Abstract
Introduction
Dislocation is one of severe complications after total hip arthroplasty (THA). Direct anterior approach (DAA) is useful for muscle preservation. Therefore, it might be also effective to reduce dislocation. The purpose of this study is to investigate the ratio and factors of dislocations after THA with DAA.
Materials & methods
Nine hundred fifity two primary THAs with DAA are examined. Mean age at operation was 64.9 yrs. 838 joints are in women and 114 (joints) in men. All THAs were performed under general anesthesia in supine position.
We reviewed the ratio, onset and frequency of dislocations, build of the patients, preoperative Japanese Orthopaedic Association (JOA) Hip scores, implant setting angles, pelvic tilt angles and diameter of inner heads.
Results
The ratio of dislocation was 14 joints (1.47%). All patients were women and mean age was 67.1 yrs. Anterior dislocation was in 9 joints and posterior was in 5 joints. Primary diagnosis for THA was the following: osteoarthritis in 9 hips and rheumatoid arthritis in 5 (hips). About primary onset, 7 joints were within 3 weeks, 5 joints from 3 weeks to 3 months and 2 joints after 3 months. About frequency, 9 joins were simple and 5 joints were multiple. Revision surgery was done in 2 joints due to ceramic fracture and cup migration.
About build of the patients, mean body height was 153.1cm, mean body weight (was) 55.6 kg and mean BMI (was) 23.6. Mean preoperative JOA score was 40.0 points.
Implant setting angles were the following: mean cup inclination was 42.4 degree, mean cup anteversion (was) 24.8 degree and mean stem anteversion (was) 18.7 degree.
Cup inclination and anteversion in the anterior dislocation group were bigger than that in no dislocation group. Stem anteversion in the posterior dislocation group was smaller than that in no dislocation group.
The difference of pelvic tilt angle between supine and standing position was 6.4 degree. It was significant bigger in the posterior dislocation group.
The most of used Inner head was 28mm in 375 joints. There was no significant difference of the dislocation rate among inner head size.
Discussion and conclusion
DAA-THA can expect the reduction of dislocation rate due to intermusclar approach; however there are some reports of high dislocation rate because of difficult technique.
In our study, dislocation ratio was 1.47%. Risk factors of dislocation after THA was rheumatoid arthritis, large cup inclination and anteversion for anterior dislocation, small stem anteversion and large difference of pelvic tilt angle between supine and standing position for posterior dislocation.
