Prospective Study Assessing Impact of Ethylene Oxide Sterilization on Endoscopic Ultrasound Image Quality.

BACKGROUND & AIMS: Duodenoscope-associated transmission of infections has raised questions about efficacy of endoscope reprocessing using high-level disinfection (HLD). Although ethylene oxide (ETO) gas sterilization is effective in eradicating microbes, the impact of ETO on endoscopic ultrasound (EUS) imaging equipment remains unknown. In this study, we aimed to compare the changes in EUS image quality associated with HLD vs HLD followed by ETO sterilization. METHODS: Four new EUS instruments were assigned to 2 groups: Group 1 (HLD) and Group 2 (HLD + ETO). The echoendoscopes were assessed at baseline, monthly for 6 months, and once every 3 to 4 months thereafter, for a total of 12 time points. At each time point, review of EUS video and still image quality was performed by an expert panel of reviewers along with phantom-based objective testing. Linear mixed effects models were used to assess whether the modality of reprocessing impacted image and video quality. RESULTS: For clinical testing, mixed linear models showed minimal quantitative differences in linear analog score (P = .04; estimated change, 3.12; scale, 0-100) and overall image quality value (P = .007; estimated change, -0.12; scale, 1-5) favoring ETO but not for rank value (P = .06). On phantom testing, maximum depth of penetration was lower for ETO endoscopes (P < .001; change in depth, 0.49 cm). CONCLUSIONS: In this prospective study, expert review and phantom-based testing demonstrated minimal differences in image quality between echoendoscopes reprocessed using HLD vs ETO + HLD over 2 years of clinical use. Further studies are warranted to assess the long-term clinical impact of these findings. In the interim, these results support use of ETO sterilization of EUS instruments if deemed clinically necessary.

Effects of axial forearm instability on force transmission across the elbow.

BACKGROUND: The interosseous membrane (IOM) and distal radioulnar joint (DRUJ) provide axial stability to the forearm. Our hypothesis was that injury to these structures alters force transmission through the elbow. METHODS: A custom-designed apparatus that applies axial loads from the wrist to the elbow was used to test 10 cadaveric upper limbs under the following simulated conditions (1) intact, (2) DRUJ injury, (3) IOM injury, or (4) IOM + DRUJ injury. IOM injury was simulated by osteotomies of the IOM attachment to the radius, and DRUJ injury was simulated by distal ulnar oblique osteotomy. We applied 160 N of axial force during cyclic and functional range of forearm rotation (40o pronation/40o supination), and force, contact pressure, and contact area through the elbow joint were measured simultaneously. RESULTS: The force across the radiocapitellar joint was significantly higher in the IOM + DRUJ injury and the IOM injury groups than in the intact and DRUJ injury groups. The mean force across the radiocapitellar joint was not significantly different between the intact and DRUJ injury groups or between the IOM + DRUJ injury and the IOM injury groups. Forces across the ulnohumeral joint showed an inverse pattern to those in the radiocapitellar joint. CONCLUSIONS: These findings suggest that injury to the IOM contributes more to the disruption of the normal distribution of axial loads across the elbow than injury to the DRUJ.

Fibrin glue mediated delivery of bone anabolic reagents to enhance healing of tendon to bone.

Tendon graft healing in bone tunnels for the fixation of intra-articular ligament reconstructions may limit clinical outcome by delaying healing. This study assesses the effects of hydrogel-mediated delivery of bone anabolic growth factors in a validated model of tendon-to-bone tunnel healing. Forty-five Wistar rats were randomly allocated into three groups (BMP2-treated, GSK126-treated, and placebo). All animals underwent a tendon-to-bone tunnel reconstruction. Healing was evaluated at 4 weeks by biomechanical assessment, micro-computed tomography (bone mineral density, bone volume, cross sectional area of bone tunnels), and traditional histology. Adverse events associated with the hydrogel-mediated delivery of drugs were not observed. Results of our biomechanical assessment demonstrated favorable trends in animals treated with bone anabolic factors for energy absorption (P = 0.116) and elongation (P = 0.054), while results for force to failure (P = 0.691) and stiffness (P = 0.404) did not show discernible differences. Cross sectional areas for BMP2-treated animals were reduced, but neither BMP2 nor GSK126 administration altered bone mineral density (P = 0.492) or bone volume in the bone tunnel. These results suggest a novel and positive effect of bone anabolic factors on tendon-to-bone tunnel healing. Histological evaluation confirmed absence of collagen fibers crossing the soft tissue-bone interface indicating immature graft integration as expected at this time point. Our study indicates that hydrogel-mediated delivery of BMP2 and GSK126 appears to be safe and has the potential to enhance tendon-to-bone tunnel healing in ligament reconstructions.

