Role of Alpha-Actinin-3 in Contractile Properties of Human Single Muscle Fibers: A Case Series Study in Paraplegics.
Role of Alpha-actinin-3 in Contractile Properties of Human Single Muscle Fibers: A Case Series Study in Paraplegics.
Filed under: Rehab Centers
PLoS One. 2012; 7(11): e49281
Broos S, Malisoux L, Theisen D, Francaux M, Deldicque L, Thomis MA
A common nonsense polymorphism in the ACTN3 gene results in the absence of ?-actinin-3 in XX individuals. The wild type allele has been associated with power athlete status and an increased force output in numeral studies, though the mechanisms by which these effects occur are unclear. Recent findings in the Actn3(-/-) (KO) mouse suggest a shift towards ‘slow’ metabolic and contractile characteristics of fast muscle fibers lacking ?-actinin-3. Skinned single fibers from the quadriceps muscle of three men with spinal cord injury (SCI) were tested regarding peak force, unloaded shortening velocity, force-velocity relationship, passive tension and calcium sensitivity. The SCI condition induces an ‘equal environment condition’ what makes these subjects ideal to study the role of ?-actinin-3 on fiber type expression and single muscle fiber contractile properties. Genotyping for ACTN3 revealed that the three subjects were XX, RX and RR carriers, respectively. The XX carrier’s biopsy was the only one that presented type I fibers with a complete lack of type II(x) fibers. Properties of hybrid type II(a)/II(x) fibers were compared between the three subjects. Absence of ?-actinin-3 resulted in less stiff type II(a)/II(x) fibers. The heterozygote (RX) exhibited the highest fiber diameter (0.121±0.005 mm) and CSA (0.012±0.001 mm(2)) and, as a consequence, the highest peak force (2.11±0.14 mN). Normalized peak force was similar in all three subjects (P?=?0.75). Unloaded shortening velocity was highest in R-allele carriers (P<0.001). No difference was found in calcium sensitivity. The preservation of type I fibers and the absence of type II(x) fibers in the XX individual indicate a restricted transformation of the muscle fiber composition to type II fibers in response to long-term muscle disuse. Lack of ?-actinin-3 may decrease unloaded shortening velocity and increase fiber elasticity. HubMed – rehab
Clinically Relevant Injury Patterns After an Anterior Cruciate Ligament Injury Provide Insight Into Injury Mechanisms.
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Am J Sports Med. 2012 Nov 9;
Levine JW, Kiapour AM, Quatman CE, Wordeman SC, Goel VK, Hewett TE, Demetropoulos CK
BACKGROUND:The functional disability and high costs of treating anterior cruciate ligament (ACL) injuries have generated a great deal of interest in understanding the mechanism of noncontact ACL injuries. Secondary bone bruises have been reported in over 80% of partial and complete ACL ruptures. PURPOSE:The objectives of this study were (1) to quantify ACL strain under a range of physiologically relevant loading conditions and (2) to evaluate soft tissue and bony injury patterns associated with applied loading conditions thought to be responsible for many noncontact ACL injuries. STUDY DESIGN:Controlled laboratory study. METHODS:Seventeen cadaveric legs (age, 45 ± 7 years; 9 female and 8 male) were tested utilizing a custom-designed drop stand to simulate landing. Specimens were randomly assigned between 2 loading groups that evaluated ACL strain under either knee abduction or internal tibial rotation moments. In each group, combinations of anterior tibial shear force, and knee abduction and internal tibial rotation moments under axial impact loading were applied sequentially until failure. Specimens were tested at 25° of flexion under simulated 1200-N quadriceps and 800-N hamstring loads. A differential variable reluctance transducer was used to calculate ACL strain across the anteromedial bundle. A general linear model was used to compare peak ACL strain at failure. Correlations between simulated knee injury patterns and loading conditions were evaluated by the ?