An analysis of Extensor Pollicis Brevis tendon excursion in different wrist positions in normal healthy subjects
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Extensor Pollicis Brevis (EPB) is a tendon of the first dorsal wrist compartment and in vitro cadaver studies have shown that it moves approximately 14-15mm over the wrist when the thumb is moved through a full range of extension to flexion. Additionally, it has been shown in vitro that wrist position has an effect on EPB excursion. To date there are no in vivo studies that have examined the excursion of this tendon, or the effect of wrist position. Greater knowledge of excursion of EPB at wrist level could provide valuable baseline information that may be utilised in further studies in relation to pathomechanics, causative factors, assessment and management of forearm conditions, for example deQuervains disorder. Additionally, in vivo excursion values may also have relevance for post-operative tendon rehabilitation, as well as tendon transfer and reconstructive surgery. Information gained may assist in further research involving similar methodology. The objectives of this study were to quantify in vivo excursion of EPB at the wrist in different wrist positions and to evaluate the reliability of the methods used. Ultrasound Imaging (USI) and a cross-correlation algorithm were utilised to assess 49 normal EPB tendons (25 subjects, mean age=40.7±12.8yrs), through full thumb extension to full flexion, in three different wrist positions (45° extension, neutral, 45° flexion). Subjects attended on two different occasions. Within-session and between-session intra-rater reliability was analysed for all data, as well as for each of the selected wrist positions. Results showed that wrist position had a significant effect on EPB tendon excursion (p≤0.05). EPB excursion in the neutral wrist position was statistically greater from the other two positions (p<0.05). Mean excursions for each position were: Neutral=2.78mm±1.89, Extension=1.67mm±1.15mm, Flexion=1.62±1.4mm. Intraclass Correlation Coefficients (ICC) for all data within-session 1 and within-session 2 were high [ICC=0.88, 95% Confidence Interval (CI) 0.84-0.91 and ICC=0.87, 95% CI 0.92-0.90 respectively]. The neutral wrist position demonstrated excellent reliability for within-session 1 and within-session 2 [ICC=0.93, 95% CI 0.88-0.96 and ICC=0.91, 95% CI 0.84-0.95]. Between-session analyses was found to be acceptable for all data [ICC=0.76, 95% CI 0.66-0.83] and high for the neutral wrist position [ICC=0.80, 95% CI 0.64-0.89]. In conclusion, in vivo EPB tendon excursion measures have, for the first time, been quantified and significant effects of wrist position on EPB tendon excursion have been found. These measures have been found to be significantly less than those found in in vitro studies. Reliability analyses demonstrated high to excellent ICC values for both within-session and between-session data. USI and a cross-correlation algorithm are therefore considered to be reliable methods for measuring tendon excursion. Further studies evaluating and comparing EPB tendon excursion in a pathologically affected population are recommended. The methodology could also be utilised in evaluating longitudinal excursion of other tendons.