The effect of a gerontology nurse specialist for high needs older people in the community on healthcare utilisation: a controlled before-after study.

BACKGROUND: Nurse-led models of comprehensive geriatric assessment and care coordination can improve health management as well as reduce hospitalisations for high risk community dwelling older people. This study investigated the effect on healthcare utilisation of systematic case finding to identify high risk older people in the community with a subsequent comprehensive assessment and care coordination intervention by a Gerontology Nurse Specialist based in primary care. METHODS: This was a controlled before-after study design located within primary healthcare practices in Auckland, New Zealand. An intervention model was initiated within two primary healthcare practices and involved a screening tool to identify high risk older people with succeeding gerontology nurse specialist assessment and care coordination. The comparison group included older people who received usual care at three comparable primary healthcare practices. The primary outcome measure was acute hospital admissions. Secondary outcomes included hospital re-admissions, length of stay, emergency department presentations, residential care admissions, and community contacts. RESULTS: A total of 579 older people were posted the screening tool in the intervention group, with 517 completed screens (89% response rate) formulating the intervention group. A total of 101 older people were identified as high risk from these screens (20%). The comparison group comprised 883 older people. Comparing the intervention and comparison group, no statistical differences were found for hospital admissions, emergency department presentations, hospital re-admissions, length of stay, or residential care admission. Community physiotherapy showed a statistically significant increase for the intervention compared to the comparison group (p = 0.03). Non-significant findings revealed decreased risk of entering residential care and fewer frequent hospital re-admissions for the intervention group when compared with the comparison group. CONCLUSIONS: This specialist nurse-led intervention involving comprehensive assessment and care coordination care did not appear superior to usual care, however, there is benefit to exploring a more robust randomised controlled trial design. TRIAL REGISTRATION: Retrospectively registered on 18/09/2017 with the Australian New Zealand Clinical Trials Registry (ANZCTR). Registration number ACTRN12617001332314.

A mechanism of injury to the forefoot in car crashes.

OBJECTIVE: The purpose of this study was to determine a mechanism of injury of the forefoot due to impact loads and accelerations as noted in some frontal offset car crashes. METHODS: The impact tests conducted simulated knee-leg-foot entrapment, floor pan intrusions, whole-body deceleration, muscle tension, and foot/pedal interaction. Specimens were impacted at speeds of up to 16 m/s. To verify this injury mechanism research was conducted in an effort to produce Lisfranc type injuries and metatarsal fractures. A total of 54 lower legs of post-mortem human subjects were tested. Two possible mechanisms of injury were investigated. For the first mechanism the driver was assumed to be braking hard with the foot on the brake pedal and at 0 deg plantar flexion (Plantar Nominal Configuration) and the brake pedal was in contact with the foot behind the ball of the foot. The second mechanism was studied by having the ball of the foot either on the brake pedal or on the floorboard with the foot plantar-flexed 35 to 50 deg (Plantar Flexed Configuration). RESULTS: The Plantar Nominal injury mechanism yielded few injuries of the type the study set out to produce. Out of 13 specimens tested at speeds of 16 m/s, three had injuries of the metatarsal (MT) and tarsometatarsal joints. The Plantar Flexed Configuration injury mechanism yielded 65% injuries at high (12.5-16 m/s) and moderate (6-12 m/s) speeds. CONCLUSION: It is concluded that Lisfranc type foot injuries are the result of impacting the forefoot in the Plantar Flexed Configuration. The injuries were consistent with those reported by physicians treating accident victims and were verified by an orthopedic surgeon during post impact x-ray and autopsy. They included Lisfranc fractures, ligamentous disruptions, and metatarsal fractures.

Head injuries in airbag-equipped motor vehicles with special emphasis on AIS 1 and 2 facial and loss of consciousness injuries.

