Clinical Outcome and Subsidence of the Wagner Cone femoral Component in Patients with Challenging Proximal Femoral Anatomy

Background:
Total hip arthroplasty (THA) in patients with unusual proximal femoral anatomy can be challenging secondary to sizing issues, control of version, and implant fixation. The Wagner Cone is a monoblock, fluted, tapered stem that has a track record of success in this difficult patient population. However, prior studies have provided limited information on the frequency and severity of subsidence, a common radiographic feature with cementless stems.

Methods:
We retrospectively reviewed our cases using the modified Wagner Cone (Zimmer, Warsaw, IN) implanted over a 13-year period (2006-2019) in patients with small or abnormal proximal femoral anatomy. During this time, we performed 144 primary THAs in 114 patients using this prosthesis. The mean follow-up was 4.5 ± 3.4 years (range, 1-13 years). The most common reason for implantation was hip dysplasia (52%), and the second most common reason was osteoarthritis in patients with small femoral proportions (22%). Analysis of outcome included collection of hip scores and radiographic analysis, including assessment of stem subsidence and stability.

Results:
Survival was 98.6% in aseptic cases, and revision free survival was 97.9%. Femoral subsidence was observed in 84 cases (58%). No subsidence progressed after 3 months. Of those that subsided the mean distance was 2.8 ± 2.0 mm. There was less subsidence in stems that stabilized prior to 6 weeks (2.2 ± 1.4 mm) when compared to those that continued until 12 weeks (3.9 ± 1.6, p = 0.02). Harris Hip Scores, UCLA and WOMAC scores significantly improved from pre-operative evaluation (p< 0.001, p<0.003, p<< 0.001 respectively; there was no significant difference between patients with and without subsidence (p=0.430, p=0.228, p=0.147 respectively).

Conclusion:
The modified Wagner Cone demonstrates excellent clinical outcomes in patients with challenging proximal femoral anatomy. Minor subsidence occurs frequently, stops by 3 months, but does not compromise patient reported outcome.