Knee joint kinematics, fixation and function related to joint area design in total knee arthroplasty

Abstract

The aim was to study the influence of different designs of the joint area on tibial component fixation, kinematics and clinical outcome after a cemented total knee arthroplasty (TKA). The HSS score and a special questionnaire were used at the clinical examination. Conventional radiography was done to record the positioning of the implants and development of radiolucencies. The migration and inducible displacement were evaluated using radiostereometry (RSA). The kinematics of the knee during active extension was studied using dynamic RSA. In randomised and prospective studies 87 knees in 83 patients (28 male, 55 female, age 69, range 50-83) received an AMK (DePuy, Johnson&Johnson) TKA. The patients were divided into two groups. In group 1 the patients had varus/valgus deformities of £ 5° and the PCL was retained. The PCL was resected in group 2 where the patients had deformities exceeding 5° and/or fixed flexion deformities of more than 10°. In group 1 a flat (F, n=20) or a concave (C, n=20) design was implanted (study 3). In group 2 (study 4) the patients received a concave (n=25) or a posterior-stabilised (PS, n=22) tibial plateau. The migration of the tibial component, positioning of the prosthesis, development of radiolucencies and the clinical outcome were evaluated after one and two years. Twenty-two patients (11F, 11C) in group 1 (study 1) and 22 knees in 20 patients in group 2 (study 2; 11C, 11PS) were examined one year postoperatively to evaluate the kinematics of the knee. Eleven normals served as controls. During active extension of the knee the inducible displacements of the tibial component were recorded in 16 knees (15 patients). Based on successful RSA examinations 5 knees (4F, 1C) from group 1 and 11 knees (5C, 6PS) from group 2 were selected (study 5).Abnormal kinematics and especially increased AP translations compared to normals (p< 0.0005) were recorded in all designs. The concave design showed the widest AP-translations in both studies. The clinical outcome in terms of HSS score did not differ between the flat versus the concave designs in study 1 and between the concave versus the PS implants in study 2. Up to two years the migration of the tibial component and the development of radiolucent lines were of the same magnitude for the flat versus the concave inserts in study 3 and the concave versus the PS designs in study 4. The positioning of the implant and the fulfilment of the patients expectations on the surgery preoperatively did not differ. The AMK prosthesis migrated at about the same amount as reported earlier for similar designs. In study 5 all implants showed a correlation between some of the inducible displacements (anterior-posterior tilting and maximum total point motion) and the corresponding migration up to 2 years. The more the anterior tilt the more the migration in the same direction. If the PCL was sacrificed during the knee replacement the change into increased anterior tilt occurred earlier (i.e. at more degree of flexion) if a concave insert was used compared with the PS design. When the active extension reached 25 degrees there was more anterior tilt of the tibial component in the concave design (p=0.001, r2=0.62) and if the tibial plateau centre had a medial position (p<0.0005, r2=0.78).Compared with normal knees all prosthetic designs showed abnormal pattern of motion. The extent of this abnormality was influenced by the design of the joint area. A corresponding influence on the fixation of the tibial component could not be verified. The choice of joint area and recorded kinematics had no or small influence on the clinical results. Feelings of instability could to some extent be related to the kinematics of the knee joint.