Flexor tendon and pulley injuries in athletes present a unique challenge to the treating clinician. An understanding of the anatomy and mechanism of injury helps the clinician appropriately diagnose and treat the injury. Treatment may become more complicated when associated with delays in diagnosis, in-season considerations, and an athlete’s desire to return to play. Two injuries involving the flexor tendon-pulley system, avulsion injuries of the flexor digitorum profundus tendon from its insertion onto the base of the distal phalanx and flexor pulley injuries, are examined in detail in this article.
Key points
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A thorough understanding of the anatomy and mechanism of injury are critical for diagnosis, treatment, and postoperative management.
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Jersey finger injuries should be promptly diagnosed to allow timely surgical repair and prevention of complications.
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Meticulous suturing, tensioning, bony reduction, and fixation techniques are critical to postoperative tendon tracking and outcomes.
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It is important to understand the demands and treatment goals of injured athletes to allow them to make informed treatment decisions.
Introduction
Finger injuries make up more than a third of all upper extremity injuries presenting to emergency rooms in the United States. Given its location and need for function, the finger is not only particularly vulnerable to athletic injuries but may result in significant functional consequences after injury. Although the exact incidence of athletic-related flexor tendon and flexor pulley injuries has not been described, they can be debilitating to the athletes. An understanding of the anatomy, mechanism, diagnosis, and treatment options of such injuries can ensure appropriate and efficient treatment.
Two injuries involving the flexor tendon-pulley system, namely avulsion injuries of the flexor digitorum profundus (FDP) tendon from its insertion onto the base of the distal phalanx (eg, jersey finger) and flexor pulley injuries are described given their high incidence within this patient population.
Anatomy and mechanism
An understanding of the anatomy of the digital flexor tendon and pulley system is critical to understanding the principles of injury, diagnosis, and treatment of FDP avulsion injuries and flexor pulley injuries. The extrinsic flexor muscles (FDP, flexor digitorum superficialis [FDS], and flexor pollicis longus) originate in the volar forearm and insert onto the volar base of the distal phalanx of the index through small fingers, the radial and ulnar aspect of the proximal half of the middle phalanx of these digits, and the volar base of the distal phalanx of the thumb, respectively. In these digits, the FDS tendon splits into 2 slips volar to the proximal phalanx through which the FDP passes (termed the Camper chiasm). At this level, the flexor tendons receive nutrition from both vascular perfusion (via the vincular system) and synovial diffusion (via the parietal paratenon). The vincular system, composed of short and long connections to the FDS and FDP, has implications for treatment of jersey finger injuries based on their disruption, as described in more detail later ( Fig. 1 ). Given that the vincular system and synovial diffusion via the parietal paratenon are the predominant vascular supply to the tendons proximal to their insertion, the vascular supply at the bone-tendon interface has relevance for injuries at this interface. Leversedge and colleagues evaluated the vascular anatomy of the FDP insertion and found a consistent and dense vascular supply to the palmar and dorsal regions from the distal phalanx and the vinculum brevis profundus ( Fig. 2 ).
Five flexor tendon zones were described based on anatomy that help dictate treatment principles ( Fig. 3 ). , An avulsion injury of the FDP off the distal phalanx occurs in zone 1, identified as the region in the finger that is distal to the FDS insertion. This injury, aptly termed jersey finger, describes an injury in which there is forced extension of the finger against flexion (eg, when a player, usually in rugby or football, grabs or gets a finger stuck in another player’s jersey). The ring finger is especially susceptible to injury for a variety of proposed reasons: (1) the ring finger extends more prominently than the other digits during power grip, , (2) its biomechanical load to failure is significantly less than that of the long finger, (3) it is anatomically restrained by the lumbrical muscles in the palm but shares a common muscle belly with the long and small fingers in the forearm. ,
The FDS and FDP tendons course through the fibro-osseous flexor pulley system, which runs from the metacarpal neck to just distal to the distal interphalangeal (DIP) joint. It is made up of 5 thicker annular pulley and 3 thinner cruciate pulleys ( Fig. 4 ). , The pulleys provide a mechanical advantage to the flexor tendons and improve motion by keeping the tendons opposed to the bone and preventing bowstringing. , The A2 and A4 pulleys originate from the proximal third of the proximal phalanx and the middle phalanx in the digits and overlie the proximal and middle phalanges, respectively. Although these 2 pulleys have been shown to be the most important biomechanically, , further study has shown that, if the other pulleys are intact, each of these 2 pulleys may be vented or released in isolation during flexor tendon repair with maintenance of function. Although more applicable in zone II flexor tendon injures, pulley release may improve intraoperative exposure and/or prevent triggering or adhesions postoperatively. Mitsionis and colleagues, in evaluating the biomechanical effect of A2 and A4 pulley excision, showed that each pulley may be excised up to 25% alone or in combination without affecting angular rotation. The effect of residual pulley strength and location of pulley release were not addressed in that article and are current areas of study. Although rare in the general population, pulley attenuation and ruptures most classically occur in rock climbers, and occasionally in pitchers, from the contraction of the flexor tendons against the pulley system. The A2 pulleys in the ring and middle digits are the most commonly involved in rock climbers, whereas the A4 pulley is most frequently involved in pulley injuries in baseball pitchers. The crimp position, in which the proximal interphalangeal (PIP) joints are flexed 90° or more and the DIPs are slightly hyperextended, is common in rock climbing to allow maximum holding contact. Pitchers with pulley ruptures have typically thrown fastballs in a similar mechanism that places an extension force on the DIP joint of a flexed digit. In this position, the flexor tendons are contracting under high loads, which places a great amount of force on the pulley system. It is not clear why A4 pulley injuries may be more common in pitchers and A2 pulley injuries are more common climbers, but a biomechanical study of 19 fingers placed in the crimp position and loaded showed that, of those with isolated pulley ruptures, 82.4% failed at the A4 pulley, whereas the remaining digits (17.6%) failed at the A2 pulley.
