Subchondral insufficiency fractures of the femoral head

Bone Marrow Edema: Overview of Etiology and Treatment Strategies

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Bone marrow edema (BME) is a nonspecific but relevant finding, usually indicating the presence of an underlying pathology.

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The gold standard technique for detecting BME is magnetic resonance imaging (MRI), as it allows for a correct diagnosis to be made, which is extremely important given the heterogeneity of BME-related diseases.

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Depending on the severity of painful symptomatology and the MRI evidence, different treatment strategies can be followed: physical modalities, pharmacological options, and surgical therapy.

Rapid Destruction of the Hip Joint After Acetabular Fracture in an Elderly Patient

Cases of rapidly progressive destruction of the hip joint after acetabular fractures are rarely reported. A 78-year-old woman fell from a chair. There was no fracture diagnosis; however, retrospective evaluation of the plain radiograph showed a slightly displaced fracture of the acetabulum. Her pain worsened after experiencing additional minor falls. The left hip joint had severe bone defects at 3 months after the initial injury. She underwent total hip arthroplasty using a KT-plate with an autogenous bone graft for acetabular bone defects. This case indicates that rapid destruction of the hip joint may occur after acetabular fracture from minor falls and bone fragility in elderly patients. In such cases, closer follow-up with advanced imaging can lead to early surgical intervention before severe destruction develops.

Nomenclature of Subchondral Nonneoplastic Bone Lesions

OBJECTIVE. The purpose of this article is to summarize the nomenclature of nonneoplastic conditions affecting subchondral bone through a review of the medical literature and expert opinion of the Society of Skeletal Radiology Subchondral Bone Nomenclature Committee. CONCLUSION. This consensus statement summarizes current understanding of the pathophysiologic characteristics and imaging findings of subchondral nonneoplastic bone lesions and proposes nomenclature to improve effective communication across clinical specialties and help avoid diagnostic errors that could affect patient care.

Fat-suppressed T2-weighted MRI appearance of subchondral insufficiency fracture of the femoral head

OBJECTIVE

Our aims were to investigate the imaging appearance of subchondral insufficiency fracture (SIF) of the femoral head based on fat-suppressed T2-weighted MRI, and evaluate its correlation with the clinical outcomes following conservative treatment.

MATERIALS AND METHODS

We retrospectively evaluated 40 hips in 37 patients with SIF of the femoral head (12 males and 25 females; mean age 55.8 years, range 22-78 years). MRI examinations were performed within 3 months after the onset of hip pain. Using fat-suppressed T2-weighted imaging, we evaluated the hips for the intensity of the subchondral bone (corresponding to the area superior to the low intensity band on T1-weighted images) as well as bone marrow edema, joint effusion, and presence of the band lesion. We then correlated the intensity of the subchondral bone with clinical outcomes.

RESULTS

The hips were classified into three types based on subchondral intensity on fat-suppressed T2-weighted images: type 1 (21 hips) showed high intensity, type 2 (eight hips) showed heterogeneous intensity, and type 3 (11 hips) showed low intensity. The mean period between pain onset and MRI examination was significantly longer for type 2 hips than for type 1. Healing rates were 86 % for type 1, 75 % for type 2, and 18 % for type 3.

CONCLUSION

SIF cases were classified into three types based on subchondral intensity on fat-suppressed T2-weighted imaging performed within 3 months after pain onset. Type 3 SIF tended to be intractable to conservative treatment compared to type 1 and type 2.

The clinicopathologic findings of a subchondral insufficiency fracture of the femoral head in a male patient: a case report

There are few reports describing the clinicopathologic characteristics of subchondral insufficiency fractures of the femoral head (SIF) in men over 50 years of age. A 59-year-old man experienced a sudden onset of the left hip pain without any antecedent trauma. The hip pain did not improve despite conservative treatments, and he underwent a total hip arthroplasty. The mid-coronal cut section of the resected femoral head revealed a fracture line paralleling the subchondral bone endplate beneath the articular cartilage. In addition, the subchondral fracture broadly underlaid the weight bearing area of the femoral head. Histopathologically, reparative tissue including fracture callus and granulation tissue, as well as thin disconnected bone trabeculae were observed. These clinicopathological findings were similar to those of previously described SIF in women. It is therefore important to consider SIF in cases of acute hip pain, even in middle-aged men.

