MR imaging of fatigue stress injuries to bones: intra- and interobserver agreement

[Stress fractures]

Bone stress injuries are due to repetitive mechanical overuse of the skeleton and occur as a result of microscopic lesions sustained when bone is subjected to repeated submaximal stress. Over time accumulation of such injuries can lead to bone failure and fractures. Stress-related bone injuries are relatively common among otherwise healthy persons who have recently started new or intensified forms of physical training activities. Stress injuries lead to typical findings on radiography, bone scintigraphy, computed tomography (CT) and magnetic resonance imaging (MRI) and need to be discriminated from other conditions, in particular infections and neoplasms. Stress fractures must be differentiated from insufficiency fractures that occur in bones with reduced mechanical resistance or disturbed structure.

Diagnosis, treatment, and rehabilitation of stress fractures in the lower extremity in runners

Stress fractures account for between 1% and 20% of athletic injuries, with 80% of stress fractures in the lower extremity. Stress fractures of the lower extremity are common injuries among individuals who participate in endurance, high load-bearing activities such as running, military and aerobic exercise and therefore require practitioner expertise in diagnosis and management. Accurate diagnosis for stress fractures is dependent on the anatomical area. Anatomical regions such as the pelvis, sacrum, and metatarsals offer challenges due to difficulty differentiating pathologies with common symptoms. Special tests and treatment regimes, however, are similar among most stress fractures with resolution between 4 weeks to a year. The most difficult aspect of stress fracture treatment entails mitigating internal and external risk factors. Practitioners should address ongoing risk factors to minimize recurrence.

Assessing diagnostic tests: how to correct for the combined effects of interpretation and reference standard

We describe a general solution to the problem of determining diagnostic accuracy without the use of a perfect reference standard and in the presence of interpreter variability. The accuracy of a diagnostic test is typically determined by comparing its outcomes with those of an established reference standard. But the accuracy of the standard itself and those of the interpreters strongly influence such assessments. We use our solution to examine the effects of the properties of the standard, the reliability of the interpreters, and the prevalence of abnormality on the measured sensitivity and specificity. Our results provide a method of systematically adjusting the measured sensitivity and specificity in order to estimate their true values. The results are validated by simulations and their detailed application to specific cases are described.

The role of MRI in musculoskeletal practice: a clinical perspective

This clinical perspective presents an overview of current and potential uses for magnetic resonance imaging (MRI) in musculoskeletal practice. Clinical practice guidelines and current evidence for improved outcomes will help providers determine the situations when an MRI is indicated. The advanced competency standard of examination used by physical therapists will be helpful to prevent overuse of musculoskeletal imaging, reduce diagnostic errors, and provide the appropriate clinical context to pathology revealed on MRI. Physical therapists are diagnostically accurate and appropriately conservative in their use of MRI consistent with evidence-based principles of diagnosis and screening.

Tibial stress injury: relationship of radiographic, nuclear medicine bone scanning, MR imaging, and CT Severity grades to clinical severity and time to healing

PURPOSE

To examine the relationship between severity grade for radiography, triple-phase technetium 99m nuclear medicine bone scanning, magnetic resonance (MR) imaging, and computed tomography (CT); clinical severity; and recovery time from a tibial stress injury (TSI), as well as to evaluate interassessor grading reliability.

MATERIALS AND METHODS

This protocol was approved by the Griffith University Human Research Ethics Committee, the Stanford University Panel on Human Subjects in Medical Research, the U.S. Army Human Subjects Research Review Board, and the Australian Defense Human Research Ethics Committee. Informed consent was obtained from all subjects. Forty subjects (17 men, 23 women; mean age, 26.2 years ± 6.9 [standard deviation]) with TSI were enrolled. Subjects were examined acutely with standard anteroposterior and lateral radiography, nuclear medicine scanning, MR imaging, and CT. Each modality was graded by four blinded clinicians. Mixed-effects models were used to examine associations between image severity, clinical severity, and time to healing, with adjustments for image modality and assessor. Grading reliability was evaluated with the Cronbach α coefficient.

