Modern Treatment of Neurogenic Thoracic Outlet Syndrome: Pathoanatomy, Diagnosis, and Arthroscopic Surgical Technique.

Compressive pathology in the supraclavicular and infraclavicular fossae is broadly termed "thoracic outlet syndrome," with the large majority being neurogenic in nature. These are challenging conditions for patients and physicians and require robust knowledge of thoracic outlet anatomy and scapulothoracic kinematics to elucidate neurogenic versus vascular disorders. The combination of repetitive overhead activity and scapular dyskinesia leads to contracture of the scalene muscles, subclavius, and pectoralis minor, creating a chronically distalized and protracted scapular posture. This decreases the volume of the scalene triangle, costoclavicular space, and retropectoralis minor space, with resultant compression of the brachial plexus causing neurogenic thoracic outlet syndrome. This pathologic cascade leading to neurogenic thoracic outlet syndrome is termed pectoralis minor syndrome when primary symptoms localize to the infraclavicular area. Making the correct diagnosis is challenging and requires the combination of complete history, physical examination, advanced imaging, and ultrasound-guided injections. Most patients improve with nonsurgical treatment incorporating pectoralis minor stretching and periscapular and postural retraining. Surgical decompression of the thoracic outlet is reserved for compliant patients who fail nonsurgical management and respond favorably to targeted injections. In addition to prior exclusively open procedures with supraclavicular, infraclavicular, and/or transaxillary approaches, new minimally invasive and targeted endoscopic techniques have been developed over the past decade. They involve the endoscopic release of the pectoralis minor tendon, with additional suprascapular nerve release, brachial plexus neurolysis, and subclavius and interscalene release depending on the preoperative work-up.

Intramedullary Metacarpal Fracture Fixation: A Biomechanical Study of Screw Diameter and Comparison With Intramedullary Wire Stabilization.

PURPOSE: Interest in intramedullary metacarpal fracture fixation (IMFF) with screws is increasing. However, the optimal screw diameter for fracture fixation is not yet established. In theory, larger screws should be more stable, but there is concern about long-term sequelae of larger metacarpal head defects and extensor mechanism injury created during insertion as well as implant cost. Therefore, the purpose of this study was to compare different diameter screws for IMFF to a popular and more cost-effective alternative of intramedullary wiring. METHODS: Thirty-two cadaveric metacarpals were used in a transverse metacarpal shaft fracture model. Treatment groups consisted of IMFF with 3.0 × 60 mm, 3.5 x 60 mm, and 4.5 x 60 mm screws as well as 4 1.1-mm intramedullary wires. Cyclic cantilever bending was performed with the metacarpals mounted at 45° to simulate physiologic loading. Cyclical loading at 10, 20, and 30 N was performed to determine fracture displacement, stiffness, and ultimate force. RESULTS: At 10, 20, and 30 N of cyclical loading, all screw diameters tested provided similar stability as measured by fracture displacement and were superior to the wire group. However, ultimate force under load to failure testing was similar between the 3.5- and 4.5-mm screws and superior to 3.0-mm screws and wires. CONCLUSIONS: For IMFF, 3.0, 3.5, and 4.5-mm diameter screws provide adequate stability for early active motion and are superior to wires. When comparing the different screw diameters, 3.5- and 4.5-mm diameter screws offer similar construct stability and strength superior to the 3.0-mm diameter screw. Therefore, to minimize metacarpal head morbidity, smaller screw diameters may be preferable. CLINICAL RELEVANCE: This study suggests that IMFF with screws is biomechanically superior to wires in cantilever bending strength in the transverse fracture model. However, smaller screws may be sufficient to permit early active motion while minimizing metacarpal head morbidity.

Reverse shoulder arthroplasty in upper extremity ambulators: a matched-cohort analysis.

