Migration and wear of hydroxyapatite-coated press-fit cups in revision hip arthroplasty: A radiostereometric study

Screw-fixated and hydroxyapatite-coated press-fit cups were studied using radiostereometry in 29 revision and 14 primary arthroplasties. The acetabular defects in the revision cases varied from none to type 3 (wall defects) according to Gustilo—Pasternak. Morsellized allograft was used in 25 revisions. Nine of these cups rested on less than 50% living bone. After 2 years, the mean migration in the revised group reached 0.36, 0.21, and 0.49 mm in the horizontal, longitudinal, and anteroposterior (AP) directions. The mean rotations varied between 0.5° and 0.7° depending on direction. The primary implants displayed smaller mediolateral migration and AP tilt. The mean proximal wear rate for the whole group was 0.11 mm/y. A central gap on the postoperative AP view implied less migration. The size of the preoperative bone defects or amount of bone—graft used had no influence on the migration. Despite extensive use of morsellized allograft, this implant displayed the smallest migration so far reported in revision hip arthroplasty.     

Evaluation of micromotion in cemented vs uncemented knee arthroplasty in osteoarthrosis and rheumatoid arthritis. Randomized study using roentgen stereophotogrammetric analysis

Twenty-four patients (25 knees) with osteoarthrosis (OA) and 19 patients (20 knees) with rheumatoid arthritis (RA) were operated with bi-tricompartmental knee arthroplasty. The patients were randomized to cemented or cementless fixation of the tibial component. The fixation of the tibial components was examined with roentgen stereophotogrammetric analysis (RSA) up to 24 months after operation. The following parameters representing tibial component micromotion were measured: (1) maximum migration of the prosthetic edge (maximum total point motion, MTPM); (2) distal migration of the prosthetic center (subsidence); (3) maximum proximal movements of the prosthetic edge ("lift-off"); and (4) prosthetic rotations, corresponding to internal/external rotation, adduction/abduction, and forward/backward tilt of the tibial component. All prostheses displayed significant micromotions, which tended to decrease 3-6 months after the operation. The average migration after 2 years, when measured as maximum single axis rotation, and MTPM were about 0.9 degrees-1.5 degrees and 1.0-1.5 mm, respectively, in all four groups. There were no statistically significant differences between cemented and cementless prostheses in either the OA or the RA group. The fixation in the RA patients did not significantly differ from that of the OA patients, perhaps because the RA patients had lower weight and were living a more sedentary life.     

Inducible displacements of the cup and the femoral head during active range of motion: Dynamic RSA studies of cemented total hip replacements

We evaluated changes in position of the femoral head relative to the cup and of the cup relative to the pelvis in total hip replacement patients during hip motion 2 years postoperatively. Two patient groups with nine patients in each group were studied. Hip motions, translations of the femoral head center, and cup displacements were recorded with dynamic radiostereometric examination (RSA, 2 exposures/s) during abduction in Group 1 and with use of static RSA exposures at increasing flexion of the hip in Group 2. Conventional radiographic examinations were used to evaluate any radiolucent lines around the cups at 2 years. During active abduction the femoral head center moved medially (median 0.04 mm) and the cup tilted anteriorly (median 0.09 mm). Increments in radiolucent lines at 2 years correlated to medial femoral head penetration, posterior tilt, and retroversion of the cup at 20° of abduction. The extension of radiolucent lines at 2 years showed a positive correlation with proximal inducible displacement of the cup and posterior translation of the femoral head center at maximum hip flexion. Our observations may be of value in understanding the pathogenesis of the loosening process and may be used to facilitate the development of prosthetic designs that optimize hip kinematics. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1686–1693, 2013     

Stable Fixation but Unpredictable Bone Remodelling Around the Lord Stem : Minimum 23-Year Follow-Up of 66 Total Hip Arthroplasties

Early designs of uncemented hip implants turned out to be failures mainly because the prerequisites for durable implant fixation were unknown. One exception was the chrome–cobalt stem of the Madreporic Lord prosthesis. We prospectively studied this prosthetic design in 107 hips that underwent surgery in 1979–1986. At the last follow-up, five stems and 54 cups had been revised, corresponding to stem and cup survival rates of 92% ± 3% and 45% ± 5% at 26 years. In all, 66 hips with remaining Lord stems were available for clinical follow-up 26 years (24–29) after the index operation. The mean total Harris hip and pain scores were 81 (SD 14) and 41 (SD 5).     

