Functions and Effectiveness of Unloader, Patellofemoral, and Knee Sleeve Orthoses: A Review

Abstract

Background

Knee orthoses have been extensively used as a nonsurgical approach to improving knee deficiencies. Currently, arthritic knee conditions remain the leading cause of disability, and this number is expected to increase. As the use of knee orthoses varies widely, so has their effectiveness which is still largely debatable. Here, we present the functions and effectiveness of the three most prominent knee orthotic models dedicated to supporting knee osteoarthritis—unloader, patellofemoral, and knee sleeves.

Purpose/Research Question

Considering the depth and diversity of the many clinical studies and documented laboratory reports published to date, this literature review was created to educate the clinician, patient, and researcher on common knee orthoses used for the management of arthritic knee conditions. In doing so, we discuss their design, biomechanical effects, and clinical efficacy, as well as broader outcomes, limitations, and recommendations for use.

Results/Synthesis

The knee orthoses discussed within the scope of this paper are dedicated to protecting the knee against strenuous compressive loads that may affect the patellofemoral and tibiofemoral joints of the knee. Since the knee has multiple axes of motion and articulating surfaces that experience different loads during functional activities, it can be implied that, to a large extent, knee brace designs can differ drastically. Unloader knee orthoses are designed to decrease tibiofemoral and patellofemoral joint pressures. Patellofemoral knee orthoses are designed to decrease strain on the patellofemoral and quadriceps tendons while stabilizing the patella. Knee sleeves are designed to stabilize movements, reduce pain in joints, and improve proprioception across the knee joint.

Conclusion

Although patients often report benefits from wearing braces, these benefits have not been confirmed by clinicians and scientific investigators. Results from these three orthosis types show that clinical efficacy is still elusive due to the different methodologies used by researchers.

Layman Summary

Knee orthoses also referred to as knee brace are commonly used for support and stability of the knee. Unloader knee braces are designed to relieve and support those suffering from knee osteoarthritis by improving physical impairment and reducing pain. Patellofemoral knee braces aim to help patients manage patellofemoral pain syndrome. Rehabilitative compression sleeves, also known as knee sleeves, are often used to assist patients suffering from knee pain and laxity. Important findings on the three knee braces discussed show discrepancies in results. Their effectiveness and validity are yet to be understood.

Introduction

Arthritic knee conditions remain one of the leading causes of pain and disability [1–3], predisposing the knee to a variety of syndromes and deficiencies. Oftentimes, this poses substantial healthcare expenses relating to surgery, lengthy and costly rehabilitative care, long-term disability, or progression to severe cartilage disease known as osteoarthritis (OA) [4]. Today’s conservative orthopedic management of arthritic knee injuries focuses on pain alleviation, tissue restoration, and injury prevention. The use of knee orthoses as a conservative treatment approach for knee injuries uses mechanical forces to alter lower limb biomechanics, such as three- and four-point bending systems or hinges that support the unloading or stabilization of the knee joint. Consequently, the altered biomechanics within the deranged knee joint reduces the compressive loads on the affected compartment and relieve pain in misaligned knees, which can slow disease progression [5–12]. Knee orthoses improve proprioception for subjects suffering from knee instability and dysfunctions of the lower limb extremities [13–16].

Conservative treatment of knee OA has focused on the use of knee orthoses as an alternative therapeutic measure in treating OA, especially for young adults lesser than 60 years of age who are not good candidates for knee replacement surgery due to the high risk of surgical revision resulting from limited implant survival [10]. However, many controversies surround their effectiveness and the lack of consistent methodologies employed in their experimental study, proving a great deal of heterogeneity. Despite patient support, some authors have reported that there are little to no beneficial effects reported regarding their use under physiological conditions [6]. Even so, clinicians must still make evidence-based decisions about their use for patients. Hence, brace recommendations require an understanding of both injury etiology and prognosis, as well as knowledge of design functions, effectiveness, and limitations of the orthosis. The goal of this article was to present peer-reviewed clinical studies and documented laboratory reports of the three most frequently used knee brace types: unloader, patellofemoral, and knee sleeves. Here, we discuss their design, biomechanical effects, and clinical efficacy, as well as broader outcomes, limitations, and recommendations for use.

Design and Biomechanics of Orthotic Joints

Knee orthoses are assistive devices that aim to meet the biomechanical needs of individuals with physical disabilities of the knee or lower limb. Except for knee sleeves, current knee orthoses are designed to resist aberrant joint motions, supplement normal knee mechanical stability, and restore mechanical stability in an injured or rehabilitating knee [6]. Each brace type is designed to perform a predetermined function; of the three design features considered, we found that selection is determined by the brace fit, hinge design, and the mechanical properties of the brace. Knee orthoses elicit specific effects that vary in function, cost, duration of use, and the mechanism of support. Generally, braces come in two forms: off-the-shelf braces, commonly manufactured in four to five preset standard sizes, and custom braces that are individually fitted to the patient’s knee anatomy.

Generally, the knee joint undergoes varying degrees of displacement, rotation, and abduction-adduction that accompany flexion-extension motions [17, 18]. Knee motion may be visualized as the rotation of the femur about a series of three-dimensional instantaneous axes rather than just a simple fixed axis [19, 20]. As a result, the motion exhibited by the knee is much more complex than flexion about a simple hinge or fixed axis of rotation [21]. Thus, knee motion with proper joint stability is a result of complex interactions of the ligamentous and capsular structures surrounding the joint, mainly consisting of opposing articular surfaces, and musculotendinous activity across the joint [20]. For most activities being performed, the path or locus of the axis varies, influencing the amount of inherent laxity in an individual’s knee. Moreover, brace competence is significantly undermined by challenges in obtaining proper congruence between the brace and bony surfaces, the evolving morphology of soft tissue, and obtaining an appropriate balance between the rigidity and flexibility of the brace [22].

In this article, we classify unloader, patellofemoral, and knee sleeves as the three most often used orthoses in treating knee OA and, in some cases, assist in resisting soft tissue strain. Except for knee sleeves, most rigid/static knee braces exert control on skeletal positioning by applying mechanical leverage using uprights, hinges, and calf and thigh cuffs and straps [6]. It has been suggested that whenever possible, the leverage application point should provide purchase directly upon sub-cutaneous bone, such as the tibial tuberosity or the medial and lateral condyles [4]. Consideration must also be made for brace durability and brace comfort with regards to the mechanical compatibility with the patient’s knee, as these factors impact the practice of donning and doffing the brace [21, 23].

