Exertional heat stroke causes long-term skeletal muscle epigenetic reprogramming, altered gene expression, and impaired satellite cell function in mice.

The effect of exertional heat stroke (EHS) exposure on skeletal muscles is incompletely understood. Muscle weakness is an early symptom of EHS but is not considered a major target of multiorgan injury. Previously, in a preclinical mouse model of EHS, we observed the vulnerability of limb muscles to a second EHS exposure, suggesting hidden processes contributing to declines in muscle resilience. Here, we evaluated the possible molecular origins of EHS-induced declines in muscle resilience. Female C57BL/6 mice [total n = 56; 28/condition, i.e., EHS and exercise control (EXC)] underwent forced wheel running at 37.5°C/40% relative humidity until symptom limitation (unconsciousness). EXC mice exercised identically at room temperature (22-23°C). After 1 mo of recovery, the following were assessed: 1) specific force and caffeine-induced contracture in soleus (SOL) and extensor digitorum longus (EDL) muscles; 2) transcriptome and DNA methylome responses in gastrocnemius (GAST); and 3) primary satellite cell function (proliferation and differentiation). There were no differences in specific force in either SOL or EDL from EXC. Only EHS solei exhibited lower caffeine sensitivity. EHS GAST exhibited higher RNA expression of genes encoding structural proteins of slow fibers, heat shock proteins, and myogenesis. A total of ∼2,500 differentially methylated regions of DNA that could potentially affect many cell functions were identified. Primary satellite cells exhibited suppressed proliferation rates but normal differentiation responses. Results demonstrate long-term changes in skeletal muscles 1 mo after EHS that could contribute to declines in muscle resilience. Skeletal muscle may join other, more recognized tissues considered vulnerable to long-term effects of EHS.NEW & NOTEWORTHY Exertional heat stroke (EHS) in mice induces long-term molecular and functional changes in limb muscle that could reflect a loss of "resilience" to further stress. The phenotype was characterized by altered caffeine sensitivity and suppressed satellite cell proliferative potential. This was accompanied by changes in gene expression and DNA methylation consistent with ongoing muscle remodeling and stress adaptation. We propose that EHS may induce a prolonged vulnerability of skeletal muscle to further stress or injury.

Delayed metabolic disturbances in the myocardium after exertional heat stroke: contrasting effects of exertion and thermal load.

Epidemiological studies report higher risks of cardiovascular disease in humans exposed to heat stroke earlier in life. Previously, we explored mechanistic links between heat stroke and developing cardiac abnormalities using a preclinical mouse model of exertional heat stroke (EHS). Profound metabolic abnormalities developed in the ventricles of females but not males after 2 wk of recovery. Here we tested whether this lack of response in males could be attributed to the lower exercise performances or reduced thermal loads they experienced with the same running protocol. We systematically altered environmental temperature (Te) during EHS to manipulate heat exposure and exercise performance in the males. Three groups of adult C57BL/6 male mice were studied: "EHS-34" (Te = 34°C), "EHS-41" (Te = 41°C), and "EHS-39.5" (Te = 39.5°C). Mice ran until symptom limitation (unconsciousness), reaching max core temperature (Tc,max). After a 2-wk recovery, the mice were euthanized, and the ventricles were removed for untargeted metabolomics. Results were compared against age-matched nonexercise controls. The EHS-34 mice greatly elevated their exercise performance but reached lower Tc,max and lower thermal loads. The EHS-41 mice exhibited equivalent thermal loads, exercise times, and Tc,max compared with EHS-39.5. The ventricles from EHS-34 mice exhibited the greatest metabolic disturbances in the heart, characterized by shifts toward glucose metabolism, reductions in acylcarnitines, increased amino acid metabolites, elevations in antioxidants, altered TCA cycle flux, and increased xenobiotics. In conclusion, delayed metabolic disturbances following EHS in male myocardium appear to be greatly amplified by higher levels of exertion in the heat, even with lower thermal loads and max core temperatures.NEW & NOTEWORTHY Epidemiological data demonstrate greater cardiovascular risk in patients with previous heat stroke exposure. Using a preclinical mouse model of exertional heat stroke, male mice were exposed to one of three environmental temperatures (Te) during exercise. Paradoxically, after 2 wk, the mice in the lowest Te, exhibiting the largest exercise response and lowest heat load, had the greatest ventricular metabolic disturbances. Metabolic outcomes resemble developing left ventricular hypertrophy or stress-induced heart disease.

The Biomechanical Role of the Deltoid Ligament on Ankle Stability: Injury, Repair, and Augmentation.

BACKGROUND: Deltoid ligament injuries occur in isolation as well as with ankle fractures and other ligament injuries. Both operative treatment and nonoperative treatment are used, but debate on optimal treatment continues. Likewise, the best method of surgical repair of the deltoid ligament remains unclear. PURPOSE: To determine the biomechanical role of native anterior and posterior components of the deltoid ligament in ankle stability and to determine the efficacy of simple suture versus augmented repair. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric ankles (mean age, 51 years; age range, 34-64 years; all male specimens) were mounted on a 6 degrees of freedom robotic arm. Each specimen underwent biomechanical testing in 8 states: (1) intact, (2) anterior deltoid cut, (3) anterior repair, (4) tibiocalcaneal augmentation, (5) deep anterior tibiotalar augmentation, (6) posterior deltoid cut, (7) posterior repair, and (8) complete deltoid cut. Testing consisted of anterior drawer, eversion, and external rotation (ER), each performed at neutral and 25° of plantarflexion. A 1-factor, random-intercepts, linear mixed-effect model was created, and all pairwise comparisons were made between testing states. RESULTS: Cutting the anterior deltoid introduced ER (+2.1°; P = .009) and eversion laxity (+6.2° of eversion; P < .001) at 25 degrees of plantarflexion. Anterior deltoid repair restored native ER but not eversion. Tibiocalcaneal augmentation reduced eversion laxity, but tibiotalar augmentation provided no additional benefit. The posterior deltoid tear showed no increase in laxity. Complete tear introduced significant anterior translation, ER, and eversion laxity (+7.6 mm of anterior translation, +13.8° ER and +33.6° of eversion; P < .001). CONCLUSION: A complete deltoid tear caused severe instability of the ankle joint. Augmented anterior repair was sufficient to stabilize the complete tear, and no additional benefit was provided by posterior repair. For isolated anterior tear, repair with tibiocalcaneal augmentation was the optimal treatment. CLINICAL RELEVANCE: Deltoid repair with augmentation may reduce or avoid the need for prolonged postoperative immobilization and encourage accelerated rehabilitation, preventing stiffness and promoting earlier return to preinjury activity.

Outcomes Following Repair of Achilles Midsubstance Tears: Percutaneous Knotless Repair vs Open Repair.

BACKGROUND: Optimum treatment for acute Achilles tendon rupture results in high mechanical strength, low risk of complications, and return to preinjury activity level. Percutaneous knotless repair is a minimally invasive technique with promising results in biomechanical studies, but few comparison clinical studies exist. Our study purpose was to compare functional outcomes and revision rates following acute Achilles tendon rupture treated between percutaneous knotless repair and open repair techniques. METHODS: Patients 18 years or older with an acute Achilles tendon rupture, treated by a single surgeon with either open repair or percutaneous knotless repair, and more than 2 years after surgery were assessed for eligibility. Prospective clinical data were obtained from the data registry and standard electronic medical record. Additionally, the patients were contacted to obtain current follow-up questionnaires. Primary outcome measure was Foot and Ankle Ability Measure (FAAM) activities of daily living (ADL). Secondary outcome measures were FAAM sports, 12-Item Short Form Health Survey (SF-12), Tegner activity scale, patient satisfaction with outcome, complications, and revisions. Postoperative follow-up closest to 5 years was used in this study. RESULTS: In total, 61 patients were included in the study. Twenty-four of 29 patients (83%) in the open repair group and 28 of 32 patients (88%) in the percutaneous knotless repair group completed the questionnaires with average follow-up of 5.8 years and 4.2 years, respectively. We found no significant differences in patient-reported outcomes or patient satisfaction between groups (FAAM ADL: 99 vs 99 points, P = .99). Operative time was slightly longer in the percutaneous knotless repair group (46 vs 52 minutes, P = .02). Two patients in the open group required revision surgery compared to no patients in the percutaneous group. CONCLUSION: In our study, we did not find significant differences in patient-reported outcomes or patient satisfaction by treating Achilles tendon midsubstance ruptures with percutaneous knotless vs open repair. LEVEL OF EVIDENCE: Level IlI, retrospective cohort study.

Broström Repair With and Without Augmentation: Comparison of Outcomes at Median Follow-up of 5 Years.

BACKGROUND: An augmented Broström repair with nonabsorbable suture tape has demonstrated strength and stiffness more similar to the native anterior talofibular ligament (ATFL) compared to Broström repair alone at the time of repair in cadaveric models for the treatment of lateral ankle instability. The study purpose was to compare minimum 2-year patient-reported outcomes (PROs) following treatment of ATFL injuries with Broström repair with vs without suture tape augmentation. METHODS: Between 2009 and 2018, patients >18 years old who underwent primary surgical treatment for an ATFL injury with either a Broström repair alone (BR Cohort) or Broström repair with suture tape augmentation (BR-ST Cohort) were identified. Demographic data and PROs, including Foot and Ankle Ability Measure (FAAM) with activities of daily living (ADL) and sport subscales, 12-Item Short Form Health Survey (SF-12), Tegner Activity Scale, and patient satisfaction with surgical outcome, were compared between groups, and proportional odds ordinal logistic regression was used. RESULTS: Ninety-one of 102 eligible patients were available for follow-up at median 5 years. The BR cohort had 50 of 53 patients (94%) completed follow-up at a median of 7 years. The BR-ST cohort had 41 of 49 (84%) complete follow-up at a median of 5 years. There was no significant difference in median postoperative FAAM ADL (98% vs 98%, P = .67), FAAM sport (88% vs 91%, P = .43), SF-12 PCS (55 vs 54, P = .93), Tegner score (5 vs 5, P = .64), or patient satisfaction (9 vs 9, P = .82). There was significantly higher SF-12 MCS (55.7 vs 57.6, P = .02) in the BR-ST group. Eight patients underwent subsequent ipsilateral ankle surgery, of which one patient (BR-ST group) was revised for recurrent lateral ankle instability. CONCLUSION: At median 5 years, patients treated for ATFL injury of the lateral ankle with Broström repair with suture tape augmentation demonstrated similar patient-reported outcomes to those treated with Broström repair alone. LEVEL OF EVIDENCE: Level II, retrospective cohort study.

Amino acid solution mitigates hypothermia response and intestinal damage following exertional heat stroke in male mice.

Increased gut permeability is implicated in the initiation and extent of the cytokine inflammatory response associated with exertional heat stroke (EHS). The primary objective of this study was to determine if a five amino acid oral rehydration solution (5AAS), specifically designed for the protection of the gastrointestinal lining, would prolong time to EHS, maintain gut function and dampen the systemic inflammatory response (SIR) measured during EHS recovery. Male C57/BL6J mice instrumented with radiotelemetry were gavaged with 150 µL of 5AAS or H2 O, and ≈12 h later were either exposed to an EHS protocol where mice exercised in a 37.5°C environmental chamber to a self-limiting maximum core temperature (Tc,max) or performed the exercise control (EXC) protocol (25°C). 5AAS pretreatment attenuated hypothermia depth and length (p < 0.005), which are indicators of EHS severity during recovery, without any effect on physical performance or thermoregulatory responses in the heat as determined by percent body weight lost (≈9%), max speed (≈6 m/min), distance (≈700 m), time to Tc,max (≈160 min), thermal area (≈550°C∙min), and Tc,max (42.2°C). EHS groups treated with 5AAS showed a significant decrease in gut transepithelial conductance, decreased paracellular permeability, increased villus height, increased electrolyte absorption and changes in tight junction protein expression pattern suggestive of improved barrier integrity (p < 0.05). No differences were witnessed between EHS groups in acute phase response markers of liver, circulating SIR markers, or indicators of organ damage during recovery. These results suggest that a 5AAS improves Tc regulation during EHS recovery through maintaining mucosal function and integrity.

Syndesmotic Suture Button Fixation Results in Higher Tegner Activity Scale Scores When Compared to Screw Fixation: A Multicenter Investigation.

BACKGROUND: Suture buttons and metal screws have been used and compared in biomechanical, radiographic, and clinical outcome studies for syndesmotic injuries, with neither implant demonstrating clear superiority. The aim of this study was to compare clinical outcomes of both implants. METHODS: Patients who underwent syndesmosis fixation at 2 separate academic centers from 2010 through 2017 were compared. Thirty-one patients treated with a suture button and 21 patients treated with screws were included. Patients in each group were matched by age, sex, and Orthopaedic Trauma Association fracture classification. Tegner Activity Scale (TAS), Foot and Ankle Ability Measure (FAAM), patient satisfaction score, surgical failure, and reoperation rates were compared. RESULTS: Patients who underwent suture button fixation had significantly higher TAS scores than those who underwent screw fixation (p < 0.001). There was no significant difference in FAAM ADL scores between cohorts (p = 0.08). Symptomatic hardware removal rates were similar (3.2% suture button cohort vs 9.0% in screw cohort). One patient (4.5%) underwent revision surgery secondary to syndesmotic malreduction after screw fixation, for a reoperation rate of 13.5%. CONCLUSION: Patients with unstable syndesmotic injuries treated with suture button fixation had higher mean TAS scores compared to patients treated with screws. Foot and Ankle Ability Measure and ADL scores in these cohorts were similar.Level of Evidence: Level 3 Retrospective Matched Case-Cohort.

Are Prospective Criteria or Objective Clinical Measures Utilized in Return to Play (RTP) Decision Making After Ankle Surgery? A Scoping Review.

Background: Manuscripts discussing return to play (RTP) following ankle surgery are common. However, the definition for RTP and the method by which it is determined remains unclear. The purpose of this scoping review was to clarify how RTP is defined following ankle surgery in physically active patients, to identify key factors informing RTP decision making (such as objective clinical measures), and make recommendations for future research. Methods: A scoping literature review was performed in April 2021 using PubMed, EMBASE, and Nursing and Allied Health databases. Thirty studies met inclusion criteria: original research following ankle surgery reporting at least 1 objective clinical test and documentation of RTP. Data were extracted for study methods and outcomes (RTP definition, RTP outcomes, and objective clinical tests). Results: The scoping review found studies on 5 ankle pathologies: Achilles tendon rupture, chronic lateral ankle instability, anterior ankle impingement, peroneal tendon dislocation, and ankle fracture. RTP criteria were not provided in the majority of studies (18/30 studies). In the studies that provided them, the RTP criteria were primarily based on time postsurgery (8/12) rather than validated criteria. Objective clinical outcome measures and patient-reported outcome measures (PROMs) were documented for each surgery when available. Both clinical outcomes and PROMs were typically measured >1 year postsurgery. Conclusion: In physically active patients who have had ankle surgery, RTP remains largely undefined and is not consistently based on prospective objective criteria nor PROMS. We recommend standardization of RTP terminology, adoption of prospective criteria for both clinical measures and PROMs to guide RTP decision making, and enhanced reporting of patient data at the time of RTP to develop normative values and determine when the decision to RTP is not safe. Level of Evidence: Level IV, scoping review.

Methods for Biomechanical Testing of Posterior Malleolar Fractures in Ankle Fractures: A Scoping Review.

