Mid-term outcomes after distally locked-to-standard primary stem exchange in 29 hip-prosthesis patients

Cementless locked femoral stems are used for revision surgery in patients with bone loss to induce spontaneous bone reconstruction, allowing subsequent replacement by a standard primary stem. The small number of patients and short follow-ups available to date preclude a valid assessment of this strategy.

After distally locked stem revision, replacement by a standard primary stem does not induce complications, and the quality of the bone reconstruction allows strong fixation of a regular primary stem.

We retrospectively evaluated 29 patients in whom a distally locked femoral stem was replaced by a standard primary stem between 1998 and 2010 (cemented in 27, cementless in 2 cases). The reason for the procedure was stem breakage, stem migration, or thigh pain. Mean patient age was 63 years (range, 39-78 years). Outcomes were evaluated based on the Postel-Merle d'Aubigné [PMA] score and Harris Hip Score [HHS]. In addition, radiographs were obtained to assess prosthesis fixation and the Hofmann cortical index measured the bone reconstruction.

The distally locked stem was removed via a postero-lateral approach without femoral osteotomy in all the 29 cases. In one patient, an intra-operative fracture occurred during femoral preparation. Mean follow-up after the exchange procedure was 75 months (range, 3-188 months). Postoperative ccomplications occurred in 9 (32%) patients and consisted of chronic infection in 2 patients (after 3 and 76 months), post-traumatic peri-prosthetic fractures treated with internal fixation in 3 patients (after 100, 138, and 182 months), aseptic loosening in 3 patients (after 13, 39, and 122 months), and recurrent instability in one patient (after 63 months). All cause revision stem survival after 75 months was 72% (95% confidence interval, 47%-87%). In the 19 patients who still had their revision stem at last follow-up, the mean PMA score was 16.7 (range, 13-18) and the mean HHS was 88.2 (range, 59-99). The Hofmann index remained unchanged [36.5% (range, 28%-58%) before the exchange and 32.9% (range, 20%-57%) after the exchange; P=0.129].

This study confirms the feasibility of substituting a distally locked stem with a standard primary stem. No specific complications occurred and no technical difficulties arose when extracting the long stems. However, the 32% complication rate and, more specifically, the occurrence of loosening in 10% (3/29) of patients mandates caution in the use of this technique, which should not be proposed routinely, and suggests a need for considering cementless fixation of the standard primary stem.

Level IV, retrospective study.