Musculoskeletal Imaging

Fracture Healing ( Fig. 5.1 )

Phases of healing:

• Inflammatory phase

  • Torn periosteum

  • Blood clots in fracture line

  • Inflammatory reaction

• Reparative phase

  • Granulation tissue replaces clot.

  • Periosteum forms immature callus.

  • Internal callus forms within granulation tissue.

  • Cartilage forms around fracture.

• Remodeling phase

  • Woven bone in callus is replaced by compact bone (cortex) and cancellous bone (medullary cavity).

Terminology for Description of Fractures

• Anatomic site of fracture

  • In long bones, divide the shaft into thirds (e.g., fracture distal third of femur).

  • Use anatomic landmarks for description (e.g., fracture near greater tuberosity).

• Pattern of fracture

  • Simple fracture: no fragments. Describe the direction of the fracture line: transverse, oblique, spiral, longitudinal

  • Comminuted fracture (more than two fragments): T-, V-, Y-shaped patterns, butterfly fragments, segmental

  • Complete or incomplete fractures

• Apposition and alignment: defined in relation to distal fragments

  • Displacement (e.g., medial, lateral, posterior, anterior)

  • Angulation (e.g., medial, lateral, posterior, anterior)

  • Rotation (internal, external)

  • Overriding: overlap of fragments (bayonet apposition)

  • Distracted: separated fragments

• Adjacent joints

  • Normal

  • Dislocation

  • Subluxation

  • Intraarticular extension of fracture line

Specific Fractures

• Stress fractures:

  • Fatigue fracture: abnormal muscular stress applied to normal bone (e.g., march fracture)

  • Insufficiency fracture: normal muscular stress applied to abnormal bone (e.g., osteoporotic vertebral fracture)

• Pathologic fracture: fracture superimposed on underlying bone disease

• Intraarticular fracture: fracture line extends into joint

• Salter-Harris fracture: fractures involving growth plate

• Pseudofracture: fissure like defects in osteomalacia (Looser zones)

• Occult fracture: suspected but nonvisualized fracture on plain radiograph; demonstrated by ^99m technetium (Tc) methylene diphosphonate (MDP) scintigraphy or magnetic resonance imaging (MRI)

• Hairline fracture: nondisplaced fracture with minimal separation

• Avulsion fracture: fragment pulled away from bone at tendinous and ligament insertion (commonly at tuberosity)

• Apophyseal fracture: at growth centers such as ischial tuberosity and medial epicondyle; commonly avulsion fractures

Long Bones

• Epiphysis

• Metaphysis

• Diaphysis

Types of Joints

• Synovial joint (diarthrosis)

  • Appendicular skeleton

  • Facet joints of spine

  • Atlantoaxial joints

  • Lower two-thirds of sacroiliac (SI) joints

  • Acromioclavicular (AC) joint

  • Uncovertebral joints

• Cartilaginous joint (amphiarthrosis)

  • Synchondroses (temporary: physis; permanent: ribs, first sternocostal joint)

  • Pubic symphysis

  • Intervertebral disks

• Fibrous joint (synarthrosis)

  • Tibiofibular and radioulnar syndesmosis

  • Cranial sutures

  • Gomphoses (dentoalveolar joints)

  • Superior portions of SI joints

Synovial Joint ( Fig. 5.3 )

In contradistinction to fibrous and cartilaginous joints, synovial joints allow wide ranges of motion and are classified according to axes of movement. The articular cartilage is hyaline. The most superficial layer has collagen fibrils parallel to the surface with microscopic pores to allow passage of electrolytes. This is also referred to as the armor plate. Deeper in the cartilage, collagen fibrils are arranged in arcades to give flexibility and allow for compression. Proteoglycans within the cartilage bind water to give a cushion effect.

Cartilaginous Joint

Cartilaginous joints are covered with fibrocartilage, and allow for limited range of motion. There is no synovial lining and there is often a central disk.

Fibrous Joint

Fibrous joints are the strongest joints, allowing almost no motion. Fibrous tissue is between bones.

Types of Repair

• Reduction

  • Closed: skin intact; may be performed in surgery under general anesthesia

  • Open: requires exposing the fracture site in surgery

• Fixation

  • Internal: using fixation devices such as plates, screws, rods; a subsequent operation is usually necessary to remove hardware.

  • External: cast or external fixator

Orthopedic Hardware

• Intramedullary rods: most of the intramedullary rods are hollow, closed nails; proximal and distal interlocking screws prevent rotation and shortening of bone fragments.

• Kirschner wires (K-wires): unthreaded segments of wires drilled into cancellous bone; if more than one wire is placed, rotational stability can be achieved; the protruding ends of the K-wire are bent to prevent injury; K-wires are most frequently used for:

  • Provisional fixation

  • Fixation of small fragments

  • Pediatric metaphyseal fractures

• Cerclage wires are used to contain bone fragments.

• Staples are commonly used for osteotomies.

• Plates

• Nails

• Screws

Biomechanics ( Figs. 5.4–5.5 )

Pearls

• 20% of spinal fractures are multiple.

• 5% of spinal fractures are at discontinuous levels.

• Spinal cord injury occurs:

  • At time of trauma, 85%

  • As a late complication, 15%

• Cause of spinal fractures

  • Motor vehicle accident (MVA), 50%

  • Falls, 25%

  • Sports related, 10%

• Most spinal fractures occur in upper (C1–C2) or lower (C5–C7) cervical spine and thoracolumbar (T10–L2) region.

