Discussion

We identified a 38% incidence of late ulnar neuropathy following ORIF of a distal humerus fracture, supporting our first hypothesis. This was most common in AO type C, followed by AO type A injuries. There were no cases of AO type B injuries resulting in late ulnar nerve dysfunction. The presence of a preoperative history of ulnar nerve paresthesias led to a 100% incidence of late symptoms. In no case was there a McGowan stage 3 finding, but 56% were type 1 and 44% were type 2. All type 2 injuries ultimately required a second surgery to address ulnar nerve function. There was no statistical significance difference as to the development of late ulnar neuropathy and the surgical exposure, but there was a trend toward olecranon osteotomy. Supporting our second hypothesis, there was no statistical significance difference in general between the use of an in situ release versus transpositions and the development of late ulnar neuropathy, except for the single case using a submuscular transposition that ultimately led to late symptoms.

Ulnar Neuropathy Incidence

Nerve injuries, especially involving the ulnar nerve, are considered to be more often associated with severe fracture patterns. High-energy fractures dissipate their forces through the soft tissue and can also result in greater bone displacement. This can result in both direct and indirect nerve injury at the time of fracture. The incidence of ulnar neuropathy following distal humerus fracture fixation is variable. Occurrence presenting in the immediate postoperative period ranges from the low values of 0% to 6.6% to higher values of 10.1% to 21%. Most of these reported postoperative neuropathies resolve with late ulnar neuropathy incidences ranging only from 0% to 3.3% but they have been documented at higher ranges of 11.7% to 16%.

Helfet and Schmeling retrospectively reviewed their experience with bicondylar intraarticular distal humerus fractures and identified, among other complications, a 7% incidence of late ulnar neuropathy but it was unclear from their series whether these were early or late neuropathies. More recently, Vazquez and colleagues retrospectively examined 69 distal humerus fractures (both AO type A and C) without preoperative ulnar nerve symptoms to determine the incidence of late ulnar nerve dysfunction at a minimum of 12-months postoperatively. They identified an incidence of 10.1% immediately postoperatively and 16% at final follow-up. Also, using McGowan staging, they identified that 57% were grade I and 43% were grade II and, similar to our series, no development of grade III stages. They also did not identify any specific risk factors for the development of late ulnar neuropathy. Moreover, Ruan and colleagues retrospectively examined 117 consecutive AO type C distal humerus fractures at two centers to evaluate late ulnar nerve dysfunction and found that no patients without preoperative ulnar nerve symptoms developed late symptoms, whereas, among the 29 patients with preoperative ulnar nerve symptoms, there were 31% that continued to demonstrate late ulnar nerve symptoms.

Ulnar Nerve Management

There are inherent advantages and disadvantages to either releasing the ulnar nerve in situ or transposing it. In situ release affords surgical simplicity, decreased nerve handling, avoiding devascularization of the nerve, and iatrogenic traction injury. However, it maintains the nerve in close proximity to hardware in the cubital tunnel and tensioned around the medial epicondyle, in which case the native anatomy may also be altered. Transposition avoids contact of the nerve from fracture inflammation, callous formation, periarticular fibrosis, and soft tissue edema, as well as decreasing its tension along its path. However, transposition requires increased nerve handling, potential devascularization, traction injury, and late compressive neuropathy from inadequate decompression of soft tissue restraints.

Numerous recommendations have been made regarding when to transpose the ulnar nerve in distal humerus fracture management. An article reviewing distal humerus fractures from 1985 to 2003 advised transposition in those fractures with preoperative ulnar nerve symptoms, or when internal fixation requires extension over the medial epicondyle. One investigator used indications of preoperative palsy, possible implant irritation, or intraoperative traction. There continues to be no clear consensus as to when an ulnar nerve is transposed during surgery. The investigators’ terminology in their decisions to transpose include “if hardware came to lie in the ulnar groove,” “if during elbow flexion, ulnar nerve was noted to impinge on hardware,” or “the ulnar nerve was mobilized if necessary to prevent iatrogenic damage.” Some investigators prefer to routinely transpose the ulnar nerve in all intrarticular distal humerus fractures, whereas some investigators transpose without citing particular reasoning and, in some cases, the investigators make no mention of their ulnar nerve management.

The controversy is apparent when comparing studies analyzing similar fractures. The surgeons involved in the type C distal humerus fracture study by Athwal and colleagues preferred to routinely anteriorly transpose the ulnar nerve in all cases with subcutaneous placement in 98%. Six patients (19%) had preoperative ulnar nerve injuries. Similar to our transposition results, five patients (16%) had postoperative neuropathies (four ulnar and one radial sensory). The symptoms of three out of these five patients resolved at a mean of 4.5 months. The study did not specifically comment on the outcome of the preoperative neuropathic patients but did question whether the routine anterior transposition contributed to the increased incidence of postoperative ulnar neuropathy. However, another study by Luegmair and colleagues with all type C fractures only transposed the nerve in two patients (12%). They reported only one (6%) of their 17 patients with preoperative ulnar symptoms and two (12%) postoperative ulnar neuropathies in patients without nerve transposition. Of note, the percentages of postoperative neuropathies is similar without transposition as reported by Luegmair and colleagues and with transposition, in both the results of our study and Athwal and colleagues’ study. Results, or without transposition as reported by Luegmair and colleagues.

