Effect of Bone Coverage on Acetabular Implant Stresses in Standard and Dual-Mobility Total Hip Arthroplasty Constructs: A Finite Element Model.

Although mechanical stress in total hip arthroplasty modular head-neck junctions is thought to contribute to the risk of trunnionosis and related metal ion disease in total hip arthroplasty, little is known about mechanical stress in the modular acetabular components. Recent retrieval analyses of dual-mobility constructs have demonstrated corrosion between liner and shell in some dual-mobility acetabular components. The objective of this study was to evaluate acetabular stress as a function of acetabular bone coverage, component modularity, and femoral head diameter. A parametric finite element model was created. The acetabulum was set at 40° of abduction and 15° of anteversion; superolateral bone loss up to 50° was modeled; and 28-mm, 32-mm, 36-mm, and 40-mm head sizes were simulated in stance phase of gait. Fixed polyethylene-bearing, monoblock and modular dual-mobility (MDM) acetabular components were evaluated. For traditional fixed-bearing components, the largest peak stress, 49.5 MPa, was observed with 50° of bone loss and a 28-mm head. The lowest peak stress, 6.3 MPa, occurred with complete bone coverage and a 36-mm head. Peak stress in the MDM construct, 25.1 MPa, concentrated in the chromium-cobalt portion of the construct. Larger head diameters are associated with decreased stress in the acetabular component when bone loss is present. An MDM construct with a stiff inner liner may decrease overall stress in the acetabular construct, but focally increased stress near the rim of uncovered acetabular components may increase the risk of metal-on-metal corrosion. [Orthopedics. 2021;44(5):280-284.].

Protective Effects of Controlled Mechanical Loading of Bone in C57BL6/J Mice Subject to Disuse.

Prolonged reduction in weightbearing causes bone loss. Disuse of bone is associated with recovery from common musculoskeletal injury and trauma, bed rest resulting from various medical conditions, and spaceflight. The hindlimb-suspension rodent model is popular for simulating unloading and disuse. We hypothesized that controlled mechanical loading of the tibia would protect against bone loss occurring from concurrent disuse. Additionally, we hypothesized that areas of high mechanical peak strains (midshaft) would provide more protection than areas of lower strain (distal shaft). Adult C57BL6/J mice were suspended for 3 weeks, with one limb subjected to tibial compression four times per week. µCT imaging was completed at days 0, 11, and 21, in addition to serum analysis. Significant bone loss caused by hindlimb suspension was detected in trabecular bone by day 11 and worsened by day 21 (p < 0.05). Bone loss was also detected in cortical thickness and area fraction by day 21. However, four short bouts per week of compressive loading protected the loaded limb from much of this bone loss. At day 21, we observed a 50% loss in trabecular bone volume/total volume and a 6% loss in midshaft cortical thickness in unloaded limbs, but only 15% and 2% corresponding losses in contralateral loaded limbs (p = 0.001 and p = 0.02). Many bone geometry parameters of the loaded limbs of suspended animals did not significantly differ from non-suspended control limbs. Conversely, this protective effect of loading was not detected in cortical bone at the lower-strained distal shaft. Analysis of bone metabolism markers suggested that the benefits of loading occurred through increased formation instead of decreased resorption. This study uniquely isolates the role of externally applied mechanical loading of the mouse tibia, in the absence of muscle stimulation, in protecting bone from concurrent disuse-related loss, and demonstrates that limited bouts of loading may be highly effective during prolonged disuse. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Collagen-infilled 3D printed scaffolds loaded with miR-148b-transfected bone marrow stem cells improve calvarial bone regeneration in rats.

Differentiation of progenitors in a controlled environment improves the repair of critical-sized calvarial bone defects; however, integrating micro RNA (miRNA) therapy with 3D printed scaffolds still remains a challenge for craniofacial reconstruction. In this study, we aimed to engineer three-dimensional (3D) printed hybrid scaffolds as a new ex situ miR-148b expressing delivery system for osteogenic induction of rat bone marrow stem cells (rBMSCs) in vitro, and also in vivo in critical-sized rat calvarial defects. miR-148b-transfected rBMSCs underwent early differentiation in collagen-infilled 3D printed hybrid scaffolds, expressing significant levels of osteogenic markers compared to non-transfected rBMSCs, as confirmed by gene expression and immunohistochemical staining. Furthermore, after eight weeks of implantation, micro-computed tomography, histology and immunohistochemical staining results indicated that scaffolds loaded with miR-148b-transfected rBMSCs improved bone regeneration considerably compared to the scaffolds loaded with non-transfected rBMSCs and facilitated near-complete repair of critical-sized calvarial defects. In conclusion, our results demonstrate that collagen-infilled 3D printed scaffolds serve as an effective system for miRNA transfected progenitor cells, which has a promising potential for stimulating osteogenesis and calvarial bone repair.

