Composite Hydrogel Sealants for Annulus Fibrosus Repair.

Intervertebral disc (IVD) herniation is a leading cause of disability and lower back pain, causing enormous socioeconomic burdens. The standard of care for disc herniation is nucleotomy, which alleviates pain but does not repair the annulus fibrosus (AF) defect nor recover the biomechanical function of the disc. Existing bioadhesives for AF repair are limited by insufficient adhesion and significant mechanical and geometrical mismatch with the AF tissue, resulting in the recurrence of protrusion or detachment of bioadhesives. Here, we report a composite hydrogel sealant constructed from a composite of a three-dimensional (3D)-printed thermoplastic polyurethane (TPU) mesh and tough hydrogel. We tailored the fiber angle and volume fraction of the TPU mesh design to match the angle-ply structure and mechanical properties of native AF. Also, we proposed and tested three types of geometrical design of the composite hydrogel sealant to match the defect shape and size. Our results show that the sealant could mimic native AF in terms of the elastic modulus, flexural modulus, and fracture toughness and form strong adhesion with the human AF tissue. The bovine IVD tests show the effectiveness of the composite hydrogel sealant for AF repair and biomechanics recovery and for preventing herniation with its heightened stiffness and superior adhesion. By harnessing the combined capabilities of 3D printing and bioadhesives, these composite hydrogel sealants demonstrate promising potential for diverse applications in tissue repair and regeneration.

Biomechanical and Histological Study of Retrieved LARS Synthetic Ligaments.

BACKGROUND: Synthetic grafts have been used for a number of years in anterior cruciate ligament (ACL) reconstruction surgery. One of the more recent additions to the stable of synthetic ligaments is the Ligament Augmentation and Reconstruction System (LARS) ligament. PURPOSE: To analyze the biomechanics and histology of LARS grafts retrieved due to failure of the device. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 22 LARS ligament grafts that were explanted from patients were sent for analysis. Five new, unused samples of the standard LARS ACL graft were also analyzed. Biomechanical testing was performed: ultimate tensile force, force versus displacement, and stress versus strain were recorded. Histopathological examination was performed looking for degree of fibrous tissue ingrowth as well as the presence of a foreign body reaction. RESULTS: Of the 22 grafts retrieved, 14 were used for ACL grafts, 1 for a lateral collateral ligament graft, 2 for medial collateral ligament grafts, 4 for gluteal tendon augmentation, and 1 for a supraspinatus augmentation. A severe foreign body reaction was found in 86% of the grafts (18/22) and a mild foreign body reaction in the remaining 14% (4/22). Tissue ingrowth was minimal in the majority of ACL grafts; the other grafts showed moderate tissue ingrowth. Maximal tensile force was significantly higher for the new ACL grafts (mean ± SD, 1667 ± 845 N) compared with the retrieved grafts (897 ± 395 N; P < .05). CONCLUSION: This study demonstrated that the vast majority of retrieved LARS artificial ligaments had a florid foreign body reaction. There was minimal tissue ingrowth in ACL grafts and moderate ingrowth in other grafts. Retrieved grafts had a decreased ultimate tensile force, which increased their risk of rupture. CLINICAL RELEVANCE: Surgeons should be cautious in choosing to use these grafts in reconstructive surgery for patients.

Finite element analysis of patient-specific additive-manufactured implants.

Introduction: Bone tumors, characterized by diverse locations and shapes, often necessitate surgical excision followed by custom implant placement to facilitate targeted bone reconstruction. Leveraging additive manufacturing, patient-specific implants can be precisely tailored with complex geometries and desired stiffness, enhancing their suitability for bone ingrowth. Methods: In this work, a finite element model is employed to assess patient-specific lattice implants in femur bones. Our model is validated using experimental data obtained from an animal study (n = 9). Results: The results demonstrate the accuracy of the proposed finite element model in predicting the implant mechanical behavior. The model was used to investigate the influence of reducing the elastic modulus of a solid Ti6Al4V implant by tenfold, revealing that such a reduction had no significant impact on bone behavior under maximum compression and torsion loading. This finding suggests a potential avenue for reducing the endoprosthesis modulus without compromising bone integrity. Discussion: Our research suggests that employing fully lattice implants not only facilitates bone ingrowth but also has the potential to reduce overall implant stiffness. This reduction is crucial in preventing significant bone remodeling associated with stress shielding, a challenge often associated with the high stiffness of fully solid implants. The study highlights the mechanical benefits of utilizing lattice structures in implant design for enhanced patient outcomes.

