The response of posteroanterior lumbar stiffness to repeated loading

Inter-rater and test-retest reliabilities of lumbar stiffness measurement in the postero-anterior direction using a portable algometer and the Kinovea program

Background

Back pain negatively impacts a person's quality of life and can cause major disability or even death. The measurement of spinal stiffness can be utilized as a promising tool to guide therapeutic decisions regarding physical therapy that result in effective back pain management. This study aimed to determine the reliability of instrumented postero-anterior (PA) stiffness assessment of the lumbar spine in asymptomatic participants by novice assessors using a portable algometer and the Kinovea program.

Methods

Thirty asymptomatic participants aged 18-25 years were enrolled in this study. Two novice assessors examined the participants for lumbar spinal stiffness at L1-L5 for two consecutive days. The algometer was applied to measure the PA force that applied to each lumbar. The stiffness assessment of each lumbar region was recorded as a video. The 600 data sets of assessment videos were imported into the Kinovea program to perform displacement measurements of each lumbar level. Spinal displacement values at 15 N were defined by graph plotting between force and displacement. The spinal stiffness values were defined by slope calculation. Both variables were analyzed for inter-rater and test-retest reliabilities using intra-class correlation coefficients (ICCs) and standard error of measurement (SEM). Bland-Altman analysis was applied to assess the inter-rater and test-retest systematical bias and limits of agreement of measuring displacement and stiffness.

Results

The inter-rater reliability of measuring the displacement and the stiffness of L1-L5 was moderate to good (displacement ICCs: 0.67-0.83, stiffness ICCs: 0.60-0.83). The test-retest reliability of measuring the displacement and stiffness of L1-L5 were moderate to good, ICCs: 0.57-0.86 and ICCs: 0.51-0.88, respectively. The inter-rater analysis's Bland-Altman plot showed that the systematic bias was 0.83 when measuring displacement and 0.20 when measuring stiffness and the bias of both parameters were in both directions. While the test-retest systematically biased measurements of displacement and stiffness were -0.26 mm and 0.22 N/mm, respectively, and the bias of both parameters were in both directions.

Conclusions

The moderate-to-good inter-rater and test-retest reliabilities of the portable instrumented spinal stiffness assessment using a digital algometer and the Kinovea program by novice assessors were demonstrated in this study. Bland-Altman analysis showed that measuring stiffness was more stable and had less systematic bias than measuring displacement. To figure out how reliable the device is in general, more comprehensive studies should be comparatively conducted in the future on subgroups of patients with normal vertebra, hypomobile or hypermobile conditions.

A Comparison of Clinical Spinal Mobility Measures to Experimentally Derived Lumbar Spine Passive Stiffness

Spinal stiffness and mobility assessments vary between clinical and research settings, potentially hindering the understanding and treatment of low back pain. A total of 71 healthy participants were evaluated using 2 clinical assessments (posteroanterior spring and passive intervertebral motion) and 2 quantitative measures: lumped mechanical stiffness of the lumbar spine and local tissue stiffness (lumbar erector spinae and supraspinous ligament) measured via myotonometry. The authors hypothesized that clinical, mechanical, and local tissue measures would be correlated, that clinical tests would not alter mechanical stiffness, and that males would demonstrate greater lumbar stiffness than females. Clinical, lumped mechanical, and tissue stiffness were not correlated; however, gradings from the posteroanterior spring and passive intervertebral motion tests were positively correlated with each other. Clinical assessments had no effect on lumped mechanical stiffness. The males had greater lumped mechanical and lumbar erector spinae stiffness compared with the females. The lack of correlation between clinical, tissue, and lumped mechanical measures of spinal stiffness indicates that the use of the term "stiffness" by clinicians may require reevaluation; clinicians should be confident that they are not altering mechanical stiffness of the spine through segmental mobility assessments; and greater resting lumbar erector stiffness in males suggests that sex should be considered in the assessment and treatment of the low back.

The effect of real-time feedback on learning lumbar spine joint mobilization by entry-level doctor of physical therapy students: a randomized, controlled, crossover trial

OBJECTIVE

To examine the effects of real-time, objective feedback on learning lumbar spine joint mobilization techniques by entry-level Doctor of Physical Therapy (DPT) students.

METHODS

A randomized, controlled, crossover design was used. Twenty-four 1st Year DPT students were randomized into two groups. Group 1 (n = 12) practiced with the real-time feedback device first and then without it, while Group 2 (n = 12) practiced without the device first and then with it. Both practice periods with and without the device were 4 weeks long. Data were collected at Baseline, 5 weeks, 11 weeks, and 16 weeks. The crossover period was 5 weeks long, during which neither group practiced with or without the device. Eight force parameters were measured: R1 force; R2 force; Grade III and Grade IV mean peak force, frequency, and amplitude.

RESULTS

When students practiced with the real-time feedback device, they more closely matched the reference standard for two outcomes: 1) the mean difference in R2 force between student and reference standard was better with device (38.0 ± 26.7 N) than without it (51.0 ± 38.5 N); P = .013; and 2) the mean difference in Grade III peak to peak amplitude force was also better with device (8.9 ± 9.3 N) than without it (11.8 ± 11.0); P = .026. All other force parameters improved when students practiced with the real-time feedback device, however, the differences between when they practiced without the device were not statistically significant.

DISCUSSION

Real-time, objective feedback using a direct force measurement device improved learning for some aspects of lumbar spine joint mobilization by entry-level physical therapy students.

LEVEL OF EVIDENCE

2b.

Reliability of a new loaded rolling wheel system for measuring spinal stiffness in asymptomatic participants

BACKGROUND

Few, if any, patient reported symptoms have been shown to be related to objective measures of spine function. Recently, patient-reported measures of disability following spinal manipulative therapy have been associated with an immediate decrease in spinal stiffness obtained by instrumented L3 indentation. Given this novel relation, we anticipate that stiffness measures obtained from locations in addition to L3 may yield valuable information. As such, our research team has developed a new technique to acquire stiffness data continuously over an entire spinal region. The reliability of stiffness measurements obtained by this new technique has yet to be quantified.

METHODS

Continuous stiffness testing employs a weighted roller that moves uninterrupted over the spine while measuring the resulting spinal deflection along a subject-specific, laser-defined trajectory. A volunteer sample of asymptomatic participants were assessed in 2 sessions occurring 1 to 4 days apart, with each session scheduled at the same time of day. Each session consisted of 3 trials each beginning at a baseline of ~ 17 N then progressing to a maximally tolerable load as defined from pre-test familiarization trials (~ 61, 72 or 83 N). Reliability was evaluated with the intraclass correlation coefficient, the standard error of measurement and Bland & Altman analysis.

RESULTS

A total of 17 asymptomatic participants (mean age 29.2 +/- 6 years, 53% female) took part in the study. Overall, the within and between-session reliability of lumbar spine stiffness measures at the maximal tolerable load was excellent ranging from 0.95-1.00 and good to excellent ranging from 0.82-0.93, respectively. Trial averaging was found to reduce standard error of measurement by a mean of 35.2% over all measurement conditions compared to a single trial. Bland and Altman plots for agreement in lumbar spine stiffness measurements varied from - 0.3 +/- 1.2 at unloaded condition to - 0.2 +/- 1.2 at loaded condition. Data from two participants were removed due to the development of back pain between two sessions.

CONCLUSION

This study introduced a new technique for measuring spinal stiffness over an entire spinal region in asymptomatic human participants. The new technique produced reliable measurements quantifying the load-displacement values for within-session and between-session assessments.