Bone cement with reduced proportion of monomer in total hip arthroplasty: Preclinical evaluation and randomized study of 47 cases with 5 years' follow-up

Bone cement with reduced amount of monomer and low curing temperature may improve implant fixation due to reduced toxicity. We analyzed the mechanical, chemical and thermal properties of such a cement (Cemex Rx) using Palacos R as control. The in vivo performance of the 2 cements was also evaluated in a prospective randomized study of 47 hips, where either of the cement types was used to fixate Lubinus SP2 prostheses with the stem made of titanium alloy. Cemex Rx had a reduced tensile strength, probably because this cement was manually mixed, as recommended by the manufacturer. A standardized laboratory test showed lower curing temperature for Cemex, but measurements at 37° and with prechilled Palacos R and Cemex Rx, as in clinical work, showed no difference. In the clinical study radiostereometric measurements of cup and stem migration showed similar values in the 2 groups up to 5 years after the operation. The cement mantle was stable in both groups, but the stems migrated similarly inside the cement mantle regardless of the type of cement used. Proximal wear was low (0.04-0.05 mm/year) and tended to be lower in the Cemex group (p = 0.02). Aluminum and vanadium levels in serum increased 5 years after the operation, but no difference was noted between the 2 groups. Collagen markers (PICP, ICTP) showed similar increases in bone turnover 6 weeks and 6 months after operation in both groups.     

Changed gait pattern in patients with total knee arthroplasty but minimal influence of tibial insert design

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° 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° varus-valgus alignment and/or extension defect of 10° 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.     

Increase in early polyethylene wear after sterilization with ethylene oxideRadiostereometric analyses of 201 total hips

We evaluated polyethylene wear by measuring femoral head penetration in 201 THA (median age 62 (31-81) years, 117 women) extracted from 5 randomized studies aimed to assess various fixation principles. There were 30 cemented all-polyethylene Lubinus cups sterilized by gamma irradiation in a reduced oxygen environment, 65 porous-coated Trilogy cups with liners gamma-sterilized in inert gas. Moreover, 37 cemented cups were sterilized with ethylene oxide (Reflection all-poly) and 69 porous-coated cups had liners sterilized in ethylene oxide (Reflection). 28 mm femoral heads were used in all cups. The patients were followed with repeated radiostereometric measurements (RSA) up to 2 years. The activity level of the patients was evaluated by a questionnaire. After 2 years, cups with polyethylene sterilized in EtO had almost twice the proximal and 3D penetration rates, as compared with gamma-sterilized polyethylene. The penetration did not differ between the gamma-irradiated designs. Using stepwise linear regression analysis, we found that the type of sterilization, age and weight were the most important predictors and that they determined the direction of the proximal penetration rate. Activity score, male gender and proximal migration of the cup had little effect. The accelerated wear observed with the EtO-sterilized polyethylene causes concerns about long-term problems and especially in younger patients.     

Kinematics and laxity of the knee joint after anterior cruciate ligament reconstruction: pre- and postoperative radiostereometric studies

BACKGROUND: Injury of the anterior cruciate ligament changes the kinematics of the knee joint. In studies of cadaveric knees, investigators have examined the effect of anterior cruciate ligament reconstruction on knee kinematics, but the effect on dynamic knee motion is not known. HYPOTHESIS: Reconstruction of the anterior cruciate ligament restores knee kinematics to normal. STUDY DESIGN: Prospective cohort study. METHODS: Nine patients were examined preoperatively and 1 year after reconstruction. Continuous radiostereometric exposures were performed at a speed of two to four exposures per second while the patients ascended an 8-cm high platform. Tibial rotation and tibial and femoral translation were measured with radiostereometric analysis. RESULTS: Tibial rotation and tibial and femoral translation were not significantly different after anterior cruciate ligament reconstruction compared with preoperative measurements. A radiostereometric evaluation of anterior knee laxity revealed restoration to within 1 mm of that on the uninjured side. Further evaluation of knee function using the Lysholm score, the Tegner activity level score, the International Knee Documentation Committee evaluation system score, and measurements of laxity using the KT-1000 arthrometer revealed significant improvements after reconstruction. CONCLUSION: Kinematics of the anterior cruciate ligament injured knee did not change significantly after ligament reconstruction, but the functional results were satisfactory and knee laxity was diminished.