Magnetic resonance imaging of the knee. Current techniques and spectrum of disease

The relationship of proximal lateral collateral ligament hyperintensity with knee joint ligament and meniscus pathologies

BACKGROUND

Hyperintensity in the proximal lateral collateral ligament (LCL) is often confusing. This appearance may be alone or accompany other pathologies.

PURPOSE

To investigate the relationship between the signal intensity (SI) change in the proximal LCL and the knee joint pathologies.

MATERIAL AND METHODS

The knee MRI scans taken between 2020 and 2022 were queried retrospectively. Patients with acute trauma, instability, knee surgery, or high-grade osteoarthritis were excluded. Included patients were divided into two groups as normal SI and increased SI according to proximal LCL. The difference in ligamentous and meniscal pathologies between the two groups was analyzed using a chi-square test. Inter-observer agreement analysis was performed on 50 randomly selected patients.

RESULTS

A total of 351 patients (139 men [39.6%], 212 women [60.4%]; median age = 37 years; interquartile range = 67 years) were included. There were 114 (32.5%) LCLs with normal SI and 237 (67.5%) LCLs with increased SI. Normal SI and increased SI groups had a significant difference in terms of joint side, median age, patellar tendon SI, anterior cruciate ligament SI, and medial collateral ligament SI (P = 0.004, P = 0.004, P = 0.001, P = 0.011, P = 0.004, respectively). A significant difference between the results of two separate LCL examinations in coronal + axial and coronal-only planes (P <0.001). Inter-observer agreement was found to be good to excellent.

CONCLUSION

Hyperintensity in the proximal LCL was more common on the right joint side, in older patients, and patients with hyperintensity in the proximal patellar tendon, anterior cruciate ligament, and medial collateral ligament. Evaluating the LCL only in the coronal plane overestimates the hyperintensity.

Clinical versus MRI grading of the medial collateral ligament in acute knee injury

Sensitivity, specificity, and agreement between clinical and magnetic resonance imaging (MRI) gradings of the medial collateral ligament (MCL) after acute knee injury were evaluated in 362 patients. Ninety-seven per cent were injured during sports/recreation. Sensitivity and specificity of MRI for grade II or III MCL injury was 68% (95% CI 58-77%) and 90% (95% CI 86-93%), respectively. Weighted Kappa analysis showed moderate agreement between clinical and MRI grading (0.56 [95% CI 0.48-0.65]). Findings were similar for patients with and without concomitant cruciate ligament rupture (0.57 [95% CI 0.48-0.66] and 0.55 [95% CI 0.35-0.75], respectively) and for specialists in orthopaedics and knee sub-specialists (0.55 [95% CI 0.39-0.70] and 0.57 [95% CI 0.47-0.67], respectively). Agreement between clinical and MRI grading of MCL injuries by orthopaedic specialists in a general hospital is at least moderate regardless of the presence of cruciate ligament injury.

Clinical, patient-reported, radiographic and magnetic resonance imaging findings 11 years after acute posterior cruciate ligament injury treated non-surgically

BACKGROUND

Long-term consequences of posterior cruciate ligament (PCL) injury such as persistent posterior tibial translation and risk of osteoarthritis development are unclear. Additionally, little data is available describing the natural history of structural morphology of the ruptured PCL. The purpose of the study was to determine the long-term outcome after non-operatively treated PCL injury.

METHODS

Over 6-years, all acute knee injuries were documented by subacute MRI (median 8 days [5-15, 25th - 75th percentile] from injury to MRI). Twenty-six patients with acute PCL injury were identified of whom 18 (69%) participated in the long-term follow-up after 11 years. Follow-up included radiographic posterior tibial translation (RPTT) determined using the Puddu axial radiograph. weight-bearing knee radiographs, MRI and KOOS (Knee injury and Osteoarthritis Outcome Score).

