Comparing femoral bone remodeling after total hip arthroplasty using collarless POLARSTEM◊ for different Dorr types

Using bone-cemented stems is recommended for femurs with severe osteoporosis and a large medullary cavity. This study aimed to evaluate postoperative bone changes around a collarless POLARSTEM◊ using simple X-ray images and the bone mineral density and compare them according to the medullary cavity geometry. The data used in this study consisted of 50 patients (54 joints in total) who underwent total hip arthroplasty with POLARSTEM◊ (Dorr type A: 19 joints, Dorr type B: 19 joints, and Dorr type C: 16 joints) between January 2018 and December 2021. Clinical evaluations included Harris' hip score, blood loss, radiological evaluation, and bone mineral density changes. The postoperative Harris hip score was better than that preoperatively in Dorr types A, B, and C. Radiolucent lines were observed in two joints, but there was no evidence of subsidence greater than 3 mm or cortical hypertrophy. Stress shielding was found proximally in zones 1 and 7, while cancellous condensation was found distally in zones 3, 4, and 5. The postoperative bone mineral density of the femoral condyle was greater than that preoperatively in all zones, with the highest and lowest bone mineral density in zones 5 and 1, respectively, in all medullary configurations. In Dorr type C, there was no postoperative femoral pain or stem subsidence. Good bone remodeling also occurred, suggesting that POLARSTEM◊ may be a valuable option for hip arthroplasty in older adults.