Pressure-sensitive Film Research Articles

A Novel Inflatable Belt-Type Clamp in Open Heart Surgery

ABSTRACTIn this study, a novel inflatable belt-type clamp is introduced and its performance is verified. Finite element simulations are performed to compare the performance of three different aorta clamping systems. In every case, the aorta is modeled as a simple hollow cylinder made of linearly elastic material. For a traditional surgical clamp in which the jaws remain inclined to one another as they close around the aorta, the maximum normal stress within the aorta wall is found to be 806kPa. It is shown that the numerical results are in good qualitative agreement with the experimental results obtained using a pressure sensitive film. The simulation results for a modified clamp in which the jaws remain parallel during the clamping operation show that the maximum normal stress is reduced to 222kPa. However, two regions of maximum stress are induced within the aorta wall. Finally, the numerical results for a novel inflatable belt-type clamp show that the maximum normal stress is equal to approximately 221kPa. In contrast to the modified clamp, the stress is uniformly distributed around the perimeter of the aorta, and thus the risk of aortic dissection is significantly reduced.

Relationship between masseter muscle size and maxillary morphology

The aim of this study was to investigate the relationship between masseter muscle size and craniofacial morphology, focusing on the maxilla. Twenty-four patients (11 males and 13 females; mean age 27.6 ± 5.6 years) underwent cephalometric analyses. Ultrasonography was used to measure the cross-sectional area (CSA) of the masseter muscle and bite force was measured using pressure sensitive film. The results showed that CSA-relaxed was positively correlated with upper anterior face height (UAFH)/total anterior face height (TAFH) and negatively with lower anterior face height (LAFH)/TAFH and LAFH (P < 0.05). CSA-clenched was correlated positively with SN-palatal, FH-palatal, UAFH/TAFH, and lower posterior face height (LPFH)/total posterior face height (TPFH) and negatively with LAFH/TAFH, LAFH, upper posterior face height (UPFH)/TPFH, and UPFH (P < 0.05). Bite force was positively correlated with LPFH/TPFH and negatively with UPFH/TPFH (P < 0.05). As the masseter became larger, the anterior maxillary region tended to shift downwards relative to the cranial base, whereas the posterior region tended to shift upwards. The decrease in LAFH/TAFH and increase in LPFH/TPFH as the size of the masseter muscle increases may be influenced not only by the inclination of the mandibular plane but also by the clockwise rotation of the maxilla.

ハシブトガラスとハシボソガラスにおける最大突刺力と最大引張力

We investigated whether there are significant differences in neck muscle mass, maximum peck force, pressure and maximum pull force between Jungle Crows Corvus macrorhynchos and Carrion Crows C. corone. The maximum peck force and pressure were measured using pressure sensitive film. The maximum pull force was measured with spring balances. For male Jungle Crows, neck muscle mass, maximum peck force, pressure and maximum pull force were 8.27 g, 26.8 N, 80.4 MPa and 9.54 N; for females they were 6.82 g, 22.3 N, 69.7 MPa and 8.25 N. Those values for male Carrion Crows were 6.69 g, 22.3 N, 59.7 MPa and 4.07 N;, whereas for females they were 4.50 g, 15.1 N, 53.2 MPa and 2.71 N. Furthermore, neck muscle mass, maximum peck force and maximum pull force were positively correlated with body mass in both species. There were no significant differences in the ratio between the cervical levator mass and the cervical depressor mass, and the maximum peck force exerted by one unit of the cervical depressor mass between Jungle and Carrion Crows. However, the maximum pull force exerted by one unit of the cervical lavator and depressor mass of Jungle Crows was significantly larger than that of Carrion Crows.

