Plinth padding confounds measures of posteroanterior spinal stiffness

The development and evaluation of a novel repurposing of a peripheral gaming device for the acquisition of forces applied to a hydraulic treatment plinth

This technical note details the stages taken to create an instrumented hydraulic treatment plinth for the measurement of applied forces in the vertical axis. The modification used a widely available low-cost peripheral gaming device and required only basic construction and computer skills. The instrumented treatment plinth was validated against a laboratory grade force platform across a range of applied masses from 0.5-15 kg, mock Gr I-IV vertebral mobilisations and a dynamic response test. Intraclass correlation coefficients demonstrated poor reliability (0.46) for low masses of 0.5 kg improving to excellent for larger masses up to15 kg respectively; excellent to good reliability (0.97-0.86) for the mock mobilisations and moderate reliability (0.51) for the dynamic response test. The study demonstrates how a cheap peripheral gaming device can be repurposed so that forces applied to a hydraulic treatment plinth can be collected reliably when applied in a clinically reasoned manner.

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.

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.

Posteroanterior spinal stiffness at T5, T10, and L3 levels in normal subjects

OBJECTIVE

To measure, by using standardized device and protocol, posteroanterior (PA) spinal stiffness at the 5th and 10th thoracic (T5 and T10) and 3rd lumbar (L3) vertebral levels in asymptomatic adult volunteers.

DESIGN

A cross-sectional study.

SETTING

Osteopathic Heritage Foundation Physical Medicine Core Research Laboratory where the Therapeutic Spinal Mobilizer was fabricated to standardize the testing protocol.

PARTICIPANTS

Sixteen asymptomatic adult volunteers.

METHODS

Volunteers were in the prone position on the treatment plinth and the loading block of the loading piston was placed at T5, T10, and L3. The subjects were instructed to remain still, to not contract any muscle, and to stop breathing mid cycle for 15 seconds when the data acquisition was initiated for a 10-second test cycle. The force was measured by using the load cell, and the spinal deformation was measured by the linear variable differential transducer. The data were extracted and subjected to descriptive statistics and analysis of variance to determine the effect of independent variables on spinal stiffness.

RESULTS

The PA spinal stiffness at 3 spinal levels was significantly different (P < .0001). The spinal stiffness was significantly affected by the testing load, age, gender, and body weight of the subjects (P < .0001). The PA stiffness of the entire sample at 3 spinal levels ranged from 4.8-8.8 N/mm. The spinal stiffness values could be predicted as the function of testing load and body weight (P < .01).

CONCLUSIONS

Results of this experiment suggest that the standardized and repeatable methodology will result in reliable stiffness values. Because the spinal stiffness is an indicator of patient's symptoms and it is an important variable in selection of treatment regimen, it is important to be able to measure this variable with a standardized protocol. Values from asymptomatic subjects can be used to study and to compare the symptomatic patients.

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.

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.

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.

Aberrant protective force generation during neural provocation testing and the effect of treatment in patients with neurogenic cervicobrachial pain

BACKGROUND

Observation of the occurrence of protective muscle activity is advocated in assessment of the peripheral nervous system by means of neural provocation tests. However, no studies have yet demonstrated abnormal force generation in a patient population.

OBJECTIVES

To analyze whether aberrations in shoulder girdle-elevation force during neural tissue provocation testing for the median nerve (NTPT1) can be demonstrated, and whether possible aberrations can be normalized following cervical mobilization.

STUDY DESIGN

A single-blind randomized comparative controlled study.

SETTING

Laboratory setting annex in a manual therapy teaching practice.

PARTICIPANTS

Twenty patients with unilateral or bilateral neurogenic cervicobrachial pain.

METHODS

During the NTPT1, we used a load cell and electrogoniometer to record continuously the shoulder-girdle elevation force in relation to the available range of elbow extension. Following randomization, we analyzed the immediate treatment effects of a cervical contralateral lateral glide mobilization technique (experimental group) and therapeutic ultrasound (control group).

RESULTS

On the involved side, the shoulder-girdle elevation force occurred earlier, and the amount of force at the end of the test was substantially, though not significantly, greater than that on the uninvolved side at the corresponding range of motion. Together with a significant reduction in pain perception after cervical mobilization, a clear tendency toward normalization of the force curve could be observed, namely, a significant decrease in force generation and a delayed onset. The control group demonstrated no differences.

CONCLUSIONS

Aberrations in force generation during neural provocation testing are present in patients with neurogenic pain and can be normalized with appropriate treatment modalities.

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 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.

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.