REVIEW

A Review of the Anatomy of the Hip AbductorMuscles, Gluteus Medius, Gluteus Minimus, and

Tensor Fascia Lata

NATASHA AMY MAY SPARKS FLACK,1* HELEN D. NICHOLSON,1,2 AND

STEPHANIE JANE WOODLEY1

1Department of Anatomy, University of Otago, Dunedin, New Zealand2School of Medical Sciences, University of Otago, Dunedin, New Zealand

The hip abductor muscles have the capability to contribute to numerousactions, including pelvic stabilization during gait, and abduction and rotation atthe hip joint. To fully understand the role of these muscles, as well as theirinvolvement in hip joint dysfunction, knowledge of their anatomical structureis essential. The clinical literature suggests anatomical diversity within thesemuscles, and that gluteus medius (GMed) and gluteus minimus (GMin), inparticular, may be comprised of compartments. This systematic review of theEnglish literature focuses on the gross anatomy of GMed, GMin, and tensorfascia lata (TFL) muscles. Although studies of this muscle group have gener-ated useful descriptions, comparison of results is hindered by methodologicallimitations. Furthermore, there is no single comprehensive anatomical investi-gation of all three muscles. Several aspects of the morphology of attachmentsites are unknown or unclear. There is little data on fascicle orientation, theinterface between fascicles and tendons, and the specific patterning of thesuperior gluteal nerve. Consequently, the existence of anatomical compart-mentalization within the hip abductor muscles is difficult to assess. Furtherresearch of the architecture and innervation of the hip abductor muscle groupis required; a better understanding of the precise anatomy of these musclesshould improve our understanding of their specific functions and their contri-bution to the pathogenesis of disorders affecting the hip joint. Clin. Anat.

:000–000, 2012. VVC 2011 Wiley Periodicals, Inc.

Key words: gluteus medius; gluteus minimus; tensor fascia lata; morphology;compartmentalization

INTRODUCTION

Muscle architecture is an important determinantof function, and it has been demonstrated in bothanimal and human studies that skeletal muscles maybe divided into distinct morphological regions (Eng-lish and Letbetter, 1982; Windhorst et al., 1989;Segal, 1992; English et al., 1993; Bakkum et al.,1996; Woodley and Mercer, 2005; Becker et al.,2010). Division of a muscle into compartments orpartitions, based on architectural parameters suchas fascicular orientation, attachment sites, and pat-terns of innervation, may indicate the capability for

differential activation (English et al., 1993). The hipabductor muscle group, gluteus medius (GMed), glu-teus minimus (GMin), and tensor fascia lata (TFL)play a significant role in pelvic stabilization during

*Correspondence to: Natasha A.M.S. Flack, Department of Anat-omy, University of Otago, 275 Great King Street, Dunedin 9016,New Zealand. E-mail: natasha.flack@anatomy.otago.ac.nz

Received 29 June 2011; Revised 16 October 2011; Accepted 26October 2011

Published online in Wiley Online Library (wileyonlinelibrary.com).DOI 10.1002/ca.22004

VVC 2011 Wiley Periodicals, Inc.

Clinical Anatomy 00:000–000 (2012)

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gait, by contracting to maintain the level of thecontralateral pelvis during single leg stance (Gray,1858; Soderberg and Dostal, 1978; Lyons et al.,1983; Gottschalk et al., 1989; Kumagai et al.,1997; Anderson and Pandy, 2003). In addition totheir abduction role, GMed and GMin contribute torotatory actions at the hip joint. Although it iswidely accepted that both of the deep glutealmuscles function to internally rotate the hip joint,it has also been proposed that with respect toGMed, the anterior portion of the muscle performsinternal rotation while the posterior part functionsduring external rotation (Knox, 1831; Gray, 1858;Dostal et al., 1986; Conneely et al., 2006). Thispremise is also apparent clinically, whereby com-partmentalization of GMed forms the basis forsome treatment regimes, with the posterior part ofthe muscle being the target of specific strengthen-ing exercises (Fredericson et al., 2000; Bewyer andBewyer, 2003; Mascal et al., 2003; Cowan et al.,2008). Similarly, there is evidence to suggest thatthe anterior two-thirds of GMin is susceptible to at-rophy following total hip joint replacement, whilethe posterosuperior part of the muscle is more sus-ceptible to atrophy in those who also present withsymptoms of lateral hip pain postsurgery (Pfirr-mann et al., 2005).

These examples highlight the necessity for adetailed understanding of anatomy to appreciateboth the function of these muscles and any changesthat may occur secondary to dysfunction or pathol-ogy. However, it is unclear whether existing, robustanatomical evidence supports the apparent compart-mentalization of the hip abductor muscles. There-fore, a systematic review of the literature was under-taken with the purpose of assessing morphologicalinformation important in determining compartmen-talization such as attachment sites, fascicle architec-ture, and innervation patterns. Investigations usingEMG are not included in this review; however, it isimportant to note that an improved understanding ofthe detailed anatomy of the hip abductor muscleswill determine what further information may bederived from EMG.

