Thermally treated 1st generation highly crosslinked polyethylenes (HXLPE) have demonstrated reduced penetration and osteolysis rates, however, concerns still remain with respect to oxidative stability and mechanical properties of these materials. To address these concerns, manufacturers have introduced the use of antioxidants to quench free radicals while maintaining the mechanical properties of the HXLPE. Two common antioxidants are α-tocopherol (Vitamin-E) and pentaerythritol tetrakis (PBHP). These may be either mixed prior to consolidation, or diffused throughout the polymer after consolidation and irradiation. Between 2010 and 2015, 73 anti-oxidant HXLPE components were collected as a part of an IRB approved, multi-institutional retrieval analysis program during routine revision surgery. Of the seventy-three components, 30 (41%) were acetabular liners, whereas, 43 were tibial inserts. The components were fabricated from three different materials: Vitamin-E Diffused HXLPE (n=30; E1, Biomet), Vitamin-E Blended (n = 41; Vivacit-E, Zimmer) and PBHP blended (n = 2, AOX, DePuy). The hip and knee components were implanted for 0.7 ± 0.8 years (Range: 0.0–2.25 years) and 0.8 ± 1.1 years (Range: 0.0–4.5 years), respectively. Implantation time, patient weight, age, gender, and activity levels were similar between hip and knee components (Table 1). For oxidation analysis, thin slices (∼200μm) were taken from medial condyle and central eminence of the tibial inserts or the superior/inferior axis from hip components. The slices were boiled in heptane for six hours to extract lipids absorbed Introduction
Methods
A variety of porous coatings and substrates have been used to obtain fixation at the bone-implant interface. Clinical studies of porous tantalum, have shown radiographically well-fixed implants with limited cases of loosening. However, there has been limited retrieval analysis of porous tantalum hip implants. The purpose of this study was to investigate factors affecting bone ingrowth into porous tantalum hip implants. 126 porous tantalum acetabular shells and 7 femoral stems, were collected under an IRB-approved multicenter retrieval program. Acetabular shells that were grossly loose, cemented or complex revisions were excluded. Shells with visible bone on the surface were chosen. 20 acetabular shells (10 primary) and all femoral stems were dehydrated, embedded, sectioned, polished and bSEM imaged (Figure-1). Main shell revision reasons were infection (n=10,50%), femoral loosening (n=3,15%) and instability (n=3,15%). Analyzed implants were implanted for 2.3±1.7 years (shells) and 0.3±0.3 years (stems). Eight slices per shell and 5–7 slices per stem were analyzed. The analysis included bone area/pore area (BA/PA), BA/PA zonal depth analysis, extent of ingrowth and maximum depth of bone ingrowth. BA/PA zone depths were: Zone-1 (0–500um), Zone-2 (500–1000um) and Zone-3 (1000um-full depth). Nonparametric statistical tests investigated differences in bone measurements by location within an implant and implant type (Friedman's Variance and Kruskal-Wallis). Post-hoc Dunn tests were completed for subsequent pairwise comparisons. Spearman's rank correlation identified correlations between bone measurements and patient related variables (implantation time, age, height, weight, UCLA Activity Score). Statistical analyses were performed using PASW Statistics package.Introduction
Methods
The debate about retaining or sacrificing the posterior cruciate ligament (PCL) in total knee arthroplasty continues. Benefits of PCL retention cited by researchers include increased flexion, improved posterior rollback, improved quadriceps function, decreased post-tibial subluxation and reduced interface stress. On the other hand, other researchers contend that sacrificing the PCL affords latitude for correction of fixed deformity, improves exposure, ligament balancing, flexion and stability. This paper reports on a bilateral knee study that is currently in progress and involves three separate sites/investigators. It describes Knee Society scores, range of motion and intra-operative metrics for 100 patients followed up for one to four years.
A multicentre prospective study in the USA involves more than 75 investigators who have enrolled over 1 800 cases over nearly four years. In a subset of this group, the performance of a tapered, cementless, porous stem is being evaluated. One surgeon has used this stem in 301 hips in 282 patients, of whom 141 are at one-year follow-up and 51 at two-year follow-up. An optional large proximal body stem was often used to optimise proximal femoral fill. Clinical and radiological examinations were carried out immediately after surgery and at 6, 12 and 24 months, and demographic, Health Status (SF-12), and Harris Hip Score (HSS) data noted. From a preoperative mean of 41, the HSS improved to 88 and 92 at one-year and two-year follow-ups respectively. No progressive radiolucency, implant migration, gross loosening, osteolysis or polyethylene wear has been observed.
Unicompartmental knee arthroplasty has been in use since the 1970s. In spite of early enthusiasm, the procedure soon fell into disfavour, particularly in the USA. Early failures were a result of improper indication, poor technique and in some cases and poor prosthetic design. A new instrument system for use with the MG unicompartmental knee arthroplasty has been designed, with guides for accurate and reproducible alignment, sizing and resection. Potential benefits include early mobilisation, rapid rehabilitation, improved range of motion and shortened hospital stay. This paper briefly reviews the literature and discusses indications and surgical techniques.
This paper reviews the potential advantages and disadvantages of minimal incision total hip arthroplasty (THA). A ‘mini-incision’ approach has been developed, with incision size decreasing to 7.5 mm to 8.5 mm over the past four years. This allows for adequate exposure and proper component positioning, and consistently good results have been achieved in over 400 patients. Using a posterior approach, an oblique skin incision is made. The approach permits insertion of acetabular fixation screws, and the technique can be used for both cemented and non-cemented implants. New retractors have been developed to protect the proximal angle of the incision and elevate the femur for femoral preparation, and a new acetabular inserter developed to protect the distal pole of the incision. Results have been excellent. There have been no dislocations and no cases of sciatic nerve palsy. The mean length of hospital stay is three days and mean operative time (skin to skin) 44.9 minutes.
