A Novel and Accurate Palpation Method for Identification of the L4 Spinous Process: A Preliminary Study of Accuracy.

OBJECTIVE: The purpose of this study was to assess a novel method of lumbar spinous process (SP) palpation by using magnetic resonance imaging (MRI) high-signal marker reference standards for verification. METHODS: Clinicians (doctors of chiropractic) in this study used either: (1) the standard/traditional method of identifying the L4 SP using the supracristal plane (n = 14) or (2) a novel method that manually induced sacral motion to identify the L5 and then the L4 SP (n = 54). The clinicians, blinded to the results of each other, used a grease pencil to mark the location identified as the L4 SP. An MRI high-signal marker then was taped across this location. The MRI scans were assessed by a radiologist, blinded to the palpation method, who extended a line posteriorly from the superior and inferior extent of the L4 SP and determined whether the high-signal marker was within the lines bordering the L4 SP (ie, "on-target"). RESULTS: Palpation using the traditional method showed a 35.7% accuracy, with 5 of 14 "on target" and all "off target" being too superior. Palpation using the novel method showed 77.8% accuracy, with 42 of 54 "on target" and 3 "off target" being too superior and 9 "off target" too inferior. CONCLUSIONS: The novel method performed better than the traditional method. The novel method shows promise. Additional prospective research should be conducted to fully assess the accuracy of the novel method compared with traditional methods of palpation.

Reliability of Human Lumbar Facet Joint Degeneration Severity Assessed by Magnetic Resonance Imaging.

OBJECTIVE: The purpose of this study was to determine the reliability of the assessment of lumbar facet joint degeneration severity by analyzing degeneration subscales using magnetic resonance imaging (MRI) in human participants. METHODS: The reliability of articular cartilage degeneration, subchondral bone sclerosis, and osteophyte formation subscales of lumbar facet joint degeneration severity was assessed in MRI images from n = 10 human participants. Each scale was applied to n = 20 lumbar facet joints (L4/5 level). Three examiners were trained. A first assessment of MRI images was provided by the examiners followed by a second assessment 30 days later. Intraobserver and interobserver reliability were determined using percent agreement, the weighted kappa coefficient κw for paired comparisons, and the overall weighted kappa κo. The minimum threshold for reliability was set at moderate levels of agreement, κw > 0.40, based upon previous recommendations. RESULTS: The articular cartilage subscale had acceptable intraobserver (κo = 0.51) and interobserver (κo = 0.41) reliability. Scales for subchondral bone sclerosis (intraobserver κo = 0.28; interobserver κo = 0.10) and osteophyte formation (intraobserver κo = 0.26; interobserver κo = 0.20) did not achieve acceptable reliability. CONCLUSION: Of the 3 subcategories of lumbar facet joint degeneration, only articular cartilage degeneration demonstrated acceptable reliability. Subscales of lumbar facet joint degeneration should be considered independently for reliability before combining subscales for a global degeneration score. Owing to the inherent difficulty of assessing lumbar facet joint degeneration, the use of multiple examiners independently assessing degeneration with reliable scales and then coming to a consensus score upon any disagreements is recommended for future clinical studies.

A Feasibility Study to Assess Vibration and Sound From Zygapophyseal Joints During Motion Before and After Spinal Manipulation.

