Orthoses and the Dynamic Knee: A Basic Overview
Carrie Louise Beets, C.O. *
Frank W. Clippinger, M.D. *
Patricia R. Hazard, C.O. *
David W. Vaughn, C.P.O. *
The knee is one of the most complex joints of the human body, permitting flexion, extension, internal and external rotation. It serves as the core and foundation for a system of levers and pulleys that allow man the ability to ambulate.
The knee is susceptible to a wide variety of externally induced injuries and internal disease processes which substantially affect its ability to perform as designed. Damage to the knee can result in an excessive or limited range of motion, decrease in strength, flexibility, and pain. These effects in many cases are incapacitating.
TYPES OF INJURY
Of the internal disease processes affecting the knee, the one that we as practitioners most often see is arthritis, which, through pain and inflammation, causes self-limiting range of motion and loss of flexibility of the knee. It is generally accepted that the sufferer often benefits from the use of an orthosis.
Various forms of arthritis can afflict the knee:
- Degenerative arthritis is a common malady of the knee. Patients complain of aching, stiffness, and crepitation on movement. Valgus or varus deformities are often seen in accompaniment of degenerative arthritis. Activities involving knee flexion (low chairs, deep knee bends, stairs) generally aggravate symptoms.
- Rheumatoid arthritis is a systemic disease which first involves the soft tissues. Symptoms include swelling, pain, and limited motion. As the disease progresses, flexion deformities usually occur.
- Chondromalacia patellae is a degenerative arthritis of the patellofemoral joint. Patients usually complain of retropatellar aching, crepitation, a sensation of their knees giving way, and pain on weight-bearing during flexion. Chondromalacia patellae is frequently a complication of other knee pathologies such as degenerative arthritis, cruciate or collateral ligament injuries. Treatment is geared towards preventing activities that will aggravate the patient's symptoms.
In the externally induced injury category, ligamentous damage from sports related activities is the most common injury seen by orthotists. The knee joint itself is reinforced with ligaments which restrict the extent to which the knee can move in a particular direction. These restrictions dictate the maximum limits of motion that can be achieved, while maintaining a stable mechanical system. Injury to any of these incorporated ligaments often results in laxity of the ligament. The damaged ligament then permits a greater than normal range of motion to occur within the knee complex; creating unstable, potentially pathophysiologic, and oftentimes painful motion in the dynamic knee.
Trauma to the knee resulting in ligamentous injury rarely produces an isolated injury. A combination of injuries to the soft tissues is typical, and the particular combination affects the type of orthosis that may be used. An understanding of the structural contributions that individual ligaments provide the knee establishes a base from which the orthotist can choose orthotic design components.
Following are descriptions of areas susceptible to traumatic injuries.
- The medial collateral ligament provides the primary medio-lateral stabilization for the knee. It is also the main structure responsible for prevention of excessive anteromedial rotation of the tibia. The medial collateral ligament is commonly injured by a direct blow to the lateral aspect of the knee which creates a valgus stress with resulting sprain. The extent of injury is determined by the degree of force and duration of the blow. Patients complain of localized pain and sometimes of a wobbling sensation.
- The most frequent severe damage to the knee results from anterior cruciate ligament injury. A direct blow is not necessary, as injury may occur when an individual makes a sudden stop or directional change while running. A torn anterior cruciate ligament often requires surgery in order to have a chance of healing, and even then it does not necessarily heal correctly.
This ligament is primarily responsible for preventing excessive anterior placement and excessive internal rotation of the tibia. When damaged, the amount of resulting anterior instability is also affected by the integrity of the secondary ligamentous capsular structures.
- The posterior cruciate ligament restrains the tibia from backward motion and hyperextension of the knee. Injury can occur through dislocation of the knee or a posterior blow to the proximal tibia when the knee is flexed. Though the injury can create instability, patients are usually asymptomatic unless the injury is accompanied by other ligamentous injury.
- The lateral collateral ligament restrains medial angulation of the knee. It is injured less often than the medial collateral ligament due to its intimate reinforcement by the biceps femoris and the fact that varus force injuries are less common than valgus force injuries. If the lateral collateral ligament is injured, the biceps femoris is usually damaged as well and common peroneal nerve damage may also be involved.
- The menisci are two cartilaginous structures located medially and laterally between the femur and tibia. Their function is to provide shock absorption and synovial fluid. The medial meniscus is attached to the medial collateral ligament, while the lateral meniscus is attached to the posterior cruciate ligament. The menisci are susceptible to tearing injury from rotational stress. They can receive isolated damage or injury associated with ligaments. In isolated injuries, small tears, depending on their location, may heal with non-operative procedures and rehabilitation. Tears that do not interfere with joint motion may be amenable to surgical repair, while injuries that interfere with joint motion present an urgent surgical problem which can often be handled arthroscopically. Injury to the menisci in conjunction with other ligamentous injury of the knee is common.
