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DOI: 10.1148/radiol.2211001634
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(Radiology. 2001;221:469-477.)
© RSNA, 2001

Musculoskeletal Imaging

Greater Trochanter of the Hip: Attachment of the Abductor Mechanism and a Complex of Three Bursae—MR Imaging and MR Bursography in Cadavers and MR Imaging in Asymptomatic Volunteers1

Christian W. A. Pfirrmann, MD, Christine B. Chung, MD, Nicolas H. Theumann, MD, Debra J. Trudell, RA and Donald Resnick, MD

1 From the Department of Radiology, Veterans Administration Medical Center, San Diego, Calif. Received October 9, 2000; revision requested December 5; revision received April 27, 2001; accepted May 2. Supported by the Swiss National Science Foundation. Address correspondence to C.W.A.P., Department of Radiology, University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland (e-mail: christian@pfirrmann.ch).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To evaluate trochanteric anatomy with magnetic resonance (MR) imaging, bursography, MR bursography, and anatomic analysis.

MATERIALS AND METHODS: T1-weighted and fat-saturated T2-weighted (transverse, sagittal, coronal, and coronal oblique planes) MR imaging of the greater trochanter was performed in 10 cadaveric hips and 12 hips of asymptomatic volunteers. Three bursae comprising the trochanteric bursa complex were injected, and conventional radiography and MR imaging were performed. The specimens were sectioned for anatomic analysis, corresponding to the MR imaging planes. Tendon attachments and bursal localization were related to the facets of the greater trochanter.

RESULTS: The bony surface of the greater trochanter consists of four facets: anterior, lateral, posterior, and superoposterior. The gluteus medius muscle attaches to the superoposterior and lateral facets. The gluteus minimus muscle attaches to the anterior facet. The trochanteric bursa covered the posterior facet and the lateral insertion of the gluteus medius muscle. The subgluteus medius bursa was located in the superior part of the lateral facet, underneath the gluteus medius tendon. The subgluteus minimus bursa lies in the area of the anterior facet, underneath the gluteus minimus tendon, medial and cranial to its insertion, and extends medially covering the distal anterior part of the hip joint capsule. The trochanteric bursa is delineated with fat on both sides and can be seen on transverse nonenhanced T1-weighted images as a fine line curving around the posterior part of the trochanter.

CONCLUSION: MR imaging and bursography provide detailed information about the anatomy of tendinous attachments of the abductor muscles and the bursal complex of the greater trochanter.

Index terms: Femur, MR, 449.121411, 449.12143 • Hip, anatomy, 449.92 • Hip, MR, 449.121411, 449.12143


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
The hip joint, much like the glenohumeral joint, boasts one of the widest ranges of motion in the human body, with its greater trochanter serving as the main attachment site for strong tendons, facilitating complex movement such as postural gait (1). This complex motion is achieved with the sophisticated attachment architecture of the abductor mechanism in the trochanteric surface and its three interposed bursae (2–4). Despite the importance of the integrity of the greater trochanteric structures for normal gait (5), reports describing the tendon insertions and the bursal anatomy are sparse. Furthermore, to our knowledge, the magnetic resonance (MR) appearance of the tendon attachments in the greater trochanter and even the precise localization of the three main trochanteric bursae have not been described.

Although pain over the lateral aspect of the hip has been commonly attributed to a trochanteric bursitis, the spectrum of pathologic abnormalities about the hip has broadened with the identification of entities such as rotator cuff tears of the hip, a term referring to a tear of the gluteus medius or minimus tendon (6,7). Despite similar clinical presentations, treatment of tears or bursitis can be different, emphasizing the need for accurate diagnosis.

The objectives of our cadaveric and human volunteer study were to (a) describe the normal MR imaging appearance of the attachment sites of the abductor mechanism and (b) to analyze the location, extent, and appearance of the bursal complex of the greater trochanter.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Analysis of Femoral Bones
Femoral bones derived from 10 human skeletons were visually inspected to determine the presence of osseous landmarks of the greater trochanter that represented sites of musculotendinous attachments (1,3,4,8–10). The following anatomic observations comprise the basis for the remaining methodology. Four distinct facets could be differentiated in all trochanters (Fig 1); the anterior facet is located on the anterolateral surface of the trochanter. It is oval and shares a medial border with the intertrochanteric line. The lateral facet has an inverted triangular shape, with the most caudal portion (the tip of the triangle) comprising the palpable part of the trochanter at physical examination. The posterior superior border is in contact with the superoposterior facet; this facet forms the most cranial part of the trochanter and has an oblique transverse orientation. The posterior facet is the most posterior aspect of the trochanter. It borders the lateral and superoposterior facets and has a curved shape in a mediolateral direction.



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  		Figure 1a. Schematics of the proximal part of the femur in the frontal view (left image), lateral view (middle image), and posterior view (right image) display (a) the four facets: the anterior facet (AF), lateral facet (LF), posterior facet (PF), and superoposterior facet (SPF); (b) osseous attachment sites of the gluteus medius (GMe) and gluteus minimus (GMi) tendons; and (c) locations of the bursae: TrB, SGMeB, and SGMiB.