Zone 1 Flexor Digitorum Profundus Avulsions
Clinical evaluation and diagnosis
A thorough history and physical examination are critical for managing athletes. For example, recognizing concomitant or associated injuries may affect overall management, whereas an understanding of the chronicity of the injury may affect an athlete’s treatment options. Patients may present with a painful and/or swollen digit that lacks isolated DIP joint flexion. Digital tenodesis shows relative extension of the involved distal phalanx ( Fig. 5 ). Stabilizing the proximal and middle phalanxes and asking the patient to flex the finger isolates the FDP and allows evaluation of the tendon ( Fig. 6 ). Critical to note is that an injured FDP may weakly flex the DIP via a bony avulsion trapped at the A5/A4 pulley or through an intact volar plate and distal vinculum ( Fig. 7 ). , For this reason, some investigators advocate conducting this examination with resistance. , Palpation of the digit and palm is likely to elicit pain at the FDP insertion site (although patients with chronic injuries may be pain free) and may provide information as to the level of tendon retraction.
Although a diagnosis can typically be made based on history and physical examination alone, plain radiographs may help to identify an avulsion of a bony fragment, associated fractures, and/or dislocations. Advanced modalities such as ultrasonography and MRI may be useful adjuncts to help identify the level of retraction, especially in chronic injuries ( Fig. 8 ). Ultrasonography is a dynamic and inexpensive modality; however, it is operator dependent. MRI is less operator dependent but with an added expense.
Classification
Understanding the mechanism and nature of zone 1 flexor tendon injuries is important because it helps guide further work-up, prognosis, and treatment. The Leddy and Packer classification schema, which was later augmented by Robins and Dobyns is frequently used and includes 4 primary injury types based on the level of tendon retraction , ( Table 1 ).
| Type | Level of Retraction | Notes |
|---|---|---|
| I | Palm | Vincula disrupted, prognosis poor |
| II | PIP joint | Vincula intact, prognosis fair |
| III | A5/A4 pulley | Vincula intact, prognosis good |
| IIIa/IV | Bone: A5/A4 pulley, Tendon: PIP joint or palm | Prognosis fair/poor |
In type I injuries, the FDP tendon retracts into the palm and the vincula are disrupted, thereby compromising the vascular supply. Type II injuries are the most common and occur when the tendon is retracted to the level of the PIP joint, leaving the long vinculum intact. It may be difficult to differentiate between type I and II injuries without advanced imaging. In addition, type II injuries may become type I injuries with continued activity. Type III injuries occur when a large bony fragment has been avulsed that prevents retraction proximal to the distal aspect of the A4 pulley. In these scenarios, the vincula remain intact. Type IV is the least common type and includes both a fracture and an avulsion in which the FDP tendon has avulsed from the fracture fragment. In these injuries, the bony fragment retracts to the same level as that of a type III injury and the tendon retracts into the palm or to the PIP level.
Treatment
Type I
Because the blood supply is disrupted in type I injuries, the prognosis is poor compared with that of type II and III injuries, and prompt (within 7 to 10 days) surgical treatment is recommended. A midlateral or Brunner-style incision is used to expose the distal flexor pulley system and the distal insertion of the FDP. The retracted portion of the tendon is retrieved through another incision made near or proximal to the A1 pulley. It may be necessary to extend this incision proximally or create transverse windows to identify and retrieve the reacted tendon. The retracted tendon may be “milked” distally within its sheath and held in place with a 25-gauge needle. Alternatively, a pediatric feeding tube may be used to help bring the tendon distal through the pulley system. The edges of the FDP tendon may need to be trimmed to healthy tendon. Although it is best to preserve the A4 pulley, it may be safely vented to prevent complications related to tendon gliding, as described earlier. The bony insertion site of the tendon should be prepared and the tendon stump should be carefully debrided. Although various techniques exist to reinsert the FDP tendon to the distal phalanx, no one technique has proved to be superior. A pullout suture sutured through the tendon and transosseous tunnels may be used. Sutures may be secured with or without a button on the nail plate dorsally ( Fig. 9 ). The button and suture are typically removed after 4 to 6 weeks. Alternatively, if the distal phalanx is large enough, miniature suture anchors may be used ( Fig. 10 ). An all-inside repair using two 3-0 Ethibond sutures to attach to the distal FDP via a Massachusetts General Hospital (MGH)/modified method to bone with 2 Keith needles, and a knot tied over the dorsal distal phalanx, has also been described ( Fig. 11 ). In each technique, it is critical to ensure the FDP tendon is well approximated to the bony footprint when the knot is tied. In order to minimize the risk of nail bed deformity when using the pullout or suture anchor technique is to ensure the needle (in the pullout suture and transosseous tunnel technique) and the tip of the suture anchor (in the suture anchor technique) do not exit through or penetrate the germinal or sterile matrices.
