Long-term results of the metaphyseal-loading anterolaterally flared anatomic femoral stem for total hip arthroplasty.

BACKGROUND

Patients with secondary hip osteoarthritis due to developmental dysplasia of the hip (DDH) often have abnormal femoral morphology, making stem design critical for long-term outcomes. The FMS-anatomic stem previously demonstrated favourable mid-term results. Its successor, the Anatomic Fit stem, was developed with a reduced hydroxyapatite-coated area to enhance proximal load transfer and a narrower lateral flare to facilitate insertion. This study aimed to analyze the long-term clinical and radiographic outcomes of these stems.

METHODS

The one-hundred seventy-eight hips underwent total hip arthroplasty using either the FMS-anatomic or Anatomic Fit stem. After applying exclusion criteria, 119 hips (36 FMS-anatomic and 83 Anatomic Fit) were analyzed. Clinical and radiographic outcomes were assessed, and stem survival was evaluated using Kaplan-Meier analysis with stem revision as the endpoint.

RESULTS

The 15- and 20-year survival rates were 97.2% and 94.4% for the FMS-anatomic stem, and 98.8% for the Anatomic Fit stem at both time points, with no significant difference. Spot welds were observed in nearly all cases, but their distribution differed significantly: zones 2 and 6 in the FMS-anatomic group and zones 1 and 7 in the Anatomic Fit group (P < 0.05). Stress shielding of Grade 3 or higher occurred in 16.5% of FMS-anatomic stems and 33.7% of Anatomic Fit stems (P < 0.05).

CONCLUSIONS

Both stems showed excellent long-term survival and proximal fixation. However, the Anatomic Fit stem did not reduce stress shielding, despite its modified design intended to improve load transfer.