Osteolytic changes around biodegradable cement restrictors in hip surgery

Abstract

Background and purpose - Biodegradable cement restrictors are widely used in hip arthroplasty. Like others, we observed osteolytic reactions associated with a specific cement restrictor (SynPlug; made of PolyActive) and reviewed our patients. Patients and methods - We identified 703 patients with suitable radiographs from our database (2007 to 2012) who underwent cemented hip arthroplasty and received a SynPlug biodegradable cement restrictor. We reviewed all available radiographs to determine the incidence, severity, and progression of osteolysis. Mean postoperative follow-up was 1.8 (1-7) years Results - 1 year after implantation, the femoral cortex showed thinning by 12% in the anterior-posterior view and by 8% in the axial view. This had increased to 14% and 12%, respectively, at the latest available follow-up postoperatively (at a mean of 4 years). Cortical thinning of less than 10% was found in 37% of patients, but cortical thinning of 10-30% was found in 56% of patients. In the remaining 7%, a reduction of more than 30% of the original cortical thickness was observed. Interpretation - Osteolytic changes associated with the SynPlug biodegradable bone restrictors are inconsistent and highly variable. While some patients showed increased weakening of the femoral cortex with the potential risk of periprosthetic fracture, in others the degree of osteolysis only increased slightly or stabilized after 2 or more years. Any cortical bone loss after total hip replacement should be avoided, so the use of PolyActive biodegradable cement restrictors should be discontinued. Patients with a PolyActive cement restrictor in place should be followed up closely after surgery.

Figure 1.

Measurements were performed using the AP view (A) and the lateral view (B). The relationship between inner and outer diameter was calculated from below the tip of the prosthesis. When osteolysis was found, the center of the oval osteolysis was measured.

Figure 2.

Graph depicting the amount of loosening over time. After 1 year, a decrease of 8% in both the AP view and the axial view could be observed. At the latest available radiographic follow-up (average 3.9 years), a decrease in cortical thickness of 14% in the AP view and of approximately 12% in the lateral view was found. The osteolytic process appears to be most apparent during the first year, but then it continues at a slower rate. All changes were statistically significant (^a p < 0.01).

Figure 3.

A 74-year-old woman 4 years postoperatively, in whom osteolysis showed a marked sagittal pattern. In the AP view (A), only minor osteolysis was seen.

Figure 4.

A. An 84-year old woman immediately postoperatively with an unremarkable cemented prosthesis. B. 2 years after implantation, a discrete osteolysis was found distal to the prosthesis. C. The amount of osteolysis as seen in a CT. In a standard radiograph, there might be underestimation of the amount of loosening, which we noted often shows in an anterior-posterior pattern, weakening the linea aspera.

Figure 5.

A 90-year-old man at 8 weeks (panels A and B) and 7 years (C and D) postoperatively. The images after 7 years (C and D) revealed osteolytic changes in the area of the SynPlug cement restrictor. Progressive radiolucencies first appeared distally around the prosthetic stem just proximal to the osteolytic changes in zone 4.