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Water pollution from nonpoint sources is increasingly a focal point for efforts to reduce water quality impairments. These efforts often require or subsidize riparian buffer strips. However, the costs of these buffer strips are not always well understood. This article estimates the annualized costs of establishing and maintaining 45.7-meter (150-feet) riparian buffer strips on all agricultural land adjoining a waterway in Tennessee's Harpeth River watershed. A mandatory requirement for buffer strips of this width would result in 4,955 hectares (12,245 acres) of buffer strips at an annualized cost of $1 .3 million. A supply curve for buffer strips is also constructed. Since the passage of the Clean Water Act (CWA), largely unregulated nonpoint sources (NPS) of pollution have contributed to an increasing share of the nation's water quality problems (Copeland). While the amount of agricultural land in the United States has remained relatively constant over the past thirty years, agricultural production has increased because of technological advances and increasingly fertilizer-intensive agricultural practices. These fertilizerintensive practices have been a major contributor to a threefold increase in the nitrate load in the Mississippi River entering the Gulf of Mexico (Greenhalgh and Sauer). When the states and territories surveyed the nation's rivers and streams, they found 39% of the segments surveyed impaired for one or more uses. Agriculture was listed as a contributor to 48% of these impairments - more than twice as much as any other source (USEPA 2002).

The effects of migrating seniors on the provision of local public services in rural communities is growing in importance because of the large number of retiring baby boomers and the increasing rate at which these retirees are locating outside traditional retirement destinations. Some communities are optimistic about attracting and retaining retirees as an economic development strategy, but others are concerned that inmigrating seniors may be reluctant to support local public services, such as education, bringing with them “Gray Peril.” This article attempts to clarify questions regarding the Gray Peril hypothesis and local ability and willingness to fund education in Tennessee, an increasingly popular retirement destination. To this end, county per pupil education expenditure growth is explained by growth trends in local property tax assessment and sales tax revenue, and migration patterns of the retirement-aged population from 1962 to 2002.

This research analyzes spatial and temporal variation in the effects of lot size and proximity to open space on residential home values in a single Tennessee county. The findings show that the value of proximity to greenways, parks, and water bodies increased over time, while the value of lot size and proximity to golf courses fell. Proximity to open space is found to be a substitute for lot size, although the degree of substitutability has weakened over time. Geographic variation in the marginal effects of lot size and proximity to open space is analyzed using locally weighted regression analysis.

Trading in water pollution reduction credits, or “water quality trading,” (WQT) has been touted as a cost-effective solution to water quality impairments caused by nutrients and other oxygen-demanding pollutants. However, trading programs require buyers and sellers to be successful. Whether a particular source of pollutants is capable of participating in a trading program depends upon the spatial relationship of that source to both impairments and other sources. This paper analyzes these spatial relationships for all of Tennessee's watersheds to evaluate the feasibility of water quality trading and to identify areas where trading programs are most likely to be successful. Copyright 2008, Oxford University Press.

