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Transcript of A functional model to describe the action of the adductor ... A functional model to describe the

A functional model to describe the action of the

adductor muscles at the hip in the transverse plane

R. Dennis Leighton, DPT, PTAssociate Professor, Department of Physical Therapy, University of New England, Portland, ME, USA

Anatomical texts agree on most muscle actions, with a notable exception being the action of theadductors of the hip in the transverse plane. Some texts list an action of the adductor brevis (AB),adductor longus (AL), and=or adductor magnus (AM) as internal rotation, whereas others list anaction of external rotation. The purpose of this article is to present a functional model in support ofthe action of external rotation. Transverse plane motion of the femur at the hip during normal gaitis driven by subtalar joint motion during the loading response, terminal stance, and preswing phases.During the loading response, the subtalar joint pronates, and the talus adducts. This talar adductionresults in the lower leg, and subsequently the femur, internally rotating. During terminal stance and pre-swing, the opposite occurs; the subtalar joint supinates as the talus abducts in response to forces gen-erated from the lower extremity and in the forefoot. Electromyographic (EMG) studies indicate variedactivity in the AB, AL, and AM during the loading response, terminal stance, and preswing phases ofthe gait cycle. A careful analysis of EMG activity and kinematics during gait suggests that, in the trans-verse plane, the adductors may be eccentrically controlling internal rotation of the femur at the hip dur-ing the loading response, rather than the previously reported role as concentric internal rotators. Inaddition, these muscles may also concentrically produce external rotation of the femur at the hip duringterminal stance and preswing. Physical therapists should consider this important function of the hipadductors during gait when evaluating a patient and designing an intervention program. Anatomicaltexts should consider listing the concentric action of external rotation of the femur at the hip as oneaction of the AB, AL, and AM, particularly when starting from the anatomic position.

Introduction

Knowledge of normal muscular anatomy isessential for the physical therapist in the examin-ation, evaluation, diagnosis, and development ofintervention programs for his or her patients(APTA, 2001). Beyond anatomical knowledge,the therapist must also be aware of the contribu-tions of each muscle as the patient functions byinteracting with the environment. Generally, atherapist will find agreement on human anatom-ical structure in the literature. However, theaction of one muscle groupthe hip adduc-

torshas been the subject of disagreement.Authors agree that the hip adductor musclegroup, consisting of the adductor longus (AL),adductor brevis (AB), and adductor magnus(AM), adduct the femur in relation to the pelvisalong the frontal plane. Furthermore, someauthors describe the AL, the AB, and theanterior (superior) fibers of the AM as actingalong the sagittal plane by flexing the femur inrelation to the pelvis, and the posterior (inferior)fibers of the AM as extending the femur inrelation to the pelvis. For motion along thefrontal and sagittal planes, then, there is no

Accepted for publication 25 July 2005.

Address correspondence to Dennis Leighton, DPT, PT, Department of Physical Therapy, University of New England, 716

Stevens Avenue, Portland, Maine 04103. E-mail: dleighton@une.edu

Physiotherapy Theory and Practice, 22(5):251262, 2006Copyright # Informa HealthcareISSN: 0959-3985 print/1532-5040 online

DOI: 10.1080/09593980600927385

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disagreement about the actions of the hip adduc-tors (Basmajian, 1975, 1982, 1989; Grant, 1958,1971; Hislop and Montgomery, 1995; Kapandji,1988; Lindner, 1989).

There is not universal agreement, however,about the action of these muscles along thetransverse plane. Some authors describe theaction as internal rotation (Basmajian, 1982;Basmajian and DeLuca, 1985; Basmajian andSlonecker, 1989; Hislop and Montgomery,1995), whereas others describe the action asexternal rotation (Grant, 1958; Grant andBasmajian, 1971; Kapandji, 1988). Still othersdescribe actions of both internal and externalrotation (Guy, 1998; Lindner, 1989).