Effects of spinal manipulative therapy biomechanical parameters on clinical and biomechanical outcomes of participants with chronic thoracic pain: a randomized controlled experimental trial

BACKGROUND

Spinal manipulative therapy (SMT) includes biomechanical parameters that vary between clinicians, but for which the influence on the therapy clinical effects is unknown. This parallel-randomized controlled trial aimed to investigate the effect of SMT biomechanical parameters on the outcomes of participants with chronic thoracic pain (CTP) following three treatment sessions (follow-up at one week).

METHODS

Adults reporting CTP (pain within the evaluated region [T6 to T8] for ≥3 months) were asked to participate in a four-session trial. At the first session, participants were randomly assigned to one of three experimental groups (different SMT doses) or the control group (no SMT). During the first three sessions, one SMT was executed at T7 for the experimental groups, while a 5-min rest was provided to the control group. SMT were delivered through an apparatus using a servo-controlled linear actuator motor and doses consisted of peak forces, impulse durations, and rates of force application set at 135 N, 125 ms and 920 N/s (group 1), at 250 N, 125 ms and 1840 N/s (group 2), and at 250 N, 250 ms, 920 N/s (group 3). Disability and pain intensity were evaluated at each session (primary outcomes). Spinal stiffness was assessed before-and-after each SMT/rest and at follow-up. Tenderness and muscle activity were evaluated during each spinal stiffness trial. Improvement was evaluated at follow-up. Differences in outcomes between groups and sessions were evaluated as well as factors associated with clinical improvement.

RESULTS

Eighty-one participants were recruited and 17, 20, 20 participants of the three experimental groups and 18 of the control group completed the protocol. In exception of higher pain intensity at baseline in the control group, no between-group differences were found for any of the outcomes. A decrease in pain intensity, disability, spinal stiffness, and tenderness during spinal stiffness were observed (p-values< 0.05). At follow-up, 24% of participants were classified as 'improved'. Predictors of improvement were a greater decrease in pain intensity and in tenderness (p-values< 0.05).

CONCLUSIONS

In an experimental setting, the delivery of a SMT does not lead to significantly different outcomes in participants with CTP than a control condition (spinal stiffness assessment). Studies are still required to explore the mechanisms underlying SMT effects.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03063177 , registered 24 February 2017).

Changes in spinal stiffness with chronic thoracic pain: Correlation with pain and muscle activity

Objective

The objective was to compare thoracic spinal stiffness between healthy participants and participants with chronic thoracic pain and to explore the associations between spinal stiffness, pain and muscle activity. The reliability of spinal stiffness was also evaluated.

Material and methods

Spinal stiffness was assessed from T5 to T8 using a mechanical device in 25 healthy participants and 50 participants with chronic thoracic pain (symptoms had to be reported within the evaluated region of the back). The spinal levels for which spinal stiffness was measured were standardized (i.e. T5 to T8 for all participants) to minimize between-individual variations due to the evaluation of different spinal levels. The device load and displacement data were used to calculate the global and terminal spinal stiffness coefficients at each spinal level. Immediately after each assessment, participants were asked to rate their pain intensity during the trial, while thoracic muscle activity was recorded during the load application using surface electromyography electrodes (sEMG). Within- and between-day reliability were evaluated using intraclass correlation coefficients (ICC), while the effects of chronic thoracic pain and spinal levels on spinal stiffness and sEMG activity were assessed using mixed model ANOVAs. Correlations between pain intensity, muscle activity and spinal stiffness were also computed.

Results

ICC values for within- and between-day reliability of spinal stiffness ranged from 0.67 to 0.91 and from 0.60 to 0.94 (except at T5), respectively. A significant decrease in the global (F_1,73 = 4.04, p = 0.048) and terminal (F_1,73 = 4.93, p = 0.03) spinal stiffness was observed in participants with thoracic pain. sEMG activity was not significantly different between groups and between spinal levels. Pain intensity was only significantly and "moderately" correlated to spinal stiffness coefficients at one spinal level (-0.29≤r≤-0.51), while sEMG activity and spinal stiffness were not significantly correlated.

Conclusion

The results suggest that spinal stiffness can be reliably assessed using a mechanical device and that this parameter is decreased in participants with chronic thoracic pain. Studies are required to determine the value of instrumented spinal stiffness assessment in the evaluation and management of patients with chronic spine-related pain.

Assessment of cervical stiffness in axial rotation among chronic neck pain patients: A trial in the framework of a non-manipulative osteopathic management

BACKGROUND

Cervical stiffness is a clinical feature commonly appraised during the functional examination of cervical spine. Measurements of cervical stiffness in axial rotation have not been reported for patients with neck pain. The purpose of this study was to investigate cervical spine stiffness in axial rotation among neck pain patients and asymptomatic subjects, and to analyze the impact of osteopathic management.

METHODS

Thirty-five individuals (17 patients) were enrolled. Measurements were carried out for left-right axial rotation using a torque meter device, prior and after intervention. Passive range of motion, stiffness, and elastic-and neutral zone magnitudes were analyzed. Pain intensity was also collected for patients. The intervention consisted in one single session of non-manipulative osteopathic treatment performed in both groups.

FINDINGS

A significant main effect of intervention was found for total range of motion and neutral zone. Also, treatment by group interaction was demonstrated for neutral-, elastic zone, stiffness in right axial rotation, and for total neutral zone. Significant changes were observed in the clinical group after intervention, indicating elastic zone decrease and neutral zone increase. In contrast, no significant alteration was detected for the control group.

INTERPRETATIONS

Stiffness characteristics of the cervical spine in axial rotation are prone to be altered in patients with neck pain, but seem to be relieved after a session of non-manipulative manual therapeutic techniques. Further investigations, including randomized clinical trials with various clinical populations and therapeutic modalities, are needed to confirm these preliminary findings.

The intra-rater reliability of a revised 3-point grading system for accessory joint mobilizations

OBJECTIVES

Joint mobilizations are often quantified using a 4-point grading system based on the physiotherapist's detection of resistance. It is suggested that the initial resistance to joint mobilizations is imperceptible to physiotherapists, but that at some point through range becomes perceptible, a point termed R1. Grades of mobilization traditionally hinge around this concept and are performed either before or after R1. Physiotherapists, however, show poor reliability in applying grades of mobilization. The definition of R1 is ambiguous and dependent on the skills of the individual physiotherapist. The aim of this study is to test a revised grading system where R1 is considered at the beginning of range, and the entire range, as perceived by the physiotherapists maximum force application, is divided into three, creating 3 grades of mobilization.

METHOD

Thirty-two post-registration physiotherapists and nineteen pre-registration students assessed end of range (point R2) and then applied 3 grades of AP mobilizations, over the talus, in an asymptomatic models ankle. Vertical forces were recorded through a force platform. Intra-class Correlation Coefficients, Standard Error of Measurement, and Minimal Detectable Change were calculated to explore intra-rater reliability on intra-day and inter-day testing. T-tests determined group differences.

RESULTS

Intra-rater reliability was excellent for intra-day testing (ICC 0.96-0.97), and inter-day testing (ICC 0.85-0.93). No statistical difference was found between pre- and post-registration groups.

DISCUSSION

Standardizing the definition of grades of mobilization, by moving R1 to the beginning of range and separating grades into thirds, results in excellent intra-rater reliability on intra-day and inter-day tests.

LEVEL OF EVIDENCE

3b.

Association of lumbar spine stiffness and flexion-relaxation phenomenon with patient-reported outcomes in adults with chronic low back pain - a single-arm clinical trial investigating the effects of thrust spinal manipulation

Background

Spinal manipulation (SM) is used commonly for treating low back pain (LBP). Spinal stiffness is routinely assessed by clinicians performing SM. Flexion-relaxation ratio (FRR) was shown to distinguish between LBP and healthy populations. The primary objective of this study was to examine the association of these two physiological variables with patient-reported pain intensity and disability in adults with chronic LBP (>12 weeks) receiving SM.