BACKGROUND: Upper extremity ambulators (UEAs) who require prolonged use of assistive devices for mobility have a high incidence of shoulder pathology secondary to increased stress across the shoulder joint with upper extremity weight-bearing. Reverse shoulder arthroplasty (RSA) for rotator cuff arthropathy has historically been associated with increased complications in UEA, but more recent studies have shown more promising outcomes. The objective of this study is to evaluate clinical outcomes and complication rates between these 2 groups to define the relative risk of RSA in the UEA population and identify opportunities to improve treatment outcomes. METHODS: An institutional review board-approved retrospective chart review was performed in patients who underwent RSA at our institution by the senior author from 2004 to 2019. UEAs were defined as patients who used regular upper extremity assistive devices for community ambulation before initial consultation for the surgical extremity. Pre- and postoperative range of motion, visual analog scale scores, American Shoulder and Elbow Surgeons scores, Constant-Murley scores, and Simple Shoulder Test scores were measured at defined intervals. Complications including infection, instability, and need for revision surgery were also compared. All patients were followed for a minimum of 2 years postoperatively. RESULTS: A total of 159 RSA procedures (70 UEAs, 89 controls) were performed during the study period. On average, UEA patients had more preoperative pain and less shoulder function than controls, with statistically significant differences in visual analog scores (6.897 vs. 5.532, P = .0010) and American Shoulder and Elbow Surgeons scores (33.50 vs. 40.20, P = .0290), respectively. Despite the lower baseline values, UEA patients experienced excellent postoperative improvement, leading to similar postoperative pain and shoulder function except for a lower average forward flexion in the UEA group (127° vs. 135°, P = .0354). Notching and complication rates were also similar between the 2 groups, with notching rates of 59% and 50% and complication rates of 14.3% and 13.5% in the UEA and control groups, respectively. CONCLUSIONS: RSA in the UEA population can achieve similar pain and functional outcomes as compared with age-matched controls without a significant increase in complication rates; however, further studies are required to assess long-term comparative outcomes in this challenging patient population.

Volar versus dorsal approach for supinator to posterior interosseous nerve transfer: An anatomical study in cadavers.

INTRODUCTION: Supinator to posterior interosseous nerve (SPIN) transfer allows reconstruction of finger/thumb extension and thumb abduction for low radial nerve palsy, incomplete C6 tetraplegia, and brachial plexus injury affecting C7-T1. No study has compared dorsal versus volar approach to perform SPIN transfer. This comparison is studied in the present work, assessing supinator motor branch length and ability to achieve nerve transfer from either approach. METHODS: Ten fresh frozen cadavers were randomly allocated to receive either a dorsal or volar approach to PIN and supinator radial and ulnar branches (RB = radial, UB = ulnar). Supinator head innervation patterns were documented. RB and UB lengths, forearm lengths measured from ulnar styloid to olecranon, visualization of extensor carpi radialis brevis (ECRB) motor nerve without additional dissection, and ability to perform tension-free nerve transfer were assessed. RESULTS: Nine of 10 specimens had supinator branches innervating both heads. The ECRB nerve was visualized in all volar but only one dorsal approach. No significant differences in forearm length were found. Volar with elbow extended: mean RB length was 35 ± 7.8 mm and UB was 37.8 ± 9.3 mm. Dorsal with elbow extended: mean RB length was 30 ± 4.1 mm and UB was 38.8 ± 7.3 mm. Dorsal with elbow flexed 90°: RB was 25.6 ± 3.8 mm and UB was 34.8 ± 4.8 mm. No significant differences were found in branch lengths between approaches (dorsal vs. volar UB, p = .339; dorsal vs. volar RB, p = .117). All limbs achieved tension-free coaptation. CONCLUSION: Neither approach demonstrated superiority in achieving tension-free nerve transfer. Volar permitted immediate identification of ECRB nerve whereas this was only visualized in one dorsal specimen without additional dissection. Overall, the volar approach allows direct coaptation in elbow extension, mimicking maximal physiologic tension for neurorrhaphy. It simultaneously permits additional procedures for pinch reconstruction via single exposure, circumventing limb/microscope maneuvering, dorsal dissection, and increased operative time. Ultimate choice of approach should depend on surgeon familiarity and potential need for additional simultaneous transfers.

Dupuytren's Contracture Recurrence and Treatment Following Collagenase Clostridium Histolyticum Injection: A Longitudinal Assessment in a Veteran Population.

