JCO Oncol Pract. 2020 Oct;16(10):643-653. doi: 10.1200/OP.20.00266.
Restricted mouth opening or trismus is often encountered in patients with head and neck cancer. The restriction may be the presenting sign of malignancy, a sequela of tumor site or growth, an adverse effect of oncologic treatment, or a first sign of tumoral recurrence. In general, any insult to the temporomandibular joint, masticatory muscles, or their neural innervation may cause limitation in mouth opening. The etiologies leading to trismus are as follows: myospasm secondary to tumor
infiltration; reflectory myospasm; radiation-induced myositis and myofibrosis; temporomandibular joint involvement with tumor; unfavorable postsurgical scarring; muscle and joint atrophy secondary to immobilization; pain; jaw fracture and hardware failure; and infection. Preventive measures should be implemented before, during, and after treatment. These measures include identification of high-risk patients, utilization of dose-sculpting radiation techniques whenever possible, performing reconstruction at the same time of resective surgery whenever feasible, and initiating mobilization exercises as early as possible. When trismus develops, treatments are often challenging and disappointing. These include physical therapy, mouth opening appliances, drug therapy, and release surgery. All medical specialties dealing with head and neck cancer should be familiar with the diagnosis and prevention of trismus and make an effort to ensure patients are referred to the appropriate care when needed. Trismus should not be considered a trivial sequela of head and neck cancer.