BACKGROUND: The treatment of posterior malleolar fractures (PMFs) is debated, including the need for surgery and method of fixation. Recent literature has suggested that fracture pattern, rather than fragment size, may be an important predictor for ankle biomechanics and functional outcome. Biomechanical studies have been conducted to provide evidence-based treatment on the effects of fracture and fixation on contact pressure and stability. The objective of this scoping review is to summarize the methodologies used in biomechanical studies on PMFs and assess whether they are sufficient to test the need for surgery and method of fixation. METHODS: A scoping review of publications before January 2022 was performed. PubMed/Medline and Embase Ovid were searched for cadaver or finite element analysis (FEA) studies that created and tested the effects of PMFs in ankle fractures. Both cadaver and FEA studies were included. Data about fragment characteristics, mode of testing, and outcomes were charted by 2 persons from the study group. The data were synthesized when possible and compared. RESULTS: We included 25 biomechanical studies, including 19 cadaver studies, 5 FEA studies, and 1 cadaver and FEA study. Aside from the fragment size, few other fragment characteristics were reported. Mode of testing varied with different loads and foot positions. Strong conclusions on the effects of fracture and fixation on contact pressure and stability could not be made. CONCLUSION: Biomechanical studies on PMFs demonstrate wide variability in fragment characteristics and mode of testing, which makes it difficult to compare studies and draw conclusions on the need for surgery and method of fixation. Additionally, limited reporting of fragment measurements questions the applicability to clinical practice. The biomechanical literature on PMFs would benefit from the use of a standard classification and universal fragment measurements to match clinical injuries in future biomechanical studies. Based on this review, we recommend the Mason classification, which addresses the pathomechanism, and use of the following fragment measurements in all 3 anatomic planes when creating and describing PMFs: fragment length ratio, axial angle, sagittal angle or fragment height, and interfragmentary angle. The testing protocol needs to reflect the purpose of the study. CLINICAL RELEVANCE: This scoping review demonstrates wide methodological diversity of biomechanical studies. Consistency in methodology should enable comparison of study results, leading to stronger evidence-based recommendations to guide surgeons in decision making and offer PMF patients the best treatment.

Effect of Posterior Malleolar Fixation on Syndesmotic Stability.

BACKGROUND: Transsyndesmotic fixation with suture buttons (SBs), posterior malleolar fixation with screws, and anterior inferior tibiofibular ligament (AITFL) augmentation using suture tape (ST) have all been suggested as potential treatments in the setting of a posterior malleolar fracture (PMF). However, there is no consensus on the optimal treatment for PMFs. PURPOSE: To determine which combination of (1) transsyndesmotic SBs, (2) posterior malleolar screws, and (3) AITFL augmentation using ST best restored native tibiofibular and ankle joint kinematics after 25% and 50% PMF. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty cadaveric lower-leg specimens were divided into 2 groups (25% or 50% PMF) and underwent biomechanical testing using a 6 degrees of freedom robotic arm in 7 states: intact, syndesmosis injury with PMF, transsyndesmotic SBs, transsyndesmotic SBs + AITFL augmentation, transsyndesmotic SBs + AITFL augmentation + posterior malleolar screws, posterior malleolar screws + AITFL augmentation, and posterior malleolar screws. Four biomechanical tests were performed at neutral and 30° of plantarflexion: external rotation, internal rotation, posterior drawer, and lateral drawer. The position of the tibia, fibula, and talus were recorded using a 5-camera motion capture system. RESULTS: With external rotation, posterior malleolar screws with AITFL augmentation resulted in best stability of the fibula and ankle joint. With internal rotation, all repairs that included posterior malleolar screws stabilized the fibula and ankle joint. Posterior and lateral drawer resulted in only small differences between the intact and injured states. No differences were found in the efficacy of treatments between 25% and 50% PMFs. CONCLUSION: Posterior malleolar screws resulted in higher syndesmotic stability when compared with transsyndesmotic SBs. AITFL augmentation provided additional external rotational stability when combined with posterior malleolar screws. Transsyndesmotic SBs did not provide any additional stability and tended to translate the fibula medially. CLINICAL RELEVANCE: Posterior malleolar fixation with AITFL augmentation using ST may be the preferred surgical method when treating patients with acute ankle injury involving an unstable syndesmosis and a PMF ≥25%.