RESULTS

Image assessment reliability was high for all grading systems except radiography, which was moderate (α = 0.565-0.895). Clinical severity was negatively associated with MR imaging severity (P ≤ .001). There was no significant relationship between time to healing and severity score for any imaging modality, although a positive trend existed for MR imaging (P = .07).

CONCLUSION

TSI clinical severity was negatively related to MR imaging severity. Radiographic, bone scan, and CT severity were not related to time to healing, but there was a positive trend for MR imaging.

Validation of MRI classification system for tibial stress injuries

OBJECTIVE

The purpose of our study was to compare an MRI classification system for tibial stress injuries with semiquantitative MR features of injury severity and clinical outcome.

MATERIALS AND METHODS

Two musculoskeletal radiologists retrospectively reviewed in consensus the MR findings of 142 tibial stress injuries to quantify the degree of periosteal and bone marrow edema and grade the injuries using the Fredericson classification system (grade 1 = periosteal edema only, grade 2 = bone marrow edema visible on T2-weighted images, grade 3 = bone marrow edema visible on T1-weighted and T2-weighted images, grade 4a = multiple focal areas of intracortical signal abnormality, and grade 4b = linear areas of intracortical signal abnormality). Kruskal-Wallis tests were used to determine the relationship between the grade of stress injury and the degree of periosteal and bone marrow edema and the time to return to sports activity.

RESULTS

Grade 4b injuries had significantly (p < 0.002) more severe and grade 1 injuries less severe periosteal and bone marrow edema than grades 2, 3, and 4a injuries. Grade 4b injuries had significantly (p < 0.002) longer time and grade 1 injuries shorter time to return to sports activity than grades 2, 3, and 4a injuries. There was no significant difference (p = 0.06-0.79) among grades 2, 3, and 4a injuries in the degree of periosteal and bone marrow edema and the time to return to sports activity.

CONCLUSION

Grades 2, 3, and 4a stress injuries had similar degrees of periosteal and bone marrow edema and similar time to return to sports activity, which suggests that these three grades can be combined into a single category in an abbreviated Fredericson classification system.

High-resolution axial MR imaging of tibial stress injuries

Purpose

To evaluate the relative involvement of tibial stress injuries using high-resolution axial MR imaging and the correlation with MR and radiographic images.

Methods

A total of 33 patients with exercise-induced tibial pain were evaluated. All patients underwent radiograph and high-resolution axial MR imaging. Radiographs were taken at initial presentation and 4 weeks later. High-resolution MR axial images were obtained using a microscopy surface coil with 60 × 60 mm field of view on a 1.5T MR unit. All images were evaluated for abnormal signals of the periosteum, cortex and bone marrow.

Results

Nineteen patients showed no periosteal reaction at initial and follow-up radiographs. MR imaging showed abnormal signals in the periosteal tissue and partially abnormal signals in the bone marrow. In 7 patients, periosteal reaction was not seen at initial radiograph, but was detected at follow-up radiograph. MR imaging showed abnormal signals in the periosteal tissue and entire bone marrow. Abnormal signals in the cortex were found in 6 patients. The remaining 7 showed periosteal reactions at initial radiograph. MR imaging showed abnormal signals in the periosteal tissue in 6 patients. Abnormal signals were seen in the partial and entire bone marrow in 4 and 3 patients, respectively.

Conclusions

Bone marrow abnormalities in high-resolution axial MR imaging were related to periosteal reactions at follow-up radiograph. Bone marrow abnormalities might predict later periosteal reactions, suggesting shin splints or stress fractures. High-resolution axial MR imaging is useful in early discrimination of tibial stress injuries.

Stress fractures in the young athlete: a pictorial review

Stress fractures are an uncommon but important source of pain and disability in young athletes. The presentation and differential diagnosis of stress fractures in young athletes differs from that of older athletes. This pictorial review outlines the pathogenesis and imaging features of stress fractures. Other pathologies that can mimic stress fractures and the advantages of the use of magnetic resonance imaging will be discussed. An imaging algorithm for a suspected stress fracture is suggested.

