Larry D. Haugh

Causality in temporal systems: Characterization and a survey

A time series {Yt} ‘causes’ another time series {Yt}, in the sense defined by C.W.J. Granger, if present Y can be predicted better by using past values of X than by not doing so, other relevant information (including the past of Y) being used in either case. In this paper we (1) classify the possible causality relationships between two series X and Y, using an analogy to events in a sample space; (2) review existing work and present some new results on alternative characterizations of the more important causality events; and (3) compare several recent procedures for the empirical detection of causality.

Morphometry of the Thoracic and Lumbar Spine Related to Transpedicular Screw Placement for Surgical Spinal Fixation

Vertebral transpedicular screws provide secure attachment for posterior spinal fixation devices. Screw design details, biomechanics, and implantation safety depend upon anatomic constraints, especially from the pedicle and body. Previous morphometric data were limited; thus, a retrospective study was undertaken using computerized axial tomograms (CT) of 91 vertebrae (T9–L5). In addition, eight cadaver vertebrae were CT scanned and then cut transversely to compare x-ray measurements with direct physical measurements. Measured parameters included pedicle width, pedicle length, angle of pedicle axis to sagittal plane, and transpedicular cortex-to-cortex chord length. Good correlation is shown to occur between CT scan and direct physical measurements of human vertebrae. Implications for spinal implant screw dimensions and safety of implantation are discussed. Comparison with previously available data is made.

Identification of Dynamic Regression (Distributed Lag) Models Connecting Two Time Series

Abstract A methodology is introduced for identifying dynamic regression or distributed lag models relating two time series. First, specification of a bivariate time-series model is discussed, and its relationship to the usual dynamic regression model is indicated. Then, a two-stage identification procedure is presented which involves fitting univariate time-series models to each series, and identifying a dynamic shock model relating the two univariate model innovation series. The models obtained at these two stages are combined to identify a dynamic regression model, which may then be fitted in the usual ways. Two systems of economic time series illustrate the methodology.

Determinants of return-to-work among low back pain patients

&NA; This prospective study identifies physical, behavioral, and psychosocial correlates of subsequent employment status in a sample of low back pain patients. The sample of 150 subjects was drawn from 2 populations of persons with chronic low back pain: 87 individuals who were receiving care at a university low back pain clinic, and 63 individuals who had applied for (but not yet received) Social Security compensation on the basis of low back pain. All subjects had worked at least 3 months prior to their latest unemployment period and were currently out of work. Initial assessment included a medical history, physical examination, biomechanical testing, psychiatric interview, and MMPI testing. All subjects were followed up 6 months later to determine whether they had returned to work. Cross‐sectional group comparisons at the time of initial assessment showed that, after controlling for the effects of age, the two samples differed on several physical and biomechanical measures, the Social Security group reflecting a more chronic picture. Group differences on physical variables were found, but most significant differences disappeared when adjusted for length of time out‐of‐work. Longitudinal analyses showed that few objective physical or biomechanical measures were associated with return‐to‐work at 6 months, while a number of psychosocial variables were significant predictors of 6‐month work status. The data suggest that exclusive reliance on the physical examination to determine level of disability, without consideration of psychosocial conditions, and without adjusting for the confounding effects of age and length of time out‐of‐work, is not empirically justified. Logistic regression analysis was used to ascertain the relative contribution of each predictor to outcome and to illustrate the hypothetical effects of changes in the levels of selected risk factors on the likelihood of return‐to‐work. Implications for interventions with low back pain patients are discussed and future research directions suggested.

Early prediction of chronic disability after occupational low back injury

Study Design An inception cohort design was used to study a consecutive sample of back‐injured workers. Objective To refine and to test the Vermont Disability Prediction Questionnaires ability to indicate an individuals relative risk for chronic disability after occupational low back injury. Summary of Background Data Although most back‐injured workers return to work quickly, the minority who do not account for the majority of associated costs and health care. Early identification of workers at high risk for disability would facilitate intervention strategies. Methods During the study recruitment period, people aged 18–60 years reporting occupational low back injury to the Vermont Department of Labor and Industry within 11 days of onset were eligible. A Vermont Disability Prediction Questionnaire was mailed to the 442 subjects who could be contacted and who gave informed consent. One hundred sixty‐three of the 166 subjects who completed and returned the questionnaire within 15 days of initial injury were telephoned 3 months later to determine work status. Those who returned the questionnaire were compared with those who would not consent or did not return the questionnaire in time according to age, sex, residence, wages, work hours per week, and length of employment. Employment status (inability to work because of low back pain) was evaluated by telephone interview 3 months after initial injury. Results The follow‐up interviewer was blinded to the Vermont Disability Prediction Questionnaire scores. Of the 163 subjects, 16 (10%) were not working because of low back pain. Using a simple dichotomous scoring system for 11 questionnaire items, a cut‐off score of 0.48 identified 3‐month postinjury work status, with 0.94 sensitivity and 0.84 specificity. Conclusions The Vermont Disability Prediction Questionnaire is a brief, easily administered and scored tool for identifying back‐injured workers at relative risk for chronic disability. Such early identification should increase the efficiency of disability prevention strategies by directing them toward people who need them most. The accuracy of the questionnaire needs to be tested in a variety of different clinical and socioeconomic settings.

