An orthotic device (commonly just referred to as an orthotic) is an external device applied on the body to limit motion, correct deformity, reduce axial loading, or improve function in a certain segment of the body.
Design characteristics of an orthotic device are crucial to function. Most important features include the following:
Weight of the orthosis
Ability to fit various sizes of patients
Ease of putting on (donning) and taking off (doffing)
Access to tracheostomy site, peg tube, or other drains
Access to surgical sites for wound care
Aeration to avoid skin maceration from moisture
Indications for recommending orthotic devices include the following:
Maintenance of orthosis: Orthosis should be simple and durable as possible.
Patient should be taught for:
Cleaning the leather.
Oiling the joints.
Wash the orthosis if possible.
Physicians must understand the biomechanics of the spine and each individual orthosis. The cervical spine is the most mobile spinal segment with flexion greater than extension. The occiput and C1 have significant flexion and extension with limited side bending and rotation. The C1-C2 complex accounts for 50% of rotation in the cervical spine. The C5-C6 region has the greatest amount of flexion and extension. The C2-C4 region has the most side bending and rotation.
When compared to the cervical and lumbar spine, the thoracic spine is the least mobile. The thoracic spine has greater flexion than extension. Lateral bending increases in a caudal direction, and axial rotation decreases in a caudal direction.
The lumbar spine has minimal axial rotation. The greatest movement in the lumbar spine is flexion and extension. Immobilization of the spine increases erector spinae muscle activity since normal rotation that occurs with ambulation is limited by the orthosis.
Biomechanichal principles of orthotic design
The biomechanical principles of orthotic design assist in promoting control, correction, stabilization, or dynamic movement.
All orthotic design are based on three relatively principles:
The pressure principle:
the pressure should be equal to the total force per unit area.
Area of Application
It means that the greater the area of a pad or plastic shell of an orthosis, the less force will be placed on the skin.
Therefore, any material that creates a force against the skin should be of dimension to minimize the force on the tissue.
The equilibrium principle:
The sum of the forces and the bending moments created must be equal to zero.
This means that three-point pressure or loading system occurs when three forces are applied to a segment in such a way that a single primary force is applied between two additional counter forces with the sum of all three forces equalizing zero.
The primary force is of a magnitude and located at a point where movement is either inhibited or facilitated, depending on the functional design of the orthosis
The lever arm principle:
The farther the point of force from the joint the greater the moment arm and the smaller the magnitude of force required to produce a given torque at the joint.
This why most orthosis are designed with long metal bars or plastic shells that are the length of adjacent segment.
The greater the length of the supporting orthotic structure, the greater the moment or torque that can be placed on the joint or unstable segment.
These three principles act dependently on each other So when designing or evaluating an orthotic devise we should check that: There is adequate padding covering the greatest area possible for comfort.
The total forces acting on the involved segment is equal to zero or there is equal pressure throughout the orthosis and no areas of skin irritation.
The length of the orthosis is suitable to provide an adequate force to creat the desired effect and to avoid increased transmission of shear forces against the anatomic tissues.
General othotic considerations:
The forces at the interface between the orthotic materials and the skin.
The degrees of freedom of each joint.
The number of joint segments.
The neuromuscular control of a segment, including strength and muscle tone.
The material selected for orthotic fabrication.
The activity level of the client.
The goal of orthotic fitting is to meet the functional requirements of the client with minimal restriction.
Functional orthotic considerations: Alignment:
A) Assistance with joint motion.
B) Resistance with joint motion.
3) Weight bearing:
4) Protection: The biomechanical principles in orthotic design include balance of horizontal forces, fluid compression, distraction, construction of a cage around the patient, placement of an irritant to serve as a kinesthetic reminder, and skeletal fixation. Construction of a cage around the patient, like a thoracolumbar brace, increases intraabdominal pressure. Increased intraabdominal pressure converts the soft abdomen into a semirigid cylinder, which helps to relieve part of the vertebral load. In general, structural damage to posterior elements of the spine creates more instability with flexion, whereas damage to anterior elements creates more instability with extension.
Orthotic devices (orthoses) are generally named by the body regions that they span. For example, a CO is a cervical orthosis, while a CTLSO is a cervicothoracolumbosacral orthosis, spanning the entire length of the spine. Many of these devices are also known by eponyms.
Several drawbacks to cervical orthotic (CO) use have been noted. The soft tissue structures around the neck (eg, blood vessels, esophagus, trachea) limit application of aggressive external force. The high level of mobility at all segments of the cervical spine makes it difficult to restrict motion. Cervical orthoses offer no control for the head or thorax; therefore, motion restriction is minimal. Cervical orthoses serve as a kinesthetic reminder to limit neck movement.
Observe appropriate precautions associated with orthotic use. Keep in mind that continued long-term use has been associated with decreased muscle function and dependency.
The soft collar is a common orthotic device made of lightweight material, polyurethane foam rubber, with a stockinette cover. It has Velcro closure strap for easy donning and doffing. Patients find the collar comfortable to wear, but it is soiled easily with long-term use.
Indications for use of the soft collar include the following benefits for the patient:
Support to the head during acute neck pain
Relief with minor muscle spasm associated with spondylolysis