 


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  		Figure 1b. Schematics of the proximal part of the femur in the frontal view (left image), lateral view (middle image), and posterior view (right image) display (a) the four facets: the anterior facet (AF), lateral facet (LF), posterior facet (PF), and superoposterior facet (SPF); (b) osseous attachment sites of the gluteus medius (GMe) and gluteus minimus (GMi) tendons; and (c) locations of the bursae: TrB, SGMeB, and SGMiB.

 


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  		Figure 1c. Schematics of the proximal part of the femur in the frontal view (left image), lateral view (middle image), and posterior view (right image) display (a) the four facets: the anterior facet (AF), lateral facet (LF), posterior facet (PF), and superoposterior facet (SPF); (b) osseous attachment sites of the gluteus medius (GMe) and gluteus minimus (GMi) tendons; and (c) locations of the bursae: TrB, SGMeB, and SGMiB.

 
Cadaveric Specimens
Ten fresh human hips were harvested from eight nonembalmed cadavers (two women, six men; mean age at death, 75 years; age range at death, 67–81 years). The specimens consisted of a hemipelvis and the proximal portion of the femur, including intact soft tissues. Radiography was performed on all specimens to exclude abnormalities from previous trauma, surgery, or severe osteoarthritis. The specimens were immediately deep-frozen at -40°C (Bio-Freezer; Forma Scientific, Marietta, Ohio). All specimens were allowed to thaw for 24 hours at room temperature prior to MR imaging.

MR Imaging
MR imaging was performed with a 1.5-T MR imager (Signa; GE Medical Systems, Milwaukee, Wis) with two receive-only 5-inch gradient coils centered laterally over the palpable greater trochanter. T1-weighted MR images were acquired in the transverse, sagittal, coronal, and coronal oblique (parallel to the femoral neck) planes centered at the level of the greater trochanter. Sequence parameters were 500/22 (repetition time msec/echo time msec), section thickness of 3 mm, two signals acquired, field of view of 14 x 14 cm, and matrix of 512 x 256. Subsequently, transverse and coronal T2-weighted fat-saturated fast spin-echo images were obtained with the following parameters: 4,000/120, an echo-train length of eight, section thickness of 3 mm, three signals acquired, field of view of 14 x 14 cm, and matrix of 512 x 256.

Bursography
After acquisition of the initial MR images, bursography was performed (C.W.A.P.) in nine cadaveric hips. The first cadaveric hip underwent anatomic analysis without bursography. In eight cadaveric hips, a single bursa (trochanteric bursa [TrB]) (n = 3), the subgluteus medius bursa (SGMeB) (n = 2), and the subgluteus minimus bursa (SGMiB) (n = 3) were injected. In one cadaveric hip, TrB and SGMeB were injected simultaneously. The injections were performed by one of the authors (C.W.A.P.) with fluoroscopic guidance, with the specimen in a prone position for the TrB and in the supine position for the SGMeB and the SGMiB. The needle trajectories for bursography of the different bursae are displayed in Figure 2 as dotted lines. In each case, a 20-gauge, 0.91 x 8.89-mm spinal needle (Terumo Medical, Somerset, NJ) was used.



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  		Figure 2. Schematic of the anatomy on sectional images. Sagittal, transverse, coronal image through the anterior part of the greater trochanter, and coronal image through the posterior part of the greater trochanter (a,b,c,d, respectively). The dotted lines display the needle paths for bursography. AF = anterior facet, G. Medius = gluteus medius, G. Minimus = gluteus minimus, LF = lateral facet, oe = obturator externus, oi = obturator internus, p = piriformis muscle, PF = posterior facet, SPF = superoposterior facet.

 
The expected position of the TrB is immediately posterior to the cortex of the posterior facet of the greater trochanter. The needle was inserted from a posterolateral approach, targeting the posterior facet at the level where the trochanter is best palpated. The SGMeB was accessed through a lateral approach with the needle inserted in the coronal plane, tilted 30° inferiorly (Fig 2b). The target was the upper part of the lateral facet, 3 mm underneath the cranial end of the trochanter (Fig 2b, 2d). For the injection of the SGMiB, the needle was inserted from an anterolateral approach, targeting the anterior facet at a point 3 mm beneath the cranial end of the greater trochanter and just medial to the intertrochanteric line. In all cases, the needle was advanced until bony contact was felt.

The position of the tip of the needle was verified with a test injection of a small amount of iodinated contrast material (Omnipaque 350; Nycomed Amersham, Princeton, NJ). After the verification of intrabursal localization, a mixture of one part 4-mmol/L gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany), one part iodinated contrast material (Omnipaque 350), and one part 15% concentrated solution of gelatin were slowly injected with fluoroscopic monitoring into the TrB (6.3–9.5 mL), SGMeB (1.0–2.5 mL), and SGMiB (1.5–2.5 mL). MR imaging of the nine cadaveric hips was performed within 30 minutes after the injection by using T1-weighted fat-saturated spin-echo sequences in the transverse, coronal, and sagittal planes, with the same parameters as previously described.