Methods

A single-arm trial provided 12 sessions of side-lying thrust SM in the lumbosacral region over 6 weeks. Inclusion criteria included 21–65 years old, Roland-Morris Disability Questionnaire (RMDQ) score ≥ 6 and numerical pain rating score ≥ 2. Spinal stiffness and FRR were assessed pre-treatment at baseline, after 2 weeks and after 6 weeks of treatment. Lumbar spine global stiffness (GS) were calculated from the force-displacement curves obtained using i) hand palpation, ii) a hand-held device, and iii) an automated indenter device. Lumbar FRR was assessed during trunk flexion-extension using surface electromyography. The primary outcomes were RMDQ and pain intensity measured by visual analog scale (VAS). Mixed-effects regression models were used to analyze the data.

Results

The mean age of the 82 participants was 45 years; 48% were female; and 84% reported LBP >1 year. The mean (standard deviation) baseline pain intensity and RMDQ were 46.1 (18.1) and 9.5 (4.3), respectively. The mean reduction (95% confidence interval) after 6 weeks in pain intensity and RMDQ were 20.1 mm (14.1 to 26.1) and 4.8 (3.7 to 5.8). There was a small change over time in the palpatory GS but not in the hand-held or automated GS, nor in FRR. The addition of each physiologic variable did not affect the model-estimated changes in VAS or RMDQ over time. There was no association seen between physiological variables and LBP intensity. Higher levels of hand-held GS at L3 and automated GS were significantly associated with higher levels of RMDQ (p = 0.02 and 0.03, respectively) and lower levels of flexion and extension FRR were significantly associated with higher levels of RMDQ (p = 0.02 and 0.008, respectively) across the 3 assessment time points.

Conclusions

Improvement in pain and disability observed in study participants with chronic LBP was not associated with the measured GS or FRR.

Trial registration

NCT01670292 on clinicaltrials.gov, August 2, 2012

Posterior-anterior(PA) pressure Puffin for measuring and treating spinal stiffness: Mechanism and repeatability

BACKGROUND

Posterior-anterior (PA) pressure technique is widely used for assessing and treating spinal segments. PA pressure is manually applied and stiffness is subjectively assessed. The method has been deemed unreliable and is associated with occupational strain.

OBJECTIVES

To introduce a new ergonomically designed hand-held device measuring spinal stiffness, and to assess its repeatability.

DESIGN

Quasi experimental study.

METHOD

A convenience sample of 30 university students, 20-30 years old was used. The participants were tested two consecutive days by two physical therapy students using the new device; the PA pressure Puffin. The spinal segments under study were L1, Th12, Th7 and Th6 which all were tested three times with 9 kg force by both testers, both days. Intra-class correlation coefficients (ICC3,k) were used to assess intra- and inter-tester repeatability and analysis of variance with alpha-level at 0.05 was used to assess differences in joint mobility at the four segments measured. Linear regression analyses were used to assess repeatability.

RESULTS

Inter-tester and intra-tester coefficients (ICCs) ranged from 0.88 to 0.97 and from 0.83 to 0.97, respectively. There was no significant difference in displacement between Th6 and Th7 but all other joints were significantly different from each other. Displacement was always significantly greater the second day compared with day one (p < 0.05).

CONCLUSIONS

This close to final prototype of the PA pressure Puffin measures segmental spinal stiffness and its ergonomically designed handle provides a promising tool for physical therapists applying PA pressure. Further research is needed for validation and reliability assessments.

The effect of application site of spinal manipulative therapy (SMT) on spinal stiffness

BACKGROUND CONTEXT

Like other factors that can influence treatment efficacy (eg, dosage, frequency, time of day), the site of treatment application is known to affect various physical interventions such as topical anesthetics and cardiopulmonary resuscitation. Like these examples, spinal manipulative therapy (SMT) is a physical intervention that may exhibit maximal benefit when directed to a specific site. Whereas numerous studies of SMT efficacy have produced mixed results, few studies have taken into account the site of SMT application.

PURPOSE

To determine if the site of SMT application modulates the effect of SMT in an anesthetized feline model.

STUDY DESIGN

Spinal manipulative therapy applied to specific anatomic locations randomized in a Latin square design with a no-SMT control.

OUTCOME MEASURES

Physiologic measures (spinal stiffness).

METHODS

Simulated SMT was delivered by a validated mechanical apparatus to the intact lumbar spine of eight anesthetized felines at four unique sites: L6 spinous process, left L6 lamina, left L6 mammillary process, and L7 spinous process. To measure spinal stiffness, a separate indentation load was applied mechanically to the L6 spinous process before and after each SMT application. Spinal stiffness was calculated from the resulting force-displacement curve as the average stiffness (k) and terminal instantaneous stiffness (TIS).

RESULTS

Relative to the no-SMT control, significant decreases in spinal stiffness followed the SMT when L6 spinous and L6 lamina were used as the contact site. Terminal instantaneous stiffness significantly decreased -0.48 N/mm (upper, lower 95% confidence interval [-0.86, -0.09]) with L6 spinous as the contact site and decreased -0.44 N/mm (-0.82, -0.05), with the L6 lamina as the contact site. k increased 0.44 N/mm (-0.01, 088), using L6 spinous as the contact site.

CONCLUSIONS

Decreases in terminal spinal stiffness were observed after SMT delivered at some application sites but not the others. The results suggest that SMT contact site modulates SMT's effect on spinal stiffness in a feline model. Changes in spinal terminal instantaneous spinal stiffness were similar in magnitude and direction to those observed in symptomatic human subjects who report benefits after SMT.

Comparison of cervical spine stiffness in individuals with chronic nonspecific neck pain and asymptomatic individuals

STUDY DESIGN

Clinical measurement, cross-sectional.

OBJECTIVE

To determine if spinal joint stiffness is different in individuals with nonspecific neck pain, and whether stiffness magnitude is associated with pain intensity and disability.

BACKGROUND

Manual therapists commonly evaluate spinal joint stiffness in patients presenting with nonspecific neck pain. However, a relationship between stiffness and neck pain has not yet been demonstrated.

METHODS

Spinal stiffness at C7 was objectively measured in participants with chronic nonspecific neck pain whose symptomatic spinal level was identified as C7 (n = 12) and in age- and sex-matched asymptomatic controls (n = 12). Stiffness (slope of the linear region of the force-displacement curve) was quantified using a device that applied 5 standardized mechanical force cycles to the C7 spinous process, while concurrently measuring displacement and resistance to movement. Stiffness was compared between groups using an independent t test. Spearman rho and Pearson r were used to determine the extent to which stiffness magnitude was associated with pain intensity (visual analog scale) and level of disability (Neck Disability Index), respectively, in the group with neck pain.

RESULTS

Participants with nonspecific neck pain had greater spinal joint stiffness at C7 compared with asymptomatic individuals (mean difference, 1.78 N/mm; 95% confidence interval: 0.28, 3.27; P = .022). However, stiffness magnitude in the group with neck pain was not associated (P>.05) with pain intensity or level of disability.

CONCLUSION

These preliminary results suggest that cervical spine stiffness may be greater in the presence of nonspecific neck pain. However, judgments regarding pain intensity and level of disability should not be inferred from examinations of spinal joint stiffness.