RESULTS

On subacute MRI, 11 knees displayed total and 7 partial ruptures. At 11 (SD 1.9) years, the median RPTT was 3.7 mm (1.5-6.3, 25th - 75th percentile). Seven knees displayed radiographic osteoarthritis approximating Kellgren-Lawrence grade ≥ 2. All follow-up MRIs displayed continuity of the PCL. Patients with more severe RPTT (> 3.7 mm), had worse scores in the KOOS subscales for symptoms (mean difference 14.5, 95% CI 7-22), sport/recreation (30, 95% CI 0-65) and quality of life (25, 95% CI 13-57) than those with less severe RPTT (≤ 3.7 mm). This was also the case for the KOOS₄ (22, 95% CI 9-34).

CONCLUSION

Acute PCL injuries treated non-surgically display a high degree of PCL continuity on MR images 11 years after injury. However, there is a large variation of posterior tibial translation with higher values being associated with poorer patient-reported outcomes.

Incidence and concomitant chondral injuries in a consecutive cohort of primary traumatic patellar dislocations examined with sub-acute MRI

PURPOSE

To present age- and sex-specific cumulative annual incidences of primary traumatic lateral patellar dislocation (LPD) and to detail patient characteristics and concomitant chondral injuries including osteochondral fractures, as visualized on magnetic resonance imaging (MRI), in a large consecutive cohort of knee-injured individuals.

METHODS

Data on primary traumatic lateral patellar dislocations were collected from a large consecutive cohort of knee injuries examined with sub-acute MRI in a single centre with a well-defined catchment area. Annual incidences for different age-groups in relation to gender were calculated together with the risk of concomitant chondral and osteochondral injury, during sports and in general.

RESULTS

A total of 184 primary patellar dislocations were identified in the cohort of 1145 acute knee injuries (n=175) and surgical records (n=9). Knee MRI was performed within a median of six days of injury. Median age of patients with primary LPD was 16 years (interquartile range, 14-21; range, 9-47) and 41% were females. Males were significantly older than females at the time of injury (median age 17 vs. 15, P = 0.021) and sustained their primary LPD during sports more often than females (65 vs. 40%, P < 0.001). Primary LPD occurred most frequently at the age of 13 to 15 years where the annual incidence was 125 (95% CI, 96-160) per 100,000 persons. The overall annual incidence of primary LPD was 14 (95% CI, 12-16) per 100,000 persons, with a predominance of males versus females (17 vs. 11, P = 0.01). Concomitant lesions to joint surfaces were displayed on MRI or during surgery in 75 (43%) knees. Osteochondral fractures were seen in 32 knees (18%). We found no statistically significant difference in the risk of osteochondral fracture between those injured during sports or during leisure activity (14 vs. 24%, P = 0.08).

CONCLUSIONS

The annual incidence of first-time patellar dislocation was found to be 14 per 100,000 individuals with the highest incidence found among those aged 13-15 years. Primary LPD was more common among males and was sustained during sports activity in 55% of the cases. Associated injuries to the chondral surfaces should be expected in 43% of knees with primary LPD where 18% represent osteochondral fractures.

Intra-Articular Ganglion Cysts of the Knee

➢

Magnetic resonance imaging (MRI) without contrast is sufficient to diagnose an intra-articular ganglion cyst of the knee. MRI with intravenous contrast may be considered for cysts in the infrapatellar fat pad, which are not a typical presentation.

➢

The current literature supports treating symptomatic cases or those discovered accidently during knee arthroscopy with arthroscopic excision.

➢

Although aspiration of these cysts results in a higher recurrence rate than excision, it is associated with quicker recovery. Thus, aspiration might be chosen as an initial treatment for anyone who would like to avoid surgery or requires a rapid recovery, including professional athletes.

➢

Open excision may be considered for infrapatellar fat pad cysts that are &gt;4.5 cm in size.

Agreement Between Clinical Examination and Magnetic Resonance Imaging in Acute Knee Trauma With Hemarthrosis

OBJECTIVE

Hemarthrosis after knee trauma often indicates serious joint injury. Few studies have evaluated agreement between clinical examination and findings from magnetic resonance imaging (MRI). We aimed to describe the agreement between acute clinical examination and subacute MRI findings after acute knee trauma with hemarthrosis and the importance of the subspecialty of the examiner.

DESIGN

Longitudinal cohort study. Agreement with MRI findings was evaluated by logistic regression.

SETTING

Helsingborg hospital.