Neuromotor deficits and altered physiological responses to repeated exertional heat stroke exposures in mice.

Exertional heat stroke (EHS) is a life-threatening illness that can lead to negative health outcomes. Using a "severe" preclinical mouse model of EHS, we tested the hypotheses that one EHS exposure results in altered susceptibility to a subsequent EHS and reduced neuromotor performance. Female C57BL/6 mice underwent two protocols, 2 wk apart, either an EHS trial (EHS) or a sham exercise control trial (EXC). For EHS, mice ran in a forced running wheel at 37.5°C/40% relative humidity until loss of consciousness, followed by a slow cooling protocol (2 h recovery at 37.5°C). EXC mice exercised equally but in ∼22°C. Mice were randomized into three groups: 1) EXC-EXC (two consecutive EXC, n = 6, 2) EHS-EXC (EHS followed by EXC, n = 5), and 3) EHS-EHS (repeated EHS, n = 9). Mice underwent noninvasive neuromotor and behavioral tests during recovery and isolated soleus force measurements at the end of recovery. At the first EHS, mice reached average peak core temperatures (Tc,max) of 42.4°C, (46% mortality). On the second EHS, average Tc,max was reduced by ∼0.7°C (P < 0.05; mortality 18%). After the first EHS, both EHS-EX and EHS-EHS showed significant reductions in maximum strength (24 h and 1 wk post). After the second EHS, strength, horizontal rotation, hindlimb tone, suspended hindlimb splay, trunk curl, and provoked biting continued to decline in the EHS-EHS group. In conclusion, exposure to a second EHS after 2 wk leads to increased exercise times in the heat, symptom limitation at a lower Tc,max, and greater deficits in neuromotor and behavioral function during recovery.

Long-term epigenetic and metabolomic changes in the mouse ventricular myocardium after exertional heat stroke.

Evidence from human epidemiological studies suggests that exertional heat stroke (EHS) results in an elevated risk of long-term cardiovascular and systemic disease. Previous results using a preclinical mouse model of EHS demonstrated severe metabolic imbalances in ventricular myocardium developing at 9-14 days of recovery. Whether this resolves over time is unknown. We hypothesized that the long-term effects of EHS on the heart reflect retained maladaptive epigenetic responses. In this study, we evaluated genome-wide DNA methylation, RNA-Seq, and metabolomic profiles of the left ventricular myocardium in female C57BL/6 mice, 30 days after EHS (exercise in 37.5°C; n = 7-8), compared with exercise controls. EHS mice ran to loss of consciousness, reaching core temperatures of 42.4 ± 0.2°C. All mice recovered quickly. After 30 days, the left ventricles were rapidly frozen for DNA methyl sequencing, RNA-Seq, and untargeted metabolomics. Ventricular DNA from EHS mice revealed >13,000 differentially methylated cytosines (DMCs) and >900 differentially methylated regions (DMRs; ≥5 DMCs with ≤300 bp between each CpG). Pathway analysis using DMRs revealed alterations in genes regulating basic cell functions, DNA binding, transcription, and metabolism. Metabolomics and mRNA expression revealed modest changes that are consistent with a return to homeostasis. Methylation status did not predict RNA expression or metabolic state at 30 days. We conclude that EHS induces a sustained DNA methylation memory lasting over 30 days of recovery, but ventricular gene expression and metabolism return to a relative homeostasis at rest. Such long-lasting alterations to the DNA methylation landscape could alter responsiveness to environmental or clinical challenges later in life.

Summary Report of the Arthritis Foundation and the American Orthopaedic Foot & Ankle Society's Symposium on Targets for Osteoarthritis Research: Part 1: Epidemiology, Pathophysiology, and Current Imaging Approaches.

