Evaluation of Mid-term Outcomes Following Shoulder Hemiarthroplasty for Avascular Necrosis of the Humeral Head in Patients 40 Years and Younger.

In order to evaluate postoperative function and failure rates among younger patients undergoing hemiarthroplasty for humeral head avascular necrosis (AVN), data from patients < 40 years treated between December 2008 - January 2018 was retrospectively analyzed. Pain was assessed preoperatively and at final follow up using a visual analogue scale (VAS). The American Shoulder and Elbow Surgeons (ASES) standardized assessment, single assessment numeric evaluation (SANE) score, and patient satisfaction were assessed at final follow up, as well as surgical revision rates. In total, eight shoulders were included in the final analysis, with a follow up of 6.6 + 3.6 years. Analysis indicated a statistical improvement in VAS pain (p = 0.001), while comparison of postoperative function between surgical and non-surgical limbs did not demonstrate statistical differences in SANE or ASES averages (p > 0.05). At final follow up, 25% of patients expressed dissatisfaction; however, there were no cases of revision surgery. In conclusion, younger patients undergoing hemiarthroplasty for humeral head AVN experienced pain improvement and no revisions at short-to-mid-term follow up, but one-in-four indicated dissatisfaction. Level of evidence: IV, case series. (Journal of Surgical Orthopaedic Advances 32(2):118-121, 2023).

Is Grit Associated with Burnout and Well-being in Orthopaedic Resident and Faculty Physicians? A Multi-institution Longitudinal Study Across Training Levels.

BACKGROUND: Grit has been defined as "perseverance and passion for long-term goals" and is characterized by maintaining focus and motivation toward a challenging ambition despite setbacks. There are limited data on the impact of grit on burnout and psychologic well-being in orthopaedic surgery, as well as on which factors may be associated with these variables. QUESTIONS/PURPOSES: (1) Is grit inversely correlated with burnout in orthopaedic resident and faculty physicians? (2) Is grit positively correlated with psychologic well-being in orthopaedic resident and faculty physicians? (3) Which demographic characteristics are associated with grit in orthopaedic resident and faculty physicians? (4) Which demographic characteristics are associated with burnout and psychologic well-being in orthopaedic resident and faculty physicians? METHODS: This study was an institutional review board-approved interim analysis from the first year of a 5-year longitudinal study of grit, burnout, and psychologic well-being in order to assess baseline relationships between these variables before analyzing how they may change over time. Orthopaedic residents, fellows, and faculty from 14 academic medical centers were enrolled, and 30% (335 of 1129) responded. We analyzed for the potential of response bias and found no important differences between sites in low versus high response rates, nor between early and late responders. Participants completed an email-based survey consisting of the Duckworth Short Grit Scale, Maslach Burnout Inventory-Human Services (Medical Personnel) Survey, and Dupuy Psychological Well-being Index. The Short Grit Scale has been validated with regard to internal consistency, consensual and predictive validity, and test-retest stability. The Psychological Well-being Index has similarly been validated with regard to reliability, test-retest stability, and internal consistency, and the Maslach Burnout Inventory has been validated with regard to internal consistency, reliability, test-retest stability, and convergent validity. The survey also obtained basic demographic information such as survey participants' age, gender, race, ethnicity, marital status, current year of training or year in practice (as applicable), and region of practice. The studied population consisted of 166 faculty, 150 residents, and 19 fellows. Beyond the expected age differences between sub-populations, the fellow population had a higher proportion of women than the faculty and resident populations did. Pearson correlations and standardized ß coefficients were used to assess the relationships of grit, burnout, psychologic well-being, and continuous participant characteristics. RESULTS: We found moderate, negative relationships between grit and emotional exhaustion (r = -0.30; 95% CI -0.38 to -0.21; p < 0.001), depersonalization (r = -0.34; 95% CI -0.44 to -0.23; p < 0.001), and the overall burnout score (r = -0.39; 95% CI -0.48 to -0.31; p < 0.001). The results also showed a positive correlation between grit and personal accomplishment (r = 0.39; 95% CI 0.29 to 0.48; p < 0.001). We also found a moderate, positive relationship between grit and psychologic well-being (r = 0.39; 95% CI 0.30 to 0.49; p < 0.001). Orthopaedic surgeons with 21 years or more of practice had higher grit scores than physicians with 10 to 20 years of practice. Orthopaedic surgeons in practice for 21 years or more also had lower burnout scores than those in practice for 10 to 20 years. Married physicians had higher psychologic well-being than unmarried physicians did. CONCLUSION: Among orthopaedic residents, fellows, and faculty, grit is inversely related to burnout, with lower scores for emotional exhaustion and depersonalization and higher scores for personal accomplishment as grit increases. CLINICAL RELEVANCE: The results suggest that grit could be targeted as an intervention for reducing burnout and promoting psychologic well-being among orthopaedic surgeons. Other research has suggested that grit is influenced by internal characteristics, life experiences, and the external environment, suggesting that there is potential to increase one's grit. Residency programs and faculty development initiatives might consider measuring grit to assess for the risk of burnout, as well as offering curricula or training to promote this psychologic characteristic.

