Introduction to MSK Imaging
D Magid, MD, M.Ed
(Common abbreviations: pt= patient, L/R= left, right, CXR =chest radiograph, AP= anteroposterior view, PA=posteroanterior view, w/= with, w/o =without, fx=fracture, hx=history)
APPROACH TO MSK TRADITIONAL IMAGES
Musculoskeletal plain film (a misnomer in the digital age, but conventionally accepted) imaging interpretation requires good habits including consistency, meticulous search patterns and checklists specific both to the anatomic area imaged and to the potential diagnostic/clinical concern, habitual double-checks and surveys of ‘miss’ areas, and the adherence to ‘Describe First Diagnose Second’. Precise verbal capture (“telephone model’-someone hearing this description could draw the findings) of the visual findings is necessary both because the chosen diagnosis may be elusive, and because the process of expression subconsciously jump-starts synaptical connections and deep-seated knowledge that may fine-tune the evolving differential (think of ‘Jeopardy’— bewildering yet somehow correct answers often pop up ‘out of nowhere’ in response to key clue word triggers).
TALKING THE TALK
Musculoskeletal imaging and Orthopaedic descriptors adhere to the convention of describing the distal portion relative to the more proximal portion when a bone, bone fragment, articular surface, or other identifiable landmark is displaced from conventional anatomic position. All positional descriptors are referenced to anatomic position (supine, arms and legs extended straight, hands supinated, feet plantigrade ie at right angles to ankles). Vague non-medical terms such as ‘near’, ‘behind’, ‘next to’ or ‘in front of’ are imprecise and can lead to significant miscommunication or misunderstanding. Because the hands are supinated the palmar surface of the hand can be referred to as anterior, palmar, ventral or volar; the ‘back’ of the hand as posterior or dorsal. The ulnar side of anything in the hand is medial, the radial side lateral. Hand specialists continue to disagree as to whether we have five fingers, four fingers and a thumb, or five digits; for absolute clarity uses names rather than numbers: thumb, index, LONG (no ‘middle’ if only 4 fingers!), ring, and small. The sole of the foot is plantar, the ‘top’ of the foot dorsal; since its right-angle position renders ‘anterior/posterior’ more confusing than clarifying. The hind foot is proximal, distal references towards the toes. The tibia and first toe (no need to name, numbers ok) are medial, the 5th toe and fibuLa always Lateral (Great toe vs thumb end up medial vs lateral because of embryonic rotations…but that is another chapter). Given the three-dimensionality of the bony pelvis, the scarum and SI joints are both posterior ring and superior pelvis; the symphysis part of the anterior ring and also inferior portion pelvis.
FRACTURE DESCRIPTORS adhere to these conventions and use several other terms.
Displacement: described in terms of where the DISTAL portion went in transaxial (ant/post, med/lat) plane (“3 mm lateral displacement” accurate, but “3 mm lateral displacement of major distal fibular fragment” or “3 mm lateral displacement of distal relative to more proximal fragment” add clarity and specificity although technically slightly redundant).
Angulation refers to deviation introducing an angle from the zero degree long axis of a bone or extremity
- described as ‘minimal/moderate/marked’ (exact degree measurement preferred)
- direction referenced to where DISTAL piece went relative to PROXIMAL
Rotation refers to relative clockwise or counterclockwise rotation of a fragment or bone relative to the more proximal point; eg, a femoral diaphyseal fracture rotating laterally or externally would position the knee externally rotated relative to the hip. Even in children rotation does not remodel, unlike angulation or displacement, and must be noted and reduced.
Override, telescoping, shortening refer to proximal displacement of the distal portion relative to the more proximal portion.
- Tolerance or significance of override depend on pt. age (eg, some override actually desired in pediatric femur fractures or length overgrows from exuberant healing, small degrees of override or ultimate bone length differences less critical in upper than lower extremity.)
Comminuted - fracture with three or more fragments.
Simple or closed fractures – retain soft tissue/skin integrity, not contamination from outside world.
Compound or open fractures communicate with the external world
- bones may disrupt skin (‘insideàout”), or integrity of skin/soft tissue punctured or ruptured from externally (‘outsideàin’)
- significant contamination, greatly increased risk of infection, osteomyelitis, and/or septic arthritis
‘Greenstick’ fracture - incomplete, single-cortex, or bowing fracture deformity typical of children’s more elastic bone tissue
Pathologic fracture- through pre-existing bony abnormality (eg, through cyst, tumor, infection, drill hole or hardware)
Stress fracture- Result either of abnormal repetitive forces on a normal bone (eg new military recruits on 20-mile march), or normal repetitive stress on abnormal bone (eg, osteopenia or prior radiation therapy weakening bone)
Reduction- manipulation to reduce fracture to more-anatomic alignment (position)
Closed reduction- without surgery; often with cast, brace, boot, or splint
Open reduction- surgical, often with hardware
Internal fixation- surgically or percutaneously placed hardware (pins, plates, screws, etc)
OTHER MSK DESCRIPTORS
Location with in bone- Epiphyseal, intraarticular, metaphyseal, cortical, medullary, periosteal (on cortical external surface), endosteal (cortical internal or medullary surface)
Periosteal reaction- define linear extent of reaction, nature and presence of layers vs solidity, to assess aggressiveness and age of the reaction. Used to date fracture healing, detect change, and assess aggressiveness of neoplastic or inflammatory lesion.
Margins or borders- sharp vs ill-defined; marginal sclerosis; permeative or moth eaten
Matrix- contents of a visualized lesion/finding; homogeneous vs heterogenous, stippled, loculated, calcified (cartilage-forming, arc and whorls and smoke rings) vs ossified (bone-forming, trabeculated, corticated)) vs amorphous (featureless, like milk)
*** (MADEWELL REFC**)
Radiolucent, radiodense- strictly descriptive, does not imply ‘worry/don’t worry’ or diagnosis
Sclerotic- radiodense new or reactive bone or bony reaction, often marginal, does not imply benign vs malignant
Lytic- radiolucent, implying destroyed or resorbed bone; implies aggressive process (infection, neoplasm). Describe first (“Well-defined oval area of bone loss or radiolucency..”).
Blastic – radiodense lesions, implying neoplasm. Again, describe first (“Sharply defined oval area of homogenous cortical radiodensity…”) first since ‘blastic’ implies pathology/neoplasm.
Ill-defined – finding with poor marginal/border definition or interface with adjacent tissues
Well-defined- interface with adjacent tissue readily defined; could outline easily with pencil
“ORDERING” STUDIES: Not!
CONVENTIONAL RADIOGRAPHY, or plain film, remains the entrance point to the assessment of acute and chronic musculoskeletal conditions. Remember that the Radiology requisition is not an ORDER but a PHYSICIAN CONSULTATION REQUEST. Be as precise and specific as possible in such requests. “R/O trauma” or ‘pain’ are not only inadequate but will also get your study disallowed by third party payers. Include history such as mechanism of injury, site-specific detail, and signs and symptoms leading to the request. While ‘trauma foot’ will trigger the standard 3-view exam, for example, remember that even this apparently-defined anatomic region encompasses at least 26 bones and 57 joints; and in terms of ‘trauma’ may be crushed, twisted, stubbed, chronically forced into stupid shoes, stress fractured or impinged against foreign matter. “Jumped from 3rd story balcony, heel pain” triggers a different targeted search pattern than ‘Stubbed first two 3 days ago”. While certainly the Radiologist is responsible for all findings on any film, most (especially in the Emergency Department or with sicker in-patients) prefer to focus on the urgent/historically-driven aspect first and then lean back for the second unbiased total-content look.
