Posteroanterior stiffness in the lumbosacral spine. The correlation between adjacent vertebral levels

Prevalence and Risk Factors of Degenerative Spondylolisthesis and Retrolisthesis in the Thoracolumbar and Lumbar Spine - An EOS Study Using Updated Radiographic Parameters

STUDY DESIGN

Single centre, cross-sectional study.

OBJECTIVES

The objective is to report the prevalence of spondylolisthesis and retrolisthesis, analyse both conditions in terms of the affected levels and severity, as well as identify their risk factors.

METHODS

A review of clinical data and radiographic images of consecutive spine patients seen in outpatient clinics over a 1-month period is performed. Images are obtained using the EOS® technology under standardised protocol, and radiographic measurements were performed by 2 independent, blinded spine surgeons. The prevalence of both conditions were shown and categorised based on the spinal level involvement and severity. Associated risk factors were identified.

RESULTS

A total of 256 subjects (46.1% males) with 2304 discs from T9/10 to L5/S1 were studied. Their mean age was 52.2(± 18.7) years. The overall prevalence of spondylolisthesis and retrolisthesis was 25.9% and 17.1% respectively. Spondylolisthesis occurs frequently at L4/5(16.3%), and retrolisthesis at L3/4(6.8%). Majority of the patients with spondylolisthesis had a Grade I slip (84.3%), while those with retrolisthesis had a Grade I slip. The presence of spondylolisthesis was found associated with increased age (P < .001), female gender (OR: 2.310; P = .005), predominantly sitting occupations (OR:2.421; P = .008), higher American Society of Anaesthesiology grades (P = .001), and lower limb radiculopathy (OR: 2.175; P = .007). Patients with spondylolisthesis had larger Pelvic Incidence (P < .001), Pelvic Tilt (P < .001) and Knee alignment angle (P = .011), but smaller Thoracolumbar junctional angle (P = .008), Spinocoxa angle (P = .007). Retrolisthesis was associated with a larger Thoracolumbar junctional angle (P =.039).

CONCLUSION

This is the first study that details the prevalence of spondylolisthesis and retrolisthesis simultaneously, using the EOS technology and updated sagittal radiographic parameters. It allows better understanding of both conditions, their mutual relationship, and associated clinical and radiographic risk factors.

Reliability of a New Indentometer Device for Measuring Myofascial Tissue Stiffness

Changes in tissue stiffness are associated with pathological conditions such as myofascial pain and increased risk of muscle injury. Furthermore, they have been shown to modify performance indicators such as running economy or jump height. Indentometry is an affordable way to assess tissue stiffness. However, to date, there is a paucity of studies examining the measurement properties of available devices. With this trial, we aimed to evaluate the reliability of the “IndentoPro”. Two investigators repeatedly measured the stiffness of the lateral head of the gastrocnemius muscle in healthy participants (N = 35), using 5 and 10 mm indentation depths. Intraclass Correlation Coefficients (ICC) revealed moderate inter-rater reliability (5 mm: ICC3,1 0.74, 95%CI = 0.54 to 0.86, p < 0.001; 10 mm: ICC3,1 0.59, 95%CI = 0.27 to 0.78, p < 0.001) and good intra-rater reliability (5 mm: ICC3,1 0.84, 95%CI = 0.71 to 0.92, p < 0.001; 10 mm: ICC3,1 0.83, 95%CI = 0.69 to 0.91, p < 0.001). No correlations between age, height, weight, BMI, skinfold thickness and myofascial tissue stiffness were observed (p > 0.5). In conclusion, the IndentoPro is reliable in assessing calf tissue stiffness, but the predictors of stiffness remain unclear.

Effects of muscle activity on lumbar spinal stiffness in asymptomatic adults: An investigation using a novel rolling device

BACKGROUND

Device-based measurement of lumbar spinal stiffness has the potential to identify patients with low back pain who are more likely to improve with spinal manipulative therapy. This study evaluates how voluntary contraction of spine muscles may impact stiffness measures.

OBJECTIVE

To determine how the contraction of different spinal muscles may influence spinal stiffness at all lumbar levels.

DESIGN

Experimental study.

METHOD

A mechanical device was used to measure spinal stiffness (N/mm) from L1 to L5 in 12 asymptomatic participants, while muscle activity from four pairs of thoracolumbar muscles was recorded. A baseline measurement was collected with the participants holding their breath at normal exhalation. Participants stiffness was then measured while performing (1) an isometric hip extension, (2) an isometric shoulder flexion, and (3) a deep held inhalation. Mixed-model ANOVAs were used to evaluate the effects of the perturbations on spinal stiffness at each lumbar level. Friedman's test was then computed to evaluate the differences in muscle activity between the perturbations.

RESULTS

Globally, the designed perturbations generated activity in different muscles with different magnitudes (P-values≤0.05). Increased spinal stiffness was observed at each spinal level during the hip extension, and at L5 during the held inhalation (P-values<0.05). A differential effect of the spinal levels on the spinal stiffness was observed during the hip extension and held inhalation (P-values<0.05).

CONCLUSION

This study provides evidence that the magnitude of muscle activity influences spinal stiffness, but not equally between lumbar levels.

Analysis of Surgical Forces Required to Gain Access Using a Probe for Minimally Invasive Spine Surgery via Cadaveric-Based Experiments Towards Use in Training Simulators

INTRODUCTION

Virtual Reality haptic-based surgical simulators for training purposes have recently been receiving increased traction within the medical field. However, its future adoption is contingent on the accuracy and reliability of the haptic feedback.

