KNEE CONTROL DURING A PIVOT-SHIFT SIMULATING TASK FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION – A CROSS-SECTIONAL AND LONGITUDINAL INVESTIGATION

Y. Grinberg¹, J.L. Markström^1,2, G. Sole³, C.K. Häger¹

¹Umeå University, Department of Community Medicine and Rehabilitation, Section of Physiotherapy, Umeå, Sweden, ²Umeå University, Department of Statistics, Umeå School of Business, Economics and Statistic, Umeå, Sweden, ³University of Otago, Centre for Health, Activity and Rehabilitation Research, School of Physiotherapy, Dunedin, New Zealand

Background: Anterior cruciate ligament injury may result in devastating consequences partially due to knee rotational instability. This is often assessed passively using the pivot shift test or similar. Full weight-bearing active tests have been investigated in the later stages of rehabilitation following an anterior cruciate ligament reconstruction (ACLR) but with contrasting results. Functional assessment of knee rotational stability early on is warranted, as well as throughout rehabilitation.

Purpose: To evaluate whether individuals after ACLR early and throughout rehabilitation exhibit an altered movement pattern compared to non-injured controls when performing a knee pivot-shift inducing task.

Methods: Participants following ACLR and non-injured controls performed a step-down and cross-over task: they descended two stairs and upon reaching the floor, they performed a cross-over step in an intended angle of 45° and continued walking in the new direction. Knee angles, angular velocities and moments in the sagittal and transverse-planes as well as knee muscle activation were recorded during the cross-over phase. Thirty-five individuals following ACLR were tested at: 1. Early-rehabilitation (2.9±1.1 mean±SD post-reconstruction) and compared to 35 controls. Follow up at two additional occasions throughout rehabilitation, based on functional criteria, were conducted for most individuals at: 2. Mid-rehabilitation (so far n=27, 8.8±2.9) and 3. Post-rehabilitation (so far n=25, 13±3.5). Time-normalized curves of the cross-over phase were compared between groups and legs applying functional t-tests with interval-wise testing-adjusted P values. Secondary discrete outcomes illustrating the cross-over phase performance (completion time, foot rotation angles, cross-over angle and step length) were compared using t-tests.

Results: For Early-rehabilitation compared to controls, in the final ~50% of the cross-over phase, the injured leg showed significantly greater knee flexion angle (4.0-8.1 degrees) and moment (0.17-0.23 Nm/kg), lower flexion-extension angular velocity (21-41 degrees/s) and internal rotation moment (0.05-0.10 Nm/kg). Further, the injured leg had greater muscle activation for biceps femoris and vastus medialis for the same period. Similar results, although less pronounced, were observed when comparing the injured and non-injured legs. There was no asymmetry for the controls and no differences were detected between the non-injured leg and controls. Further, the ACLR group demonstrated lower cross-over angles for both legs, greater preparatory foot rotation of the injured leg towards the new walking direction and longer time to complete the task for the injured leg compared to controls. Analysis is currently ongoing for the longitudinal data and will also be presented.

Conclusions: Individuals early after ACLR adopt a knee-protective strategy when performing an active full weight-bearing and knee pivot-shift inducing task. This strategy seems indeed most evident in the final ~50% of the cross-over phase, where knee internal rotation occurs.

Implications: Evaluation of and training for controlling cross-over manoeuvres should be implemented early in rehabilitation following ACLR. Clinicians should however, be careful when interpreting a weight-bearing task such as a step-down and cross-over, as individuals may exhibit knee protective strategy, thus concealing rotational instability.

Funding acknowledgements: Swedish Research Council; Region Västerbotten; Swedish Research Council for Sports Science; Umeå University; King Gustaf V and Queen Victoria's Foundation

Keywords:
Knee stability
Motion analysis
Biomechanics

Topics:
Sport & sports injuries
Musculoskeletal: lower limb
Orthopaedics

Did this work require ethics approval? Yes

Institution: Regional authority of the state

Committee: Regional ethical review board in Umeå

Ethics number: 2015/67-31