Peripheral Nerve Injury After Elbow Arthroscopy: An Analysis of Risk Factors.

PURPOSE: To identify risk factors associated with peripheral nerve injury after elbow arthroscopy and provide an updated incidence of those complications. METHODS: The elbow arthroscopies that were performed at our institution between 2006 and 2016 were identified. Over a 10-year period, 253 elbow arthroscopies were performed at our institution. Two hundred twenty-seven cases had a minimum follow-up of 4 weeks, and were included in our analysis. Minor and major nerve-related complications were recorded. The surgeon's experience and training, body max index of the patients, surgical tourniquet time, type of anesthesia or surgery, radiographic appearance of the elbow, diagnosis at the time of surgery, and presence of diabetes were analyzed. RESULTS: There were 12 reported peripheral nerve injuries, 10 minor (4.4%) and 2 major complications (0.9%). The risk factors examined in this study were not correlated with a higher rate of complications. CONCLUSIONS: The minor nerve-related complication rate was 4.4%, with a 0.9% incidence of major peripheral nerve injury. Based on these findings, we conclude that elbow arthroscopy is a relatively safe procedure. The risk factors examined in this study had no association with the rate of complications. This finding could be potentially related to type II or beta error in the analysis of risk factors for nerve injury. The exact reasons for nerve injury are not known from this study. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Shoulder Strength Requirements for Upper Limb Functional Tasks: Do Age and Rotator Cuff Tear Status Matter?

Understanding upper limb strength requirements for daily tasks is imperative for early detection of strength loss that may progress to disability due to age or rotator cuff tear. We quantified shoulder strength requirements for 5 upper limb tasks performed by 3 groups: uninjured young adults and older adults, and older adults with a degenerative supraspinatus tear prior to repair. Musculoskeletal models were developed for each group representing age, sex, and tear-related strength losses. Percentage of available strength used was quantified for the subset of tasks requiring the largest amount of shoulder strength. Significant differences in strength requirements existed across tasks: upward reach 105° required the largest average strength; axilla wash required the largest peak strength. However, there were limited differences across participant groups. Older adults with and without a tear used a larger percentage of their shoulder elevation (p < .001, p < .001) and external rotation (p < .001, p = .017) strength than the young adults, respectively. Presence of a tear significantly increased percentage of internal rotation strength compared to young (p < .001) and uninjured older adults (p = .008). Marked differences in strength demand across tasks indicate the need for evaluating a diversity of functional tasks to effectively detect early strength loss, which may lead to disability.

Assessments of Fatty Infiltration and Muscle Atrophy From a Single Magnetic Resonance Image Slice Are Not Predictive of 3-Dimensional Measurements.

PURPOSE: To (1) determine whether standard clinical muscle fatty infiltration and atrophy assessment techniques using a single image slice for patients with a rotator cuff tear (RCT) are correlated with 3-dimensional measures in older individuals (60+ years) and (2) to determine whether age-associated changes to muscle morphology and strength are compounded by an RCT. METHODS: Twenty older individuals were studied: 10 with an RCT of the supraspinatus (5 men and 5 women) and 10 matched controls. Clinical imaging assessments (Goutallier and Fuchs scores and cross-sectional area ratio) were performed for participants with RCTs. Three-dimensional measurements of rotator cuff muscle and fat tissues were obtained for all participants using magnetic resonance imaging (MRI). Isometric joint moment was measured at the shoulder. RESULTS: There were no significant associations between single-image assessments and 3-dimensional measurements of fatty infiltration for the supraspinatus and infraspinatus muscles. Compared with controls, participants with RCTs had significantly increased percentages of fatty infiltration for each rotator cuff muscle (all P ≤ .023); reduced whole muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles (all P ≤ .038); and reduced fat-free muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles (all P ≤ .027). Only the teres minor (P = .017) fatty infiltration volume was significantly greater for participants with RCTs. Adduction, flexion, and external rotation strength (all P ≤ .021) were significantly reduced for participants with RCTs, and muscle volume was a significant predictor of strength for all comparisons. CONCLUSIONS: Clinical scores using a single image slice do not represent 3-dimensional muscle measurements. Efficient methods are needed to more effectively capture 3-dimensional information for clinical applications. Participants with RCTs had increased fatty infiltration percentages that were likely driven by muscle atrophy rather than increased fat volume. The significant association of muscle volume with strength production suggests that treatments to preserve muscle volume should be pursued for older patients with RCTs. LEVEL OF EVIDENCE: Level II, diagnostic study, with development of diagnostic criteria on the basis of consecutive patients with universally applied reference gold standard.