Unloader Knee Braces

Unloader knee braces are designed to provide patients with knee osteoarthritis (KOA) relief through unicompartmental support. Unloader knee orthoses aim to reduce compressive loads in the medial or lateral tibiofemoral and patellofemoral compartments [10, 24, 25]. Studies have shown that patients with knee OA demonstrate increased pain, decreased physical function, and impaired joint proprioception [26–28]. Therefore, orthoses designed for the management of knee OA are made to reduce excessive loading of the damaged compartment, decrease pain, reduce stiffness, improve physical function, and impede disease progression [29–31]. Pain relief of the tibiofemoral joint is thought to be mediated by the unicompartmental distraction of the involved compartment through external varus- or valgus-mediated forces applied to the knee joint [32]. As a result, tibiofemoral joint realignment is established, and the load is shifted off the degenerative compartment with this brace type. This effect redistributes loads across the knees of patients with lower limb malalignments and/or KOA.

Unloader knee braces are composed of external stems, hinges, and straps that decrease loads on the tibiofemoral and patellofemoral joints [26, 33]. These knee braces usually require a prescription and are specifically designed to treat OA [34]. This type of brace facilitates pain management as well as injury prevention and improves knee proprioception where deficient [26]. Extensive analyses suggest that valgus knee unloader braces, which are designed to reduce medial contact forces about the knee, improve quality of life, knee proprioception, quadriceps strength, and knee gait symmetry while decreasing pressure on the medial tibiofemoral compartment. These braces have demonstrated reductions in net external knee adduction moment (KAM) and pain reports with noted effects on gait mechanics [35–38]. Results concerning patient compliance remain sparse; however, some studies support the use of valgus knee braces as a treatment for patients with medial compartment knee OA. Notably, unloader knee braces appear to have a greater effect when worn for extended periods [32, 39]. However, short- and mid-term follow-up indicates that valgus knee bracing tends to decrease pain and disability in the medial tibiofemoral compartment of the knee in patients with knee OA [26, 40].

A major shortcoming of unicompartmental unloader knee braces is their limited effectiveness in addressing multicompartmental KOA. Knee OA often presents itself as a multicompartmental disease involving the patellofemoral as well as tibiofemoral joints [41]. Thus, the majority of patients who experience multicompartmental KOA disease will only achieve sub-optimal relief from the use of unicompartmental unloader knee braces. To address this gap in care, a novel bracing mechanism was developed using the tri-compartmental distraction of the tibiofemoral and patellofemoral joints. Through the brace’s unloading mechanism, researchers reported reduced joint contact forces about the patellofemoral and tibiofemoral joints [22, 38–40].

Mechanism of Action

Unloader knee braces have a unique design that delivers force to the knee to maintain proper alignment. These orthoses aim to decrease compressive loads transmitted to the joint surfaces, either in the medial or lateral tibiofemoral compartment, depending on the valgus or varus position of the device [26, 33, 42]. Valgus bracing eases medial compartment compressive loads through the application of an external valgus force on the knee while eliminating subsequent pain and improving knee function in knee OA patients [10]. In theory, valgus knee unloader braces correct the varus alignment of the knee, by applying an external abduction moment that counteracts the adduction moment at the joint, thereby reducing medial compartment loads [4]. It uses a three-point bending system with preset brace hinge components [40, 43, 44].

Medial compartment unloading normally occurs through forces laterally applied at the knee and mid-thigh and midtibia medially. The hinge attachments at the lower and upper positions of the leg account for 2 points of leverage, a diagonal strap transverse over the knee accounting for the third point of leverage. The medially directed force is applied at the lateral side of the knee joint; this creates an opposing reaction force through the straps anchored to the thigh and shank of the leg. These points of leverage result in an abduction moment that forces the knee into valgus alignment [45]. This effect reduces the mediolateral knee loading ratio and KAM during weight-bearing by 9–30% and 8% respectively [13, 46].

This type of orthotic reduces the knee adduction angle by decreasing the distance between the center of gravity and the axis of rotation of the knee joint, thus decreasing the lever arm of the ground reaction force vector [13, 40, 46, 47]. An example of this brace is illustrated in Fig. 1. Studies by Pagani et al. and Pollo et al. demonstrated that adjusting valgus angulation from 4 to 8° had a significant effect on reducing the medial compartment load of the knee [10, 37, 46]. Furthermore, in the management of concomitant patellofemoral OA symptoms, Budarick et al. [25] reported that a multicompartmental unloader knee brace is capable of simultaneously reducing the patellofemoral and tibiofemoral joint contact forces during flexed-knee weight-bearing activity when joint forces are known to be highest [25, 48–50]. This multicompartmental effect is accomplished by a spring-loaded hinge mechanism that assists knee extension during knee flexion and weight-bearing activities [25].

Fig. 1.

OA unloader knee brace with front and back plug-in stops and angle adjustment blocks to help control knee ROM, neoprene anti-slip lining, and built-in hex key for varus and valgus alignment adjustment. OA unloader knee brace for medial or lateral support

Clinical Efficacy

Unloader knee orthoses used in valgus corrective bracing have shown great potential in improving the isokinetic strength of the quadriceps, as well as vertical propulsive force and gait symmetry, yet no improvements in gait velocity [13, 51]. On the contrary, Toriyama et al. alleged that patients with unloader knee braces displayed higher walking speed and pace than those without bracing, which further highlights their inconsistencies [33]. Further analyses suggested that valgus braces cause functional limitations, such as reduced knee flexion during swing phase gait mechanics [13]. This restriction, possibly secondary to the bulkiness of single-hinge designs, can result in reduced foot clearance and shorter stride length. Furthermore, in consideration of the lower kinetic chain, the authors contended that relieving the compressive loads on the medial compartment of the knee joint may contribute to lower back pain and hip joint OA [33]. Recent analyses suggest that the effectiveness of unloader knee braces on pain and physical function is limited in patients with knee OA [11].

The psychological effects provided by brace hinge impact knee stability, suggesting that knee confidence enhances stability in people with knee OA [13, 52]. Similar effects have been reported in studies involving ankle taping/bracing while executing a dynamic balance task [53, 54]. It is important to note that poor confidence and knee instability are commonly associated with quadriceps weakness and altered neuromuscular activation patterns in non-traumatic knee OA subjects [52, 55, 56]. These pieces of evidence suggest that a knee brace can enhance quadriceps muscle performance by modifying proprioceptive feedback [28, 55]. Other beneficial effects of an unloader knee brace on pain and confidence may be a result of biomechanical modifications that can significantly diminish the KAM [13, 30, 57].