Communities in most states are under pressure to reduce the amount of solid waste going into landfills. Many are making efforts to encourage their citizens to practice backyard composting. A logit regression analysis was conducted to identify factors associated with backyard composting of yard and food wastes in a case study area. Sample data were obtained through a September 1997 telephone survey of 865 households residing in single-family dwellings in Knox County, Tennessee. Findings indicate that a number of variables reflecting complementary behavior, attitudes, knowledge, and peer influence were significantly related to composting behavior. Policy implications of these findings are outlined. Key Words: composting, food waste, solid waste, yard waste During the 1990s, most states enacted municipal solid waste management legislation establishing a goal to achieve a certain recycling rate or to reduce the amount of waste reaching landfills or incinerators by a certain percentage relative to a base year. As of 2001, very few states had met or even come close to achieving their goals (Goldstein and Madtes, 2001). A general recognition now exists that substantial further increases in recycling rates for traditional materials (e.g., aluminum, steel, glass, plastics, and newsprint) will be difficult to achieve. Attention in recent years has thus been increasingly focused upon organic materials which can be composted, especially yard waste and food scraps. Based on U.S. Environmental Protection Agency (EPA) estimates, 230 million tons of municipal solid waste were generated in 1999. Of this amount, 12.1 % was estimated to be yard waste, and 10.9% food waste (U.S. EPA, 2002). To address the yard waste component, 21 states have implemented some form of ban on disposal of yard wastes in landfills, and many communities have established programs providing curbside collection and composting of yard wastes (Goldstein and Madtes, 1999). According to EPA, about 45% of the yard waste in the United States was collected, composted, or recycled in some way in 1999, but at an estimated cost of nearly $90 per ton (U.S. EPA, 1999). With regard to food waste, EPA estimated only 5% was composted or recycled in 1999, while a 2000 study in Seattle found that the largest portion of waste not already addressed by recycling programs is compostable food, representing about 31 % (Bagby and Tarnecki, 2001). Results of pilot programs have shown curbside collection of food residuals adds another level of complexity and cost to a solid waste management system (Farrell, 2001). Consequently, some solid waste management specialists have emphasized the potential contribution backyard composting (BYC) can make. A study of 20 BYC programs operating during 1993-1994 concluded their cost per ton of waste diverted-at generally less than $20 per ton-was much lower than the cost per ton for traditional collection and disposal systems (Applied Compost Consulting, 1996). Tennessee's 1991 Solid Waste Management Act required solid waste regions (one or more counties) to reduce the tonnage of disposed waste per capita by 25% by 1996. About half of the 63 regions in the state failed to achieve the goal by that date, and were granted a five-year extension. In 1998, the methodology for calculating progress toward the 25% waste reduction goal was modified to account for the differential impact of economic growth across regions, and the deadline was extended to 2003. Many regions projected in their original plans to achieve as much as 10% waste reduction by diverting yard waste and other organic material through BYC programs. However, very little progress in this regard can be documented to date. A number of articles in waste industry magazines have described community programs designed to encourage BYC. Some have reported estimates of the percentage of households practicing BYC ranging from 2% to 60% (Riggle, 1996a, b; Sherman, 1996a, b; Vossen and Rilla, 1997). …

How relatively painless it was to agree 18 months ago to be nominated for the position of President-Elect of the Southern Agricultural Economics Association (SAEA). Preparing for this address, the most daunting task faced by holders of this office, has been anything but painless. At the same time I can say unequivocally that it has been a productive exercise for me. I hope that something I say will make your time spent listening worthwhile as well.

This study determines the likely effect of cost-share incentives on participation in the Tennessee forest Stewardship Program and identifies other factors that may contribute to participation. A random utility model is used to determine the probability that a landowner will choose to participate in the program. A binary choice model is specified to represent the dichotomous decision and a logit procedure is used to fit the model. Data are obtained from mail surveys of 4,000 randomly selected landowners. Results indicate that attitudes and knowledge of forestry programs may be more influential in a landowner's decision to participate than monetary incentives.

