Faculty Bibliography

Purpose: To see if failure of arthroscopic shoulder stabilization can be predicted by the evaluation of bipolar bone loss on MRI Methods: A retrospective review of 39 consecutive patients (40 shoulders) who underwent arthroscopic capsulolabral repair for recurrent, traumatic, anterior shoulder instability was performed. There were a total of 40 MRIs from 39 patients (31males, 8 females, mean age 31.7 yrs.). Mean follow-up was 19 months. Pre-operative plain radiographs, MRI scans, operative reports, arthroscopic photos, and post-operative records were reviewed for each patient. Surgical failure was defined as recurrent shoulder dislocation and/or persistent apprehension during normal range of motion. Each preoperative MRI scan was evaluated for bipolar bone loss by one musculoskeletal radiologist using the on-track/off-track (OOT) method in which the glenoid track (GT) and Hill-Sachs interval (HSI) aremeasured. According to this technique, the GT is calculated as 0.83D-d in which "D" represents the diameter of the intact glenoid and "d" corresponds to the amount of glenoid bone loss. The HSI represents the width of the Hill-Sachs lesion plus the width of the intact bone bridge between the rotator cuff attachment and the lateral aspect of the Hill-Sachs lesion. All measurements were in millimeters. Lesions were considered "off-track" if the HSI exceeded the GT and "on-track" if the HSI was less than the GT. These findings were then compared to the corresponding post-operative outcomes. Statistical analysis was carried out using the Fisher exact test.
Result(s): Of the 40 shoulders evaluated, 6 were considered surgical failures (3 with recurrent dislocation and 3 with persistent apprehension). The OOT method correctly predicted 1 of these failures and falsely predicted 6 failures in shoulders that were clinically stable. There was no significant difference when comparing stable to unstable shoulders with regards to age, size of GTand HSI. Overall, the OOT method sensitivity was 16.7% (1/6), specificity 82.4% (28/34), positive predictive value 14.3% (1/7), negative predictive value 84.9% (28/33) and overall accuracy 72.5% (29/40).
Conclusion(s): MRI evaluation of bipolar (humeral and glenoid) bone loss using the on-track/off-track method is a moderately accurate and specific, but insensitive technique to predict surgical failure after arthroscopic capsulolabral repair for shoulder instability

OBJECTIVE. The article reviews a select group of traumatic upper extremity injuries that can be easily misinterpreted on radiographs. CONCLUSION. The awareness of these specific injuries and an understanding of their underlying pathophysiology and the role that radiographs can play in their evaluation will give the reader the best opportunity to make the important imaging findings and guide appropriate treatment.

The mechanics of the throwing shoulder are complex, resulting in a variety of adaptations that can lead to increased performance for the athlete. These adaptations can eventually fail and result in pathology to the stabilizing structures of the shoulder, most notably the rotator cuff and glenoid labrum. The understanding of the relationship between the mechanisms and injuries is evolving, resulting in improved diagnostic, therapeutic, and preventative measures. Our goal is to clarify the relationship between the mechanisms, common types of injury, and their appearance on imaging, specifically MRI, in a comprehensive, easy-to-understand manner that will leave you more confident when evaluating this subset of patients.

OBJECTIVE. The purpose of this article is to review the current understanding of the underlying pathophysiology of the Hill-Sachs lesion and anterior glenoid bone loss and to discuss the role of imaging in identifying and accurately describing these injuries. CONCLUSION. Understanding the underlying mechanics of anterior shoulder instability that result in Hill-Sachs lesions and glenoid bone loss, the strengths and weaknesses of the different imaging modalities ordered for their evaluation, and the methods used to characterize these osseous injuries on imaging are essential for the radiologist in this clinical setting.

