Abstract
Objectives Throughout the 20th Century, it has been postulated that the knee moves on the basis of a four-bar link mechanism composed of the cruciate ligaments, the femur and the tibia. As a consequence, the femur has been thought to roll back with flexion, and total knee arthroplasty (TKA) prostheses have been designed on this basis.
Recent work, however, has proposed that at a position of between 0 degrees and 120 degrees the medial femoral condyle does not move anteroposteriorly whereas the lateral femoral condyle tends, but is not obliged, to roll back - a combination of movements which equates to tibial internal/femoral external rotation with flexion. The aim of this paper was to assess if the articular geometry of the GMK Sphere TKA could recreate the natural knee movements in situ/in vivo.
Methods The pattern of knee movement was studied in 15 with 16 GMK Sphere implants. The motions of all 16 knees were observed using pulsed fluoroscopy during a number of weight-bearing and non-weight-bearing static and dynamic activities.
Results During maximally flexed kneeling and lunging activities, the mean tibial internal rotation was 8 degrees. At a mean 112 degrees flexion during lunging, the medial and lateral condyles were a mean of 2 mm and 8 mm 4) posterior to a transverse line passing through the centre of the medial tibial concavity.
With a mean flexion of 117 degrees during kneeling, the medial and lateral condyles were a mean of 1 mm anterior and 6 mm 4) posterior to the same line. During dynamic stair and pivoting activities, there was a mean anteroposterior translation of 0 mm to 2 mm of the medial femoral condyle.
Backward lateral condylar translation occurred and was linearly relate d to tibial rotation. Conclusion The GMK Sphere TKA in our study group shows movements similar in pattern, although reduced in magnitude, to those in recent reports relating to normal knees during several activities.