Biomechanical properties of the repaired and non-repaired rat supraspinatus tendon in the acute postoperative period.

PURPOSE: The rat rotator cuff (RC) model is used to study RC pathology and potential treatment; however, native scar-mediated healing allows the rat RC to recover at 4-6 weeks but little is known about acute healing. This study characterized the properties of the repaired and non-repaired rat RC following surgical detachment. MATERIALS AND METHODS: Forty-eight rats underwent surgical RC detachment and received surgical repair (Repair) or left unrepaired (Defect) to either 12 or 19 days. Healthy controls were obtained from contralateral limbs. Biomechanical properties were assessed using stress relaxation and failure testing and mechanical modeling performed using quasilinear viscoelastic (QLV) and structurally based elastic models. Histology and micro-magnetic resonance imaging were used to qualitatively grade tendon-to-bone healing. RESULTS: Repair and Defect exhibited significantly inferior mechanical properties compared to Healthy at both time points. Repair had significant increases in peak, equilibrium, and ultimate stress, modulus, and stiffness and significant decreases in cross-sectional area, % relaxation, and QLV constant "C" between 12 and 19 days, whereas Defect showed no change. CONCLUSIONS: This study demonstrates acute differences in mechanical properties of the rat supraspinatus tendon in the presence and absence of surgical repair. Understanding the longitudinal recovery of mechanical properties can facilitate more accurate characterization of RC pathology or future treatments.

Widespread cryptic viral infections in lotic biofilms.

Viruses have important impacts on aquatic microbial ecology and have been studied at length in the global ocean. However, the roles of bacteriophages in lotic ecosystems, particularly in benthic biofilms, have been largely under-studied. The main goals of this work were to determine whether viruses are consistent members of natural benthic biofilm communities of freshwater streams; whether temperate phages are present and active in such biofilms; and whether community profiling approaches like RAPD-PCR can be adapted to characterize biofilm virus communities. Results from both field and laboratory experiments suggest that viruses are consistent members of lotic biofilm communities. Interestingly, prophage induction was statistically significant but only a small percentage of the total bacterial population appeared to harbor prophage or engaged in induction. Finally, while the use of RAPD-PCR for the community level profiling of biofilm viral communities suggests temporal change in response to biofilm maturity, further refinements are required for broad-scale quantitative application.

Investigation of RNA interference to suppress expression of full-length and fragment human huntingtin.

The use of RNA interference (RNAi) to suppress the expression of genes has drastically improved the ability to examine gene function and is now being considered as a therapeutic approach for many diseases including genetic forms of neurodegenerative disease. Recently, research has focused on RNAi for the treatment of Huntington's and other polyglutamine diseases. In this work we explored the efficacy and specificity of short hairpin RNAs to target human huntingtin mRNA. We found two sequences that are specific for, and efficiently suppress human huntingtin mRNA. Mouse cell lines that stably harbored human short hairpin RNA constructs specifically inhibited the expression of human huntingtin supplied by transfected expression plasmids. However, these same constructs were unable to stably suppress endogenous human huntingtin when stably transfected into human 293 cells, despite effectively knocking down expression of huntingtin in transient transfection. These results demonstrate the efficacy and specificity of RNAi as a tool to target human huntingtin in RNAi-based therapies but point toward potential problems, possibly cell-type specific, regarding stable suppression of human huntingtin.

Retropharyngeal Steroids and Dysphagia Following Multilevel Anterior Cervical Surgery.

