High rate of fracture in the cementless modular Extrême™ (Mark I) femoral prosthesis in revision total hip arthroplasty: 33 cases at more than 5 years' follow-up.

INTRODUCTION: The modular concept has been recommended in femoral revision surgery with extensive bone loss, but entails mechanical complications: disassembly and fracture. The present retrospective study assessed the Mark I Extrême™ modular prosthesis at a minimum 5 years' follow-up.

HYPOTHESIS: A cementless modular femoral stem facilitates revision in case of extensive bone loss, providing satisfactory results without risk of junction failure.

MATERIALS AND METHODS: Thirty-three prostheses presenting aseptic loosening, including 3 with periprosthetic fracture, in 23 female and 9 male patients, with a mean age of 65 years (range, 49-83 years), were reviewed at a mean 6.3 years' follow-up (range, 5-9 years). Bone loss was assessed on the SOFCOT (17/33 grade 3 or 4) and Paprosky classifications (19/33 grade III or IV). One patient died; another was lost to follow-up, leaving 31 hips for analysis. Clinical assessment comprised Postel Merle d'Aubigné (PMA) and Harris Hip scores (HHS); radiological assessment used the Engh score and corticomedullary index (CMI).

RESULTS: There were 15 complications requiring surgery: 9 (27%) unrelated to the implant (1 hematoma, 2 infections, 2 dislocations, 1 femoral non-union, 3 asymptomatic trochanteric non unions) and 6 (18%) implant-related (four 3-level fractures and 2 epiphyseal-metaphyseal disassemblies, requiring 3 total exchanges and 3 proximal component replacements). PMA and HHS scores showed significant improvement, PMA rising from 10.4 (6-18) to 14.4 (11-18) and HHS from 50 (19-88) to 80.9 (52-100). Bone regrowth was "certain" on the Engh classification in 11 cases (44%). There was no diaphyseal component subsidence, even in case of fracture or dissociation. CMI at the 3 junctions between the 4 quarters of the stem showed no significant change: 32.9 and 32.7, 41.2 and 38.7, and 41.6 and 39.9 respectively. Six-year survivorship was 81% (95% CI: 68-94%).

DISCUSSION: In other series for the same type of implant, the rates of fracture (always metaphyseal-diaphyseal) were much lower: 0.8-3.8%. This stem ensures diaphyseal fixation in case of extensive bone loss, but incurs excessive risk of disassembly and fracture.