Retrospective Clinical and Radiological Outcomes of Total Hip Arthroplasty in 51 Patients After a Mean 8.2 Years Using the Nanos® Short-stem Prosthesis

Introduction: Over the past several years, femoral short-stem hip implants have become more popular as a treatment option in the field of primary hip arthroplasty for younger and more active patients. Current data on clinical outcomes and the implant survival rates in patients with short-stem implants cover a maximum of five to six years. The aim of this study was to assess the survival rates, as well as clinical and functional outcomes, in total hip arthroplasty (THA) using the Nanos® short-stem implant (Smith & Nephew, Marl, Germany) over a follow-up period exceeding 5 y. Materials and Methods: This single-center retrospective study included the first 100 patients who were treated at the Department of Orthopedics at the University Hospital Halle (Saale) between January 2008 and February 2009. Ultimately, the complete data of 51 patients (54 hips) were reviewed. The follow-up period was from May to November 2017. We evaluated patient satisfaction regarding pain and function using a grading system. The Harris Hip Score and Forgotten Joint Score were obtained to evaluate functional outcome after THA. Postoperative radiographic evaluation included the measurement of leg-length discrepancy, changes in the shaft axis, femoral offset and horizontal or vertical center of rotation. Potential postoperative shaft angulation or axial shaft migration was also determined. Radiographic images were checked for radiolucent lines and heterotopic ossification using the classification systems outlined by Green and Brooker. Results: The average follow-up was 97.8 months (8.2 y). The mean patient age at follow-up was 68 y and the body mass index was 28.2 kg/m2. The mean Harris hip score at follow-up was 92.0 and the Forgotten Joint Score was 91.7 %. Survey results showed that patient satisfaction and pain perception were rated very good. No significant change in leg length was observed (mean: 0.1 mm shortening). Overall, a rather varus stem positioning was detected postoperatively (mean: 3.1°). The femoral offset was slightly reduced on average in the entire patient group (mean: -1.8 mm). In the horizontal plane, lateralization of the center of rotation was detected overall (mean: 0.7 mm). In the vertical plane, cranialization was noted (mean: 1.4 mm). The CCD angle did not change. There was no further stem migration postoperatively. Radiolucent lines occurred in 10 cases in Gruen zones 1 and 7. Heterotopic ossification occurred in stages 1 to 3 according to the Brooker classification system. We found no cases of aseptic loosening or other reasons for revision. Conclusion: The outcomes after a mean follow-up of 97.8 months (8.2 y) showed that high levels of patient satisfaction and functional outcome can be achieved with the use of a short-stem endoprosthesis. Sufficient restoration of the patient's individual anatomy paired with high survival rates makes this short-stem prosthesis a reliable implant in total hip arthroplasty.