Micro-CT, Mechanical, and Histological Examination of the Effect of Local Adjuvants on Porcine Cortical Bone Following Intralesional Curettage of Bone Tumors.

BACKGROUND AND OBJECTIVES: Curettage is the removal of a tumor from the bone while preserving the surrounding healthy cortical bone, and is associated with higher rates of local recurrence. To lower these rates, curettage should be combined with local adjuvants, although their use is associated with damage to nearby healthy bone. OBJECTIVE: The purpose of this analysis is to determine the effect of local adjuvants on cortical porcine bone by using micro-computed tomography (micro-CT) along with histological and mechanical examination. METHODS: Local adjuvants were applied to porcine specimens under defined conditions. To assess changes in bone mineral density (BMD), a micro-CT scan was used. The pixel gray values of the volume of interest (VOI) were evaluated per specimen and converted to BMD values. The Vickers hardness test was employed to assess bone hardness (HV). The depth of necrosis was measured histologically using hematoxylin and eosin-stained tissue sections. RESULTS: A noticeable change in BMD was observed on the argon beam coagulation (ABC) sample. Comparable hardness values were measured on samples following electrocautery and ABC, and lowering of bone hardness was obtained in the case of liquid nitrogen. Extensive induced depth of necrosis was registered in the specimen treated with liquid nitrogen. CONCLUSION: This study determined the effect of local adjuvants on cortical bone by using micro-CT along with histological and mechanical examination. Phenolization and liquid nitrogen application caused a decrease in bone hardness. The bone density was affected in the range of single-digit percentage values. Liquid nitrogen induced extensive depth of necrosis with a wide variance of values.

Determination of stress and displacement on human composite pelvis under static and dynamic loading.

This case study describes the experimental determination of displacements and stresses on a composite model of a pelvis that was modified to represent a healthy intact pelvic ring. The modified model was stressed statically up to 1750 N to simulate standing on one leg and also cyclically to model walking. For two different model settings in the loading machine the values of displacements and stresses at the pelvic ring were determined. The two different settings correspond to two different loading vectors applied on the pelvic ring, boundary conditions and degrees of freedom. The experimentally determined values of displacements in both settings are very similar and in accordance with the knowledge on the behaviour of a real human pelvis. The modified model is thus suitable for testing of newly developed implants for pelvis treatment and experimental determination of displacements and stresses in pelvic ring which are caused by application of implants.

Lapidus arthrodesis in combination with arthrodesis of the first metatarsophalangeal joint-biomechanical cadaver study comparing two methods of fixation.

AIMS: To assess the results of a biomechanical test of cadaveric specimens, comparing 2 methods of fixation of modified Lapidus arthrodesis in combination with arthrodesis of the first metatarsophalangeal joint. METHODS: A total of 12 cadaveric specimens were used in the test. Arthrodesis of the first MTP joint was in all patients fixed with a Variable Angle LCP 1st MTP Fusion Plate 2.4/2.7. Two methods of fixation of the Lapidus arthrodesis were compared, i.e. fixation with two screws in the PS (plate-screw) version versus fixation with X-Locking Plate 2.4/2.7 in the PP (plate-plate) version. Measurements were obtained with the use of a testing machine ZWICK Z 020-TND with an optical device Mercury RT for measuring deformities. Each specimen was subjected to 3 loading options, a. displacement 5 mm, the support is placed under the proximal phalanx, b. displacement 5 mm, the support is placed under the first metatarsal head and c. load to failure, the support is placed under the first metatarsal head. RESULTS: In all specimens the PS construct showed a statistically considerably higher stiffness than the PP construct. In all specimens treated with the PP construct the load to failure was lower than in the PS construct. For loading mode a., at a significance level of 0.05 (P<0.05), the P-value was 0.036, for mode b. the P-value was 0.007 and for loading mode c. the P-value was 0.006. In addition, age-related decrease in stiffness of the specimen was proved at a significance level of 5% (P=0.004). CONCLUSION: In all the three loading modes, the PS (plate-screw) construct showed a statistically higher stiffness than the PP (plate-plate) construct.

Efficiency of Plasticity Correction in the Hole-Drilling Residual Stress Measurement.

This paper focuses on the analysis of the plasticity effect in the measurement of the residual stress by the hole-drilling method. Relaxed strains were evaluated by the computational simulation of the hole-drilling experiment using the finite element method. Errors induced by the yielding were estimated for uniaxial tension, plane shear stress state and equi-biaxial stress state at various magnitudes of residual stress uniformly distributed along the depth. The correction of the plasticity effect in the evaluation of residual stress was realized according to the method proposed by authors from the University in Pisa, which was coded in MATLAB. Results obtained from the MATLAB script were compared to the original input data of the hole-drilling simulation and discussed. The analyses suggested that the plasticity effect is negligible at the ratio of applied equivalent stress to yield stress, being 0.6, and that the correction of the plasticity effect is very successful at the previous ratio, being 0.9. Failing to comply with the condition of the strain gauge rosette orientation according to the principal stresses directions causes an increase in the relative error of corrected stresses only for the case of uniaxial tension. It affects the relative error negligibly for the plane shear and equi-biaxial stress states.

