Single synovial compartment including radius-humeral capitellum, ulna-humeral trochear and proximal radioulnar joints.
Imaging Techniques and Applications
- Lateral – Flexed at 90 deg to detect for effusion.
- Oblique radial head- For subtle fractures.
- Radial head-capitellar
- Cubital tunnel
- Stress for MCL instability
US for effusion
CT for complex fractures, intra-articular bodies, osteophytes, malaligment.
MRI usually in extension
- High resolution coronal for collateral ligaments
MR/CT arthrography for collateral ligament injury, chondral and osteochondral lesions
Radial neck aligns with capitellum on any view (radiocapitellar line). Anterior humeral line intersects middle 1/3 capitellum. Normal valgus (carrying angle) ~165 deg, increased in cubitus valgus, less in varus.
- Small normal pseudodefect/notch ulnar articular surface and dorsal capitellum.
- Os supratrochleare dorsale – In olecranon fossa, may cause impingement/pain in extension, identical to intra-articular loose body.
- Supracondylar process/avian spur – Rare bony protrusion anteromedial aspect distal humerus associated with ligament of Struthers connecting to medial humeral epicondyle, may entrap median nerve.
Distended joint capsule (effusion, haemarthrosis, pus, pannus, PVNS) causes displacement of olecranon fossa fat pad (posterior fat pad sign) or bulging of anterior fat pad (spinnaker sail or anterior fat pad sign). In adult trauma, effusion almost always indicates fracture, slightly less specific in children. Often fracture is not visualised (on XR, CT or MR) and treatment is identical as long as no obvious deformity or loose body present (hence no further tests required, unless infection or arthritide likely).
Supinator fat pad sign – Raised or obliterated supinator fat pad esp in radial head fracture.
Paediatric Elbow Fracture/Dislocation
Ossification order CRITOE (Capitellum, Radial head, Internal epicondyle, Trochlea, Olecranon, External epicondyle at ~1,3,5,7,9,11 yrs). 75% of those with effusion but no fracture seen have an occult fracture. Paediatric fractures usually FOOSH with hyperextension or valgus. Baumann’s angle (humeral capitellar angle) is between humeral shaft and capitellar physis (for predicting final carrying angle), normal 85-90deg; greater than this or difference >5deg from contralateral side results in residual varus deformity.
- Supracondylar fracture (>60% cf radial neck most common in adults) – Hyperextension FOOSH. Usually associated with joint effusion, posterior displacement relative to anterior humeral line (should bisect middle 1/3 of capitellum). 25% incomplete, subtle on XR. Gartland type I nondisplaced; II posterior displaced with intact posterior cortex; III posterior displaced with no cortical contact; IV anteriorly displaced.
- Lateral humeral condyle (20%) – Varus stress in extended elbow with avulsion-like fracture epidondyle, humeral physis ± metaphyseal fragment. May be true SH4 involving capitellar growth centre, incomplete involving physis and extending medial to capitellum, or complete through condylar cartilage to articular surface (potentially unstable requiring fixation, difficult to diagnose on XR and may need US/MRI/arthrography).
- Avulsion of medial epicondyle ossification centre (10%) – Valgus stress. Don’t usually see fracture line. May be acute with displacement or chronic stress from repetitive traction (litle leaguer’s elbow). Fragment displaced distally by MCL and flexor/pronator muscles, if >5mm may require fixation. May be entirely extra-articular hence no effusion.
- Medial epicondyle entrapment – Transient posterolateral dislocation during medial epicondylar avulsion, allowing fragment to entrap between trochlear and ulnar, preventing realignment. May simulate normal trochlear ossification (trochlear should never appear before medial epicondyle and is last to fuse). Fragment may fuse to ulnar within a few weeks causing disability.
- Little league elbow – Chronic repeditive traction (esp throwing athletes) with displacement, fragmentation or sclerosis of the medial epicondyle.
- Separation of the humeral condyles (fracture-separation of the entire distal humeral physis) – Medially or posteromedially displaced SH1 (rarely SH2, cf post-lat in adults). Requies significant force ± twisting, eg difficult delivery, child abuse.
- Elbow dislocation most common traumatic paediatric dislocation, usually posterior. FOOSH in slight flexion. If only radial head is dislocated then check for Monteggia’s fracture. May be congenital with radial head overgrowth and dysplasia; sporadic or associated with onycho-osteodysplasia.
- Subluxation of the radial head (jerked/pulled/nursemaid’s elbow) – Anterior subluxation/dislocation with no/partial disruption of annular ligament. Distraction in extension pulls radial head out of annular ligament collar. Displacement of the radiocapitellar line from radial neck, which should pass through capitellum on all views. Typically 2-3yo, doesn’t require excessive force. XR frequently normal. Usually self-limited with spontaneous reduction, otherwise reduction by flexion and supination (eg positioning for XR).
Adult Elbow Fracture/Dislocation
Usually FOOSH with axial load impacting capitellum against radial head with head/neck fracture. May be subtle on XR. Effusion very sensitive and specific
- Single longitudinal fracture proximal radial head ± distal impaction. Tx immobilisation with sling, but if >2mm articular step then ORIF to prevent secondary OA.
- Impaction of intact radial head into neck ± angulation.
- Terrible triad – Fractures of radial head, coronoid process and rupture medial collateral ligament. Usually associated with brachialis injury/rupture. Very unstable, little to keep elbow reduced.
