Myositis ossificans traumatica in the chewing muscles: a case study and an overview of the literature

Introduction: Traumatic occurrences in the area of the chewing muscles, involving subsequent temporary functional restrictions, may be caused by the impact of external forces, or may have their origin in iatrogenic surgery. This includes, in particular, not only the consequences of dental surgical operations, such as extractions and operations to remove teeth, but also complications arising from the use of local anaesthetics. Rare complications are also well-known, such as inflammatory swellings and a temporary trismus. Any long-term trismus, however, is rather associated with a craniomandibular dysfunction. What is less well-known is an ossification of the chewing muscles as a result of a traumatic or idiopathic incident, such as can occur with myositis ossificans. A distinction must be made between a local, traumatic form (myositis ossificans traumatica) and a progressive form with genetic causes (myositis ossificans progressive). Case study: In April 2016, a 28-year-old male patient came to us because of a long-term trismus which showed no pain symptoms. This had been preceded by dental fillings in the right mandible which had involved a block anaesthesia. Approximately four weeks later, the patient noticed a clear restriction in his ability to open his mouth. After conservative treatment had failed, an operation was carried out under intubation anaesthesia to remove 18 and 48. Immediately after the surgery there was an extensive remission of the functional restrictions. About two weeks after the surgery, the patient's restricted ability to open his mouth returned. The patient was taken into hospital, where a coronoidectomy was carried out on the right side. This too resulted in a temporary improvement in the patient's ability to open his mouth, followed, however, by a relapse. A second operation was carried out at our clinic with the working diagnosis of myositis ossificans traumatica. A genetic cause in the sense of myositis ossificans progressiva was ruled out beforehand. Summary: The etiology of myositis ossificans traumatica has not been conclusively explained so far. The literature mostly contains case studies from the field of orthopaedics. There are only sporadic reports on myositis ossificans traumatica in the chewing muscles. Any clear recommendations on strategies for treatment are either absent or contradictory. The intention of this case study is to add further information to the few cases described and to provide an overview of the existing literature. Keywords: myositis ossificans, myosistis ossificans traumatica, heterotopic ossification