Abstract
Introduction
Total hip arthroplasty (THA) dislocation has been associated with different risk factors. The main difficulty in analysing dislocation is its low rate of incidence, necessitating large series for study.
We assessed factors related with patients, implant characteristics, and quality of the hip reconstruction to better identify their influence on the THA dislocation rate.
Material and Methods
Dislocations in 2,732 THAs performed between 2001 and 2016 were assessed with regard to factors related with the patient (gender, age, preoperative diagnosis, lumbar pathology); the implant (femoral head size, bearing surface, stem offset, femoral head/neck ratio); and the surgical technique (approach, cup and stem position, and abductor mechanism reconstruction). Regression analysis was used for different risk factors and Kaplan-Meier for survival analysis.
Results
After ERAS implementation, opioid consumption decreased for hospital day one (49.5MME to 35.4MME; p=0.000) and overall hospitalization (79.5MME to 59.5MME; p=0.000). Average LOS decreased (57.84hrs to 51.87hrs; p=0.011), blood transfusion rate was unchanged (4.25% to 3.81%; p=0.725), and disposition to home over skilled nursing facility increased (80.4% to 82.5%; p= 0.022). Unplanned return-to-hospital encounters were unchanged (8.51% to 8.88%; p=0.8486). Readmission trended up during postoperative days 0–30 and trended down during postoperative days 31–90. (1.42% to 2.96%; p=0.1074) and (1.21% to 0.85%; p=0.5748), respectively.
There were 92 dislocations (3.4%), of these, 62 were treated conservatively (2.3%) and 30 surgically (1.1%). Survivorship analysis for dislocation was 96.0% (95% CI:95.0–97.0) at 17 years. Among patient-related factors, greater age (p=0.001), lower activity level (p=0.001) and lumbar fusion (p<0.001) were associated with a higher dislocation rate. Among implant-related factors, a ceramic-on-ceramic THA (p<0.001) and a femoral size of 32 or 36 mm in diameter had lower dislocation rates. With regards to surgical technique, a greater acetabular abduction angle (p=0.001) and a greater distance to the hip anatomic center (p=0.006) had higher dislocation rates. A cup position outside Lewinnek´s safe zone (p<0.001) and the abductor mechanism window (p<0.001) also had a higher dislocation rate. Multivariate analysis revealed that only significant lumbar pathology (p=0.001) and lumbar fusion (p<0.001) were significant dislocation-related factors among patient-related factors. Poor reconstruction of the hip rotation (p=0.035), a cup position outside of Lewinnek's safe zone (p<0.001) and the abductor mechanism window (p<0.001) were significantly associated with a higher dislocation risk among surgical technique-associated factors.
Conclusions
Significant lumbar spine pathology increases the rate of dislocation. A proper reconstruction of the hip, including appropriate cup position and rotation centre reconstruction of the hip are essential to decrease the risk of dislocation after primary THA. The weakness of the abductor muscles is also an important cause for dislocation.