Load-Bearing at the Meniscofemoral Joint: An in vitro Study in the Canine Knee

ABSTRACT Background The role of the menisci on tibial load transmission and stress distribution has been extensively studied, but few studies have focused on the meniscofemoral joint during physiologic weightbearing. The objective of this study was to determine the contact areas and local contact stresses at the meniscofemoral interface during physiologic range of motion and axial-loading in the canine knee and to determine the influence of a partial or total meniscectomy. Methods Both fresh-frozen knees of 3 hound-type canines were tested in a universal testing machine configured for an axial-load of 90-120 N. Measurement of the contact area and the local contact stress were done at three different knee angles (30; 50; 70) and with both menisci intact, after partial meniscectomy, and after total meniscectomy. Pressure distribution was estimated by using pressure sensitive film inserted above the menisci. Results After partial meniscectomy, contact areas at 50° of knee flexion decreased approximately 25% on both femoral condyles, and local contact stress increased 30% on the medial femoral condyle but remained unchanged on the lateral. After total meniscectomy, contact areas at 50° of knee flexion decreased approximately 75% on both femoral condyles, and local contact stress increased approximately 60% on the medial compartment and 100% on the lateral compartment. Conclusions These data suggest that a conservative partial meniscectomy leaves the meniscus with an inferior weight distribution function; decreasing, but not canceling the protection on the femoral hyaline cartilage. A dramatic decrease of contact area followed by an increase of local contact stress was noted after a total meniscectomy. The clinical value of this study is to emphasize the biomechanical value of surgical procedures addressing the repair of damaged menisci.

Pure Passive Hyperextension of the Human Cadaver Knee Generates Simultaneous Bicruciate Ligament Rupture

Knee hyperextension has been described as a mechanism of isolated anterior cruciate ligament (ACL) tears, but clinical and experimental studies have produced contradictory results for the ligament injuries and the injury sequence caused by the hyperextension loading mechanism. The hypothesis of this study was that bicruciate ligament injuries would occur as a result of knee hyperextension by producing high tibio-femoral (TF) compressive forces that would cause anterior translation of the tibia to rupture the ACL, while joint extension would simultaneously induce rupture of the posterior cruciate ligament (PCL). Six human knees were loaded in hyperextension until gross injury, while bending moments and motions were recorded. Pressure sensitive film documented the magnitude and location of TF compressive forces. The peak bending moment at failure was 108 N m±46 N m at a total extension angle of 33.6 deg±11 deg. All joints failed by simultaneous ACL and PCL damages at the time of a sudden drop in the bending moment. High compressive forces were measured in the anterior compartments of the knee and likely produced the anterior tibial subluxation, which contributed to excessive tension in the ACL. The injury to the PCL at the same time may have been due to excessive extension of the joint. These data, and the comparisons with previous experimental studies, may help explain the mechanisms of knee ligament injury during hyperextension. Knowledge of forces and constraints that occur clinically could then help diagnose primary and secondary joint injuries following hyperextension of the human knee.

Simulation and experimental analysis of large area substrate overmolding with epoxy molding compounds

This paper presents new experimental and numerical methods to characterize the transfer overmolding of substrates with epoxy polymer. We investigated Multi Chip Modules on ceramic panels as well as on printed circuit boards encapsulated as a Mold Array Package (MAP). Experiments show that the polymer flow during the overmolding process depends significantly on the mold height: While standard MAP-type mold cavities are filled homogeneously and symmetrically in most cases, low cavity heights (<500 μm) can cause the flow front to concentrate on a few flow paths (flow front fingering). We developed a numerical method to describe this inhomogeneous polymer flow. The reason for flow front fingering seems to be local variations of polymer viscosity which enforces a necking on distinct flow paths. Fingering can cause the formation of air traps and excessive wire sweep. We also developed new experimental methods to measure the pressure distribution within cavities: our sensor is based on commercially available, passive pressure sensitive films from FUJUFILM and is operational at temperatures up to 180°.

Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction Restores Patellofemoral Contact Areas and Pressures More Closely Than Nonanatomic Single-Bundle Reconstruction

To investigate the effects of anterior cruciate ligament (ACL) deficiency and nonanatomic single-bundle (SB) and anatomic double-bundle (DB) ACL reconstruction on the contact characteristics of the patellofemoral (PF) joint. By use of a materials testing system, 7 fresh-frozen human cadaveric knees were tested. The following states were tested: ACL-intact knee, nonanatomic SB ACL reconstruction, anatomic DB ACL reconstruction, and ACL-deficient knee. Hamstring autografts were used. PF contact pressures and areas were measured with pressure-sensitive film at 30°, 60°, and 90° of knee flexion with a constant 100-N load on the quadriceps tendon. The total contact area of ACL-deficient and nonanatomic SB ACL-reconstructed knees (123.8 ± 63.9 and 149.6 ± 79.3 mm(2), respectively) significantly decreased when compared with those of the intact knee (206.1 ± 83.6 mm(2)) at 30° of knee flexion. The lateral-facet peak pressure of ACL-deficient and nonanatomic SB ACL-reconstructed knees (1.12 ± 0.52 and 1.22 ± 0.54 MPa, respectively) significantly decreased when compared with those of the intact knee (0.68 ± 0.38 MPa) at 90° of knee flexion. Anatomic DB ACL reconstruction restored the contact pressures and areas to values similar to those of the intact knee (no significant difference). ACL deficiency resulted in a significant decrease in the total and medial PF contact areas and in an increase in the lateral PF contact pressure. Anatomic DB ACL reconstruction more closely restored normal PF contact area and pressure than did nonanatomic SB ACL reconstruction. Our findings suggest that the changes in the PF contact area and pressures in ACL deficiency and after nonanatomic SB ACL reconstruction may be one of the causes of PF osteoarthritis or other related PF problems found at long-term follow-up. Anatomic DB ACL reconstruction may reduce the incidence of PF problems by closely restoring the contact area and pressure.

The development of air-breathing proton exchange membrane fuel cell (PEMFC) with a cylindrical configuration

A small air-breathing proton exchange membrane fuel cell with a cylindrical configuration (Cy-PEMFC) and a helical flow-channel was developed to provide a uniform contact pressure to the membrane electrode assembly (MEA) with a thin cathode current collector. A comparison of the contact pressure and performance of the Cy-PEMFC and general planar PEMFC was performed to determine the effect of the cylindrical configuration. For the contact pressure comparison, numerical analysis was performed using commercial software. Numerical analysis showed that the Cy-PEMFC has its own structural advantage of changing the applied clamping pressure to a uniformly distributed contact pressure. The actual pressure measurements were carried out with pressure-sensitive film to support results of numerical analysis. These results also showed that the Cy-PEMFC had a uniformly distributed contact pressure, whereas the planar PEMFC did not. The polarization curves of both PEMFCs were measured to determine the performance variations caused by the uniform contact pressure and better mass transfer. The maximum power density of the Cy-PEMFC was 220 mW/cm 2, which was approximately 24% higher than the planar PEMFC.

Three-dimensional Contact Analysis of Human Wrist Joint using MRI

The wrist is a complex joint, consisting of the eight small carpal bones that articulate with each other, the metacarpals distally, and the radius, ulna, and triangular fibrocartilage complex proximally. The wrist joint carries out complicated motions that combine palmar/dorsal flexion with radio/ulnar deviation. Knowledge of in vivo joint mechanics is important for understanding pathological mechanisms and the treatment of various joint problems. To examine wrist joint contact mechanisms, in vitro cadaveric studies have been performed using pressure-sensitive film. Investigations on in vivo joint contact mechanisms for wrist motion have rarely been reported. The aim of this study is to investigate in vivo wrist joint contact mechanisms during palmar/dorsal flexion by magnetic resonance imaging (MRI). Magnetic Resonance scanning was performed on the left wrist of twelve participants using a 1.5T-MRI system (Achieva, Philips Medical Systems, Best, Netherlands). The wrist joint was scanned at 5 positions (palmar flexion, –30 degree; neutral, 0 degree; and dorsal flexion, 30, 60 and 90 degrees). Quantitative analysis of wrist joint contact mechanisms was performed for 12 normal radioscaphoid and radiolunate joints. The in-plane motions of the scaphoid and lunate were measured. The contact area at the radioscaphoid joint was significantly greater than that at the radiolunate joint in all wrist positions. The contact area increased with increasing wrist angle, and the contact distributions indicated by 3–D models of the scaphoid and lunate were moved during palmar/dorsal flexion. Contributions of the scaphoid and lunate to in-plane motion at 60 degrees of dorsal flexion were 74% and 52%, respectively.