OBJECTIVE: To assess the ability of 3D MR shoulder reconstructions to accurately quantify glenoid bone loss in the clinical setting using findings at the time of arthroscopy as the gold standard. MATERIALS AND METHODS: Retrospective review of patients with MR shoulder studies that included 3D MR reconstructions (3D MR) produced using an axial Dixon 3D-T1W-FLASH sequence at our institution was conducted with the following inclusion criteria: history of anterior shoulder dislocation, arthroscopy (OR) performed within 6 months of the MRI, and an estimate of glenoid bone loss made in the OR using the bare-spot method. Two musculoskeletal radiologists produced estimates of bone loss along the glenoid width, measured in mm and %, on 3D MR using the best-fit circle method, which were then compared to the OR measurements. RESULTS: There were a total of 15 patients (13 men, two women; mean age, 28, range, 19-51 years). There was no significant difference, on average, between the MRI (mean 3.4 mm/12.6 %; range, 0-30 %) and OR (mean, 12.7 %; range, 0-30 %) measurements of glenoid bone loss (p = 0.767). A 95 % confidence interval for the mean absolute error extended from 0.45-2.21 %, implying that, when averaged over all patients, the true mean absolute error of the MRI measurements relative to the OR measurements is expected to be less than 2.21 %. Inter-reader agreement between the two readers had an IC of 0.92 and CC of 0.90 in terms of percentage of bone loss. CONCLUSIONS: 3D MR reconstructions of the shoulder can be used to accurately measure glenoid bone loss.

In the shoulder, the advantages of range of motion are traded for the disadvantages of vulnerability to injury and the development of instability. Glenohumeral instability encompasses a broad spectrum of clinical complaints and presentations. The diagnosis can be obvious or entirely unsuspected. Imaging findings depend on numerous factors and range from gross osseous defects to equivocal labral abnormalities and undetectable capsular lesions. This review focuses on the imaging findings in three distinct clinical scenarios: acute first-time shoulder dislocation, chronic instability with repeated dislocation, and chronic instability without repeated dislocation. The biomechanics of dislocation and the pathophysiology of labral-ligamentous injury are discussed. The authors distinguish the findings that occur in the acutely traumatized shoulder from those that typify the chronic unstable joint. The roles of different imaging modalities are also distinguished, including magnetic resonance arthrography and the value of specialized imaging positions. The goal of imaging depends on the clinical scenario. Image interpretation and reporting may need to emphasize diagnosis and the identification of lesions that are associated with instability or the characterization of lesions for treatment planning.

OBJECTIVE. The objective of our study was to see whether there is an association between engagement on physical examination and the location or size of a Hill-Sachs lesion and the presence and degree of glenoid bone loss as assessed on MRI. MATERIALS AND METHODS. Thirty-three consecutive patients (32 males and one female) with a history of anterior shoulder dislocation who underwent preoperative MRI and arthroscopy at our institution and were tested for engagement on physical examination over a 9-month period were included in the study. Two blinded readers reviewed each study independently and documented the presence and size of the Hill-Sachs lesion, location of the Hill-Sachs lesion with a modified biceps angle, and presence and size of glenoid bone loss. Statistical analysis included the Mann-Whitney, logistic regression, Pearson correlation, and intraclass correlation tests. RESULTS. Eleven patients had evidence of an engaging Hill-Sachs lesion on physical examination and 22 did not. There was no statistically significant difference between any of the dimensions or overall area of the Hill-Sachs lesion when comparing the group with an engaging Hill-Sachs lesion and the group with a nonengaging lesion (surface area, 3.60 vs 3.23 cm(3), respectively; p = 0.272). There was a trend for a larger biceps angle in the engaging group without a statistically significant difference (mean, 154.5 degrees vs 143.9 degrees ; p = 0.069). There was a statistically significant difference in the amount of glenoid bone loss in the engaging group compared with the nonengaging group (mean, 20.2% vs 6.0%; p = 0.001). CONCLUSION. There is a significant association between an engaging Hill-Sachs lesion on physical examination and the degree of glenoid bone loss as well as a trend toward increased engagement with more medially oriented Hill-Sachs lesions. These findings show the importance of considering both the Hill-Sachs lesion and glenoid bone loss when evaluating patients with engagement.