STUDY DESIGN: A retrospective case-control study. OBJECTIVE: The aim of this study was to determine the effect of retropharyngeal steroids on postoperative dysphagia scores and clinical outcomes following multilevel anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA: Dysphagia is a well-known complication following ACDF surgery and increased rates of dysphagia are seen with increased levels of surgery. Retropharyngeal steroids have been shown to decrease painful swallowing and prevertebral soft tissue (PSTS) swelling in 1- and 2-level anterior cervical surgery. METHODS: A retrospective review of 44 patients undergoing multilevel (2-, 3-, 4-level) ACDF. Twenty-two patients who received retropharyngeal steroids (methylprednisone) placed on a collagen sponge at the time of surgery were compared with a matched cohort of controls who did not receive local steroids. Postoperative day 1 and 6-week radiographs were analyzed for differences in PSTS. Clinical outcomes were measured pre-operatively, 6 weeks, and 3 months postoperatively utilizing the Neck Disability Index (NDI), the Bazaz-Yoo Dysphagia Scoring System, and Eat Assessment Tool (EAT-10). RESULTS: Significant improvement in dysphagia scores were seen utilizing both outcome measures. Bazaz-Yoo scores were significantly better at both 6 weeks and 3 months in patients receiving local steroids compared with controls (P = 0.008 and P = 0.022, respectively). EAT-10 showed similar improvement of the steroid group versus control at 6 weeks and 3 months (P = 0.067 and P = 0.012, respectively). A trend toward decreased PSTS was found with locally delivered steroids on initial postoperative radiographs (P = 0.07), but was no longer evident at 6 weeks. NDI, although improved from pre-operative scores, failed to demonstrate significant differences between groups. No differences in length of stay or complications were observed between the groups. CONCLUSION: The use of retropharyngeal steroids resulted in decreased rates of dysphagia following multilevel ACDF. Locally delivered methylprednisone did not result in increased rates of short-term postoperative complications. LEVEL OF EVIDENCE: 4.

The influence of testing angle on the biomechanical properties of the rat supraspinatus tendon.

Rotator cuff tears are a common shoulder pathology. The rat supraspinatus tendon model is commonly employed for preclinical assessment of rotator cuff pathology or regeneration. However, there is a lack of a standardized biomechanical testing protocol; previous studies have tested the tendon at abduction angles ranging from -15° to 90°. This study aimed to assess the effect of abduction/testing angle on the biomechanical properties of the rat supraspinatus tendon. Fourty-eight shoulders (n=12/group) from healthy Sprague-Dawley rats were randomized to 4 testing angle groups: 0° (corresponding to 90° abduction), 30°, 60°, and 90° (0° abduction). Biomechanical testing of the supraspinatus was performed, consisting of stress-relaxation and load-to-failure. Mechanical properties were calculated, and nonlinear tensile modeling was performed via the Quasilinear Viscoelastic (QLV) and Structurally Based Elastic (SBE) models. Results indicate that testing angle significantly affects supraspinatus tendon biomechanics. Stiffness and modulus significantly decreased with increasing testing angle (stiffness: 20.93±5.8N/mm at 0° vs. 6.12±1.0N/mm at 90°, P<.001; modulus: 59.51±34.0MPa at 0° vs. 22.37±7.4MPa at 90°, P=.002). Testing angle correlated significantly to ultimate strain, yield strain, and all coefficients of the SBE and QLV models, implying differences in collagen fiber crimp patterns and viscoelastic behavior as a function of testing angle. These results suggest that differences in testing methodology, in particular testing angle, significantly affect the measured mechanical properties of the supraspinatus tendon. Future studies may consider utilizing testing angles of 0°-30°, at which tendon stiffness is maximized, and full standardization of rat rotator cuff testing protocols is necessary.

The impact of rotator cuff deficiency on structure, mechanical properties, and gene expression profiles of the long head of the biceps tendon (LHBT): Implications for management of the LHBT during primary shoulder arthroplasty.

The long head of the biceps tendon (LHBT) occupies a unique proximal intra-articular and distal extra-articular position within the human shoulder. In the presence of a rotator cuff (RC) tear, the LHBT is recruited into an accelerated role undergoing potential mechanical and biochemical degeneration. Intra-articular sections of the LHBT were harvested during primary shoulder arthroplasty from patients with an intact or deficient RC. LHBTs were stained (H&E, Alcian Blue) and subjected to histologic analysis using the semiquantitative Bonar scale and measurement of collagen orientation. LHBTs (n = 12 per group) were also subjected to gene-expression analyses via an RT(2) -PCR Profiler Array quantifying 84 genes associated with cell-cell and cell-matrix interactions. LHBTs (n = 18 per group) were biomechanically tested with both stress-relaxation and load-to-failure protocols and subsequently modeled with the Quasilinear Viscoelastic (QLV) and Structural-Based Elastic (SBE) models. While no histologic differences were observed, significant differences in mechanical testing, and viscoelastic modeling parameters were found. PCR arrays identified five genes that were differentially expressed between RC-intact and RC-deficient LHBT groups. LHBTs display signs of pathology regardless of RC status in the arthroplasty population, which may be secondary to both glenohumeral joint arthritis and the additional mechanical role of the LHBT in this population.

