Radiographic appearance of Hunter tendon rod implant during staged flexor tendon reconstruction of the hand.

We report a case of staged flexor tendon reconstruction using a silicon Hunter tendon rod implant. This implant is placed during the first stage of the two-stage procedure to facilitate formation of a pseudotendon sheath. The implant is removed and the tendon graft placed during the second stage of the procedure. Radiography after the first stage of the procedure assesses healing of concomitant bony injury and evaluates the position and integrity of the tendon implant. It is important that radiologists recognize the Hunter tendon rod implant and understand potential complications when interpretating images in these patients.

Case report

We report the case of a 26-year-old right-handed butcher who sustained near-total amputation of his right index finger when he slipped while cutting pork chops. Physical examination showed an open fracture of the proximal phalanx, with compromised vascularity of the digit. Radiography confirmed a mildly comminuted, displaced fracture through the proximal phalanx of the index finger (Fig. 1). At surgical exploration, the radial and ulnar digital arteries and nerves were found to be lacerated, as were the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons. In addition, the A2 pulley was torn.

Figure 1

26-year-old male with meat-cutting injury to the hand. Lateral and oblique radiograph of the right index finger demonstrates partial amputation of the digit through the proximal phalanx. Displaced oblique fracture through the proximal phalanx and soft tissue defect are noted.

The ends of the lacerated flexor tendons were identified. Distally, the tendons had retracted beneath the distal extent of the A4 pulley and could not be pulled into the wound to allow primary repair. Further dissection distally to free the tendons was avoided because of concern for the viability of the distal soft tissues of the finger. The decision was made to pursue a staged flexor tendon reconstruction.

The proximal phalanx fracture was reduced and fixed with Kirschner wires (K-wires). The ulnar and radial arteries and digital nerves were directly repaired. A 4-mm Hunter rod was passed under the A4, A2, and A1 pulleys of the finger. The rod was secured to the tendon stump distally and left free proximally. The A2 pulley was repaired. The proximal FDP and FDS tendon stumps were debrided.

Postoperative radiographs demonstrate K-wires spanning the reduced phalanx fracture (Fig. 2). The Hunter tendon rod is visualized as a uniform-caliber rod along the palmar aspect of the finger that is slightly denser than adjacent soft tissue. The rod passes from the palm across the metacarphalangeal joint and distally across the distal interphalangeal joint along the expected course of the flexor tendon sheath.

Figure 2

26-year-old male with meat-cutting injury to the hand. Two views of the right index finger demonstrate reduction and K-wire fixation of the oblique proximal phalanx fracture. Silicon Hunter tendon rod (arrows) along the volar surface of the index finger are best seen on the lateral view.

The patient subsequently developed reduced motion of the injured digit despite rigorous hand physical therapy. He then underwent a second stage of surgical treatment, but unfortunately he progressively lost range of motion and function in the digit and eventually required amputation.

Discussion

Severe tendon injuries and partial amputations of the fingers can result in significant functional impairment. One procedure for salvaging fingers with tendon injuries is staged flexor tendon and pulley reconstruction as described by Hunter (1). Indications for this procedure include scarring of the tendon bed such that primary repair is contraindicated, extensive damage of the tendon sheath, and failure of primary repair (2). Best results are achieved in patients who are motivated to actively participate in hand therapy to preserve motion, and in the absence of infection, muscle paralysis, and contractures (3).

During the first stage of reconstruction, the flexor pulley system is repaired. A reinforced silicone passive tendon implant, often called a Hunter tendon rod, is placed along the expected course of the injured flexor tendon sheath to encourage formation of a new pseudotendon sheath around the implant. Repair of injuries to the flexor tendon pulleys, particularly the A2 and A4 pulleys, is vital to preserving flexor function of the finger. These pulleys maintain the tendon in proper position to adequately transmit forces from the flexor muscles of the forearm to the bones of the finger.

The temporary implant is secured only at the distal end, often to the FDP tendon stump, to allow passive movement of the digit. The proximal portion ends in the palm or distal forearm, up to several cm above the wrist crease. The distal portion is fixed, but the proximal portion should glide freely with movement of the digit with a range of motion of 3-4 cm at the proximal end (1). This allows for hand therapy, with the goal of preserving or improving range of motion in the interim between the first and second stages of the procedure.

During the second stage of tendon repair, at least three months later (3, 4), the implant is removed and replaced with a tendon graft. Active patient involvement in rehabilitation is vital to the success of this operation.

The passive tendon rod implant is a tube composed of silicone elastomer that may be reinforced with polyester mesh. The implant is available in diameters ranging from 2 to 6 mm, depending on the size of the planned final tendon graft (3). The graft can be cut to length. The implant is constructed of radioopaque material. The passive tendon rod implant is FDA-approved for use during staged reconstruction of the flexor tendons of the fingers, thumb, and wrist. The device is approved as a temporary implant, to be removed after 2 to 6 months.

Radiographs are obtained during the course of treatment to monitor healing of fractures, and it is important to recognize the presence of the tendon rod implant. The Hunter tendon rod is visible radiographically as a moderate-density tube extending down the expected course of the flexor tendon. The tendon rod implant may terminate in the palm or forearm. There should be no buckling or discontinuity of the rod. Particular attention should be paid to the proximal and distal placement of the tendon rod, which latter should extend to the fingertip.

Complications of the first stage of the procedure include skin necrosis, infection, and synovitis. Radiographically evident complications include rod buckling, rupture of the distal end of the silicon implant, and rod migration (2, 4, 5, 6). Rod buckling can occur if the reconstructed pulleys are too tight, preventing smooth passage of the tendon rod (2). Rod migration occurs if the distal attachment fails, allowing the rod to migrate up the palm or forearm due to finger motion. If this happens, the rod can be found curled up in the palm or proximally displaced into the forearm, sometimes completely (4, 5). If the rod migrates too far proximally, it is no longer in a position to facilitate pseudotendon formation in the digit. In addition, it can be difficult to retrieve at the time of the second operation.

Patients are sometimes lost to followup between first and second stages (7), and the Hunter tendon rod implant can remain in place for some time. In fact, one case report describes a silicon tendon rod implant that was removed 25 years after insertion, after it eroded through the soft tissues of the finger tip (8). In these circumstances, it may be useful for the radiologist to properly identify the Hunter tendon rod if it is discovered on radiograph to evaluate as a foreign body.

Awareness of the purpose and radiographic appearance of silicon flexor tendon sheath implants in the repair of flexor tendon injuries is important to allow recognition of possible complications. This case report demonstrates the typical appearance of a Hunter tendon rod insert used in a patient with near amputation of the index finger and flexor tendon injury.