Cardan angle rotation sequence effects on first-metatarsophalangeal joint kinematics: implications for measuring hallux valgus deformity.
BACKGROUND
There currently are no recommended standards for reporting kinematics of the first-metatarsophalangeal joint. This study compared 2 different rotation sequences of Cardan angles, with implications for understanding the measurement of hallux valgus deformity.


METHODS
Thirty-one women (19 hallux valgus; 12 controls) participated. All were scanned in an open-upright magnetic resonance scanner, their foot posed to simulate the gait conditions of midstance, heel-off, and terminal stance. Using computer processes, selected tarsals were reconstructed into virtual bone models and embedded with principal-axes coordinate systems, from which the rotation matrix between the hallux and first metatarsal was decomposed into Cardan angles. Joint angles were then compared using a within factors (rotation sequence and gait condition) repeated-measures analysis of variance (ANOVA).


RESULTS
Only the transverse plane-first sequence consistently output incremental increases of dorsiflexion and abduction across gait events in both groups. There was an interaction (F ≥ 25.1; p < 0.001). Follow-up comparisons revealed angles were different (p < 0.05) at terminal stance.


CONCLUSIONS
Different rotation sequences yield different results. Extracting the first rotation in the transverse plane allows for the resting alignment of the hallux to deviate from the sagittal plane. Therefore, representing first-metatarsophalangeal joint kinematics with the transverse plane-first rotation sequence may be preferred, especially in cases of hallux valgus deformity.
Program in Physical Therapy, Medical School University of Minnesota, Mayo Mail Code 388, 420 Delaware St SE, Minneapolis, MN 55455, USA.
Ward M
WM
Glasoe
Orthopaedic Surgery, Medical School University of Minnesota, Riverside Campus, 2512 Seventh St. S, Minneapolis, MN 55454, USA.
Fernando A
FA
Pena
Program in Physical Therapy, Medical School University of Minnesota, Mayo Mail Code 388, 420 Delaware St SE, Minneapolis, MN 55455, USA.
Vandana
V
Phadke
Biomechanics measurement; Bunion deformity; Gait simulation