OBJECTIVES: Safety of the airbag supplemental restraint system (airbag) is a well-known concern. Although many lives are saved each year through airbag use, injuries continue to occur, especially to the head. Airbag safety research has focused primarily on severe injuries, while minor and moderate injuries have been largely ignored. METHODS: In this study, 205,977 injury cases from the 1995 to 2001 National Automotive Sampling System (NASS)/ Crashworthiness Data System (CDS) were surveyed to determine the prevalence of AIS 1 and 2 facial and brain loss of consciousness (LOC) injuries and determine if these injuries are a concern. The query was focused on frontal impacts in vehicles equipped with airbags. Only occupants wearing appropriate seatbelts were included in this study so that the airbag would provide occupant protection under optimal conditions. Of the 205,977 injury cases studied, 2.4% met this criterion. RESULTS: From the data gathered, the trends seem to indicate an increase in these specific injuries, both in terms of the total number and the proportion to all injury cases. In 1995, AIS 1 and 2 head injuries accounted for 96.5% of all head injuries caused by airbags. By 2001, the percentage had risen 3.0% to 99.5%. Injuries occurring in vehicles equipped with first-generation versus second generation airbags were compared, and data seem to suggest that there is a higher rate of minor and moderate head injuries when occupants are in second-generation airbag-equipped vehicles, even when appropriate lap and shoulder belts are used. CONCLUSIONS: The short timeframe surveyed prevents drawing meaningful conclusions about statistical significance, but the graphical representations of the data in this study underscore an urgent need for further investigation based on current trends in order to understand the issue of minor and moderate head injury prevention in regard to airbags.

Downy Mildew Caused by Peronospora radii on Marguerite Daisy (Argyranthemum frutescens) in California.

In California, marguerite daisy (Argyranthemum frutescens [= Chyrsanthemum frutescens]) is an important, commercially grown, perennial flowering plant that is used as a potted plant, cutflower, and landscape plant. For two seasons (2003 and 2004), a downy mildew disease has been affecting marguerite daisy at wholesale container and field cutflower nurseries and retail nurseries in coastal California (Monterey, Santa Cruz, and San Mateo counties). The disease occurred early in the season (January) and continued to infect new foliage throughout the year whenever cool, foggy weather occurred. The disease primarily affected newly expanded young leaves on shoot tips. Such leaves were chlorotic, twisted and bent, and stunted. In some cases, leaflet tips turned black and necrotic. The abaxial sides of affected leaves were heavily colonized by the extensive purplish brown growth of downy mildew. Older, fully expanded foliage was unaffected. Flowers could be infected with the fungus growing on the undersides of petals and resulting in slightly twisted, bent shapes. Symptomatic plants and cutflower stems were unmarketable. Hyaline conidiophores emerged from stomata, branched dichotomously (rarely trichotomously), and had branches ending in slender, curved branchlets that did not have swollen tips. Conidia were slightly brown, ovoid, mostly nonpapillate, and measured 28.5 to 40.0 × 19.0 to 28.0 µm. Oospores were not observed in plant tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Peronospora radii (1,2). To prove pathogenicity, plants were spray inoculated with conidial suspensions, incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C).After 18 to 20 days, symptoms and signs of downy mildew developed only on the newest foliage of inoculated plants, and the pathogen morphology matched that of the originally observed pathogen. Untreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew caused by P. radii on marguerite daisy in California and the United States. The pathogen has not been reported on other hosts in California. P. radii is found on marguerite daisy in England, Germany, Israel, Mexico, and the former Yugoslavia (1,2). References: (1) I. S. Ben-Ze'ev et al. Phytoparasitica 15:51, 1987. (2) O. Constantinescu. Sydowia Ann. Mycol. 41:79, 1989.

Fundamentals of impact biomechanics: Part 2--Biomechanics of the abdomen, pelvis, and lower extremities.

This is the second of two chapters (the first chapter appeared in the Annual Review of Biomedical Engineering, 2000, 2:55-81) dealing with some 60 years of accumulated knowledge in the field of impact biomechanics. The regions covered in the first chapter were the head, neck, and thorax. In this chapter, the abdomen, pelvis, and lower extremities are discussed. The thoracolumbar spine is not covered because of length limitations and the low frequency of injury to this area from automotive accidents. Again, in the cited results, the reader needs to be keenly aware of the wide variation in human response and tolerance. This is due primarily to the large biological variations among humans and to the effects of aging. Average values that are useful in design cannot be applied to individuals.

Biomechanics of neurotrauma.

This paper reviews the traditional areas of impact biomechanics as they relate to brain injury caused by blunt impact. These areas are injury mechanisms, human response to impact, human tolerance to impact and the use of human surrogates. With the advent of high-speed computers, it is now possible to add computer models to the list of human surrogates that used to be limited to animals and human cadavers. The advantages and shortcomings of current computer models are discussed. One of the computer models was used to predict the pressures and shear stresses developed in the brain and the extent of stretch of the bridging veins in the brains of American football players who sustained severe helmet-to-helmet head impact during the game. It was found that increases in intracranial pressure were more dependent on translational acceleration while the primary determinant for the development of shear stresses in the brain is rotational acceleration. Although the current head injury criterion is based almost entirely on translational acceleration, it is recommended that any new criterion should reflect the contribution of both translational and rotational acceleration.

