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Perthes lesion Radiology

A Perthes lesion was defined as a torn anterior labrum that on at least one imaging plane on MR images appeared to be partially attached to the glenoid, with or without visualization of an intact scapular periosteum The best initial test for the diagnosis of Perthes is a pelvic radiograph. In a small number of patients with Perthes, the radiograph will be normal and persistent symptoms will trigger further imaging, e.g. MRI Here is a case of Perthes lesion one of the types of anterior glenolabral injuries. Others include Bankart, ALPSA, and GLAD lesions 4 article feature images from this case 1 public playlist includes this cas The anterior labrum is detached form the cartilage but remains attached to the periosteum, consistent with a Perthes lesion (best seen on the ABER view). This is 3 to 5 o'clock. The tear extends superiorly into the bicipitolabral anchor causing a type III slap appearance. Humeral stripping of the central portion of the IGHL Shoulder arthrograms are most frequently performed to assess for glenoid labrum tears. Chondrolabral separation or detachment is when the bone and the labrum disconnect, with fluid extending between them and a Perthes lesion has chondrolabral separation with intact periosteum. 1 article features images from this cas

Perthes Lesion (A Variant of the Bankart Lesion

Perthes lesions. Adding the abduction-external rota-tion position to the protocol in patients in whom Perthes lesion is suspected will increase diagnostic accuracy and may reveal a Perthes lesion not visible on axial images, as was the case in 50% of the patients in our series. variation of the Bankart lesion, the Perthes lesion occurs whe A Perthes lesion is a labroligamentous avulsion like a Bankart, but with a medially stripped intact periosteum. On images of the shoulder with the arm in a neutral position, the torn labrum may be held in its normal anatomic position by the intact scapular periosteum, which thereby prevents contrast media from entering the tear

Perthes disease Radiology Reference Article

The lesion may also be difficult to diagnose during arthroscopy because the labrum is still in its correct anatomic position, thus emphasizing the critical role of imaging in diagnosis of this lesion (20,63). Figure 11a. Perthes lesion. (a) Axial MR arthrogram shows contour irregularity (arrowhead) at the chondrolabral junction A Perthes lesion (17a) is a variant of the Bankart, where the anterioinferior labrum is avulsed from the glenoid and the scapular periosteum remains intact but is stripped medially. 17 Figure 17: A fat suppressed axial T1-weighted MR arthrographic image of a Perthes lesion demonstrates an avulsed anteroinferior labrum (arrow) The aim of this study was to evaluate the use of MR imaging in the characterization of the Perthes lesion by correlating MR findings with findings at arthroscopy. CONCLUSION. The use of a combination of axial and abduction—external rotation position sequences on MR images can be helpful in the diagnosis of a Perthes lesion

Perthes lesion, described by Perthes in 1905, is defined as a tear of the glenoid labrum with intact scapular periosteum. The torn anterior labrum is often undisplaced and visualized in its normal location on conventional MR imaging Conclusion: The use of a combination of axial and abduction-external rotation position sequences on MR images can be helpful in the diagnosis of a Perthes lesion. A fluid-filled joint with capsular distension, caused by either a large amount of effusion or MR arthrography, was found to be helpful in outlining Perthes lesions

Perthes lesion Radiology Case Radiopaedia

Evaluation of developmental dysplasia, Perthes disease, and neuromuscular dysplasia of the hip in children before and after surgery: an imaging update. AJR 1995; 164:1067-1073. Crossref, Medline, Google Scholar; 16 Kaniklides C. Diagnostic radiology in Legg-Calvé-Perthes disease. Acta Radiol 1996; 406:1-28. Google Schola Radiology department of the Rijnland hospital, Leiderdorp and the Onze Lieve Vrouwe Gasthuis, Amsterdam, the Netherlands. Publicationdate 2012-04-02. Perthes lesion (arrow) Images in the ABER position are obtained in an axial way 45 degrees off the coronal plane (figure)

