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Several pathologic conditions may manifest as an osteochondral lesion of the knee that consists of a localized abnormality involving subchondral marrow, subchondral bone, and articular cartilage. Although understanding of these conditions has evolved substantially with the use of high-spatial-resolution MRI and histologic correlation, it is impeded by inconsistent terminology and ambiguous abbreviations. Common entities include acute traumatic osteochondral injuries, subchondral insufficiency fracture, so-called spontaneous osteonecrosis of the knee, avascular necrosis, osteochondritis dissecans, and localized osteochondral abnormalities in osteoarthritis. Patient demographics, the clinical presentation, and the role of trauma are critical for differential diagnosis. A localized osteochondral defect can be created acutely or can develop as an end result of several chronic conditions. MRI features that aid in diagnosis include the location and extent of bone marrow edema, the presence of a fracture line, a hypointense area immediately subjacent to the subchondral bone plate, and deformity of the subchondral bone plate. These findings are essential in diagnosis of acute traumatic injuries, subchondral insufficiency fracture, and its potentially irreversible form, spontaneous osteonecrosis of the knee. If the lesion consists of a subchondral region demarcated from the surrounding bone, the demarcation should be examined for completeness and the presence of a "double-line sign" that is seen in avascular necrosis or findings of instability, which are important for proper evaluation of osteochondritis dissecans. Subchondral bone plate collapse, demonstrated by the presence of a depression or a fluid-filled cleft, can be seen in advanced stages of both avascular necrosis and subchondral insufficiency fracture, indicating irreversibility. Once the diagnosis is established, it is important to report pertinent MRI findings that may guide treatment of each condition. © RSNA, 2018 An earlier incorrect version of this article appeared online. This article was corrected on August 23, 2018.

Purpose: To assess potentially predictive factors that were evaluated 1 year after the onset of symptoms in patients with spontaneous osteonecrosis of the knee (SONK) and to determine receiver operating characteristic (ROC) curve cut-off values., Methods: Within 1 year of symptom onset, patients with SONK-selected treatment options, mainly based on severity of pain, chose either conservative treatment (n = 27 knees) or operative treatment (n = 27 knees). Knee and whole-leg radiographs, knee MRIs and bone mineral density scans of the lumbar spine, femoral neck and femoral condyles were obtained. The parameters measured were: (1) anatomical angle on whole-leg radiograph and (2) lesion size and medial meniscus extrusion on MRI., Results: The anatomical angle and lesion size in the sagittal section (depth) on MRI were markedly larger in the operative treatment group than those in the conservative treatment group. The anatomical angle and depth on MRI of SONK at Stages 1-3 were significantly different between groups, with odds ratios (95 % confidence intervals) of 1.16 (1.18-2.34) and 1.11 (1.01-1.23). One year after symptom onset, ROC curve cut-off value for anatomical angle was 180° and depth on MRI was 20 mm., Conclusion: An anatomical angle >180° and depth >20 mm on MRI were predictive factors for a poorer prognosis 1 year after symptom onset in patients with SONK. Our results on radiographs and MRI provided a predictive prognosis for patients with SONK at the initial visit to their orthopaedic surgeons., Level of Evidence: III.

Background: Avascular necrosis after arthroscopic surgery of the knee has already been published. The purpose of this article is to report on the frequently misdiagnosed entity of osteonecrosis of the medial tibial plateau., Case Presentation: Charts and radiographs of a consecutive series with isolated medial tibial plateau osteonecrosis were analyzed. The criterion for inclusion was the absence of trauma. Six caucasian female patients with an average age of 76.5 years complied with this criterion. Three of these cases had had arthroscopic intervention for medial meniscal lesion within the previous year., Conclusions: The etiology of these necroses remains unclear. Osteonecrosis must be taken into account as a possible cause of persistent knee pain after surgery. Correlation between arthroscopic treatment and necrotic processes in the tibial plateau must still be regarded with skepticism.

Bone marrow lesions (BMLs) around the knee are a common magnetic resonance imaging (MRI) finding. However, despite the growing interest on BMLs in multiple pathological conditions, they remain controversial not only for the still unknown role in the etiopathological processes, but also in terms of clinical impact and treatment. The differential diagnosis includes a wide range of conditions: traumatic contusion and fractures, cyst formation and erosions, hematopoietic and infiltrated marrow, developmental chondroses, disuse and overuse, transient bone marrow oedema syndrome and, lastly, subchondral insufficiency fractures and true osteonecrosis. Regardless the heterogeneous spectrum of these pathologies, a key factor for patient management is the distinction between reversible and irreversible conditions. To this regard, MRI plays a major role, leading to the correct diagnosis based on recognizable typical patterns that have to be considered together with coexistent abnormalities, age, and clinical history. Several treatment options have been proposed, from conservative to surgical approaches. In this manuscript the main lesion patterns and their management have been analysed to provide the most updated evidence for the differential diagnosis and the most effective treatment.

We histopathologically examined a surgically resected full specimen obtained from an early-stage spontaneous osteonecrosis of the knee (SPONK). On a mid-coronal cut section of the resected medial femoral condyle, a linear fracture line paralleling the subchondral bone endplate was found. Histopathologically, prominent callus formation was seen comprising of reactive woven bone and granulation tissue on both sides of the fracture. Fracture-related bone debris was focally observed at the osteochondral side of the fracture. Definitive features of antecedent bone infarction such as creeping substitution and bone marrow necrosis were not detected. These findings suggested that SPONK was the result of a subchondral fracture rather than primary osteonecrosis.

Reports in the literature have suggested a causal relationship between knee arthroscopy and spontaneous osteonecrosis of the knee (SONK). We conducted a study to determine if there are imaging characteristics associated with SONK and if there is a relationship between arthroscopy and SONK. In this retrospective review, we compared preoperative and postoperative findings in 11 patients (12 joints) who developed SONK after arthroscopy with findings in 11 age- and sex-matched controls who did not develop SONK after arthroscopy. There were no significant preoperative radiologic differences between the SONK and control groups. All 12 SONK lesions seen on magnetic resonance imaging were in the medial femoral condyle. Six SONK knees developed the lesion after arthroscopy, and 6 had SONK lesions before arthroscopy. Eleven of the 12 SONK knees had a medial meniscal tear, compared with 8 medial meniscal tears and 3 lateral meniscal tears in the control group. Eight SONK knees and 5 control patients had medial meniscal extrusion of more than 3 mm. A causal relationship between knee arthroscopy and SONK is questionable.

