Moment arms of spinal musculature determined from CT scans

Sagittal and coronal moment arm lengths of spinal extensors, flexors, and rotators were measured from the cross-sectional CT scans of 56 patients (35 males and 21 females) with no musculoskeletal disorders at 7th and 12th thoracic vertebral levels and 3rd and 5th lumbar vertebral levels. The sample had a mean age of 58·6 years (s.d. 15·5 years, range 23-90 years), mean body weight 73·15 kg (s.d. 13·9 kg, range 49·5-11·28 kg) and a mean body height of 169·9cm (s.d. 11·9cm, range 130-189cm). Transverso spinalis (TS), erectores spinae (ES), quadratus lumborum (QL), psoas (PS), rectus abdominis (RA), internal obliques (10), and external obliques (EO) were measured at L3 and L5 levels. TS, ES, RA and combined obliques (CO) were measured at the T12 level; however, at T7 level only TS and ES were measured. The extensor moment arm measured (6·0cm) was significantly different from the conventional value (5·0 cm). The moment arms of these muscles on the right and left sides did not differ significantly. The effect of age on the moment arm was significant only with respect to people over 60 years on the coronal plane measurements of the obliques. The gender significantly influenced the moment arms. The height, weight, and height-weight product did not regress significantly on moment arms.