Hamstring Strength Recovery is Worse in Women than Men following ACL Reconstruction with Hamstring Autografts
Authors: Bodkin Stephan G. , Casp Aaron Joseph , Kew Michelle Elizabeth , Brockmeier Stephen F. , Diduch David R. , Hart Joseph M. 
Published: July 2019

Objectives: Graft choice in ACL reconstruction (ACLR) and post-operative rehabilitation may influence strength recovery and return to sports differently in men versus women. Persistent muscle weakness, impaired function, and poor patient reported outcomes are a concern for patients early after reconstruction and impact a timely and successful return to unrestricted physical activity without re-injury. However, little is known about the effect of graft choice and sex on short term ACLR recovery and return-to-play assessment. The purpose of this study was to compare knee extensor and flexor strength between male and female patients in isolated ACLR across both patellar tendon and hamstring autografts. Methods: A total of 166 patients with primary, unilateral and uncomplicated ACL reconstructions (22.6±9.9 years, 87 females, 5.94±.46 months post ACLR) were recruited for participation. There were 100 patients with bone patellar tendon bone (BPTB) autografts and 66 hamstring (HS) autografts. All patients completed the Tegner activity Scale and underwent bilateral isokinetic (90°/sec) tests of the knee extensor and flexor groups. Outcomes were recorded in a single session as part of a return-to-sport test battery. Strength was expressed as torque normalized to mass (Nm/kg) and limb-symmetry was expressed as a percentage of (involved/uninvolved)*100. Surgical Notes were obtained to determine the patient’s sex and type of autograft used at the time of ACLR. Strength measures were compared using 2x2 ANCOVAs (Sex by Graft Type) with the patient’s current activity level as a covariate. Post-hoc Cohen’s D effect sizes and 95% CI were calculated and statistical significance was defined as p-values of .05 or less. Results: There was a significant sex*graft type interaction for normalized knee flexor torque (P=.017) (Figure 1). Females with a HS graft (.592±.49 Nm/kg) had significantly less knee flexor torque compared to females with a BPTB graft (.910±.24 Nm/kg, Cohen’s d= .90[.45, 1.36]) and all males (HS: .937±.35, Cohen’s d=.87 [.45, 1.30]). There were significant main effects for graft type for knee flexor (P=.001) and extensor (P=.008) symmetry. Patients with a BPTB graft demonstrated less knee extensor symmetry (65.7±17%) and greater knee flexor symmetry (98.7±18%) compared to patients with a HS graft (Extension: 77.1±32%, Cohen’s d=.47[.16, .79]) (Flexion: 82.9±33%, Cohen’s d=.63[.31,.95]). We also observed a significant main effect for sex (P=.028) and graft type (P=.048) for normalized knee extensor strength. On average, males (1.67±.60 Nm/kg) demonstrated significantly greater normalized extensor torque than females (1.44±.75 Nm/kg, Cohen’s d= .34 [.03, .64]), and patients with a HS graft (1.66±.34 Nm/kg) demonstrated greater normalized extensor strength than those with a BPTB graft (1.45±.42 Nm/kg, Cohen’s d= .54 [.22, .85]). Conclusion: At approximately 6 months following ACLR, female patients reconstructed with hamstring autografts demonstrated weaker hamstring strength compared to females with a BPTB autograft. There were no differences in hamstring strength between graft types in males. Females appear to be recovering hamstring strength differently than males when using a hamstring autograft. These findings may have implications in surgical planning, post-operative rehabilitation and return to sports decision making. [Figure: see text]