Radiographic Features

• Key radiographic view: anteroposterior (AP) open-mouth

• Displacement of C1 lateral masses

  • <2 mm bilateral is always abnormal in adults.

  • <1–2 mm or unilateral displacement can be due to head tilt/rotation.

• CT required for:

  • Defining full extent of fracture

  • Detecting fragments in spinal cord

Radiographic Features

• Anterior tilt of odontoid on lateral view is highly suggestive of fracture.

• Plain radiograph tomograms or CT with reformations are helpful to delineate fracture line.

• Prevertebral soft tissue swelling (may be the only sign)

• Os odontoideum (type II)

  • Congenital or posttraumatic

  • May be mechanically unstable

• Os terminale (type I)

• Ossification center that normally fuses by age 12, but may remain persist unfused simulating a type I dens fracture.

Causes

• Hanging

• MVA (chin hits dashboard)

Radiographic Features

• Best demonstrated on lateral view

• Bilateral C2 pars (common) or pedicle (less common) fractures

• Anterior dislocation or subluxation of C2 vertebral body

• Avulsion of anterior inferior corner of C2 (ruptured anterior longitudinal ligament)

• Prevertebral soft tissue swelling

Radiographic Features ( Fig. 5.11 )

• Teardrop fragment is major shear fragment from anteroinferior vertebral body.

• All ligaments are disrupted.

• Posterior subluxation of vertebral body

• Bilateral subluxated or dislocated facets

• Severe compromise of spinal canal secondary to subluxation of body and facets

• Not to be confused with:

  • Extension teardrop fracture (stable avulsive injury)

  • Burst fracture (stable comminuted fracture of centrum with variable neurologic involvement)

Radiographic Features

• Fracture through spinous process, best seen on lateral view

• If C6–C7 is not demonstrated on lateral view, obtain swimmer's view and/or CT.

• AP view: ghost sign (double-spinous process on C6–C7 caused by caudal displacement of the fractured tip of the spinous process)

Radiographic Features

• Loss of height of anterior vertebral body

• Buckled anterior cortex

• Anterosuperior fracture of vertebral body

• Differentiate from burst fracture

  • Lack of vertical fracture component

  • Posterior cortex intact

Radiographic Features

• Teardrop fragment: avulsion by the anterior longitudinal ligament

• Vertical height of fragment ≥ horizontal width

  • Do not confuse with limbus vertebra, which are a result of herniation of the nucleus pulposus through the endplate beneath the ring apophysis. Appear well corticated.

Radiographic Features

• Complete anterior dislocation of the affected vertebral body by half or more of the vertebral body AP diameter

• Batwing or bowtie configuration of locked facets

• Disruption of posterior ligament complex, intervertebral disk, and anterior longitudinal ligament

Radiographic Features

• Anterior dislocation of vertebral body less than half the AP diameter of the vertebral body

• Evidence of discordant rotation above and below involved level

• Disrupted “shingles-on-a-roof” on oblique view

• Facet within intervertebral foramen on oblique view

• Disrupted posterior ligament complex

• Best demonstrated on lateral and oblique views

Radiographic Features

• Localized kyphotic angulation

• Widened interspinous/interlaminar distance (fanning)

• Posterior widening of disk space

• Subluxation at facet joints

• Anterior vertebral body may be displaced.

• In equivocal findings, voluntary flexion/extension views are helpful.

Radiographic Features

• Mild anterior vertebral displacement

• Comminuted articular mass fracture

• Contralateral facet subluxation

• Disrupted anterior longitudinal ligament and partial posterior ligamentous disruption

Radiographic Features

• Prevertebral soft tissue swelling; a gap of more than 5 mm between the occipital condyles and the condylar surface of the atlas is highly suggestive of craniocervical injury.

• Wackenheim clivus line: a line drawn along the posterior aspect of the clivus toward the odontoid process. An abnormality is suspected when this line does not intersect or is tangential to the odontoid process.

• The traditional methods used to identify occipitoatlantal articulation injury included the power ratio (X/Y, see Fig. 5.17 ) and the “X” line of Lee. Each is dependent on identifying the opisthion and the spinolaminar line of C1. Anatomic variation and inconsistent visualization preclude consistent use of these methods.

• The current method uses the basion-axial interval (BAI) and is an easy and reliable method for assessing the occipitoatlantal relationship in patients of all ages. BAI is the distance between the basion and upward extension of the posterior axial line. Normally the BAI should not exceed 12 mm as determined on a lateral radiograph of the cervicocranium obtained at a target radiograph distance of 1 meter.

• The vertical basion-dens distance should also be <12 mm.

• Anterior dissociation is more common.

• Posterior dissociation (subluxation) can be very subtle, especially if partial.

In atlantoaxial fixation ( Fig. 5.18 ), the normal rotation of C1 on C2 cannot occur and the abnormal relationship between the atlas and the axis becomes fixed. Fielding and Hawkins have classified atlantoaxial rotatory subluxation into four categories:

• Type I, the most common type, demonstrates no displacement of C1.

• Type II demonstrates 3–5 mm of anterior displacement of C1 and is associated with abnormality of the transverse ligament.

• Type III demonstrates over 5 mm of anterior displacement of C1 on C2 and is associated with deficiency of the transverse and alar ligaments.

• Type IV, a rare entity, demonstrates C1 displacement posteriorly.

• Occipital condyle fracture ( Fig. 5.19 )

  • Often requires CT for diagnosis (coronal views). May involve the hypoglossal canal or jugular foramen.

  • Unstable if avulsion of the alar ligament attachment site.

