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

Abstract

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.

Keywords: Direct anterior approach; Functional outcomes; Hip arthroplasty; Short metaphyseal-fitting stem; Standard-length stem.