Fractional Lengthening of Forearm Flexor Tendons: A Cadaveric Biomechanical Analysis.

PURPOSE: Multiple procedures have been described for wrist and finger flexion contractures and spasticity. Fractional lengthening of forearm flexor tendons involves making parallel transverse tenotomies at the musculotendinous junction to elongate the muscle. Currently, there is limited literature to define the biomechanical consequences of this lengthening technique. METHODS: Forty-eight flexor tendons were harvested from eight paired upper limbs including flexor carpi radialis, flexor carpi ulnaris, flexor pollicis longus, and flexor digitorum superficialis tendons. Each tendon that was lengthened was paired with the contralateral tendon as a control. A pair of transverse tenotomies were completed for the fractional lengthening. The first tenotomy was performed at the musculotendinous junction where the tendon narrowed to 75% of its maximal width. The second tenotomy was made 1 cm distal to the first. Tendon length was measured before and after fractional lengthening at a constant resting tension of 1 N. The maximum load at failure of each tendon and the mechanism of failure were each measured and compared with the contralateral side. RESULTS: After fractional lengthening, the mean increase in resting tendon length was 4 mm. When loaded to failure, the mean maximum load of fractionally lengthened tendons was 42% of the mean maximum load of intact tendons. All lengthened tendons failed at the distal tenotomy site. CONCLUSIONS: Fractional lengthening resulted in an increase of 3-6 mm (mean: 4 mm) in tendon length at resting tension. There was a significant loss in tensile strength and load to failure following fractional lengthening compared with an intact musculotendinous unit. CLINICAL RELEVANCE: The reduction in tensile strength following fractional lengthening results in loads at failure that are, in some cases, lower than the estimated forces required to perform basic tasks. Caution during the healing and rehabilitation period is warranted.

Comparison of four in vitro test methods to assess nucleus pulposus replacement device expulsion risk.

Background: Nucleus replacement devices (NRDs) are not routinely used in clinic, predominantly due to the risk of device expulsion. Rigorous in vitro testing may enable failure mechanisms to be identified prior to clinical trials; however, current testing standards do not specify a particular expulsion test. Multiple methods have therefore been developed, complicating comparisons between NRD designs. Thus, this study assessed the effectiveness of four previously reported expulsion testing protocols; hula-hoop (Protocol 1), adapted hula-hoop (Protocol 2), eccentric cycling (Protocol 3), and ramp to failure (Protocol 4), applied to two NRDs, one preformed and one in situ curing. Methods: Nucleus material was removed from 40 bovine tail intervertebral disks. A NRD was inserted posteriorly into each cavity and the disks were subjected to one of four expulsion protocols. Results: NRD response was dependent on both the NRD design and the loading protocol. Protocol 1 resulted in higher migration and earlier failure rates compared to Protocol 2 in both NRDs. The preformed NRD was more likely to migrate when protocols incorporated rotation. The NRDs had equal migration (60%) and expulsion (60%) rates when using unilateral bending and ramp testing. Combining the results of multiple tests revealed complimentary information regarding the NRD response. Conclusions: Adapted hula-hoop (Protocol 2) and ramp to failure (Protocol 4), combined with fluoroscopic analysis, revealed complimentary insights regarding migration and failure risk. Therefore, when adopting the surgical approach and animal model used in this study, it is recommended that NRD performance be assessed using both a cyclic and ramp loading protocol.

The infraacetabular screw versus the antegrade posterior column screw in acetabulum fractures with posterior column involvement: a biomechanical comparison.

