Comparison of radiographic changes in rectangular curved short stem with thin versus thick porous coating for cementless total hip arthroplasty: a retrospective study with a propensity score matching

BACKGROUND: Radiographic changes that appear relatively quickly after fixation of cementless stem in total hip arthroplasty (THA) vary depending on the stem design and fixation style. The present study compared radiographic changes between two types of rectangular curved short stems of similar shape. METHODS: This retrospective study included 118 hips that underwent primary cementless THA with an anterolateral supine approach using a rectangular, curved, short stem performed by the same surgeon between June 2015 and June 2019. Among the examined hips, 39 had a thicker porous coating stem (thicker group) and 66 had a thinner porous coating and reduced tip stem (thinner group) and at least 12-month follow-up. Radiographs taken during the final course observation were assessed. Propensity score matching was performed based on demographic data and comparisons were made using pairs of 25 hips each. Statistical analysis was performed using chi-square test and p values ≤ 0.05 indicated statistical significance. RESULTS: The pattern of the radiolucent lines showed a significant difference after matching (p = 0.0044). A “proximal and distal” pattern was most common in the thicker group and a “distal only” pattern was most common in the thinner group. There was notable and significant difference in cortical hypertrophy in the thicker group after matching (p = 0.024). CONCLUSIONS: Although the two short stems were similar shapes, the short-term radiographic changes were different. The thinner group showed fewer radiographic changes than the thicker group, making it a more “silent” stem.