Disruption of finger flexor pulleys in rock climbers: prevalence, diagnosis and strategies for rehabilitation - page 3 The general finding from the studies described above is that PIP joint injuries among rock climbers are most prevalent on the middle and ring fingers. It is likely that this is because these fingers are most often used on ‘pocket’ holds, which can only accommodate two fingers. Other pathologies in this area, which have been described, include tenosynovitis (Bannister & Foster 1986) and abnormalities of the phalanges (Bollen & Wright 1994). The radiographic changes included formation of thickenings of the proximal phalangeal cortices at the attachment of the distal edge of the A2 flexor pulley. Given the range of injuries experienced by rock climbers centring around the fingers and the PIP joint in particular, there is a clear need for application of detailed knowledge of the functional anatomy of the fingers in diagnosis of finger injuries. Furthermore, there needs to be an establishment of sound and thorough diagnostic techniques for climbing related injuries to ensure appropriate treatment is subsequently applied. Functional anatomy of the flexor pulley system The flexor tendon sheath of the fingers is a continuous connective tissue structure running from the metacarpophalangeal joint to the DIP joint. The transverse fibres of the palmar aponeurosis may also be considered part of the pulley system (Phillips et al 1996). The flexor pulley system is a series of thickened fibrous tunnels running across the flexor tendons that maintain and stabilise the position of the flexor tendons close to the phalanges during flexion (Martinoli et al 2000). There are five annular pulleys, A1-A5, positioned where the sheath is required to be stiff. Three cruciate pulleys, C1-C3, are aligned over the tendons where the sheath must flex. The continuous flexor sheath contains a synovial membrane that allows tendon gliding and assists (along with the vinculae tendinum) with tendon nutrition. The A1 pulley is situated anteriorly to the metacarpophalangeal joint capsule. The A2 pulley lies over the proximal phalanx. This pulley is the longest pulley and has a well-developed distal free edge containing synovial fluid. A2 is considered the most important pulley as flexor pulley system function is most affected by excision of this pulley. There are well-defined ridges on the proximal phalanx where the A2 pulley attaches, particularly at the distal edge. These attachments can become thickened in climbers as age advances (Bollen & Wright 1994). A1 and A2 must absorb bowstringing forces from both the FDS and FDP flexor tendons. The A3 is a narrow pulley overlying the PIP joint capsule. The A4 pulley, again slightly longer than the joint pulleys, lies over the centre of the middle phalanx. The smaller and only recently described A5 pulley lies over the DIP joint (Phillips et al 1996). During flexion, the cruciate fibres become more transversely aligned and the edges of the annular pulleys draw together to become a continuous fibrous tunnel. The length of each pulley varies with the length of the digit and thickness varies with the relative length of the pulley. The mechanical advantage or moment arm of the flexor tendons depends on the perpendicular distance between the joint and tendon. The flexor pulley system effectively reduces the moment arm of the tendons over the finger joints by keeping them very closely apposed to the phalanges. By doing this, the tendon excursion required to provide a given range of joint flexion is greatly reduced. The pulley system permits 180 degrees of angular motion across the PIP and DIP joints for 2.5 cm of tendon excursion (Rispler et al 1996). This function is important and makes physiological sense as muscles are capable of producing extremely large forces but incapable of shortening many times their own length (Hunter et al 1984). Thus, an intact pulley system is considered essential for normal hand function and pulley ruptures are regularly treated by surgical reconstruction (Lin et al 1990). Sectioning of the A2 and A4 pulleys results in a need for 30% greater tendon excursion to obtain an equivalent PIP joint flexion (Le Viet et al 1996). In addition to its importance in maintenance of appropriate lever arms, an intact pulley system, through its effects on tendon excursion, is essential for flexor tendon function and health. The flexor tendons of the hand do not ‘glide’ as such through the synovial and fibro-osseous sheath. The tendons are attached to the paratenon that surrounds it (Hunter et al 1984). This relatively elastic tissue is relaxed during the mid-point of tendon motion. When the fingers are more flexed or extended, thus the peritendinous structures are stretched. This stretching uses energy and has been recognised as an important factor in tendon transfer. Furthermore, abnormal patterns of tendon excursion (the result of pulley malfunction) cause the phenomenon of ‘creep’, where the surrounding structures become permanently stretched. This effect causes an inflammatory reaction that eventually results in additional fibrous tissue deposits. It has also been shown that fibrous tissue deposits form under the bowstringing flexor tendons in the presence of pulley tears. Both these phenomena lead to flexion contracture, a condition that has been described in rock climbers suffering from pulley injury.
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