Perthes lesion is defined as an avulsion of the IGHL and labrum with intact periosteum; the intact but stripped periosteum connects to the IGHL (Fig. 17.17a, b). Perthes lesions are better visualized in ABER position Legg-Calvé-Perthes (LCP) disease is a common cause of hip pain and limp in preadolescent children. Early in its course, this condition, a form of idiopathic osteonecrosis (or osteochondrosis), may be difficult to diagnose both clinically and radiographically. MRI is a useful tool for the evaluation of LCP disease that may assist with prompt. In the Perthes lesion, the labral complex is detached from the glenoid, but the stripped peri osteum remains intact. The labral complex can often be in a normal position on conventional sequences. The ABER position can separate the base of the labrum and therefore help visualize Perthes lesions (Fig. 8A, 8B) Perthes lesion is a variant of Bankart lesion, presenting as an anterior glenohumeral injury that occurs when the scapular periosteum remains intact but is stripped medially and the anterior labrum is avulsed from the glenoid but remains partially attached to the scapula by intact periosteum Perthes lesion (a variant of the Bankart lesion): MR imaging and MR arthrographic findings with surgical correlation. AJR Am J Roentgenol 2002 ;178:233-237. Crossref , Medline , Google Schola

Perthes Lesion Courtesy-Stoller, Diagnostic Imaging Orthopaedics Courtesy Martin L. Schwartz, MD Clinical Prof. of Radiology, UAB . ALPSA (Anterior Labroligamentous Periosteal Sleeve Avulsion) Lesion Courtesy-Stoller, Diagnostic Imaging Orthopaedics Courtesy Martin L. Schwartz, MD Clinical Prof. of Radiology, UAB . GLAD (Glenoid Labrum Articula Perthes Lesion •Detached, labro-ligamentous complex •Medial stripping of anterior scapular periosteum. Perthes Lesion •Sometimes only seen Topics in Magnetic Resonance Imaging. 14(1): 35-50 • Waldt et al. Anterior Shoulder Instability. Radiology 2005; 237:578-58 Wischer TK, Bredella MA, Genant HK, Stoller DW, Bost FW, Tirman PF (2002) Perthes lesion (a variant of the Bankart lesion): MR imaging and MR arthrographic findings with surgical correlation. AJR Am J Roentgenol 178(1):233-237. doi: 10.2214/ajr.178.1.178023 Background: Osteochondritis dissecans (OCD) is estimated to occur in 2% to 7% of patients with Legg-Calvé-Perthes disease (LCPD). Unstable osteochondral fragments secondary to LCPD may produce mechanical symptoms requiring surgical intervention. Reattachment of the fragment with open reduction and internal fixation (ORIF) may provide good clinical outcomes Perthes lesion MRI imaging Perthes lesion , described by Perthes in 1905, is defined as a tear of the glenoid labrum with intact scapular periosteum. The torn anterior labrum is often undisplaced and visualized in its normal location on conventional MR imaging

Purpose: The purpose of this article is to report a new clinical entity of posterior instability of the shoulder and the results of its treatment. Type of study: Case series. Methods: The Kim's lesion, which is an incomplete and concealed avulsion of the posteroinferior labrum, was arthroscopically identified in 15 patients who presented with posterior or multidirectional posteroinferior. A plain radiograph is the initial imaging modality for diagnosis and management of shoulder dislocation and its associated osseous abnormalities such as Hill-Sachs deformity or osseous Bankart lesion. However, advanced imaging techniques such as multidetector CT (MDCT) with three-dimensional (3D) volume rendering and MRI can be helpful in. Perthes lesion (a variant of the Bankart lesion): MR imaging and MR arthrographic findings with surgical correlation. AJR Am J Roentgenol. 2002;178(1):233-7. PubMed Google Scholar 23. Bernhardson AS, Bailey JR, Solomon DJ, Stanley M, Provencher MT. Glenoid bone loss in the setting of an anterior labroligamentous periosteal sleeve avulsion tear

Metaphyseal lesion had low signal intensity in T1 weighted images and high signal intensity in inversion recovery images suggesting fluid or oedema in that area. There was no abnormality on the left hip joint (Fig 3a,b). The diagnosis of Perthes disease was made according to the radiological findings The Perthes lesion (Fig. 2c) is a variant of the Bankart lesion, which also occurs in patients with acute anterior instability. In the Perthes lesion the anteroinferior labro-ligamentous complex is detached from the glenoid, but unlike in the injury described by Bankart, the periosteum remains intact and is stripped anteromedially [ 27 , 31 , 36 ] Perthes lesion (Figure 11), described by Perthes in 1905, is defined as a tear of the glenoid labrum with intact scapular periosteum. The torn anterior labrum is often undisplaced and visualized in its normal location on conventional MR imaging Arthroscopy through the posterior portal (d) confirmed a complex ALPSA/Perthes lesion with a medially displaced labrum with granulation tissue (white arrows; lower half) and Perthes lesion (black arrows; upper half). This was a false-positive case of a classic Bankart lesion, and a false-negative case of a Perthes lesion