Parametric Finite Element Analysis of Intramedullary Nail Fixation of Proximal Femur Fractures.

Proximal femur fracture fixation with intramedullary nailing relies on stability at the fracture site and integrity of the fixation construct to achieve union. The biomechanics that dictate fracture site stability and implant stress depend on fracture type as well as implant features such as nail length, nail diameter, presence of distal fixation screws, and material composition of the implant. When deciding how to fix a fracture, surgeons have choices in these implant-related design variables. This study models all combinations of a range of implant variables for nine standard AO/OTA proximal femur fractures using finite element analysis. Under simulated maximum load during gait, the maximum stress in the implant and screws as well as interfragmentary motions at the fracture site in the axial and shear directions were computed. The results were separated by fracture type to show the influence of each design variable on measured biomechanical outcomes. Filling the reamed canal with the largest fitting nail diameter reduced axial and shear interfragmentary motion for all fracture types. Nail length was less predictive of shear interfragmentary motion for most simulated fracture types than other construct variables. Furthermore, gapping at the fracture site predisposed the construct to higher implant stresses and larger interfragmentary motions. Clinical significance: Biomechanical outcomes from this computational study can aid in surgical decision-making for optimizing hip fracture fixation with IM nailing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2358-2366, 2019.

Comminuted olecranon fractures: biomechanical testing of locked versus minifragment non-locked plate fixation.

INTRODUCTION: Open reduction and internal fixation has long been accepted as optimal treatment for displaced olecranon fractures based on poor results seen with conservative management. With the presence of comminution, tension-band wiring constructs are contraindicated due to tendency to compress through fragments, thereby shortening the articular segment. Therefore, plate fixation is typically employed. Our hypothesis was that in a comminuted fracture model, 2.7 mm reconstruction plating without locking screws will perform equally to 3.5 mm locked plating in terms of fracture displacement and rotation (shear). MATERIALS AND METHODS: A three-part comminuted olecranon fracture pattern was created in nine matched pairs of cadaveric specimen using an oscillating saw in standardized, reproducible fashion. Each matched pair was then randomized to receive either 2.7 mm reconstruction plating or 3.5 mm proximal ulna locked plating. Random allocation software was used to assign the 2.7 mm plate construct to either the right or left side of each pair with the contralateral receiving the 3.5 mm plate construct. Specimens were cyclically loaded simulating passive range of motion exercises commonly performed during rehabilitation. Displacement and rotation in relation to the long axis of the ulna were measured through motion capture. Fragment gapping and rotation was quantified following 100 cycles at 10 N and again following 100 cycles at 500 N. RESULTS: No significant differences were detected between the 2.7 and 3.5 mm plates in fracture rotation or gapping following loads at 10 N (0.5° and 0.7°; 0.6 and 1.2 mm; respectively; p > 0.05) or 500 N (2.3° and 1.6°; 3.8 and 3.1 mm; respectively; p > 0.05) loading. Fragment rotation and gapping were positively correlated within each plate construct (R 2 > 0.445; p < 0.05). CONCLUSIONS: 2.7 mm plating is an alternative to 3.5 mm locked plating with decreased plate prominence without significantly sacrificing displacement and rotational control. This is beneficial in fracture patterns where the traditional dorsal plating does not offer optimal screw trajectory.

Kinematics of passive flexion following balanced and overstuffed fixed bearing unicondylar knee arthroplasty.