Indicating spinal joint mobilisations or manipulations in patients with neck or low-back pain: protocol of an inter-examiner reliability study among manual therapists

BACKGROUND

Manual spinal joint mobilisations and manipulations are widely used treatments in patients with neck and low-back pain. Inter-examiner reliability of passive intervertebral motion assessment of the cervical and lumbar spine, perceived as important for indicating these interventions, is poor within a univariable approach. The diagnostic process as a whole in daily practice in manual therapy has a multivariable character, however, in which the use and interpretation of passive intervertebral motion assessment depend on earlier results from the diagnostic process. To date, the inter-examiner reliability among manual therapists of a multivariable diagnostic decision-making process in patients with neck or low-back pain is unknown.

METHODS

This study will be conducted as a repeated-measures design in which 14 pairs of manual therapists independently examine a consecutive series of a planned total of 165 patients with neck or low-back pain presenting in primary care physiotherapy. Primary outcome measure is therapists' decision about whether or not manual spinal joint mobilisations or manipulations, or both, are indicated in each patient, alone or as part of a multimodal treatment. Therapists will largely be free to conduct the full diagnostic process based on their formulated examination objectives. For each pair of therapists, 2×2 tables will be constructed and reliability for the dichotomous decision will be expressed using Cohen's kappa. In addition, observed agreement, prevalence of positive decisions, prevalence index, bias index, and specific agreement in positive and negative decisions will be calculated. Univariable logistic regression analysis of concordant decisions will be performed to explore which demographic, professional, or clinical factors contributed to reliability.

DISCUSSION

This study will provide an estimate of the inter-examiner reliability among manual therapists of indicating spinal joint mobilisations or manipulations in patients with neck or low-back pain based on a multivariable diagnostic reasoning and decision-making process, as opposed to reliability of individual tests. As such, it is proposed as an initial step toward the development of an alternative approach to current classification systems and prediction rules for identifying those patients with spinal disorders that may show a better response to manual therapy which can be incorporated in randomised clinical trials. Potential methodological limitations of this study are discussed.

Within- and between-day reliability of spinal stiffness measurements obtained using a computer controlled mechanical indenter in individuals with and without low back pain

Instrumented spinal stiffness measurements have shown high test-retest reliability. However, factors that may affect reliability have yet to be investigated. The objective of this study was to compare the: 1) within- and between-day reliability of a mechanical indentation device (MID) in measuring spinal stiffness, 2) measurement precision of averaging multiple measurements, and 3) reliability of stiffness measurements between individuals with and without low back pain (LBP). The spinal stiffness of 26 volunteers with and without LBP was measured 3 times by MID in each of two visits 1-4 days apart. Two stiffness measures were calculated from the resulting force-displacement data: global stiffness and terminal stiffness. Intraclass correlation coefficients (ICCs) were used to estimate reliability. Measurement precision was measured by minimal detectable changes, bias and 95% limits of agreement. Using the mean of three spinal stiffness measurements, the measurement precision was improved by 33.7% over a single measurement. Averaging three measurements, the within- and between-day reliability point estimates of both global and terminal stiffness were 0.99 and 0.98, respectively. The reliability estimates of spinal stiffness measurement using MID were not significantly altered by the participants' LBP status across all circumstances (95% confidence intervals overlapped). With our experimental protocol, averaging three spinal stiffness measurements using MID produces reliable stiffness measurements regardless of individuals' LBP status.

The effect of duration and amplitude of spinal manipulative therapy (SMT) on spinal stiffness

The aim of this study was to determine the effect of spinal manipulative therapy (SMT) force magnitude and force duration on the spinal stiffness of a feline preparation. A mechanical device performed simulated SMTs at the L6 spinous process in 22 anesthetised felines. Animals were divided into four groups. Two groups (no preload, preload) received SMT having maximal displacements of 1.0 mm, 2.0 mm and 3.0 mm of total displacement (displacement control). In two other groups (preload, no preload), SMTs were applied with maximal loads of 25%, 55% and 85% body weight (force control). Each of the SMTs were applied in order of increasing displacement or force amplitudes, at increasing durations ranging from 25 to 250 ms. Spinal stiffness was quantified by applying an indentation load to external surface of the back. Linear mixed effects models were fit for post-SMT stiffness variables. When SMT was applied under displacement control with and without a preceding preload, a significant interactive effect occurred between force magnitude and force duration (p ≤ 0.05) for some of the stiffness variables. The findings from this experiment demonstrate that spinal stiffness in a feline model was affected by the interaction of the force amplitude and force duration parameters but the exact nature of this interaction remains unclear. This study provides guidance for further investigation given other SMT parameters not tested here may facilitate the ability of SMT to alter spinal stiffness.

Development and evaluation of tetrapod-shaped granular artificial bones

We have developed a novel form of granular artificial bone "Tetrabones" with a homogeneous tetrapod shape and uniform size. Tetrabones are four armed structures that accumulate to form the intergranular pores that allow invasion of cells and blood vessels. In this study we evaluated the physicochemical characteristics of Tetrabones in vitro, and compared their biological and biomechanical properties in vivo to those of conventional β-tricalcium phosphate (β-TCP) granule artificial bone. Both the rupture strength and elastic modulus of Tetrabone particles were higher than those of β-TCP granules in vitro. The connectivity of intergranular pores 100, 300, and 400 μm in size were higher in Tetrabones than in the β-TCP granules. Tetrabones showed similar osteoconductivity and biomechanical stiffness to β-TCP at 2 months after implantation in an in vivo study of canine bone defects. These results suggest that Tetrabones may be a good bone graft material in bone reconstruction.

A structured review of spinal stiffness as a kinesiological outcome of manipulation: its measurement and utility in diagnosis, prognosis and treatment decision-making

PURPOSE

To review and discuss the methods used for measuring spinal stiffness and factors associated with stiffness, how stiffness is used in diagnosis, prognosis, and treatment decision-making and the effects of manipulative techniques on stiffness.

METHODS

A systematic search of MEDLINE, EMBASE, CINAHL, AMED and ICL databases was conducted. Included studies addressed one of four constructs related to stiffness: measurement, diagnosis, prognosis and/or treatment decision-making, and the effects of manipulation on stiffness. Spinal stiffness was defined as the relationship between force and displacement.

RESULTS

One hundred and four studies are discussed in this review, with the majority of studies focused on the measurement of stiffness, most often in asymptomatic persons. Eight studies investigated spinal stiffness in diagnosis, providing limited evidence that practitioner-judged stiffness is associated with radiographic findings of sagittal rotational mobility. Fifteen studies investigated spinal stiffness in prognosis or treatment decision-making, providing limited evidence that spinal stiffness is unlikely to independently predict patient outcomes, though stiffness may influence a practitioner's application of non-thrust manipulative techniques. Nine studies investigating the effects of manipulative techniques on spinal stiffness provide very limited evidence that there is no change in spinal stiffness following thrust or non-thrust manipulation in asymptomatic individuals and non-thrust techniques in symptomatic persons, with only one study supporting an immediate, but not sustained, stiffness decrease following thrust manipulation in symptomatic individuals.

CONCLUSIONS

The existing limited evidence does not support an association between spinal stiffness and manipulative treatment outcomes. There is a need for additional research investigating the effects of manipulation on spinal stiffness in persons with spinal pain.

Learning lumbar spine mobilization: the effects of frequency and self-control of feedback

STUDY DESIGN

Controlled laboratory study, longitudinal.

OBJECTIVES

To investigate the effects of frequency and self-control of feedback on physiotherapy students learning lumbar spinal mobilization.

BACKGROUND

Posterior-to-anterior mobilization is included in most physiotherapy curricula. However, force application varies between therapists and the optimal feedback for learning is unknown.