Variants of the Bankart lesion, where the scapular periosteum remains intact, are the anterior labroligamentous periosteal sleeve avulsion lesion, the Perthes lesion and the glenolabral articular disruption lesion. Anterosuperior labral tears are uncommon and must be differentiated from a normal sublabral foramen Bankart lesions are usually easily demonstrated by routine MRI workup, however, the other clinically significant labral injury types are less clear and may be missed, namely Perthes and ALPSA lesions.11, 12. In Perthes lesion - which was diagnosed in 6 patients - there is only minimal displacement of the torn anterior labrum due to still. 1. J Magn Reson Imaging. 2006 Jan;23(1):29-35. Anterior-inferior labral lesions of recurrent shoulder dislocation evaluated by MR arthrography in an adduction internal rotation (ADIR) position. Song HT(1), Huh YM, Kim S, Lee SA, Kim SJ, Shin KH, Suh JS

Perthes Lesion (A Variant of the Bankart Lesion

  1. MRA yielded 16 diagnoses of Bankart lesions, 5 of ALPSA lesions, and 14 of Perthes lesions. Albeit invasive, MRA seems to be a more reliable and accurate diagnostic imaging modality for the classification and treatment of instabilities compared to standard MRI
  2. Normal anatomical variants include: - sublabral foramen - sublabral recess - buford complex - capsular insertionsShoulder instability includes: - anterior glenohumeral instability: (a) anteroinferi..
  3. ALPSA lesion MRI imaging. November 29, 2012 Leave a comment. ALPSA lesion (described by Neviaser) is defined as an avulsion and medial rolling of the inferior labroligamentous complex along the scapular neck secondary to a chronic injury . The main differentiating point of ALPSA from a Perthes lesion is the displacement of the torn.

Perthes lesion. a T1-weighted FFE MR arthrography image in an axial plane at the level of the inferior glenoid labrum with the arm in neutral position demonstrates no obvious anteroinferior labroligamentous lesion.b T1-weighted fat suppressed TSE MR arthrography image of the same patient in an oblique axial plane in ABER position clearly demonstrates the avulsed anteroinferior labrum with. With GLAD lesions the articular cartilage defect can be subtle and often missed on imaging. A high index of suspicion is needed to appreciate the articular cartilage defect. Additionally, the piece of cartilage from the defect can occasionally be seen as in Fig. 12.3b, c. It is important to identify the articular cartilage lesion to prepare for.

The Radiology Assistant : Shoulder instability - MR

Imaging the Glenoid Labrum and Labral Tears RadioGraphic

Classification of Bankart and Bankart variant lesions. a Bankart lesion, b bony Bankart lesion, c Perthes lesion, d ALPSA (anterior labro-ligamentous periosteal sleeveavulsion) lesion, e GLAD (glenolabral articular disruption) lesion, f HAGL (humeralavulsion of glenohumeral ligaments) lesion.(LLC anteroinferior labro-ligamentous complex, P scapular periosteum, HH humeral head, AC articular. Perthes disease were analyzed retrospectively. Lateral subluxation was measured as the tear drop distance on radiographs. We focused on joint fluid, medial articular cartilage thickening, and abnormal lesion on MRI. Lateral subluxation continued significantly in patients with poor results. Among the MRI findings, the presence of an abnormal lesion was associated significantly with the. LESION BANKART HOMBRO PDF. En ortopedia, la lesión de Bankart es una rotura de la parte anteroinferior del reborde glenoideo o labrum glenoideo de la escápula, a consecuencia de una luxación anterior de hombro. Perthes lesion is variant of Bankart lesion, presenting as an anterior glenohumeral injury that occurs when the scapular periosteum. Perthes lesion of the shoulder: Perthes lesion is a variant of Bankart lesion where there is a tear of the glenoid labrum, but with an intact scapular periosteum [Figure 3] 6). There is only minimal displacement of the torn anterior labrum, and hence the lesions are difficult to diagnose on routine MRI or MRA

