TMJ Surgeon: Splints and MRI imaging, Part II. TMJ impingement

The above two coronal scans depict the same TM joint with and without an orthotic or ARA. Note how the device "decompresses" the TM joint disc/capsule when in place in the upper image. The lower image is with the teeth in normal occlusion, in the position during chewing loading of the joint. Note the significant increase in joint space with the orthotic. The left side of each image is the lateral joint regions. Note in the upper image how the joint space is congruous and the lateral attachment of the disc/capsule intact. Compare with images in previous blogs and the images below to discern the difference between a normal joint (above) with no imingement and the images below with impingement.

The previous blog discussed MRI imaging in the 3rd dimension or coronal plane with orthotic devices. (bite splints, ARAs etc.)  When introduced in the 80's, the Schellhas/Wilkes/Piper classifications of TMJ derangements examined two dimensions of imaging information.  These sagittal images formed the cornerstone of a classification systmem which should be used by all clinicians and researchers when communicating responses to treatment of painful and impairing orthopedic joint dysfunction or derangements (Wilkes II-V), whether surgical or non surgical,  when various treatment is studied.

Occasionally, if sagittal imaging is the only imaging obtained, normal scans can be seen, yet the patient still exhibits pain and dysfunction despite a “normal” imaging study.  This can be frustrating for provider and patient.  The following case is an example of misdiagnosis of a “normal”  TMJ MRI imaging study.  The cause of pain and dysfunction can only be appreciated when images in the 3rd dimension or coronal plane are obtained.

This is a case presentation of  a patient with several years instbility of  one TMJ.  Competent non-surgical treatment has been exhausted and yet the patient still can not eat or open the mouth without pain and joint locking.  The sagittal scan appears relatively unremarkable.  If a clinician were to rely only on a two dimensional view of the joint, or a radiologist comment only on this view, the diagnosis would not be that impressive….or would it (?)….what is the cause of the joint instability and pain (?)

The clinician orders the MRI in the coronal plane or 3rd dimension as well.  This is revealing.  The MRI  reveals a significant lateral  impingement in the joint.  Note a growth of bone downward from the lateral rim of the fossa or socket of the joint.  This boney ledge reveals near bone on bone contact between the lateral pole of the condyle and the fossa rim when the teeth are in contact.  Note lack of joint space in the extreme lateral aspects of the joint compared to the central and medial regions of the joint.  The articular disc can be seen between the fossa and condyle curvatures.  (Lateral is the left side of the MRI image)

The MRI is repeated in the coronal plane with the orthotic or the ARA in place.  Note how the joint space increases dramatically in the central and medial aspects, but not in the lateral joint space.  In fact, the image reveals more clearly a developing osteophytic change of the lateral pole of the condyle of the mandible in near contact with the lateral rim of the glenoid fossa.  Note how the cornal plane curvature of the fossa does not match the coronal plane curvature of the mandibular condyle.  Note also the normal disc dimension in the central and medial aspects of the joint but its extreme atrophy laterally….(See blog of surgical relief of an impingement for visualization of what these processes really look like and the damage they cause to the disc capsule)

COMMENT

Clinicians and patients sometimes are frustrated when orthotics and all types of non surgical treatment  does not work or the patient gets worse.  Sometimes the recommended solution is “a different type of splint” designed to “deprogram chronic muscle spasm” in a different way.  Unfortunately, rarely is a true orthopedic problem within the joint suspected  and joints imaged in 3 dimensions.

In reality, an impingement of the human jaw joint is not too dissimilar from impingements that occur in the shoulder joint that create different levels of tearing of the rotator cuff.   Many people are familiar with that orthopedic reality , having experienced the shoulder problem personally or knew of someone who has.  The mechanism for developing impingement in the jaw joint is yet to be worked out, but here are some possibilities.

1.  The jaw is the only bone in the body in which one single bone has a dual joint operating “orthopedic system” that has to be complimentary in all movements of the jaw.  Computer studies of jaw/joint function have shown that on mouth opening, the joint is loaded maximally. (1) Biomechanical studies of the TMJ have shown that tension forces predominate in the joint during maximal joint function.  Bone grows when placed under tension.  It is possible that during periods of orthopedic TMJ dysfunction, tension forces are maximized in the lateral most aspect of the joint, creating stimulus for bone spurring or osteophyte formation.  The mechanism is similar in the shoulder where the 360 degrees of arm rotation and 180 degrees of arm abduction (up/down/lifting) loads placed on the perimeter of the shoulder joint create stimulative tension forces which invite procuction of osteophytes that project from the rim of the shoulder down into the rotator cuff creating arm movement impairment and pain. 

2.  Impingements can be seen in growing patients.  (See blog with MRI of 11 year old patient with developing impingement).  In these cases, it is possible that a congenital or developmental impingement develops due to growth differentials between the base of the skull (TMJ glenoid fossa develops as the base of the skull develops and morphologically is completed its growth/development by age 8-12). (2)  The condyle of the jaw is one of the major growth centers for development of lower jaw growth and generally does not cease its active growth and development until late teens.

A developmental impingement is often first appreciated in adolescents….when patients are going into their most accelerated rate of growth and development…and when final mandibular growth and development is taking place.  A developmental impingement may simply be a mis-match in the width of the fossa from medial to lateral  as it relates to a larger medial/lateral dimension of the condyle and the congruent disc/capsule that is attached to the condyle.  Impingements create a significant increase in points of contact load of these structures, particularly on mouth opening , and rather than distributed load throughout the disc/capsule, it is concentrated , the disc/capsule becomes unstable and vulnerable to  increase in shear damage during mouth opening.

During chewing function, the condyle of the jaw will also move laterally, from side to side as it rotates and loads the joint during chewing loading. This lateral shifting increases in deranged joints. (3) One cardinal sign of an impingement is a joint that becomes more unstable during side to side movement or pain increases with lateral jaw movement toward the side of the expected impingement.

Finally, many studies have confirmed that significant pathologies or early osteoarthritic destructive processes begin in the lateral most aspect of TM joints. (4) This is surmised to be due to biomechanical confirmation movements of force fields from medial to lateral during  joint function and increased loads in this region.  Developmental impingements should be looked for, especially in younger symptomatic patients, who show the same predominance of significant  TMJ derangements in orthodontic studies…..as adult populations in multiple epidemiologic studies. (5)

BIBLIOGRAPHY
1. Tuijt M, Koolstra JH, Lobbezoo F, and Naeje M: Differences in loading of the temporomandibular joint dring opening and closing of the jaw. Jnl of Biomechanics, 43 (2010) 1048-1054.
2. Nickel JC, McLachlan KR, Smith DM: Eminence Development of the postnatal human temporomandibular joint. Journal of Dental Research, 67(6): 896-902, 1988.
3. Gallo LM: Modeling of temporomandibular joint function using MRI and jaw-tracking technologies-mechanics. Cells Tissues Organs (2005); 180:54-68.
4. KondohT, Westesson PL, TakahashiT, et al. : Prevalence of morphologic changes in the surfaces of the temporomandibular joint disc associated with internal derangement. J Oral Maxillofac Surg, 1998; 56: 339-344.
5. Nebbe B, Major,PW: Prevalence of TMJ disc displacement in a pre-orthodontic adolescent sample. Angle Orthod, 2000, 70: 454-463.