## 8 Discussion
Once the resting distance was measured, a measurement was taken with finger flexion against resistance, recreating a crimp grip as in climbing. However, there were differences in finger positions during measurements. For example, in three studies [21; 27], the authors argued that metacarpophalangeal joint (MCP) flexion should be 0\({}^{\circ}\), proximal interphalangeal (PIP) 40\({}^{\circ}\), and distal interphalangeal (DIP) 10\({}^{\circ}\). Other studies preferred a 30\({}^{\circ}\) flexion for DIP, while some positioned the MCP in maximum extension and the PIP and DIP with a 30\({}^{\circ}\) flexion [26]. Another difference in the evaluation protocol was the force exerted by fingers during active flexion: cadaver studies used variable passive force, while in vivo studies required patients to exert maximum resistance, which could be limited by pain and swelling caused by the injury. The most important value measured in individual studies using ultrasound was the minimum TBD to diagnose finger flexor pulley injury. Considering the TBD values for a healthy non-climbing subject, for A2 pulley in forced active flexion, it is 0.5 mm and at rest, 0.4 mm, while for A4 pulley, it is 1.4 mm in forced active flexion and 1.1 mm at rest [26]. For a complete A2 pulley injury, the TBD value in forced active flexion ranges from 1.9 mm to 5.1 mm, and at rest, it ranges from 1.1 mm to 3.1 mm. For a complete A4 pulley injury, the values in forced active flexion range from 1.8 mm to 3.1 mm; at rest, they range from 1.5 mm to 2 mm. However, it seems that the most accepted criterion as a threshold to diagnose both A2 and A4 pulley injuries is a 2 mm distance from the flexor tendon to the bone [19]. For a partial pulley injury, minimum TBD values start from 1.6 mm [24]. In the A3 pulley, TBD measurements showed low sensitivity (<50-76%) [23]. In diagnosing with only clinical examination, studies are highly heterogeneous. Four studies [11; 18; 28; 29] focused on the clinical bowstringing sign. The bowstringing sign is visible in clinical examination when at least a total A2 pulley injury is present. However, this clinical sign is limited because pain and swelling follow the injury, leading to a false negative [29]. Clear bowstringing is possible after rupturing A2, A3, and A4 pulleys. A sole A2 pulley injury may not be sufficient, and no additional studies for certainty exist. A case report described diagnosing an isolated A2 pulley injury using a silicone ring on the suspected injury region, immediately regaining lost joint range of motion (ROM). However, if used alone, this method does not demonstrate the severity of the injury and may underdiagnose a more severe injury requiring surgical intervention. This silicone ring could also compromise the neurovascular bundle, making this diagnostic method questionable [13]. A review considered a classification scheme for A2 pulley injuries [31]. Unfortunately, this scheme lacks scientific evidence as it relies on empirical concepts but could be a good starting point for a primary study. This classification model could be very useful in clinical examination to identify the right degree of severity and, consequently, the right treatment. An observational study suggests that diagnosing finger pulley injuries is more comprehensive when clinical signs, ultrasounds, and finger grip strength are considered together [30]. Indeed, this study demonstrates that an A2 or A4 pulley injury significantly drops grip strength, specifically when crimping with a single finger. A single finger strength deficit exceeding 41.4% is equivalent to a high-resolution ultrasound measurement of a TBD greater than 2 mm. As mentioned, a TBD greater than 2 mm equals an A2 or A4 pulley injury.