The medical choices of treatment for a debilitated knee are several: external reinforcement, surgical repair, and surgical replacement. As orthotists, we provide the external reinforcement for the ailing knee through the use of orthoses. There are many knee orthosis designs available. The function, goal (therapeutic vs. prophylactic), design criteria, and any special considerations of the individual patient must be evaluated in the selection of the appropriate orthosis. It is imperative that the practitioner be aware of available design concepts and understand their functions and uses. The ultimate responsibility for the appropriate choice of orthosis rests on the orthotist by virtue of his in-depth knowledge of design and his ability to make decisions with regard to design application.
The following basic overview of knee orthosis designs and intended applications is by no means exhaustive. It is meant to be categorical in its orientation and to present a logical approach to the consideration of design and function in the selection and application of knee orthoses.
Function: Minimal knee joint stability; patellar control is an option in open knee designs.
Design: Can be fabricated with jointed side bars for added medio-lateral stability (Fig. 1 ). Various designs of prefabricated elastic orthoses are available. Patellar alignment control can be an added function through the use of control pads affixed to an open knee design (Fig. 2 ). A suprapatellar strap is often incorporated into the design for added suspension. In fairly inactive patients, circulatory constriction can present problems. Adequate suspension on persons with large tapered thighs frequently presents problems.
RECURVATUM CONTROL ORTHOSES
Function: To prevent mild hyperextension and provide moderate medio-lateral control.
Fig. 3, Fig. 4, Fig. 5
Design: Prefabricated of metal, webbing, elastic, and VelcroŽ closures. The TeufelŽ (TKS) design has the advantage of a pivoting posterior band with proximal anterior band and wider side bars.
Function: Antero-posterior and medio-lateral stability, rotary control, post operative protection (adjustable joints) and patellar control is standard on the LermanŽ design.
Design: The LermanŽ design has plastic cuffs with adjustable metal polycentric knee joints, gum rubber straps, and VelcroŽ closures (Fig. 1 and Fig. 2 ). One can alternate the gum rubber strap placement for appropriate rotary control. Elastic webbing is located above and below the patellar control pads. The Lenox HillŽ has heavy metal sidebars with gum rubber closures (Fig. 6 and 7 ). Oblique heavy elastic provides rotary control. Elastic is interfaced with rubber above and below the patella for suspension. The External Cruciate Ligament Orthosis is laminated or has thermoplastic cuffs with polypropylene rods instead of metal joints. Originally designed with laced closures, VelcroŽ is an acceptable alternative in conjunction with thermoplastic cuffs. Heavy elastic oblique straps provide ligamentous support. The TRIO (Tennessee Rotational Instability Orthosis) is fabricated of a SubortholenŽ femoral and tibial cuff, gum rubber closure straps for rotational control and a medial supracondylar wedge for suspension; adjustable joints for post-operative use (Fig. 8 ). All of the above are custom fabricated from a cast of the patient's leg.
The LermanŽ knee orthosis is available commercially prefabricated in small, medium, and large. It is the authors' preference to utilize custom fabricated variety with wider cuffs, thus better distributing forces and affording greater protection through the extended level system.
THERMOPLASTIC KNEE IMMOBILIZATION ORTHOSIS
Function: Restriction of knee joint motion.
Design: Molded thermoplastic bivalved full cylinder or partial cylinder with anterior opening. It has VelcroŽ closures and a medial supracondylar wedge for suspension. If a supracondylar wedge is not suitable for suspension due to edematous or deformed knee, a waist suspension or posterior leaf ankle extension may be utilized.
KNEE ORTHOSIS WITH SUPRAPATELLAR SUSPENSION
Function: Medio-lateral stability, Antero-posterior stability; can be used for limited knee motion.
Design: Molded thermoplastic cuffs, metal or thermoplastic knee joints, VelcroŽ closures and a latex suprapatellar strap for suspension of orthosis (Fig. 9 and 10 ).
Due to the anatomical complexities of the knee and the biomechanical stresses to which it is subjected, it is not surprising that the human knee is frequently injured. By comparison, the percentage of impaired knees that are treated surgically is low. Orthotics practitioners often play a major role in rehabilitating the debilitated knee. Many knee orthoses exist, and new design variations are continually being introduced. A thorough understanding of the biomechanics of individual knee structures and how orthotic techniques, designs, and components allow control over specific motions permits the practitioner to select the design most appropriate for the individual diagnosis of a given patient.
Prefabricated orthoses offer the timely convenience of being "off-the-shelf." They provide an approximate fit for a lot of patients, but they do not truly fit anyone. Custom knee orthoses provide a much more critical anatomical and mechanical alignment union. Prefabricated orthoses are often satisfactory as interim devices; however, custom knee orthoses are indicated, appropriate, and far superior for definitive use. It is the authors' opinion that when possible, a custom knee orthosis is the choice that is most beneficial, which can be provided the patients for their specific condition and requirements.
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