Electromyographic Evidence of Excessive Achilles Tendon Elongation During Isometric Contractions After Achilles Tendon Repair.

Abstract

Background:Weakness in end-range plantarflexion has been demonstrated after Achilles tendon repair and may be because of excessive tendon elongation. The mean frequency (MNF) of surface electromyogram (EMG) data during isometric maximum voluntary contraction (MVC) increases with muscle fiber shortening.Hypothesis:During isometric plantarflexion, MNF during MVCs will be higher on the involved side compared with the uninvolved side after Achilles tendon repair because of excessive tendon elongation and greater muscle fiber shortening.Study Design:Case series; Level of evidence, 4.Methods:Isometric plantarflexion MVC torque was measured at 20° and 10° dorsiflexion, neutral, and 10° and 20° plantarflexion in 17 patients (15 men, 2 women; mean age, 39 ± 9 years) at a mean 43 ± 26 months after surgery. Surface EMG signals were recorded during strength tests. MNF was calculated from fast Fourier transforms of medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) EMG signals.Results:Patients had marked weakness on the involved side versus the uninvolved side in 20° plantarflexion (deficit, 28% ± 18%; P < .001) but no significant weakness in 20° dorsiflexion (deficit, 8% ± 15%; P = .195). MNF increased when moving from dorsiflexion to plantarflexion (P < .001), but overall, it was not different between the involved and uninvolved sides (P = .195). However, differences in MNF between the involved and uninvolved sides were apparent in patients with marked weakness. At 10° plantarflexion, 8 of 17 patients had marked weakness (>20% deficit). MNF at 10° plantarflexion was significantly higher on the involved side versus the uninvolved side in patients with weakness, but this was not apparent in patients with no weakness (side by group, P = .012). Mean MNF at 10° plantarflexion across the 3 muscles was 13% higher on the involved side versus the uninvolved side in patients with weakness (P = .012) versus 3% lower in patients with no weakness (P = .522).Conclusion:Higher MNF on the involved side versus the uninvolved side in patients with significant plantarflexion weakness is consistent with greater muscle fiber shortening. This indicates that weakness was primarily because of excessive lengthening of the repaired Achilles tendon. If weakness was simply because of atrophy, a lower MNF would have been expected and patients would have had weakness throughout the range of motion. Surgical and rehabilitative strategies are needed to prevent excessive tendon elongation and weakness in end-range plantarflexion after Achilles repair.