A randomized trial of diagnostic ultrasound to improve outcomes in focal neuropathies.

INTRODUCTION: Neuromuscular ultrasound is valid, reliable, and accurate, but it is not known whether combining it with electrodiagnostic studies leads to better outcomes in individuals with focal neuropathies. METHODS: One hundred twenty individuals with focal neuropathy, based on history, examination, and electrodiagnosis, were enrolled in this study. All patients underwent neuromuscular ultrasound and were randomized to either have their ultrasound results sent to the referring physician or not have them sent. Outcomes were assessed at 6 months by evaluators blinded to group assignment. RESULTS: The Overall Disability Sum Score and 7 of 8 domains of the Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) showed more improvement in the "report sent" group, although only the general health perception domain was significant (P = 0.005). CONCLUSIONS: Most 6-month outcomes did not reach statistical significance between the 2 groups. However, the "report sent" group had trends toward better outcomes, with significance being reached in the general health perception domain of the SF-36.

Age-related changes affect rat rotator cuff muscle function.

BACKGROUND: The influence of age on rotator cuff function and muscle structure remains poorly understood. We hypothesize that normal aging influences rotator cuff function, muscle structure, and regulatory protein expression in an established rat model of aging. METHODS: Seventeen rats were obtained from the National Institute on Aging. The supraspinatus muscles in 11 middle-aged (12 months old) and 6 old (28 months old) rats were studied for age-related changes in rotator cuff neuromuscular function by in vivo muscle force testing and electromyography (EMG). Changes in muscle structure and molecular changes were assessed with quantitative immunohistochemistry for myogenic determination factor 1 (MyoD) and myogenic factor 5 (Myf5) expression. RESULTS: Old animals revealed significantly decreased peak tetanic muscle force at 0.5 N and 0.7 N preload tension (P < .05). The age of the animal accounted for 20.9% of variance and significantly influenced muscle force (P = .026). Preload tension significantly influenced muscle force production (P < .001) and accounted for 12.7% of total variance. There was regional heterogeneity in maximal compound motor action potential (CMAP) amplitude in the supraspinatus muscle; the proximal portion had a significantly higher CMAP than the middle and distal portions (P < .05). The expression of muscle regulatory factors MyoD and Myf5 was significantly decreased in old animals compared with middle-aged animals (P < .05). CONCLUSIONS: The normal aging process in this rat model significantly influenced contractile strength of the supraspinatus muscle and led to decreased expression of muscle regulatory factors. High preload tensions led to a significant decrease in force production in both middle-aged and old animals.

The science of rotator cuff tears: translating animal models to clinical recommendations using simulation analysis.

PURPOSE: The purpose of this article is to review basic science studies using various animal models for rotator cuff research and to describe structural, biomechanical, and functional changes to muscle following rotator cuff tears. The use of computational simulations to translate the findings from animal models to human scale is further detailed. METHODS: A comprehensive review was performed of the basic science literature describing the use of animal models and simulation analysis to examine muscle function following rotator cuff injury and repair in the ageing population. RESULTS: The findings from various studies of rotator cuff pathology emphasize the importance of preventing permanent muscular changes with detrimental results. In vivo muscle function, electromyography, and passive muscle-tendon unit properties were studied before and after supraspinatus tenotomy in a rodent rotator cuff injury model (acute vs chronic). Then, a series of simulation experiments were conducted using a validated computational human musculoskeletal shoulder model to assess both passive and active tension of rotator cuff repairs based on surgical positioning. CONCLUSION: Outcomes of rotator cuff repair may be improved by earlier surgical intervention, with lower surgical repair tensions and fewer electromyographic neuromuscular changes. An integrated approach of animal experiments, computer simulation analyses, and clinical studies may allow us to gain a fundamental understanding of the underlying pathology and interpret the results for clinical translation.

