An in vitro dynamic evaluation of prophylactic knee braces during lateral impact loading

A Biomechanical Comparison Shows No Difference Between Two Knee Braces used for Medial Collateral Ligament Injuries

Purpose

The purpose of this study was to assess the ability of 2 commonly used knee braces to control knee valgus motion and subsequent strain on the medial collateral ligament (MCL) in a laboratory-controlled environment.

Methods

Twenty healthy individuals (6 male, 14 female; mean age, 23 ± 3 years) with no history of knee injury or brace use performed a jump landing task while wearing either no brace or 1 of 2 braces: the Playmaker and Total Range of Motion . Three-dimensional joint kinematics and kinetics were measured in our biomechanics laboratory.

Results

Significantly less knee dynamic valgus angulation was noted when using either brace (−0.51° ± 3.9° and −1.3° ± 3.2°) compared no brace (4.8° ± 3.0°). Dynamic valgus angulation did not differ significantly between the 2 braces tested, which were both not statistically different from baseline alignment. There were significant differences seen in peak knee flexion angle between each brace (77.9° ± 8.8°and 83.1° ± 8.4°), as well as between both braces and no brace (90.6° ± 11.1°). There was no significant difference in knee frontal plane moment or peak vertical ground reaction force loading among all 3 testing conditions.

Conclusions

Compared to no brace, both braces allowed significantly less dynamic valgus angulation of the knee under physiological vertical loads but were not significantly different from one another.

Clinical Relevance

Knee braces are commonly used to protect the MCL when placed under physiological loads. It is important to know which braces effectively reduce valgus stress to provide the best outcomes.

Effect of Prophylactic Knee Bracing on Anterior Cruciate Ligament Agonist and Antagonist Muscle Forces During Perturbed Walking

Background:

Anterior cruciate ligament (ACL) injuries most commonly occur after a perturbation. Prophylactic knee braces (PKBs) are off-the-shelf braces designed to prevent and reduce the severity of knee injuries during sports, yet their effectiveness has been debated.

Purpose:

To identify differences in ACL agonist and antagonist muscle forces, during braced and unbraced conditions, while walking with the application of unexpected perturbations.

Study Design:

Controlled laboratory study.

Methods:

A total of 20 recreational athletes were perturbed during walking at a speed of 1.1 m/s, and motion analysis data were used to create patient-specific musculoskeletal models. Static optimization was performed to calculate the lower-limb muscle forces. Statistical parametric mapping was used to compare muscle forces between the braced and unbraced conditions during the stance phase of the perturbed cycle.

Results:

The brace reduced muscle forces in the quadriceps (QUADS), gastrocnemius (GAS), and soleus (SOL) but not in the hamstrings. The peak QUADS muscle force was significantly lower with the brace versus without at 49% to 60% of the stance phase (28.9 ± 12.98 vs 14.8 ± 5.06 N/kg, respectively; P < .001) and again at 99% of the stance phase (1.7 ± 0.4 vs 3.6 ± 0.13 N/kg, respectively; P = .049). The SOL muscle force peak was significantly lower with the brace versus without at 25% of the stance phase (1.9 ± 1.7 vs 4.6 ± 3.4 N/kg, respectively; P = .031) and at 39% of the stance phase (1.9 ± 1.4 vs 5.3 ± 5.6 N/kg, respectively; P = .007). In the GAS, there were no significant differences between conditions throughout the whole stance phase except between 97% and 100%, where the braced condition portrayed a smaller peak force (0.23 ± 0.13 vs 1.4 ± 1.1 N/kg for unbraced condition; P = .024).

Conclusion:

These findings suggested that PKBs that restrict knee hyperextension and knee valgus/varus motion can alter neuromuscular patterns, which result in a reduction of QUADS force.

Clinical Relevance:

Understanding the way PKBs alter muscle function and knee mechanics can provide invaluable information that will help in making decisions about their use. Further studies should investigate different types of braces and perturbations to evaluate the effectiveness of PKBs.

The effect of knee brace misalignment on the anterior cruciate ligament: An experimental study

BACKGROUND

Protective knee braces are used for rehabilitation or prevention. Due to poor patient compliance or slippage, the brace might be misaligned with the knee axis.