There is also the legal and medical obligation to provide Diagnostic Imaging with other relevant detail: absolutely accurate patient name and identifying information (history number, date of birth, location, gender, side and body part of interest, etc) as well as clinical factors such as possible pregnancy, HIV or Hep C status, known underlying conditions such as diabetes, anticoagulation, chronic disease, neoplasm, neurologic disease, any precautions in place (fall, respiratory, wound), recent invasive procedures or indwelling implants, etc.
While learning the rudiments of image interpretation are essential to any clinician requesting studies, remember that the Radiologist no doubt has far higher resolution monitors and far more training and experience than the average clinician. As with any medical test it is clinically and legally imperative that the clinician check final results in a timely manner. As a rule emergent or life-threatening findings or changes would be rapidly communicated to the ordering physician, meaning contact information (names, phone numbers, etc) must be accurate and legible.
The first and most critical decision the Radiologist makes—and the one which determines the subsequent flow chart of interpretation, reporting and communication- is ‘Worry/Don’t Worry”. Everything else evolves from that call.
Plain films of the musculoskeletal system are, as elsewhere, a pattern of black, white and grays reflecting both the path length (thickness) and atomic numbers (density) of substances (patient) interposed between the xray beam and the radiosensitive digital cassette (previously film). Thicker areas will be less radiolucent (allowed more xrays through, leading to blacker or darker gray areas on image) than thinner areas of similar tissue makeup; while cortical bone, with a higher proportion of higher-atomic number calcium than an equal thickness of soft tissue immediately anterior to it, will appear far more radiodense (attenuated more xrays, producing relatively white areas). The increased radiation necessary to pass through densely calcified and/or thicker bony structures (such as the pelvis or lumbar spine), the predominance of red (active) bone marrow in the axial skeleton, and the propinquity of other radiosensitive tissues or organs (thyroid, gonads) must be acknowledged and assessed particularly when imaging children, young adults, and potentially pregnant females. This chapter will focus on adult musculoskeletal imaging.
Digital imaging has multiple advantages over traditional analogue (‘hard copy’) film imaging. Studies can be reviewed or interpreted remotely, in various locations simultaneously, and/or made available for surgery, consultation, attending review, or image-guided procedures instantly. Computer enhancement features allow the viewer to magnify areas of interest, reorient films to a standardized viewing position, measure distances and angles, annotate areas of interest or concern, or readjust the gray scale and image contrast to enhance areas such as soft tissue, lung, or fascial planes that were less readily assessed on analogue films. Archiving and retrieval are also more efficient and ‘green’ although, as with all computerized tasks, not without their own pitfalls.
The most consistent and effective film interpreters follow set checklists and habitual patterns when reviewing studies:
- confirm patient identity, date, film labels, history/indications, assessing positional adequacy and technical aspects of the exam
- systematic review of areas and findings on each view
- focus on area of alleged interest
AMERICAN COLLEGE OF RADIOLOGY APPROPRIATENESS CRITERIA (ACR AC)
Increasing imaging sub-specialization and rapid evolution of sophisticated imaging techniques makes it difficult for even the most seasoned clinicians to keep up with what to order when for suspected clinical conditions. This is another reason to consider the requisition a consultation, not an order; and to give adequate information about the patient to allow the Radiologist to assess need for contrast, decide whether the optimal study has been requested, and to factor in patient safety and comfort considerations. Another valuable resource for on-going education and problem-solving is the ACR AC (at www.acr.org), a constantly-updated on-line resource currently covering 167 topics across 800 commonly encountered clinical scenarios (eg chronic neck pain, suspected metastatic bone disease, acute ankle injury, imaging post hip arthroplasty), with a condensed version down-loadable to handheld electronic devices. Habitual reference to this resource enhances clinical understanding of the imaging process in diagnosis and therapy.
“If it is really there the Radiologist will find it”: hopefully true, but specific clinical and historical input and precise localization of area of interest enhances the batting average.
“Cover as much anatomy as possible on fewest number of films”: This is most commonly misapplied to the lower extremity and forearm (eg, ‘tibia-fibula’ ordered, not ‘knee’ and ‘ankle’). If both knee and ankle may be of interest, order coned (small collimated views) and centered (film center corresponds with point of maximum tenderness or interest) films of each joint. Long bone views literally or virtually cut off the joints at each end of the bone, since the angle of the beam at the edge of a field distorts detail and geometry the way the setting sun low in the sky elongates and distorts shadows. Even if the joint seemingly appears on the film, the report is likely to start with ‘Limited exam of the ankle and knee….”.
“One view can rule out significant abnormality and save radiation and cost”. At least two views at 90’ to each other are necessary to assess bulky 3D structures such as bones and joints. Getting one view only will lead to significantly under-calling or missing fractures (eg, slipped capital femoral epiphyses or proximal femoral fractures), and other serious injuries or conditions. Once a study is indicated, do it properly.
“Negative films rule out fracture”. Many fractures initially are extremely subtle or microscopic. Certain fractures (scaphoid, proximal femur, femoral neck, c spine) are notorious for initially unremarkable plain film appearance (and subsequent law suits). Treat patients, not films. Prophylactically treat or immobilize and get follow up exam and re-imaging at 10-14 days.
- USE ALL RESOURCES to maximize patient care, imaging accuracy, and to place a finding along the ‘worry/don’t worry’ scale.
- Review available current and prior pt. records, notes, and labs
- When necessary compare indeterminate findings to the Normal Variants Which Simulate Disease atlas (KEATS***) – is possible finding is a variant, a positional effect, just something you never noticed before, or a true finding.
- Even abnormal findings, if not changed after careful point-by-point comparisons, are less worrisome/urgent once put on a longer time line, as long as they have already been properly acknowledged/addressed (eg previously seen metastasis, hardware complication, old fracture).
- In bone, older findings tend to be smooth, well-defined, rounded, corticated ( more like river rocks than fragments); unchanged from older exams; adjacent fascial planes or soft tissues are undisturbed. Acute findings are less sharply defined, more irregular, disrupt trabeculae or cortex, may have associated soft tissue changes, and may correlate with hx/exam.
PLAIN FILM IMAGING BY REGION
No matter what the body part or clinical indication, interpreting Radiologist first surveys images to ascertain positioning, exposure and if all areas of interest are shown.
Cervical spine: 3 views= lateral from occiput to T1 (for c& nerve root), AP, and open-mouth odontoid (for frontal of C1-2, not seen on true AP). Additional views (not usually allowed as part of initial acute screen unless ordered by Orthopaedist or Neurosurgeon): flexion/extension laterals, obliques.
DO NOT KILL tip:
- Radiologists clear adequate and unremarkable lateral IMAGES not PATIENTS.
- Patient can only be cleared by a clinician and by meticulous exam of awake/sober pt.
- Collar does not come off until both film and patient ‘pass’. Collars can go to CT or MR
DO NOT KILL tip: Flexion/extension films may be requested to assess acute vs chronic or stable vs unstable when either film findings or mechanism of injury require
- DO NOT ASSIST the patient. DO NOT TOUCH patient. DO NOT HELP.
- Only sober, cooperative, ‘with-it’, comprehending patients should be asked to flex/extend.
