Christopher J. Cleary1, Bryan G. Vopat2, Ashley A. Herda1,2

1University of Kansas Edwards Campus, Overland Park, Kansas; 2University of Kansas Health Systems, Overland Park, Kansas

After orthopedic knee surgeries, deficiencies in lower-limb skeletal muscle size and strength are commonly observed within an individual between the operative (OP) and non-operative (NOP) limbs upon return to sport clearance following injury, surgery, and rehabilitation (ISR). These deficiencies often present as asymmetries when compared to healthy, never-injured individuals acting as controls (H-Con). PURPOSE: The purpose of this investigation was to assess the differences and relationships between quadriceps and hamstring muscle cross-sectional area (mCSA) and strength of ISR and age-and sex-matched H-Con individuals. METHODS: Muscle size was determined using panoramic ultrasound images and quantified as the sum of the mCSA of three superficial quadriceps and the hamstrings muscles in 18 individuals (mean±SD: 19.4±6.7 years). Muscle strength was assessed by handheld dynamometry for the quadriceps and hamstrings through maximal voluntary isometric contractions (MVIC). The ISR group was assessed at the time of their return to sport testing after a course of rehabilitation. Both groups were assessed on each leg with the OP limb defined as the non-dominant limb when matched to the H-Con group. Separate 2x2 mixed-factorial analyses of variance (ANOVA) with the factors of group (ISR vs. H-Con) and leg (OP vs. NOP) analyzed differences in MVIC and mCSA of the quadriceps and hamstrings. Linear mixed-effect regression models assessed if the mCSA-MVIC relationship differed based on group and leg status. Statistical significance was determined at p≤0.05. RESULTS: No significant interactions or effects were observed for the hamstrings MVIC or mCSA (p>0.05). There was also no interaction or effect for quadriceps MVIC (p>0.05). However, there was a 2-way interaction (p=0.014) for the quadriceps mCSA. Model decomposition revealed that NOP mCSA was greater than OP by 8.2±2.1 cm-2 in the ISR group. The linear mixed-effect regression models indicated that quadriceps mCSA influenced quadriceps MVIC independent of group or leg [estimate (95% confidence interval); 1.04 kg (0.02-2.05 kg)]. CONCLUSION: Once cleared to return to sport, muscle strength and the mCSA-MVIC relationship in the quadriceps and hamstrings appears to be similar between H-Con and ISR individuals despite mCSA differences between legs in ISR.

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