# A Cadaveric Study of Ulnar Nerve Movement and Strain around the Elbow Joint
## 4 Discussion
The ulnar nerve may be strongly anchored to the forearm flexors by multiple branches. We assumed that these branches fixed the ulnar nerve distal to the medial epicondyle and suppressed the movement and strain of the nerve with elbow flexion. [PERSON] et al. also reported little or no nerve sliding in the upper arm. In this study, nerve movement was small both at 8 cm proximal to the medial epicondyle and in the forearm. [PERSON] et al. attributed this phenomenon to the non-straight, snaking segment of the nerve that reduces the load on the nerve caused by the flexion movement of the elbow, which was referred to as the 'high compliance segment' [19]. Straightening the high compliance segment near the elbow reduces the effect of elbow flexion. Consequently, the effect on the segment away from the elbow may be reduced, as would the amount of movement away from the elbow. The findings of this study indicate that ulnar neuropathy due to over-traction of the valgus elbow may occur on the proximal side of the elbow. When a nerve is inflamed, even a 3% increase in nerve strain can produce ectopic impulses, which can cause pain and paresthesia [22]. Our findings suggest that the inching electrodiagnosis method [23] may be useful for early neuropathy due to over-traction. This study was performed at 60\({}^{\circ}\) of shoulder abduction, and the upper limb position at maximum elbow flexion was similar to the upper limb position of the motion of eating with a spoon (70\({}^{\circ}\) of shoulder abduction and 130\({}^{\circ}\) of elbow flexion), which is a daily activity with maximum ulnar nerve strain, as reported by [PERSON] et al. [13]. They reported that this motion caused 7% to 19% strain when the gliding of the ulnar nerve was restricted. In this study, we observed 18% ulnar nerve strain even in the presence of ulnar nerve gliding, which is close to the value they reported with restricted nerve gliding. They excised the fascia at the measurement site, whereas in our study, a small window was created only at the insertion site of the sensor needle to preserve the fascia, and the tension of the fascia associated with joint movement may have affected the increase in ulnar nerve strain. [PERSON] et al. reported that a 12% strain on the nerve lasting for 1 h caused nerve conduction disturbance with only a minimal recovery [3], and prolonged continuation of a limb position that increases the strain on the ulnar nerve even in daily activities may cause nerve damage. In addition, restriction of ulnar nerve gliding increases nerve strain by 50 to 154% compared to the condition with nerve gliding [12; 18]. Therefore, ulnar nerve adhesions near the elbow due to trauma or surgical manipulation are more likely to cause nerve over-traction than those at sites far from the elbow. In our study, the ulnar nerve exhibited considerable movement at 2-4 cm proximal to the medial epicondyle and 14% strain 6-8 cm proximal to the medial epicondyle in deep elbow flexion; therefore, it may be necessary to devise strategies for the prevention of nerve adhesions on a wide range, such as nerve wrapping [24; 25]. In the future, revealing the changes in strain due to nerve adhesions around the elbow over a wide area of the ulnar nerve may aid in identifying areas where nerve adhesions need to be prevented. This may help prevent ulnar nerve neuropathy in the elbow, and further studies are thus required. This study has several limitations. First, we observed differences in ulnar nerve strain at different sites; however, the sample size was small. Second, caution was exercised not to damage the soft tissues, such as para-neurium, that are crucial for nerve gliding [26] during the study; however, over time, the properties of the fascia and nerves may change due to drying, and the environment may become different from that in vivo. Third, we amputated all specimens at the shoulder joint and fixed the proximal ulnar nerve to the humeral head.