Age-related degenerative functional, radiographic, and histological changes of the shoulder in nonhuman primates.

BACKGROUND: Nonhuman primates have similar shoulder anatomy and physiology compared to humans, and may represent a previously underutilized model for shoulder research. This study sought to identify naturally occurring bony and muscular degeneration in the shoulder of nonhuman primates and to assess relationships between structural and functional aspects of the shoulder and measures of physical function of the animals. We hypothesized that age-related degenerative changes in the shoulders of nonhuman primates would resemble those observed in aging humans. METHODS: Middle-aged (n = 5; ages 9.4-11.8 years) and elderly (n = 6; ages 19.8-26.4 years) female vervet monkeys were studied for changes in mobility and shoulder function, and radiographic and histologic signs of age-related degeneration. RESULTS: Four out of 6 (4/6) elderly animals had degenerative changes of the glenoid compared to 0/5 of the middle-aged animals (P = .005). Elderly animals had glenoid retroversion, decreased joint space, walked slower, and spent less time climbing and hanging than middle-aged vervets (P < .05). Physical mobility and shoulder function correlated with glenoid version angle (P < .05). Supraspinatus muscles of elderly animals were less dense (P = .001), had decreased fiber cross-sectional area (P < .001), but similar amounts of nuclear material (P = .085). Degenerative rotator cuff tears were not observed in any of the eleven animals. DISCUSSION AND CONCLUSION: The vervet monkey naturally undergoes age-related functional, radiographic and histological changes of the shoulder, and may qualify as an animal model for selected translational research of shoulder osteoarthritis.

Rotator cuff injuries in professional and recreational athletes.

Professional and recreational athletes involved in contact sports and sports with repetitive overhead motion are at increased risk for rotator cuff tears. Shoulder anatomy, pathology, and biomechanics place unique stress on the rotator cuff tendons during sports activity. Athletes demand effective treatment to quickly return to elite competition. A PubMed search assessed treatment options providing expedited recovery time and return to competition. Twelve of 231 articles fit the objective criteria; 90.5% of professional contact athletes, 40% of professional overhead athletes, and 83.3% of recreational athletes fully recovered following rotator cuff tear surgical repair. Prompt surgical treatment for full-thickness rotator cuff tears may be appropriate for contact athletes and recreational overhead athletes. Although professional overhead athletes have low recovery rates, surgical repair of full-thickness rotator cuff tears may still be indicated. The authors propose a treatment algorithm based on the limited literature (mainly level 4 and 5 evidence).

Hand and body radiation exposure with the use of mini C-arm fluoroscopy.

PURPOSE: To determine whole body and hand radiation exposure to the hand surgeon wearing a lead apron during routine intraoperative use of the mini C-arm fluoroscope. METHODS: Four surgeons (3 hand attending surgeons and 1 hand fellow) monitored their radiation exposure for a total of 200 consecutive cases (50 cases per surgeon) requiring mini C-arm fluoroscopy. Each surgeon measured radiation exposure with a badge dosimeter placed on the outside breast pocket of the lead apron (external whole body exposure), a second badge dosimeter under the lead apron (shielded whole body exposure), and a ring dosimeter (hand exposure). RESULTS: Completed records were noted in 198 cases, with an average fluoroscopy time of 133.52 seconds and average cumulative dose of 19,260 rem-cm(2) per case. The total measured radiation exposures for the (1) external whole body exposure dosimeters were 16 mrem (for shallow depth), 7 mrem (for eye depth), and less than 1 mrem (for deep depth); (2) shielded whole body badge dosimeters recorded less than 1 mrem; and (3) ring dosimeters totaled 170 mrem. The total radial exposure for 4 ring dosimeters that had registered a threshold of 30 mrem or more of radiation exposure was 170 mrem at the skin level, for an average of 42.5 mrem per dosimeter ring or 6.3 mrem per case. CONCLUSIONS: This study of whole body and hand radiation exposure from the mini C-arm includes the largest number of surgical cases in the published literature. The measured whole body and hand radiation exposure received by the hand surgeon from the mini C-arm represents a minimal risk of radiation, based on the current National Council on Radiation Protection and Management standards of annual dose limits (5,000 mrem per year for whole body and 50,000 mrem per year to the extremities).

Chemical denervation with botulinum neurotoxin a improves the surgical manipulation of the muscle-tendon unit: an experimental study in an animal model.