INTRODUCTION: Dupuytren's contracture is a connective tissue disease characterized by an abnormal proliferation of collagen in the palm and fingers, which leads to a decline in hand function because of progressive joint flexion. In addition to surgical and percutaneous interventions, collagenase clostridium histolyticum (CCH, trade name Xiaflex) is an intralesional enzymatic treatment for adults with palpable cords. The objectives of this study are to evaluate factors predictive of recurrence following treatment with CCH and to review the outcomes of repeat treatments with CCH for recurrent contracture. MATERIALS AND METHODS: An institutional review board-approved retrospective chart review was conducted for patients between 2010 and 2017 who received CCH injections for Dupuytren's contracture at a Veterans Affairs hospital. Demographics, comorbidities, affected finger and joint, pre/posttreatment contracture, time to recurrence, and treatment of recurrence were recorded. Successful treatment was defined as contracture ≤5° following CCH, and improvement was defined as ≥20° reduction from baseline contracture. Study cohorts were followed after their secondary treatment, and time to recurrence was recorded and plotted using a Kaplan-Meier curve. A Cox proportional hazards model was used to compare treatment group risk factors for recurrence with a P-value less than .05 defined as statistical significance. RESULTS: Of 174 injections performed for the correction of flexion deformities in 109 patients, 70% (121) were successfully treated with CCH, and an additional 20% (35) had improvement. There was a recurrence of contractures in 43 joints (25%). Of these, 16 contractures were treated with repeat CCH, whereas another 16 underwent limited fasciectomy. In total, 75% (12 of 16) of the repeat CCH group and 75% of the fasciectomy group were successfully treated. Pre-injection contracture of ≥25° was found to be predictive of recurrence (P < .05). CONCLUSIONS: Initial treatment of contracture with CCH had a 70% success rate with 25% recurrence during the study period. Compared with limited fasciectomy, CCH had decreased efficacy. Based on the findings of this study, we believe that the treatment of primary and/or recurrent Dupuytren's contracture with CCH is a safe and less invasive alternative to fasciectomy in the era of telemedicine. CCH treatment requires no suture removal, which allows the ability to assess motion virtually, and the potential consequences of CCH treatment such as skin tears can be assessed and managed conservatively. In the veteran and active duty population, CCH can facilitate faster recovery and return to service. Strengths of this study include a large series of veteran populations with longitudinal follow-up to determine treatment efficacy for primary Dupuytren's contracture and recurrence. Limitations include a smaller sample size compared to previous trials, a lack of standardized follow-up, and the retrospective nature of our study that prohibits randomization to compare outcomes between CCH treatment and fasciectomy efficacy over time. Directions for future research include stratification of patients by joint and specific digit involvement as well as comparison with percutaneous needle fasciotomy, another minimally invasive technique that could benefit the veteran population at increased risk for developing Dupuytren's disease.

Dupuytren Disease: Surgical Tips, Optimizing Outcomes, and Cost Considerations.

Dupuytren disease is associated with benign fibroproliferative changes to the palmar fascia of the hand sometimes resulting in progressive contractures of the fingers. The earliest descriptions of these contractures date back to the 18th century. Much has been learned about the condition since the clawing condition was first described; however, optimal treatment still poses significant challenges to modern-day surgeons. It is important to examine the treatment options for Dupuytren disease and highlight the current evidence, techniques, and cost considerations of open fasciectomy, needle aponeurotomy, and recently described minimally invasive treatment.

Novel Diagnostic and Treatment Techniques for Neurogenic Thoracic Outlet Syndrome.

Neurogenic thoracic outlet syndrome is a challenging condition to diagnose and treat, often precipitated by the triad of repetitive overhead activity, pectoralis minor contracture, and scapular dyskinesia. The resultant protracted scapular posture creates gradual repetitive traction injury of the suprascapular nerve via tethering at the suprascapular notch and decreases the volume of the brachial plexus cords and axillary vessels in the retropectoralis minor space. A stepwise and exhaustive diagnostic protocol is essential to exclude alternate pathologies and confirm the diagnosis of this dynamic pathologic process. Ultrasound-guided injections of local anesthetic or botulinum toxin are a key factor in confirming the diagnosis and prognosticating potential response from surgical release. In patients who fail over 6 months of supervised physical therapy aimed at correcting scapular posture and stretching of the pectoralis minor, arthroscopic surgical release is indicated. We present our diagnostic algorithm and technique for arthroscopic suprascapular neurolysis, pectoralis minor release, brachial plexus neurolysis, and infraclavicular thoracic outlet decompression.

Upper extremity firearm injuries: epidemiology and factors predicting hospital admission.

