Musculoskeletal injuries are commonplace in family practice patients, and many knee joint disorders are common among them. The knee is the largest joint in the body, and its exposed position makes it vulnerable to injury during athletic activities.^1,2 While strength, flexibility and technique have historically been important components of knee injury management, the use of knee braces as preventive and therapeutic adjuncts has gained recent attention.^3,4 The occurrence of knee injuries among high-profile athletes and the aggressive marketing of braces by manufacturers have also contributed to interest in the use of knee braces. As a result, patients may consult their family physicians for accurate, unbiased information about knee braces.

According to the American Academy of Orthopaedic Surgeons,⁵ knee braces fit into several categories: (1) prophylactic—braces intended to prevent or reduce the severity of knee injuries in contact sports; (2) functional—braces designed to provide stability for unstable knees; and (3) rehabilitative—braces designed to allow protected and controlled motion during the rehabilitation of injured knees. A fourth category includes patellofemoral braces, which are designed to improve patellar tracking and relieve anterior knee pain.

Knee braces may minimize knee injuries, but their true effectiveness remains debatable.^1,2,6–9 The current situation is one of confusion among players, coaches, parents and physicians about when knee braces should be used, if at all. This article critically examines prophylactic, functional and patellofemoral knee braces and attempts to assist primary care physicians in selecting the appropriate brace for their active patients.

Prophylactic Knee Braces

After prophylactic knee braces were successfully tested in the National Football League, many athletes wanted access to similar products for use during contact activities. The prophylactic knee brace had been intended to protect the medial collateral ligament (MCL) during a valgus knee stress and to support the cruciate ligaments during a rotational stress.³ Their initial popularity has waned as increasing evidence has questioned their effectiveness, particularly considering the high cost of universal application.

BENEFITS AND LIMITATIONS

Shortly after the introduction of prophylactic braces, several national studies attempted to determine whether they reliably prevent knee injuries. In general, inadequate control groups, subjective biases, variable rules of football, alternative treatment modalities for MCL injuries and inconsistent methods of data collection have limited comparison among most studies of prophylactic knee braces.^10–12 Some researchers have concluded that prophylactic knee braces significantly reduce MCL injuries,^11–13 while others have noted few beneficial effects with regular use.¹⁰

As with many types of athletic braces, reported subjective benefits often exceed objective findings. Brace wearers also have noted significant differences in joint position sense between braced and unbraced legs, but this noted difference has not been consistently confirmed.¹⁰

At best, prophylactic knee braces offer limited resistance to lateral knee impact and provide little meaningful rotational stress protection. At worst, they may generate increased forces that augment associated injuries to the medial knee.^3,10 The benefits and limitations of prophylactic knee braces are summarized in Table 1.

Despite a lack of conclusive research, many players and coaches still consider using prophylactic knee braces. “Skill players” in football (receivers, kickers and running backs) have voiced the concern that prophylactic knee braces limit speed and agility, so they typically avoid routine brace wear. On the other hand, offensive and defensive linemen who are at greatest risk for injury wear prophylactic knee braces more frequently.^11,12 Many players wear prophylactic knee braces in practices but not in games, because of feared performance limitations.

OBTAINING AND FITTING A PROPHYLACTIC KNEE BRACE

Currently, most prophylactic knee braces use unilateral or bilateral bars with hinges. Examples of both types are shown in Figure 1.

In choosing a prophylactic knee brace, physicians should select the longest brace that fits the athlete's leg, as shorter braces provide less MCL protection.³ Trying on several different braces before purchase may be helpful for determining the best fit. Cost is greater for custom braces than for off-the-shelf models; however, custom models provide few additional benefits. In addition, physicians may wish to contact several distributors or suppliers, as prices vary considerably. Details of various braces are given in Table 2. Brace efficacy depends on proper application. Regular tightening of straps, tape or hook-and-pile fasteners helps reduce unwanted brace migration. Also, shaving leg hair and fitting a brace closely to the contours of the leg may improve brace-skin contact and limit unwanted slippage. Correctly placing the hinge(s) relative to the femoral condyles is essential for optimal brace performance with minimal range of motion diminishment. Finally, prophylactic knee braces should be assessed daily by trainers and players for positioning and structural integrity. A broken or damaged prophylactic knee brace should be replaced to ensure maximum functionality.

PROPHYLACTIC BRACE SUMMARY

The American Academy of Orthopaedic Surgeons and the American Academy of Pediatrics

have concluded that prophylactic knee braces lack sufficient evidence of efficacy in reducing the incidence or severity of ligamentous knee injuries.^1,5 A prophylactic knee brace may offer a subjective sense of protection, but it is unable to protect an MCL during a direct lateral impact. Researchers have found that prophylactic brace usage is less important in MCL injury prevention than strength training, conditioning, technique refinement and flexibility.¹⁰ Additional well-designed studies are needed to identify the proper role for prophylactic braces. Currently, the regular use of a prophylactic knee brace at any level of athletic competition is not recommended.

