Superior Gemellus Research Articles

Deep External Rotator Muscles of the Hip: An Anatomical and Architectural Study

The arrangement of sarcomeres within a muscle (referred to as the muscle architecture) can be used to predict a muscle's functional capability. Parameters that are measured when studying muscle architecture are muscle fascicle length, sarcomere length, and the mass of the contractile tissue. Using these measured values, physiological cross‐Sectional Area (PCSA, representative of sarcomeres arranged in‐parallel) and normalized fascicle length (LFn, representative of sarcomeres arranged in‐series) can be calculated. PCSA is currently the best predictor of the relative force production capability of a muscle, and LFn is the best predictor of the excursion potential of a muscle. Additionally, based on the well‐known force‐length relationship for human muscle, sarcomere length at a given posture can be used to predict the percentage of maximal force generating capability that the muscle can produce.In this study, the architectural parameters of six deep external rotator muscles of the hip (Piriformis, Quadratus Femoris, Obturator Internus, Obturator Externus, Gemellus Superior and Gemellus Inferior) were measured, and each muscle's anatomical pathway was photographed using high quality digital imaging. These muscles are primarily external rotators and stabilizers of the hip joint, and may be affected during hip surgery if the anatomical attachments or pathways are altered. Previously, there had been no detailed architectural data measured for these six deep hip external rotator muscles. The six muscles were removed from 12 embalmed cadavers on one side of the body (n=12, 6 male and 6 female, age 56–88 years). Each muscle was carefully removed from the cadaver using dissection hand tools and had all external fat, fascia and tendon removed. Muscle mass was measured using a digital scale. Three fascicles were isolated from different locations on the muscle and fascicle length was measured using a digital caliper. Three small biopsies were taken from each fascicle and were subjected to laser diffraction to measure sarcomere length. Table 1 shows all measured and calculated results. Obturator Internus is predicted to have the highest force generating capability (based on PCSA), and Piriformis is predicted to have the highest excursion potential (based on LFn). All of the six deep hip external rotator muscles have an average sarcomere length, measured in the neutral cadaveric posture, ranging between 2.41 um – 2.54 um. This suggests an ability for the muscles to produce 91 – 95% of their maximal force, on the ascending limb of the force‐length curve, in this posture. These data, in conjunction with modelling software, can be used to predict force generating capabilities throughout the hip range of motion, and will be valuable to predict changes in the muscles' behavior after being displaced from their respective anatomical attachments during hip surgery.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pelvic limb and tail musculature of the red kangaroo (Macropus rufus)

Most members of the marsupial mammalian family Macropodidae move around in their environments using a bipedal form of hopping and are instantly recognizable by their elongated lower limbs and long, robust, nonprehensile tails. Paleontologists rely on anatomical descriptions of living species to make inferences about locomotor evolution and how anatomical specializations in kangaroos vary with body size. Even though the locomotor anatomy of the smaller eastern grey kangaroo (Macropus giganteus) is well documented, a review of the literature demonstrates a near absence of documentation of the musculoskeletal anatomy of the red kangaroo (Macropus rufus), the largest living marsupial. To fill this gap in knowledge, this work describes the musculoskeletal anatomy of the pelvic limb and tail of the red kangaroo and documents anatomical differences from the eastern grey kangaroo and other large terrestrial marsupials. We performed two complete pelvic limb and tail dissections on two lightly embalmed red kangaroos: one male adult obtained from Grant's Farm nature park (St. Louis, MO), and one juvenile male obtained from Louisiana State University School of Veterinary Medicine. Anatomical features and attachments of all muscles were recorded and photographed during the dissection; skeletal remains were macerated and cleaned after dissection by a dermestid beetle colony. Our studies of the pelvic and tail musculature of red kangaroos demonstrated differences between eastern grey and red kangaroos in attachments for two specific muscles of the proximal pelvic limb: The attachments of the ischiofemoralis in the red kangaroo differ in that this muscle's proximal and distal attachments form broad aponeuroses, as opposed to narrower tendinous attachments in the eastern kangaroo. The small lateral rotators of the hip (obturator internus, obturator externus, piriformis, and the two gemellus muscles) in the red kangaroo are more distinct from one another, and the distal attachment of the piriformis is distal to the greater trochanter of the femur instead of medial to it, as described in the literature for the eastern grey kangaroo. Additionally, prominent muscle bellies for three muscles originating in the distal pelvic limb and attaching to the pes are nonexistent or inconsistent with the literature: the extensor digiti II and III longus, peroneus digiti IV, and peroneus digiti V are not found in either red kangaroo specimen, even though they've been described for the eastern red kangaroo. Ultimately, more specimens are necessary to verify these differences and address inconsistencies in the literature before we can make any inferences about how these differences may subtly affect locomotion in these closely related taxa.Support or Funding InformationThis research was supported by Indiana University School of Medicine.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Access to the Ischium: A Simple Extension of the Posterior Approach in Revision Hip Arthroplasty

