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The use of a polyglycolide lactide cement plug restrictor in cemented femoral fixation during total hip arthroplasty was evaluated. Femoral cement pressurization was evaluated in vitro in a cadaveric model and the host response to polymer degradation was evaluated in vivo in a canine total hip arthroplasty model. Sixteen embalmed anatomic specimen femurs were prepared for cement femoral fixation. The intramedullary canal was plugged with either an ultrahigh molecular weight polyethylene cement plug restrictor or a polyglycolide lactide cement plug restrictor. Peak pressures in the proximal, mid, and distal portions of the cement mantle were recorded during cement insertion, cement pressurization, and implant insertion. There was no difference between the two plug groups in peak pressures throughout the cement mantle during cement insertion, pressurization, or implant insertion. Total hip arthroplasty using a cementless acetabular component and a cemented femoral stem was performed in 24 dogs. The femoral intramedullary canal was plugged with a polyethylene or a biodegradable cement plug restrictor. The dogs were sacrificed at 7 weeks, 10 months, or 15 months. Radiographically, no osteolytic lesions were seen around either plug type. Histomorphometrically, the polyglycolide lactide plugs appeared intact at 7 weeks and partially degraded by 10 and 15 months. In both plug groups, a mild fibrohistiocytic reaction with infiltration of fibrocytes, histocytes, and endothelial cells was seen. No osteolysis was observed. The results of the current study show that femoral cement pressurization can be attained in vitro using a biodegradable cement plug restrictor and that for as long as 15 months in the in vivo canine model there were no adverse reactions associated with use of these plugs compared with conventional ultrahigh molecular weight polyethylene plugs.

Cementless total hip arthroplasty was performed in 13 dogs. The acetabular component was anchored with two biodegradable devices (polylactic acid) in seven dogs and with two titanium screws in six dogs. At 14 weeks, histomorphometric determinations of bony ingrowth into the porous coating of the acetabular weight bearing dome was 54.4% when fixed with the biodegradable devices and 58.9% when fixed with the titanium screws (no statistically significant difference; p = 0.556). At the sites of fixation, less bony ingrowth occurred with the biodegradable devices. The use of biodegradable devices in total hip arthroplasty should overcome the potential metal corrosion of titanium screws that can lead to polyethylene wear.

Load-bearing porous-surfaced implants in dogs which failed were not incorporated by bone ingrowth. The implants were incorporated only by fibrous tissue ingrowth. Collagen fiber orientation within this fibrous tissue and Sharpey's fiber-like features at the interface between the fibrous tissue and a surrounding layer of dense bone suggest the adequacy of the fibrous tissue attachment for support of a loaded implant. The surrounding dense bone layer could be distinguished radiographically within three months of the operation. This radiopaque line is similar to that observed around some porous surfaced hip implants in humans. Observations of animal mobility up to six months postoperatively suggest that fibrous connective tissue growth into porous implants can provide adequate mechanical support for weight-bearing dogs.

Load-bearing porous-surfaced implants in dogs which failed were not incorporated by bone ingrowth. The implants were incorporated only by fibrous tissue ingrowth. Collagen fiber orientation within this fibrous tissue and Sharpey's fiber-like features at the interface between the fibrous tissue and a surrounding layer of dense bone suggest the adequacy of the fibrous tissue attachment for support of a loaded implant. The surrounding dense bone layer could be distinguished radiographically within three months of the operation. This radiopaque line is similar to that observed around some porous surfaced hip implants in humans. Observations of animal mobility up to six months postoperatively suggest that fibrous connective tissue growth into porous implants can provide adequate mechanical support for weight-bearing dogs.