Legg-Calvé-Perthes disease (LCPD) is a condition in which the blood supply of the femoral head epiphysis is disrupted, resulting in epiphyseal osteonecrosis and chondronecrosis with cessation of growth of the ossific nucleus. It was independently recognized in 1910 by Arthur Legg of the United States, Jacques Calvé of France, Georg Perthes of. Legg-Calvé-Perthes disease was originally described independently in 1910 by Legg of the United States, Calvé of France, and Perthes of Germany. The condition is a disease of children in which the essential lesion is not simply ischemia, but also includes the resulting process of resorption, collapse, and repair, which may result in a painful. Angiography in Legg-Calvé-Perthes disease. Angiography in Legg-Calvé-Perthes disease. Théron, J 1980-04-01 00:00:00 Eleven cases of Legg-Calv#{233}-Perthes disease were studied angiographically by opacifying the femoral or medial circumflex artery. In the early stages of the disease, obstruction of the superior capsular arteries and devascularization of the epiphysis is shown

Legg-Calvé-Perthes disease | Image | Radiopaedia

The Bankart lesion is an injury of the Glenohumeral Joint. This is a ball-and-socket joint binds the scapular and the humerus. Parts of the joint are the labrum, a fibrocartilaginous structure around the glenoid, the capsule and ligaments and supporting muscle tendons Interestingly, postoperative imaging showed an immediate improvement in Goutallier scores and tendon atrophy scores, suggesting that repositioning the tendon had a substantial effect on both. Subjectivity of the grading system is an additional limitation, which some researchers have attempted to improve on by using quantitative analysis of.

Glenohumeral Instability - Radsourc

Phillip Tirman. S.A. Rubin. A 53-year-old man presented with a three-week history of left shoulder pain, pain and numbness in the left side of the neck, weakness in the left arm, and a 25-pound. The glenohumearal joint has a greater range of motion than any other joint in the body. The small size of the glenoid fossa and the relative laxity of the joint capsule renders the joint relatively unstable and prone to subluxation and dislocation. MR is the best imaging modality to examen patients with shoulder pain and instability Perthes lesions can be occult on both conventional non-arthrographic MRI and arthroscopy. The abduction external rotation (ABER) sequence of the MRI increased tension on the inferior glenohumeral ligament (IGHL) and hence exaggerate the pathology. Thus, increase sensitivity in detection. Case 8 (Perthes lesion Perthes disease (Necrosis of the femoral head) Other cases by these authors: A. Nordwig (4) . 1: Perthes disease (Necrosis of the femoral head) 2: Submucous hemangioma of the subglottic trachea 3: Adrenal hemorrhage in a Newborn 4: Primary sclerosing cholangitis (PSC) H. Hetschko (3) . 1: Glioblastoma multiforme in a newborn 2: Perthes disease (Necrosis of the femoral head The bony Bankart lesion is an avulsion fracture of the glenoid rim that carries with it the capsulolabral complex. Perthes, prior to Bankart in 1906 described a lesion with incomplete avulsion of the labrum and capsular stripping from the scapular neck. Because of the intact periosteum these lesions may be occult at both imaging and surgery

Perthes lesion MRI imaging Radiology Imaging Technique

  1. Perthes lesion visualized with ABER positioning. Upon abduction and external rotation of the shoulder, the labrum demonstrates a defect at the base on a fat suppressed T1-weighted image (arrow). There is still labral attachment to scapular periosteum. These findings are consistent with a Perthes lesion
  2. Perthes lesion (a variant of the Bankart lesion): MR imaging and MR arthrographic findings with surgical correlation AJR , 178 ( 2002 ) , pp. 233 - 237 CrossRef View Record in Scopus Google Schola
  3. In our study Perthes lesion (Fig. 15, Fig. 19) was the most prevalent labral injury and detected in 28 cases out of the 96 patients included in our study.MRA showed very high sensitivity in detecting all the 28 lesions with 100% sensitivity while CTA showed less capability detecting only 16 cases out of the 28 lesions by an accuracy of 57%
  4. Glenoid labrum articular disruption (GLAD) lesions are an uncommon concomitant injury associated with labral tears, occurring in 1.5-2.9% of cases. In previous reported cases, the articular lesion is debrided during repair of the labral injury, which may predispose patients to osteoarthritis, a longitudinal complication seen in articular debridement of the hip
  5. Start studying Diagnostic Imaging. Learn vocabulary, terms, and more with flashcards, games, and other study tools
  6. lesions, of ALPSA lesions, and of Perthes lesions. Albeit invasive, MRA seems to be a more reliable and accurate diagnostic imaging modality for the classi cation and treatment of instabilities compared to standard MRI. 1. Introduction Anterior shoulder instability is one of the most common orthopedic problems. Glenohumeral (GH) instability occur
  7. Imaging Shoulder joint II Lesions of the anterior labrum and inferior Perthes Lesion Small tear at the base of a non displaced or slightly displaced anterior labrium Young patient with history of dislocation . Perthes lesion; Avulsed labrum with intact perostium . ALPS