OBJECTIVE: This feasibility study used novel accelerometry (vibration) and microphone (sound) methods to assess crepitus originating from the lumbar spine before and after side-posture spinal manipulative therapy (SMT). METHODS: This study included 5 healthy and 5 low back pain (LBP) participants. Nine accelerometers and 1 specialized directional microphone were applied to the lumbar region, allowing assessment of crepitus. Each participant underwent full lumbar ranges of motion (ROM), bilateral lumbar SMT, and repeated full ROM. After full ROMs the participants received side-posture lumbar SMT on both sides by a licensed doctor of chiropractic. Accelerometer and microphone recordings were made during all pre- and post-SMT ROMs. Primary outcome was a descriptive report of crepitus prevalence (average number of crepitus events/participant). Participants were also divided into 3 age groups for comparisons (18-25, 26-45, and 46-65 years). RESULTS: Overall, crepitus prevalence decreased pre-post SMT (average pre = 1.4 crepitus/participant vs post = 0.9). Prevalence progressively increased from the youngest to oldest age groups (pre-SMT = 0.0, 1.67, and 2.0, respectively; and post-SMT = 0.5, 0.83, and 1.5). Prevalence was higher in LBP participants compared with healthy (pre-SMT-LBP = 2.0, vs pre-SMT-healthy = 0.8; post-SMT-LBP = 1.0 vs post-SMT-healthy = 0.8), even though healthy participants were older than LBP participants (40.8 years vs 27.8 years); accounting for age: pre-SMT-LBP = 2.0 vs pre-SMT-healthy = 0.0; post-SMT-LBP = 1.0 vs post-SMT-healthy = 0.3. CONCLUSIONS: Our findings indicated that a larger study is feasible. Other findings included that crepitus prevalence increased with age, was higher in participants with LBP than in healthy participants, and overall decreased after SMT. This study indicated that crepitus assessment using accelerometers has the potential of being an outcome measure or biomarker for assessing spinal joint (facet/zygapophyseal joint) function during movement and the effects of LBP treatments (eg, SMT) on zygapophyseal joint function.

Grading Osteoarthritic Changes of the Zygapophyseal Joints from Radiographs: A Reliability Study.

OBJECTIVE: This study tested the reliability of a 5-point ordinal scale used to grade the severity of degenerative changes of zygapophyseal (Z) joints on standard radiographs. METHODS: Modifications were made to a Kellgren grading system to improve agreement for grading the severity of osteoarthritic changes in lumbar Z joints. These included adding 1 grade of no degeneration, multiple radiographic views, and structured examiner training. Thirty packets of radiographic files were obtained, which included representation of all 5 grades including no degeneration (0) and Kellgren's 4-point (1-4) joint degeneration classification criteria. Radiographs were digitized to create a radiographic atlas that was given to examiners for individual study and blinded evaluation sessions. Intrarater and interrater agreement was determined by weighted κ (κw) from the examination of 79 Z joints (25 packets). RESULTS: Using the modified scale and after training, examiners demonstrated a moderate-to-substantial level of interrater agreement (κw = 0.57, 0.60, and 0.68). Intrarater agreement was moderate (κw = 0.42 and 0.54). CONCLUSIONS: The modified Kellgren 5-point grading system provides acceptable intrarater and interrater reliability when examiners are adequately trained. This grading system may be a useful method for future investigations assessing radiographic osteoarthritis of the Z joints.

US chiropractors' attitudes, skills and use of evidence-based practice: A cross-sectional national survey.

BACKGROUND: Evidence based practice (EBP) is being increasingly utilized by health care professionals as a means of improving the quality of health care. The introduction of EBP principles into the chiropractic profession is a relatively recent phenomenon. There is currently a lack of information about the EBP literacy level of US chiropractors and the barriers/facilitators to the use of EBP in the chiropractic profession. METHODS: A nationwide EBP survey of US chiropractors was administered online (Nov 2012-Mar 2013) utilizing a validated self-report instrument (EBASE) in which three sub-scores are reported: attitudes, skills and use. Means, medians, and frequency distributions for each of the sub-scores were generated. Descriptive statistics were used to analyze the demographic characteristics of the sample. Means and proportions were calculated for all of the responses to each of the questions in the survey. RESULTS: A total of 1,314 US chiropractors completed the EBASE survey; the sample appeared to be representative of the US chiropractic profession. Respondents were predominantly white (94.3%), male (75%), 47 (+/- 11.6) years of age, and in practice for more than 10 years (60%). EBASE sub-score means (possible ranges) were: attitudes, 31.4 (8-40); skills, 44.3 (13-65); and use, 10.3 (0-24). Survey participants generally held favorable attitudes toward EBP, but reported less use of EBP. A minority of participants indicated that EBP coursework (17%) and critical thinking (29%) were a major part of their chiropractic education. The most commonly reported barrier to the use of EBP was "lack of time". Almost 90% of the sample indicated that they were interested in improving their EBP skills. CONCLUSION: American chiropractors appear similar to chiropractors in other countries, and other health professionals regarding their favorable attitudes towards EBP, while expressing barriers related to EBP skills such as research relevance and lack of time. This suggests that the design of future EBP educational interventions should capitalize on the growing body of EBP implementation research developing in other health disciplines. This will likely include broadening the approach beyond a sole focus on EBP education, and taking a multilevel approach that also targets professional, organizational and health policy domains.

