Jeffrey C. Posnick, DMD, MD

• It generally affects girls and women who are between the ages of 15 and 35 years.

• It is most frequent among teenage girls during the pubertal growth spurt.

• It typically results in bilateral symmetric condylar involvement followed by stabilization (remission). In the majority of affected individuals, limited further resorption occurs. Unfortunately, in some, a second episode will result in the further loss of condylar height.

• There is no agreed-upon and proven etiology. ICR frequently seems to occur as part of the natural course of events rather than in conjunction with active therapy or treatment. It may also coincide with or be observed during or after active dental restorative, orthodontic, or surgical interventions.

• During the active phase of condylar resorption, TMJ and masticatory muscle discomfort is expected. The active phase often subsides within 6 to 12 months.

• When the condition becomes quiescent, the individual is generally left with satisfactory TMJ function without significant limitations in mouth opening or intracapsular pain. Persistent joint noise is frequent.

• Head and neck functions are likely to be negatively impacted including: chewing; breathing; speech articulation; and body image.

• When the condition is in remission, a cartilaginous cap over an intact cortical rim can generally be documented. A deflated or diminished condylar head is generally seen on imaging (e.g., magnetic resonance imaging or computed tomography scanning). The glenoid fossa and the articular disc typically remain biologically intact.

• Change in the shape of the condylar heads (i.e., flattening and thinning)

• Decrease in condylar height

• Loss of overall posterior facial height

• Mandibular retropositioning with clockwise rotation (high angle)

• Angle Class II anterior open bite, excess overjet malocclusion

Theories of Etiology

The current dominant theory holds that the etiology of ICR is hormonally mitigated, immunologically controlled and may arise in genetically susceptible individuals in conjunction with environmental factors.* Sex hormones are thought to modulate biochemical changes within the TMJ, which may then result in condylar resorption. For some time, it has been suggested that there is alteration in the serum hormonal levels in at least some affected girls and women with ICR.³¹ Gunson and colleagues described endocrine function among women who arrived at their clinic with a history, physical examination, and radiographic findings that were consistent with ICR. The average age at presentation was 26 years (range, 15 to 45 years).³¹ Twenty-five of the 27 patients (93%) had low levels of serum 17-beta estradiol at the mid-menstrual cycle. Two subgroups were further differentiated. The first group did not produce estrogen naturally (8 out of 27 patients), and the second group (19 out of 27 patients) had low 17-beta estradiol levels that were presumed to be the result of oral contraceptive pill usage. The authors theorize that, whether the condition is induced by ethinyl estradiol (i.e., oral contraceptive pills) or by premature ovarian failure, a low circulating 17-beta estradiol serum level negatively affects the natural reparative capacity of the condyles. The authors believe that, when 17-beta estradiol deficiency is coupled with the presence of local factors that cause compressive forces, condylar lysis is more likely to occur and to ultimately result in the observed condition called ICR.^{8,14,27,46,64} Unfortunately, the study did not include a control group for oral contraceptive pill use or precise knowledge of the phase of the menstrual cycle at the time of hormone serum sampling. Although hormone influences no doubt play a role, an autoimmune aspect is also likely.³¹

Gunson and Arnett comment that whatever the underlying etiology of ICR, all bone loss at the condylar level involves a common resorptive pathway that includes cytokine-activated osteoblasts that then recruit and promote the activity of osteoclasts.³² This in turn results in the secretion of enzymes that are responsible for the breakdown of hydroxyapatite and collagen. A case in point is juvenile idiopathic arthritis (ex. polyarticular arthritis, rheumatoid factor positive), which is caused by a B-cell–mediated autoimmune reaction to synovial tissues.^33,80,105 A consequence of this reaction is the presence of local inflammatory cells, which secrete cytokines that cause the activation of osteoblast-mediated osteoclast catabolism.⁸⁹ The end result is bone breakdown through the common resorptive pathway.³⁰ In patients with juvenile idiopathic arthritis (JIA), a current treatment approach is to minimize articular bone loss by using pharmacologic drugs that interfere with specific cytokines and enzymes along the common resorptive pathway rather than open joint or joint replacement procedures. This may include non-steroidal anti-inflammatories (NSAIDS) or other drugs such as methotrexate or a newer class of medications called biologicals. ^{10,35,36,39,48,52,80,105} Gunson and Arnett point out that a similar approach to ICR may prove to be useful.³²

