Limited mouth opening of unknown cause cured by diagnostic coronoidectomy: a new clinical entity?

Limited mouth opening is a constant annoyance and can be life-threatening should intubation be needed. The causes are numerous and are categorised as intra-articular or extra-articular, which are often difficult to distinguish. We present what we regard as a new clinical entity - long-standing limited mouth opening of unknown cause - and describe our treatment. Four female patients presented with limited mouth opening and lateral and protrusive movements within normal limits, which were typical of restriction of extra-articular origin. However, the radiological findings were within normal limits, with no visible cause of the restriction. All four were treated by bilateral coronoidectomy that resulted in the immediate return of mouth opening to within normal limits that was preserved over subsequent years. Histopathological examination showed atrophy and degenerative changes in the temporalis band that had been attached to the coronoid, which accounts for the stiffness of the temporalis muscle but does not explain the pathogenesis. In the light of this "diagnostic coronoidectomy" further studies are required to document the underlying pathological changes and to develop more accurate imaging that will enable correct diagnosis in future.