METHODS

Sixty-two physiotherapy students were randomized to 3 feedback groups: constant (100% of practice trials), intermittent (33%), and self-controlled (varied according to student choice) feedback. Students performed 12 practice trials of grade II posterior-to-anterior mobilization to the third lumbar vertebra while receiving real-time feedback. The differences between students' force parameters (mean peak force [N], force amplitude [N], and oscillation frequency [Hz]) and those of a physiotherapist expert were compared between groups posttest and at a follow-up of 5 to 7 days using analysis of covariance. Students completed a survey regarding their perceptions of feedback.

RESULTS

Students in the self-controlled group applied mean peak force (mean difference between student and expert, 6.7 N; 95% confidence interval [CI]: 4.4, 9.0) and force amplitude (6.3 N; 95% CI: 4.2, 8.4) that more closely matched the expert's than those applied by the constant group (13.7 N; 95% CI: 8.7, 18.6; P = .021, and 13.1 N; 95% CI: 8.9, 17.4; P = .028) at posttest, with similar results at follow-up for force amplitude only (self-controlled, 9.5 N; 95% CI: 5.8, 18.1; constant, 21.0 N; 95% CI: 13.3, 28.7; P = .018). There were no other significant differences. All students reported a better understanding of manual force application, but feedback preferences varied.

CONCLUSION

Self-controlled feedback appears to be more beneficial than constant feedback for students learning to apply forces during lumbar mobilization.

Preliminary investigation of the mechanisms underlying the effects of manipulation: exploration of a multivariate model including spinal stiffness, multifidus recruitment, and clinical findings

STUDY DESIGN

Prospective case series.

OBJECTIVE

To examine spinal stiffness in patients with low back pain (LBP) receiving spinal manipulative therapy (SMT), evaluate associations between stiffness characteristics and clinical outcome, and explore a multivariate model of SMT mechanisms as related to effects on stiffness, lumbar multifidus (LM) recruitment, and status on a clinical prediction rule (CPR) for SMT outcomes.

SUMMARY OF BACKGROUND DATA

Mechanisms underlying the clinical effects of SMT are poorly understood. Many explanations have been proposed, but few studies have related potential mechanisms to clinical outcomes or considered multiple mechanisms concurrently.

METHODS

Patients with LBP were treated with two SMT sessions over 1 week. CPR status was assessed at baseline. Clinical outcome was based on the Oswestry disability index (ODI). Mechanized indentation measures of spinal stiffness and ultrasonic measures of LM recruitment were taken before and after each SMT, and after 1 week. Global and terminal stiffness were calculated. Multivariate regression was used to evaluate the relationship between stiffness variables and percentage ODI improvement. Zero-order correlations among stiffness variables, LM recruitment changes, CPR status, and clinical outcome were examined. A path analysis was used to evaluate a multivariate model of SMT effects.

RESULTS

Forty-eight patients (54% women) had complete stiffness data. Significant immediate decreases in global and terminal stiffness occurred post-SMT regardless of outcome. ODI improvement was related to greater immediate decrease in global stiffness (P = 0.025), and less initial terminal stiffness (P = 0.01). Zero-order correlations and path analysis supported a multivariate model suggesting that clinical outcome of SMT is mediated by improvements in LM recruitment and immediate decrease in global stiffness. Initial terminal stiffness and CPR status may relate to outcome though their relationship with LM recruitment.

CONCLUSION

The underlying mechanisms explaining the benefits of SMT appear to be multifactorial. Both spinal stiffness characteristics and LM recruitment changes appear to play a role.

Reliability of joint mobility and pain assessment of the thoracic spine and rib cage in asymptomatic individuals

Despite the importance of correctly diagnosing a spinal dysfunction, limited research exists related to physical therapists' ability to reliably identify a joint exhibiting signs of dysfunction. The purpose of this investigation was to determine the inter- and intra-examiner reliability of a thoracic spine and rib cage joint mobility and pain assessment between two experienced manipulative physical therapists. Nine healthy subjects (3 male, 6 female; ages 23-35) without history of mid- or low back pain participated. Posterior-to-anterior pressures were applied to the thoracic spine and rib articulations with anterior-to-posterior pressures applied to the costosternal joints of each subject by two examiners to evaluate joint mobility and pain provocation. Both examiners assessed all subjects twice and were blinded to subject identity. Kappa statistics were calculated using a strict and expanded definition of agreement to determine the between- and within-examiner reliability for each outcome. Intra-examiner reliability of joint mobility assessment ranged from slight to fair based on the strict agreement but improved to good when findings were compared across +/- 1 spinal/rib level. Pain provocation reliability increased to very good under the expanded agreement; however, this finding should be viewed with caution due to limited pain prevalence in the subject sample. Selected clinical prediction rules, applied to the care of individuals with back pain, characterize the patient's regional mobility simply as hypomobile, normal, or hypermobile; consequently, we feel the results of an expanded definition of agreement may be more appropriate for clinic practice. Further research is needed to determine the reliability in individuals with thoracic spine and rib cage symptoms.

Changes in bending stiffness and lumbar spine range of movement following lumbar mobilization and manipulation

OBJECTIVE

The purpose of this study was to investigate the effects of lumbar rotational manipulation and lumbar central posteroanterior mobilization on lumbar bending stiffness and flexion and extension range of motion (ROM).

METHODS

A same-subject, repeated-measures, crossover design was used using 32 asymptomatic subjects (16 female and 16 male; mean [SD] age, 25.5 [4.5] years; weight, 65.7 [11.8] kg; and height, 1.70 [0.08] m). Each subject received mobilization or manipulation on 2 different occasions. Bending stiffness was calculated using a 3-point bending model using an electromagnetic tracking device and a force platform; lumbar flexion and extension ROM was measured using an electromagnetic tracking device. All variables were measured pre- and postintervention. Their effect was compared using paired t tests.

RESULTS

Manipulation and mobilization did not significantly alter either bending stiffness or lumbar flexion and extension ROM (mobilization: P = .175, P = .613, and P = .535; manipulation: P = .973, P = .323, and P = .439). Bending stiffness changes were not correlated to changes in ROM (Pearson r for stiffness-flexion = -0.102, P = .586; Pearson r for stiffness-extension = 0.014, P = .941).

CONCLUSIONS

Manipulation and mobilization had no significant effect on bending stiffness or flexion and extension ROM for this group of subjects. Some individual variations in effect were observed.

Computer assisted learning in manipulative therapy education

Teaching manipulative therapy is one of the most relevant issues in a physiotherapy course. However, for an effective instruction of this topic practical experience is considered fundamental. To achieve this purpose, this paper presents a computer assisted environment for the practical learning of manipulative therapy. The implementation of such a laboratory includes standard Personal Computers (PCs), the popular software package Matlab, a digital camera and gloves with embedded strength sensors located in the thumb and near the wrist. The students wear a glove that measures the applied force in the patient. These signals are acquired and stored in a computer providing the teachers with the necessary information to analyze the applied force and verify if the manual therapy was successful. A digital camera is also used to record the images of the student's movements during the manual therapy application. The developed system has an autonomy of 15h allowing the application of thirty therapies and the corresponding data analysis.

The effects of thoracic manipulation on posteroanterior spinal stiffness

STUDY DESIGN

Controlled laboratory study, with measurements taken before and after a standardized clinical intervention.

OBJECTIVES

To determine if thoracic manipulation alters the posteroanterior (PA) spinal stiffness of the thoracic spine, and the factors associated with any potential changes in stiffness.