Another theory of the cause of ICR is avascular necrosis of the condyle as a result of the compression of specific vessels that supply the condyle followed by condylysis, loss of condyle height with secondary jaw deformity and malocclusion.16,17,45,62,72,81–84 Piper and Choung had speculated that pathologic compressive forces of the posterior aspect of the condyle on the ligamentous retrodiscal soft tissues constrict the small vessels, thereby limiting circulation to the condyles with resulting in aseptic necrosis that accounts for the observed condylysis in patients with ICR.^17,72 They went on to hypothesize that either a chronically dislocated non-reducing disc or specific patterns of malocclusion may also cause this cycle of events. As an extension of this thinking, preventative open-joint procedures were offered to alleviate the theoretical compression of the condylar circulation. Those of us that are skeptical of the non-reducing disc cause of ICR point out that the almost universally observed bilateral symmetric simultaneous nature of this condition and its occurrence only in females make the theory an improbable explanation.

Clinical Perspectives

The foregoing theories remain unproven, but the effects of estrogen on condylar resorption and repair with or without an autoimmune component seem indisputable. Further studies will be required to determine the additive effects of occlusion and masticatory muscle forces on the TMJ in the presence of hormonal imbalance, autoimmune influences, genetic predisposition and other environmental factors.

Some clinicians suggest that, with a lack of clarity about either the etiology of the condition or the effects of various treatment modalities and without a guaranteed endpoint to the condylar degeneration in any given patient, it is best to remove the affected condyles and either reconstruct them with a costochondral (rib) graft or to remove the whole joint (i.e., the condyle, the disc, and the glenoid fossa) and replace it with an alloplastic total joint. Proponents of a partial or total joint replacement approach to the management of ICR are correct in their thinking that the only way to be certain that a further loss of posterior facial height will not continue is to remove and replace the condyle.55,56,107,110 For the great majority of patients with ICR, joint replacement treatment seems radical on the basis of the following: 1) the unlikely probability of long-term TMJ pain 2) the expected satisfactory long-term mandibular (mouth) opening 3) the expected condylar stabilization (“burn-out”) that is typically seen and 4) the known potential for perioperative complications with invasive open joint procedures and the long-term failure rates of total joint replacement.

Mercuri presents an alternative point of view with a recommendation for total joint replacement to “eliminate the variable issue of ongoing condylar resorption.”55,56 He offers total alloplastic reconstruction as a definitive solution. He also states that the non-alloplastic (biologic) condyle option (e.g., costochondral grafting) requires stabilization of the graft with minimal mobility while integration (union) to the host mandibular occurs. This limits early masticatory muscle rehabilitation, which he feels is contrary to the tenets of physical rehabilitation after joint surgery. The disadvantages of alloplastic total TMJ reconstruction include the following: 1) the cost of the device 2) the expected material wear 3) the potential for long-term instability and failure 4) the incidence of both early and late complications including infections with the associated need for device removal and 5) the fact that alloplastic implants will not follow a patient’s normal growth pattern. Joint replacement advocates admit that patients must be advised that alloplastic total TMJ reconstruction devices are expected to have a limited functional life. In addition, the total joint replacement approach requires the removal of the functional glenoid fossa and disc along with excision of the condylar head, neck, and posterior ramus on both sides.

Recommendations regarding how best to limit progression of condylar resorption and then how to treat the consequences of ICR depend on the clinician’s beliefs about the following 1) the disorder’s likely etiology 2) the effects of malocclusion and the masticatory muscle forces and 3) the natural history of the degenerative process.

