The temporomandibular joint (TMJ) is a complex joint connecting the lower jawbone, or mandible, to the skull, facilitating essential functions like talking and chewing. A common disorder affecting this joint is internal derangement, which is defined by an abnormal positional relationship of the articular disc relative to the mandibular condyle and the temporal bone. This disc acts as a cushion and smooth gliding surface, and its displacement disrupts the joint’s normal mechanics. To standardize the description and progression of this disorder, the Wilkes Classification system was developed, providing a structured way to categorize the increasing severity of this internal derangement.
Why This Classification Exists
Before the widespread use of advanced imaging, diagnosing temporomandibular joint disorders was challenging because a patient’s symptoms often did not directly correspond to the actual physical damage inside the joint. The Wilkes Classification, introduced by Dr. Clyde Wilkes in 1989, was created to establish an objective link between clinical presentation, surgical findings, and imaging results. The system provides a common language for healthcare providers, allowing for better communication and a more accurate prognosis based on objective pathology rather than just subjective pain reports.
The Five Stages of Wilkes
The Wilkes Classification organizes internal derangement into five distinct stages, describing a continuum from a minor, reversible displacement to severe, irreversible joint degeneration. This progression is characterized by changes in the disc’s position, its ability to return to normal, and the integrity of the surrounding bone.
Stage I: Early Stage
This initial stage is often characterized clinically by a painless reducing disc, meaning the disc is slightly anteriorly displaced when the mouth is closed, but it recaptures its normal position upon opening. Patients typically report a soft, reciprocal clicking sound, which occurs when the disc moves onto the condyle during opening and moves off it again during closing. Radiographic imaging usually shows a slight forward displacement of the disc, but the disc itself maintains a normal biconcave shape and the surrounding bone remains structurally intact.
Stage II: Early/Intermediate Stage
Progression to Stage II introduces occasional pain and joint tenderness, often accompanied by headaches. The clicking sound persists and may become louder, occurring later in the opening movement compared to Stage I. The patient may also experience transient subluxation, a brief catching sensation, or intermittent locking of the jaw. Pathologically, the disc is still displaced anteriorly but reduces, now showing a slight thickening of its posterior band, which represents the beginning of anatomical deformity.
Stage III: Intermediate Stage
In Stage III, the condition transitions to a non-reducing disc displacement, commonly known as a closed lock. The characteristic clicking sound disappears because the disc never returns to its correct position on the condyle. Clinically, this leads to frequent pain, joint tenderness, and a significant restriction in mouth opening, often less than 30 millimeters. The displaced disc acts as a physical barrier to the condyle’s forward movement. Imaging reveals a clearly displaced disc that remains anterior to the condyle even when the mouth is wide open, and the disc is visibly deformed.
Stage IV: Intermediate/Late Stage
This stage is marked by the onset of chronic pain, persistent headaches, and continued restricted motion, though the limitation may be less severe than in the acute phase of Stage III. A new sound, crepitus—a grating or grinding noise—may be heard, signaling bone-on-bone contact. The non-reducing disc is now severely deformed and displaced. The major distinguishing factor is the appearance of degenerative osseous changes, such as flattening, erosion, or osteophyte formation, on the condyle and temporal bone.
Stage V: Late Stage
Stage V represents the most advanced form of the disorder, with a variable clinical presentation that may include episodic pain, chronic crepitus, and severely limited function. The joint is characterized by severe disc deformity and displacement without reduction, along with progressive, advanced degenerative osseous changes. In this late stage, the posterior attachment tissues or the disc itself may have perforated, allowing communication between the upper and lower joint compartments.
Guiding Treatment Decisions
The Wilkes Classification serves as a practical blueprint for determining the appropriate management strategy for temporomandibular joint internal derangement. Treatment philosophy generally follows a sequential path, moving from the least invasive options to more aggressive surgical interventions based on the stage of the disease.
For early stages, specifically Stage I and Stage II, the focus is typically on conservative, non-surgical approaches. This includes patient education, physical therapy, and the use of oral appliance therapy, such as splints, designed to unload the joint or encourage disc recapture.
When the derangement progresses to Stage III, the acute non-reducing disc displacement often requires more direct intervention to relieve the closed lock and restricted opening. Procedures like arthrocentesis, which involves flushing the joint space with fluid, are commonly used to improve mobility and wash out inflammatory mediators.
Later stages, Stage IV and Stage V, which involve chronic displacement and significant bony changes, often indicate a failure of conservative therapy and may necessitate more definitive surgical solutions. Arthroscopy (keyhole surgery) or open joint surgery may be considered to address the advanced pathology, such as repairing or removing the severely deformed disc, correcting osseous deformities, or addressing perforations.