# Internal Derangement of the TMJ

## Overview

Internal derangement (ID) refers to an abnormal positional relationship of the articular disc relative to the mandibular condyle, fossa, and articular eminence. The most common form is anterior disc displacement. Internal derangement affects approximately 25-30% of the general population, though many are asymptomatic. There is a female predominance of 3:1 to 5:1. The condition represents a spectrum ranging from mild displacement with reduction to advanced degenerative joint disease.

## Normal TMJ Disc-Condyle Anatomy and Function

The articular disc is a biconcave fibrocartilaginous structure. In its normal position, the posterior band sits at the 12 o'clock position relative to the condylar head when the mouth is closed. During opening, the disc translates anteriorly with the condyle, maintaining its position on the condylar head. The disc is attached posteriorly to the bilaminar zone (retrodiscal tissue) and laterally and medially to the condylar poles. The superior head of the lateral pterygoid inserts into the anterior band and capsule. Disc stabilization depends on the collateral ligaments, disc shape, and coordinated muscular function.

## Classification

### Wilkes Staging System

| Stage | Name | Disc Position | Disc Morphology | Osseous Changes | Clinical Features |
|---|---|---|---|---|---|
| I | Early | DDwR | Normal | None | Clicking, minimal symptoms |
| II | Early-Intermediate | DDwR | Early deformity | None | Intermittent locking |
| III | Intermediate | DDwR or DDwoR | Significant deformity | None or early | Persistent pain, mechanical dysfunction |
| IV | Intermediate-Late | DDwoR | Severe deformity | Beginning DJD | Chronic pain, limited opening |
| V | Late | DDwoR / perforation | Perforation | Advanced DJD (osteophytes, erosion, sclerosis) | Crepitus, bone-on-bone |

Stage I (Early) is characterized by disc displacement with reduction, no morphologic changes, and minimal symptoms. Stage II (Early-Intermediate) features disc displacement with reduction, early disc deformity, and intermittent locking. Stage III (Intermediate) involves disc displacement with or without reduction, significant disc deformity, and persistent symptoms with pain and mechanical dysfunction. Stage IV (Intermediate-Late) shows disc displacement without reduction, severe disc deformity, and the beginning of degenerative osseous changes. Stage V (Late) presents with disc displacement without reduction or perforation, advanced degenerative changes, disc perforation, crepitus, and bone-on-bone articulation.

### Disc Displacement with Reduction (DDwR)

In DDwR, the disc is displaced (usually anteriorly) at closed mouth. During opening, the condyle translates anteriorly and recaptures the disc, a process called reduction. Clinically, this produces reciprocal clicking -- a click on opening represents reduction and a click on closing represents re-displacement. DDwR is often asymptomatic or mildly symptomatic and may progress to displacement without reduction or may remain stable for years.

### Disc Displacement without Reduction (DDwoR) -- Closed Lock

In DDwoR, the disc is displaced and does not reduce during mandibular opening. The displaced disc acts as a mechanical block to full condylar translation. In the acute form, there is sudden onset of limited opening (typically less than 30 mm), deviation to the affected side, and pain. In the chronic form, limited opening may partially improve as retrodiscal tissue undergoes metaplasia (pseudodisc formation), but degenerative changes may progress.

### Other Displacement Patterns

Less common patterns include lateral disc displacement, medial disc displacement, posterior disc displacement (rare, usually post-traumatic), and rotational disc displacement.

<image>Sagittal MRI sequences of the TMJ showing normal disc position at closed and open mouth positions compared with anterior disc displacement with reduction (disc recaptured on opening) and anterior disc displacement without reduction (disc remains displaced with limited condylar translation)</image>

## Etiology and Pathogenesis

### Multifactorial

The etiology is multifactorial. Trauma can be macrotrauma (blow to the chin, hyperextension injury) or microtrauma (parafunction, bruxism). Excessive or asymmetric joint loading contributes. Ligamentous laxity from collateral ligament elongation allows the disc to displace. Disc morphology changes include thinning of the posterior band and loss of biconcavity. Retrodiscal tissue changes involve stretching and loss of elasticity of the superior retrodiscal lamina. The role of occlusal factors is controversial and likely minimal in isolation. Hormonal factors, specifically the prevalence of estrogen receptors in TMJ tissues, may explain the female predominance.

### Pathologic Cascade (Wilkes)

The pathologic cascade progresses from disc attachment elongation and early disc displacement, through disc deformity and progressive displacement, retrodiscal tissue breakdown, articular surface fibrillation and degradation, osteoarthritic remodeling (osteophytes, erosion, sclerosis, flattening), and finally end-stage degenerative joint disease.

## Diagnosis

### Clinical Examination

The history should assess for clicking, locking, preauricular pain, limited opening, and deviation. Palpation includes lateral and posterior auricular palpation of the TMJ. Range of motion is measured, with normal maximum interincisal opening exceeding 40 mm and normal lateral excursions exceeding 7 mm per side. Joint sounds are assessed, with reciprocal clicking in DDwR and crepitus in degenerative joint disease. The deviation pattern shows deflection to the affected side in DDwoR and an S-shaped path in DDwR. The dynamic loading test uses bilateral manual manipulation (Dawson technique) to load the joint.