PURPOSE: The chemical denervation that results from botulinum neurotoxin A (BoNT-A) causes a temporary, reversible paresis that can result in easier surgical manipulation of the muscle-tendon unit in the context of tendon rupture and repair. The purpose of the study was to determine whether BoNT-A injections can be used to temporarily and reversibly modulate active and passive skeletal muscle properties. METHODS: Male CD1 mice weighing 40-50 g were divided into a 1-week postinjection group (n = 13: n = 5 saline and n = 8 BoNT-A) and a 2-week postinjection group (n = 17: n = 7 saline and n = 10 BoNT-A). The animals had in vivo muscle force testing and in vivo biomechanical evaluation. RESULTS: There was a substantial decline in the maximal single twitch amplitude (p < .05) and tetanic amplitude (p < .05) at one week and at 2 weeks after BoNT-A injection, when compared to saline-injected controls. BoNT-A injection significantly reduced the peak passive properties of the muscle-tendon unit as a function of displacement at one week (p < .05). Specifically, the stiffness of the BoNT-A injected muscle-tendon unit was 0.417 N/mm compared to the control saline injected group, which was 0.634 N/mm, a 35% reduction in stiffness (p < .05). CONCLUSIONS: Presurgical treatment with BoNT-A might improve the surgical manipulation of the muscle-tendon unit, thus improving surgical outcomes. The results implicate neural tone as a substantial contributor to the passive repair tension of the muscle-tendon unit. The modulation of neural tone through temporary, reversible paresis is a novel approach that might improve intraoperative and postoperative passive muscle properties, allowing for progressive rehabilitation while protecting the surgical repair site.

Early to midterm radiographic loosening of the press fit radial head prosthesis.

BACKGROUND: Radiographic loosening is frequently seen around the radial head (RH) implant. The hypothesis of this study was that radiographic loosening will be more frequent in patients in which the RH prosthesis was implanted due to elbow trauma leading to instability that required lateral collateral ligament repair (LCL). MATERIALS AND METHODS: A retrospective review of the patients who had RH implantation between 2012 and 2019 was performed. Evaluation included evidence of radiographic loosening, stress shielding, formation of heterotopic ossification, and rate of removal of the implant. Range of motion of the elbow at the latest follow up was also recorded. RESULTS: At a mean follow up of 18 months (range 1.4 - 80) eight out of 25 patients had radiographic loosening around the implant. The radial head implant was removed in 8 patients (in 3 due to painful radiographic loosening, in 4 due pain without radiographic loosening and in 1 due to infection). Radiographic loosening around the RH implant had no association with LCL repair (p=0.18) or future removal of implant (p=0.18) or the diagnosis of Monteggia lesion (p=0.68). In addition, removal of the RH implant had no association with prior LCL repair (p=0.60) or the diagnosis of Monteggia lesion (p=0.15). Stress shielding was seen in 5 patients and was of no clinical significance. Heterotopic ossification was seen in 12 patients and was classified as Class I in 3, IIA in 3, IIC in 6, according to the Hastings Classification. The average flexion-extension arc was 23° to 130°, and average pronation-supination was 76° to 69°. CONCLUSION: One third of the patients had radiographic loosening around the RH implant at a mean follow up of 18 months. Pain with or without radiographic loosening were the main reasons for removal of the implant. No associations were found between the development of radiographic loosening and LCL repair at the time of RH replacement. Limitations of this study are: (a) the retrospective design (b). the small sample size and the possibility of a type II statistical error.

Sonography of the coracohumeral interval: a potential technique for diagnosing coracoid impingement.

OBJECTIVE: Coracoid impingement has been recognized as an etiology for anterior shoulder pain; however, no imaging reference standard exists. We used sonography to compare the coracohumeral interval (CHI) in asymptomatic volunteers with the CHI in patients with coracoid impingement. METHODS: Bilateral shoulder sonography was performed in 19 asymptomatic volunteers (10 men and 9 women) and in 8 shoulders in 7 patients (6 men and 1 woman) with a clinical diagnosis of coracoid impingement. With the arm adducted across the chest, the interval between the coracoid process and the lesser tuberosity of the humerus was measured using a linear array ultrasound transducer with a peak frequency of 13 MHz. RESULTS: In the asymptomatic volunteers, the mean +/- SD for the CHI was 12.2 +/- 2.5 mm (range, 7.8-17.5 mm). In the symptomatic shoulders, the mean +/- SD for the CHI was 7.9 +/- 1.4 mm (range, 5.9-9.6 mm). Repeated measures analysis of variance revealed the CHI to be significantly narrower in symptomatic shoulders than in asymptomatic volunteers (P < .0001). CONCLUSIONS: These data suggest a role for sonography in diagnosing coracoid impingement.

