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.

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.

Introducing the external link model for studying spine fixation and misalignment: part 1--need, rationale, and applications.

This is the first article in a series introducing a new animal model, the External Link Model that we propose will allow researchers to produce and study spine lesions with the cardinal biomechanical features of the chiropractic subluxation: fixation (hypomobility) and misalignment.

Degenerative changes following spinal fixation in a small animal model.

OBJECTIVE: The objective of this study was to evaluate changes of the lumbar vertebral column following fixation. DESIGN: Using an established small animal (rat) model of spinal fixation (hypomobility), 3 contiguous lumbar segments (L4, L5, L6) were fixed with a specially engineered vertebral fixation device. Spinal segments of control rats were compared with those of animals with 1, 4, or 8 weeks of fixation. Subgroups of these fixation animals subsequently had the fixation device removed for 1, 2, 4, 8, or 12 weeks to evaluate the effects of attempting to reestablish normal forces to the vertebral segments following hypomobility. SETTING: This Institutional Animal Care and Use Committee (IACUC) approved study was conducted in a university animal facility. ANIMALS: Eighty-seven animals (23 controls animals and 64 fixation animals) were used in this study. Main Outcome Measures Outcome measures were degenerative changes of the vertebral bodies (VBs) and intervertebral disks (IVDs), zygapophysial (Z) joint osteophyte formation, and Z joint articular surface degeneration (ASD). Changes found in vertebral segments that were fixed (hypomobile) were compared with changes in adjacent nonfixed vertebral segments, and changes among fixation animals were compared with nonfixed controls. Main Results Very few degenerative changes were identified on the VBs and IVDs. Z joint changes were significant, both for osteophyte formation (analysis of variance [ANOVA], P <.0001) and ASD (ANOVA, P <.0001). Fixed segments had more degenerative changes than nonfixed segments for all Z joint parameters (ANOVA, P <.0001). Osteophyte formation and ASD were directly dependent on duration of fixation. CONCLUSIONS: These findings indicate that fixation (hypomobility) results in time-dependent degenerative changes of the Z joints.

The impact of a newly implemented PBL curriculum on the National Board of Chiropractic Examiners Part I Examinations at the National University of Health Sciences.

BACKGROUND: Performance differences between students of traditional lecture-based curricula and students of problem-based learning (PBL) curricula on standardized National Board Examinations have been studied. PURPOSE: To assess the impact and effectiveness of a change from a traditional lecture-based curriculum to a PBL curriculum. METHODS: Student performance in a traditional lecture-based curriculum (entering class of 1997) was compared to student performance in a PBL curriculum (entering class of 1998) on the standardized National Board of Chiropractic Examiners Part I Examination. RESULTS: There was a difference between the two curricula, with the PBL curriculum students outperforming the traditional lecture-based curriculum students on each individual part (d =.36-.95) of the National Board Examination and overall (d =.96). CONCLUSION: A comparison of student performance on a standardized National Board Examination has proved a useful tool at quantifying the impact of a newly implemented PBL curriculum.