MR and Anatomic Comparison
After imaging, all cadaveric hips were immediately positioned, with the hip joint in neutral position, frozen at -65°C for at least 24 hours, and subsequently cut with a band saw into 3-mm-thick sections that corresponded in thickness and orientation to those of the MR images: coronal (n = 3), sagittal (n = 3), or transverse (n = 4) planes. The tendon insertion sites in the greater trochanter were recorded by two musculoskeletal radiologists (C.W.A.P., C.B.C.) by means of consensus. On each section, the bursal spaces were slightly distended, allowing documentation of the extent and topographic location of each bursa. The size of the bursa was measured with a ruler.

Asymptomatic Volunteers
Twelve hips (six right, six left) in 12 asymptomatic volunteers (five men, seven women; mean age, 35.1 years; age range, 21–51 years) were imaged. Institutional review board approval and informed consent were obtained prior to MR imaging. Only hips with no history of trochanteric pain or other local symptoms or trauma to this region were included in the study. The MR imaging protocol was the same as described previously. The imaging was performed with a 1.5-T imager (Siemens Symphony; Siemens Medical Systems, Erlangen, Germany).

Analysis of Images
All 22 MR studies without injection in the bursae (cadaveric hips, n = 10; volunteers, n = 12) were analyzed independently by two musculoskeletal radiologists. Reader 1 (C.W.A.P.) was involved in the anatomic study, and reader 2 (C.B.C.) was not involved in the anatomic study and received only a description of the facet anatomy and a diagram of the bursal topography (Fig 2). All sequences used before bursography were evaluated. Image analysis included both facet and bursal identification. Detectability of the facet was rated from one to four on a continuous scale: 1, not detectable; 2, poor detectability; 3, fair detectability; and 4, good detectability. The best plane for the detection of each facet was recorded. The visibility of the three bursae on images before enhancement was rated by using the same scale, and the best plane was also recorded. For the cadaveric studies, the dimensions of all facets were measured. The exact orientation of the abductor tendons attaching to the trochanter was recorded, and the diameter of the tendons 3 mm proximal to their insertion was measured.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Facet Anatomy of the Greater Trochanter on MR Images
The results regarding the detectability of facets on MR images are summarized in Table 1. The detectability of all facets in the cadaveric and living human hips was fair to good for both readers. A schematic of the cross-sectional appearance of the facets is displayed in Figure 2. Table 2 displays the dimensions of the facets in the cadaveric hips.


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  		TABLE 1. Detectability of the Facets of the Greater Trochanter on MR Images

 

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  		TABLE 2. Dimensions of the Facets and Bursae of the Greater Trochanter in the Cadaveric Study

 
The anterior facet was usually best seen on transverse images (Fig 3a). It was also easily identified on anterior coronal and sagittal images (Fig 3b). This facet corresponded to the insertion of the gluteus minimus tendon. The anterior border was formed by the intertrochanteric line just posterior to the capsular insertion of the hip. On transverse images, a distinct tubercle was usually present at this insertion point (Fig 4b, 4c).



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  		Figure 3a. Facet anatomy on T1-weighted MR images (500/22). (a) Human study. Transverse image demonstrates the anterior (thin black arrows), lateral (black arrowheads), and posterior (white arrowheads) facets. The gluteus minimus tendon (large white arrow) is attached to the anterior facet and is surrounded by the anterior part of the gluteus minimus muscle (thick black arrows). The TrB (small white arrows) can be identified as a thin line. (b-d) Cadaveric study. (b) Coronal image through the anterior part of the greater trochanter shows the anterior facet (arrowheads) with the gluteus minimus tendon (curved arrow) attached to it. (c) Coronal image through the posterior part of the greater trochanter displays the lateral facet (arrowheads), the lateral part of the gluteus medius tendon (curved arrow), and the iliotibial tract (straight arrow). (d) Sagittal image shows the superoposterior facet (black arrowheads), with the main tendon (curved white arrow) of the gluteus medius muscle attached to it, and the posterior facet (white arrowheads). The piriformis tendon (straight white arrow), the obturator internus tendon (straight black arrow), and the obturator externus tendon (curved black arrow) are also seen.