Matsuno et al. [40] report that subjects’ who demonstrated moderate-to-severe varus deformities showed improved clinical efficacy with unloader brace use. Some reports suggest that the knee-function score for walking improved significantly with an increase in the strength of the quadriceps muscle [38, 58]. These pieces of evidence show that unloader knee braces can significantly improve physical functions, valgus moment, and self-confidence. Dessery et al. [5] compared three different unloader knee braces and concluded that there were significant improvements in comfort, pain alleviation, kinematics, and kinetics while walking with valgus unloader ACL-brace types. Hence, the use of a valgus unloader knee brace holds promise for subjects with medial compartment OA. This can potentially prolong or prevent the need for surgical intervention. Moreso, a retrospective analysis study exploring the clinical benefits associated with the use of a tri-compartment offloader (TCO) (Levitation^™, Spring Loaded Technology Inc., Halifax, NS) brace in patients with heterogeneous symptoms of KOA, found that participants experienced statistically significant improvements in pain and function after brace use. Findings from this study demonstrated significant improvements in lower extremity function scores (LEFS), decreased VAS pain scores, increased reported physical activity levels, and decreased reported pain medication [48]. A summary of relevant clinical and documented experimental studies is presented in Table 1.

Table 1.

Summary of outcomes of unloader knee brace used in clinical and documented experimental studies

Author, year	Sample	Sample size	Study design	Age, mean SD (years)	Study duration	Outcome measures	Results
Budarick et al., 2020 [48]	Tri-compartmental offloader brace Subjects with multicompartmental knee OA	40	Retrospective analysis	59.4 ± 10.2	3–5 months, 4 days/week	Pain scores, lower extremity function, physical activity levels, medication use, use of other therapies	Statistically significant reduction in knee pain Statistical improvement in participant’s physical function, increased physical activity levels Significantly decreased weekly frequency of medication use Decreased reported use of other therapies across all categories
Thoumie et al., 2018 [118]	Unloader knee brace Medial knee OA	Male (23) Female (44)	Randomized clinical trial	65 ± 9.6	6 weeks	VAS Lequesne index score	Decreased pain Excellent safety and observance Better improvement in Lequesne index score
Lee et al., 2017 [39]	Unloader knee brace	Male (26) Female (37)	Prospective Study	50.9 ± 9.7	8 years	EQ-5D QALYs Cost	A mean increase in EQ-5D with an average duration of 26.1 months Improved QALYs Unloader knee brace is a cost-effective treatment option for 4 months or more
Hart et al., 2016 [32]	Unloader knee brace Subjects with knee OA after ACL reconstruction	Immediate: Male (6) Female (12) 4-week effects (11) Male (6) Female (5)	2 within-subject randomized studies	Immediate Female: 42 ± 12 4 weeks Female: 37 ±7	4 weeks	VAS	Unloader braces produced immediate improvements in knee confidence during hop for distance and knee pain during step-down After 4 weeks, bracing improved knee confidence, perceived task difficulty, and stability during hop for distance, knee pain, perceived task difficulty, confidence, and stability during step-down
Dessery et al., 2014 [5]	Unloader knee brace Functional knee brace Medial knee OA	Male (14) Female (10)	Cross-over study (valgus brace (V3P), unloader brace with valgus+ER functions (VER), functional knee brace)	57.2 (8.6)	3 months	VAS WOMAC Kinematics & kinetics of lower limbs during gait	Knee pain was reduced with all 3 braces The VER and ACL braces showed a significant reduction in peak KAM during terminal stance but not for the V3P brace Reduced knee adduction, lower ankle, and knee external rotation were observed with V3P brace but not with the VER brace
Hart et al., 2013 [55]	Unloader knee brace (varus knee brace) Lateral tibiofemoral joint OA and valgus malalignment after ACL reconstruction	1	Case study	48	Immediate	VAS Quantitative Gait Analysis Knee Kinematics Net Joint Moment	Improved pain (3%), task difficulty (41%), stability (46%), and confidence (49%) when performing a step-down task with braces Varus brace resulted in immediate reductions in knee abduction angle (24%), internal rotation angle (56%), and increased knee adduction moment (18%)
Toriyama et al., 2011 [33]	Unloader knee brace Medial compartment KOA	Male (12) Female (2)	Biomechanics study Non-randomized	68.43 (7.83)	Immediate	Kinematic gait data	Participants with bracing showed a significantly higher walking speed and cadence than those without bracing
Ramsey et al., 2007 [56]	Unloader knee brace Genu varum+medial compartment OA	16	Biomechanical study Cross-over study (no brace/brace)	54.9 ± 8.8	2-time points	Kinematic data GRF data EMG data Self-reprted Questionnaires: KOOS	Knee function and stability scored best with the brace in the neutral setting compared with the valgus setting Co-contraction of vastus lateralis-lateral and vastus medialis-medial hamstrings were significantly reduced from baseline in both neutral and valgus conditions and with the valgus setting respectively
Richards et al., 2005 [13]	Unloader knee brace Unilateral OA of the medial compartment	Male (7) Female (5)	Cross-over, RCT study (no brace/non-valgus bracing/valgus bracing)	60.2 (50 to 75)	6 months	Knee kinematics GRF VAS HHS activity and functional questionnaires	Valgus bracing demonstrated significantly greater loading forces and propulsive vertical forces Non-valgus bracing showed improvement in vertical and posterior loading but not to the same extent Valgus bracing demonstrated a significant improvement in pain and function scores
Draper et al., 2000 [51]	Valgus knee brace Medial compartment knee OA	Male (18) Female (12)	Clinical trial	56.2 (35–70)	3 months	VAS Modified HSS knee score	Symmetry indices of stance and swing phase of gait showed consistent and immediate improvement at 0 and 3 months Significant improvement at 3 months in the mean HHS knee score

HSS hospital for special surgery, VAS visual analog scale of pain, GRF ground reaction force, WOMAC Western Ontario and McMaster University Osteoarthritis Index, KOOS knee outcome survey, KOA knee osteoarthritis, EQ-5D EuroQol five dimensions, QALYs quality-adjusted years

Limitations

Although there has been significant evidence supporting the clinical efficacy of unloader knee brace use, they do have some limitations. Current designs create discomfort for patients after prolonged use, and other reported side effects include thrombophlebitis of the lower limbs [24]. Also, most unloader knee braces are limited to applying distraction to one compartment of the joint, while research demonstrates an increased prevalence of multicompartment knee OA [37].

Patellofemoral Knee Braces

Patellofemoral knee braces are designed to address patellofemoral pain syndrome (PFPS). PFPS is a broad term used to describe pain in the front of the knee and around the patella or kneecap due to inflamed articular cartilage located between the posterior patella and femoral trochlea [59–61]. Other terms used to describe patellofemoral pain syndrome include chondromalacia patella, anterior knee pain syndrome, and runner’s or jumper’s knee [59, 62]. Patellofemoral pain (PFP) is considered one of the most common forms of knee pain, with a prevalence between 15 and 45% [59, 61]. Symptoms include reports of dull, aching pain in the front of the knee which may progress in intensity and frequency with functional activities, such as climbing stairs, kneeling, and squatting. PFPS may be caused by physical activities or adverse strains that cause repeated stress to the knee [63]. PFPS may also be caused by a sudden change in physical activity (i.e., increasing intensity and frequency of exercise activity).