- Proprioception in the neck is excellent; should the pt. complain “My head feels like it might fall off”, STOP and replace the collar.
DO NOT KILL tip: Do not hesitate to get CT to visualize any inadequately seen area or possible finding.
Checkpoints: adequacy of views (position, extent, exposure)
- Flowing posterior vertebral body lordosis (straightening often position, collar, muscle spasm)
- Similar flowing lordosis spinolaminar lines and spaces. Thecal space defined by these two lines, should be ~17 mm at C1-2 and taper or ‘funnel’ slightly distally.
- Vertebral body contour, trabeculae, and heights
- Prevertebral soft tissue (posterior oropharynx) ~ ¼ AP vertebral body diameter at C1-4, triples C4-5 as common airway bifurcates to trachea and esophagus
- C1-C2 anterior relationship (ADA, atlanto-dens interval) <2.5 mm and stable
- Posterior odontoid margin ‘straight-backed’
- Other areas on film:soft tissues neck, sphenoid sinus, sella turcica (possible life-threatening ‘incidentalomas’ include basal skull fracture, air/fluid level sinus, pituitary adenoma, metastasis
- Assess position/rotation: vertical spinous process line, trachea, both midline and equidistant from medial clavicle borders; mandible horizontal, head nonrotated
- Air column: symmetric margins and caliber from piriform sinuses distal
- Undulating symmetrical ‘flowing’ lateral margins (lateral processes)
- C7 transverse processes directed caudal, T1 directed cephalad; assess symmetry, r/o cervical ribs or proximal rib fractures, mets, etc.
- Lung apex for pneumothorax, mass, aymmetry
- Not all pts. able (in collar, injuries, arthritis or fusion, noncompliant) ; two attempts then revert to CT
- Odontoid peg centered, upright, symmetric, intact
- Lateral margins C1, C2: less than 3 mm total medial/lateral step off, R and L
- Old films, hx, where possible pre-existing trauma seen.
- CT if any doubts
- CT for any limited or indeterminate exam in a trauma setting or any clinical question involving skeletal structures. Usually rapidly available.
- MR best if cord, nerve roots, soft tissue of primary hx, exam, or plain film interest.
Soft tissue technique:
- If the primary clinical interest is the prevertebral soft tissues or epiglottis.
- Hx of anticoagulation, trauma, surgery, instrumentation, fevers, psychiatric, etc.
- Proprioception in the neck/esophagus is very sensitive.
- Studies rarely identify conventional ingested matter—fish and many chicken bones would be difficult to see radiographically
- If foreign matter ingestion/inhalation identified/suspected get both AP and lateral to assess if in trachea or esophagus
Initial plain film study =AP and lateral (invariably limited of most proximal T spine because of superimposed shoulders).
- Count 12 pairs ribs to ascertain number of T spine bodies, r/o vertebral anomalies or cervical ribs.
- Check end plates and body heights,
- Uniformity of disc spaces, definition of smooth endplates
- Paraspinous soft tissue (parallels lateral margins)
- Relative uniform bone density and bony definition from level to level,
- XR bone technique will accentuate lung markings and make film more ‘black/white’ than CXR.
- Normal kyphosis is ~20-40’, slowly increasing with age, osteopenia, individual variance
- Proximal few levels NEVER adequately seen (imposed shoulders-too bulky)
- End plates smooth (straight or slightly concave), similar level to level
- Disc spaces similar level to level
- Vertebral bodies, trabecular bone defined and comparable level to level
- Posterior vertebral line continuous, flowing, no anterior/posterior displacements
- Posterior elements, facet joints, and spaces ‘shingled’ or stacked, similar level to level
- Coned lateral gives best detail of L3-4-5-S1 (high incidence of findings, LBP)
- Other tissues on film: aortic, mediastinal contours, lung, calcifications, upper abdomen
- Old films assess acute vs chronic or stable vs progressive changes; may increase sensitivity to subtle findings such as moving or changing hardware, increasing kyphosis or scoliosis, or appearing/disappearing/enlarging findings.
- Obliques rarely useful esp. in acute/trauma setting; not routinely obtained
- Flexion/extension laterals also uncommon, may help assess dynamic aspects of possible finding in posterior column or vertebral body alignment or hardware issue.
Low back pain is ubiquitous; up to 80% of adults have had one episode of ‘significant’ back pain by age 45, the majority of which can be managed conservatively in reliable pt. populations. Judgment of signs, symptoms, and pt. characteristics (age, level of activity, other clinical problems such as neoplasm, fevers, or osteopenia, reliability as historian) help drive imaging tree of local or low-grade pain in adults. Radicular pain (‘electric’, shooting down to the lower extremity) or bladder/bowel/sphincter changes mandate complete assessment including MRI.
Routine initial study = AP, lateral, and coned lateral (L3-S1). While spine plain films are relatively high dose (about 2x abdomen, 30x CXR film), the 3rd (coned) view is validated by the high incidence of pathology involving the most distal lumbar spine (eg herniated L4-5 disc, pars defect) and the improved detail obtained by coning and centering. Possible pregnancy must be ruled out historically or by lab prior to imaging females.
- SPONDYLOSIS: degenerative disc disease and/or osteophytes vertebral bodies, aka ‘degenerative disc disease’ or ‘degenerative change’ but NOT ‘arthritis” –only true synovial joints in L spine are posterior facet joints which CAN get ‘arthritis”
- SPONDYLOLYSIS: acute, chronic, or developmental defect in pars interarticularis, best seen on obliques (bilaterals show up on lateral view) and associated with dynamic instability (ie vertebral body relationship changes/subluxes, flexion/extension laterals).
- SPONDYLOLISTHESIS: the anterior/posterior subluxation of one vertebral body over another, assessed at posterior body margins. Graded I (25%) through IV (75-100%) or V (>100%, rare). Grade does not imply etiology, which may include chronic stress, inflammation or infection, degenerative changes, developmental dysplasia/elongation, neoplasm, or acute trauma. Flexion/extension laterals assess dynamic instability.
- PSEUDARTHROSIS: Apposed cephalo-caudal expanded L5 transverse process and superior S1 ala acquire fine sclerotic margins creating appearance of ‘joint’; implying sufficient biomechanic interaction both to trigger bony response and possible pain.
- Document 5 lumbar bodies (T12 ribs); segmentation anomalies at L5-S1 very common.
- L5-S1 pseudarthrosis may cause chronic intermittent LBP and is easily overlooked.
- Spinous processes should line up vertically/straight in the midline.
- Assess body heights and disc spaces for similarity level-to-level
- SI joints symmetric and unremarkable (3-4 mm, undulating, fine cortical margins). True synovial SI (diarthrodial) joint is only distal 1/3-1/4, more superior = syndesmotic, ie stabilizing ligaments restricting motion and contributing to postural stability.
- Usually 2-3 pairs sacral neural foramina roofs visible (“eyebrows’)
- Psoas lines usually (not 100%) visible, abnormal/absent may = abscess, hemorrhage, silhouetting by ascites, obscured by air/feces bowel but nl. reassuring
- Other tissues on film: aorta, iliac wings, medial hips, renal outlines, fascial planes of obturator internus and bladder, calcifications (renal, GU, GI, soft tissue, vascular), medical, ingested, or ambient foreign matter
- Compare to old films (or abdomen, GI,GU studies too) to enhance sensitivity to change.
