LENGTH AND TORSION OF THE LOWER-LIMB

Corrective osteotomies are often planned and performed on the basis of normal anatomical proportions. We have evaluated the length and torsi on of the segments of the lower limb in normal individuals, to analyse the differences between left and right sides, and to provide toleranc e figures for both length and torsion. We used CT on 355 adult patient s and measured length and torsion by the Ulm method. We excluded all p atients with evidence of trauma, infection, tumour or any congenital d isorder. The mean length of 511 femora was 46.3 +/- 6.4 cm (+/-2SD) an d of 513 tibiae 36.9 +/- 5.6 cm; the mean total length of 378 lower li mbs was 83.2 +/- 11.4 cm with a tibiofemoral ratio of 1 to 1.26 +/- 0. 1. The 99th percentile level for length difference in 178 paired femor a was 1.2 cm, in 171 paired tibiae 1.0 cm and in 60 paired lower limbs 1.4 cm. In 505 femora the mean internal torsion was 24.1 +/- 17.4 deg rees, and in 504 tibiae the mean external torsion was 34.9 +/- 15.9 de grees. For 352 lower limbs the mean external torsion was 9.8 +/- 11.4 degrees. The mean torsion angle of right and left femora in individual s did not differ significantly, but mean tibial torsion showed a signi ficant difference between right (36.46 degrees of external torsion) an d left sides (33.07 degrees of external torsion). For the whole legs t orsion on the left was 7.5 +/- 18.2 degrees and 11.8 +/- 18.8 degrees, respectively (p < 0.001). There was a trend to greater internal torsi on in femora in association with an increased external torsion in tibi ae, but we found no correlation. The 99th percentile value for the dif ference in 172 paired femora was 13 degrees; in 176 pairs of tibiae it was 14.3 degrees and for 60 paired lower limbs 15.6 degrees. These re sults will help to plan corrective osteotomies in the lower limbs, and we have re-evaluated the mathematical limits of differences in length and torsion.