PFPS is typically managed conservatively with physical therapy; rest, ice, compression, and elevation (RICE); taping; non-steroidal anti-inflammatory drugs (NSAIDs); and orthotics. Surgical treatments typically include debridement and lateral release of the lateral retinaculum tendon [63]. One of the primary indications for a patellofemoral knee brace is to address abnormal tracking of the kneecap in the trochlear groove, which is believed to also cause PFPS. In PFPS, the patella is believed to be shifted toward one side of the trochlear groove as the knee bends. This aberrant motion causes increased pressure between patellar and trochlear contact surfaces, resulting in soft tissue irritation [62]. Poor patellar tracking may be caused by malalignment of the legs between the hips and ankles or muscular weakness or imbalances, particularly of the quadriceps muscles which act to stabilize the knee [62].

Knee braces are most used to treat PFPS due to their availability and multitude of designs that provide support for varying conditions. For example, the DonJoy neoprene sleeve Adjustable Patella Donut Brace provides full-circumference support for patellar chondromalacia, patellar tracking, and patellar tendonitis [60]. An adjustable buttress composed of rubber offers proximal, distal, medial, and lateral stability of the kneecap. Another model of the patellofemoral brace is the Tru-Pull Advanced System Brace, designed to relieve pain caused by patellofemoral dysfunction, lateral malalignment, and patellar tendonitis. This brace has an elastic strap that actively pulls the patella when the knee extends, and its independent anchors prevent it from rotating [60]. Other models of patellofemoral (PF) knee braces include designs that function to stabilize patellar frontal plane motion while enabling normal flexion and extension motion of the knee with the use of padded buttresses, adjustable thighs, and frontal straps.

Mechanism of Action

Excessive patellofemoral joint stress appears to be the cause of PF pain [64]. The joint stress can be caused by abnormal anatomy or alignment, abnormal patellar tracking, lower kinetic chain factors, and general overuse [65]. The PFP knee brace is designed to protect against abnormal patellar joint stress by applying a medially directed force to the patella that resists lateral displacement during patellar tracking as the knee flexes and extends, thus preventing pain and dysfunction [66–68]. It is important to note that brace effectiveness depends on proper fit and design according to its use case. As previously defined, PFPS is believed to be caused by inflammation of the articular cartilage between the posterior patella and the femoral trochlea. The mechanisms of action of these braces may slow the progression of PF OA through protection from non-physiologic loads on patellar and trochlear articular cartilage during functional mobility [69].

Through the alteration of patellar position, patellar braces have been found to increase the contact area between the patella and the femoral trochlea during patellar tracking, thus reducing stress forces on the patella [70]. Using MR imaging, the use of patellar realignment braces demonstrated significantly reduced patella height ratios, patella tilt angles, and bisect offsets at full extension and 15 and 30° flexion in the upright standing position [71]. The analgesic effects provided by patellofemoral braces may be secondary to changes in regional temperature, neuro-sensory feedback, or circulation about the knee joint [72]. The design of the brace utilizes either straps or buttresses to stabilize the patella and as shown in Fig. 2 [68].

Fig. 2.

Patellofemoral knee brace with pull straps above and below the patella, and buttress that provide stabilizing forces to the lateral aspects of the patella during functional activities

Clinical Efficacy

Several studies have reported improved patellar tracking during knee flexion-extension range of motion (ROM), diminished lateral patellar forces, decreased frequency and severity of anterior knee pain, and enhanced performance and confidence during physical activity [68]. In a study published in 2019, researchers investigated the effect of a knee brace compared with patient education about PFPS in self-reported kinesiophobia and function in people with PFPS [61]. Using the Tampa Scale for Kinesiophobia, the Anterior Knee Pain Scale, International Physical Activity Questionnaire, and objective functional tests such as a forward step-down test, researchers were able to measure improvements in subjective and objective outcomes surrounding the patient’s knee function [61]. Results of this study showed reduced kinesiophobia at 2-week and 6-week follow-up time points in people with PFPS in the knee brace group, compared to the patient education group. However, there were no significant differences in the self-reported objective function and physical activity levels [61].

A randomized controlled clinical trial comparing the efficacy of a patella-stabilizing, motion-restricting knee brace versus a neoprene non-hinged knee brace for the treatment of a first-time traumatic patellar dislocation demonstrated no significant reduction in re-dislocations versus a neoprene non-hinged knee brace [73]. Knee immobilization in the patella-stabilizing, motion-restricting knee brace (solely allowing 0–30°of flexion) for 4 weeks after initial injury was associated with quadriceps muscle atrophy, less knee ROM, and worse functional outcomes in the first 6 months after injury. Although, no clinically significant differences were found at 3 years of follow-up.

Other studies have found patellofemoral braces to be ineffective [74, 75]. Studies have reported increased skin irritation, insignificant pain relief, and inflated subjective findings in comparison to objective findings with regular brace use, noting that brace effectiveness depends on the correct application and use of patellofemoral braces [68]. A 2015 Cochrane systematic review on the management of PFPS using knee orthoses found that there was an overall lack of evidence to inform the use of knee orthoses for treating PFPS [76]. Additionally, there is low-quality evidence from clinically heterogenous trials that demonstrate no reduction in knee pain or improvement in knee function in the short term (less than 3 months) in adults who used different knee orthoses while also undergoing an exercise program for treating PFPS [77]. Some relevant clinical and documented experimental studies are presented in Table 2.

Table 2.

Summary of outcomes of patellofemoral knee braces used in clinical and documented experimental studies

Author, year	Sample	Sample size	Study design	Age, mean SD (years)	Study duration	Outcome measures	Results
Honkonen et al., 2022 [72]	First-time traumatic patella dislocation	64	Randomized control trial; level of evidence, 1	28 ± 9.3 29 males, 35 females	4 weeks	Redislocation Tegner score Kujala score ROM, degree Quadricep muscle atrophy	No statistically significant difference in the risk of dislocation among groups Less knee ROM for patients assigned patella-stabilizing, the motion-restricting knee brace Knee immobilization resulted in quadricep muscle atrophy, less ROM, and worse functional outcomes
Priore et al., 2020 [61]	Patellofemoral knee brace Patients with patellofemoral pain	50	Single-blind randomized controlled trial (knee brace vs. patient education)	–	6 weeks	Tampa Scale for Kinesiophobia Anterior Knee Pain Scale International Physical Activity Questionnaire Forward step-down test	Knee brace reduced kinesiophobia in people with PFP compared with non-brace groups with moderate effect size at 2 wk and 6 wk time points There was no significant difference in the self-reported and objective function and physical activity level
Mäenpää et al., 1997 [75]	Patellofemoral knee brace Non-operative management for primary acute patellar dislocations	Male (37) Female (63)	Randomized clinical trial (plaster cast/posterior splint/patellar bandage or brace)	Woman median age: 23 (10 to 64) Men median Age: 22 (11 to 47)	13 years on average	Knee joint movement: Retro-patellar crepitation Apprehension test: Number of re-dislocations and problems Subjective symptoms and functional limitations	No statistically significant difference between groups of treatment modalities (sex, age, BMI) Plaster casts and bandages or braces experienced restricted extension and flexion than posterior splints groups Retro-patellar crepitation in the patellar compression and sliding tests in patients treated with plaster casts Higher rates of re-dislocations per follow-up in a patellar bandage or brace groups Subjects with patellar casts reported increased rates of dissatisfaction and patellofemoral pain and patellar subluxation

