Watters AL, et al. - In patients with head and neck cancer, researchers determined the prevalence of trismus by searching four (Cochrane Library, MEDLINE, EMBASE, and Web of Science) electronic databases up to April 2018. A total of 636 abstracts were evaluated. The study sample consisted of 2,786 head and neck cancer patients treated with surgery, radiotherapy, and/or chemotherapy either alone or in combination. Based on individual studies, having a primary site of the oral cavity or oropharynx was linked to a greater risk of trismus. To further examine the prevalence of trismus secondary to head and neck cancer treatment, prospective cohort studies or randomized controlled trials with multiple objective trismus measurements, evaluation of disease features, and treatment variables are required.