Characterization of the pre-force-generation state in the actomyosin cross-bridge cycle.

Myosin is an actin-based motor protein that generates force by cycling between actin-attached (strong binding: ADP or rigor) and actin-detached (weak binding: ATP or ADP.P(i)) states during its ATPase cycle. However, it remains unclear what specific conformational changes in the actin binding site take place on binding to actin, and how these structural changes lead to product release and the production of force and motion. We studied the dynamics of the actin binding region of myosin V by using fluorescence resonance energy transfer (FRET) to monitor conformational changes in the upper-50-kDa domain of the actin binding cleft in the weak and strong actin binding states. Steady-state and lifetime data monitoring the FRET signal suggest that the cleft is in a more open conformation in the weak actin binding states. Transient kinetic experiments suggest that a rapid conformational change occurs, which is consistent with cleft closure before actin-activated phosphate release. Our results have identified a pre-force-generation actomyosin ADP.P(i) state, and suggest force generation may occur from a state not yet seen by crystallography in which the actin binding cleft and the nucleotide binding pocket are closed. Computational modeling uncovers dramatic changes in the rigidity of the upper-50-kDa domain in different nucleotide states, which suggests that the intrinsic flexibility of this domain allows myosin motors to accomplish simultaneous tight nucleotide binding (closed nucleotide binding pocket) and high-affinity actin binding (closed actin binding cleft).

Glenohumeral internal rotation deficit in throwing athletes: current perspectives.

Glenohumeral internal rotation deficit (GIRD) is an adaptive process in which the throwing shoulder experiences a loss of internal rotation (IR). GIRD has most commonly been defined by a loss of >20° of IR compared to the contralateral shoulder. Total rotational motion of the shoulder is the sum of internal and external rotation and may be more important than the absolute value of IR loss. Pathologic GIRD has been defined as a loss of IR combined with a loss of total rotational motion. The leading pathologic process in GIRD is posterior capsular and rotator-cuff tightness, due to the repetitive cocking that occurs with the overhead throwing motion. GIRD has been associated with numerous pathologic conditions, including posterior superior labral tears, partial articular-sided rotator-cuff tears, and superior labral anterior-to-posterior tears. The mainstay of treatment for patients with GIRD is posterior capsular stretching and strengthening to improve scapular mechanics. In patients who fail nonoperative therapy, shoulder arthroscopy can be performed. Arthroscopic surgery in the high-level throwing athlete should be to restore them to their functional baseline with the minimum amount of intervention possible.

Arthroscopic Mechanical Chondroplasty of the Knee Is Beneficial for Treatment of Focal Cartilage Lesions in the Absence of Concurrent Pathology.

BACKGROUND: Articular cartilage lacks the ability for intrinsic repair after acute injury, and focal articular cartilage lesions cause significant morbidity worldwide. Arthroscopic debridement (chondroplasty) represents the majority of cartilage procedures of the knee; however, limited data exist regarding outcomes after chondroplasty performed in isolation of concurrent procedures or not as a primary treatment for osteoarthritis (OA). HYPOTHESIS: Arthroscopic mechanical chondroplasty is beneficial for patients with a focal cartilage lesion of the knee in the absence of meniscal pathology or OA. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Potential participants were identified by querying billing data from a 3-year period in a single-surgeon practice, and eligible patients were verified to meet inclusion criteria through electronic medical record review. OA was quantified through Kellgren-Lawrence (KL) scoring. Subjective patient-reported outcome (PRO) scores, including International Knee Documentation Committee (IKDC), Knee injury and Osteoarthritis Outcome Score (KOOS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), Tegner, Lysholm, and Veterans RAND 12-Item Health Survey (VR-12), were collected preoperatively and at follow-up intervals. International Cartilage Repair Society (ICRS) grade and lesion size were determined at arthroscopy. Linear regression was used to determine the effect of baseline score on final follow-up score. Correlated regression equations were used to assess the relationship of covariates and change in PRO scores. RESULTS: Fifty-three of 86 (62%) eligible participants completed postoperative questionnaires at an average of 31.5 months (range, 11.5-57 months). The mean patient age was 37.3 ± 9.7 years and mean body mass index (BMI) was 27.7 ± 5.6 kg/m2; 33 (62%) participants were women. The mean treated lesion size was 3.3 ± 1.9 cm2, of these, 36 (68%) were ICRS grade 2 or 3, and 42 (79%) patients had a KL score of 0 to -2. On average, the cohort demonstrated significant improvement from baseline for almost all PRO scores. Regression analysis of change in score versus baseline indicated participants with lower preoperative scores gained more benefit from chondroplasty. Correlated regression equations showed KL score >0 and male sex had a consistent positive effect on change in PRO scores, high ICRS grade had a consistent negative effect, and lesion size, age, and obesity had no effect. Eight patients (15%) required further surgical intervention within the follow-up period. CONCLUSION: The clinical efficacy of chondroplasty for repair of focal cartilage defects of the knee has not been studied in isolation from concurrent orthopaedic procedures. Our data show that arthroscopic mechanical chondroplasty is beneficial to patients, and response to surgical intervention is correlated with baseline PRO scores, sex, ICRS grade, and KL score.

A prospective randomized comparison of two distinct allogenic tissue constructs for anterior cruciate ligament reconstruction.

