José Montero Vilela, Francisco Parra González, Salvador Pitarch Corresa, David Garrido Jaén, Ignacio Bermejo Bosch*, Javier Andrade Celdrán, Eduardo Parrilla Bernabé, Juan Alfonso Gómez Herrero

Instituto de Biomecánica  (IBV). Universitat Politècnica de Valencia. Edificio 9C. Camino de Vera s/n (46022) Valencia (Spain)

* IBV’s Healhcare Technology Group, CIBER in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN)

Instituto de Biomecánica (IBV) has developed the Test FRP Lumbar software application, which is specifically designed to customize and streamline the execution and the delivery of results in the lumbar flexion-relaxation protocol.

The application allows users to easily define, through a graphical and intuitive interface, their own protocol execution requirements, and to obtain the results automatically and immediately.

To record the variables that show the existence of the flexion-lumbar relaxation phenomenon, TestFRP/Lumbar uses a system to analyze the movements of the spine and lower limbs, and surface electromyography (SEMG) equipment to record muscle activity.

INTRODUCTION

Since the beginning of 2000, the Instituto de Biomecánica (IBV) offers the NedLumbar/IBV application for the functional assessment of low back pain. Many users of this application have expressed an interest in performing a lumbar flexion-relaxation test on their patients as a complementary test. The first reference to the flexion-relaxation phenomenon (FRP) of the lumbar spine is found in the article The function of the erectores spinae muscles in certain movements and postures in man (Floyd & Silver, 1955). This phenomenon consists of a significant decrease in the electrical activity of the lumbar extensor muscles reflected in a significant electromyographic silence towards the final phase of the lumbar spine flexion movement, which persists for as long as the subject maintains the position of maximum voluntary flexion (MVF). In this position, the trunk is passively supported by the bone-ligamentous elements.

However, in patients suffering from low back pain, this electromyographic silence phenomenon does not normally occur (Figure 1).

The works extracted from the bibliography allow us to conclude that:

♦ The presence of a FRP phenomenon makes it possible to detect normal subjects with a high degree of specificity.

♦ The absence of a FRP phenomenon makes it possible to detect, with a high sensitivity, subjects with chronic low back pain.

Figure 1. Presence/absence of electromyographic silence in lumbar flexion-relaxation test

The FRP phenomenon can be quantitatively evaluated by comparing the amplitude of the SEMG signal in the different phases of the gesture: rest standing, flexion, MVF, and extension to return to the initial position. The ratios are calculated for both the signal amplitudes in the different phases and their effective values (RMS).

THE GESTURE ANALYZED

The phases of the gesture analyzed are described in figure 1.

There is considered to be a general consensus as regards the phases of the kinematics of gesture execution:

Phase1. Initial orthostatic: The subject remains at rest in the orthostatic position.

Phase2. Flexion: From the orthostatic position, the subject performs a flexion to the MVF position.

Phase3. MVF: The subject maintains the MVF position during a preset period of time.

Phase4. Extension: The subject performs the extension movement to recover the orthostatic position.

Phase5. Final orthostatic: The subject reaches and maintains the orthostatic position. In the case of continuous repetitions of the gesture, this phase matches the initial orthostatic phase of the next repetition.

Figure 2. Sequence of positions during the execution of the gesture in the lumbar flexion-relaxation test

In FRP tests, two or four SEMG channels are usually recorded. The TestFRP/Lumbar application records up to four channels, obtaining both the raw signals and their effective values (RMS). Figure 2 shows an example of the record of these signals against the kinematic record of movement (lumbar flexion angle). These graphs show the different repetitions of the gesture (green areas), as well as the phases within each of these repetitions (vertical dashed lines).

Figure 3. Signals of the lumbar flexion angle and SEMG during a TestFRPLumbar test performed on a normal subject

VALIDATION CRITERIA OF THE PROTOCOL

There is no consensus in the scientific literature as to what conditions cause the FRP. The main points of discussion focus on the lumbar range, the execution speed of the gesture, and the time in MVF phase that are required for this phenomenon to occur.

In order to make it easier for users to perform the tests according to their own criteria, the TestFRP/Lumbar application makes it possible to define the limits that are valid for the execution parameters of the tests (Figure 3):

♦ Minimum range of lumbar flexion.

♦ Speed during the flexion phase.

♦ Duration of the MVF phase.

♦ Speed during the flexion phase.

Figure 4. Configuration of the lumbar flexion-extension protocol in TestFRPLumbar/IBV

ASSESSMENT OF THE FRP EXISTENCE

Scientific literature also shows controversy regarding the criteria to assess the presence/absence of the FRP. Some authors argue that the level of activity of the SEMG in absolute terms is a robust parameter; however, other authors have developed different ratios for the levels of SEMG activity in different phases of the gesture.

As part of the protocol customization, users can also define what results they want to be shown, both on the screen and in the reports generated by the application (Figure 5):

♦ Ranges and speeds of the lumbar spine, pelvis, and both together.

♦ Mean and maximum RMS signals in the orthostatic, flexural, MVF, and extension phases.

♦ Main ratios published in the scientific literature.

Figure 5. Protocol configuration. Selection of the results to be obtained

THE TestFRPLumbar/IBV APPLICATION

TestFRP/Lumbar is a software application for the execution of protocols intended to analyze the phenomenon of lumbar flexion-relaxation, that was specially designed to give versatility and speed to the experts in instrumented functional assessment.

The base technology of TestFRP/Lumbar is a video photogrammetry system to analyze the spine and lower limbs movements, and SEMG equipment to record muscle activity.

Given the diversity of proposals in the scientific literature, TestFRP/Lumbar allows users to define their own protocols and to record the data from both the movement kinematic analysis system and the SEMG system. Once the data are recorded, the application will automatically present the parameters related to the execution of the protocol (Figure 6 and Figure 7). The test report is also automatically generated, with the user being able to configure which parameters are of interest and should be included.

In short, TestFRP/Lumbar brings to the users of the IBV functional assessment methodologies a tool that allows them to perform a 2-minute test, versatile and easy to use, which automatically generates results and reports.

Figure 6. Automatic segmentation of the test and graphs of lumbar FE angle with 4 SEMG channels

Figure 7. Kinematic parameters of the various segments with one SEMG channel

CONCLUSIONS

The lumbar flexion-relaxation test is widely accepted as a complementary test in the field of functional assessment of low back pain.

The diversity of criteria regarding the execution of the gesture of the lumbar flexion-relaxation protocol (lumbar FRP) makes it necessary to have an application that provides flexibility when configuring the execution requirements, while maintaining the automation of both the analysis and the delivery of results.

TestFRP/Lumbar is useful for the members of the IBV User Community, that is, mutual insurance companies that collaborate with the Social Security, hospital services with rehabilitation and physiotherapy units, and any professionals specialized in Bodily Harm Assessment, since it is a tool that facilitates the performance of FRP tests, combined with the functional assessment tests carried out using NedLumbar/IBV.

ACKNOWLEDGEMENTS

We would like to thank Egarsat (mutual insurance company collaborating with Social Security nº 276); Mutua Montañesa (mutual insurance company collaborating with Social Security nº 7), and MAZ (mutual insurance company collaborating with Social Security Nº11) for providing feedback on the usefulness of TestFRP/Lumbar in the activities of their biomechanical assessment laboratories.