GOAL

This study describes and analyzes the implementation of a set of haptic-tailored experiments to extract the force feedback of a medical probe used in minimally invasive spinal lumbar interbody fusion surgeries.

METHODS

Experiments to extract linear, lateral and rotational insertion, relaxation and extraction of the tool within the spinal muscles, intervertebral discs and lumbar nerve on two cadaveric torsos were conducted.

RESULTS

Notably, mean force-displacement and torque-angular displacement curves describing the different tool-tissue responses were reported with a maximum force of 6.87 (±1.79) N at 40 mm in the muscle and an initial rupture force through the Annulus Fibrosis of 20.550 (±7.841) N at 6.441 mm in the L₄/L₅ disc.

CONCLUSION

The analysis showed that increasing the velocity of the probe slightly reduced and delayed depth of the muscle punctures but significantly lowered the force reduction due to relaxation. Decreasing probe depth resulted with a reduction to the force relaxation drop. However, varying the puncturing angle of attack resulted with a significant effect on increasing force intensities. Finally, not resecting the thoracolumbar fascia prior to puncturing the muscle resulted with a significant increase in the force intensities.

SIGNIFICANCE

These results present a complete characterization of the input required for probe access for spinal surgeries to provide an accurate haptic response in training simulators.

Dose optimization for spinal treatment effectiveness: a randomized controlled trial investigating the effects of high and low mobilization forces in patients with neck pain

STUDY DESIGN

Randomized controlled trial. Objective To determine if force magnitude during posterior-to-anterior mobilization affects immediate and short-term outcomes in patients with chronic, nonspecific neck pain.

BACKGROUND

The optimal dose of mobilization to effectively treat patients with neck pain is not known.

METHODS

Patients with neck pain of at least 3 months in duration (n = 64) were randomized to receive a single treatment of posterior-to-anterior mobilization applied with 30 N or 90 N of mean peak force (3 sets of 30 seconds) or a placebo (detuned laser) on the spinous process at the painful spinal level. Pressure pain threshold, pain measured with a visual analog scale (range, 0-100 mm), cervical range of motion, and spinal stiffness at the painful spinal level (measured with a custom device and normalized as a percentage of C7 stiffness) were assessed before, immediately after, and at a mean ± SD follow-up of 4.0 ± 1.8 days following treatment. Repeated-measures analysis of covariance and Bonferroni-adjusted post hoc tests determined group differences for each outcome measure after treatment and at follow-up.

RESULTS

At follow-up, the 90-N group had less pain than the 30-N group (mean difference, 11.3 mm; 95% confidence interval: 0.1, 22.6 mm; P = .048) and lower stiffness than the placebo group (mean difference, 17.5%; 95% confidence interval: 4.2%, 30.9%; P = .006). These differences were not present immediately after treatment. There were no significant between-group differences in pressure pain threshold or range of motion after treatment or at follow-up.

CONCLUSION

A specific dose of mobilization, in terms of applied force, appears necessary for reducing stiffness and potentially pain in patients with chronic neck pain. Changes were not observed immediately after mobilization, suggesting that its effects are not directly mechanical.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry ( http://www.anzctr.org.au/): ACTRN12611000374965.

LEVEL OF EVIDENCE

Therapy, level 1b-.

Effects of unilateral facet fixation and facetectomy on muscle spindle responsiveness during simulated spinal manipulation in an animal model

OBJECTIVES

Manual therapy practitioners commonly assess lumbar intervertebral mobility before deciding treatment regimens. Changes in mechanoreceptor activity during the manipulative thrust are theorized to be an underlying mechanism of spinal manipulation (SM) efficacy. The objective of this study was to determine if facet fixation or facetectomy at a single lumbar level alters muscle spindle activity during 5 SM thrust durations in an animal model.

METHODS

Spinal stiffness was determined using the slope of a force-displacement curve. Changes in the mean instantaneous frequency of spindle discharge were measured during simulated SM of the L6 vertebra in the same 20 afferents for laminectomy-only and 19 laminectomy and facet screw conditions; only 5 also had data for the laminectomy and facetectomy condition. Neural responses were compared across conditions and 5 thrust durations (≤ 250 milliseconds) using linear-mixed models.

RESULTS

Significant decreases in afferent activity between the laminectomy-only and laminectomy and facet screw conditions were seen during 75-millisecond (P < .001), 100-millisecond (P = .04), and 150-millisecond (P = .02) SM thrust durations. Significant increases in spindle activity between the laminectomy-only and laminectomy and facetectomy conditions were seen during the 75-millisecond (P < .001) and 100-millisecond (P < .001) thrust durations.

CONCLUSION

Intervertebral mobility at a single segmental level alters paraspinal sensory response during clinically relevant high-velocity, low-amplitude SM thrust durations (≤ 150 milliseconds). The relationship between intervertebral joint mobility and alterations of primary afferent activity during and after various manual therapy interventions may be used to help to identify patient subpopulations who respond to different types of manual therapy and better inform practitioners (eg, chiropractic and osteopathic) delivering the therapeutic intervention.

The immediate effect of posteroanterior mobilization on reducing back pain and the stiffness of the lumbar spine

OBJECTIVE

To study the immediate effect of posteroanterior mobilization on back pain and the associated biomechanical changes in the lumbar spine.

DESIGN

An experimental between-group study.

SETTING

A biomechanics laboratory.

PARTICIPANTS

Subjects with low back pain (n=19) and healthy subjects (n=20).

INTERVENTIONS

Grade III posteroanterior mobilization (3 cycles of 60s) was applied at the L4 level in people with or without back pain on 1 occasion.

MAIN OUTCOME MEASURES

Pain intensity, active lumbar range of motion, the magnitude of the posteroanterior mobilization loads, bending stiffness of the lumbar spine, and the lordotic curvature of the lumbar spine before and after 3 cycles of posteroanterior mobilization.

RESULTS

The magnitude of pain of the patients was found to decrease significantly after posteroanterior mobilization treatment. There was also a significant decrease in the bending stiffness of the lumbar spine of the patients, which was derived from the posteroanterior load and the associated change in spine curvature. The stiffness was restored to a level that was similar to that of the asymptomatic subjects. A strong correlation was found between the magnitude of pain and the bending stiffness of the spine before (r=.89) and after posteroanterior mobilization (r=.98).

CONCLUSIONS

Posteroanterior mobilization was found to bring about immediate desirable effects in reducing spinal stiffness and the magnitude of back pain. The restoration of the mechanical properties of the spine may be a possible mechanism that explains the improvement in pain after manual therapy.

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.

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.

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.

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.

Reliability of assisted indentation in measuring lumbar spinal stiffness

The reliability of manual methods to assess spinal stiffness is modest at best. In response, instrumentation has been developed which may be reliable, but is often difficult to use in clinical settings. The purpose of this study was to determine the intra-rater reliability of assisted indentation (AI), a smaller, less automated technique of measuring spinal stiffness in vivo. Twenty-three asymptomatic subjects were included in the study. The AI device was placed over the 4th lumbar spinous process in each prone, resting subject. Ten indentations were performed at approximately 2-min intervals while load and displacement data were collected simultaneously. From these data, two outcome variables were calculated: Global Stiffness (GS; slope of the force-displacement data) and Mean Maximal Stiffness (MMS; peak force/peak displacement). Intra-class correlation coefficient values for 10 consecutive measures of GS and MMS were 0.93 and 0.91, respectively. A repeated measures analysis of variance (ANOVA) did not demonstrate significant differences between any indentation trials from the same subject. Measurement of spinal stiffness using AI demonstrated excellent intra-rater reliability. These data, in addition to specific features of AI (small, transportable, relatively low cost, ease of operation) suggest that AI may be of benefit within clinical environments.

Comparison of posteroanterior spinal stiffness measures to clinical and demographic findings at baseline in patients enrolled in a clinical study of spinal manipulation for low back pain

OBJECTIVE

A system for measuring posterior-to-anterior spinal stiffness (PAS) was developed for use in clinical trials of manipulation for low back pain (LBP). The current report is an analysis of the baseline PAS data, with particular emphasis on relationships between PAS and clinical and demographic characteristics.

METHODS

Posterior-to-anterior spinal stiffness measurements were recorded over the spinous processes of the lumbar spines from patients who had LBP. The system uses electronic sensors to record displacement and force, whereas a human operator provides the force of indentation. Clinical and outcome measures were compared with spinal stiffness.

RESULTS

We recruited 192 patients (89 female and 103 male; average age, 40.0 years; SD, 9.4 years). The average Roland-Morris score was 9.7 (SD, 3.2) on a 24-point scale. The Visual Analog Scale pain scores were 55.7 (SD, 20.9) on a 100-mm scale. Stiffness values ranged from 4.16 to 39.68 N/mm (mean, 10.80 N/mm; SD, 3.72 N/mm). Females' lumbar spines were, on the average, 2 N/mm more compliant than males (P < .001).

CONCLUSIONS

The PAS system of computer-monitored equipment with human operation performed well in this clinical study of LBP. Spinal stiffness was found to be different between males and females, and age and body mass index were related to PAS. We found no significant relationship between the severity or chronicity of the LBP complaint and spinal stiffness. There was little agreement between the stiff or tender segments identified by the clinicians using palpation and the segment that measured most stiff using the PAS device.

Manual Application of Controlled Forces to Thoracic and Lumbar Spine With a Device: Rated Comfort for the Receiver's Back and the Applier's Hands

PURPOSE

High volumes of manual therapy work can lead to overuse hand and wrist injuries. This study evaluated hand and back comfort in asymptomatic volunteers during spinal mobilization carried out with an instrumented manual therapy tool.

METHODS

This crossover design study examined 36 asymptomatic physiotherapy students that were tested in pairs. One participant assumed the role of the simulated therapist and the other the simulated patient, before reversing roles. Posteroanterior mobilization conditions formed by using 2 spinal segments (thoracic/lumbar), 2 force application methods (hands/device), and 3 grades of mobilization were applied in a random order. After each combination, both participants in each pair rated hand or back comfort, respectively, on a 100-mm visual analogue scale. Data were analyzed by analysis of variance.

RESULTS

Rated back comfort was greater for hands than for the device and decreased with greater applied force. When the original hard rubber device tip was changed to one of soft molded rubber, both back and hand comfort improved significantly. Although tool mobilization was still rated as significantly less comfortable than mobilization with hands only, this difference was approximately half the discomfort experienced as the grade of mobilization increased from grade I to grade III. For hand comfort when using the softer device tip, the method of force application was no longer a significant determinant of comfort.

CONCLUSIONS

The mobilizing tool with a molded rubber tip was acceptably comfortable in use with asymptomatic backs and hands. Further research is indicated in manual therapy settings with therapists who have experienced hand pain.

Response of lumbar paraspinal muscles spindles is greater to spinal manipulative loading compared with slower loading under length control

BACKGROUND CONTEXT

Spinal manipulation (SM) is a form of manual therapy used clinically to treat patients with low back and neck pain. The most common form of this maneuver is characterized as a high-velocity (duration <150 ms), low-amplitude (segmental translation <2 mm, rotation <4 degrees , and applied force 220-889 N) impulse thrust (high-velocity, low-amplitude spinal manipulation [HVLA-SM]). Clinical skill in applying an HVLA-SM lies in the practitioner's ability to control the duration and magnitude of the load (ie, the rate of loading), the direction in which the load is applied, and the contact point at which the load is applied. Control over its mechanical delivery is presumably related to its clinical effects. Biomechanical changes evoked by an HVLA-SM are thought to have physiological consequences caused, at least in part, by changes in sensory signaling from paraspinal tissues.

PURPOSE

If activation of afferent pathways does contribute to the effects of an HVLA-SM, it seems reasonable to anticipate that neural discharge might increase or decrease in a nonlinear fashion as the thrust duration approaches a threshold value. We hypothesized that the relationship between the duration of an impulsive thrust to a vertebra and paraspinal muscle spindle discharge would be nonlinear with an inflection near the duration of an HVLA-SM delivered clinically (<150 ms). In addition, we anticipated that muscle spindle discharge would be more sensitive to larger amplitude thrusts.

STUDY DESIGN/SETTING

A neurophysiological study of spinal manipulation using the lumbar spine of a feline model.

METHODS

Impulse thrusts (duration: 12.5, 25, 50, 100, 200, and 400 ms; amplitude 1 or 2 mm posterior to anterior) were applied to the spinous process of the L6 vertebra of deeply anesthetized cats while recording single unit activity from dorsal root filaments of muscle spindle afferents innervating the lumbar paraspinal muscles. A feedback motor was used in displacement control mode to deliver the impulse thrusts. The motor's drive arm was securely attached to the L6 spinous process via a forceps.

RESULTS

As thrust duration became shorter, the discharge of the lumbar paraspinal muscle spindles increased in a curvilinear fashion. A concave-up inflection occurred near the 100-ms duration eliciting both a higher frequency discharge compared with the longer durations and a substantially faster rate of change as thrust duration was shortened. This pattern was evident in paraspinal afferents with receptive fields both close and far from the midline. Paradoxically, spindle afferents were almost twice as sensitive to the 1-mm compared with the 2-mm amplitude thrust (6.2 vs. 3.3 spikes/s/mm/s). This latter finding may be related to the small versus large signal range properties of muscle spindles.

CONCLUSIONS

The results indicate that the duration and amplitude of a spinal manipulation elicit a pattern of discharge from paraspinal muscle spindles different from slower mechanical inputs. Clinically, these parameters may be important determinants of an HVLA-SM's therapeutic benefit.

Muscular contributions to dynamic dorsoventral lumbar spine stiffness

Spinal musculature plays a major role in spine stability, but its importance to spinal stiffness is poorly understood. We studied the effects of graded trunk muscle stimulation on the in vivo dynamic dorsoventral (DV) lumbar spine stiffness of 15 adolescent Merino sheep. Constant voltage supramaximal electrical stimulation was administered to the L3-L4 interspinous space of the multifidus muscles using four stimulation frequencies (2.5, 5, 10, and 20 Hz). Dynamic stiffness was quantified at rest and during muscle stimulation using a computer-controlled testing apparatus that applied variable frequency (0.46-19.7 Hz) oscillatory DV forces (13-N preload to 48-N peak) to the L3 spinous process of the prone-lying sheep. Five mechanical excitation trials were randomly performed, including four muscle stimulation trials and an unstimulated or resting trial. The secant stiffness (k (y) = DV force/L3 displacement, kN/m) and loss angle (phase angle, deg) were determined at 44 discrete mechanical excitation frequencies. Results indicated that the dynamic stiffness varied 3.7-fold over the range of mechanical excitation frequencies examined (minimum resting k (y) = 3.86 +/- 0.38 N/mm at 4.0 Hz; maximum k (y) = 14.1 +/- 9.95 N/mm at 19.7 Hz). Twenty hertz muscle stimulation resulted in a sustained supramaximal contraction that significantly (P < 0.05) increased k (y) up to twofold compared to rest (mechanical excitation at 3.6 Hz). Compared to rest, k (y) during the 20 Hz muscle stimulation was significantly increased for 34 of 44 mechanical excitation frequencies (mean increase = 55.1%, P < 0.05), but was most marked between 2.55 and 4.91 Hz (mean increase = 87.5%, P < 0.05). For lower frequency, sub-maximal muscle stimulation, there was a graded change in k (y), which was significantly increased for 32/44 mechanical excitation frequencies (mean increase = 40.4%, 10 Hz stimulus), 23/44 mechanical excitation frequencies (mean increase = 10.5%, 5 Hz stimulus), and 11/44 mechanical excitation frequencies (mean increase = 4.16%, 2.5 Hz stimulus) when compared to rest. These results indicate that the dynamic mechanical behavior of the ovine spine is modulated by muscle stimulation, and suggests that muscle contraction plays an important role in stabilizing the lumbar spine.

Active Trunk Extensor Contributions to Dynamic Posteroanterior Lumbar Spinal Stiffness

BACKGROUND

Assessments of posteroanterior (PA) spinal stiffness using mobilization apparatuses have demonstrated an increase in PA spine stiffness during voluntary contraction of the lumbar extensor muscles; yet, little work has been done to this degree in symptomatic subjects.

OBJECTIVE

To use a previously validated dynamic mechanical impedance procedure to quantify changes in PA dynamic spinal stiffness at rest and during lumbar isotonic extension tasks in patients with low back pain (LBP).

METHODS

Thirteen patients with LBP underwent a dynamic spinal stiffness assessment in the prone-resting position and again during lumbar extensor efforts. Stiffness assessments were obtained using a handheld impulsive mechanical device equipped with an impedance head (load cell and accelerometer). PA manipulative thrusts (approximately 150 N, <5 milliseconds) were delivered to skin overlying the L3 left and right transverse processes (TPs) and to the L3 spinous process (SP) in a predefined order (left TP, SP, right TP) while patients were at rest and again during prone-lying lumbar isotonic extension tasks. Dynamic spinal stiffness characteristics were determined from force and acceleration measurements using the apparent mass (peak force/peak acceleration, kg). Apparent mass measurements for the resting and active lumbar isotonic task trials of each patient were compared using a 2-tailed, paired t test.

RESULTS

A significant increase in the PA dynamic spinal stiffness was noted for thrusts over the SP (apparent mass [17.0%], P=.0004) during isotonic trunk extension tasks compared with prone resting, but no statistically significant changes in apparent mass were noted for the same measures over the TPs.

CONCLUSIONS

These findings add support to the significance of the trunk musculature and spinal posture in providing increased spinal stability.

Influence of standardized mobilization on the posteroanterior stiffness of the lumbar spine in asymptomatic subjects

BACKGROUND AND PURPOSE

Spinal mobilization is commonly used to relieve pain and assist recovery of mobility in individuals with low back pain. Fundamental to this concept is the belief that spinal mobilization will influence the mechanical properties of the symptomatic motion segment. The objective of the present study was to examine the segmental effects of a standardized mobilization procedure on the posteroanterior (PA) stiffness of the lumbar spine.

METHOD

Audio and visual feedback was used to train a physiotherapist to perform PA mobilization at a consistent load and frequency. After training, twenty-four subjects without low back pain were recruited for the intervention phase of the study. The spinal posteroanterior mobilization (SPAM) apparatus was used to measure the PA stiffness of the lumbar spine at three measurement sites (L1, L3 and L5). The trained physiotherapist then applied the standardized PA mobilization technique via the L3 spinous process for two minutes. Following mobilization, PA stiffness was measured three times at the three locations.

RESULTS

The physiotherapist was able to apply a standardized mobilization with a mean force of 146 N (standard deviation (SD) 8 N) at a frequency of 1.5 Hz. The first trial on each assessment demonstrated a pre-condition effect. Two minutes' PA mobilization resulted in no significant change in the PA stiffness of the lumbar spine at the level to which the mobilization was applied, or at the L1 and L5 segments. The 95% confidence intervals (CI) of the difference in PA stiffness before and after testing included zero at each measurement site.

CONCLUSIONS

Clinicians should pre-condition the spine when assessing PA stiffness both before and after interventions. A standardized mobilization of 150 N at 1.5 Hz for two minutes had no segmental effect on spinal PA stiffness. Subsequent studies need to consider other mechanisms that may contribute to the changes that occur after PA spinal mobilization.

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.

Comparison of dynamic posteroanterior spinal stiffness to plain film radiographic images of lumbar disk height

BACKGROUND

Assessments of spinal stiffness have become more popular in recent years as a noninvasive objective biomechanical means to evaluate the human spine. Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Such measures may be important determinants to discriminate between patients with low back pain (LBP) and asymptomatic subjects.

OBJECTIVE

To determine the relationships between dynamic PA spinal stiffness and radiographic measures of lower lumbar disk height and disk degeneration.

METHODS

L4 and L5 posterior disk height (PDH), vertebral body height (PVH), anterior disk height (ADH), and vertebral body height (AVH) were obtained from digitized plain film anteroposterior (AP) and lateral radiographs of 18 symptomatic LBP patients presenting to a chiropractic office (8 female patients and 10 male patients, aged 15-69 years, mean 44.3, SD 15.4 years). Disk degeneration (DD) and facet arthrosis (FA) were qualitatively assessed from the films by an independent examiner. Anterior disk height ratios (ADHR = ADH/AVH) and posterior disk height ratios (PDHR = PDH/PVH) were calculated from the disk height measurements and were compared to L4 and L5 posteroanterior spinal stiffness obtained using a previously validated mechanical impedance stiffness assessment procedure.

RESULTS

One third of the subjects were found to have radiographic evidence of mild or moderate DD and approximately two thirds of the subjects showed signs of mild or moderate FA. The L4 and L5 anterior disk height and posterior disk height were approximately one half and one fifth of the respective vertebral body heights, and the PA stiffness was greater at L4 than at L5. Male subjects had a greater ADHR than female subjects, but female subjects had a greater L4 and L5 PA stiffness in comparison to male subjects; however, these differences were not statistically significant. Posteroanterior L5 vertebral stiffness was found to be significantly correlated to the L5 PDHR.

CONCLUSIONS

Computations of spinal input impedance are relatively simple to perform, can provide a noninvasive measure of the dynamic mechanical behavior of the spine, appear to have potential to discriminate pathologic changes to the spine, and warrant further study on a larger sample of normal subjects and patients.

Contribution of ribcage movement to thoracolumbar posteroanterior stiffness

OBJECTIVE

To investigate (1) whether thoracolumbar posteroanterior (PA) stiffness differs between 2 conditions of ribcage movement: unconstrained and constrained, and (2) whether the effect of ribcage constraint on PA stiffness varies according to where the PA force is applied.

DESIGN

Two-factor within-subjects design.

SETTING

Spinal Mechanics Laboratory, University of Sydney.

INTERVENTION

A convenience sample of 41 subjects, asymptomatic for back pain, participated. PA stiffness at T12-L4 was measured in the unconstrained and constrained ribcage conditions with a mechanical device. For the constrained condition, we used a clamping device to apply a force to the subject's lower thorax to reduce movement.

MAIN OUTCOME MEASURES

PA stiffness at T12-L4 under both ribcage conditions.

RESULTS

PA stiffness at T12-L4 significantly increased when the ribcage was constrained (P<.05). However, the effect of ribcage movement did not depend on the location of the PA force.

CONCLUSIONS

These findings suggest that the properties of the ribcage influence measures of PA stiffness in the thoracolumbar (T12-L4) spine uniformly. Variations in PA stiffness in segments T12-L4 may reflect the properties of the intervertebral joints.

Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization

OBJECTIVE

To develop a mathematical model capable of describing the static and dynamic motion response of the lumbar spine to posteroanterior forces.

DESIGN

Static, impulsive and oscillatory forces with varying thrust angles and offsets were applied to the model, and the resulting motion responses were compared to experimental data published for spinal mobilization and manipulation of prone-lying subjects.

BACKGROUND

Methods are sought to improve understanding of the dynamic force-induced displacement response of the lumbar spine during spinal mobilization and manipulation treatment.

METHODS

The thorax, pelvis and five lumbar vertebrae were represented as seven rigid structures and eight flexible joint structures. Flexible joint structures were modeled using spring and damper elements with three displacement degrees-of-freedom (posterior-anterior and axial displacement, and flexion-extension rotation). The resulting 21 degrees-of-freedom lumped parameter model was solved in modal space.

RESULTS

The fundamental natural frequency of vibration was 5.24 Hz. Simulations performed using 100 N static and dynamic posteroanterior forces applied to the L3 vertebrae indicated that peak L3 segmental displacements were up to 2.40 mm (impulsive) and 8.23 mm (oscillatory at 2 Hz). Appreciable axial displacements (0.41 mm) and flexion-extension rotations (1.49 degrees ) were also observed for oscillatory forces at L3. The posteroanterior motion response of the lumbar vertebrae was relatively insensitive to both the thrust force angle and thrust force offset, but axial displacements and flexion-extension rotations showed a large change (2-fold or greater) for thrust angles greater than -5 degrees (caudal) in comparison to vertical thrusts. Intersegmental motion responses for static, impulsive and oscillatory loads were more comparable than their segmental counterparts.

CONCLUSIONS

The model predicts lumbar segmental and inter-segmental motion responses to manipulative forces that are otherwise difficult to obtain experimentally.

RELEVANCE

This study assists clinicians to understand the biomechanics of posteroanterior forces applied to the lumbar spine of prone-lying subjects. Of particular clinical relevance is the finding that greater spinal mobility is possible by targeting specific load-time histories.

The response of posteroanterior lumbar stiffness to repeated loading

Lumbar posteroanterior (PA) responses are determined by manual examination and are used to guide treatment decisions and interpret changes in symptoms within and between treatments. Mechanical devices that simulate manual assessment have been developed to measure lumbar PA responses. The two variables used to describe lumbar PA responses to mechanical loading are stiffness coefficient K and displacement D30. The purpose of this study was to investigate the behaviour of lumbar PA responses with repeated loading over time. Lumbar PA responses at L4 were measured in 18 pain-free subjects using a mechanical device. Measurements were made for five consecutive loading cycles on three test occasions. The responses were compared between the five cycles within a single test occasion and between three test occasions. An identical procedure was also used to test a set of elastic springs for comparison. There was a significant increase in both stiffness coefficient K and displacement D30 between the first cycle and subsequent cycles of a single test occasion on human subjects. This response which demonstrates an increase in stiffness and displacement between the first and subsequent cycles can be considered a normal response to PA loading. PA stiffness remains constant over several tests both within one day and between days.

Contribution of pelvic rotation to lumbar posteroanterior movement

Variability in lumbar PA stiffness has been found to relate to many factors. Sagittal pelvic rotation has been suggested as one determinant of lumbar PA stiffness. Previous studies have shown that decreased pelvic rotation is associated with increased lumbar PA stiffness. However, it is not known whether variations in pelvic rotation cause changes in PA stiffness. This study aimed to investigate the role of pelvic rotation in determining lumbar PA stiffness, and to investigate whether this role varies with vertebral level of the applied load. A mechanical device was used to apply PA forces to the skin overlying the spinous processes of L2-L5 with the pelvis constrained and unconstrained in 37 subjects without low back pain. Significantly higher PA stiffness (P<0.05) was found when the pelvis was constrained. The degree of increase in PA stiffness depended upon the vertebral level being loaded, with loads at L5 producing the greatest increase in stiffness (24%) and loads at L2 producing a non-significant increase (6%). The findings indicate that sagittal pelvic rotation plays a significant part in the lumbar PA stiffness at L5 but has a lesser influence at more cephalad vertebral levels.

Stiffness and neuromuscular reflex response of the human spine to posteroanterior manipulative thrusts in patients with low back pain

BACKGROUND

Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Such measures may be important determinants in discriminating between patients who are asymptomatic and those who have low back pain. However, little objective evidence is available concerning variations in PA stiffness and their clinical significance. Moreover, although several studies have assessed only load input in relation to stiffness, a more complete assessment based on dynamic stiffness measurements (force/velocity) and concomitant neuromuscular response may offer more information concerning mechanical properties of the low back.

OBJECTIVE

To determine the stiffness and neuromuscular characteristics of the symptomatic low back.

STUDY DESIGN

This study is a prospective clinical study investigating the in vivo mechanical and muscular behavior of human lumbar spinal segments to high loading rate PA manipulative thrusts in research subjects with low back pain (LBP).

METHODS

Twelve men and 10 women, aged 15 to 73 years (mean age of 42.8 +/- 17.5 years) underwent physical examination and completed outcome assessment instruments, including Visual Analog Scale, Oswestry Low Back Disability Index, and SF-36 health status questionnaires. Clinical categorization was made on the basis of symptom frequency and LBP history. A hand-held spinal manipulation device, equipped with a preload control frame and impedance head, was used to deliver high-rate (<0.1 millisecond) PA manipulative thrusts (190 N) to several common spinal landmarks, including the ilium, sacral base, and L5, L4, L2, T12, and T8 spinous and transverse processes. Surface, linear-enveloped, electromyographic (sEMG) recordings were obtained from electrodes (8 leads) located over the L3 and L5 paraspinal musculature to monitor the bilateral neuromuscular activity of the erector spinae group during the PA thrusts. Maximal-effort isometric trunk extensions were performed by the research subjects before and immediately after the testing protocol to normalize sEMG data. The accelerance or stiffness index (peak acceleration/peak force, kg-1) and composite sEMG neuromuscular reflex response were calculated for each of the thrusts.

RESULTS

Posteroanterior stiffness obtained at the sacroiliac joints, transverse processes, or spinous processes was not different for subjects grouped according to LBP chronicity. However, in those with frequent or constant LBP symptoms, there was a significantly increased spinous process (SP) stiffness index (7.0 kg-1) (P <.05) in comparison with SP stiffness index (6.5 kg-1) of subjects with only occasional or no LBP symptoms. Subjects with frequent or constant LBP symptoms also reported significantly greater scores on the visual analog scale (P =.001), Oswestry (P =.001), and perceived health status (P =.03) assessments. The average SP stiffness index was 6.6% greater (P <.05) and 19.1% greater (P <.001) than the average sacroiliac stiffness index and average transverse process stiffness index, respectively.

CONCLUSIONS

This study is the first to assess erector spinae neuromuscular reflex responses simultaneously during spinal stiffness examination. This study demonstrated increased spinal stiffness index and positive neuromuscular reflex responses in subjects with frequent or constant LBP as compared with those reporting intermittent or no LBP.

Stiffness properties of the human lumbar spine: a lumped parameter model

OBJECTIVE

To characterise with a mechanical model, the force-displacement response of the human lumbar spine to postero-anterior loading.

DESIGN

Single case with repetition.

BACKGROUND

Previous attempts to characterise the spine's force-displacement response have been simplistic and only considered the loading curve. These approaches ignored valuable information such as viscosity, non-linear elasticity and inertia of the lumbar spine.

METHODS

The Spinal Assessment Machine applied a postero-anterior load to the spines of 23 asymptomatic subjects and measured the force-displacement response. The data was analysed by two methods; by a traditional linear regression of part of the loading curve and by a new method where an equation including non-linear stiffness and damping was used to characterise the whole force-displacement relationship.

RESULTS

The equation developed was found to account for virtually all of the variance in the raw data (R2 > 0.993). Four elements derived by the equation determine the contributions of linear elasticity, non-linear elasticity, linear viscosity and non-linear viscosity to the overall stiffness.

CONCLUSIONS

Considering the excellent fit of the new equation to the raw data and its poor correlation with existing measures, it is proposed that the traditional measures provide an incomplete description of the force-displacement response. Relevance. Therapists use their perception of the force-displacement response of the spine to select the type of manipulative treatment to apply. To study this aspect of patient care, devices capable of measuring spinal stiffness have been developed, however to date the obtained data has been analysed only simply. A lumped parameter mechanical model incorporating non-linear damping and stiffness provides a more complete description of the force-displacement response and thus may offer added insight into the manipulative treatment of spinal pain.

Sources of variation in spinal indentation testing: indentation site relocation, intraabdominal pressure, subject movement, muscular response, and stiffness estimation

BACKGROUND

Force-displacement properties of spinal tissues assessed by blunt indentation are thought to have clinical relevance; however, numerous variables with respect to spinal indentation have yet to be identified or characterized completely.

OBJECTIVE

To identify and quantify, where possible, previously unidentified or incompletely characterized variables with respect to spinal indentation.

DESIGN

Multiprotocol design.

METHODS

Four experiments were performed: (1) Twelve asymptomatic subjects were indented with concurrent electromyography during conditions of rest, held inspiration, increased intraabdominal pressure and lumbar extension. (2) Changes in the recumbent position of 12 subjects were measured while a series of movements was performed in restrained and unrestrained conditions. (3) Ten clinicians attempted to locate, and to relocate, a subcutaneous anatomical landmark through visualization/palpation and ultrasonic imaging. (4) Performances of 3 methods of force-displacement curve modeling were compared with respect to stiffness estimation.

RESULTS

(1) Spinal stiffness increased significantly in a minority of subjects awaiting indentation and in a majority of subjects during increases in intraabdominal pressure. (2) Changes in subject position were significantly reduced by a restraint system. (3) With respect to interclinician error in locating and relocating an indentation site, there was significant improvement with the use of ultrasonic visualization. (4) The error associated with linear techniques used to model curvilinear force-displacement data plots increased with increasing linear intervals.

CONCLUSION

Several sources of variation in spinal indentation were identified: indentation site relocation, intraabdominal pressure, subject movement, muscular response, and stiffness estimation. These variables, which have been unaccounted for in previous indentation studies, might be responsible for the change or lack of change in force-displacement properties between preintervention and postintervention indentation trials.