OBJECTIVES:: To determine the lowest estimated radiation dose necessary to reproducibly detect intra-articular air in the knee joint of a cadaver model. METHODS:: 10 adult fresh-frozen cadaver knees with intact joint capsules provided by Science Care(R), Phoenix, AZ. were thawed and scanned at 5 decreasing radiation doses (decreasing by approximately half from 8.42 mGy to 0.74 mGy) after introducing increasing volumes (0 cc, 0.1 cc, 0.3 cc, 0.5 cc, 0.7 cc, 0.9cc) of intra-articular air. Scans were performed using 2.0 mm slice-thickness from the distal 1/3 of the femur to the proximal 1/3 of the tibia. Sagittal and coronal reconstructions of each scan using 1.0 mm slice-thickness were rendered. All scans were reviewed by 1) a single attending radiologist, 2) a single attending orthopedic surgeon, and 3) a single chief resident, for the presence of intra-articular air. RESULTS:: The sensitivity and specificity of CT scan to detect intra-articular air at each volume of intra-articular air (0.1 cc, 0.3 cc, 0.5 cc, 0.7 cc, 0.9cc) was 100% at 0.74 mGy - the radiation threshold dose (RadTH) (scan parameters: voltage 80kV, current: 33mA, and scan time: 12.17 sec). The effective radiation dose at 0.74 mGy for a CT scan of the knee is approximately 0.10 mSV CONCLUSIONS:: CT scan to detect traumatic knee arthrotomies can be successfully accomplished at a threshold radiation dose of 0.74 mGy and for an intra-articular volume of 0.1cc of air. This low radiation dose protocol and volume of intra-articular air should be taken into consideration with future studies evaluating the use of CT scan to detect traumatic arthrotomies.

Objective: To determine the accuracy of MR imaging for the evaluation of the subscapularis tendon as well as define imaging findings that will increase accuracy. MATERIALS AND METHODS: Retrospective review of the MR and operative (OR) reports of 286 patients was conducted and reviewed for the presence/degree (partial (PT)/full-thickness (FT)) of tearing; only PT articular tears were included. The presence of a supraspinatus tear and time interval between surgery and MRI were also documented. All of the PT tears called on MRI were also reviewed to see if there was a statistically significant association between certain imaging characteristics and the presence of a tear in surgery. Statistical analysis included 95 % confidence intervals, Fisher's exact, and exact Mann-Whitney tests. RESULTS: A total of 244 patients were included in the study with a total of 25 subscapularis tears, 16 PT and nine FT, and 219 intact tendons in arthroscopy; 20/25 tears and 200 intact sensitivity of 80%, specificity of 91%, accuracy of 90%, positive predictive value of 51%, and negative predictive value of 98 %. There was a significant association between the presence of a PT tear during arthroscopy and fluid-like signal within the tendon on more than one imaging plane (p<0.001) with an accuracy of 90%. CONCLUSIONS: This study reflects a musculoskeletal radiology section's experience with the diagnosis of subscapularis tendon pathology, demonstrating that MRI could be used to accurately evaluate the subscapularis tendon. An understanding of certain imaging pitfalls and the presence of fluid-like signal on multiple imaging planes should increase the diagnostic accuracy of the radiologist evaluating the subscapularis tendon for the presence of a tear.

OBJECTIVE. The purpose of this study was to define and correlate the appearance of the rotator cable on MRI with arthroscopy, band-saw cadaveric sections, and histology. MATERIALS AND METHODS. Two cadaveric shoulders underwent 3-T MRI, band-sawing, and histologic evaluation. Three readers evaluated the MRI for the presence of the cable, and the same readers and a pathologist reviewed the macroscopic and microscopic specimens for a structure that corresponded to the cable. Cadaver 1 underwent arthroscopic evaluation to evaluate for the presence of a cable. Seventy consecutive shoulders that underwent 1.5- or 3-T MRI were also reviewed for the presence of the cable and evaluation of its characteristics (location, thickness, and width). RESULTS. A linear band of hypointense signal intensity was found along the undersur-face of the supraspinatus and infraspinatus tendons on both cadaveric MR images, which correlated to a linear band of tissue in the same location on macroscopic and microscopic evaluation and linear thickening along the cuff articular surface on arthroscopy consistent with the cable. The cable was seen in 74.3% of the MRI studies in both sagittal and coronal planes with a mean (+/- SD) distance of the cable from the medial margin of the enthesis of 1.33 +/- 0.27 cm, a mean width of the cable of 1.24 +/- 0.31 cm, and a mean thickness of 0.19 +/- 0.05 cm. CONCLUSION. The rotator cable is a structure that can be consistently seen on gross anatomic and histologic analysis, arthroscopy, and MRI in the intact rotator cuff. Familiarity with the typical location and morphology of the cable may allow easier characterization of disease that can involve the cable, such as rotator cuff tears.