Perthes lesion (a variant of the Bankart lesion): MR

  1. LEGG-CALVE-PERTHES DISEASE Comparison of conventional radiography, MR imaging, bone scintigraphy and arthrography COSTA KANIKLIDES' , TORSTEN LONNERHOLMI , ANDERS MOB ERG^ and Bo SAHLSTEDT' Abstract In a prospective study of 22 patients (24 hips) with Legg-Calve-Perthes dis- ease (LCPD) the findings at conventional radiography, arthrography, bon
  2. Perthes lesion 115. Perthes lesion• Bankart variant (uncommon 5-10 % of Bankart lesions)• Detached IGHLC with intact scapular periosteum, which is stripped medially• Etio-pathology similar to Bankart lesion 116
  3. Pulmonary venous hypertension 46. Imaging features of pericardial lesion 47. Ultrasonographic evaluation of peripheral arterial diseases 2 3. BONES MAJOR QUESTIONS 1. Describe the calcium metabolism and radiological changes in hyperparathyroidism. 2. Discuss etiopathogenesis, clinical features and imaging appearances in Perthes disease. 3
  4. Perthes-Like Lesion in Wrist Joint: Stripping of Ulnar Collateral Ligament. It requires high resolution, high signal-to-noise, high contrast with a small field of view imaging for accurate assessment of anatomy and pathology, because each structure of the wrist is small and thin. In addition, MRI of the collateral ligaments of the wrist has.

Humeral avulsion of anterior glenohumeral ligament lesion MRI imaging. November 29, The main differentiating point of ALPSA from a Perthes lesion is the displacement of the torn labroligamentous tissue, which is undisplaced or shows minimal displacement in Perthes lesion. An ALPSA lesion differs from a Bankart lesion in that an ALPSA lesion. The affected breeds were mostly small-sized as shown in Figure 1. The weight of affected dogs varied from 1.3 kg to 17.3 kg, with 97.82% of the animals (n = 45) weighing from 1.3 kg to 7.1 kg. The age at which clinical manifestation occurred was from 2 to 24 months, and 67.39% (n = 31) were between 2 and 10 months old Imaging characteristics that suggest instability include T2 bright fluid surrounding the fragment, disruption of the subchondral bone and a 5mm or larger cyst adjacent to the lesion. 19 An unstable or displaced fragment is managed surgically. Small, stable lesions and open physes are associated with better outcomes. 2 During this process, X-rays are used to help the doctor position the needle and make sure the dye is injected in the right spot. Once the dye is absorbed, X-ray pictures are taken. You may be asked to lie still, or to move to different positions. A CT scan and MRI scan may also be taken while the dye is in your system

Anterior shoulder dislocation with Perthes lesion and HAGL

Video: Beyond the Cuff: MR Imaging of Labroligamentous Injuries

The Radiology Assistant : Hip pathology in Childre

Start studying NBCE Part III Radiology Findings Summary. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Soap-bubble osteolytic lesion filled with blood, Ballooning of cortex Most commonly found in the distal femur Legg-Calve Perthes AVN. Head of the Femur in a Child (AVN name) Osteochondritis Dessicans. Radiology: SA Musculoskeletal. STUDY. Flashcards. Learn. Write. Spell. Test. PLAY. Match. Gravity. Created by. csh1442. Terms in this set (84) 3 things that classify a bone lesion as aggressive. 1. cortical destruction 2. active/irregular periosteal reaction 3. indistinct transition zone. T/F Geographic, moth-eaten and permeative lysis patterns. Perthes disease, also called Legg-Calvé-Perthes disease, is a rare condition of the hip that affects only children. It develops when there is a temporary loss of blood supply to the rounded head of the femur (thigh bone) - the ball part of the ball and socket hip joint. Blood supply is important for bone, as it delivers oxygen.

