Precompressed Spring Units Making a Huge Difference
- Safe and Free-Handed Standing and Walking
The main purpose of an orthosis for a calf muscle weakness is to restore safety when standing and walking without depending on additional walking aids. For this purpose, the orthosis must activate the forefoot lever that has been lost due to the weakened calf muscles in order to provide the required resistance to counteract the body weight. Only the precompressed spring units of the system joints of the NEURO SWING product range offer a basic resistance at the required level.
If the basic resistance is overcome during movement, the resistance increases with increasing dorsiflexion due to the additional compression of the spring unit. By individually combining two spring units, different basic resistances can be used in both directions of movement. This way a high basic resistance required in the direction of dorsiflexion can be combined with a low basic resistance in the direction of plantar flexion. The diagram above shows two examples of typical spring characteristics of precompressed spring units with a tibial progression of 8°.
Variable Spring Force
We provide a total of five different spring units for each system width, with forces ranging from normal to extra strong and a range of motion from 15°(normal) to 5° (extra strong).
The spring unit with the yellow colour marking and “very strong” spring force offers a basic resistance with a 10° range of motion, which usually is enough to counteract the body weight appropriate for the system width.
The spring unit with the blue colour marking and the “normal” spring force and 15° range of motion is usually used for patients with a peroneal palsy and a low activity level. It is strong enough to lift
the foot in swing phase and counteract stumbling.
The spring unit with the white colour marking and the “strong” spring force and 10° range of motion can be used to reduce the basic resistance compared to the spring unit with the yellow colour marking and increase it in comparison to the spring unit with the green colour marking.
The spring unit with the red colour marking and the “extra strong” spring force and 5° range of motion almost doubles the basic resistance compared to the spring unit with the yellow colour marking. It can be used for patients with a crouch gait, for example.
The spring unit with the green colour marking and “medium” spring force and 15° range of motion cannot only be used to control the foot lifting but also the plantar flexion and knee flexion in loading response. This spring unit is often used for patients with a peroneal palsy and a higher activity level.
Mounting Precompressed Spring Units
This video contains further information on the different properties of the precompressed spring units in the FIOR & GENTZ product range. The focus is on the resistance and inclination angle as well as the effects of typical errors during assembly.
Independent Adjustment Options
The system joints in the NEURO SWING product range offer five colour-coded, interchangeable spring units with different spring forces. The graph above shows the basic resistance of the spring units using the coloured spring characteristics. If the lower leg-to-plumb line angle is changed (e.g. 1 → 2), these spring characteristics shift. The adjustment of the tibial inclination does not change the basic resistance and spring force of the selected spring unit. This clearly shows that the different settings work independently of each other. The original NEURO SWING system ankle joint allowed such independent adjustment for the first time and this unique advantage is still an integral part of the NEURO SWING product range system joints today.
The spring effect of the NEURO SWING system joints can be adjusted to optimise the resistance in both directions of movement of the ankle joint to counteract the body weight as well as the weakness of the calf and foot lifting muscles. The tibial inclination, as starting point for the specific resistances, can easily be adjusted with two alignment screws. This allows defining a stable position and a secure stance.
Individual Adjustment
Should the gait change, a quick response is possible at any time through the adaptable adjustments, exchangeable spring units or even a conversion to another system joint with plug + go modularity.
Calculation of the Spring Force
The FIOR & GENTZ Orthosis Configurator determines, based on the muscle strength, the spring force with the corresponding precompression that is best suited for the needs of your patients.
Problems with Conventional Treatments
- Non-Precompressed Springs
Standard springs in conventional joints are not precompressed and therefore offer no basic resistance. In case of a weakness of the calf muscles (plantar flexors), it is therefore impossible to activate the forefoot lever. Usually, such springs are compressed late due to the low resistance, which does not achieve the desired effect. If the anterior spring is compressed, it changes the orthosis’ alignment, as the posterior spring is automatically compressed as well. This increases the potential for a hyperextended knee, which should be avoided in case of weak calf muscles. An additional posterior spring compression is required to restore the physiologically optimal tibial inclination. This increases the spring constant (increase in resistance during movement, illustrated by the lines in the diagram). At the same time, the range of motion is reduced. The spring constant is inevitably the same in both directions of movement. This effect can be increased until the range of movement is completely blocked. The basic resistance cannot be increased by this measure as long as the physiological tibial inclination is maintained. The necessary basic resistance is only achieved with complete compression and thus a simultaneous movement blockage. Orthoses in which conventional joints with standard springs are used should therefore not be used to treat a weakness of the calf muscles.
- Jointless Orthoses
All jointless orthoses have the same effect as orthoses with conventional joints with standard, non-precompressed, springs. They offer either low or high rigidity. The spring constant is inevitably the same in both directions of movement. If orthoses without joints are not produced completely rigidly, they cannot generate the necessary basic resistance. If a high rigidity is required to achieve balance, the orthosis restricts the range of motion of the upper ankle joint. If they aim at a higher mobility of the upper ankle joint, a high rigidity is not sufficient to activate the forefoot lever in order to achieve a stable balance. This classic predicament leads to necessary compromises. Therefore, such orthoses are usually produced with high rigidity and a low anterior inclination angle. Although this design increases the basic resistance in a physiological tibial inclination, it also increases the potential for hyperextension, which should be reduced with the right orthotic treatment in case of a weakness of the calf muscles. Jointless orthoses cannot generate any basic resistance when they are produced with the physiologically optimal tibial inclination. Therefore, all types of orthoses without joints are not suitable for treatments that are intended to compensate a calf muscle weakness, as they cannot generate a stable balance.
