K-W Limited-Motion Brace for Knee Instability

RUSSELL F. WARREN, MD*, ANDHERBERT E. KRAMER, BS, CPO**New York, New York


Knee instability continues to be one of the most common problems affecting adolescents and adults, particularly those engaged in athletics. Chronic anterior cruciate ligament insufficiency can result in knee collapse in deceleration or highload activities. The affected leg is weighted and the knee approaches extension combined with internal tibial rotation.

Many knee orthoses designed to prevent collapse have long been on the market. Most offer insufficient support. Other appliances are expensive and require time-consuming custom casting and fabrication. Based on experience with the Public School Athletic League, we developed the K-W brace which consists of a laced hinge knee support with specially modified polycentric hinges (Fig. 1 , Fig. 2 , Fig. 3 ). The joints permit one to set knee excursion and limit knee extension. Restricting extension by means of an extension stop decreases the tendency of the tibia to rotate as the knee approaches extension. An internal or external rotation-control strap may be added. The strap controls instability by providing kinesthetic feedback that allows the wearer to avoid rotation, thus preventing or modifying the pivot shift.

Clinical experience with the K-W brace is substantial. It has been fitted to more than 2000 patients during the past four years, including high school, college and professional athletes; children with congenital knee mediolateral instability; and patients with arthritis and genu recurvatum secondary to poliomyelitis.

The advantages of the K-W brace include:

  1. Maximum support of the knee
  2. Excellent patient tolerance
  3. Good control of edema
  4. Easy adjustment to accommodate changes in knee function
  5. Incorporation of prefabricated components and materials which are readily available
  6. Rapid assembly and fitting to permit earlier patient treatment
  7. Few repairs needed.

Although experience has been overwhelmingly successful, one patient rejected the K-W brace because she felt it was too snug and she could not become accustomed to it. Elastic components sometimes require replacement after a year of hard use.

The K-W brace is indicated for preoperative, postoperative and nonoperative management of knee instability. Patients with acute injury to the anterior (ACL) or posterior cruciate or medial or lateral collateral ligaments have been fitted. In injury confined to the collateral ligaments, we prefer nonoperative treatment. In grades Ila or b with mild to moderate instability, bracing is used either in the first week or after a period of two weeks of immobilization, depending on the degree of instability. In grade III medial collateral injury after four weeks of immobilization, the brace is worn for two months during the rehabilitation program and in the early stages after returning to sports activity.

In acute ACL injury, if a nonoperative course has been selected, the knee is immobilized for four weeks. Subsequently, the brace is applied with the stops set at -10 deg. extension and a rotation strap is utilized, exerting an external rotation force on the lower leg. As the activity level increases after three months, the brace is used with an exercise program emphasizing the hamstrings rather than the quadriceps.

Patients who have undergone surgery for ACL injury, with or without medial collateral damage, are casted in 30 deg. flexion for six weeks followed by bracing. At the start of orthosis use, the stops are set to allow 30 to 60 deg. flexion, supplemented by an external rotation-control strap. The orthosis is removed four times a day for flexion exercises, avoiding full extension. After six weeks the stops are reset at -10 deg. extension, and the rotation strap retained. The orthosis is worn until nine months after reconstruction. Thereafter it is needed only for running activities which are gradually increased. All sports are resumed at one year. Many patients report their ability to participate in activities that were not possible prior to bracing. The main objective of the K-W brace is to prevent sudden hyper extension or flexion from overstressing the repair. Use of the orthosis plus exercise reduces the frequency and severity of knee-collapsing episodes. Most individuals discard the orthosis within two years.

In patients who present chronic ACL insufficiency, exercise and bracing are the most frequent initial approaches. The patient will perform hamstring as well as quadriceps exercises and wear the orthosis for all sports activities. The orthotic knee joints are set at -10 deg. extension, and a rotation strap is attached. For those individuals in whom giving way persists and ACL reconstruction is performed, the K-W brace is an important part of the postoperative program.