Percutaneous versus open pedicle screw fixation for treatment of type A thoracolumbar fractures.

BACKGROUND: The purpose of this study was to evaluate the effectiveness between percutaneous and open pedicle screw fixation without fusion for treating type A3 and A4 thoracolumbar fractures. Traumatic thoracolumbar burst fracture is a common pathology without a consensus on the best treatment approach. Percutaneous pedicle screw fixation (PPSF) systems have been recently introduced in the treatment of spinal fractures to reduce the adverse effects associated with the conventional open approaches, such as iatrogenic muscle denervation and pain. METHODS: A prospective analysis was made to evaluate consecutive 46 patients with type A3 and A4 thoracolumbar fractures. Patients were divided into a percutaneous pedicle screw fixation group (PPSF) and an open pedicle screw fixation group (OPSF). The mean age of patients in PPSF group (12 men, 11 woman) was 49.9 years and in OPSF group (10 men, 13 women) 52.2 years. For the purpose of evaluation, the radiological assessment of the bisegmental Cobb angle, the loss of correction, the volume of blood loss, operation time, cumulative radiation time and dose were recorded and compared. RESULTS: All patients were followed up for 12 months. There were no significant differences between OPSF and PPSF in the Cobb angle preoperative and postoperative angle and the loss of bisegmental correction. In PPSF group, the mean preoperative Cobb angle was 10.9° and improved by 4.5° postoperatively, and in OPSF group the preoperative angle was 12.1° and postoperatively improved by 3.8°. Significant differences between OPSF and PPSF were found in the mean cumulative radiation time, radiation dose and operation time. PPSF group also had a significantly lower perioperative blood loss. CONCLUSIONS: Both open and percutaneous short-segment pedicle fixation were safe and effective methods to treat thoracolumbar burst fractures. Percutaneous fixation without fusion seems to be suitable for type A3 and A4 fractures.

Biomechanical Testing of Spinal Segment Fixed by Arcofix System on the Swine Spine.

STUDY DESIGN: An in vitro biomechanical study. PURPOSE: To evaluate the mechanical properties of the spinal segment in the intact, injured, and stabilized state after fixation by an Arcofix implant. OVERVIEW OF LITERATURE: Several types of thoracolumbar spine injury necessitates anterior instrumentation. The Arcofix plate represents the latest generation of angular stablity systems. The biomechanical properties of these implants have not been sufficiently studied yet. METHODS: A total of ten porcine specimens (levels Th12-L3) were prepared. The tests were performed for intact, injured, and implanted specimens. In each state, the specimen was subjected to a tension load of a prescribed force, and subsequently, twisted by a given angle. The force load was 200 N. The torsion load had a deformation character, i.e., the control variable was the twisting angle and the measured variable was the moment of a couple. The amplitude of the load alternating cycle was 3°. Another parameter that was evaluated was the area of the hysteresis loop. The area corresponds to the deformation energy which is dissipated during the cycle. RESULTS: A statistically significant difference was found between the intact and injured states as well as between the injured and implanted specimens. The statistical evaluation also showed a statistically different value of the hysteresis loop area. In the case of instability, the area decreased to 33% of the physiological value. For the implanted sample, the area increased to 170% of the physiological value. CONCLUSIONS: The Arcofix implant with its parameters appears to be suitable and sufficiently stable for the treatment of the anterior column of the spine.

In situ measurements of thin films in bovine serum lubricated contacts using optical interferometry.

The aim of this study is to consider the relevance of in situ measurements of bovine serum film thickness in the optical test device that could be related to the function of the artificial hip joint. It is mainly focussed on the effect of the hydrophobicity or hydrophilicity of the transparent surface and the effect of its geometry. Film thickness measurements were performed using ball-on-disc and lens-on-disc configurations of optical test device as a function of time. Chromatic interferograms were recorded with a high-speed complementary metal-oxide semiconductor digital camera and evaluated with thin film colorimetric interferometry. It was clarified that a chromium layer covering the glass disc has a hydrophobic behaviour which supports the adsorption of proteins contained in the bovine serum solution, thereby a thicker lubricating film is formed. On the contrary, the protein film formation was not observed when the disc was covered with a silica layer having a hydrophilic behaviour. In this case, a very thin lubricating film was formed only due to the hydrodynamic effect. Metal and ceramic balls have no substantial effect on lubricant film formation although their contact surfaces have relatively different wettability. It was confirmed that conformity of contacting surfaces and kinematic conditions has fundamental effect on bovine serum film formation. In the ball-on-disc configuration, the lubricant film is formed predominantly due to protein aggregations, which pass through the contact zone and increase the film thickness. In the more conformal ball-on-lens configuration, the lubricant film is formed predominantly due to hydrodynamic effect, thereby the film thickness is kept constant during measurement.