METHODS

A review of the primary literature was undertakenin a systematic manner to ensure all relevant articleswere evaluated. Papers published between 1947 andJune 20, 2011 were selected for review, if they con-tained specific morphological information includingdata on attachment sites, muscle architecture, orinnervation of GMed, GMin, or TFL. Surgical paperswere included only when primary observations wereoffered. Papers providing EMG data were notincluded, as there was no accompanying primary an-atomical information on the morphology of thesemuscles. Figure 1 provides details regarding thedatabases searched, search terms, and exclusion cri-teria. In addition, information from a selection ofnine anatomical textbooks available from the Univer-sity of Otago library catalogue were included (publi-cation date range, 1763–2008).

RESULTS

Selection of Studies

Using the specified search terms (Fig. 1), after re-moval of duplicate articles, 1207 papers (English)were retrieved. Ninety-two scientific articles met theinclusion criteria, of which, 43 were classified as pri-mary papers, providing quantitative data and rela-tively detailed anatomical descriptions. The remain-ing 54 were deemed secondary papers because,although morphological features were mentioned,anatomical details of the muscles were not the focusof research. Only the primary papers were includedin this review. With nine anatomical textbooksselected for analysis, a total of 52 references, pro-viding information on hip abductor anatomy, wereexamined. The following section provides firstly, abrief critique of the literature and then a concisesummary of the anatomical data under the subhead-ings of attachment sites, muscle architecture, inner-vation, and compartmentalization.

Critique of the Literature

The aims and methods of each primary studywere variable. Of the 43 primary papers, 26 pro-vided anatomical information derived from cadav-eric dissections, 11 used imaging and the remain-ing six were accounts of surgical techniques. Themedian sample size for the dissection studies wasapproximately 10 specimens (range 2–28); how-ever, two did not specify specimen number(Kaplan, 1958; Jovanovic et al., 2004). Commonlimitations typically included, missing specimen in-formation (age, sex, and embalming fluid composi-tion), and details pertaining to measurement pa-rameters. In addition, terminology differed acrossinvestigations, making comparison of data difficult(e.g., fascicle vs. fiber). In terms of attachmentsites, muscle architecture, volume, and innerva-tion, 10 papers were deemed to provide the mostanatomical information (Gottschalk et al., 1989;Friederich and Brand, 1990; Akita et al., 1992a,b,1993, 1994a,b; Duparc et al., 1997; Beck et al.,2000; Ward et al., 2009), but none have compre-hensively investigated the anatomy of all three hipabductor muscles.

Imaging studies present an advantage overcadaveric investigations in that muscle anatomy canbe observed in vivo. Despite this, investigationswere often limited to one or two morphological char-acteristics, such as muscle volume (Jaegers et al.,1992; Jaegers et al., 1995; Inan et al., 2005;Grimaldi et al., 2009a,b; Sudhoff et al., 2009), andmodalities were variable (e.g., computed tomogra-phy versus magnetic resonance imaging). The sixsurgical techniques papers also contributed specificanatomical detail such as quantitative data for themuscle length of TFL, GMed and GMin proximalattachment and innervation patterns. Overall,however, little information was found within thesepublications.

Anatomical textbooks provide a variety of mor-phological descriptions. Commonly, GMed and GMin

2 Flack et al.

Fig. 1. Search strategy including databases and keywords used, number ofpapers retrieved and exclusion criteria. GMed, gluteus medius; GMin, gluteus mini-mus; TFL, tensor fascia lata.

3An Anatomical Review of the Hip Abductor Muscles

are described together, meaning the individualanatomy of GMin is overlooked. Likewise, detailregarding TFL is scarce, and in general the reviewedtextbooks did not usually provide primary evidenceor reference to original work to support theirdescriptions.

Attachment Sites

Although similar in general insertion sites, varia-tion is evident within the current literature regardingthis anatomical parameter for all three hip abductormuscles. A summary of the provided descriptions ofattachment sites for GMed, GMin, and TFL are sum-marized in Figures 2–4, respectively.

Proximal Attachments

There is widespread agreement that both GMedand GMin arise from the external iliac surface. Allreviewed textbooks note GMed attaching from theanterior to the posterior gluteal lines, and thosethat present information on GMin agree that itattaches between the anterior and inferior gluteallines (Winslow, 1763; Gray, 1858; Frazer, 1920;Woodburne and Burkel, 1988; Moore and Dalley,1999; Sinnatamby, 2006; Standring et al., 2008).In addition, specific to GMed, two other sites ofproximal attachment are commonly cited; the glu-teal aponeurosis (GA) (Winslow, 1763; Knox, 1831;Gray, 1858; Hollinshead, 1967; Clark and Haynor,1987; Woodburne and Burkel, 1988; Standring etal., 2008; Al-Hayani, 2009), and the iliac crest(Knox, 1831; Gray, 1858; Little et al., 1983; Gott-schalk et al., 1989; Jacobs and Buxton, 1989;Jaegers et al., 1992; Bos et al., 1994; Duparc et al.,1997; Nork et al., 2005; Basarir et al., 2008; Zhanget al., 2008).

On closer inspection, it is apparent that not alldetails are present. For example, the morphology,and the extent of GMed insertion into the GA are notdescribed. Contradictions also arise when the attach-ment to the iliac crest is considered. For example,GMed may attach to the anterior three quarters ofthe crest (Duparc et al., 1997), more posteriorly(Zhang et al., 2008), or along the entire length ofthe crest (Gottschalk et al., 1989; Little et al., 1983;Nork et al., 2005).

