A novel method of measuring passive quasi‐stiffness in the first metatarsophalangeal joint

Abstract

BackgroundFirst metatarsophalangeal joint (MTPJ) mobility is commonly assessed by its angular displacement (joint angle) or subjectively rated as ‘hypermobile’, ‘normal’ or ‘stiff’ by a clinician. Neither of these methods is ideal because displacement alone does not take into account the force required to displace the joint and subjective evaluation is not always reliable. This study presented a novel method to determine the passive quasi-stiffness of the first MTPJ. The reliability of the proposed method was also assessed. The first MTPJ passive quasi-stiffness of 13 healthy subjects were measured at two occasions, 7 days apart, by two testers (experienced and inexperienced). A tactile pressure sensing system was used to measure the force applied to dorsiflex the first toe by the testers. The torque (in Nmm) about the first MTPJ was calculated as the applied force (in N) multiplied by a moment arm (in mm), where moment arm was the length of the first proximal phalanx. A video camera recorded the motion of the first MTPJ, simultaneously with force measurements, to determine the joint angular displacement (in degrees) using the Dartfish software. The quasi-stiffness (in Nmm/degrees) was calculated as the slope of a graph where torque was plotted against first MTPJ angular displacement. Descriptive statistics of the first MTPJ quasi-stiffness were calculated. Intra-rater and inter-rater reliability were assessed using Bland and Altman plot, intraclass correlation coefficients (ICC), and standard error of measurement (SEM).ResultsFirst MTPJ quasi-stiffness of the subjects ranged widely from 0.66 to 53.4 Nmm/degrees. Intra-rater reliability for experienced tester was moderate (Session 1: 14.9 ± 14.6 Nmm/degrees, Session 2: 14.2 ± 8.5 Nmm/degrees, ICC = .568, SEM = 7.71 Nmm/degrees). Inter-rater reliability between experienced (12.6 ± 8.4 Nmm/degrees) and non-experienced (19.9 ± 9.2 Nmm/degrees) testers was poor (ICC = -.447, SEM = 11.29 Nmm/degrees).ConclusionsFirst MTPJ passive quasi-stiffness can be quantified from torque and angular displacement measurements using simple equipment in a clinical setting. The tester’s experience affected the consistency in joint quasi-stiffness measurements.Electronic supplementary materialThe online version of this article (doi:10.1186/s13047-016-0173-2) contains supplementary material, which is available to authorized users.

Fiber Bragg Grating Sensors for Clinical Measurement of the First Metatarsophalangeal Joint Quasi-Stiffness

“…At each interval, the first toe was kept stationary for several seconds so that stable wavelengths drift of the FBG could be recorded. This method of pausing the first toe at multiple intervals along the working range of motion closely followed that described by Heng et al [9] for stable MTPJ angle measurements via offline video analysis. As the toe moved, MTPJ motion was concurrently recorded by the FBG device and the 3D motion capture system.…”

“…In a laboratory setting, each eligible subject wore a new pair of disposable garment and laid in a supine position on an examination table [9]. The cable embedded with FBG sensors was attached to the testing foot.…”

“…The following calibration procedures were performed on each subject. These procedures were used based on the study by Heng et al [9] in which quasi-stiffness of subjects were measured using a tactile pressure sensing system. A tester applied a dorsiflexion force to flex the first toe at four intervals, gradually increased to maximum degree of dorsiflexion.…”

“…Since these earlier devices are bulky and impractical for clinical practice, Farhadi [8] proposed an enhanced design of a light-weight, portable measuring unit that can be strapped onto the subject's foot to measure MTPJ stiffness. One method that most closely represents the clinical examination practice is the approach by Heng [9] who used video analysis together and a sleeve embedded with pressure sensor on the clinician's thumb. This method does not require any device attached to the subject and allows the quantification of MTPJ quasi-stiffness in a non-weight-bearing position on an examination table as in a regular clinical examination routine.…”

“…Rao [6] calculated the slopes only during the early (first 25%) and late (last 25%) phases but not the middle portion. In contrast, Heng [9] excluded data near the end points and used only the middle 'working range-of-motion' to calculate the slope during the unloading phase. These inconsistencies among studies suggested the MTPJ quasi-stiffness over different ranges of motion may have different clinical implications, since the non-linear and varying stiffness in human joints had been long recognized [10,11].…”