Flat vs. concave tibial joint surface in total knee arthroplasty - Randomized evaluation of 39 cases using radiostereometry

40 patients with non-inflammatory arthrosis and minor preoperative deformit y (less than or equal to 5 degrees) were operated on with an AMK type (DePu y, Johnson & Johnson) total knee arthroplasty (TKA), The posterior cruciate ligament was retained, The patients were divided into those with a Rat (te rminology of the manufacturer: standard) or a concave (terminology of the m anufacturer: constrained) polyethylene insert (20 in each group), Radioster eometric (RSA) examinations were done postoperatively and after 3, 12 and 2 4 months, The median absolute rotations of the tibial inserts varied betwee n 0.12 and 0.24 (range 0.00-1.54) degrees, with no differences between the 2 groups, The median maximum total-point motions (flat/concave = 0.41/0.42 mm), the maximum subsidence or lift-os did not differ, The Hospital for Spe cial Surgery knee score and the patients' opinion about the operation, base d on their preoperative expectations, showed little, if any, differences, A t 2 Sears, 10 of 20 patients with flat and 13 of 19 with concave inserts re garded their knee function as normal or almost so.