AbstractReconstruction of acetabular defects in revision total hip arthroplasty (THA) requires excellent exposure. Most extensile approaches to the acetabulum were described in the trauma literature and are not beneficial for revision THA. This article describes a modification of the standard posterior surgical approach to improve visualization of the ischium as required for acetabular defect reconstruction, insertion of standard and custom triflange cages as well as posterior column plating. The current surgical technique utilizes an intermuscular plane between the gemellus inferior muscle and the obturator externus muscle. This intermuscular plane leads the surgeon directly to the ischium and facilitates easy extension toward the insertion of the hamstring muscles without compromising the insertion of the external rotator muscles along the ischium. This article describes a novel surgical approach to the posterior column and ischium under special consideration of the sciatic nerve, superior gluteal vessels, and medial femoral circumflex artery. This simple extension of the standard posterior approach optimizes exposure of the posterior column during revision THA using a posterior approach.

LENGTH CHANGE OF THE SHORT EXTERNAL ROTATORS OF THE HIP IN COMMON STRETCH POSITIONS: A CADAVERIC STUDY.

Stretching of the deep rotators of the hip is commonly employed in patients with lumbosacral, sacroiliac, posterior hip, and buttock pain. There is limited research demonstrating the effectiveness of common stretching techniques on the short external rotators of the hip. The objective of this study was to evaluate length change during stretching of the superior and inferior fibers of the piriformis, superior gemellus, obturator internus, and inferior gemellus. Repeated-measures laboratory controlled cadaveric study. Seventeen hip joints from nine embalmed cadavers (5 male; 4 female) with an age between 49-96 years were skeletonized. Polypropylene strings were attached from the origin to insertion sites of the short external rotators. The change of length (mm) noted by excursion of the strings was used as a proxy for change in muscle length, when the hip was moved from the anatomical position to four specific stretch positions: 1) 45 ° internal rotation from hip neutral flexion/extension, 2) 45 ° external rotation from 90 ° hip and knee flexion, 3) 30 ° adduction from 90 ° of hip and knee flexion, and 4) 30 ° of adduction with the hip and knee flexed so the lateral malleolus contacted the lateral femoral epicondyle of the contralateral limb , were recorded. There was a significant effect on string displacement by stretch position, F (15,166) = 14.67, p < .0005; Wilk's L = .097, partial n2 = .540. The greatest displacement of the strings corresponding to the superior piriformis, inferior piriformis, and the superior gemellus occurred in 30 ° adduction from 90 ° of hip and knee flexion. The obturator internus and inferior gemellus had the largest string displacement with 45 ° internal rotation from neutral flexion/extension. While all stretch positions caused a significant string displacement indicating length changes of the deep rotators of the hip, the three stretch positions that caused the greatest change were: 1) 30 ° adduction from 90 ° of hip and knee flexion, 2) 45 ° internal rotation from neutral flexion/extension, and 3) 45 ° external rotation with 90 ° hip and knee flexion. This study has clinical implications for the effectiveness of specific stretching techniques on the short external rotators of the hip with the potential to improve the validity of stretching protocols for patients with posterior hip or buttock pain. The piriformis and superior gemellus had a larger change in length when adducting the hip from 90 ° degrees of hip and knee flexion. The obturator internus and inferior gemellus had a greater length change when internally rotating the hip from neutral flexion/extension. 3.

High division of sciatic nerve associated with a double superior gemellus muscle

Abstract Introduction: The superior gemellus muscle is a lateral rotator of the thigh, functioning together with other muscles of the region such as the piriformis muscle. The sciatic nerve is the largest nerve of the human body. It arises from the lumbosacral plexus and divides into two nerves: the tibial and common fibular nerves, which normally appear near the apex of the popliteal fossa. It is responsible for the innervation of the muscles of the posterior compartment of the lower limb. Case report: We report a doubled superior gemellus muscle associated with a high division of the sciatic nerve on the left side of a cadaveric specimen. The other muscles of the region showed no abnormality. Conclusion: This variation may offer information to piriformis muscle syndrome and be of importance in radiology and surgery of the region.

