2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


Influence of Knee Flexors on Joint Stability During the Ligamentization Phase Post-ACLR

Magdalena Stawinska, MPT, Warsaw POLAND
Marcin Plenzler, MPT, Warsaw POLAND
Robert Smigielski, MD, PhD, Warsaw, masovian POLAND
Beata Ciszkowska-Lyson, PhD, Warsaw POLAND

Life Medical Center, Jozef Pilsudski University of Physical Education in Warsaw, Warsaw, POLAND

FDA Status Not Applicable

Summary

This study examines the role of knee flexor strength and activation in maintaining stability during the ligamentization phase after ACL reconstruction, emphasizing the importance of intensive flexor training while delaying extensor training

Abstract

Background

Anterior cruciate ligament (ACL) reconstruction is a widely performed procedure aimed at restoring knee stability and function. The ligamentization process, during which the graft transforms into a biological and functional substitute for the native ligament, is crucial for optimal outcomes. During this critical phase, the role of knee flexor muscles becomes increasingly significant, as their strength and activation directly impact joint stability. Understanding the interplay between flexor muscle function and knee stability is essential for developing effective rehabilitation protocols and enhancing post-operative recovery. This study aims to explore how the strength and activation of the knee flexors contribute to maintaining knee stability during the ligamentization phase following ACL reconstruction.

Methods

Twenty-five patients (14 men, 11 women) who underwent anterior cruciate ligament reconstruction using an autologous quadriceps tendon graft were evaluated 12 months post-operatively. The study focused on assessing the strength of the knee flexor muscles at angles of 30 and 90 degrees of flexion, as well as the strength of the knee extensor muscles at 90 degrees of flexion.The control group consisted of the contralateral uninjured limbs. Knee stability was assessed at a 30-degree flexion angle by analyzing tibial translation in relation to the femur using a Rolimeter arthrometer at 3, 6, 9, and 12 months post-operatively.
The rehabilitation protocol included regular exercises to strengthen the knee flexor muscles through concentric-eccentric contractions, particularly during the intensive graft ligamentization period (3 to 6 months post-surgery). Concurrently, exercises for the knee extensor muscle group were limited to closed kinetic chain activities, extending until a minimum of 9 months post-operatively.

Results

Analysis of the results revealed no statistically significant difference in muscle strength of the knee flexors at both 30 and 90 degrees of flexion when comparing the operated limb to the contralateral limb. However, the results at 30 degrees of flexion were significantly better (p<0.001) than those at 90 degrees of flexion. The strength values for the knee extensors were significantly weaker in the operated limb compared to the non-operated limb (p<0.001), with an average deficit of 17% (SD 12%).
Analysis of tibial translation measurements demonstrated similar values for the operated limb compared to the non-operated limb at each observation point. Notably, there was no significant change (increase in tibial translation) between 3 and 6 months, as well as between 3, 9, and 12 months post-surgery. The average values ranged from 8.4 to 8.7 mm for the non-operated limb and from 6.6 to 7.5 mm for the operated limb. All values remained within the accepted normative range.
Importantly, none of the patients reported experiencing instability during activities of daily living or while engaging in dynamic physical activities.

Conclusion

The obtained results regarding muscle strength and stability seem to support the rationale for implementing intensive training of the knee flexor muscles, particularly during the critical graft ligamentization phase. Delaying the introduction of intensive strength training for the knee extensors in an open kinetic chain until a minimum of 6 months post-surgery, while concurrently engaging in intensive training of the flexors, may contribute to the preservation of clinical knee stability.