TEMPOROMANDIBULAR-JOINT INJURY POTENTIAL IMPOSED BY THE LOW-VELOCITY EXTENSION-FLEXION MANEUVER

Purpose: It has been proposed that significant temporomandibular joint injury can occur as a result of rapid extension-flexion motion of the neck (whiplash). This motion, which is experienced by passengers in v ehicles that undergo rear-end collisions, has been described as causin g rapid protrusion and opening of the mandible. It has been speculated that this relative motion between the mandible and the cranium produc es forces at the temporomandibular joint (TMJ) that injure the articul ar elements. The objective of this study was to measure these forces b y an experimental method. Materials and Methods: Accelerometer sensor and high-speed cinematographic data were obtained from the kinematic r esponses of live human test subjects positioned as occupants in motor vehicles that underwent staged low-velocity rear-end collisions. Linea r and moment forces generated at the TMJs were obtained from the resul tant acceleration pulse at the craniomandibular complex, estimation of the mass properties of the mandible and its appended soft tissues, an d the application of Newton's Second Law of motion. Results: The maxim um linear forces generated at the TMJ in a rear-end collision resultin g in a velocity change of the test subject of 8 km/h (5 mph) were in t he 7 to 10 N (1.6 to 2.2 lb) range, Moment forces at the joint peaked briefly at 0.55 N.m (4.87 lb-in.). Conclusions: These force magnitudes generated at the TMJ constitute a minor fraction of the forces experi enced at the joint during normal physiologic function, It is a conclus ion of this study that injuries to the TMJ attributed to low-velocity ''whiplash'' cannot be accounted for by the joint forces produced by t his maneuver.