New Orthotic Method For Treatment Of Angular Deformity Of The Knee In Children

Presenter: Britt-Mary Guerre-Aguilar, CPO
Authors: Britt-Mary Guerre-Aguilar, CPO, Michael Davidson, CPO, William Bunnell, MD
Loma Linda University
Department of Orthopaedic Surgery, Department of Orthotics and Prosthetics
Loma Linda, California

Angular deformity of the knee is a common problem in the pediatric population. While some causes are self-limited, others progress to severe and debilitating deformity. The purpose of this paper is to review currently available methods of non-operative treatment and to propose a new orthotic device for treatment of these conditions.

Angular alignment of the knee evolves through a number of stages in the normal growing child. All knees are in varus at birth although not always obvious since the child does not stand. Weight-bearing changes the knee alignment to valgus very quickly in most children, but always by age two in normal children. Many children "overcompensate" in this conversion and appear to have excessive valgus in the early juvenile years. This too usually normalizes by age ten. Normal adult alignment is 7º valgus allowing knees and ankles to touch each other when standing even though the hip joints are approximately 12 inches apart.

Angular deformity of the knee may be physiologic, i.e. normal for the stage of development. Thus, a child under age two may normally appear bow-legged and a child between ages two and six may appear excessively knock-kneed. Persistence of this physiologic alignment outside the given age parameters may signal pathology which may require treatment.

In addition to normal developmental variations, a number of pathologic conditions must be recognized which lead to deformity. One of the most common disorders causing pathologic bow leg is Blount's disease, a condition recognized after age two in which there is varus deformity, lateral thrust of the knee in stance, and significant internal tibial torsion. X-rays demonstrate an abnormality of the proximal medial tibial growth plate. Failure to treat nonsurgically at an early age (between age two and three) often results in the need for corrective tibial osteotomy.

A number of other pathologic conditions cause angular deformity of the knee. Metabolic bone disease such as rickets (a common outcome of chronic renal disease), skeletal dysplasias (such as achondroplasia), trauma and infections are common causes. Advanced stages of deformity require surgical correction and are not the subject of this paper. The goal of orthotic treatment is to prevent progression of a deformity to a stage requiring surgical treatment.

Many valid concepts of orthotic treatment were developed early on although the devices appear very primitive to us. The major biomechanical principle is the application of three points of force against the deformity and many clever methods of application have been used. Examples include those from Kolbe (1), Bradford (2), Beely (3), Hoffa (4) and Becker (5).

Netter illustrates that the brace in most common use today is a Blount's Brace and an Aframe variation (6). Goldberg, Hsu and Supan et al describe a KAFO frequently used for up to 23 hours a day (7, 8)

Image 1

They are all theoretically capable of applying the requisite valgus force at the knee. In practicality, it is nearly impossible to maintain an appropriate amount of force with these braces due to short fat legs, constant growth and incessant activity. If both legs are immobilized and linked as in a Blount's Brace, the children do not tolerate the brace well and sleep is frequently interrupted.

Our design requirements included: ability for the Orthotist to apply an appropriate amount of valgus or varus correction, adjustability for the parents, ease of donning and doffing and comfort for the child.

The primary component of the brace we designed was a one-way locking hinge called the Monodos hinge1 (Image 1). The internal mechanism is a one-way clutch allowing free rotation in one direction, no motion in the opposite direction and an infinite number of locking positions. It is placed anterior to the knee to allow force and motion in the coronal plane rather than in the sagittal plane. This valgus force at the knee prevents flexion and extension. In addition to the Monodos hinge, we included a range of motion joint, posteriorly aligned with the anterior joint. Locking screws on the posterior joint allowed a limitation setting to avoid over correction.

Image 2

The secondary feature of the KAFO was the modification of the cast to facilitate placement of the anterior and posterior hinges to apply the requisite forces. In order to attach the upright distally to the anterior shell, we custom molded a thermoplastic tibial cuff and from the medial aspect, encompassed the foot with a long foot plate. For the proximal upright attachment, the thermoplastic femoral cuff was placed medially with an anterior extension. Both cuffs were made of plastic Modified Polyethylene2, lined with Volara3 foam to increase comfort and included Velcro4 strapping (Image 2). A sole was added to the plantar aspect of the AFO to allow minimal ambulating if needed at night time.

