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.     

The effect of posteroanterior mobilisation on sagittal mobility of the lumbar spine

The purpose of this study was to investigate the effect of a posteroanterior central vertebral pressure (PA mobilisation) on sagittal mobility of the lumbar spine in asymptomatic subjects. On 3 separate days an experienced manipulative physiotherapist stood on a force platform and applied a PA mobilisation to L3 spinous process for 2 minutes on 18 female subjects. Prior to this, subjects acted as their own control by lying prone for the same length of time but without receiving mobilisation treatment. The force platform was used to indirectly measure the minimum and maximum peak forces, and the frequency of oscillation of the applied PA mobilisation. A CA-6000 Spine Motion Analyser (SMA) was used to measure lumbar spine flexion and extension before and after the mobilisation and control treatments. Prior to the main experiment, intra-therapist reliability of the SMA was found to be good, with no significant difference (p > 0.05) in flexion or extension range of movement between 3 days of testing and root mean square error (RMSE) values of 7.43 degrees for flexion and 8.6 degrees for extension. The results indicated that a PA mobilisation with a mean maximum force of 92.5 N, amplitude of force oscillation of 9.6 N and a frequency of oscillation of 4.5 Hz had no significant affect (p > 0.05) on sagittal mobility of the lumbar spine in the asymptomatic subject population.     

Real-time feedback improves accuracy of manually applied forces during cervical spine mobilisation

PurposeTo determine if real-time feedback enables students to apply mobilisation forces to the cervical spine that are similar to an expert physiotherapist.MethodsAn instrumented treatment table collected mobilisation force data with feedback about forces displayed on a computer screen. An expert physiotherapist performed posteroanterior mobilisation of C7 on 21 asymptomatic subjects while forces were recorded. These data were used as force targets for 51 students who mobilised one of the asymptomatic subjects on two occasions. Students' forces were recorded before and after practice either with (experimental group) or without real-time feedback (control group). Improved performance was defined as a smaller difference between expert and student forces, comparing groups with non-parametric statistics.ResultsStudents receiving feedback applied more accurate forces than controls (median difference between student and expert forces in the experimental group, 4.0 N, inter-quartile range (IQR) 1.9–7.7; in controls, 14.3 N, IQR 6.2–26.2, difference between groups p < 0.001). One week later, these students still applied forces that more closely matched the expert's compared to controls (p < 0.01), but the differences between the students' and expert's forces were greater (6.4 N, IQR 3.1–14.7).ConclusionPractice with real-time objective feedback enables students to apply forces similar to an expert, supporting its use in manual therapy training.     

Bending stiffness of the lumbar spine subjected to posteroanterior manipulative force

This study measured the bending stiffness of the spine when it is subjected to posteroanterior mobilization force. The lumbar spine was modeled as an initially curved beam column supported over the rib cage and the pelvis. Posteroanterior mobilization was assumed to be three-point bending of the beam. The mobilization force was measured by the mounting of a force plate onto the manipulation couch, where electromagnetic sensors measured the change in spinal curvature. The bending stiffness of the spine was derived from the force and curvature data. The technique developed in this study provided highly repeatable data. The theoretical analysis suggests that the pelvic rotation produced by mobilization may be used clinically to indicate the magnitude of the mobilization force. Future research may employ the present method to determine how back pain may affect the bending stiffness of the spine. The bending stiffness values reported in this study will be valuable to future modeling work.     

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.     

A rigid body model of the dynamic posteroanterior motion response of the human lumbar spine

BACKGROUND: Clinicians apply posteroanterior (PA) forces to the spine for both mobility assessment and certain spinal mobilization and manipulation treatments. Commonly applied forces include low-frequency sinusoidal oscillations (<2 Hz) as used in mobilization, single haversine thrusts (<0.5 seconds) as imparted in high-velocity, low-amplitude (HVLA) manipulation, or very rapid impulsive thrusts (<5 ms) such as those delivered in mechanical-force, manually-assisted (MFMA) manipulation. Little is known about the mechanics of these procedures. Reliable methods are sought to obtain an adequate understanding of the force-induced displacement response of the lumbar spine to PA forces. OBJECTIVE: The objective of this study was to investigate the kinematic response of the lumbar spine to static and dynamic PA forces. DESIGN: A 2-dimensional modal analysis was performed to predict the dynamic motion response of the lumbar spine. METHODS: A 5-degree-of-freedom, lumped equivalent model was developed to predict the PA motion of the lumbar spine. Lumbar vertebrae were modeled as masses, massless-spring, and dampers, and the resulting equations of motion were solved by using a modal analysis approach. The sensitivity of the model to variations in the spring stiffness and damping coefficients was examined, and the model validity was determined by comparing the results to oscillatory and impulsive force measurements of vertebral motion associated with spine mobilization and 2 forms of spinal manipulation. RESULTS: Model predictions, based on a damping ratio of 0.15 (moderate damping) and PA spring stiffness coefficient ranging from 25 to 60 kN/m, showed good agreement with in vivo human studies. Quasi-static and low-frequency (<2.0 Hz) forces at L3 produced L3 segmental and L3-L4 intersegmental displacements up to 8.1 mm and 3.0 mm, respectively. PA oscillatory motions were over 2.5-fold greater for oscillatory forces applied at the natural frequency. Impulsive forces produced much lower segmental displacements in comparison to static and oscillatory forces. Differences in intersegmental displacements resulting from impulsive, static, and oscillatory forces were much less remarkable. The latter suggests that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting therapeutic responses. CONCLUSIONS: The simple analytical model presented in this study can be used to predict the static, cyclic, and impulsive force PA displacement response of the lumbar spine. The model provides data on lumbar segmental and intersegmental motion patterns that are otherwise difficult to obtain experimentally. Modeling of the PA motion response of the lumbar spine to PA forces assists in the understanding the biomechanics of therapeutic PA forces applied to the lumbar spine and may ultimately be used to validate chiropractic technique procedures and minimize risk to patients receiving spinal manipulative therapy.     

