An understanding of the anatomic path of the ulnar nerve is critical to understand how to avoid ulnar nerve problems during fixation or replacement of distal humeral fractures. The first important concept regarding the anatomy of the ulnar nerve is the extreme variability of its course in the distal part of the humerus. Because of this variability, it is dangerous to blindly rely on precise anatomical landmarks when handling the ulnar nerve, without exploring its real position.

The ulnar nerve runs initially in the anterior compartment of the arm and goes posteriorly through the medial intermuscular septum at an average distance of about 6–8 cm proximal to the medial epicondyle with a range of between 5 and 11 cm [4, 5]. In approximately 40 % of cases, however, the ulnar nerve passes posteriorly without crossing the medial intermuscular septum and then transitions from anterior to posterior at a more distal point [6].

Further complicating the picture, the point of passage through the medial intermuscular septum can occur through a simple hole in the membrane or a fibrous channel formed by a splitting of the medial intermuscular septum. In some cases, the presence of a fibrous tissue in the vicinity of the medial intermuscular septum, particularly evident at the level of the passage of the nerve, led to the coining of the term arcade of Struthers whose existence and description, however, remain unclear. Several anatomical studies on cadavers have investigated the existence of the arcade of Struthers and have described its anatomical variants. The great variability reported in some articles is largely dependent on the terminology used to describe this structure. In articles in which the presence of any fibrous structure between the medial triceps and the medial intermuscular septum has been defined as the arcade of Struthers, the prevalence of this arcade exceeds 80 % in cadavers [4, 5].

In articles in which the description of the arcade is more adherent to the original description of the ligament of Struthers, the percentage drops to 0 % [7]. According to our clinical experience, the presence of a clear structure of a dense, fibrous, tendon-like membrane, stretched between the medial intermuscular septum and medial head of the triceps, is extremely rare. However, it is important to explore the nerve proximally, even in the absence of a clear ligament of Struthers, until it passes through the medial intermuscular septum, to avoid tardy neuropathies of the ulnar nerve.

At the level of the elbow, the ulnar nerve engages in the cubital tunnel, which is comprised proximally by the Osborne ligament (a fibrous structure stretched between the two heads of the FCU) and is formed distally by the deep flexor/pronator aponeurosis (approximately 5 cm distal to the medial epicondyle).

Considering the great variability of the ulnar nerve and its proximity to the medial epicondyle and the distal humerus, a cautious exploration of the ulnar nerve is usually recommended before proceeding with the treatment of the fracture. In elective surgery cases, the identification of the ulnar nerve is not particularly difficult. However, in fracture cases—especially those treated several days after the trauma—the identification of the ulnar nerve can be tricky because of the local edema and hematoma that usually infiltrates the triceps. To simplify the identification of the ulnar nerve, we recommend the application of a sterile tourniquet and to begin the identification of the ulnar nerve from proximal to distal (Fig. 23.1a, b).

In extremely difficult cases, the identification of the nerve is made simpler by extending the exploration more proximally. Once isolated, the ulnar nerve must be released distally in order to allow a complete exposure of the medial epicondyle and to avoid a more distal compression. The exposure of the medial epicondyle is especially crucial for the synthesis of distal humeral fractures using parallel precontoured plates (Fig. 23.2). We recommend a neurolysis extending at least until the first motor branch followed by a transposition into a large subcutaneous pocket. During surgery, great care must be taken to avoid excessive traction on the nerve. For this reason, we prefer not to place heavy tools to clamp the vessel loop but instead use a simple knot (Fig. 23.3).

The postoperative management is extremely important to avoid tardy ulnar nerve complications. In this regard, we believe that it is important a drain be kept in place for 24 h to prevent the formation of large hematomas that may compress the ulnar nerve. The elbow must also be kept in extension for 24 h, hung above the head, to facilitate the resolution of local edema.