INTRODUCTION: Progression of osteoarthritis in the unreplaced compartment following unicondylar knee arthroplasty (UKA) may be hastened if kinematics is disturbed following UKA implantation. The purpose of this study was to analyze tibiofemoral kinematics of the balanced and overstuffed UKA in comparison with the native knee during passive flexion since this is a common clinical assessment. METHODS: Ten cadaveric knees were mounted to robotic manipulator and underwent passive flexion from 0 to 90°. The kinematic pathway was recorded in the native knee and in the balanced, fixed bearing UKA. The medial UKA was implanted using a measured resection technique. Additionally, a one millimeter thicker tibial insert was installed to simulate the effects of overstuffing. Tibial kinematics in relation to the femur was recorded. RESULTS: Following UKA the tibia was externally rotated, and in valgus relative to the native knee near extension. In flexion, installing the UKA caused the knee to be translated medially and anteriorly. The tibia was translated distally through the entire range of flexion after UKA. Compared to the balanced UKA, overstuffing further increased valgus at full extension and distal translation of the tibia from full extension to 45° flexion. CONCLUSIONS: UKA implantation altered tibiofemoral kinematics in all planes. Differences were small; nevertheless, they may affect tibiofemoral loading patterns. CLINICAL RELEVANCE: Alterations in tibiofemoral kinematics following UKA might have implications for prosthesis failure and progression of osteoarthritis in the remaining compartment. Overstuffing should be avoided as it further increased valgus and did not improve the remaining kinematics.

Frontal plane stability following UKA in a biomechanical study.

INTRODUCTION: Function and kinematics following unicondylar knee arthroplasty (UKA) have been reported to be close to the native knee. Gait, stair climbing and activities of daily living expose the knee joint to a combination of varus and valgus moments. Replacement of the medial compartment via UKA is likely to change the physiologic knee stability and its ability to respond to varus and valgus moments. It was hypothesized that UKA implantation would stiffen the knee and decrease range of motion in the frontal plane. MATERIALS AND METHODS: Six fresh frozen cadaver knees were prepared and mounted in a six-degrees-of-freedom robot. An axial load of 200 N was applied with the knee in 15°, 45° and 90° of flexion. Varus and valgus moments were added, respectively, before and after implantation of medial UKA. Tests were than redone with a thicker polyethylene inlay to simulate overstuffing of the medial compartment. Range of motion in the frontal plane and the tibial response to moments were recorded via the industrial robot. RESULTS: The range of motion in the frontal plane was decreased with both, balanced and overstuffed UKA and shifted towards valgus. When exposed to valgus moments, knees following UKA were stiffer in comparison with the native knee. The effect was even more pronounced with medial overstuffing. CONCLUSION: In UKA, the compressive anatomy is replaced by much stiffer components. This lack of medial compression and relative overstuffing leads to a tighter medial collateral ligament. This drives the trend towards a stiffer joint as documented by a decrease in frontal plane range of motion. Overstuffing should strictly be avoided when performing UKA.

Accuracy of Individualized Custom Tibial Cutting Guides in UKA.

BACKGROUND: Component malposition is one of the major reasons for early failure of unicompartmental knee arthroplasty (UKA). QUESTIONS/PURPOSES: It was investigated how reproducibly patient-specific instrumentation (PSI) achieved preoperatively planned placement of the tibial component in UKA specifically assessing coronal alignment, slope and flexion of the components and axial rotation. PATIENTS AND METHODS: Based on computer tomography models of ten cadaver legs, PSI jigs were generated to guide cuts perpendicular to the tibial axis in the coronal and sagittal planes and in neutral axial rotation. Deviation ≥3° from the designed orientation in a postoperative CT was defined as outside the range of acceptable alignment. RESULTS: Mean coronal alignment was 0.4 ± 3.2° varus with two outliers. Mean slope was 2.8 ± 3.9° with six components in excessive flexion. It was noted that the implants were put in a mean of 1.7 ± 8.0° of external rotation with seven outliers. CONCLUSIONS: PSI helped achieve the planned coronal orientation of the component. The guides were less accurate in setting optimal tray rotation and slope.

Endothelial retention and phenotype on carbonized cardiovascular implant surfaces.

Heart valve disease is an increasing clinical burden for which there is no effective treatment outside of prosthetic replacement. Over the last 20 years, clinicians have increasingly preferred the use of biological prosthetics to mechanical valves despite their superior durability because of the lifelong anticoagulation therapy that is required. Mechanical valve surface engineering has largely focused on being as non-thrombogenic as possible, but despite decades of iteration has had insufficient impact on the anticoagulation burden. In this study, we systematically evaluate the potential for endothelialization of the pyrolytic carbon surface used in mechanical valves. We compared adsorbed adhesion ligand type (collagen I, fibronectin, laminin, and purified adhesion domain fragments GFOGER and FN7-10) and concentration on endothelial adhesion rates and adhesion strength on Medtronic-Hall prosthetic valve surfaces. Regardless of ligand type or concentration, endothelial adhesion strengthening was insufficient for their intended ultra-high shear stress environment. We then hypothesized that microfabricated trenches would reduce shear stress to tolerable levels while maintaining endothelial access to the flow stream, thereby promoting a confluent and anticoagulant endothelial monolayer. Computational fluid dynamics simulations predicted an empirical relationship of channel width, depth, and spacing that would maintain interior surface shear stress within tolerable levels. Endothelial cells seeded to confluence in these channels retained a confluent monolayer when exposed to 600 dyn/cm(2) shear stress for 48 h regardless of applied adhesive ligand. Furthermore, sheared EC expressed a mature anti-coagulant profile, including endothelial nitric oxide synthase (eNOS), VE-cadherin, and significantly downregulated plasminogen activator inhibitor-1 (PAI-1). As a final test, channeled pyrolytic carbon surfaces with confluent EC reduced human platelet adhesion 1000-fold over pyrolytic carbon alone. These results advance a promising biohybrid approach to enable active moderation of local coagulative response in mechanical heart valves, which could significantly extend the utility of this important treatment for heart valve disease.