Other studies seem to favor anterior transposition of the ulnar nerve for both prevention and treatment of neuropathy. Gofton and colleagues conducted another study analyzing type C fractures by assessed sensorimotor ulnar nerve outcomes with the 28-item Patient-Rated Ulnar Nerve Evaluation. Preoperatively, six patients (26%) had ulnar neuropathy. The investigators did not define the time frame for resolution but reported four of six patients’ neuropathies resolving quickly. The other two preoperative neuropathies were categorized as subjective complaints after not finding any functional or objective deficits. Only one patient (4.3%) developed neuropathy after surgery, which could be classified as subacute or postoperative depending on the specific time-frame of symptom presentation. The investigators credit the low rate of objective ulnar neuropathy to routine transposition. Kinik and colleagues also routinely transposed the ulnar nerve in their patients and had similar postoperative results. Three patients (6.5%) had ulnar neurapraxia caused initially by the fracture, whereas only two patients (4.3%) developed postoperative neuropathy. After transposition, the preoperative symptoms resolved and one of the two postoperative neuropathies improved during follow-up. One study by Wang and colleagues, who performed anterior transposition during fixation of type C fractures, found none of their 20 patients developed postoperative or delayed ulnar neuropathies after adequate follow-up. Their results could be credited to small study group or other variables. No mention was made concerning the incidence of any preoperative symptoms.

In contrast, Robinson and colleagues did not primarily transpose the ulnar nerve during treatment of distal humerus fractures—even with preoperative symptoms. Eight of their 320 patients (2.5%) had preoperative ulnar symptoms. One went on to have symptoms 3-months postinjury and treatment. Postoperatively, six patients (1.9%) developed ulnar neurapraxia and the investigators associated the palsy with surgical treatment of type C fractures. All but two palsies recovered postoperatively over 6 to 10 weeks. An additional study, in which transposition was not routinely performed in all but two patients, also found good ulnar nerve recovery. Although it is not known which patients received the primary transpositions, it can be assumed that only the two postoperative neuropathic (11.7%) patients were not primarily transposed because they underwent additional ulnar nerve surgeries to treat their symptoms. Therefore, both studies had a small percentage of patients develop postoperative neuropathy without transposing the nerve.

In other studies, some investigators transposed the ulnar nerve based on simple criteria and produced favorable results. Two age-demographic studies of distal humerus fractures by Huang and colleagues transposed the nerve with indications of preoperative palsy, possible implant irritation, and/or intraoperative traction of the nerve. In their study of elderly patients, they transposed the nerve based on their indications in 4.5%, 22.7%, and 4.5% of the patients. In their larger study of all adult ages, they transposed the nerve in 5.0%, 12.5%, and 7.5% of patients based on their indications. Overall, only one patient (5.3%) from their study of elderly patients and two patients (5%) from their study of adult patients developed a postoperative neuropathy. Ultimately, all patients with neuropathies resolved within 3 months. A group of surgeons in one study mobilized the ulnar nerve, if necessary, to prevent iatrogenic damage, although they did not give specific criteria. Their rate of postoperative ulnar neurapraxia was 17%; however, all patients had resolved during follow-up.

The ulnar nerve can also be managed with in situ decompression. In a study by Russell and colleagues, the surgeon initially performed what was described as an in-situ release of the ulnar nerve and would transpose the nerve only if during elbow flexion the nerve impinged on the hardware or subluxed. A total of seven patients (29%) had transpositions. Only one patient with transposition developed postoperative ulnar neuropathy, but symptoms resolved within 3 months. However, three patients (12.5%) without transposition postoperatively developed what the investigators called ulnar neuritis and attributed the results to the plating around the medial epicondyle.

A recent study by Ruan and colleagues compared in situ decompression versus anterior subfascial (intramuscular) transposition of the ulnar nerve. The investigators chose a subfascial location because of its vascular bed as well as its decreased vulnerability to irritation and scarring when compared with submuscular alternatives. The 29 patients with preoperative ulnar symptoms (24.8%) were randomized to receive either ulnar nerve procedure. The Bishop rating system was used to classify ulnar nerve function. In the transposition group, 80% of the patients recovered completely, whereas the remaining 20% recovered partially. The in situ group had 57% of patients with complete recovery and 43% with only partial recovery. Furthermore, their rating system determined excellent and good results in 86.7% of the transposition group versus 57.1% of the in situ group. The results of this study advocate subfascial transposition over in situ release. Interestingly, the subfascial transposition was also performed on patients without preoperative symptoms and found no incidence of postoperative or delayed ulnar neuropathy.