Electromyography of Pectineus Muscle KYOICHI TAKEBE,l MATHIAS VITTI AND JOHN V. BASMAJIAN Regional Rehabilitation Research and Training Center and Department of Anatomy, Emory University, Atlanta, Georgia ABSTRACT Using bipolar fine-wire electrodes, we investigated the function of the pectineus muscle. Electromyography revealed that the main function of pectineus muscle is flexion, adduction and medial (not lateral) rotation of the hip joint. These functions suggest that the spasm of this muscle may be important in the cause of deformities in cerebral palsy. Modern electromyographic studies on the muscles around the hip joint have neglected the role of the pectineus muscle because of its inaccessibility and the proximity to femoral vessels. Most authors agree that it flexes and adducts the hip joint. However, some textbooks (e.g. Woodburne, '65) state that pectineus is mainly an adductor, while Duchenne (1867) and Wells ('69) gave flexion as its main function. Other possible functions have been suggested sporadically and with little or no confirmation. Goss ('69), among others, stated that pectineus rotates the hip medially, although Edwards ('56) and Woodburne accepted the view of Duchenne who believed the opposite. Clinical views of the muscle and its neighbors make it of greater importance than its small size would suggest. Lamb and Pollock ('62) offered iliopsoas and pectineus overactivity as a primary cause of the flexion deformity of the hip joint in children with cerebral palsy. Prompted by these divergent anatomical opinions and growing clinical interest, we undertook a limited electromyographic investigation of the function of the pectineus muscle. Dissections demonstrated the feasibility of percutaneously implanting electrodes without special risk. The pectineus is a thin quadrangular muscle which is the highest adductor. It arises from the superior ramus of the pubis and runs downward, backward and lateralward to insert into a rough line that descends from the lesser trochanter. MATERIALS AND METHODS Two of the investigators acted as subANAT. REC.,180: 281-284. jects. The bipolar fine-wire electrodes (Basmajian and Stecko, '62) were inserted upwards and medially into the muscle 2 cm lateral to the public tubercle and 3 cm below the inguinal ligament. (The needle is removed leaving the 25-micron wires in situ for the duration of experiments.) Action potentials were amplified and recorded on FM magnetic tape. Simultaneously both subject behavior and muscle activity were videotaped by split-screen methods for later validation of results. Records were made according to a protocol in the standing and supine positions and during walking. Foot contact-switches were used to record the heel- and toe-strikes during walking. RESULTS Moderate or marked activity of the muscle occurred equally in free flexion, adduction and medial rotation. Against resistance these movements showed much greater activity than the free movements. Each of these resisted isometric efforts and free movements showed much more activity when the hip was at 90 degrees of flexion compared with when it was extended or slightly flexed. Neglible or nil activity occurred in both free lateral rotation and the same movement against resistance. Neither was activity recorded during quiet sitting, standing on both feet, and standing on the ipsilatReceived Jan. 25, '74. Accepted Mar. 26, '74. 1 On leave of absence from the Department of Orthopedic Surgery, Kobe University School of Medicine, Kobe, Japan. 2 On leave of absence from the Department of Morphology, Faculdade de Odontologia de Piracicaba, U.E.C.,Siio Paulo, B r a d . Fellowship from FundaqHo de Amparo B Pesquisa do Estado de SZo Paulo, Proc. med. 71/1045. 281 282 K. TAKEBE, M. VITTI AND J. V. BASMAJIAN 3 Fig. 1 EMG of the pectineus, showing marked activity in flexion (tracing 2) adduction (3) and medial rotation ( 4 ) of the hip, but none in lateral rotation (1). eral foot. Sit-ups from the supine position showed slight activity, but flexion of the trunk in the standing position did not. During normal walking, moderate activity was recorded in the stance phase from the middle of heel strike to the end of toe strike; and slight activity was noted during the swing phase. the swing phase. Finally, our findings suggest that contracture or spasticity of this muscle could be a cause of the deformity of the hip joint in children with cerebral pdsy-which typically is flexion, adduction and DISCUSSION We are grateful to Mr. James Perry for technical assistance. Our results show that this muscle participates equally in flexion, adduction and medial rotation of the hip. They contradict those authors who have surmised from its morphology that its function is lateral rotation. We believe that in walking the pectineus works as a stabilizer and possible medial rotator of the hip in the stance phase, and contributes to flexion during ACKNOWLEDGMENTS LITERATURE CITED Basmajian, J. V., and G. A. Stecko 1962 A new bipolar indwelling electrode for electromyography. J. Appl. Physiol., 17: 849. Bleck, E. E. 1972 Postural and gait abnormalities caused by hip-flexion deformity in spastic cerebral palsy. J. Bone and Joint Surg., 53-A: 1468-14aa. EMG O F PECTINEUS MUSCLE Duchenne, G. B. 1867 Physiology of Motion. Translated by E. B. Kaplan ('59) Philadelphia W. B. Saunders, p. 266. Edwards, L. E. 1956 Concise Anatomy, 2nd ed. McGraw-Hill Book Co., New York, p. 191. Goss, C. M. 1969 Gray's Anatomy of the Human Body. 28th ed., Lea and Febiger, Philadelphia, p. 498. 283 Lamb, D. W., and G. A. Pollock 1962 Hip deformities in cerebral palsy and their treatment. Develop. Med. Child. Neural., 4: 488498. Wells, W. F. 1969 Kinesiology, 4th ed., W. B. Saunders, Philadelphia, p. 310. Woodburne, R. T. 1965 Essentials of Human Anatomy, 3rd ed., Oxford Univ. Press, New York, p. 579.