Some clinicians speculate that, if “decompressive” TMJ treatment is initiated early during the clinical course of active ICR, then less condylar resorption will occur. Others believe that, after the resorptive process has begun, it runs its course despite any attempt to “unload” the joint. Even with a lack of evidence-based research into the subject, most clinicians recommend attempts to limit mechanical compressive TMJ forces through the use of conservative measures (i.e., splints, muscle relaxants, medications and, diet modifications) in the hopes that less resorption (condylysis) will occur.11,12,19,21,25,37,40,47,63,66,101 Some authors believe that counterclockwise rotation of the maxillomandibular complex as part of the orthognathic correction will increase the compressive condylar forces, whereas others state that it is actually a method of “unloading” the joint.^{20,22,41,44,50,57,61,71,85,88,105,108} I agree with the published studies that document long-term skeletal stability when counterclockwise rotation of the maxillomandibular complex is carried out as part of the correction of mandibular-deficient dentofacial deformity.^74,75,77,109 A common concern is that TMJ “loading” (i.e., the presence of compressive forces) will occur if the condyles are “overseating” or if medial or lateral condylar torquing is allowed to occur during orthognathic surgery.^3–6 Some clinicians speculate that individuals who have persistent TMJ symptoms (e.g., popping, clicking) after the orthodontic treatment and corrective orthognathic surgery are at higher risk for progression.² Most published studies confirm that joint noise (e.g., popping, clicking, grating) is not in itself an indicator of future condylar resorption.^60,87,104

Current Clinical Approach to Correction of the Secondary Jaw Deformities

After the diagnosis of ICR is made, non-invasive measures (e.g., splint therapy, muscle relaxants, medications, and diet modification) to “unload” and “stabilize” the condyles or at least to relieve masticatory muscle hyperactivity and discomfort are initiated. Orthognathic procedures and orthodontic treatment carried out to correct the secondary malocclusion, the facial dysmorphology, and to open the airway are more likely to be maintained if the condylar resorption process has been stable for a period of time.49,77,112 Stability can be documented by minimal ongoing change in the occlusion, an intact cartilaginous cap, and an underlying rim of cortical bone over the partially resorbed condyle. The judicious use of technetium-99m methylene diphosphonate quantitative condylar bone scintigraphy can be a helpful tool for assessing whether or not condylysis is active.^{9,18,26,53,69,70,73,78,90,103} Unfortunately, these and other tests only confirm the current anatomy and activity level; they cannot predict the future.

The resulting maxillomandibular dysmorphology observed in patients with ICR can affect speech, swallowing, chewing, breathing, and lip closure. ICR rarely results in disabling facial or TMJ pain or significant limitations in vertical mouth opening. The observed facial aesthetic consequences of ICR are the result of the maxillo-mandibular changes which distort but do not actually deform the soft-tissue envelope. The overlying soft tissues of the lips, cheeks, and neck and the underlying soft tissues of the tongue and soft palate can be normalized only by correcting the skeletal deformities. The achievement of favorable facial aesthetics and the opening of the airway generally require the surgical repositioning of the maxilla (Le Fort I osteotomy), the mandible (ramus osteotomies), and the chin region (oblique osteotomy). Limiting the surgery to either the maxilla or the mandible with the idea of achieving a more stable occlusal result is not substantiated in the literature and is likely to result in suboptimal results. The key to achieving a successful outcome (i.e., enhanced aesthetics, improved occlusion, and an open airway) for the majority of patients with ICR is to surgically accomplish adequate horizontal advancement of the entire maxillomandibular complex often with counterclockwise rotation.

The suggestion that, for the patient who has experienced ICR, the use of distraction osteogenesis techniques rather than standard orthognathic procedures will achieve a more stable long-term occlusion is not supported by the literature.38,54,68,91,94,95,102 The distraction approach 1) generally limits the region of reconstruction to the mandible 2) it requires greater patient convalescences and compliance, and 3) it may increase (rather than decrease) the compressive forces on the condyles.

When the condylar resorption process is believed to be “burnt out,” a comprehensive approach to correct the secondary deformities that involves an orthodontist, an orthognathic surgeon, a TMJ specialist, and appropriate imaging studies is recommended. Periodontal and restorative dental work may also be needed. Evaluation by a rheumatologist should also be considered. A thorough evaluation of the upper airway is essential to clarify any day and nighttime breathing difficulties. The simultaneous correction of chronic nasal airway obstruction and any baseline obstructive sleep apnea should be a primary objective (see Chapters 10 and 26).