BACKGROUND

Spinal manipulation is commonly used to treat thoracic pain and dysfunction. Therapists use manual assessment of PA spinal stiffness to determine the appropriateness and effectiveness of treatment, with potential changes in spinal stiffness possibly contributing to symptomatic improvement following manipulation.

METHODS

Thoracic PA spinal stiffness was measured at 5 vertebral levels (manipulated level and 2 levels above and below), in 24 asymptomatic subjects, before and after manipulation. Five cycles of standardized mechanical PA force were applied to the spinous process while recording resistance to movement and concurrent displacement, with stiffness defined as the slope of the linear portion of the force-displacement curve. A 2-way repeated-measures analysis of variance determined differences between premanipulation and postmanipulation among multiple spinal levels. Linear regression determined the relationship between stiffness magnitude and its change following manipulation. Generalized linear mixed models were used to determine if subject age, gender, spinal level, premanipulation stiffness, or manipulative thrust parameters were associated with postmanipulation stiffness.

RESULTS

Thoracic spine PA stiffness differed between spinal levels (F4,92=21.1, P<.001) but was not significantly different following manipulation. The mean change in spinal stiffness correlated with stiffness magnitude at the manipulated spinal level only but not other levels (Pearson r, –0.65; P<.001). Greater postmanipulation stiffness was associated with being male (regression coefficient, 1.16; 95% CI: 0.52, 1.79; P<.001) and with higher premanipulation stiffness (regression coefficient, 0.63; 95% CI: 0.49, 0.77; P<.001). Manipulation force parameters were not associated with postmanipulation stiffness.

CONCLUSION

In asymptomatic individuals, thoracic PA spinal stiffness is not significantly different when measured before and after thrust manipulation, but any potential mechanical effects appear associated with the manipulated spinal level rather than other levels.

Cervical spine mobilisation forces applied by physiotherapy students

OBJECTIVES

Postero-anterior (PA) mobilisation is commonly used in cervical spine treatment and included in physiotherapy curricula. The manual forces that students apply while learning cervical mobilisation are not known. Quantifying these forces informs the development of strategies for learning to apply cervical mobilisation effectively and safely. This study describes the mechanical properties of cervical PA mobilisation techniques applied by students, and investigates factors associated with force application.

PARTICIPANTS

Physiotherapy students (n=120) mobilised one of 32 asymptomatic subjects.

METHODS

Students applied Grades I to IV central and unilateral PA mobilisation to C2 and C7 of one asymptomatic subject. Manual forces were measured in three directions using an instrumented treatment table. Spinal stiffness of mobilised subjects was measured at C2 and C7 using a device that applied a standard oscillating force while measuring this force and its concurrent displacement. Analysis of variance was used to determine differences between techniques and grades, intraclass correlation coefficients (ICC) were used to calculate the inter- and intrastudent repeatability of forces, and linear regression was used to determine the associations between applied forces and characteristics of students and mobilised subjects.

RESULTS

Mobilisation forces increased from Grades I to IV (highest mean peak force, Grade IV C7 central PA technique: 63.7N). Interstudent reliability was poor [ICC(2,1)=0.23, 95% confidence interval (CI) 0.14 to 0.43], but intrastudent repeatability of forces was somewhat better (0.83, 95% CI 0.81 to 0.86). Higher applied force was associated with greater C7 stiffness, increased frequency of thumb pain, male gender of the student or mobilised subject, and a student being earlier in their learning process. Lower forces were associated with greater C2 stiffness.

CONCLUSION

This study describes the cervical mobilisation forces applied by students, and the characteristics of the student and mobilised subject associated with these forces. These results form a basis for the development of strategies to provide objective feedback to students learning to apply cervical mobilisation.

Measuring the posteroanterior stiffness of the cervical spine

An essential part of improving manual therapy treatment for cervical spine disorders is the identification of the mechanical effects of manual techniques. The aims of this research were to develop a reliable and safe instrument for measuring cervical spine stiffness, and to document stiffness in a group of asymptomatic individuals. A device for measuring cervical spine stiffness was designed and tested. The stiffness of the cervical spine of 67 asymptomatic individuals was measured at C2 and C7 on one or more occasions. Stiffness was defined as the slope of the linear region of the force-displacement curve (coefficient K). For C2, the linear region of the force-displacement curve was from 7 to 40 N, and for C7, 20-70 N. The mean stiffness (coefficient K) on the first measurement occasion at C2 was 4.58 N/mm (95% CI 4.30-4.85), and at C7 was 7.03 N/mm (95% CI 6.50-7.57). ICC(2,1) for repeated measurements was 0.84 (95% CI 0.74-0.90). Stiffness measurements in the cervical spine were generally lower than those previously reported for the lumbar spine. Age was positively associated with C2 stiffness (p=0.01). Males were stiffer at C7 than females (p<0.001). This research provides a basis for future studies investigating the effects of manual techniques on cervical spine stiffness, potentially leading to improved outcomes for patients treated by manual therapy.

Force-displacement relationship during anteroposterior mobilization of the ankle joint

OBJECTIVE

The purpose of this study was to determinate the correlation between force and displacement during passive anteroposterior mobilization of the talus and the effect of this treatment technique on ankle dorsiflexion range of motion (ROM).

METHODS

This is an exploratory, methodological study. Maitland grades III and IV mobilization were applied on the right ankle of 25 healthy subjects (mean age +/- standard deviation, 25.08 +/- 3.01 years) by 2 randomized raters (A and B). Applied forces were measured using a small force plate and displayed for the rater on a computer monitor. Linear displacement of the ankle joint was quantified by a motion analysis system. Synchronization of these 2 systems was obtained by software. Dorsiflexion active ROM, before and after mobilization, was assessed using a biplane goniometer. Statistical analysis was performed using the Pearson correlation coefficient for force and displacement variables and the paired t test to compare dorsiflexion ROM mean values.

RESULTS

A fair positive correlation was found between force range and displacement (r = 0.370; P = .049, 1-tailed), and a fair negative correlation was found between minimum forces and displacement (r = 0.404; P = .035, 1-tailed), only for rater A data. Significant increase in dorsiflexion was found in the right ankle (P = .035), comparing ROM before and after mobilization, which did not occur in the left ankle.

CONCLUSIONS

These data do not support a linear force-displacement relationship during Maitland grades III and IV passive joint mobilization, although they confirmed an increase in ankle dorsiflexion ROM immediately after joint mobilization. The use of visual feedback may increase interrater reliability of forces applied during ankle joint mobilization.

Relationship between spinal stiffness and outcome in patients with chronic low back pain

Many manual therapists assess and treat spinal stiffness of people with low back pain. The objectives of this study were to investigate: (i) whether spinal stiffness changes after treatment; (ii) the relationship between pre-treatment spinal stiffness and change in stiffness with treatment; (iii) the relationship between spinal stiffness, pain, disability and global perceived effect of treatment; (iv) whether spinal stiffness predicts outcome of treatment or response to treatment in chronic low back pain patients. One hundred and ninety-one subjects with chronic low back pain were randomly allocated to groups that received either spinal manipulative therapy, motor control exercise, or a general exercise program. Spinal stiffness was assessed before and after intervention. All three groups showed a significant decrease in stiffness following treatment (p<0.001). No difference between groups was observed. There was a significant negative correlation between pre-treatment stiffness and change in stiffness (r=-0.61; p<0.001). There was a significant but weak correlation (r=0.18; p=0.02) between change in stiffness and change in global perceived effect of treatment, and a significant but weak correlation between change in stiffness and change in function for subjects in the spinal manipulative therapy group (r=-0.28; p=0.02). No significant association was observed between initial stiffness score and any of the final outcome measures following treatment. Initial stiffness did not predict response to any treatment. In conclusion, spinal stiffness decreases over the course of an episode of treatment, more so in those with the stiffest spines, but the decrease is not dependent on treatment and is not generally related to outcome.