Disparities in the effectiveness of patellofemoral braces could be secondary to differences in brace design, mode of use, and wear time. A randomized clinical trial in 2016 found that the use of medially directed patellar realignment braces in combination with supervised physical therapy for 6 and 12 weeks led to better outcomes than exercise alone in patients with PFPS. Patients scored significantly better in KOOS subscales, functional Kujala score, and pain ratings during functional activities at 6- and 12-week time points [78]. In another randomized trial, subjects with PF OA were braced for 6 weeks, for a mean duration of 7.4 h/day, and the bone marrow lesion (BML) volume change in the PF joint was measured. The results of this study found significantly lower knee pain and reduced PF BML volume compared to the control group [79].

Limitations

As stated earlier, there is an overall lack of evidence on the efficacy of the use of knee orthoses for treating PFPS [76]. Evidence from heterogeneous trials failed to demonstrate short-term (less than 3 months) improvements in knee pain or function in adults who were also undergoing an exercise program for the treatment of PFPS [80]. Due to the complex interior characteristics of the patellofemoral joint, current patellar bracing fails to reduce the compressive force on the patella, stabilize the joint, or properly ensure that muscles do not exhibit atrophy as a result of treatment [25]. However, users may report subjective decreases in pain due to changes in the patellofemoral contact area with the use of a patellofemoral brace [70, 81].

Knee Sleeves

Knee sleeves are knee rehabilitation compressive sleeves/orthoses that are the most recognizable, easy to acquire (off-the-shelf), and typically do not require a prescription from an orthotist or doctor [31]. They are often used to assist and stabilize movements, reduce pain in joints, and diminish excessive knee loads or laxities during sports activities but do not provide any structural support [24, 82, 83]. These sleeves are simple, less cumbersome, and used as an inexpensive alternative that improves balance and proprioception and have been accepted clinically based on subjective performance [84]. Due to the inability of the knee sleeve to provide stiff support, this knee brace provides negligible effects on the skeletal system; thus, it is important to remind readers that knee sleeves are insufficient for the treatment of an unstable knee [82].

Although the knee sleeve is unable to impact skeletal alignment, its functional and neuromuscular effects are believed to help maintain dynamic joint stability [22]. They are usually soft neoprene sleeves made from elastic materials [24, 85]. Documented reports from persons with arthritis and sportsmen with ligament injuries have endorsed feelings of improved stability with knee sleeve use [26]. Generally, knee sleeves provide minimal support and alignment through compression of the knee joint, yet they are frequently patronized because of their ease of use and are recommended as an appropriate treatment for the nonsurgical management of knee OA. This can be attributed to reports that knee sleeve braces incite effects via improvement in proprioception by the simulation of the cutaneous mechanoreceptors [14, 86].

Comparative evaluation of different knee sleeve braces with varying characteristics, for example, knee sleeves with heat-retaining capabilities versus ordinary sleeve braces and sleeve braces with patellar realignment straps, has demonstrated that their fundamental functionalities remain unchanged and provide no additional benefits in improving pain or physical function [11, 87, 88]. Knee sleeves provide an immediate pain-relieving effect for treatment targeting patients with knee OA and have proven to be successful in improving proprioception via joint position sense where this is deficient; this may be due to an increased sense of security during physical activities [11, 89]. Additionally, some studies suggested that wearing knee sleeves can reduce pain in the short term with prolonged improvement in both pain and dynamic function of daily activities [89]. Though improvements in performance-based physical function in patients with knee OA remain inconclusive, patients wearing knee sleeves show better control of balance in static and dynamic conditions [11, 84, 86, 89].

Mechanism of Action

Knee sleeves apply compression to the knee that can help stabilize the patella when deficient. Some sleeve designs apply medial force to the patella that aims to improve patellofemoral tracking and reduce the possibility of lateral patellar dislocation, while others contain lateral hinges that integrate an extension stop [6, 68, 72]. Sleeves modified with straps help decrease traction forces on the tibial tuberosity and patellar tendon in treating patellar tendonitis [84]. When a strap is placed inferior to the patella, it may be used to treat Osgood-Schlatter disease and patellar tendonitis [77], as it decreases the traction forces at the tibial tuberosity [84]. The knee sleeve may also be modified to include an opening for the patella, one or more movable straps, or a buttress [90]. The buttress may be circular, C-shaped, J-shaped, or H-shaped. With these modifications, the knee sleeve is often referred to as an extensor mechanism counterforce brace and is used to treat patellofemoral joint disorders, including patellar subluxation, patellar dislocation, and patellofemoral syndrome, all of which are very common in athletes [84]. An example of such orthosis is represented in Fig. 3.

Fig. 3.

Knee sleeve or compressive sleeve is made from neoprene material, they are made to incite effects by stimulating cutaneous mechanoreceptors to provide immediate pain-relieving effects

Clinical Efficacy

Some reports have acknowledged the possibility of knee sleeves promoting a biomechanical balance between knee joint structures, significantly lowering knee adduction moments in unilateral knee OA, and decreasing the pressure in the extensor mechanism [58, 91, 92]. This effect helps reduce the pressure on the infrapatellar fat pad, which is often inflamed in knee OA [58, 82, 91]. Some researchers have concluded that significant reductions in loading rates accompanied by increased knee flexion and decreased muscular co-contraction are possibly due to a greater sense of stability provided by the proprioception-enhancing effects of knee sleeves [93]. Their use has also demonstrated feelings of increased knee stability. A recent study to determine the immediate effect and 6-week effect on the biomechanics of the knee after an anterior cruciate ligament reconstruction (ACLR) showed an improvement in a step-down hop task [94].

