Speaking as a clinician that often sees patients several weeks, even months after they have been involved in a traumatic event such as an automobile accident, I believe that temporomandibular joint trauma is an injury that is often overlooked in patients transported to the emergency room following the traumatic episode. The incidence of this type of injury would appear to be relatively high in automotive trauma cases, but it is seems that it is not routinely investigated as a potential injury, nor treated with much intensity in the vast majority of victims. It is assumed that this seeming neglect may be: (1.) related to the fact that many victims of automotive accidents may often sustain severe injuries to the limbs and body that require immediate and focused medical attention to ensure the victim's survival rather than to true omission, and (2.) that there is really not much that the emergency room physician, or anyone else in the hospital environment can offer in regard to the immediate treatment of this type of injury. The purpose of this paper is not to criticize anyone involved with helping people who are victims of trauma, but to direct attention towards a particular type of injury that appears to be given a form of second class status in the immediate post-trauma time frame. Temporomandibular joint trauma commonly presents it's unique type of aggravation to the trauma victim at a time when it is clear they have been successfully guided through what may have been life-threatening injuries and have supposedly arrived at a less dramatic period in the recuperative process when the plaster casts and bandages have been removed and they should be thinking about resuming normal life. A study at the University of Toronto in 1992 (1) found that patients who developed TMD following an automotive accident were among the most difficult to treat both from the viewpoint of response to therapy and length of treatment, and often showed cognitive impairments including depression, similar to symptoms seen in patients with post-concussion syndrome.

It is relatively easy to understand how trauma injury to the jaw joints could occur when an accident victim's face is suddenly propelled into the steering wheel, into the dashboard, or even into another individual inside the vehicle. What is harder to envision is the effect that a violent change of direction can have on the same structures - even without a direct impact into another object, or portion of the car interior. Significant trauma is possible due to sudden acceleration, or sudden deceleration of the head in medium velocity incidents like automotive crashes. Medium velocity incidents should be defined as those traumatic events which occur at, or near the relative velocity at which automotive vehicles travel, and run into themselves and other objects, and for the sake of this discussion, can be thought of being anywhere between 20 and 60 miles per hour, or roughly 30 to 88 feet per second. Vehicular accidents can occur at velocities both above and below these limits, and are only limited by the creativity of their participants.

Mandibular whiplash is a very specific injury that can occur alone, in concert with cervical whiplash, or along with any other traumatic injuries. Cervical whiplash injury is considered to be the result of sudden violent change in the direction of motion of the head and neck that can occur in relatively low velocity automotive collisions. It is most often associated with impact coming from the rear of the victim's auto, but can also occur when impact comes from any direction. Whiplash injuries can even take place in the arms, hands, and fingers given the right set of circumstance. Newtonian physics states that a body in motion (in a certain direction) tends to stay in motion (in that direction). In the typical rear end collision often associated with the cervical whiplash the sudden forward acceleration imparted to the physical mass of the victim's automobile, and by direct extension, his body, by the collision process results in the head being suddenly, and perhaps violently, hyper extended on the cervical spine. The victim's body moves with the rest of the auto in the direction imparted to it by the impacting vehicle because it is usually firmly seated and supported by the contours of the seat itself. In actuality, the head tends to stay exactly where it was in space at the time of the initial impact and the automobile, seat, and seat supported body of the victim are all propelled to a different position in space. At the same time, the mandible, because it is somewhat free to move independently of the head, also tends to keep moving in the original direction, usually toward the front of the vehicle. Because collisions with the victims auto can take place from any relative direction of the compass, violent forces can come from any original direction, and indeed, many other subsequent directions during any single automotive collision. The physical analysis of the potentially damaging effects of these forces on the victim's head , jaw, and neck are very complex to say the least. Every traumatic incident produces it's own unique set of circumstances for the unfortunate victim, and the precise type of injury, degree of injury, and degree of morbidity that results can be just as variable.