Less information is available regarding GMin.Although four studies supplement textbook accounts(Little et al., 1983; Nazarian et al., 1987; Gottschalket al., 1989; Beck et al., 2000), only one compre-hensively describes the morphology of the proximalattachments of this muscle (n ¼ 9 cadavers) (Becket al., 2000). GMin is described as attachingproximally to the external ilium, beginning 3–5 mmanterior to the anterior superior iliac spine (ASIS),running parallel to the iliac crest reaching to the iliactubercle. Following the anterior gluteal line, the mus-cle attachment extends to the greater sciatic notch.The muscle covers the posterosuperior acetabulumand follows the inferior gluteal line to the anteriorinferior iliac spine (AIIS) anteriorly. The anteriorborder attaches along the bony ridge between theASIS and AIIS.

TFL is most commonly recorded as attaching prox-imally along the iliac crest (Kaplan, 1958; Hill et al.,1978; Woodburne and Burkel, 1988; Moore andDalley, 1999; Sinnatamby, 2006; Standring et al.,2008; Al-Hayani, 2009), at a width between 15 and76 mm (Frazer, 1920; Kaplan, 1958; Pare et al.,1981; Weber and Ganz, 2002; Sinnatamby, 2006;Standring et al., 2008). Mostly, it is described asbeing restricted to the anterior lateral portion of thecrest, including only the lateral aspect of the ASIS(Hill et al., 1978; Pare et al., 1981; Woodburne andBurkel, 1988; Jaegers et al., 1992; Horch et al.,1998; Moore and Dalley, 1999; Weber and Ganz,2002; Standring et al., 2008; Al-Hayani, 2009). Theiliac tubercle (Sinnatamby, 2006), a notch locatedbelow the superior spine of the ilium (Frazer, 1920;Woodburne and Burkel, 1988; Standring et al.,2008), the anterolateral iliac fossa just below thecrest (Frazer, 1920; Kaplan, 1958; Sinnatamby,

Fig. 2. Variation in the locations of the bony proxi-mal and distal insertion sites of GMed as portrayed inthe current literature. Shaded areas denote sites ofbony insertion onto the ilium and the greater trochanteras described in anatomical textbooks and scientificarticles. Areas common to more than one publicationare indicated by darker regions. An additional proximalinsertion site includes the deep surface of the glutealaponeurosis (not shown in this figure). AIIS, anterior in-ferior iliac spine; ASIS, anterior superior iliac spine;IGL, inferior gluteal line; MGL, middle gluteal line; PGL,posterior gluteal line; PIIS, posterior inferior iliac spine;PSIS, posterior superior iliac spine; a, anterior facet; b,lateral facet; c, posterosuperior facet; d, posteriorfacet, of the greater trochanter (as defined by Pfirr-mann et al. [2005]).

4 Flack et al.

2006), and the deep surface of the fascia lata of thethigh (Kaplan, 1958; Hill et al., 1978; Pare et al.,1981; Standring et al., 2008) are also suggestedsites of proximal insertion for this muscle. The mor-

phology of the proximal insertion is described asbeing tendinous in nature (Knox, 1831; Pare et al.,1981; Clark and Haynor, 1987), but most referencesdo not discuss this feature. Also, it is not clearwhether such tendinous tissue belongs to the fascialata, or is the muscle’s own tendon.

Distal Attachments

The distal insertion sites for GMed and GMin maybe split primarily into two parts: (1) tendinous inser-tion into bone and (2) fascicular insertion onto ten-don. In addition, muscle and tendinous tissue ofGMin inserts into the hip joint capsule, while distallyTFL is associated with the fascia lata.

Insertion of tendon onto bone. There is con-sensus that the tendons of GMed and GMin insertonto the greater trochanter (GT) of the femur (Knox,1831; Gray, 1858; Frazer, 1920; Hollinshead, 1967;Nazarian et al., 1987; Delp et al., 1990; Jaegers etal., 1992; Akita et al., 1994a; Moore and Dalley,1999; Nork et al., 2005; Sinnatamby, 2006; Solo-mon et al., 2010; Molini et al., 2011; low, 1763; g etal., 2008). However, the precise point of each ofthese attachment sites varies (Figs. 2 and 3). Mostcommonly, GMed is noted as attaching to the lateralsurface (Winslow, 1763; Knox, 1831; Gray, 1858;Frazer, 1920; Nazarian et al., 1987; Akita et al.,1993; Heimkes et al., 1993; Moore and Dalley,1999; Pfirrmann et al., 2001; Sinnatamby, 2006;Basarir et al., 2008; Al-Hayani, 2009; Solomonet al., 2010); however, the anterosuperior (Gottschalket al., 1989; Connell et al., 2003), posteromedial(Molini et al., 2011), posterosuperior (Hollinshead,1967) and superior (with GMin) (Little et al., 1983)aspects, and the apex (Perez et al., 2004) of the GThave also been described. In contrast, the mostcommonly noted site for GMin insertion is onto theanterior surface (Winslow, 1763; Knox, 1831; Gray,1858; Nazarian et al., 1987; Heimkes et al., 1993;Moore and Dalley, 1999; Pfirrmann et al., 2001;Molini et al., 2011), but alternate locations include:the anterosuperior angle (Woodburne and Burkel,1988; Gottschalk et al., 1989); anterolateral ridge(Beck et al., 2000; Walters et al., 2001; Sinnatamby,2006; Standring et al., 2008; Al-Hayani, 2009);lateral surface (with GMed) (Basarir et al., 2008);

Fig. 3.