Stress fractures in athletes

Stress fractures that occur in the young active population typically represent an overuse injury, and may lead to prolonged periods of restriction from play if they are not treated appropriately. Several risk factors have been identified and must be addressed when treating these patients. Low-risk stress fractures can be successfully treated with activity restriction and a stepwise return to sport. Several pharmacologic and nonoperative treatment modalities have been described. However, high-risk stress fractures are more difficult to treat because they may have an increased rate of delay and nonunion, and often require surgical stabilization. When treating an athlete with a stress fracture, the objective is a safe and quick return to sport; therefore, special considerations must be made in this population, particularly when dealing with the in-season athlete.

Stress fractures presenting as tumours: a retrospective analysis of 22 cases

Frequently, the imaging features of stress fractures may be misinterpreted as tumour-like lesions. The aim of this study was to analyse the quality of different examinations in detecting stress fractures mimicking tumour-like lesions in magnetic resonance imaging (MRI). We evaluated 22 cases which were referred to our department with the suspected diagnosis of bone tumours turning out to be stress fractures. Whenever the MRI did not lead to a diagnosis after a second review, computed tomography (CT) scans and, if still required, additional examinations were performed until the fracture was detected. A stress fracture was diagnosed in 15 cases after the additional CT scan, in five cases with the review of the MRI and in two cases with a combination of several examinations. Especially in stress fractures of the tibia and the femur, CT scanning was essential for making a diagnosis by detecting the fracture line. Bone scans and biopsies, in contrast, were not helpful in making a correct diagnosis.

Significance of radiographic abnormalities in patients with tibial stress injuries: correlation with magnetic resonance imaging

OBJECTIVE

The objective was to correlate radiographic findings with magnetic resonance imaging (MRI) findings in patients with suspected tibial stress injuries in order to determine the significance of radiographic signs of stress injury in these individuals.

PATIENTS AND METHODS

The study group consisted of 80 patients with suspected tibial stress injuries who underwent a radiographic and MR examination of the tibia. Nineteen patients had bilateral involvement. Thus, a total of 99 tibias were evaluated. All radiographs and MR examinations were retrospectively reviewed, 1 month apart, in consensus by two musculoskeletal radiologists. The radiographs were reviewed without knowledge of the site of the clinical symptoms. Fisher's exact tests were used to determine the association between a positive radiograph and the presence of various MRI signs of a high-grade stress injury.

RESULTS

There was a strong association between the presence of periosteal reaction on radiographs at the site of the clinical symptoms and a Fredericson grade 4 stress injury on MRI.

CONCLUSIONS

The presence of periosteal reaction on radiographs at the site of clinical symptoms is predictive of a high-grade stress injury by MRI criteria.

High-Resolution CT Grading of Tibial Stress Reactions in Distance Runners

OBJECTIVE

The purpose of this study was twofold: to determine whether asymptomatic distance runners exhibit cortical tibial abnormalities on CT and to determine the diagnostic accuracy of CT in athletes with medial tibial stress syndrome.

MATERIALS AND METHODS

A cross-sectional study with high-resolution CT of both tibiae was performed on 41 subjects: 20 asymptomatic distance runners, 11 distance runners with unilateral or bilateral pain due to medial tibial stress syndrome (14 painful tibiae), and 10 volunteers not involved in a sport. The group was composed of 13 women and 28 men, ranging in age from 18 to 26 years. A total of 82 tibiae, 14 painful and 68 painless, were evaluated. On the basis of CT findings, tibiae were classified in three groups, and correlation between CT classification and symptoms was made.

RESULTS

Among distance runners, the presence of CT abnormalities was found in 14 (100%) of 14 painful tibiae in patients with medial tibial stress syndrome and in 8 (16.6%) of 48 painless tibiae. The difference was statistically significant (p < 0.001, Fisher's exact test). Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of CT in diagnosing medial tibial stress syndrome were 100%, 88.2%, 63.6%, 100%, and 90.2%, respectively.

CONCLUSION

High-resolution CT has high diagnostic accuracy in depicting medial tibial stress syndrome. Cortical abnormalities can also be seen in some asymptomatic distance runners.