The aging population of the United States has long been a subject of debate and inquiry for development planners, policy makers, and researchers. The doubling of the population of Americans older than 65 since 1960 (while the population younger than 65 has grown by only one half) (Fuguitt et al. 2002), has prompted interest in their effect on the economies in which they live (Serow 2003) and their potential as a resource for rural economic development (Fagan 1988; Fagan and Longino 1993; Reeder 1998). Interest in these issues intensified as the baby boomer generation approached retirement age. The retirement of this age cohort is likely to have profound effects on the nation and its economy as this cohort is not only much larger than previous age cohorts, but also healthier and wealthier due to economic growth and advances in the quality of healthcare. Older Americans increasingly have the means and the motivation to migrate to a different area upon retirement. For example, it is estimated that over the next 18 years, approximately 400,000 retirees each year – with an average of $320,000 to spend on a new home – will choose to relocate beyond their state borders (Vestal 2006). The South and West have been and continue to be popular destinations for these migrants (Serow 2001; He and Schachter 2003), although more are choosing to locate outside of the traditional retirement areas of Florida and Arizona (Vestal 2006). One driving force of this shift is the “halfback” phenomenon in the Southeast where retirees who had previously migrated to the coast are returning halfway back to their ancestral homes by relocating to areas such as the Southern Appalachian mountain regions of eastern Tennessee, western North Carolina, and northern Georgia (Park et al. 2007). Further, later-life migrants are frequently settling in rural places or small towns (Fuguitt et al. 2002). For example, in 2000 a half million more persons above 60 moved into non-metro counties than out of them (Beale 2005). These trends beg the question of how the recent in-migration of older Americans is affecting local economies, particularly in rural areas where the marginal effect of in-migration may be proportionally greater than in more populous urban areas.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a unique source of reach spectral information useful for many applications. It provides observations in 36 spectral bands ranging in wavelengths from 0.4μm to 14.4μm with a spatial resolution from 250m to 1km. The standard MODIS data processing system and products cover the basic operational needs for a number of products and applications. Implemented globally they, however, cannot always make the best use of MODIS 250m and 500m land channels required for terrestrial monitoring and climate change applications. To address the need of regional users in enhanced MODIS data, especially in terms of spatial resolution, an independent technology for processing MODIS imagery has been developed. It uses MODIS level 1B top of the atmosphere swath data as input. The system includes the following steps: 1) fusion (downscaling) of MODIS 500m land channels B3-B7 with 250m bands B1-B2 to obtain consistent 250m imagery for all seven bands B1-B7; 2) re-projection of 250m bands into standard geographic projection; 3) scene identification at 250m spatial resolution to obtain mask of clear-sky, cloud and cloud shadows; 4) compositing clear-sky pixels over 10-day intervals; 5) atmospheric correction; 6) landcover-based BRDF fitting procedure. The fusion technique is designed to work with MODIS/TERRA data due to known problems with band-to-band registration accuracy on MODIS/AQUA. The developed method is applied to generate MODIS clear-sky land products in the Lambert Conformal Conical (LCC) projection for Canada and the Lambert Azimuthal Equal-Area (LAEA) projection for the North America and the Arctic circumpolar zone. The novel clear-sky compositing approach is proposed that significantly reduces impact of BRDF effect on raw composites by separation of pixels into two ranges of relative azimuth angle within 90°-270° and outside of this interval.

A new technology has been developed at the Canada Centre for Remote Sensing (CCRS) for generating North America continental scale clear-sky composites at 250 m spatial resolution of all seven MODIS land spectral bands (B1-B7). The MODIS Level 1B (MOD02) swath level data were used as input to circumvent the problems with image distortion in the mid-latitude and polar regions inherent to the sinusoidal (SIN) projection utilized for the standard MODIS data products. The new data products are stored in the Lambert Conformal Conical (LCC) projection for Canada and the Lambert Azimuthal Equal-Area (LAEA) projection for North America. The MODIS 500m data (B3-B7) were downscaled to 250m resolution using an adaptive regression algorithm. The clear-sky composites are generated using scene identification information produced at 250m resolution and multi-criteria selection which depends on pixel identification. Cloud shadows were also identified and removed from output product. It is demonstrated that new approach provides better results than any scheme based on a single compositing criterion, such as maximum NDVI, minimum visible reflectance, or combination of them. To account for surface bi-directional properties, two clear-sky composites for same time period are produced for the relative azimuth angles within 90°-270° and outside of this interval. Comparison with Landsat imagery and MODIS standard composite products demonstrated advantages of new technique for screening cloud and cloud shadow and providing the high spatial resolution. The final composites were produced for every 10-day intervals since March 2000. The composite products have been used for mapping albedo and vegetation properties as well as for land cover and change detections applications at 250m scale.

Migrating seniors are choosing to live in nonmetropolitan areas. Many nonmetropolitan communities are, in turn, focusing on recruiting retirees as an economic development strategy. This paper applies a regional growth model to measure the impact of migrating seniors (between 1995 and 2000) on employment and business establishment growth in the southeastern United States from 2000 to 2004. This region is a popular senior destination due to low taxes, mild climate, inexpensive housing, and proximity to friends and families. The economic impacts of senior migration are spatially heterogeneous across the region, suggesting alternative policy implications for urban and nonurban communities.

A two-stage multinomial logit selection model is used to model the relationship between demographic characteristics and housing density across Tennessee's six metropolitan statistical areas. The study finds that there is both spatial correlation and heterogeneity in the spatial distribution of housing both within and across the six areas. For example, Memphis, the most densely populated area, has the least amount of spatial correlation among housing density at the neighborhood level, while Johnson City, which has the lowest overall housing density, has the highest degree of spatial correlation.

