Direct anterior approach in total hip arthroplasty: influence of stem length on clinical and radiological outcomes at medium-term follow-up.

Purpose To evaluate the influence of short versus long stems implanted through a Direct Anterior Approach (DAA) on clinical and radiological outcomes in THA at medium-term follow-up (average follow-up of 44.8 months). Methods 167 consecutive total hip arthroplasties treating patients affected by primary hip osteoarthritis were retrospectively evaluated. A standard-length stem (H-MAXs) was used in 70 patients, while a short metaphyseal—fitting femoral stem (MINIMA) was used in 97 patients. The Harris Hip Score (HHS) and Forgotten Joint Score-12 (FJS) were used as outcomes measurements. Post-operatively, Engh’s score and Brooker classification were analyzed at 6 months, 1 year and every 2 years until the final FU. The correct size of the implant was evaluated determining the canal fill index (CFI), and all undersized stems were classified according to Magra classification. Results The average HHS was 83±13.4 in the standard stems group and 87±14.1 for short stems group (p=0.148). The average FJS was 87.9±15.2 for patients in the standard stems group and 84.5±17.7 with no significant differences (p=0.327). None of the stems showed radiographic signs of instability (standard stems mean Engh’s score: 19.25 versus short stems mean Engh’s score: 19.50—p=0.41). According to Brooker classification, no significant difference in severity was found using different stems (p=0.715). A high rate of undersized stems was found (standard stems 24%—short stems 25%) but without statistical difference between groups (p=0.078), while a different trend in malposition following the recent classification proposed by Magra et al. was observed evaluating all undersized stems (p=0.0387). Conclusions Both groups achieved good and comparable patient-reported outcome measurements (PROMs) and radiographic stability with fixation observed by bone ingrowth. A high rate of undersized stems was found with a correlation between femoral stem length and specific pattern of malposition. Malalignment in Varus was frequent in shorter stems in contact proximally with medial calcar and distally with lateral cortex, while a uniform undersizing was observed for longer ones with a continuous margin around the stem. However, the stems never presented progressive radiolucent lines over the whole surface of the stem.