Pre-operative knee extensor and flexor torque after secondary ACL rupture: a comparative retrospective analysis

Abstract

Background: Secondary anterior cruciate ligament (ACL) ruptures are a relevant clinical concern after surgical treatment of a primary ACL rupture. However, there is a lack of scientific evidence related to the role of muscle strength prior to revision surgery in a second ACL rupture. The aim of this study was to assess differences in knee extensor and flexor strength in patients before primary and secondary ACL reconstruction compared to healthy controls.

Methods: In total, n = 69 age, weight and sex matched individuals were included in the study: n = 23 patients with isolated primary ACL rupture, n = 23 with secondary ACL rupture, and n = 23 matched healthy controls. Maximal isokinetic knee extension and flexion torque normalized to body mass was assessed for both legs.

Results: For patients with secondary ACL ruptures, torques were reduced in the non-injured (extension: 1.94 Nm/kg vs. 2.46 Nm/kg, p < 0.05, flexion: 1.25 Nm/kg vs. 1.59 Nm/kg, p < 0.05) and the injured leg (extension: 1.70 Nm/kg vs. 2.46 Nm/kg, p < 0.05, flexion: 1.14 Nm/kg vs. 1.59 Nm/kg, p < 0.05) compared to healthy controls. For patients with a primary ACL rupture torques were reduced in the non-injured (extension: 1.92 Nm/kg vs. 2.46 Nm/kg, p < 0.05, flexion: 1.24 Nm/kg vs. 1.59 Nm/kg, p < 0.05) and the injured leg (extension: 1.38 Nm/kg vs. 2.46 Nm/kg, p < 0.05, flexion: 1.01 Nm/kg vs. 1.59 Nm/kg, p < 0.05) compared to healthy controls. There were no differences between patients with primary and secondary ruptures, except of the knee extension on the injured leg showing higher values after a secondary ACL rupture (1.38 Nm/kg vs. 1.70 Nm/kg, p < 0.05).

Conclusions: The findings indicate that maximal knee torques were significantly reduced in patients with primary and secondary ACL ruptures before surgical reconstruction for the non-injured and injured leg as compared to healthy controls. Further investigations are needed to assess strength abilities before and after a second revision within a prospective design.

Keywords: ACL re-rupture; ACL revision; Isokinetic; Pre-rehabilitation; Strength.

Fig. 1

Flow chart diagram—description of the study population

Fig. 2

Pre-operative normalized knee extension A and flexion B torque (Nm/kg body weight) of the non-injured leg. Bars show the mean and error-bars standard error. Points indicate the tendon type (n = 69). Filled and colored dots represent primary tendon grafts; * indicates significant differences following one-way ANOVA (p < 0.05); BTB = bone-to-bone, ST = Semitendinosus, BW = body weight

Fig. 3

Pre-operative normalized knee extension A and flexion B torque (Nm/kg body weight) of the injured leg. Bars show the mean and error-bars the standard error. Points indicate individual data points (n = 69). Filled and colored dots represent primary tendon grafts; * indicates significant differences following one-way ANOVA (p < 0.05); BTB = bone-to-bone, ST = Semitendinosus, BW = body weight