Axial load transmission through the elbow during forearm rotation.

BACKGROUND: Forearm rotation is closely associated with the axiorotational force transmission through the elbow joint. A technique has been developed to study the transmission of force across the radiocapitellar and ulnotrochlear joints during forearm rotation. METHODS: Ten human cadaveric upper limbs were prepared on a custom-designed apparatus that permits the application of extrinsic axial loads across an intact cadaveric elbow joint. A force-sensitive transducer was inserted into the elbow joint of each cadaver. A 160 N axial force was applied to the specimen during cyclic forearm rotation while the force, contact pressure, and contact area through the elbow joint were measured. RESULTS: The mean force across the radiocapitellar joint showed no significant difference between pronation and supination (P = .3547). The radiocapitellar joint showed significantly higher contact area (P = .0001) and lower contact pressure (P = .0001) in pronation than in supination. The mean values for contact pressure, area, and force across the ulnotrochlear joint were not significantly different between supination and pronation. CONCLUSION: The contact pressure and contact area of the radiocapitellar joint in the cadaveric model changed according to forearm rotation while the force remained constant. The mean contact pressure of the radiocapitellar joint in pronation was significantly lower than that in supination because the force across it did not change significantly and its contact area decreased significantly. These findings may suggest that the pronated elbow can play an important role in protecting the radiocapitellar joint in high-impact activities like delivering punch in martial arts or falling on an outstretched arm.

Coronoid reconstruction using osteochondral grafts: a biomechanical study.

HYPOTHESIS: The purposes of this study were to test the hypothesis that coronoid deficiency in the setting of posteromedial rotatory instability (PMRI) must be reconstructed to restore articular contact pressures to normal and to compare 3 different osteochondral grafts for this purpose. METHODS: After creation of a anteromedial fracture, six cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads and to passively flex the elbow. Mean articular surface contact pressure data were collected and processed using TekScan sensors and software. After testing of the intact specimen (intact condition), a PMRI injury was created (PMRI condition). Testing was repeated after reconstruction of the lateral collateral ligament (LCL) (LCL-only condition), followed by reconstruction of the coronoid with 3 different osteochondral graft techniques (reconstructed conditions). RESULTS: Contact pressure was consistently significantly higher in the PMRI elbow compared with the intact, LCL-only, and reconstructed conditions (P < .006). The LCL-only elbow contact pressure was significantly higher than that of the intact and reconstructed conditions from 5° to 55° of flexion (P = .018). The contact pressure of the intact elbow was never significantly different from that of the reconstructed elbow, except at 5° of flexion (P ≤ .008). No significant difference was detected between each of the reconstructed techniques (P ≥ .15). However, the annular surface of the radial head was the only graft that yielded contact pressures not significantly different from normal at any flexion angle. CONCLUSION: Isolated reconstruction of the LCL did not restore native articular surface contact pressure, and reconstruction of the coronoid using osteochondral graft was necessary. There was no difference in contact pressures among the 3 coronoid reconstruction techniques.

Role of the lateral collateral ligament in posteromedial rotatory instability of the elbow.

