What did the study look at?
In total hip replacement (total hip arthroplasty), the inclination and anteversion angles of the cup placed in the pelvis (acetabular cup) are, as the authors note, linked to range of movement, dislocation risk and implant wear.
Pelvic incidence (PI) is an angle describing the shape of the pelvis seen from the side; it is not affected by posture and equals the sum of the sacral slope (SS) and sagittal pelvic tilt (SPT). The aim was to assess how hip replacement affects these pelvic angles, and how they affect cup position.
How was it done?
- 123 patients who had total hip replacement for one-sided osteoarthritis (coxarthrosis) between March 2011 and March 2015 were screened; those with bilateral disease, surgery on the other hip, previous spinal surgery, fixed hip contracture, or arthritis due to dysplasia or fracture were excluded, leaving 86.
- Prospectively collected data were evaluated retrospectively. All patients were operated on by the same team using a posterolateral approach.
- Cup inclination was measured on a front-to-back pelvic X-ray and anteversion on CT; SS, SPT and PI were compared on standing side X-rays before and after surgery.
- Patients were grouped by preoperative PI as low (<50°), normal (50°–60°) or high (>60°).
What did it find?
- The Harris Hip Score rose from a mean of 45.3 before surgery to 92.2 after. No dislocations occurred. Median follow-up was 32 months.
- SS did not change after surgery (43.7° versus 43.2°); SPT increased slightly but significantly (9.7° to 11.0°), and PI also increased significantly.
- Cup inclination was 40.2°, 41.7° and 44.1° in the PI groups; the difference was not significant (p=0.343).
- Cup anteversion was 9.2° in the low PI group, 19.3° in the normal group and 21.1° in the high group; the difference was significant (p=0.001).
- Low anteversion was seen in 50% of the low PI group, 6.7% of the normal PI group and 16.7% of the high PI group.
- In 32.6% of patients, both inclination and anteversion were within the defined safe limits.
The authors' conclusion
The authors conclude that differing PI values affect cup anteversion in total hip replacement, so preoperative assessment of PI is important in preventing malposition of the cup after surgery.
Limitations
- The study was limited to 86 patients with a mean follow-up of 32 months; more patients and longer follow-up are needed.
- Rotation of the femoral component was not assessed.
- Spinal morphology and disease were not evaluated.
Reference
Sahin A, Simsek ME, Gürsoy S, Akkaya M, Isik C, Bozkurt M. Three-dimensional analysis of acetabular cup orientation and an evaluation of the relationship with pelvic sagittal parameters. Journal of Orthopaedic Surgery (Hong Kong). 2019;27(2):2309499019861225. Published under a Creative Commons Attribution-NonCommercial 4.0 (CC BY-NC 4.0) licence.
Free full text: Journal of Orthopaedic Surgery (SAGE)
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
