Effects of anterior cruciate ligament (ACL) injury on postural control and muscle activity of head, neck and trunk muscles S. TECCO*, V. SALINI † , V. CALVISI ‡ , C. COLUCCI † , C. A. ORSO † , F. FESTA* & M. D’ATTILIO* Departments of *Oral Sciences and † Orthopaedy and Traumatology, University ‘G.d’Annunzio’, Chieti/Pescara and ‡ Department of Orthopaedy and Traumatology, University de L’Aquila, L’Aquila, Italy SUMMARY The aim of the study was to evaluate the effects that an anterior cruciate ligament injury of the knee has on postural control and activity of neck, head and trunk muscles to investigate the existence of connections between the masticatory system and body posture. Surface electromyograph- ic activity of the muscles at mandibular rest posi- tion, and during maximal voluntary clenching and posturometric and stabilometric measurements of 25 adult patients having pathology on the left knee were compared with a control non-pathological group. At rest, the patients showed a higher mus- cular activity of anterior temporalis, masseter, ster- nocleidomastoid and lower trapezius, compared with the control subjects (P <0Æ05). At maximal voluntary clenching, the patients showed a lower muscular activity of the right anterior temporalis and masseter and a higher muscular activity of the lower trapezius, compared with the control sub- jects. For the stabilometric measurements, all the subjects showed a significant reduction in the postural centre of pressure path length during the test with eyes open and cotton rolls, compared with the test with eyes closed and mandibular rest position (P <0Æ05). In addition, the patients showed a significant displacement of the postural centre of pressure in a forward direction (P <0Æ05) and into the right side (P <0Æ05), compared with the control subjects. Anterior cruciate ligament injury appears to be associated to a change in the activity of head, neck and trunk muscles and to a change in the position of the postural centre of pressure. Cotton rolls seem to improve the stability of the subject. KEYWORDS: anterior cruciate ligament (ACL) of the knee, body posture, head, neck and trunk muscles, stabilometry, surface electromyography Accepted for publication 24 September 2005 Introduction The existence of connections between the masticatory system and the body posture has been discussed previously (1–15). Part of these studies showed that an alteration of the body muscular equilibrium can influence both the mandibular position (4–9) and the facial morphology (10). To date, the dental literature includes several articles on the influence of head and body postures on mandibular rest position and range of functional movements (4, 11–12). Then, Mintz observed that temporomandibular joint (TMJ) disorders can develop because of an orthopaedic postural prob- lem (13). He found that a severe back injury or chronic lower back problems may alter the position of the cranium and finally result in a mandibular malposture, which can affect the muscles of mastication and cause spasm or chronic irritation. By this mechanism, it may be understood that a TMJ dysfunction can also be caused by a repetitive maintenance of an unorthodox position during a job or/and an exercise that may tend to overstimulate any of the muscles in the previously described chain reaction. However, other authors sug- gested that body postural control does not influence mandibular rest position in young adults without occlusal problems, as the range of body postural changes that can be compensated for is generally greater in subjects without occlusal problems, than in ª 2006 Blackwell Publishing Ltd doi: 10.1111/j.1365-2842.2005.01592.x Journal of Oral Rehabilitation 2006 33; 576–587