BACKGROUND: Posteromedial rotatory instability (PMRI) of the elbow consists of an anteromedial coronoid fracture with lateral collateral ligament (LCL) and posterior bundle of the medial collateral ligament (PMCL) tears. We hypothesized that the LCL tear is required for elbow subluxation/joint incongruity and that an elbow affected by an anteromedial subtype 2 coronoid fracture and a PMCL tear exhibits contact pressures different from both an intact elbow and an elbow affected by PMRI. MATERIALS AND METHODS: Six cadaveric elbows were tested under gravity varus stress using a custom-made machine designed to simulate muscle loads and to passively flex the elbow from 0° to 90° and measure joint contact pressures. After testing of the intact specimen (INTACT-elbow), an anteromedial subtype 2 coronoid fracture with a PMCL tear (COR+PMCL-elbow) and a PMRI injury (PMRI-elbow), after adding an LCL tear, were tested. The highest values of mean contact pressure were used for the comparison among the 3 groups. RESULTS: Neither subluxation nor joint incongruity was observed in the COR+PMCL-elbow. The addition of an LCL detachment consistently caused subluxation and joint incongruity. Mean contact pressures were higher in the COR+PMCL-elbow compared with the INTACT-elbow (P < .03) but lower than in the PMRI-elbow (P < .001). CONCLUSIONS: The LCL lesion in PMRI is necessary for elbow subluxation and causes marked elevations in contact pressures. Even without subluxation, the COR+PMCL-elbow showed higher contact pressures compared with the INTACT-elbow. Treatment of PMRI should be directed toward prevention of joint incongruity, whether by surgical or nonsurgical means, to prevent high articular contact pressures.

Effect of Off-Axis Fluoroscopy Imaging on Two-Dimensional Kinematics in the Lumbar Spine: A Dynamic In Vitro Validation Study.

Spine intersegmental motion parameters and the resultant regional patterns may be useful for biomechanical classification of low back pain (LBP) as well as assessing the appropriate intervention strategy. Because of its availability and reasonable cost, two-dimensional (2D) fluoroscopy has great potential as a diagnostic and evaluative tool. However, the technique of quantifying intervertebral motion in the lumbar spine must be validated, and the sensitivity assessed. The purpose of this investigation was to (1) compare synchronous fluoroscopic and optoelectronic measures of intervertebral rotations during dynamic flexion-extension movements in vitro and (2) assess the effect of C-arm rotation to simulate off-axis patient alignment on intervertebral kinematics measures. Six cadaveric lumbar-sacrum specimens were dissected, and active marker optoelectronic sensors were rigidly attached to the bodies of L2-S1. Fluoroscopic sequences and optoelectronic kinematic data (0.15-mm linear, 0.17-0.20 deg rotational, accuracy) were obtained simultaneously. After images were obtained in a true sagittal plane, the image receptor was rotated in 5 deg increments (posterior oblique angulations) from 5 deg to 15 deg. Quantitative motion analysis (qma) software was used to determine the intersegmental rotations from the fluoroscopic images. The mean absolute rotation differences between optoelectronic values and dynamic fluoroscopic values were less than 0.5 deg for all the motion segments at each off-axis fluoroscopic rotation and were not significantly different (P > 0.05) for any of the off-axis rotations of the fluoroscope. Small misalignments of the lumbar spine relative to the fluoroscope did not introduce measurement variation in relative segmental rotations greater than that observed when the spine and fluoroscope were perpendicular to each other, suggesting that fluoroscopic measures of relative segmental rotation during flexion-extension are likely robust, even when patient alignment is not perfect.

Influence of radial head prosthetic design on radiocapitellar joint contact mechanics.

