Comparison of external load compensation during rhythmic arm movements and rhythmic jaw movements in humans.

Experiments were performed on human elbow flexor and extensor muscles and jaw-opening and -closing muscles to observe the effect on rhythmic movements of sudden loading. The load was provided by an electromagnetic device, which simulated the appearance of a smoothly increasing spring-like load. The responses to this loading were compared in jaw and elbow movements and between expected and unexpected disturbances. All muscles showed electromyographic responses to unexpected perturbations, with latencies of approximately 65 ms in the arm muscles and 25 ms in the jaw. When loading was predictable, anticipatory responses started in arm muscles approximately 200 ms before and in jaw muscles 100 ms before the onset of loading. The reflex responses relative to the anticipatory responses were smaller for the arm muscles than for the jaw muscles. The reflex responses in the arm muscles were the same with unexpected and expected perturbations, whereas anticipation increased the reflex responses in the jaw muscles. Biceps brachii and triceps brachii showed similar sensory-induced responses and similar anticipatory responses. Jaw muscles differed, however, in that the reflex response was stronger in masseter than in digastric. It was concluded that reflex responses in the arm muscles cannot overcome the loading of the arm adequately, which is compensated by a large centrally programmed response when loading is predictable. The jaw muscles, particularly the jaw-closing muscles, tend to respond mainly through reflex loops, even when loading of the jaw is anticipated. The differences between the responses of the arm and the jaw muscles may be related to physical differences. For example, the jaw was decelerated more strongly by the load than the heavier arm. The jaw was decelerated strongly but briefly, <30 ms during jaw closing, indicating that muscle force increased before the onset of reflex activity. Apparently, the force-velocity properties of the jaw muscles have a stabilizing effect on the jaw and have this effect before sensory induced responses occur. The symmetrical responses in biceps and triceps indicate similar motor control of both arm muscles. The differences in reflex activity between masseter and digastric muscle indicate fundamental differences in sensory feedback to the jaw-closing muscle and jaw-opening muscle.

Heterotopic ossification after severe burns: a report of three cases and review of the literature.

Heterotopic ossification (HO) is a rare complication of head and spinal injuries, polio, orthopaedic surgery and burns. Three patients are reported, who developed severe HO following major, life-threatening burn injury. The aetiology, diagnosis and treatment of this condition are discussed. Particular attention is given to measures which may help reduce morbidity.

Squamous cell carcinoma in a tube pedicle forty years after jaw reconstruction.

Forty years following extensive jaw resection for adenocarcinoma in a young man, and innovative mandibular reconstruction, a squamous cell carcinoma developed in the tubed pedicle flap used to provide lining for the floor of the mouth. The case is described and a brief history of the early methods of mandibular reconstruction is presented.

Immediate reconstruction of the helical rim after bite injury using the posterior auricular flap.

A local flap of auriculomastoid skin and subcutaneous tissue, based on the posterior auricular artery, has been used to reconstruct as a primary procedure defects of the helical rim following animal and human bites. The principles of the reconstruction and three illustrative case reports are presented.