Pelvic Tilt Angle Differences Between Symptom-Free Young Subjects and Elderly Patients Scheduled for THA: The Rationale for Tilt-Adjusted Acetabular Cup Implantation.

Josef Kozak,Andrzej Kochman,Carlos J Marques,Frank Lampe,Viktor Breul,Adrian Goral,Tobias Martin

doi:10.2174/1874325001812010364

Abstract

Background:The question whether Pelvic Tilt (PT) angles measured in the supine position are adequate for the alignment of the acetabular cup without an adjustment for anatomical differences between patients is of clinical importance. The aim of this work was to test for factors that can significantly affect PT angles.Methods:In the present retrospective cohort comparison, the PT angles of 12 Symptom-Free Young Subjects (SFYS) and 45 patients scheduled for Total Hip Arthroplasty (THA) were compared. The data was collected during two studies with the use of a novel smartphone-based navigated ultrasound measurement system. Multi-factorial analysis of variance was run to determine which factors significantly affect PT.Results:Body position (F= 126.65; P< 0.001) and group (SFYS vs. THA patients) (F= 17.52; P< 0.001) had significant main effects on PT. There was also a significant interaction between body position and group (F= 25.59; P< 0.001). The mean PT increased by 8.1° from an interiorly to a neutral tilted position (P< 0.001) and 21.4° from a neutral to a posteriorly tilted position (P< 0.001) with the transition from the supine into the upright position for the SFYS and THA patients, respectively.Conclusion:In both groups, PT changed significantly with a transition from the supine to the upright position. A position-dependent mean PT increase in the patient group showed that acetabular cup alignment based on PT in the supine position is not reliable without taking into consideration the inclination of the pelvis in standing position. This may lead to instability and dislocations.

Highlights

Hip dislocation is a major cause of complications after Total Hip Arthroplasty (THA), with reported prevalence rates ranging from 0.3 to 3% [1]
In the present retrospective cohort comparison, the pelvic tilt angle (PT) angles of 12 Symptom-Free Young Subjects (SFYS) and 45 patients scheduled for Total Hip Arthroplasty (THA) were compared
A position-dependent mean PT increase in the patient group showed that acetabular cup alignment based on PT in the supine position is not reliable without taking into consideration the inclination of the pelvis in standing position

Summary

Introduction

Hip dislocation is a major cause of complications after Total Hip Arthroplasty (THA), with reported prevalence rates ranging from 0.3 to 3% [1]. Acetabular component alignment is considered to play a determinant role in THA dislocation [3]. According to Lewinnek et al the acetabular component should be placed within a 40° ± 10° inclination and a 15° ± 10° anteversion safety zone, inside which the greatest range of motion of the hip with the minimum dislocation risk should be achieved [4]. The APP has been used as a reference plane for implantation of the acetabular component during non-navigated THA. The angle between the APP and the coronal (frontal) plane is defined as pelvic tilt angle (PT) (Fig. 1a). The question whether Pelvic Tilt (PT) angles measured in the supine position are adequate for the alignment of the acetabular cup without an adjustment for anatomical differences between patients is of clinical importance. The aim of this work was to test for factors that can significantly affect PT angles

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