No differences in clinical and radiographic outcomes between standard and shortened versions of a same cementless femoral stem in Dorr type A femurs

PURPOSE: In Dorr type A femurs (DTAF), the flared anatomy renders proximal femoral filling (PFF) with a standard-length stem (STA) challenging, although this is essential to ensure favourable outcomes. This study compared clinical and radiographic outcomes between standard and shortened versions of a same cementless stem in DTAF. Our hypothesis was that there would be no differences in clinical outcomes, PFF or osseointegration between the 2 stems. METHODS: We reviewed 87 THA files performed in DTAF from 2013 to 2015 for STA and from 2015 to 2019 for shortened-length stems (SHO). At minimum 2-year follow-up, 8 patients were unavailable for evaluation, leaving 79 THA: 34 STA and 45 SHO. Femoral morphology was assessed preoperatively with the canal-calcar ratio (CCR) and canal bone ratio (CBR). Outcomes included: Oxford Hip Score (OHS) and PMA, proximal canal fill ratio (CFR)(A) and (B), stem subsidence and alignment, distal cortical hypertrophy, and Engh score. RESULTS: There were no significant differences in clinical outcomes, PFF and osseointegration between the 2 groups. Greater migration was observed in STA. Distal cortical hypertrophy was seen exclusively in SHO and was significantly associated with a worse OHS. CCR was significantly correlated with proximal CFR. Aligned stems were significantly associated with higher CFR(B). CONCLUSIONS: There were no differences in clinical or radiographic outcomes of STA and SHO in DTAF. Increasing CFR enhanced stem alignment, while femoral morphology significantly influenced PFF. SHO migrated less, but exhibited distal cortical hypertrophy, which may indicate early stress-shielding and challenge the stem's "short" designation.