Criterion for trismus in head and neck cancer patients: a verification study

PURPOSE: Several cut-off points for trismus in head and neck cancer patients have been used. A mouth opening of 35 mm or less is most frequently used as cut-off point. Due to the variation in cut-off points, prevalence, risk factors and treatment outcomes of trismus cannot be studied in a uniform manner. To provide uniformity, we aimed to verify the cut-off point of 35 mm or less. Additionally, we aimed to determine associated covariates with reported difficulties when opening the mouth. METHODS: In a cross-sectional design, we measured the mouth opening in 671 head and neck cancer patients at the Department of Oral and Maxillofacial Surgery, at the University Medical Center Groningen. The cut-off point was determined using the receiver operating characteristic curve and Youden index, with reported difficulties when opening the mouth as criterion for trismus. Cut-off points for significant covariates were also determined. RESULTS: The Youden index was highest at 35 mm, with a sensitivity of 0.71 and a specificity of 0.86. Of the covariates analysed, type of treatment modality was significantly associated with reported difficulties when opening the mouth. The highest Youden index for patients treated with surgery alone was 37 mm and for patients treated with radiotherapy alone 33 mm. CONCLUSIONS: The cut-off point of 35 mm or less for trismus was confirmed in a head and neck cancer population and is recommended to be used in future studies. Patients receiving different treatment modalities experience difficulty when opening the mouth differently.