Shared Distal Insertion of the Gluteus Medius and Piriformis Muscles and Implications for Rehabilitation Exercises

Motivation for this study was prompted by the discovery of bilateral shared tendinous insertion of the gluteus medius (GM) and piriformis (PM) muscles into the anterior trochanteric crest during routine dissection of the gluteal region of a 58-year -old male cadaver. We therefore asked, what is the frequency of GM and PM shared insertions into the greater trochanter, and how could this impact physical therapy interventions for piriformis syndrome? In 23 specimens from either side of 16 embalmed human cadavers, we dissected and characterized the detail of GM and PM insertions. We discovered that just over 50% of the specimens dissected exhibited shared tendinous insertions between the two muscles, and in one specimen, we observed additional fusion of fibers of the superior gemellus (SG) and obturator internus (OI) muscles into the PM. The distal attachments of the GM and PM are more complex than traditionally understood and should be considered when prescribing rehabilitation exercises to treat piriformis syndrome.

Bilateral Absence of Gemelli Muscles: Case Report

Bilateral Absence of Gemelli Muscles: Case Report

A superior gemellus tear in a degenerative hip: Is it relevant?

A superior gemellus tear in a degenerative hip: Is it relevant?

Comparative anatomy of the gluteal muscles of Sapajus libidinosus 1

ABSTRACT: New World primates Sapajus sp. unexpectedly display cognitive aspects, tool use, social behavior, memory and anatomical aspects similar to Old World primates, such as chimpanzees and baboons. Convergent evolutionary aspects must have occurred between Sapajus and Old World primates and should be verified not only in terms of behavior analysis, but also of anatomical structure. The pelvic region can provide data for evolutionary verification trends, since taking standing position is one of the characteristics associated to the use of tools by early humans and pongids. We used eight specimens of Sapajus libidinosus to describe the deep muscular structure of the pelvis. Unlike humans, the gluteus medius muscle in S. libidinosus is completely covered by the gluteus maximus and elongated as compared to humans and chimpanzees, putatively by the elongated pelvis of S. libidinosus. Considering origin and insertion, the gluteus maximus muscle resembles more its counterpart in baboons than in humans and chimpanzees, since this muscle in baboons is associated to semibiped posture and to the tail. Gluteus minimum, piriformis, superior gemellus, internal shutter, gemellus and lower square muscles are positioned in this order in relation to the cranial-caudal axis, with all of its tendons converging for a common insertion in the greater trochanter. The muscles of the gluteal region of S. libidinosus are similar to the baboon, especially regarding the gluteus maximus, which points to the evolutionary kinship of these animals.

Une complication musculaire rarissime de l’hémophilie: la myosite ossifiante

Circumscribed myositis ossificans is a benign condition characterized by heterotopic growth of bone in soft tissues. It usually occurs in adolescents or young adults. Very rare cases have been described among children. Its etiopathogenesis is not clear, however, it seems that a focal muscle necrosis or a hematoma may cause the lesion. The most common sites are the quadriceps and biceps brachii. We report the case of a 20-year-old patient with a personal history of hemophilia A, admitted in our Department of Physical Medicine and Functional Rehabilitation to receive treatment for both hip mobility limitation. This one was caused, one year before, by a fall of patient own height: the patient impacted on both hips with resulting pain and swelling to their level. Evolution was marked by progressive mobility limitation of both hips, resulting in functional impairment and reduction in walking space. Clinical examination objectified a painful limitation of both hip range of motion with no further accompanying sign. Standard radiographs and pelvic TC scan showed a muscle ossification around both hips, whose appearances was compatible with progressive myositis ossificans of femoris square muscle of both sides and of right inferior gemellus muscle. Surgery was proposed but rejected by the patient. He then received medical treatment and pain rehabilitation. Evolution was marked by a slight improvement in function.

