The role of spinal tissues in resisting posteroanterior forces applied to the lumbar spine

Does the application site of spinal manipulative therapy alter spinal tissues loading?

BACKGROUND CONTEXT

Previous studies found that the intervertebral disc (IVD) experiences the greatest loads during spinal manipulation therapy (SMT).

PURPOSE

Based on that, this study aimed to determine if loads experienced by spinal tissues are significantly altered when the application site of SMT is changed.

STUDY DESIGN

A biomechanical robotic serial dissection study.

SAMPLE

Thirteen porcine cadaveric motion segments.

OUTCOME MEASURES

Forces experienced by lumbar spinal tissues.

METHODS

A servo-controlled linear actuator provided standardized 300 N SMT simulations to six different cutaneous locations of the porcine lumbar spine: L2-L3 and L3-L4 facet joints (FJ), L3 and L4 transverse processes (TVP), and the space between the FJs and the TVPs (BTW). Vertebral kinematics were tracked optically using indwelling bone pins; the motion segment was removed and mounted in a parallel robot equipped with a six-axis load cell. Movements of each SMT application at each site were replayed by the robot with the intact specimen and following the sequential removal of spinal ligaments, FJs and IVD. Forces induced by SMT were recorded, and specific axes were analyzed using linear mixed models.

RESULTS

Analyses yielded a significant difference (p<.05) in spinal structures loads as a function of the application site. Spinal manipulative therapy application at the L3 vertebra caused vertebral movements and forces between L3 and L4 spinal segment in the opposite direction to when SMT was applied at L4 vertebra. Additionally, SMT applications over the soft tissue between adjacent vertebrae significantly decreased spinal structure loads.

CONCLUSION

Applying SMT with a constant force at different spinal levels creates different relative kinetics of the spinal segments and load spinal tissues in significantly different magnitudes.

Influence of Spinal Manipulative Therapy Force Magnitude and Application Site on Spinal Tissue Loading: A Biomechanical Robotic Serial Dissection Study in Porcine Motion Segments

OBJECTIVE

In order to define the relation between spinal manipulative therapy (SMT) input parameters and the distribution of load within spinal tissues, the aim of this study was to determine the influence of force magnitude and application site when SMT is applied to cadaveric spines.

METHODS

In 10 porcine cadavers, a servo-controlled linear actuator motor provided a standardized SMT simulation using 3 different force magnitudes (100N, 300N, and 500N) to 2 different cutaneous locations: L3/L4 facet joint (FJ), and L4 transverse processes (TVP). Vertebral kinematics were tracked optically using indwelling bone pins, the motion segment removed and mounted in a parallel robot equipped with a 6-axis load cell. The kinematics of each SMT application were replicated robotically. Serial dissection of spinal structures was conducted to quantify loading characteristics of discrete spinal tissues. Forces experienced by the L3/L4 segment and spinal structures during SMT replication were recorded and analyzed.

RESULTS

Spinal manipulative therapy force magnitude and application site parameters influenced spinal tissues loading. A significant main effect (P < .05) of force magnitude was observed on the loads experienced by the intact specimen and supra- and interspinous ligaments. The main effect of application site was also significant (P < .05), influencing the loading of the intact specimen and facet joints, capsules, and ligamentum flavum (P < .05).

CONCLUSION

Spinal manipulative therapy input parameters of force magnitude and application site significantly influence the distribution of forces within spinal tissues. By controlling these SMT parameters, clinical outcomes may potentially be manipulated.

Spinal Tissue Loading Created by Different Methods of Spinal Manipulative Therapy Application

STUDY DESIGN

Comparative study using robotic replication of spinal manipulative therapy (SMT) vertebral kinematics together with serial dissection.

OBJECTIVE

The aim of this study was to quantify loads created in cadaveric spinal tissues arising from three different forms of SMT application.

SUMMARY OF BACKGROUND DATA

There exist many distinct methods by which to apply SMT. It is not known presently whether different forms of SMT application have different effects on spinal tissues. Should the method of SMT application modulate spinal tissue loading, quantifying this relation may help explain the varied outcomes of SMT in terms of effect and safety.

METHODS

SMT was applied to the third lumbar vertebra in 12 porcine cadavers using three SMT techniques: a clinical device that applies forces through a hand-held instrument (INST), a manual technique of applying SMT clinically (MAN) and a research device that applies parameters of manual SMT through a servo-controlled linear actuator motor (SERVO). The resulting kinematics from each SMT application were tracked optically via indwelling bone pins. The L3/L4 segment was then removed, mounted in a parallel robot and the resulting kinematics from SMT replayed for each SMT application technique. Serial dissection of spinal structures was conducted to quantify loading characteristics of discrete spinal tissues.