 


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  		Figure 3b. Facet anatomy on T1-weighted MR images (500/22). (a) Human study. Transverse image demonstrates the anterior (thin black arrows), lateral (black arrowheads), and posterior (white arrowheads) facets. The gluteus minimus tendon (large white arrow) is attached to the anterior facet and is surrounded by the anterior part of the gluteus minimus muscle (thick black arrows). The TrB (small white arrows) can be identified as a thin line. (b-d) Cadaveric study. (b) Coronal image through the anterior part of the greater trochanter shows the anterior facet (arrowheads) with the gluteus minimus tendon (curved arrow) attached to it. (c) Coronal image through the posterior part of the greater trochanter displays the lateral facet (arrowheads), the lateral part of the gluteus medius tendon (curved arrow), and the iliotibial tract (straight arrow). (d) Sagittal image shows the superoposterior facet (black arrowheads), with the main tendon (curved white arrow) of the gluteus medius muscle attached to it, and the posterior facet (white arrowheads). The piriformis tendon (straight white arrow), the obturator internus tendon (straight black arrow), and the obturator externus tendon (curved black arrow) are also seen.

 


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  		Figure 3c. Facet anatomy on T1-weighted MR images (500/22). (a) Human study. Transverse image demonstrates the anterior (thin black arrows), lateral (black arrowheads), and posterior (white arrowheads) facets. The gluteus minimus tendon (large white arrow) is attached to the anterior facet and is surrounded by the anterior part of the gluteus minimus muscle (thick black arrows). The TrB (small white arrows) can be identified as a thin line. (b-d) Cadaveric study. (b) Coronal image through the anterior part of the greater trochanter shows the anterior facet (arrowheads) with the gluteus minimus tendon (curved arrow) attached to it. (c) Coronal image through the posterior part of the greater trochanter displays the lateral facet (arrowheads), the lateral part of the gluteus medius tendon (curved arrow), and the iliotibial tract (straight arrow). (d) Sagittal image shows the superoposterior facet (black arrowheads), with the main tendon (curved white arrow) of the gluteus medius muscle attached to it, and the posterior facet (white arrowheads). The piriformis tendon (straight white arrow), the obturator internus tendon (straight black arrow), and the obturator externus tendon (curved black arrow) are also seen.

 


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  		Figure 3d. Facet anatomy on T1-weighted MR images (500/22). (a) Human study. Transverse image demonstrates the anterior (thin black arrows), lateral (black arrowheads), and posterior (white arrowheads) facets. The gluteus minimus tendon (large white arrow) is attached to the anterior facet and is surrounded by the anterior part of the gluteus minimus muscle (thick black arrows). The TrB (small white arrows) can be identified as a thin line. (b-d) Cadaveric study. (b) Coronal image through the anterior part of the greater trochanter shows the anterior facet (arrowheads) with the gluteus minimus tendon (curved arrow) attached to it. (c) Coronal image through the posterior part of the greater trochanter displays the lateral facet (arrowheads), the lateral part of the gluteus medius tendon (curved arrow), and the iliotibial tract (straight arrow). (d) Sagittal image shows the superoposterior facet (black arrowheads), with the main tendon (curved white arrow) of the gluteus medius muscle attached to it, and the posterior facet (white arrowheads). The piriformis tendon (straight white arrow), the obturator internus tendon (straight black arrow), and the obturator externus tendon (curved black arrow) are also seen.

 


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  		Figure 4a. Cadaveric study. (a) Transverse T1-weighted fat-saturated MR image (500/22) obtained after bursography shows the SGMiB (black and white arrowheads) deep to the main tendon of the gluteus minimus (curved black arrow) and extending medially to merge with the hip capsule. Contrast material is present in the hip joint space (curved white arrow). (b) The corresponding nonenhanced transverse T1-weighted MR image (500/22) shows the SGMiB (black arrowheads) as a hypointense thin line medial to the main tendon of the gluteus minimus (curved black arrow). The tubercle (straight white arrow) at the medial end of the anterior facet is the attachment site of the hip capsule. (c) The corresponding transverse anatomic section shows the distended SGMiB (black arrowheads) and TrB (white arrowheads). Note the close relationship between the SGMiB (black arrowheads) and the hip joint space (curved arrow). The osseous tubercle (straight arrow) with the attachment of the hip capsule can be easily identified. (d) Coronal T1-weighted fat-saturated MR image (500/22) through the anterior part of the trochanter after SGMiB bursography shows the relation of the contrast material in the bursal space (curved arrow) and the contrast material in the joint space (straight arrow), which had resulted from a previous inadvertent injection. (e) The corresponding coronal anatomic section shows the gluteus minimus muscle and tendon (white arrows) and the SGMiB (black arrowheads) deep to the gluteus minimus tendon. The anterior part of the gluteus medius attachment (black arrow) covers the gluteus minimus tendon.