- Read all as L lateral (pt facing to yr left) for consistency, ‘pattern-recognition’
- Posterior vertebral line: normal flowing and continuous lordosis; straightening =postural, muscle spasm, brace
- Spondylolisthesis: anterior or posterior displacement from level-to-level; describe precisely (“3 mm, Grade I anterior spondylolisthesis of L4 over L5’)
- Disc height maximum at L4-5, ~2 mm less L3-4 and L5-S1 (if L4-5 =s these, ‘narrowed’)
- Endplates slightly concave, similar level-to-level; very concave or irregular or zig-zagged abnormal, as would be lytic/blastic changes
- Vertebral body trabecular pattern similar level-to-level, account for possible focal lucencies/densities and see if also discernable on AP to confirm IN, not superimposing.
- Vertebral body height, shape, proportions, contours similar level-to-level; spondylosis at several levels very common by 40-45.
- If pars defect apparently visible, suspect bilateral pars defect.
- Spinous process presence/absence (laminectomy, laminotomy), deformity
- Facet joints, posterior arthritis
- Other tissues: aorta (aneurysm, change); bowel contents or abnormalities; calcifications in GI,GU, vascular; surgery or foreign matter
- Old studies to confirm possible findings, assess stability or change, set ‘worry’ level.
PELVIS AND HIPS: SEVERE ACUTE TRAUMA
Due to the severity of force required to disrupt such a biomechanically (multiple arches) strong and bulky osseous structure, close proximity to major organ systems, and intensely rich vascularization, pelvic ring fractures are the third leading cause of shock and death following blunt trauma, with high (in some studies up to 31%) early mortality. Proximal femu and acetabular fractures, while less urgently life-threatening initially, also have well-documented high 6 month mortality and morbidity. Rapid and accurate initial clinical and radiographic assessment are key to reducing morbidity and mortality in all pelvic injuries.
While there are 9 standard plain film views (AP, R/L coned AP and lateral, R/L obliques, and inlet/outlet), the initial screening film is an AP pelvic, followed (if clinically, historically, and radiographically warranted) by either further exam of the hip (proximal femur lateral) and/or pelvic ring (inlet/outlet, which DO NOT require pt. repositioning—a safety consideration). The obliques require rolling the patient, and may either contribute to hemorrhage or may impinge sharp bone fragments against or through neurovascular, GU, GU, or other vulnerable structures. Rapid and thorough assessment mandates CT once baseline views have been obtained.
VOCABULARY POINTER: “Hip” refers to the entire joint ie, acetabulum, and proximal femoral head and neck. What lay people refer to as ‘hip fractures’ usually means ‘proximal femoral neck fractures’, which are both common and the source of great morbidity and mortality in the elderly.
- Assess pelvic ring position for rotation and adequacy; obturator foramina symmetric, Obesity, pain, scoliosis, produce subtle rotation therefore distort landmarks.
- Obesity, markedly osteopenia, layers of transport immobilization, and/or marked air and feces colon, may all limit initial exams. When in doubt go to CT.
- Follow pelvic inlet ilio-pubic line SI joint to symphysis; ilio-ischial line SI joint to lateral margin obturator foramin (defines anterior and posterior colums respectively).
- Symphysis 3-4 mm, no superior step-off, learn characteristics of osteitis symphysis from parity
- ‘Teardrop” demarcates entire pelvic sidewall (quadrilateral plate surface)not always defined, in non-rotated should be symmetric “J’ or fine loop neither filled-in (blastic) nor disrupted (lytic , fractured, destroyed)
- Acetabular roof= weight-bearing condensation from ’10 to 2 o’clock’ over femoral head.
- Acetabular dome= cone of criss-crossing trabeculae with roof as base, demonstrating transfer of weight-bearing forces into the roof, hip and femur.
- Femoral neck has two corresponding (tensile and compressive) arrays of trabeculae, (relative sparing centrally =Ward triangle); flowing into lateral/medial cortices femur.
- Femoral head and acetabulum approximate 2/3 perfect sphere, deep ball-and-socket, rarely dislocates in normal adult without accompanying acetabular fracture.
- Medial pelvic wall soft tissue assessment for fascial planes, muscles and bladder; hemorrhage, ascites, edema, bladder rupture, may all obscure (as may air/feces)
- “Good for fracture, good for patient”: Even in pt. with other severe injuries prompt fracture reduction may simplify pt. stabilization. Vascular supply to femoral head retrograde from intertrochanteric capsule in adults; rapid reduction of proximal femoral displacement required to decrease risk of avascular necrosis. Rapid pelvic ring reduction necessary to tamponade/control hemorrhage and shock.
- Gross or obvious pelvic ring or acetabular deformity should trigger prompt CT.
- Pelvic ring integrity can be rapidly assessed without moving pt, by tilting tube caudal from cephalad position (pelvic inlet, ie iliopubic lines, stretched out) or moving tube caudal and shooting cephalad, thereby elongating anterior ring (symphysis, pubic rami, obturator foramina). Inlet/outlet sometimes obtained even when CT indicated, or immediately after surgical reduction, bec. will provide simple inexpensive lower dose baseline for further f/u over recovery.
HIP (ACETABULUM AND PROXIMAL FEMUR): AP and ‘LATERAL’
DO NOT KILL tip: Never clear inadequately seen femoral neck; unacceptable medical and legal risk. Pts. with fractures do not cooperate with positioning. Proximal femoral fracture one of most expensive diseases to pt, society, and physicians.
- Repeat/coned AP may help if initial pelvic AP inadequate
- Several lateral or 2nd views proximal femur, with minimal pt. movement or cooperation (cross-table, O.R., frog leg); but NOT acetabulum;à CT
- Follow both trabecular arrays in neck for disruption, irregularity, smudging, blurring, thickening (subtle fracture, destruction, blastic change); the proximal femur, like the proximal humerus, contains red marrow, subject to neoplasm or infection similar to red marrow of axial skeleton. Bilateral comparison to assess prominent Ward triangle (osteopenic) vs ‘lytic lesion’.
PELVIS AND HIPS: LESS EMERGENT TRAUMA
Pts. may self-present following less severe trauma. Ability to ambulate, denial of pain, absence of significant soft tissue bruising, even apparent adequate passive range of motion, do not r/o significant pelvic or hip trauma. Intoxicated, post-ictal, shocked, confused, neurologically or intellectually compromised, unduly stoic, or self-medicating pts. may all have falsely reassuring presentations. Pts. are also poor historians; ‘hip pain’ may refer to a different part of the pelvis or lower trunk than examining physician assumes. Careful systematic review of the plain film exam, complete physical exam exceeding just the pt-denoted area of interest, and if indicated additional studies and/or f/u are mandated to avoid serious medical and legal complications.
Clearing a pelvic views with incompletely seen femoral necks (inadequately-internally rotated proximal femurs is inexcusable. Hip pain is the primary cause of external rotation at presentation. While we currently see over 352,000 proximal femur fractures a year, the aging US population will average 650,000 such fx/yr by 2050—1800 a day. Know the pt. at highest risk: older, taller, thin post-menopausal females, following even seemingly minor trauma or no trauma at all (stress fx not uncommon as the population takes to aggressive walking routines, survives longer following pelvic irradiation fro tumor, etc). The risk begins to double every 5 yrs over 50 yrs of age, (Amer Acad Orthop Surgery, www.aaos.com***)
When in doubt get additional/adequate views, or go to MR (AVNEESH)
HIP AND PELVIS: COMMON “Do Not Miss” ENTITIES
YOUNG ADOLESCENT, intermittent pain/limp :
- 1/150,000 peri-adolescents (10-13) will experience slipped capital femoral epiphysis (SCFE), a slow-motion failure of the proximal femur physeal plate
- Head slips (usually posteriorly, inferiorly, and/or medially) off the metaphysis.