Unlike other joints in several ways, the temporomandibular joint has a sliding as well as a rotational motion during function. Because of the requirements associated with the sliding movement, the joint does not have a complete fibrous capsule, or binding structure, all around the periphery. The anterior, or forward-most area of the joint has an incomplete capsule that allows the condyle the freedom to slide forward and downward on the articular eminence of the skull. It is possible, especially under the unusual circumstances seen in automotive accidents, for condyles to be forced completely forward, even out of the joint socket in the skull by the forces produced during a relatively mild collision. Normal range of motion would rarely, if ever, encroach on this portion of the joint capsule, but an abnormal set of circumstances could result in the condyles being violently drawn beyond the normal range of motion. For example, placing the sharp point of a stevedore's cargo hook into the bone behind the chin and pulling forward with vigor might result in sufficient movement to bring the condyles out of their normal relation. It should be easy to envision that scene and the forces that could be applied by the person on the handle of the hook. What that represents is just plain brute force in action, but of relatively low velocity. Remember the Newtonian physics referred to above, e.g., a body in motion tending to stay in motion. A mandible, with it's associated appurtenances of facial tissues, teeth and tongue might weigh something like one pound, possible a pound and a half. Consider that mass, loosely constrained, and in it's normal attachment to the head traveling along at about , say 30 miles per hour. Suddenly, the head portion (forehead) runs into a large tree limb hanging down in the path. What is going to happen to the mandible, forgetting what is going to happen to the forehead? Of course, it is going to tend to keep moving in the original direction at 30 miles per hour. But what importance can that have? Now envision a carpenter's hammer...weight, or mass, in this case, usually about one pound (16 oz). For the sake of illustration, put your left hand on the table and very carefully, and with predetermined accuracy, take that same hammer in your right hand and give it an acceleration to 30 miles per hour toward your left hand. What do you think the net result of that action is going to be - especially if you were dumb enough to actually keep your left hand on the table? Another example illustrating the physical effects of much the same overall velocity of 30 miles per hour would be jumping off of a three story building. Whether this jump in terminated on dirt, or a concrete sidewalk, the physical effect is about the same when it comes to analyzing the effect of a body in motion coming to a sudden halt. Beginning to get the point? Physics is unforgiving! Always was, and always will be.

First of all, the normal anatomy of the joint usually presupposes that a small, roughly dime sized disc of articular fibrocartilage is interposed between the football-shaped condyles and their bony sockets in the skull (fossi). That is probably the usual starting point for maybe 50% of the populace, the others usually having some degree of abnormal articular disc-condyle relationship due to many other factors beyond their control. This would seem to indicate that many people can go through life with an abnormal disc/condyle relation, but do not necessarily have any pain or dysfunction as a result. The articular disc itself is a relatively tiny mass when compared to the whole mandible, and is normally elastically attached to the condyle toward the medial and lateral poles. One image to keep in mind is the way a handle attaches to a bucket. The disc can slide back and forth over the condyle in an arc similar to the way the bucket handle moves in an arc.

While a joint such as a knuckle has a tough connective tissue capsule completely surrounding the joint, condyles are somewhat loosely attached to the surrounding joint structure in the skull with relatively thin and weak capsular ligaments. The anterior, or forward facing portion of these joints does not have a complete capsule surrounding the joint parts. Remember, the purpose of this apparent structural weakness is to allow the sliding motion that normally occurs on opening.

Consider what happens when the mandible is violently snapped forward as described above. Are the condyles going to make this violent readjustment of position while still maintaining a "normal" relation with the articular discs and the capsular ligaments, or are they going to possibly tend to leave the discs, as well as capsular ligaments, behind, in the dust, so to speak? Also, in the process, would the normal constraints on condylar motion tend to be somewhat strained? Remember that one pound hammer? Envision that a piece of string, possibly made of nylon or polyester, was suspended 6-8 inches above your left hand. Would you bet that string would be sufficient to stop that onrushing hammerhead before it actually hit you hand? Or would you still do your best to get the hand out of the way? No question about it, you'd be crazy to keep your hand as such an inviting target. Without any doubt that hammer would go through that string faster than a congressional pay raise. Unfortunately, in the vehicular trauma situation, the victim almost never gets a break, and that mandibular "hammer" can tear right through the capsular restraints (the string) as a simple Newtonian system in action. The one pound mass, once put into motion in a certain direction tends to stay in motion in that direction. Practically speaking, there are limits placed on the system in most cases where the mandible has to reach some limit of movement. These limiting factors are the joint capsule, the muscles, and eventually even the fascia and skin of the lower face. The posterior restraints on the articular discs are rarely exceeded because of elasticity and lack of mass, but the condyles have no such restraint and may bring the discs with them because of their lateral and medial polar attachments. Velocity is the major factor in analyzing the whole system. When the velocity of any incident reaches a certain point, it is easy to see that the mandibular mass could easily exceed any constraints placed on it by mere human tissues and end up quite a ways away from the scene.

To further complicate the whole issue, add the additional possibilities that come into play with sudden changes in the direction of applied forces after the initial impact. The realization that the forces directed at the victim can be applied many times over during the same incident, especially if the victims vehicle proceeds to inconveniently roll over a nearby embankment, or bashes into a nearby immovable object, and you begin to appreciate the potential for damages that can occur to just one small part of the human anatomy. The level of the forces applied, the direction of force application, and the number of times that force is applied in a small period of time can eventually add up and result in a serious problem.

