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PATTERNS OF EXTRA-SPINAL LEFT-RIGHT SKELETAL ASYMMETRIES IN ADOLESCENT GIRLS WITH LOWER SPINE SCOLIOSIS: III. ILIO-FEMORAL LENGTH ASYMMETRY ASSOCIATED WITH SACRAL ALAR HEIGHT ASYMMETRY AND UNRELATED TO LOWER SPINAL SCOLIOSIS

¹ The Centre for Spinal Studies and Surgery, Queen’s Medical Centre, Nottingham, UK , ² Department of Orthopaedic Surgery, King’s Mill Hospital, Mansfield, UK (Supported by AO).

In schoolchildren screened for scoliosis about 40% have minor, non-progressive, lumbar scolioses secondary to pelvic tilt with leg-length and/or sacral inequality [1] not reported with preoperative thoracic curves [2]. Forty-nine of 108 consecutive adolescent patients referred from routine scoliosis school screening during 1996–1999 had lower spinal scoliosis with measurable radiological sacral alar and hip tilt angles – lumbar scoliosis 18, thoracolumbar scoliosis 31 (girls 41, boys 8, mean Cobb angle 16 degrees, range 4–38 degrees). In standing full spine antero-posterior radiographs measurements were made of Cobb angle and pelvic asymmetries as sacral alar and iliac heights (left minus right). From anthropometric measurements derivatives were calculated as ilio-femoral length (total leg length minus tibial length) and several length asymmetries, namely: ilio-femoral length asymmetry, total leg length inequality and tibial length asymmetry (all left minus right). Ilio-femoral length asymmetry correlates significantly with sacral alar height asymmetry (girls negatively r= – 0.456, p=0.002, boys positively r=0.726 p=0.041) but not iliac height asymmetry (girls p=0.201) from which three types are identified. Total leg length inequality but not tibial length asymmetry in the girls is associated with sacral alar height asymmetry (r= – 0.367 p=0.017 & r=0.039 p=0.807 respectively). Interpretation is complicated by total leg lengths each including some ilium in which there is asymmetry [3]. But lack of association between ilio-femoral length asymmetry and iliac height asymmetry suggests that the femoral component is more important than iliac component in determining the associations between sacral alar height asymmetry and each of ilio-femoral length asymmetry and total leg length inequality.

Conclusions:

1. Sacral alar height asymmetry and leg length asymmetries. The evidence suggests that sacral alar height asymmetry is not secondary to the leg length inequalities at least in most girls (negative correlations) and is more likely to result from primary skeletal changes in femur(s) and sacrum.
   
2. Sacral alar height asymmetry and Cobb angle. Scoliosis progression and iliac height asymmetry [3] appear to need factors additional to those that determine ilio-femoral length asymmetry – for in the girls Cobb angle is associated with both sacral alar height asymmetry and iliac height asymmetry (each p<0.001) but not with either ilio-femoral length asymmetry (p=0.249) or total leg length inequality (p=0.650). The additional factors may be biomechanical [4], and/or biological in the trunk [5] and central nervous system [6].
   

Correspondence should be addressed to Jeremy C T Fairbank at The Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX7 7LD, UK