INTRODUCTION: Traditionally, plate osteosynthesis of the anterior column combined with an antegrade posterior column screw is used for fixation of anterior column plus posterior hemitransverse (ACPHT) acetabulum fractures. Replacing the posterior column screw with an infraacetabular screw could improve the straightforwardness of acetabulum surgery, as it can be inserted using less invasive approaches, such as the AIP/Stoppa approach, which is a well-established standard approach. However, the biomechanical stability of a plate osteosynthesis combined with an infraacetabular screw instead of an antegrade posterior column screw is unknown. MATERIAL AND METHODS: Two osteosynthesis constructs were compared in a synthetic hemipelvis model with an ACPHT fracture: Suprapectineal plate + antegrade posterior column screw (APCS group) vs. suprapectineal plate + infraacetabular screw (IAS group). A single-leg stance test protocol with an additional passive muscle force and a cyclic loading of 32,000 cycles with a maximum effective load of 2400 N was applied. Interfragmentary motion and rotation of the three main fracture lines were measured. RESULTS: At the posterior hemitransverse fracture line, interfragmentary motion perpendicular to the fracture line (p < 0.001) and shear motion (p < 0.001) and at the high anterior column fracture line, interfragmentary motion longitudinal to the fracture line (p = 0.017) were significantly higher in the IAS group than in the APCS group. On the other hand, interfragmentary motion perpendicular (p = 0.004), longitudinal (p < 0.001) and horizontal to the fracture line (p = 0.004) and shear motion (p < 0.001) were significantly increased at the low anterior column fracture line in the APCS group compared to the IAS group. CONCLUSIONS: Replacing the antegrade posterior column screw with an infraacetabular screw is not recommendable as it results in an increased interfragmentary motion, especially at the posterior hemitransverse component of an ACPHT fracture.

The Injection of Gels Through an Intact Annulus Maintains Biomechanical Performance without Extrusion Risk.

For autologous-disc-derived chondrocyte transplantation (ADCT) a transglutaminase crosslinked gelatine gel and an albumin hyaluronic acid gel, crosslinked with bis-thio-polyethylene glycol, were injected through a syringe into a degenerated intervertebral disc, where they solidified in situ. This biomechanical in vitro study with lumbar bovine motion segments evaluated disc height changes, motion characteristics in a quasi-static spine loading simulators, and the potential extrusion risk of these biomaterials in a complex dynamic multi-axial loading set-up with 100,000 loading cycles. After the injection and formation of the gel in the center of the nucleus, the disc height increase was about 0.3 mm. During cyclic testing, a gradual decrease in height could be detected due to viscoelastic effects and fluid loss. No gel extrusion could be observed for all specimens during the entire test procedure. A macroscopic inspection after dissections showed an accumulation of the solidified gel in the center of the nucleus. The results demonstrate that the injection of in situ solidifying gels through the intact annulus allows for the stable maintenance of the injected gel at the target location, with high potential for use as a suitable scaffold to anchor therapeutically applied cells for disc regeneration within the treated nucleus pulposus.

A Comparative Biomechanical Study of Alternative Medial Collateral Ligament Reconstruction Techniques.

BACKGROUND: There is little evidence of the biomechanical performance of medial collateral ligament (MCL) reconstructions for restoring stability to the MCL-deficient knee regarding valgus, external rotation (ER), and anteromedial rotatory instability (AMRI). HYPOTHESIS: A short isometric reconstruction will better restore stability than a longer superficial MCL (sMCL) reconstruction, and an additional deep MCL (dMCL) graft will better control ER and AMRI than single-strand reconstructions. STUDY DESIGN: Controlled laboratory study. METHODS: Nine cadaveric human knees were tested in a kinematics rig that allowed tibial loading while the knee was flexed-extended 0° to 100°. Optical markers were placed on the femur and tibia and displacements were measured using a stereo camera system. The knee was tested intact, and then after MCL (sMCL + dMCL) transection, and loaded in anterior tibial translation (ATT), ER, varus-valgus, and combined ATT + ER (AMRI loading). Five different isometric MCL reconstructions were tested: isolated long sMCL, a short construct, each with and without dMCL addition, and isolated dMCL reconstruction, using an 8 mm-wide synthetic graft. RESULTS: MCL deficiency caused an increase in ER of 4° at 0° of flexion (P = .271) up to 14° at 100° of flexion (P = .002), and valgus laxity increased by 5° to 8° between 0° and 100° of flexion (P < .024 at 0°-90°). ATT did not increase significantly in isolated MCL deficiency (P > .999). All 5 reconstructions restored native stability across the arc of flexion apart from the isolated long sMCL, which demonstrated residual ER instability (P≤ .047 vs other reconstructions). CONCLUSION: All tested techniques apart from the isolated long sMCL graft are satisfactory in the context of restoring the valgus, ER, and AMRI stability to the MCL-deficient knee in a cadaveric model. CLINICAL RELEVANCE: Contemporary MCL reconstruction techniques fail to control ER and therefore AMRI as they use a long sMCL graft and do not address the dMCL. This study compares 5 MCL reconstruction techniques. Both long and short isometric constructs other than the long sMCL achieved native stability in valgus and ER/AMRI. Double-strand reconstructions (sMCL + dMCL) tended to provide more stability. This study shows which reconstructions demonstrate the best biomechanical performance, informs surgical reconstruction techniques for AMRI, and questions the efficacy of current popular techniques.