The results of sudden changes in velocity and direction are most dramatic in the case of aircraft crashes. An impact at 300+ miles per hour into a mountainside and that mandible being discussed may keep going forward - possibly even several hundred feet beyond where the rest of the head effectively comes to a stop. In these crashes bodies are pulverized to the extent that teams of forensic experts may spend weeks examining and assembling assorted parts in order to place them with the proper victim, e.g. U.S. Air Flight 427 in Pittsburgh in September, 1994. Automobile trauma is seldom as dramatic when compared to airplane crashes, but the simple act of surviving the automobile crash often has long-term repercussions that are never problems to those who are victims of the later.

When the mandible is suddenly accelerates away from the rest of the skull in the initial milliseconds of the crash, it can actually tear the joint capsule as a simple application of the physics described before. The mandibular condyles, being part of the total structure can violently pinch, one, or both articular discs between themselves and the slopes of the articular eminences of the skull. This "pinch" can assume the seriousness of a hammer blow, or it can be of lesser violence, again depending on the factor of velocity. This pinching, besides causing damage to the cartilage lining of the bony portions of the joinsts can also cause violent impingement of any tissues caught between the hard parts. This sudden impact can minimally produce bruising of the discs or marginal tissues, or, in the case where a partial disc dislocation may already exist (remember, this can be the case in a significant number of people to begin with ) can produce a hematoma (bruising), and even varying degrees of crushing of the marginal attachment, or disc itself. Maceration, or crushing, of the tissues can lead to the eventual development of a frank perforation of the articular cartilage disc and associated tissues immediately, or at some time after the injury.

It is generally accepted that damaged cartilage surfaces within the joint are unrepairable by normal healing processes in adults (2), so these injuries do not improve with the passage of time. Remember when we established that the mandible had a mass of somewhere between a pound and possibly a pound-and-a -half, and we compared that to the carpenter's hammer? A "loose cannon" of this mass, accelerated at the velocities often encountered in the typical auto crash is capable of doing severe injury to associated joint parts even without reaching levels of force where nearby bone (condylar neck) exceeds it's elastic limits and fractures.

It is easy to envision the fact that direct blows, even multiple direct blows, can often occur during the same violent incident, especially when the victim's head happens to strike interior portions of the car, or other occupants. Imagine a side impact collision where the victims auto proceeds to roll over several times. The best image would be somewhat similar to what you would see looking through the window of a clothes dryer in action. Speed up the action, however. The opportunities for the production of significant temporomandibular joint trauma are numerous, and few victims have enough retained awareness of the incident afterwards to remember just what did happen to them during their particular crack up.

Another set of conditions come into play during the second portion of the classic whiplash incident. The first is when the head and neck appear to be violently thrown toward the rear of the car. Remember the Newtonian physics? Actually, the head, attached to the somewhat flexible neck, tends to stay where it was in space - but the rest of the automobile, plus the victim's body, is suddenly driven forward by the rear-impacting vehicle giving much the same impression to the victim. The mandible and condyle, after first having the rear wall of the joint fossa appear to leap forward to violent contact, also tends to stay where it was during the moment of impact, but the rest of the head and neck tend to then be accelerated violently to the rear. The net effect is that the mandible appears to first slam backward to contact with the rear wall of the joint fossa, then to instantly change direction to follow the rest of the head, and then to keep going in the forward direction for another short period of time until it reaches the limits of it's constraints.

Cartoon characters make excellent illustrations of physics in action. When a speeding Daffy Duck runs, neck first, into a protruding fence rail, his neck stops, and his head and body stretch out until Daffy's cartoon based elastic limit is reached. The rebound portion of Daffy's encounter with the rail bring head and body back toward the point of impact, often with a little embellishment of the action. Thus, the victim's head apparently remains stationary, and his mandible is being violently thrown forward. His mandibular condyles seem to apparently accelerate forward up the slopes of the articular eminences of their sockets in the skull. Unhappily, any soft tissues trapped between these violently disturbed bony structures may end up being pinched, or even crushed. This is only a partial description of the effects seen in the first few microseconds of the whiplash event when natural laws assert themselves into the situation. Simple physics in action. The end result of the application of physical forces according to the laws of physics can be immediate damage to the internal parts of the temporomandibular joints. This damage occurs first to the relatively thin cartilage surfaces of the condyle and fossa, which can easily be crushed, or the damage may be to the fibrocartilagenous articular disc itself. Immediately posterior to the condyle is an area of tissue that is loaded with numerous fine blood vessels and nerves. Traumatic impingement on this tissue often leads to development of additional symtoms such as vertigo. Assessing the degree of damage resulting from any single occurrence is difficult because every accident has it's own peculiar set of causative factors. Some people are basically tougher than other people. Some people are luckier. Unfortunately, this realization of multifactorial causation does not end the episode.

