Regaining satisfactory digital function after flexor tendon laceration and repair within the digit has long been one of the most difficult problems in hand surgery. Until the 1960s it was universally recommended that tendons divided in the digit (then referred to as “no man’s land”) should not be repaired. Bunnell taught that “it is better to remove the tendons entirely from the finger and graft in new tendons smooth throughout its length.” That dictum remained sacrosanct until the 1960s when reports by Verdan, Kleinert et al, and Kessler and Nissim challenged the concept that flexor tendons should not be repaired primarily. These investigators noted that when done correctly, immediate tendon suture would outperform secondary free tendon grafting. Armed by those encouraging reports, there was a gradual and cautious development of the concept and practice of primary flexor tendon repair. Initially, primary tendon repair was often combined with anecdotal protocols by Duran et al, Lister et al, and Strickland and Glogovac for applying varying amounts of early post-repair motion to the repaired tendons. As often happens with advances in medicine, the efforts to improve the performance of flexor tendon repairs were based almost entirely on individual experience and clinical experimentation with little or no scientific support. The last 25 years, however, have heralded an enormous amount of basic research designed to improve our knowledge of the structure of tendons, including the kinesiology, the biomechanics of their action on the joints they move, their biologic response to injury and repair, the mechanical characteristics of various tendon suture constructs, and the effect of post-repair motion stress on tendon strength and healing. These investigative efforts have given rise to improved methods of tendon repair, a greater emphasis on flexor sheath preservation and restoration, and protocols for the early application of passive and active wrist and digital motion as a means to more rapidly increase the strength and gliding of repaired tendons. The following sections will provide a concise review of some of the most important of these reports.

Development of flexor tendon surgery: twenty-five years of progress.

The scientific basis for advances in flexor tendon surgery.

To examine the precise conformation of the annular and oblique pulleys of the thumb flexor sheath, anatomic dissections were undertaken on 14 hands. In all specimens a distinct pulley was found between the A1 and oblique pulleys. This is named the variable annular pulley or Av pulley. There appear to be 3 discrete forms of this pulley designated type I to III. The biomechanical study was done on 8 limbs by using linear strain transduction techniques. The analysis showed that the strain in the oblique pulley was greater in extension than in flexion of the thumb. This statement remains true even after division of either the A1 or Av pulley and after section of both pulleys. The oblique pulley does not prevent bowstringing of the flexor pollicis longus when A1 and Av pulleys have been sectioned. These studies challenge current concepts of both the anatomy and mechanics of the thumb pulley system with implications for clinical procedures such as trigger thumb release and pulley reconstruction.

The pulley system of the thumb: Anatomic and biomechanical study

Flexor pulley injuries are most commonly seen in avid rock climbers; however, reports of pulley ruptures in nonclimbers are increasing. In addition to traumatic disruption, corticosteroid-induced pulley rupture has been reported as a complication of treating stenosing tenosynovitis. Over the last decade, there have been 2 new developments in the way hand surgeons think about the flexor pulley system. First, the thumb pulley system has been shown to have 4 component constituents, in contrast to the classic teaching of 3 pulleys. Second, in cases of zone II flexor tendon injury, the intentional partial A2 and/or A4 pulley excision or venting is emerging as a component for successful treatment. This is challenging the once-held dogma that preserving the integrity of the entire A2 and A4 pulleys is indispensable for normal digit function.

Flexor Pulley System: Anatomy, Injury, and Management

Pediatric trigger thumb and trigger finger represent distinct conditions and should not be treated like adult acquired trigger finger. Over the last two decades, our understanding of the natural history of pediatric trigger thumb and the etiology and surgical management of pediatric trigger finger has improved. Pediatric trigger thumb may spontaneously resolve, although resolution may take several years. Open surgical release of the A1 pulley of the thumb is an alternative option that nearly uniformly restores thumb interphalangeal joint motion. Surgical management of pediatric trigger finger with isolated release of the A1 pulley has been associated with high recurrence rates. Awareness of the anatomic factors that may contribute to triggering in the pediatric finger and willingness to explore and address other involved components of the flexor mechanism can prevent surgical failure.

Management of pediatric trigger thumb and trigger finger

The purpose of this study was to quantify the contributions of the thumb flexor pulleys on the mechanical efficiency and angular joint displacement of the human thumb. Fourteen human (below elbow) cadaveric specimens were divided into two study groups. Four experimental trials were performed with each thumb. Group 1 was tested with an intact pulley system, as well as after sequential sectioning of the oblique, A1, and A2 pulleys. Group 2 was tested with all pulleys intact and following the sequential sectioning of the (A1), oblique, and (A2) pulleys. Each forearm was mounted to a dynamic testing apparatus, and an 815 g load was applied at the thumb tip. The flexor pollicus longus tendon was attached to a force transducer and computer-driven stepper motor, and tension was recorded through full range of motion of the interphalangeal and metacarpophalangeal joints. The initial sectioning of either the A1 or oblique pulley did not significantly alter the thumb efficiency or its interphalangeal or metacarpophalangeal joint angular displacement. When both the A1 and oblique pulleys were cut, significant bowstringing was observed, as well as decreased interphalangeal flexion and increased metacarpophalangeal flexion; total angular motion remained unchanged. The tension required to achieve a given displacement also decreased following the sectioning of both the A1 and oblique pulleys. There was no statistical difference between an isolated, intact A2 pulley and no intact pulleys. These findings indicate that repair or reconstruction of either the A1 or oblique pulley after injury will restore normal thumb kinematics.

Kent E. Yinger

Papers

Biomechanics of the thumb flexor pulley system