Fig. 3. Variation in the locations of the proximal (i)and distal (ii) insertion sites of GMin as portrayed in thecurrent literature. Shaded areas denote sites of bonyinsertion onto the ilium (i) and the greater trochanterand hip joint capsule (ii) as described in anatomicaltextbooks and scientific articles. Areas common to morethan one publication are indicated by darker regions.AIIS, anterior inferior iliac spine; ASIS, anterior superioriliac spine; IGL, inferior gluteal line; MGL, middle glutealline; PGL, posterior gluteal line; PIIS, posterior inferioriliac spine; PSIS, posterior superior iliac spine; a, ante-rior facet; b, lateral facet; c, posterosuperior facet; d,posterior facet, of the greater trochanter (as defined byPfirrmann et al. [2005]).

5An Anatomical Review of the Hip Abductor Muscles

and superior aspect (with GMed) (Little et al., 1983)of the GT.

In addition, controversy exists as to whetherGMed has a single tendon or two or more distal sitesof attachment (Srivastava and Joshi, 1969; Wood-burne and Burkel, 1988; Duparc et al., 1997; Pfirr-mann et al., 2001; Standring et al., 2008). As wellas the lateral GT, a second, superiorly located, tendi-nous attachment has been reported; but the specificattachment site is again, variable. Some reportattachment only to the superior (Srivastava andJoshi, 1969; Duparc et al., 1997; Standring et al.,2008), while others specify the superoposterior(Woodburne and Burkel, 1988; Pfirrmann et al.,2001) GT. Finally, Jaegers et al. (1992) describesthe muscle belly of GMed as being comprised ofthree parts, with three corresponding sites of inser-tion onto the GT: dorsal, ventral, and lateral.

Attachment of fascicles onto tendon. Docu-mentation of this aspect of morphology is not com-mon despite its potential importance in delineatinganatomical compartments (Segal et al., 1991). Mus-cle fascicles are often described as converging toinsert onto the distal tendons of GMed and/or GMin(Winslow, 1763; Gray, 1858; Clark and Haynor,1987; Gottschalk et al., 1989; Beck et al., 2000;Connell et al., 2003; Sinnatamby, 2006; Standringet al., 2008). Some sources have observed that thefascicles of GMed insert into both the superficial anddeep surfaces of the tendon (Knox, 1831), while twosources state that those of GMin converge to insertonly into the deep surface of the tendon (Gray,1858; Standring et al., 2008). However, anothersource provides information for the attachment sitesof different parts GMin, describing the middle andposterior regions as attaching to the deep surfacewhile the anterior region attaches to the ‘‘outer part’’of the tendon (Knox, 1831). The concept of ‘‘ante-rior’’ and ‘‘middle’’ fascicle attachments within GMedcan be compiled from the combined observations ofthree primary sources, but none provide details forthe entire muscle (Akita et al., 1993; Duparc et al.,1997; Pfirrmann et al., 2001).

Attachment into the hip joint capsule (GMin).While referred to in only three textbooks (Winslow,1763; Sinnatamby, 2006; Standring et al., 2008), acapsular component of the distal attachment of GMinis often noted within the primary literature (Clarkand Haynor, 1987; Nazarian et al., 1987; Beck etal., 2000; Pfirrmann et al., 2001; Walters et al.,

2001; Weber and Ganz, 2002; Connell et al., 2003).However, there is a paucity of literature describingor quantifying this attachment site; the frequency ofa capsular insertion has solely been investigated byWalters et al. (2001) and the extent of the capsularattachment is reported upon only by Beck et al.(2000). Medial-lateral (10–15mm) and cranial-cau-dal (20–25mm) measurements, from nine cadavers,are provided, but measurement parameters are notstipulated. With respect to the location of the capsu-lar insertion, the superior (or lateral) capsule is usu-ally specified (Nazarian et al., 1987; Pfirrmann et al.,2001; Walters et al., 2001; Sinnatamby, 2006), andsuch a connection has been histologically determinedin both adults and fetuses (Walters et al., 2001).Attachment to the anterior aspect of the joint cap-sule has also been documented (Pfirrmann et al.,2001; Standring et al., 2008).

Tensor fascia lata. The distal insertion of TFLinto the fascia lata has been widely noted within theliterature, but the location of this insertion is notclearly documented (Table 1). Although Pare et al.(1981) observed the tendinous fibers of TFL join themiddle longitudinal layer of the fascia lata, it is notclear whether these fuse immediately into the ITB,just distal to the inferior aspect of the muscle belly(Winslow, 1763; Kaplan, 1958; Moore and Dalley,1999), or continue to interweave with the patellarretinaculum or the tubercle of the tibia (Pare et al.,1981). Standring et al. (2008) suggest that botharrangements may exist.

Muscle Architecture

Within the reviewed literature, the terms ‘‘fasci-cle’’ and ‘‘fiber’’ appear to be used interchangeably.Determination of fiber length requires microscopicdissection, and with the exception of one paper(Friederich and Brand, 1990), no study has specifiedthe use of this technique. Therefore, it is possiblethat where the term ‘‘fiber’’ has been written, a ‘‘fas-cicle’’ has been measured. Consequently (apart fromthe aforementioned exception), the term ‘‘fascicle’’will be used when referring to this literature.