RESULTS

In terms of load magnitude, SMT application with MAN and SERVO created greater forces than INST in all conditions (P < 0.05). Additionally, MAN and SERVO created comparable posterior forces in the intact specimen, but MAN created greater posterior forces on IVD structures compared to SERVO (P < 0.05).

CONCLUSION

Specific methods of SMT application create unique vertebral loading characteristics, which may help explain the varied outcomes of SMT in terms of effect and safety.

LEVEL OF EVIDENCE

N/A.

Tissue loading created during spinal manipulation in comparison to loading created by passive spinal movements

Spinal manipulative therapy (SMT) creates health benefits for some while for others, no benefit or even adverse events. Understanding these differential responses is important to optimize patient care and safety. Toward this, characterizing how loads created by SMT relate to those created by typical motions is fundamental. Using robotic testing, it is now possible to make these comparisons to determine if SMT generates unique loading scenarios. In 12 porcine cadavers, SMT and passive motions were applied to the L3/L4 segment and the resulting kinematics tracked. The L3/L4 segment was removed, mounted in a parallel robot and kinematics of SMT and passive movements replayed robotically. The resulting forces experienced by L3/L4 were collected. Overall, SMT created both significantly greater and smaller loads compared to passive motions, with SMT generating greater anterioposterior peak force (the direction of force application) compared to all passive motions. In some comparisons, SMT did not create significantly different loads in the intact specimen, but did so in specific spinal tissues. Despite methodological differences between studies, SMT forces and loading rates fell below published injury values. Future studies are warranted to understand if loading scenarios unique to SMT confer its differential therapeutic effects.

Isolation and Characterization of Human Mesenchymal Stem Cells From Facet Joints and Interspinous Ligaments

STUDY DESIGN

A descriptive in vitro study on isolation and differentiation of human mesenchymal stem cells (MSCs) derived from the facet joints and interspinous ligaments.

OBJECTIVE

To isolate cells from the facet joints and interspinous ligaments and investigate their surface marker profile and differentiation potentials.

SUMMARY OF BACKGROUND DATA

Lumbar spinal canal stenosis and ossification of the posterior longitudinal ligament are progressive conditions characterized by the hypertrophy and ossification of ligaments and joints within the spinal canal. MSCs are believed to play a role in the advancement of these diseases and the existence of MSCs has been demonstrated within the ligamentum flavum and posterior longitudinal ligament. The aim of this study was to investigate whether these cells could also be found within facet joints and interspinous ligaments.

METHODS

Samples were harvested from 10 patients undergoing spinal surgery. The MSCs from facet joints and interspinous ligaments were isolated using direct tissue explant technique. Cell surface antigen profilings were performed via flow cytometry. Their lineage differentiation potentials were analyzed.

RESULTS

The facet joints and interspinous ligaments-derived MSCs have the tri-lineage potential to be differentiated into osteogenic, adipogenic, and chondrogenic cells under appropriate inductions. Flow cytometry analysis revealed both cell lines expressed MSCs markers. Both facet joints and interspinous ligaments-derived MSCs expressed marker genes for osteoblasts, adipocytes, and chondrocytes.

CONCLUSION

The facet joints and interspinous ligaments may provide alternative sources of MSCs for tissue engineering applications. The facet joints and interspinous ligaments-derived MSCs are part of the microenvironment of the human ligaments of the spinal column and might play a crucial role in the development and progression of degenerative spine conditions.

Efficacy of segmental stabilization exercise for lumbar segmental instability in patients with mechanical low back pain: A randomized placebo controlled crossover study

Background:

Lumbar segmental stability is an important biomechanical component that influences symptoms amongst patients with Mechanical low back pain.

Aims:

To compare the efficacy of segmental stabilization exercises utilizing multifidus and transversus abdominis muscles versus a placebo treatment in patients with lumbar segmental instability.

Materials and methods:

The study was an observer-blinded randomized placebo-controlled cross-over study of 18 adults (12 men, 6 women), of mean age 22.5 ± 1.09 yrs who scored 7/13 in subjective aspects and 8/14 in objective aspects of Delphi criteria for lumbar segmental instability. The selected subjects were then randomized to receive either placebo-control (prone lying) or experimental (lumbar segmental stabilization) as a first treatment. Each treatment was followed by a wash-out period of 24 hours. Outcomes were measured four times- pre- and post- first intervention, pre- and post- second intervention. The outcome measures used were pain on Visual analogue scale, Pressure pain threshold and Joint play grading scale (0-6 scale) on that level.

