Objectives Controversy still exists on whether knee hyperextension affects the outcome following anterior cruciate ligament reconstruction (ACL-R). Therefore, the purpose of the present study was to determine if maximum knee extension angle of ACL-R knees and contralateral uninjured knees during walking is related to the clinical outcome following ACL-R. It was hypothesised that maximum knee extension angle would not be significantly correlated with patient-reported outcome measures (PROMs) following ACL-R.
Methods Forty-two patients (age at surgery: 23±9 years, 23 male and 19 female) underwent unilateral ACL-R. Twenty-four months after surgery, subjects performed level walking on a treadmill while biplane radiographs were acquired at 100 Hz. Three-dimensional tibiofemoral motion was determined using a validated model-based tracking process. Tibiofemoral rotations were calculated from foot strike through early stance. The primary kinematic outcome measure was maximum knee extension angle of ACL-R and contralateral uninjured knees during walking, with positive values indicating hyperextension. The side-to-side difference (SSD) in maximum knee extension angle was calculated by subtracting the angle of the contralateral uninjured knee from that of the ACL reconstructed knee. PROMs (International Knee Documentation Committee Subjective Knee Form, Knee Injury and Osteoarthritis Score and Marx Activity Rating Scale) were obtained at 24 months after surgery. Correlations between PROMs and maximum dynamic knee extension angle in ACL-R and contralateral knee were evaluated (P<0.05).
Results Maximum knee extension angle during walking was 2.3±4.5° in ACL-R knees and 4.3±4.2° in contralateral uninjured knees at 24 months after surgery, indicating hyperextension during walking on average. SSD in maximum knee extension angle was −2.0±3.7°. No significant correlation was observed between maximum knee extension angle and the PROMs.
Conclusion Maximum knee extension angle during walking was not significantly correlated with PROMs, suggesting that clinically, physiologic knee hyperextension can be restored after ACL-R and not adversely affect PROMs.
Level of evidence Level III.
- anterior cruciate ligament reconstruction
- knee extension angle
- dynamic stereo X-ray system
- patient-reported outcome measures
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Contributors KN, EH and YT conceived the study. KN, EH and TG performed data and statistical analysis. KN, EH and WA wrote the manuscript. JJI and FHF obtained funding. FHF supervised this study. All authors participated in the design of the study, interpretation of the data and performed critical revision of the manuscript for important intellectual content. All authors read and approved the final manuscript.
Funding This research was funded by NIH/NIAMS, grant # R01 AR 056630.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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