Fascicle and Fiber Lengths

For all three hip abductor muscles, fascicle lengthis not normally reported; no quantitative data areavailable for GMed and TFL, and only one study pro-

TABLE 1. Information Regarding the Location of the Distal Insertion of TFL into the Fascia Lata

Author (year) Location of distal insertion

Winslow (1763) At the point where the fascia lata adheres to the GT and the tendon of GMaxKnox (1831) 3 inches distal to the GTKaplan (1958) Blends with fascia lata below the GTHill et al. (1978) At the junction of the proximal mid-thighJaegers et al. (1992) Caudal to the GTStandring et al. (2008) 1/3 of the way down the thighAl-Hayani (2009) Slightly inferior and anterior to the GTMolini et al. (2011) Just below the GT

GMax, gluteus maximus; GT, greater trochater.

6 Flack et al.

vides a mean fascicle length of 40 mm for GMin(Beck et al., 2000). In contrast, fiber length hasbeen derived from cadaveric dissections, for all threemuscles (Friederich and Brand, 1990; Ward et al.,2009). Friederich and Brand (1990) first report meanfiber lengths of 58.2, 42.0, and 98.3 mm for GMed,GMin, and TFL, respectively. Because of their fanshape, additional measurements for GMed and GMinwere taken from the anterior, middle, and posteriorparts of the muscles (GMed: 5.0 cm, 4.2 cm, 3.4cm; GMin: 5.0 cm, 4.2 cm, 3.4 cm, respectively);however, data are limited by sample size (n ¼ 2). Incontrast, Ward et al. (2009) having investigated 21cadaveric specimens, report a larger mean fiberlength of 73.3 mm 6 15.7 mm for GMed. Fiberlengths were sampled from three different regions ofthe muscle, and a coefficient of variation (20.3% 611.8%) is also presented to indicate the variation inregional differences. No specific regional fiber length

data are provided nor is there information availablefor GMin or TFL; however, fiber length has been nor-malized to sarcomere length in an attempt to cir-cumvent length changes that may occur with varia-tions in the position of fixation (Lieber et al., 1994).

Whole Muscle Length

Muscle lengths are not available for GMed or GMinwithin anatomical textbooks, and only one providesdata for TFL (approximately 150 mm) (Moore andDalley, 1999). Within the primary literature, meanGMed muscle length data range from 117 to 199.9mm (Delp et al., 1990; Friederich and Brand, 1990;Duparc et al., 1997; Nork et al., 2005; Ward et al.,2009), while GMin length ranges from 80.0 to 95.0mm (Friederich and Brand, 1990). Similar to fasciclelength, mean muscle lengths for three subdivisionsof GMed (117.5 mm, 117.5 mm, and 130.0 mm) andGMin (80.0 mm, 90.0 mm, and 82.5 mm) were pro-vided in the paper by Friederich and Brand (1990),but again the authors do not provide reasons forthese divisions. TFL is reported to measure between120 and 180 mm in length (Friederich and Brand,1990; Ihara et al., 1997; Brenner and Krebs, 2001;Gosain et al., 2002; Jovanovic et al., 2004).

Fascicle Direction

The line of action of a muscle is influenced by thedirection and arrangement of fascicles within themuscle belly (Gans, 1982). Despite such functionalsignificance, there is a dearth of corresponding dataregarding fascicle direction within the hip abductormuscles. While some anatomical textbooks providewritten portrayals of GMed and/or GMin as radiatingmuscles (Winslow, 1763; Knox, 1831; Gray, 1858;Hollinshead, 1967; Moore and Dalley, 1999; Sinna-tamby, 2006; Standring et al., 2008), the specificitybetween sources varies and only Knox (1831) pro-vides an overview of whole muscle fascicle orienta-tion for both muscles. Information on TFL fascicledirection is limited to the orientation of the wholemuscle within the thigh, rather than individual fas-cicles and the muscle is described as being arrangedvertically (Knox, 1831) or posteroinferiorly (Winslow,1763).

Little information regarding fascicle direction ofthe hip abductor muscles is available within the pri-mary literature. Although all authors agree thatGMed fascicle orientation differs across the musclebelly (Knox, 1831; Nazarian et al., 1987; Gottschalket al., 1989; Friederich and Brand, 1990; Akita etal., 1993; Duparc et al., 1997; Al-Hayani, 2009), of-ten only the direction of the anterior portion of themuscle is specified (Nazarian et al., 1987; Akita etal., 1993; Duparc et al., 1997). However, the poster-oinferior direction of these anteriorly located fas-cicles is consistently recorded. Three of the primaryinvestigations state that GMed is comprised of threeparts, each with its own individual fascicular direc-tion, but only the vertical arrangement of the fas-cicles within the middle regions is agreed upon(Knox, 1831; Gottschalk et al., 1989; Al-Hayani,2009). The muscle belly of GMin is usually noted as

Fig. 4. Variation in the locations of the bony proxi-mal insertion sites of tensor fascia lata as portrayed inthe current literature. Shaded areas denote sites ofbony insertion onto the ilium as described in anatomicaltextbooks and scientific articles. Areas common to morethan one publication are indicated by darker regions. Anadditional proximal insertion site included the deepsurface of the fascia lata of the thigh (not shown in thisfigure). AIIS, anterior inferior iliac spine; ASIS, anteriorsuperior iliac spine; IGL, inferior gluteal line; MGL,middle gluteal line; PGL, posterior gluteal line; PIIS,posterior inferior iliac spine; PSIS, posterior superioriliac spine; a, anterior facet; b, lateral facet; c, postero-superior facet; d, posterior facet, of the greatertrochanter (as defined by Pfirrmann et al. [2005]).