Comparison of brain responses between frontal and lateral impacts by finite element modeling.

This study was conducted to investigate differences in brain response due to frontal and lateral impacts based on a partially validated three-dimensional finite element model with all essential anatomical features of a human head. Identical impact and boundary conditions were used for both the frontal and lateral impact simulations. Intracranial pressure and localized shear stress distributions predicted from these impacts were analyzed. The model predicted higher positive pressures accompanied by a relatively large localized skull deformation at the impact site from a lateral impact when compared to a frontal impact. Lateral impact also induced higher localized shear stress in the core regions of the brain. Preliminary results of the simulation suggest that skull deformation and internal partitions may be responsible for the directional sensitivity of the head in terms of intracranial pressure and shear stress response. In previous experimental studies using subhuman primates, it was found that a lateral impact was more injurious than a frontal impact. In this study, shear stress in the brain predicted by the model was much higher in a lateral impact in comparison with a frontal impact of the same severity. If shear deformation is considered as an injury indicator for diffuse brain injuries, a higher shear stress due to a lateral impact indicate that the head would tend to have a decreased tolerance to shear deformation in lateral impact. More research is needed to further quantify the effect of the skull deformation and dural partitions on brain injury due to impacts from a variety of directions and at different locations.

Development of a computer model to predict aortic rupture due to impact loading.

Aortic injuries during blunt thoracic impacts can lead to life threatening hemorrhagic shock and potential exsanguination. Experimental approaches designed to study the mechanism of aortic rupture such as the testing of cadavers is not only expensive and time consuming, but has also been relatively unsuccessful. The objective of this study was to develop a computer model and to use it to predict modes of loading that are most likely to produce aortic ruptures. Previously, a 3D finite element model of the human thorax was developed and validated against data obtained from lateral pendulum tests. The model included a detailed description of the heart, lungs, rib cage, sternum, spine, diaphragm, major blood vessels and intercostal muscles. However, the aorta was modeled as a hollow tube using shell elements with no fluid within, and its material properties were assumed to be linear and isotropic. In this study fluid elements representing blood have been incorporated into the model in order to simulate pressure changes inside the aorta due to impact. The current model was globally validated against experimental data published in the literature for both frontal and lateral pendulum impact tests. Simulations of the validated model for thoracic impacts from a number of directions indicate that the ligamentum arteriosum, subclavian artery, parietal pleura and pressure changes within the aorta are factors that could influence aortic rupture. The model suggests that a right-sided impact to the chest is potentially more hazardous with respect to aortic rupture than any other impact direction simulated in this study. The aortic isthmus was the most likely site of aortic rupture regardless of impact direction. The reader is cautioned that this model could only be validated on a global scale. Validation of the kinematics and dynamics of the aorta at the local level could not be done due to a lack of experimental data. It is hoped that this model will be used to design experiments that can reproduce field relevant aortic ruptures in the laboratory. Only after such experiments have been run, can local validation be examined and the model judged to be acceptable or unacceptable.

Investigation of Head Injury Mechanisms Using Neutral Density Technology and High-Speed Biplanar X-ray.

The principal focus of this study was the measurement of relative brain motion with respect to the skull using a high-speed, biplanar x-ray system and neutral density targets (NDTs). A suspension fixture was used for testing of inverted, perfused, human cadaver heads. Each specimen was subjected to multiple tests, either struck at rest using a 152-mm-diameter padded impactor face, or stopped against an angled surface from steady-state motion. The impacts were to the frontal and occipital regions. An array of multiple NDTs was implanted in a double-column scheme of 5 and 6 targets, with 10 mm between targets in each column and 80 mm between columns. These columns were implanted in the temporoparietal and occipitoparietal regions. The impacts produced peak resultant accelerations of 10 to 150 g, and peak angular accelerations between 1000 and 8000 rad/s(2). For all but one test, the peak angular speeds ranged from 17 to 22 rad/s. The relative 3D displacements between the skull and the NDTs were analyzed. The localized motions of the brain generally followed loop or figure eight patterns, with peak displacements on the order of +/- 5 mm. These results can be used to further finite-element modeling efforts.

Recent advances in brain injury research: a new human head model development and validation.

