“To understand motion is to understand nature.”1
The orthotic profession has been trying to understand the motion of human lower limbs for decades. Not only do the motions themselves need to be understood, but outside forces that react on these motions also need to be comprehended. Neuromuscular disorders such as Charcot Marie Tooth, congenital hypotonia, Frederick's ataxia, Kugelber Weldander, muscular dystrophy, Werding-Hoffman, polio, Guillain-Barre, amyotrophic lateral sclerosis, femoral neuropathy, and others can lead to lower extremity weakness or paralysis that can be devastating to the infant, young child, adolescent, adult, and geriatric patient. Neuromuscular deficiencies present over an extended time can induce musculoskeletal abnormalities, which in turn lead to abnormally directed forces on skeletal structures, in addition to leaving muscles weak and paralyzed.
Technical advances combined with a better understanding of biomechanics have enabled scientists, engineers, and orthotists to develop new and improved methods of orthotic treatment. For centuries, orthotists were limited to two basic knee joint types: free motion and manually locked (in full extension). Over time, many variations of the locked joints were developed. Very recently, stance control knee joints have become available for orthotists to incorporate into knee-ankle-foot orthosis (KAFO) designs. The challenge is to make the right decision, based on thorough evaluation of each patient's unique constellation of biomechanical deficiencies.
Orthotists today have a good understanding of basic mechanics and physics and can use that knowledge, along with medical/anatomical knowledge, to reduce the forces that orthoses apply to persons with neuromuscular deficiencies, thereby minimizing the risk of causing damage to the structures of their musculoskeletal system. It is important to realize that “…disturbances of the neurological control mechanisms, motor input, and structural skeletal alignment can have a significant effect on dynamic stability…”2 The purpose of orthotic intervention must be clearly understood and is typically to provide stability for the limb at risk for further damage in the sagittal, coronal, and transverse planes. For this population, proprioception is an important consideration. Some neuromuscular deficiencies, such as poliomyelitis, involve only the anterior horn cell of the spinal cord. So long as the posterior horn cell is intact, these patients retain proprioception. Having a sense of where the limb is in space seems to help in mastering ambulation with a KAFO.
In addition to providing safety and stability, KAFOs must provide sufficient comfort for a full day of activities. “Knee stability during standing is normally achieved by alignment. The normal knee extends slightly beyond a straight line so that the center of knee rotation can be displaced behind the weight-bearing line.… Muscle activity is not required (not even quadriceps) unless the knee center is displaced anterior to the weight bearing line”3; Patients who were skeletally mature before developing a neuromuscular disorder can often benefit from an orthosis that maintains the knee center behind the weight-bearing line. Because of their mature skeletal development, their knees tend to be stable in the frontal/coronal plane and the transverse planes. They can often learn to recruit muscles such as hip extensors or ankle plantar flexors to assist in pulling the knee posteriorly, thus aiding in standing stability.
Patients who developed neuromuscular disorders as children commonly have tri-planar musculoskeletal abnormalities that must be considered in KAFO design to ensure unfailing stability in all environments and may not be able to utilize ground reaction forces as readily. These patients are very challenging to fit and require highly skilled orthotic care to manage their complex deficiencies. “Recommendations about orthotic options are based on four types of information: (1) an understanding of the patient's diagnosis and prognosis; (2) a thorough assessment of gait, muscle function and motor control, range of motion, and alignment of the limb; (3) an understanding of the patient's general medical condition and level of fitness; and (4) discussion of the patient's typical or desired vocational and leisure activities.”4 Once these four issues are well understood, the patient and caregiver can work together to formulate a design/protocol that provides quality of life/stability that might not otherwise be present.
Patients who need orthotic care are often interested in new technology, hoping it can offer them a better quality of life due to improved gait, stability, and independence. However, not everyone can benefit from the latest innovations. The role of stance control orthoses for persons with neuromuscular deficiencies is not fully clear at this time but seems promising. However, many will remain best served by less sophisticated orthoses. The challenge for rehabilitation professionals in the next few years will be to obtain sufficient clinical experience and scientific evidence to determine the optimal KAFO designs to enable people with neuromuscular disorders to achieve the highest level of independence and the greatest quality of life with an orthosis that is safe and comfortable and allows participation in the full range of normal daily activities.
1.Bunch WH, Keagy RD. Principles of Orthotic Treatment
, St. Louis: CV Mosby; 1976.
2.Evans GE, editor. Biomechanical Studies of the Muscular-Skeletal System
, Springfield, IL: Charles C. Thomas; 1961.
3.Fish DJ, Nielson JP. Clinical assessment of human gait. J Prosthet Orthot
4.Lusardi MM, Nielsen CC. Knee-ankle-foot orthoses. In: DiBello TV, ed. Orthotics and Prosthetics in Rehabilitation.
Boston: Butterworth-Heinemann; 2000:191–202.