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.     

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.     

Effect of position on the posteroanterior stiffness of the lumbar spine

SUMMARY. Physiotherapists commonly use motion testing techniques in the assessment of patients with spinal disorders. One of the techniques considered important in the assessment of low back pain is the application of posteroanterior (PA) forces to the lumbar spinous processes to evaluate spinal stiffness and symptom response. The purpose of this study was to investigate the effect of spinal position on the measured lumbar PA stiffness. The PA stiffness at the L3 and L5 vertebral levels was assessed in 12 painfree subjects in three prone lying positions (flexion, neutral and extension). PA forces were applied to the spinous processes, under quasi-static loading conditions, using a specifically built apparatus. The stiffness coefficient was calculated from the slope of the regression line fitted to the truncated (35N-80N) force-displacement curves. At both vertebral levels, the PA stiffness was position dependent, with the lowest values obtained in the neutral position. The mean stiffness increased by 12.4% in extension and 31.9% in flexion. In all positions PA stiffness was significantly greater at L5 than at L3. These results suggest that clinical assessments of lumbar PA stiffness may be influenced by the patient position in which the test is performed. Comparative assessments of PA stiffness over time should be performed with the spine supported in the same position. Copyright 1998 Harcourt Publishers Ltd.     

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.     

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

OBJECTIVE: To determine the effects of the dissection of spinal tissues on the mechanical behavior of motion segments under the application of posteroanterior forces. DESIGN: A cadaveric motion segment study. SETTING: A tissue mechanics research laboratory. PROCEDURE: Anterior shear and extension moment were applied to 10 motion segments to simulate the clinical situation when posteroanterior forces were applied to the spine. The movements of the specimens in the sagittal plane were studied by a camera. Spinal tissues were dissected sequentially, and the mechanical testing was repeated after the dissection of each tissue. RESULTS: The most significant movements produced were extension and superior translation of the anteroinferior corner of the superior vertebral body. Translational movements in the other directions were small. The dissection of the posterior ligaments and zygapophyseal joints did not lead to significant changes in the movements. CONCLUSIONS: Injuries of the posterior ligaments are unlikely to alter the mechanical response of the spine to posteroanterior forces. However, these posterior tissues are pain sensitive and may be subjected to large strains and elicit symptoms.     

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.     

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.     

Paraganglioma metastatic to the cervical spine

Paragangliomas are usually benign tumors which may be locally invasive. Only 10% of these tumors are malignant. When metastases occur the most common sites are lung, liver and bone. When bony metastases occur the spine is a common site. In the present case cervical spine metastases with resultant bony encroachment: and epidural extension of tumor with cord compression was diagnosed with myelography and CT.     

Analysis of the mechanical response of damaged human cervical spine ligaments

BackgroundCervical spine ligaments that protect the spinal cord and stabilize the spine are frequently injured in motor vehicle collisions and other traumatic situations. These injuries are usually incomplete, and often difficult to notice. The focus of the presented study is placed on analysis of the effect of subfailure load on the mechanical response of the three main cervical spine ligaments: the anterior and the posterior longitudinal ligament and the ligamentum flavum.MethodsA total of 115 samples of human cadaveric ligaments removed within 24–48 h after death have been tested. Uniaxial tension tests along the fiber direction were performed in physiological conditions on a custom designed test equipment. The ligaments were loaded into an expected damage zone at two different subfailure values (based on previously reported reference group of 46 samples), and then reloaded to failure.FindingsThe main effect of a high subfailure load has proven to be the toe elongation change. The toe elongation increase is affected by the subfailure load value. While anterior and posterior longitudinal ligament showed similar changes, the smallest subfailure effect was found in ligamentum flavum.InterpretationsThe normal physiological region of the cervical spine ligaments mechanical response is modified by a high subfailure load. The observed ligament injury significantly compromises ligament ability to give tensile support within physiological spinal motion.     

Cervical spine mobilisation forces applied by physiotherapy students

Objectives

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

Participants

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

Methods

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

Results

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

Conclusion

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