Many finite element models have been developed by several research groups in order to achieve a better understanding of brain injury. Due to the lack of experimental data, validation of these models has generally been limited. Consequently, applying these models to investigate brain responses has also been limited. Over the last several years, several versions of the Wayne State University brain injury model (WSUBIM) were developed. However, none of these models is capable of simulating indirect impacts with an angular acceleration higher than 8,000 rad/s(2). Additionally, the density and quality of the mesh in the regions of interest are not detailed and sensitive enough to accurately predict the stress/strain level associated with a wide range of impact severities. In this study, WSUBIM version 2001, capable of simulating direct and indirect impacts with a combined translational and rotational acceleration of the head up to 200 g and 12,000 rad/s(2) has been developed. This new finely meshed model, consisting of more than 314,500 elements and 281,800 nodes, also simulates an anatomically detailed facial bone model. An additional new feature of the model is the damageable material property representation of the facial bone and the skull, allowing it to simulate bony fractures. The model was subjected to extensive validation using published cadaveric test data. These data include the intracranial and ventricular pressure data reported by Nahum et al. (1977) and Trosseille et al. (1992), the relative displacement data between the brain and the skull reported by King et al. (1999) and Hardy et al. (2001), and the facial impact data reported by Nyquist et al. (1986) and Allsop et al. (1988). With the enhanced accuracy of model predictions offered by this new model, along with new experimental data, it is hoped that it will become a powerful tool to further our understanding of the mechanisms of injury and the tolerance of the brain to blunt impact.

Lower Limb: Advanced FE Model and New Experimental Data.

The Lower Limb Model for Safety (LLMS) is a finite element model of the lower limb developed mainly for safety applications. It is based on a detailed description of the lower limb anatomy derived from CT and MRI scans collected on a subject close to a 50th percentile male. The main anatomical structures from ankle to hip (excluding the hip) were all modeled with deformable elements. The modeling of the foot and ankle region was based on a previous model Beillas et al. (1999) that has been modified. The global validation of the LLMS focused on the response of the isolated lower leg to axial loading, the response of the isolated knee to frontal and lateral impact, and the interaction of the whole model with a Hybrid III model in a sled environment, for a total of nine different set-ups. In order to better characterize the axial behavior of the lower leg, experiments conducted on cadaveric tibia and foot were reanalyzed and experimental corridors were proposed. Future work will include additional validation of the model using global data, joint kinematics data, and deformation data at the local level.

Qualitative analysis of neck kinematics during low-speed rear-end impact.

OBJECTIVE: To analyze neck kinematics and loading patterns during rear-end impacts. DESIGN: The motion of each cervical vertebra was captured using a 250 frame/s X-ray system during a whole body rear-end impact. These data were analyzed in order to understand different phases of neck loading during rear-end impact. BACKGROUND: The mechanism of whiplash injury remains largely unknown. An understanding of the underlying kinematics of whiplash is crucial to the identification of possible injury mechanisms before countermeasures can be designed. METHODS: Metallic markers were inserted into the vertebral bodies and spinous processes of each of the seven cervical vertebrae. Relative displacement-time traces between each pair of adjacent cervical vertebrae were calculated from X-ray data. Qualitative analyses of the kinematics of the neck at different phase of impact were performed. RESULTS: The neck experiences compression, tension, shear, flexion and extension at different cervical levels and/or during different stages of the whiplash event. CONCLUSIONS: Neck kinematics during whiplash is rather complicated and greatly influenced by the rotation of the thoracic spine, which occurs as a result of the straightening of the kyphotic thoracic curvature. RELEVANCE: Understanding the complicated kinematics of a rear-end impact may help clinicians and researchers shed some light on potential mechanisms of whiplash neck injury.

Kinematics of human cadaver cervical spine during low speed rear-end impacts.

