3.1. Basic conditions of surgery
No significant difference was observed in the operation time, hospitalization time, blood loss, and blood transfusion between the two groups (P > 0.05). A comparison of the intraoperative data between the two groups is shown in Table 2.
3.2. Clinical results
A total of 120 patients were followed up with an average of 74.8 months (12–114 months). At the last follow-up, the Harris Hip Score in the cylindrical and tapered groups increased from 41.1 ± 6.1 to 84.3 ± 4.4 (P < 0.05) and from 40.1 ± 6.6 to 85.5 ± 3.8 (P < 0.05), respectively. The VAS score in the cylindrical and tapered groups decreased from 7.6 ± 1.6 to 2.0 ± 0.4 (P < 0.05) and from 7.5 ± 1.2 to 1.8 ± 0.2 (P < 0.05), respectively. At the last follow-up, no significant difference was observed in the Harris Hip Score between the two groups (P > 0.05), but the VAS score of the cylindrical group was higher than that of the tapered group (P = 0.047) (Figure 1). Moreover, no significant difference was observed in the overall satisfaction of recent follow-up results between the cylindrical group (87.3%) and the tapered group (90.1%) (Table 3).
3.3. Radiographic results
At the last follow-up, prosthesis subsidence in the cylindrical and tapered groups was 0–15 mm with an average of (4.17 ± 4.20) mm and 0–8 mm with an average of (2.17 ± 1.49) mm, respectively (Figure 2). A significant difference was observed in prosthesis subsidence between the two groups. All prosthesis subsidence stopped within 1 year after operation. Ten hips in the tapered group (15.2%) and seven hips in the cylindrical group (13.0%) experienced subsidence of more than 5 mm (P > 0.05). Among the 10 hips in the tapered group, eight had type ⅢA femoral defects, and two had type IIIB femoral defects. Among the seven hips in the cylindrical group, six hips had type IIIA femoral defects, and one had a type IIIB femoral defect.
In the cylindrical group, 45 hips (84.1%) were fixed by bone growth, seven (13.0%) were fixed by fibers, and one (1.8%) was unstable. In the tapered group, 64 hips (98.4%) were fixed by bone growth, one (1.5%) was fixed by fibers, and one (1.5%) was unstable. The failure rate of osseointegration (fibrous or unstable) in the cylindrical group was significantly higher compared with that in the tapered group (P < 0.05).
In the imaging changes of proximal femoral host bone, the proportion of bone repair type in the tapered group (39.4%) was significantly higher than that in the cylindrical group (7.4%, P < 0.05), and the proportion of bone loss type in the tapered group (13.6%) was significantly lower than that in the cylindrical group (43.6%, P < 0.05; Table 4).
In the cylindrical group, 21 hips (38.9%) had stress-shielded bone resorption of degrees I and II in the greater trochanter, which was manifested by femoral moment atrophy or decreased cortical bone mineral density from the sharply blunt margin to the trochanter level. However, in the tapered group, nine hips (13.6%) had stress-shielded bone resorption of degrees I and II in the greater trochanter. A significant difference was observed between the two groups (P < 0.05; Table 5).
3.4. Survivorship
The 8-year cumulative survival rate was defined as the end point of any reoperation for any reason. The 8-year cumulative survivorship of the cylindrical and tapered stems was 94.43% (95% confidence interval [CI], 86.13%–97.82%) and 96.69% (95% CI, 91.39%–98.75%), respectively. No significant difference was observed between the two groups (Figure 3).
3.5. Postoperative complications
Intraoperative fractures were found in eight cases (14.8%, Figure 4) in the cylindrical group and three cases (4.5%, Figure 5) in the tapered group. A significant difference was observed between the two groups (P < 0.05). In the cylindrical group, five cases had femoral trochanteric fractures (with steel wire binding), and three cases had femoral shaft fractures (with steel wire binding). All fractures were healed. In the tapered group, three cases had femoral shaft fractures (with steel wire binding), and the fractures healed after operation.
Periprosthetic fractures were observed in two cases (3.7%) in the cylindrical group and one case (1.5%) in the tapered group (P > 0.05). These fractures were treated with open reduction and internal fixation.
Two cases (3.7%) of hip dislocation were observed in the cylindrical group after operation. One patient underwent cup exchange with recurrent instability, whereas the other was treated with closed reduction, regaining hip stability. Two cases (3.0%) of hip dislocation occurred in the tapered group (P > 0.05). One case of frequent dislocation after closed reduction was treated with replacement of lining and femoral head size.
One hip in the cylindrical group was revised due to osteolysis around the cup 9 years after surgery (Figure 6). The last follow-up radiography showed osteolysis around the cup, and cup revision arthroplasty was conducted for an osteolytic lesion.
Three out of 66 cases in the tapered group had mild thigh pain after operation (VAS score l–3), but most of the symptoms disappeared 1 year after operation. Seven out of 54 cases in the cylindrical group had mild thigh pain (VAS score 1–4), 2 of which developed persistent thigh pain. The rate of postoperative thigh pain was higher in the cylindrical group (12.9%) than in the tapered group (4.5%) (P < 0.05).