 


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  		Figure 4b. Cadaveric study. (a) Transverse T1-weighted fat-saturated MR image (500/22) obtained after bursography shows the SGMiB (black and white arrowheads) deep to the main tendon of the gluteus minimus (curved black arrow) and extending medially to merge with the hip capsule. Contrast material is present in the hip joint space (curved white arrow). (b) The corresponding nonenhanced transverse T1-weighted MR image (500/22) shows the SGMiB (black arrowheads) as a hypointense thin line medial to the main tendon of the gluteus minimus (curved black arrow). The tubercle (straight white arrow) at the medial end of the anterior facet is the attachment site of the hip capsule. (c) The corresponding transverse anatomic section shows the distended SGMiB (black arrowheads) and TrB (white arrowheads). Note the close relationship between the SGMiB (black arrowheads) and the hip joint space (curved arrow). The osseous tubercle (straight arrow) with the attachment of the hip capsule can be easily identified. (d) Coronal T1-weighted fat-saturated MR image (500/22) through the anterior part of the trochanter after SGMiB bursography shows the relation of the contrast material in the bursal space (curved arrow) and the contrast material in the joint space (straight arrow), which had resulted from a previous inadvertent injection. (e) The corresponding coronal anatomic section shows the gluteus minimus muscle and tendon (white arrows) and the SGMiB (black arrowheads) deep to the gluteus minimus tendon. The anterior part of the gluteus medius attachment (black arrow) covers the gluteus minimus tendon.

 


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  		Figure 4c. Cadaveric study. (a) Transverse T1-weighted fat-saturated MR image (500/22) obtained after bursography shows the SGMiB (black and white arrowheads) deep to the main tendon of the gluteus minimus (curved black arrow) and extending medially to merge with the hip capsule. Contrast material is present in the hip joint space (curved white arrow). (b) The corresponding nonenhanced transverse T1-weighted MR image (500/22) shows the SGMiB (black arrowheads) as a hypointense thin line medial to the main tendon of the gluteus minimus (curved black arrow). The tubercle (straight white arrow) at the medial end of the anterior facet is the attachment site of the hip capsule. (c) The corresponding transverse anatomic section shows the distended SGMiB (black arrowheads) and TrB (white arrowheads). Note the close relationship between the SGMiB (black arrowheads) and the hip joint space (curved arrow). The osseous tubercle (straight arrow) with the attachment of the hip capsule can be easily identified. (d) Coronal T1-weighted fat-saturated MR image (500/22) through the anterior part of the trochanter after SGMiB bursography shows the relation of the contrast material in the bursal space (curved arrow) and the contrast material in the joint space (straight arrow), which had resulted from a previous inadvertent injection. (e) The corresponding coronal anatomic section shows the gluteus minimus muscle and tendon (white arrows) and the SGMiB (black arrowheads) deep to the gluteus minimus tendon. The anterior part of the gluteus medius attachment (black arrow) covers the gluteus minimus tendon.

 


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  		Figure 4d. Cadaveric study. (a) Transverse T1-weighted fat-saturated MR image (500/22) obtained after bursography shows the SGMiB (black and white arrowheads) deep to the main tendon of the gluteus minimus (curved black arrow) and extending medially to merge with the hip capsule. Contrast material is present in the hip joint space (curved white arrow). (b) The corresponding nonenhanced transverse T1-weighted MR image (500/22) shows the SGMiB (black arrowheads) as a hypointense thin line medial to the main tendon of the gluteus minimus (curved black arrow). The tubercle (straight white arrow) at the medial end of the anterior facet is the attachment site of the hip capsule. (c) The corresponding transverse anatomic section shows the distended SGMiB (black arrowheads) and TrB (white arrowheads). Note the close relationship between the SGMiB (black arrowheads) and the hip joint space (curved arrow). The osseous tubercle (straight arrow) with the attachment of the hip capsule can be easily identified. (d) Coronal T1-weighted fat-saturated MR image (500/22) through the anterior part of the trochanter after SGMiB bursography shows the relation of the contrast material in the bursal space (curved arrow) and the contrast material in the joint space (straight arrow), which had resulted from a previous inadvertent injection. (e) The corresponding coronal anatomic section shows the gluteus minimus muscle and tendon (white arrows) and the SGMiB (black arrowheads) deep to the gluteus minimus tendon. The anterior part of the gluteus medius attachment (black arrow) covers the gluteus minimus tendon.

 


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  		Figure 4e. Cadaveric study. (a) Transverse T1-weighted fat-saturated MR image (500/22) obtained after bursography shows the SGMiB (black and white arrowheads) deep to the main tendon of the gluteus minimus (curved black arrow) and extending medially to merge with the hip capsule. Contrast material is present in the hip joint space (curved white arrow). (b) The corresponding nonenhanced transverse T1-weighted MR image (500/22) shows the SGMiB (black arrowheads) as a hypointense thin line medial to the main tendon of the gluteus minimus (curved black arrow). The tubercle (straight white arrow) at the medial end of the anterior facet is the attachment site of the hip capsule. (c) The corresponding transverse anatomic section shows the distended SGMiB (black arrowheads) and TrB (white arrowheads). Note the close relationship between the SGMiB (black arrowheads) and the hip joint space (curved arrow). The osseous tubercle (straight arrow) with the attachment of the hip capsule can be easily identified. (d) Coronal T1-weighted fat-saturated MR image (500/22) through the anterior part of the trochanter after SGMiB bursography shows the relation of the contrast material in the bursal space (curved arrow) and the contrast material in the joint space (straight arrow), which had resulted from a previous inadvertent injection. (e) The corresponding coronal anatomic section shows the gluteus minimus muscle and tendon (white arrows) and the SGMiB (black arrowheads) deep to the gluteus minimus tendon. The anterior part of the gluteus medius attachment (black arrow) covers the gluteus minimus tendon.

