Tibial bowing in children - what is normal? A radiographic study

To define osseous landmarks on tibia radiographs in order to establish age-related normal values characterizing physiological tibial bowing in children.

Five hundred and twenty-six patients aged 0-17 years with normal radiographs of the lower legs were identified and retrospectively reviewed by two blinded radiologists. In anteroposterior (ap)/lateral (lat)-views, 3 lines defined tibial length and angulation. Line-A connecting proximal to distal corner of tibial metaphysic, lines B and C corresponding to corners of tibial metaphysis. Angle A/B defines proximal, A/C distal tibial-angulation. Tibial curvature is defined by distance of line-D parallel to A and tangential to tibial cortex. Normal values were calculated with linear-regression. Intra-/Interreader agreement were tested with a Bland-Altman-plot.

Intrareader-agreement: Reader 1 showed a bias of -0.1, standard-deviation of bias was 1.9 and 95 %-limits-of-agreement -3.9- 3.7. Reader 2: -0.01, 2.4 and -4.7- 4.7. Interreader: 0.2, 1.6 and -2.9- 3.3. Angle-A/B ap was 80-100°, increasing with age (86.5-88); angle-AC ap was 82-107°(96.8-90.5), angle-AB lat was 81-107°(93.0-98.0); angle-AC lat was 76-102 (89.5-86.5); depth of curve ap was 0-11 % (8-3.5) and lat 2-13 %, (8.5-3.5).

Age dependent tibial bowing can be assessed with this new measurement system and age-related normal-values characterizing physiological tibial bowing in children is established.

• Tibial Bowing is diagnosed on conventional radiographs. • Existing Methods provide limited level of confidence. • New methods provide easy to assess landmarks in all patient ages. • Existing methods require higher radiation dose compared to new method presented.