Regulation of the patellofemoral contact area: An essential mechanism in patellofemoral joint mechanics?

Although the relationship between contact area and pressure under physiological loading has been described in the feline patellofemoral joint, this interaction has only been examined under simplified loading conditions and/or considerably lower forces than those occurring during demanding activities in humans. We hypothesized that patellofemoral contact area increases non-linearly under an increasing joint reaction force to regulate patellofemoral pressure. Eight human cadaveric knees were ramp loaded with muscle forces representative of the stance phase of stair climbing at 30° knee flexion. Continuous pressure data were acquired with a pressure sensitive film that was positioned within the patellofemoral joint. While pressure was linearly dependent upon the resulting joint reaction force, contact area asymptotically approached a maximum value and reached 95% of this maximum at patellofemoral forces of 349–723 N (95% CI). Our findings indicate that the regulatory influence of increasing contact area to protect against high patellofemoral pressure is exhausted at relatively low loads.

Development of an efficient numerical model for hail impact simulation based on experimental data obtained from pressure sensitive film

Aircraft are subjects to a number of unpredictable loadings that can seriously affect their performance. In the spirit of ever increasing the safety of passengers, hail impact has been studied. This paper shows the progress that has been made using pressure sensitive film to measure the hail impact event. Moreover, the smooth particle hydrodynamics (SPH) method in LS-DYNA is used to create a numerical model in order to validate the numerical hail model so that it can be used in future advanced simulations of hail impact on components of aircraft. Results show that the SPH method can be effectively used to create a numerical hail model and that pressure sensitive film is a simple and inexpensive tool to capture the experimental data.

Interface contact profiles of a novel locking plate and its effect on fracture healing in goat

Objective To evaluate the interface characteristics of the new-designed locking plate (LP) and limited contact-dynamic compression plate (LC-DCP) and compare the fracture healing between LP and LC-DCP in a goat tibia fracture model. Methods Eight-hole LP and LC-DCP were applied to fix fresh goat tibiae in a reproducible manner. The average pressure, force and interface contact area were calculated using Fuji prescale pressure sensitive film interposed among the plate and the bone and image analysis system. Eight-hole LP and LC-DCP were applied to each tibia in a goat tibia fracture model. The fracture healing was evaluated by X-ray photography at postoperative 8 weeks. The goats were sacrificed at postoperative 12 weeks. Three-point bending test was conducted in the tibiae. Results The interface contact of LP system was smaller than that of LC-DCP ( P<0.05), while interface contact force of LP system was higher than that of LC-DCP ( P<0.05). Radiographs revealed that the fracture line disappeared in the LP group, while the fracture line was visible in DCP group at postoperative 8 weeks. At postoperative 12 weeks, the bending strength and bending load of fractured tibia were higher in LP group than in DCP group, respectively. Conclusion The new-designed locking plate can significantly decrease the contact area on the bone interface, which further provides better fracture healing than conventional plates.

