# Comparison of quadriceps and hamstring muscle size and strength between young athletes following knee surgery and healthy controls

## TL;DR

This study found that young athletes who had knee surgery had stronger hamstrings than healthy controls, but no differences in quadriceps strength or size.

## Contribution

The study demonstrates the feasibility of using ultrasound imaging in return-to-sport evaluations after knee surgery in a small sample.

## Key findings

- The POST group had greater hamstrings absolute and relative strength than the SAM group.
- There were no significant differences in quadriceps strength or size between the POST and SAM groups.
- Rehabilitation may have effectively restored quadriceps function and enhanced hamstrings strength.

## Abstract

This study compared the size and strength of the quadriceps and hamstring muscles in young athletes who had undergone previous knee surgery (POST) to sex- and age- matched, healthy controls (SAM).

A total of 18 (nine POST and nine SAM) participants volunteered to participate in the study’s procedures. Of the nine POST participants, six had underwent anterior cruciate ligament reconstruction, two underwent medial patellofemoral ligament reconstruction and one had undergone patellar tendon repair. Maximal voluntary isometric contractions assessed absolute strength (MVICABS) of the quadriceps and hamstrings. Muscle size was quantified as muscle cross-sectional area (mCSA) from panoramic ultrasound images. Relative strength (MVICREL) was calculated as a ratio of strength to muscle size. Separate 2-way mixed-factorial analyses of variance leg (operative or non-dominant (O-ND) vs. non-operative or dominant (NO-D)) and group (POST vs. SAM) assessed statistical differences at p ≤ 0.05.

There were no significant two-way interactions (p-range: 0.142–0.74) for any variables. Further, there were no significant main effects for the quadriceps (p-range: 0.127–0.605) nor was there a main effect for leg in any hamstrings variables (p-range: 0.126–0.367). However, the POST group had greater MVICABS and MVICREL than SAM for the hamstrings by 69.8 ± 30.7 N (p = 0.037) and 2.21 ± 1.02 N cm−2 (p = 0.045).

These findings indicate that there was no difference in quadriceps muscle strength or size between the POST and SAM groups. However, the POST group had greater hamstrings strength than SAM yet no differences in muscle size. These results suggest that the rehabilitation program may have been effective in restoring quadriceps function and enhancing hamstrings strength in young athletes following knee surgery. However, future studies should continue to elucidate the physiological effects of knee surgeries in larger, more diverse samples to attenuate the negative musculoskeletal outcomes experienced even after successful surgery and rehabilitation. Yet, these results can be considered as preliminary findings that demonstrate the feasibility of the inclusion of ultrasound imaging in return-to-sport evaluation in a small sample.