Total Hip Instability and the Spinopelvic Link.

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Spine Surgery

Background:

• Total hip arthroplasty (THA) has seen reduced dislocation rates due to technological and surgical advancements.
• Instability in THA without clear causes may be linked to spinopelvic interrelationships.

Purpose of the Study:

• To review the biomechanics, diagnosis, classification, management, and outcomes of hip instability related to spinopelvic alignment.
• To explore the role of spinopelvic alignment in prosthetic dislocations without known etiologies.

Main Methods:

• Review of current literature on spinopelvic alignment and its effect on THA.
• Analysis of biomechanical changes during standing and sitting, focusing on pelvic tilt and acetabular anteversion.
• Classification of spinopelvic mechanics based on sacral motion from lateral radiographs.

Main Results:

• Decreased lumbar lordosis and posterior pelvic tilt during sitting increase acetabular anteversion.
• Spinal fusion can lead to abnormal hip motion, impingement, and dislocation.
• Classifying spinopelvic mechanics aids in optimizing acetabular cup positioning to prevent dislocation.

Conclusions:

• Understanding spinopelvic mechanics is crucial for managing THA instability.
• Surgical considerations include acetabular positioning, high-offset implants, dual mobility, and removal of impinging structures.
• Further research is needed on concomitant hip and spine pathology management and long-term dislocation rates.