Pressure-sensitive molecular film for investigation of micro gas flows

For the development of micro- and nano-technology, it has been strongly desired to understand thermo-fluid phenomena inside or around micro- and nano-devices. An optical measurement technique based on the absorption and the emission of photons by molecules is useful for experimental analyses of thermo-fluid phenomena of micro and nanoflows. The pressure-sensitive paint (PSP) technique is a potential diagnostic tool for pressure measurements of micro/nano gas flows because it works as a so-called “molecular sensor”. However, the micro-scale measurement of PSP has been limited by the aggregation of the luminescent molecules and their thick film due to the use of a polymer binder. In our previous work, we adopted the Langmuir–Blodgett (LB) technique to fabricate pressure-sensitive molecular film (PSMF) with ordered molecular assemblies, and investigated properties of PSMF. In this study, a novel approach to enhance the luminescent intensity of PSMF is proposed, and the pressure distribution in a micro-nozzle is successfully measured by using PSMF. Moreover, we compared the pressure distribution measured by PSMF with that numerically analyzed by the direct simulation monte carlo (DSMC) method, showing good agreement with each other.

Near-Surface Composition Profiles and the Adhesive Properties of Statistical Copolymer Films Being Model Systems of Pressure Sensitive Adhesive Films

Statistical copolymer films that consist of two types of monomers, a sticky and a glassy monomer, are investigated. These model systems of pressure-sensitive adhesive films are probed with X-ray reflectivity and mechanical tack measurements. For the first time, composition profiles along the surface normal in the near-surface region are monitored. The influence of the type of monomers being copolymerized, the monomer ratio, and the sample age on the near-surface composition as well as the resulting adhesive performance of the films are analyzed. The copolymers contain ethylhexyl acrylate as the majority component and styrene, maleic acid anhydride, or methylmethacrylate as a minority component. Regardless of the composition, we find a surface enrichment of one component in all samples. In the case of freshly prepared samples, this enrichment is driven by solubility due to the preparation based on solution casting. The minimization of the surface free energy results in an internal reorganization and the component of the statistical copolymer with the lower surface tension enriches at the free surface. The mechanical behavior is not dominated by the surface but by the surface-near part of the composition profile.

A Comparison of Screw Insertion Torque and Pullout Strength

Pullout strength of screws is a parameter used to evaluate plate screw fixation strength. However, screw fixation strength may be more closely related to its ability to generate sufficient insertion because stable nonlocked plate-screw fracture fixation requires sufficient compression between plate and bone such that no motion occurs between the plate and bone under physiological loads. Compression is generated by tightening of screws. In osteoporotic cancellous bone, sufficient screw insertion torque may not be generated before screw stripping. The effect of screw thread pitch on generation of maximum insertion torque (MIT) and pullout strength (POS) was investigated in an osteoporotic cancellous bone model and the relationship between MIT and POS was analyzed. Stainless steel screws with constant major (5.0 mm) and minor (2.7 mm) diameters but with varying thread pitches (1, 1.2, 1.5, 1.6, and 1.75 mm) were tested for MIT and POS in a validated osteoporotic surrogate for cancellous bone (density of 160 kg/m(3) [10 lbs/ft(3)]). MIT was measured with a torque-measuring hex driver for screws inserted through a one-third tubular plate. POS was measured after insertion of screws to a depth of 20 mm based on the Standard Specification and Test Methods for Metallic Medical Bone Screws (ASTM F 543-07). Five screws were tested for each failure mode and screw design. The relationship between MIT and compressive force between the plate and bone surrogate was evaluated using pressure-sensitive film. There was a significant difference in mean MIT based on screw pitch (P < 0.0001), whereas POS did not show statistically significant differences among the different screw pitches (P = 0.052). Small screw pitches (1.0 mm and 1.2 mm) had lower MIT and were distinguished from large pitches (1.5 mm, 1.6 mm, and the 1.75 mm) with higher MIT. For POS, only the 1-mm and 1.6-mm pitch screws were found to be different from each other. Linear regression analysis of MIT revealed a moderate correlation to the screw pitch (R(2) = 0.67, P < 0.0001), whereas the analysis of POS suggested no correlation to the screw pitch (R(2) = 0.28, P = 0.006). Pearson correlation analysis indicated no correlation between MIT and POS (P = 0.069, r = -0.37). A linear relationship of increased compression between the plate and bone surrogate was found for increasing screw torque (R(2) = 0.97). These results indicate that the ability of different screw designs to generate high screw insertion torque in a model of osteoporotic cancellous bone is unrelated to their pullout strength. Therefore, extrapolation of results for POS to identify optimal screw design for osteoporotic bone may not be valid. Screw designs that optimize MIT should be sought for fixation in osteoporotic bone.