Purpose: Magnetic resonance (MR) imaging offers the highest sensitivity for detecting bone necrosis. We evaluated osteonecrosis in rabbit models by calculating the percentage of fat to (fat + water) [F/(F+W)] on MR spectroscopy (MRS) and compared MR spectroscopy and imaging findings with corresponding histological results., Methods: To model the natural course of articular osteonecrosis, we removed the fourth tarsal bone in 45 rabbits, froze it for 5 min in liquid nitrogen to produce complete cellular necrosis, and then replaced the bone into the knee joint. We performed Carr-Purcell-Meiboom-Gill proton spectroscopic imaging to assess necrotic bone at 3 days and one, 2, 3, 4, 8, 12, 16, and 20 weeks after osteonecrosis and calculated the percentage of F/(F+W) of each bone. We also performed conventional T1- and T2-weighted imaging and compared all data to histological findings to analyze the natural course of necrosis., Results: T1-weighted MR imaging demonstrated obvious low signal intensity at 2 to 8 weeks and recovery at 12 to 20 weeks, whereas T2-weighted imaging demonstrated inconsistent intensities throughout the period. The postoperative percentage of F/(F+W) measured using line scan MRS decreased to 8.88% at 3 weeks, 6.22% at 8 weeks, and 34.40% at 20 weeks results that were mostly consistent with MR imaging findings. Histological findings demonstrated complete absence of osteocyte nuclei and loss of osteoid-osteogenesis at 3 to 8 weeks. Recovery of bone marrow was identified as an increase in the area of fat after 12 weeks., Conclusion: Osteonecrosis delineated by T1-weighted MR imaging demonstrated fat content in the bone marrow that correlated with histology. The present MRS modality can be used to calculate the percentage of F/(F+W) of osteonecrosis to enable objective assessment of recovery and quantification of osteonecrosis to provide a numerical value for osteonecrosis.

Between 2003 and 2007, 99 knees in 77 patients underwent opening wedge high tibial osteotomy. We evaluated the effect of initial stable fixation combined with an artificial bone substitute on the mid- to long-term outcome after medial opening-wedge high tibial osteotomy (HTO) for medial compartmental osteoarthritis or spontaneous osteonecrosis of the knee in 78 knees in 64 patients available for review at a minimum of five years (mean age 68 years; 49 to 82). The mean follow-up was 6.5 years (5 to 10). The mean Knee Society knee score and function score improved from 49.6 (SD 11.4, 26 to 72) and 56.6 (SD 15.6, 5 to 100) before surgery to 88.1 (SD 12.5, 14 to 100) and 89.4 (SD 15.6, 5 to 100) at final follow-up (p < 0.001) respectively. There were no significant differences between patients aged ≥ 70 and < 70 years. The mean standing femorotibial angle was corrected significantly from 181.7° (SD 2.7°, 175° to 185°) pre-operatively to 169.7° (SD 2.4°, 164° to 175°) at one year's follow-up (p < 0.001) and 169.6° (SD 3.0°, 157° to 179°) at the final follow-up (p = 0.69 vs one year). Opening-wedge HTO using a stable plate fixation system combined with a bone substitute is a reliable procedure that provides excellent results. Although this treatment might seem challenging for older patients, our results strongly suggest that the results are equally good.

Background: [corrected] To develop a successful treatment modality for osteonecrosis, an appropriate animal model is essential. We have proposed a new osteonecrosis model that shows the total amount of necrosis and in which we observed new bone formation after transplanting autologous cultured osteoblasts., Materials and Methods: The femoral condyles of the right knees of New Zealand white rabbits were exposed after dissecting the ligaments surrounding the distal femur. After which, the metaphyseal-diaphyseal junction was cut using a saw, and the entire femoral condyle was isolated. After three liquid nitrogen treatments, the isolated femoral condyle was internally fixated to the femoral shaft using two or three Kirschner wires. Bone marrow isolated from the iliac crest was cultivated to differentiate it into osteoblasts, and the cultured cells were then injected into the necrotic bone., Results: Viable osteocytes with well-stained nuclei were not present in the necrotic areas at any stage of the development of the osteonecrosis model within 24 wk after osteonecrosis induction. However, new bone formation with osteocytes and blood vessels was observed in the necrotic bone 12 wk after transplanting the autologous cultured osteoblasts., Conclusions: The distal femoral condyle of the rabbit is an appropriate model for demonstrating osteonecrosis and treatment evaluation owing to its easy reproducibility and treatment interpretation. Therefore, autologous cultured osteoblast treatment would seem to be a potentially successful treatment modality for osteonecrosis., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Hematogenous Salmonella osteomyelitis is uncommon in immunocompetent hosts, but occurs with some regularity in immunosuppressed patients affected by systemic lupus erythematosus (SLE). Surgical debridement with resection of compromised tissue is central to the surgical management of osteomyelitis. Persistence of septic arthropathy may result from inadequate debridement, areas of osteonecrosis (ON), and an abnormal cellular and humoral dysregulation characteristic of SLE. We describe a 53-year-old Hispanic female with SLE on immunosuppressive therapy, who developed acute salmonella-induced septic arthritis and osteomyelitis of both knees associated with ON and recurrent SLE synovitis. She received prolonged antibiotic therapy and an extensive surgical debridement as part of a successful two-stage bilateral total knee replacement. This report illustrates the significance of Salmonella enterica infection in SLE patients, and the role of underlying bone and joint pathology such as bone infarcts, sub-acute osteomyelitis, and SLE synovitis.

Bone marrow signal changes on magnetic resonance imaging (MRI) after meniscectomy have been reported as evidence of postmeniscectomy osteonecrosis, but this pathology is unclear. We conducted a study to follow-up cases with bone marrow signal changes on MRI after meniscectomy and investigate the pathology of underlying lesions. Of 136 patients with no presurgical evidence of osteonecrosis, 29 had juxta-articular bone marrow signal changes on MRI after arthroscopic meniscectomy and subsequently underwent conservative therapy. In 6 of these 29 patients, clinical symptoms and radiographic changes began deteriorating. Based on the Koshino classification, 4 of the 6 patients had Stage-2 knee osteonecrosis and 2 had Stage-3. Arthroscopic and pathologic examinations were performed. Arthroscopic findings were fibrillation (all 6 cases), fissuring (4), ulceration (2), and eburnation (2). Histologic analysis confirmed subchondral bone fractures in all 6 cases, but osteonecrotic lesions were detected only in 2 cases with obvious radiologic deterioration. Postmeniscectomy osteonecrosis might result from subchondral bone fractures. Fracture healing is worse in patients with comorbidities than in those without it; comorbidities might be a risk factor for osteonecrosis.