### Imaging

#### MRI (Gold Standard for Soft Tissue)

MRI is the best modality for assessing disc position, morphology, and joint effusion. Sagittal and coronal oblique sequences through the TMJ are obtained, and open and closed mouth views evaluate disc mobility. Findings include disc position, disc morphology (normal, thickened, or perforated), joint effusion, and retrodiscal tissue status. Sensitivity and specificity for disc displacement exceed 90%.

#### CBCT / CT

CBCT and CT are best for osseous pathology including condylar morphology, osteophytes, erosion, sclerosis, and subcortical cysts. They do not visualize the disc directly but are useful for surgical planning and evaluating degenerative changes.

#### Panoramic Radiograph

The panoramic radiograph is a screening tool with limited sensitivity for early changes. It can show condylar flattening, osteophytes, or erosion in advanced disease.

<image>Coronal and sagittal MRI of the TMJ demonstrating the Wilkes staging progression: Stage I with subtle anterior disc displacement and normal condylar morphology, Stage III with disc deformity and early osseous changes, and Stage V with disc perforation, osteophyte formation, and condylar flattening</image>

## Management

### Non-Surgical Management (First Line)

Patient education emphasizes the self-limiting nature of many cases and provides reassurance. Behavioral modification includes a soft diet, jaw rest, avoidance of wide opening, and habit cessation. Pharmacotherapy involves NSAIDs (ibuprofen 600-800 mg TID for 2-4 weeks), muscle relaxants (cyclobenzaprine 5-10 mg QHS), low-dose tricyclic antidepressants (amitriptyline 10-25 mg QHS) for chronic pain, and rarely short-course corticosteroids for acute flares. Physical therapy includes jaw exercises, manual therapy, ultrasound, and moist heat. Occlusal splint therapy uses a stabilization splint (flat plane, full coverage, maxillary or mandibular) to reduce joint loading and provide muscular relaxation; anterior repositioning splints for DDwR are controversial due to the risk of posterior open bite. Intra-articular injections include corticosteroid injection for short-term relief (with concern for repeated use causing condylar resorption) and hyaluronic acid injection for viscosupplementation.

### Arthrocentesis

Arthrocentesis is indicated for DDwoR (closed lock) failing conservative therapy. It involves lysis and lavage of the superior joint space, can release disc adhesions and reduce inflammatory mediators, and is a simple office-based procedure under local anesthesia or sedation. The success rate is 70-85% for pain relief and improved function.

### Arthroscopy

Arthroscopy offers both diagnostic and operative capabilities, including lysis, lavage, and disc mobilization under direct visualization. It can perform disc repositioning, posterior attachment cauterization, and synovectomy. The success rate is 80-90% for pain relief and functional improvement, with advantages over arthrocentesis including direct visualization and the ability to address intra-articular pathology.

### Open Joint Surgery (Disc Repositioning / Discectomy)

Open joint surgery is reserved for cases failing arthroscopic management. Disc repositioning (plication) involves repositioning the displaced disc and securing it with sutures to the posterior attachment or lateral capsule, though there is a risk of re-displacement and limited long-term data. Discectomy (disc removal) is performed for severely deformed, perforated, or non-repositionable discs. Fibrous tissue (pseudodisc) forms in the joint space, and the procedure may be performed with or without an interpositional graft (dermis, fat, or temporalis fascia). Outcomes are generally good for pain relief despite disc removal.

### Alloplastic TMJ Replacement

End-stage management for severe degenerative joint disease with failed previous interventions involves total joint replacement with custom or stock prostheses, discussed in detail in Topic 27.

## Clinical Pearls

The majority of patients with internal derangement improve with conservative management, and surgery is needed in only 5-10% of cases. MRI is the gold standard but should be ordered only when it will change management -- not every clicking joint needs imaging. Clicking alone, without pain or functional limitation, does not require treatment. Acute closed lock (DDwoR) in a young patient is a relative urgency, and early arthrocentesis within 2-4 weeks may prevent chronic changes. Repeated corticosteroid injections should be avoided due to the risk of condylar resorption, especially in young females. Progressive condylar resorption (idiopathic condylar resorption) is a separate entity from internal derangement and requires different management. Other causes of limited opening (coronoid hyperplasia, myofascial pain, neoplasia) should always be excluded before attributing it to closed lock.

<image>Algorithmic flowchart for the management of TMJ internal derangement showing the progression from conservative management (education, pharmacotherapy, splints, physical therapy) through arthrocentesis and arthroscopy to open joint surgery and total joint replacement, with decision points based on symptom severity, imaging findings, and response to treatment</image>

## References
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- Dimitroulis G. Management of temporomandibular joint disorders: a surgeon's perspective. Br J Oral Maxillofac Surg. 2018.
- Al-Moraissi EA, et al. Arthroscopy versus arthrocentesis in the management of internal derangement of the TMJ: a systematic review. Int J Oral Maxillofac Surg. 2015.
- Schiffman E, et al. Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). J Oral Facial Pain Headache. 2014.
- Guo C, et al. Prevalence of temporomandibular joint disc displacement: a systematic review and meta-analysis. J Dent Res. 2020.
- Liu F, Steinkeler A. Epidemiology, diagnosis, and treatment of temporomandibular disorders. Dent Clin North Am. 2013.