Acetabular Inclination : Wheeless' Textbook of Orthopaedics

Acetabular Component Abduction / Inclination:

when cup is abducted < 30 degrees, impingement occurrs in flexion;
when cup is abducted > 50 deg, head tended to sublux out of acetabulum by "climbing the wall"
note that the abduction angle of the cup is an important technical factor contributing to the amount of wear;
- cups with an abduction angle of less 40 deg had the lowest annual rates of linear and volumetric wear
- cups with an abduction angle of greater than 50 deg had the highest rates of wear;
Udomkiat P, et al, the authors found the abduction angle of the cup to be an important factor contributing to amount of wear; angle of >50 deg had the highest rates of wear;
- cups with an abduction angle of >50° had an average volumetric wear rate of 160 mm 3 /yr, which exceeds the critical rate of 150 mm 3 /yr that can be expected to result in osteolysis and loss of fixation 18;
- this accelerated wear in cups with an abduction angle of >50° was also reported by Schmalzreid, et al;
McCollum, et al
- safe range for cup abduction that would allow physiologic ROM w/o impingement was 30-50 deg abduction w/ cup in 30 deg flexion;
- note that in lateral position on OR table, superior acetabulum is adducted toward foot of table consistently between 10 deg to 15 deg;
- if cup is placed in position of 45 deg of horizontal abduction to table w/ pelvis in adducted position, when pt stood up cup was abducted an additional 10-15 deg placing it in 55 degrees -60 degrees of abduction, which is an unstable position;