INTRODUCTION: Civilian gun violence is a public health crisis in the USA that will be an economic burden reported to be as high as $17.7 billion with over half coming from US taxpayers dollars through Medicaid-related costs. The purpose of this study is to review the epidemiology of upper extremity firearm injuries in the USA and the associated injury burden. METHODS: The Inter-university Consortium for Political and Social Research's Firearm Injury Surveillance Study database, collected from the National Electronic Injury Surveillance System, was queried from 1993 to 2015. The following variables were reviewed: patient demographics, date of injury, diagnosis, injury location, firearm type (if provided), incident classification, and a descriptive narrative of the incident. We performed chi-square testing and complex descriptive statistics, and binomial logistic regression model to predict factors associated with hospital admission. RESULTS: From 1993 to 2015, an estimated 314,369 (95% CI: 291,528-337,750; 16,883 unweighted) nonfatal firearm upper extremity injuries with an average incidence rate of 4.76 per 100,000 persons (SD: 0.9; 03.77-7.49) occurred. The demographics most afflicted with nonfatal gunshot wound injuries were black adolescent and young adult males (ages 15-24 years). Young adults aged 25-34 were the second largest estimate of injuries by age group. Hands were the most commonly injured upper extremity, (55,014; 95% CI: 75,973-89,667) followed by the shoulder, forearm, and upper arm. Patients who underwent amputation (OR: 28.65; 95% CI: 24.85-33.03) or with fractures (OR: 26.20; 95% CI: 23.27-29.50) experienced an increased likelihood for hospitalization. Patients with a shoulder injury were 5.5× more likely to be hospitalized than those with a finger injury (OR:5.57; 95% CI:5.35-5.80). The incidence of upper extremity firearm injuries has remained steady over the last decade ranging between 4 and 5 injuries per 100,000 persons. Patients with proximal injuries or injuries involving the bone were more likely to require hospital admission. This study should bring new information to the forefront for policy makers regarding gun violence.

Rotator cuff repair in upper extremity ambulators: an assessment of longitudinal outcomes.

Background: Individuals who rely on wheelchairs, walkers, and crutches for ambulation have an increased incidence of rotator cuff tears due to altered shoulder biomechanics and increased force transmission across the shoulder joint. The purpose of our study is to review our longitudinal outcomes treating upper extremity ambulators to guide patient expectations and identify risk factors for rotator cuff repair failure. Methods: A total of fifteen patients were included after a cohort of thirty-nine patients were identified. The mean age was 54.9 years at the time of index rotator cuff repair, with each patient requiring either wheelchair, cane, walker, or crutches for ambulation. Clinical outcomes were measured (strength, range of motion, and pain scores), and patient-reported outcome scores (American Shoulder and Elbow Surgeons, Simple Shoulder Test, and University of California Los Angeles functional shoulder assessment tool) were obtained. No follow-up imaging was obtained unless indicated by a change in clinical status. Results: Within our cohort, 14 of 15 (93%) presented with supraspinatus tears, 7 of 15 (47%) with infraspinatus tears, and only 3 of 15 (20%) with subscapularis pathology. Additionally, the rates of concurrent biceps pathology or acromioclavicular joint pathology were significant at 53% and 73%, respectively. Only one patient in our cohort experienced known failure of cuff repair, despite longitudinal follow-up at an average of 97 months following surgery, however, routine follow-up imaging was not obtained. There were statistically significant improvements in visual analog scale pain scores, forward flexion ROM and strength, and abduction ROM. Additionally, statistically significant improvements were noted in all patient-reported outcome scores measured. Conclusion: Despite the apparent risks associated in rotator cuff repair in upper extremity ambulators, these patients demonstrate clinically significant improvements following surgery. Appreciating additional pathology beyond the rotator cuff is important in formulating a treatment plan.

Arthroscopic Management of Kienböck Disease.

Wrist arthroscopy represents the most recent development in the diagnosis and treatment of Kienböck disease. Through direct visualization of lunate and adjacent carpal articulations, a more accurate diagnosis can be obtained and, ultimately, a more precise treatment decision. Treatments that are based on bypassing, fusing, or excising "nonfunctional" articulations can be done with less morbidity than traditional open techniques by using arthroscopy. Given the minimal capsular and soft tissue scarring, this potentially improves early pain and functional recovery. Although technically demanding, long-term outcomes studies have shown that the benefits of an arthroscopic approach may be worth the learning curve.

A Retrospective Comparison of Above- vs Below-the-Knee Cast Treatment for Salter Harris-II Distal Tibia Fractures.

BACKGROUND: Distal tibia fractures are common in the pediatric patient population. Recent reports suggest that patients with closed low-energy distal tibial fractures treated with short leg casts (SLCs) have similar radiographic outcomes with improved functional outcomes compared to those treated with long leg casts (LLCs). However, to date there has not been a study comparing these treatment modalities for Salter-Harris (SH) II distal tibia fractures. The purpose of this study was to compare the radiographic and time to weightbearing outcomes between patients with SH-II tibial ankle fractures treated with an SLC vs an LLC. METHODS: A retrospective review on SH-II distal tibia fractures was performed at a Level I pediatric trauma center from 2013 to 2020. Primary outcomes included final coronal angulation, sagittal angulation, and time to weightbearing. RESULTS: A total of 59 patients with SH-II distal tibia fractures were treated with an SLC (22 patients, median age 11.79 years) or an LLC (37 patients, median age 12.17 years). There was no statistically significant difference between the 2 treatment groups for coronal angulation at final follow-up, sagittal angulation at final follow-up, or percentage of patients fully weightbearing at 6 weeks (P > .05). No patients required subsequent remanipulation or operative treatment in either treatment group. CONCLUSION: In this retrospective review with relatively short-term follow-up, SLCs were found to be noninferior to LLCs for treatment of reduced SH-II distal tibia fractures. This casting option may still be considered by surgeons who are nonoperatively managing pediatric distal tibia fractures. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Pectoralis minor syndrome - review of pathoanatomy, diagnosis, and management of the primary cause of neurogenic thoracic outlet syndrome.

Thoracic outlet syndrome is an umbrella term for compressive pathologies in the supraclavicular and infraclavicular fossae, with the vast majority being neurogenic in nature. These compressive neuropathies, such as pectoralis minor syndrome, can be challenging problems for both patients and physicians. Robust understanding of thoracic outlet anatomy and scapulothoracic biomechanics are necessary to distinguish neurogenic vs. vascular disorders and properly diagnose affected patients. Repetitive overhead activity, particularly when combined with scapular dyskinesia, leads to pectoralis minor shortening, decreased volume of the retropectoralis minor space, and subsequent brachial plexus compression causing neurogenic thoracic outlet syndrome. Combining a thorough history, physical examination, and diagnostic modalities including ultrasound-guided injections are necessary to arrive at the correct diagnosis. Rigorous attention must be paid to rule out alternate etiologies such as peripheral neuropathies, vascular disorders, cervical radiculopathy, and space-occupying lesions. Initial nonoperative treatment with pectoralis minor stretching, as well as periscapular and postural retraining, is successful in the majority of patients. For patients that fail nonoperative management, surgical release of the pectoralis minor may be performed through a variety of approaches. Both open and arthroscopic pectoralis minor release may be performed safely with effective resolution of neurogenic symptoms. When further indicated by the preoperative workup, this can be combined with suprascapular nerve release and brachial plexus neurolysis for complete infraclavicular thoracic outlet decompression.

Management of Acute Distal Radioulnar Joint Instability Following a Distal Radius Fracture: A Systematic Review and Meta-Analysis.

Purpose: We sought to review the clinical outcomes of conservative and operative treatment options for acute distal radioulnar joint (DRUJ) instability associated with distal radius fractures in adult patients. Methods: A systematic search of PubMed, MEDLINE, and EMBASE for articles published between 1990 and 2020 involving DRUJ instability associated with distal radius fractures was performed. The primary outcomes analyzed included clinical grip strength; range of motion; the disability of the arm, shoulder and hand (DASH) score; and the modified Mayo wrist score (MMWS). Results: Of the 531 articles identified in the literature search, 8 met our defined criteria and were included in the final analysis. The cumulative sample size was 258 patients at a mean follow-up of 11.1 months (range, 3-16.9 months). Treatment groups included cast immobilization in supination, K-wire stabilization, and triangular fibrocartilage complex (TFCC) repair. Statistical analysis revealed no difference across groups in active flexion-extension or DASH scores. A significant decrease in grip strength was found in patients who underwent TFCC repair compared with that in those who underwent both cast immobilization (P = .04) and K-wire stabilization (P = .02). Furthermore, we found a significant decrease in active pronation-supination between patients who underwent TFCC repair and those who underwent cast immobilization (P = .03). Patients who underwent TFCC repair were also found to exhibit decreased MMWS as compared with those who underwent K-wire stabilization (P = .05). Overall, persistent DRUJ instability was only found in 4 patients (1.5%), without a significant difference between treatment groups. Conclusions: This study suggests functional advantages of certain treatment modalities over others, with the range of motion being highest in patients who underwent cast immobilization and grip strength being highest in patients who underwent K-wire stabilization. However, the mean DASH scores showed no difference across all groups, calling into question the clinical need to pursue operative treatment via K-wire stabilization or TFCC repair over conservative treatment via cast immobilization. This study will hopefully serve as a foundation for future prospective studies to help improve and standardize treatment algorithms in patients with DRUJ instability and distal radius fractures.Type of study/level of evidence: Therapeutic II.