 
The lateral facet was easily identified on the coronal and coronal oblique images through the posterior half of the trochanter (Fig 3c). It had to be carefully distinguished from the anterior facet, which had a similar configuration in the coronal plane but was clearly a more anterior structure (Fig 2, c, d; Fig 3b). On transverse images, the lateral facet appeared broader at its superior extent, being consistent with its inverted triangular shape. The superior border was in contact with the superoposterior facet, which constituted the most cranial part of the trochanter. The lateral facet was identified best on sagittal images. This facet was covered completely by the main tendon of the gluteus medius muscle (Fig 3d).

The sagittal plane was best for visualizing the posterior facet (Fig 3d). The contour was usually straight on sagittal images and curved on transverse images. On transverse images, the border between the lateral facet and the posterior facet was sometimes not well defined (Fig 3a). No tendon insertion was present on this facet, which was covered by the TrB.

Cadaveric Study: Abductor Attachments in the Greater Trochanter
The attachment sites of the gluteus medius and minimus muscles in relation to the facet anatomy are displayed in Figure 1b.

The gluteus medius attachment could be divided into three parts. The main tendon arose from the central posterior portion of the muscle and had a strong insertion covering the superoposterior facet (Fig 5). The main tendon in the transverse plane was flat and oval, with a coronal to coronal oblique orientation. This tendon was thicker medially than laterally. The mean anteroposterior diameter was 19.3 mm (range, 11–26 mm), and the mean mediolateral diameter was 7.0 mm (range, 4–12 mm). The lateral part of the gluteus medius tendon insertion was obliquely orientated in the lateral facet from posterior to anterior, and this tendon continued anteriorly covering the insertion of the gluteus minimus tendon. The lateral part of the gluteus medius tendon arose from the undersurface of the muscle and was usually thin or almost purely muscular in nature (Fig 3c). The anterior tendon was surrounded by and attached to the gluteus minimus tendon (Fig 3a) but was not visible macroscopically.



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  		Figure 5a. MR images (500/22) of the TrB in cadaveric study. (a) Transverse, (b) coronal, and (c) sagittal T1-weighted fat-saturated MR images obtained after bursography of the TrB (curved white arrow). (d) Transverse T1-weighted nonenhanced MR image shows TrB (white arrowheads) and SGMiB (black arrowheads) as thin hypointense lines, the gluteus minimus tendon (curved arrow), and the iliotibial tract (straight arrow).

 


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  		Figure 5b. MR images (500/22) of the TrB in cadaveric study. (a) Transverse, (b) coronal, and (c) sagittal T1-weighted fat-saturated MR images obtained after bursography of the TrB (curved white arrow). (d) Transverse T1-weighted nonenhanced MR image shows TrB (white arrowheads) and SGMiB (black arrowheads) as thin hypointense lines, the gluteus minimus tendon (curved arrow), and the iliotibial tract (straight arrow).

 


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  		Figure 5c. MR images (500/22) of the TrB in cadaveric study. (a) Transverse, (b) coronal, and (c) sagittal T1-weighted fat-saturated MR images obtained after bursography of the TrB (curved white arrow). (d) Transverse T1-weighted nonenhanced MR image shows TrB (white arrowheads) and SGMiB (black arrowheads) as thin hypointense lines, the gluteus minimus tendon (curved arrow), and the iliotibial tract (straight arrow).

 


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  		Figure 5d. MR images (500/22) of the TrB in cadaveric study. (a) Transverse, (b) coronal, and (c) sagittal T1-weighted fat-saturated MR images obtained after bursography of the TrB (curved white arrow). (d) Transverse T1-weighted nonenhanced MR image shows TrB (white arrowheads) and SGMiB (black arrowheads) as thin hypointense lines, the gluteus minimus tendon (curved arrow), and the iliotibial tract (straight arrow).

 
The gluteus minimus attachment could be divided into two distinct components. The main tendon demonstrated a consistent insertion in the anterior facet of the trochanter on its lateral and inferior aspect. In contrast with the gluteus medius muscle, the main tendon arose from the superficial part of the muscle fascia. The morphology of the tendon in the transverse plane was flat and biconcave. The main tendon usually was separated from the cortical bone by a thin linear region with a signal intensity isointense to the muscle. The mean anteroposterior diameter at 3 mm above the insertion site was 17.4 mm (range, 12–23 mm), and the mean mediolateral diameter was 4.0 mm (range, 2–6 mm). The transverse orientation of the tendon at the level of the acetabular roof was coronal oblique and parallel to the iliac wing. The tendon orientation twisted approximately 90° in an inward direction during its course to the insertion in the anterior facet. The second part of the gluteus minimus insertion was a muscular insertion in the ventral and superior capsule of the hip joint.

