title: Bone mineral density of the proximal femur after hip resurfacing arthroplasty: 1-year follow-up study.
abstract: BACKGROUND
  Hip resurfacing arthroplasty (HRA) is considered a bone-preserving procedure and may eliminate proximal femoral stress shielding and osteolysis. However, in addition to implant-related stress-shielding factors, various patient-related factors may also have an effect on bone mineral density (BMD) of the proximal femur in patients with HRA. Thus, we studied the effects of stem-neck angle, demographic variables, and physical functioning on the BMD of the proximal femur in a one-year follow-up.
  
  
  METHODS
  Thirty three patients (9 females and 24 males) with a mean (SD) age of 55 (9) years were included in the study. BMD was measured two days and 3, 6, and 12 months postoperatively and 10 regions of interest (ROI) were used. Stem-neck angle was analyzed from anteroposterior radiographs.
  
  
  RESULTS
  Three months postoperatively, BMD decreased in six out of 10 regions of interest (ROI) on the side operated on and in one ROI on the control side (p<0.05) compared to the second postoperative day. At 12 months, BMD had increased in 7 ROIs on the operated side and one ROI on the control side (all p<0.001). Correlation was found between the stem-neck angle and BMD in ROIs 2, 3, 7, and 9 (r=0.36-0.61). In multiple regression analysis, stem-neck angle, age, sex, body mass index, and walking distance did not explain the BMD changes.
  
  
  CONCLUSIONS
  After an early drop, the BMD of the upper femur was restored and even exceeded the preoperative level at one year follow-up. From a clinical standpoint, the changes in BMD in these HRA patients could not be explained by stem-neck angle or patient related factors.
authors: Department of Physical Medicine and Rehabilitation, Jyväskylä Central Hospital, and Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland. arja.hakkinen@jyu.fi
authors: Arja
authors: A
authors: Häkkinen
authors: Håkan
authors: H
authors: Borg
authors: Mikko
authors: M
authors: Hakulinen
authors: Jukka
authors: J
authors: Jurvelin
authors: Esa
authors: E
authors: Anttila
authors: Tapani
authors: T
authors: Parviainen
authors: Ilkka
authors: I
authors: Kiviranta
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