Plain knee sleeves may be used to treat postoperative knee effusions and patellofemoral pain syndrome [77]. Used in this capacity, the knee sleeve decreases knee pain by promoting blood circulation [68, 74, 95]. When a knee pad is added, it provides protective cushioning to the patella and anterior knee [84]. Although knee sleeves provide little mechanical support to the knee, it is thought that the feelings of improved stability and reduced pain are largely due to an improvement in joint proprioception. Some researchers have suggested that compressive forces exerted by knee sleeves stimulate mechanoreceptors around the joints, leading to improvements in proprioception and balance [95–97].

Additional benefits of knee sleeves include their ability to be used regardless of the degree of knee deformity [35]. Although these orthoses do not provide structural support to the deformed knee, factors such as increases in skin temperature and provision of mild compression contribute to the therapeutic effects of knee sleeves [82, 86, 89, 98]. It is believed that knee sleeves provide local thermal effects to the skin that lead to less muscle contracture, as well as improved joint stability through its mild compressive forces. These mechanisms enable increased confidence and symptomatic relief to the user [81]. Healthy joints similarly gain better joint position sense with the use of knee sleeves [82]. The underlying mechanism for these effects is likely a heightened sensory input from tactile stimulation provided by knee sleeve compression [14, 15, 82]. However, these effects are limited to activities with relatively low motor skills such as walking and balancing [82].

There are documented reports showing improved clinical outcomes with the use of knee sleeves [58, 88]. Perlau et al. reported that knee joint proprioception was improved while wearing elastic bandages in a group of uninjured subjects [14]. Similarly, knee sleeves have been found to elicit immediate improvement in early and late stance KAM, increase walking speed after 6 weeks of sleeve use, and improve arthritic joints and tibial rotation of healthy joints [92, 99, 100]. Some studies assessed gait, balance, and proprioception with sleeve brace use and have reported functional improvements [92, 93, 99–104]. Injury prevention effects are documented with neoprene knee sleeve use as well, demonstrating improvements in repositioning error in fatigued knee joints [87, 89]; however, this effect is not demonstrated in non-fatigued knees. There are also reports of improvements to ipsilateral postural control and static-dynamic balance among knee sleeve users [82, 89, 95].

Likewise, some studies focused on balance and functional performances [58, 89, 98, 99]. A 2019 study by Mohd Sharif et al. studied the effects of two different types of knee sleeves, a simple knee sleeve and a simple sleeve with patella cutout, on knee adduction moment using a motion capture system and force plates in patients with clinically diagnosed knee OA. Results of the study showed a significant reduction in pain, early stance and late stance knee adduction moment, and increased walking speed after 6 weeks of both knee sleeve applications [92]. Collins et al. conducted a study to measure the effect of neoprene knee sleeves used in concurrence with stochastic resonance electrical stimulation (SRES) on postural control. The results of the study indicate that knee sleeves cannot influence postural control in those with KOA and neither does SRES improve balance [105]. A summary of relevant clinical and documented experimental studies is presented in Table 3.

Table 3.

Summary of outcomes of knee sleeve used in clinical and documented experimental studies