Background: The literature suggests survivorship of unicompartmental knee arthroplasties (UKAs) for spontaneous osteonecrosis of the knee ranges from 93% to 97% at 10 to 12 years. However, these data arise from small series (23 to 33 patients), jeopardizing meaningful conclusions., Questions/purposes: We determined (1) the longer-term survivorship of UKAs in a larger group of patients with spontaneous osteonecrosis of the knee; (2) their subjective, symptomatic, and functional outcomes; and (3) the percentage of failures and reasons for failures to identify relevant indications, contraindications, and technical parameters for treatment with a modern implant design., Methods: We retrospectively evaluated all 84 patients with late-stage spontaneous osteonecrosis of the knee who had a medial UKA from 1998 to 2005. All patients had preoperative MRI to confirm the diagnosis, exclude metaphyseal involvement, and confirm the absence of major degenerative changes in the lateral and patellofemoral compartments. The mean age of the patients at surgery was 66 years and mean BMI was 28.9. We conducted Kaplan-Meier survival analysis using revision for any reason as the end point. Minimum followup was 63 months (mean, 98 months; range, 63-145 months)., Results: Ten-year survivorship was 89%. Ten revisions were performed; the most common reasons were subsidence of the tibial component (four) and aseptic loosening of the tibial component (three). No patient underwent revision for progression of osteoarthritis in the lateral or patellofemoral compartments., Conclusions: Our data suggest spontaneous osteonecrosis of the knee may be an indication for UKA, provided secondary osteonecrosis of the knee is ruled out, preoperative MRI documents the absence of disease in other compartments, and there is no overcorrection in any plane., Level of Evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Introduction: Subchondral bone cysts (SBC) have been identified in patients with knee osteoarthritis (OA) as a cause of greater pain, loss of cartilage and increased chance of joint replacement surgery. Few studies monitor SBC longitudinally, and clinical research using three-dimensional imaging techniques, such as magnetic resonance imaging (MRI), is limited to retrospective analyses as SBC are identified within an OA patient cohort. The purpose of this study was to use dual-modality, preclinical imaging to monitor the initiation and progression of SBC occurring within an established rodent model of knee OA., Methods: Eight rodents underwent anterior cruciate ligament transection and partial medial meniscectomy (ACLX) of the right knee. In vivo 9.4 T MRI and micro-computed tomography (micro-CT) scans were performed consecutively prior to ACLX and 4, 8, and 12 weeks post-ACLX. Resultant images were co-registered using anatomical landmarks, which allowed for precise tracking of SBC size and composition throughout the study. The diameter of the SBC was measured, and the volumetric bone mineral density (vBMD) was calculated within the bone adjacent to SBC. At 12 weeks, the ACLX and contralateral knees were processed for histological analysis, immunohistochemistry, and Osteoarthritis Research Society International (OARSI) pathological scoring., Results: At 4 weeks post-ACLX, 75% of the rodent knees had at least 1 cyst that formed in the medial tibial plateau; by 12 weeks all ACLX knees contained SBC. Imaging data revealed that the SBC originate in the presence of a subchondral bone plate breach, with evolving composition over time. The diameter of the SBC increased significantly over time (P = 0.0033) and the vBMD significantly decreased at 8 weeks post-ACLX (P = 0.033). Histological analysis demonstrated positive staining for bone resorption and formation surrounding the SBC, which were consistently located beneath the joint surface with the greatest cartilage damage. Trabecular bone adjacent the SBC lacked viable osteocytes and, combined with bone marrow changes, indicated osteonecrosis., Conclusions: This study provides insight into the mechanisms leading to SBC formation in knee OA. The expansion of these lesions is due to stress-induced bone resorption from the incurred mechanical instability. Therefore, we suggest these lesions can be more accurately described as a form of OA-induced osteonecrosis, rather than 'subchondral cysts'.

Background: Osteonecrosis is a major treatment complication of pediatric leukemias owing to its potential to cause joint deterioration. Because of potential long-term effects of osteonecrosis on joints, information regarding its progression and collapse in different patients can be used to identify high-risk groups, advise the patients and parents of this complication, and potentially consider the risk for development of osteonecrosis in planning primary treatment., Questions/purposes: We therefore determined: (1) the incidence of joint collapse and/or pain in young patients with hematologic malignancies diagnosed with ON of the knee; (2) risk factors associated with collapse; and (3) the relationship between size and location of osteonecrotic knee lesions and the likelihood of joint collapse., Patients and Methods: We retrospectively reviewed 109 patients with hematologic malignancies and MRI-confirmed knee osteonecrosis. The median age was 11.5 years (range, 2.3-18.8 years) at primary diagnosis of hematologic malignancy and a median age of 13.4 years (range, 2.7-23.3 years) at diagnosis of osteonecrosis of the knee. For analyses, we used the first and last MR images. Minimum clinical followup was 2.3 years after diagnosis of knee osteonecrosis (median, 6 years; range, 2.3-7.17 years)., Results: Joint collapse occurred in 22% (24 of 109). Older age, pain at osteonecrosis presentation, and lesions extending to the articular surface of distal femoral epiphyses were associated with joint collapse., Conclusions: Younger patients and those without extensive femoral epiphyseal involvement have a better prognosis for osteonecrosis of the knee., Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Magnetic resonance imaging (MRI) is the imaging modality of choice used to assess bone marrow not only in the knee but throughout the musculoskeletal system. Its ability to characterize marrow makes it an essential imaging tool in the evaluation of patients with suspected marrow pathology. In this article, we describe the MRI appearance of normal bone marrow and its pathology in the knee., ((c) Thieme Medical Publishers.)

