Introduction: Anterior Cruciate Ligament Reconstruction (ACLR) is crucial for knee stability in ACL-injured individuals and for resuming pre-injury physical activities. Despite advancements, achieving symmetrical movement patterns during rehabilitation, particularly in stair negotiation, poses challenges. This study examines lower limb kinematics during stair negotiation at various rehabilitation stages post-ACLR, employing inertial measurement units (IMUs) and Statistical Parametric Mapping (SPM) for in-depth analysis outside the laboratory. Methods: This cohort study longitudinally assessed stair ambulation kinematics in patients aged 18-40, three (n=26) and five months (n=18) post-ACLR, using IMUs to track sagittal plane movement during stair ascent and descent. The participants ambulated on a flight of 20 stairs outside the laboratory. Results: At three months post-ACLR, the injured knee was less flexed compared to the contralateral knee during stair ascent (mean difference = -11.3, CI [-14.4, -8.1], p<.001) and descent (mean difference = -6.3, CI [-10.2, -2.4], p=.002). SPM analysis identified clusters where the injured knee showed decreased flexion at 0-35% and 87-99% of the stair ascent cycle (p<.005). By five months, flexion differences during ascent improved (mean difference = -4.7, CI [-8.1, -1.4], p=.008), but significant asymmetry persisted, with decreased flexion at 10-32% of the cycle during ascent and 20-29% during descent (p<.017). Improvements between three and five months were observed in knee flexion during ascent (mean increase = 6.1, p<.001) and descent (mean increase = 9.3, p=.004). Ankle and hip joint movements also exhibited persistent asymmetries, with minimal improvements over time. Conclusions: Persistent lower limb kinematic asymmetries remain five months post-ACLR during stair ascent and descent.

The authors have declared no competing interest.

NCT05001594

Arielle Fischer was supported by the Zuckerman STEM Leadership Program. In addition, this research was supported by the Israel Science Foundation (grant No. 2070658).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

approved by the Rambam health care campus Helsinki committee (0089-21-RMB)

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors