Hip and groin injuries in athletes

Although athletic injuries about the hip and groin occur less commonly than injuries in the extremities, they can result in extensive rehabilitation time. Thus, an accurate diagnosis and well-organized treatment plan are critical. Because loads of up to eight times body weight have been demonstrated in the hip joint during jogging, presumably even greater loads can occur during vigorous athletic competition. The available imaging modalities are effective diagnostic tools when selected on the basis of a thorough history and physical examination. Considerable controversy exists as to the cause and optimal treatment of groin pain in athletes, or the so-called "sports hernia." There has also been significant recent attention focused on intraarticular lesions that may be amenable to hip arthroscopy. This article briefly reviews several common hip and groin conditions affecting athletic patients and highlights some newer topics.

Selective management of flail chest and pulmonary contusion

Four hundred and twenty-seven patients with severe blunt chest trauma were treated resulting in (1) flail chest, (2) pulmonary contusions, (3) pneumothorax, (4) hemothorax, or (5) multiple rib fracture. The need for endotracheal intubation and mechanical ventilation was determined selectively by standard clinical criteria. Avoidance of fluid overload and vigorous pulmonary toilet was attempted in all patients. Three hundred and twenty-eight patients were treated by nonintubation; 318 patients (96.6%) had a successful outcome, while ten required intubation. Only one patient died. The 99 patients who required intubation and mechanical ventilation had a high mortality because of associated shock and head injury; however, the total mortality for the entire group of patients was 6.5%, with only 1.4% mortality caused by pulmonary injury. The incidence of pneumonia was high (51%), but there was only a 4% incidence of tracheostomy complications. Flail chest and pulmonary contusion without flail chest occurred in 95 and 135 patients, respectively. Half of the flail chest patients were intubated, but 69.5% were intubated less than three days. Twenty per cent of the patients with pulmonary contusion required mechanical ventilation, usually for less than three days. This study demonstrates that patients with severe blunt chest trauma can be managed safely by selective intubation and mechanical, ventilation and that the incidence of complications associated with controlled mechanical ventilation can be greatly reduced.

Diagnosing cardiac contusion: old wisdom and new insights

Cardiac contusion is usually caused by blunt chest trauma and therefore is frequently suspected in patients involved in car or motorcycle accidents. The diagnosis of a myocardial contusion is difficult because of non-specific symptoms and the lack of an ideal test to detect myocardial damage. Cardiac contusion can cause life threatening arrhythmias and cardiac failure. Many diagnostic methods, such as ECG, biochemical cardiac markers, transthoracic and transoesophageal echocardiography, and radionuclide imaging studies, have been investigated to determine their use in predicting such complications. Recently, cardiac troponin I and T were found to be highly sensitive for myocardial injury. Troponin I and T have also proved to be useful in the stratification of patients at risk for complications. Nevertheless, diagnosis of a cardiac contusion and identification of patients at risk remain a challenge. In this review the current diagnostic tests will be discussed. Also, based on these diagnostic tests, a screening strategy containing data from the latest studies is presented, with the intention of detecting patients at risk.

Posttraumatic brain hypothermia provides protection from sensorimotor and cognitive behavioral deficits

The purpose of this study was to determine the degree of sensorimotor and cognitive protection conferred by posttraumatic brain hypothermia. Baseline measurements were taken on sensorimotor tasks involving forelimb placing and beam-walking, as well as on a spatial navigational task utilizing the water maze. Twenty-four hours after the last baseline measurements, normothermic (37 degrees C) animals were subjected to a fluid percussion pulse (1.9-2.4 atm) over the right parietal sensorimotor cortex. Following trauma, brain temperature was maintained for 3 h at either normothermic (37 degrees C, group TBI-N, n = 12) or hypothermic levels (30 degrees C, group TBI-H, n = 11). Shams (n = 10) underwent all surgical procedures including posttraumatic brain injury (TBI) temperature manipulation, but were not subjected to the fluid percussive pulse. Beam-walking and forelimb placing measures were begun 24 h post-TBI and continued for 2 weeks. Animals were tested on the water maze task for 2 days beginning 24 h post-TBI. TBI produced substantial deficits in contralateral limb placing, which recovered over approximately one week. Hypothermia provided partial protection from these deficits, with TBI-H animals exhibiting intermediate scores that differed from both sham and TBI-N animals (p < 0.03). In the water maze, there was a distinction between groups in the ability to navigate 48 h after TBI. TBI-N animals performed significantly worse than sham and TBI-H animals (both p < 0.01), whereas there was no significant difference between the scores of sham and TBI-H animals. The present data demonstrate that moderate postinjury brain hypothermia can provide protection from sensorimotor and cognitive behavioral deficits as well as neuropathology in a model of traumatic brain injury associated with early neuronal and microvascular injury.

Long-term effects of two different ventilatory modes on oxygenation in acute lung injury. Comparison of airway pressure release ventilation and volume-controlled inverse ratio ventilation

A total of 18 patients with acute lung injury (ALI) were sequentially ventilated with two different modes of mechanical ventilation, each applied for a period of 24 h: (1) volume-controlled inverse ratio ventilation (VC-IRV), (2) airway pressure release ventilation (APRV). The individual sequence of both ventilatory modes was randomized. Ventilatory minute volume was adjusted for a PaCO2 of 35 to 45 mm Hg at the beginning of the study during the first ventilatory mode and then kept constant within preset limits. Hemodynamic variables were stable and similar during the 24-h periods of VC-IRV and APRV as well. Despite the lower sedation and spontaneous breathing during APRV, oxygen uptake was similar during both ventilatory modes. During the 24-h period of VC-IRV there was no relevant change of either airway pressures, alveolo-arterial O2 tension difference (AaDO2)/fraction of inspired oxygen (FIO2) or venous admixture. In contrast, peak airway pressures (Pawmax) during APRV were significantly lower (about 30%; p < 0.01), and decreased further within 24 h (p < 0.05). During APRV AaDO2/FIO2 and venous admixture improved significantly with time after more than 8 h (AaDO2/FIO2: 487 versus 414 mm Hg; p < 0.01; venous admixture: 20.6 versus 13.9%; p < 0.01; medians of onset versus end). The improvement was significantly different between both ventilatory modes (p < 0.01). We conclude that this indicates a progressive alveolar recruitment over time during ventilation with APRV.(ABSTRACT TRUNCATED AT 250 WORDS)

Quadriceps contusions. West Point update

A 3 year study of 117 quadriceps contusions in West Point cadets was undertaken to document the effectiveness of a three-phased therapy program to return these young athletes to full activity with a normal knee range of motion and without recurrence of injury. The treatment protocol of this study was modeled after the 1973 West Point study of Jackson and Feagin with two major changes: 1) resting the injured leg in flexion (versus extension) and 2) emphasizing early flexion exercises (versus extension). Classification of contusions was based on knee range of motion at 12 to 24 hours after the injury (mild, greater than 90 degrees; moderate, 45 degrees to 90 degrees; severe, less than 45 degrees). The average disability time was 13 days for mild, 19 days for moderate, and 21 days for severe contusions. Myositis ossificans developed in 9% of cadets and was associated with five risk factors (knee motion less than 120 degrees, injury occurring during football, previous quadriceps injury, delay in treatment greater than 3 days, and ipsilateral knee effusion.

Pulmonary contusions: quantifying the lesions on chest X-ray films and the factors affecting prognosis

OBJECTIVES

To quantify pulmonary contusions on chest x-ray film and to evaluate factors correlating with the size of the pulmonary contusions, changes in the first 24 hours, the need for ventilatory assistance, and death.

METHODS

The medical records and chest x-ray films of 103 patients with blunt chest trauma diagnosed as having a pulmonary contusion were reviewed.

RESULTS

A pulmonary contusion score was developed (3 = one third of a lung; 9 = an entire lung). In the emergency department, pulmonary contusions were not present in 11, were mild (one ninth to two ninths of a lung) in 15 patients, moderate-severe (three ninths to nine ninths of a lung) in 53 patients, and very severe in 24 patients. Within 24 hours, the pulmonary contusion score increased in 26 patients by 7.9 +/- 5.5 (SD). The 26 patients with an increasing contusion had a higher mortality rate (38% vs. 17%) (p = 0.044) and tended to need ventilatory assistance more frequently (73% vs. 49%) (p = 0.061). The 35 patients with very severe pulmonary contusions (pulmonary contusion score = 10-18) had the lowest PaO2:FIO2 ratio at 24 hours (175 +/- 103 mm Hg), longest hospital length of stay (28 +/- 35 days), and the highest Injury Severity Score (26 +/- 9). The factors correlating highest with a need for ventilatory support (57/103) were the 24 hour or initial PaO2/FIO2 ratio < 300, an Injury Severity Score > or = 24, Revised Trauma Score < 6.4, Glasgow Coma Scale score < or = 12, and shock or need for blood in the first 24 hours (p < 0.001). Death correlated highly with a need for ventilatory assistance, Injury Severity Score > or = 26, Revised Trauma Score < or = 6.3, and Glasgow Coma Scale score < or = 11 (p < 0.001).

CONCLUSION

Quantifying and noting changes in the extent of the pulmonary contusions and PaO2/FIO2 ratio during the first 24 hours may be of value in determining the need for ventilatory assistance and predicting outcome.

Determinants of outcome after pulmonary contusion

During the past 5 1/2 years, 86 patients were treated for pulmonary contusion resulting from blunt trauma. Injury mechanism was motor vehicle in 65 patients (76%), farming in nine (10%), fall in eight (9%), and miscellaneous in four (5%). There were 68 males (79%) and 18 females. Ages ranged from 4 to 75 years (mean, 32 years). Twenty-two patients (26%) presented in hypovolemic shock. Injury Severity Score (ISS) averaged 26 (range, 9-57). Intubation was performed in the Emergency Department in 21 patients (24%), 19 of whom were severely hypoxic with pO2/FIO2 ratio less than 300. Thirty-four patients were ultimately treated with mechanical ventilation for 1 to 103 days (mean, 9.1 days). The average hospital stay was 22 days. Eleven patients (13%) died. Mortality was significantly greater (p less than 0.05) in patients with ISS greater than or equal to 25, initial Glasgow Coma Scale less than or equal to 7, transfusion of greater than three units of blood, and pO2/FIO2 less than 300. Mortality was not correlated with either presence of shock or amount of intravenous fluid administration. Eighteen patients with concomitant flail chest demonstrated no increase in mortality but were likely to require mechanical ventilation (p less than 0.05). The extent of contusion assessed on admission chest roentgenogram was not predictive of mortality or need for intubation. We recommend aggressive treatment of associated injuries, craniocerebral trauma, and selective mechanical ventilation based upon degree of intrapulmonary shunt.

Effects of Schwann cell transplantation in a contusion model of rat spinal cord injury

Cultured Schwann cells were transplanted at various delays into a spinal cord contusion injury performed at low thoracic level in adult female rats. The Schwann cells were purified from the dorsal root ganglia of adult syngeneic animals. the transplants were well tolerated, and the transplanted Schwann cells invaded the injured spinal cord. As quantified using video image analysis, the survival and growth of the transplanted cells were poor when the grafting procedure was performed 3-4 days after injury and very good when performed immediately or 10 days after injury, in which cases post-traumatic micro- and macrocavitation were strongly reduced. In animals grafted immediately after injury but not in animals grafted after 10 days, post-traumatic astrogliosis was much reduced. The Schwann cells transplanted area was invaded by numerous regenerating axons, the vast majority of which were, based on the neurotransmitter (CGRP and SP) profile, originating from dorsal root ganglion. No regeneration of the corticospinal tract as assessed after anterograde tracing or of descending aminergic fibers could be demonstrated.

Treatment of Muscle Injuries by Local Administration of Autologous Conditioned Serum: Animal Experiments Using a Muscle Contusion Model

Muscle contusions represent a major part of sports injuries. The suggested treatments are generally sufficient to support muscle healing, but require a relatively long period of time. Given that autologous blood products are safe treatments, we have used a technique which stimulates the release of certain growth factors in the autologous conditioned serum (ACS). Those growth factors are known to improve the proliferative activity of myogenic precursor cells. Mice were subjected to an experimental contusion injury to their gastrocnemius muscle; one group received local injections of ACS at 2 hrs, 24 hrs, and 48 hrs after injury, a control group received saline injections. The histology results showed that satellite cell activation at 30/48 hrs post injury was accelerated and the diameter of the regenerating myofibers was increased compared to the controls within the first week after injury. ELISA results on the ACS have shown that the elevations in FGF-2 (460 %) and TGF-beta1 (82 %) could be partly responsible for the accelerating effects on regeneration due to proliferative and chemotactic properties. We conclude that ACS injection is a promising approach to reduce the time of recovery from muscle injury. In terms of clinical targets, this new approach could be used in the treatment of sports injuries and may also be interesting in postoperative situations.

Chest injuries in children: an analysis of 100 cases of blunt chest trauma from motor vehicle accidents

One hundred twenty-eight cases of chest injury were seen in a Paediatric Trauma Unit over a 5 1/2-year period. One hundred patients sustained motor vehicle accident (MVA)-related blunt chest injuries, 91 of them as pedestrians. Nine children had blunt chest injuries from falls, 10 had stab wounds (3 assault, 7 accidental), and 9 had gunshot injuries (6 from birdshot used by police during civil disturbance). MVA-related injuries were studied separately, as an etiologically homogeneous group. Sixty-five of these patients were under the age of 6. All but 3 also had serious extrathoracic injuries. The mean injury severity score (ISS) in MVA-related injuries was 25. Eight patients died, all with an ISS of 34 or more, 7 of whom had fatal head injuries. In MVA-related injuries, pulmonary contusion (n = 73) was the most frequent lesion seen, followed by rib fracture (n = 62), posttraumatic effusion (n = 58), pneumothorax (n = 38), and pneumatocele (n = 5). In MVA-related injuries, 18 children required ventilation. Thirty-nine (69%) of 56 children with radiologically evident posttraumatic pleural effusion had intercostal chest drainage. Analysis suggests that lung injury is a central event in MVA-related blunt chest trauma. Primary lung injury, radiologically visible as contusion, is complicated by hematoma, posttraumatic effusion, and pneumothorax.

Lung contusion: inflammatory mechanisms and interaction with other injuries

This article reviews current animal models and laboratory studies investigating the pathophysiology of lung contusion (LC), a common and severe condition in patients with blunt thoracic trauma. Emphasis is on studies elucidating cells, mediators, receptors, and processes important in the innate pulmonary inflammatory response that contribute to LC injury. Surfactant dysfunction in the pathogenesis of LC is also discussed, as is the potential role of epithelial cell or neutrophil apoptosis. Studies examining combination injuries where LC is exacerbated by secondary insults such as gastric aspiration in trauma patients are also noted. The need for continuing mechanism-based research to further clarify the pathophysiology of LC injury, and to define and test potential therapeutic interventions targeting specific aspects of inflammation or surfactant dysfunction to improve clinical outcomes in patients with LC, is also emphasized.

Muscle contusion injuries: current treatment options

Muscle contusion is second only to strain as the leading cause of morbidity from sports-related injuries. Severity depends on the site of impact, the activation status of the muscles involved, the age of the patient, and the presence of fatigue. The diagnosis has traditionally been one of clinical judgment; however, newer modalities, including ultrasonography, magnetic resonance imaging, and spectroscopy, are becoming increasingly important in both identifying and delineating the extent of injury. Although controlled clinical studies are scarce, animal research into muscle contusions has allowed the description of the natural healing process, which involves a complex balance between muscle repair, regeneration, and scar-tissue formation. Studies are being performed to evaluate the effects of anti-inflammatory medications, corticosteroids, operative repair, and exercise protocols. Prevention and treatment of complications such as myositis ossificans have also been stressed, but recognition may improve the outcome of these ubiquitous injuries.

Management of primary blast injury

Blast waves are produced following the detonation of munitions, the firing of large caliber guns, or from any type of explosion. These blast waves can be powerful enough to injure the individuals exposed to them. This type of injury is called primary blast injury (PBI) and the organs most vulnerable to PBI are the gas-filled organs, namely the ear, the lungs and the gastrointestinal tract. The approach to the casualty with PBI is the same as it would be for any trauma victim, i.e. the initiation of life support measures. Attention should be directed to the common life-threatening manifestation of thoracic and abdominal PBI. Pulmonary manifestations would include hemorrhage, barotrauma and arterial air embolism, while abdominal manifestations would include hemorrhage and hollow organ rupture. Therapy is directed at the specific manifestations as well as avoiding additional iatrogenic injury.

Renal trauma

The pertinent literature on renal trauma for the last 25 years has been analyzed. An evolutionary pattern is seen in the development of diagnostic methods, while surgical and medical management of renal trauma has become much more precise for specific lesions. Various subareas of interest within the field have emerged, such as pediatric trauma, associated injuries and the subdivisions of blunt and penetrating trauma. Furthermore, therapy has been extended to include those severe vascular lesions that previously were considered untreatable. Various new and experimental concepts are described. Specific recommendations regarding the diagnosis and the therapeutic management are offered in an attempt to bring perspective to these new developments.

Alveolar recruitment in combination with sufficient positive end-expiratory pressure increases oxygenation and lung aeration in patients with severe chest trauma

OBJECTIVE

Investigation of oxygenation and lung aeration during mechanical ventilation according to the open lung concept in patients with acute lung injury or acute respiratory distress syndrome.

