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NAVIGATION KINEMATICS-THE OBLIQUE KNEE JOINT

The South West London Elective Orthopaedic Centre, Epsom, KT18 7EG, UK.

Computer navigation systems enable precise measurement and intra- operative knee range of movement analysis. We present a series of five knees that demonstrated unusual kinematics.

Five of 80 computer navigated knee replacements that were part of a prospective randomised trial were found to have unusual joint lines. Range of motion assessment was performed with computer assisted navigation after exposure and registration of bony landmarks and before bony resection was commenced. This revealed valgus alignment in extension that drifted into varus with knee flexion. We referred to these unusual patterns as ‘oblique joint lines’.

The data from the navigation log files of these five knees was analysed in detail. Average age of patients in this series was 68years and all were female. The average pre- operative angle between femoral axis and distal femoral articular surface was 101 degrees. All five knees had a tibial varus with average angle between the tibial axis and articular surface being 85 degrees. In two knees, more bone was resected from the medial posterior femoral condyle using 4 degrees external rotation. These two knees showed improved kinematics and horizontal joint line post- operatively.

Computer assisted navigation provides a precise understanding of the pre- operative knee kinematics. Bony cuts can be tailored to suit the pre- operative deformity. Increased external rotation of the femur with adequate medial soft tissue release is an alternate approach for difficult knees with ‘oblique joint lines’.

Correspondence should be addressed to Mr K Deep, General Secretary CAOS UK, Dept of Orthopaedics, Golden Jubilee National Hospital, Glasgow G81 4HX, Scotland. Email: caosuk{at}gmail.com