Complex Femoral Reconstruction Following Pathologic Subtrochanteric Femur Fracture Secondary to Paget's Disease of the Bone: A Case Report with Long-Term Follow-up.

INTRODUCTION: Paget's disease (PD) is the most common metabolic bone disorder after osteoporosis. Clinically, it can result in pain, bony deformity, pathologic fractures, and, in the late stage, progression to malignancy. At a pathophysiological level, PD manifests as an imbalance between the homeostasis of bone destruction and formation. Bones most often involved with this disease process include the pelvis, femur, tibia, vertebra, and skull. The goals of orthopedic intervention in PD are two-fold: Prevention of pathologic fracture with internal stabilization and reconstruction following fracture, which is often complicated by poor bone quality and advanced deformity. In this case report, authors detail a patient with PD who presented with a pathologic left subtrochanteric femur fracture requiring a novel complex femoral reconstruction with a 29-year follow-up period. To the best of our knowledge, no such report exists, particularly with this degree of long-term follow-up. CASE REPORT: A 70-year-old Caucasian man with PD presented with an atypical subtrochanteric femur fracture after a ground level fall. Due to his significant femoral deformity and osteopenia, proximal femoral resection followed by composite femoral allograft reconstruction with total hip arthroplasty was performed. Long-term durability of this novel reconstruction method as well as longitudinal clinical and radiographic outcomes is described. CONCLUSION: Complex pathologic fractures in patients with PD can be effectively treated with composite femoral allograft reconstruction and total hip arthroplasty with good long-term radiographic and clinical outcomes. Broadly, it is important to note the unique healing pattern seen in PD bone and to consider the implications it may have when planning surgical intervention.

Quantifying Craniometric Change Early After Fronto-Orbital Advancement in Metopic Synostosis.

Frontal orbital advancement (FOA) for metopic synostosis results in cranial vault expansion, supporting underlying growth of the developing brain and improving head shape. Previous studies have shown that FOA in younger infants leads to a greater incidence of long-term growth restriction of intracranial volume; however, it is still unknown as to whether this is due to undercorrection at the time of surgery versus primary suture pathology. The purpose of our study is to provide a method for objective analyses of intracranial volumes in the early post-FOA period. A retrospective chart review was conducted on patients who underwent FOA over a 10-year period by a single surgeon. Data collected included patient characteristics and clinical outcomes. Radiological analysis of intracranial volumes pre- and post-FOA was determined using Amira volume-rendering software. Average increase in intracranial volume at 6 weeks post-FOA was 139.27 mL (80.01-225.25 mL) with average relative cranial vault expansion of 18.1% (3.3-48%). Patients who underwent FOA older than 12 months of age had an average increase in intracranial volume of 8.5% (3.3-13.1%). Patients younger than 12 months had a statistically higher average increase of 25% (12.8-48%). Frontal orbital advancement effectively increases intracranial volume in patients with metopic synostosis. When compared with older patients, patients younger than 1 year of age have a greater relative increase in intracranial volume in the immediate postoperative period. Quantifying cranial vault expansion after FOA can assist surgeons in surgical planning as well as in measuring and monitoring clinical outcomes within and across craniofacial centers regardless of technique.

Neurobiology of empathy and callousness: implications for the development of antisocial behavior.

Information on the neurobiology of empathy and callousness provides clinicians with an opportunity to develop sophisticated understanding of mechanisms underpinning antisocial behavior and its counterpart, moral decision-making. This article provides an integrated in-depth review of hormones (e.g. peripheral steroid hormones such as cortisol) and brain structures (e.g. insula, anterior cingulate cortex, and amygdala) implicated in empathy, callousness, and psychopathic-like behavior. The overarching goal of this article is to relate these hormones and brain structures to moral decision-making. This review will begin in the brain, but will then integrate information about biological functioning in the body, specifically stress-reactivity. Our aim is to integrate understanding of neural processes with hormones such as cortisol, both of which have demonstrated relationships to empathy, psychopathy, and antisocial behavior. The review proposes that neurobiological impairments in individuals who display little empathy are not necessarily due to a reduced ability to understand the emotions of others. Instead, evidence suggests that individuals who show little arousal to the distress of others likewise show decreased physiological arousal to their own distress; one manifestation of reduced stress reactivity may be a dysfunction in empathy, which supports psychopathic-like constructs (e.g. callousness). This integration will assist in the development of objective methodologies that can inform and monitor treatment interventions focused on decreasing antisocial behavior.