DESIGN

Retrospective analysis.

SETTING

Surgical intensive care unit of a university hospital.

PATIENTS

We retrospectively identified 17 patients with acute lung injury/acute respiratory distress syndrome due to pulmonary contusion who had thoracic helical computed tomography scans before and after ventilation with the open lung concept.

INTERVENTIONS

Baseline ventilation consisted of low tidal volumes (< or =6 mL/kg) and positive end-expiratory pressure (PEEP; 5-17 cm H2O). We briefly applied high inspiratory pressures for opening up collapsed alveoli. External PEEP and intrinsic PEEP were combined to keep recruited lung units open. We generated intrinsic PEEP by pressure-cycled high-frequency inverse ratio ventilation (80 min, inspiratory/expiratory ratio 2:1) and maintained our ventilatory strategy for 24 hrs. Then, after reducing total PEEP by decreasing respiratory rate, Pao2/Fio2 ratio was reevaluated. If it remained >300 mm Hg, weaning was started. If not, previous ventilator settings were resumed for another 24 hrs after recruiting the lungs once again.

MEASUREMENTS AND MAIN RESULTS

Physiologic variables and ventilator settings were obtained from routine charts. Data from computed tomography before and after the open lung concept were analyzed for volumetric quantification of lung aeration and collapse. All results are presented as median and range. During baseline ventilation, PEEP was 10 (range, 5-17) cm H2O and after recruitment 21 (range, 18-26) cm H2O. Opening pressures were 65 (range, 50-80) cm H2O. After recruitment, Pao2/Fio2 ratio was higher in all patients. Total lung volume increased from 2915 (range, 1952-4941) to 4247 (range, 2285-6355) mL and normally aerated volume from 1742 (range, 774-2941) to 2971 (range, 1270-5232) mL. Atelectasis decreased significantly from 604 (range, 147-1538) to 106 (range, 0-736) mL. Hyperinflation increased significantly from 5 (range, 0-188) to 62 (range, 1-424) mL, whereas poor aeration did not change substantially from 649 (range, 302-1292) to 757 (range, 350-1613) mL. No hemodynamic problems occurred.

CONCLUSIONS

Lung recruitment increased arterial oxygenation, normally aerated lung volume, and total lung volume while decreasing the amount of collapsed tissue. These results indicate that the open lung concept is a reasonable mode of ventilation for patients with severe chest trauma.

Blunt thoracic trauma in children: review of 137 cases

OBJECTIVE

Thoracic injuries are uncommon in children and few report present on blunt ones.

METHODS

Between 1994 and 2003, 137 children with blunt thoracic injury were reviewed.

RESULTS

The mean age of children was 6.9+/-7.3 (1-16) years. Etiology was falls in 46.7%, traffical accidents in 51% and abuse in 2.2%. Average height in fallen-down cases was 6.4+/-2 (range: 3-11) m. Calculated mean kinetic energy transfer to body was 1923+/-1056 J. When first seen, 70% (82/117) of the patients had vital signs that were within normal limits. Forty-two (35.9%) children had isolated thoracic injury. Associated injuries were present in 75 (64.1%) children. Head injury was the most common associated injury present in 33 (28.2%). Pulmonary contusion was the most common thoracic injury with 68 (49.6%). Seventeen (12.4%) required surgery, 11 (8%) of them were thoracic (4 for diaphragmatic tear, 2 for flail chest, 2 for tracheobronchial injuries, 2 for laceration, 1 for esophageal rupture). Surgical group had higher ISS (26.8 vs 36.2, P = 0.001). Fifteen were lost (10.9%): There were lethal injuries in 7; chest tube treatment in 3; intensive care unit management in 2; mechanical support in 2 and observation in 1 patient. No death occurred for operations. Mortality rate was the lowest at injuries to chest alone and the highest for multi-system injuries (P < 0.05). The hospital length of stay for averaged 13.4+/-8.8 (range: 4-49) days.

CONCLUSION

Associated injury is the most important mortality factor. Thoracic operations can be performed with minimal morbidity and without mortality in children with blunt thoracic trauma.

