br Acknowledgments We acknowledge the Natural Sciences and

Acknowledgments
We acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for Grants 034685 and 034813 (UBC), which supported this project. We also thank the Centre for Hip Health and Mobility for providing the lab facilities and the Institute for Computing, Information and Cognitive Systems for program support.

Introduction
The flexor tendon pulley system of the finger functions to maintain the flexor Atractyloside Dipotassium Salt of the fingers close to the phalanges, enabling full range of motion in finger flexing movements (Amis and Jones 1988; Roloff et al. 2006). These structures are subjected to extreme forces in sports such as rock climbing (Bollen 1988), and their rupture is a frequent consequence. Accurate diagnosis of pulley injuries depends on the use of crucial imaging techniques, but these are often accompanied by challenges.
The most widely employed technique for visualizing the finger flexor pulley system is ultrasound, as it enables the physician to examine these structures in real time and in a dynamic fashion (Hauger et al. 2000). For a better understanding of how the pulleys are visualized using ultrasound, Figure 1 compares the anatomic structures to their respective ultrasound images. Pulleys have traditionally been difficult to visualize directly using ultrasound, causing dependence on indirect symptoms such as the distance between flexor tendons and phalanx in a flexed finger position for pulley rupture diagnosis. However, with newer ultrasound equipment offering better visualization using higher frequency probes, direct visualization of the pulleys has achieved greater significance as a diagnostic (Klauser et al. 2002). For instance, Kovacs and Bodner (2002) were able to visualize all of the annular pulleys, including A3 and A5, as well as the cruciate pulleys. Boutry et al. (2005) were able to consistently visualize the A2 and A4 pulleys, the A3 pulley in 65% of cases and the C3 pulley in 45% of cases using a 17 MHz probe, concluding that a minimum frequency of 17 MHz is necessary for the visualization of the A3 pulley. Direct visualization of the A2 and A4 pulleys has subsequently reached a high diagnostic value. However, direct visualization of the A3 pulley remains accompanied by challenges and is limited to 17 MHz probes—instruments not typically available to normal clinicians, which restricts their use in clinical studies.
As the direct visualization of the A3 pulley remains difficult and with 65% rather random, ultrasound cannot be relied on as a secure method of diagnosing ruptures of the A3 pulley or those in which the A3 pulley is a component. In a magnetic resonance imaging cadaver study using the same specimens as used in this study, Bayer et al. (2015) were able to use a new, indirect approach for diagnosing A3 pulley ruptures. They included measurements involving the volar plate (VP), and were able to show that diminished translation distances of the VP relative to the middle phalanx base, as well as augmented VP tendon distances in the crimp grip position, were suitable indirect indicators for A3 pulley rupture. So far, this approach has not been applied to ultrasound imaging.
This study thus focused on the visualization of each pulley and its location with regards to the proximal interphalangeal (PIP) joint, crucial when considering a repair (Roloff et al. Atractyloside Dipotassium Salt 2006), as well as on determining the accuracy of the ultrasound technique in determining correct pulley rupture—particularly of the A3 pulley. In order to achieve this, particular attention was paid to the visualization of the VP to determine whether the indirect approach from the magnetic resonance image could be applied to the ultrasound technique. For improved visualization, a picture enhancing technique (speckle reduction) was employed, leading to a high resolution of small structures (Wunsch et al. 2007).

Materials and Methods
All measurements were completed using a GE Logic 9 (GE Healthcare, Buckinghamshire, United Kingdom) with a linear M12 L Matrix probe, an aperture of 3.9 cm and a frequency of 14 MHz. The cross beam settings were set to “low,” and the speckle reduction was left at “2” to maintain comparability with an in vivo environment. A 14-MHz probe, readily available to every clinician, was used to ensure the relevance of these research results to the improvement of diagnostic tools in clinical settings.