Rising landfill costs have forced solid waste managers to consider waste stream reduction alternatives such as household recycling. Explaining the factors which motivate households to recycle is important to regions where households must bear a large portion of the recycling cost because unit-based garbage disposal fees and curbside recycling are not feasible options. Empirical results indicate that residents are responsive to constraints introduced by the household production technology, such as time costs and storage space, but are not responsive to variables measuring a recycling promotional program. Promotion efforts should switch focus from broader “public good” benefits of recycling to reducing household-level household production constraints.

Carriker, Infanger, and Shabman and Stephenson have provided a set of papers related to the current debate over environmental regulatory reform. Each paper stands alone as a distinct and valuable contribution to the literature on this subject. Yet as a set they complement one another and form a whole that is greater than the sum of its parts.Carriker, in his comprehensive overview of federal environmental policy in the U.S., painstakingly describes the origins, evolution, and impacts of nine major pieces of environmental legislation, and thus sets the stage for discussion of current issues and professional perspectives in the other two papers. Carriker's paper is well documented and should also serve as a good primer for students taking natural resource and environmental economics courses or contemplating graduate research in this area.

A contingent valuation model is developed to estimate the value of the recreational experience for visitors to Reelfoot Lake in northwestern Tennessee. Hicksian compensating variation measures of consumer surplus were estimated. Individual willingness-to-pay and aggregate willingness-to-pay were calculated for the lake.

I intend to accomplish three things with my discussion of this paper. First, I offer a summary of Jim’s basic line of reasoning, as I understand it, and then suggest what I believe to be the most important contributions his paper makes. Second, I use his paper as a jumping off point to offer my assessment of a likely shift to privatization in the provision of one traditionally “public” service in rural communities, with which I am particularly interested. Third, I comment briefly on the possible role of an intermediate institutional arrangement-public, but with market type incentives--for that same public service.

agement strategy. Also, external cost estimates Much of the solid waste stream in the United States could provide insight into alternative incentive and is generated by metropolitan areas, while associated mitigation strategies designed to facilitate landfill landfills are often located in adjacent rural commu- siting. nities. Landfill disposal of municipal solid waste Much of the solid waste stream is generated by often creates external costs to nearby residents. Con- metropolitan areas, while associated landfills are tingent valuation was used to estimate external costs often located in adjacent rural communities that are of siting a landfill in the Carter community of Knox more sparsely populated. The Carter community of County, Tennessee. Estimates of annual external Knox County, Tennessee, is an example of such a costs were $227 per household. Household income, community where the landfill siting issue has been size, years in the community, and distance from the debated In 1987, the siting issue emerged when proposed landfill and the respondent's education, county administrators considered a request by sex, and perception of health risks were important Browning Ferris, Inc. (BFI), to site a new landfill on in determining a household's willingness to pay to land in the center of that community for which BFI avoid having a landfill in the Carter community. had purchased an option to buy. The proposed site Also, households whose drinking water supplies was located within 1,000 feet of the community were at risk of contamination were willing to pay recreation facilities and the high school. The BFI $141 more than those who used piped city water or request was denied by the Knox County Commisbottled water. sion partly because of strong public opposition from Carter community residents. BFI sued for permisfavor of Knox County and against BFI. Subsequently, an appeals court overturned the decision Increased perception of health and other risks as- of the lower court and granted permission for BFI to sociated with solid waste disposal facilities has construct the landfill. made the siting of new municipal landfills techni- The objectives of this study were (1) to estimate cally difficult and in some cases socially and politi- the external costs accruing to nearby residents from cally unacceptable. Landfill disposal practices siting a municipal landfill in the Carter community create external costs to nearby residents who per- and (2) to investigate the relationship between ceive risks associated with groundwater contamina- household characteristics and the level of external tion, truck traffic, odor, noise, and litter, as well as costs borne by Carter community households. The other nonmarket costs not borne by waste disposal contingent valuation method was used to accomfirms and producers of garbage. These external costs plish these objectives. This approach has been used result in an inefficient allocation of resources (too to evaluate changes in hazardous waste risks (Smith

Twenty selected patients with spondylolysis have been studied following apophyseal joint arthrography. In each instance a communication with the defect of the pars interarticularis was demonstrated by the extension of contrast medium from injection into the adjacent facet joint. The clinical and radiological features are described. The anatomical basis of the abnormality is presented using macroscopic and radiographic correlation from a dissected cadaveric specimen of spondylolysis. Sixty-five per cent of the patients experienced significant relief of pain symptoms when long-acting local anaesthetic was introduced into the facet joint.

