Which of the following typically produces INTRACAPSULAR restriction of mandibular movement?

Correct answer: A. Ankylosis

• A. CORRECT. ANKYLOSIS is by definition an INTRACAPSULAR pathology — a fibrous or bony union between the condyle and the glenoid fossa within the joint itself. It produces a severe, fixed, mechanically absolute limitation of opening that does NOT improve with muscle relaxants, heat, or time, and which cannot be overcome under general anaesthesia. Causes are trauma (most common), prior joint infection, rheumatoid arthritis and previous joint surgery.
• B. Myofascial pain disorder is a MUSCLE disorder — extracapsular by definition. Limitation is soft, variable through the day, and typically improves with heat, NSAIDs and a splint.
• C. Coronoid hyperplasia restricts opening by impingement of the enlarged coronoid process against the zygomatic arch — an EXTRACAPSULAR mechanical obstruction outside the joint.
• D. Infection of the masticatory spaces produces trismus through inflammatory MUSCLE splinting and oedema, which is EXTRACAPSULAR. It resolves as the infection is treated.

Note: The clinical discriminator: apply gentle stretch at maximum opening. A soft, springy end-feel that gains a few millimetres means a MUSCULAR (extracapsular) restriction. A hard, abrupt end-feel with no give means an INTRACAPSULAR problem — ankylosis or a non-reducing disc displacement — and warrants imaging.