OBJECTIVES

Does a misaligned knee brace stress the anterior cruciate ligament?

STUDY DESIGN

It is an experimental study.

METHODS

A strain sensor was implanted on the anterior cruciate ligament in eight limbs. The limbs were mounted in a knee simulator, muscle forces were applied and a cyclic motion from 10° to 60° flexion was performed under three conditions: unbraced, braced and with a misaligned brace.

OUTCOME MEASURES

The outcome measures were anterior cruciate ligament strain and three-dimensional kinematics of the knee joint.

RESULTS

The correctly aligned brace significantly reduced the anterior cruciate ligament strain at 10° compared to the unbraced condition from 0% to -1.54% (standard deviation = 1.4). The misaligned brace neutralised the effect of bracing to -0.06% (standard deviation = 1.1) anterior cruciate ligament strain. At 60° flexion angle, bracing had no statistically significant effect on the anterior cruciate ligament strain compared to the unbraced knee: -2.58% (standard deviation = 0.8) versus -1.64% (standard deviation = 1.0). The anterior cruciate ligament in the misaligned braced knee at 60° flexion with a strain of -1.1% (standard deviation = 0.9) was significantly more stressed than in the correctly aligned condition. An effect of bracing on knee kinematics was not detected.

CONCLUSION

A correctly aligned knee brace reduced anterior cruciate ligament strain. By contrast, a misaligned brace tended to increase the anterior cruciate ligament strain compared to the unbraced knee.

CLINICAL RELEVANCE

The correct alignment of the brace was identified as a key factor decisively influencing the effectiveness of bracing.

Do neoprene sleeves and prophylactic knee braces affect neuromuscular control and cutting agility?

OBJECTIVES

To evaluate the effects of neoprene sleeves (NSs) and prophylactic knee braces (PKBs) on neuromuscular control and cutting agility.

DESIGN

Markerless motion-capture technology tracked subjects (1) without a brace as a control (2) with NSs and (3) with PKBs during single-leg drop vertical jump (SLDVJ), single-leg squat (SLS), Y-excursion, and cutting movements. Movements were recorded five times per bracing condition in three different sessions.

SETTING

University laboratory.

PARTICIPANTS

Ten healthy, active subjects (5 male, 5 female; age range, 22-26 years).

MAIN OUTCOME MEASURES

Degrees of motion and time to completion.

RESULTS

Use of NSs and PKBs reduced subjects' hip internal rotation in the loading phase of SLDVJ (p = 0.026, 0.02) and SLS (p = 0.005, <0.001), reduced knee flexion in the loading phase of SLDVJ (p = 0.038, <0.001), and reduced knee frontal plane abduction (FPA) with SLS (p = 0.015, 0.024) and Y-excursion (p = 0.002, 0.005) compared to control. Use of PKBs decreased subjects' hip internal rotation in the Y-excursion (p = 0.024) and reduced knee FPA in the SLDVJ loading phase (p = 0.014) compared to control. There was no difference in cutting agility for either group (p = 0.145, 0.347).

CONCLUSION

Both NSs and PKBs positively impacted neuromuscular control without impacting cutting agility.

Do Prophylactic Knee Braces Protect the Knee Against Impacts or Tibial Moments? An In Vitro Multisensory Study

BACKGROUND

Knee braces are prescribed by physicians to protect the knee from various loading conditions during sports or after surgery, even though the effect of bracing for various loading scenarios remains unclear.

PURPOSE

To extensively investigate whether bracing protects the knee against impacts from the lateral, medial, anterior, or posterior directions at different heights as well as against tibial moments.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight limb specimens were exposed to (1) subcritical impacts from the medial, lateral, anterior, and posterior directions at 3 heights (center of the joint line and 100 mm inferior and superior) and (2) internal/external torques. Using a prophylactic brace, both scenarios were conducted under braced and unbraced conditions with moderate muscle loads and intact soft tissue. The change in anterior cruciate ligament (ACL) strain, joint acceleration in the tibial and femoral bones (for impacts only), and joint kinematics were recorded and analyzed.