In developing strategies for nonpoint pollution control in designated 208 areas, one of the issues facing planners is the relative emphasis which should be placed upon urban versus agricultural non-point control. Five criteria which should be considered in designing an appropriate BMP strategy mix are discussed: 1) BMP cost effectiveness; 2) information and administrative cost; 3) flexibility, which relates to the cost of reversibility given substantial uncertainties; 4) associated effects, both direct and indirect; and 5) acceptability to local jurisdictions and groups. Whatever an evaluation on the basis of the first four criteria may suggest, acceptance of agricultural BMPs will be difficult to achieve, thus favoring urban oriented strategies, unless local revenue sources are developed to offer payments to farmers for BMP adoption.

Arthrography following hip replacement has been reviewed. The problems encountered have been analysed with particular reference to technique and accuracy. The accepted criteria for loosening have not been consistently reliable and have led to false positive interpretation of loosening of the acetabular component. The reasons for false negative results are also considered.

Clinically silent cervicodorsal fracture may occur following upper-thoracic injury in the presence of a characteristic buckling injury to the sternum. Failure to recognise the association may result in gross kyphotic deformity. Three examples are provided, illustrating the role of radiology in the management of this complex traumatic lesion.

and the logic behind them. Second, best Th art r on analyses of the cost management practice (BMP) options and costs effhstivlenes of three soil erosion cosntrl are specified for representative farm units in a effectiveness of three soil erosion control case study area. Third, an integer program- policy alternatives, specifically 1) uniform- ming mdel is emloyed to simulateer prograe rate cost sharing, 2) variable-rate cost shar- smingod strategies ne d allow comparison of ing, and 3) fixed subsidy payments per unit s s an a ing, and 3) fixed subsidy payments per unit their cost effectiveness. Finally, conclusions reduction in erosion. A brief discussion of the thr cost effectiveness. Finally, c onclusions place of these alternative subsidy strategies erosion control policy. within the context of the current policy en- vironment is presented. Integer programming THE SOIL EROSION CONTROL voluntary adoption of BMPs appears likely to be the general policy approach for the Soil erosion control policy in the United foreseeable future (Sharp and Bromley; States has received much criticism in recent AAEA Task Force). Subsidy programs have years, with the cost effectiveness of major generally been designed to compensate far- programs being questioned (USGAO). A num- mers by an amount equal to or greater than ber of innovative changes in these programs their net BMP cost, that is, gross costs for have been introduced or suggested. This arti- BMP adoption less the economic return from cle reports on comparative analyses of the on-site productivity benefits of soil erosion cost effectiveness of the traditional strategy control, though Michalson and Brooks have of uniform-rate cost sharing to induce volun- argued for off-site damages as a basis for sub- tary adoption of soil erosion control practices sidy amounts. Cost effectiveness in the use of and two alternative subsidy strategies. One is public funds for subsidization is a matter of variable-rate cost sharing, where rates de- concern because these funds are limited. pend on characteristics of the practice and the The question of how to define cost effec- field to which it is applied. The other involves tiveness with regard to soil erosion control offering a fixed subsidy per ton of erosion has received a great deal of attention reduction. The primary hypothesis tested is (USGAO). Ideally, cost effectiveness should that cost effectiveness is improved in shifting be defined in terms of damages avoided, both from uniform- to variable-rate cost sharing to on- and 'off-site. However, given the limita- the fixed subsidy payment approach. What tions on such information, the focus in this follows first is a discussion of the policy en- study is on cost effectiveness as reflected by vironment in which these alternatives arose cost per unit reduction in the annual average

Pain following total hip replacement is a significant clinical and diagnostic problem. Technetium scanning has proved a sensitive indicator of infection or loosening but does not differentiate between them. This study assessed the value of gallium-67 to aid this differentiation. Thirty patients underwent revision surgery. Fourteen were proven to be infected and 13 had positive gallium scans as also did two patients without infection. The implications of these false interpretations are discussed. Increased gallium activity was correlated with the patterns of the 99m Tc scans and arthrographic appearances. It is concluded that gallium-67 scanning is a valuable adjunct to the assessment of the painful hip replacement when infection is suspected.