Biomechanical Analysis of Headless Compression Screw Versus Tension Band Wiring for Proximal Interphalangeal Joint Arthrodesis.

PURPOSE: Proximal interphalangeal (PIP) joint arthrodesis is a procedure employed to address arthritis, instability, and deformity. Multiple fixation methods are available to maintain stability across the arthrodesis interval, including headless compression screws (HCSs), tension band wiring (TBW), plating, and Kirschner wire constructs. The purpose of this study was to compare the biomechanical properties of the HCS and TBW techniques. METHODS: Thirty-two nonthumb digits from the paired upper limbs of four fresh frozen cadavers were divided into pairs, matching contralateral digits from the same specimen. One PIP joint of each pair was fused with an antegrade 3.5 mm HCS, and the second was fused with TBW using 0.035 in. Kirschner wires with 24-gauge dental wire. Each construct was then stressed to 10 N in the radial deviation, ulnar deviation, flexion, and extension planes, and stiffness (N/mm) was calculated. The fingers were stressed to failure in extension with the ultimate load and mode of failure recorded. RESULTS: When stressed in extension, the HCS construct had a significantly greater mean stiffness than the TBW construct (16.4 N/mm vs 10.8 N/mm). The stiffness in all other planes of motion were similar between the two constructs. The mean ultimate load to failure in extension was 91.4 N for the HCS and 41.9 N for the TBW. The most common mode of failure was fracture of the dorsal lip of the proximal phalanx (13/16) for the HCS and bending of the K-wires (15/16) for TBW. CONCLUSIONS: Arthrodesis of the PIP joint using a HCS resulted in a construct that was significantly stiffer in extension with greater than double the load to failure compared to TBW. CLINICAL RELEVANCE: Although the stiffness required to achieve successful PIP joint arthrodesis has not been well quantified, the HCS proved to be the most favorable construct with respect to initial strength and stability.

Biomechanical effects of cranial closing wedge osteotomy on joint stability in normal canine stifles: an ex vivo study.

BACKGROUND: Cranial closing wedge osteotomy (CCWO) is a functional stabilisation technique for cranial cruciate ligament (CrCL) ruptures. This biomechanical study aimed to evaluate the influence of CCWO on the stability of the stifle joint. Eighteen Beagle stifle joints were divided into two groups: control and CCWO. The stifle joints were analyzed using a six-degree-of-freedom robotic joint biomechanical testing system. The joints were subjected to 30 N in the craniocaudal (CrCd) drawer and proximal compression tests and 1 Nm in the internal-external (IE) rotation test. Each test was performed with an extension position, 135°, and 120° of joint angle. RESULTS: The stifle joints were tested while the CrCLs were intact and then transected. In the drawer test, the CCWO procedure, CrCL transection, and stifle joint flexion increased CrCd displacement. The CCWO procedure and CrCL transection showed an interaction effect. In the compression test, the CCWO procedure decreased and CrCL transection and stifle joint flexion increased displacement. In the IE rotation test, CCWO, CrCL transection, and stifle joint flexion increased the range of motion. CONCLUSIONS: CCWO was expected to provide stability against compressive force but does not contribute to stability in the drawer or rotational tests. In the CCWO-treated stifle joint, instability during the drawer test worsened with CrCL transection. In other words, performing the CCWO procedure when the CrCL function is present is desirable for stabilizing the stifle joint.

An additively manufactured model for preclinical testing of cervical devices.

Purpose: Composite models have become commonplace for the assessment of fixation and stability of total joint replacements; however, there are no comparable models for the cervical spine to evaluate fixation. The goal of this study was to create the framework for a tunable non-homogeneous model of cervical vertebral body by identifying the relationships between strength, in-fill density, and lattice structure and creating a final architectural framework for specific strengths to be applied to the model. Methods: The range of material properties for cervical spine were identified from literature. Using additive manufacturing software, rectangular prints with three lattice structures, gyroid, triangle, zig-zag, and a range of in-fill densities were 3D-printed. The compressive and shear strengths for all combinations were calculated in the axial and coronal planes. Eleven unique vertebral regions were selected to represent the distribution of density. Each bone density was converted to strength and subsequently correlated to the lattice structure and in-fill density with the desired material properties. Finally, a complete cervical vertebra model was 3D-printed to ensure sufficient print quality. Results: Materials testing identified a relationship between in-fill densities and strength for all lattice structures. The axial compressive strength of the gyroid specimens ranged from 1.5 MPa at 10% infill to 31.3 MPa at 100% infill and the triangle structure ranged from 2.7 MPa at 10% infill to 58.4 MPa at 100% infill. Based on these results, a cervical vertebra model was created utilizing cervical cancellous strength values and the corresponding in-fill density and lattice structure combination. This model was then printed with 11 different in-fill densities ranging from 33% gyroid to 84% triangle to ensure successful integration of the non-homogeneous in-fill densities and lattice structures. Conclusions: The findings from this study introduced a framework for using additive manufacturing to create a tunable, customizable biomimetic model of a cervical vertebra.

