First metatarsophalangeal joint range of motion is associated with lower limb kinematics in individuals with first metatarsophalangeal joint osteoarthritis

Participants for this study were drawn from a larger randomised trial evaluating the effectiveness of shoe-stiffening inserts for 1st MTP joint OA, the details of which have been published previously [9]. The La Trobe University Human Ethics Committee provided ethical approval (number HEC15–128) and all participants provided written informed consent prior to enrolment. Briefly, individuals with 1st MTP joint OA were recruited by advertisements placed in local newspapers, posters placed in senior citizens’ centres and retirement villages, mail-out advertisements to health-care practitioners in Melbourne, mail-outs to people currently accessing podiatry services at the La Trobe University Health Sciences Clinic, and through social networking media (e.g. Facebook, Twitter). Inclusion criteria were: (i) 18 years of age or older, (ii) pain in the 1st MTP joint on most days for at least 12 weeks, (iii) pain rated at least 30 mm on a 100 mm visual analogue scale (VAS), (iv) pain upon palpation of the dorsal aspect of the 1st MTP joint, (v) able to walk household distances (> 50 m) without the aid of a walker, crutches or cane, and (vi) willing to have their foot x-rayed. Exclusion criteria included: (i) previous first MTP joint surgery, (ii) currently pregnant, (iii) significant first MTP joint deformity including hallux valgus, (iv) presence of any systemic inflammatory condition such as gout or rheumatoid arthritis, (v) an inability to speak and read English, and (vi) cognitive impairment.

Participant characteristics (such as age, sex, weight, height, education and income level), major medical conditions and number of medications were obtained via a structured questionnaire. Height and weight were measured using a stadiometer and digital scales, and body mass index (BMI) was calculated as weight (kg) / height (m)². Static foot posture was assessed using the Foot Posture Index [10]. Passive NWB 1st MTP joint maximum dorsiflexion as measured using a reliable goniometric technique [11]. The first metatarsal and proximal phalanx of the hallux were bisected in the sagittal plane. A dorsiflexion force was applied to the hallux until end range of motion was reached, allowing the first ray to maximally plantarflex. The angle between the two lines was then measured via a handheld goniometer (see Fig. 1). The reliability of this test has been shown to be excellent in healthy individuals [12] and individuals with 1st MTP joint OA [11] (intra-class correlation coefficient = 0.95). Clinical features associated with 1st MTP joint OA (pain on palpation, dorsal exostosis, joint effusion, pain on motion, hard-end feel and crepitus) were documented [11]. The presence of radiographic 1st MTP joint OA was determined at baseline using the La Trobe University radiographic atlas [13]. The atlas incorporates weightbearing dorso-plantar and lateral radiographs to document the presence of OA based on observations of osteophytes and joint space narrowing. Osteophytes were recorded as absent (score = 0), small (score = 1), moderate (score = 2) or severe (score = 3). Joint space narrowing was recorded as none (score = 0), definite (score = 1), severe (score = 2) or joint fusion (score = 3). Radiographic OA using this atlas is defined as a score of 2 or more for osteophytes or joint space narrowing on either dorso-plantar and lateral views. The atlas has been shown to have good to excellent intra- and inter-rater reliability for grading 1st MTP joint OA (ĸ range 0.64 to 0.95) [13].

Biomechanical assessment was performed to evaluate sagittal plane kinematics of the 1st MTP, hip, knee and ankle joints. Kinematics were measured using a 10-camera infrared motion analysis system (Vicon Motion Systems Ltd., UK). Dorsiflexion of the hallux during walking was measured by attaching six passive retro-reflective markers to the medial forefoot (3 markers) and proximal phalanx of the hallux (3 markers) as required for calculation of 1st MTP joint kinematics using a modification of the Salford Foot Model [14]. This model has been used to assess 1st MTP joint kinematics with acceptable reliability [14]. In addition, 32 markers were fixed to anatomical landmarks of the trunk, pelvis and lower limb based on the modified Helen Hayes marker set [15, 16], as well as a customised model to allow for segmental definition and functional joint calibration. Marker trajectories were collected at a frequency of 100 Hz, and all lower limb joint kinematics were calculated based on Euler angles and described in terms of movement of the distal segment relative to the proximal segment. Data were collected and averaged from the middle stride of six 10-m walking trials for each condition at self-selected walking speed. Participants were equipped with ‘gait shoes’ with a laced fastening and canvas upper, customised with cut-outs in order to allow clear visualisation of the foot markers (Fig. 2). The minimum and maximum angles throughout the stance phase of gait were extracted from each of the six strides and averaged to represent gait for each individual. The range of motion of each joint was calculated by subtracting the minimum angle from the maximum angle.

Statistical analysis was undertaken using SPSS version 26.0 (IBM Corp, NY, USA). We included one foot only for each participant. The symptomatic side was included (either right or left), and in the case of bilateral symptoms, the most symptomatic foot only was analysed. All data were screened for normality and outliers. Analysis was then undertaken in three stages. Firstly, associations between passive NWB 1st MTP joint maximum dorsiflexion, participant characteristics (age, height, weight, BMI and pain severity), temporo-spatial gait characteristics (velocity, cadence and step length) and the kinematic gait variables were analysed using Pearson’s r correlation coefficients, as these variables were considered to be possible confounders. Secondly, associations between passive NWB 1st MTP joint maximum dorsiflexion and the kinematic gait variables were analysed, and where necessary, adjusted for confounders using partial Pearson’s r correlation coefficients. Statistical significance was set at p < 0.05. Correlation coefficients were interpreted using the following cut-off values: 0 to 0.29 (weak), 0.30 to 0.49 (moderate), 0.50 to 1.00 (large) [17]. Finally, for all significant correlations, r² values were calculated to express the proportion of variance in kinematic variables explained by 1st MTP joint maximum dorsiflexion. Sagittal plane kinematic variables that were included in the analysis were: 1st MTP joint maximum dorsiflexion, ankle joint maximum plantarflexion, ankle joint maximum dorsiflexion, ankle joint excursion, knee joint maximum extension, knee joint maximum flexion, knee joint excursion, hip joint maximum extension, hip joint maximum flexion and hip joint excursion.

One hundred participants (45 men and 55 women, age 24 to 82 years, mean 57.5 [SD 10.3]) were recruited for the randomised trial. Of these, 54 participants were available and consented to biomechanical analysis, and complete data were available for 48 participants (24 males and 24 females). Characteristics of these participants are reported in Table 1.

Sagittal plane kinematics of the 1st MTP, ankle, knee and hip joints in individuals with 1st MTP joint OA are reported in Table 2 and visually presented in Fig. 3. Mean dynamic 1st MTP joint maximum dorsiflexion was 25.4 (SD 6.7) degrees.

There were no significant associations between passive NWB 1st MTP joint maximum dorsiflexion and participant characteristics (age, height, weight, BMI) or temporo-spatial gait characteristics (velocity, cadence and step length), so no adjustment for confounding was required. Associations between passive NWB 1st MTP joint maximum dorsiflexion and sagittal plane kinematics are shown in Table 3. Passive NWB 1st MTP joint maximum dorsiflexion was moderately associated with dynamic 1st MTP joint maximum dorsiflexion (r = 0.486, p < 0.01; r² = 0.236), ankle joint maximum plantarflexion r = 0.383, p < 0.01; r² = 0.147), and ankle joint excursion (r = 0.399, p < 0.01; r² = 0.159). A scatterplot of the association between passive NWB 1st MTP joint maximum dorsiflexion and 1st MTP joint maximum dorsiflexion during stance phase is shown in Fig. 4.