The Effect of Peroneal Muscle Strength on Functional Outcomes After the Modified Brostrom Procedure for Chronic Ankle Instability

Background: Although the peroneal muscles are known to be the major dynamic lateral stabilizers of the ankle, little information is available regarding the change in muscle strength and relation with the outcomes after lateral ligament repair surgery. The purpose of this study was to identify the effects of peroneal strength on the validated functional outcome measures after the modified Brostrom procedure (MBP) for chronic ankle instability. Methods: Forty-one patients (41 ankles) who underwent MBP using suture anchors were eligible and followed up to 2 years postoperatively. Functional evaluation consisted of the Foot and Ankle Outcome Score (FAOS), and Foot and Ankle Ability Measure (FAAM). The changes of peroneal strength were evaluated using an isokinetic dynamometer. Differences in the functional outcomes between the 3 groups divided according to the recovery rate of peroneal strength were analyzed. Results: Peak torque and total work for eversion in 60 degrees/s angular velocity significantly improved from a mean 8.1 and 5.2 Nm preoperatively to 11.4 and 6.9 Nm at postoperative 2 years, respectively (P < .001, P = .038). The deficit ratio of peak torque for eversion significantly improved from a mean 38.6% to 17.4%, and a significant side-to-side difference was found (P = .011). There were no significant differences in FAOS, FAAM, and measurements of stress radiograph between the 3 groups. Conclusions: Although restoration of peroneal strength postoperatively was about 82.6% of the unaffected ankle, patient-reported function in daily and sport activities were satisfactorily improved. Postoperative isokinetic strength of the peroneals demonstrated no statistically significant effects on the functional outcomes after MBP. Level of Evidence: Level III, prospective comparative case series.