ELBOW, WRIST, AND HAND
Injuries of the elbow, wrist, and hand are common in the athletic population. Approximately 25% of all sports injuries involve injuries to the elbow, forearm, and wrist (1). Sex differences associated with the anatomy and biomechanics of elbow, wrist, and hand structures have been reported in the literature. These differences can have implications in various traumatic and overuse injuries seen in athletes. To understand and treat injuries of the musculoskeletal system, it is important to first understand the “normal” functioning of the involved body part among different populations, such as males and females. This can help providers identify risk factors for injury in order to optimize treatment and/or injury prevention. This chapter provides an overview of gender and sex differences in elbow, wrist, and hand anatomy and biomechanics and looks specifically at various injuries in which sex differences have been reported in the literature.
ANATOMY AND BIOMECHANICS
The elbow joint involves three articulations: the proximal radioulnar joint, the ulnohumeral joint, and the radiocapitellar joint. It has two degrees of freedom: flexion-extension and pronation-supination. Stability of the elbow joint is accomplished primarily by the congruity of the articulations, the capsule, as well as the ligament complexes. Myotendinous units that cross the joint also provide dynamic stability.
Normal elbow range of motion (ROM) is approximately 0° to 150° of flexion and 80° of pronation and supination (2). Golden et al. evaluated 600 elbows (300 participants) of healthy children and adolescents and found females to have greater total ROM, greater flexion, and greater extension than males (3). Chapleau et al. demonstrated similar findings of greater elbow ROM in females compared with males in an adult population (4).
The elbow has a relative valgus alignment, formed between the long axis of the humerus and the long axis of the ulna when in full extension and supination, called the carrying angle. This angle is approximately 5° to 10° (2). Numerous studies have demonstrated an increased carrying angle in females (5–11). This difference has often been considered to be a secondary sex characteristic. Not all studies, however, have noted this difference. Beals conducted a radiographic study of the carrying angle in 422 patients and found no real differences in males and females (12). The author suggested that the clinical observation of an increased carrying angle in females may be explained by increased joint laxity, allowing for a greater degree of extension (Figure 3.1).
An increased carrying angle, when combined with the significant valgus and extension forces generated in overhead throwing motions, can lead to stress injuries of the elbow. Continued valgus stress can cause ligament damage, formation of olecranon tip osteophytes, loose bodies, articular damage, flexor-pronator tendonitis, ulnar neuritis, and medial epicondylitis or apophysitis (13).
The wrist consists of the distal ulna, distal radius, eight carpal bones, and the bases of the metacarpals. It is divided into three primary joint regions: distal radioulnar, radiocarpal, and midcarpal. It has two primary degrees of freedom: flexion-extension and radial/ulnar deviation. Normal wrist palmar flexion is 75° to 80° and normal dorsal extension is 75° to 85° (2). Normal radial deviation is 20° to 25°; normal ulnar deviation is 35° to 40° (2). Allander et al. analyzed wrist joint ROM in 517 females and 203 males, all ranging in age from 33 to 70, and found that females had significantly larger ROM in the wrist than males (14).
The relative length of the ulna in relation to the radius at the level of the wrist is called ulnar variance (Figure 3.2). Ulnar variance may be positive (ulnar projects distally), negative (ulnar projects more proximally), or neutral (both the ulnar and radial articular surfaces are the same length).
Ulnar variance has been associated with various pathological states. Positive ulnar variance has been associated with ulnar impaction syndromes and triangular fibrocartilage complex (TFCC) injury. Negative ulnar variance has been associated with Kienbock’s disease, avascular necrosis of the scaphoid, and scapholunate dissociations.
Goldfarb et al. assessed ulnar variance in the adolescent population and found that young adolescent boys demonstrated a greater degree of negative ulnar variance compared with young adolescent girls (15). Nakamura et al. measured ulnar variance in 325 normal wrists, consisting of 203 males and 122 females ranging in age from 14 to 79 years (16). The study found that males had a lower mean value (i.e., greater degree of negative ulnar variance) in all age groups compared with females.
