Abstract
Introduction and aims: Increasingly the accurate reconstruction of the hip in total hip arthroplasty is planned using pre-operative pelvic radiographs. The accuracy of reconstruction is assessed using post-operative pelvic radiographs. This study defines significant variations in the offset, hip joint centre and femoral head centre-trochanteric height relations in normal radiographs.
Method: One hundred standard normal pelvic radiographs were examined based on a defined criterion. The medial offset, the vertical height of hip joint centre with reference to the ischial tuberosity and the femoral head centre-trochanterc height relation were measured for both hips. The differences in measurements were evaluated to determine the normal variation in offset and the hip joint centre. The relationship of the femoral head centre to the tip of the greater trochanter was determined.
Results: On average, the right hip and left hip differed by 2.54mm in their offset .The standard deviation of differences was 2.31. Therefore the offset of one hip will predict the offset of the other hip to within 4.62mm, with 95% accuracy. If the reconstructed hip has an offset to within + 4.62 to – 4.62mm of the contra lateral side, then the offset should be considered to be reconstructed as normal. The average difference in height of the hip joint centres of right hip from left hip with reference to bi-ischial line was found to be 3.49mm. The standard deviation of differences was 3.15. Therefore the hip joint centre height measured in one hip will predict the hip joint centre height of the opposite hip to within 6.3mm with 95% accuracy. Thus the hip joint centre height of one hip may differ from the opposite hip by 6.3mm in normal individuals. The tip of greater trochanter was on average 8mm higher than the centre of rotation of the femoral head. The greater trochanter was not at the same level as the femoral head centre as commonly believed.
Conclusion: This study demonstrates considerable variation in the medial offset and the hip joint centre location on pelvic wall. The femur head centre is lower than commonly assumed. These factors should be taken into account when pre-operative planning using pelvic radiographs and assessing the quality of the post-operative reconstruction.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
