Acetabular cup position and risk of dislocation in primary total hip arthroplasty

Abstract

Background and purpose — Hip dislocation is one of the most common complications following total hip arthroplasty (THA). Several factors that affect dislocation have been identified, including acetabular cup positioning. Optimal values for cup inclination and anteversion are debatable. We performed a systematic review to describe the different methods for measuring cup placement, target zones for cup positioning, and the association between cup positioning and dislocation following primary THA.Methods — A systematic search of literature in the PubMed database was performed (January and February 2016) to identify articles that compared acetabular cup positioning and the risk of dislocation. Surgical approach and methods for measurement of cup angles were also considered.Results— 28 articles were determined to be relevant to our research question. Some articles demonstrated that cup positioning influenced postoperative dislocation whereas others did not. The majority of articles could not identify a statistically significant difference between dislocating and non-dislocating THA with regard to mean angles of cup anteversion and inclination. Most of the articles that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rate. Alternative target ranges have been proposed by several authors.Interpretation— The Lewinnek safe zone could not be justified. It is difficult to draw broad conclusions regarding a definitive target zone for cup positioning in THA, due to variability between studies and the likely multifactorial nature of THA dislocation. Future studies comparing cup positioning and dislocation rate should investigate surgical approach separately. Standardized tools for measurement of cup positioning should be implemented to allow comparison between studies.

The Effects of Body Position on Pelvic Tilt Angles Measured with a Smartphone-Based Navigated Ultrasound System in Symptom-Free Young Adults

“…In a systematic review, most of the included studies could not identify significant differences between dislocating and non-dislocating THA with regard to the mean cup anteversion and inclination angles. Furthermore, the studies that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rates [13].…”

“…According to their investigations, an inclination of 40 • ± 10 • and anteversion of 15 • ± 10 • should enable the greatest possible range of motion of the hip with the minimum dislocation risk. However, the validity of Lewinnek safe zones has been challenged by recent studies [12,13]. In a systematic review, most of the included studies could not identify significant differences between dislocating and non-dislocating THA with regard to the mean cup anteversion and inclination angles.…”

Accuracy and Precision of an Ultrasound‐Based Device to Measure the Pelvic Tilt in Several Positions

“…[1][2][3][4][5] Dislocation is the second most common cause of complications. [4][5][6][7] Many factors can have an influence on postoperative dislocations 8 ; one of these is the orientation of the cup: ie, the orientation of the acetabular prosthetic component. It has been considered for several decades that the cup should be oriented within a safe zone defined as 15 AE 10 of anteversion and 40 AE 10 of inclination according to the anterior pelvic plane (APP).…”

Intra‐ and Inter‐rater Reliability of Navigated Ultrasound in the Assessment of Pelvic Tilt in Symptom‐Free Young Adults

“…According to their investigations based on anteroposterior radiographs, an inclination of 40° ± 10° and an anteversion of 15° ± 10° should enable the greatest possible range of motion of the hip joint with the minimum dislocation risk. Recent studies have challenged the validity of Lewinnek safe zones . In a systematic review on the association between cup positioning and dislocation after primary THA, 28 studies were included.…”

“…Most of the studies could not identify significant differences between dislocating and nondislocating THA with regard to mean angles of cup anteversion and inclination. Furthermore, the studies that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in the dislocation rate . Hence, the optimum acetabular component position is still a controversial issue needing further investigation.…”