Loss of the knee-ankle coupling and unrecognized elongation in Achilles tendon rupture: effects of differential elongation of the gastrocnemius tendon.

PURPOSE: The biarticular anatomy of the gastrocnemii is an important mechanism of knee-ankle coupling and differential elongation may affect this function leading to weakness of the push-off phase during the gait. Achilles tendon ruptures may cause detachment of the gastrocnemius tendon from the soleus aponeurosis with subsequent differential elongation of the individual subtendons. This study investigated the effects of such detachment by investigating tendon fusion levels of the two muscle groups, and the effect of sequential differential elongation of the gastrocnemius on the Achilles tendon resting angle (ATRA) and to the knee-ankle coupling. METHODS: Conjoined tendon length (CTL) was measured in 23 cadavers. ATRA in knee extension (ATRA 0) and 90-degree knee flexion (ATRA 90) was measured with the gastrocnemius tendons (GT) intact, transected and with the gap reduced in 5-mm increments. In 15 specimens, knee-ankle coupling was examined. RESULTS: Considerable anatomical variation was present with CTL ranging from 2 to 40% of fibular length. In the intact triceps, surae ATRA 0 differed from ATRA 90 by 6 degrees (p < 0.001). Cutting the gastrocnemius caused an immediate separation of the tendon ends by 19 mm. ATRA 0 and ATRA 90 increased 8 and 4 degrees (p < 0.001), significantly larger increase for ATRA 0 (p < 0.001). Lengthening the gastrocnemius 10 mm altered the coupling point 10 degrees towards dorsiflexion. Transfixing the gastrocnemius at the level of the gap where the Achilles was sectioned, decoupled the knee-ankle coupling in all but two specimens. A moderate correlation between CTL and length of the medial gastrocnemius tendon was found. CONCLUSIONS: A greater relative ATRA 0 than relative ATRA 90 indicates differential elongation of the gastrocnemius. By elongating the gastrocnemius the knee-ankle coupling point shifts dorsally, and 20 mm elongation completely decouples the knee-ankle coupling. Independent lengthening of the gastrocnemius may explain the loss of power experienced by some patients following acute Achilles tendon rupture despite what would appear to be appropriate approximation of the ruptured tendon ends. Recognizing this occurrence is crucial when treating Achilles tendon ruptures and such patients require surgical correction in order to avoid long-term weakness of push-off strength.

Deep Peroneal Nerve Injury Following Hardware Removal for Lisfranc Joint Injury.

BACKGROUND: Surgical exposure of the Lisfranc joint complex is within close proximity to the deep peroneal nerve, which can be injured in this approach. Common clinical practice is to remove Lisfranc hardware at 3 to 4 months postoperatively. However, it is unknown if this provides a clinical benefit or risks injury to the deep peroneal nerve. The rate of nerve injury is currently unknown from the published literature. This study clarifies rates of neurological injury to the deep peroneal nerve during primary surgery and hardware removal. METHODS: This retrospective study was performed on all patients of a single surgeon from 2012 to 2018. Fixation was performed with locking plates or screws depending on the injury pattern. All patients who required open reduction and internal fixation routinely underwent hardware removal during this time. Neurological injury was assessed in a binary fashion (normal or abnormal) at 2, 6, and 12 weeks after the primary surgery and 2 and 12 weeks after hardware removal. McNemar's test was performed to compare the rates of injury. Patients were contacted at a minimum follow-up of 15 months (range, 15-87 months) to assess persistent nerve injury and satisfaction. Fifty-seven patients with an average age of 29.8 years were included in the final analysis; all had documentation at 3 months postsurgery. RESULTS: All patients had normal neurology before surgery. The rate of nerve injury for the primary surgery (11%) was significantly lower than the rate for patients with nerve injury following hardware removal (23%). However, the rate of spontaneous neurological recovery was low, with symptoms persisting in 5 of 6 patients between the primary operation and subsequent hardware removal. When these patients were excluded from the analysis, the rate of new nerve injury following hardware removal (15%) was not significantly different from the primary surgery rate. Seventy-one percent of nerve injuries persisted at the minimum 15-month final follow-up, with all patients with nerve injury being very or partially satisfied. CONCLUSION: The rate of deep peroneal nerve injury from primary Lisfranc fixation was 11%, and when routine hardware removal was planned the overall rate of nerve injury rose to 23%. This may be useful information during the patient consent process. LEVEL OF EVIDENCE: Level IV, case series.