Stress fractures in adolescent competitive athletes with open physis

There have been no studies devoted exclusively to stress fractures in competitive athletes with immature skeletal systems so far. The object of this case series was to describe special features of stress fractures in athletes with immature skeletal systems, with special reference to sport-specific strain, diagnosis and treatment results. The study population was made up of 19 children and adolescents with a total of 21 stress fractures. The average observation period was 4.83 years [standard deviation (SD) 2.69] and the average age at diagnosis, 14.04 years (SD 4.7). The lower extremity was affected in most of our cases. In adolescent athletes, endurance sports appear to lead preferentially to stress fractures in the region of the metatarsal bones, while sports requiring sudden stops at high speed appear to increase the risk of fractures in the region of the tibial diaphysis (P=0.0322). Most (20 of 21) of the fractures in this study were treated conservatively with refraining from athletic activity and reduction of stress/weight-bearing for an average of 6.73 weeks (SD 2.91). In five cases the extremity was in addition immobilized in a plaster cast for 5.32 weeks (SD 2.21). Complete healing was achieved in 14 cases. In seven cases, however, the treatment did not lead to a satisfactory outcome. Most of the patients whose symptoms persisted over a long period had fractures in the tibia and were engaged in sports requiring frequent sudden stops. Our data suggest that stress fractures in athletes, whose skeletal systems are still immature, lead to a clinical picture that does not always culminate in a good outcome of treatment. We therefore recommend a thorough and early diagnostic investigation (including MRI) and consistent treatment whenever a patient's history and clinical picture give any indication that a stress fracture might be present.

Musculoskeletal imaging in physical therapist practice

This article presents an overview of current concepts of evidence-based diagnosis using a variety of imaging modalities for a broad spectrum of musculoskeletal conditions and syndromes. There is limited but increasing evidence that physical therapists appropriately use diagnostic studies in clinical practice. Pathology revealed by diagnostic studies must be viewed in the context of the complete examination, as pathology is common in the asymptomatic population. Special diagnostic challenges are presented by patients with areas of referred pain, multiple injuries or multiple areas of pathology, neoplasms, and infections. Plain film radiographs have been overused in the clinical management of many conditions, including low back pain. Clinical decision rules provide simple evidence-based guidelines for the appropriate use of imaging studies.

CT and MR imaging findings in athletes with early tibial stress injuries: comparison with bone scintigraphy findings and emphasis on cortical abnormalities

PURPOSE

To prospectively compare computed tomography (CT), magnetic resonance (MR) imaging, and bone scintigraphy in athletes with clinically suspected early stress injury of tibia.

MATERIALS AND METHODS

Medical ethics committee approval and informed consent were obtained. A total of 42 patients experiencing tibial pain due to early stress injuries were evaluated. Eight patients had bilateral involvement; thus, 50 tibiae were evaluated. All patients underwent initial radiography that was negative for injury. MR imaging, CT, and bone scintigraphy were performed in all patients within 1 month of onset of symptoms. Ten asymptomatic volunteers served as the control group. Location of stress injuries, types of bone alterations, and presence of periosteal and bone marrow edema were evaluated. Sensitivity, specificity, accuracy, and positive and negative predictive values of MR imaging and CT were assessed, as was sensitivity of bone scintigraphy. McNemar test was used to detect statistically significant differences.

RESULTS

Sensitivity of MR imaging, CT, and bone scintigraphy was 88%, 42%, and 74%, respectively. Specificity, accuracy, and positive and negative predictive values were 100%, 90%, 100%, and 62%, respectively, for MR imaging and 100%, 52%, 100%, and 26%, respectively, for CT. Significant difference in detection of early tibial stress injuries was found between MR imaging and both CT and bone scintigraphy (McNemar test; P < .001 and P = .008, respectively).

CONCLUSION

MR imaging is the single best technique in assessment of patients with suspected tibial stress injuries; in some patients with negative MR imaging findings, CT can depict osteopenia, which is the earliest finding of fatigue cortical bone injury.