Changes in postural activity of the trunk muscles following spinal manipulative therapy

Spinal manipulative therapy (SMT) is common in the management of low back pain (LBP) and has been associated with changes in muscle activity, but evidence is conflicting. This study investigated the effect of SMT on trunk muscle activity in postural tasks in people with and without LBP. In 20 subjects (10 with LBP and 10 controls), EMG recordings were made with fine-wire electrodes inserted into transversus (TrA), obliquus internus (OI), and externus (OE) abdominis. Rectus abdominis (RA) and anterior deltoid EMG was recorded with surface electrodes. Standing subjects rapidly flexed an arm in response to a light, before and after a small amplitude end range rotational lumbar mobilization at L4-5. In controls, there was no change in trunk muscle EMG during the postural perturbation after SMT. In LBP subjects there was an increase in the postural response of OI and an overall increase in OE EMG. There was no change in TrA or RA EMG. These results indicate that SMT changes the functional activity of trunk muscles in people with LBP, but has no effect on control subjects. Importantly, SMT increased the activity of the oblique abdominal muscles with no change in the deep trunk muscle TrA, which is often the target of exercise interventions.

Manual Forces Applied During Cervical Mobilization

OBJECTIVE

Manual therapists routinely use passive accessory mobilization techniques to treat patients with mechanical neck disorders, but little is known about the manual forces applied. The aim of this study was to quantify the manual forces applied to the cervical spine during joint mobilization.

METHODS

Ten physiotherapists performed posterior-to-anterior mobilizations to C2 and C7 (both centrally and unilaterally, 1 right and 1 left, grades I-IV) on a single asymptomatic male subject. Manual forces were measured in 3 planes using an instrumented treatment table.

RESULTS

The instrumented table showed excellent reliability (intraclass correlation coefficient [2,1], 0.99; 95% confidence interval, 0.97-1.00) and accuracy (mean absolute error; vertical force, 1.1 N; SD, 1.5). There were considerable differences between therapists for mean peak force, force amplitude, and oscillation frequency for each technique and grade. Mean peak forces (grade I, 21.8 N; SD, 15.0; grade II, 34.9 N; SD, 20.9; grade III, 58.2 N; SD, 27.5; grade IV, 61.0 N; SD, 29.9) were considerably lower than previously reported lumbar mobilization forces. Intratherapist repeatability for all mobilization parameters was high. Force amplitude and oscillation frequency measures indicated that therapists generally adhered to the published definitions of the grades of mobilization when applying force, but when asked, provided quite different definitions of the grades.

CONCLUSIONS

This study provides preliminary evidence that cervical mobilization forces vary considerably between therapists, but intratherapist repeatability is high.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited

OBJECTIVE

The objectives of this white paper are to review and summarize the basic science literature relevant to spinal fixation (subluxation) and spinal adjusting procedures and to make specific recommendations for future research.

METHODS

PubMed, CINAHL, ICL, OSTMED, and MANTIS databases were searched by a multidisciplinary team for reports of basic science research (since 1995) related to spinal fixation (subluxation) and spinal adjusting (spinal manipulation). In addition, hand searches of the reference sections of studies judged to be important by the authors were also obtained. Each author used key words they determined to be most important to their field in designing their individual search strategy. Both animal and human studies were included in the literature searches, summaries, and recommendations for future research produced in this project.

DISCUSSION

The following topic areas were identified: anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system. A relevant summary of each topic area and specific recommendations for future research in each area were the primary objectives of this project.

CONCLUSIONS

The summaries of the literature for the 6 topic sections (anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system) indicated that a significant body of basic science research evaluating chiropractic spinal adjusting has been completed and published since the 1997 basic science white paper. Much more basic science research in these fields needs to be accomplished, and the recommendations at the end of each topic section should help researchers, funding agencies, and other decision makers develop specific research priorities.

Manual Forces Applied During Posterior-to-Anterior Spinal Mobilization: A Review of the Evidence

OBJECTIVE

The objective of this review was to evaluate the evidence for the consistency of force application by manual therapists when carrying out posterior-to-anterior (PA) mobilization techniques, including the factors that influence the application and measurement of mobilization forces.

METHODS

Studies were identified by searching 6 electronic databases up to April 2005, screening the reference lists of retrieved articles, and contacting experts by e-mail. Relevant articles were defined as those that described the measurement of forces applied during spinal mobilization or discussed the reliability of measurement of manual forces.

RESULTS

Twenty studies described the quantitative measurement of applied force during a PA mobilization technique, with most focusing on the lumbar spine. When defined by magnitude, frequency, amplitude, and displacement, PA mobilization forces are extremely variable among clinicians applying the same manual technique. Variability may be attributed to differences in techniques, measurement or reporting procedures, or variations between therapists or between patients.

CONCLUSIONS

The inconsistency in manual force application during PA spinal mobilization in existing studies suggests that further studies are needed to improve the clinical standardization of manual force application. Future research on mobilization should include forces applied to the cervical and thoracic spines in addition to the lumbar spine while thoroughly describing force parameters and measurement methods to facilitate comparison between studies.

Dynamic dorsoventral stiffness assessment of the ovine lumbar spine

Posteroanterior spinal stiffness assessments are common in the evaluating patients with low back pain. The purpose of this study was to determine the effects of mechanical excitation frequency on dynamic lumbar spine stiffness. A computer-controlled voice coil actuator equipped with a load cell and LVDT was used to deliver an oscillatory dorsoventral (DV) mechanical force to the L3 spinous process of 15 adolescent Merino sheep. DV forces (48 N peak, approximately 10% body weight) were randomly applied at periodic excitation frequencies of 2.0, 6.0, 11.7 and a 0.5-19.7 Hz sweep. Force and displacement were recorded over a 13-22 s time interval. The in vivo DV stiffness of the ovine spine was frequency dependent and varied 3.7-fold over the 0.5-19.7 Hz mechanical excitation frequency range. Minimum and maximum DV stiffness (force/displacement) were 3.86+/-0.38 and 14.1+/-9.95 N/mm at 4.0 and 19.7 Hz, respectively. Stiffness values based on the swept-sine measurements were not significantly different from corresponding periodic oscillations (2.0 and 6.0 Hz). The mean coefficient of variation in the swept-sine DV dynamic stiffness assessment method was 15%, which was similar to the periodic oscillation method (10-16%). The results indicate that changes in mechanical excitation frequency and animal body mass modulate DV spinal stiffness.

Intra-abdominal pressure increases stiffness of the lumbar spine

Intra-abdominal pressure (IAP) increases during many tasks and has been argued to increase stability and stiffness of the spine. Although several studies have shown a relationship between the IAP increase and spinal stability, it has been impossible to determine whether this augmentation of mechanical support for the spine is due to the increase in IAP or the abdominal muscle activity which contributes to it. The present study determined whether spinal stiffness increased when IAP increased without concurrent activity of the abdominal and back extensor muscles. A sustained increase in IAP was evoked by tetanic stimulation of the phrenic nerves either unilaterally or bilaterally at 20 Hz (for 5 s) via percutaneous electrodes in three subjects. Spinal stiffness was measured as the force required to displace an indentor over the L4 or L2 spinous process with the subjects lying prone. Stiffness was measured as the slope of the regression line fitted to the linear region of the force-displacement curve. Tetanic stimulation of the diaphragm increased IAP by 27-61% of a maximal voluntary pressure increase and increased the stiffness of the spine by 8-31% of resting levels. The increase in spinal stiffness was positively correlated with the size of the IAP increase. IAP increased stiffness at L2 and L4 level. The results of this study provide evidence that the stiffness of the lumbar spine is increased when IAP is elevated.