Now that you have an appreciation of the first part of the picture, we have the rebound portion of the incident to consider. Once the head and neck reach the maximum rearward portion of their initial reaction, the next phase of the action is a forward rebound. If it is of significant magnitude, this rebound can result in the victim's head and face impacting into the steering wheel, dash, or other parts of the automobile. Often some of this reaction is intercepted and modified by the presence of seat belts and shoulder restraints, but even when these items are in use and doing their job, the victim's head is not restrained and is thrown forward and flexes toward the chest. In incidents where the violence of the impact is sufficient, the chin can impact on the chest wall. This reaction can be very insignificant, or it can, again, be a violent impact on the mandible with the whole mass of the head swinging along behind it like a ten pound hammer. Under this scenario, the force generated is transmitted through the mandible toward the temporomandibular joints. Depending on the level of this force, the result, as far as the temporomandibular joint structures is concerned, can vary from a negligible effect, to a severely traumatic event, e.g. ,with bruising, maceration of tissues, or even fracture of the condylar neck, or on to any of several degrees of seriousness. Any trauma that produces internal bleeding and an organized blood clot within the joint spaces can, as a result of normal healing, produce a fibrous tag, or a fibrous adhesion between the condyle and disc, or the disc and the fossa. Adhesions, or fibrous tags severely limit the normal motion of the joint and can greatly interfere with normal joint functioning. Adhesions usually develop when the blood clot formed "matures" in the normal healing process to form scar tissue, but adhesions generally take the form of the tissue type closest to the lesion, so the case of a joint, the adhesion can be scar tissue, excessive synovial tissue, cartilage or bone.

The relatively poor blood supply to the fibrocartilage articular disc, as well as to the fibrocartilage lining the surface of the condyle and fossa, almost guarantees future chronic problems after any crushing, or macerating injury. Incomplete fractures of the condylar neck (green stick fracture) would probably have the best chance of uneventful bone healing, but forces sufficient to cause the initial fracture would positively have crushing, or macerating effect on the cartilage surfaces lining the surface of the condyle and this injury never heals.

Condylar fractures can occur as the result of any part of the conditions described above. Condylar fractures that are severe enough to allow the broken segment to displace freely are then further complicated by the action of the attachment of the superior head of the external pterygoid muscle to the condyle and articular disc. This muscular action tends to draw the broken condylar segment forward, downward, and medially. In effect, this functionally destroys the function of the joint as a simple hinge and results in the total imbalance of the joint and the whole mandible.

The mandible is unique among the bones of the body in that it has the same functional joint on both of it's ends. The two temporomandibular joints form, in effect, two legs of a tripod, and the teeth are assumed to form the third. Losing one leg of a tripod results in a totally unstable situation. Just as your Nikon, or favorite Camcorder would tend to rush earthward toward the imbalanced leg, so would the mandible tend to shift out of a normally balanced condition toward the side showing the loss of support. Instead of gravity as the main unbalancing and destructive force, the mandible responds to the imbalance created in the musculature. The net result is a functional disaster to basic jaw functions like chewing, speaking, and swallowing. In addition, the disturbance of normal mandibular muscle function also involves these same muscles in their role as part of the postural system of the head and neck. Therapy for cervical whiplash, alone, cannot address the total muscular problem any more than treatment just directed to the temporomandibular joint apparatus. Physical therapists can't make dental appliances.

The author's personal opinion is that any trauma to the face, or jaws should be classed as at least "keep on observation" for any clinician involved. Any injury to the lower jaw has the potential for turning into a significant problem for the patient at some future time after the incident. Ignoring even relatively minor injury is one sure way to cause the invocation of Murphy and his book of laws.

Significant trauma, or that level of injury that produces visible external bruising as an initial finding, has a high probability of having secondary consequences. Symptoms may begin immediately, but it is not uncommon to have them begin to be noticed within a few hours of injury. Again, the onset of symptoms does not have to coincide with the immediate injury. Symptoms may not fully develop for many weeks, even months, after the injury. Why? Because everyone has some capability to tolerate a minor injury for an individual's own period of tolerance. That coping ability varies with the individual, and must be recognized as an important factor in the future consequence of any injury.

The condyle is considered to be an important growth center for the mandible. A condylar fracture in a growing individual can have disastrous consequences on facial growth producing degrees of visible facial asymmetry depending on when the injury takes place. This is another way of saying that a condylar fracture at age 8 is potentially much more damaging to the individual than one at age 18. Unfortunately, this is another area where proper treatment is rarely given, or allowance made for correcting growth problems when the child matures. Typically, combined surgical and/or orthodontic correction of facial asymmetry is the only solution after the fact, and if an accidental injury is only thought of as of immediate concern, the individual is often left without proper financial resources when the need for orthognathic surgery arrives in the late teen years.

© R. E. Brossman 1995

References Cited:

1. Tenenbaum, H. Cited from A. D. A. News, J. A. D. A., 124:22-23, October, 1993.

2. Hasselbacher, P. Joints. Normal structure and function, in Kelly, W. N. (ed.) Textbook of Internal Medicine, Philadelphia, PA, Lippincott, 1989, pp: 968-971.