Using the transverse acetabular ligament as a landmark for acetabular anteversion: an intra-operative measurement

PURPOSE. To measure the transverse acetabular ligament (TAL) anteversion in hips with severe deformity, using fluoroscopy-computed tomographic navigation. METHODS. 31 hips in 10 men and 19 women aged 40 to 78 (mean, 58.7) years who underwent total hip arthroplasty for primary osteoarthritis (n=6) or osteoarthritis secondary to developmental hip dysplasia (n=19) or congenital hip dislocation (n=6) were included. The severity of hip dislocation was classified according to the Crowe classification; 15 hips were grade 1, 7 were grade 2, 3 were grade 3, and 6 were grade 4. The TAL anteversion was measured using fluoroscopy-computed tomographic navigation. The difference in TAL anteversion between non-dislocated hips (Crowe grade 1, n=15) and dislocated hips (Crowe grades 2-4, n=16) was compared. RESULTS. In all 31 hips, the TAL could be visualised intra-operatively. No patient reported severe pain, early wear, loosening, or dislocation after 2 years. The mean TAL anteversion and inclination angles measured by the navigation system were 26.5 (SD, 8.9; range, 8-42) degrees and 41.5 (SD, 4.6; range, 32-49) degrees, respectively. 22 of the 31 hips were in the safe zone. TAL anteversion in non-dislocated and dislocated hips was not significantly different. Inter- and intra-observer mean absolute differences in TAL anteversion were 0.3 and 0.4 degree, respectively. CONCLUSION. The TAL is a useful anatomic landmark for total hip arthroplasty in dislocated hips.