Introduction: First extensor compartment has been always of a great relevance due to its anatomical variations and their consequences in De Quervain disease. These anatomical variations are defined not only by their length and the presence of septa inside but also by its contents. We often require an interposition graft in hand surgery for many clinical procedures as osteoarthritis of the base of the thumb and also for tendon injury reconstructions and chronic ligamentous injuries of the hand. Bravo showed how the accessory abductor pollicis longus (AAPL) proportions are suitable for its use as tendon graft donor in hand surgery. Hypothesis and Objectives: The presence and length of the abductor polllicis longus (APL) muscle belly can be precisely determined by sonography, which could help to its use as an autologous tendon graft in many hand procedures. We proposed to evaluate in this research the anatomical concordance between the sonographic observations and those examined after the dissection. Material and Methods: First of all, a sonographic survey is performed, and then we proceed with an anatomical dissection in 19 upper limb specimens at the human anatomy department of the Medicine Faculty of Murcia. Anatomical variations in the first extensor compartment are analyzed. All variables with categoric information are described by their frequency and percentage. The quantitative variables defined are the mean average, standard deviation, median, interquartile range, and range. Kappa concordance coefficient is calculated to analyze qualitative variables in the relation between the sonography and the dissection. To analyze quantitative variables, an intraclass correlation coefficient (ICC) from a 2-factor mix model is calculated, and so Bland-Altman graphics are constructed. The statistical analysis is performed using the SPSS program, version 19.0. Results: The results obtained comparing sonographic and open dissection showed a moderate concordance for the length of the first extensor compartment; a good concordance in determining the length of the APL, AAPL, and extensor pollicis brevis (EPB) from the insertion to the myotendinous junction; it is possible to calculate the caliber of the APL and AAPL tendons distal to the first extensor compartment, with a moderate concordance. We observed a good concordance identifying the number of tendons within the first extensor compartment (kappa index, 0.746) and very good concordance identifying the septa in its interior. However, we observed a poor concordance identifying their distal insertions. APL and AAPL intramuscular length were evaluated showing a median of 54 mm, with a range between 43 and 95 mm for the first one, and 30 to 95 mm for the second one. Conclusions: A 12-MHz lineal-probe sonography allows, with a high reliability, identifying the anatomical variations within the first extensor compartment of the wrist and also studying and identifying tendinous width and myotendinous length of APL, AAPL tendons. However, it is not feasible, a good visualization of the distal tendinous insertion of the AAPL tendons. We also prove that APL and AAPL muscles show an intramuscular tendon portion very useful for many surgical procedures in hand surgery, to achieve longer tendon grafts compared with those available to date.