Finite element analysis for the evaluation of the structural behaviour, of a prosthesis for trans-tibial amputees.

The finite element analysis (FEA) has been identified as a useful tool for the stress and strain behaviour determination in lower limb prosthetics. The residual limb and prosthetic socket interface was the main subject of interest in previous studies. This paper focuses on the finite element analysis for the evaluation of structural behaviour of the Sure-flex™ prosthetic foot and other load-bearing components. A prosthetic socket was not included in the FEA. An approach for the finite element modelling including foot analysis, reverse engineering and material property testing was used. The foot analysis incorporated ground reaction forces measurement, motion analysis and strain gauge analysis. For the material model determination, non-destructive laboratory testing and its FE simulation was used. A new, realistic way of load application is presented along with a detailed investigation of stress distribution in the load-bearing components of the prosthesis. A novel approach for numerical and experimental agreement determination was introduced. This showed differences in the strain on the pylon between the experimental and the numerical model within 30% for the anteroposterior bending and up to 25% for the compression. The highest von Mises stresses were found on the foot-pylon connecting component at toe off. Peak stress of 216MPa occurred on the posterior adjusting screw and maximum stress of 156MPa was found at the neck of the male pyramid.

A biomechanical study of a suture between the deltoid muscle and a free tendon graft for reconstruction of the elbow extension.

AIMS: It is possible to reconstruct the elbow motion in tetraplegic patients using the posterior portion of the deltoid muscle. In this surgery however, it is a problem to achieve a firm suture between the deltoid muscle and the tendon graft which extends the muscle and is sewn in order to compensate for the plegic musculus triceps brachii function. This study assesses two methods of attachment between muscle and free tendon graft from the biomechanical point of view. METHODS: The assessment was made on 7 fresh-frozen cadaveric samples where the rear portion of the deltoid muscle was sewn with the strip of fascia lata (A1-A7) and 7 samples (B1-B7) where the free tendon graft was attached with a strengthened part of deltoid fascia. The character of the attachment defect was evaluated as strength and elongation parameters using the device Zwick Z020-TND. RESULTS: The ANOVA showed a statistically significant greater suture solidity connecting the muscle and tendon for group B (B1-B7) than group A. The deformation of the actual suture location was smaller in group B than the deformation of attachment surroundings. CONCLUSION: From the biomechanical solidity point of view, it is more efficient to use the strengthened fascia of the deltoid muscle on its inner side for the suture with the tendon graft for reconstruction of the elbow extension in tetraplegic patients.

Biomechanical testing of spinal segment fixed by thoracolumbar spine locking plate on the swine lumbar spine.

BACKGROUND: The aim of the experiment was to compare the mechanical properties of intact spinal segment with impaired intervertebral disc and impaired intervertebral disc fixed by TSLP (Thoracolumbar Spine Locking Plate). METHODS AND RESULTS: Spinal specimens were taken from domestic swine. A total of 8 test mechanical states (intact, impaired and fixed) were modeled and the mechanical properties, expressed by the value of moment of couple necessary to twist the specimen at tensile force F = 200 N and the value of moments necessary for extension straining, were determined. The study was based on in vitro biomechanical testing of the TSLP plate used to stabilize the front thoracolumbar column of spinal segments taken from a pig. The plate was used for monosegmental fixation. The disc was cut by scalpel to simulate the Type A injury to front spinal column. In each state (intact, impaired or fixed), specimens were subjected to a tension load of prescribed force and, then, twisted by a given angle. Subsequently, extension load of intact, impaired and impaired & fixed segment was measured. Statistical evaluation verified the hypothesis of the different behavior of intact, impaired and fixed specimens - both for tension & torsion load and extension load. The analyses did not indicate different mechanical behavior of intact and fixed specimens. In other words, monosegmental fixation of both impaired and intact specimens by TSLP Synthes implant will lead to similar mechanical behavior of these specimens. Further, we found that intact and fixed specimens show non-symmetric behavior at positive and negative twisting angles. This was not observed for impaired specimens. CONCLUSION: Several stabilization systems were developed to stabilize the front thoracolumbar spinal column. Surgery of the anterior column of injured spine should restore the correct position of the spine, ensure decompression of vertebral canal when neural structures are compressed, and stabilize the spine to allow immediate loading and mobilization of the patient. The aim of this study was to compare mechanical properties of intact spinal segment, impaired spinal segment and impaired spinal segment stabilized by TSLP Synthes implant. The problems were solved by experimental modeling using a testing machine that simulated loads for several mechanical states of the spinal segment. Favorable mechanical properties of TSLP Synthes fixator were demonstrated. The experimental results will be used for subsequent computational modeling of the spinal segment in all experimentally solved states.