5MRI and autopsy sections: upper row oblique sagittal MRI, asymptomatic volunteer: left lateral, middle medial, rightopened mouth
6Internal Derangements General orthopedic term implying a mechanical fault that interferes with the smooth action of a jointThe most common internal derangement is disc displacementClinical FeaturesClicking sounds from joint(s)Restricted or normal mouth opening capacityDeviation on openingPain
7Internal Derangements Imaging FeaturesAnterior disc displacement: posterior band of the disc located anterior to the superior portion of the condyle at closed mouth on oblique sagittal imagesDisc may have normal (biconcave) or deformed morphologyIn opened mouth position disc may be in a normal position (“with reduction”) or continue to be displaced (“without reduction”)
8Partial anterior disc displacement at baseline lateral sectionscentral sectionsopen-mouth
13Osteoarthritis Definition Non-inflammatory focal degenerative disorder of synovial joints, primarily affecting articular cartilage and sub-condylar bone; initiated by deterioration of articular soft-tissue cover and exposure of bone.Clinical FeaturesCrepitation sounds from joint(s)Restricted or normal mouth opening capacityPain or no pain from joint areas and/or of mastication musclesOccasionally, joints may show inflammatory signsWomen more frequent than men
14anteriorly displaced and deformed, degenerated disc and irregular cortical outline with osteophytosis and sclerosis of condyle .
15Advanced osteoarthritis and anterior disc displacement, with joint effusion
16Bone Marrow Abnormalities DefinitionBone marrow edema: serum proteins within marrow interstitium surrounded by normal hematopoietic marrow.Osteonecrosis: complete loss of hematopoietic marrow.
17Imaging FeaturesAbnormal signal on T2-weighted image fromcondyle marrow: increased signal indicates marrow edema; reduced signal indicates marrow sclerosis or fibrosisCombination of marrow edema signal and marrow sclerosis signal in condyle most reliable sign for histologic diagnosis of osteonecrosisMarrow sclerosis signal may indicate advancedosteoarthritis without osteonecrosis, or osteonecrosis
18Arthritides Definition Inflammation of synovial membrane characterized by edema, cellular accumulation, and synovial proliferation (villous formation).Clinical FeaturesSwelling of joint area, not frequently seen in TMJPain (in active disease) from jointsRestricted mouth opening capacityMorning stiffness, in particular stiff neckDental occlusion problems; “my bite doesn’t fit”Crepitation due to secondary osteoarthritis
20Rheumatoid arthritis. A MRI shows completely destroyed disc, replaced by fibrous or vascular pannus and cortical punched-out erosion (arrow) with sclerosis in condyle.
21Psoriatic arthropathy Psoriatic arthropathy. Oblique coronal and oblique sagittal CT images show punched-out erosion in lateral part of condyle (arrow).Psoriatic arthropathy. MRI shows contrast enhancementwithin bone erosion and in joint space, consistent with thickened synovium/pannus formation. OpenmouthMRI shows reduced condylar translation but normallylocated disc (and normal bone in this section)
27Inflammatory or Tumor-like Conditions Calcium Pyrophosphate Dehydrate CrystalDeposition Disease (Pseudogout)
28Benign Tumors Synovial Chondromatosis Benign tumor characterized by cartilaginous metaplasia of synovial membrane, usually in knee, producing small nodules of cartilage, which essentially separate from membrane to become loose bodies that may ossify.