This first of a 2-part series of articles recounts the key points presented in a collaborative symposium sponsored jointly by the Arthritis Foundation and the American Orthopaedic Foot & Ankle Society with the intent to survey the state of scientific knowledge related to incidence, diagnosis, pathologic mechanisms, and injection treatment options for osteoarthritis (OA) of the foot and ankle. A meeting was held virtually on December 3, 2021. A group of experts were invited to present brief synopses of the current state of knowledge and research in this area. Part 1 overviews areas of epidemiology and pathophysiology, current approaches in imaging, diagnostic and therapeutic injections, and genetics. Opportunities for future research are discussed. The OA scientific community, including funding agencies, academia, industry, and regulatory agencies, must recognize the needs of patients that suffer from arthritis of foot and ankle. The foot and ankle contain a myriad of interrelated joints and tissues that together provide a critical functionality. When this functionality is compromised by OA, significant disability results, yet the foot and ankle are generally understudied by the research community. Level of Evidence: Level V - Review Article/Expert Opinion.

Summary Report of the Arthritis Foundation and the American Orthopaedic Foot & Ankle Society's Symposium on Targets for Osteoarthritis Research: Part 2: Treatment Options.

This second of a 2-part series of articles recounts the key points presented in a collaborative symposium sponsored jointly by the Arthritis Foundation and the American Orthopaedic Foot & Ankle Society with the intent to survey current treatment options for osteoarthritis (OA) of the foot and ankle. A meeting was held virtually on December 10, 2021. A group of experts were invited to present brief synopses of the current state of knowledge and research in this area. Topics were chosen by meeting organizers, who then identified and invited the expert speakers. Part 2 overviews the current treatment options, including orthotics, non-joint destructive procedures, as well as arthroscopies and arthroplasties in ankles and feet. Opportunities for future research are also discussed, such as developments in surgical options for ankle and the first metatarsophalangeal joint. The OA scientific community, including funding agencies, academia, industry, and regulatory agencies, must recognize the importance to patients of addressing the foot and ankle with improved basic, translational, and clinical research. Level of Evidence: Level V, review article/expert opinion.

The impact of castration on physiological responses to exertional heat stroke in mice.

INTRODUCTION: The capability of male mice to exercise in hot environments without succumbing to exertional heat stroke (EHS) is markedly blunted compared to females. Epidemiological evidence in humans and other mammals also suggests some degree of greater vulnerability to heat stroke in males compared to females. The origins of these differences are unknown, but testosterone has previously been shown to induce faster elevations in core temperature during acute, passive heat exposure. In this study, we tested the hypothesis that loss of testosterone and related sex hormones through castration would improve the performance and heat tolerance of male mice during EHS exposure. METHODS: Twenty-four male mice were randomly divided into 3 groups, untreated EHS mice (SHAM-EHS), castrated EHS mice (CAS+EHS) and naïve exercise controls (NAIVE). Exercise performance and physiological responses in the heat were monitored during EHS and early recovery. Two weeks later, blood and tissues were collected and analyzed for biomarkers of cardiac damage and testosterone. RESULTS: Core temperature in CAS+EHS rose faster to 39.5°C in the early stages of the EHS trial (P<0.0001). However, both EHS groups ran similar distances, exhibited similar peak core temperatures and achieved similar exercise times in the heat, prior to symptom limitation (unconsciousness). CAS+EHS mice had ~10.5% lower body mass at the time of EHS, but this provided no apparent advantage in performance. There was no evidence of myocardial damage in any group, and testosterone levels were undetectable in CAS+EHS after gonadectomy. CONCLUSIONS: The results of these experiments exclude the hypothesis that reduced performance of male mice during EHS trials is due to the effects of male sex hormones or intact gonads. However, the results are consistent with a role of male sex hormones or intact gonads in suppressing the early and rapid rise in core temperature during the early stages of exercise in the heat.