# A Cadaveric Study of Ulnar Nerve Movement and Strain around the Elbow Joint
## 4 Discussion  
The ulnar nerve slides during elbow motion and stretching, and nerve slacking repeatedly occurs [6, 8]. Nerve strain of 5-10% impairs intraneural blood flow [2, 14, 15], axonal transport [16], and nerve conduction [3, 17]. Recent studies wherein a strain gauge was used reported that ulnar nerve strain changes at different upper limb positions. [PERSON] et al. reported that the greatest ulnar nerve strain is observed during the acceleration phase of the pitching motion [1]. [PERSON] et al. found that composite upper extremity joint movement caused more than 15% strain on the ulnar nerve [6]. [PERSON] et al. observed that the maximum strain was behind the medial epicondyle during maximal elbow flexion [9]. [PERSON] et al. and [PERSON] et al. measured strain changes after in situ decompression and medial epicondylectomy and showed that the medial epicondyle plays a major role in increasing ulnar nerve strain [10, 11]. Although [PERSON] et al. did not use strain gauges, they reported that daily activities involving the elbow and shoulder joints increased the strain on the ulnar nerve; however, no permanent nerve damage was observed [12]. Conversely, these studies measured only one site in or near the cubital tunnel. [PERSON] et al. measured nerve strain by placing markers on the ulnar nerve over a wide area of the upper arm and forearm [18]. They removed the fascia and Osborne ligament around the nerve to place the markers, which may be far from the in vivo environment. Thus, it remains unclear how the strain changes depending on the location around the elbow joint. The present study measured the longitudinal movement of the ulnar nerve at several sites near the elbow by preserving the soft tissue around the ulnar nerve as much as possible. The results revealed that ulnar nerve movement differs according to the measuring site, and the degree of strain changes across sites at the elbow joint position. Proximal to the medial epicondyle, movement of the ulnar nerve during elbow flexion increased nearer to the elbow and decreased with an increase in the distance from the elbow. This result is consistent with our hypothesis. [PERSON] et al. observed that the ulnar nerve moves 12.4 mm with maximum elbow flexion at the site 3 cm proximal to the cubital tunnel [1]. Our study demonstrated that at 2 cm proximal to the medial epicondyle, the ulnar nerve moved 10.4 mm with full elbow flexion. These findings suggest that at least 10 mm of ulnar nerve movement occurs on the proximal side of the medial epicondyle with elbow flexion. Ulnar nerve strain proximal to the medial epicondyle demonstrated the maximum value near the elbow (p20-40). Major strain associated with elbow flexion near the elbow (p20-40) occurred before 60\({}^{\circ}\) of elbow flexion; however, major strain in the more proximal section (p60-80) occurred with deep flexion of 60\({}^{\circ}\) or more. This result did not support our hypothesis; nevertheless, it was an interesting finding. [PERSON] et al. reported that major strain change in the ulnar nerve at the site 3 cm proximal to the cubital tunnel occurred before 90\({}^{\circ}\) of elbow flexion, which is consistent with the results of this study [1]. The ulnar nerve distal to the medial epicondyle moved proximally with elbow flexion; however, the movement was small compared with the proximal part of the medial  
Figure 6: Comparison of ulnar nerve strain with elbow flexion divided into mild flexion (0–60\({}^{\circ}\)) and deep flexion (60–120\({}^{\circ}\)). p20–40: 15% versus 3%, *: \(p<0.01\); p60–80: 5% versus 9%, **: \(p<0.05\).**epicondyle. [PERSON] et al. used an ultrasound machine to measure sliding of the ulnar nerve in elbow flexion and reported slight sliding of the nerve in the forearm [19; 20]. Similar results were obtained in our study. [PERSON] et al. reported that the ulnar nerve distal to the elbow has two to five muscular branches to the flexor carpi ulnaris and one to two muscular branches to the flexor digitorum profundus [21].