Predicting the Recovery of Isokinetic Knee Strength 6 Months After Anterior Cruciate Ligament Reconstruction

Markus Wenning; Ghislain N Sofack; Daniela Zöller; Marlene Mauch; Albrecht H Heitner; Jochen Paul; Peter Zahn; Ramona Ritzmann

doi:10.1177/23259671241264845

Predicting the Recovery of Isokinetic Knee Strength 6 Months After Anterior Cruciate Ligament Reconstruction

Orthop J Sports Med. 2024 Sep 4;12(9):23259671241264845. doi: 10.1177/23259671241264845. eCollection 2024 Sep.

Authors

Markus Wenning^{1

2}, Ghislain N Sofack³, Daniela Zöller³, Marlene Mauch^{4

5}, Albrecht H Heitner⁴, Jochen Paul⁴, Peter Zahn¹, Ramona Ritzmann^{4

6}

Affiliations

¹ Department of Orthopaedic and Trauma Surgery, University Medical Center, Faculty of Medicine, University of Freiburg, Germany.
² Orthopaedic Surgery, BDH Klinik Waldkirch, Waldkirch, Germany.
³ Institute of Medical Biometry and Statistics, Faculty of Medicine, University of Freiburg, Germany.
⁴ Praxisklinik Rennbahn, Basel, Switzerland.
⁵ Department of Orthopaedics and Traumatology, University Hospital Basel, Basel, Switzerland.
⁶ Department of Sport and Sport Science, University of Freiburg, Germany.

Abstract

Background: The limb symmetry index (LSI) is a metric of strength restoration. It is key to successfully return to sports after anterior cruciate ligament (ACL) reconstruction. The threshold for return to sports is generally considered an LSI of ≥85%.

Purpose: To develop a statistical model for predicting the recovery of knee extension and flexion strength (with LSI ≥85%) at 6 months after ACL reconstruction.

Study design: Case-control study; Level of evidence: 3.

Methods: Patients who underwent arthroscopic ACL reconstruction between November 2015 and December 2020 were included. The patients were classified into 2 groups: "pass" if the LSI at 6 months postoperatively was ≥85% and "fail" if the LSI was <85%. Factors in 25 categories with 74 levels, including patient characteristics, periarticular procedures, intra-articular lesions and treatment, and perioperative management, were collected. A multivariable logistic regression combined with backward variable elimination was used to determine the predictive parameters for recovery of knee extension and flexion strength.

Results: A total of 948 patients were included. Graft site, preoperative isokinetic strength, treatment of meniscal injury, and injured side (left vs right) were identified as general predictors for both knee extension and flexion strength. For knee extension strength, age at injury and partial weightbearing duration were identified as additional predictors. For knee flexion strength, type of meniscal injury, surgeon volume, cartilage procedures, and periarticular procedures were identified as additional predictors. The Nagelkerke R ² of the final model was 0.178, and the c-statistic was 0.716 (95% CI, 0.676-0.754). The Hosmer-Lemeshow test indicated good calibration (P = .879).

Conclusion: Several factors including preoperative isokinetic strength, treatment of meniscal injuries, left vs. right side and graft site were found to predict recovery of ≥85% LSI in knee extension and flexion strength. Despite the numerous factors that were analyzed, the predictive power was moderate (c-statistic = 0.716), indicating there were other nonincluded factors that significantly influence strength performance at 6 months postoperatively.

Keywords: ACL reconstruction; isokinetic strength; prediction model; return to sports.