The migration pattern and initial stability of the Optimys short stem in total hip arthroplasty: a prospective 2-year follow-up study of 33 patients with RSA

Background and purpose: The consensus that bone stock preservation and optimal restoration of offset and leg length is important in total hip arthroplasty is now widespread, especially for young and active patients. Short stems seem promising in this aspect, though implant stability is still of concern. This study looked at the migration pattern of the Optimys short stem through RSA analysis. Patients and methods: 40 patients were included. RSA images were made directly postoperatively (within 5 days), at 6 weeks and at 3, 6, 12 and 24 months. Double examinations were made for precision measurement. HOOS and pain scores were obtained preoperatively and at 2 years. 4 patients were excluded due to protocol violation and 1 patient was excluded for RSA analysis with a CN number >110. 2 patients were lost to follow-up after 3 and 6 months (n = 1 lost, n = 1 deep infection, respectively). Results: Mean age was 60 years with a mean BMI of 27. RSA analysis of 34 patients showed a significant initial median proximodistal translation (subsidence) of 0.21 mm (IQR 0.64–0.06) and anteversion-retroversion rotation of 0.59° (IQR 0.01–1.34) at 6 weeks, after which the stem stabilises and showed no further significant movement. Median migration in other directions was small. 4 patients had an initial subsidence of >2 mm, all showed secondary stabilisation. HOOS outcomes were satisfactory, with the domain symptoms and pain showing a median score of 95/100 at 2 years. Conclusions: After initial migration the Optimys achieves secondary stabilisation, suggesting low risk on long-term aseptic loosening. Clinical trials registration: NL47055.048.13.