  

• Longus colli muscle calcific tendinopathy ( Fig. 5.20 )

  • Calcium hydroxyapatite deposition leads to an inflammatory response.

  • Lateral C-spine view or CT shows amorphous calcification of the longus colli muscle tendons at the level C1–C2, often with small retropharyneal/prevertebral effusion.

  • Do not mistake for retropharyngeal abscess or trauma.

  

Radiographic Features

• Widened interpedicular distance

• Paraspinal hematoma

• Unstable fractures:

  • Compression fracture >50%

  • Widened interlaminar space

  • Disrupted posterior elements

  • All fracture-dislocations

Radiographic Features ( Fig. 5.22 )

• Separation of pars interarticularis

• Spondylolisthesis common in bilateral spondylolysis

• If patient looks to right, the left pars is visualized by X-ray.

• Oblique view is usually diagnostic.

• CT or single photon emission computed tomography (SPECT) may be helpful in confirming diagnosis.

Pure Orbital Blow-Out Fracture ( Fig. 5.26 )

Isolated fracture of the orbital floor or less commonly the medial wall; the orbital rim is intact. Mechanism: sudden increase in intraorbital pressure (e.g., baseball, fist).

Clinical Findings

• Diplopia on upward gaze (inferior rectus muscle entrapment)

• Enophthalmos (may be masked by edema)

Radiographic Features ( Figs. 5.27–5.28 )

• Displacement of bone fragments into maxillary sinus (trap door sign)

• Opacification of maxillary sinus (hematoma)

• Orbital emphysema

• Caldwell and Waters views best demonstrate fractures.

• Using CT, evaluate for muscle entrapment and orbital content herniation.

Impure Orbital Blow-Out Fracture

Associated with fracture of orbital rim and other facial fractures.

Orbital Blow-In Fracture

Impact to frontal bone causes blow-in of orbital roof. Associated with craniofacial fractures and frontal lobe contusion.

Radiographic Features

• Most fractures are transverse and are depressed or displaced.

• Dislocation of septal cartilage is diagnosed by occlusal view or CT.

• Anterior nasal spine fracture is best evaluated by occlusal view.

• Do not mistake sutures and nasociliary grooves for fractures.

Flail Mandible ( Fig. 5.31 A–B )

Symphysis fracture with bilateral subcondylar, angle, or ramus fracture. Tongue may prolapse and obstruct airway.

Simple Arch Fractures

Simple fractures of the zygomatic arch are less common than complex fractures. Fracture lines occur most commonly:

• Anteriorly at temporal process

• In midportion near zygomaticotemporal suture

• Posterior and anterior to condylar eminence

Complex Arch Fractures (Tripod Fracture)

• Diastasis of zygomaticofrontal suture

• Posterior zygomatic arch fracture

• Fracture of inferior orbital rim and lateral maxillary wall

Dentoalveolar Fracture

Fracture of the alveolar process of maxilla secondary to direct blow. May present clinically as loose teeth; managed as open fracture.

Sagittal Maxillary Fracture

Usually occurs with other injuries such as Le Fort fracture.

Le Fort Type I

This fracture produces a floating palate; fracture lines extend through:

• Nasal septum (vomer and septal cartilage)

• Medial, anterior, lateral, posterior walls of maxillary sinus

• Pterygoid plates of sphenoid

Le Fort Type II

This fracture produces a floating maxilla; zygomatic arches are not included in this fracture; fracture line extends through:

• Nasal bone and nasal septum

• Frontal process of maxilla

• Medial orbital wall (ethmoid, lacrimal, palatine)

• Floor of orbit (inferior orbital fissure and canal)

• Infraorbital rim

• Anterior, lateral, posterior wall of maxillary sinus

• Pterygoid plates of sphenoid

Le Fort Type III

This fracture separates face from cranial vault and produces a floating face; the fracture line extends through:

• Nasal bone and septum

• Frontal process of maxilla

• Medial wall of orbit (lacrimal, ethmoid, palatine)

• Infraorbital fissure

• Lateral wall of orbit

• Zygomaticofrontal suture

• Zygomatic arch

• Pterygoid plates of sphenoid

Complications

• Laceration of vessels

• Nerve injuries

• Other associated fractures

Do not mistake rhomboid fossa (irregular concavity at the undersurface of the medial clavicle), a normal anatomic variant, for a fracture or lytic lesion.

Anterior Dislocation ( Fig. 5.39 )

Most common type (95%) of dislocation. Usually caused by indirect force from abduction, external rotation, and extension.

Radiographic Features

• Humeral head lies inferior and medial to glenoid.

• Two lesions can occur as humeral head strikes the glenoid:

  • Hill-Sachs lesion (posterosuperior and lateral) of humeral head (best seen on AP view with internal rotation) and bony Bankart lesion (anteroinferior) of glenoid (may require CT)

• Bulbous distortion of the scapulohumeral arch (Moloney arch)

• Tear of the inferior glenohumeral ligament (IGHL) from its humeral attachment = humeral avulsion of the glenohumeral ligament (HAGL) lesion

• Associated labral tears ( Fig. 5.40 ):

  • Abduction and external rotation (ABER) view: stretches the IGHL, improves detection of anterior-inferior labral tears.

  • Bankart lesion: complete detachment of anterior inferior labrum and often IGHL or middle glenohumeral ligament (MGHL)

  • Perthes lesion: labral tear with periosteal stripping, labrum remains attached to periosteum

  • Anterior labral periosteal sleeve avulsion (ALPSA): basically a medially displaced Perthes lesion, labrum remains attached to periosteum

  • Glenolabral articular disruption (GLAD), superficial labral tear with glenoid cartilage injury. In contrast to the above labral tears, it is not associated with shoulder instability.