7An Anatomical Review of the Hip Abductor Muscles

being comprised of two parts, with the anterior fas-cicles arranged vertically and posterior fascicles ori-ented horizontally (Nazarian et al., 1987; Beck etal., 2000; Al-Hayani, 2009), but little more informa-tion is available. Finally, descriptions of TFL fascicleorientation are also variable across sources and aredescribed as being arranged obliquely (Winslow,1763; Phillips and Lindseth, 1992), or vertically (Al-Hayani, 2009) within the thigh, as well as divergingin an anteroposterior direction, distally (Knox, 1831;Pare et al., 1981).

Friederich and Brand (1990) provide quantitativefascicle angle ranges for both GMed (08–198) andGMin (08–218), respectively. Ward et al. (2009) givea pennation angle of 20.58 6 17.38 for GMed, andBeck et al. (2000) state that the two bundles ofGMin (anterior and posterior) form an angle of 758with one another during hip extension, but no valuesfor fascicular angles are provided. No paper explainshow angles were measured and no angle data cur-rently exists for TFL.

Muscle Volume and PhysiologicalCross-sectional Area

Although GMed is portrayed as the largest of thethree muscles followed by GMin then TFL, anatomicaltextbooks do not provide quantitative data. Unfortu-nately, there are also discrepancies within the pri-mary literature. Mean volumetric data for GMed fallswithin two different value ranges (95–130.4 cm3 and311–398.9 cm3). In contrast, the first publishedmean volumetric data for GMin, taken from cadav-ers, was 35 ml (Friederich and Brand, 1990), whichequates to approximately one-third of the value,taken from MR images, published by Jaegers et al.(1992, 1995) (102.5 cm3 6 30.1 cm3, 120.2 cm3 616.2 cm3, respectively), and less than half the vol-ume calculated by Grimaldi et al. (2009b) (82.5cm3), also from MR images. TFL volumes obtainedfrom MR imaging are similar in value (72.7–87.0cm3), despite sex and age differences (Jaegers etal., 1992, 1995; Grimaldi et al., 2009a; Sudhoff etal., 2009) but are more than double one of the twovalues (25 ml) derived from cadaveric dissections(Friederich and Brand, 1990).

Mean physiological cross-sectional area (PCSA)data are similarly diverse for GMed: 15.9 cm2 (n ¼6) (Heimkes et al., 1993), 27.78 cm2 (n ¼ 2) (Frie-derich and Brand, 1990), and 33.8 cm2 (n ¼ 21)(Ward et al., 2009), and TFL: 8.0 cm2 and 2.5 cm2

(Friederich and Brand, 1990) but surprisingly, GMinPCSAs are relatively similar: 10.1 cm2 (Heimkeset al., 1993) and 8.5 cm2 (Friederich and Brand,1990). All data are limited to cadaveric specimens.

Innervation

Throughout the literature, a commonly investi-gated feature of the hip abductor muscles is the pat-tern of innervation by the superior gluteal nerve(SGN). Typically, in anatomical textbooks, the SGNis described as emerging from the greater sciatic fo-ramen (Knox, 1831; Gray, 1858; Woodburne andBurkel, 1988; Moore and Dalley, 1999; Standring et

al., 2008), above the piriformis muscle (Knox, 1831;Gray, 1858; Hollinshead, 1967; Moore and Dalley,1999; Standring et al., 2008), running anteriorly(Hollinshead, 1967) between GMed and GMin (Hol-linshead, 1967; Moore and Dalley, 1999) and sup-plying both muscles (Knox, 1831; Hollinshead,1967; Woodburne and Burkel, 1988; Moore and Dal-ley, 1999; Standring et al., 2008). The nerve contin-ues through the intermuscular plane between GMedand GMin to enter TFL and either terminates immedi-ately (Hollinshead, 1967; Woodburne and Burkel,1988) or extends to the inferior end of the muscle(Gray, 1858). Descriptions of the course of the SGNwithin the primary literature are very similar. Sup-plementary data regarding the exit of the nerve fromGMed (approximately 1 cm distal and posterior tothe ASIS) (Phillips and Lindseth, 1992), and that theSGN enters TFL at its mid-length (Hill et al., 1978;Ihara et al., 1997) in an anterior to posterior direc-tion (Hill et al., 1978), are also available.

However, inconsistencies are evident in the num-ber and specific distribution patterns of branches ofthe SGN. For example, while the existence of threebranches has been reported within the literature(Bos et al., 1994; Perez et al., 2004; Nork et al.,2005; Zhang et al., 2008), the most commonlyacknowledged configuration is that the SGN splitsinto two main branches (Gray, 1858; Hollinshead,1967; Nazarian et al., 1987; Akita et al., 1992b,1993, 1994a,b; Duparc et al., 1997; Moore and Dal-ley, 1999; Weber and Ganz, 2002; Perez et al.,2004; Basarir et al., 2008; Standring et al., 2008).The origins of the two primary nerve branches havealso been evidentially identified (Akita et al., 1992b),and the branch which originates from root levels L4to S1 is, accordingly, named ‘‘cranial,’’ while theother, originating from S1 and S2 is termed ‘‘cau-dal.’’

