Kent N. Bachus

A Water-Borne Adhesive Modeled after the Sandcastle Glue of P. californica

Polyacrylate glue protein analogs of the glue secreted by Phragmatopoma californica, a marine polycheate, were synthesized with phosphate, primary amine, and catechol sidechains with molar ratios similar to the natural glue proteins. Aqueous mixtures of the mimetic polyelectrolytes condensed into liquid complex coacervates around neutral pH. Wet cortical bone specimens bonded with the coacervates, oxidatively crosslinked through catechol sidechains, had bond strengths nearly 40% of the strength of a commercial cyanoacrylate. The unique material properties of complex coacervates may be ideal for development of clinically useful adhesives and other biomaterials.

The effects of drilling force on cortical temperatures and their duration: an in vitro study.

Bone loss due to thermonecrosis may weaken the purchase of surgically placed screws and pins, causing them to loosen post-operatively. The goal of this study was to determine how differences in applied drilling forces affect the temperature of cortical tissue near the drilling site. Results from thermocouples placed into fresh cortical bone indicate that increasing the applied drilling force resulted in a significant decrease (P=0.001) of maximum cortical temperatures. Furthermore, increasing the drilling force resulted in a significant decrease (P=0.001) in the average duration of temperature elevations above 50 degrees C. The results of the current study demonstrate that by the application of a larger force to the drill, both maximum cortical temperatures and their duration above 50 degrees C may be effectively reduced, decreasing the potential for thermal necrosis in the neighboring cortical bone.

Determining mineral content variations in bone using backscattered electron imaging

The mechanical properties of bones are greatly influenced by the ratio of organic constituents to mineral. Determination of bone mineral content on a macroscopic scale is straightforward, but microscopic variations, which can yield new insights into remodelling activities, mechanical strength, and integrity, are profoundly more difficult to measure. Measurement of microscopic mineral content variations in bone material has traditionally been performed using microradiography. Backscattered electron (BSE) imaging is a technique with significantly better resolution than microradiography with demonstrated consistency, and it does not suffer from projection-effect errors. We report results demonstrating the applicability of quantitative BSE imaging as a tool for measuring microscopic mineral content variations in bones representing a broad range of mineralization. Bones from ten species were analyzed with Fourier-transformed infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectrometry, ash measurements, and BSE imaging. BSE image intensity (graylevel) had a very strong positive correlation to mineral (ash) content. Compositional and crystallographic variations among bones had negligible influence on backscattered electron graylevels. The present study confirms the use of BSE imaging as a tool to measure the microscopic mineral variability in a broad range of mineralized tissues.

The effect of reconstruction of the medial patellofemoral ligament on patellar tracking.

We evaluated patellar tracking in six cadaveric knees with the medial restraints intact and then sectioned to determine their contribution to lateral translation of the patella with and without a lateral force on the patella. The medial patellofemoral ligament was then reconstructed with a gracilis tendon graft and patellar tracking was again evaluated. The knees were extended using a materials testing machine, and patellar tracking was measured with a position sensing system. With no lateral force applied to the patella, patellar tracking was unaffected by the presence or absence of the medial restraints or by reconstruction of the medial patellofemoral ligament. With a lateral force applied to the patella, patellar tracking was changed significantly by the loss of the medial restraints. Normal patellar tracking was substantially restored by reconstruction of the medial patellofemoral ligament.

