Condylar Hyperplasia (CH) is a condition characterized by excessive, prolonged growth of the lower jawbone, or mandible. This overgrowth primarily affects the mandibular condyle, which is the rounded end of the jaw that connects to the skull at the temporomandibular joint (TMJ). The result of this disproportionate growth is a progressive facial asymmetry, where one side of the face becomes noticeably larger or longer than the other.
Understanding the Mandibular Condyle
The mandibular condyle is a crucial part of the temporomandibular joint, acting as the primary growth center for the lower jaw after birth. It is composed of a specialized type of cartilage that continues to grow and shape the mandible through childhood and adolescence. Normal jaw growth is a carefully balanced process, with both condyles growing symmetrically until skeletal maturity is reached, typically in late adolescence or early adulthood.
Condylar hyperplasia develops when this normal growth process becomes disrupted, causing growth to continue past the usual time frame or to occur at an accelerated rate. Since the condition is usually unilateral, meaning it affects only one side, the excessive growth on the affected side leads to a lengthening of the entire jaw on that side. This uncontrolled proliferation of cartilage and bone results in the physical manifestations of the disorder.
Prevalence and Classification
Condylar hyperplasia is generally considered a rare disorder in the overall population, although precise, large-scale prevalence data is difficult to establish. A rough administrative estimate suggests the condition may affect between 2.4 to 9.6 individuals per 100,000 people annually, highlighting its relative infrequency. The condition is most commonly diagnosed in adolescents and young adults, typically between the ages of 10 and 30, when the body is undergoing significant growth spurts.
While uncommon, condylar hyperplasia is a frequent finding among patients presenting with facial asymmetry, accounting for an estimated 30% to 50% of these cases in specialized clinics. Clinicians often categorize the condition based on the pattern of abnormal growth, which helps guide treatment planning. One widely used system classifies the condition into two primary types: hemimandibular elongation and hemimandibular hyperplasia.
Hemimandibular elongation is characterized by excessive growth in the horizontal direction, causing the entire jaw to lengthen and the chin to deviate away from the affected side. Conversely, hemimandibular hyperplasia involves a larger, more vertical overgrowth of the condyle and its neck, resulting in a generally enlarged half of the face. These classifications help distinguish the underlying growth pattern, which determines the specific surgical approach required to correct the deformity.
Recognizing the Physical Manifestations
The most apparent sign of condylar hyperplasia is a progressively worsening facial asymmetry. Because the condition typically affects only one side, the lower third of the face appears longer and fuller on the affected side. This excessive growth also forces the chin to deviate noticeably toward the unaffected side of the face.
The overgrowth also disrupts the patient’s bite, leading to various forms of malocclusion. In cases of hemimandibular elongation, the horizontal growth often results in a posterior crossbite, where the upper teeth sit inside the lower teeth on the side opposite the overgrowth. Alternatively, the vertical overgrowth seen in hemimandibular hyperplasia frequently causes an anterior open bite, where the front upper and lower teeth cannot touch. Although the condition is often painless, some patients may experience functional issues like clicking, restricted movement, or discomfort in the temporomandibular joint.
Management and Treatment Pathways
The management of condylar hyperplasia begins with determining whether the condition is still actively growing or has become inactive. This distinction is crucial because the treatment strategy changes significantly depending on the growth status. A single-photon emission computed tomography (SPECT) bone scan is the most common diagnostic tool used to assess activity, identifying areas of increased bone metabolism. An uptake difference of 10% or more between the two condyles typically indicates active growth.
If the condition is confirmed to be active and progressive, the primary goal is to stop the abnormal growth, usually through a surgical procedure called a condylectomy. This involves removing the excessive growth center of the condyle, often through a high condylectomy or a smaller condylar shaving procedure. Once the growth is arrested, or if the condition is already inactive, the focus shifts to correcting the resulting facial and dental deformities.
Correction of the asymmetry and malocclusion typically involves a combination of orthodontics and orthognathic surgery, which repositions the jawbones. This corrective surgery, often performed after growth has ceased, aims to restore facial symmetry and a functional bite. In certain cases of mild asymmetry where the bite is unaffected, a less invasive procedure to reduce the height of the lower border of the jaw may be used to improve the facial contour.