Biofeedback load technique in the rehabilitation of osteoporotic patients (Biomechanical analysis)

Summary

Based on a simple bio­mechanical analysis, available to physicians, the article recommends carrying a backpack regularly as a part of the complex rehabilitation of osteoporotic patients. Carrying a backpack in front or on the back is recommended for patients with uncomplicated osteoporosis, carrying a backpack only on the back is recommended for patients with osteporotic vertebrae fractures. The importance of carrying a backpack is based upon remove the muscular dysbalance of the trunk muscles and upon increasing the bone strength by compressive force acting upon the vertebrae and proximal femur and activating osteoblasts to osteoformation. The backpack load magnitude is differentiated – patients with vertebrae fractures put a weight up to 1 kg into the backpack, patients without vertebrae fractures up to 2 kg.

Key words:
osteoporosis – vertebral fracture – bio­mechanics – rehabilitation – backpack – muscular dysbalance

Introduction

The aim of this short statement is to explain the benefits of carrying a backpack in the rehabilitation of osteoporotic patients on the basis of a simple bio­mechanical analysis available to physicians.

Carrying a backpack alternately in front and on the back is recommended for patients:

• with vertebral ostepenia and osteoporosis (without vertebrae fractures) and muscular dysbalance of the trunk muscles (fig. 1),

effect: remove the muscular dysba­lance of the trunk musculature, activating osteoblasts to neoformation of bone by compressive forces acting upon vertebrae [1–5], increasing the bone strength;

• with osteopenia and osteoporosis in the area of proximal femur,

effect: stimulation of osteoblasts to osteoformation by compressive forces acting upon the area of pro­ximal femur [1–5], increasing the bone strength.

• Carrying a backpack on the back only:

for patients with osteoporotic vertebrae fractures [6].

Patients with osteoporotic vertebrae fractures

Osteoporotic vertebrae fractures represent the most frequent complication of osteoporosis and contribute to a partial or full invalidation of patients. Kyphosis, as a consequence of wedge-shaped deformation of fractured osteoporotic vertebrae in the thoracic or lumbosacral area, conditions bio­mechanical changes in the organism with consequent grave clinical symptomatology:

• deviation of body’s gravity centre from its normal position (fig. 2a),
• muscular dysbalance of trunk muscles,
• ileocostal friction syndrome (the rib arches rub on ala ossis ilii by walking and by motion) (fig. 3),
• pathological position of disci intervertebrales in the kyphosis and their non‑physiological load (decrease of compressive forces upon ventral part and decrease of tension forces upon dorsal part of intervertebral discs),
• growth of compressive forces upon pulmonary parenchyma,
• development of cor pulmonale chronicum,
• ischemia or venostasis in intraabdominal organs, non‑specific intermittent abdominal pain, chronic constipation,
• chronic backache [6].

It is recommended to carry a backpack on the back for patients with osteoporotic fractures. The following positive effects can be achieved:

• careful stretching of shortened pectoral muscles,
• strengthening the stretched and weakened dorsal muscles (balancing the muscular dysbalance),
• potentiating a moderate straightening of a spine and so mild the ileo­costal friction syndrome and reducing tension forces acting upon dorsal muscles,
• reducing compressive forces acting upon organs of abdominal cavity,
• displacement of the deflected gravity centre closer to its physiological position – improving the patient’s stability,
• reducing compressive forces acting upon ventral part and tension forces acting upon dorsal part of intervertebral discs in the site of pathological kyphosis,
• rise of the maximal breathing capacity,
• restriction of pain intensity in the back [6].

Impaired stability of body in osteoporotic patient with fractured vertebrae (explanation to fig. 2a and 2b)

Definitions

From the mechanical point of view the balance constancy in any posture of a man is determined by:

• the magnitude of the support area,
• the position of the body’s gravity centre in relation to the support area,
• the distance of the body’s median (the gravity centre projection) from the edge of the support area,
• the magnitude of the stability angle.

The support area of a man is repre­sented by the area delimited by the outer limit of the body’s contact area with the ground. The outer limit of this support area is called the edge of the support area or the stability limit. The gravity centre (T) of the body is re­presented by a mass point, concentrating the whole force of the body’s gravity (the body mass). It is called also the mass centre. The body mass is equally distributed from this point to all sides. The median (t) is a vertical line passing through the gravity centre. The gravity centre projection (PT) is the point in the support area, crossed by the median.