Functional Knee Braces

Functional knee braces gained popularity among football players after Joe Namath used one in his successful comeback after a knee injury.^14,15 The braces are designed to reduce knee instability following injury to the anterior cruciate ligament (ACL) and to decrease additional injuries during athletic activities.^4,5,7 They were initially marketed for use by athletes with knee joint instability who participated in activities that required rapid direction changes.⁸ More recently, functional knee braces have been recommended following reconstructive surgery to reduce strain in an ACL graft.^8,16

BENEFITS AND LIMITATIONS

Few standardized, controlled studies have assessed the clinical efficacy of functional knee braces.^2,7,14 Brace manufacturers cite laboratory tests using cadavers or surrogate leg models that demonstrated limitations of tibial rotation and anteroposterior translation, but these effects rapidly diminished during physiologic stress loads.^{2,4,8,10,16,17} Nonetheless, many persons who use functional knee braces report subjective improvements that exceed objective measurements of knee stability, pain attenuation, performance enhancement and confidence during athletics.^4,7,17

Some researchers found that energy expenditure increased with functional knee brace use during lengthy athletic endeavors, but others reported no adverse performance effects.^3,14,16,17 The regional muscle ischemia and lactic acid build-up observed with brace use may precipitate an increase in muscle fatigue.^4,17 Researchers have also concluded that functional braces provide few proprioceptive effects and may expose athletes to additional risk by imparting a false sense of confidence.^4,8,14,17 Strengths and weaknesses of functional knee braces are outlined in Table 1.

OBTAINING AND FITTING A FUNCTIONAL KNEE BRACE

Functional knee braces are available in custom or presized models. Both categories use a “hinge-post-shell” or a “hinge-post-strap” design, which differ in their thigh and calf enclosures. The former uses a molded shell of plastic and foam, while the latter uses a system of straps around the thigh and calf.³ Some studies have suggested that hinge-post-shell designs provide improved tibial-displacement control, greater rigidity, enhanced durability and better soft tissue contact.^2,14,16 Examples of functional knee braces are shown in Figure 2.

Custom braces require several measurements of the affected leg to be taken to produce a brace that closely conforms to the desired size. Presized braces are sized by measuring the thigh circumference 6 in above the mid-patella and selecting the corresponding brace size. Presized braces may be desirable for use in patients who have changing limb girths during rehabilitation. In contrast, custom functional knee braces are more appropriate for abnormal limb contours and high-level athletes, or for enhanced patient comfort.²

Because studies comparing prefabricated and custom braces have found few significant clinical differences, presized braces may be better when cost or rapid availability is important.^8,17 Costs vary considerably, so several suppliers should be contacted before a brace is purchased. Details of various functional knee braces are given in Table 2.

Accurate sizing will limit brace migration and improve brace effectiveness. Most companies make braces of different lengths, and the longest length the athlete can comfortably wear should be chosen. Setting 10 to 20 degrees of extension limitation may help minimize hyperextension of the knee joint.² Attention to correct hinge placement relative to the femoral condyles improves the overall brace performance and efficacy.⁸ Finally, any exposed metal should be covered to limit brace-induced injuries to others, and more durable materials should be chosen for contact sports.

FUNCTIONAL BRACE SUMMARY

Functional knee braces deserve consideration as a component of the treatment and rehabilitation for ligamentous knee instability. They offer some control of external knee rotation and anteroposterior joint translation.¹⁷ Functional knee braces are also useful adjuncts to muscular rehabilitation for graft protection following ACL reconstruction.⁷ Although brace wearers consistently report subjectively improved knee stability and function, the objective effects of functional knee braces appear to diminish at physiologic stress levels.^4,8

While functional knee braces have not been shown to be harmful, their correct application depends on appropriate rehabilitation and activity modification. Overall, lower extremity muscle strengthening, flexibility improvements and technique refinement are more important than functional bracing in treating ligamentous knee injuries.

Patellofemoral Braces

Anterior knee pain is a common disorder among active persons of all ages. Although definitions vary, the painful anterior knee syndrome is most often thought to originate from a malalignment of the patellofemoral joint.^9,18–20 Patellofemoral braces were introduced to resist lateral displacement of the patella, maintain patellar alignment and, theoretically, decrease knee pain.^3,15 Low cost, ease of use and availability promoted their widespread use. Nevertheless, many efficacy claims made by brace companies are not based on objective evidence.^6,21

BENEFITS AND LIMITATIONS

General agreement exists regarding the utility of conservative therapy in the initial management of anterior knee pain.^9,22 Less clear is the role of bracing as part of the therapeutic regimen. Several studies have demonstrated significant improvements in patellofemoral pain symptoms with the use of patellofemoral knee braces,^18,19,21,23 but others have found them to be ineffective.^6,24

This lack of consensus stems from the absence of well-controlled studies addressing their efficacy. Nonetheless, patients appear to welcome patellofemoral braces and report significant subjective improvements in pain and disability with brace wear.^18,21,23,25 A compilation of reported benefits and limitations of patellofemoral braces is outlined in Table 1.

OBTAINING AND FITTING A PATELLOFEMORAL BRACE

Many different patellofemoral knee braces are currently available, and some examples are shown in Figure 3. They usually incorporate an elastic material such as neoprene and may include straps or buttresses that help to stabilize the patella. For most persons, an off-the-shelf version can be successfully fitted and used without the need for customization.³ A more active person may prefer a patellofemoral brace with a lateral hinge and adjustable patellar buttress. Details of various braces are given in Table 2.

Brace effectiveness depends on correct application and use, and steps for accurately fitting patellofemoral braces are listed in Table 3. Counterbalancing straps are usually secured superiorly but may be placed inferiorally for infrapatellar tendonitis. Buttresses are typically placed laterally, but medial placement may diminish medial patellar subluxation. Shoe orthotics should be considered in addition to a brace for patients with recalcitrant patellofemoral pain syndrome.²²

PATELLOFEMORAL BRACE SUMMARY

Patellofemoral braces are an inexpensive, subjectively helpful component of anterior knee pain therapy. Their mechanism of action remains unclear, but most appear to improve patellar tracking through a medially directed force.²⁵ Changes in regional temperature, neurosensory feedback or circulation may also contribute to their effects.²³ Overall, patellofemoral braces should be used in conjunction with a comprehensive knee rehabilitation program that includes strengthening, flexibility and technique improvements.