HYPOTHESIS: Our aim was to test whether anatomically designed metallic radial head implants could better reproduce native radiocapitellar contact pressure and areas than nonanatomic implants. METHODS: The distal humerus and proximal radius from 6 cadaveric upper extremities were serially tested in supination with 100 N of compression force at 4 angles of flexion (0°, 30°, 60°, and 90°). By use of a thin flexible pressure transducer, contact pressures and areas were measured for the native radial head, an anatomic implant, a nonanatomic circular monopolar implant, and a bipolar nonanatomic implant. The data (mean contact pressure and mean contact area) were modeled using a 2-factor repeated-measures analysis of variance with P ≤ .05 considered to be significant. RESULTS: The mean contact areas for the prosthetic radial heads were significantly less than those seen with the intact radial heads at every angle tested (P < .01). The mean contact pressures increased significantly with all prosthetic radial head types as compared with the native head. The mean contact pressures increased by 29% with the anatomic prosthesis, 230% with the monopolar prosthesis, and 220% with the bipolar prosthesis. Peak pressures of more than 5 MPa were more commonly observed with both the monopolar and bipolar prostheses than with the anatomic or native radial heads. CONCLUSIONS: The geometry of radial head implants strongly influences their contact characteristics. In a direct radius-to-capitellum axial loading experiment, an anatomically designed radial head prosthesis had lower and more evenly distributed contact pressures than the nonanatomic implants that were tested.

Biomechanical analysis of a novel locking plate with smooth pegs versus a conventional locking plate with threaded screws for proximal humerus fractures.

BACKGROUND: Repair of proximal humeral fractures with locking plates has greatly improved outcomes. However, an alarming rate of complications including screw cutout and impingement under the acromion has recently been reported. A novel locking plate with smooth pegs was developed to reduce these risks. The purpose of this study was to compare these 2 fixation methods with a cadaveric biomechanical study. MATERIALS AND METHODS: Fourteen pairs of cadaveric proximal humeri (mean age, 77 years) were harvested, and bone density was measured. Osteosynthesis was performed on each pair using either a locking plate with threaded screws (TS group) or smooth pegs (SP group) on the contralateral side. Seven pairs of humeri were tested for cyclic bending, and 7 pairs for cyclic torsional evaluation: TS bending, SP bending, TS torsion, and SP torsion. The bending protocol consisted of cyclically loading to a maximum of 7.5 Nm bending moment for 10,000 cycles. The torsion protocol consisted of ±2 Nm of axial torque for 10,000 cycles. Surgical neck fractures were simulated by excising a 10-mm wedge of bone. RESULTS: No implant failure or screw cutout was observed in any of the groups tested. Under bending loads, mean displacement of the distal fragment was significantly less for the SP group than that for the TS group over 5,000 cycles. In torsion tests, no significant differences were observed between the 2 fixation methods. DISCUSSION: The SP group demonstrated superior biomechanical characteristics to the TS group in regards to cyclic bending.

Evaluation of fracture resistance in aqueous environment of four restorative systems for posterior applications. Part 1.

PURPOSE: The goals of this study were to: (1) establish a range of the performance of four restorative systems for posterior single-tooth crowns under single load to fracture submerged in an aqueous environment, (2) identify restorative system(s) of interest to be examined in the second study phase under sliding contact step-stress fatigue as full-contour anatomically appropriate single posterior tooth restoration(s), (3) establish a range for loading/testing for phase 2. MATERIALS AND METHODS: Forty specimens (n = 10/group) of 2 mm uniform thickness were tested. Group 1: monolithic lithium disilicate IPS e.max Press; group 2: IPS e.max ZirPress, 0.8 mm zirconia core with 1.2 mm pressed veneering porcelain; group 3: IPS e.max ZirPress, 0.4 mm zirconia core with 1.6 mm pressed veneering porcelain; group 4: IPS InLine PoM. Specimens were bonded to a block of polycast acrylic resin on a 30° sloped surface with resin cement. Specimens were axially single loaded to failure while submerged under water. RESULTS: There was a statistically significant difference (p < 0.001) in failure load among the four restorative systems. Lithium disilicate showed a mean failure load similar to mean maximum posterior bite forces (743.1 ± 114.3 N). IPS e.max Zirpress with a 0.4 mm zirconia core exhibited the lowest mean failure load (371.4 ± 123.0 N). CONCLUSION: Fracture resistance of monolithic lithium disilicate in an aqueous environment is promising and requires second phase testing to evaluate the potential of various thicknesses appropriate for posterior single tooth applications. Doubling the IPS e.max Zirpress zirconia core from 0.4 mm to 0.8 mm increased the fracture resistance of this restorative system threefold.