Contact Area and Pressure Changes in the Medial Compartment of the Knee in Horizontal Cleavage Tears of the Medial Meniscus (SS-36)

Contact Area and Pressure Changes in the Medial Compartment of the Knee in Horizontal Cleavage Tears of the Medial Meniscus (SS-36)

Loading and knee alignment have significant influence on cartilage MRI T2 in porcine knee joints

Physiological magnetic resonance imaging (MRI) under loading or knee malalignment conditions has not been thoroughly investigated. We assessed the influence of static loading and knee alignment on T2 (transverse relaxation time) mapping of the knee femoral cartilage of porcine knee joints using a non-metallic pressure device. Ten porcine knee joints were harvested en bloc with intact capsules and surrounding muscles and imaged using a custom-made pressure device and 3.0-T MRI system. Sagittal T2 maps were obtained (1) at knee neutral alignment without external loading (no loading), (2) under mechanical compression of 140 N (neutral loading), and (3) under the same loading conditions as in (2) with the knee at 10 degrees varus alignment (varus loading). T2 values of deep, intermediate, and superficial zones of the medial and lateral femoral cartilages at the weight-bearing area were compared among these conditions using custom-made software. Cartilage contact pressure between the femoral and tibial cartilages, measured by a pressure-sensitive film, was correlated with cartilage T2 measurements. In the medial cartilage, mean T2 values of the deep, intermediate, and superficial zones decreased by 1.4%, 13.0%, and 6.0% under neutral loading. They further decreased by 4.3%, 19.3%, and 17.2% under varus loading compared to no loading. In the lateral cartilage, these mean T2 values decreased by 3.9%, 7.7%, and 4.2% under neutral loading, but increased by 1.6%, 9.6%, and 7.2% under varus loading. There was a significant decrease in T2 values in the intermediate zone of the medial cartilage under both neutral and varus loading, and in the superficial zone of the medial cartilage under varus loading (P<0.05). Total contact pressure values under neutral loading and varus loading conditions significantly correlated with T2 values in the superficial and intermediate zones of the medial cartilages. The response of T2 to change in static loading or alignment varied between the medial and lateral cartilages, and among the deep, intermediate, and superficial zones. These T2 changes were significantly related to the contact pressure measurements. Our results indicate that T2 mapping under loading allows non-invasive, biomechanical assessment of site-specific stress distribution in the cartilage.

The SNaP System: Biomechanical and Animal Model Testing of a Novel Ultraportable Negative-Pressure Wound Therapy System

Negative-pressure wound therapy is traditionally achieved by attaching an electrically powered pump to a sealed wound bed and applying subatmospheric pressure by means of gauze or foam. The Smart Negative Pressure (SNaP) System (Spiracur, Inc., Sunnyvale, Calif.) is a novel ultraportable negative-pressure wound therapy system that does not require an electrically powered pump. Negative pressure produced by the SNaP System, and a powered pump, the wound vacuum-assisted closure advanced-therapy system (Kinetic Concepts, Inc., San Antonio, Texas), were compared in vitro using bench-top pressure sensor testing and microstrain and stress testing with pressure-sensitive film and micro-computed tomographic scan analysis. In addition, to test in vivo efficacy, 10 rats underwent miniaturized SNaP (mSNaP) device placement on open wounds. Subject rats were randomized to a system activation group (approximately -125 mmHg) or a control group (atmospheric pressure). Wound measurements and histologic data were collected for analysis. Bench measurement revealed nearly identical negative-pressure delivery and mechanical strain deformation patterns between both systems. Wounds treated with the mSNaP System healed faster, with decreased wound size by postoperative day 7 (51 percent versus 12 percent reduction; p < 0.05) and had more rapid complete reepithelialization (21 days versus 32 days; p < 0.05). The mSNaP device also induced robust granulation tissue formation. The SNaP System and an existing electrically powered negative-pressure wound therapy system have similar biomechanical properties and functional wound-healing benefits. The potential clinical efficacy of the SNaP device for the treatment of wounds is supported.