S3-Guideline non-traumatic adult femoral head necrosis

INTRODUCTION

The treatment of adult non-traumatic avascular necrosis of the femoral head (AVN; N-ANFH) within an estimated incidence of 5000-7000 cases per annum in Germany remains a challenge. Risk factors include steroids, alcohol abuse, chemotherapy and immunosuppressive medication, but a genetic predisposition has been suggested. Early diagnosis of this often bilateral disease process is essential for successful conservative or joint preserving surgical management. In this review, we present the update German consensus S3 guideline "diagnosis and management for N-ANFH" as a concise summary.

MATERIALS AND METHODS

This systematic review is based on the published literature from January 1, 1970 to April 31, 2013 (German and English language). Inclusion criteria were systematic reviews, meta-analyses and relevant peer review publications. We identified a total of 3715 related publications, of which 422 were suitable according to the SIGN criteria, but only 159 fulfilled our inclusion criteria.

RESULTS AND CONCLUSIONS

Clinical suspicion of N-ANFH mandates radiographic evaluation. If radiographs are normal MRI scans are recommended, which should be evaluated according to the ARCO-classification. Differential diagnoses include transient osteoporosis, bone bruise, insufficiency fracture and destructive arthropathy. Untreated, subchondral fractures commonly occur within 2 years, during which the risk for contralateral involvement is high-thereafter unlikely. Conservative management with Ilomedin and Alendronat can be tried, but other pharmacological or physical treatments are inappropriate. No specific joint preserving procedure can be recommended, but core decompression should be considered in early stages if necrosis is <30 %. In ARCO stages IIIc or IV total hip arthroplasty (THA) should be contemplated, which offers similar outcome compared to osteoarthritis. Young age is the main risk factor for higher revision rates after THA for N-ANFH.

Regional Articular Cartilage Abnormalities of the Hip

OBJECTIVE

Imaging of hip cartilage is challenging because of its limited thickness and complex geometry and therefore requires advanced MRI techniques. However, cartilage abnormalities are found in a number of disease entities, and their diagnosis may impact patient management. This article will provide pertinent information about the motivation to image hip cartilage, which imaging techniques to use, and how to analyze cartilage; finally, we will discuss disease entities with regional cartilage lesions, including the typical MRI findings.

CONCLUSION

Because the detection and quantification of regional cartilage abnormalities are critical for guidance of operative and nonoperative management of hip disorders, radiologists should be familiar with imaging and analysis techniques for assessing hip cartilage.

THE IMPORTANCE OF THE DIAGNOSIS OF SUBCHONDRAL FRACTURE OF THE FEMORAL HEAD, HOW TO DIFFERENTIATE IT FROM AVASCULAR NECROSIS AND HOW TO TREAT IT

Subchondral fracture of the femoral head is an uncommon and underdiagnosed affection. The abrupt or gradual onset of groin pain with functional disability on weight-bearing that improves with a resting period should alert the orthopedic surgeon to the possibility of this diagnosis. The differential diagnosis from osteonecrosis of the femoral head can be provided by assessing the different patterns of bone edema on MRI studies of the hip, thus avoiding unnecessary invasive operations on the hip.

Subchondral insufficiency fractures of the femoral head: associated imaging findings and predictors of clinical progression

OBJECTIVES

To characterize the morphology and imaging findings of femoral head subchondral insufficiency fractures (SIF), and to investigate clinical outcomes in relation to imaging findings.

METHODS

Fifty-one patients with hip/pelvis magnetic resonance (MR) images and typical SIF characteristics were identified and reviewed by two radiologists. Thirty-five patients had follow-up documentation allowing assessment of clinical outcome. Subgroup comparisons were performed using regression models adjusted for age and body mass index.

