Achilles tendon biomechanics in psoriatic arthritis patients with ultrasound proven enthesitis.

OBJECTIVE: To investigate Achilles tendon (AT) biomechanics in psoriatic arthritis (PsA) patients with ultrasound confirmed features of enthesitis. METHOD: PsA patients and healthy control subjects underwent three-dimensional (3D) gait analysis to measure walking speed, rotational joint motion and the moments, power, and AT force at the ankle-subtalar joint complex. The Glasgow Ultrasound Enthesitis Scoring System (GUESS) was used to score the presence of enthesophytes, erosions, retrocalcaneal bursitis, and tendon thickening. Power Doppler ultrasound signal (PDUS) was used to detect active disease. Peripheral joint arthritis, acute-phase reactants, global health, disability, and foot impairments were recorded. A core set of biomechanical variables that influence the insertion of the AT and indirect estimates of tendon loading were compared between PsA patients and control subjects with and without enthesitis. RESULTS: Forty-two PsA patients with a mean disease duration of 10.6 (SD 9.4) years and 29 control subjects were studied. Seventeen (40%) PsA patients had clinically detectable AT entheseal pain. Twenty-eight (67%) PsA patients and nine (31%) control subjects had one or more GUESS enthesitis features, predominantly enthesophytes. PsA patients with enthesitis walked significantly more slowly than control subjects (p = 0.019) and generated lower peak ankle joint moments (p = 0.006), power (p = 0.001), and AT force (p = 0.003). Ankle-subtalar joint complex motion was comparable and no between-group differences were found for peak dorsiflexion (p = 0.59), eversion (p = 0.05), and internal rotation (p = 0.19). CONCLUSIONS: In this group of PsA patients, the AT insertional angle was not influenced by ankle-subtalar joint motion in those with and without enthesitis. Moreover, the PsA patients with enthesitis had significantly lower AT loading.

A novel device for improving marker placement accuracy.

BACKGROUND: Repeatability of marker placement has been acknowledged as a major factor affecting the reliability of multi-segment foot models. A novel device is proposed that is intended to reduce marker placement error and its effect on the reliability of inter-segmental foot kinematic data is investigated. METHOD: The novel device was tested on eight healthy subjects. Landmarks were identified and indicated on the subject's foot at the start of testing using pen, and these points were used to guide placement. Markers were twice attached by a podiatrist using a standard approach, and twice by a researcher who used the novel device. Replacement accuracy and the kinematic reliability of the foot model data for both techniques were analysed. RESULTS: The mean marker placement variability using the novel device placement device was 1.1mm (SD 0.28) compared to 1.4mm (SD 0.23) when using standard placement techniques. Results suggest that these reductions in placement error tended to improve the overall reliability of the multi-segment data from the foot model. DISCUSSION: The novel device is a simple and inexpensive tool for improving the placement consistency of skin-mounted markers.