Extensive Hand Thermal and Blast Injury From Electronic Cigarette Explosion: A Case Report.

Background: As the use of electronic cigarettes rises, more reports of injuries related to device explosion are surfacing. Methods: Presented here is the case of a 35-year-old man sustaining extensive thermal and blast injuries to his hand when the device exploded while he was holding it. He required multiple surgeries involving groin flap coverage, tendon transfer, and nerve grafting to optimize his postinjury function. Results: While much of his hand function has been restored, he has continued deficits in range of motion and sensation as a result of the incident. Conclusions: With increasing numbers of such injuries, hand surgeons must be aware of the blast mechanism involved so as to avoid missing deep soft tissue injury or disruption of deep structures, as demonstrated in this case.

Modeling a rotator cuff tear: Individualized shoulder muscle forces influence glenohumeral joint contact force predictions.

BACKGROUND: Rotator cuff tears in older individuals may result in decreased muscle forces and changes to force distribution across the glenohumeral joint. Reduced muscle forces may impact functional task performance, altering glenohumeral joint contact forces, potentially contributing to instability or joint damage risk. Our objective was to evaluate the influence of rotator cuff muscle force distribution on glenohumeral joint contact force during functional pull and axilla wash tasks using individualized computational models. METHODS: Fourteen older individuals (age 63.4 yrs. (SD 1.8)) were studied; 7 with rotator cuff tear, 7 matched controls. Muscle volume measurements were used to scale a nominal upper limb model's muscle forces to develop individualized models and perform dynamic simulations of movement tracking participant-derived kinematics. Peak resultant glenohumeral joint contact force, and direction and magnitude of force components were compared between groups using ANCOVA. FINDINGS: Results show individualized muscle force distributions for rotator cuff tear participants had reduced peak resultant joint contact force for pull and axilla wash (P ≤ 0.0456), with smaller compressive components of peak resultant force for pull (P = 0.0248). Peak forces for pull were within the glenoid. For axilla wash, peak joint contact was directed near/outside the glenoid rim for three participants; predictions required individualized muscle forces since nominal muscle forces did not affect joint force location. INTERPRETATION: Older adults with rotator cuff tear had smaller peak resultant and compressive forces, possibly indicating increased instability or secondary joint damage risk. Outcomes suggest predicted joint contact force following rotator cuff tear is sensitive to including individualized muscle forces.

Basic Shoulder Arthroscopy: Beach Chair Patient Positioning.

Shoulder arthroscopy is an orthopaedic procedure that has grown significantly in popularity over the last 40 years. The 2 principle patient positions during shoulder arthroscopy include the beach chair position and lateral decubitus position. This Technical Note details the operating room setup for shoulder arthroscopy in the beach chair position. Proper positioning for this procedure will minimize potential complications and facilitate ease of surgical intervention.

Quantitative Analysis of Three-Dimensional Distribution and Clustering of Intramuscular Fat in Muscles of the Rotator Cuff.

The purpose of this study was to (1) develop and present a technique to quantitatively assess three-dimensional distribution and clustering of intramuscular fat and (2) use the technique to compare spatial characteristics of intramuscular fat in rotator cuff muscles of older adults with and without a supraspinatus tear. Moran's Index (I), an existing quantitative measure of clustering, was extended for use with MRI to allow comparisons across individuals with different size muscles. Sixteen older adults (>60 years) with (N = 6) and without (N = 10) a degenerative supraspinatus tear participated. Following 3D Dixon MRIs of the shoulder, which separates fat from water, rotator cuff muscles were segmented and sectioned and fat% and Moran's I were calculated to assess distribution and clustering, respectively. Moran's I ranged was 0.40-0.92 and 0.39-0.76 for the tear and control subjects, respectively. Compared to uninjured controls, tear subjects demonstrated increased fat distribution (p = 0.036) and clustering (p = 0.020) distally in the supraspinatus. Tear subjects had more pronounced distribution (p < 0.001) and clustering distally (p < 0.001) than proximally. Other rotator cuff muscles exhibited different patterns of fat clustering and distribution. This technique, which we applied to quantify spatial characteristics of intramuscular fat, can be applied to assess clustering of fat in other pathologies and tissues.