The purposes of this study were to measure the relative linear and angular displacements of each pair of adjacent cervical vertebrae and to compute changes in distance between two adjacent facet joint landmarks during low posterior-anterior (+Gx) acceleration without significant hyperextension of the head. A total of twentysix low speed rear-end impacts were conducted using six postmortem human specimens. Each cadaver was instrumented with two to three neck targets embedded in each cervical vertebra and nine accelerometers on the head. Sequential x-ray images were collected and analyzed. Two seatback orientations were studied. In the global coordinate system, the head, the cervical vertebrae, and the first or second thoracic vertebra (T1 or T2) were in extension during rear-end impacts. The head showed less extension in comparison with the cervical spine. Relative motion for each cervical motion segment went from flexion at the upper cervical levels to extension at the lower cervical levels, with a transition region at the mid-cervical levels. This rotational pattern formed an "S" shape in the cervical spine during the initial phase of low-speed rear impacts. A pair of facet joint landmarks on each cervical motion segment was used to measure the distance across the joint space. Uni-axial facet capsular strains were calculated by dividing changes in this distance over the original distance in seven tests using three specimens. In 20-degree seatback tests, the average strain was 32+/-11% for the C2/C3 facet joint (17%-43% range), and 59+/-26% for the C3/C4 facet joint (41%-97% range). The C4/C5 and C5/C6 facet joints exhibited peak tensile or compressive strains in different specimens. In 0-degree seatback tests, the average strain was 28+/-11% for the C2/C3 facet joint (21%-41% range), 30+/-9% for the C3/C4 facet joint (21%-39% range), 22+/-4% for the C4/C5 facet joint (19%-25% range), and 60+/-13% for the C5/C6 facet joint (51%-69% range). In 20-degree seatback tests, there was less initial cervical lordosis, more upward ramping of the thoracic spine, and more relative rotation of each cervical motion segment in comparison with the 0-degree seatback tests. Relative to T1, the head went from flexion to extension for 20-degree seatback tests while stayed in extension for 0-degree seatback tests.

Development of a finite element model of the human shoulder.

Previous studies have hypothesized that the shoulder may be used to absorb some impact energy and reduce chest injury due to side impacts. Before this hypothesis can be tested, a good understanding of the injury mechanisms and the kinematics of the shoulder is critical for occupant protection in side impact. However, existing crash dummies and numerical models are not designed to reproduce the kinematics and kinetics of the human shoulder. The purpose of this study was to develop a finite element model of the human shoulder in order to achieve a deeper understanding of the injury mechanisms and the kinematics of the shoulder in side impact. Basic anthropometric data of the human shoulder used to develop the skeletal and muscular portions of this model were taken from commercial data packages. The shoulder model included three bones (the humerus, scapula and clavicle) and major ligaments and muscles around the shoulder. This model was then integrated into a human thorax model developed at Wayne State University (WSU) along with pre-existing models of other body parts such as the pelvis and the lower extremities. Material properties used for the model were taken from the literature. The model was first used to simulate lateral shoulder impact study by the Association Peugeot- Renault (APR) followed by simulations of several of the 17 rigid and padded cadaveric impacts conducted on a side impact sled at WSU. Contact forces measured at the levels of shoulder, thorax, abdomen and pelvis were used as response variables to validate the model. Additionally, a cadaveric test involving the deployment of a generic side airbag was also used to check the validity of the model. Model prediction of accelerations of the shoulder matched well against those measured experimentally. The role of the shoulder in side impact protection and the reduction of injury to the ribcage are discussed, based on model results.

Fundamentals of impact biomechanics: Part I--Biomechanics of the head, neck, and thorax.

This is the first of two chapters dealing with some 60 years of accumulated knowledge in the field of impact biomechanics. The regions covered in this first chapter are the head, neck, and thorax. The next chapter will discuss the abdomen, pelvis, and the lower extremities. Although the principal thrust of the research has been toward the mitigation of injuries sustained by automotive crash victims, the results of this research have applications in aircraft safety, contact sports, and protection of military personnel and civilians from intentional injury, such as in the use of nonlethal weapons. The reader should be keenly aware of the wide variation in human response and tolerance data in the cited results. This is due primarily to the large biological variation among humans and to the effects of aging. Average values are useful in design but cannot be applied to individuals.

Effects of phospholipase A2 on lumbar nerve root structure and function.