With regard to distribution, the most recent obser-vations state that the cranial branch supplies theposterior regions (Duparc et al., 1997) of GMed andends in GMin (Perez et al., 2004). Meanwhile, thecaudal branch innervates the anterior region (Duparcet al., 1997) of GMed and ends in TFL, without con-tribution to GMin (Duparc et al., 1997; Perez et al.,2004). However, this differs to the observationsmade by Nazarian et al. (1987) who state that thecaudal branch of the SGN supplies all three muscles,and to a group of dissection studies using Japanesecadaveric specimens (Akita et al., 1992b, 1993,1994a,b). The authors of the later studies describethe cranial branch as continuing inferiorly betweenthe muscles, being distributed to the middle and an-terior regions of GMed, and all of GMin and TFL,while the caudal branch exclusively supplied the pos-terior region of GMed.

Compartmentalization

Although compartmentalization of GMed and GMinis alluded to through descriptions of differing fascicleorientation (Winslow, 1763; Knox, 1831), function(Wilson et al., 1976; Dostal et al., 1986; Delp et al.,1990; Anderson and Pandy, 2003), or innervation

8 Flack et al.

(Jacobs and Buxton, 1989; Akita et al., 1992b,1993, 1994a, 1994b; Perez et al., 2004), the divisionof these two muscles into distinct anatomical com-partments based upon the guidelines recommendedby Segal et al. (1991), has not been formally investi-gated. These authors state that for a muscle to beanatomically subdivided into compartments, eachsubdivision must be innervated by its own primarynerve branch and one feature of its architecture(e.g., fascicle angle and/or attachment sites) shouldbe distinct from surrounding compartments. Regard-less, some authors have suggested that GMed maybe comprised of two (Duparc et al., 1997) compart-ments, while others denote three (Gottschalk et al.,1989; Jaegers et al., 1992; Al-Hayani, 2009).Similarly, although most authors depict GMin as ahomogenous structure, based upon patterns ofinnervation (Akita et al., 1993, 1994a,b), function(Delp et al., 1990) or attachment sites (Jaegers etal., 1992), a contemporary anatomical textbook(Standring et al., 2008) suggests the muscle may becomprised of two (anterior and posterior) compo-nents. Finally, while the EMG recordings of Pareet al. (1981) infer differential activation of the ante-rior and posterior aspects of TFL, this muscleis not normally considered to be anatomicallycompartmentalized.

DISCUSSION

The primary aim of this systematic review was tocritique and summarize the available literatureregarding the anatomy of the hip abductor muscles:GMed, GMin, and TFL. Initially, there appears to beample research presenting the basic morphology ofthese muscles; however, when specific details areassessed, it is apparent that there is limited informa-tion provided by both anatomical textbooks and theprimary literature.

There were several identifiable weaknesses withinthe reviewed literature but the main issue was thatfew studies had comprehensively described each ofthe muscles’ anatomical features. In particular, thekey components which define compartmentalizationwithin a muscle (i.e., primary nerve branch patternand one or more architectural features such as fasci-cle angle, length, or attachment site [Segal et al.,1991]) have not been investigated simultaneously tosee if GMed, GMin, and TFL may be subdivided, ana-tomically. As a result, it is difficult to confirm theproposition that these muscles are capable of differ-ential activation during various movements at thehip joint (particularly rotation). Although compart-mentalization is the basis of some descriptions, oftenonly one anatomical feature influences the authors’decisions to subdivide these muscles. Thereby, therequirements of anatomical compartmentalizationare not met.

In addition, to obtain a complete overview of theanatomy of GMed, GMin, and TFL, information wasextracted from a number of investigations where dif-ferences in methods meant that comparison of datawas limited. Despite muscle length data being rela-tively similar across studies, differences in measure-

ment parameters need to be considered so appropri-ate comparisons can be made. For example, in twostudies regarding GMed muscle length (Duparc etal., 1997; Nork et al., 2005), clarification is requiredof the reference point from where measurementswere taken along the ilium. For TFL, discrepanciessurround the point of fusion of the muscle into theITB. It appears as though the issue surrounding thedescription of this anatomical feature lies, not neces-sarily in defining the area, but trying to compare thedifferent descriptions; the variable use of terminol-ogy and missing defined anatomical landmarks makecomparisons difficult.

The pattern of innervation is another area wheredifferences in descriptions, terminology, and meth-odology lead to difficulty in comparison across stud-ies. The in-depth account, presented through thecombination of a group of cadaveric dissections(Akita et al., 1992b, 1993, 1994a,b), thoroughlydescribes the anatomy of the SGN; however, morerecent investigations have published conflicting in-formation (Nazarian et al., 1987; Duparc et al.,1997; Perez et al., 2004). According to Akita et al.(1992b), the cranial nerve branch (root origin L4,L5) is said to continue as the inferior branch of theSGN when identified in the plane between GMed andGMin. Consequently, the caudal branch (root originL5, S1) is the nerve branch that continues superiorlythrough the gluteal region. As Nazarian et al.(1987), Duparc et al. (1997), and Perez et al. (2004)did not trace the nerve origins back to the spinalcord, it is difficult to determine whether the primarynerve branches were named in the same way asAkita et al. (1992b), or whether they were namedrelative to one another while running within theintermuscular plane. If the latter is true, then no-menclature adapted by the more recent papers ismost likely to be opposite to that used by Akita et al.(1992) as the two nerve branches cross paths whencoursing through the intermuscular plane (Akita etal., 1993). Anatomical textbooks also use differentterms compared to the primary literature; it can onlybe assumed that ‘‘superior’’ is used in place of‘‘cranial,’’ and ‘‘inferior’’ in place of ‘‘caudal.’’

