Abstract
Background
Tapered cementless femoral components have been used in total hip arthroplasty (THA) constructs for more than 20 years. The Synergy femoral component was introduced in 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets to better restore femoral offset at THA (Figure 1). The purpose of this study was to evaluate the outcome of the authors' experience using the Synergy stem at minimum 15 years of follow-up.
Material and methods
We retrospectively reviewed a consecutive series of 102 patients (112 hips) who underwent surgery between November 1996 and October 1998 for primary THA using cementless Synergy stem with a minimum 15-years follow-up. The mean age at the time of surgery was 61 years, and the mean duration of follow-up was 16.3 years. Seventeen patients were lost at FU (8 died before the 15 years mark, 8 changed residency, 1 not willing to be seen) with no problems related to the replaced hip. Ninety-four hips in 85 patients were available for clinical and radiologic analysis. Clinical results of the 94 THAs with more than 15 years of follow-up were assessed preoperatively and postoperatively at 5, 10 and 15 years by means of standard evaluation tools: SF12, WOMAC and Harris Hip Score. Thigh pain frequency and intensity were also recorded. Radiographic analysis (Figure 2) was focused on stem alignment, bone ingrowth, radiolucent lines presence, width and progression, stress-shielding and heterotopic ossification (HTO). Student paired test and Kaplan-Meier survival analysis were used for statistical analysis.
Results
All clinical evaluation tools showed at 5-year FU, 10-year FU and at latest FU (15–17 years) a statistically significant improvement compared to the preoperative scores. We observed a not constant thigh pain in 5 hips (4.75%). Nine stems were revised due to polyethylene wear (3 cases), late periprosthetic fracture (2 cases), infection (2 cases), subsidence (1 case) and instability (1 case). Stem related revision was a case of subsidence, related to occult intraoperative calcar crack and early revised (within 1 year); cumulative stem-related survival rate at 15 years was 99%. Alignment was varus in 5 cases and valgus in 1. Bone in-growth was observed in 93 hips (98%). Radiolucent lines were uncommon, non progressive, less than 2 mm, in Gruen zones 2 and 6. Stress-shielding was present as cortical reaction in 5 femurs in Gruen zones 3 and 5. Fifteen cases of HTO (grade I and II in 12 case and grade III in 3 cases) were observed.
Conclusions
The Synergy stem demonstrated excellent clinical and radiographic results at 15–17 years FU in 85 patients. Survivorship (with stem revision as end point) was 99% at 15 years. Thigh pain was uncommon and the level of activity and autonomy is excellent. Radiographically bone ingrowth is evident in all stems and radiolucent lines are “benign” with no aseptic loosening.