Biomechanical evaluation of posterior lumbar dynamic stabilization: an in vitro comparison between Universal Clamp and Wallis systems.

Treatment of chronic low back pain due to degenerative lumbar spine conditions often involves fusion of the symptomatic level. A known risk of this procedure is accelerated adjacent level degeneration. Motion preservation devices have been designed to provide stabilization to the symptomatic motion segment while preserving some physiologic motion. The aim of this study was to compare the changes in relative range of motion caused as a result of application of two non-fusion, dynamic stabilization devices: the Universal Clamp (UC) and the Wallis device. Nine fresh, frozen human lumbar spines (L1-Sacrum) were tested in flexion-extension, lateral bending, and axial rotation with a custom spine simulator. Specimens were tested in four conditions: (1) intact, (2) the Universal Clamp implanted at L3-4 (UC), (3) the UC with a transverse rod added (UCTR), and (4) the Wallis device implanted at L3-4. Total range of motion at 7.5 N-m was determined for each device and compared to intact condition. The UC device (with or without a transverse rod) restricted motion in all planes more than the Wallis. The greatest restriction was observed in flexion. The neutral position of the L3-4 motion segment shifted toward extension with the UC and UCTR. Motion at the adjacent levels remained similar to that observed in the intact spine for all three constructs. These results suggest that the UC device may be an appropriate dynamic stabilization device for degenerative lumbar disorders.

The biomechanical effect of the distal interosseous membrane on distal radioulnar joint stability: a preliminary anatomic study.

PURPOSE: The distal interosseous membrane (DIOM) is a secondary stabilizer of the distal radioulnar joint (DRUJ) and has a considerably variable morphology. The purpose of this study was to investigate whether innate DRUJ stability is influenced by the anatomic variation of the DIOM. METHODS: Ten fresh-frozen cadaver upper extremities were used in this study. The humerus and the ulna were affixed rigidly to a custom-made apparatus, with the elbow in 90° of flexion. Testing was performed by translating the radius in volar and dorsal directions relative to the ulna, with a 20-N applied force in neutral forearm alignment, 60° pronation, and 60° supination. Total translation of the radius was measured as DRUJ laxity. After the experiment, we investigated anatomic variation of the DIOM, especially regarding the existence of the distal oblique bundle (DOB), which is a notably thick fiber within the DIOM. We compared the DRUJ stability between the groups with and without the DOB. RESULTS: The DOB was found in 4 of 10 specimens. The group with a DOB demonstrated a significantly greater DRUJ stability in the neutral position than the group without a DOB. In pronated and supinated forearm positions, no significant difference in DRUJ stability was obtained between the groups with and without a DOB. CONCLUSIONS: Innate DRUJ stability in the neutral forearm position was greater in the group with a DOB than in those without a DOB. CLINICAL RELEVANCE: This study suggests that considerable variation exists in DRUJ laxity and that it partially depends on anatomical variations of the DIOM.

Radial head prosthesis micromotion characteristics: Partial versus fully grit-blasted stems.

BACKGROUND: Compared to fully textured prosthetic stems, partial texturing lessens bone loss due to stress shielding and makes removal easier. However, initial press-fit stability is necessary for bone ingrowth. HYPOTHESIS: There is no significant difference in the initial stability of radial head prostheses that are partially grit-blasted compared to those that are fully grit-blasted. MATERIALS AND METHODS: Cadaveric radii were implanted with partial or fully grit-blasted radial head prostheses. Micromotion of the stem at the isthmus of the canal and stem tip were measured under circumstances simulating eccentric loads. RESULTS: Micromotion was not significantly different in the fully grit-blasted stems (isthmus, 11 ± 1 µm; tip, 21 ± 2 µm) and partially grit-blasted stems (isthmus, 13 ± 2 µm; tip, 25 ± 2 µm) (P = 0.4). The direction of loading had no effect on micromotion characteristics in either the fully or partially grit-blasted stems (P = .07). DISCUSSION: Micromotion is comparable in partially and fully grit-blasted radial head prosthetic stems. For both stem surfaces, micromotion was well within the range that is conducive for bone ingrowth. A partially textured stem might have less bone loss due to stress shielding, making it easier to remove without destroying bone. CONCLUSION: The initial stability of a radial head stem that is partially grit-blasted only at the proximal end is comparable to that of a radial head stem that is grit-blasted along its entire length.