Nonpenetrating thoracic injuries

In patients with nonpenetrating thoracic trauma, the rib fractures and other chest wall lesions may distract the physician from dangerous internal injuries in the chest or abdomen which may not be noted unless looked for very carefully. Early vigorous correction of any ventilatory problem is essential, particularly if there is any evidence of impaired tissue perfusion. Shock is frequently due to extrathoracic injuries, particularly intraabdominal bleeding. The flail associated with multiple rib fractures may seem mild initially, but severe underlying pulponary contusion and/or associated extrathoracic injuries make early ventilatory assistance extremely important. Rupture of the thoracic aorta should be suspected in rapid deceleration injuries, but is often not considered unless there is widening of the superior mediastinum on hte chest x-ray. Aortography to confirm the aortic tear should be done if time permits, and early repair of the injury provides the best results.

Pathophysiology of pulmonary contusion in dogs

We produced a localized right lower lobe (RLL) contusion in 14 anesthetized ventilated dogs, 7 of which were treated with positive end-expiratory pressure (PEEP group). We measured gas exchange, pulmonary mechanics, and regional function before and 5 h after the contusion. Arterial PO2 decreased by 20 Torr and venous admixture doubled in both groups during air breathing. The shunt fraction (Qs/Qt) was minimally increased, despite a large lobar Qs/Qt (0.43) in the contused RLL. These results were explained by reduced ventilation per unit volume (VA/V), and ventilation-to-perfusion ratios of the contused RLL measured with 133Xe technique. We conclude that pulmonary contusion causes a leak of blood and plasma, flooding 25% of the air spaces of the RLL at FRC, reducing the compliance of adjacent air spaces, and resulting in a reduced VA/V and a large RLL Qs/Qt. These results are consistent with the observed reduction in regional volume and perfusion in the contused RLL, and suggest that Qs/Qt was not increased because blood flow was markedly reduced to flooded air spaces. PEEP reduced the hypoxemia, but increased the contusion.

The multiple injured patient with bladder trauma

Trauma of the bladder from external force is associated with severe multiple injuries and the resulting mortality rate is substantial. The major associated injury was fracture of the pelvic bones which was present in 346 (83%) of the 417 patients with bladder trauma. Contusion of the bladder was present in 280 (67%), intraperitoneal rupture in 53 (13%), extraperitoneal rupture in 76 (18%), and both intra- and extraperitoneal rupture in eight (2%). Radiologic evaluation of the bladder by a retrograde cystogram using 400 ml of dye is recommended to diagnose the type of bladder injury. Nonoperative (catheter) management of extraperitoneal rupture of the bladder was used in 18 patients and resulted in complications in four of the 18.

Development of Approaches to Improve the Healing following Muscle Contusion

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of β-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion. © 1998 Elsevier Science Inc.

Bone Marrow Stromal Cell-Derived Exosomes Promote Muscle Healing Following Contusion Through Macrophage Polarization

Skeletal muscle contusion is among the most common injuries in traumatology and clinics of sports medicine. The injured muscle is vulnerable to re-injury owing to fibrosis formation. Given that the bone marrow stromal cell-derived exosomes (BMSC-Exos) displayed promising therapeutic effect for various tissues, we used BMSC-Exos to treat skeletal muscle contusion and investigated its effects on muscle healing. In this study, the in vivo model of skeletal muscle contusion was established by subjecting the tibialis anterior of young male mice to hit injury, and the in vitro inflammation model was established by lipopolysaccharide treatment on macrophages. Macrophage depletion model was built by intraperitoneal injection with clodronate-containing liposomes. Exosomes were isolated and purified from the supernatant of BMSCs using gradient centrifugation. Nanoparticle tracking analysis, transmission electron microscope, and western blot were used to identify the exosomes. HE stain, Masson stain, immunofluorescence, and biomechanical testing were carried out on the muscle tissue. In addition, enzyme-linked immunosorbent assay (ELISA) assays, real-time qPCR, flow cytometry, and PKH67 fluorescence trace were conducted in vitro. Intramuscular injection of BMSC-Exos to mice after muscle contusion alleviated inflammation level, reduced fibrosis size, promoted muscle regeneration, and improved biomechanical property. After macrophages depletion, the effects of BMSC-Exos were inhibited. In vitro, PKH-67 fluorescence was internalized into macrophages. BMSC-Exos promoted M2 macrophages polarization both in vivo and in vitro. At the same time, BMSC-Exos reduced the production of inflammatory cytokines under the inflammatory microenvironment and upregulated anti-inflammatory factors expression. In conclusion, BMSC-Exos attenuated muscle contusion injury and promoted muscle healing in mice by modifying the polarization status of macrophages and suppressing the inflammatory reaction.