Effect of direction of applied mobilization force on the posteroanterior response in the lumbar spine

OBJECTIVE

The purpose of this study was to investigate whether changing the direction of applied force affects measured posteroanterior stiffness and associated pelvic (sacral) and lower thoracic rotations.

DESIGN

A repeated measures design was used.

SETTING

University biomechanical laboratory.

PARTICIPANTS

Twenty-four subjects (14 male, 10 female) with no history of recent low back pain or contraindications to mobilization volunteered for testing.

MAIN OUTCOME MEASURE

Posteroanterior stiffness was assessed at vertebral levels L3 and L5 through use of 3 sagittal plane directions of applied force; the directions differed by 10 degrees. The amount of sacral and lower thoracic rotation that occurred during loading between 30 and 100 N was also recorded.

RESULTS

A small but significant variation of stiffness with direction of applied force was found. At L3, mean stiffness was greatest when the posteroanterior force was applied in a base direction; it was 11% less when the force was applied 10 degrees more caudad than the base direction and 14% less when the force was applied 10 degrees more cephalad than the base direction. There was no significant effect of direction when the force was applied at L5. Both sacral and thoracic rotations displayed significant variation with direction of force when load was applied at L5, with decreasing rotation as the force was applied in a more caudal direction.

CONCLUSION

Posteroanterior stiffness in individuals without back pain is affected by the sagittal plane direction in which the posteroanterior force is applied to the lumbar spine. Remote (thoracic and sacral) movements are also affected by the direction of posteroanterior force. Direction of applied force should therefore be controlled, particularly in the research setting.

Indenter head area and testing frequency effects on posteroanterior lumbar stiffness and subjects' rated comfort

Although several mechanical devices have been developed to objectively assess posteroanterior (PA) stiffness of the lumbar spine, no standardized testing protocol has been adopted. Two factors that may vary across protocols, and that effect measured stiffness and the comfort of the test subject, are the size of the indenter head used to apply the PA pressure, and indenting frequency. Three variables; PA stiffness, defined as the slope of the stiffness curve (K), the displacement of the indenter at 30N (D30), and rating of perceived comfort, were measured in 36 subjects asymptomatic for low back pain. For each subject nine tests were conducted, using three different indenter head sizes (300mm(2), 720mm(2)and 1564mm(2)) at each of three different testing frequencies (0.25 Hz, 0.5 Hz and 2 Hz). Machine testing with a large indenter head produced a lower K value, an increased D30 value and higher perceived comfort, while a fast testing frequency produced a higher K value and a lower D30 value. An indenter size by frequency interaction showed small indenter heads to be least comfortable at slow speed. The differences found suggest that the indenter head size and the testing frequency should be standardized during mechanical spinal stiffness testing.

Ultrasonic quantification of osseous displacements resulting from skin surface indentation loading of bovine para-spinal tissue

OBJECTIVE

To validate an ultrasound-based technique which quantifies uni-planar subcutaneous displacement of an osseous object resulting from an externally applied load.

BACKGROUND

Many spinal conditions are thought to be characterized by aberrant vertebral displacements yet the invasive nature of many investigative techniques has left the clinical significance of this relation incompletely understood.

METHOD

Six bovine bone/paravertebral tissue preparations were indented by one of two ultrasonic transducers (5 and 7 MHz) fitted to an electromechanical actuator. The resulting osseous displacement along the principal indentation axis was calculated by subtracting the change in transducer/bone distance between ultrasonic images collected at tissue contact and maximal load from the change in actuator displacement. A dial gauge contacting the bone was used as a displacement criterion measure.

RESULTS

Using the 7 MHz transducer, the mean error of the technique was 6.74% (SD=3.98) while the mean error associated with the 5 MHz transducer was 12.73% (SD=7.49).

CONCLUSIONS

This non-invasive technique is capable of quantifying subcutaneous uni-planar bone displacement with an accuracy comparable to similar invasive techniques over a comparable displacement range. RelevanceThis non-invasive technique may be beneficial in assessing the significance of vertebral displacements in conditions such as hypermobility and osteoarthritis, as well as in studies of manipulative therapy.

Comparison of ribcage and posteroanterior thoracic spine stiffness: an investigation of the normal response

Evaluation of the movement response to posteroanterior (PA) loads applied to the spinous processes is a recognized part of the physical examination of the thoracic spine. During this clinical procedure the thoracic spine is supported by the ribcage which may contribute to the movement response. However, the contribution of ribcage stiffness to the PA stiffness of the thoracic spine has not been established. The purpose of this study was to measure the PA stiffness of the thoracic spine and compare this to the stiffness of the ribcage under anteroposterior load. Using force-displacement analysis, this study measured the PA stiffness of the thoracic spine at T4, T7 and T10 in 20 asymptomatic individuals, and compared this to the ribcage stiffness measured through sternal compression. The mean PA stiffness at T7 (10.7 N/mm) was significantly greater than at T4 (9.1 N/mm, P < 0.001), and there was a non-significant increase between T7 and T10 (11.4 N/mm, P = 0.08). The stiffness of the ribcage measured via sternal compression (7.6 N/mm) was significantly lower than the thoracic PA stiffness at all levels (P < 0.01). A significant proportion (33%) of the thoracic spine PA stiffness was accounted for by the stiffness of the ribcage (P < 0.01). In young, asymptomatic subjects, the PA stiffness of the thoracic spine is significantly greater than the stiffness of the ribcage. This suggests that the response to PA load application in the thoracic spine can be attributed to factors relating to the spine as well as the ribcage. Defining consistent patterns of PA stiffness in the thoracic spine may assist in the interpretation of clinical measurements of patients with mechanical dysfunction of the thoracic spine.