- Typically seen in overweight African American males (females and other ethnic groups rapidly catching up), perhaps related to activity or time of day (“Tuesdays after soccer he limps for a few hrs then he’s fine in AM”); and eventually bilateral in about 20%.
- Suspect it or miss it in this age group, and when imaging is indicated get AP and frogleg lateral (which is more sensitive) of BOTH hips at f/u until the risk period (physeal immaturity) ends.
- Diagnosis considered emergency; surgery for stabilization usually within 24 hrs.
- Physes are open.
- On AP lateral neck line should inter
- Cephalo-caudal heights of R/L capital epiphyses (heads) may be subtly asymmetric as abnomal side slips posteriorly (‘setting sun”).
- Widening, irregularity, asymmetry, or reaction along the metaphyseal neck physis suggests non-acute slip—meaning far greater risk pf AVN if reduced—and must be noted.
- The head may be more readily seen to overhang the medial metaphyseal margin; uncovering the lateral metaphysis margin which may be forced into a weight-bearing position over time and which accounts for the leg length discrepancy often seen ( both factors contributing to subsequent degenerative changes)
- Again, reactive changes along physis suggest sub-acute or chronic slip even if sx alleged to be acute
FOLLOW UP IMAGING
- Always look at BOTH hips; 20% asynchronous but bilateral
- Confirm screw tip within head on both views
- Assess progression of physeal maturation/fusion BOTH hips
- Assess capital epiphysis for early AVN (sclerosis, subchondral crescent radiolucency, radiodensity changes in head)
Lytic lesions in adults over 45 are ‘mets or myeloma til proven otherwise’, statistically speaking. Lesions in the pelvis may be masked by the superimposed air and feces, soft tissue, and inability to see all the bulky structures on at least two views at 90’. Look carefully for disruption or distortion of any of the guidelines to the pelvis (see Pelvic Fracture, above), to the fine etched trabecular pattern of the femoral necks, tiny cortical disruptions or distortions, or apparent ‘air and feces’ which does not move between exams. Old films are vital to enhance sensitivity to otherwise-overlooked changes (or failures to change) over time.
It is more important to get the ‘worry/don’t worry’ call correct than to be familiar with the spectrum of primary and metastatic neoplasms in the pelvis. Differential is dependent on history, age, gender, location within pelvis or hip, and other modifying factors. See SKELETAL NEOPLASM: GENERAL PRINCIPLES.
In general CT is obtained to confirm presence of a bone lesion, bony and soft tissue involvement or integrity, risk of impending or pathologic fracture, progression or regression of bony disease, and to help determine ‘compartments’ for possible biopsy or excisional surgery. MR is warranted when soft tissue, marrow, vascular, and neural tissue questions predominate. (AVNEESH*** bx planning here or under ‘NEOPLASM”) )
KNEES: TRAUMA and ARTHRITIS
The knee includes articulations between the femur and tibia, femur and patella, and tibia and fibula. As with other 3D joints, two views (AP, lateral) are necessary for adequate basic plain film assessment or screening. Arthritis or specific hx/findings also mandate additional views, most commonly patello-femoral or ‘sunrise’ views, or flexed-AP views.
- §Always start with the lateral, facing L, for consistency and pattern acquisition.
- §Assess rotation; condyles should be superimposed and patella profiled
- §Suprapatella bursa (a misnomer—it communicates with joint space unlike true bursa) should be radiolucency between flat or concave quadriceps (superior patellar) tendon and anterior cortex distal diametaphyseal femur. Focal oval radiodensity posterior to this tendon, or ill-defined increased radiodensity possibly ‘silhouetting’ the posterior tendon margin, and/or anterior bulge/displacement of the tendon, all imply joint effusion and warrant increased vigilance.
- §If cross-table lateral taken, acute hemorrhage or penetrating trauma may produce suprapatellar air/fluid or fat/fluid level (also seen on MR after hemarthrosis and prolonged immobility as blood components settle into layers with gravity). Again—vigilance!
- §Follow all cortical margins endosteally (internally) and periosteally, assess trabecular bone patterns, look for loss of definition or evidence of destruction, reaction, disruption.
- §Look for smooth integrity of posterior (articular) surface patella (anterior surface is nonarticular, may be rougher).; integrity of trabecular patterns in patella
- §Inferior patellar tendon extends from inferior pole patella to anterior tibial tuberosity, posterior margin should be well-defined by apposed anterior fat pad.
- §Use Normal Variant book (KEATS***) to define possible or unfamiliar findings (eg, normal variant posterior sesamoid called fabella, seen in 8%); correlate with hx and exam and if possible, old films.
- §Vascular calcifications are usually posterior. Loose body calcifications/ossifications are usually rounded, possibly layered or lamellated, may be anywhere within joint capsule and may have moved since previous exam. Common sx are intermittent sudden pain and ‘locking’, particularly on steps. Size of a loose body may well exceed any possible corresponding visible source or defect since osteochondral fragments can survive and grow in synovial fluid without vascular supply.
- §Periosteal reaction, if noted, must be characterized in terms of activity, extent, layers, appearance or change from prior exams
- §Soft tissue edema, plane effacement or displacement, or unexpected soft tissue densities/lucencies/air/mass effect must all be characterized, clinically correlated, and if indicated further assessed.
- Critique position and technique
- Follow cortical margins, trabecular patterns, articular surfaces
- Assess integrity of articular medial, lateral plateau and subchondral trabecular pattern for subtle fx
- Medial and lateral joint space: medial narrows first in osteoarthritis, decreasing anatomic axis (shaft-shaft angle) from normal 6-8’ valgus towards zero or varus.
- Look at medial and lateral joint spaces for early chondrocalcinosis (meniscal and cartilage calcifications), loose bodies.
- Patella difficult to see on AP but try to trace periphery, trabecular pattern to r/o fx.
- Follow fibula for signs of fx or old/new trauma
- Medullary spaces; calcifications (often infarct or enchondroma), endosteal changes, trabecular disruptions, lytic/blastic/reactive lesions
- Periosteal reactions, soft tissue changes
SUNRISE or SKYLINE or MERCHANT VIEW PATELLA
- With knee flexed, a tangential cephalo caudal beam film profiles the patello-femoral joint, allowing visualization of the medial and lateral articular patellar facets (TIP: The Lateral is Longer) and the femur’s trochlear groove in which it articulates.
- The articular surfaces = parallel rounded V’s, articular cartilage/space symmetric from medial to lateral margins; posterior patella centered in groove .
- Osteophytes or cartilage loss seen with patello femoral arthritis
- Subluxations (almost always lateral), fractures, old trauma also seen
STANDING FLEXION FRONTAL
- Most often used if arthritis suspected, the pt. is weight-bearing and stands with knees flexed 30-45’ for a tangential AP view of femoral-tibial articular surfaces, notch.
