Clinical results of the midstem porous-coated anatomic uncemented femoral stem in primary total hip arthroplasty: a five- to nine-year prospective study

J L Knight, R D Atwater, J Guo
Journal of Arthroplasty 1998, 13 (5): 535-45
The clinical and radiologic results of an inclusive series of 60 patients (70 hips) who had primary total hip arthroplasty using the porous-coated anatomic (PCA) midstem femoral prosthesis was prospectively studied. The midstem component features a proximal circumferential porous bead coating similar to the PCA primary stem; but increased proximal thickness, increased length, and a distal anterior curve for additional rotational stability. The mean Harris Hip Score rose from 39.5 points before surgery to 91.3 points at a minimum follow-up of 5 years (average, 69 months); 88% were good or excellent. Moderate or severe thigh pain on a visual analogue scale was reported by 30% of cases, and was more common in women. Radiographic analysis indicated preservation of proximal bone stock and bony ingrowth in 87%, but stem subsidence in 9%. One stem has been revised for subsidence and thigh pain (1.4%), and one stem is radiographically loose, but the patient refuses surgical revision. Endosteal osteolysis was rarely seen (2.8%) and was benign in appearance. Acetabular components used included 63 nonmodular PCA metal-backed cups and 7 hemispherical porous ingrowth cups fixed with screws. One PCA cup was revised for loosening (1.4%), and one is radiographically loose but stable (1.4%). Only one cup exhibited an area of osteolysis. At this intermediate follow-up the clinical outcome of the midstem component is stable and excellent. The radiographic results appear superior to the PCA primary stem, with a lower incidence of stem subsidence and osteolysis. The prevalence of thigh pain is a concern and we recommend regular follow-up of patients with the midstem femoral implant, and the use of a visual analogue thigh pain scale when any femoral prosthesis is evaluated.

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