Dynamic Cervical Plates: Biomechanical Evaluation of Load Sharing and Stiffness

Study Design. An in vitro biomechanical study using a simulated cervical corpectomy model to compare the load-sharing properties and stiffnesses of two static and two dynamic cervical plates. Objectives. To evaluate the load-sharing properties of the instrumentation with a full-length graft and with 10% graft subsidence and to measure the stiffness of the instrumentation systems about the axes of flexion–extension, lateral bending, and axial torsion under these same conditions. Summary of Background Data. No published reports comparing conventional and dynamic cervical plates exist. Methods. Six specimens of each of the four plate types were mounted on ultra-high molecular weight polyethylene-simulated vertebral bodies. A custom four-axis spine simulator applied pure flexion–extension, lateral bending, and axial torsion moments under a constant 50 N axial compressive load. Load sharing was calculated through a range of applied axial loads up to 120 N. The stiffness of each construct was calculated in response to ±2.5 Nm moments about each axis of rotation with a full-length graft, a 10% shortened graft, and no graft. ANOVA and Fisher’s post hoc test were used to determine statistical significance (alpha ≤ 0.05). Results. The two locked cervical plates (CSLP and Orion) and the ABC dynamic plate were similar in flexion–extension, lateral bending, and torsional stiffness. The DOC dynamic plate was consistently less stiff. The Orion plate load shared significantly less than the other three plates with a full graft. Both the ABC and the DOC plates were able to load share with a shortened graft, whereas the conventional plates were not. Conclusions. All plates tested effectively load share with a full-length graft, whereas the two dynamic cervical plates tested load share more effectively than the locked plates with simulated graft subsidence. The effect of dynamization on stiffness is dependent on plate design.

Effect of the Tibial Cut on Subsidence Following Total Knee Arthroplasty

In 33 total knee arthroplasties (TKAs) using instrumentation designed to cut the tibia with 0 degree posterior slope, ten tibial components demonstrated at least 2 mm of tibial component subsidence. These subsided components were implanted onto tibiae with an average of 8 degrees +/- 2 degrees difference between the preoperative, anatomic posterior slope and their postoperative posterior slope. The remaining 23 components, without subsidence, were implanted onto tibiae cut within 2 degrees +/- 2 degrees of their anatomic slope. To help understand these clinical observations, a laboratory study was performed to compare the load carrying capacity and the stiffness of tibial subchondral bone following two types of tibial cuts: one made perpendicular to the long axis of the tibia and the other made parallel to the articular surface of the tibia. Mock tibial baseplates mounted on paired cadaver tibiae were loaded in compression and force displacement curves were recorded. Tibiae cut parallel to the surface exhibited 40% greater load carrying capacity and 70% greater stiffness than the paired tibiae cut perpendicular to the long axis. The biomechanical data of this study indicated that cutting the tibia perpendicular to the long axis results in weaker bone that may be inadequate to support a tibial component. This may explain the higher incidence of clinical subsidence if the tibial cut is not made approximately parallel to the anatomic slope.

The influence of tendon length and fit on the strength of a tendon-bone tunnel complex. A biomechanical and histologic study in the dog.

Using a dog model, we examined the influence of tendon length and fit within a bone tunnel on the pull-out strength of a tendon-bone tunnel complex at 6 weeks after fixation. Fourteen adult mongrel dogs (weight, 25 to 30 kg) underwent bilateral hindlimb surgery in which the extensor digitorum longus tendon was transplanted into an extraarticular metaphyseal bone tunnel. Our findings demonstrated that pull-out strength at 6 weeks was enhanced by increasing the length of tendon within the tunnel. The average load to failure with 1 cm of tendon within the tunnel was 153.7 78.6 N, compared with 265.5 93.3 N for the specimens with 2 cm of tendon in the tunnel. Tendon fit within the tunnel was also found to be important. The average load to failure when a tendon was placed in a 4.2-mm diameter tunnel was 301 61 N at 6 weeks. The average load to failure when the tendon was placed within a 6-mm diameter tunnel was 228 65 N. These differences were statistically different. Histologically, the interface between the tendon and bone appeared to be most mature when there was intimate bone-to-tendon contact. These data suggest that maximizing tendon length within a bone tunnel and minimizing tendon-tunnel diameter mismatch will maximize the strength of a tendon-bone tunnel complex at 6 weeks.