The skeletal anatomy of the hand consists of phalanges, metacarpal bones, and carpal bones. These 27 bones serve as attachment and insertion sites for muscles and ligaments that can produce a vast array of movements and tasks through complex interactions (17).
Mallon et al. assessed the ROM of fingers in young healthy adults. The study found that females showed an increased amount of both active and passive extension at all joints on all digits (18).
Overarm Throwing Kinematics
The position of the hand, shoulder, and elbow during overarm throwing all play a role in the amount of stress experienced across the elbow. Van den Tillaar and Cabri investigated the throwing velocity and kinematics of overarm throwing in elite female and male handball players (19). The analysis consisted of maximal joint angles, angles at ball release, maximal angular velocities of the joint movements, and maximal linear velocities of the distal endpoints of segments and their timing during the throw. No major differences in kinematics were found, except for the maximal endpoint velocities of the hand and wrist segment (19). The authors conclude that male and female handball players throw with the same technique, and differences in throwing velocity are generally not the result of changes in kinematics in the joint movements.
The perception that sex alone causes suboptimal throwing mechanics appears false. “Throwing like a girl” may simply be an immature throwing mechanic and not a specific gender-related anatomic or physiologic finding (20). Multiple studies have reported that the pace of developing a mature throwing mechanic may be delayed in females compared with males (21,22). While gender has generally been a reasonable predictor when evaluating throwing velocity, if grouped by stages of development, gender explains no more than 2% additional variance (23). This finding is discussed in greater depth elsewhere in this textbook, in Chapter 4 on upper limb mechanics: throwing.
The golf swing is a complex movement utilizing the whole body in a coordinated fashion. Repeated motion can result in injury in both professional and amateur golfers. Female golfers have been found to have twice as many wrist injuries as males (24). Zheng et al. compared the golf swing kinematics between 25 female and 25 male professional golfers (25). Significant differences were found in the maximum angular velocity of both wrists, the maximum angular velocity of the right elbow extension, and the timing when the maximum left wrist angular velocity occurred. These velocity differences may account for the difference in wrist injury incidence.
Reported sex differences in specific injuries/pathology of the elbow, wrist, and hand are somewhat limited in the literature. However, the injuries described in the following sections have been found to have differing incidence in males and females.
Valgus Extension Overload
Valgus extension overload (VEO) is a constellation of symptoms and pathology seen with overarm throwing athletes as a result of high repetitive stresses generated by overarm throwing motions. There is increased incidence of VEO in males, given the high association with baseball pitchers. With each pitch, the elbow joint is subject to a valgus torque reaching an average of 64 Nm, of which approximately 50% is taken up by the ulnar collateral ligament (UCL) (26). Overhead sports requiring similar motions, such as a tennis serve, football pass, or volleyball spike, can also produce tensile forces to the medial elbow. The valgus carrying angle of the elbow, which can be increased in females, may predispose the medial elbow to overuse injuries.
A valgus torque of 45 Nm is generated at the elbow during underhand softball pitching (27). Although a smaller magnitude of force is exerted on the softball pitcher’s elbow compared with a baseball pitcher, Barrentine et al. suggest that the underhand throwing motion in softball may not be as safe from overuse injuries as previously thought (27).
Compression at the Elbow/Cubital Tunnel
At the level of the elbow, the ulnar nerve enters the ulnar groove formed between the medial epicondyle of the humerus and the olecranon process of the ulna. Distal to this groove, the ulnar nerve travels under the two heads of the flexor carpi ulnaris muscle, known as the cubital tunnel (Figure 3.3). Ulnar neuropathy at the elbow may be caused by compression at the ulnar groove or at the cubital tunnel.
