Abstract
Background
Cup inclination is a major factor in the success of a total hip replacement. An open cup position can lead to dislocation or increased wear from rim loading and a closed cup position lead to impingement against the femoral neck or psoas. Although the ideal inclination for cup position is recommended as between 40 and 45 degrees, accurate positioning of the implant might be influenced by pelvic flexion and movement of the patient's pelvis during the procedure. We wanted to examine if the transvers acetabular ligament (TAL) could be used to determine cup inclination intra-operatively.
Methods
16 hips from 9 cadaveric specimens were used for the study. A computer navigation system (Brain lab) was used to measure and document the exact inclination and version of the acetabular trial component in three positions: flush with the transvers acetabular ligament (TAL), with the rim of the cup 5 mm from the TAL in a cranial direction and with the rim of the cup 5 mm caudally displaced. Statistical analysis of the results was performed by the Department of Biostatistics.
Findings
With the cup positioned flush with the TAL, the average version was 43 degrees (range 37 to 47 degrees.) When there was a 5 mm gap between the TAL and the cup the average inclination was 28 degrees (21 to 35 degrees.) When the cup was opened so it covered the TAL by 5 mm the average inclination increased to 64 degrees (55 to 75 degrees.) The average anteversion angle was 18 degrees (range 15 to 25 degrees.)
Conclusion
We found the transverse acetabular ligament to be an accurate landmark for positioning of the femoral implant as far as version and inclination was concerned. We recommend positioning the acetabular component flush with the TAL as cup inclination was shown to be ideal in all cases when we adhered to that principle.
NO DISCLOSURES
