Tendon split lengthening technique for flexor hallucis longus tendon rupture

Five patients with a total rupture of the FHL tendon, having tendon defect distal to the knot of Henry and the fibrous slip, were treated with split tendon lengthening between May 2012 and September 2015. Two patients had laceration on the great toe, and primary repair was initially performed at the local hospitals. The patients were referred to our hospital when the loss of active flexion at the great toe IP joint was detected. Other two patients had dislocation of the IP joint, and closed reduction with trans-articular fixation was performed. FHL tendon rupture was detected 6 weeks later, when K-wire was removed. The last one had a history of IP joint dislocation, which was reduced at a local hospital 2 months ago. The patient had extension deformity at the IP joint and complained of the big toe rubbing against the toe box inside his shoe. The mean duration of time from the initial injury to FHL reconstruction surgery was 6.2 weeks. The mean defect size was 18.4 mm.

Under ankle block anesthesia, the patient was placed in a supine position with a pneumatic tourniquet prepared around the calf for later use during tendon length determining procedure. After routine sterile drape was placed, a rubber tourniquet was applied around the ankle. In cases of lacerated rupture, when the proximal end of the ruptured tendon could not be found because of retraction, incision was extended proximally through the medial or lateral side of the first metatarsal head longitudinally to avoid injury to the fat pad and the neurovascular bundle underneath the first metatarsal head. Degenerative tendon tissue was excised at the proximal and the distal ends of the ruptured FHL tendon, and the defect size was measured between both ends of the tendon, with the ankle joint in plantigrade neutral position and with the first MTP joint and the IP joint in neutral 0 degree position (Fig. 1).

In the midfoot, a longitudinal incision was made along the upper border of abductor hallucis muscle (Fig. 2a). The FHL and flexor digitorum longus (FDL) tendons were identified at the knot of Henry. The fibrous slip connecting the FHL and FDL was divided and released. A split incision was made to divide FHL longitudinally into half (Fig. 2b) [14]. The split incision was started at the knot of Henry and advanced distally 1.5 cm longer than the measured size of the tendon defect to facilitate later overlap for suturing after lengthening of the split tendon. Before the vertical cut at the end of the split incision, the whip stitch was made at both ends of the split tendon to secure the tendon from retracting proximally (Fig. 2c). The vertical cut at the end of the split incision made the distal part of the FHL tendon move distally for lengthening (Fig. 3). The whip stitch was made at the distal end of the ruptured tendon and was pulled down distally (Fig. 4). Care was taken to hold the whip stitch at both ends and not to pull the tendon entirely out of the foot. If it was pulled out from the foot, it would be difficult to reinsert the tendon to its anatomical position, unless by means of open surgery. In two cases, there was some fibrous connection underneath the MTP joint that we had to release in order to pull down the tendon distally. When the distal stump of the ruptured FHL was healthy and long enough for a secure repair, end-to-end direct repair was possible. However, when the distal stump was degenerated or was too short, a bone hole was made to insert the distal end of the split FHL tendon. By using the pull-out technique, the two ends of the whip stitch were pulled out through the bone hole and were sutured on the dorsum of the distal phalanx. Finally, the length of the FHL tendon was determined at the midfoot, where the FHL was split. When the tendon is reconstructed too tight, it can cause clawing of the great toe and limit dorsiflexion, which can be problematic during walking. When it is too loose, a patient is not able to plantarflex the great toe IP joint, and it does not provide enough push-off strength during walking. To measure the appropriate length of the FHL tendon, we used ankle block anesthesia instead of general or spinal anesthesia to let the patient actively move the great toe to test balance. Overlap area of the split tendon was temporarily sutured in neutral position of the ankle, MTP joint, and IP joint and was tested for balance with patient’s movement (Fig. 5). The length was adjusted when the tendon was too tight or loose. During this procedure, pneumatic tourniquet was inflated at the calf, and the rubber tourniquet applied around the ankle was released, because we found that compression around the ankle plantarflexed the great toe making the tendon too tight to measure the balance. Patients could withstand 250 mmHg of pneumatic pressure around the calf even with ankle block anesthesia. In a single case with hyperextension deformity at IP joint, we repaired the plantar plate before the FHL reconstruction.

Postoperatively, short leg cast was applied for 3 weeks with a window made on the plantar area of the great toe to allow active plantarflexion exercise but to limit extension. Active extension exercise was encouraged after cast removal for the next 3 weeks. Weightbearing was allowed in a functional brace at 6 weeks postoperatively. Patients were invited to a final follow-up office visit for a detailed evaluation for the study.