The effect of cyclic loading simulating oscillatory joint mobilization on the posterior capsule of the glenohumeral joint: a cadaveric study.

STUDY DESIGN: Experimental laboratory design. OBJECTIVES: To examine the effect of force and repetition during oscillatory joint mobilizations on the posterior capsule of the glenohumeral joint. BACKGROUND: The optimal external force and frequency to be used during joint mobilization to elongate the posterior capsule of the glenohumeral joint has yet to be identified. METHODS: Twenty-one posterior capsules were harvested from fresh-frozen shoulders. A cyclic loading test simulating oscillatory posterior joint mobilization on the shoulder specimens was performed with a material testing machine. The specimens were assigned to 3 different loading groups simulating joint mobilization in the toe (5 N), transition (20 N), and beginning of the linear regions (40 N) of the load displacement curve. Displacement of the humeral head at an applied load of 5 N was recorded at the 1st, 100th, 200th, 300th, 400th, 500th, and 600th cycles and at 1 hour after completion of the cyclic loading. Furthermore, stiffness was calculated after the 1st and 600th cycles and 1 hour after testing. RESULTS: Humeral head displacement was significantly greater for the 100th to 600th cycle, compared to the 1st cycle, for all 3 loading groups. Significant increases in displacement and stiffness were observed between the 1st cycle and 1 hour after completion of the cyclic tests for both the 20-N and 40-N loading groups. CONCLUSION: While oscillatory joint mobilization to a force of 5 N resulted in temporary elongation of the posterior capsule, mobilization to loads of 20 and 40 N resulted in sustained elongation of the capsule for up to 1 hour. Our findings also suggest that mobilization up to loads that represent the beginning of the linear region of the load displacement curve could be performed without serious damage to the posterior capsule.

Biomechanical evaluation of the dynamic radioulnar convergence after ulnar head resection, two soft tissue stabilization methods of the distal ulna and ulnar head prosthesis implantation.

INTRODUCTION: The biomechanical performance of the Darrach procedure, its stabilizing methods and the effectiveness of an ulnar head prosthesis was evaluated in this experiment. PURPOSE: The purpose of this study was to: (1) analyze the dynamic effects of the resection of the distal ulna on radioulnar convergence; and (2) evaluate the mechanical performance of two soft tissue stabilizing procedures (pronator quadratus advancement flap and ECU/FCU tenodesis) for the unstable distal ulnar stump and the implantation of an ulnar head prosthesis (uHead) following a distal ulnar resection (Darrach procedure) on radioulnar convergence. METHOD: With a dynamic PC-controlled forearm simulator, cadaveric forearm rotation was actively and passively performed while simultaneously loading the relevant muscles. The resultant total forearm torque and the three-dimensional kinematics of the ulna, radius and third metacarpal were simultaneously recorded in seven fresh-frozen cadaver upper extremities. RESULTS: The resection of the distal ulna created an extreme instability of the forearm with movement of the radius toward the ulna (0.92-0.38 cm compared to the intact state) in each particular loading condition. The implantation of the ulnar head prosthesis effectively restored the stability of the DRUJ by simulating the geometry of the ulnar head. There were significantly better results after the implantation of the prosthesis compared with the Darrach and the soft tissue stabilization procedures. CONCLUSION: This study provides laboratory validity to the option of implanting an ulnar head endoprosthesis as an attempt to stabilize the distal forearm with instability after Darrach resection in lieu of performing soft tissue stabilization techniques.

Biomechanical muscle stiffness measures of extensor digitorum explain potential mechanism of McArdle sign.

BACKGROUND: McArdle sign is a phenomenon of impaired gait and muscle weakness that occurs with neck flexion, immediately reversible with neck extension. A recent report measured the specificity of this sign for multiple sclerosis by measuring differences in peak torque of the extensor digitorum between neck extension and flexion. METHODS: This substudy included 73 participants (29 multiple sclerosis, 20 non-multiple sclerosis myelopathies, 5 peripheral nerve disorders, and 19 healthy controls). The effect of neck position was assessed on muscle stiffness and neuromechanical error of the extensor digitorum. FINDINGS: Patients with multiple sclerosis had greater neuromechanical error (sum of squared error of prediction) compared to controls (P = 0.023) and non-multiple sclerosis myelopathies (P = 0.003). Neuromechanical error also provided improved sensitivity/specificity of McArdle sign. Peak torque, muscle stiffness, and neuromechanical error could distinguish multiple sclerosis from other myelopathies with 80% specificity and 97% sensitivity (AUC = 0.95). INTERPRETATION: A decrease in muscle stiffness and neuromechanical error in neck flexion compared to extension are additional indicators for a diagnosis of multiple sclerosis. Analysis of muscle stiffness may provide insights into the pathophysiology of this specific clinical sign for multiple sclerosis. Furthermore, muscle stiffness may provide an additional accurate, simple assessment to evaluate multiple sclerosis therapeutic interventions and disease progression.

Biomechanical evaluation of a new fixation device for the thoracic spine.

The technology used in surgery for spinal deformity has progressed rapidly in recent years. Commonly used fixation techniques may include monofilament wires, sublaminar wires and cables, and pedicle screws. Unfortunately, neurological complications can occur with all of these, compromising the patients' health and quality of life. Recently, an alternative fixation technique using a metal clamp and polyester belt was developed to replace hooks and sublaminar wiring in scoliosis surgery. The goal of this study was to compare the pull-out strength of this new construct with sublaminar wiring, laminar hooks and pedicle screws. Forty thoracic vertebrae from five fresh frozen human thoracic spines (T5-12) were divided into five groups (8 per group), such that BMD values, pedicle diameter, and vertebral levels were equally distributed. They were then potted in polymethylmethacrylate and anchored with metal screws and polyethylene bands. One of five fixation methods was applied to the right side of the vertebra in each group: Pedicle screw, sublaminar belt with clamp, figure-8 belt with clamp, sublaminar wire, or laminar hook. Pull-out strength was then assessed using a custom jig in a servohydraulic tester. The mean failure load of the pedicle screw group was significantly larger than that of the figure-8 clamp (P = 0.001), sublaminar belt (0.0172), and sublaminar wire groups (P = 0.04) with no significant difference in pull-out strength between the latter three constructs. The most common mode of failure was the fracture of the pedicle. BMD was significantly correlated with failure load only in the figure-8 clamp and pedicle screw constructs. Only the pedicle screw had a statistically significant higher failure load than the sublaminar clamp. The sublaminar method of applying the belt and clamp device was superior to the figure-8 method. The sublaminar belt and clamp construct compared favorably to the traditional methods of sublaminar wires and laminar hooks, and should be considered as an alternative fixation device in the thoracic spine.

Stem diameter and micromotion of press fit radial head prosthesis: a biomechanical study.

BACKGROUND: Aseptic loosening of the stem, ranging from mild periprosthetic lucency to symptomatic loosening leading to implant removal, has been reported in press fit radial head prostheses. HYPOTHESIS: The purpose of this study was to determine the effect of the stem diameter and insertion force on initial stability with a press fit radial head prosthesis designed for bone ingrowth. MATERIALS AND METHODS: Cadaveric radii were implanted with radial head prostheses of increasing stem diameter. The insertion forces for each rasp and stem were measured. Micromotion of the stem at the isthmus of the canal and stem tip were measured under circumstances simulating eccentric loads. RESULTS: Insertion forces for all submaximum-sized rasps were similar. However, the insertion force for the maximum-sized rasp was approximately twice as large, and the insertion force for the oversized rasp was twice as large again, potentially indicating that the insertion force may be useful as a guide for determining appropriate stem size. Micromotions of the maximum diameter stem (isthmus, 41 microm; tip, 64 microm) were near the threshold for bone ingrowth, whereas the micromotions of the submaximum stem (isthmus, 253 microm; tip, 394 microm) were above this threshold. DISCUSSION: The maximum diameter stem achieved greater stability (minimum micromotion) compared with the submaximum diameter stem. CONCLUSION: The best fixation strength in the press fit radial head prosthesis was achieved by maximum sizing in the neck canal.

