Lower limb compensation in adult spinal deformity: can we identify different patterns?

Area of Science:

• Orthopedics
• Biomechanical Engineering
• Radiology

Background:

• Lower limbs play a crucial role in compensating for sagittal malalignment in adult spinal deformity (ASD).
• Understanding the specific patterns and influencing factors of lower limb compensation is essential for managing ASD.
• Existing knowledge on the distinct types of lower limb compensation strategies remains limited.

Purpose of the Study:

• To identify and categorize different patterns of lower limb compensation in adult spinal deformity (ASD) patients.
• To investigate the relationship between various patient parameters and the recruitment of knee flexion versus hip extension for compensation.

Main Methods:

• A multicentric prospective database of adult spinal deformity (ASD) patients with full-body X-rays was utilized.
• K-means cluster analysis was performed on sacro-femoral angle (SFA) and knee flexion angle (KA) to identify compensation patterns.
• Demographics, clinical scores, and radiographic parameters (pelvic incidence-lumbar lordosis mismatch, T1 pelvic angle, osteoarthritis grade) were analyzed across identified clusters.

Main Results:

• Four compensation patterns were identified: 'No compensators', 'Recliners' (hip extension), 'Squatters' (knee flexion), and 'Mixed compensators'.
• 'Squatters' and 'Mixed' groups showed higher BMI, while 'Squatters' had the highest rates of hip and knee osteoarthritis (OA).
• Significant differences in sex distribution, pelvic incidence, PI-LL mismatch, and T1 pelvic angle were observed across the clusters, with 'Squatters' exhibiting poorer clinical outcomes.

Conclusions:

• Four distinct lower limb compensation patterns exist in adult spinal deformity (ASD): 'Recliners', 'Squatters', 'Mixed', and 'No compensators'.
• The recruitment of lower limb compensatory mechanisms is multifactorial.
• Factors influencing compensation include age, sex, BMI, frailty, knee and hip osteoarthritis, pelvic incidence, and spinal alignment.