Biomechanical Comparison of Distal Radioulnar Joint Reconstruction Graft Preparation Techniques.

Background Graft preparation techniques for the Adams-Berger distal radioulnar joint (DRUJ) reconstruction vary among surgeons with insufficient evidence to support any specific technique. Questions/Purposes We compared survival with cyclic loading, absolute elongation, elongation rate, and modes of failure of four graft preparation techniques. Methods Fifteen porcine extensor tendons were divided into three equal groups: tendon only; tendon augmented along its full length with nonlocking 2-0 FiberLoop suture spaced at 6 mm intervals; and tendon with suture at 12 mm intervals. Suture only was also tested. Samples were woven through custom radius- and ulna-simulating jigs mounted on a mechanical testing machine. Samples underwent a staircase cyclic loading protocol and were then inspected visually for the mode of failure. Survival with cyclic loading, absolute elongation, and elongation rate was compared. Results Average survival with cyclic loading of suture-augmented tendon was significantly higher than tendon only. All tendon groups had significantly higher survival compared with suture only. Absolute elongation was subject to variability due to initial nonlinear elongation behavior of samples. The elongation rate was significantly lower with suture compared with all tendon groups. Modes of failure included rupture of the tendon and/or suture at the simulated graft-bone interface and elongation of the entire construct without rupture. Conclusions In this biomechanical study, augmentation of porcine tendons with suture spaced at either 6 or 12 mm for DRUJ reconstruction significantly increased survival to a staircase cyclic loading protocol Clinical Relevance For the Adams-Berger reconstruction, tendon grafts augmented along their entire length by nonabsorbable braided suture are biomechanically superior to tendon alone.

Triple contrast computed tomography reveals site-specific biomechanical differences in the human knee joint-A proof of concept study.

Cartilage and synovial fluid are challenging to observe separately in native computed tomography (CT). We report the use of triple contrast agent (bismuth nanoparticles [BiNPs], CA4+, and gadoteridol) to image and segment cartilage in cadaveric knee joints with a clinical CT scanner. We hypothesize that BiNPs will remain in synovial fluid while the CA4+ and gadoteridol will diffuse into cartilage, allowing (1) segmentation of cartilage, and (2) evaluation of cartilage biomechanical properties based on contrast agent concentrations. To investigate these hypotheses, triple contrast agent was injected into both knee joints of a cadaver (N = 1), imaged with a clinical CT at multiple timepoints during the contrast agent diffusion. Knee joints were extracted, imaged with micro-CT (µCT), and biomechanical properties of the cartilage surface were determined by stress-relaxation mapping. Cartilage was segmented and contrast agent concentrations (CA4+ and gadoteridol) were compared with the biomechanical properties at multiple locations (n = 185). Spearman's correlation between cartilage thickness from clinical CT and reference µCT images verifies successful and reliable segmentation. CA4+ concentration is significantly higher in femoral than in tibial cartilage at 60 min and further timepoints, which corresponds to the higher Young's modulus observed in femoral cartilage. In this pilot study, we show that (1) large BiNPs do not diffuse into cartilage, facilitating straightforward segmentation of human knee joint cartilage in a clinical setting, and (2) CA4+ concentration in cartilage reflects the biomechanical differences between femoral and tibial cartilage. Thus, the triple contrast agent CT shows potential in cartilage morphology and condition estimation in clinical CT.

Biomechanical characterization of the passive porcine stomach.

