High incidence of early subtrochanteric lateral cortical atrophy after hip arthroplasty using bone-conserving short stem.

PURPOSE: Load transfer to the bone is believed to be more physiological around the short stem in total hip arthroplasty (THA). However, we found unusual bony remodeling around the shortened tapered stem. This study was performed to investigate the extent and frequency of this phenomenon and to find the possible risk factors of it.

METHODS: Among 121 consecutive THA using the same short stem, 80 THAs were enrolled. Radiographic measurements were made using anteroposterior (AP) radiographs taken immediately and at two years after surgery. The thickness of the lateral cortex at the level of the distal end of the coated surface and at 10, 20, 30, and 40 mm proximal to it were measured.

RESULTS: Significant atrophy was noted in all regions (P < 0.001 each). In 46 cases, this presented as an intra-cortical osteolytic line (IOL). Sixty-one cases showed either an IOL or atrophy >10%. The risk of a mean reduction >20% was related to an increased operating time (odds ratio [OR] = 0.981; 0.966 < 95% confidence interval [CI] < 0.996) and lower body mass index (BMI) (OR = 1.216; 1.043 < 95% CI < 1.417). Periprosthetic fracture through the lateral cortex occurred in one case.

CONCLUSION: Even with THA using a shortened stem, high incidence of proximal stress shielding was noted in the form of lateral cortical atrophy, especially for the patient with low BMI.