Part 3: Upper Extremity Radiology Ke

iability of Perthes, and along with the age of the patient when first affected, is useful in predicting long-term outcomes. Published reports of treatment strategies and their success depend on effective classification of the disease severity and radiographic result at final follow-up concerning head sphericity, congruency with the acetabulum, and arthritis. This article reviews published. On the MR image, the lesion is visible as a disruption of the normal hypointense linear signal intensity of the subchondral bone (arrowheads). 46. Osseous Bankert. 47. A large Hill-Sach lesion as seen on a CT arthrogram 48. Perthes lesion. (a) Axial MR arthrogram shows contour irregularity (arrowhead) at the chondrolabral junction Radiology. 2008 Aug. 248(2):571-8. . Anderson IF, Crichton KJ, Grattan-Smith T. Osteochondral fractures of the dome of the talus. J Bone Joint Surg [Am]. 1989 Sep. 71(8):1143-52. . [Guideline] Griffith JF, Lau DT, Yeung DK, Wong MW. High-resolution MR imaging of talar osteochondral lesions with new classification

Imaging in Anterior Glenohumeral Instability Radiolog

Perthes lesion A Perthes lesion is a labroligamentous avulsion like a Bankart, but with a medially stripped intact periosteum. On images of the shoulder with the arm in a neutral position, the torn labrum may be held in its normal anatomic position by the intact scapular periosteum, which thereby prevents contrast media from entering the tear Conventional Radiology: Radiographic images are the most common method to start the study of a painful hip or pelvis, on suspicion of Perthes disease or another nosological entity, as it is a simple method to achieve, cheap and relatively easy to interpret. 2 With the clinical and radiological suspicion of Perthes disease, the study should be completed with more complex examinations that a. Synonyms: Calvé-Legg-Perthes disease, Perthes-Calvé-Legg disease. Introduction. This is a self-limiting hip disorder caused by varying degrees of ischaemia and subsequent necrosis of the femoral head . Characteristic features include: The essential lesion is loss of blood supply (avascular necrosis) of the nucleus of the proximal femoral. Advanced imaging is an umbrella term that refers to anatomy-based (structural), physiology-based (functional), and hybrid imaging methods that offer greater spatial and/or contrast resolution relative to conventional imaging methods in radiology such as radiography or ultrasound. Examples of advance History. 1890 - Broca and Hartmann gave a good description of the lesion, but their work was neglected. [5, serie IV, 312-336.June 1890]. 1906 - Perthes recognised that the inferior glenoid fracture with detachment of the labrum caused instability of the shoulder and emphasized reattachment of the labrum to stabilize the joint

Shoulder labral tears MRIHow is Perthes disease Diagnosed?Shoulder Mri Scan in Delhi by Dr Shekhar ShrivastavMRI of traumatic anterior injuries of the shoulderThe Radiology Assistant : Shoulder MR - InstabilityBankart Lesion Cases | eORIF

The case was recognised clinically as possibly one of Perthes' disease and treated accordingly. Subsequent radiographs proved this to be correct; the classical picture of Perthes' disease developed. The only definite abnormality to be detected in this film is the convexity of the upper border of the neck of the right femur on comparison with. Avascular necrosis (AVN), also called osteonecrosis or bone infarction, is death of bone tissue due to interruption of the blood supply. Early on, there may be no symptoms. Gradually joint pain may develop which may limit the ability to move. Complications may include collapse of the bone or nearby joint surface.. Risk factors include bone fractures, joint dislocations, alcoholism, and the use. Interesting Radiology Cases from Daily Practice and a Personal Reference. Monday, February 6, 2012. Bankart and Bankart variant lesion Legg-Calvé-Perthes disease (LCPD) is avascular necrosis (AVN) of the proximal femoral head resulting from compromise of the tenuous blood supply to this area. LCPD usually occurs in children aged 4-10 years. The disease has an insidious onset and may occur after an injury to the hip. In the vast majority of instances, the disorder is unilateral