Author, year	Sample	Sample size	Study design	Age, mean SD (years)	Study duration	Outcome measures	Results
Mohd Sharif et al., 2019 [92]	Simple knee sleeve vs knee sleeve with patella cutout	Female (15), Male (2)	Comparative study	47.7 ± 9.7	6 weeks	WOMAC	Significant reduction in pain, early stance, and late stance knee adduction moment
Schween et al., 2015 [100]	Knee Sleeve Osteoarthritis of the medial tibiofemoral joint	Male (19) Female (8)	A prospective comparative study (with/without elastic knee sleeve)	50 ± 9	Immediate	Kinetic gait analysis	Knee adduction angle at ground contact was reduced by 1.9 ± 2.1° with the use of a sleeve Peak knee adduction was reduced by 1.5 ± 6°
Kwon et al., 2014 [95]	Knee sleeve Patients with a history of ACL reconstruction	Male (13)	Randomized controlled trial (pre/post-silicon sleeve application)	28.27	Immediate	Dynamic balance tests, TUG, stair step test, vertical jump test, proprioception test, isokinetic knee strength test	Application of silicone sleeve showed significant effects in proprioceptive function on the operated side compared to both taping and control conditions Muscle strength on the operated side of the quadriceps and hamstring was significantly improved compared with none or taping
Giotis et al., 2013 [99]	Knee sleeve Patients with a history of unilateral ACL reconstruction with BPTB autograft	Male (20)	A prospective comparative study (prophylactic brace/patellofemoral brace (sleeve)/non-braced)	27.1 ± 3.4	Immediate	Kinematic data	The range of motion of tibial rotation was significantly lower in the intact knee compared with all 3 conditions of the ACL-reconstructed knee Placing a brace or a sleeve on the ACL-reconstructed knee resulted in lower rotation than in the non-braced condition
Collins et al, 2012 [93]	Knee sleeve Knee OA	Male (22) Female (30)	Counterbalanced, repeated measures with SRES	61.2 ±9.6	Immediate	Center of pressure displacement	Neoprene knee sleeves show no significant improvement in knee balance
Mortaza et al, 2012 [119]	Knee sleeve and prophylactic knee brace Healthy male collegiate athletes	Male (31)	Cross-over randomized controlled trial Prophylactic knee brace with neoprene knee sleeves	21.2 ± 1.5	Immediate	Single-leg vertical jump test Cross-over hop tst. Isokinetic Strength Test	No statistical significance was found between the 4 (non-braced control, a neoprene sleeve, a neoprene sleeve with four metal supports, and prophylactic knee brace) testing conditions while performing the single-leg vertical jump test and the cross-over hop tests
Collins et al., 2011 [93]	knee sleeve Stochastic resonance ES+knee sleeve Knee OA	Male (22) Female (30)	Counterbalance sequence design of two treatment conditions (stochastic resonance ES+knee sleeve/knee sleeve/no sleeve+ES)	61.2 (9.6)	Immediate	Kinetic gait data Kinematic gait data EMG data	75% threshold/sleeve and sleeve-only conditions resulted in increased knee flexion at contact and reduced loading rates compared to the control condition Muscle co-contraction was found to decrease with the 75% threshold/sleeve condition compared to the other conditions
Bryk et al., 2011 [58]	Knee sleeve Knee OA	74	Randomized controlled trial (with or without knee sleeves)	–	–	SCPT, TUG test, 8MW test, VAS for pain	Statistically significant reduction in pain with knee sleeve use compared to without knee sleeve use Statistically significant improvements in 8MW and TUG tests sleeve use compared to without knee sleeve use
Wilson et al., 2010 [97]	Knee sleeve Cadaver lower extremities	Male (4) Female (5)	Cross-over study (knee sleeve, patellar stabilization sleeve, patellar stabilization brace, control)	62.7 (52–75)	Immediate	Contact area & pressure	All braces increased contact area, but the wrap-style patellar stabilization brace decreased peak pressure on the PF joint A decrease in magnitude and proximal shift in the location of the peak PF pressure was demonstrated with a wrap-style patellar stabilization brace Both patellar stabilization sleeves and the knee sleeve significantly increased contact area compared with the wrap-style patellar stabilization brace
Birmingham et al., 2008 [120]	Functional knee brace compared to knee sleeve	Brace: Male (36) Female (40) Sleeve: Male (37) Female (37)	Randomized controlled clinical trial (functional knee brace/neoprene sleeve)	Brace: 26.8 ± 8.9 Sleeve: 28.2 ± 10.1	2 years	ACL-Quality of Life Questionnaire Anterior tibial translation single limb forward hop test. Tegner Activity Scale Subjective questionnaire	No significant difference between brace and sleeve drops for any outcomes at 1- and 2-year follow-ups Subjective ratings of confidence in the knee provided by the brace/sleeve were higher for the brace group than the sleeve group
Van Tiggelen et al., 2008 [l02]	Knee sleeve Healthy subjects	Male (49) Female (15)	A prospective comparative study (with/without elastic knee sleeve)	24.44 ± 4.56	Immediate	Proprioception	On the braced side, no significant differences were observed between the baseline assessment and the third assessment Neoprene knee sleeves compensate for the deficit in joint position sense due to fatigue
Chuang et al., 2007 [89]	Knee sleeve Knee OA	Male (8) Female (42)	Cross-over randomized controlled trial (with or without neoprene sleeve)	61.24 ± 8.8 (group A) 64.32 ± 10.4 (group B)	Immediate	Static & dynamic balance tests	Knee OA subjects wearing knee sleeves showed better balance control in static and dynamic conditions than those without neoprene sleeves
Miller et al., 2005 [98]	Knee sleeve D1 collegiate athletes	Male (12) Female (12)	A 2 × 2 × 3 × 5 factorial design with replicated measures on 3 variables	21.79	Immediate	Skin (an anterior aspect of thigh) and muscle (vests lateralis) temperature	Thigh sleeve showed no effect on intramuscular temperature before or during exercise, but post-exercise temperatures averaged 0.5 °C higher Exercise intensity showed 1.3 to 2.0 °C increases in temperature with sleeve use Females showed higher intramuscular temperatures than males when donning sleeves; however, males had higher skin temperatures than females
Mazzuca et al., 2004 [88]	Knee sleeve Knee OA	Male (12) Female (40)	Double-blind, randomized controlled trial (verum sleeve/placebo sleeve)	62.7 ± 11.2	8 weeks Don sleeves for 12 h daily for 4 weeks	WOMAC	Subjects with verum sleeves reported a decrease in mean WOMAC pain score relative to baseline No statistically significant difference between groups
Hassan et al., 2002 [86]	Knee bandage Knee OA	Male (19) Female (49)	Cross-over, within-subject study (randomized, standard-sized/loose-sized bandages, pre- and post-time points)	67.1 (36–87)	2 weeks/treatment arm	VAS WOMAC Static postural sway Proprioceptive acuity	The standard-sized bandage did not affect knee pain, proprioception, or postural sway Proprioceptive acuity and postural sway improved with looser bandages, but the benefit was lost upon removal
Kirkley et al., 1999 [38]	Knee sleeve Patients with varus gonarthrosis+knee OA	Male (86) Female (33)	Prospective, parallel group, randomized clinical trial (unloader knee brace/neoprene sleeve/control)	59.5	6 months	WOMAC MACTAR Assess function: 6-MWT, 30-second stair-climbing test	Improvement in disease-specific quality of life and function in both knee brace groups compared with the control group A significant difference between the unloader brace group and the neoprene-sleeve group in pain after 6-MWT and 30-s stair-climbing test Te unloader brace was, on average, more effective than the neoprene sleeve
McNair et al., 1996 [15]	Knee sleeve Healthy subjects	Male (10) Female (10)	2 × 2 Latin square cross-over design (with/without knee sleeve)	28 (5)	Immediate	Angle and force data	11 % improvement in tracking when subjects wore the knee brace

Limitations

Considering the biomechanical impacts of the knee sleeve, its benefits are not well established [82]. Knee sleeves can cause swelling through heat retention around the knee or obstruction of venous and lymphatic return below the sleeve. Knee sleeves should only be worn during sports activities if these complications occur [93]. Differences in the study designs used to evaluate different knee sleeve designs may contribute to mixed results [82]. Some studies used only simple knee sleeves, while other studies used semi-rigid knee sleeves (i.e., with patellar reinforcement, with laterally placed thin metal bars) [58, 89, 96]. These advancements alter mechanical joint forces because of the additional forces on the patella, as well as additional compression to the knee [82].

Different sleeve designs, materials, and constriction characteristics may elicit different effects on knee proprioception as compressive forces can improve coordination through restriction of range of motion (ROM) [96, 106]. Sleeves with a patella cutout may restrict patellar mobility but may also help with patellar stabilization [82]. The thin metal bars, if present, may increase lateral reinforcement to improve stability [104]. Shortcomings in their effectiveness can also be attributed to the scarcity of literature and studies dedicated to evaluating their efficacy. Therefore, additional high-quality studies are required to warrant their usefulness in addressing pain reduction and improvement of physical function.

Discussion

These knee orthoses are designed to address arthritic conditions by resisting muscular laxity, patellar instability, and load imbalances, as the knee sustains different loads during functional activities. Multiple models of knee orthoses have been devised to restrict or support different ranges of motion and deliver varying loading abilities on different structures of the knee. This implies that not all knee braces are the same to a large extent. For instance, unloader knee braces are designed to protect against compressive loads, while patellofemoral knee braces are tailored to restrict patellar deviation during functional bending activities. Thus, when choosing any knee brace, there should be an accurate diagnosis of the injury, the expectations of the user (i.e., physical activity demands and wear time tolerance), an understanding of the mechanism of action of the brace, and the clinical benefit and limitations associated with its use.

Albeit patients often report benefits from wearing braces, these benefits have not been significantly verified by clinical and scientific investigations. Therefore, an ideal knee brace in any of the three categories discussed here should produce a synergism with the innate knee-stabilizing muscles and ligaments throughout the normal ROM. It should increase resistance to injury from valgus, varus, rotational, or anterior-posterior translation forces and should not interfere with normal knee function or increase the risk of injury to other parts of the lower extremity. Therefore, the following steps must be considered in the brace selection process: first, define the instability or abnormal function that the brace must control. Greater physical demands require increased mechanical support from the braces chosen. Second, determine the functional role of the brace and the expectations of the patient; is the brace needed to prevent further injury, overcome pain, or compensate for chronic instability due to KOA? Third, identify the physical demands that the brace must withstand in consideration of the current injured state of the patient’s knee; is the brace to be used for activities of daily living, or does the patient have goals to return to active sports participation? The fourth step is to provide patient education and ensure patient compliance.

