Joint area constraint had no influence on bone loss in proximal tibia 5 years after total knee replacement.

After total knee replacement (TKR) the bone mineral density (BMD) decreases in the proximal tibia. Our aim was to evaluate if changes in constraint of the cemented AMK TKR (DePuy, Johnson & Johnson, Leeds, UK) had any effect on postoperative bone remodeling in the proximal tibia. We used dual-energy X-ray absorptiometry in 43-53 knees to record changes in BMD in three regions of interest around the tibial component up to 5 years after operation with the AMK (DePuy) TKR. The knees had been randomly allocated to receive a flat or a concave tibial insert with retention of the posterior cruciate ligament when preoperative deformity was less severe, and either a concave or a posterior-stabilized (PS) insert with resection of the posterior cruciate ligament when deformity was more pronounced. All designs were associated with loss of BMD in the proximal tibia. The mean bone loss varied from 5 to 23% depending on the region of interest. There were no statistically significant differences between the groups, and the alteration of tibial insert constraint did not influence the bone remodeling. However, low precision values may have impaired the detection of differences.

Influence of joint area design on tibial component migration: comparison among a fixed symmetrical, asymmetrical, and moveable bearing.

Fifty-four knees (50 patients) were allocated to three different tibial polyethylene inserts (standard/rotating platform/FS1000) in the Freeman-Samuelson (Finsbury Orthopaedics Ltd, Surrey, United Kingdom) total knee arthroplasty. The FS1000 design has a spherical medial and a roller-in-trough configuration laterally. Radiostereometric examinations were done postoperatively and after 3, 12, and 24 months. The median migration of the metal-backing and the Hospital for Special Surgery scores did not differ between the three groups. At 2 years, the median external/ internal displacements for the rotating platforms were 2.8 degrees and 0.2 degrees, respectively (rotating platforms versus standard inserts/rotating platforms versus FS1000: P < .0005). Longitudinal rotations above the detection limits for radiostereometry were observed in some of the fixed implants (standard and FS1000 designs), indicating conditions for backside wear.

Posterior stabilized component increased femoral bone loss after total knee replacement. 5-year follow-up of 47 knees using dual energy X-ray absorptiometry.

After total knee replacement (TKR) bone mineral density (BMD) commonly decreases behind the anterior flange of the femoral component, which may increase the risk for supracondylar fracture. Our aim was to evaluate if changes in femoral design and joint area constraint had any effect on the postoperative bone remodeling in the distal femur. We used dual-energy X-ray absorptiometry in 47 knees up to 5 years after operation with the AMK (DePuy, Johnson and Johnson Leeds, UK) TKR. The knees had been randomly allocated to receive a flat or a concave tibial insert with retention of the posterior cruciate ligament when preoperative deformity was less severe, and either a concave or a posterior-stabilized (PS) insert with resection of the posterior cruciate ligament when deformity was more pronounced. The most pronounced relative reduction (15-38%) in bone mineral density (BMD) was seen posterior to the anterior flange. There were no significant differences in relative change in BMD between flat and concave inserts. Knees operated with PS inserts had more reduction posterior to the flange than knees with concave inserts in the subgroup with more advanced preoperative deformity (23% and 38% respectively). Use of posterior stabilized insert may increase the risk of supracondylar fracture compared to concave insert in knees with advanced preoperative deformity.

Influence of polyethylene constraint on tibial component fixation in total knee arthroplasty: follow-up report after 5 years.

The influence of articulating surface design of AMK total knee prosthesis (DePuy, Johnson & Johnson) on migration and radiographic outcome at 5 years was evaluated. The knees were randomly allocated to receive a flat or a concave insert with retention of the posterior cruciate ligament when preoperative deformity was less severe and either a concave or a posterior-stabilized insert with resection of the posterior cruciate ligament when deformity was more pronounced. In 64 knees, migration was measured with radiostereometry. The posterior-stabilized component displayed more varus-valgus tilting than the concave insert. Other statistically significant differences in migration were not seen. Radiolucent lines were frequently seen without differences between prosthesis groups.

Changed gait pattern in patients with total knee arthroplasty but minimal influence of tibial insert design: gait analysis during level walking in 39 TKR patients and 18 healthy controls.