Severe back-ache in young adults may present a difficult clinical problem when the absence of neurological signs results in delayed diagnosis. Fourteen patients, with discographic evidence of posterior annular fissuring are reported. The discrepancy between painful disability and negative radiographic examination including radiculography is stressed. Discography has proved to be the investigation of choice in these patients. This will demonstrate the morphology of the lesion and reproduce the symptomatology in the majority of cases. The clinical implications are discussed.

An economically efficient, nonpoint pollution control strategy for a multijurisdictional 208 area may result in a benefit-cost distribution that will prohibit its acceptance. Vesting financial authorities in a regional water quality management agency would allow for implementation of a local compensation scheme designed to facilitate acceptance. Such a scheme would involve raising revenues from water quality beneficiaries that would, in turn, be paid as inducements for implementation of nonpoint control practices. These propositions are first defended with a theoretical argument. Then a linear programming model is applied for an empirical case analysis.

A travel cost model is developed to estimate the potential reductions in recreational benefits from sedimentation in Reelfoot Lake in northwestern Tennessee. In addition to the consumer surplus estimates generated by the model, three other aspects of the study were significant. First, the study applied a relatively untested methodology for deriving the opportunity cost of travel time. The study resulted in a value that is less than one-half of the Water Resource Council's “one-third of the wage rate” rule-of-thumb. Second, water quality perceptions were unsuccessfully incorporated into the model as a demand shifter. This raised questions as to the appropriate manner in which perceptions could be included in a travel cost model. Finally, a simple methodology was outlined by which estimates of the recreational value of Reelfoot Lake could be used to suggest how much cost could be justified for soil erosion control on agricultural land surrounding the lake.

There is a long standing hypothesis that overdevelopment has occurred in the nation's floodplains due to imperfect information about the potential flood hazard, an expectation of disaster relief and anticipation of future structural protection. This hypothesis is investigated with multiple regression analysis of data for a case study area. In particular the question of whether floodplain residential property values are fully discounted for expected flood damages is addressed by considering the impact of the National Flood Insurance Program on property values. The extent to which flooding risk perceptions are based on low cost information such as distance from and elevation above the river is also considered. Finally, implications for floodplain management policy are discussed.

Bone scintigraphy has been studied in two groups of patients presenting with low back pain. In one group of 38 patients suffering "nonspecific" back pain, bone scintigraphy and laboratory findings were negative in 24. There were abnormal laboratory findings in all of the remaining 14 and 7 had positive bone scans indicative of clinically significant disease. Selection of patients for bone scintigraphy in this group should therefore be influenced by abnormal laboratory findings and elevation of the erythrocyte sedimentation rate in particular. By comparison, the bone scans were reviewed from another group of patients suffering previously known malignancy. Out of 138 patients, nearly 40% showed a positive bone scan due to subsequently proven metastasis. Bone scintigraphy was positive in a further 14% as a result of osteoporotic rib fracture and vertebral body collapse. In half of these, it was not possible to exclude malignancy by scintigraphy. The present findings indicate that bone scintigraphy is not a useful procedure in patients with long-standing low back pain who have normal radiographs and normal laboratory findings.

The radiological features, clinical findings and mortality rates of patients with ankylosing spondylitis complicated by cervical trauma have been reviewed. All patients had long-standing disease and half had sustained their fractures as a result of trivial accidents. There were 19 cervical fractures in 18 patients, which were chalkstick in type and occurred predominantly at the 6th and 7th cervical levels. Ten fractures passed through the upper part of the vertebral body, one through the mid-vertebral body and the final eight were through the disc space. The site of the fracture line was related to neurological outcome. Those patients whose fracture line ran through the disc space had significantly less neurological injury and a much better prognosis. Distraction at the fracture site had some relation to prognosis but horizontal displacement and angulation were not found to be of importance. This study confirms that cervical fracture with neurological complications may follow minor trauma in ankylosing spondylitis. The site of the fracture in relation to the vertebral bodies and discs appears to be of some prognostic relevance and careful radiological assessment of all patients with ankylosing spondylitis and cervical injury should be undertaken.