PATIENTS

Thousand one hundred forty-five consecutive patients with hemarthrosis after knee trauma.

INTERVENTIONS

Clinical examination and MRI.

MAIN OUTCOME MEASURES

agreement between clinical examination and findings from MRI. We considered the radiologist's report as the gold standard.

RESULTS

Median time (25th, 75th percentile) from injury to clinical examination was 2 (1, 7) days, and from injury to imaging was 8 (5, 15) days. The overall sensitivity and specificity of clinical examination versus MRI for major ligament injury or lateral patella dislocation (LPD) were 70% [95% confidence interval 67-73) and 66% (61-72), respectively. Orthopedic subspecialist knee had the highest agreement with anterior cruciate ligament rupture (adjusted odds ratios were 1.7 (95% confidence interval 1.2-2.3), 1.9 (1.2-3.0) and 5.9 (3.7-9.5) for orthopedic trainees, orthopedic subspecialists other, and orthopedic subspecialist knee, respectively]. For other ligament injuries and LPD, we did not find statistically significant differences.

CONCLUSIONS

Clinical diagnosis after acute knee injury is relatively unreliable versus MRI findings even when performed by orthopedic specialists. However, the agreement is improved when the examination is performed by an orthopedic knee subspecialist.

Epidemiology of intra- and peri-articular structural injuries in traumatic knee joint hemarthrosis - data from 1145 consecutive knees with subacute MRI

OBJECTIVE

In patients with traumatic knee distorsion and hemarthrosis, to investigate the panorama of structural injury, as visualized on magnetic resonance imaging (MRI).

DESIGN

Cohort study of 1145 consecutive patients with traumatic knee distorsion who underwent MRI within median 8 days after injury. We present structural injury as visualized on MRI in relation to age, sex and activity at injury. Population based gender specific annual incidences of common structural injuries were calculated.

RESULTS

The majority of injuries (72%) occurred during sports. Overall, anterior cruciate ligament (ACL) rupture was the most common structural injury (52%), followed by meniscal tear (41%) and lateral patella dislocation (LPD, 17%). Only 12% of ACL tears were isolated with meniscal tear being the most common associated injury (55%). The annual incidence of ACL injury was 77 (70-85, 95% CI) per 100,000 inhabitants with significant differences between men (91, 80-103) and women (63, 53-73). In those aged 16 years and younger, LPD was the most frequent structural injury, both in boys (39%) and girls (43%). In this age group, the annual incidence of LPD was 88 (68-113) and higher in boys (113, 81-154) than in girls (62, 39-95).

CONCLUSIONS

ACL injury occurs in one out of two knees with traumatic hemarthrosis but only 12% are without concomitant structural injury. The overall rate of traumatic knee hemarthrosis and ACL injury is higher in men. In those aged 10-19 years, ACL rupture is more common among girls than boys whereas in those 16 years and younger, LPD is more common among boys than girls.

Correlation of clinical examination, ultrasound sonography, and magnetic resonance imaging findings with arthroscopic findings in relation to acute and chronic lateral meniscus injuries

PURPOSE

The aim of this study was to evaluate whether ultrasound sonography (USS) performed by orthopedic surgeons is a reliable method of investigating lateral meniscus (LM) knee lesions as compared to magnetic resonance imaging (MRI), and arthroscopy, which is the gold standard in clinical practice.

METHODS

In total, 107 patients were involved in this study. They were hospitalized for arthroscopy due to LM injury of the knee. Clinical examination (McMurray's, Apley's, and joint line tenderness tests), USS, and MRI were performed prior to arthroscopy. We compared the results of clinical examination, USS, and MRI with the arthroscopic findings for the knee, which were considered the reference values.

RESULTS

McMurray's clinical test, which is the most sensitive method of detecting lateral meniscus lesions, gave the same sensitivity rate for both acute and chronic LM injuries: 65%. USS was observed to be more sensitive and specific for chronic LM injuries (85 and 90%, respectively) than for acute LM injuries (71 and 87%). MRI also yielded higher values of sensitivity and specificity for chronic lateral meniscus injuries (75 and 95%, respectively) than for acute LM injuries (68 and 87%).