Objective: Spontaneous osteonecrosis of the knee affects patients typically over the age of fifty-five years. Evidence exists that this process may not be true necrosis. The purpose of this study was to characterize the demographic, radiographic, and pathologic features of this condition., Materials and Methods: Twenty-one patients (twenty-two knees) consecutively treated for spontaneous osteonecrosis of the knee were studied., Results: Only one of twenty-two specimens demonstrated evidence of bone necrosis. No specimens showed fat necrosis, marrow necrosis, fibrous change or appositional bone repair. Fourteen of twenty-two specimens (64%) showed significant osteopenia and fifteen of twenty-two specimens (68%) showed evidence of osteoarthritis., Conclusions: This study demonstrated that spontaneous osteonecrosis of the knee is not an osteonecrotic condition and has been misnamed. Osteopenia and osteoarthritis may play a role in the pathogenesis of this disease.

Although osteochondral grafting surgery is believed to replace damaged cartilage with healthy-looking normal cartilage, no study focuses on ultrasound quantification of those cartilage immediately after the surgery. It is unknown whether the ultrasound properties of damaged cartilage from trauma or osteonecrosis are same with each other. We have examined ultrasound properties of damaged cartilage, adjacent intact cartilage and plug cartilage during osteochondral grafting surgery for 15 knees of 15 patients, mean age of 43.4 (range, 14-61) years. Results showed that signal intensities of ultrasound (a measure of superficial cartilage integrity) of intact cartilage, damaged cartilage, and plug cartilage were 1.91 (arbitrary unit), 0.40, and 2.13, respectively, in 11 knees of 11 patients of traumatic cartilage lesions. Interval between signals of ultrasound (a parameter related to thickness) were 2.79 (micros), 1.90, and 2.85, respectively. The signal intensity and the interval between signals of plug cartilage were 533% (P < 0.01) and 150% (P < 0.01) of damaged cartilage, respectively. In four knees of four patients of osteonecrosis, the signal intensities of intact cartilage, damaged cartilage, and plug cartilage were 1.25, 0.30, and 1.39, respectively. The interval between signals were 2.36, 2.00, and 2.69, respectively. The signal intensity and the interval between signals of plug cartilage were 463% (P < 0.01) and 135% (P < 0.05) of damaged cartilage. We conclude that ultrasound properties of the damaged cartilage from trauma or osteonecrosis did not differ a lot especially in the late stages of osteonecrosis and that the osteochondral grafting surgery replaced the damaged cartilage with plug cartilage that had greater superficial cartilage integrity and greater thickness parameter immediately after the surgery. Long-term effect of the osteochondral grafting surgery should be verified in further study.

Introduction: The aim was to investigate the relationship of cartilage loss (change in medial femorotibial cartilage thickness measured with magnetic resonance imaging (MRI)) with compartment-specific baseline radiographic findings and MRI cartilage morphometry features, and to identify which baseline features can be used for stratification of fast progressors., Methods: An age and gender stratified subsample of the osteoarthritis (OA) initiative progression subcohort (79 women; 77 men; age 60.9 +/- 9.9 years; body mass index (BMI) 30.3 +/- 4.7) with symptomatic, radiographic OA in at least one knee was studied. Baseline fixed flexion radiographs were read centrally and adjudicated, and cartilage morphometry was performed at baseline and at one year follow-up from coronal FLASH 3 Tesla MR images of the right knee., Results: Osteophyte status at baseline was not associated with medial cartilage loss. Knees with medial joint space narrowing tended to show higher rates of change than those without, but the relationship was not statistically significant. Knees with medial femoral subchondral bone sclerosis (radiography), medial denuded subchondral bone areas (MRI), and low cartilage thickness (MRI) at baseline displayed significantly higher cartilage loss than those without, both with and without adjusting for age, sex, and BMI. Participants with denuded subchondral bone showed a standardized response mean of up to -0.64 versus -0.33 for the entire subcohort., Conclusions: The results indicate that radiographic and MRI cartilage morphometry features suggestive of advanced disease appear to be associated with greater cartilage loss. These features may be suited for selecting patients with a higher likelihood of fast progression in studies that attempt to demonstrate the cartilage-preserving effect of disease-modifying osteoarthritis drugs.

Spontaneous osteonecrosis of the knee (SPONK) usually involves a single condyle or plateau. The medial femoral condyle (MFC) is most often involved and spontaneous osteonecrosis of the medial tibial plateau (MTP) is a rare condition, representing only 2% of all necroses reported in the knee. SPONK involving both the MFC and the MTP is extremely rare. SPONK occurring in either the MFC or the MTP individually might extend to the corresponding side of the knee in the advanced end-stage; however, in that situation, significant degenerative changes would exist and it might be difficult to differentiate end-stage SPONK form severe osteoarthritis. SPONK affecting both the MFC and the MTP without significant secondary osteoarthritic changes has not been reported, even though it is difficult to know which occurs first. We have cared for three patients with histologically proven osteonecrosis of the MFC and MTP and report their radiologic features.

Magnetic resonance imaging (MRI) is considered the most sensitive tool for the detection of osteonecrosis at early stages. We report about 3 patients with high suspicion of osteonecrosis at the knees in whom an initial MRI was normal, but the condition was apparent in a subsequent study. The time between the initial insult and the appearance of diagnostic alterations in MR studies remains undefined and, in patients at risk an initial MRI, if done too early, may fail to detect this condition.

Unlabelled: Unicompartmental knee arthroplasty is a logical procedure when the lesion is limited to one femorotibial compartment. The procedure can now be performed through a mini-incision to provide quicker recovery because the extensor mechanism disruption is minimized. We have found the length of the incision varies according to patient mass and muscle tone. Specific instrumentation limited to the replaced compartment and using either an intra- or extramedullary femoral technique provides femorotibial component alignment and allows slight undercorrection of the deformity. Radiographic assessment demonstrates precise implantation of the components is possible with a mini-incision, which is believed important for the long-term results of the arthroplasty. The functional evaluation of patients implanted with unicompartmental knee arthroplasty performed through a mini-incision suggests appropriate kinematics can be restored after the procedure, enhancing the importance of a functional anterior cruciate ligament., Level of Evidence: Level V, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The development of osteonecrosis after arthroscopic surgery has been associated with meniscectomy, chondral surgery, and the use of thermal energy. This paper presents five cases, four of which fulfilled the temporal criteria for postarthroscopy necrosis, i.e. presurgical magnetic resonance imaging was obtained at least four weeks after the onset of symptoms). Four cases were treated conservatively while one underwent arthroscopic debridement and microfracturing. The diagnosis of osteonecrosis should be kept in mind in osteoarthritic patients whose knee symptoms manifest a sudden increase without trauma, and in cases with worsening knee symptoms after arthroscopic surgery. The optimal treatment strategy in these patients is still debatable.