RESULTS

SIF were frequently associated with cartilage loss (35/47, 74.5 %), effusion (33/42, 78.6 %), synovitis (29/44, 66 %), and bone marrow oedema pattern (BMEP) (average cross-sectional area 885.7 ± 730.2 mm(2)). Total hip arthroplasty (THA) was required in 16/35 patients, at an average of 6 months post-MRI. Compared to the THA cohort, the non-THA group had significantly (p < 0.05) smaller overlying cartilage defect size (10 mm vs. 29 mm), smaller band length ratio and fracture diameters, and greater incidence of parallel fracture morphology (p < 0.05). Male gender and increased age were significantly associated with progression, p < 0.05.

CONCLUSIONS

SIF were associated with synovitis, cartilage loss, effusion, and BMEP. Male gender and increased age had a significant association with progression to THA, as did band length ratio, fracture diameter, cartilage defect size, and fracture deformity/morphology.

KEY POINTS

• Femoral head subchondral insufficiency fractures (SIF) frequently require total hip arthroplasty (THA). • SIF frequently coexist with synovitis, cartilage loss, and bone marrow oedema pattern. • SIF cartilage defect size, band length ratio, and fracture diameter/morphology can predict progression risk.

Stress fracture of the pelvis and lower limbs including atypical femoral fractures-a review

Stress fractures, that is fatigue and insufficiency fractures, of the pelvis and lower limb come in many guises. Most doctors are familiar with typical sacral, tibial or metatarsal stress fractures. However, even common and typical presentations can pose diagnostic difficulties especially early after the onset of clinical symptoms. This article reviews the aetiology and pathophysiology of stress fractures and their reflection in the imaging appearances. The role of varying imaging modalities is laid out and typical findings are demonstrated. Emphasis is given to sometimes less well-appreciated fractures, which might be missed and can have devastating consequences for longer term patient outcomes. In particular, atypical femoral shaft fractures and their relationship to bisphosphonates are discussed. Migrating bone marrow oedema syndrome, transient osteoporosis and spontaneous osteonecrosis are reviewed as manifestations of stress fractures. Radiotherapy-related stress fractures are examined in more detail. An overview of typical sites of stress fractures in the pelvis and lower limbs and their particular clinical relevance concludes this review.

Teaching Points

• Stress fractures indicate bone fatigue or insufficiency or a combination of these.

• Radiographic visibility of stress fractures is delayed by 2 to 3 weeks.

• MRI is the most sensitive and specific modality for stress fractures.

• Stress fractures are often multiple; the underlying cause should be evaluated.

• Infratrochanteric lateral femoral fractures suggest an atypical femoral fracture (AFF); endocrinologist referral is advisable.

Magnetic resonance perfusion and diffusion imaging characteristics of transient bone marrow edema, avascular necrosis and subchondral insufficiency fractures of the proximal femur

PURPOSE

To evaluate magnetic resonance (MR) perfusion and diffusion imaging characteristics in patients with transient bone marrow edema (TBME), avascular necrosis (AVN), or subchondral insufficiency fractures (SIF) of the proximal femur.

MATERIALS AND METHODS

29 patients with painful hip and bone marrow edema pattern of the proximal femur on non-contrast MR imaging were examined using diffusion-weighted and dynamic gadolinium-enhanced sequences. Apparent diffusion coefficients (ADCs) and perfusion parameters were calculated for different regions of the proximal femur. Regional distribution and differences in ADC values and perfusion parameters were evaluated.

RESULTS

Seven patients presented with TBME, 15 with AVN and seven with SIF of the proximal femur. Perfusion imaging showed significant differences for maximum enhancement values (Emax), slope (Eslope) and time to peak (TTP) between the three patient groups (p<0.05). In contrast, no significant differences for ADC values were calculated when comparing TBME, AVN, and SIF patients.

CONCLUSION

Diffusion weighted imaging of bone marrow of the proximal femur did not show significant differences between patients with TBME, AVN or SIF. In contrast, MR perfusion imaging demonstrated significant differences for the different patient groups and may as a complementary imaging technique add information to the understanding of the pathophysiology of diseases associated with bone marrow edema.

Imaging of musculoskeletal disorders related to pregnancy

OBJECTIVE

This article provides an overview of the typical appearance of biomechanical and physiologic changes in pregnancy and an update on related pathophysiology. Conditions occurring during the childbearing, delivery and postpartum periods will be reported separately.

