Study of Windlass Mechanism in the Lower Limb Using Inertial Sensors.

AIMS: This study aimed to quantify the degrees of movement that occur in the lower limb using a kinematic system after taking two measurements of 45° and 60° of extension at the first metatarsophalangeal joint (1st MTPJ) and to test the validity of this sensor system using radiography. METHODOLOGY: This was a quasi-experimental test-post-test study with a single intervention group (25 subjects). Four inertial sensors were placed on the proximal phalange of the first toe, dorsum of the foot, medial-lateral of the leg (level of tibia), and medial-lateral of the thigh (level of femur). The extension of the 1st MTPJ produced movements of supination in the foot and rotation at the level of leg and thigh. We studied this mechanism in three situations (relaxed, 45°, and 60°) both with the sensors and with X-rays. RESULTS: With the kinematic system, there was an increase in the range of movement in each of the variables, with a value of p < 0.05. The relationship between the kinematic system and the radiography was tested using Spearman's rho test, obtaining a correlation coefficient of 0.624 and a value of p < 0.05, and the Bland-Altman graph, with 90% of the cases within the tolerance limits. CONCLUSIONS: The extension of the 1st MTPJ generated kinematic changes associated with supination movement in the midfoot and external rotation on the tibia and femur level. Both measurement techniques were very similar in the way that they quantified the degrees of extension of the 1st MTPJ. If we extrapolate this result to the measurement technique used by the inertial sensors, we could affirm that the values recorded in the supination and external rotation movements were reliable.

Static Range of Motion of the First Metatarsal in the Sagittal and Frontal Planes.

The first metatarsal and medial cuneiform form an important functional unit in the foot, called "first ray". The first ray normal range of motion (ROM) is difficult to quantify due to the number of joints that are involved. Several methods have previously been proposed. Controversy exists related to normal movement of the first ray frontal plane accompanying that in the sagittal plane. The objective of this study was to investigate the ROM of the first ray in the sagittal and frontal planes in normal feet. Anterior-posterior radiographs were done of the feet of 40 healthy participants with the first ray in a neutral position, maximally dorsiflexed and maximally plantarflexed. They were digitalized and the distance between the tibial malleolus and the intersesamoid crest in the three positions mentioned was measured. The rotation of the first ray in these three positions was measured. A polynomic function that fits a curve describing the movement observed in the first ray was obtained using the least squares method. ROM of the first ray in the sagittal plane was 6.47 (SD 2.59) mm of dorsiflexion and 6.12 (SD 2.55) mm of plantarflexion. ROM in the frontal plane was 2.69 (SD 4.03) degrees of inversion during the dorsiflexion and 2.97 (SD 2.72) degrees during the plantarflexion. A second-degree equation was obtained, which represents the movement of the first ray. Passive dorsiflexion and plantarflexion of the first ray were accompanied by movements in the frontal plane: 0.45 degrees of movement were produced in the frontal plane for each millimeter of displacement in the sagittal plane. These findings might be useful for the future design of instruments for clinically quantifying first ray mobility.