The NANOS short stem in total hip arthroplasty: a mid term follow-up

A number of short stems for total hip arthroplasty have been introduced during the last decade. We describe our experience with the NANOS prosthesis (Smith and Nephew, Marl, Germany). The potential increase of bone mass around a femoral short stem using bone densitometry may be an indicator for secondary ingrowth. We report the outcome of 72 NANOS short stems in 65 patients between March 2003 and October 2007. The mean follow-up was 5.2±0.7 years and the mean age of the patients was 63±8.3 years. Along with demographic data and co-morbidities, the Harris Hip Score, the Merle d'Aubigné mobility score, and a patient-centred questionnaire were evaluated pre-operatively and during follow-up. The Mean Harris Hip Score increased from 47.3±12.2 pre-operatively to 97.6±0.6 at the final follow-up. The Merle d'Aubigné mobility score increased from 7.6±1.4 pre-operatively to 11.8±0.3 at the final follow-up. None of the 72 stems were revised, providing a survival rate of 100%. Radiolucent lines were visible rasiographically in two patients during follow-up. The NANOS short stem demonstrated a satisfactory outcome at mid term follow-up. The clinical and radiological results support to the principle of metaphyseal anchorage of a short stem prosthesis. Long term evaluation will be of interest to determine if these encouraging trends are reflected by prolonged survivorship.