  

Posterior Dislocation ( Fig. 5.41 )

• Less common (5%); usually caused by direct or indirect force (fall on flexed and abducted arm). Associated with seizures or electrical shock (bilateral).

• Lightbulb sign: appearance of the internally rotated humeral head on AP radiograph

• Bennett lesion: rim of calcification along posterior glenoid, associated with posterior capsule avulsive injury (baseball pitchers or other overhead throwing athletes)

Radiographic Features

• Humeral head lies superior to glenoid.

• Trough sign: compression fracture of the anterior humeral surface, 15% (best seen on AP view with external rotation or axillary view)

• Sharp angle of the scapulohumeral arch (Moloney arch)

• Posterior displacement is best seen on axillary view.

• 40-degree posterior oblique (Grashey view) may be needed: loss of glenohumeral space is diagnostic.

• Fixed in internal rotation

Inferior Dislocation

Also called luxatio erecta: the humeral head is located below the glenoid and the shaft of the humerus is fixed in extreme abduction. Complications of luxatio erecta include injuries to the brachial plexus and axillary artery.

Causes

• Degeneration

• Trauma

• Impingement

Radiographic Features

• Narrowing of acromiohumeral space to <6 mm (chronic rupture)

• Eroded inferior aspect of acromion (chronic rupture)

• Flattening and atrophy of the greater tuberosity of the humeral head (chronic rupture)

  • Acromial undersurface contour, Bigliani classification (assessed on sagittal oblique MR, type 3 strongly associated with rotator cuff impingement) ( Fig. 5.44 ):

    • Type 1: flat

    • Type 2: concave, without subacromial space narrowing

    • Type 3: acute inferior downslope (hooked) with narrowing.

    • Type 4: convex

    

• Arthrogram

  • Opacification of subacromial-subdeltoid bursa

  • Contrast may leak into the cuff in partial tears

• MRI features:

  • MR arthrography is most accurate diagnostic study

  • MR can distinguish full thickness (perforating tear, part of the tendon is intact) from complete (complete tendon interruption) tears.

  • Full-thickness tears are often associated with fluid in the subacromial/subdeltoid bursa.

  • Partial-thickness tears may be articular surface, bursal surface, or intrasubstance tears.

  • High-grade partial thickness tears >50%

  • Tendon retraction should be reported because retraction >3–4 cm reduces potential for surgical repair.

  • Fatty atrophy of a rotator cuff muscle indicates chronic tear.

  • Medial dislocation/subluxation of the biceps from the intertubercular groove indicates subscapularis tear

Radiographic Features

• Decreased size of joint capsule

• Obliteration of axillary and subscapular recesses

• Disuse osteoporosis

• Arthrogram if persistent

Radiographic Features

• Technique

  • AP view with 15 degree cephalad angulation is the preferred view for diagnosis.

  • May need opposite shoulder for comparison

  • May need stress views (2- to 10-kg weights)

• Normal

  • AC distance ≤8 mm

  • Coracoclavicular distance ≤13 mm

  • Inferior margin of clavicle lines up with inferior acromion.

• AC joint injury

  • Downward displacement of scapula/extremity

  • Downward displacement and AC separation worsen with stress weights.

  • AC widening = disrupted AC ligament

  • Craniocaudad (CC) widening because of disrupted AC ligament

• Six grade classifications (Rockwood):

  • Grade I (mild sprain): normal radiograph

  • Grade II (moderate sprain): increased AC distance; normal CC distance

  • Grade III (severe sprain): increased AC and CC distance

  • Grade IV: total dislocation; clavicle displaced superoposteriorly into the trapezius

  • Grade V: total dislocation; clavicle displaced superiorly into neck

  • Grade VI: total dislocation; clavicle displaced interiorly to subacromial or subcoracoid position

Radiographic Features

• Superior displacement of clavicle

• Many injuries occur as Salter fractures of medial clavicular epiphysis.

• CT is the examination of choice: thin section with coronal reformation.

• Angled AP plain radiograph (serendipity view) is not as helpful.

Four-Segment Neer Classification ( Fig. 5.47 )

Based on number and type of displaced segments. 4 segments: anatomic neck, surgical neck, greater tuberosity, lesser tuberosity. Displacement defined as (1) >1 cm separation of fragments or (2) >45-degree angulation.

• 1-part: no displacement (regardless of comminution); treated with sling

• 2-part: displacement of 1 segment; closed reduction

• 3-part: displacement of 2 segments, 1 tuberosity remains in continuity with the head; closed reduction

• 4-part: displacement of 3 segments; open reduction and internal fixation or humeral head replacement

• 2-, 3-, and 4-part fractures may have anterior or posterior dislocation.

Radiographic Features

• Fracture lines according to Neer classification

• Pseudosubluxation: inferior displacement of humeral head because of hemarthrosis

• Subacromial fat-fluid level: lipohemarthrosis

• Transthoracic or transscapular views useful to accurately determine angulation

Classification

• Supracondylar-extraarticular fracture (three types)

  • Type I: nondisplaced

  • Type II: displaced with posterior cortical continuity

  • Type III: totally displaced

• Transcondylar-intraarticular fracture

• Intercondylar (bicondylar)-intraarticular fracture (four types)

  • Type I: nondisplaced

  • Type II: displaced

  • Type III: displaced and rotated

  • Type IV: displaced and rotated and comminuted

Complications

• Volkmann ischemic contracture (usually secondary to supracondylar fracture)

• Malunion (results in “cubitus varus” deformity)

Treatment

• No displacement: splint, cast

• >3-mm displacement on lateral view: open reduction and internal fixation (ORIF)

• Comminuted: excision of radial head

Radiographic Features ( Fig. 5.50 )

• Positive fat pad sign

  • Anterior fat pad has the appearance of a sail (sail sign).