Nontraumatic avascular necrosis (AVN) of bone is a well-reported complication of glucocorticoid therapy for immunologic and malignant disease. We present the case of a 13-year-old girl with no history of trauma who presented with a 5-day history of increasing pain in both knees after cord blood transplantation for acute lymphoblastic leukemia. Plain film and magnetic resonance imaging (MRI) were reported as normal. Bone scintigraphy revealed evidence of bilateral avascular necrosis in the distal femora. MRI subsequently became abnormal several weeks later. The case illustrates the natural history of AVN, in which changes that are detected by MRI can take several weeks to develop. The scintigraphic findings influenced early management of the condition.

The research presents pathogenesis of the chrono osseous necrosis of the knee joint with accompanying clinical, histological and radiological symptoms; as well as its treatment. The results of treatment have been analyzed. The method - site of bone abrasion and stabilization of parted fragment with a metal screw; as well as rebuilding of the stabilized part. Ten results were very positive and two were satisfying. No poor results have been noticed. The conclusion from the above work - the stabilization of a free fragment by a screw is an advisable and preferable method. The present methods of filling the chrono osseous defects have been revised.

Purpose: To estimate the accuracy and consistency of a method using a voxel-based MR image registration algorithm for precise monitoring of knee joint diseases., Materials and Methods: Rigid body transformation was calculated using a normalized cross-correlation (NCC) algorithm involving simple manual segmentation of the bone region based on its anatomical features. The accuracy of registration was evaluated using four phantoms, followed by a consistency test using MR data from the 11 patients with knee joint disease., Results: The registration accuracy in the phantom experiment was 0.49+/-0.19 mm (SD) for the femur and 0.56+/-0.21 mm (SD) for the tibia. The consistency value in the experiment using clinical data was 0.69+/-0.25 mm (SD) for the femur and 0.77+/-0.37 mm (SD) for the tibia. These values were all smaller than a voxel (1.25 x 1.25 x 1.5 mm)., Conclusion: The present method based on an NCC algorithm can be used to register serial MR images of the knee joint with error on the order of a sub-voxel. This method would be useful for precisely assessing therapeutic response and monitoring knee joint diseases; normalized cross-correlation; accuracy., (J. Magn. Reson. Imaging 2005. (c) 2005 Wiley-Liss, Inc.)

Background: Spontaneous osteonecrosis of the knee (SONK) is a distinct clinical condition occurring in patients without any associated risk factors. There is controversy as to the best method of treatment, and the available literature would suggest that patients with SONK have a worse outcome than those with primary osteoarthrosis when arthroplasty is performed. We assessed the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK; Ahlbäck grades III and IV)., Patients and Methods: We assessed 29 knees (27 patients) with spontaneous osteonecrosis of the knee using the Oxford Knee Score. 26 knees had osteonecrosis of the medial femoral condyle and 3 had osteonecrosis of the medial tibial plateau. All had been operated on using the Oxford Medial Unicompartmental Knee Arthroplasty (UKA). This group was compared to a similar group (28 knees, 26 patients) who had undergone the same arthroplasty, but because of primary osteoarthrosis. Patients were matched for age, sex and time since operation. The mean length of follow-up was 5 (1-13) years., Results: There were no implant failures in either group, but there was 1 death (from unrelated causes) 9 months after arthroplasty in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 38, and it was 40 in the group with osteoarthrosis., Interpretation: Use of the Oxford Medial UKA for spontaneous focal osteonecrosis of the knee is reliable in the short to medium term, and gives results similar to those obtained when it is used for patients with primary osteoarthrosis.

Osteonecrosis of the medial tibial plateau is characterized by acute pain on the medial aspect of the knee. Progression can lead to articular collapse and requires early diagnosis and treatment. We studied seven patients affected of idiopathic osteonecrosis of the tibial plateau. The mean age was 62 years and the mean follow-up 42 months. We performed roentgenograms in all patients, bone scans in three patients and magnetic resonance image (MRI) in five. MRI shows T1-weighted low-intensity signal and T2-weighted high-intensity signal with a surrounding area of intermediate low-intensity signal. An increased focal uptake was seen at bone scan. Histological findings showed necrotic bone with empty lacunae. Surgical treatment consisted of tibial subchondral drilling in four patients-two of them by failure of conservative treatment, and a total knee arthroplasty in other two. One patient had a satisfactory evolution with conservative treatment. Idiopathic osteonecrosis of the tibial plateau must be considered in elderly patients with knee pain over the medial tibial plateau. At early stages, decompression with tibial drilling must be considered. This procedure allows a prompt and effective relief of symptoms.

Objective: To investigate the MR characteristics of SONK-like (spontaneous osteonecrosis of the knee) subchondral abnormalities in the adult atraumatic knee and to recategorize these patients into two subgroups: a subacute to chronic process associated with osteoarthritis and an acute process associated with insufficiency fractures., Design: We retrospectively examined the knee MRIs of 39 patients with non-specific interpretations of osteochondral abnormalities., Patients: There were a total of 52 subchondral lesions without any known traumatic event and no prior surgery. All lesions evaluated had MR features previously ascribed to SONK. Several MR characteristics were then assessed: presence or absence of a line, size, zonal location, T1 and T2 signal, associated marrow edema, associated ipsilateral meniscal tear, and associated ipsilateral cartilage defects., Results and Conclusions: The abnormalities with linear components (insufficiency fractures) tended to be larger (P<0.01) and were associated with a severe amount of marrow edema (P<0.0001) consistent with an acute process. The non-linear abnormalities were more associated with cartilage defects (P=0.01) and less marrow edema consistent with osteoarthritis and a subacute to chronic process. This association of SONK-like abnormalities with osteoarthritis and insufficiency fractures casts doubt on the validity of the term "spontaneous osteonecrosis" as it is currently applied, and further investigation into the separate etiologies of these subchondral marrow lesions is needed.

