The purpose of this study was to evaluate trabecular bone response, at fifty-two week follow-up, to four different synthetic graft materials (CaSO4 and CaSO4 – HA/TCP composites) as compared to autograft in a canine defect model. The group with the highest HA/ TCP proportion had the greatest amount of residual graft material and total mineralized material. Increasing the proportion of HA/TCP reduces the rate of dissolution, and appears to have little effect on bone formation at long term follow-up. This study further suggests that a range of composites could be created to match the spectrum of resorption rates demanded by clinical applications.

The purpose of this study was to evaluate trabecular bone response to four synthetic graft materials (CaSO4 and CaSO4 – HA/TCP composites) as compared to autograft in a canine defect model, at long term follow-up.

Both 85% CaSO4 – 15% HA/TCP and 65% CaSO4 – 15% HA/TCP showed bone formation similar to autograft. The group with the highest proportion of HA/TCP lasted longer than the other formulations. The results suggest that increased HA/TCP proportions reduce the rates of dissolution, without compromising bone formation in the current model.

Results suggests that a range of composites could be created to match the spectrum of resorption rates demanded by clinical applications.

In this REB-approved RCT, bilateral humeral and femoral cylindrical defects were filled with one of four types of pellets with varying proportions of CaSO4 – HA/TCP, autograft bone, or left unfilled. After sacrifice at six, twelve, twenty-six or fifty-two weeks, defect sites were evaluated histologically for tissue and inflammatory response, area fractions of residual graft material, and bone ingrowth in the defects.

The area of the defect occupied by residual graft material in the group with the highest percentage of HA/TCP was greater than in other composite groups (p< 0.0001). This group contained the greatest amount of total mineralized material (graft material + bone) (p< 0.03. The extent of new bone formation increased from twelve to twenty-six weeks (p< 0.0001). Both 85% CaSO4 – 15% HA/TCP and 65% CaSO4 – 15% HA/TCP showed bone formation similar to autograft.

Funding: Research grant from Stryker Howmedica, Matwah, NJ.

The results of wear testing using hip simulators have suggested that highly cross-linked polyethylene (PE) is more resistant to abrasive wear than “conventional” polyethylene that has been sterilized by 2.5 – 4 Mrad of radiation. Optimum methods for testing other mechanical properties of PE are controversial, but some studies have suggested that highly cross-linked polyethylenes have reduced impact strength when compared to either “conventional” PE or PE that has never been cross-linked. T he principle mechanism of loosening of most total hip prostheses is bone loss induced by debris particles that have been generated by abrasive wear, hence the rationale for using highly cross-linked PE for total hip arthroplasty. The principle mechanism of failure of bipolar hips, however, is less clear. If abrasive wear is important in bipolars, then the use of highly cross-linked PE is reasonable, but if impingement is an important complication of bipolar arthroplasty, then the use of highly cross-linked polyethylene might We revewied the implant registry of the Cleveland Clinic and identified 62 retrieved bipolar implants. The peripheral rim of each was evaluated, and a previously published scoring system used to grade the extent of rim damage due to impingement. A subset of implants were disassembled, and the shadowgraph method was used to measure the extent and rate of polyethylene abrasive wear. Adequate clinical information and radiographs were available in relatively few cases, but when available, the results of implant evaluation were correlated with clinical and radiographic findings.

The results suggest that both abrasive wear and rim damage due to impingement are common findings in retrieved bipolar devices. Further studies with better clinical and radiographic correlation are needed to clarify the most significant factors with respect to osteolysis and implant failure, but our results suggest caution in implementing highly cross-linked polyethylene for bipolar devices.