Joint motion restrictions and exaggerate muscular activities during fingertip-to-floor test in case of patients with chronic low back pains? A pilot study

Keywords:

• Chronic low back pain
• fingertip-to-floor test
• external work
• functional restoration program

1. Introduction

The physical examination of patients with chronic Low Back Pain (cLBP) is mainly relying on physical impairment tests. Enhancement of hip and spinal flexibility is often a treatment goal of exercise therapy in patients with cLBP. Thus validated tests, like Fingertip-to-Floor (FTF) test, is needed. For that, the patient bend forward and attempt to reach for the floor with their fingertips. In relation to radiography and level of pain (evaluated with Visual Analog Scale or VAS), FTF test has been previously shown reliable in patients with LBP and validated (Perret et al. 2001). So this test is currently used before and after Functional Restoration Program (FRP). However, this test has been criticized for not measuring isolated lumbar flexion Range of Motion. Forward bending range is effectively also based on pelvic, hip, thoracic spine, dural and shoulder mobility, as illustrated with Index of Trunk Mobility (Delpierre et al. 2018). Participation in a FRP results in improved muscle strength, endurance, and physical activity. So, FTF-test give limited information of the strategies used by patients, independently of limiting parameters as joint motions restrictions and muscular activity. These two limiting parameters could be evaluated with external work (W_ext) in walking condition. W_ext corresponds to the mechanical work performed to move the Center of Mass (CoM), a point assimilated to the body, affected by the mass of body and subjected to external forces. In case of gait analysis, W_ext is dependent of joint motion restrictions (Mahaudens and Mousny 2010) and muscular activity (Zollinger et al. 2016). But, gait is associated to higher displacements of CoM in comparison to FTF-test. It seems interesting to evaluate W_ext before and after FRP. So, based on retrospective data, considering that FRP tends to limit joint motion restriction and strategies of avoidance that improves FTF test, the purpose of this pilot study was to compare VAS, FTF measure and W_ext before and after FRP. We hypothesized that, associated to lower FTF outcome measure, W_ext is significantly lower after FRP.

2. Methods

2.1. Population

Following ethical approval from Ethics Committee of Angers, France (2017/07), a group of 12 patients with CLBP (8 women and 4 men; mean 36.71 years (Standard deviation 7.25 years); mean 65.00 Kg (SD 9.73 kg); mean 165.42 cm (SD 6.42 cm)) has been considered. All patients reported the site of the injury to be within the lumbar or lumbosacral region, but none of them reported radicular symptoms. These patients participated in a 5-week multidisciplinary FRP involving muscle development, stretching, posture, cardiovascular, and proprioceptive exercises. The program also included ergonomics and psychosocial care. The dropout rate was null. None subjects had any apparent neurological or orthopedic disorders (like scoliosis) or previous surgery likely to interfere with movement. Motion caption data were recorded during the first and final week of the program.

2.2. Material& method

A 3 D motion capture system (ViconT10, 100 Hz, Oxford, United Kingdom) equipped with 8 cameras recorded data for 34 passive markers (14 mm) to define a plug-in gait model. A Ground Reaction Force GRF (AMTI, 1000 Hz) was also used. To filter trajectories and forces, a double-pass Butterworth filtering method was applied (low-pass filter 3 Hz). Subjects were asked to perform 4 sets of FTF at the speed of their choice and were given rest periods of 5 seconds between each set. The 5-second interval was implemented to make certain that all markers were captured correctly, to ensure that the subject began a movement in an orthostatic posture.

Subjects began movements in a comfortable standing position: they stood in an erect posture looking forward, their arms hanging freely, both before and after each movement. They were asked to avoid compensatory movements of the lower limbs (e.g., knee flexion or extension) and of the trunk in order to isolate hip and trunk mobility. Subjects were asked to perform these movements to maximum voluntary ranges. FTF measure was calculated from marker on hand (dorsum of the hand just below the medial head of metacarpal). To obtain W_ext, Cavagna’s method was used to compute CoM displacement (Cavagna 1975). From GRF, vertical and forward accelerations were calculated in reference to Equations (1)(1) $$F_v=m.a_v+\mathit{frictional}\mathrm{ }\mathit{forces}+\mathit{weight}\mathrm{ }$$(1) and (2)(2) $$F_f=m.a_f+\mathit{frictional}\mathrm{ }\mathit{forces}$$(2) : (1) $$F_v=m.a_v+\mathit{frictional}\mathrm{ }\mathit{forces}+\mathit{weight}\mathrm{ }$$(1) (2) $$F_f=m.a_f+\mathit{frictional}\mathrm{ }\mathit{forces}$$(2)

Frictional forces correspond to the force opposite to CoM displacement in relation to muscular force or nonelastic deformation of the body itself and air resistance (Cavagna 1975). We considered these forces as limited. So, from vertical acceleration ($a_v$) and forward acceleration ($a_f$), we computed CoM with double integrations. Based on F (the result of the external forces applied to the body), D (the displacement of CoM), according (Cavagna 1975), W_ext is given by: (3) $$W_{\mathit{ext}}\mathrm{ }=\mathrm{ }\overrightarrow{F}\mathrm{ }.\mathrm{ }\overrightarrow{D}$$(3)

Descriptive statistics were used to report mean, standard deviation (SD). Statistical analyses were performed using Statistica (version 13, USA). The Wilcoxon’s test was used to identify differences between data before and after FRP. The chosen level of significance was p ≤ 0.05.

3. Results and discussion

VAS and FTF measures were significantly lower after FRP (Table 1). W_ext presented no significant difference before and after FRP (p≤.05) and limited values.

Table 1. VAS, FTF measure (mm) and W_ext (mJ kg⁻¹ m⁻¹) before/after FRP.

	Before FRP	After FRP	p
VAS	4.63 (2.33)	2.31 (1.64)	0.02*
FTF	290.1 (141.4)	155.1 (113.3)	<0.001*
Wext	10.2 (1.0)	9.8 (1.0)	0.09

* Significant difference.

So, FRP induces significant effects on pain levels and contribute to perform larger movements. Even if we had not significant difference on W_ext, this result could certainly be explained with our small number of patients or restrictive hypothesis on W_ext (as detailed on limitations). If the FTF test is impacted, the location and pain score should be documented (Perret et al. 2001). It is important to remember that there are no “normative” values for this test, as forward bending flexibility is highly variable even in the asymptomatic population (Perret et al. 2001).

Furthermore, it seems interesting to develop specific model to evaluate relation between clinical data (like psycho-social scales in particular scales which evaluate fear-avoidance behaviours) and W_ext in order to quantify the impact of W_ext on these psycho-social parameters as it was observed in case of kinematical index (Delpierre et al. 2018).

We note three main limitations. Firstly, the CoM was obtained from the GRF. Frictional forces presented in Equations (1) and (2) were considered negligible. This part could be tested with asymptomatic subjects and limited flexion (Cavagna 1975). Secondly, muscle activity was not analyzed here but we associated W_ext to muscular activity and joint motion restrictions. Thirdly, this pilot study was based on limited number of patients, without controls.

4. Conclusions

This first pilot study based on FTF test and W_ext shows a positive trend but need other validations to consider W_ext as dependant of joint motion restrictions and muscular activity during fingertip-to-floor test.

Acknowledgements

All patients included in this retrospective study.