302. EVALUATION AT MORE THAN ONE YEAR OF A PRESS-FIT REVISION FEMORAL STEM: PFM-R, A PROSPECTIVE CONSECUTIVE SERIES OF 154 PATIENTS

Abstract

Purpose of the study: The PFM-R (Zimmer) prosthesis is a straight modular stem made of sanded titanium designed to favour spontaneous bone reconstruction. The purpose of this work was to analyse the clinical and radiographic results of this implant.

Material and methods: This was a consecutive prospective series of 154 patients who underwent surgery from 1998 to 2007 (15 first-intention prostheses and 139 revisions for severe loosening [Paprosky stages 3 and 4]). Revision included a clinical evaluation (PMA score) and radiographic assessment (migration, bone regeneration, stress shielding, osteointegration, Le Béguec score) as well as a survival analysis.

Results: At mean 4.6 years follow-up (1–10 years), three patients had died, two were lost to follow-up and 18 implants were removed, 11 for infection, six for migration and one for defective technique. The PMA score improved from 8 (0–16) to 15.8 (5–18). Mean pivot impaction was 4 mm (0–50), statistically dependent on initial bone stock, form of the isthma, the corticomedullary index in the implantation zone, length of anchor, and time to weight bearing, but not femorotomy nor zone of primary stability. Bone stock was good in 73% at poor in 27% (15 stress shielding, nine infectious osteolysis, 16 absence of bone regeneration). Stress shielding was related to length and diameter of the implanted pivot (p< 0.05). Bone regrowth was statistically dependent on the number of prior operations, type of stem explanted (cemented), initial bone stock, form of the isthma and quality of the surgical reconstruction. The implant was osteointegrated in 128 cases (86%). The analysis of the prosthetic anchoring showed that primary stability was mainly diaphyseal (90%) then secondarily global (83%). Osteointegration depended statistically on the number of prior operations, initial bone stock, form of the isthma and bone regrowth, but not femorotomy. The overall Le Béquec score reached 14.7 (2–20) at last follow-up.

Discussion: The PFM-R enabled bone regeneration and osteointegration in the majority of patients. The quality of the femoral reconstruction around the implant appears to be fundamental. Massive stems should be avoided as they lead to stress shielding. The limits for use of this implant are osteopenia and absence of an isthma.