Failure characteristics of the thoracic spine with a posteroanterior load: investigating the safety of spinal mobilization

STUDY DESIGN

In vitro biomechanical study of human cadaveric thoracic spine segments and one intact cadaver and applied load measurements in human volunteers.

OBJECTIVES

To quantify failure load and pattern of midthoracic vertebrae under a posteroanterior load and to compare failure load in vitro with applied load in vivo.

SUMMARY OF BACKGROUND DATA

Osteoporosis and back pain are common alone and in combination among older adults. Spinal mobilization techniques have been shown to relieve back pain and improve function in various clinical settings. However, whether controlled spinal mobilization can cause vertebral fracture in individuals with osteoporosis is not known.

METHODS

Twelve T5-T8 cadaveric specimens (mean age, 77 years) were scanned using bone densitometry, radiographed, and measured for bone size. The authors measured failure load, failure site, and intervertebral motion (using a precision optoelectronic camera system) when a posteroanterior load was applied at the spinous process of T6 using a servohydraulic material testing machine. Post-test radiography and CT scan were used to verify failure site. These tests were repeated in an intact cadaver using a Tekscan I-Scan sensor to measure applied loads. The authors also quantified in vivo applied loads during posteroanterior mobilization during seven trials by two experienced physiotherapists.

RESULTS

Mean (SD) in vitro failure load of 479 N (162 N) was significantly higher than the mean (SD) in vivo applied load of 145 N (38 N) (P = 0.0004). Macroscopic observation revealed a fracture at the T6 spinous process in 11 specimens and one at the T7 spinous process. These fractures were detected by plain radiography in three of 12 cases and by CT scan in six of 12 cases.

CONCLUSIONS

The results suggest a reasonable margin between failure load in vitro and applied mobilization load in vivo.

Biomechanical and neurophysiological responses to spinal manipulation in patients with lumbar radiculopathy

OBJECTIVE

The purpose of this study was to quantify in vivo vertebral motions and neurophysiological responses during spinal manipulation.

METHODS

Nine patients undergoing lumbar decompression surgery participated in this study. Spinal manipulative thrusts (SMTs) ( approximately 5 ms; 30 N [Sham], 88 N, 117 N, and 150 N [max]) were administered to lumbar spine facet joints (FJs) and spinous processes (SPs) adjacent to an intraosseous pin with an attached triaxial accelerometer and bipolar electrodes cradled around the S1 spinal nerve roots. Peak baseline amplitude compound action potential (CAP) response and peak-peak amplitude axial (AX), posterior-anterior (PA), and medial-lateral (ML) acceleration time and displacement time responses were computed for each SMT. Within-subject statistical analyses of the effects of contact point and force magnitude on vertebral displacements and CAP responses were performed.

RESULTS

SMTs (>/= 88 N) resulted in significantly greater peak-to-peak ML, PA, and AX vertebral displacements compared with sham thrusts (P <.002). SMTs delivered to the FJs resulted in approximately 3-fold greater ML motions compared with SPs (P <.001). SMTs over the SPs resulted in significantly greater AX displacements compared with SMTs applied to the FJs (P <.05). Seventy-five percent of SMTs resulted in positive CAP responses with a mean latency of 12.0 ms. Collectively, the magnitude of the CAP responses was significantly greater for max setting SMTs compared with sham (P <.01).

CONCLUSIONS

Impulsive SMTs in human subjects were found to stimulate spinal nerve root responses that were temporally related to the onset of vertebral motion. Further work, including examination of the frequency and force duration dependency of SMT, is necessary to elucidate the clinical relevance of enhanced or absent CAP responses in patients.

Neuromechanical characterization of in vivo lumbar spinal manipulation. Part I. Vertebral motion

OBJECTIVE

To quantify in vivo spinal motions and coupling patterns occurring in human subjects in response to mechanical force, manually assisted, short-lever spinal manipulative thrusts (SMTs) applied to varying vertebral contact points and utilizing various excursion (force) settings.

METHODS

Triaxial accelerometers were attached to intraosseous pins rigidly fixed to the L1, L3, or L4 lumbar spinous process of 4 patients (2 male, 2 female) undergoing lumbar decompressive surgery. Lumbar spine acceleration responses were recorded during the application of 14 externally applied posteroanterior (PA) impulsive SMTs (4 force settings and 3 contact points) in each of the 4 subjects. Displacement time responses in the PA, axial (AX), and medial-lateral (ML) axes were obtained, as were intervertebral (L3-4) motion responses in 1 subject. Statistical analysis of the effects of facet joint (FJ) contact point and force magnitude on peak-to-peak displacements was performed. Motion coupling between the 3 coordinate axes of the vertebrae was examined using a least squares linear regression.

RESULTS

SMT forces ranged from 30 N (lowest setting) to 150 N (maximum setting). Peak-to-peak ML, PA, and AX vertebral displacements increased significantly with increasing applied force. For thrusts delivered over the FJs, pronounced coupling was observed between all axes (AX-ML, AX-PA, PA-ML) (linear regression, R(2) = 0.35-0.52, P <.001), whereas only the AX and PA axes showed a significant degree of coupling for thrusts delivered to the spinous processes (SPs) (linear regression, R(2) = 0.82, P <.001). The ML and PA motion responses were significantly (P <.05) greater than the AX response for all SMT force settings. PA vertebral displacements decreased significantly (P <.05) when the FJ contact point was caudal to the pin compared with FJ contact cranial to the pin. FJ contact at the level of the pin produced significantly greater ML vertebral displacements in comparison with contact above and below the pin. SMTs over the spinous processes produced significantly (P <.05) greater PA and AX displacements in comparison with ML displacements. The combined ML, PA, and AX peak-to-peak displacements for the 4 force settings and 2 contact points ranged from 0.15 to 0.66 mm, 0.15 to 0.81 mm, and 0.07 to 0.45 mm, respectively. Intervertebral motions were of similar amplitude as the vertebral motions.

CONCLUSIONS

In vivo kinematic measurements of the lumbar spine during the application of SMTs over the FJs and SPs corroborate previous spinous process measurements in human subjects. Our findings demonstrate that PA, ML, and AX spinal motions are coupled and dependent on applied force and contact point.

Spinal stiffness changes throughout the respiratory cycle

Posteroanterior stiffness of the lumbar spine is influenced by factors, including trunk muscle activity and intra-abdominal pressure (IAP). Because these factors vary with breathing, this study investigated whether stiffness is modulated in a cyclical manner with respiration. A further aim was to investigate the relationship between stiffness and IAP or abdominal and paraspinal muscle activity. Stiffness was measured from force-displacement responses of a posteroanterior force applied over the spinous process of L2 and L4. Recordings were made of IAP and electromyographic activity from L4/L2 erector spinae, abdominal muscles, and chest wall. Stiffness was measured with the lung volume held at the extremes of tidal volume and at greater and lesser volumes. Stiffness at L4 and L2 increased above base-level values at functional residual capacity (L2 14.9 N/mm and L4 15.3 N/mm) with both inspiratory and expiratory efforts. The increase was related to the respiratory effort and was greatest during maximum expiration (L2 24.9 N/mm and L4 23.9 N/mm). The results indicate that changes in trunk muscle activity and IAP with respiratory efforts modulate spinal stiffness. In addition, the diaphragm may augment spinal stiffness via attachment of its crural fibers to the lumbar vertebrae.