Comparison of in vitro motion and stability between techniques for index metacarpophalangeal joint radial collateral ligament reconstruction.

PURPOSE: To evaluate a technique using interference screws to secure a tendon graft for reconstruction of the radial collateral ligament (RCL) of the index finger metacarpophalangeal (MCP) joint. We hypothesized that this technique would provide equivalent stability and flexion as a 4-tunnel reconstruction. METHODS: We isolated the RCL in 17 cadaveric index fingers. A cyclic load was applied to the intact RCL across the MCP joint to assess flexion, ulnar deviation at neutral (UD 0), and ulnar deviation at 90° of MCP joint flexion (UD 90). The RCL was excised from its bony origin and insertion. We performed each reconstruction (4-tunnel and interference screw) sequentially on each specimen in a randomized order using a palmaris longus tendon graft. We repeated testing after each reconstruction and compared differences from the intact state between techniques using paired t-tests for all joint positions (flexion/UD 0/UD 90). RESULTS: There was no statistically significant difference in UD 0 or UD 90 between the intact state and after interference screw reconstruction. Compared with the intact state, there was significantly less UD 0 and significantly more UD 90 after 4-tunnel reconstruction. There was no statistically significant difference between techniques when we compared changes in -UD 0 or UD 90. Change in flexion was statistically significantly different, which indicates that the interference screw technique better replicated intact MCP joint flexion compared with the 4-tunnel technique. CONCLUSIONS: Interference screw reconstruction of the index RCL provides stability comparable to 4-tunnel reconstruction and is less technically challenging. These results substantiate our clinical experience that the interference screw technique provides an optimal combination of stability and flexion at the index MCP joint. CLINICAL RELEVANCE: Using an interference screw to reconstruct the index RCL is less challenging than 4-tunnel reconstruction and provides stability and range of motion that closely resemble the native MCP joint.

Anatomy of the radial collateral ligament of the index metacarpophalangeal joint.

PURPOSE: To describe the origin and insertion of the radial collateral ligament (RCL) of the index metacarpophalangeal (MP) joint, relative to the MP joint line and other landmarks readily discernible intraoperatively. METHODS: We dissected 17 fresh-frozen human cadaveric index fingers. We removed all overlying soft tissue from the MP joint except for the proper RCL. We dissected the RCL from its original insertion under loupe magnification while concurrently marking the ligamentous origin and insertion points. We measured distances of these points in relation to the bony landmarks (dorsal, articular, and volar surfaces) using digital photo analysis. The same observer recorded all measurements to reduce systematic error. RESULTS: The center of the metacarpal attachment of the RCL was located 5.4 ± 1.1 mm from the dorsal border of the metacarpal, 8.0 ± 2.2mm from the volar border of the metacarpal, and 10.3 ± 3.2mm from the articular surface of the MP joint. The total width and height of the metacarpal origin site were 5.8 ± 1.6 and 6.4 ± 1.4 mm, respectively. The center of the proximal phalanx attachment of the RCL was located 6.8 ± 1.4 mm from the dorsal border of the proximal phalanx, 5.7 ± 0.9 mm from the volar border of the proximal phalanx, and 4.4 ± 0.8mm from the articular surface of the MP joint. The total width and height of the phalangeal origin site were 5.0 ± 1.1 and 5.7 ± 0.9 mm, respectively. CONCLUSIONS: Our study defines the anatomic origin and insertion of the RCL of the index MP joint in relation to landmarks that are identifiable during surgery. CLINICAL RELEVANCE: We believe this information will be useful to surgeons when repairing or reconstructing the RCL, allowing for recreation of normal RCL anatomy.