The stability angle is the angle formed by the median and the line passing through the gravity centre and the edge of the body’s support area.

The stability of the skeleton is increased by:

• the enlargement of the support area,
• the approximation of the gravity centre to the support area,
• the approximation of the median (gravity centre projection) to the centre of the support area,
• the enlargement of the stability angle.

When the gravity centre projection gets over the edge of the support area, i.e., beyond the stability limit, the man is in an unbalanced position and falls down to the ground. In patients with osteoporotic vertebral fractures the projection of the gravity centre into the support area gets close to the stability limit of the support area in the upright position, and so these patients are prone to falls when bending forward or to sides [7].

Biomechanical analysis [7–9]

The importance of carrying a backpack can be explained by a simple bio­mechanical model, represented in fig. 4 and 5. The force F, situated in front of vertebrae, simulates the external load (e. g., a backpack, worn in front). To determine the way, how the force F is transferred into the vertebrae, the model example is solved by situating a couple of forces in the axis of vertebrae. The couple of forces are two forces of the same magnitude, acting in the same ray and in the same point of application, however, they are of the opposite direction and sense, while it holds true that:

F = F1 = F₂

The equilibrium status of forces does not change, as the effects of both added forces are mutually cancelled. This couple is also called the couple of zero forces.

Forces F₁ and F₂ produce a positive bending moment M on the arm r (acting clockwise) and the force F₂ is transferred as compressive force into lower situated vertebrae and through both hip joints into both lower limbs.

Solution result: External load by the force F is transferred to the vertebrae as a bending moment M and compressive force F₂.

Carrying the backpack regularly (about an hour daily) and alternatingits position in front and on the back balances the muscular dysbalance of the torso musculature. Simultaneously, the compressive force in the vertebrae and in the proximal femur area is increased. The compressive force stimulates osteoblasts to production of bone tissue (activation of oesteoformation), increasing so the bone strength.

Load magnitude

According to all, that we can not calculate the individual safe load for patient, we do not know the ultimate strength limit for osteoporotic and fractured vertebra in vivo, we can re­commend only the very low load.

The patients with vertebrae fractures put a load of up to 1 kg into their backpacks [10], the patients without vertebrae fractures up to 2 kg.

Carrying a backpack in front

The backpack simulates the external load, stressing the spine to bend and press. The body defends itself against the bending moment of the backpack’s gravity force (M), pulling the trunk to bend forward, by firstly isometric contraction of the abdominal and less dorsal muscles. These muscles are strengthened and the compressive force (F₂) is symmetrically (if the pelvis is in horizontal line) distributed from the spine through hip joints into both lower limbs. Carrying a backpack in front makes, at the same time, the shortened pectoral muscles to stretch [6,11].

Carrying a backpack on the back

The body defends itself against the bending moment of the backpack’s gravity force (M), pulling the trunk to bend backwards, by firstly isometric contraction of the dorsal muscles and less abdominal muscles, and in doing so, strengthens them. The backpack’s gravity force also carefully stretches the shortened pectoral muscles and the compressive force (F₂) is also symmetrically distributed from the spine through the hip joints into both lower limbs [6,11].

In the Fig.  4  the force F (external load) will be situated in the back of the spine and the bending moment M will be negative (acting counter – clockwise).

Conclusion

Carrying a backpack regularly represents for the patient with uncomplicated osteoporosis as well as for the patient with osteoporotic vertebrae fractures a low-cost, easily accessible and effective daily rehabilitation, which is a part of a complex kinesitherapy of the patient. It allows the patient to carry a backpack while making a small shopping, walking in a park or in easy terrain.

It is necessary to be aware that du­ring the combination of carrying a back-pack and Nordic walking certain magnitude of compressive forces is transferred from the patient into the poles and the rehabilitation effect of carrying a backpack is diminished [12].

Declaration – conflict of interests

The author declares, that she has no competing interests (financial or non financial).

Fig.  1 and 3 are modified by author from original anatomical pictures. Fig.  2a, 2b, 4, 5 are original – created by author.

Figurants: Ass. Prof. PhDr. Bohuš Hatiar, CSc. and Martin Petrik

Doručeno do redakce: 17. 5. 2010

ass. Prof. Jaroslava Wendlová, MD, PhD.

www.nspr.sk/Nemocnica-Kramare

e‑mail: jwendlova@mail.t-com.sk