CONCLUSION

Pregnancy causes biomechanical and physiologic changes that may be responsible for a wide spectrum of musculoskeletal disorders in the mother.

Subchondral insufficiency fracture of the femoral head in elderly people

We evaluated the clinical course of subchondral insufficiency fracture of the femoral head (SIFFH) and its characteristic findings with special regard to joint space narrowing (JSN). Thirty-one cases of SIFFH of mean age 68.9 yr initially underwent limited weight-bearing conservative treatment. During the follow-up period, the patients with intractable pain underwent total hip arthroplasty (THA). For radiographic evaluation, lateral center-edge angle, JSN and femoral head collapse (FHC) were documented, and the extent of FHC was classified as mild (<2 mm), moderate (2-4 mm), and severe (>4 mm). The progression or new development of FHC more than 2 mm was evaluated on sequential plain radiographs. The relationship between radiographic parameters and clinical outcomes were evaluated. THAs were performed in 15 cases (48.4%). There was no significant correlation between clinical outcomes and the extent of initial FHC. However, a significantly larger proportion of patients that underwent THA showed JSN and FHC progression compared to the symptom improvement group. The risk factor significantly associated with failed conservative treatment was JSN (P=0.038; OR, 11.8; 95% CI, 1.15-122.26). Clinical results of conservative treatment for SIFFH in elderly patients are relatively poor. The patients with JSN are at higher risk of failed conservative treatment.

Subchondral impaction fractures of the non-weight-bearing portion of the lateral femoral condyle

OBJECTIVE

To document the first report of intra-articular, non-weight-bearing, impaction fractures of the lateral femoral condyle.

MATERIALS & METHODS

Institutional Review Board and Regional Ethics Committee approval for this study was obtained and patient informed consent deemed unnecessary. We prospectively documented all potential cases of non-weight-bearing posterior subchondral impaction fractures of the femoral condyles diagnosed on magnetic resonance imaging (MRI) of the knee performed at our institution between January 2006 and December 2011. The cases were reviewed and discussed by three experienced musculoskeletal radiologists and only cases satisfying pre-defined MRI criteria were included.

RESULTS

Sixteen cases of intra-articular impaction fractures in a posterior, non-weight-bearing area of the lateral femoral condyle were diagnosed in patients with a mean age of 40. Eight were associated with recreational sports activities and 4 with repeated kneeling. There were no fractures documented in the non-weight-bearing aspect of the medial femoral condyles. Proposed underlying mechanisms for development of this type of fracture are presented.

CONCLUSION

Awareness, along with a high level of suspicion, that non-specific knee pain, especially in patients involved in athletic activities, could be due to intra-articular impaction fractures of the non-weight-bearing posterior aspect of the lateral femoral condyle is essential and MRI is the mainstay of diagnosis.

Destructive discovertebral degenerative disease of the lumbar spine

The uncommon variant of degenerative hip joint disease, termed rapidly progressive osteoarthritis, and highlighted by severe joint space loss and osteochondral disintegration, is well established. We present a similar unusual subset in the lumbar spine termed destructive discovertebral degenerative disease (DDDD) with radiological features of vertebral malalignment, severe disc resorption, and "bone sand" formation secondary to vertebral fragmentation. Co-existing metabolic bone disease is likely to promote the development of DDDD of the lumbar spine, which presents with back pain and sciatica due to nerve root compression by the "bone sand" in the epidural space. MRI and CT play a complimentary role in making the diagnosis.