The natural history of spontaneous osteonecrosis of the medial tibial plateau remains controversial and incomplete. We have studied 21 patients (aged between 53 and 77 years) with clinical and scintigraphic features of spontaneous osteonecrosis of the medial tibial plateau who were observed prospectively for at least three years (37 months to 8.5 years). The mean duration of follow-up was 5.6 years. The mean duration of symptoms at presentation was 4.7 weeks (3 days to 12 weeks). Radiographs of the affected knee at the first visit were normal in 15 patients and mildly arthritic in six. The characteristic radiographic lesion of osteonecrosis was noted at presentation in five of the mildly arthritic knees and during the evolution of the disease in eight of the radiographically normal knees. During the follow-up, subchondral sclerosis of the affected medial tibial plateau was noted in 16 knees. There are three distinct patterns of outcome: 1) acute extensive collapse of the medial tibial plateau in two knees within three months of onset; 2) rapid progression to varying degrees of osteoarthritis in 12 knees, in eight within a year, in all within two years and deterioration of the pre-existing osteoarthritis in three; and 3) complete resolution in four knees, two of which were normal at presentation and two mildly osteoarthritic. The two patients with acute extensive collapse and three who had rapid progression to severe osteoarthritis required total knee arthroplasty. We conclude that osteonecrosis of the medial tibial plateau progresses in most cases to significant degenerative disease of the knee.

Purpose: To evaluate if osteonecrosis diagnosed on MR images of the knee relates to reduced bone mineral density (BMD) and may be caused by an insufficiency fracture., Material and Methods: Thirty-two consecutive patients (8 men, 24 women; age range 27-82 years, mean 62 years) with MR findings of osteonecrosis of the femoral or tibial condyle were prospectively included. Trabecular and cortical BMD were measured with high resolution peripheral quantitative CT in the non-dominant distal radius and the tibia of the involved extremity. One tibia was not measured due to posttraumatic deformity., Results: The mean trabecular BMD of the radius was 81% of the young-adult average peak BMD (range 19-160%). The mean cortical BMD in the radius was 86% (range 63-108%). The mean trabecular BMD in the tibia was 92% (range 28-160%). The mean cortical BMD in the tibia was 86% (range 49-132%). The values of the trabecular bone of the distal radius (tibia) were normal in 11 (15) patients, osteopenic in 12 (4), and osteoporotic in 9 (12), respectively. The cortical bone values of the distal radius (tibia) were normal in 12 (13) patients, osteopenic in 12 (12), and osteoporotic in 8 (6), respectively., Conclusion: Osteoporosis and osteopenia are commonly found in patients with osteonecrosis of the knee as diagnosed on MR images. This indicates that for some patients an insufficiency mechanism may be responsible for the MR findings. However, in the patients with normal bone density other reasons for osteonecrosis may be present.

MRI is clearly the imaging modality of choice for detecting and exploring joint, osseous, and soft tissue injuries in the lower extremity and throughout the musculoskeletal system. Its ability to detect and differentiate the various forms of marrow pathology is unrivaled, and as such it should be obtained early in the work-up of a patient with a suspected marrow abnormality. Additionally, the radiologist must be familiar with the MRI appearances of normal marrow and the most common types of marrow pathology if its diagnostic power is to be fully realized.

Objective: To assess the value of joint fluid analysis for determining cartilage degradation and prognosis in spontaneous osteonecrosis (ON) of the knee., Methods: Synovial fluid was obtained from 30 knees with spontaneous ON (26 medial femoral condyles, 4 medial tibial plateaus) as well as from 50 knees with medial compartmental osteoarthritis (OA) as a control. Levels of chondroitin 6-sulfate (C6S), C4S, and hyaluronic acid were measured with high-performance liquid chromatography. The lesion size, appearance of the articular cartilage, and results of magnetic resonance imaging (MRI) were compared with the results of joint fluid analysis., Results: The mean +/- SD level of C6S was 82.2 +/- 36.6 nmoles/ml in joint fluid from ON knees, which was significantly higher than the levels in knees with grade 2 (47.2 +/- 20.0 nmoles/ml) and grade 3 (55.8 +/- 29.2 nmoles/ml) OA. The C6S:C4S ratio was highest in lesions with mild articular changes and reflected the macroscopic alteration of cartilage overlying the ON lesion. The concentration of C6S in the 9 knees with lesions that covered > or = 40% of the condyle (99.0 +/- 32.9 nmoles/ml) was higher than that in the 17 knees with lesions that covered <40% of the condyle (67.2 +/- 31.7 nmoles/ml). Knees with bone marrow edema on MRI had a higher level of C6S than did knees with a fibrous-like appearance., Conclusion: While radiologic staging was useful for indicating the size of the ON lesion, it was less valuable for determining articular cartilage damage. Joint fluid analysis may provide more precise information about articular cartilage degradation in ON, and the findings may also be of prognostic significance.

In the last few years, postmeniscectomy osteonecrosis has been reported, especially in elderly patients, with low incidence, unclear physiopathology, and without long periods of follow-up. We report a case diagnosed and followed-up for a 3-year period using magnetic resonance imaging. In the initial phase, a large area of intramedullary edema was evident; after 3 months, the edema had decreased (it was no longer evident at 1 year examination) and a clearly defined area of osteonecrosis was evident with very high signal intensity on high-contrast sequences. After 3 years, the lesion showed a degenerative cyst appearance with an osteosclerotic rim and completely disrupted cartilage.

We report a case story where IDDM was diagnosed in a young man due to late complications such as ischaemia in a toe, retinopathy and nephropathy. Due to a prior minor knee trauma he developed osteonecrosis/Charcot joint in his knee eighteen months after diagnosis of IDDM.

Background: Spontaneous osteonecrosis of the knee is a superficial subchondral lesion classically seen in the medial femoral condyle; in general, it is markedly different in its clinicopathological presentation from the classic wedge-shaped subchondral osteonecrotic lesions seen in the hip, knee, and other joints. Recent reports on subchondral insufficiency fracture of the femoral head, which has marked morphological similarities with spontaneous osteonecrosis of the knee, led us to reevaluate a series of patients who had had operative treatment because of a clinical and pathological diagnosis of spontaneous osteonecrosis of the knee., Methods: We reviewed the cases of fourteen patients who had had operative treatment of spontaneous osteonecrosis of the knee in order to reevaluate the gross and histological morphology of this lesion. The patients included eight women and six men who ranged in age from fifty-nine to eighty-eight years. In all patients, the diagnosis of spontaneous osteonecrosis of the knee had been based on clinical presentation, imaging studies, and pathological findings. The appearance of the lesion on plain radiographs was categorized into four stages, which corresponded to the gross and histological findings. In stage 1, the radiographic appearance is normal; in stage 2, a radiolucent oval area is seen subchondrally or there is slight flattening of the convexity of the condyle, or both; in stage 3, the radiolucent area is expanded and is surrounded by a sclerotic halo; and in stage 4, secondary osteoarthritic changes are apparent., Results: No patient had a stage-1 lesion. Three patients, all of whom had a stage-2 lesion, were considered to have a subchondral insufficiency fracture of the medial femoral condyle. Another six patients, all of whom had a stage-3 lesion, were considered to have a subchondral fracture and associated focal osteonecrosis that was confined to the area between the fracture line and the articular surface. The remaining five patients, three of whom had a stage-3 lesion and two of whom had a stage-4 lesion, had indeterminate findings because the lesion had become detached from the condyle., Conclusions: Our histopathological findings suggest that the primary event leading to spontaneous osteonecrosis of the knee is a subchondral insufficiency fracture and that the localized osteonecrosis seen in association with this disease is the result of a fracture.

