July 2012 - Donna Magid, M.D., M.Ed.
Elbow for Pragmatists
- Actually = 2 joints with communicating synovial spaces/capsule
- “Ginglymus” or HINGE joint: flexion-extension at humeral-ulnar articulation
- ROTATION ONLY at proximal radial-ulna joint for pronation/supination
AP forearm supinated, elbow extended) and Lateral (90 degree flexion); obliques, radial-capitellum may be added to look for subtle fractures. The R-C view is particularly helpful if radial head fx. suspected. On lateral the humerus should angle anteriorly like a hockey stick and the anterio humeral cortex line should intercept about ¼-1/3 of the humeral head (useful in children where this subtle posterior angulation and ‘straightening’ may be only clue, aside from joint effusion, to supracondylar fracture.)
Radiographically RADIAL HEAD always aligns with CAPITELLUM: R-C axis = constant, any position/view. If R-C articular relationship disrupted→ suspect dislocation, subluxation, fx.
FAT PADS: Anterior and posterior fat pads are INTRAARTICULAR but EXTRASYNOVIAL. Normally slumped into the anterior and posterior aspects of the olecranon fossa, they are elevated up and out if the synovial volume increases (inflammation, hemarthrosis, iatrogenic). The anterior may be seen as a thin radiolucency parallel to the anterior cortex on some normal lateral but elevates as a triangle, ‘spinnaker’, or ‘sail sign’with joint effusion. The posterior, rarely visible on normal true lateral, may also become visible as joint distends. In CHILDREN fat pad should be assumed to indicate fracture; in ADULTS it is highly likely to suggest fx., especially of the radial head/neck—the most common adult elbow fracture. One-finger correlation over the radial head in supination/pronation increases diagnostic accuracy (and usually greatly increases the 1st year resident’s respect for the fat pad sign).
Fall on an outstretched hand is most common mechanism of injury from toddlers through adulthood. Toddlers tend to get buckle fractures of the distal radius and ulna with such an axial-load/fall. School age children 5-9 y.o. → supracondylar fractures; account for `60% of elbow fractures. 2-3% are open, 1% may have other fractures same limb; 0.5% get compartment syndrome, radial nerve injury, or other complication. By puberty such falls may lead to posterior dislocation instead.
OSSIFICATION CENTERS: “CRITOE” Developmental maturation of the elbow is predictable with 2dary ossification centers becoming visible infancy through age 10, starting with:
- Capitellum (3-5 months)
- Radial head, Medial (or Internal) epicondyle `5 yrs
- Trochlea `8 yrs.
- Lateral (External) epicondyle
Salter type injuries in young children may displace ossified or non ossified growth centers; failure to diagnose can lead to permanent deformity and disability. Assume fracture if fat pad elevated and advise f/u 10-14 days. When in doubt images of the normal contralateral elbow help, as will the Normal Variants text since the trochlea may appear ‘fragmented’, the olecranon bifid, etc.
ADULT: Radial head and neck fxs are the most common adult elbow fxs. (10-20%); olecranon fxs are 2nd.
RADIAL HEAD: most common elbow fx in adults; fall on outstretch arm. Pattern may involve articular surface, or be extremely subtle impaction of head on neck: attention to trabecular detail and cortical flow on magnified image helps. Clinical exam more convincing than radiograph early on; if effusion, EXAMINE PT. when possible, and suggest f/u 10-14 days. Morbidity usually from impaired supination/pronation. Initially missed (subtle) fxs. may displace as osteoclasts kick in, requiring surgery, and producing impaired function…and lawsuits. The radial-capitellum view may be requested if there is high clinical/radiographic suspicion; it is an oblique angled lateral (akin to the scaphoid view), which elongates the radial head and trabeculae and removes the superimposition of radial head/proximal ulna which can limit assessment on lateral.
OLECRANON FRACTURES: can be indirect violence with triceps contraction/avulsion; often direct posterior blow (to olecranon) eg, fall onto flexed elbow. The contraction of triceps displaces proximal ulnar fragment proximally; usually requires internal fixation to re-appose and stabilize articular olecranon against triceps tug. Isolated acute triceps rupture (intact ulna) rare but check triceps soft tissue routinely on laterals. “Javelin thrower’s elbow” (more commonly due to pitching, tennis, volleyball, or other forceful repeated throwing motions)= triceps repetitive injury; chronic strain with or without olecranon process damage or changes.
SUPRACONDYLAR FRACTURES: 2nd most common elbow fracture in Pediatrics; #1 for 5-8 yr olds. (Both-bones forearm fractures, BBFF, or buckle fractures of the distal radius and ulna, remain slightly more common—but in kids under 5) Fall on outstretched hand, 98% L>R, M>F (although females catching up—gymnastics). 2-3% compound (open), 1% have 2d fracture same limb 0.5% get compartment syndrome (consider mechanism of injury, magnitude of forces, for risks). Radial nerve more likely than medial or ulnar to be involved. PREDISPOSING FACTORS at this age: period of rapid growth and remodeling; gracility, thinned cortices. Hyperextensibility, slightly lax ligaments common. Axial load on forearm becomes bending force at olecranon fossa
DISLOCATION (of forearm from humerus through joint): 20% of all dislocated joints. (2nd only to glenohumeral dislocations) 5-25 yr old most common (maturing bone finallystronger than restraining ligaments and capsule; forces that were producing supracondylar fractures now instead disrupt restraining soft tissues). Usually humerus-ulnar disruption; most POSTERIOR (of ULNA relative to HUMERUS). Anterior dislocation (of ulna) rare implies direct posterior/ulnar blow (e.g. baseball bat). Capsule distorted or disrupted, ligaments injured. Associated avulsions epicondyles, coronoid process.
Radial HEAD fracture often seen in adult, radial NECK fracture child. COMPLICATIONS: Neurovascular compromise; this is EMERGENCY. Clinicians should document vascular and neurologic exam early and often. Articular surface damage (bone or cartilage) may impair range of motion (ROM) and contribute to premature arthritis over time. Myositis Ossificans or heterotopic bone can form and block ROM or impinge nerves, vessels, muscles.
July 2012 - Donna Magid, M.D., M.Ed.