Abstract
Purpose
In an effort to increase the durability of cemented total hip arthroplasties (THA), femoral stems were precoated using polymethlymethacrylate (PMMA). One such design is Harris precoat plus and centralign design (Zimmer, Warsaw, Indiana). The reports on these particular designs are variable, ranging from good survival to early failures, studied over short to medium term. Early failures have been attributed, most of the time to debonding at cement-bone interface. In view of lack of long term and variable results, we reviewed the results of primary hybrid THA performed during October 1990 to December 1995, using a PMMA coated, cemented femoral prosthesis and contemporary cementing techniques.
Materials and Methods
121 patients (136 hips) underwent primary THA using one of the precoated femoral stems during the study period. Thirty-five patients (36 hips) died and 23 patients (23 hips) were lost to follow-up due to some reasons. Two hips (2 patients) were revised for postoperative infection and hence, not included in study. Collectively, 75 hips (61 patients) were available for clinical and radiological reviews until the last follow-up, with an average follow-up period of 15.5 years (range, 14 to 18.3 years). The average age of the patients at the time of the index surgery was 53.6 years (range, 24 to 82 years). There were 43 males (55 hips) and 18 females (20 hips). Acetabular components used in these 75 hips were Harris Galante porous (HGP) cups in 69 hips and CLS Expansion cup (Protek, AG, Bern) in six hips. The mean age of 61 patients (75 hips) who were available for latest follow-up at December 2009, was 46 years (range, 22-65 years). Third generation cementing techniques and distal cement plug but no centralizer was used in all cases. All surgeries were performed by same surgeon at a single institute.
Results
23 femoral stems were revised, 20 for aseptic loosening (8 Precoat plus and 12 Centralign) and 3 for periprosthetic fracture with loosening (1 Precoat plus and 2 Centralign). The cementing of the femoral stem was grade A in 29 hips (39%), grade B in 16 (21%), C1 in 6 (8%) and grade C2 in 24 (32%). 21 of 24 hips which showed definitive loosening in radiogram had had cement grade C2 cementing. There were 22 acetabular revisions. 11 hips underwent isolated liner exchange for severe wear and osteolysis and in remaining 11 hips, complete acetabular component revision was performed. Indications for acetabular component revisions were aseptic loosening in five, severe lysis in four, extensive wear and metallosis in one, and liner dissociation in one. In one hip, with a fractured acetabular component due to severe pelvic bone defect, both the components were revised.
Conclusion
Our results suggest that an early failure of the precoated femoral stem was mainly precipitated due to insufficient cementing technique (a thin cement mantle). Inherent flaws of the stem design may also accelerate the mechanism of failure.
