Impact of Hip Damage on Lower Limb Compensation in AS Patients Pre- and Post-PSO

Overview

This study evaluated how hip structural damage affects pelvic and lower limb compensatory mechanisms in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis undergoing pedicle subtraction osteotomy (PSO). Findings indicate that severe hip involvement limits pelvic retroversion and alters lower limb compensation both before and after surgery.

Background

Ankylosing spondylitis is a chronic autoimmune disease causing progressive spinal and sacroiliac joint ossification, often resulting in thoracolumbar kyphosis and impaired quality of life. Pedicle subtraction osteotomy is a surgical technique used to restore sagittal spinal alignment in these patients. Compensatory mechanisms involving the pelvis and lower limbs play a critical role in maintaining sagittal balance, but hip structural damage, common in AS, may restrict these compensations and complicate surgical planning.

Data Highlights

Key Findings

• Approximately 30% to 50% of AS patients have hip structural damage, with nearly 90% showing bilateral involvement.
• Severe hip involvement (BASRI-hip grades 3–4) is associated with restricted pelvic retroversion and altered compensatory mechanisms in the lower limbs.
• Preoperative sagittal parameters including pelvic tilt and lower extremity angles differ significantly between mild and severe hip involvement groups.
• Postoperative improvements in spinal alignment via PSO are influenced by the degree of hip structural damage, affecting the extent of lower limb compensation.
• The sacrofemoral angle (SFA) and femoral obliquity angle (FOA) are useful parameters to assess lower limb compensations in AS patients.

Clinical Implications

Clinicians should carefully evaluate hip structural damage in AS patients when planning PSO surgery, as severe hip involvement may limit pelvic and lower limb compensatory capacity. Incorporating lower extremity sagittal parameters into preoperative assessment can improve surgical planning and postoperative outcomes. Awareness of these compensatory limitations is essential to optimize correction strategies and patient rehabilitation.

Conclusion

Hip structural damage significantly impacts pelvic and lower limb compensatory mechanisms in AS patients with thoracolumbar kyphosis undergoing PSO. Comprehensive assessment of hip involvement and lower extremity parameters is crucial for accurate surgical planning and improved postoperative sagittal balance.

References

1. Modified New York criteria for AS diagnosis
2. Bath Ankylosing Spondylitis Radiology Hip Index (BASRI-h) grading
3. Previous studies on sagittal parameters and compensatory mechanisms [10]