A pilot randomized controlled trial of flexion-distraction dosage for chiropractic treatment of lumbar spinal stenosis.

OBJECTIVE: The purpose of this pilot clinical trial was to assess the feasibility of recruiting older adults with lumbar spinal stenosis (LSS) into a clinical trial that used different dosages of flexion-distraction manipulation. METHODS: This randomized controlled trial used a 4-group design. Three groups consisted of chiropractic flexion-distraction manipulation applied at different dosages (8, 12, or 18 treatments). The fourth group was given 8 treatments of placebo care. Feasibility measures included recruitment goals, adherence to various treatment schedules, credibility of the placebo treatment, and rates of adverse events. The primary outcome measure was the Swiss Spinal Stenosis Questionnaire, a validated self-report of LSS symptom severity and physical function. RESULTS: The recruitment and adherence goals of the study were met with a total of 60 subjects randomized (n = 15 per group) and most subjects attending at least 75% of their scheduled visits. No adverse events were reported by any of the subjects in the trial. Our placebo treatment did not appear to be credible; most subjects correctly guessed that they were receiving a placebo treatment. Between-group effect size estimates were small, indicating larger samples are needed for future studies. CONCLUSION: This pilot study showed that it is feasible to recruit patients with LSS and that most subjects will adhere to a 6-week treatment schedule. The information gained from this trial will be useful to inform the design of larger trials.

Development of a student-mentored research program between a complementary and alternative medicine university and a traditional, research-intensive university.

The global need to develop clinician-scientists capable of using research in clinical practice, translating research knowledge into practice, and carrying out research that affects the quality, efficacy, and efficiency of health care is well documented. The complementary and alternative medicine (CAM) professions embrace the call to develop physician-researchers to carry out translational and applied research for CAM modalities. CAM universities face unique challenges when implementing research training compared with traditional, research-intensive (TRI) universities and medical centers where the majority of medical research is carried out.The authors present the development and outcomes of a mentored research program (MRP) between a CAM and a TRI institution, the National University of Health Sciences and the University of Illinois at Chicago School of Public Health, between 2006 and 2012. CAM predoctoral students engaged in a full-immersion semester at the TRI, including didactic courses and active research with a TRI faculty research mentor. Half of the participating doctor of chiropractic (DC) students continued on to PhD programs, and half established integrative medicine, primary care clinical careers.Establishing rigorous criteria for mentors and mentees, communicating expectations, developing solid relationships between the mentor, mentee, and home school advisor, responding quickly to impediments, and providing adequate support from CAM and TRI investigators were key to the MRP's success. To sustain research opportunities, coordinated degree programs for the DC and master of public health and master of clinical and translational research were established.

Magnetic resonance imaging zygapophyseal joint space changes (gapping) in low back pain patients following spinal manipulation and side-posture positioning: a randomized controlled mechanisms trial with blinding.