  • A positive posterior fat pad is a good indicator of a fracture that is not normally seen.

• Fracture line may be difficult to see on standard projections. If in doubt, obtain radial head view, oblique views, or tomograms.

Olecranon Fracture

Result from direct fall on flexed elbow. Treated conservatively if nondisplaced. ORIF if displaced (by pull of triceps). Best view: lateral.

Coronoid Fracture

Usually in association with posterior elbow dislocations. Best view: radial head or oblique views.

Monteggia Fracture-Dislocation

Ulnar shaft fracture and radial head dislocation

Galeazzi Fracture-Dislocation

Distal radial shaft fracture and distal radioulnar dislocation

Essex-Lopresti Fracture-Dislocation

Comminuted radial head fracture and distal radioulnar subluxation/dislocation

Radiographic Features

• Extraarticular fracture (in contradistinction to Barton fracture)

• Distal radius is dorsally displaced/angulated.

• Ulnar styloid fracture, 50%

• Foreshortening of radius

• Impaction

Complications

• Median, ulnar nerve injury

• Posttraumatic radiocarpal arthritis

Barton Fracture

Intraarticular fracture of the dorsal margin of the distal radius. The carpus usually follows the distal fragment. Unstable fracture requiring ORIF and/or external fixation.

Smith Fracture

• Same as a Colles fracture except there is volar displacement and angulation of the distal fragment

• Three types

  • Type 1: horizontal fracture line

  • Type 2: oblique fracture line

  • Type 3: intraarticular oblique fracture = reverse Barton fracture

Reverse Barton Fracture (see Fig. 5.53 )

Intraarticular fracture of the volar aspect of the articular surface.

Chauffeur's (or Hutchinson) Fracture ( Fig. 5.54 )

Fracture of the styloid process. Either by direct blow to back of wrist (hand crank of old cars started by hand) or forced dorsiflexion and abduction. Often associated with scapholunate disassociation and ulnar styloid process fracture.

Elbow MRI Pearls

• Ulnar collateral ligament (UCL)

  • Three components: anterior (most important), posterior, and transverse bands

  • UCL tear = baseball pitcher injury. Anterior band attaches to sublime tubercle of medial epicondyle and lies deep to common flexor tendon of elbow. Posterior band attaches to lateral aspect of ulna at supinator crest. MRI: T1 globular signal, increased T2 signal.

• Radial collateral ligament complex

  • Four components: annular (torn with elbow dislocation), radial collateral, lateral ulnar collateral ligament (LUCL, most important), and accessory collateral ligaments

• Common extensor tendon originates from lateral epicondyle (repetitive varus stress leads to lateral epicondylitis or tennis elbow, often associated with LUCL injury)

• Common flexor tendon originates from medial epicondyle (repetitive valgus stress leads to medial epicondylitis or golfer's elbow)

• Avascular necrosis (AVN) of capitellum: Panner disease, occurs in boys 7–12 years of age before complete capitellar ossification.

• Osteochondral defect (OCD) of capitellum: caused by repetitive valgus stress in young competitive athletes (12–16 years), most often involves anterior capitellum (do not mistake for normal “pseudodefect” that is caused by sharp angulation of posterior capitellum)

Ulnar Variance

• Neutral ulnar variance (normal) 80% load by radius, 20% by ulna

• Negative ulnar variance (abnormal). Associated with Kienböck disease

• Positive ulnar variance (abnormal). Associated with:

  • Scapholunate instability

  • Ulnar impaction syndrome

  • Triangular fibrocartilage tear

  • Previous radial head excision

  • Aging

Standard radiographic assessment to quantify deformities associated with distal radius fractures should also consist of three radiographic measurements, which correlate with patient outcome:

• Radial length (radial height): on posteroanterior (PA) view, distance between line perpendicular to the long axis of the radius passing through the distal tip of the sigmoid notch at the distal ulnar articular surface of the radius and a second line at the distal tip of the radial styloid. This measurement is normally 10–13 mm. A shortening of >3 mm is usually symptomatic and leads to positive ulnar variance.

• Radial inclination (radial angle): on PA view, angle between line connecting the radial styloid tip and the ulnar aspect of the distal radius and a second line perpendicular to the longitudinal axis of the radius. The normal radial inclination ranges between 21 and 25 degrees. Loss of radial inclination increases load across the lunate.

• Volar tilt of the distal radius (palmar tilt): on lateral view, the angle between a line along the distal radial articular surface and the line perpendicular to the longitudinal axis of the radius at the joint margin. The normal volar tilt averages 11 degrees and has a range of 2 to 20 degrees. Dorsal intercalated segment instability (DISI) (see later) may result from an angle >25 degrees.

Radiographic Features

• Fracture may be difficult to detect on plain radiograph.

• Scaphoid views (PA view in ulnar deviation) may be useful to demonstrate fracture.

• Loss of navicular fat stripe on PA view.

