IF YOU COULD SEE INSIDE THE KNEE, WHAT WOULD YOU SEE IN KNEELING? VISUALISATION OF 4-DIMENSIONAL ARTHROKINEMATICS IN DEEP FLEXION

Scarvell J.1,2, Hribar N.1, Galvin C.1,3, Pickering M.4, Lynch J.3, Smith P.3,5, Perriman D.1,3,5
1University of Canberra, Physiotherapy, Bruce, Australia, 2Canberra Hospital, Trauma and Orthopaedic Research Unit, Canberra, Australia, 3Canberra Hospital, Trauma and Orthopaedic Research Unit, Woden, Australia, 4University of New South Wales, Canberra, School of Electrical Engineering and Information Technology, Canberra, Australia, 5Australian National University, College of Medicine, Canberra, Australia

Background: Kneeling is a culturally important activity for many people, yet people over the age of 45 may lose this ability due to osteoarthritis, joint stiffness or pain. Knee replacement design has focused on increased knee flexion ability without great success. However, some of the limitations of post knee replacement arthrokinematics may be due to the natural arthrokinematics of older people, or kinematics due to their existing osteoarthritis. There have been some studies of arthrokinematics of deep flexion, but not in older people. The characteristics of deep flexion in older people are not known.

Purpose: This study aims to describe the deep flexion arthrokinematics of healthy older people in order to understand the requirements of six degrees of freedom kinematics, and in particular, potential coupled motions that make deep flexion possible.

Methods: 30 participants between 45 and 80 years participated. The study is part of a registered clinical trial called PICKLeS (ANZCTR) looking at knee replacement design and healthy ageing. A clinical examination including pain, range of motion, knee stability, functional tests and patient reported outcomes excluded participants with knee symptoms. Imaging was captured by fluoroscopy during a kneeling activity, and computerised tomography resting in supine. Images were imported into Orthovis for registration and determination of the axes of tibia and femur. The resultant 4-dimensional rendered model was analysed for six degrees of freedom in Matlab.

Results: Participants achieved 142+/-6.4 degrees in kneeling. At 90 degrees knee flexion there was 8+/-5.7 degrees of internal rotation, at 120 degrees rotation had increased to 11+/-5 degrees and 16+/-5 degrees at 150 degrees of flexion. Flexion was coupled to the rotation (r=0.469, p 0.001). Abduction was minimal from 1+/-1.7 degrees at 90 degrees flexion to 2.2+/-2.5 degrees at 150 degrees flexion. Translations were slight in the axial plane- from 2+/-3.1mm medial translation at 90 degrees flexion to 4.8+/-3.8mm lateral translation at 150 degrees of flexion. Anterior/posterior translation was most interesting with the femur beginning 12.8 +/-2.6mm anterior to the tibia and moving posteriorly in a linear relationship (r= 0.955, p 0.001) so that at 120 degrees of flexion the femur is almost central at 1.2+/-2.8mm, and at 150 flexion the femur was 23+/-3.4mm posterior to the tibia. The posterior translation was coupled to internal rotation for deep flexion (R2= 0.920). Visually this appears as the femur moving far back on the tibia, so the femoral condyles are resting on the posterior horns of the menisci, with internal rotation so that the posterior margin of the medial tibial plateau rotates around into the fossa of the posterior femur.

Conclusion(s): Flexion, internal rotation and posterior translation of the femur are coupled powerfully in deep knee flexion.

Implications: Osteoarthritis of the knee limits both rotation and posterior translation of the knee. This potentially drives the loss of knee flexion. Damage to the posterior horns of the menisci may likewise limit flexion by pain or stiffness. To restore knee flexion, internal rotation and posterior translation will be essential. Manual therapy should consider a P-A glide to the tibia for flexion with internal rotation and some distraction.

Funding acknowledgements: Canberra Hospital Private Practice Fund
Biomet Pty Ltd Australia

Topic: Musculoskeletal: peripheral

Ethics approval: ACT Health Directorate and University of Canberra Research Ethics Committees (ETH4.11.071).


All authors, affiliations and abstracts have been published as submitted.

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