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We investigated the effects of pelvic rotation and femoral head diameter on the anterior stability of the hip joint after total hip replacement. Computer navigation and cadaveric bone were used to simulate the range of motion after total hip replacement. The hip was put at 0 degrees of flexion and it was gradually externally rotated until the hip dislocated. The degree of external rotation when the hip was dislocated was recorded. The test was repeated with the hip at +10, -10, -20, -30, -40 and -50 degrees of flexion. The acetabular component was positioned with abduction of 45 degrees and anteversion at 20 degrees. There was a significant difference amongst each group of pelvic rotation from 0 to -50 degrees in the degree of external rotation when the hip was dislocated. The degree became insignificant when pelvic rotation was increased from 0 to 10 degrees. From -10 to -50 degree of pelvic rotation, 36mm head had significant better stability compared with 32mm and 28mm femoral heads. The presence of significant pelvic sagittal malrotation can increase the risk of anterior dislocation. A larger femoral head is more stable than smaller heads. When pelvic sagittal malrotation is not present, there is no difference in stability between large and small femoral heads.

The size of the femoral head and acetabular anteversion are crucial for stability in total hip replacements. This study examined the effects of head diameter and acetabular anteversion on the posterior instability after total hip replacement in an in vivo setting. The acetabular shell was inserted at 0-20° of anteversion at five degree intervals. By using different head sizes (28 mm, 32 mm, 36 mm), the degrees of dislocation were recorded by computer navigation. The 36-mm group consistently showed better stability compared with the 32- and 28-mm groups, regardless of the degree of cup anteversion. Within each group of head size, the hip was significantly more stable when the cup anteversion increased from 0° to 10°. The difference became insignificant when it increased from 15° to 20°.

Purpose: To report the radiological and clinical results of revision total hip arthroplasty (THA) with femoral impaction bone grafting (IBG)., Methods: 4 men and 9 women (15 hips) aged 38 to 84 years underwent revision THA with femoral IBG using Elite plus stems for aseptic loosening or infection., Results: The mean follow-up duration was 7.7 years. The Harris hip score improved from 61.7 to 83.7. There was no pain in 11 hips and slight pain in 4. The mean subsidence was 5.7 mm. The mean change of alignment was 1.2 degrees. There was no radiological evidence of stem loosening. One stem was revised due to a peri-prosthetic fracture. Cortical healing was noted in 11 hips, and trabecular incorporation in 10., Conclusion: Although intra- and post-operative complications were not uncommon, femoral IBG is a safe procedure in carefully selected patients and offers good medium-term results.