Initial stability and bone response at 6 months post-operation in the Avenir complete stem: a comparative study by femoral canal shape

OBJECTIVE: To compare the initial postoperative fixation and bone response at 6 months among different femoral canal morphologies in patients implanted with a specific fully hydroxyapatite-coated femoral stem. METHODS: This study included 95 hip joints of patients who underwent primary total hip arthroplasty between 19 October 2020 and 20 October 2023 (17 male and 78 female). Femoral canal shapes were categorised into Dorr types A, B, and C using the canal flare index. RESULTS: Dorr types A, B, and C were observed in 17, 76, and 25 cases, respectively, and averaged -0.17 ± 1.99°, 0.71 ± 2.24°, and 1.57 ± 1.25°, respectively in the coronal plane, indicating a trend toward varus insertion. The medullary cavity occupancy rate was highest in Dorr type C (17.6 ± 9.81%). The bone contact rates were higher in Zones 3 and 7 for Dorr type C than for types A and B. At 6 months, spot welds indicative of fixation appeared in all cases, with Dorr type A showing an absence of spot welds in Zones 1 and 7, suggesting a risk of distal fixation. CONCLUSIONS: Although the implant generally provides satisfactory fixation, the risk of malalignment and distal fixation associated with specific femoral canal morphologies should be carefully considered.