It should be noted at this point that the construction of the Monodos hinge allows it to provide either varus or valgus force on either right or left side depending on the orientation of the hinge on the brace. Improper orientation of the hinge will cause the wrong force to be applied!

We have treated 25 children with angular deformity of the knee. The etiology of the deformities included Blount's disease, physiologic valgus, and metabolic bone disease. Indications for use included failure to resolve physiologic deformity, progressive deformity, failure of a simpler brace (eg. Dennis-Brown Bar5).

Since the knee cannot flex, the brace is usually worn only at night although some daytime use can be achieved in younger children. The Monodos hinge can be set to allow free motion in either direction making donning simpler. Once applied, a gentle correcting force is applied to the brace by the parent to tighten the brace against the deformity. Caution needs to be used to avoid over-tightening.

We have obtained X-rays of the deformity in the standing position both prior to and after application of the brace demonstrating the ability of the brace to effect the desired realignment.

We have done clinical follow-ups on several children who have completed treatment, resulting in satisfactory realignment of the knee. Once this has been accomplished, the brace may be discontinued without relapse except in the case of metabolic bone disease where continued soft bone may allow either a relapse or over-correction into the opposite deformity.

We have encountered some clinical problems. Care must be taken to have the hinges directly anterior and posterior so that a pure varus or valgus force is applied. Location of the hinge should be centered over the knee joint rather than attempting to locate it over the point of maximum deformity. The plastic components of the brace will fit against the leg in different ways depending on the amount of correction achieved and may cause discomfort at the point of contact. This is easily accommodated by minor modifications.

A major advantage of the Monodos hinge is its versatility. The same hinge can be oriented to produce either varus or valgus, flexion or extension, and can do so on either right or left upper or lower extremity. This greatly reduces the need to maintain a large inventory. It is manufactured in two sizes, the smaller one being appropriate for nearly all pediatric needs. Two hinges can be combined on the same brace for complex needs such as one at the knee to increase extension and one at the ankle to increase dorsiflexion. We have used one on the bottom of an AFO to increase heel varus.

With the introduction of the new Monodos hinge and the subsequent modifications on a KAFO, this application has been found to be beneficial in the treatment of angular deformity of the knee in children. This new approach has been well tolerated by the patient. It is straightforward in its fabrication, and effective in clinical practice.

1 Monodos hinge from Becker Orthopedic, Troy, MI 48083-4576I.
2 Modified Polyethylene Plastic 3/16.inch thickness from American Plastics, TX, 76011.
3 Volara 1/4 inch thickness from Atlas International Orthopedic supplies and equipment. Rancho Cordova, CA, 95742.
4 Velcro from Cascade Orthopedic Supply, Chico, CA, 95973.
5 Dennis Browne Bar from Fillauer, Chattanooga, TN 37406

References

  1. DW Kolbe Apparatus for Deformities of the Lower Extremities, 6th edition, 1879.

  2. EH Bradford, RW Lovett. Orthopedic Surgery, 5th edition. 1915.

  3. F Beely, Trans American Orthopedic Association. 6:157, 1893.

  4. A. Hoffa, The first treatment for bone fractures and dislocations. From the series on" First Medical Treatment" occasioned by the Central Committee for Medical Education in Prussia (Winter Semester 1904-05).

  5. David L. Becker, MD, Blount Orthopaedic Clinic at, Milwaukee, WI 53202.

  6. Frank H. Netter, M.D., The Ciba Collection of Medical Illustrations, Volume 8, Musculoskeletal System, Part II, Developmental Disorders, Tumors, Rheumatic Diseases and Joint Replacement, 1990, Section I Plate 78: 82.

  7. B. Goldberg, M.D. John D. Hsu, M.D., Atlas of Orthoses and Assistive Devices, 3rd edition, 1997, P.495.

  8. T. Supan CPO "Orthotic Correction of Blount's Disease", Clinical Orthotics and Prosthetics. 9:3-6, 1985.