- Medial compartment narrows first in most osteoarthritis, this is most accurate view; use lateral compartment and if indicated contralateral knee for baseline
- Flexion also best profiles marginal osteophytes around femoral notch, also seen with OA , and spurring or sharpening of tibial spines (of indeterminate prognostic significance in OA)
- Not used in emergency/trauma setting; requires compliant pt able to stand.
Ankle injuries are common and account for millions of Emergency Department visits annually. Serious injury may involve the bones and/or stabilizing ligaments making up the ‘ring’. There are criteria for determining when to order ankle imaging but as in all appropriately ordered trauma imaging, a certain per cent of negative films reassures that the criteria are pragmatic, not overly-exclusive. About 90% get radiographed, 15% require immobilization/follow-up. Three views are commonly obtained.
- True frontal view of the distal tibia and fibula (fibula partially obscures lateral talus).
- Soft tissue over and proximal to medial, lateral malleolus should be symmetric and preserve fascial planes (subcutaneous fat, deeper muscle).
- No obvious step-offs or deformity of visualized articular surfaces or cortical margins.
- Assess trabecular patterns (‘hand-etched graph paper’)
- Visualized mortise and relationships unremarkable, symmetric
- Shallow internal-oblique (foot internally rotated on ankle) to profile mortise
- 3-sided articular space 3-4 mm and uniform, smooth articular surfaces
- TIP: Even small (1mm) asymmetries in medial/lateral width very significant, imply relative talar subluxation under tibial plafond, loss of tibio-talar surface apposition.
- TIP: follow articular surface talar dome for small defects or subchondral lucencies; osteochondral fracture/defect common cause of ‘sprain that still hurts’ months later
- TIP: trabecular pattern again should approximate hand-drawn graph paper; subtle crumples or smudges may imply subtle impaction, fracture or abnormality
- Check soft tissues
- Check gastrocnemius (“Achilles”) tendon first, common ‘miss’ zone with severe clinical consequences
- Tendon should be smooth, regular, flat margins; relatively sharp and smooth interface with radiolucent pre-tendinous triangle (‘clear space’). If clinical/radiographic suspicion of tendon injury get MR. (AVNEESH???)
- Smooth regular curved articular surfaces and space, tibia-talus
- Joint effusion may be seen as ‘dumbbell’ like radiodensity immediate anterior and/or posterior to tibio-talar joint
- Assess subtalar (talar-calcaneal) joint, anterior process calcaneus (another common-miss point), calcaneal trabecular symmetry and flow for subtle trauma
- Describe calcaneal spur (size, smoothness) but usually ‘incidentaloma’
- OTHER MISS ZONES: base of 5th MT, tibio-fibular joint, anterior superior talar margin
STRESS VIEWS = optional frontal views to assess ligamentous stability of ankle ring, with the foot forced into varus/valgus (medial/lateral) stress on the stabilized distal tibia, usually by (lead-gloved) 2nd person. May confirm suspicion of loss of ligamentous integrity/stability. Up to 10 degrees change in usually-parallel plafond (horizontal articular platform distal tibia) and superior talar dome can be normal; obtain contralateral (normal) side stress view if indeterminate.
CT with coronal and sagittal 2D reformatting best to assess fracture or alignment/articular relationship changes, tibio-fibular, tibio-talar, fibular-talar, or calcaneus. (AVNEESH??)****
MR best for gastrocnemius injury or tear, plantar fascia, early osteomyelitis.
- Fall into 3 general categories, all (mis)posted as 'ARTHROGRAMS", with slight modifications of technique: ASPIRATION (r/o infection), PAIN STUDIES, and GADOLINIUM FOR MRI.
- Each requires slightly different modifications but similar consent, preparation, risks, and radiation (minimal)
- None requires special preparation or pre-medication unless there are known contrast allergies
- Post-procedure discomfort should not exceed usual discomfort, usual measures (heat, anti inflammatories) suffice. Resume baseline activities as comfortable, protect anesthetic joints.
ASPIRATION FOR POSSIBLE INFECTION may be warranted when signs, symptoms or initial radigraphs suggest possible infection involving the joint. Patients about to undergo primary or, more commonly, revision arthroplasty may have baseline aspirations.
- Provide adequate information to justify procedure and clarify clinical questions: hx, underlying conditions (HIV, IV drug abuse, MRSA, endocarditis, steroid therapy, etc), physical and lab findings; prior surgery or interventions.
- If unusual agents suspected clarify what additional tests are hoped-for. Remember there may be very limited fluid and therefore limits to tests possible.
- A ‘dry’ tap (no frank fluid) can still lead to successful culture; the needle tip is ‘walked’ or rubbed along bone/implant surfaces and then stabbed into the culture medium. A few cc’s of non-bacteriostatic saline can also be injected and retrieval for culture attempted.
- Total shoulder arthroplasty: culture for P.acnes: add “P.acnes: Hold 10 days’ on req (‘finicky’)
- Injecting intraarticular bupivacaine for temporary pain relief does not interfere with cultures and is appreciated by patients with chronic pain. Admonish care while joint ‘anesthetic’.
“PAIN STUDY” (Therapeutic injection to test response)
- Performed either to confirm joint of interest is actually source of pain (eg, ‘hip’ pain may actually be SI joint, bursitis, knee, or other peri-articular source), and/or
- To provide temporary (hours to days to weeks, response not predictable) relief from pain and/or improved range of motion. Pt. must continue to limit activities to pre-injection levels.
- Pt. expectations- explain injection may leave pt. improved ,unchanged, or even more uncomfortable but that all test responses are ‘correct’ and useful for the clinical assessment.
- High level of psychologic input; both technical and interpersonal sophistication needed.
- Lower extremity (hip) injections: risk of ‘leg numbness’ or decreased proprioception; explain to and warn pt to exercise care on steps, uneven ground, pavement.
- Pt. with initial good response (pain relief over days, weeks, even months) more likely to have subsequent good responses. Injection can be repeated several times over months/years, but is usually not long-term answer to pain resolution.
- Initial response gauged in procedure room but pt. must track response in ‘pain diary’ to discuss w/ clinician; some relief responses have delayed onset.
GADOLINIUM INJECTION PRIOR TO MRI (most often hip, shoulder, wrist, elbow)
- Markedly dilute (1:100-200, literature varies) Gd in either sterile saline or sensorcaine (for short term relief)
- Minimize test injections, number of punctures, as best possible
- Coordinate scheduling of injection and MR to follow; long delays compromise outcome
- Minimize joint motion once injected; hydraulic pressure on distended joint capsule will extrude contrast . Take pt. to MR by wheelchair, remaining in hospital gown.
BIOPSY or TISSUE SAMPLE FOR TUMOR, INFECTION
CT and/or MR best determine the nature of the lesion, the safest (blood-free, nerve-free skin-to-lesion approach; most characteristic part of lesion for best biopsy; number and choice of compartments breeched; optimal excisable needle track if neoplasm suspected).
Joint fluid (R/O septic arthritis, eg) is best sampled by percutaneous procedure by a Radiologist, most often under fluoroscopy (Arthrogram Service, MSK Imaging Fellows) but in certain situations, also by US.
CRoss Sectional IMaging - A. Chhabra, MD
Although conventional radiograph is important for initial screening and diagnosis of musculoskeletal (MSK) pathologies, cross-sectional imaging has revolutionized the care of these patients. It is essential to understand the potential advantages and pitfalls of each of the various cross-sectional modalities for optimal utilization, while maximizing their advantages.