1. Passive straight-leg raising may induce pain in the back or leg or a combination of both in patients with acute lower lumbar disc lesions. Clinical, myelographic and operative observations were carried out prospectively in fifty such cases to investigate the relation of the pattern of pain on straight-leg raising to the site of the protrusion. 2. In patients with central protrusion straight-leg raising induced mainly back pain. In patients with intermediate protrusion, lying in contact with both dura and nerve root, a combination of back and leg pain predominated. Patients with lateral protrusion usually experienced only pain in the leg. This correlation was found in 80 per cent of cases. 3. Production of pain in the leg by straight-leg raising is of practical significance in lateral protrusions where myelography may be normal. 4. Pain in the back and pain in the leg on straight-leg raising may be related respectively to dural and nerve root sensitivity.

Reported cases of avascular necrosis of the head of the femur associated with pregnancy are rare. Two further cases are presented, and a review of the previously reported cases suggests that other known predisposing causes of avascular necrosis may be incriminated in the aetiology. The possibility that a normal pregnancy may very rarely be associated with avascular necrosis is suggested by one of our patients and receives some support from the previously reported cases.

Twenty-five out of 41 adult patients suffering from their first attack of acute low-back pain were subjected to local anesthetic injection into the maximally tender lumbar apophyseal joints under controlled conditions. Two clinical syndromes can be identified according to whether the patients responded to the facet injection or not. Various clinical differences were statistically significant and included a wider than normal spinal canal in the responding group. The clinical significance of these two distinct groups is discussed in detail.

SUMMARY A series of fifty-one cases of lumbo-sacral spondylolisthesis under the age of thirty years were followed up for a minimum period of one year. The overall progression rate in this series was 24%, but more significantly, the incidence of progression in adolescence was 38%. Furthermore, there was a marked difference in the incidence of progression in the dysplastic type (32%) compared with the isthmic type (4%). Radiological studies showed that adolescent progression occurred concurrently with significant structural changes in both the 5th lumbar vertebra and the sacrum. It was felt that the loss of support of the posterior vertebral complex in dysplastic spondylolisthesis resulted in an interference in the vertebral growth once displacement exceeded 25%, demonstrating that progression may occur before a fusion becomes sound. Late progression was not accompanied by structural changes, and was due to a loss of posterior ligamentous and disc integrity.

The clinical, radiologic, and discographic findings are reviewed in eight patients with acute traumatic intraosseous disc herniation. The syndrome should be considered in adolescent patients having severe back pain with limited radiation to the upper thigh, following significant compression/flexion stress to the spine. The intraosseous disc herniation can be confirmed by discography and reproduction of symptoms during the procedure is a helpful confirmatory feature. The radiologic natural history of the lesion is presented, and the role of bone scintigraphy is discussed. This type of injury may be responsible for considerable pain and disability in the adolescent age group and has proved extremely difficult to manage except by conservative treatment and analgesics.

Long-term immobilisation in serial plasters for scoliosis, including the period of the adolescent growth spurt, leads to an increase in height of the vertebral bodies and a decrease of their height to width ratio. These changes are at the expense of the disc which is reduced in thickness. This stimulating effect on the vertebral body growth is probably due to the changes in mechanical factors.

The features of abdominal aortography in a small group of severely affected children with spina bifida cystica and kyphosis are presented. The examination was done prior to spinal fusion as earlier surgical reports had indicated a close relationship between the aorta and the vertebral bodies forming the apex of the kyphosis. The abdominal aorta was shown to bridge the apex of the kyphosis, thus it was outside the field of surgery and was not a potential hazard. Three vascular abnormalities emerged. First, the position of the aortic bifurcation, as judged by the vertebral level, was shown to be rather lower than usual, although lumbar kyphosis masked a relative aortic shortening. Second, the aorta was abnormally small in calibre with hypoplastic limb vessels. Third, abnormal segmentation of lumbar arteries was found in four of the eight in whom they were visualised, and correlates with the presence of vertebral body maldevelopment as opposed to neural arch maldevelopment. The possible pathogenic significance is discussed.

Three patients with synovial haemangioma of the knee were examined by thermography. This technique disclosed extensive subcutaneous distribution of haemangiomata which had been unsuspected clinically. Localised and diffuse lesions can be differentiated by this method. This information is important in planning surgery and in assessment of prognosis.