Neuropathic Pain Following Sagittal Split Ramus Osteotomies of the Mandible: Prevalence, Risk Factors, and Clinical Course

Neuropathic pain (NPP) is characterized by paradoxical pain and abnormal sensory function following sensory nerve injury. NPP has been reported as a complication of many surgical procedures including sagittal split ramus osteotomies (SSRO) of the mandible.¹ While studies have examined the prevalence of and risk factors for NPP following thoracic, abdominal, gastrointestinal and gynecologic surgeries, there is limited knowledge about NPP following SSRO of the mandible. Prevalence estimates have ranged from 5-10%, but these have been derived from just a few small case series.² Our current understanding of NPP following SSRO has been further limited by the methodologic heterogeneity of studies and a lack of consensus regarding the characteristics of NPP. Therefore we sought to identify the prevalence of, risk factors for, and clinical course of NPP following SSRO in a large group of patients.

 We assembled a retrospective cohort of all patients undergoing SSRO from January 2007 through September 2012 at Kaiser Permanente Oakland and Santa Clara Medical Centers to identify those with NPP. The International Association for the Study of Pain has defined NPP as "pain caused by a lesion or disease of the somatosensory nervous system." We defined NPP as paradoxical pain in the distribution of V₃ in conjunction with reduced sensory function. Demographic, clinical, and surgical factors were abstracted from medical records and relevant co-morbidities identified. We calculated the prevalence of NPP in our cohort and noted the frequency of clinical signs, symptoms, temporal characteristics, and treatment response in affected patients. Standard descriptive statistics were used to describe the characteristics of the cohort and Kolmogorov-Smirnov and chi-squared tests were used for comparison between NPP and non-NPP subgroups.

 We identified 1,778 patients who underwent  sagittal split ramus osteotomies of the mandible and excluded 107 patients according to predefined criteria. The remaining 1,671 patients had a median age of 24 years (interquartile range, 19-35) and 62.4% were women. Seven patients of 1,671 developed NPP, which is an overall prevalence of 0.42%. All patients with NPP in our cohort were women. The risk factors for developing NPP after this surgery were older age (P = 0.002), surgical site infection and/or hematoma (P = 0.008),  depression (P= 0.002), and female gender. Neuropathic pain developed an average of 30 days postoperatively (range 18-56) and persisted a median duration of 52 days (range 22-72). All patients responded favorably to anticonvulsant (N = 6) or tricyclic medications (N = 1) and no patients developed chronic post-surgical pain.

Overall, we found that neuropathic pain was an infrequent complication that occurred in 1 of 238 patients. The short duration and positive response to medication are reassuring findings in those who develop NPP after sagittal mandibular osteotomies. The results of this investigation highlight the need for prospective studies to further understand the spectrum of postoperative NPP.

1. Popat H, Herdman W, Cronin AJ et al. Management of chronic neuropathic pain following mandibular advancement surgery. Int J Oral Maxillofac Surg 2012; 41: 1374-1377
2. Jaaskelainen SK, Teerijoki-Oksa T, Virtanen A et al. Sensory regeneration following intraoperatively verified trigeminal nerve injury. Neurology 2004; 62: 1951-7.