Reproducibility of image interpretation in MRI of the prostate: application of the sextant framework by two different radiologists

The aim of this study was to reproduce prostate cancer (PCA) localization by MRI based on prostatic sextants (right and left base, middle, and apex) with minimal systematic error. Combined endorectal/body-phased-array-coil MRI of the prostate at 1.5 T was retrospectively evaluated twice, with an interval of more than 1 month, by each of two independent radiologists (R1 readings R11 and R12, and R2 readings R21 and R22) in 23 patients (age 51-75 years) who had radical prostatectomy within 1 month of MRI. PCA stage was pT2 in 14 patients, and pT3 in nine. Median Gleason score was 7 (range 5-9). Histopathology showed 83 sextants with PCA and 55 without. Reproducibility of sextant positions was within one MRI slice (3 mm) in over 80% of cases. For PCA localization, ROC analysis (AUC=0.584+/-0.048-0.724+/-0.043) yielded no significant intra-reader differences. R11 and R21 differed slightly (P=0.035). Intra-observer agreement (kappa=0.52-0.58) exceeded inter-observer agreement (kappa=0.35-0.45). Intra-observer Spearman correlation (r=0.72-0.74) exceeded inter-observer correlation (r=0.43-0.51) for sextants with PCA, but not for sextants without (r=0.69-0.74). Per-sextant localization and reporting provides a highly reliable framework in MRI of the prostate. MRI of the prostate should be followed up by the same radiologists to minimize systematic error of interpretation.

Bone stress injuries in asymptomatic elite recruits: a clinical and magnetic resonance imaging study

BACKGROUND

The occurrence and clinical significance of asymptomatic bone stress injuries is unknown.

HYPOTHESIS

To evaluate by clinical and magnetic resonance imaging follow-up the occurrence of asymptomatic bone stress injuries, their clinical significance, and whether they all progress to stress fractures in subjects undergoing intensive physical training.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 1.

METHODS

Twenty-one male elite-unit military recruits voluntarily underwent clinical examination and magnetic resonance imaging before their intensive training period, 6 weeks into it, and on completion of the 5-month training program.

RESULTS

Based on magnetic resonance imaging, a total of 75 bone stress injuries were detected. Only 40% (30/75) of the bone stress injuries had been symptomatic. Symptoms depended on location and magnetic resonance imaging grade of injury, with higher grades usually more symptomatic. Repeated clinical and magnetic resonance imaging assessment indicated that asymptomatic grade I bone stress injuries healed (21/25, 84%) or remained grade I and asymptomatic (3/25, 12%). The numbers of bone stress injuries, symptomatic cases, and recruits with bone stress injury increased toward the end of the intensive training period.

CONCLUSIONS

Asymptomatic grade I bone stress injuries seem common in subjects undergoing intensive physical training. Such bone stress injuries heal or remain asymptomatic grade I bone stress injuries even if intensive physical activity continues. They are therefore of no clinical significance. Only subjects who exhibit symptoms need undergo imaging studies. Subjects with an asymptomatic grade I bone stress injury may continue training but should be clinically monitored for symptoms.

Asymptomatic Tibial Stress Reactions: MRI Detection and Clinical Follow-Up in Distance Runners

OBJECTIVE

The purpose of this study was twofold: to determine if asymptomatic elite distance runners exhibit stress reactions of the tibia on MR images and to determine if the presence of bone stress lesions predicts later development of symptomatic tibial stress injuries.

CONCLUSION

Signs of a tibial stress reaction were found on MRI in 43% of the 21 asymptomatic college distance runners in this study. The presence of these changes was not found to be a predictor of future tibial stress reactions or stress fractures. Our findings underscore the importance of correlating MRI findings with clinical findings before making therapeutic decisions.

MR imaging of sports-related hip disorders

Hip arthroscopy is being used increasingly for the diagnosis and treatment of hip disorders. MR imaging performed with appropriate technical considerations may aid not only in preoperative planning but in the appropriate selection of patients, which tends to lead to better postoperative results. Although the painful hip is imaged most commonly by radiography, MR imaging is considered the next imaging test of choice for evaluation of most common hip abnormalities in athletes, including labral injuries, ligament injuries, osteochondral injuries, fractures, bursitis, and musculotendinous injuries. MR arthrography can be a particularly useful technique for dedicated assessment of hip joint internal derangements.