Ulnar neuropathy at the elbow is the second most common entrapment neuropathy of the upper extremity. Richardson et al. compared characteristics of patients with and without ulnar neuropathy at the elbow and found that men were more likely to have an ulnar neuropathy at the elbow than women (28). The study also found that more women with a body mass index (BMI) of less than or equal to 22.0 had ulnar neuropathy at the elbow when compared to women with a BMI greater than 22.0, suggesting that thin women are at increased risk for ulnar neuropathy at the elbow, presumably due to susceptibility to external compression. This trend was not seen among men. The authors suggested that any mechanical protective effect of an increased BMI in males may be offset by increased forearm muscle mass and grip strength that produce greater pressures over the ulnar nerve (28).
Contreras et al. also looked at sex differences and their relationship to ulnar neuropathy at the elbow (29). They found significantly larger (2 to 19 times greater) fat content on the medial aspect of the elbow in women compared to men. In addition, the tubercle of the coronoid process was approximately 1.5 times larger in men. These two anatomical findings suggest two mechanisms by which the ulnar nerve may be predisposed to increased risk of compression in males compared to females.
There has been increased use of ultrasound in the evaluation of nerves, including the ulnar nerve. Multiple studies have demonstrated increased cross-sectional areas and increased cross-sectional diameters in healthy males when compared with healthy females (30,31).
Compression at the Wrist/Guyon’s Canal
At the level of the wrist, the ulnar nerve enters a canal formed proximally/medially by the pisiform bone and distally/laterally by the hook of the hamate, called Guyon’s canal. In the canal, the nerve divides into the superficial sensory and deep palmar motor branches.
Ulnar neuropathy at the wrist/Guyon’s canal is much less common than ulnar neuropathy at the elbow. It is most commonly due to a ganglion cyst within Guyon’s canal that compresses the ulnar nerve. Women are three times more likely to be affected by hand and wrist ganglions than men (32). Ulnar neuropathy at the wrist/Guyon’s canal can also be associated with trauma and fractures.
Olecranon bursitis is inflammation of the subcutaneous synovial-lined sac of the bursa overlying the olecranon process of the ulna. Annual incidence is approximately 10/100,000 and predominantly affects male patients (80%) aged 40 to 60 years (33). Most cases of nonseptic bursitis seen in athletes are posttraumatic or due to overuse.
Lateral and Medial Epicondylosis
Lateral epicondylosis, often referred to as tennis elbow, is a common cause of lateral elbow pain. It is an overuse syndrome affecting the wrist extensors, particularly the extensor carpi radialis brevis tendon. The literature is mixed regarding incidence of lateral epicondylosis between males and females. Several studies note an increased incidence in females (34–36). Other studies note equal incidence in males and females (37–39).
Medial epicondylosis, often referred to as golfer’s elbow, is a common cause of medial elbow pain. It is less common than lateral epicondylosis. It is an overuse syndrome affecting the wrist flexors. There appears to be equal incidence in males and females (38–40).
Triangular Fibrocartilage Complex
TFCC consists of the articular disc, the meniscus homologue, the dorsal and palmar radioulnar ligaments, the ulnolunate and ulnotriquetral ligaments, and the extensor carpi ulnaris tendon sheath. The TFCC plays a key role in stabilization, rotation, translation, and loading transmission to the wrist and acts as an essential pivot point (41). It is prone to injuries because of its anatomical location and involvement in rotation and load bearing. Positive ulnar variance is associated with degeneration of the TFCC, while negative ulnar variance is associated with less degenerative wear (41).
Mallet finger, also known as baseball finger, is a deformity caused by rupture of the extensor tendon after sudden passive flexion of the distal interphalangeal joint when the finger is extended. Peak incidence has been found to vary between sexes, occurring in young to middle-age men and in older women (42).
Boxer’s fracture is a fracture of the metacarpal neck/shaft that may be seen after a person strikes a wall or another person with poor technique. It may occur at any digit but is commonly seen in the fifth digit. Gudmundsen and Borgen reviewed 271 fifth metacarpal fractures and found 48% were related to aggression, with males comprising 93.1% of the aggression group as well as 70.2% of the nonaggression-related group (43).