- Nuclear Medicine
Knowledge of the suspected underlying MSK pathology is helpful to set appropriate scan protocols. In general, bony imaging requires high-resolution techniques and thin (2-3 mm) slices. The scans are acquired as the Xray tube in the gantry rotates around the patient. The images, thus obtained, can be displayed in multiple planes and multiple contrast settings for optimal visualization of both bony and soft tissue pathology. Axial images are used for finer soft tissue and bony details and coronal and sagittal images are used for overall alignment and longitudinal extent of the pathology. Contrast enhanced scans should be obtained to look for abnormal enhancement in suspected infections or tumors. MDCT scanners enable the machine to collect data for multiple slices for each revolution of the X-ray tube assembly.
- Extremely rapid imaging- hundreds of slices acquired in less than a minute.
- Volumetric 3D imaging using sub-millimeter slices provides excellent spatial resolution, reduces the need for precise patient positioning and scans can be obtained in any desired orientation- aids in better pre-operative planning and increases diagnostic accuracy.
- 4D imaging possible to evaluate derangement during kinematic imaging of various joints.
- Trauma- For pre-operative evaluation, persistent significant clinical findings with negative radiographs, spine trauma, tendon entrapment at the fracture site. Enhanced imaging to assess clinically suspected vascular injuries.
- Infection- Look for cortical destruction, soft tissue extent, foreign body and sequestrum.
- Tumors- Useful in periosteal or cortical lesions, such as, osteoid osteoma demonstrating a lucent or partially calcified nidus; flat bone, such as chest wall, sternal and scapular lesions; fluid-fluid levels in aneurymal bone cyst; fat containing lesions, such as lipoma, liposclerosing myxofibrous tumor, lipoblastoma or liposarcoma; mineralizing lesions, such as enchondroma, chondrosarcoma and; ossifying lesions, such as, osteoblastoma and osteosarcoma.
- Prosthesis Imaging- requires thinnest slice acquisition with thickest slice reconstitution with imaging along the metal to effectively suppress beam-hardening artifacts. CT is useful to assess the spine hardware complications such as loosening, malalignment, migration and bone / metal fracture as an adjunct to conventional radiographs.
- Kinematic joint studies- for distal radioulnar joints subluxation, patellofemoral maltracking disorders and spine flexion-extension studies.
- CT guided procedures- useful for bone and deep soft tissue biopsies, ablation of osteoid osteoma, steroid injections for unicameral bone cysts, spine injections and facet blocks as an alternative to fluoroscopic guidance.
- Contraindication to MRI- For patients who cannot undergo MRI due to claustrophobia, pacemakers, cochlear implants, etc. The indications include, CT arthrogram for the labro-ligamentous injuries, rotator cuff tears, chondral and meniscal injuries; avascular necrosis and soft tissue extent of infection or malignancy.
Pitfalls and Disadvantages
- CT may miss isodense (similar density to muscle) soft tissue lesions.
- Marrow pathology is sub optimally assessed- marrow infiltration / replacement disorders, such as leukemia, lymphoma, metastasis, etc may be missed; stress injuries, such as, stress response / transient osteoporosis / trabecular and subchondral fractures may not be apparent.
- Radiation- ALARA (as low as reasonably achievable) principal should be followed to the extent possible. Pediatric dose should be limited to 120 KVp.
MRI is a significant advance in the arena of MSK imaging for the diagnosis and treatment of a whole host of bone, joint and soft tissue pathologies. MRI scans are obtained by exciting patient’s body protons in the selected imaging field of view. Computer generates images from the signals received, as the protons go back to their relaxed state. Basically, T1-weighted (T1W) and T2-weighted (T2W) images are obtained. T1W images are useful for anatomy as fluid is dark (hypointense) and fat is markedly bright (hyperintense) on these images, thus beautifully outlining the other musculofascial structures. On T2W images, both fluid and fat are bright. Therefore, fat suppressed T2W (fsT2W) imaging is critical in MSK MRI for best detection of pathology. fsT2W images are extremely fluid sensitive and are useful for detection of abnormality because most of the pathologies lead to abnormal T2 hyperintensity. Gadolinium enhanced fsT1W scans should be obtained in suspected infections, inflammatory / infectious arthritis or tumors to look for abnormal enhancement. With the availability of new high field scanners (1.5-3 Tesla), better coil designs and novel imaging sequences, high resolution and superb soft tissue contrast imaging can be obtained enabling exquisite detailed evaluation of the labro-ligamentous and articular cartilage anatomy. 3D MRI with isotropic resolution is now possible allowing multiplanar image reconstruction and evaluation similar to MDCT imaging.
- Trauma- For evaluation of spinal cord compression, muscle, tendon, meniscal, chondral and labral injuries. Peripheral nerve entrapment and injuries. Enhanced scans for suspected vascular injuries.
- Infection- Optimal modality for the assessment of soft tissue extent including sinus tract, fistula and abscess, joint involvement, foreign body, devitalized soft tissue and sequestrum.
- Tumors- Optimal modality for the assessment of extent of tumor including bone marrow, soft tissue, neurovascular and joint involvement; blood-fluid levels in aneurysmal bone cyst; vascular malformation and hemangioma; fat containing lesions showing complete or partial suppression on fsT2W images, such as lipoma, liposclerosing myxofibrous tumor, lipoblastoma or liposarcoma; cartilaginous lesions, such as enchondroma, chondrosarcoma and; satellite lesions / epiphyseal involvement in osteosarcoma and ewing’s sarcoma; chest wall involvement in pancoast tumors; hemosiderin in giant cell tumor of tendon sheath; differentiation of cystic versus solid lesions, such as ganglion versus sarcoma and indolent versus malignant appearing bone lesions by excluding associated bone marrow edema, cortical invasion and soft tissue mass.
- Arthritis- As an adjunct to conventional radiographs for diagnosis; early detection of inflammatory / infectious arthritis, early identification of articular cartilage abnormality in osteoarthritis, specific diagnostic features of T2 hypointensity seen with hemosiderin deposition in pigmented villonodular synovitis and hemophilia, detection of synovial chondromatosis, loose bodies and, follow-up for treatment response and prognosis.
- Marrow Disorders- Best assessed due to excellent soft tissue contrast and available fat suppression, thus enhancing marrow pathology. MRI is more sensitive than radiographs and more specific than nuclear scans for these pathologies. Red marrow reconversion, marrow infiltration by malignancy, infection, edema due to stress injuries and subchondral fractures and avascular necrosis is easily identified.
- Kinematic joint studies- For distal radioulnar joints subluxation, patellofemoral maltracking disorders and spine flexion-extension studies. Advantage over CT includes additional assessment of ligamentous structures and lack of radiation. Disadvantage includes- longer acquisition time and suboptimal bone resolution.
- MR guided procedures- Currently being explored for spine injections, perineural injections and facet blocks as an alternative to fluoroscopic guidance. Currently not many centers are performing such procedures.
Pitfalls and Disadvantages
- Small cortical and periosteal lesions may not be identified due to lack of appreciable signal abnormality and associated bone marrow edema.
- Intralesional mineralization is hard to identify as compared to radiographs and CT.
- Patients may not tolerate MRI scans due to longer imaging time, claustrophobia, etc and motion artifacts may degrade imaging.