Introduction: The most frequent site for aseptic bone necrosis and osteochondrosis dissecans in the human knee joint is the medial femoral condyle. The aim of this study is to analyze the three-dimensional vascularization of the human knee joint and to find out if there are any differences in the blood supply of the medial and lateral femoral condyles which may explain the preponderance of aseptic bone necrosis in the medial side., Material and Methods: The femoral arteries of 14 unfixed lower extremities have been injected with epoxy resin. After documentation of the extraosseous course of the blood vessels the bone was macerated with 10% formic acid. The insertions of tendons and ligaments were investigated by light microscopy and immunohistochemistry., Results: The arterial supply of the lateral femoral condyle originates from the upper lateral geniculate artery, the terminal ends of which penetrate the bone from lateral. Branches of the middle geniculate artery reach the bone from the medial wall of the intertubercular notch. The subchondral bone of the medial femoral condyle draws its blood supply mainly from the descending geniculate artery. Branches of the middle geniculate artery penetrate the medial femoral condyle only in the posterior part of the intercondylar fossa. These posterior vessels do not contribute to the supply of the subchondral bone. In the anterior part of the medial wall of the intercondylar fossa there is the wide femoral insertion of the posterior cruciate ligament. Injection techniques and immunohistochemical investigations show that the fibrocartilage of the chondral apophyseal insertion of the posterior cruciate ligament is avascular and acts as banier which impedes blood vessels to penetrate the bony surface in this region. The subchondral bone adjacent to the femoral insertion of the posterior cruciate ligament receives its blood supply from vessels that penetrate the bone at the medial wall of the medial femoral condyle. The blood vessels which supply the lateral parts of the medial condyle have the longest intraosseous course. The density of vessels within this region is largely reduced., Conclusions: The region adjacent to the femoral insertion of the posterior cruciate ligament is the most frequent site for osteochondrosis dissecans in the knee joint. Our results show that the arterial supply of the subchondral bone may be considered as a cofactor for the etiology of osteochondrosis dissecans.

Symptoms in patients suffering from spontaneous osteonecrosis of the knee (SONK) may be reduced by high tibial osteotomy (HTO). However, the fate of the necrotic lesion is unknown and needs further investigation. We conducted a prospective study to evaluate magnetic resonance imaging (MRI) changes after operative and nonoperative treatment. Ten consecutive patients suffering from SONK of the medial compartment were given two treatment options: either HTO (n = 6) or conservative treatment with partial weight bearing for 3 months (n = 4). We measured the greatest extent of well-defined subchondral low signal intensity abnormality, considered to represent necrosis, and the surrounding area of intermediate signal intensity, considered to represent perifocal bone marrow edema, on T1-weighted coronal MRI images before and after treatment. The MRI follow-up period was 17.5 months (range 12-27) in the HTO group and 14.5 months (range 8-25) in the nonoperative group. At follow-up the MRI evaluation revealed a decrease in the low signal intense areas (necrosis) in five of the six patients in the HTO group. Only one of the four nonoperative patients showed a decrease in the low signal intense area. The intermediate intense areas (edema) decreased in all patients in the HTO group and in three of four in the nonoperative group. The mean decrease in the area of perifocal edema was significantly greater in the HTO group than in the nonoperative group (P = 0.019). No statistically significant difference was found for the area of necrosis between the two groups (P = 0.171). A clinical improvement was observed in all patients of the HTO group but in only two of the four patients of the nonoperative group. We conclude that the decrease in perifocal bone marrow edema seems to be associated with improved patient comfort. The MRI appearance of the necrotic lesion does not alter with either treatment mode.

Objective: To demonstrate the contribution of magnetic resonance imaging to the elucidation of mechanisms involved in "osteonecrosis-like syndrome of the medial tibial plateau"., Patients and Methods: A magnetic resonance study with sagittal and coronal sections was done in 13 patients (age range, 57-95 years) two weeks to four months into a painful syndrome meeting the definition of "osteonecrosis-like syndrome of the medial tibial plateau". Gadolinium injection was used in nine patients. Clinical symptoms resolved within a few weeks in all 13 cases., Results: T1-weighted images without gadolinium showed diffuse low signal from the epiphysis (n = 12) containing an area of even lower signal seen either as a crescent-shaped subchondral image (n = 3/12) or as a linear image (n = 9/12). On postgadolinium images, the low signal was abolished except for a line of low signal parallel to the subchondral bone. T2-weighted images demonstrated diffuse high signal from the medial tibial plateau with persistence of the line of low signal (n = 8/12)., Conclusion: Magnetic resonance imaging allows to analyze the anatomic lesion responsible for "osteonecrosis-like syndrome of the medial tibial plateau". Our magnetic resonance findings were similar to those seen in stress fractures at other sites.