Cadaveric Study: MR Anatomy of the Trochanteric Bursae
The localization of the bursae is shown in Figures 1 and 2. Table 2 summarizes the mean size of each bursa. The results regarding the detection of bursae on nonenhanced MR images are shown in Table 3.


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  		TABLE 3. Detectability of the Bursae of the Greater Trochanter on Nonenhanced MR Images

 
The TrB was the largest of the three bursae. It covered the posterior facet, the distal lateral part of the gluteus medius tendon (lateral facet), and the proximal part of the vastus lateralis insertion. The bursa was located beneath the gluteus maximus muscle and the iliotibial tract (Figs 4c, 5). The TrB did not extend over the anterior border of the lateral facet. This bursa was lined by a small layer of fat on both sides. Therefore, it could be routinely identified on nonenhanced transverse MR images as a fine linear structure paralleling the posterior facet (Figs 3a, 5d).

The SGMeB was found deep to the lateral part of the gluteus medius tendon (Fig 6). The SGMeB covered an area of the superior part of the lateral facet. Its superior extent was marked by the tip of the trochanter; its anterior extent, by the lateral facet; and its posterior and inferior extent, by the tendinous insertion of the gluteus medius muscle. In one case, this bursa communicated with the SGMiB. The collapsed bursa could not be reliably identified on most nonenhanced MR images.



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  		Figure 6a. Cadaveric study. (a) Coronal T1-weighted fat-saturated MR image (500/22) through the lateral facet of the greater trochanter after bursography shows the SGMeB (arrowheads) deep to the lateral part of the gluteus medius tendon and muscle (arrows). (b) On the corresponding anatomic section, the SGMeB (arrowheads) is filled with gelatin.

 


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  		Figure 6b. Cadaveric study. (a) Coronal T1-weighted fat-saturated MR image (500/22) through the lateral facet of the greater trochanter after bursography shows the SGMeB (arrowheads) deep to the lateral part of the gluteus medius tendon and muscle (arrows). (b) On the corresponding anatomic section, the SGMeB (arrowheads) is filled with gelatin.

 
The SGMiB was found in the area of the anterior facet (Fig 4). The bursa lay beneath the gluteus minimus tendon, medial and superior to its insertion. The bursa extended medially, covering the distal anterior portion of the capsule of the hip joint (Fig 4a). Its close relationship to the joint capsule resulted in an intraarticular injection in one cadaver on the first attempt at bursography. A more lateral position allowed the entry of the needle into the bursa. The SGMiB was sometimes detected as a fine linear structure adjacent to the gluteus medius tendon on nonenhanced transverse MR images (Fig 4b). In most cases, however, these two structures were not distinguishable.

Human Study: MR Anatomy of the Trochanteric Bursae
The results regarding the detection of bursae on nonenhanced MR images of the volunteers are shown in Table 3. The TrB could be seen in almost all cases. Only in one volunteer with increased muscle mass and little fat was the bursa not seen. The detectability and visibility rates were in the same range for the cadaveric study and the human study.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
The greater trochanter of the femur demonstrates a complex but consistent topographic anatomy. An understanding of the anatomy of the four facets of the greater trochanter is essential because each facet has specific tendinous attachments and specific nearby bursae. In cadaveric specimens, the facets are easily delineated at gross inspection, and their appearance is also constant on cross-sectional MR images.

It is generally believed that muscular attachments to the bone demonstrate four consistent zones composed of tendon, unmineralized fibrocartilage, mineralized fibrocartilage, and Sharpey fibers (11). Although little variability is noted in the presence of these zones, wide variability can be noted in the extent in different tendons. This variability can make identification of distinct tendinous fibers difficult, as in the case of the gluteus medius and minimus attachments, which have large curving insertion sites in the trochanteric surface, each with strong tendinous as well as macroscopically evident, almost purely muscular attachments (3,4,10). Although differences in the function of both of these gluteal muscles have been emphasized in the literature (1,3,8), there are no specific clinical tests that can differentiate between dysfunction of these muscles.

Recently, an expanded spectrum of pathologic abnormalities affecting the soft tissues of the hip has been noted, with such findings including not only trochanteric bursitis but also the so-called rotator cuff tears of the hip (6,7). This term refers to a tear in one or more of the tendons of the abductor mechanism of the hip, similar to that seen in rotator cuff tears of the shoulder. Bunker et al (6) described the typical appearance of this tear as a circular or oval defect in the gluteus minimus tendon, which extended posteriorly in the lateral part of the gluteus medius tendon. In this report, the tear appeared to originate in the gluteus minimus tendon (6).

In a second series by Kagan (7), the rotator cuff tears of the hip were located in the anterior part of the gluteus medius tendon. During surgical exploration, signs of trochanteric bursitis and gluteal tendon tears often coexisted. In a reported series (12) of 35 patients with MR imaging evidence of either tendinosis or tendon tears in the abductor mechanism, all lesions were found in the gluteus medius tendon. However, 10 lesions extended into the gluteus minimus tendon.