STUDY DESIGN: To investigate the effects of phospholipase A2 on the neurophysiology and histology of rat lumbar spinal nerves and the corresponding behavioral changes. OBJECTIVES: To study possible mechanisms of sciatica. SUMMARY OF BACKGROUND DATA: The pathophysiology of sciatica is uncertain, although mechanical, chemical, and ischemic factors have been proposed. METHODS: Phospholipase A2 was injected into the rat L4-L5 epidural space, and the rats were observed for 3 or 21 days. Behavioral studies were conducted daily during the survival period. On the 3rd or 21st day, extracellular nerve recordings were made from dorsal roots, to determine discharge properties and mechanical sensitivity. The nerve roots were then sectioned for a light-microscopic examination. RESULTS: Motor weakness of hind limbs and altered sensation were observed. In the 3-day phospholipase A2 groups, squeezing the dorsal roots at the L4-L5 disc level (force = 0.8 g) evoked sustained ectopic discharge that lasted approximately 8 minutes. Squeezing the roots distal to the L4-L5 area did not result in sustained discharges. In sham, control, and 21-day phospholipase A2 groups, squeezing the dorsal roots elicited only a transient firing that lasted approximately 0.1 second. Loss of myelin was seen in the nerve root cross sections in the 3-day group, and remyelination was observed in the 21-day group. No abnormality was found in the control groups. CONCLUSIONS: Based on these studies, it is hypothesized that phospholipase A2 causes demyelination that results in hypersensitive regions where ectopic discharge may be elicited by mechanical stimulation. These ectopic discharges may be a source of sciatica. We believe that, as long as these irritating factors are present, the hypersensitive nerve root nerve will continue to fire, and sciatic pain will persist.

Mechanisms of low back pain: a neurophysiologic and neuroanatomic study.

Idiopathic low back pain has confounded health care practitioners for decades. The cellular and neural mechanisms that lead to facet pain, discogenic pain, and sciatica are not well understood. To help elucidate these mechanisms, anesthetized New Zealand white rabbits were used in a series of neurophysiologic and neuroanatomic studies. These studies showed the following evidence in support of facet pain: an extensive distribution of small nerve fibers and endings in the lumbar facet joint, nerves containing substance P, high threshold mechanoreceptors in the facet joint capsule, and sensitization and excitation of nerves in facet joint and surrounding muscle when the nerves were exposed to inflammatory or algesic chemicals. Evidence for pain of disc origin included an extensive distribution of small nerve fibers and free nerve endings in the superficial annulus of the disc and small fibers and free nerve endings in adjacent longitudinal ligaments. Possible mechanisms of sciatica included vigorous and long lasting excitatory discharges when dorsal root ganglia were subjected to moderate pressure, excitation of dorsal root fibers when the ganglia were exposed to autologous nucleus pulposus, and excitation and loss of nerve function in nerve roots exposed to phospholipase A2.

The relationship between loading conditions and fracture patterns of the proximal femur.

In an attempt to test the hypothesis of spontaneous hip fracture, seven pairs of femurs, with ages ranging from 59 to 90, were tested under two loading conditions designed to simulate muscular contraction. Simulated iliopsoas contraction produced femoral neck fractures at an average normalized ultimate load of 5.2 +/- 0.8 times body weight. Simulated gluteus medius contraction produced sub-/inter-trochanteric fractures at an average normalized ultimate load of 4.1 +/- 0.6 times body weight. The average ultimate load for all specimens was 3040 +/- 720 N. Fracture patterns produced by both loading conditions were clinically relevant. The results from this study suggest that abnormal contraction produced by major rotator muscles could induce hip fracture.

Lumbar facet pain: biomechanics, neuroanatomy and neurophysiology.

Idiopathic low back pain has confounded health care practitioners for decades. Although there has been much advance in the understanding of the biomechanics of the lumbar spine over the past 25 years, the cellular and neural mechanisms that lead to facet pain are not well understood. An extensive series of experiments was undertaken to help elucidate these mechanisms and gain a better understanding of lumbar facet pain. Biomechanic and neuroanatomic studies were performed in human cadaveric facet joints and neurophysiologic studies were performed in New Zealand White rabbits. These studies provide the following evidence to help explain the mechanisms of lumbar facet pain: (1) The facet joint can carry a significant amount of the total compressive load on the spine when the human spine is hyperextended. (2) Extensive stretch of the human facet joint capsule occurs when the spine is in the physiologic range of extreme extension. (3) An extensive distribution of small nerve fibers and free and encapsulated nerve endings exists in the lumbar facet joint capsule, including nerves containing substance P, a putative neuromodulator of pain. (4) Low and high threshold mechanoreceptors fire when the facet joint capsule is stretched or is subject to localized compressive forces. (5) Sensitization and excitation of nerves in facet joint and surrounding muscle occur when the joint is inflamed or exposed to certain chemicals that are released during injury and inflammation. (6) Marked reduction in nerve activity occurs in facet tissue injected with hydrocortisone and lidocaine. Thus, the facet joint is a heavily innervated area that is subject to high stress and strain. The resulting tissue damage or inflammation is likely to cause release of chemicals irritating to the nerve endings in these joints, resulting in low back pain.