OBJECTIVE: The purpose of this study was to quantify lumbar zygapophyseal (Z) joint space separation (gapping) in low back pain (LBP) subjects after spinal manipulative therapy (SMT) or side-posture positioning (SPP). METHODS: This was a controlled mechanisms trial with randomization and blinding. Acute LBP subjects (N = 112; four n = 28 magnetic resonance imaging [MRI] protocol groups) had 2 MRI appointments (initial enrollment and after 2 weeks of chiropractic treatment, receiving 2 MRI scans of the L4/L5 and L5/S1 Z joints at each MRI appointment. After the first MRI scan of each appointment, subjects were randomized (initial enrollment appointment) or assigned (after 2 weeks of chiropractic treatment appointment) into SPP (nonmanipulation), SMT (manipulation), or control MRI protocol groups. After SPP or SMT, a second MRI was taken. The central anterior-posterior joint space was measured. Difference between most painful side anterior-posterior measurements taken postintervention and preintervention was the Z joint "gapping difference." Gapping differences were compared (analysis of variance) among protocol groups. Secondary measures of pain (visual analog scale, verbal numeric pain rating scale) and function (Bournemouth questionnaire) were assessed. RESULTS: Gapping differences were significant at the first (adjusted, P = .009; SPP, 0.66 ± 0.48 mm; SMT, 0.23 ± 0.86; control, 0.18 ± 0.71) and second (adjusted, P = .0005; SPP, 0.65 ± 0.92 mm; SMT, 0.89 ± 0.71; control, 0.35 ± 0.32) MRI appointments. Verbal numeric pain rating scale differences were significant at first MRI appointment (P = .04) with SMT showing the greatest improvement. Visual analog scale and Bournemouth questionnaire improved after 2 weeks of care in all groups (both P < .0001). CONCLUSIONS: Side-posture positioning showed greatest gapping at baseline. After 2 weeks, SMT resulted in greatest gapping. Side-posture positioning appeared to have additive therapeutic benefit to SMT.

Quantification of cavitation and gapping of lumbar zygapophyseal joints during spinal manipulative therapy.

OBJECTIVES: The purpose of this study was to use previously validated methods to quantify and relate 2 phenomena associated with chiropractic spinal manipulative therapy (SMT): (1) cavitation and (2) the simultaneous gapping (separation) of the lumbar zygapophyseal (Z) joint spaces. METHODS: This was a randomized, controlled, mechanistic clinical trial with blinding. Forty healthy participants (18-30 years old) without a history of low-back pain participated. Seven accelerometers were affixed to the skin overlying the spinous processes of L1 to L5 and the S1 and S2 sacral tubercles. Two additional accelerometers were positioned 3 cm left and right lateral to the L4/L5 interspinous space. Participants were randomized into group 1, side-posture SMT (n = 30), or group 2, side-posture positioning (SPP, n = 10). Cavitations were determined by accelerometer recordings during SMT and SPP (left side = upside for both groups); gapping (gapping difference) was determined by the difference between pre- and postintervention magnetic resonance imaging scan joint space measurements. Results of mean gapping differences were compared. RESULTS: Upside SMT and SPP joints gapped more than downside joints (0.69 vs -0.17 mm, P < .0001). Spinal manipulative therapy upside joints gapped more than SPP upside joints (0.75 vs 0.52 mm, P = .03). Spinal manipulative therapy upside joints gapped more in men than in women (1.01 vs 0.49 mm, P < .002). Overall, joints that cavitated gapped more than those that did not (0.56 vs 0.22 mm, P = .01). No relationship was found between the occurrence of cavitation and gapping with upside joints alone (P = .43). CONCLUSIONS: Zygapophyseal joints receiving chiropractic SMT gapped more than those receiving SPP alone; Z joints of men gapped more than those of women, and cavitation indicated that a joint had gapped but not how much a joint had gapped.

Distribution of cavitations as identified with accelerometry during lumbar spinal manipulation.