The complex mechanics of the gastric wall facilitates the main digestive tasks of the stomach. However, the interplay between the mechanical properties of the stomach, its microstructure, and its vital functions is not yet fully understood. Importantly, the pig animal model is widely used in biomedical research for preliminary or ethically prohibited studies of the human digestion system. Therefore, this study aims to thoroughly characterize the mechanical behavior and microstructure of the porcine stomach. For this purpose, multiple quasi-static mechanical tests were carried out with three different loading modes, i.e., planar biaxial extension, radial compression, and simple shear. Stress-relaxation tests complemented the quasi-static experiments to evaluate the deformation and strain-dependent viscoelastic properties. Each experiment was conducted on specimens of the complete stomach wall and two separate layers, mucosa and muscularis, from each of the three gastric regions, i.e., fundus, body, and antrum. The significant preconditioning effects and the considerable regional and layer-specific differences in the tissue response were analyzed. Furthermore, the mechanical experiments were complemented with histology to examine the influence of the microstructural composition on the macrostructural mechanical response and vice versa. Importantly, the shear tests showed lower stresses in the complete wall compared to the single layers which the loose network of submucosal collagen might explain. Also, the stratum arrangement of the muscularis might explain mechanical anisotropy during tensile tests. This study shows that gastric tissue is characterized by a highly heterogeneous microstructure with regional variations in layer composition reflecting not only functional differences but also diverse mechanical behavior. STATEMENT OF SIGNIFICANCE: Unfortunately, only few experimental data on gastric tissue are available for an adequate material parameter and model estimation. The present study therefore combines layer- and region-specific stomach wall mechanics obtained under multiple loading conditions with histological insights into the heterogeneous microstructure. On the one hand, the extensive data sets of this study expand our understanding of the interplay between gastric mechanics, motility and functionality, which could help to identify and treat associated pathologies. On the other hand, such data sets are of high relevance for the constitutive modeling of stomach tissue, and its application in the field of medical engineering, e.g., in the development of surgical staplers and the improvement of bariatric surgical interventions.

Mechanical testing and comparison of porcine tissue, silicones and 3D-printed materials for cardiovascular phantoms.

Background: Cardiovascular phantoms for patient education, pre-operative planning, surgical training, haemodynamic simulation, and device testing may help improve patient care. However, currently used materials may have different mechanical properties compared to biological tissue. Methods/Aim: The aim of this study was to investigate the mechanical properties of 3D-printing and silicone materials in comparison to biological cardiovascular tissues. Uniaxial cyclic tension testing was performed using dumbbell samples from porcine tissue (aorta, pulmonary artery, right and left ventricle). Flexible testing materials included 15 silicone (mixtures) and three 3D-printing materials. The modulus of elasticity was calculated for different deformation ranges. Results: The modulus of elasticity (0%-60%) for the aorta ranged from 0.16 to 0.18 N/mm2, for the pulmonary artery from 0.07 to 0.09 N/mm2, and for the right ventricle as well as the left ventricle short-axis from 0.1 to 0.16 N/mm2. For silicones the range of modulus of elasticity was 0.02-1.16 N/mm2, and for the 3D-printed materials from 0.85 to 1.02 N/mm2. The stress-strain curves of all tissues showed a non-linear behaviour in the cyclic tensile testing, with a distinct toe region, followed by exponential strain hardening behaviour towards the peak elongation. The vessel samples showed a more linear behaviour comparted to myocardial samples. The silicones and 3D printing materials exhibited near-linearity at higher strain ranges, with a decrease in stiffness following the initial deformation. All samples showed a deviation between the loading and unloading curves (hysteresis), and a reduction in peak force over the first few cycles (adaptation effect) at constant deformation. Conclusion: The modulus of elasticity of silicone mixtures is more in agreement to porcine cardiovascular tissues than 3D-printed materials. All synthetic materials showed an almost linear behaviour in the mechanical testing compared to the non-linear behaviour of the biological tissues, probably due to fibre recruitment mechanism in the latter.

Differential expression of the inflammatory ciita gene may be accompanied by altered bone properties in intact sex steroid-deficient female rats.