Upon initial observation, the anatomicalarrangement of the hip adductor muscles wouldseem to indicate an action of external rotation ofthe femur on the pelvis in the transverse plane(Figures 1 and 2). The adductors originate proxi-mally from the inferior aspect of the body andramus of the pubis and the inferior ramus ofthe ischium and all three muscles insert distallyon the femur from a point beginning on the pos-terior aspect of the femur proximal to the lineaaspera, along the linea aspera, to the adductortubercle (Basmajian, 1982; Grant and Basmajian,1971; Grant, 1958; Guy, 1998; Lindner, 1989).From the anatomical standing position and witha fixed pelvis, an active concentric contraction ofthese muscles would appear to rotate the pos-terior aspect of the femur medially. This wouldresult in the entire femur rotating around thevertical mechanical axis in a direction that, bydefinition, is external rotation.

There is little scientific evidence to supportan action of the three adductors of either inter-nal or external rotation at the hip. Of the anat-omy texts cited for this review, none provide aspecific reference to support the action of thehip adductors. Some texts provide general refer-ences or a reading list at the end of the chap-ters. John Basmajian (1985) has been aproponent of an action of internal rotation,which he has supported in his classic textMuscles Alive: Their Functions Revealed byElectromyography. In this text, Basmajian citesan abstract published in 1966 by deSousa andVitti (1966) in the Archives of Mexican Anat-omy, in which deSousa and Vitti conclude thatthe AL and AM act as internal rotators ofthe hip. Other texts authored by Basmajian

(Basmajian, 1982; Basmajian and Slonecker,1989) also describe the hip adductors as internalrotators. Basmajians position on the issue isclearly demonstrated as one follows the hipadductors through the editions of Grants Anat-omy. The sixth edition of Grants Anatomy,authored by Grant (1958), and the eighth edi-tion, authored by Grant and Basmajian(1971), describe an action of external rotation.However, the ninth edition of Grants Anatomy,authored by Basmajian alone (1975), describesthe adductor action as internal rotation.

The abstract by deSousa and Vitti (1966) ledto the publication of an article in 1967 (de Sousaand Vitti, 1967). Although deSousa and Vitticonclude that the hip adductors are internalrotators, the evidence presented in their articlemay not support such a conclusion. Theseauthors studied the electromyographic (EMG)activity of the AL and AM as their subjectsactively internally and externally rotated thelower extremity while supine and while standing.When reviewing the method of data collectionfor the standing trials, it is equally reasonableto conclude an action of external rotation ifone were to consider the function of eccentriccontractions. For example, deSousa and Vittihad the subjects internally rotate the hip whilestanding and weight bearing, noting the EMGactivity that this motion produced. The con-clusion, therefore, was that since the hip wasinternally rotating when the muscles were electri-cally active, then the action of the muscles mustbe internal rotation. These results and conclu-sions are similar to those of Williams andWesley (1951). However, if these authors con-sidered an eccentric action to control the inter-nal rotation in standing, then the conclusionscould have been that the adductors may actuallyfunction as external rotators.

By citing only the abstract of the article,Basmajian was unable to critically analyze themethods of de Sousa and Vitti, and it may bepossible that Basmajian (Basmajian, 1975, 1982;Basmajian and De Luca, 1985; Basmajian andSlonecker, 1989) has incorrectly described theaction of the hip adductors as internal rotation.

de Sousa and Vitti and Williams and Wesleyalso had the subjects internally and externallyrotate the hip while lying supine. These datashould also be questioned because the authorsdo not explain if or how the supine hip rotation

252 Leighton/Physiotherapy Theory and Practice 22 (2006) 251262

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motions were done in isolation of other hipmotions. If the subjects were allowed to adductand=or flex the hip, any EMG activity couldnot be conclusively attributed to the rotationseen.

A number of biomechanical models havebeen proposed to study muscle actions. Inman(1947) used wires and x-ray to represent theaction lines of muscles. This early investigationcame to be known as the straight-line methodof describing muscle action, in which a straightline is taken from origin to insertion, and the

muscles action line is considered to fall alongthis line. The relationship of the action line tothe axis of rotation determines the action of themuscle. Authors have advocated for the straight-line method as a reasonably simple way tod