Closed Traumatic A2 Through A4 Pulley Rupture and Flexor Digitorum Superficialis Avulsion Treated With Reconstruction

DISCUSSION

The standard treatment for single pulley ruptures is conservative management; however, management principles change drastically when multiple pulley injuries are involved.^3,6 The role of the flexor pulley system is to maintain close contact between the flexor tendons and the phalanges, thus applying a short moment arm across the PIP joint.¹⁰ Subsequent tendon bowstringing results in a loss of tendon excursion, loss of active flexion, and the potential for PIP joint flexion contracture.^11,12 Biomechanical studies have shown that the A3 pulley alone is of little importance in preventing tendon bowstringing at the PIP joint.¹³

A review of pulley reconstruction techniques yields several approaches, differing by the number of fastening loops and/or autologous graft source. The Weilby technique has been shown to produce excellent functional outcomes,¹⁴ while the Widstrom loop-and-a-half technique is the strongest repair.¹² Bunnell¹⁵ was effective with the single-loop technique, while Okutsu et al¹⁶ and Mehta and Phillips¹⁷ opted for the triple-loop technique. Doyle and Blythe¹⁸ argued for the palmaris longus tendon as the ideal autologous graft, Lister¹⁹ described repairs using the flexor retinaculum, while Gabl et al⁶ and Moutet²⁰ preferred the extensor retinaculum. Karev et al²¹ described an altogether unique belt-loop approach involving 2 transverse incisions in the volar plate.

To our knowledge, this case is only the third report of combined pulley rupture and FDS avulsion (Table 2). The first case was reported in 2001 by Vandeputte and Dubert, who described a 48-year-old male who ruptured the A2 through A4 pulleys with an avulsed FDS tendon of the right ring finger while forcefully making a fist.⁸ Three months after the initial injury, the patient underwent surgical reconstruction that involved an autologous palmaris longus tendon graft. The patient experienced significant improvements in range of motion after the repair, with a full return to activities by 5 months.⁸ The second case was reported in 2014 by Johnsen et al.⁹ They described a 56-year-old male who presented with pain and swelling of the right long finger resulting from release of a bowling ball. Ultrasound confirmed A2 and A3 pulley ruptures with avulsion of the FDS tendon. Seventeen days after the injury, the patient underwent surgical reconstruction of the A2 and A3 pulleys according to the Weilby technique using an autologous palmaris longus tendon. He had increased range of motion by 2 months postoperatively and achieved a full return to activity at 15 months.

In our case, the surgeon opted for the triple-loop technique to prevent further bowstringing of the FDP tendon. The reconstruction was tested and shown to have smooth gliding of the FDP with correction of the flexion contracture. The A3 pulley was not reconstructed because of its anatomic location over the joint. A reconstructed A3 pulley would have a minimal biomechanical role in preventing further bowstringing of the FDP tendon. In cases of concomitant FDS and pulley loss, repair of the FDS avulsion has been deemed to be unnecessary because it would likely impede gliding of the FDP through zone II.⁹ Zone II refers to the area between the FDS insertion and the distal palmar crease, as described in the classification system of flexion tendon injuries by Verdan in 1960.²²

Patients with preexisting PIP joint flexion contractures are associated with less favorable functional outcomes compared to patients who undergo reconstruction before developing contractures.⁸ Contractures in pulley injuries arise from an increased lever arm at the PIP joint. Additionally, scar tissue impedes contracture resolution after pulley repair. As seen in our patient, contracture release achieved through PIP joint capsulotomy and release of the checkrein ligaments and the collateral ligaments led to full passive range of motion at the PIP joint. Such releases should be managed with postoperative dynamic extension splinting to reduce the risk of contracture recurrence.

A rapid extension force acutely applied to a flexed finger has been described as the mechanism of injury in pulley ruptures by Bowers et al.¹¹ Marco et al conducted cadaver experiments in which the flexor tendons were loaded until pulley and tendon rupture occurred, at which point they hypothesized that a transfer of force from the bowstringing profundus tendon to the superficialis led to avulsion of the FDS tendon.²³ The clinical progression of our patient from mechanism of injury to symptoms at time of presentation is consistent with similarly described cases. Compared to previously reported cases of combined pulley rupture and FDS avulsion, our patient had a worse outcome in postoperative range of motion. Timing of the reconstruction was an important factor in the patient's outcome, with 9 months from injury being less than ideal. Ultimately, the patient traded a stiff finger in flexion for a stiff finger in extension. The patient was satisfied with this new position as he stated he is more functional in daily life, such as being able to place his hands in his pockets.