The posterior skeletal thorax: rib-vertebral angle and axial vertebral rotation asymmetries in adolescent idiopathic scoliosis.

Abstract

The deformity of the ribcage in thoracic adolescent idiopathic scoliosis (AIS) is viewed by most as being secondary to the spinal deformity, though a few consider it primary or involved in curve aggravation. Those who consider it primary ascribe pathogenetic significance to rib-vertebra angle asymmetry. In thoracic AIS, supra-apical rib-vertebra angle differences (RVADs) are reported to be associated with the severity of the Cobb angle. In this paper we attempt to evaluate rib and spinal pathomechanisms in thoracic and thnoracolumbar AIS using spinal radiographs and real-time ultrasound. On the radiographs by costo-vertebral angle asymmetries (rib-vertebral angle differences RVADs, and rib-spinal angle differences RSADs), apical vertebral rotation (AV) and apical vertebral translation (AVT) were measured; and by ultrasound, spine-rib rotation differences (SRRDs) were estimated. RVADs are largest at two and three vertebral levels above the apex where they correlate significantly and positively with Cobb angle and AVT but not AVR. In right thoracic AIS, the cause(s) of the RVA asymmetries is unknown: it may result from trunk muscle imbalance, or from ribs adjusting passively within the constraint of the fourth column of the spine to increasing spinal curvature from whatever cause. Several possible mechanisms may drive axial vertebral rotation including, biplanar spinal asymmetry, relative anterior spinal overgrowth, dorsal shear forces in the presence of normal vertebral axial rotation, asymmetry of rib linear growth, trunk muscle imbalance causing rib-vertebra angle asymmetry weakening the spinal rotation-defending system of bipedal gait, and CNS mechanisms.

The English stop voicing contrast is examined in both word-initial position (via VOT) and word-final position (via the duration of the preceding vowel) in young adult speakers born and brought up in the Shetland Isles. The subjects'parents were either also from Shetland, from elsewhere in Scotland, orEngland. All have identical phonemic stop systems, unambiguously so ininitial position. The quasi-phonemic role in Scottish English of vowelduration in signalling the suffixual vs. tautomorphemic word final /d/ insteadof the /t/-/d/ contrast (the Scottish Vowel Length Rule) renders final positionmore complex. There are fine-grained interspeaker differences covering awide area of the phonetic space, exemplifying the potential forphonologically-relevant variation. The targets may be speaker-specificresponses to input, especially mismatches between the dialect of their parentsand the wider community.