• If a fracture is clinically suspected but not radiographically detected, use multidetector CT. In the absence of multidetector CT and high-quality reformations, thin-section CT may be performed along the coronal and sagittal axes of the scaphoid:

  • Coronal position is obtained by placing the patient prone, with elbow flexed 90 degrees and hand placed ulnar side down above the patient's head; images are acquired parallel to the dorsum of the wrist. Alternatively, with the palm side down, the hand and wrist are elevated 30–45 degrees and images acquired parallel to the dorsal aspect of the scaphoid.

  • Long sagittal position can be obtained by placing wrist palm down with hand, wrist, and forearm at 45-degree angle to the long axis of the CT table. Anatomically, this alignment can be recognized by identifying the base of the thumb and the hard bone prominence on the middle portion of the distal radius (Lister tubercle).

• Bone scan: highly sensitive; increased uptake may represent fracture, and decreased uptake proximally may represent possible AVN. Does not offer anatomic detail or distinguish marrow edema/bone bruise from fracture.

• MRI: highly sensitive to fractures and allows imaging of planes along the long and short axes of the scaphoid

• Cast and repeat plain radiographs in 1 week.

Prognosis

• Waist fracture: 90% heal eventually; 10% nonunion or proximal AVN

• Proximal fracture: high incidence of nonunion or AVN

• Distal fracture: usually heals without complications

Triquetrum

• Dorsal avulsion at attachment of radiocarpal ligament (most common type of fracture)

• Best seen on lateral view

Hamate

• • Hook of hamate fracture: diagnosis requires tomography, carpal tunnel view, or CT

  • Other fractures are usually part of complex fracture-dislocations.

    • Kienböck disease (lunatomalacia)

  • AVN of lunate secondary to (usually trivial) trauma

  • Associated with ulnar minus variant

  • Acute lunate fractures are rare.

    • Stahl classification (radiographs):

  • Stage 1: normal radiograph

  • Stage 2: increased lunar radiodensity

  • Stage 3: lunate collapse

  • Stage 4: degenerative changes around lunate

    • Preiser disease (scaphomalacia)

  • AVN of scaphoid secondary to (usually trivial) trauma without fracture, or drugs (e.g., steroids)

    • Type 1: complete, indicates poor outcome.

    • Type 2: partial, associated with better outcome.

    • Greater arc injury

  • Greater arc injuries extend through radial styloid and scaphoid across hamate, capitate, triquetrum, and ulnar styloid.

Lesser Arc Injury (Perilunate Injuries) ( Fig. 5.58 )

The continuum of perilunate injuries ranges from disassociation to dislocation. Mechanism: backward fall on extended hand. Each of the four successive stages progresses from radial to ulnar side with ligamentous injury around the lunate, and indicates increased carpal instability.

Scapholunate Dissociation (Stage 1) ( Fig. 5.59 )

• Rupture of scapholunate ligaments

• >3-mm gap between lunate and scaphoid (Terry-Thomas sign)

• Ring sign on PA view secondary to rotary subluxation of scaphoid

Perilunate Dislocation (Stage 2)

• Capitate dislocated dorsally, while the lunate maintains normal articulation with radius.

• Disruption of the capitolunate joint (often the radiocapitate ligament)

• May be accompanied by transscaphoid fracture, triquetrum fracture, capitate fracture, and radial styloid process fracture

Midcarpal Dislocation (Stage 3)

• Rupture of triquetrolunate ligament (or triquetrum fracture)

• Capitate and carpus are dislocated dorsally.

Lunate Dislocation (Stage 4)

• Lunate dislocates volarly.

• Disruption of the dorsal radiolunate ligament.

• Capitate appears aligned with the radius.

Carpal Instability ( Figs. 5.60–5.61 )

Most commonly caused by ligamentous injury of the proximal carpal row (trauma or arthritis). Best diagnosed by stress fluoroscopy and/or plain radiograph evaluation of the scapholunate and capitolunate relationships.

Scapholunate Dissociation

• Scapholunate angle >60 degrees

Volar Intercalated Segment Instability (VISI)

• Increased capitolunate angle

• Volar tilt of lunate

• Scapholunate angle sometimes decreased

• Much less common than DISI

Dorsal Intercalated Segment Instability

• Increased scapholunate and capitolunate angles

• Dorsal tilt of lunate

Bennett Fracture

• Dorsal and radial dislocation (force from abductor pollicis longus)

• Small fragment maintains articulation with trapezium.

Rolando Fracture

• Comminuted Bennett fracture; the fracture line may have a Y, V, or T configuration.

Baseball (Mallet) Finger

• Avulsion of extensor mechanism

• DIP flexion with or without avulsion fragment

Boutonnière (Buttonhole) Finger

• Avulsion of middle extensor slip at base of middle phalanx

• PIP flexion and DIP extension with or without avulsion fragment

Avulsion of Flexor Digitorum Profundus

• Avulsion at volar distal phalanx

• DIP cannot be flexed.

• Fragment may retract to PIP joint.

Volar Plate Fracture

• Avulsion at base of middle phalanx

• PIP hyperextension

• Nerve entrapment syndromes:

  • Carpal tunnel syndrome: most common nerve entrapment in the body, median nerve is compressed in the carpal tunnel. On US and MRI, enlargement of the median nerve >2 mm ² is seen in the carpal tunnel compared with at the level of the pronator quadratus. Contrast enhancement may be seen on MRI.