CONCLUSIONS

The accuracy of ultrasound examination is demonstrated by the high reliability of this method in the diagnosis of lateral meniscus lesions of the knee, and the evaluation performed in this study showed that ultrasound is a useful clinical tool for diagnosing knee pathology.

Management of medial-sided knee injuries, part 1: medial collateral ligament

The medial collateral ligament complex is a primary stabilizer that combines static and dynamic resistance to direct valgus stress while contributing significant restraints to rotatory motion and anterior-posterior translation. Varying opinions exist among investigators regarding injury classification and treatment algorithms. Whereas most agree that the majority of isolated medial collateral ligament complex injuries can be treated nonoperatively, isolated injuries with chronic instability and multiligament injuries may require operative intervention. Substantial confounding factors are present within published reports, making comparative analyses and systematic review challenging. This review focuses on the anatomy and biomechanics of the medial structures of the knee; it discusses the clinical evaluation of complex injuries; and it reviews nonoperative and operative treatment methods.

A randomized trial of treatment for acute anterior cruciate ligament tears

BACKGROUND

The optimal management of a torn anterior cruciate ligament (ACL) of the knee is unknown.

METHODS

We conducted a randomized, controlled trial involving 121 young, active adults with acute ACL injury in which we compared two strategies: structured rehabilitation plus early ACL reconstruction and structured rehabilitation with the option of later ACL reconstruction if needed. The primary outcome was the change from baseline to 2 years in the average score on four subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS)--pain, symptoms, function in sports and recreation, and knee-related quality of life (KOOS(4); range of scores, 0 [worst] to 100 [best]). Secondary outcomes included results on all five KOOS subscales, the Medical Outcomes Study 36-Item Short-Form Health Survey, and the score on the Tegner Activity Scale.

RESULTS

Of 62 subjects assigned to rehabilitation plus early ACL reconstruction, 1 did not undergo surgery. Of 59 assigned to rehabilitation plus optional delayed ACL reconstruction, 23 underwent delayed ACL reconstruction; the other 36 underwent rehabilitation alone. The absolute change in the mean KOOS(4) score from baseline to 2 years was 39.2 points for those assigned to rehabilitation plus early ACL reconstruction and 39.4 for those assigned to rehabilitation plus optional delayed reconstruction (absolute between-group difference, 0.2 points; 95% confidence interval, -6.5 to 6.8; P=0.96 after adjustment for the baseline score). There were no significant differences between the two treatment groups with respect to secondary outcomes. Adverse events were common in both groups. The results were similar when the data were analyzed according to the treatment actually received.

CONCLUSIONS

In young, active adults with acute ACL tears, a strategy of rehabilitation plus early ACL reconstruction was not superior to a strategy of rehabilitation plus optional delayed ACL reconstruction. The latter strategy substantially reduced the frequency of surgical reconstructions. (Funded by the Swedish Research Council and the Medical Faculty of Lund University and others; Current Controlled Trials number, ISRCTN84752559.)

The acutely ACL injured knee assessed by MRI: are large volume traumatic bone marrow lesions a sign of severe compression injury?

OBJECTIVES

To map by magnetic resonance imaging (MRI) and quantitative MRI (qMRI) concomitant fractures and meniscal injuries, and location and volume of traumatic bone marrow lesions (BMLs) in the acutely anterior cruciate ligament (ACL) injured knee. To relate BML location and volume to cortical depression fractures, meniscal injuries and patient characteristics.

METHODS

One hundred and twenty-one subjects (26% women, mean age 26 years) with an ACL rupture to a previously un-injured knee were studied using a 1.5T MR imager within 3 weeks from trauma. Meniscal injuries and fractures were classified by type, size and location. BML location and volume were quantified using a multi-spectral image data set analyzed by computer software, edited by an expert radiologist.

RESULTS

Fractures were found in 73 (60%) knees. In 67 (92%) of these knees at least one cortical depression fracture was found. Uni-compartmental meniscal tears were found in 44 (36%) subjects and bi-compartmental in 24 (20%). One hundred and nineteen (98%) knees had at least one BML, all but four (97%) located in the lateral compartment. Knees with a cortical depression fracture had larger BML volumes (P<0.001) than knees without a cortical depression fracture, but no associations were found between meniscal tears and BML volume or fractures. Older age at injury was associated with smaller BML volumes (P<0.01).

