Trismus is highly prevalent in head and neck cancer (HNC) survivorship. Current standards for trismus treatment include various stretch-based exercise protocols as a primary and single treatment modality with limited evidence regarding the role of manual therapy (MT) for this indication.

To assess the effect size and associations of response to MT to increase oral opening in the setting of radiation-associated trismus.

This retrospective case series was conducted at the University of Texas MD Anderson Cancer Center between 2016 and March 2020 (before COVID-19 interruption) and included 49 disease-free survivors of HNC who were referred for treatment of radiation-associated trismus.

Intraoral MT (including or excluding external head and neck) targeting the muscles of mastication.

Maximum interincisal opening (MIO) before and after the initial MT session compared with serial MT sessions. Covariates were examined to determine the association with response to MT for trismus.

A total of 49 survivors of HNC (13 women [27%]; 24 [49%] 64 years or younger; 25 [51%] 65 years or older; mean [range] of 6.6 [0-33] years postradiotherapy were included, 9 [18.4%] of whom underwent a single MT session; 40 [81.6%] who underwent multiple sessions [mean, 6; median (range), 3 (2-48)]). The MIO improved after a single session by a mean (SD) of 4.1 (1.9) mm (0.45 effect size) and after serial MT sessions by a mean (SD) of 6.4 (4.8) mm with an effect size of 0.7. No covariates were found to be clinically meaningfully associated with MIO improvement following MT.

The findings of this case series study suggest that MT improved MIO with a medium to large effect size in survivors of HNC with radiation-associated trismus. The results suggest that the largest increase in oral opening was achieved after the initial treatment and although gains were more modest, oral opening continued to improve with serial treatment. Covariates were not associated with MT response, suggesting that patients with clinical features often considered treatment refractory (eg, advanced disease, multiple lines of oncology treatment, ≥5 years posttreatment) may benefit from treatment with MT. Manual therapy may be a beneficial frontline or adjuvant treatment when combined with traditional stretching therapy. A clinically meaningful increase in oral opening has the potential to improve swallow function, speech, pain, and quality of life.