OBJECTIVE: The class II transactivator (CIITA), encoded by the CIITA gene, controls expression of immune response regulators, which affect bone homeostasis. Previously, we investigated a functional CIITA polymorphism in elderly women. Women carrying the allele associated with lower CIITA levels displayed higher bone mineral density (BMD), but also higher bone loss. The present exploratory study in a rat model sought to investigate effects of differential expression of Ciita on bone structural integrity and strength. Two strains DA (normal-to-high expression) and DA.VRA4 (lower expression) underwent ovariectomy (OVX) or sham-surgery at ~ 14-weeks of age (DA OVX n = 8, sham n = 4; DA.VRA4 OVX n = 10, sham n = 2). After 16-weeks, femoral BMD and bone mineral content (BMC) were measured and morphometry and biomechanical testing performed. RESULTS: In DA.VRA4 rats, BMD/BMC, cross-sectional area and biomechanical properties were lower. Ciita expression was accompanied by OVX-induced changes to cross-sectional area and femoral shaft strength; DA rats had lower maximum load-to-fracture. Thus, while lower Ciita expression associated with lower bone mass, OVX induced changes to structural and mechanical bone properties were less pronounced. CONCLUSION: The data tentatively suggests association between Ciita expression and structural and mechanical bone properties, and a possible role in bone changes resulting from estrogen deficiency.

Biomechanical Comparison of the Simple Suture Technique, Meniscal Matrix-Assisted Repair, and a Novel Meniscus Cap Suture Technique for Complex Meniscal Repair.

Background: Meniscal repair is the gold standard for simple morphology tears. However, when the morphology and chronicity of the tear are less favorable, the success of the standard techniques is reduced. Purpose/Hypothesis: To compare meniscal repair augmented by a new bioresorbable implant (Meniscus Cap) versus a traditional simple suture technique and the currently available augmented repair collagen matrix meniscus wrapping technique. It was hypothesized that the Meniscus Cap suture technique would increase ultimate failure load and less displacement during cyclic loading. Study Design: Controlled laboratory study. Methods: A total of 80 fresh porcine menisci were harvested. Complex tears were created in 60 menisci, and 20 intact menisci were tested as the control group. Repairs were performed on the 60 meniscal tears using 1 of the 3 techniques (20 menisci each): an inside-out H-suture group (SS), the collagen matrix wrapping technique (CMW), and the Meniscus Cap bioresorbable implant group (CM). The menisci were subjected to 500 loading cycles from 4 to 20 N at a frequency of 1 Hz, and the total displacement was recorded. Then, the specimens underwent load to failure testing at a rate of 3.15 mm/s, and the failure mode was noted. Results: After 500 cycles of cyclic loading, there were no significant differences in displacement between the controls and CM group (0.524 vs 0.448 mm; P = .95). The displacement after the CM was significantly smaller compared with the CMW and the SS (0.448 vs 1.077 mm [P = .0009] and 0.448 vs 0.848 mm [P = .04], respectively). The ultimate load to failure was significantly greater for the controls and the CM group compared with the SS and CMW groups (controls, 1278.7 N and CM, 628.5 N vs CMW, 380.1 N and SS, 345.1 N; P < .05). The failure mode was suture breakage (suture failure) for all repairs. Conclusion: In a porcine specimen meniscal repair model, the biomechanical properties of a novel Meniscus Cap repair technique were superior to that of the simple suture and CMW techniques. Clinical Relevance: The results suggest that the Meniscal Cap repair technique may provide sufficient primary stability of the meniscal fixation even in the cases of complex meniscal tears.

Influence of bone density on stability in TBW.

Osteoporosis is a common disease that leads to a reduction in bone density and increases the risk of fractures. Stable surgical treatment is particularly important for these fractures. The aim of this study was to examine the influence of bone density in the area of ​​the proximal ulna on the failure of the fixation technique of K-wires in tension band wiring (TBW). We provided 10 ulna specimens with TBW and biomechanically examined the pull-out strength of bi- and tricortical K-wires. Bone density measurement was performed using qCT. In the paired t-test, the tricortical group showed a significantly higher pull-out strength in relation to bone density than the bicortical group (p = 0.001). Furthermore, the Pearson correlation showed a high influence of bone density on pull-out strength in the tricortical group (r = 0.544), but without significance (p = 0.100).Our work shows that bone density has a direct effect on the pull-out strength of K-wires in TBW. TBW should therefore be used as osteosynthesis technique, especially in young patients with non-osteoporotic bones. In the case of osteoporotic fractures, alternative procedures should be preferred.

Stabilization and Gap Formation of Adjustable Versus Fixed Primary ACL Repair With Internal Brace: An in Vitro Full-Construct Biomechanical Cadaveric Study.