Fabrication Procedure

A laced hinged knee support, such as OTC Model 552*** 12 1/2 or 14 1/2in. long, is modified to accommodate the additional components in the K-W brace.

Remove the single-axis free-motion hinges provided with the support and replace them with a pair of polycentric limited-motion knee joints (United States Manufacturing Co. #1A29-LM)****. The excursion which is provided is 160-120 deg. Modify the joints to increase their range by filing the open track inside the joints. Remove the slotted screws that limit motion and substitute a #30 stainless steel rivet to provide unrestricted flexion with a 15-20-deg. extension stop. The excursion depends on the diameter of the rivet at the point of extension contact of the joint.

Cut the uprights of the polycentric hinges to the same length as the hinges provided with the knee support. For the 12 1/2 in. support, fabricate a 7.5 cm (3 in.) wide thigh cuff and a 6.5 cm (2 1/2 in.) wide calf cuff from 4 oz. leather. With the 14 1/2 in. support, two 7.5 cm (3 in.) wide cuffs are used. The length of each cuff should be sufficient to encompass the limb circumference plus 2.5 cm (1 in.). Trim any excess material at the time of fitting. Secure closure is provided by two billets and buckles attached to each cuff.

At the proximal margin of the thigh cuff sew a 5-cm-wide (2 in.) Velcro pile strip between the billets and buckles. Repeat the same procedure on the distal margin of the calf cuff. The Velcro strips will be used for attachment of an elastic rotation-control strap.

Posteriorly, in the center of the exposed leather close to the edge of each cuff insert a 5/8 in. grommet. On either side of the first grommet insert a second and third one. The grommets will provide a point of attachment for the check-lacer strap. To provide a loop for the leather cuffs, cut in a straight line the outer leather sleeve of the pouch that receives the hinges. Insert the cuffs through the loops.

The last component to be fabricated consists of a rubber rotation-control strap. From a sheet of 1 / 16 in. natural rubber, cut a strip 6.5 x 51 cm (2 1/2 x20in). Stitch a 5x6.5 cm (2x2 1/2 in.) piece of Velcro pile backed by cuff leather to each rubber strip to form a point of attachment to the cuff.

Fitting Procedure

Fit the patient with the knee support snugly. Allow a minimum of 2 cm (3/4 in.) opening between the lacer edges to ensure adjustability. The size of the appliance is determined by knee circumference and ranges from 24 cm (9 1/2 in.) for extra small to 52 cm (20 1/2 in.) or more for extra large. Once the correct size is determined, remove the support from the patient's leg. Contour the polycentric joints to the patient's knee. Accurate fit is important for success. In the process of fitting, make certain that the lateral upright does not impinge on the fibular head. The medial upright should fit closely under the medial tibial condyle.

Remove the limited-motion lock screws from the hinges, in order to flex the hinges sufficiently to fit into the pouch of the knee support. Then replace the control screws in the hinges.

Reapply the support and allow the patient to flex the knee slightly to determine whether the black anodized locking screw approximates the path of knee rotation. Lace the support snugly and buckle the leather billets on the cuffs. Have the patient stand and thread the check lacer through the appropriate holes, and buckle the check lacer strap with the knee in the desired attitude.

The entire fitting procedure takes 20 minutes.

The K-W brace accommodates to leg-volume changes readily. The elastic support tends to control edema satisfactorily. For postoperative use, a small support is required to fit the leg which is apt to be atrophied upon removal of the cast. When the atrophy subsides, the support is replaced easily with a larger one.

*Director of Sports Medicine, The Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021

**Director of the Prosthetics and Orthotics Department, The Hospital for Special Surgery

***OTC Professional Appliances, Erie Avenue, Cincinnati, OH 45208

****United States Manufacturing Co., 180 North San Gabriel Boulevard, Post Office Box 5030, Pasadena, CA 91107

Vol. 21, No Spring 1986