Limited range of motion of hip resurfacing arthroplasty due to unfavorable ratio of prosthetic head size and femoral neck diameter.
OBJECTIVE
Hip resurfacing arthroplasty is being used more and more frequently. The small ratio in size between the resurfaced femoral head and the relatively thick femoral neck raises the question of whether the range of motion is sufficient, particularly with regard to the high mobility required by younger patients. We analyzed motion in a CAD model.


METHODS
Three-dimensional CAD models of the natural hip were created from CT scans and 8 designs of hip resurfacing prostheses (head diameter between 42 mm and 54 mm combined with a hemispherical cup) were implanted in a virtual sense. We simulated 3 different leg positions and the range of motion was evaluated, considering five different implant positions.


RESULTS
The range of motion of the hip resurfacing designs analyzed was far below the range of motion of stemmed total hip prostheses. None of the resurfacing prostheses provided flexion movements of 90 degrees without impingement. The average range of motion of hip resurfacing arthroplasty was 31-48 degrees below the range of motion of a stemmed total hip replacement with 32-mm head diameter.


CONCLUSIONS
The range of motion of the hip resurfacing designs examined was substantially less than that of a conventional total hip prosthesis. Since impingement of the femoral neck on the acetabular component increases the risk of neck fractures, of dislocation and of subsequent implant loosening, the design and position of the implant should be considered before using hip resurfacing arthroplasty as a standard treatment for younger patients.
Kluess
Daniel
D
Department of Orthopedics, Institute for Biomedical Engineering, University of Rostock, Germany. daniel.kluess@uni-rostock.de
Zietz
Carmen
C
Lindner
Tobias
T
Mittelmeier
Wolfram
W
Schmitz
Klaus-Peter
KP
Bader
Rainer
R
D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods; D003198:Computer Simulation; D005270:Femur Head / Q000033:anatomy & histology; D005272:Femur Neck / Q000033:anatomy & histology; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular; D012307:Risk Factors