(2) test for independence. RESULTS:Anterior cruciate ligament failure was generated in 15 of 17 specimens (88%). A clinically relevant distribution of failure patterns was observed including medial collateral ligament tears and damage to the menisci, cartilage, and subchondral bone. Only abduction significantly contributed to calculated peak ACL strain at failure (P = .002). While ACL disruption patterns were independent of the loading mechanism, tibial plateau injury patterns (locations) were significantly (P = .002) dependent on the applied loading conditions. Damage to the articular cartilage along with depression of the midlateral tibial plateau was primarily associated with knee abduction moments, while cartilage damage with depression of the posterolateral tibial plateau was primarily associated with internal tibial rotation moments. CONCLUSION:The current findings demonstrate the relationship between the location of the tibial plateau injury and ACL injury mechanisms. The resultant injury locations were similar to the clinically observed bone bruises across the tibial plateau during a noncontact ACL injury. These findings indicate that abduction combined with other modes of loading (multiplanar loading) may act to produce ACL injuries. CLINICAL RELEVANCE:A better understanding of ACL injury mechanisms and associated risk factors may improve current preventive, surgical, and rehabilitation strategies and limit the risk of ACL and secondary injuries, which may in turn minimize the future development of posttraumatic osteoarthritis of the knee.
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Acute myocardial infarction in a young patient with hyperhomocysteinaemia.
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BMJ Case Rep. 2012; 2012(nov07_1):
Ukachukwu V, Idris S, McIlwee A
Homocysteinuria is a rare inborn error of metabolism known to be associated with an increased risk of vascular events. A 36-year-old Caucasian man presented with a 2day history of epigastric discomfort associated with nausea and sweating. He has a history of homocysteinuria and had been poorly compliant with treatment. An ECG showed ST-segment elevation and Q-waves in anterior leads. Blood tests showed markedly elevated high-sensitivity troponin and high homocysteine levels. He had a failed primary percutaneous coronary intervention due to extensive thrombus in the left anterior descending artery, which was aspirated and he received integrelin infusion for 48 h. Echocardiogram showed mild-to-moderate impairment of left ventricular function with apical akinesis extending to the mid-portion of anteroseptal walls consistent with anterior myocardial infarction. He was started on homocysteine-lowering treatment with betaine and folic acid. He is now on follow-up with clinical chemistry and cardiac rehabilitation.
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Fall risk six weeks from onset of stroke and the ability of the Prediction of Falls in Rehabilitation Settings Tool and motor function to predict falls.
Filed under: Rehab Centers
Clin Rehabil. 2012 Nov 9;
Nyström A, Hellström K
Objective:To investigate whether the Prediction of Falls in Rehabilitation Settings Tool (Predict FIRST) and motor function could be used to identify people at risk of falling during the first six weeks after stroke, and to compare the risk of falling according to Predict FIRST with real falls frequency.Design:A longitudinal, prospective study.Patients:Sixty-eight people newly diagnosed with stroke admitted to an acute stroke unit.Methods:The participants underwent an assessment of motor ability (Modified Motor Assessment Scale according to Uppsala University Hospital version 99 (M-MAS UAS-99)) and falls risk (Predict FIRST) on the first to fourth day at the acute stroke unit. Falls occurring in the acute stroke unit were recorded and falls occurring after discharge were reported by telephone follow-up. The prediction of falls was analysed with binary logistic regression.Results:Fourteen of the patients (21%) fell at least once during the first six weeks after stroke. The strongest significant predictor for falls was a high score on Predict FIRST (odds ratio 5.21, confidence interval (CI) 1.10-24.78) followed by M-MAS UAS-99 parts C-E (odds ratio 0.65, CI 0.44-0.95). Predict FIRST underestimated the risk of falling as the median fall risk was 9% according to Predict FIRST.Conclusion:Although Predict FIRST has the ability to predict falls in people with recent onset of stroke, there is some underestimation of fall risk.
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