OBJECTIVE: This project determined the location and distribution of cavitations (producing vibrations and audible sounds) in the lumbar zygapophyseal (Z) joints that were targeted by spinal manipulative therapy (SMT). METHODS: This randomized, controlled, clinical study assessed 40 healthy subjects (20 men, 20 women) 18 to 30 years of age who were block randomized into SMT (group 1, n = 30) or side-posture positioning only (group 2; control, n = 10) groups. Nine accelerometers were placed on each patient (7 on spinous processes/sacral tubercles of L1-S2 and 2 placed 3 cm left and right lateral to the L4/L5 interspinous space). Accelerometer recordings were made during side-posture positioning (groups 1 and 2) and SMT (group 1 only). The SMT was delivered by a chiropractic physician with 19 years of practice experience and included 2 high-velocity, low-amplitude thrusts delivered in rapid succession. Comparisons using χ(2) or McNemar test were made between number of joints cavitating from group 1 vs group 2, upside (contact side for SMT) vs downside, and Z joints within the target area (L3/L4, L4L5, L5/S1) vs outside the target area (L1/L2, L2/L3, sacroiliac). RESULTS: Fifty-six cavitations were recorded from 46 joints of 40 subjects. Eight joints cavitated more than once. Group 1 joints cavitated more than group 2 joints (P < .0001), upside joints cavitated more than downside joints (P < .0001), and joints inside the target area cavitated more than those outside the target area (P < .01). CONCLUSIONS: Most cavitations (93.5%) occurred on the upside of SMT subjects in segments within the target area (71.7%). As expected, SMT subjects cavitated more frequently than did subjects with side-posture positioning only (96.7% vs 30%). Multiple cavitations from the same Z joints had not been previously reported.

Evaluating the relationship among cavitation, zygapophyseal joint gapping, and spinal manipulation: an exploratory case series.

OBJECTIVE: This project determined the feasibility of conducting larger studies assessing the relationship between cavitation and zygapophyseal (Z) joint gapping following spinal manipulative therapy (SMT). METHODS: Five healthy volunteers (average age, 25.4 years) were screened and examined against inclusion and exclusion criteria. High-signal magnetic resonance imaging (MRI) markers were fixed to T12, L3, and S1 spinous processes. Scout images were taken to verify the location of the markers. Axial images of the L4/L5 and L5/S1 levels were obtained in the neutral supine position. Following the first MRI, accelerometers were placed over the same spinous processes; and recordings were made from them during side-posture positioning and SMT. The accelerometers were removed, and each subject was scanned in side-posture. The greatest central anterior to posterior Z joint spaces (gap) were measured from the first and second MRI scans. Values obtained from the first scan were subtracted from those of the second, with a positive result indicating an increase in gapping following SMT (positive gapping difference). Gapping difference was compared between the up-side (SMT) joints vs the down-side (non-SMT) joints and between up-side cavitation vs up-side noncavitation joints. RESULTS: Greater gapping was found in Z joints that received SMT (0.5 ± 0.6 mm) vs non-SMT joints (-0.2 ± 0.6 mm), and vertebral segments that cavitated gapped more than those that did not cavitate (0.8 ± 0.7 vs 0.4 ± 0.5 mm). CONCLUSIONS: A future clinical study is quite feasible. Forty subjects (30 in an SMT group and 10 in a control group) would be needed for appropriate power (0.90).

Zygapophyseal joint adhesions after induced hypomobility.

OBJECTIVE: Adhesions (ADH) have been previously identified in many hypomobile joints, but not in the zygapophyseal (Z) joints of the spine. The objective of this study was to determine if connective tissue ADH developed in lumbar Z joints after induced intervertebral hypomobility (segmental fixation). METHODS: Using an established rat model, 3 contiguous segments (L4, L5, L6) were fixed with specially engineered, surgically implanted, vertebral fixation devices. Z joints of experimental rats (17 rats, 64 Z joints) with 4, 8, 12, or 16 weeks of induced hypomobility were compared with Z joints of age-matched control rats (23 rats, 86 Z joints). Tissue was prepared for brightfield microscopy, examined, and photomicrographed. A standardized grading system identified small, medium, and large ADH and the average numbers of each per joint were calculated. RESULTS: Connective tissue ADH were characterized and their location within Z joints described. Small and medium ADH were found in rats from all study groups. However, large ADH were found only in rats with 8, 12, or 16 weeks of experimentally induced intervertebral hypomobility. Significant differences among study groups were found for small (P < .003), medium (P < .000), and large (P < .000) ADH. The average number of medium and large ADH per joint increased with the length of experimentally induced hypomobility in rats with 8 and 16 weeks of induced hypomobility. CONCLUSIONS: We conclude that hypomobility results in time-dependent ADH development within the Z joints. Such ADH development may have relevance to spinal manipulation, which could theoretically break up Z joint intra-articular ADHs.