The key to a favorable reconstruction for an individual with end-stage ICR or PCR is to define the functional disability (i.e., breathing, chewing, speech, swallowing, lip closure) and the extent of skeletal dysmorphology. The establishment of a functional occlusion that limits stress in the entire masticatory system without significant centric relation–centric occlusion discrepancies and without parafunctional habits is desirable (see Chapter 9). The successful performance of orthognathic, intranasal, and dental procedures to achieve these objectives represents our standard approach; see the case presentations later in this chapter.

Kaban and colleagues offers an alternative approach when the patient is not willing to take the risk that a degree of resorption may continue or reoccur at some point in the future.24,43,67,92,96–98 The authors completed a retrospective case series of 15 patients with the diagnosis of active bilateral ICR who chose a condylar replacement approach between 1999 and 2004. Each patient underwent bilateral endoscopic-assisted condylectomy and autogenous costochondral graft reconstruction. Patients with the following characteristics were included:

Symptoms such as myofascial pain and occlusal discomfort are managed by splint therapy, physical therapy, muscle relaxants, nonsteroidal anti-inflammatory drugs, and other modalities as indicated. Patients who respond to treatment as documented by the relief of symptoms, no occlusal radiograph changes over a 2-year period, and a negative bone scan begin orthodontic treatment in preparation for standard orthognathic surgery. Patients with active ICR who do not respond to the previously described treatment modalities or who prefer not to follow the protocol for a variety of reasons are considered candidates for condylectomy and costochondral graft reconstruction. Fifteen patients fell into this latter category and underwent bilateral endoscopic condylectomies and costochondral graft reconstruction. None of the 15 study patients suffered significant surgical complications, such as fractures or the erroneous placement of the graft within the fossa. Postoperatively, all patients showed Class I occlusion with no anterior open bite. All patients maintained a clinically acceptable and reproducible occlusion one year later with a mean maximum incisor mouth opening of 39 mm. Kaban and colleagues stressed the importance of making a distinction between active and inactive ICR and the patient’s refusal to wait for the presumed remission of the active condylar resorption phase. Only those who were unwilling to risk recurrence are offered the condylar replacement option; all others undergo a standard orthognathic approach.

Brief Overview of Author’s Current Thinking

With the osteoarthritic condition known as ICR or PCR, after the acute process “runs its course” (i.e., after 6 to 12 months for most individual’s), a degree of bilateral condylar resorption will have occurred. This is typically followed by relative condylar stability, satisfactory range of motion of the mandible, and no significant TMJ limitations. The resulting anterior open bite Class II malocclusion may be responsible for masticatory muscle discomfort during function. Temporary relief of these symptoms with a neutralizing splint is generally possible.

The definitive correction of the secondary maxillomandibular deformity through standard osteotomies in combination with appropriate orthodontics has proven beneficial to improve the occlusion, to open the airway, and to enhance facial aesthetics. Concern about further resorption of the “fragile” condyles is best managed by avoiding masticatory activities that “load” (i.e., compress) the joint and with the use of systemic medications when indicated.³²

The treatment of juvenile idiopathic arthritis (JIA) has improved dramatically during recent years with the advent of disease-modifying anti-rheumatoid drugs. The orthognathic surgeon will encounter patients on a drug regimen that consists of nonsteroidal anti-inflammatory drugs [NSAIDS], glucocorticoids, methotrexate, and biologic agents. In these cases, consultation with a rheumatologist is recommended, but the surgeon should also be aware of these medications, because their presence could affect surgical outcome. Prudent perioperative management of these drugs is necessary to optimize surgical outcome. A balance must be struck between minimizing potential surgical complications and maintaining disease control to prevent further joint damage (i.e., condylar resorption) that would negatively affect the outcome.^41A

To review, ICR should not be managed either as a standard internal derangement or as a typical temporomandibular disorder (TMD). The concept of resolving the problem through either an open-joint procedure or through joint replacement continues to seem off the mark given the known natural history of this entity for the majority of affected individuals. A joint-replacement approach is generally reserved for those few patient who have undergone failed surgical procedures with additive iatrogenic TMJ dysfunction.

Case Presentations