Spino Pelvic Mobility in THA

Courtesy: Dr Anil Oommen, Dr Ashok Shyam, Ortho TV

Overview

• Spinopelvic mobility has gained increasing attention in recent years in the field of total hip arthroplasty.
• Many cases of postoperative dislocation are now understood to be related to overlooked factors involving the interaction between the spine and the pelvis.
• Understanding this relationship is important for proper acetabular cup positioning and for reducing complications after surgery.

Relationship Between Spine and Pelvis

• Movement of the spine and pelvis is interconnected during posture changes.
• When a person moves from sitting to standing, both the spine and pelvis adjust simultaneously.
• In a normal standing posture, the pelvis usually tilts anteriorly.
• In a sitting posture, the pelvis typically tilts posteriorly.
• The degree of change between sitting and standing varies between individuals and is considered patient-specific.
• These changes are reflected in the presence or absence of lumbar lordosis on radiographic images.
• The functional orientation of the pelvis differs from one person to another due to differences in pelvic tilt.

Clinical Importance

• Certain patients are more prone to problems related to spinopelvic mobility.
• Individuals with ankylosing spondylitis often have a fused spine and reduced pelvic motion.
• In such cases, improper acetabular cup orientation can lead to instability or dislocation after total hip arthroplasty.
• Careful evaluation of spinal stiffness and spinopelvic mobility is therefore essential before surgery.

Radiographic Assessment

• Preoperative evaluation should include lateral radiographs of the spine and pelvis in both sitting and standing positions.
• These images help determine the degree of pelvic tilt change during posture transition.
• Several spinopelvic parameters can be assessed, including:
  • Lumbar lordosis
  • Pelvic tilt
  • Sacral slope
  • Pelvic inclination
• Among these, sacral slope is commonly used as a simple and reliable indicator.

Sacral Slope and Normal Motion

• In normal individuals, the sacral slope changes approximately ten to thirty degrees when moving from sitting to standing.
• This change reflects normal spinopelvic mobility.
• Limited variation indicates reduced mobility or spinal stiffness.

Influence on Acetabular Cup Orientation

• Pelvic tilt significantly affects the functional orientation of the acetabular cup.
• A change in pelvic tilt alters both cup inclination and anteversion.
• Approximately every ten degree change in pelvic tilt results in:
  • About seven degree change in anteversion
  • About three degree change in inclination
• In the sitting position, the pelvis rotates posteriorly, increasing functional anteversion.
• In the standing position, the pelvis rotates anteriorly, producing relative retroversion.

Risk of Impingement and Dislocation

• Incorrect cup orientation combined with abnormal spinopelvic motion can lead to:
  • Anterior or posterior impingement
  • Eccentric wear of the prosthesis
  • Hip dislocation
• Adjustments in cup placement may be required based on individual spinopelvic mechanics.

Patterns of Spinopelvic Mobility

Stuck Sitting Pattern

• Sacral slope remains less than approximately thirty degrees in both sitting and standing positions.
• Associated with reduced lumbar lordosis.
• Common in patients with ankylosing spondylitis.
• The pelvis remains relatively posteriorly tilted with minimal movement.

Stuck Standing Pattern

• Sacral slope remains greater than approximately thirty degrees with little change between positions.
• Persistent lumbar lordosis is present.
• Often seen in patients with degenerative spine disease or spinal instrumentation.

Clinical Implications of Mobility Patterns

Stuck Standing Pattern

• Limited spinal flexion may lead to anterior impingement.
• Increased risk of posterior hip dislocation.
• Slightly increased acetabular anteversion may help reduce this risk.

Stuck Sitting Pattern

• Limited spinal extension causes posterior impingement.
• Increased risk of anterior dislocation.
• Reduced acetabular anteversion may be recommended.

Special Considerations in Ankylosing Spondylitis

• The spine and pelvis may function as a rigid unit with minimal mobility.
• Spinopelvic parameters often remain unchanged even after hip replacement.
• Many patients demonstrate a persistent stuck sitting pattern.
• Careful adjustment of acetabular anteversion is important to prevent instability.

Implant Strategy

• Dual mobility implants are often recommended in patients with abnormal spinopelvic mechanics.
• These implants can reduce the risk of postoperative dislocation in high-risk cases.

Practical Surgical Considerations

• Spinopelvic mobility should be assessed before performing total hip arthroplasty.
• Preoperative standing and sitting lateral radiographs of the spine and pelvis are essential.
• Acetabular cup positioning should be adjusted according to individual spinopelvic characteristics.
• When advanced technology is unavailable, careful use of anatomical landmarks and surgical technique remains important.

Key Takeaways

• Spinopelvic mobility plays a critical role in the stability of total hip arthroplasty.
• Patient-specific evaluation helps guide appropriate acetabular cup positioning.
• Recognition of abnormal mobility patterns can help prevent impingement and dislocation.
• Thorough preoperative assessment and thoughtful implant strategy improve surgical outcomes.