The Effect of Foot Orthoses on Transverse Tibial Rotation During Walking.

McPoil TG, Cornwall MW (Gait Research Laboratory, Department of Physical Therapy, Northern Arizona University, Flagstaff, Ariz), J Am Podiatr Med Assoc. 2000;10:2-11.

The study's purpose was to evaluate the effect on transverse plane tibial rotation of 2 types of foot orthoses: a rigid plastic orthosis with either forefoot or rear-foot posting and a soft, pre-molded, accommodative orthosis with no posting. The study also compared the effects on tibial rotation of walking barefoot and of walking in shoes without foot orthoses.

The authors used a technique that they developed previously to measure tibial rotation during gait. They advocated the use of this technique because tibial rotation is easier to measure in people while they wear shoes than rear-foot motion. The authors measured both the maximum internal rotation of the tibia and the tibia's maximum acceleration in the direction of internal rotation. They chose these dependent variables because they correlate well with rear-foot and subtalar motion and because foot orthoses are intended to influence subtalar pronation. The authors observed that the magnitude of pronation may be related to stresses on soft and bony tissues and that the rate of pronatory acceleration may be related to stresses on contractile tissues.

After screening 110 candidates to find people without histories of congenital or traumatic limb deformity or asymmetry, the authors chose 10 subjects who had rear-foot or forefoot deformities that might require compensatory pronation during stance, but whose talocrural range of motion and range of motion of the first metatarsophalangeal joint was normal.

Using a motion analysis system that included 2 cameras and a transducer platform, the authors recorded tibial rotation as subjects walked. The platform allowed recording of stance phase pressures so that the investigators could monitor stance duration. According to the authors, stance duration reflects a subject's gait velocity, a variable they controlled so that differences in gait velocity would not confound the observed differences in tibial rotation.

The authors tested subjects under 4 conditions: walking barefoot, wearing shoes without foot orthoses, and wearing either of 2 types of orthoses. They randomized the order of testing under the 4 conditions and compared the conditions using a one-way repeated measures ANOVA. This design permitted subjects to serve as their own controls, and it removed from the analysis the sizeable intersubject variability that many authors have noted in subtalar movement. Tukey post hoc comparisons were used to evaluate differences in tibial rotation that were detected by the ANOVA.

Maximum tibial internal rotation did not differ when subjects walked barefoot (10.7 [degrees] [+ or -] 3.6 [degrees]) or wore shoes without foot orthoses (11.7 [degrees] [+ or -] 4.9 [degrees]). Subjects displayed significantly less tibial internal rotation when they walked while wearing orthoses, but similar reductions in tibial movement occurred whether subjects wore soft (8.4 [degrees] [+ or -] 3.9 [degrees]) or rigid (8.8 [degrees] [+ or -] 4.0 [degrees]) orthoses.

Maximum acceleration in tibial internal rotation was greatest when subjects walked barefoot: (3,502 [+ or -] 2,023 [degrees]/[sec.sup.2]), significantly lower when they wore shoes (2,976 [+ or -] 1,420 [degrees]/[sec.sup.2]), and even lower when they wore foot orthoses. Maximum acceleration did not differ whether subjects wore soft (2,228 [+ or -] 1,363 [degrees]/[sec.sup.2]) or rigid (2,479 [+ or -] 1,497 [degrees]/[sec.sup.2]) orthoses.

The authors related the study's results to 2 outstanding questions in the area of orthopedic practice. First, the authors believed that the results indicated that soft, accommodative orthoses controlled pronation as effectively as more rigid ones. Moreover, they suggested that orthoses that provided total contact were as effective as ones that incorporated posts or wedges.

David M Thompson, PT University of Oklahoma Health Sciences Center Oklahoma City, Okla