INTRODUCTION: Previous radiostereometric studies have revealed abnormal anterior-posterior translation of the femur in patients operated with AMK (DePuy, Johnson and Johnson, Leeds, UK) total knee arthroplasty (TKA). Based on these observations, we hypothesized that patients with TKA have an abnormal gait pattern, and that there are differences in kinematics depending on the design of the tibial joint area. METHOD: We used a gait analysis system to evaluate the influence of joint area design on the kinematics of the hip and knee during level walking. 39 TKA patients (42 knees) and 18 healthy age-matched controls were studied. Patients with 5 degrees varus/valgus alignment or less were randomized to receive either a relatively flat or a concave tibial insert with retention of the posterior cruciate ligament. Patients who had more than 5 degrees varus-valgus alignment and/or extension defect of 10 degrees or more were randomized to receive the concave or a posterior-stabilized tibial component with resection of the posterior cruciate ligament. RESULTS: Patients with TKA tended to have less hip and knee extension and decreased knee and hip extension moment than controls. They also tended to walk more slowly. TKA altered the gait pattern, but choice of implant design had little influence. INTERPRETATION: In patients with a similar degree of degenerative joint disease and within the limits of the constraints offered by the prostheses under study, the choice of joint area constraint has little influence on the gait pattern.

The effect of tibial insert design on rising from a chair; motion analysis after total knee replacement.

BACKGROUND: There are few previous studies of sit-to-stand movement following total knee arthroplasty. Aim of the study was to test the hypotheses that total knee replacement alters the maximum trunk, hip, knee and ankle flexion-extension movements during chair rising, and that the design of the tibial plateau has small influence on the kinematics. METHODS: A motion analysis system was used to evaluate kinematics of the trunk, hip, knee and ankle when rising from one chair and sitting down on another. Patients with 5 degrees varus/valgus alignment or less received either a flat or a concave tibial insert with retention of the posterior cruciate ligament. Patients who had more malalignment and /or extension defect of 10 degrees or more were randomized to receive the concave or a posterior-stabilized tibial component with resection of the posterior cruciate ligament. The two groups of patients operated with and without resection of the posterior cruciate ligament were analysed separately and compared with a control group. 28 patients (29 knees) and 16 controls were in the final analysis. FINDINGS: Decreased hip and knee extension compared to the controls was seen, but there were no statistically significant differences in kinematics between the designs. INTERPRETATION: Choice of implant design in total knee arthroplasty had no detectable effects on kinematics of hip and knee joints during sit-to-stand movement.

Total knee replacement influences both knee and hip joint kinematics during stair climbing.

A gait analysis system was used to evaluate the kinematics of the hip and knee during stair ascending and descending after operation with total knee replacement. Patients with 5 degrees varus/valgus alignment or less were selected randomly to receive either a flat or a concave tibial component with retention of the posterior cruciate ligament. Patients who had more than 5 degrees varus/valgus alignment and/or an extension defect of 10 degrees or more were selected randomly to receive the concave or posterior-stabilized tibial component with resection of the posterior cruciate ligament. Twenty patients and 17 controls were studied 1-2 years after the operation. Patients had abnormal kinematics during stair ascending and descend-ing. Both knee extension and flexion were reduced. Hip extension tended to decrease, and decreased hip extension moment was noted.

Kinematics of three variations of the Freeman-Samuelson total knee prosthesis.

The effect of changes in the articulating surfaces on the kinematics of the Freeman-Samuelson total knee replacement was evaluated. Twenty-two patients (22 knees) (median age, 69 years) were randomized to a standard design with a fixed polyethylene bearing, a design with a mobile bearing, or a new design with a spherical medial femoral condyle with a fixed bearing. The patients were studied with radiostereometry and film-exchangers at 0 degrees nonweightbearing and during active weightbearing extension from 45 degrees to 15 degrees. The center of the tibial tray with a mobile-bearing prosthesis occupied a more anterior position than observed in the designs with a fixed bearing. The medial femoral condyle center had a more posterior position in the standard design than in the design with a spherical medial condyle. From a distally displaced position at 45 degrees, the medial condylar center displaced a mean of 1.8 mm proximally during extension in the standard design and had a constant position in the meniscal design. In the spherical design the medial condyle was displaced proximally at 45 degrees and displaced a mean of 1.6 mm distally during extension. The reduced anteroposterior and proximodistal translations in the meniscal design are compatible with improved congruency between the components. The design with a spherical medial condyle stabilized anteroposterior motions, but showed more pronounced proximodistal displacement medially than did the other two designs.