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Prescribing Functional Braces for Knee Instability

Scott A. Paluska, MD; Douglas B. McKeag, MD, MS

Department Editor: William O. Roberts, MD


Functional knee braces (FKBs) have become a popular adjunct to managing ACL injuries (1). Since their introduction, functional braces have gained wide acceptance for use on ACL-deficient knees and for graft protection during rehabilitation after ACL reconstruction (2).

FKBs (figure 1: not shown) are designed to minimize internal and external tibial rotation and anterior-posterior translation. While manufacturers claim that their braces significantly reduce translation and rotation in ACL-deficient knees, many studies have not supported these assertions (3). In particular, few well-controlled studies have documented clinical benefits under real-life conditions (1,3).

Laboratory studies using surrogate models have shown that most FKBs limit some tibial rotation and anterior knee translation. However, these moderate laboratory effects rapidly disappear during typical use (3,4). Regardless, many active individuals wear the braces and report reduced pain and improved stability, performance, and confidence (5).

FKBs may increase energy expenditure during vigorous activities, but this finding has not been consistently reproducible (5). Improved proprioception has also been reported by researchers and patients, though this has not been objectively confirmed (2). Patients have differing degrees and types of instability, so brace wear and performance may depend largely on the user.

Indications. FKBs are indicated for patients who have mild-to-moderate ACL instability. Some individuals with ACL-deficient knees choose braces instead of reconstructive ligament surgery. Moreover, FKBs are popular as a postoperative support for 6 to 12 months following ACL-reconstruction surgery. FKBs should not be used for unstable or complex knee injuries that require surgical management.

Selecting a Brace

Many different models of functional braces, both custom and off-the-shelf, are currently available (table 1). Their basic designs are similar, and most use either a "hinge-post-shell" or a "hinge-post-strap" design. The former incorporates molded shells of plastic and foam connected by lateral hinges, and the latter relies on bilateral hinged supports attached to thigh and calf straps. FKBs that use "hinge-post-shell" designs seem to provide enhanced control, durability, rigidity, and soft-tissue contact (4).

Table 1. Some Examples of Functional Knee Braces

Brace Name Brace Type Company Phone Number Cost*
DonJoy Defiance CI Hinge-post-strap, custom Smith & Nephew, Vista, CA 1-800-336-6569 $525
DonJoy GoldPoint Hinge-post-strap, presized Smith & Nephew, Vista, CA 1-800-336-6569 $370
Lenox Hill Brace Hinge-post-strap, presized Seattle Orthopedic Group, Poulsbo, WA 1-800-248-6463 $330
Ortho-Tech Performer Hinge-post-shell, custom Orthopedic Technology, Inc, Tracy, CA 1-800-227-1554 $600
Pro 50 KS 5 ACL Brace Hinge-post-strap, presized Pro Orthopedic Devices, Inc, Tucson 1-800-523-5611 $105
Townsend Hinge-post-shell, custom Townsend Design, Bakersfield, CA 1-800-432-3466 $1,200

Design Premier

Townsend Hinge-post-shell, presized Townsend Design, Bakersfield, CA 1-800-432-3466 $500

Design Rebel-X

*Approximate expense to provider—actual purchase price may be higher.

In general, custom FKBs are advantageous for asymmetrically proportioned legs (calves or thighs out of proportion), high-intensity activities, maximal comfort, or aesthetic appeal. Off-the-shelf FKBs are advantageous for patients who have minimal symptoms of instability or fluctuating leg circumferences during a rehabilitation program. Comparison studies between off-the-shelf and custom functional braces have found few significant differences.

FKBs are available at sports medicine centers, medical supply stores, or manufacturers. Consumer prices often vary substantially among suppliers, so one may wish to contact several sources before buying an FKB.

Fitting an FKB

Prefabricated off-the-shelf FKBs are sized by measuring the patient's thigh circumference 6 in. above the midpatella and choosing the corresponding brace size. Specific measuring and ordering instructions are provided by brace manufacturers.

Custom braces require the measurement of thigh, knee, and calf dimensions using a company-specific instrument. The measurements are then sent to the manufacturer and used to create a brace that conforms closely to the affected leg.

The following guidelines may be helpful when fitting a functional brace:

  • Select the longest brace that fits comfortably but does not impair range of motion. Many manufacturers offer braces in two or three different lengths to allow for different inseam measurements.
  • Consider setting an extension stop at 10° to 20° of flexion to limit hyperextension.
  • Choose more durable brace materials or a brace cover for active patients to limit brace deterioration.
  • Properly position hinges and condylar pads over the femoral condyles superior to the joint line.
  • Securely fasten the brace and advise the patient to regularly adjust its position during prolonged activities.
  • Regularly inspect the brace to improve brace performance and minimize injuries to others caused by protuding broken metal or plastic.

Some ultimately may wish to consider having an FKB sized by an orthotist or other trained individual to ensure maximal comfort and function.

Satisfaction and Limitations

In general, patients report satisfaction with functional braces and note subjective benefits that exceed documented effects. Therefore, physicians must warn patients not to harbor a false sense of security.

Functional knee braces appear to be safe for use in many athletic settings, but they should be used only in conjunction with aerobic conditioning, muscle rehabilitation, and technique refinement. Patients must also be willing to limit activities as necessary, but FKBs can help athletes return to previous activity levels.


  1. Kramer JF, Dubowitz T, Fowler P, et al: Functional knee braces and dynamic performance: a review. Clin J Sports Med 1997;7(1):32-39
  2. Liu SH, Mirzayan R: Current review: functional knee bracing. Clin Orthop 1995;317(Aug):273-281
  3. Beynnon BD, Pope MH, Wertheimer CM, et al: The effect of functional knee-braces on strain on the anterior cruciate ligament in vivo. J Bone Joint Surg (Am) 1992;74(9): 122021-1312
  4. Liu SH, Lunsford T, Gude S, et al: Comparison of functional knee braces for control of anterior tibial displacement. Clin Orthop 1994;303(Jun):203-210
  5. Cawley PW, France EP, Paulos LE: The current state of functional knee bracing research: a review of the literature. Am J Sports Med 1991;19(3):226-233

Dr Paluska is a family physician in private practice in Cary, North Carolina. Dr McKeag is professor and chair of family medicine at Indiana University School of Medicine, Indianapolis. Dr Roberts is a family physician at MinnHealth SportsCare in White Bear Lake, Minnesota.