Abstract
Introduction
Resorptive bone remodeling secondary to stress shielding has been a concern associated with cementless total hip arthroplasty (THA). At present, various types of cementless implants are commercially available. The difference in femoral stem design may affect the degree of postoperative stress shielding. In the present study, we aimed to compare the difference in bone mineral density (BMD) change postoperatively in femurs after the use of 1 of the 3 types of cementless stems.
Methods
Ninety hips of 90 patients who underwent primary cementless THA for the treatment of osteoarthritis were included in this study. A fit-and-fill type stem was used for 28 hips, a tapered-rectangular Zweymüller type stem was used for 32 hips, and a tapered-wedge type stem was used for 30 hips. The male/female ratio of the patients was 7/21 in the fit-and-fill type stem group, 6/26 in the tapered-rectangular Zweymüller type stem group, and 6/24 in the tapered-wedge type stem group. The mean age at surgery was 59.9 (39–80) in the fit-and-fill type stem group, 61.7 (48–84) in the tapered-rectangular Zweymüller type stem group and 59.6 (33–89) in the tapered-wedge type stem group. To assess BMD change after THA, we obtained dual-energy X-ray absorptiometry scans preoperatively and at 6, 12, 24, and 36 months postoperatively.
Results
There were no differences in demographic data, such as gender, age at surgery, and body mass index, among the 3 groups (Table1). In terms of BMD change after THA, no differences were observed in Gruen zones 1–5 among the 3 groups during the 3-year follow-up. The BMD in Gruen zone 6 was maintained in the tapered-wedge type stem group, but decreased by 5% in the fit-and-fill type stem group and by 20% in the tapered-rectangular Zweymüller type stem group (p < 0.01). The BMD loss in Gruen zone 7 was observed in all stem types; however, the BMD loss at 36 months in the tapered-wedge type stem group (−15%) was significantly less than that of the other 2 groups (the fit-and-fill type stem group: −29%; the tapered-rectangular Zweymüller type stem group: −30%; p < 0.001 for both groups) (Figure).
Discussion and Conclusion
A difference in postoperative BMD loss was observed among the 3 stem designs. This may be a result of the different fixation concept associated with each stem design. In the present study, we compared the postoperative BMD change after THA among a fit-and-fill type stem, a tapered-rectangular Zweymüller type stem, and a tapered-wedge type stem. BMD in the medial-proximal femur was maintained 3 years after THA in the group with the tapered-wedge type stem, which is fixed in a more proximal part of the femur compared to the other stems.