A prospective randomized three-week trial of spinal manipulation, transcutaneous muscle stimulation, massage and corset in the treatment of subacute low back pain

Study Design A randomized prospective trial of manipulation, massage, corset and transcutaneous muscle stimulation (TMS) was conducted in patients with subacute low back pain. Objectives The authors determined the relative efficacy of chiropractic treatment to massage, corset, and TMS. Summary of Background Data Although all of these treatments are used for subacute low back pain treatment, there have been few comparative trials using objective outcome criteria. Patients were enrolled for a period of 3 weeks. They were evaluated once a week by questionnaires, visual analog scale, range of motion, maximum voluntary extension effort, straight leg raising and Biering-Sorensen fatigue test. The dropout rate was highest in the muscle stimulation and corset groups and lowest in the manipulation group. Rates of full compliance did not differ significantly across treatments. A measure of patient confidence was greatest in the manipulation group. Results After 3 weeks, the manipulation group scored the greatest improvements in flexion and pain while the massage group had the best extension effort and fatigue time, and the muscle stimulation group the best extension. Conclusion None of the changes in physical outcome measures (range of motion, fatigue, strength or pain) were significantly different between any of the groups.

Chronic low back pain : the relationship between patient satisfaction and pain, impairment, and disability outcomes

Study Design. Treatment outcomes for low back pain have been measured by varying standards of pain, impairment, and disability. This study examines the relationship between these three outcomes and treatment satisfaction in patients with chronic low back pain (CLBP). Methods. Ninety CLBP patients underwent initial pain (VAS), impairment (PIS), and disability (OPQ) evaluations. Results. Correlation coefficients between initial VAS, PIS, and OPQ were all less than 0.50. At 5-year follow-up, pain and disability scores were closely matched, more with lower mean scores among workers (P = 0.04 and 0.001). For 65 rehabilitation participants, 5-year patient satisfaction scores did not relate closely with VAS, PIS, and OPQ improvements during treatment (r = 0.15, 0.01, and 0.14). Five-year satisfaction correlated weakly with current pain and disability (r = 0.32, −0.36). Satisfaction levels were higher for workers after 1 year (P = 0.01), and after 5 years (P = 0.34). Conclusions. This study suggests that CLBP patients and their health care practitioners mutually set distinct pretreatment pain, impairment, and disability goals and judge outcomes accordingly.

Repeatability of Four Clinical Methods for Assessment of Lumbar Spinal Motion

Spinal motion usually is recorded from subjective observation of the fully flexed trunk using a goniometer or the distance from the fingertips to the floor. To quantify functional improvement in the low-back pain patient, the repeatability of four clinical techniques was studied: the common fingertip-to-floor distance; the modified Schober; the two-inclinometer method, and a photometric technique. Ten normal subjects (five men, five women), ages 24 to 34 years old, were examined in full flexion, full extension, and the erect position, both standing and sitting. Repeatability was poor for the fingertip-to-floor method in all postures and for the two-inclinometer method in full flexion. Although other methods for various postures had good repeatability, the modified Schober method of determining lumbar spinal motion was the most repeatable and is recommended for a routine, noninvasive, clinical evaluation of lumbar spinal motion.

A Prospective, Randomized Clinical Investigation of the Treatment of First-Time Ankle Sprains

Background Acute ankle ligament sprains are treated with the use of controlled mobilization with protection provided by external support (eg, functional treatment); however, there is little information regarding the best type of external support to use. Hypothesis There is no difference between elastic wrapping, bracing, bracing combined with elastic wrapping, and casting for treatment of acute, first-time ankle ligament sprains in terms of the time a patient requires to return to normal function. Study Design Randomized controlled clinical trial; Level of evidence, 1. Methods Patients suffering their first ligament injury were stratified by the severity of the sprain (grades I, II, or III) and then randomized to undergo functional treatment with different types of external supports. The patients completed daily logs until they returned to normal function and were followed up at 6 months. Results Treatment of grade I sprains with the Air-Stirrup brace combined with an elastic wrap returned subjects to normal walking and stair climbing in half the time required for those treated with the Air-Stirrup brace alone and in half the time required for those treated with an elastic wrap alone. Treatment of grade II sprains with the Air-Stirrup brace combined with the elastic wrap allowed patients to return to normal walking and stair climbing in the shortest time interval. Treatment of grade III sprains with the Air-Stirrup brace or a walking cast for 10 days followed by bracing returned subjects to normal walking and stair climbing in the same time intervals. The 6-month follow-up of each sprain severity group revealed no difference between the treatments for frequency of reinjury, ankle motion, and function. Conclusion Treatment of first-time grade I and II ankle ligament sprains with the Air-Stirrup brace combined with an elastic wrap provides earlier return to preinjury function compared to use of the Air-Stirrup brace alone, an elastic wrap alone, or a walking cast for 10 days.

A poroelastic-swelling finite element model with application to the intervertebral disc.

The swelling process that occurs in soft tissue is incorporated into a poroelastic finite element model. The model is applied to a spinal segment consisting of two vertebrae and a single intervertebral disc. The theory is an extension of the poroelastic theory developed by Biot7and the model is an adaptation of an axisymmetric poroelastic finite element model of the intervertebral disc by Simon.45,46The model is completely three-dimensional although the results presented here assume symmetry about the sagittal plane. The theory is presented in two stages. First the development of the poroelastic theory. Following this, the effects of swelling caused by osmotic pressure are developed and expressed as a modification of the constitutive law and initial stresses. In the case of the disc, this pressure is produced mainly by the fixed negative charges on the proteoglycans within the disc.In this development we assume that the number of fixed charges remains constant over time and that the distribution of mobile lons has reached equilibrium. The variations over time in osmotic pressure, and thus in swelling effects are therefore only dependent on the initial state and the change by changes in mobile ion concentrations will be the subject of a future paper.47The results reported in this article illustrate the dramatic effect of swelling on the load carrying mechanisms in the disc. The authors believe it is likely that this will have important useful implications for our understanding not only of normal disc function, but also of abnormal function, such as disc degeneration, herniation, and others.