Although arthritis is often associated with synovial inflammation, the osseous changes in inflammatory and degenerative arthritis are principally reactive, and typically lack an acute inflammatory component. We have recently encountered several osteoarticular specimens removed at the time of large joint arthroplasty that have shown a distinctive pattern of subchondral acute inflammation (SCAI) resembling acute bacterial osteomyelitis. These microscopic findings heretofore have not been recognized as a component of the histopathology of arthritis. To determine the frequency of SCAI, we examined slides (mean four per case) from 164 hip arthroplasties performed at one of our institutions in a single year. A total of 10 cases of SCAI, including the 4 original examples (2 humeral head specimens, 2 femoral head specimens) and 6 identified from the slide review are described in this report. Eight patients were female and two were male (ages 54-86 years, mean 70, median 70). All had severe degenerative joint disease, six had rheumatoid arthritis, and three had osteonecrosis. In none was there a clinical or intraoperative suspicion of infection. Cultures of joint fluid or bone were not performed. In all cases, the inflammation was subchondral (within 1.0 cm of the joint surface), and it was frequently associated with subchondral cysts. In osteonecrotic foci, the suppurative inflammation was diffuse within the marrow space, whereas in viable bone it was nodular and vaguely granulomatous. Special stains for organisms were negative. None of the patients was treated with long-term IV antibiotics. There has been no septic loosening of the prostheses at follow-up intervals ranging from 5 to 36 months (mean: 17 months). Our observations, to the best of our knowledge, are novel. Although we cannot definitively exclude bacterial infection as a cause of SCAI, the histologic and clinical features suggest that SCAI likely represents a noninfectious sterile form of inflammation. Subchondral acute inflammation is possibly secondary to synovial fluid insudation into subchondral cancellous bone in the setting of severe osteoarthritis and/or rheumatoid arthritis.

Osteonecrosis of the knee should be differentiated into two main categories: (1) primary, spontaneous, or idiopathic osteonecrosis and (2) secondary osteonecrosis (e.g., secondary to factors such as steroid therapy, systemic lupus erythematosus, alcoholism, Caisson decompression sickness, Gaucher's disease, hemoglobinopathies, etc.). Spontaneous or primary osteonecrosis of the knee presents with an acute knee pain in elderly patients. It is three times more common in women than in men. Traumatic and vascular theories have been proposed as a causative factor of osteonecrosis of the knee, but the precise etiology still remains speculative. High index of clinical awareness and a good history and physical examination are essential to make an early, accurate diagnosis. Plain radiographs are often normal during the early course of the disease and, in such instances, radioisotope bone scan and magnetic resonance imaging may be helpful. In the early stage of the disease, nonoperative treatment is indicated and many patients, if diagnosed early, have a benign course with a satisfactory pain relief and a good knee function. In patients with advanced stage of the disease, treatment options include arthroscopic debridement, curettage or drilling of the lesion, bone grafting, high tibial osteotomy, use of osteochondral allograft, and unicompartmental or total knee arthroplasty. The choice of treatment should be based on factors such as age of the patient, severity of symptoms, activity level and functional demands on the knee, site and stage of the lesion, and extent of deformity and secondary osteoarthritis. The clinical features and treatment of steroid-induced osteonecrosis of the knee are briefly discussed. In recent years, "postmeniscectomy" osteonecrosis has been reported, but at present its prevalence and pathophysiology remain unknown. It is possible that this may be a preexisting condition that was not recognized at the time of initial consultation or osteonecrosis may develop after meniscectomy in occasional cases.

Four cases with spontaneous osteonecrosis of the knee are reported to highlight mainly the features of the cartilage flap over the necrotic lesion. Case 1 and Case 2 showed late Stage 2 and Stage 3 spontaneous osteonecrosis in the medial femoral condyle, respectively, but featured a convex calcified plate with no flattening in the lateral view of the radiographic knee. Case 3 showed multiple small fractures in the subchondral necrotic bone of the cartilage flap. In Case 4, the cartilage flap became detached and was found in the synovium of the supra-patellar fossa; moreover, the necrotic bone of the flap seemed to be revascularized, and the small fragments were found to be united. Flattening is not always found in the early stage of the necrotic process. As spontaneous osteonecrosis progresses in the femoral condyle, it is understood that a cartilage flap with a layer of necrotic bone sustains multiple fractures and thus forms a calcified plate. Therefore, a subchondral radiolucency may appear first, followed by a calcified plate with flattening.

In the Swedish Multicenter Study of Knee Arthroplasty, 115 knees in 110 patients with knee osteonecrosis represented all reported cases treated with knee arthroplasty in the period from 1975 to 1986. Primary medial femoral condyle osteonecrosis was the most common osteonecrosis reported (89%). Preoperative roentgenograms were staged according to the type of osteonecrosis and classified according to the grade of arthrosis. Detailed measurements of the size of the lesion were also performed. For primary medial femoral osteonecrosis, the width of the lesion averaged 45% of the condyle. The mean width of the lesion (anteroposterior size) was 21 mm and the mean length (lateral size) was 34 mm. The mean depth on lateral roentgenograms was 6 mm. There was a high correlation of results among the various methods of measurement. Using regression analysis, it was possible to approximate the volume of the lesion even from a single measurement of the width on anteroposterior view. The size of osteonecrosis of the knee can be used to plan resection and select the implant design.

Between November 1985 and June 1987, 751 posterior cruciate-sparing total knee arthroplasties were performed on 523 patients who exhibited fixed varus or valgus deformities. Patients excluded from this study included the following: those with a postoperative follow-up period of less than 2 years (including patients who had died), patients who became infected, and patients with previous failed total knee arthroplasty in the same knee. A total of 473 knees left for evaluation. All arthroplasties were measured using anatomic axis for alignment measurement. The Hospital for Special Surgery scoring system was used to determine the clinical scores prior to the end of each follow-up examination. All ligament releases were performed sequentially, including balancing of the posterior cruciate ligament. All arthroplasties were divided into six separate groups depending upon the degree of varus or valgus deformity. Kaplan-Meier curves were constructed using three methods of failure definition. Curves were then compared between groups. The mean Hospital for Special Surgery score was no different between any of the groups, except for the group of 6 degrees-10 degrees varus, which was significantly higher than the mean score of the 11 degrees and higher valgus group. All other groups were the same statistically. It is concluded that severe varus and valgus deformities may be satisfactorily corrected with the use of a cruciate-retaining type of total knee arthroplasty.

Arthroplasty for primary osteonecrosis of the femoral condyle of the knee was performed in 5 patients and the resected pieces of bone were studied histologically. The patients had been given 99 mm-Tc-MDP preoperatively and the scintimetric uptake in the resected bone pieces was determined. All patients had changes typical for osteonecrosis preoperatively on radiographs and scintimetry. In one case MRI investigation was performed. The histological investigation showed necrotic bone with empty lacunae and fatty degeneration corresponding to the osteonecrosis center. A reparative bone formation, osteoblastic activity, cartilage formation and bands of fibrovascular granulation tissue were observed at the borders to intact bone. The scintimetric uptake of the resected bone pieces showed a high uptake corresponding to the osteonecrosis center. The MR examination showed a well demarcated osteonecrotic region. The findings emphasize the localized nature of the osteonecrosis disease.