Papers by Keyword: Polyethylene Wear

Abstract: Total knee arthroplasty is a successful procedure for treating chronic degenerative knee pathologies, many patients are dissatisfied with the results of the standard design. Improper tibia rotation of the implant is suspected to contribute to post-operative pain, polyethylene wears, aseptic loosening, and instability. Many factors can influence the alteration of knee kinematics after surgery including differences in implant design. Using magnetic resonance imaging, tibia rotation in a normal knee has -15.0º and -2.5º in weight-bearing males neutral tibia rotation, and tibia rotation in postoperative patients has 2.1º and 9.5º using computer tomography. In this study, a knee joint implant was developed to facilitate a high range of motion. Tibia rotation was observed with the axes of knee motion joint implants varied from 0°, 2°, 3° to 5° and knee bend measurements at 30°, 60°, 90°, 120°, and 150° of knee flexion using the knee kinematic motion simulator and the results will be compared with the results from magnetic resonance imaging and computer tomography. Using statistical analysis resulted for 0° and 2° kinematics alignment, the p-value of the development product is 0.072 and 0.054 (p > 0.05), for 3° and 5° kinematics alignment, the p-value of the development product is 0.039 and 0.031 (p ˂ 0.05). Thus, the kinematics development product at 0° and 2° kinematics alignment are similar to a normal human knee joint. Evaluation of knee kinematics implant using a knee motion simulator is expected to become a standard procedure before performing total knee arthroplasty surgery. This similarity in kinematics knee implant with a normal knee is to be expected to reduce postoperative pain, polyethylene wears, aseptic loosening, and instability during deep knee flexion and minimize the risk of implant failure.

Abstract: The Omnifit-HA femoral stem component has shown excellent results in early clinical studies. This is an independent prospective study of the outcome of a ydroxyapatite-coated femoral component implanted by one surgeon with an intermediate-term follow up. The senior author performed 103 consecutive uncemented total hip arthroplasties in 96 patients from July 1991 to December 1996. The components implanted were the Omnifit-HA femoral stem and the Omnifit PSL porous-coated acetabular shell. The mean age at the time of the index procedure was 52 years old (range, 27–78) and male:female ratio was 54:42. Three patients were deceased and four patients were lost to follow-up. The mean follow up was 10.3 years (range, 7.3–12.7 years). Clinical and radiographic evaluations were performed by an independent observer. The average preoperative and postoperative Harris Hip Scores were 55 and 92, respectively. The overall survivorship of the Omnifit-HA stem was 100% with no femoral revisions. The survivorship of the Omnifit PSL cup was 89.7% with 4 acetabular revisions for aseptic loosening and 6 polyethelene liner exchanges for osteolysis or late instability. The mean polyethylene wear rate was 0.24 mm per year. This long-term follow up shows that the use of circumferentially coated hydroxyapatite stems can protect against the migration of wear debris along the femoral stem.

Abstract: Hydroxyapatite (HA) coatings for femoral stems have been successful in short- to intermediate-term follow up. However, the outcomes of HA-coated cups have not been as successful as comparable non-HA-coated designs. This has been attributed to component design and to poor quality HA-coating processes. This is a clinical outcome study of a newer generation acetabular design with an improved plasma-sprayed HA-coat. Ninety consecutive primary total hip replacements implanted with a HA-coated metal-backed cup were prospectively followed up for 2–5 years after surgery. Mean age was 69 years, male:female ratio was 36:47; mean-weight was 77 kg. Polyethylene wear was measured on digitized images. Component position, component migration, and implant-bone interface radiolucent lines were analyzed by computerized image analysis. Hip-scores improved from preoperative mean 59(±12) to a final follow-up mean of 91(±12). One hip was revised for recurrent dislocation. No hips were revised for aseptic loosening. Mean acetabular abduction angle was 46°(±8.5) and anteversion was 18°(±8.7). Incomplete lucent lines were noted on early postoperative radiographs in 5% of the cases. With ongoing follow up radiolucent line thickness decreased by mean 13% and radiolucent line density increased by 11%. No cup had complete continuous radiolucent lines or lysis. Mean polyethylene linear and volumetric wear rates were 0.14(± 0.15) mm/year and 73(± 70) mm3/year respectively. Wear rates were higher in males (p<0.03). No other factor (age, body weight, cup abduction or anteversion angle) correlated significantly with wear rate. This study presents encouraging short-term results. The improvement in radiolucent lines suggests a beneficial effect of the HA-coat on bone ingrowth. None of the cups loosened or migrated. Wear rates were comparable to published reports of successful non-HA-coated cups. Long-term follow up is ongoing to corroborate these early findings.