2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


Evaluating Biological Recovery in ACL Reconstruction: Implications for Return to Sports

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 investigates the biological recovery of the knee following ACL reconstruction and emphasizes the importance of delaying the return to unrestricted activity from 9 months to at least 12 months to reduce the risk of re-injury.

Abstract

Background

The expected timeline for returning to unrestricted activity is between 6 and 12 months post-surgery. A second ACL injury is one of the most common complications, particularly prevalent within the first two years following ACL reconstruction (ACLR). This recurrence may be linked to graft healing, restoring knee joint homeostasis, and achieving functional recovery before resuming unrestricted sports activities.
This study aimed to investigate the biological recovery of the knee and identify the duration of biological readiness as a factor influencing the risk of re-rupture.

Methods

A total of 75 patients (42 males and 33 females) who underwent reconstruction with an autologous quadriceps tendon graft were reviewed using 3-T MRI scans at 3, 6, 9, 12, 18, and 24 months post-ACLR. A control group included 84 healthy adults with intact ACLs. To maintain homogeneity, the same orthopedic surgeon performed all surgeries, and the same physiotherapy team conducted rehabilitation.
Signal intensity (SI) was measured manually in three ROIs for the ACL and one ROI for the PCL. The ACL/PCL ratio (APR) was calculated and compared over time (3 to 24 months) and to native ACL signal intensity assessed through the same method. Bone marrow edema (BME) was evaluated in coronal STIR sections by measuring signal intensity in five areas: lateral and medial femoral and tibial condyles.
Patients were assessed postoperatively using the IKDC and Lysholm-Tegner scores. Instrumented knee testing was conducted with the Rolimeter arthrometer. Hamstring and quadriceps muscle strength were assessed under isometric conditions, measuring maximal isometric torque (IT).

Results

The native value of APR at three measurement points (dsl, mid, prx) was 2.02 ± 0.68. The peak hyper-intense signal observed at 6 months post-surgery was 3.59, with a range of 2.82–4.64 (p < 0.001). By the 12-month mark, the signal had significantly decreased, reaching 70% of the target native value (p < 0.05), with a significant difference of 15% in signal intensity observed between 9 and 12 months (p < 0.05). At the 2-year follow-up, the remodeling of the ACL graft closely resembled that of the native ACL (p < 0.01).
Bone marrow edema (BME) was evident at 3 months post-surgery, significantly reduced by 6 months (p < 0.001), with complete reduction by 12 months (p < 0.01).
Anterior knee laxity was lower at all time points compared to the contralateral healthy knee (p < 0.05). No association was found between muscle strength or IKDC scores and signal intensity. During a 4-year clinical follow-up, less than 2% experienced re-injury.

Conclusion

A year post-surgery, the biological environment of the knee is not fully restored; however, delaying the return to activity from 9 months to a minimum of 12 months might promote biological healing and enhance overall recovery, thereby reducing the risk of re-injury. Because functional recovery can occur more quickly than structural readiness, it is crucial to ensure that both the ACL graft and BME are fully healed and that functional recovery has been achieved before returning to sports.