Radiocapitellar joint stability with bipolar versus monopolar radial head prostheses.

BACKGROUND: Bipolar and monopolar designs are both available for replacement of the radial head. Few data exist comparing the biomechanical characteristics of these 2 quite different prostheses. This study evaluated the relative contribution to radiocapitellar stability by concavity compression with these 2 types of radial head prostheses. METHODS: The study used 12 fresh frozen elbow cadavers. The capitellum of the distal humerus and 3 different conditions of radial head (native, monopolar and bipolar) were tested for radiocapitellar joint stability. RESULTS: The monopolar metallic head and the native radial head behaved similarly regarding resistance to subluxation. The bipolar head behaved in an entirely opposite manner than the native and monopolar head and actually acted to facilitate subluxation. CONCLUSIONS: Mobility of radial head components, such as in the bipolar radial head, has a compromising effect on the concavity compression stability of the radiocapitellar joint. A monopolar implant is more effective in stabilizing the radiocapitellar joint than a bipolar radial head prosthesis.

Oritavancin polymethylmethacrylate (PMMA)-compressive strength testing and in vitro elution.

BACKGROUND: Polymethylmethacrylate (PMMA) is used for local antimicrobial delivery in orthopedic infection. Oritavancin is a long half-life lipoglycopeptide with broad activity against Gram-positive bacteria. Herein, we addressed if 7.5% w/w oritavancin mixed into PMMA affects PMMA strength and whether it elutes from PMMA, compared to vancomycin. METHODS: Elution was assessed by placing an oritavancin- or vancomycin-loaded bead in a flow system with human plasma. Compressive strength of bland compared to oritavancin- or vancomycin-loaded PMMA was assessed after 0, 3, and 7 days of soaking in 1 ml of pooled normal human plasma at 37 °C, by testing to failure in axial compression using a servo-hydraulic testing machine. RESULTS: Median compressive strength on days 0, 3, and 7 for bland PMMA compared to oritavancin- or vancomycin-loaded PMMA was 80.1, 79.4, and 72.4 MPa, respectively; 93.3, 86.4, and 65.3 MPa, respectively; and 97.8, 82.7, and 65.9 MPa, respectively. Oritavancin reduced PMMA compressive strength after 3 and 7 days (P = 0.0250 and 0.0039, respectively), whereas vancomycin reduced the PMMA compressive strength after 0, 3, and 7 days (P = 0.0039, 0.0039, and 0.0062, respectively) as compared to bland PMMA. Oritavancin-loaded PMMA had higher compressive strength than vancomycin-loaded PMMA on days 3 and 7 (P = 0.0039 and 0.0062, respectively). Compressive elastic moduli were 1226, 1299, and 1394 MPa for bland PMMA; 1253, 1078, and 1245 MPa for oritavancin-loaded PMMA; and 986, 879, and 779 MPa for vancomycin-loaded PMMA on days 0, 3 and 7, respectively. Oritavancin-loaded PMMA had higher compressive elastic moduli than vancomycin-loaded PMMA on days 0 and 7 (P = 0.0250 and 0.0062, respectively). Following polymerization, 1.0% and 51.9% of the initial amount of oritavancin and vancomycin were detected, respectively. Cmax, Tmax, and AUC0-24 were 1.7 µg/ml, 2 h, and 11.4 µg/ml for oritavancin and 21.4 µg/ml, 2 h, and 163.9 µg/ml for vancomycin, respectively. CONCLUSIONS: Oritavancin-loaded PMMA had higher compressive strength than vancomycin-loaded PMMA on days 3 and 7 and higher compressive elastic moduli than vancomycin-loaded PMMA on days 0 and 7. However, proportionally less oritavancin than vancomycin eluted out of PMMA.