Postoperative ulnar neuropathy is not necessarily iatrogenic: a prospective study on dynamic ulnar nerve dislocation at the elbow.

BACKGROUND: Patients who undergo surgery may develop ulnar neuropathy. Although the mechanism of ulnar neuropathy is still not clear, ulnar neuropathies are common causes of successful lawsuits against surgeons. Recently, the concept developed that endogenous patient factors can lead to postoperative peripheral neuropathies. We hypothesize that dynamic ulnar nerve dislocation at the elbow (DUNDE) may be a predisposing factor for ulnar irritation (i.e., neuropathy) in normal subjects.
METHODS: In a prospective investigation, patients aged 20 years and older presenting in our emergency department were asked to participate. Three physicians examined both elbows of subjects included in our study for evidence of DUNDE (through clinical and sonographic examination) and for clinical symptoms related to ulnar neuropathy.
RESULTS: Dynamic ulnar nerve dislocation was observed in 29.3% of examined subjects. No significant difference in its occurrence was observed in relation to gender or dominant side. Physical examination with provocation tests demonstrated significantly more positive Tinel tests and spontaneous signs of neuropathy in patients with dynamic dislocating ulnar nerves (14.7 vs. 1.1%).
CONCLUSION: Dynamic ulnar nerve dislocation may be linked to ulnar nerve irritability (i.e., ulnar neuropathy) in normal subjects without history of trauma, surgical procedure, or anesthesia. Considering the high incidence of this variant in the general population, our study supports previous investigations suggesting that many postoperative ulnar nerve deficits are traceable to chronic patient conditions. Our study suggests that dynamic ulnar nerve dislocation is a predisposing factor in the development of ulnar neuropathy in the postoperative period. NOTES: (1) neuropathy should be viewed as a broad definition as signs of nerve irritation/inflammation, and independently of the pathophysiology and etiology; (2) because no specific term exists in the international anatomic nomenclature (Nomina Anatomica) to designate this variant, several synonyms have been used in the literature, leading to confusion and misleading conclusions concerning its traumatic etiologies and their consequences: (a) recurrent or habitual ulnar nerve luxation (or subluxation); (b) recurrent or habitual ulnar nerve dislocation; (c) ulnar nerve instability; (d) laxity of the ulnar nerve; and (e) ulnar nerve hypermobility.