BACKGROUND: Conduct a prospective randomized study to compare clinical outcomes of anterior cruciate ligament (ACL) reconstruction using quadrupled hamstring tendon (HT) allograft or doubled tibialis anterior (TA) allograft. Limited level 1 data exist comparing outcomes of different soft tissue allograft constructs for ACL reconstruction. We hypothesized no difference would exist in the patient reported outcomes (PRO), arthrometric testing, or rate of re-rupture between the two constructs. METHODS: Ninety eight subjects undergoing primary ACL reconstruction were randomized to HT (n=47) or TA (n=51) allograft. Subjects completed validated (PRO) measures pre-operatively, and six months and two years post-operatively. Arthrometric testing was performed at six months to assess integrity of the reconstruction. RESULTS: Fifty-eight percent of subjects (57/98) completed a two-year follow up. Allograft re-tear rates were similar between groups (6.2% HT vs. 4.0% TA, respectively, p=1.0). The relative risk of re-tear in the HT group was 1.5 compared to the TA group (p=0.7). The TA group improved significantly more on the physical portion of the VR-12 (p=0.046) and Lysholm score (p=0.014) compared to the HT group. There was no difference in the change from baseline for the other PRO scores at two years. CONCLUSIONS: Our data indicate no difference in graft failure rate and similar improvement from baseline in most PRO scores between treatment groups after two years. Based on these findings, TA allograft appears to provide a reliable and satisfactory option for patients who elect to undergo allograft ACL reconstruction.

Bioburden after Staphylococcus aureus inoculation in type 1 diabetic rats undergoing internal fixation.

SUMMARY: Fracture stabilization in the diabetic patient is associated with higher complication rates, particularly infection and impaired wound healing, which can lead to major tissue damage, osteomyelitis, and higher amputation rates. With an increasing prevalence of diabetes and an aging population, the risks of infection of internal fixation devices are expected to grow. Although numerous retrospective clinical studies have identified a relationship between diabetes and infection, currently there are few animal models that have been used to investigate postoperative surgical-site infections associated with internal fixator implantation and diabetes. The authors therefore refined the protocol for inducing hyperglycemia and compared the bacterial burden in controls to pharmacologically induced type 1 diabetic rats after undergoing internal fracture plate fixation and Staphylococcus aureus surgical-site inoculation. Using an initial series of streptozotocin doses, followed by optional additional doses to reach a target blood glucose range of 300 to 600 mg/dl, the authors reliably induced diabetes in 100 percent of the rats (n = 16), in which a narrow hyperglycemic range was maintained 14 days after onset of diabetes (mean ± SEM, 466 ± 16 mg/dl; coefficient of variation, 0.15). With respect to their primary endpoint, the authors quantified a significantly higher infectious burden in inoculated diabetic animals (median, 3.2 × 10 colony-forming units/mg dry tissue) compared with inoculated nondiabetic animals (7.2 × 10 colony-forming units/mg dry tissue). These data support the authors' hypothesis that uncontrolled diabetes adversely affects the immune system's ability to clear Staphylococcus aureus associated with internal hardware.

The effect of nitric oxide surface flux on the foreign body response to subcutaneous implants.

Although the release of nitric oxide (NO) from biomaterials has been shown to reduce the foreign body response (FBR), the optimal NO release kinetics and doses remain unknown. Herein, polyurethane-coated wire substrates with varying NO release properties were implanted into porcine subcutaneous tissue for 3, 7, 21 and 42 d. Histological analysis revealed that materials with short NO release durations (i.e., 24 h) were insufficient to reduce the collagen capsule thickness at 3 and 6 weeks, whereas implants with longer release durations (i.e., 3 and 14 d) and greater NO payloads significantly reduced the collagen encapsulation at both 3 and 6 weeks. The acute inflammatory response was mitigated most notably by systems with the longest duration and greatest dose of NO release, supporting the notion that these properties are most critical in circumventing the FBR for subcutaneous biomedical applications (e.g., glucose sensors).

Implant healing in experimental animal models of diabetes.

Diabetes mellitus is becoming increasingly prevalent worldwide. Additionally, there is an increasing number of patients receiving implantable devices such as glucose sensors and orthopedic implants. Thus, it is likely that the number of diabetic patients receiving these devices will also increase. Even though implantable medical devices are considered biocompatible by the Food and Drug Administration, the adverse tissue healing that occurs adjacent to these foreign objects is a leading cause of their failure. This foreign body response leads to fibrosis, encapsulation of the device, and a reduction or cessation of device performance. A second adverse event is microbial infection of implanted devices, which can lead to persistent local and systemic infections and also exacerbates the fibrotic response. Nearly half of all nosocomial infections are associated with the presence of an indwelling medical device. Events associated with both the foreign body response and implant infection can necessitate device removal and may lead to amputation, which is associated with significant morbidity and cost. Diabetes mellitus is generally indicated as a risk factor for the infection of a variety of implants such as prosthetic joints, pacemakers, implantable cardioverter defibrillators, penile implants, and urinary catheters. Implant infection rates in diabetic patients vary depending upon the implant and the microorganism, however, for example, diabetes was found to be a significant variable associated with a nearly 7.2% infection rate for implantable cardioverter defibrillators by the microorganism Candida albicans. While research has elucidated many of the altered mechanisms of diabetic cutaneous wound healing, the internal healing adjacent to indwelling medical devices in a diabetic model has rarely been studied. Understanding this healing process is crucial to facilitating improved device design. The purpose of this article is to summarize the physiologic factors that influence wound healing and infection in diabetic patients, to review research concerning diabetes and biomedical implants and device infection, and to critically analyze which diabetic animal model might be advantageous for assessing internal healing adjacent to implanted devices.