Biomechanical Characterization of a Model of Noninvasive, Traumatic Anterior Cruciate Ligament Injury in the Rat.

The onset of post-traumatic osteoarthritis (PTOA) remains prevalent following traumatic joint injury such as anterior cruciate ligament (ACL) rupture, and animal models are important for studying the pathomechanisms of PTOA. Noninvasive ACL injury using the tibial compression model in the rat has not been characterized, and it may represent a more clinically relevant model than the common surgical ACL transection model. This study employed four loading profiles to induce ACL injury, in which motion capture analysis was performed, followed by quantitative joint laxity testing. High-speed, high-displacement loading repeatedly induces complete ACL injury, which causes significant increases in anterior-posterior and varus laxity. No loading protocol induced valgus laxity. Tibial internal rotation and anterior subluxation occurs up to the point of ACL failure, after which the tibia rotates externally as it subluxes over the femoral condyles. High displacement was more determinative of ACL injury compared to high speed. Low-speed protocols induced ACL avulsion from the femoral footprint whereas high-speed protocols caused either midsubstance rupture, avulsion, or a combination injury of avulsion and midsubstance rupture. This repeatable, noninvasive ACL injury protocol can be utilized in studies assessing PTOA or ACL reconstruction in the rat.

Early deprivation alters the vocalization behavior of neonates directing maternal attention in a rat model of child neglect.

Animal models of child neglect (known as maternal separation or early deprivation) have suggested a causal link to subsequent depression and/or anxiety in children. In this experiment, the acoustical features of the ultrasonic calls emitted by a rat pup when separated from its dam were analyzed as well as the maternal behavior when the dam was allowed to retrieve the pup. Bout structure and harmonic double shifts did differ between controls and "neglected" pups, as did maternal attention. This model will be used to determine neural mechanisms underlying deficits in attachment behavior.

Biomechanical evaluation of the TightRope versus traditional docking ulnar collateral ligament reconstruction technique: kinematic and failure testing.

BACKGROUND: Numerous variations of ulnar collateral ligament (UCL) reconstruction have been described since the original technique by Jobe et al. Purpose/ HYPOTHESIS: To biomechanically compare the new TightRope technique and the traditional ulnar bone tunnels as used in the docking technique. The hypothesis was that the TightRope technique would exhibit improved kinematics and comparable failure properties. STUDY DESIGN: Controlled laboratory study. METHODS: Seven matched pairs of cadaveric arms (mean age, 44.71 years) were tested in both the native state and reconstructed state. Kinematics were assessed at 15° to 90° of flexion by applying a 1.5-N·m valgus torque and measuring the resultant angular displacement. Failure testing was performed by loading to failure at 4.5 deg/s in 70° of flexion. Sides of a matched pair were randomized to the TightRope (TR) and docking (DO) techniques after testing the native state. RESULTS: There was no significant difference in kinematic results between the native state and reconstructed state in either the TR or DO group at 15° to 75° of flexion. At 90°, the TR group had significantly higher angular displacement (2.23° ± 1.0°) compared with the native state (1.31° ± 0.7°) (P = .020). The TR-reconstructed specimens had significantly lower initial stiffness (49.34 ± 19.3 N·m/rad vs 82.47 ± 36.0 N·m/rad, respectively; P = .007) and total stiffness (53.81 ± 27.8 N·m/rad vs 101.06 ± 34.4 N·m/rad, respectively; P < .001) than did the paired native specimens. In addition, the TR-reconstructed specimens had significantly lower torsional torque at 5° of valgus rotation (mean, 4.61 ± 2.2 N·m vs 7.62 ± 3.7 N·m, respectively; P = .010), at 15° of valgus rotation (12.24 ± 4.4 N·m vs 20.65 ± 6.8 N·m, respectively; P = .002), and at ultimate failure (19.18 ± 7.5 N·m vs 25.42 ± 7.1 N·m, respectively; P = .025) than did the paired native specimens. There was no significant difference in torsional torque between the TR and DO groups at 5° of valgus rotation (4.61 ± 2.2 N·m vs 4.09 ± 1.7 N·m, respectively; P = .644), at 15° of valgus rotation (12.24 ± 4.4 N·m vs 17.94 ± 7.23 N·m, respectively; P = .178), or at failure (19.18 ± 7.5 N·m vs 23.19 ± 10.6 N·m, respectively; P = .444). The DO group exhibited significantly higher angular displacement at failure than did the native state (28.12° ± 8.5° vs 18.04° ± 4.8°, respectively; P = .009), but there was no difference at 3 N·m of loading. There was no significant difference in angular displacement either at 3 N·m or at failure between the native state and reconstructed state in the TR group. CONCLUSION: Both the TR and DO techniques restored native joint kinematics from 15° to 75° of flexion under low loading conditions. While the TR technique exhibited inferior failure torque compared with the native state, the DO technique did not differ from the native state. No differences were found between the TR and DO groups when compared directly. The DO technique restored valgus stability under high loading to a greater extent than did the TR technique but also failed at higher angular displacement. CLINICAL RELEVANCE: Strong postoperative UCL reconstruction fixation is important to restore ulnotrochlear joint stability. Our study demonstrates that the new TR technique has comparable kinematic and failure properties to the traditional DO technique.