Another reported series (13) detailed the imaging findings of tears and avulsive injuries of the gluteus medius muscle specifically. Four of six patients had a bony avulsion of the trochanteric tip at the site of the attachment of the main gluteus medius tendon, corresponding to the superoposterior facet. All four patients showed atrophy of the gluteus medius muscle as an associated finding (13). This analysis of previous reported finding appears to indicate a broad spectrum of lesions that affect different parts of the abductor mechanism.

Although inflammation of the synovial lining of bursal cavities is well documented, such bursitis may lead to nonspecific symptoms, resulting in missed diagnoses. Bursal cavities are frequently underestimated in their importance, and they even have been called "the Cinderellas of the body" (2). Bursae are found where tendons move against each other or glide over bony surfaces (1). There are about 20 bursae (1,2) about the hip joint, with variable extent and prevalence. The three bursae that are located about the greater trochanter and that are investigated here are reported most commonly (1). Some reports describe a separate subgluteus maximus bursa that lies distal to the TrB (14). In the literature, the subgluteus maximus bursa is also used synonymously with the TrB. In our analysis, only one bursa was seen in this location.

In the radiologic and orthopedic literature (14–19), only the TrB has received attention. To our knowledge, our report represents the first description of the cross-sectional anatomy and MR appearance of the bursal complex of the trochanter. The TrB almost always was seen on standard transverse T1-weighted spin-echo MR images as a thin hypointense line, because it is surrounded by fat on both sides (Fig 3a). The SGMiB is depicted less frequently; such depiction relates either to a separation of the bursa from the gluteus minimus tendon by a fat layer or to a medial extension of the bursa (Fig 4b). Depiction of this bursa is improved when it is distended either with an effusion or injection of a contrast agent.

Lateral hip pain is often a challenging diagnostic and therapeutic problem, with a wide range of differential diagnostic considerations that include articular disease, soft-tissue alteration, and referred pain from a distant pathologic condition. The spectrum of pathologic abnormalities includes classic trochanteric bursitis; degeneration and tears of the tendons of the gluteus medius and minimus muscles; arthritis of the hip; insufficiency fractures of the proximal portion of the femur, a spinal source of pain; and other nerve entrapment syndromes; as well as poorly defined syndromes such as pseudotrochanteric bursitis, adiposis dolorosa, tensor fasciae femoris syndrome, abductor muscle strain, and myofascial pain (19). Many of these disorders lead to similar clinical symptoms, and imaging studies such as routine radiography and bone scintigraphy may be unrewarding. MR imaging potentially may provide useful information to initiate the appropriate treatment.

The injection of the trochanteric bursae is technically easy to perform. In our small series, enhancement of all three bursae was successful. The main purpose for an intrabursal injection is related to diagnostic or therapeutic injection of local anesthetics and corticosteroids in patients with suspected trochanteric bursitis. The classic injection site is described as the point of maximum tenderness or the point where the greater trochanter is most palpable (18,20). Our results suggest that the injection site should be slightly more posterior, with the needle approaching the greater trochanter from a posterolateral position. Fluoroscopic guidance with contrast enhancement allows verification of intrabursal injection. Fluoroscopic or CT guidance also allows accurate localization of the two other smaller bursae for diagnostic or therapeutic purposes.

This study has some limitations. It is well known that bursal cavities show great variability. Owing to the small sample, this issue cannot be appropriately addressed with the results of our study. All of our injections were performed in cadavers of elderly patients. The extent and appearance of the bursae may be different in a younger population. Further, only limited clinical data were available regarding the cadaveric specimens, and clinical symptoms of the trochanteric region could not be completely excluded.

In conclusion, MR imaging and bursography provide detailed information about the anatomy of the tendinous attachments of the abductor muscles and the bursal complex of the greater trochanter of the femur. A detailed understanding of the anatomy of the trochanteric facets is important for understanding the structure, function, and pathologic abnormalities that are seen commonly in this region.


   FOOTNOTES
 
Abbreviations: SGMeB = subgluteus medius bursa, SGMiB = subgluteus minimus bursa, TrB = trochanteric bursa

Author contributions: Guarantors of integrity of entire study, C.W.A.P., D.R.; study concepts, D.R.; study design, C.W.A.P., D.R.; literature research, C.W.A.P.; clinical studies, C.W.A.P., D.J.T.; data acquisition, C.W.A.P., C.B.C.; data analysis/interpretation, C.W.A.P., N.H.T.; statistical analysis, C.W.A.P.; manuscript preparation, C.W.A.P., N.H.T.; manuscript definition of intellectual content, C.W.A.P., C.B.C., D.R.; manuscript editing, C.W.A.P.; manuscript revision/review, D.R., C.B.C.; manuscript final version approval, D.R.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
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