Background: Many short stems for total hip arthroplasty have been introduced by the manufacturers only during the last decade. One of them is the Nanos short stem (Smith and Nephew, Marl, Germany). The development of short stems was aimed at preserving bone and soft tissue by utilizing a minimally invasive approach, thus allowing a quick return to an active life. It was purpose of this study to evaluate the radiological changes after using this device.
Methods: We present the radiological results of 202 cementless THAs which were performed in 172 patients using the Nanos stem. Radiological evaluation was performed using standing anterior-posterior (AP) and lateral radiographs of the proximal femur preoperatively, postoperatively and during the follow up. We analyzed the preoperative and postoperativ CCD angle, the subsisdence, preoperative and postoperative offset, osteolysis, bone resorption, increased density, neocortex and periarthricular ossifications.
Results: One stem had to be revised due to subsidence four days after implantation. Two cups (BiconPlus, Smith and Nephew, Marl, Germany) had to be revised during the time of follow up due to an aseptic cup loosening. Two stems showed radiolucent lines at the implant-bone-interface at the last follow-up. An increase of bone density could be detected in 18 hips (8.9%). 14 hips showed periarticular ossifications. Measurable subsidence was detected in a total of four stems (1.9%). The preoperative neck-shaft-angle angle was 133.8 ± 4.4° (range: 118.5-146.2) and the neck-shaft-angle angle at the time of follow up was 134.6 ± 4.3° (range: 123.3-147; P< 0.05). The preoperative and postoperative offset changed from 109.3 ± 11.9 mm (range: 80.9-131.6) to 109.7 ± 12.3 mm (range: 79.7-155.6; P< 0.05).
Conclusion: In summary, this study shows that a correct anatomical reconstruction is possible with a device of this design. The outcome is comparable to that of other short stems. Further studies should be performed in a prospective and randomized design to evaluate the advantage of such a device with a higher level of evidence.