Squatting, lunging and kneeling provided similar kinematic profiles in healthy knees—A systematic review and meta-analysis of the literature on deep knee flexion kinematics

Background: Understanding healthy deep flexion kinematics will inform the design of conservative clinical rehabilitation strategies for knee osteoarthritis and contribute to improved knee prosthesis design. This study is a systematic review and meta-analysis of the kinematic outcomes measured at the healthy tibiofemoral joint during loaded deep knee flexion. Methods: A computerised literature search and bibliography review without date restriction identified twelve studies with 164 participants aged 25–61 years in-vivo, and 69–93 years in-vitro. Flexion higher than 120° was achieved by squatting, lunging or kneeling. Measurement technologies in-vivo included radiographs, open MRI and 2D–3D MRI or CT image registration on fluoroscopy. Microscribe was used in-vitro. Results: Outcomes were either six degrees-of-freedom based on femur movement or contact patterns on the tibial plateau. The meta-analysis demonstrated that in-vivo, between 120° and 135° of flexion, the tibia internally rotated (mean difference (MD) = 4.6°, 95% CI 3.55° to 5.64°). Both the medial-femoral-condyle and lateral-femoral-condyle translated posteriorly, (MD = 10.4 mm, 95% CI 6.9 to 13.9 mm) and (MD = 5.55 mm, 95% CI 4.64 to 6.46 mm) respectively. There was some evidence of femoral medial translation (3.8 mm) and adduction (1.9° to 3.3°), together with medial compression (1.7 mm) and lateral distraction (1.9) mm. Conclusions: Across the in-vivo studies, consistent kinematic patterns emerged; despite the various measurement technologies and reference methods. In contrast, in-vivo and in-vitro results were contradictory. Trial registration: This systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 25 February 2017 (registration number: 42017057614).