Densitometric evaluation of periprosthetic bone resorption after surgical placement of Accolade I® TMZF® hip stem at 36 months

Purpose. The implantation of a hip prosthesis determines changes in the joint biomechanics and it alters distribution of the loads on the surrounding bone. Proximal bone resorption around femoral stems is commonly seen after cementless total hip arthroplasty. The aim of this study was to evaluate the effects of a tapered single wedge HA coated Stem on periprosthetic bone density in the seven Gruen areas to define the pattern of bone remodelling associated with this stem's design. Methods. 25 patients (11 men and 14 women) were selected in this study in accordance with specific inclusion and exclusion criteria. Patients underwent total hip replacement with Accolade I® TMZF® hip stem. They were all preoperative evaluated using the Harris Hip Score and a standard radiology examination. Clinical, radiological and bone density evaluations were performed on each patient within 6 months and at 12, 24 and 36 months after surgery. Results. The results at 36 months show a statistically significant increase (p < 0.001) of the HHS scores, from 64 during preoperative phase to 93 at 36 months. No patients underwent to revision surgery and no peri-implant radiolucency was found during radiological assessments. The bone mineral density changes in the seven Gruen zones seen with DXA scan showed a decrease of 2.9% only at the level of the calcar region (R7), a moderate increase at the level of R1, R2 and R3 and a statistically significant increase of BMD (p < 0,05) at 24 and 36 months after surgery at the level of R4 (+ 6.2%), R5 (+ 7.2%) and R6 (+ 8.15%). Conclusion. Our study showed that the use of the Accolade I® TMZF® uncemented stem after 36 months of followup is associated to a good load transfer to the preripros-thetic bone avoiding the stress shielding phenomena. It showed a definitely positive BMD evolution at the level of all Gruen's zones and especially at the level of the medial region (R5, R6). The only exception was at the level of the calcar region where there was a BMD mildly decrease (from 1.03 to 1.00) most likely due to the stem philosophy (metaphyseal fixation) and to the consequent load transfer to the metaphyseal medial regions (R5, R6).