Radiological and biomechanical evaluation of the ulnar nerve after the percutaneous application of the medial K-wire in the extended position on supracondylar humerus fractures: Does the postoperative long arm splint position matter?

Our study aimed to evaluate and compare the changes in ulnar nerve tension and strain at different elbow positions radiologically and mechanically before and after applying the medial K-wire on the supracondylar humerus fracture cadaver model. We used ten fresh frozen cadaver upper extremity specimens to measure strain and tension on the ulnar nerve in 3 different elbow positions: elbow full extension, elbow flexion-forearm supination, and elbow flexion-forearm pronation. We employed Shear wave elastography (Siemens Acuson S3000 USG, 9L4 linear probe) and a microstrain gauge (Microstrain, Inc., Burlington) to obtain our measurements. Minimum, maximum and mean stress and strain values on the nerve and its surroundings were measured and compared statistically. The mean values of elbows with full extension are statistically lower than those in elbows with 90° flexion-forearm supination and those with 90° flexion-forearm pronation positions. Statistical evaluations were performed between all of the groups. Elbow 90° flexion-forearm pronation, both minimum and maximum and mean values were statistically higher in the group, including the specimens with Kirschner applied. The mean values in the elbow full extension and elbow 90° flexion-forearm supination positions were statistically similar in the specimens with and without the K-wire applied. Despite the numerous techniques described in the literature, there is no absolute technical method to prevent ulnar nerve damage. K-wire application to the medial epicondyle with the elbow in a slightly extended position is a technique that can be applied to reduce the risk of ulnar nerve paralysis. However, it has been reported that ulnar nerve damage can be observed in cases where a splint is placed in the 90° flexion position. We hypothesize that the position of the elbow joint in the postoperative period may contribute to ulnar nerve paralysis due to soft tissue tension and strain and as a result of changing the balance of the surrounding tissues. Our findings suggest that the long arm splint applied in elbow 90° flexion and forearm pronation position should not be preferred in the postoperative period. The maximum strain values obtained in the elbow full extension were lower, suggesting that it would be appropriate to stabilize the elbow in the extension position as much as possible postoperatively. Level of evidence: Level V.