  • Guyon canal syndrome: rare, compression of ulnar nerve by space-occupying lesion in canal. Other causes: extrinsic compression (cyclist's arm), or thrombosis/aneurysm of superficial palmar branch of ulnar artery (hypothenar hammar syndrome)

Classification

• Stable fractures (single break of pelvic ring or peripheral fractures); more common

• Avulsion fractures

  • Anterior superior iliac spine: sartorius avulsion

  • Anterior inferior iliac spine: rectus femoris avulsion

  • Ischial tuberosity: hamstring avulsion

  • Pubis: adductor avulsion

• Other fractures

  • Duverney fracture of iliac wing

  • Sacral fractures

  • Fracture of ischiopubic rami: unilateral or bilateral

  • Wide-swept pelvis: external rotation (anterior compression) injury to one side and an internal rotation (lateral compression) injury to contralateral side

• Unstable fractures (pelvic ring interrupted in two places); less common. Significant risks of pelvic organ injury and hemorrhage. All unstable fractures require CT before fixation for more accurate evaluation; the extent of posterior ring disruption is often underestimated by plain radiograph.

  • Malgaigne fracture: SI joint (or paraarticular fracture) and ipsilateral ischiopubic ramus fracture. Clinically evident by shortening of the lower extremity.

  • Straddle: involves both obturator rings

  • Bucket-handle: SI fracture and contralateral ischiopubic ramus fracture

  • Dislocations

  • Pelvic ring disruptions and arterial injury

    • Sources of pelvic hemorrhage include arteries, veins, and osseous structures.

    • Arterial bleeding is usually from internal iliac artery branches. Frequency in descending order: gluteal, internal pudendal, lateral sacral, and obturator arteries.

High frequency of arterial hemorrhage in AP compression, vertical shear, crushed fracture of sacrum, and fractures extending into greater sciatic notch.

Classification (Letournel)

• Fracture of the anterior (iliopubic) column

• Fracture of the posterior (ilioischial) column

• Transverse fracture involving both columns

• Complex fracture: T-shaped, stellate

Classification

• Intracapsular fracture involving femoral head or neck

  • Capital: uncommon

  • Subcapital: common

  • Transcervical: uncommon

  • Basicervical: uncommon

• Extracapsular fracture involving the trochanters

  • Intertrochanteric

  • Subtrochanteric

Treatment

• Bed rest: incomplete fractures

• Knowles pin

• Endoprosthesis if high risk of AVN or nonunion

Complications

• AVN (in 10%–30% of subcapital fractures) occurs secondary to disruption of femoral circumflex arteries.

• Nonunion: obliquity of fracture influences prognosis (steep fractures have higher incidence of nonunion).

Treatment

• Internal fixation with dynamic compression screw

• Valgus osteotomy

Complications

• AVN is rare.

• Coxa vara deformity from failure of internal fixation

• Penetration of femoral head hardware as fragments collapse

• Arthritis

• Lesser trochanter avulsion fracture

  • Avulsion of iliopsoas in children and adolescents

  • In adults, isolated less trochanter fracture should raise suspicion for a pathologic fracture (metastatic disease)

Classification ( Fig. 5.76 )

• Posterior dislocation, 90%

  • Femoral head lateral and superior to the acetabulum

  • Femur internally rotated, greater trochanter in profile and lesser trochanter obscured on AP view

  • Posterior rim of acetabulum is usually fractured

  • Sciatic nerve injury, 10%

• Anterior dislocation, 10%

  • Femoral head displaced into the obturator, pubic, or iliac region

• Internal dislocation

  • Always associated with acetabular fracture

  • Femoral head protrudes into pelvic cavity

• Femoral stress fracture

  • Medial femoral neck proximal to lesser trochanter, linear sclerosis or periosteal bone formation can be seen radiographically. MRI is more sensitive and should be obtained if clinical suspicion is high.

  • Bisphosphonate therapy is associated with stress fractures of the lateral humeral shaft, look for linear sclerosis on radiographs.

• Femoroacetabular impingement ( Fig. 5.77 )

  • Impingement of acetabular labrum and cartilage between femoral head-neck junction and acetabular rim

  • Cam-type : more common, dysmorphic bulge/overgrowth at the anterolateral femoral head-neck junction

  • Pincer-type: less common, excessively deep acetabulum, look for cross-over sign (anterior acetabular margin projects lateral to posterior acetabular margin)

  • Associated with old developmental dysplasia of the hip (DDH) or Legg-calvé-perthes disease

  

• Morel-Lavallée lesion

  • Degloving injury commonly seen in the lateral proximal thigh and lower back

  • Subcutaneous fat is detached from muscle fascia

  • Potentially large, chronic, collections can develop

Classification

• Supracondylar

  • Nondisplaced

  • Displaced

  • Impacted

  • Comminute

• Condylar intercondylar

Classification (Müller) ( Fig. 5.78 )

• Type 1: split fracture of tibial condyle and proximal fibula (rare)

• Type 2: pure depression fracture of either plateau

• Type 3: combined types 1 and 2

• Type 4: comminuted fracture of both tibial condyles; lateral plateau is usually more severely damaged.

Radiographic Features

• Fractures of tibial plateau may not be obvious; plain radiographs often underestimate the true extent of fractures; therefore CT or tomography in AP and lateral projection is often necessary.

• Fat (marrow)-fluid (blood) interface sign (hemarthrosis) on cross-table lateral view

• Description of fractures:

  • Type of fracture: split, depression, etc.

  • Location: medial, lateral

  • Number of fragments

  • Displacement of fragments

  • Degree of depression

Complications

• Malunion (common)

• Secondary OA (common)

• Concomitant ligament and meniscus injuries (i.e., medial collateral ligament [MCL])

• Peroneal nerve injury

Radiographic Features

• Chondral fracture requires arthrography or MRI for visualization.