Reliability of zygapophysial joint space measurements made from magnetic resonance imaging scans of acute low back pain subjects: comparison of 2 statistical methods.

OBJECTIVE: This purpose of this study was to assess the reliability of measurements made of the zygapophysial (Z) joint space from the magnetic resonance imaging scans of subjects with acute low back pain using new equipment and 2 different methods of statistical analysis. If found to be reliable, the methods of Z joint measurement can be applied to scans taken before and after spinal manipulation in a larger study of acute low back pain subjects. METHODS: Three observers measured the central anterior-to-posterior distance of the left and right L4/L5 and L5/S1 Z joint space from 5 subject scans (20 digitizer measurements, rounded to 0.1 mm) on 2 separate occasions separated by 4 weeks. Observers were blinded to each other and their previous work. Intra- and interobserver reliability was calculated by means of intraclass correlation coefficients and also by mean differences using the methods of Bland and Altman (1986). A mean difference of less than +/-0.4 mm was considered clinically acceptable. RESULTS: Intraclass correlation coefficients showed intraobserver reliabilities of 0.95 (95% confidence interval, 0.87-0.98), 0.83 (0.62-0.92), and 0.92 (0.83-0.96) for each of the 3 observers and interobserver reliabilities of 0.90 (0.82-0.95), 0.79 (0.61-0.90), and 0.84 (0.75-0.90) for the first and second measurements and overall reliability, respectively. The mean difference between the first and second measurements was -0.04 mm (+/-1.96 SD = -0.37 to 0.29), 0.23 (-0.48 to 0.94), 0.25 (-0.24 to 0.75), and 0.15 (-0.44 to 0.74) for each of the 3 observers and the overall agreement, respectively. CONCLUSIONS: Both statistical methods were found to be useful and complementary and showed the measurements to be highly reliable.

Recruitment methods and costs for a randomized, placebo-controlled trial of chiropractic care for lumbar spinal stenosis: a single-site pilot study.

OBJECTIVE: The purpose of this article is to describe the methods for recruitment in a clinical trial on chiropractic care for lumbar spinal stenosis. METHODS: This randomized, placebo-controlled pilot study investigated the efficacy of different amounts of total treatment dosage over 6 weeks in 60 volunteer subjects with lumbar spinal stenosis. Subjects were recruited for this study through several media venues, focusing on successful and cost-effective strategies. Included in our efforts were radio advertising, newspaper advertising, direct mail, and various other low-cost initiatives. RESULTS: Of the 1211 telephone screens, 60 responders (5.0%) were randomized into the study. The most successful recruitment method was radio advertising, generating more than 64% of the calls (776 subjects). Newspaper and magazine advertising generated approximately 9% of all calls (108 subjects), and direct mail generated less than 7% (79 subjects). The total direct cost for recruitment was $40 740 or $679 per randomized patient. The costs per randomization were highest for direct mail ($995 per randomization) and lowest for newspaper/magazine advertising ($558 per randomization). CONCLUSIONS: Success of recruitment methods may vary based on target population and location. Planning of recruitment efforts is essential to the success of any clinical trial.

Introducing the external link model for studying spine fixation and misalignment: current procedures, costs, and failure rates.