Dynamic Ultrasonography of the Deep External Rotator Musculature of the Hip: A Descriptive Study

BackgroundNo detailed reports exist describing the methodology of ultrasound image acquisition of the deep external rotator muscles of the hip. Because gluteal pain and sciatica are common, ultrasound may be a useful dynamic imaging adjunct in the evaluation of these patients. ObjectiveTo describe dynamic ultrasonography of the deep external rotator muscles of the hip for diagnostic purposes. DesignDescriptive. SettingUniversity radiology department. ParticipantsParticipants (n = 25; 14 male) without gluteal pain or sciatica were enrolled (mean age 27.6 ± 4.7 years; mean body mass index 26.0 ± 4.1 kg/m2). MethodsUltrasonographic cine clips oriented to the long axis of each deep external rotator muscle were captured. In addition, cine clips of the piriformis tendon and obturator internus tendon were obtained. Cine clips were analyzed approximately 1 week after completion of image acquisition independently by 2 blinded raters. Main Outcome MeasuresA 5-point Likert scale to evaluate the diagnostic utility of the ultrasound image. ResultsThe modal Likert scores for rater 1 were as follows: piriformis muscle = 4; piriformis tendon = 4; superior gemellus muscle = 3; obturator internus muscle = 4; obturator internus tendon = 4; inferior gemellus muscle = 4; quadratus femoris muscle = 4. The modal scores for rater 2 were: piriformis muscle = 4; piriformis tendon = 3; superior gemellus muscle = 4; obturator internus muscle = 3; obturator internus tendon = 4; inferior gemellus muscle = 3; quadratus femoris muscle = 4. ConclusionDynamic ultrasonography may be useful to image the hip deep external rotator musculature for diagnostic purposes and therefore aid in the evaluation of gluteal pain and sciatica. Future work should investigate the reliability and validity of ultrasonography in the evaluation of pathology of these muscles.

Fetal Development of the Human Obturator Internus Muscle With Special Reference to the Tendon and Pulley.

To examine the development of the tendon pulley of the obturator internus muscle (OI), we observed paraffin sections of 26 human embryos and fetuses (∼6-15 weeks of gestation). The OI was characterized by early maturation of the proximal tendon in contrast to the delayed development of the distal tendon. At 6 weeks, the ischium corresponded to a simple round mass similar to the tuberosity in adults. At 8 weeks, before development of the definite lesser notch of the ischium, initial muscle fibers of the OI, running along the antero-posterior axis, converged onto a thick and tight but short tendon running along the left-right axis. Thus, at the beginning of development, the OI muscle belly and tendon met almost at a right angle. At 10 weeks, the OI tendon extended inferiorly along the sciatic nerve, but the distal part remained thin and loose and it was embedded in the gluteus medius tendon. At 15 weeks, in association with the gemellus muscles, the distal OI tendon was established. The mechanically strong sciatic nerve was first likely to catch the OI muscle fibers to provide a temporary insertion. Next, the ischium developing upward seemed to push the tendon to make the turn more acute along the cartilaginous ridge. Finally, the gemellus muscle appeared to provide inferior traction to the OI tendon for separation from the gluteus medius to create the final, independent insertion. Without such guidance, the piriformis tendon first attached to the OI tendon and then merged with the gluteus medius tendon.

Surgically Relevant Bony and Soft Tissue Anatomy of the Proximal Femur.

Background:Hip endoscopy facilitates the treatment of extra-articular disorders of the proximal femur. Unfortunately, current knowledge of proximal femur anatomy is limited to qualitative descriptions and lacks surgically relevant landmarks.Purpose:To provide a quantitative and qualitative analysis of proximal femur anatomy in reference to surgically relevant bony landmarks.Study Design:Descriptive laboratory study.Methods:Fourteen cadaveric hemipelvises were dissected. A coordinate measuring device measured dimensions and interrelationships of the gluteal muscles, hip external rotators, pectineus, iliopsoas, and joint capsule in reference to osseous landmarks.Results:The vastus tubercle, superomedial border of the greater trochanter, and femoral head-neck junction were distinct and reliable osseous landmarks. The anteroinferior tip of the vastus tubercle was 17.1 mm (95% CI: 14.5, 19.8 mm) anteroinferior to the center of the gluteus medius lateral insertional footprint and was 22.9 mm (95% CI: 20.1, 25.7 mm) inferolateral to the center of the gluteus minimus insertional footprint. The insertions of the piriformis, conjoint tendon of the hip (superior gemellus, obturator internus, and inferior gemellus), and obturator externus were identified relative to the superomedial border of the greater trochanter. The relationship of the aforementioned footprints were 49% (95% CI: 43%, 54%), 42% (95% CI: 33%, 50%), and 64% (95% CI: 59%, 69%) from the anterior (0%) to posterior (100%) margins of the superomedial border of the greater trochanter, respectively. The hip joint capsule attached distally on the proximal femur 18.2 mm (95% CI: 14.2, 22.2 mm) from the head-neck junction medially on average.Conclusion:The vastus tubercle, superomedial border of the greater trochanter, and the femoral head-neck junction were reliable osseous landmarks for the identification of the tendinous and hip capsular insertions on the proximal femur. Knowledge of the interrelationships between these structures is essential for endoscopic navigation and anatomic surgical repair and reconstruction.Clinical Relevance:The qualitative and quantitative clinically relevant anatomic data presented here will aid in the diagnosis of proximal femur pathology and will provide a template for anatomic repair or reconstruction.

