Experience of an Anatomic Femoral Stem in a United Kingdom Center - Excellent Survivorship and Negligible Periprosthetic Fracture Rates at Mean 12 Years Following Primary Total Hip Arthroplasty

Do all anatomic stems perform equally at long-term survival? A regional registry-based study on 12,010 total hip arthroplasty implants according to stem length and neck modularity

BACKGROUND

Anatomic stems for total hip arthroplasty (THA) have been developed to achieve a precise geometric fit between the implant and the surrounding femoral bone, aiming at the improvement of primary stability of cementless implants until osteointegration occurs. The aim of the current study is to go over the regional Registry of Orthopaedic Prosthetic Implants (RIPO) to analyze survivorship of THA implants when anatomic stems are used; moreover, separate analysis for modular and nonmodular stems, and in standard and short implants, is presented.

MATERIALS AND METHODS

This retrospective registry study involved the analysis of data collected by the RIPO registry between 2000 and 2019. The study focused on THAs performed for primary hip osteoarthritis (OA) between 2000 and 2019. All patients treated by THA within this time frame and officially registered in the RIPO registry were included in the study. Exclusion criteria were: revision THAs, cemented implants, hemiarthroplasties, resurfacing procedures, megaprostheses for neoplastic and non-neoplastic conditions, and THAs performed on patients residing outside the region.

RESULTS

A total of 12,010 cementless primary THAs using curved anatomic stems were performed in Emilia-Romagna between 2000 and 2019 and formally registered in the RIPO registry. The overall survival rate for anatomic standard stems was 96.7% at 10 years (96.1-97.3%); at 15 from the surgery, the survival rate dropped to 95.1% (93.9-96.1%). A total of 473 out of 12,010 recorded THA with anatomic stems (3.93%) experienced failure requiring revision surgery. The fixed standard stem showed the lowest failure rate (0.6%), while modular short stems had the highest (7.4%) at long-term follow-up. The most common stem-related complication was periprosthetic fracture (PF) in short stems (2.0% of cases) while in standard stems it was implant breakage (0.9% of cases); PFs were significantly more frequent in female patients (p = 0.0082), with a relative risk (RR) of 1.59 compared with male patients. Implant breakage demonstrated the highest rate of incidence among standard-modular stems (1.1% of cases).

CONCLUSIONS

This registry-based study highlights that stem length and modularity significantly affect the long-term survival of anatomic femoral stems in THA. Fixed standard stems had the lowest failure rates, while modular short stems showed the highest failure rates and complications.

LEVEL OF EVIDENCE: 3

Experience of an anatomic femoral stem in a UK orthopaedic centre beyond 20 years of follow-up

INTRODUCTION

Increasing interest in the use of anatomical stems has developed as the prevalence of periprosthetic fractures (PPFs) continues to increase. The primary aim of this study was to determine the long-term survivorship and PPF rate of an anatomical femoral stem in a single UK centre.

PATIENTS AND METHODS

Between 2000 and 2002, 94 consecutive THAs were performed using the 170 mm Lubinus SP II anatomical femoral stem in our institution. Patient demographics, operative details and clinical outcomes were collected prospectively in an arthroplasty database. Patient records and national radiographic archives were reviewed finally at a mean of 21.5 years (SD 0.7) following surgery to identify occurrence of subsequent revision surgery, dislocation or periprosthetic fracture.

RESULTS

Mean patient age at surgery was 65.8 years (SD 12.5, 34-88 years). There were 48 women (51%). Osteoarthritis was the operative indication in 88 patients (94%). Analysis of all-cause THA failure demonstrated a survivorship of 98.5% (95% confidence interval [CI], 98.0-99.3%) at 10 years and 96.7% (94.5-98.9%) at 21 years. The 20-year stem survival for aseptic loosening was 100% with no cases of significant lysis found (lucent line > 2 mm) and no stems required revision. Patient demographics did not appear to influence risk of revision (p > 0.05). There were 2 revisions in total (2 for acetabular loosening with original stems retained). There were no PPFs identified at mean 21.5 year follow-up and 5 dislocations (5%).

CONCLUSIONS

The Lubinus SP II 170 mm stem demonstrated excellent survivorship and negligible PPF rates over 20 years following primary THA.