Results:

Two-way analysis of variance and post-hoc analysis using Bonferonni test were used with level of significance set at p<.05 using Statistical package for social sciences version 12.0.1 for Windows. Visual analogue scale changed significantly in both the periods of intervention- in control (P =.016) and experimental (P =.000) periods. However this improvement was more significant in the experimental period. The Joint play grading scale scores improved only in the experimental condition compared to the control condition significantly. The Pressure pain threshold also improved significantly in the experimental condition (P =.000) while the changes in control condition was not statistically significant (P=.816).

Conclusion:

Segmental stabilization exercise was more effective than placebo intervention in symptomatic lumbar segmental instability.

Spinal Implant Development, Modeling, and Testing to Achieve Customizable and Nonlinear Stiffness

The spine naturally has a nonlinear force-deflection characteristic which facilitates passive stability, and thus there is a need for spinal implants that duplicate this behavior to provide stabilization when the spine loses stiffness through injury, degeneration, or surgery. Additionally, due to the complexity and variability in the mechanics of spinal dysfunction, implants could potentially benefit from incorporating a customizable stiffness into their design. This paper presents a spinal implant with contact-aided inserts that provide a customizable nonlinear stiffness. An analytical model was utilized to optimize the device design, and the model was then verified using a finite element model. Validation was performed on physical prototypes, first in isolation using a tensile tester and then using cadaveric testing on an in-house spine tester. Testing confirmed the performance of the implant and it was observed that the device increased mechanical stability to the spinal segment in flexion-extension and lateral-bending.

ANALYSIS OF THE BENDING BEHAVIOR OF THE LUMBAR SPINE DURING POSTEROANTERIOR MOBILIZATION

This research study aimed to measure the bending stiffness of the lumbar spine when subjected to posteroanterior mobilization. The lumbar spine was modeled as an initially curved beam column supported over the rib cage and the pelvis. Together with the posteroanterior mobilization force acted on the spine formed the three-point bending of the beam. The bending stiffness of the spine was derived from the mobilization force and the change in curvature of the spine. The mobilization force was measured by mounting a force plate onto the mobilization couch, and electromagnetic sensors were used to measure the change in spinal curvature. The mean bending stiffness of the spine was found to be 38.5 Nm2. The theoretical modelling suggested that the pelvic rotation produced by mobilization may be employed to provide an indicator of the magnitude of the mobilization force.

Manual physical assessment of spinal segmental motion: intent and validity

Validity of a clinical test can be defined as the extent to which the test actually assesses what it is intended to assess. In order to investigate the validity of manual physical assessment of the spine, it is therefore essential to establish what physical therapists intend to assess when they are applying these tests. The aims of this study were to (1) establish what manual physical therapists are intending to assess while applying passive intervertebral motion tests; and (2) examine the face validity and content validity for manual physical assessment of the spine. We surveyed 1502 members of the national manual physical therapist organisations of New Zealand and the United States of America using a web-based survey instrument. Sixty-six percent of 466 respondents believed passive accessory intervertebral motion (PAIVM) tests were valid for assessing quantity of segmental motion, and 76% believed passive physiologic intervertebral motion (PPIVM) tests were valid for assessing quantity of segmental motion. Ninety-eight percent of manual physical therapists base treatment decisions at least in part on the results of segmental motion tests. Quality of resistance to passive segmental motion was considered of greater importance than quantity of kinematic motion during PAIVM tests, while the quality of complex kinematic motion was considered of greater importance than quantity of displacement kinematics during PPIVM tests. Manual physical therapists accept the face validity of manual physical assessment of spinal segmental motion to a great extent, however a minority voice scepticism. Content validity is dominated by concepts of segmental kinematics and the force-displacement relationship. Intent of assessment does, however, vary widely between therapists. These data will inform the design of concurrent validity studies. Further work is recommended to increase consistency of intent, methodology and terminology in manual physical assessment of the spine.

The reliability of a posterior-to-anterior spinal stiffness measuring system in a population of patients with 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. The reliability of this device is under investigation in this study.

METHODS

The PAS system uses electronic sensors to record displacement and force while a human operator provides the force of indentation. A test-retest design was used with measures repeated by the same operator within 5 minutes. Posterior-to-anterior loads were applied to each lumbar spinous process of patients lying prone on a hard flat bench. Force and displacement were recorded and used to calculate PAS.

RESULTS

The subjects consisted of 22 males and 14 females; average age was 49.1 years (SD, 14.2). All subjects had low back pain of at least 4 weeks duration, with mean Roland-Morris scores of 7.6 (SD, 3.3). Spinal stiffness ranged from 4 to 26 N/mm (average, 11.2; SD, 3.5). Stiffness in the first and second tests varied on the average by 0.31 N/mm (P = .03). Standard error of the measurement was 1.62 N/mm. The single measures intraclass correlation coefficient (3,1) was 0.790 (95% confidence interval, 0.739-0.832).