Fractures of the femoral head: a long-term follow-up study

The femoral head fracture has become an increasingly frequent injury, usually sustained by individuals during high-energy trauma. Regardless of the type of treatment, long-term consequences, as avascular necrosis, post-traumatic arthritis, and heterotopic ossification, may complicate the clinical outcome leading to variable degree of disability. The aim of this study was to review the clinical and radiological long-term follow-up of patients with a fracture of the femoral head. Between January 1985 and January 2002, twenty-one patients with mean age 42.0 ± 15.9 years (range, 21-70 years) with a fracture of the femoral head were evaluated retrospectively. According to Pipkin's classification, there were four type I, nine type II, and eight type IV fractures. Functional outcomes were measured using the Merle d'Aubigné-Postel and Thompson-Epstein scoring scale. Heterotopic calcifications was graded according to the Brooker classification. All patients were followed up from 12 to 210 months, with an average of 81.19 ± 37.4 months. The average Merle d'Aubigné-Postel score was 12.9 ± 4.5. According to the Thompson-Epstein criteria, eight patients had excellent results, eight patients good, two patients fair, and three patients poor results. Overall, almost all (95. 2%) patients were determined to have radiographic criteria of post-traumatic arthritis (PA). Ten patients (47.6%) had a mild PA, seven patients (33.3%) had a moderate PA, and three patients (14.2%) had a severe PA. Open reduction and internal fixation of the fragments provided better results in comparison to excision. Although degenerative changes of the hip were observed in almost all patients, most severe case occurred in the excision group.

Hip Osteoarthritis MRI Scoring System (HOAMS): reliability and associations with radiographic and clinical findings

OBJECTIVE

To develop a semiquantitative MRI-based scoring system (HOAMS) of hip osteoarthritis (OA) and test its reliability and validity.

DESIGN

Fifty-two patients with chronic hip pain were included. 1.5T magnetic resonance imaging (MRI) was performed on all patients. Pelvic radiographs were scored according to the Kellgren-Lawrence (KL) system. Clinical outcomes were assessed by the hip osteoarthritis outcome score (HOOS). MRIs were analyzed using a novel whole-joint MRI score that incorporated 13 articular features. Reliability was determined on a random subset of 15 cases. Weighted-kappa statistics and overall agreement were used as a measure of intra- and inter-observer reliability. Associations between MRI features and radiographic OA severity were calculated using Cochran-Armitage test for trend. Ordinal logistic regression was used to assess associations between MRI features and severity of pain and functional limitation.

RESULTS

Distribution of radiographic grading was: KL 0=12 (27%), KL 1=11 (25%), KL 2=14 (32%), KL 3=5 (11%) and KL 4=2 (5%). Intra-reader reliability for the different features ranged from 0.18 (cysts) to 0.85 (cartilage). Inter-reader reliability ranged between 0.15 (cysts) and 0.85 (BMLs). Low kappas were due to low frequencies of some features as overall percent agreement was good to excellent (83.8% and 83.1%). There was a strong association between MRI-detected lesions and radiographic severity (P=0.002). Non-significant trends were observed between MRI features and clinical outcomes.

CONCLUSION

MRI-based semiquantitative assessment of the hip shows adequate reliability. Presence of more severe MRI-detected intraarticular pathology shows a strong association with radiographic OA. The results suggest possible associations between MRI-detected pathology and clinical symptoms.

[Transient bone marrow edema of the hip]

Transient bone marrow edema of the hip is characterized by moderate homogeneous low MR signal intensity with ill-defined margins that involves at least a portion of the femoral head. Spin echo T1-weighted images are helpful to exclude other underlying diseases (tumor, infection, necrosis from systemic origin…), for which marrow edema is secondary or no epiphyseal in location. High-resolution fat-suppressed T2-weighted or proton density images allow evaluation of the articular cartilage, subchondral bone and subchondal marrow: if the articular cartilage is abnormal, the lesion is irreversible (arthrosis or necrosis); if the subchondral bone is focally interrupted and/or if the femoral is no longer spherical, the lesion is irreversible (necrosis); if a focal linear fluid collection is present under the subchondral bone, the lesion is irreversible (necrosis). Finally, subchondral changes may provide useful prognostic information: the absence of any abnormality other than marrow edema typically indicates that complete resolution is likely; the presence of a focal T2-weighted hypointense lesion immediately next to the subchondral bone suggests an irreversible lesion, especially if it is equal to or thicker than 4mm or the joint space. In some instances, prognosis cannot be reliably determined requiring the need for follow-up imaging.