Insufficient and variable anatomical informationon GMed, GMin, and TFL limits the accurate extrapo-lation of their possible functions. While textbookspropose a variety of roles performed by GMed, GMin,and TFL, the supporting evidence is not always avail-able. Muscle functions may be derived from electro-myography studies (Battye and Joseph, 1966; Gott-schalk et al., 1989; Peeraer et al., 1990; Jaegers etal., 1996; Dubois et al., 1997; Walters et al., 2001;Benedetti et al., 2003; Rutherford and Hubley-Kozey, 2009). However, there are anatomical limita-tions to the use of surface electrodes; activityrecordings for GMed and GMin (due to their deeplocation) are likely to be affected by interferencefrom the overlying gluteus maximus. To minimize in-terference, fine wire electrodes inserted into theappropriate muscle tissue can be used, but theplacement of electrodes has not been anatomicallyvalidated. The use of biomechanical models to derivefunction may also be limited as there appears to be

9An Anatomical Review of the Hip Abductor Muscles

little regard for the anatomy of the muscle; or, whenanatomy has been investigated through dissection,the transfer of anatomical data to the model is notcomplete nor particularly specific (McLeish andCharnley, 1970; Dostal et al., 1986; Beck et al.,2000; Anderson and Pandy, 2003; Liu et al., 2006;Gartman et al., 2008).

The importance of having a clear understanding ofmorphological detail of the hip abductors alsobecomes apparent when considering clinical condi-tions associated with changes in these muscles.For example, gluteal tendon pathology has beenimplicated in the development of lateral hip pain(Gordon, 1961; Chung et al., 1999; Kagan, 1999;Bird et al., 2001; Connell et al., 2003; Walsh and Ar-chibald, 2003; Bewyer and Chen, 2005; Blanken-baker et al., 2008; Lequesne et al., 2008; Woodleyet al., 2008). Although it is known that tendinosis ortendon tears may affect GMed and GMin, the exactlocation of pathology within the musculotendinouscomplexes, relative to known anatomical landmarks,has not been elucidated. The lack of precisionregarding the site(s) of pathology may partially be areflection of the limited anatomical knowledge of thetendinous structure of these muscles, but such infor-mation is important as it could influence the clinicalassessment, differential diagnosis, and managementof symptoms.

Understanding ‘‘normal’’ muscle volume is rele-vant when considering changes that may occur inassociation with pathology around the hip joint. Atro-phy of GMed and GMin has been demonstrated inindividuals with conditions such as osteoarthritis andlateral hip pain (Chung et al., 1999; Cvitanic et al.,2004; Pfirrmann et al., 2005; Demant et al., 2007;Woodley et al., 2008; Grimaldi et al., 2009b) andtwo studies have specifically demonstrated a reduc-tion in the volume of these muscles (Grimaldi et al.,2009a,b). Consequently, it seems important to as-certain how changes in gluteal muscle volume affectstrength and therefore function. ‘‘Nonpathological’’volumetric data for these muscles are derived from acombination of cadaveric and imaging studies(Jensen and Metcalf, 1975; Friederich and Brand,1990; Jaegers et al., 1992; Grimaldi et al., 2009a,b;Jolivet et al., 2009) but are limited by factors suchas the age and sex of specimens/participants. Fur-ther investigation is required using a number of indi-viduals of different age ranges and sex, to acquire abetter understanding of what constitutes ‘‘normal’’gluteal muscle volume.

Similarly, anatomical knowledge of whether thehip abductor muscles are comprised of distinct mor-phological compartments will play an important rolein identifying whether pathologies may be isolated toa particular region of the muscle and thus, haveimplications for function. For example, atrophy ofGMed and GMin posthip joint surgery has been local-ized to specific parts of the muscle, but it is unclearwhether these regions are anatomically distinct(Pfirrmann et al., 2005; Muller et al., 2010; Muller etal., 2011). The anatomical validity of exercises tai-lored to strengthen specific regions of the glutealmuscles, namely the ‘‘posterior portion’’ of GMed,

will be equally influenced. As such, treatmentapproaches based upon the compartmentalizationtheory are not currently supported by morphologicalevidence (Fredericson et al., 2000; Bewyer and Bew-yer, 2003; Mascal et al., 2003; Cowan et al., 2008).An understanding of the embryology of the hip ab-ductor muscles might also help in the determinationof anatomical compartments within these muscles,but very little information is currently available in theliterature.

CONCLUSION

A number of studies provide partial informationregarding attachment sites, muscle dimensions, fas-cicle architecture, and innervation patterns forGMed, GMin, or TFL. However, no single comprehen-sive investigation of all three muscles has beenundertaken and there is a need for further evidenceregarding compartmentalization of GMed and GMin.Furthermore, the existing data are limited by samplesize, or other methodological limitations. As a result,discrepancies exist, and anatomical detail is lacking.This review supports the need for further researchinto the architecture and innervation of the three hipabductor muscles so that their specific functionalcapabilities and their involvement in the pathogene-sis of hip joint dysfunction can be better understood.

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