US is a very useful modality due to its non-invasiveness, portability, free-hand imaging, low cost and no radiation risk. High-resolution imaging is possible with new scanners and available high frequency US probes between 7.5 and 12 MHz. US frequencies lower and higher required for deep and very superficial structures, respectively. Transducers with a small footprint should be used in assessing smaller structures, (e.g., interphalangeal joints).
- Trauma- For evaluation of soft tissue hematoma, muscle and tendon injuries (especially full thickness tears), hemarthrosis, peripheral nerve entrapment and injuries. Perform doppler scans for suspected vascular injuries.
- Infection- Good modality for the assessment of soft tissue extent including sinus tract, fistula and abscess, joint involvement and foreign body.
- Tumors- Good modality for evaluation of solid (complex echotexture and shows Doppler flow) versus cystic mass (anechoic or sometimes complex but with no Doppler flow) and vascular malformations (show Doppler flow).
- Arthritis- As an adjunct to conventional radiographs for diagnosis; early detection of inflammatory / infectious arthritis, tenosynovitis and joint effusions.
- US guided procedures- Easy to perform with free hand or probe guide techniques for soft tissue lesion biopsies, ganglion or cyst aspiration, joint injections, bursal injections and treatment of patellar tendinitis, medial and lateral epicondylitits.
Pitfalls and Disadvantages
- Isoechoic soft tissue mass lesions may be missed. Most of the times, bony lesions are not picked up.
- Partial rotator cuss tears versus tendinosis may not be distinguished. MRI superseded US in evaluation of internal joint derangement.
- Operator dependent as compared to CT and MRI.
Bone scintigraphy is a highly sensitive method for demonstrating bone disease, often providing earlier diagnosis or demonstrating more lesions than are found by conventional radiographs. Methylene diphophonate can be labelled with a radionuclide tracer Technetium 99m (Tc 99m MDP) and is used for bone imaging because of their good localisation in the skeleton and rapid clearance from soft tissues. Bone scintigraphy images the distribution of a radioactive tracer in the skeletal system. Most bone forming / inflammatory / infectious / traumatic / tumor lesions are seen as increased uptake / hot on the scans. Non-bone forming lesions (myeloma) / transudates (simple ascites/pleural effusion) are cold on bone scans.
Bone scan may be performed as:
- Limited bone scintigraphy (planar images of a selected area of body); for specific clinical needs/ clarify abnormality seen on other imaging study.
- Whole-body bone scintigraphy (planar images of the entire skeleton; in anterior and posterior views); most commonly performed for oncology.
- SPECT or SPECT-CT (tomographic image of a portion of the skeleton without or with a localized CT scan); to increased specificity and diagnostic accuracy for a localized lesion in question, such as spondylosis.
- Multiphasic bone scintigraphy (angiographic, blood pool and delayed images to study blood flow and tracer retention characteristics). For trauma, inflammation, infection and complex regional pain syndrome.
- Trauma- For evaluation of stress fracture (focal trnasverse uptake on all three phases) versus shin splints (linear uptake along the periosteum on delayed phase imaging). Evaluation of complex regional pain syndrome (increased uptake on delayed image with pronounced periarticular uptake).
- Infection- Pronounced uptake on all three phases. Gallium 67 scan is good for detection of chronic infections, tumors and spine osteomyelitis; while Indium 111 labeled WBC scan is good for acute infections, and for suspected prosthesis infection evaluation.
- Tumors- Most neoplastic bone lesions, including metastases and osteoid osteoma, demonstrate uptake with few exceptions, such as hemangioma, cyst, lipoma and myeloma. Tc99m MDP bone scan is also used for monitoring of treatment response for malignancy. In addition, I131 is useful for bone and soft tissue metastases from differentiated thyroid carcinoma. F18 PET scanning is useful for lytic metastases, while bone scan is more useful for blastic metastases.
- Arthritis- As an adjunct to conventional radiographs for diagnosis and for early detection of inflammatory / infectious arthritis.
- Metabolic bone disease- Look for insufficiency fractures as areas of increased tracer uptake in osteopororsis, osteomalacia and hyperparathyroidism. Look for typical features of long areas of uptake with expansion in paget’s disease and fibrous dysplasia.
- Therapeutic procedures- Radionuclides, such as samarium-153 or strontium-89 may be used for short-term treatment of bone pain from lesions demonstrating increased uptake on bone scan. The pain relief may last as long as 6 months.
Pitfalls and Disadvantages
- Nuclear scans are very sensitive but often non-specific. A wide array of soft tissue inflammatory, infectious and neoplastic pathologies also take up Tc99m MDP. Specificity now somewhat improved with SPECT-CT imaging.
- Spatial resolution is limited as compared to CT and MRI. MRI has surpassed bone scan for evaluation of early osteonecrosis.
- Long imaging and waiting times for the patients. Associated radiation risk.
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2. Ahn JM, El-Khoury GY. Role of magnetic resonance imaging in musculoskeletal trauma. Top Magn Reson Imaging. 2007 Jun;18(3):155-68.
3. Resnick D, Kransdorf MJ, Bone and Joint Imaging. Elsevier Saunders. 2005.p78-136.
4. Finnoff JT, Smith J, Nutz DJ, Grogg BE. A musculoskeletal ultrasound course for physical medicine and rehabilitation residents. Am J Phys Med Rehabil. 2010 Jan;89(1):56-69.
5. Vijayanathan S, Butt S, Gnanasegaran G, Groves AM. Advantages and limitations of imaging the musculoskeletal system by conventional radiological, radionuclide, and hybrid modalities. Semin Nucl Med. 2009 Nov;39(6):357-68.
MAGID’S 10 COMMANDMENTS for pragmatic MSK Imaging:
1)LOCALIZE WITH ONE FINGER: as The X-Files said, ‘Trust No One Believe No One’
2)CONE AND CENTER: true area of interest gets center stage
3)ONE VIEW IS NO VIEW: again as per X-Files, “The Truth is Out There”
4)CLINICIAN, COMMUNICATE WITH RADIOLOGY:
5)EMBRACE PRECISE DESCRIPTION : “Telephone Model” of linguistic precision that allows recipient to draw findings; “Describe First, Diagnos Second” for consistency
6)VERITABLE WITNESS ONLY: no assumptions about unseen areas, no leaps of faith; describe only what is seen, acknowledge limits/unseen (if asked what color a cardboard carton is, one would say ‘The side facing me is beige”, not “It is beige”—see the difference in literal precision and avoidance of over-inclusion or assumptions?)
7)PURGE (most) ‘DEAD WHITE GUYS’, SLANG, and MALLBONICS from medical speech. Medical linguistics is both art and skill. Adieu, ‘Colles/Bennett/Kienbock’ fractures, ‘chip’ fractures, “sorta”, “near”, “Um…like..”.
8)TREAT PATIENTS NOT RADIOGRAPHS. Follow-up 10-14 days if hx/exam/gut suggestTreat presumptively and conservatively if pt. worse than radiograph.
9)LEND NO FOOTHOLD TO LAWYERS. X-File fans, “Fight The Future”. Whether in a radiographic report, medical note, or verbal communication, learn what phrasing to avoid, how to express degree of certainty/doubt, and avoid ‘always/never’—always!!
10)DISTINGUISH BETWEEN INVISIBLE ENERGY (‘x-rays’) and VISIBLE IMAGES (ie radiographs, studies, views, films…)
Chapter above excerpted from drafts (Magid, Chhabra) for Oxford University Press, Handbook of Radiology, MSK Imaging.