Revision total hip arthroplasty is often associated with acetabular bone defects. In most cases, assessment of such defects is still qualitative and biased by subjective interpretations. Three-dimensional imaging techniques and novel anatomical reconstructions using statistical shape models (SSM) allow a more impartial and quantitative assessment of acetabular bone defects [1]. The objectives of this study are to define five clinically relevant parameters and to assess 50 acetabular bone defects in a quantitative way. Anonymized CT-data of 50 hemi-pelvises with acetabular bone defects were included in the study. The assessment was based on solid models of the defect pelvis (i.e. pelvis with bone defect) and its anatomical reconstruction (i.e. native pelvis without bone defect) (Fig.1A). Five clinically relevant parameters were defined: (1) Bone loss, defined by subtracting defect pelvis from native pelvis. (2) Bone formation, defined by subtracting native pelvis from defect pelvis. Bone formation represents bone structures, which were not present in the native pelvis (e.g. caused by remodeling processes around a migrated implant). (3) Ovality, defined by the length to width ratio of an ellipse fitted in the defect acetabulum. A ratio of 1.0 would represent a circular acetabulum. (4) Lateral center-edge angle (LCE angle), defined by the angle between the most lateral edge of the cranial roof and the body Z-axis, and (5) implant migration, defined by the distance between center of rotation (CoR) of the existing implant and CoR of native pelvis (Fig. 1B).Introduction
Methods
Cross-linked polyethylene in total hip arthroplasty has demonstrated excellent long-term wear resistance, leading to its acceptance as the standard bearing used in hip replacement. Adoption in knee replacement has been tentative, as the cross-linking process can decrease the polyethylene mechanical properties. The current study's purpose was examining survivorship of a fixed bearing knee replacement system featuring a moderately cross-linked polyethylene (MXLK) bearing, a cobalt chrome (CoCr) tibial tray with a highly polished top surface, and a new polyethylene-to-tray locking mechanism. The MXLK is made of ultra-high molecular weight GUR1020 resin irradiated with 5 Mrad gamma radiation, followed by a free radical quenching remelting annealing process, above the 135 degree melting point, that provides wear and fatigue resistance, and oxidative stability. From November 2005 to June 2008, 539 PFC Sigma primary total knee replacements (TKA's) were prospectively entered into this non-comparative, multicenter, multinational study. Average age at time of surgery was 67 years, 57% were female, average body mass index was 30.4 kg/m2, and the dominant diagnosis was osteoarthritis (97%). Kaplan-Meier (KM) survivorship was the primary endpoint with primary event definition being removal of any component for any reason. The time variable was one of the following: time to revision, time to death, or time to last follow-up. Additional endpoints included: American Knee Society scores (knee and function), Oxford Knee score (range 12 to 60), SF-12 scores; radiographically assessed rates of radiolucent lines (RLL's) and osteolysis. RLL's greater than 2mm were counted. Progressive RLL's were those increasing in width from an earlier follow-up interval. Adjacent RLL's were defined as RLL's in adjacent zones. Complete RLL's were defined as RLL's completely around a component. This report provides 5-year results in this ongoing study with a 10-year final endpoint.Introduction
Materials & Methods
Revision knee arthroplasty presents a number
of challenges, not least of which is obtaining solid primary fixation
of implants into host bone. Three anatomical zones exist within
both femur and tibia which can be used to support revision implants.
These consist of the joint surface or epiphysis, the metaphysis
and the diaphysis. The methods by which fixation in each zone can
be obtained are discussed. The authors suggest that solid fixation
should be obtained in at least two of the three zones and emphasise
the importance of pre-operative planning and implant selection. Cite this article:
