The Journal of Bone and Joint Surgery, Vol 76, Issue 11 1692-1705, Copyright © 1994 by Journal of Bone and Joint Surgery, Inc
Micromotion of femoral stems in total hip arthroplasty. A randomized study of cemented, hydroxyapatite-coated, and porous-coated stems with roentgen stereophotogrammetric analysis
J Karrholm, H Malchau, F Snorrason and P Herberts
Northern University Hospital, Umea, Sweden.
The fixation of the femoral stem in a total hip arthroplasty was studied in
sixty patients (sixty-four hips) with use of roentgen stereophotogrammetric
analysis. The hips were randomly stratified on the basis of the age, sex,
and weight of the patient; the roentgenographic quality of the bone; and
the reason for the operation (primary or secondary osteoarthrosis). The
hips were then randomly assigned to one of three types of fixation of the
femoral component: insertion with cement, hydroxyapatite coating, or porous
coating. Examinations with roentgen stereophotogrammetry were done as long
as two years after the operation. Micromotion of the prostheses was
evaluated in terms of subsidence or proximal migration and rotations and
translations of the proximal-lateral (shoulder) and distal (tip) parts of
the prostheses. The clinical results at the two-year follow-up evaluation
did not differ significantly between the groups with regard to the Harris
hip score or the pain score (p > 0.05 for both; Wilcoxon rank-sum test).
There were small or no differences in rotations and micromotions of the
shoulder and the tip of the prostheses. Increased subsidence of 0.1 to 0.2
millimeter was recorded for the cemented and the porous-coated prostheses
(p = 0.002 and p = 0.02, respectively; Wilcoxon rank-sum test). Thus,
proximal hydroxyapatite coating seems to enhance the early fixation of the
stem. Conventional roentgenography revealed an increased number of
radiodense lines surrounding the porous-coated prostheses. Distal
hypertrophy of the femoral cortex was found mainly around the
hydroxyapatite-coated prostheses. Proximal resorption of bone and
heterotopic ossification occurred to approximately the same extent
regardless of the type of fixation used.
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