Sciatica and Claudication Caused by Ganglion Cyst

Case report. We report a rare case that a ganglion cyst compressed the sciatic nerve and caused sciatica and claudication in a 51-year-old male. Sciatica and claudication commonly occurs in spinal stenosis. To our knowledge, only 4 cases have been reported on sciatica resulting from posterior ganglion cyst of hip. A 51-year-old male had a 2-month history of radiating pain on his right leg. He could only walk 20 to 30 m before stopping and standing to rest for 1 to 3 minutes. Interestingly, he was able to walk longer distances (about 200 m) when walking slowly in small steps, without any rest. He had been treated as a case of lumbar disc herniation, but conservative treatment was ineffective. On buttock examination, a round, hard, and fixative mass was palpated at the exit of the sciatic nerve. MR imaging of hip revealed a multilocular cystic mass located on the posterior aspect of the superior gemellus and obturator internus, compressing the sciatic nerve. On operation, we found that the cyst extended to the superior gemellus and the obturator internus, positioned right at the outlet of the sciatic nerve. At 18 months of follow-up, the patient continued to be symptom free. He returned to comprehensive physical activity with no limitations. For an extraspinal source, a direct compression on the sciatic nerve also resulted in sciatica and claudication. A meticulous physical examination is very important for the differential diagnosis of extraspinal sciatica from spinal sciatica.

Bilateral Absence of Superior Gemellus Muscle in Elderly Cadaver

El musculo gemelo superior (SGM) que se origina de la superficie externa de la parte posterior del isquion, se une a la parte superior del tendon del musculo obturador interno, y se introduce con el en la superficie medial del trocanter mayor. En este trabajo se describe una variacion anatomica en la que el SGM esta ausente bilateralmente. Debido a la escaza descripcion de esta variacion, es relevante conocer la ausencia de la SGM, con el fin de mejorar el conocimiento anatomico y clinico de este hallazgo.

Ultrasound-guided perineural steroid injection to treat intractable pain due to sciatic nerve injury

Sciatic neuropathy is a rare but serious complication of cardiac surgery. Neuropathic pain following nerve injury can be severely debilitating and largely resistant to treatment. We present a case of this complication where ultrasound-guided perineural steroid injection at the site of the sciatic nerve injury provided excellent pain relief and facilitated subsequent rehabilitation. A 17-yr-old boy developed bilateral sciatic neuropathy after a nine-hour cardiac surgical procedure in the supine position, resulting in debilitating dysesthesia refractory to neuropathic pain therapies and leading to severe functional limitation. With magnetic resonance imaging of the lower extremities, the location of the lesion was determined to be from the level of the superior gemellus to the level of the quadratus femoris. An ultrasound-guided injection of triamcinolone 20 mg and lidocaine 40 mg around both sciatic nerves at the level of the lesion was administered two months after the surgery, and the pain score (rated on a scale 0-10) at rest decreased from 9-10 to 1 two weeks after the injection. There are a limited number of reports in the literature on sciatic nerve injuries associated with cardiac surgery. This case illustrates the efficacy of ultrasound-guided steroid injection around sciatic nerves at the level of superior gemellus in treating our patient's neuropathic pain.

