Modular femoral sleeve and stem implant provides long-term total hip survivorship

Abstract

Background: A femoral implant with a modular sleeve and stem has been designed to allow independent and complete metaphyseal-diaphyseal fit and fill as well as independent rotation to accommodate anteversion at the time of THA.

Questions/purposes: In a prospective study we asked whether such a modular femoral sleeve and stem implant used during THA could provide (1) high long-term survivorship; (2) radiographically stable implants without radiolucencies, stress shielding, or osteolysis; and (3) high clinical scores in patients 15 to 20 years after a primary THA.

Patients and methods: We prospectively evaluated 31 hips that underwent a primary THA using a modular femoral component for clinical outcome (Harris hip score) and radiographic outcome (implant stability, femoral loosening, osteolysis and stress shielding) at a minimum followup of 15 years (mean, 17 years; range, 15-20.2 years).

Results: There were no femoral revisions for aseptic loosening; all hips had radiographic evidence of bone ingrowth. Two well-ingrown components were revised for late hematogenous infection. Some degree of proximal femoral disuse atrophy from stress shielding occurred in 23 hips (74%) but was nonprogressive and did not result in any failures or complications. Femoral osteolysis occurred in 18 hips (58%), but we cannot definitively determine whether or not the modular junction contributed to this.

Conclusions: These data suggest this modular femoral stem can provide long-term survivorship with no cases of aseptic loosening at 15 to 20 years after primary THA. However, it may be prudent when using this femoral stem to consider an articulation with an alternative bearing or, if the modularity is not needed to address femoral anteversion and metaphyseal-diaphyseal mismatch, to consider a nonmodular femoral stem.

Level of evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

A Kaplan-Meier survivorship curve demonstrates the probability of survival free of femoral revision for aseptic loosening or revision for any reason at 20 years postoperatively for the original cohort of 59 consecutive primary cementless THAs with an S-ROM^® femoral component. The survival rate was 100% with revision for aseptic loosening as the end point and 84% with revision for any reason as the end point. The vertical bars represent the 95% confidence intervals.

Fig. 2

An AP hip radiograph taken 18 years postoperatively demonstrates the typical appearance of spot welds (arrows), trabecular streaming, and absence of radiolucencies adjacent to the porous-coated proximal sleeve of the S-ROM^® stem.

Fig. 3

A 20-year postoperative AP hip radiograph demonstrates bony ingrowth with severe proximal femoral stress shielding with resultant cortical bone loss and loss of calcar thickness.

Fig. 4

A 19-year postoperative radiograph of an S-ROM^® femoral component shows femoral osteolysis in Gruen Zones 1 and 7 (arrows). There is no apparent polyethylene wear of the acetabular liner.