Effect of Lateral Meniscal Allograft Sizing on Contact Mechanics of the Lateral Tibial Plateau An Experimental Study in Human Cadaveric Knee Joints

Background A mismatch of the original lateral meniscus and a lateral meniscus allograft by inaccurate preoperative radiographic sizing can have significant consequences on ultimate function. Hypothesis The size of a lateral meniscal allograft affects the contact mechanics of the femoral condyle on the tibial plateau. Study Design Controlled laboratory study. Methods Four right and 2 left knees were tested as intact joints, after meniscectomy, and after replantation with the original menisci and 16 right or 9 left human, fresh-frozen lateral meniscal allografts, respectively. The allografts were allocated into 7 groups according to their outer and inner anteroposterior and mediolateral diameters. Biomechanical testing was performed as compressive loadings with constrained motions in extension and 30° of flexion. Measurements were done with Fuji pressure-sensitive films for contact parameters of the direct femorotibial and meniscotibial contact. Results Oversized lateral meniscal allografts led to greater forces across the articular cartilage, whereas undersized allografts resulted in normal forces across the articular cartilage but greater forces across the meniscus. Two undersized transplants failed. Most of the contact parameters of allografts 10% smaller or larger than the original menisci were in the range of the intact knees. The knees after meniscectomy showed greater forces of the direct femorotibial contact areas than did the intact knees and the knees with the replanted original menisci. The contact mechanics of the knees with the replanted original menisci were close to normal. Conclusion The size of a lateral meniscal allograft has a significant effect on the contact mechanics of the tibial plateau. Clinical Relevance Preoperative radiographic sizing needs to be performed precisely to identify a suitable lateral meniscal allograft. A mismatch may be the reason for failure of the allograft or subsequent development of degenerative changes. A mismatch on graft selection of less than 10% of the size of the original meniscus may be acceptable.

Cyclic Loading of Olecranon Fracture Fixation Constructs

Background: Despite the good results that are usually reported after fixation at the sites of olecranon fractures and osteotomies, problems such as loss of fixation, nonunion, and the need for revision surgery are still encountered. Various types of fixation have been recommended, but few have been evaluated with use of clinically relevant cyclic load testing at appropriate levels of stress. The purpose of the present study was to test multiple olecranon fixation techniques under physiologic cyclic loads. Methods: We studied ten cadaveric elbows with use of cyclic loading that simulated (1) active range of motion and (2) pushing up from a chair. Each specimen underwent fixation of a simulated 50% transverse olecranon fracture with use of intramedullary and cortically fixed tension band constructs (in randomized order) followed by fixation with a 7.3-mm-diameter cancellous screw with and without a tension band. Displacement transducers were placed posteriorly on the tension side and anteriorly near the articular surface. Results: Both configurations involving the 7.3-mm-diameter cancellous screw provided the most stable fixation—nearly five times better than that provided by the Kirschner-wire techniques. Use of the tension band in conjunction with the intramedullary screw improved the stability of fixation. In none of the constructs did the AO tension band result in compression across the osteotomy gap. Conclusions and Clinical Relevance: The use of a 7.3-mm screw in conjunction with a tension band provided better fixation of simulated displaced transverse fractures than did the use of Kirschner wires in conjunction with a tension band or the use of a screw only. The AO principle of converting posterior tensile forces to articular compressive forces was not demonstrated in this study. We therefore question the validity of the tension band concept in olecranon fracture fixation and recommend passive rather than active range of motion in the immediate postoperative period to limit fracture distraction.

Analysis of particles in acetabular components from patients with osteolysis.

Acetabular polyethylene components were quantitatively analyzed for the presence of third body particles from 38 consecutively retrieved components. Backscattered electron imaging and correlated energy dispersive x-ray analysis were used for the assessments. Retrievals were divided into 4 groups based on methods of fixation and metal alloy types: 8 hydroxyapatite coated, 6 cobalt chrome porous coated, 17 titanium porous coated, and 7 cemented implants were evaluated. The backscattered electron imaging data showed that the components from the hydroxyapatite coated implants had larger particles than did the components from the cemented group. The hydroxyapatite group had 51 +/- 52 particles per mm2. The cobalt chrome alloy group had 10 +/- 9 particles per mm2, and the titanium alloy group had 9 +/- 16 particles per mm2. The cemented group had 5 +/- 4 particles per mm2. The difference between the cement group and the hydroxyapatite group was statistically significant. The elemental analysis showed that 70% of the particles in the hydroxyapatite group had calcium and phosphorus elements. Third body particles likely contribute to particulate generation. The results suggest that the hydroxyapatite coated components have the potential for producing greater amounts of particulate debris. Continued analysis of retrieved components for the presence of the third body particles is required.