Role of MRI in hip fractures, including stress fractures, occult fractures, avulsion fractures

MR imaging plays a vital role in the diagnosis and management of hip fractures in all age groups, in a large spectrum of patient groups spanning the elderly and sporting population. It allows a confident exclusion of fracture, differentiation of bony from soft tissue injury and an early confident detection of fractures. There is a spectrum of MR findings which in part is dictated by the type and cause of the fracture which the radiologist needs to be familiar with. Judicious but prompt utilisation of MR in patients with suspected hip fractures has a positive therapeutic impact with healthcare cost benefits as well as social care benefits.

Prognostic factors associated with a subchondral insufficiency fracture of the femoral head

OBJECTIVE

The aim of this study was to identify the risk factors associated with the prognosis of a subchondral insufficiency fracture of the femoral head (SIF).

METHODS

Between June 2002 and July 2009, 25 patients diagnosed with SIF were included in this study. Sequential radiographs were evaluated for the progression of collapse. Clinical profiles, including age, body mass index, follow-up period and Singh's index, were documented. The morphological characteristics of the low-intensity band on T(1) weighted MRI were also examined with regards to four factors: band length, band thickness, the length of the weight-bearing portion and the band length ratio (defined as the proportion of the band length to the weight-bearing portion of the femoral head in the slice through the femoral head centre).

RESULTS

Radiographically, a progression of collapse was observed in 15 of 25 (60.0%) patients. The band length in patients with progression of collapse [22.5 mm; 95% confidence interval (CI) 17.7, 27.3] was significantly larger than in patients without a progression of collapse (13.4 mm; 95% CI 7.6, 19.3; p<0.05). The band length ratio in patients with progression of collapse (59.8%; 95% CI 50.8, 68.9) was also significantly higher than in patients without a progression of collapse (40.9%; 95% CI 29.8, 52.0; p<0.05). No significant differences were present in the other values.

CONCLUSION

These results indicate that the band length and the band length ratio might be predictive for the progression of collapse in SIF.

Risk factors leading to total hip arthroplasty in patients with subchondral insufficiency fractures of the femoral head

PURPOSE

To retrospectively evaluate factors leading to total hip arthroplasty (THA) in patients with subchondral insufficiency fractures (SIF) of the femoral head. METHODS. 5 men and 22 women aged 51 to 85 (mean, 72) years with SIF of the femoral head initially underwent conservative treatment. THA was later performed for 13 patients, as the hip pain became worse secondary to joint space narrowing and/ or femoral head collapse. Patient demographics and radiological variables were retrieved. Risk factors leading to THA in patients with SIF of the femoral head were identified. Receiver operating characteristic curves were used to determine optimal cut-off values for the significant risk factors.

RESULTS

2 men and 11 women aged 62 to 85 (mean, 74.9) years underwent THA and were followed up for 0.2 to 62 (mean, 13) months. The remaining 3 men and 11 women aged 51 to 81 (mean, 68) years underwent conservative treatment and were followed up for 9 to 93 (mean, 28) months. Patient age was the only risk factor for THA (p = 0.047, odds ratio = 1.13), the cutoff value being 71 years (sensitivity, 77%; specificity, 64%). The survival rate was significantly lower in patients aged 71 years or older than in those aged younger than 71 years (p < 0.05).

CONCLUSION

Elderly patients with SIF of the femoral head are at higher risk of undergoing THA.

MRI evaluation of collapsed femoral heads in patients 60 years old or older: Differentiation of subchondral insufficiency fracture from osteonecrosis of the femoral head

OBJECTIVE

The purpose of this article is to verify the hypothesis that osteonecrosis and subchondral insufficiency fracture of the femoral head can be differentiated on the basis of their appearance on MRI.

SUBJECTS AND METHODS

Between May 1998 and February 2009, we reviewed 30 consecutive hips in 30 patients, 60 years old or older at the time of onset of hip pain, with radiologic evidence of subchondral collapse of the femoral head and with both MR images and histologic results available. Both clinical and radiologic appearances were investigated. The patients were divided into two groups according to the shape of low-intensity bands on T1-weighted images. The first group showed concavity of the articular surface, which is characteristic of osteonecrosis, and the second group showed an irregular convexity of the articular surface, which is characteristic of subchondral insufficiency fracture.