CONCLUSION

A majority of the ACL injured knees had a cortical depression fracture, which was associated with larger BML volumes. This indicates strong compressive forces to the articular surface and cartilage at the time of injury, which may constitute an additional risk factor for later knee osteoarthritis development.

Acute rotational trauma to the knee: poor agreement between clinical assessment and magnetic resonance imaging findings

OBJECTIVES

To determine the incidence of anterior cruciate ligament (ACL) injuries in the general population; the pathology associated with a knee sprain verified by magnetic resonance imaging (MRI); and the agreement between clinical findings and MRI.

MATERIAL AND METHODS

Inclusion criterion was an acute rotational trauma to the knee associated with effusion. One hundred and fifty-nine consecutive patients, mean age 27 years and 36% women, were included after clinical assessment at the orthopedic emergency unit. Patients were referred to an MRI examination (1.0 or 1.5 T) performed within a median of 8 days of the initial visit.

RESULTS

The annual incidence of MRI verified ACL injuries was 0.81/1000 inhabitants aged 10-64 years. Fifty-six percent (n=89) of those included had sustained an ACL injury of whom 38% had an associated medial meniscus tear. There was a poor agreement between initial clinical antero-posterior laxity and MRI verified presence of an ACL tear (kappa 0.281). Every second patellar dislocation was diagnosed as a ligament injury.

CONCLUSION

Our findings indicate that the incidence of ACL injuries is higher than previously described. We also show that the first clinical examination after an acute knee trauma has a low diagnostic value. Further assessment with MRI improves the chances of a correct diagnosis of intraarticular pathology and is recommended in the early phase after a rotational knee trauma.

MRI description of knee medial collateral ligament abnormalities in the absence of trauma: edema related to osteoarthritis and medial meniscal tears

A retrospective case series regarding the knees of 12 adult patients with MRI abnormalities of the medial collateral ligament (MCL), but without clinical history of trauma to the MCL, were collected and compared with six knee MR images from patients with clinical traumatic injuries to their MCLs. The MR images were studied for the extent of edema of the MCL, as well as other associated findings. Edema of the MCL on MRI could be found in three distinct categories of patients: (a) those with trauma to the MCL, which was an expected finding; (b) those without trauma but with medial compartment osteoarthritis; and (c) those without trauma but with degenerative medial meniscal tears. The clinical significance, if any, of the edema found in MCLs without trauma remains unclear. Atraumatic MCL edema may serve as a marker for medial knee compartment osteoarthritis or for a degenerative medial meniscal tear and should not be confused with traumatically induced MCL injuries, although this distinction can often be difficult to make based on MRI findings alone.

Magnetic resonance imaging of the elbow: update on current techniques and indications

The utility of magnetic resonance imaging of the elbow has noticeably improved over the past decade. Advances in equipment and refinement of pulse sequences has allowed for superior visualization of many pathologic processes involving the elbow joint and its surrounding structures. At this time, magnetic resonance imaging is most valuable in detecting occult fractures, osteochondritis dissecans, collateral ligament tears, nonossified intra-articular loose bodies, and soft tissue masses. It may also aid in the diagnosis of tendinous injuries, compression neuropathies, and synovial disorders. This article serves as an educational update for hand surgeons and illustrates the features of normal anatomy and specific disorders of the elbow.

Physical Examination and Imaging of the Medial Collateral Ligament and Posteromedial Corner of the Knee

The medial side is one of the most commonly injured areas of the knee. The anatomy, diagnosis, and treatment of medial collateral ligament and posteromedial corner (PMC) injuries can be challenging. Understanding the mechanism of injury and performing a thorough physical examination and radiographic evaluation is essential. Frequently, there are concomitant meniscal and other ligament injuries associated with medial-side injuries. Correct identification of all injured structures is important, as missed diagnoses can lead to significant disability. Unrecognized PMC injuries have been implicated in anteromedial rotary instability and failed anterior cruciate ligament reconstructions. Valgus stress testing is the cornerstone for the identification of medial-side knee injuries. Coronal sequences from magnetic resonance imaging are the most useful tool to view the medial collateral ligament and posteromedial structures. Stress x-rays and ultrasound may also be helpful. Thorough physical examination and imaging of injuries to the PMC should dictate the appropriate treatment for optimal results.