Generally, knee orthoses are designed to deliver dynamic support to the knee joint that is compatible with the internal joint mechanics. Knee joint motion, such as external rotation of the tibia as the knee is brought into extension, can be variable depending upon the activity and external forces applied to the knee [107]. Thus, knee joint motion must fall within the boundaries of support that are defined by the orthosis under physiological conditions for the knee brace to be effective [108–113]. Hence, it is useful that brace designs consider a central path of motion that will occur, for example, during normal gait or flexion-extension under quadriceps action, simulating rising from a chair or climbing a step [114–116]. In most studies, prominent motions apart from flexion-extension rotation and anterior-posterior translation do occur, for example, external KAM and knee flexion moment, yet most studies do not place any emphasis on the effects of these parameters.

Knee braces dedicated to the management of arthritic knee conditions have the capability of stabilizing and unloading different compartments within the knee joint. The unloader knee brace was designed to provide relief to patients with unicompartmental KOA through the reduction of excessive loading on the damaged compartment. The novel tri-compartment offloader brace was designed to address the heterogenous presentation of knee OA through multicompartment unloading forces across patellofemoral and tibiofemoral joints during flexed-knee weight-bearing activities [22, 38–40]. These unloader braces are designed for desired outcomes of less pain, reduced stiffness, improved physical function, and possibly slow disease progression [28–30]. Many of these orthoses have demonstrated significant benefits toward quality of life, knee proprioception, quadriceps strength, and knee gait symmetry [5, 32, 117]. Since this type of brace is designed for extended use; demonstrating efficacy, proper fit, and comfort is of higher importance to its users. Patients should consider the overall comfort of the brace, as well as the impact of brace use on gait mechanics when choosing to use this brace. If the use of the brace significantly alters gait mechanics, the user may experience pain or disability up or down the kinetic chain from the knee joint (i.e., low back, hip, or ankle).

Hypothetically, the patellofemoral knee brace is designed to stabilize the knee joint. This type of knee brace is used to treat a myriad of pain presentations located in the front of the knee. One of the primary indications for a patellofemoral knee brace is to address abnormal tracking of the kneecap in the trochlear groove. This knee brace application treats abnormal patellar tracking through the application of a medially directed force to the patella that resists lateral displacement of the patella during patellar tracking, ultimately preventing arthritic deterioration [62]. Studies examining the efficacy of this brace type alluded that the use of this brace may reduce kinesiophobia (fear of moving) among users [72]. However, there is a lack of evidence to support objective functional improvements. Patients who use patellofemoral knee braces should consider them as a supplement to rehabilitation programs that target muscle weakness, tissue flexibility, and movement re-education to decrease pain. Choosing a suitable patellofemoral knee brace may involve a trial of multiple brace fits that will subjectively improve comfort with activity.

Finally, knee sleeves are designed to assist and “stabilize” movements depending on their intended purpose(s) and/or design modifications. They are primarily devised to reduce pain in joints and/or to reduce excessive knee loads or laxities during sporting activities [56, 70, 82]. Research has demonstrated that knee sleeves improve proprioception, gait and balance, and functional improvements in both healthy and non-healthy knee presentations [11, 83–86, 88]. The benefits of knee sleeves are secondary to enhanced joint proprioception, as knee sleeves provide very little mechanical support [32]. Howbeit, there is variability in the literature regarding the clinical efficacy of this orthosis, possibly because of differences in the fit of the orthotic between models. Different sleeve designs, materials, and constriction characteristics may produce different stimulatory effects on the knee, thus influencing knee proprioception differently [96, 103]. Users need to restrict knee sleeve use to specific functional/sporting activities to deter the detrimental effects of prolonged compressive forces on the knee joint. Users must also consider the overall comfort and stability when choosing an appropriate knee sleeve.

A graphical representation of how each brace type compares relative to each other under different criteria is shown in Fig. 4. The criteria are comfort, ease of use, compliance, proprioception, knee alignment, cost, and durability; the composite scores are based upon extrapolation of data from the state of the literature, subjective reports, and the consequences of each brace type design. However, it is worth noting that the specific measures for each brace type may vary depending on the individual wearing it and the severity of the condition being treated. It is always best to consult with a healthcare professional before using any knee brace type, as this can help determine if a brace is suitable and which type of brace may be highly favorable.

Fig. 4.

A radar chart of the three brace types: unloader, patellofemoral, and knee sleeve braces. Each brace type is evaluated based on the following criteria: comfort, ease of use, compliance, proprioception, knee alignment, cost, and durability

Conclusion

An ideal knee brace in any of these categories discussed should produce a synergism with the innate knee, augment the joint and muscles, improve functional activities, prevent pain and OA progression, and alleviate PF pain. To enhance the state of research surrounding knee orthoses and the efficacy of their use in future studies, pre-clinical and clinical studies must be designed with the input of patients, physicians, physical therapists, orthotists, and rehabilitation researchers. This will enable proper consideration of brace material and fit, functional body mechanics, activity tolerance, and appropriate functional outcome measures for stronger study design and reproducibility.

Likewise, future orthotic design should consider working knowledge of biomechanical tenets and ligament mechanics in conjunction with designs that mimic natural joint articulating motions and anatomical behaviors with a focus on specific clinical conditions relevant to improving the patient’s overall clinical outcomes. Orthotic designs should also aim to incorporate more adaptive design (bionic) concepts that allow braces to respond to different loading conditions during locomotion and functional activities. This design concept should consider closed-feedback loop systems which help to overcome significant challenges that occur with functional activities. This can be achieved by incorporating sensors, actuators, and machine-learning algorithms that can improve knee rehabilitation.

Abbreviations

OA

osteoarthritis

AAOS

American Academy of Orthopedic Surgeons

KOA

knee osteoarthritis

ACL

anterior cruciate ligament

ALRI

anterior lateral rotary instability

AROM

active range of motion

BPTB

bone-patellar tendon-bone

CT

computed tomography

EMG

electromyographic

IKDC

International Knee Documentation Committee

MCL

medial collateral ligament

RCT

randomized controlled trials

ROM

range of motion

ACLR

anterior cruciate ligament reconstruction

PFPS

patellofemoral pain syndrome

PFP

patellofemoral pain

KAM

knee adduction moment

TCO

tri-compartment offloader

LEFS

Lower Extremity Function Scores

VAS

visual anolog scale

HSS

hospital for special surgery

GRF

ground reaction force

WOMAC

Western Ontario and McMaster University Osteoarthritis Index

KOOS

knee outcome survey

EQ-5D

EuroQol five dimensions

QALYs

quality-adjusted years

TUG

time up and go

8MW

8-m walk

6-MWT

6-min walk test