OBJECTIVE: This is the last article in a series of 3 articles introducing a new animal model, the external link model (ELM), that permits reversible, nontraumatic control of the cardinal biomechanical features of the subluxation: fixation and misalignment. A detailed description of current ELM procedures is presented and practical issues are reviewed such as expense (dollars and time) and construct failure rates during and after the surgical implant procedure. METHOD: Descriptive report of current ELM procedures, refinements to the spinous attachment units (SAUs), and tabulation of costs and failure rates drawn from recent studies. RESULTS: In contrast to the older, 1-piece stainless steel SAUs, new 3-piece titanium SAUs may be reimplanted many times without failure. Consequently, the cost per ELM ranges from $579 to $69, depending on whether the SAUs, links, and screws must be purchased or are already available for implanting. The SAU implant procedure requires between 0.5 and 1.25 hours, depending on the experience of the surgeon. The total construct failure rate for the ELM is 24.2% (6.6% at surgery failure + 17.8% postsurgery failures). This rate is consistent with that reported in spine implant studies with other devices. To date, more than 500 male Sprague-Dawley rats (350-450 g) have been implanted with SAUs for ELM studies at the Palmer Center for Chiropractic Research and the National University of Health Sciences. CONCLUSION: It has been our experience that individuals with basic animal research training will become proficient at producing the ELM after observing 3 to 4 implant procedures and performing 4 to 6 procedures on their own.

Preliminary morphological evidence that vertebral hypomobility induces synaptic plasticity in the spinal cord.

OBJECTIVE: A widely accepted theoretical model suggests that vertebral hypomobility can cause pain and abnormal spinal mechanics because of changes in sensory input from spinal and paraspinal tissues. The purpose of this pilot study was 3-fold: (1) to make a preliminary determination if chronic vertebral hypomobility at L4 through L6 in the rat would affect synaptic density and/or morphology in the superficial dorsal horn of the L2 spinal cord level, (2) to identify relevant outcome variables for future studies, and (3) to obtain preliminary data that would permit estimating an appropriate sample size for future studies. METHODS: Using an established rat model, we fixed 3 contiguous lumbar segments (L4-L6) for 8 weeks with a specially engineered vertebral fixation device. Electron micrographs were obtained from 2 animals from the experimental (fixed) group and each of 3 control groups (no surgery, surgery but no devices implanted, and devices implanted but not fixed). Synapses were randomly selected using a stereological approach and were analyzed for symmetry, curvature, type of postsynaptic profile, and perforations. The synaptic density was also estimated. RESULTS: There was increased synaptic density and percentage of positively curved synapses in the dorsal horn of experimental animals as compared with controls. Experimental animals had a lower percentage of axospinous synapses, with a concomitant increase in the percentage of synapses on dendritic shafts. CONCLUSIONS: These preliminary data suggest for the first time that chronic vertebral hypomobility at L4 through L6 in the rat affects synaptic density and morphology in the superficial dorsal horn of the L2 spinal cord level. More definitive studies are warranted, and the biologic significance of these finding should be investigated.

Introducing the external link model for studying spine fixation and misalignment: part 2, Biomechanical features.

OBJECTIVES: The purpose of this study was to characterize intervertebral stiffness and alignment changes in the external link model and evaluate it as an experimental mimic for studying the chiropractic subluxation. METHOD: A controlled test-retest design was used to evaluate rats with spine segments linked in 3 alignment configurations and controls that were never linked. Dorsal-to-ventral spine stiffness was measured with a load platform, and flexion/extension misalignment was assessed on lateral radiographs obtained with a spine extension jig. Descriptive statistics were computed for study groups, and multiple linear regression models were used to examine all potential explanatory variables for the response variables "stiffness" and "joint position." RESULTS: Rats tested with links in place had significantly higher dorsal-to-ventral stiffness in the neutral configuration than rats in the flexed configuration. This difference remained after the links were removed. Stiffness after link removal was greater for longer linked periods. Surprisingly, stiffness after link removal was also greater with longer unlinked periods. Longer linked periods also produced greater misalignments during forced spine extension testing. Although link configuration was not a statistically significant predictor of misalignments, longer times after link removal did produce greater misalignments. CONCLUSIONS: This study suggests that the external link model can be a valuable tool for studying the effects of spine fixation and misalignment, 2 cardinal features of what has been historically described as the chiropractic subluxation. Significant residual stiffness and misalignment remained after the links were removed. The progressive course of this lesion is consistent with subluxation theory and clinical chiropractic experience.