• Osteochondral fracture may be seen by plain radiograph.

Radiographic Features

• Earliest finding: joint effusion

• Radiolucent line separating osteochondral body from condyle (advanced stage)

• Normal ossification irregularity of posterior condyle may mimic osteochondritis dissecans.

• Best evaluated by MRI

Radiographic Features

• Plain radiographs can be unremarkable except for joint effusion.

• MRI is the imaging modality of choice and shows:

  • Hemarthrosis

  • Disruption or sprain of medial retinaculum

  • Lateral patellar tilt or subluxation

  • Bone contusions in lateral femoral condyle anteriorly and in medial facet of patella

  • Osteochondral injuries of patella

  • Associated injuries to ligaments and menisci in 30%

Types

• Vertical (longitudinal) tears; most commonly from acute trauma

• Horizontal tears (cleavage tears) in older patients: degenerative

• Oblique tears

• Bucket-handle: may become displaced or detached. There are characteristic signs by MRI: double posterior cruciate ligament (PCL) sign and flipped meniscus sign. The displaced fragment is typically seen within the intercondylar notch.

• Peripheral tear: meniscocapsular separation

• Truncated meniscus: resorbed or displaced fragment

MRI Grading of Tears ( Fig. 5.80 )

• Type 1: globular increased signal intensity, which does not communicate with articular surface. Pathology: mucinous, hyaline, or myxoid degeneration

• Type 2: linear increased signal intensity, which does not extend to articular surface. Pathology: collagen fragmentation with cleft formation

• Type 3: tapered apex of meniscus

• Type 4: blunted apex of meniscus

• Type 5: linear increased signal intensity, which extends to the articular surface. Pathology: tear

• Type 6: linear increased signal intensity, which extends to both articular surfaces

• Type 7: fragmented, comminuted meniscus

Pitfalls of Diagnosing Meniscal Tears by MRI ( Fig. 5.81 )

• Fibrillatory degeneration of the free concave edge of the meniscal surface is often missed by MRI because of volume averaging.

• Normal transverse ligament courses through Hoffa fat pad and may be mistaken for an anterior horn tear. The ligament connects the anterior horns of medial and lateral menisci.

• Postmeniscectomy meniscus may have linear signal extending to articular surface as a result of intrameniscal signal.

• Pseudotears

  • Lateral aspect of posterior horn of lateral meniscus (popliteus tendon); medial lateral meniscus (ligament)

Radiographic Features

• Plain radiographs may show avulsion fragment of intercondylar eminence.

• MRI is the study of choice for diagnosing ligamentous injury.

• PCL is larger than ACL and better seen by MRI.

• MRI is useful for the assessment of complications after ACL reconstruction, including the Cyclops lesion (focal fibrotic nodule in the intercondylar notch).

Radiographic Features ( Fig. 5.84 )

• MRI criteria of injury are similar to those used for ACL and PCL tears

• O'Donoghue triad (the “unhappy triad”) results from valgus stress with rotation:

  • ACL tear

  • MCL injury

  • Medial meniscal tear (lateral compartment bone bruise)

• Pelligrini-Steida lesion: curvilinear calcification or ossification at site of femoral attachment of MCL indicates old MCL injury.

Radiographic Features

• Acute tendinitis

  • Tendon enlargement

  • Fluid in synovial sheath (in tenosynovitis)

  • Abnormal MRI signal within tendon may indicate partial tear.

• Chronic tendinitis

  • Tendon thinning or thickening

  • Intratendon signal does not increase on T2W images.

Classification ( Fig. 5.86 )

Of the different classifications of injuries available, the Weber classification is the most useful. It uses the level of fibular fracture to determine the extent of injury to the tibiofibular ligament complex:

• Weber A (below tibiofibular syndesmosis)

  • Transverse fracture of lateral malleolus or rupture of LCL

  • Oblique fracture of medial malleolus

  • Tibiofibular ligament complex spared (stable)

  • Results from supination-adduction (inversion)

• Weber B (through tibiofibular syndesmosis)

  • Oblique or spiral fracture of lateral malleolus near the joint

  • Transverse fracture of medial malleolus or rupture of deltoid ligament

  • Partial disruption of tibiofibular ligament complex

  • Results from supination-lateral rotation or pronation-abduction

• Weber C (above tibiofibular syndesmosis)

  • Proximal fracture of fibula

  • Transverse fracture of medial malleolus or rupture of deltoid ligament

  • Rupture of tibiofibular ligament complex (lateral instability)

  • Results from pronation-lateral rotation

Approach

• 1

  Evaluate all three malleoli.

• 2

  Assess ankle mortise stability (3- to 4-mm space over entire talus).

• 3

  If an isolated medial malleolar injury is present, always look for proximal fibular fracture.

• 4

  Obtain MRI or arthrography for accurate evaluation of ligaments.

• 5

  Determine if the talar dome is intact.

Pilon Fracture ( Fig. 5.87 )

Supramalleolar fractures of distal tibia that extend into tibial plafond. Usually associated with fractures of distal fibula and/or disruption of distal tibiofibular syndesmosis. Mechanism is usually caused by vertical loading (e.g., in jumpers). Associated with intraarticular comminution. Complication: posttraumatic arthritis.

Tillaux Fracture ( Fig. 5.88 )

Avulsion of the lateral tibial margin. In children, the juvenile Tillaux fracture is a Salter-Harris type III because the medial growth plate fuses earlier.