- Elbow dislocation – Uncommon, usually posterior. Highly associated with fracture, significant ligamentous, neurovascular and muscular injury, myositis ossificans (esp brachialis, worse with delayed relocation causing reduced ROM).
- Olecranon – From triceps avulsion and proximal displacement. Tx ORIF with olecranon screw or wires and figure-of-eight tension band. May be stress fracture.
- Distal humerus fracture – May have longitudinal Y or T shaped fracture with intra-articular extension (usually involving trochlea). Surgical fixation may require olecranon osteotomy.
Forearm is a solid ring, hence almost always breaks/dislocates in more than one place. Children tend to have transverse/buckle/torus fracture to distal radius ± ulna; adolescents SH2/1; young adults scaphoid and/or triquetrum fracture; older adults distal radius esp Colles. Both bone fracture in children Tx usually cast, adults usually ORIF. Intra-articular step >/=2mm associated with OA.
- Colles fracture – FOOSH, fracture distal radius ± ulna with dorsal angulation and impaction. Dinner-fork deformity. Esp women with osteoporosis, associated with NOF fracture. Impaction usually worsens with casting. Heals with loss of palmar tilt and ulnar inclination and may predispose to chronic pain and OA, RSD, acquired ulnar plus with ulnar impaction syndrome.
- Smith’s fracture – FOOSH, fracture distal radius ± ulna with volar angulation. Much less common than Colles.
- Barton’s fracture – Unstable intra-articular fracture distal lip of radius with dorsal subluxation of carpus and distal radial fragment. Tx ORIF.
- Reverse Barton’s fracture – Volar displacement.
- Hutchinson’s/Chaeffeur’s fracture – Intra-articular radial styloid fracture from avulsion of radial collateral ligamnet or direct blow. Associated with scapholunate ligament tear.
- Plastic bowing derformity of the forearm – Bending without frank fracture, only seen in children. Tx surgical complete fracturing of bones and resetting. Untreated may -> reduced supination and pronation.
- Monteggia fracture – Fracture proximal ulna with dislocation of proximal radius. Untreated, radial head may -> AVN with elbow dysfunction.
- Galeazzi fracture – Fracture radial shaft with dislocation distal ulna. Much less common than Monteggia.
- Essex-Lopresti fracture – Rare comminuted fracture radial head and neck, tear of interosseous ligament, dislocation of distal radioulnar joint. Unstable.
- Nightstick fracture – Isolated fracture ulnar shaft from direct blow.
Post-traumatic radioulnar synostosis – Complication with osseous union, Tx resection of synostosis.
(Osteochondritis dessicans of the capitellum). Distal posterior capitellum vulnerable to direct impaction when elbow flexed.
Ligaments and Tendons
Collateral Ligament Injuries
MCL (anterior bundle, medial epicondyle -> coronoid) injury from acute or chronic valgus stress. Best seen on coronal in extension.
(Tennis elbow). Tendinitis of common extensor tendon and supinator, from repetitive motion (carpenters, golfers, tennis players). High T2 or thickening of tendon, occasional adjacent marrow oedema, calcification. Tear has very high T2 with defect (granulation tissue, blood or fluid). Tx conservative.
Tendinitis of common flexor tendon and pronators. In professional baseball pitches, tennis players. High T2 or thickening, occasionally adjacent marrow oedema, calcification. Associated with traction spur of anterior bundle MCL insertion into coronoid, litle leaguer’s elbow.
Distal biceps tendon injured mostly from repetitive stress, others include RA, previous steroid injection, anabolic steroids. Most tears are at the tendon insertion to radial tuberosity. Tendinosis or partial tears have high signal, thickening and surrounding oedema/fluid. Rupture/full tears are usually associated with fluid, retraction (may be limited by intact biceps aponeurosis). Transverse planes best for exclusion of tear. May be associated with haematoma (appearing like sarcoma). DDx cubital bursa tear (may also cause rupture) – between distal tendon and medial radius.
Uncommon, usually causes olecranon avulsion fracture.
Neuropathies and Nerve Injuries
Cubital tunnel syndrome – Injury in cubital tunnel (between medial epicondyle, proximal ulna, overlying retinaculum) from nerve subluxation, traction, bone spurs, ganglion/mass, fibrosis, fracture, inflammation, anatomical abnormality. Weak flexor carpi ulnaris and intrinsic muscles of hand. Signal abnormality of adjacent fat, nerve or perineural oedema. Tx of underlying cause or cubital tunnel retinaculum release.
Vulnerable between heads of pronator teres distal to elbow or as it passes through flexor carpi ulnaris. Weak 1st 3 fingers, pain on writing or weightlifting. May also be trapped by ligament of Struthers.
Prone to injury just distal to elbow where deep branches (posterior interosseus nerve) pass into supinator. Weak finger extension, pain/tenderness lateral epicondyle. From dislocation, fracture, mass, fibrosis.
Volar forearm muscles prone to compartment syndrome, requires urgent direct intracompartment pressure measurement (not MRI) and fasciotomy. Volkmann’s contracture is Cx with progressive fixed flexion deformity of fingers and wrist due to fibrosis of necrosed muscles.
Most common bursitis in body. From trauma, haemorrhage, or inflammation (RA, gout).