TMJ Condylar Hyperplasia

Condylar hyperplasia is excessive growth of the mandibular condyle, producing progressive facial asymmetry, usually unilateral. It most often begins in adolescence and may continue into the third decade.

Two main patterns exist. Hemimandibular hyperplasia is a three dimensional enlargement of one side of the mandible with vertical overgrowth. Hemimandibular elongation is horizontal overgrowth that causes the chin to deviate to the unaffected side. Mixed forms occur.

Pathophysiology. Abnormal activity of the condylar growth centre, with a thickened cartilage cap, causes overgrowth after the usual growth period. The cause is unknown, and trauma, hormonal factors and local blood supply have been proposed.

Growth can be active or stable, and the activity determines the timing and type of surgery.

Progressive facial asymmetry with the chin deviating to the side opposite the lesion (in elongation), a dental midline shift, a canted occlusal plane, a crossbite on the unaffected side, or an open bite on the affected side. Pain and joint noises are uncommon, but TMJ dysfunction may occur.

The face is lengthened on the affected side, with a prominent angle and lower border. Asymmetry increases during adolescence and is often first seen at 11 to 16 years.

• Clinical assessment of the face, bite and occlusal plane, with photographs.
• Panoramic radiograph and cephalometric views: enlarged condylar neck and head, a long ramus and body, and a deepened inferior border on the affected side.
• CT with 3D reconstruction for dimensions and symmetry.
• Single photon emission CT with technetium-99m methylene diphosphonate, comparing the condyles: a difference in uptake of 10% or more (affected side over 55% of the total) indicates active growth. Repeat after 6 to 12 months for confirmation when uncertain.
• Dental models and orthodontic records for planning.
• Histology of the condyle or cartilage cap: a cartilage cap thicker than 3 mm suggests active growth.

Differential diagnosis.

• Osteochondroma of the condyle
• Hemifacial hypoplasia of the contralateral side
• Fibrous dysplasia
• Functional mandibular shift from occlusal interference
• Condylar tumour and other neoplasm
• Posttraumatic overgrowth
• Cherubism and Paget disease (rarely)

• Active growth: high condylectomy (removal of 3 to 5 mm, or enough to remove the active cartilage cap and proportional condylectomy) to stop growth, usually followed by orthodontic treatment and orthognathic surgery to correct the asymmetry, performed after stability is confirmed.
• Inactive growth with a stable asymmetry: orthodontic treatment and orthognathic surgery (bilateral sagittal split with maxillary Le Fort I and genioplasty) to correct the bite and symmetry. Perform when growth is complete.
• Observation with serial scintigraphy at 6 to 12 months and clinical follow up for mild cases or those with uncertain activity.
• Perioperative antibiotic: cefazolin 2 g intravenously (3 g if over 120 kg) at induction, or clindamycin 600 mg intravenously in penicillin allergy.
• Analgesia after surgery: paracetamol 1 g every 6 hours (maximum 4 g daily) with ibuprofen 400 mg every 8 hours with food when appropriate.
• Treat TMJ dysfunction conservatively with splint and physiotherapy.

Monitoring. Review every 6 months until growth stops and for 12 to 24 months after surgery, with imaging and cephalometric records. Recurrence of asymmetry after condylectomy indicates residual growth.

Referral and escalation. Refer to oral and maxillofacial surgery and orthodontics. Urgent referral for rapid growth, pain, or suspected tumour.