Application of 3D-MR image registration to monitor diseases around the knee joint

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.

Abnormalities identified in the knees of asymptomatic volunteers using peripheral magnetic resonance imaging

OBJECTIVE

To estimate the prevalence of bone and soft tissue abnormalities in asymptomatic knees using peripheral magnetic resonance imaging (pMRI) and to examine the relationship between these abnormalities and Kellgren-Lawrence (K-L) graded X-rays.

METHOD

Volunteers (20-68 years) with no history of knee pain, injury or bone or joint disease were recruited. Individuals underwent a single MRI scan and radiograph of their non-dominant knee. pMR images were acquired in sagittal plane using a 3-D gradient-echo protocol. Two radiologists graded the presence and severity of cartilage degeneration, osteophytosis, meniscal and ligamentous abnormalities, bone marrow edema and subchondral cysts. X-rays were acquired using a fixed-flexion technique and graded using the K-L scale.

RESULTS

Forty-four individuals, mean age (SD) 41.1 (14.2) years, participated. K-L grading of X-rays revealed 29 individuals were grade 0, 12 were grade 1 and 3 were grade 2. Five individuals showed evidence of cartilage lesions, the femoral trochlea, medial femur and patella being those regions most commonly affected. Twelve individuals (27.3%) showed evidence of osteophytosis, nine of whom did not show evidence on X-ray. Forty-three individuals showed evidence of at least one meniscal abnormality while 27 individuals (61.4%) had abnormalities in at least three of the four regions of the knee.

CONCLUSION

Our results suggest that osteophytes may be more prevalent in this population than radiographic data suggests due to the limitations of two-dimensional imaging. Meniscal degeneration or tears, a risk factor for knee osteoarthritis, are highly prevalent in asymptomatic individuals with the medial anterior and posterior horns being the most commonly affected regions.

Long-term BMP-2-induced bone formation in rat island and free flaps

Ectopic osteoinduction by exogenous bone morphogenetic proteins (BMPs) is rapid but heretofore characterized as transient. A rat model of carrier-free recombinant human BMP-2 intramuscular implantation was used, followed by creation of either an island flap or transplantation of a free flap. BMP-2 injection into an unaltered gastrocnemius, thigh adductor, or cutaneous trunci (thoracic wall) muscle site led to bone resorption at 4 weeks. In contrast, creation of an island or free flap of the muscle/injection site caused the newly formed ossicle to maintain its bony composition with active osteoblastic presence, from 3-8 weeks. Muscle denervation or sectioning of the Achilles tendon (for gastrocnemius injections) did not prevent bone resorption at 4 weeks. There was little osteoclastic activity within de novo bone sites of island- and free flap-injected muscles at 4 and 8 weeks. These data demonstrate that simple injection of BMP-2 into a surgically isolated flap site results in the prolonged presence of de novo bone. These findings suggest that BMP-injected island or free muscle flaps may be used to generate new bone for reconstruction of a bony defect.

Imaging of early stages of osteonecrosis of the knee

Osteonecrosis of the knee can present as a spontaneous and primary or a secondary clinical entity. The natural history of osteonecrosis follows a course of several sequential stages, and the later stages of both entities seem to be irreversible. Early diagnosis of osteonecrosis is crucial: the earlier the stage of the lesion at the time of diagnosis, the better the prognosis.Clinically, early diagnosis and treatment of osteonecrosis might prevent unnecessary surgery in cases with a concomitant degenerative meniscal tear. Early-stage osteonecrosis should be ruled out before surgery, because arthroscopy has lately been associated with osteonecrosis. Not every imaging method is equally suitable for detecting pathognomonic changes in each stage of osteonecrosis. Early-stage osteonecrosis is difficult to diagnose,because various differential diagnoses must be kept in mind. Moreover, there is a diagnostic window between the onset of symptoms and the appearance of pathognomonic changes on plain radiographs and MRI.