Reduced jaw opening produced by shortening of the muscles gives a “too soft” endfeel during passive jaw opening (Groot Landeweer and Bumann 1991. Stengenge et al 1993).
• A “too hard” endfeel indicates a shortened capsule (Bumann et al. 1993). This finding can be corroborated by testing the endfeels from anterior translation and in ferior traction (Fig. 201ff).
• A “rebounding” endfeel is evidence of a nonreducing disk displacement (Fig. 160). This can be verified through MRI. However, a nonreducing disk displacement seen on a MRI is not necessarily the cause of restricted movement. Therefore the MRI cannot be relied upon as the primary diagnostic tool.
• A “bony” endfeel indicates osseous changes. Disrupted innervation can be ruled out through isometric contraction of the jaw-opening muscles.
Examination of the Joint Surfaces
The functional articulating surfaces of the temporomandibular joint are the fibrocartilaginous articular portions of the temporal bone and the condylar process of the mandible as well as the articular disk. Because the resultant force of the muscles of mastication is directed anterosuperiorly (Chen and Xu 1994), this is where the functional joint surfaces are found.
The proteoglycans in the fibrous cartilage are responsible for the disk’s resistance to compression (Kopp 1978, Axels-son et al. 1992). Although a reduced content of proteoglycan significantly alters the compressive characteristics of cartilage, it has no negative effect on its frictional properties (Pickard et al. 1998). The ability of the joint surfaces to deform serves to cushion and distribute peaks of stress. It also helps lubricate the contacting joint surfaces to minimize friction and wear (Mow et al. 1993, Murakami et al. 1998). The conformity of the joint surfaces plays a decisive role in the lubrication process (Nickel and McLachlan 1994b). The coefficient of friction of a healthy joint is 0.007. Lavage can cause this to increase three-fold, and following introduction of hyaluronic acid friction is reduced again by half(Mabuchi et al. 1994).
162 Form for recording signs and symptoms
Excerpt from the manual functional analysis examination form for recording the results of the dynamic compression and dynamic translation tests for the current degree of adaptation of the joint surfaces. The upper row is for the results of the dynamic compression test and the lower row is for the dynamic translation test. With these findings one can differentiate between osteoarthrosis, osteoarthritis, and capsulitis of the bilaminar zone with nonreducing disk displacement.
The joint surfaces in the temporomandibular joint become deformed when loaded (Moffet 1984). Destructive changes in the joint surfaces occur six to eight times more frequently in women than in men (Toller 1973, Rasmussen 1981, Tegelberg and Kopp 1987), which indicates that either the adaptability of women’s joints is less or the harmful influences are stronger. The effect of a force depends on its amplitude, frequency, and duration (Gradishar and Porterfield 1989, Bell 1990).
Motion reduces the deforming effects. Conversely, restrictions of movement intensify the deforming effects. As long as the adaptability of the tissue is not exceeded, the articulating surfaces of the temporal bone and condyle can become remodeled (adapted), but otherwise degenerative changes will occur in the joint surfaces (Moffet et al. 1964, Solberg 1986, Copray et al. 1988). The capacity for progressive and regressive adaptation of the osseous portions of the joints is present throughout life (Griffen et al. 1975). Surgical osteotomies on one or both jaws are followed by distinct adaptive changes of the condyle in approximately 23% of adult patients (Hoppenreijs et al 1998). Adaptive changes of the condyle and fossa could also be found in more than half the joints after mandibular midline osteodistraction treatment to stimulate osteogenesis (Harper et al. 1997). The disk, on the other hand, is not capable of cellular remodeling (Moffet 1984). Therefore, loading of the disk can produce only reversible (elastic) or irreversible (plastic) deformation.
Histologically, slightly elevated levels of functional loading lead to thickening of the cartilage on the joint surfaces (Muir 1977. Radin et al. 1978). A further increase in loading interferes with fluid exchange and disrupts the supply of nutrients (Gradishar and Porterfield 1989, Haskin et al. 1995), thereby causing increased tissue degeneration (Ateshian and Wang 1995). Short term loading (less than 2 minutes) of the articular cartilage lowers the coefficient of friction, whereas a load applied for 45 minutes causes a five-fold increase in friction! Cyclic short-term loads allow a high water content in the cartilage and are accompanied by reduced friction (Nickel and McLachlan 1994a). Neither occlusal attrition nor the thickness of the cortical layer of bone as seen in a radiograph provides any reliable indication of the current thickness of the fibrocartilaginous joint surfaces (Pullinger et al. 1990). Contours of the bone seen on the radiograph do not correspond to the actual contours of the joint surfaces!
A noninvasive determination of the stages of regressive adaptation of the joint surfaces can only be made clinically, not by imaging procedures. For this we use the so-called dynamic compression and dynamic medial and lateral translation (sometimes with compression). The fundamentals and clinical procedures are described on the following pages.
163 Examination techniques and their usefulness in differentiating between injuries/lesions of the joint surfaces
Active movements, dynamic compressions, and medial and lateral dynamic translations are all used to serve as nonmanipulated references for specific testing of the joint surfaces. Through the findings from the dynamic compression test it is possible to conclude whether there is an adapted joint surface, osteoarthrosis, osteoarthritis, or capsulitis of the bilaminar zone in the presence of a nonreducing disk displacement (pp. 70–74). Use of the dynamic translation test permits further determination of whether a regressive adaptation and its associated loading vector lie more medially or laterally. This knowledge is essential later during clinical testing of influences to determine whether or not there is a causal relation with occlusal disturbances.
Frequently temporomandibular joints with obvious radiographic changes in the bone show only insignificant clinical symptoms or none at all (Mejersjö and Hollender 1984). Because of this the purpose of a specific functional joint-surface test is only to determine whether or not the joint surfaces are adapted or not. Diagnostically and therapeutically, it is of minor importance how the structures are represented by imaging procedures.
There is a close correlation between regressive adaptations of the functional joint surfaces and crepitus (Boering 1994, Hansson and Nilner 1975, Bates 1993, Pereira et a!. 1994). Controlled studies indicate that crepitus is a reliable clinical sign of osteoarthritis (Holmlund and Axelsson 1996). Within a selected group of temporomandibular joint patients, 3-24% were found to exhibit rubbing sounds (Bates et al. 1994, Zarb and Carlsson 1994).
Sometimes the degeneratively altered joint surfaces are also painful. Even though in the 20th embryonic week the disk is supplied with numerous nerve endings, no innervating structures remain to be seen after birth (Ramieri et al. 1996). Therefore the disk can be excluded as a source of pain. As long as the temporal and condylar joint surfaces are still covered with cartilage, they too are unable to give rise to pain. It is only when subchondral bone is exposed that the nociceptors transmit corresponding pain sensations (Quinn 1989, Kamminishi and Davis 1989).
Conventional clinical examination methods can diagnose initial osteoarthrotic changes only with a low degree of specificity and sensitivity. Therefore manual functional analysis employs not only active protruding and opening movements, but also