Undescribed variation of the sciatic nerve

Piriformis muscle syndrome has been increasingly recognized as a cause of leg pain. Overuse, strain, or anatomical variations of the relationship between the nerve and the piriformis muscle are thought to be the underlying causes of the entrapment of the sciatic nerve. We report a previously undescribed variation found during a routine dissectionDuring a routine dissection of the left gluteal region of an adult male cadaver we observed a high division of the sciatic nerve and the presence of an accessory piriformis muscle. The sciatic nerve divided beneath the piriformis muscle and the common fibular nerve passed over the accessory piriformis muscle, whereas the tibial nerve reflected anteriorly to pass between the accessory piriformis and the superior gemellus muscle. Additionally, both nerves communicated with a side branch under the inferior border of the accessory piriformis muscle and the inferior gluteal nerve originated from the fibular nerve.Anatomical variations in the relationship between the piriformis muscle and the sciatic nerve may be present in up to 17% of the population. Six different variations have been described and none of them is similar to our description. Though complete understanding of the physiopathology of the piriformis muscle syndrome remains to be elucidated, knowledge of the possible anatomical variations may be useful for its adequate diagnosis and treatment.

Clinical Significance of Pathophysiology in Piriformis Syndrome Due to Multiple Variations in the Deep Gluteal Region

A relationship between the piriformis muscle and the sciatic nerve, which is observed to be unusual has been suggested to be a cause of piriformis syndrome. During dissection of a male cadaver, several anatomical variations were encountered. These variations consist of atypical organization of the sacral plexus, unusual origins, trajectories of common fibular, tibial, and inferior gluteal nerves. It is also observed that the presence of a common tendon formed by the deep gluteal muscles (obturator internus, superior gemellus, inferior gemellus, and both piriformis muscles, a duplication of the piriformis muscle) inserts on the greater trochanter of the femur. Additionally, an early division of the sciatic nerve, where a common fibular nerve that runs between the two variant piriformis muscles, and the tibial nerve which is making its way below the inferior piriformis, is also observed. These anatomical variations are found to be bilateral. In these casses the unusual pathway of this sciatic nerve and its relationship with the piriformis may predispose to its impingement at the gluteal region. The prevalence of the piriformis and the sciatic nerve anomalies is 16.2% in surgical cases. Thus, clinicians and surgeons should be aware of the potential complications from these unique variations.

Analysis of the sensory innervations of the greater trochanter for improving the treatment of greater trochanteric pain syndrome

In medical practice, greater trochanteric pain syndrome has an incidence of 5.6 per 1,000 adults per year, and affects up to 25% of patients with knee osteoarthritis and low back pain in industrialized nations. It also occurs as a complication after total hip arthroplasty. Different etiologies of the pain syndrome have been discussed, but an exact cause remains unknown. The purpose of this study was to obtain a better understanding of the sensory innervations of the greater trochanter in attempt to improve the treatment of this syndrome. Therefore, we dissected the gluteal region of seven adult and one fetal formalin fixed cadavers, and both macroscopic and microscopic examination was performed. We found a small sensory nerve supply to the periosteum and bursae of the greater trochanter. This nerve is a branch of the n. femoralis and accompanies the arteria and vena circumflexa femoris medialis and their trochanteric branches to the greater trochanter. This nerve enters the periosteum of the greater trochanter directly caudal to the tendon of the inferior gemellus muscle. This new anatomical information may be helpful in improving therapy, such as interventional denervation of the greater trochanter or anatomically guided injections with corticosteroids and local anesthetics.

Anatomic Mapping of Short External Rotators Shows the Limit of Their Preservation During Total Hip Arthroplasty

The direct anterior approach in THA requires no detachment of muscle insertions. However, damage to the short external rotator muscles may occur when attempting to elevate the femur for exposure. Although the anatomic insertions of these muscles are approximately known, there are no quantitative data regarding their locations. We therefore asked where and how the tendons attach to the inner aspect of the greater trochanter. In 20 cadaveric hips we identified the attachments of the short external rotator tendons on the medial aspect of the greater trochanter. Mapping of the attachment site was performed by defining coordinate axes; the total width and height of the greater trochanter represented 100% and distances of the attachment from the anteroinferior reference point were given. The mean anterior border location of the conjoined tendon (obturator internus, gemellus superior, and gemellus inferior) attachment was located at 29% (13 mm from the anteroinferior reference point), its posterior border at 53% (23 mm), its mean superior border at 70% (15 mm), and its mean inferior border at 24% (5 mm). The mean anterior border of the piriformis tendon attachment was located at 57% (25 mm), its mean posterior border at 78% (34 mm), its mean superior border at 64% (17 mm), and its inferior border at 55% (12 mm). There was considerable variation in these attachment sites among individuals. The insertion of the conjoined tendon extends to the anterosuperior aspect of the greater trochanter. Together with the considerable variation of the attachment site, external rotator muscles remain at risk of being damaged during the capsular release.