CONCLUSIONS

The equipment and method produced repeatable results over the short-term. The system may be sensitive enough to detect changes in spinal stiffness that occur with care.

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.

Measurement of Lumbar Spine Loads and Motions During Rotational Mobilization

OBJECTIVES

To measure the loads acting at the lumbar spine and the resulting motions during rotational mobilization.

METHODS

Twenty healthy subjects were subjected to right rotational mobilization of different grades. The magnitude and frequency of mobilization loads were decided by an experienced manipulative therapist to be appropriate for each mobilization grade. Subjects were positioned on a specially constructed plinth capable of measuring forces and moments about 3 axes. The 3-dimensional movements of the lumbar spine were captured by an electromagnetic tracking device.

RESULTS

In the starting positions, the lumbar spines were found to be flexed, axially rotated to the right, and laterally bent to the left. As the mobilization grade increased, the spine was axially rotated further into the range. Rotational mobilization was found to induce oscillatory moments and movements of the spine in all 3 anatomical planes. The twisting moment and movement were generally accompanied by lateral bending moment and movement in the opposite direction. The mean amplitudes of the moment and movement oscillations were small and found to be largest for grade III mobilization.

CONCLUSION

The mechanical effects of rotational mobilization are not restricted to axial rotation of the spine as the name may have suggested. Rotational mobilization may be able to restore lost movements of the lumbar spine in any of the 3 planes. The method developed in this study showed good reliability and may be considered to assess treatment outcome and changes in spinal stiffness after therapy.

Dynamic response of the cervical spine to posteroanterior mobilisation

BACKGROUND

Posteroanterior mobilisation is a manual therapy technique that is commonly used in the examination and treatment of neck pain, but little is known about its biomechanical effect. The purpose of this study was to determine the intervertebral movements of the cervical spine produced by posteroanterior mobilisation.

METHODS

The cervical spines of nineteen healthy subjects were scanned using an open interventional magnetic resonance imaging scanner. Posteroanterior mobilisation forces were applied to the fifth cervical vertebra whilst they were in the prone position. Sagittal images of the spine were obtained before and during mobilisation.

FINDINGS

It was shown that posteroanterior mobilisation of the cervical spine generally produced extension of the upper motion segments and flexion of the lower segments. The middle segments were inconsistent in the direction of rotation. The cervical lordosis was found to increase with repeated PA loading cycles.

INTERPRETATION

The magnitude of intervertebral movement produced by mobilisation is small. Forces applied at one spinous process produced not only movements at the target vertebra but also movements of the entire cervical spine resulting in an increase in lordosis. Mobilisation should be interpreted as three-point bending of the entire cervical spine, rather than simple gliding of one vertebra upon another.

Loads in the lumbar spine during traction therapy

The purpose of the present study was to determine the loads acting on the lumbar spine when traction therapy was given in the Fowler's position. The study had two parts: a theoretical analysis which showed that traction produced a flexion moment on the spine as well as axial distraction; and an experimental study which measured the flexion moment induced by the adoption of the Fowler's position. The Fowler's position is clinically essential in that it flexes the spine and takes up the slack of the posterior tissues before the traction force is applied. Hence the axial tension and flexion moment generated by the traction force are more effective in stretching the posterior tissues. The angle of pull on the traction harness influences the friction between the body and the couch. However, this consideration is not necessary if a split traction table is used. The mechanical effects of traction are compared with those produced by postero-anterior mobilisation. The relative magnitude and direction of loads produced, and their variation with segmental level should be considered by therapists when choosing a technique for treating low back pain.

Kinematics of rotational mobilisation of the lumbar spine

OBJECTIVE

The purposes of this study were to measure the movements of the lumbar spine produced by rotational mobilisation, and to study the effects of different grades of mobilisation on the movements produced.

DESIGN

Kinematics of rotational mobilisation was assessed with an electromagnetic tracking device.

BACKGROUND

Rotational mobilisation is frequently used in the treatment of back pain, but there was no information on its mechanical effects.

METHODS

Movements of the lumbar spine were measured in 14 healthy volunteers when they were subjected to grades I to IV left rotational mobilisation.

RESULTS

In the starting positions, the spines were found to be flexed, axially rotated to the left and laterally bent to the right. As the mobilisation grade increased, the spine was axially rotated further into the range. Rotational mobilisation was found to produce oscillatory movements of the lumbar spine in all three anatomical planes. It produced axial rotation which was accompanied by lateral bending in the opposite direction and sagittal rotation. The mean frequency of the oscillatory movements was 1.4 Hz. The amplitude of the oscillations was small, and was found to be increased in grades II and III mobilisation.

CONCLUSION

Rotational mobilisation may be able to restore lost movements of the lumbar spine in any of the three anatomical planes.