Misalignment of Total Ankle Components Can Induce High Joint Contact Pressures

A major cause of the limited longevity of total ankle replacements is premature polyethylene component wear, which can be induced by high joint contact pressures. We implemented a computational model to parametrically explore the hypothesis that intercomponent positioning deviating from the manufacturer's recommendations can result in pressure distributions that may predispose to wear of the polyethylene insert. We also investigated the hypothesis that a modern mobile-bearing design may be able to better compensate for imposed misalignments compared with an early two-component design. Two finite element models of total ankle replacement prostheses were built to quantify peak and average contact pressures on the polyethylene insert surfaces. Models were validated by biomechanical testing of the two implant designs with use of pressure-sensitive film. The validated models were configured to replicate three potential misalignments with the most version of the tibial component, version of the talar component, and relative component rotation of the two-component design. The misalignments were simulated with use of the computer model with physiologically relevant boundary loads. With use of the manufacturer's guidelines for positioning of the two-component design, the predicted average joint contact pressures exceeded the yield stress of polyethylene (18 to 20 MPa). Pressure magnitudes increased as implant alignment was systematically deviated from this reference position. The three-component design showed lower-magnitude contact pressures in the standard position (<10 MPa) and was generally less sensitive to misalignment. Both implant systems were sensitive to version misalignment. In the tested implants, a highly congruent mobile-bearing total ankle replacement design yields more evenly distributed and lower-magnitude joint contact pressures than a less congruent design. Although the mobile-bearing implant reduced susceptibility to aberrant joint contact characteristics that were induced by misalignment, predicted average contact stresses reached the yield stress of polyethylene for imposed version misalignments of >5 degrees.

Development of a Model Based Method for Investigating Facet Articulation

Reported investigations of facet articulation in the human spine have often been conducted through the insertion of pressure sensitive film into the joint space, which requires incision of the facet capsule and may alter the characteristics of interaction between the facet surfaces. Load transmission through the facet has also been measured using strain gauges bonded to the articular processes. While this method allows for preservation of the facet capsule, it requires extensive instrumentation of the spine, as well as strain-gauge calibration, and is highly sensitive to placement and location of the strain gauges. The inherently invasive nature of these techniques makes it difficult to translate them into medical practice. A method has been developed to investigate facet articulation through the application of test kinematics to a specimen-specific rigid-body model of each vertebra within a lumbar spine segment. Rigid-body models of each vertebral body were developed from CT scans of each specimen. The distances between nearest-neighboring points on each facet surface were calculated for specific time frames of each specimen's flexion/extension test. A metric describing the proportion of each facet surface within a distance (2 mm) from the neighboring surface, the contact area ratio (CAR), was calculated at each of these time frames. A statistically significant difference (p<0.037) was found in the CAR between the time frames corresponding to full flexion and full extension in every level of the lumbar spine (L1-L5) using the data obtained from the seven specimens evaluated in this study. The finding that the contact area of the facet is greater in extension than flexion corresponds to other findings in the literature, as well as the generally accepted role of the facets in extension. Thus, a biomechanical method with a sufficiently sensitive metric is presented as a means to evaluate differences in facet articulation between intact and treated or between healthy and pathologic spines.