The GraftLink ulnar collateral ligament reconstruction: biomechanical comparison with the docking technique in both kinematics and failure tests.

BACKGROUND: Ulnar collateral ligament (UCL) reconstruction aims to restore valgus stability, and numerous techniques have been described in the literature. HYPOTHESIS/ PURPOSE: To biomechanically compare the GraftLink (GL) technique with traditional bone tunnels used in the docking (DO) technique. It is hypothesized that the GL method will offer a stiffer, less lax construct compared with the DO. STUDY DESIGN: Controlled laboratory study. METHODS: Native and reconstructed states were tested in 7 matched pairs of cadaveric arms. To test kinematics, a 1.5-N·m valgus torque was applied and the resultant displacement at 15° to 90° of flexion was measured. Dissipated energy and the torque at the peak of the 10th cycle of preconditioning were analyzed during kinematic tests. Failure testing was performed by internal rotation of the humerus at 4.5 deg/s in 70° of flexion. Ulnotrochlear joint (UTJ) gapping was quantified during failure tests by use of video tracking. RESULTS: Kinematics testing revealed no differences between the native state and the reconstructed state in either the DO or the GL group at any flexion angle. Stiffness was lower in the reconstructed specimens in both the DO (39.92 N·m/rad) and GL (50.74 N·m/rad) groups compared with their matched native states (DO Native, 71.41 N·m/rad, P = .005; GL Native, 86.36 N·m/rad, P = .002). There was no difference in stiffness between DO and GL. Reconstructed specimens in the GL group had lower torque at failure compared with native specimens (17.404 N·m vs 24.63 N·m, P = .038), but there was no difference in the DO group at failure. There was no difference in torque at failure between DO and GL. The DO exhibited higher angular displacement at failure compared with the native state (34.21° vs 21.79°, P = .010) and compared with the GL when normalized (1.58-fold vs 1.19-fold, P = .039). Compared with their native states, both DO and GL had significantly higher UTJ gapping at 3 N·m and at failure. The DO had significantly higher normalized UTJ gapping than the GL at 3 N·m (P = .037) and at failure (P = .043). CONCLUSION: The DO and GL both restored joint kinematics under low loading conditions. Although less stiff, the GL exhibited lower joint gapping and laxity than did the DO. CLINICAL RELEVANCE: Understanding the biomechanics of UCL reconstruction has significant implications for postoperative management as it relates to early rehabilitation. Biomechanically inferior constructs could risk graft failure or early loosening during rehabilitation, and comparing the biomechanics of new techniques to established, widely used procedures such as the docking technique can provide important information about the immediate postoperative performance.