Background: A knotless, tensionable primary anterior cruciate ligament (ACL) repair system preloaded with an internal brace has been released. Currently, there is no biomechanical data on the stabilization and gap formation behavior of the adjustable system when compared with fixed repairs in human ACL tissue. Hypothesis: That knotless adjustable suture repair with an internal brace would provide overall higher construct stability and greater load share on the ACL with less gap formation compared with fixed repair. Study Design: Controlled laboratory study. Methods: Human cadaveric knees were utilized for internal braced ACL repair constructs (each group n = 16). Two fixed groups consisting of a single-cinch loop (SCL), cortical button (SCL group), and knotless suture-anchor (anchor group) were compared with an SCL-adjustable loop device (SCL-ALD) group. Testing was performed at 4 different peak loads (50, 150, 250, 350 N) over 4000 cycles at 0.75 Hz including suture repair preconditioning (10 cycles at 0.5 Hz) for SCL-ALD. Specimens were ultimately pulled to failure with a cut internal brace. The final loading situation of the construct and ACL repair with gap formation and ultimate strength were evaluated. Results: Peak elongation at various peak loads showed a significantly higher (P < .001) stabilization of SCL-ALD when compared with both fixed groups. There was a significantly higher (P < .001) load share of SCL-ALD, especially at lower loads (48% of 50 N), and the gap formation remained restricted up to 250 N. With only a little load share on the fixed constructs (<6%) at lower loads (50, 150 N), gap formation in these groups started at a load of 150 N, leading to significantly higher gaps (P < .001). The ultimate failure load for SCL-ALD and anchor groups was significantly increased (P < .001) as compared with SCL. The stiffness of SCL-ALD (62.9 ± 10.6 N/mm) was significantly increased (P < .001). Conclusion: Internal braced knotless adjustable fixation for ACL repair with preconditioning of the suture repaired ligament increased the overall stabilization with higher load share on the ACL and restricted gap formation (<0.5 mm up to 350 N) compared with fixed suture repair. All internal braced repairs restored stability according to native ACL function. Clinical Relevance: Adjustable ACL repair improved the mechanical characteristics and reduced gap formation, but the overall clinical significance on healing remains unclear.

Biomechanical comparison of shoelace suture technique for repairing calcaneal tendon.

BACKGROUND: The biomechanical assessment of tendon repair is essential for the evaluation of different tendon suturing techniques. The shoelace suture technique with absorbable Vicryl® is a modified technique of Achilles tendon repair that may have biomechanical advantages depending on the number of threads used and the direction of the suture. PURPOSE: To evaluate the creep under constant pre-load, the stiffness, the maximum strength, and the failure mode for three different configurations of the shoelace suture in a bovine tendon biomechanical model. STUDY DESIGN: Controlled Laboratory Study. METHODS: 36 bovine Achilles tendon specimens were acquired and divided into three test groups of 12 Achilles tendons each. A model of the calcaneal tendon rupture was created through a transverse cut with a scalpel, performed 5 centimeters proximal to the calcaneal bone insertion. Group 1 was repaired using the simple shoelace technique with just one suture. Group 2 was repaired using the shoelace technique with three sutures individually sutured from distal to proximal at the site of rupture. Group 3 was repaired using the shoelace technique with three sutures individually sutured from proximal to distal at the site of rupture. RESULTS: System creep after constant pre-load was 5.9 ± 2.5 mm, 3.0 ± 0.4 mm and 2.9 ± 0.4 mm for groups 1, 2 and 3, respectively. The system's stiffness was 23.2 ± 2.8 N/mm, 30.3 ± 1.1 N/mm and 29.8 ± 2.3 N/mm for groups 1, 2 and 3, respectively. In the final load-to-failure test, the ultimate load force (ULF) was 158.2 ± 27.5 N, 346.5 ± 47.6 N and 358.1 ± 41.6 N for groups 1, 2 and 3, respectively. There was statistical significance in the comparative tests between groups 1-2 and 1-3 in terms of means of creep, system stiffness and maximum system strength. No statistically significant difference was found between groups 2 and 3 when analyzing creep, system stiffness and ULF. Suture breakage was the prevalent mode of failure for all tested groups. CONCLUSION: The shoelace with three sutures significantly reduced creep in the preloading phase and increased the stiffness and ultimate load force. The biomechanical results demonstrate better overall mechanical performance of the technique than the simple shoelace technique. The better mechanical performance indicates that the shoelace with three sutures could result in early postoperative rehabilitation. CLINICAL RELEVANCE: This study indicates that the shoelace suture technique with three sutures is biomechanically strong and stiff, being a possible therapeutic option to be used.