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Why does outer joint motion predominate in bipolar hip prosthesis? Experimental and clinical studies
Sung Man Rowe1, Jae Yoon Chung, Eun Sun Moon
1Department of Orthopedics, Chonnam National University Hospital, Gwangju, Korea. smrowe@chonnam.ac.kr
Acta Orthopaedica Scandinavica
|March 15, 2005
Summary
Bipolar hip prostheses show more outer joint motion than inner, contrary to theory. This is due to impingement and joint differences, suggesting design adjustments can reduce acetabular erosion.
Area of Science:
- Orthopedic biomechanics
- Biomaterials science
Background:
- Theoretical models predict equal friction coefficients lead to inner joint motion in bipolar hip prostheses.
- Clinical observations suggest outer joint motion is more prevalent.
Purpose of the Study:
- To analyze motion distribution in bipolar hip prostheses.
- To identify factors influencing motion distribution between inner and outer joints.
Main Methods:
- Cadaveric bone model analysis.
- Fluoroscopic examination of 50 patients during motion.
Main Results:
- Motion distribution varied significantly among patients.
- A consistent preponderance (63-90%) of outer joint motion was observed across all movement directions.
- 44 out of 50 patients exhibited persistent motion at both joints.
- Outer motion preponderance resulted from early acetabular cup impingement and structural joint differences.
Conclusions:
- Adjusting positive eccentricity and reducing inner joint frictional torque can improve motion distribution.
- Enhanced lubrication and smoothness of the inner joint may reduce acetabular erosion.