Introduction Trismus, or limited mouth opening, is a well-known complication of head and neck cancer and its treatment. It may be caused by tumour infiltration into the masticatory muscles or by treatment like surgery and radiotherapy. A limited mouth opening may have a negative effect on nutrition, phonation, dental hygiene and treatment, and quality of life. The severity of this complication depends on the location of the tumour, the type of reconstruction, the total radiation dose, fractionation, and treatment techniques. If there is no intervention, these changes may be progressive and persist for life. There are no specific treatments for trismus. Current strategies emphasize prevention and, in instances of existing trismus, collaboration between health care professionals to establish pain control, prevent the progression of trismus, and restore function. The prevalence of trismus in head and neck cancer patients ranges from 5% to 38%. Despite numerous studies, reliable data on the aetiology of trismus and appropriate treatment for it are scarce. Case report We describe a patient with squamous cell carcinoma of the oropharynx who developed trismus after surgery and radiotherapy. A multidisciplinary treatment strategy including analgesics, regional blocks, hyperbaric oxygenation therapy, external dynamic bite opener and physiotherapy, increased the mouth opening from 5 mm to 22 mm, however, the patient still suffered from xerostomia and had problems with intake of solid food. Material and methods A systematic literature search (starting January 1., 1980, and ending June 1., 2009) was performed to identify evidence-based interventions for the treatment of trismus in head and neck cancer patients. A total of 244 articles were identified from the databases. Of these, eight were excluded because of the absence of an English abstract and 214 were excluded because they were of marginal relevance to the inclusion criteria. The remaining 22 articles were evaluated independently by two experts using the Scottish Inter-collegiate Guidelines Network criteria for quality and evidence. Results There were few studies of good methodological quality on this topic. Two systematic reviews and two RCTs were identified. The other reports involved cohorts, case series, and expert opinions. Discussion Evidence in the form of clinical studies on therapeutic interventions is scarce. Numerous pharmacological treatment modalities have been described, but few are supported by the results of comparative trials involving control groups. Few studies have documented therapeutic effects for longer than a year. Better evidence was found for non-pharmacological methods, especially for physical therapy with passive and active stretching exercises, an important first-line strategy. The interincisal distance criterion for trismus varies between authors from 15 to 40 mm, which renders comparison between studies difficult. The absence of a standardized assessment protocol may also have contributed to variation between studies. An interincisal distance of 35 mm has been proposed as a definition of trismus. Explicit and precise treatment algorithms could not be established based on the available literature. However, a coordinated multidisciplinary approach in order to estimate and understand patient dysfunction is recommended; a systematic treatment plan should result in good symptom control and patient care. Prevention of trismus is more desirable than treatment for trismus.

Wranicz, Herlofson, Evensen, Kongsgaard, , , , , (2010). Prevention and treatment of trismus in head and neck cancer: A case report and a systematic review of the literature. Scandinavian journal of pain, 2010 Apr;1(2):84-88. https://www.ncbi.nlm.nih.gov/pubmed/29913945