An orthosis is a mechanical device used to correct/maintain the anatomical or functional position of any target region. They protect the joint from deforming forces, and distortion, and reduce pain by holding them in place. Two basic forms of orthotics are brace and splint. Braces are long-term therapeutic devices used to correct or support the injured joint. A splint is a rehabilitation device used to immobilize the joints, reduce pain by restricting movements and prevent bone fragments to cause injuries to soft tissues.

Principle of working of orthosis

The key principle of working orthosis relies on the Jordan principle, which states that the body must have a point with pressure opposed by two equal points of counter pressure in order to be stable. Orthotics work by applying equal and opposite pressure to correct the deformity. If the area is considered, then large pressure is applied over a small area and vice versa.

A good example to explain this is the case of heels. As the height of the heel increases, the pressure applied increases due to a reduction in area and hence results in pain. People wearing high heels would experience pain for a shorter duration compared to those with flat shoes. An example of orthosis is the use of plastic as a material to reduce the pressure applied to the target region.

There are four different ways by which an orthotic device works. They control the rotational moments, translation, and axial forces and control the line of action of ground reaction force by suitable modifications. Orthotic devices can do the following

  • Correct deformities (club foot boot for infants)
  • relieve pain (lumbosacral belt for lower back pain)
  • prevent substitution of function (hip flexors by adductors and abductors)
  • protect (rigid four post collar for cervical fracture)
  • prevent weight bearing (for fracture calcaneum, where weight is shifted to patellar tendon region away from injury).
  • strengthen muscles (tendon splint)
  • support (caliper to stabilize injured joints)
  • functional (stabilize and provide a function for injured part- foot drop splint)

General purposes of orthotics

There are general and specific functionalities for an orthosis. The general purposes include the usage of forces for joint biomechanics, decrease sensory feedback, a corrective force for proximal and distal counter forces, adjustability for children and adults, maintenance and cleaning, easy donning and doffing, reduction of pain by limiting movement, allowing appropriate movement, usage for the indicated duration, appealing cosmesis, easy use and comfort, and proper utility. The orthosis must prevent the progression of the deformity in the case of fixed deformity where the movement in opposite direction is absent.

Certain factors like gravity play an important role in the functioning of orthosis, especially to those joints where the heaviest movement masses are present. For example, a Rolyan shoulder cuff (large arm sling) can be used in hemiplegia to prevent subluxation of the shoulder, which is the largest joint prone to the deleterious effects of gravity.

Specific purposes of orthotics

Apart from the above-mentioned general purposes, orthosis also performs specific purposes as explained in certain use cases mentioned below.

  • Radial nerve glow acting as wrist drop splint to hold in the extended position
  • Knuckle duster splint that maintains flexion of metacarpophalangeal joints and extension at the interphalangeal joint with a lumbrical bar
  • Opponens splint to maintain thumb in an abducted position
  • Swedish knee cage to correct genu recurvatum
  • Pediatric orthosis for spinal Bifida or T12 lesion or cerebral palsy
  • Parapodium to correct the severe paralytic disorder
  • Arm slings to prevent shoulder dislocation
  • Static three-point proximal interphalangeal orthosis for Boutonniere deformity in case of rheumatoid arthritis
  • Splint to prevent stiffening of finger joints in case of burns
  • Twister to control the rotation of joints in the lower limb
  • Reciprocating gait orthosis that provides hip contralateral extension and ipsilateral lesion

Certain disadvantages of orthosis include callus, ulcer formations, lack of cosmetic appearance, weakening of muscles, physiological dependence, skin infection, limitation in lifestyle, and lack of motivation. The next blog will deal in detail with upper and lower limb orthosis.

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