RESULTS

Sixteen hips (53.3%) showed evidence of osteonecrosis, and 14 (46.7%) showed evidence of subchondral insufficiency fracture, which was consistent with the corresponding histopathologic diagnoses. In all cases of osteonecrosis, the patient had a history of either corticosteroid intake or alcohol abuse. Among patients with subchondral insufficiency fracture, the proportion of women was significantly higher than that among patients with osteonecrosis. A crescent sign (subchondral fracture) was present radiographically in about half of all cases in both groups.

CONCLUSION

The results of the present study suggest that the shape of the low-intensity band on MRI is useful for the differentiating subchondral insufficiency fracture from osteonecrosis. In addition, among osteoporotic elderly women without any history of corticosteroid intake or alcohol abuse, a diagnosis of subchondral insufficiency fracture should be considered.

Bicondylar spontaneous osteonecrosis of the knee: A case report

Spontaneous osteonecrosis of the knee was originally described as a distinct disorder in 1968. Characteristic imaging findings and distinctive demographic and clinical factors help distinguish this disease from other osteonecrotic conditions, with which it can be confused. This report presents a rare, atypical case of bicondylar spontaneous osteonecrosis of the knee in a young patient, and highlights the importance of a clear understanding of the clinical and radiographic characteristics of this condition to accurately diagnose and treat it when evaluating osteonecrotic lesions of the knee.

Magnetic resonance imaging of the hip

Standard magnetic resonance imaging (MRI) as well as MR arthrography (MRA) have been important diagnostic tools to assess for a spectrum of clinical presentations related to the hip. MRA has allowed the radiologist to closely examine intracapsular structures such as the acetabular labrum. In this article, we provide a general review of soft tissue and osseous anatomy of hips, especially focusing on the MR appearances of the acetabular labrum and the osseous morphology of the greater trochanter and ischial tuberosity with their muscle and tendon attachments. In addition, current topics in recent literature will be discussed such as femoroacetabular impingement (FAI) and rotator cuff tears of the hip.

Bone marrow edema of the femoral head and transient osteoporosis of the hip

The current article of this issue aims at defining the generic term of bone marrow edema of the femoral head as seen at MR imaging. It must be kept in mind that this syndrome should be regarded, not as a specific diagnosis, but rather as a sign of an ongoing abnormal process that involves the femoral head and/or the hip joint. We aim at emphasizing the role of the radiologists in making a specific diagnosis, starting from a non-specific finding on T1-weighted images and by focusing on ancillary findings on T2-weighted SE or fat-saturated proton-density weighted MR images.

Looking beyond low bone mineral density: multiple insufficiency fractures in a woman with post-menopausal osteoporosis on alendronate therapy

Insufficiency fractures occur most commonly in the pelvic girdle and in the sacrum, followed by the tibia and the femoral neck. Insufficiency fractures of the femoral diaphyses are rare, with only few reported cases in the literature. The strongest associations exist with untreated osteoporosis. We describe an unusual case of multiple insufficiency fractures in a 73-yr-old Chinese woman who presented with a 10-month history of bilateral groin pain and difficulty with walking in the absence of trauma, diagnosed 18 months following the commencement of anti-resorptive therapy with alendronate. The pathogenesis of such insufficiency fractures is poorly understood, but next to low bone mineral density and micro-architectural damage likely involves other components such as changes in bone turnover and patient-related factors (e.g. non-compliance). This case report and review of the literature draws attention to some of the challenges in the diagnosis and management of such rare insufficiency fractures.

MR Imaging of the Hip: Osseous Lesions

Because of the exquisite soft tissue contrast resolution of MR imaging combined with recent technologic developments, a variety of conditions involving the hip joint and adjacent bony structures can be well evaluated using MR imaging, with or without contrast material. Among the different conditions, hip trauma and avascular necrosis are the most frequent indications. Other entities for which MR imaging has proven its usefulness include subchondral fractures, osteochondritis dissecans, transient osteoporosis, bone tumors, inflammatory and infectious processes, and a variety of bone marrow disorders.