RESULTS

Bracing reduced joint acceleration for medial and lateral center impacts. The ACL strain change was decreased for medial superior impacts and increased for anterior inferior impacts. Impacts from the posterior direction had substantially less effect on the ACL strain change and joint acceleration than anterior impacts. Bracing had no effect on the ACL strain change or kinematics under internal or external moments.

CONCLUSION

Our results indicate that the effect of bracing during impacts depends on the direction and height of the impact and is partly positive, negative, or neutral and that soft tissue absorbs impact energy. An effect during internal or external torque was not detected.

CLINICAL RELEVANCE

Bracing in contact sports with many lateral or medial impacts might be beneficial, whereas athletes who play sports with rotational moments on the knee or anterior impacts may be safer without a brace.

Dynamically tensioned ACL functional knee braces reduce ACL and meniscal strain

PURPOSE

The effectiveness of ACL functional knee braces to reduce meniscal and ACL strain after ACL injury or reconstruction is not well understood. A new dynamic knee tensioning brace system has been designed to apply an active stabilizing force to the knee. The ability of this system to reduce tissue strains is unknown. The purpose of this study was to test the ability of the dynamically tensioned brace to reduce strain in both the ACL and meniscus during rehabilitation activities.

METHODS

A combined in vivo/in silico/in vitro method was used to study three activities: gait, double leg squat, and single leg squat. Muscle forces and kinematics for each activity were derived through in vivo motion capture and applied to seven cadaveric knee specimens fitted with custom braces. Medial meniscal strain and ACL strain were measured in ACL intact, deficient and reconstructed conditions.

RESULTS

The brace lowered peak and average meniscal strain in ACL deficient knees (P < 0.05) by an average of 1.7%. The brace was also found to lower meniscal strain in reconstructed knees (1.1%) and lower ACL strain in ACL intact (1.3%) and reconstructed knees (1.4%) (P < 0.05).

CONCLUSIONS

This study supports the use of a brace equipped with a dynamic tensioning system to lower meniscal strain in ACL-deficient knees. Its use may help decrease the risk of subsequent meniscal tears in chronic ACL deficiency or delayed reconstruction. In ACL-intact and reconstructed knees, the brace may be beneficial in injury prophylaxis or in protecting the ACL graft following reconstruction. These results will aid clinicians make informed recommendations for functional brace use in patients with unstable knees.

LEVEL OF EVIDENCE

II.

Compression-rate-dependent nonlinear mechanics of normal and impaired porcine knee joints

Background

The knee joint performs mechanical functions with various loading and unloading processes. Past studies have focused on the kinematics and elastic response of the joint with less understanding of the rate-dependent load response associated with viscoelastic and poromechanical behaviors.

Methods

Forty-five fresh porcine knee joints were used in the present study to determine the loading-rate-dependent force-compression relationship, creep and relaxation of normal, dehydrated and meniscectomized joints.

Results

The mechanical tests of all normal intact joints showed similar strong compression-rate-dependent behavior: for a given compression-magnitude up to 1.2 mm, the reaction force varied 6 times over compression rates. While the static response was essentially linear, the nonlinear behavior was boosted with the increased compression rate to approach the asymptote or limit at approximately 2 mm/s. On the other hand, the joint stiffness varied approximately 3 times over different joints, when accounting for the maturity and breed of the animals. Both a loss of joint hydration and a total meniscectomy greatly compromised the load support in the joint, resulting in a reduction of load support as much as 60% from the corresponding intact joint. However, the former only weakened the transient load support, but the latter also greatly weakened the equilibrium load support. A total meniscectomy did not diminish the compression-rate-dependence of the joint though.

Conclusions

These findings are consistent with the fluid-pressurization loading mechanism, which may have a significant implication in the joint mechanical function and cartilage mechanobiology.

Can a knee brace reduce the strain in the anterior cruciate ligament? A study using combined in vivo/in vitro method

BACKGROUND AND AIM

It is unknown whether prophylactic knee braces can reduce the strain in the anterior cruciate ligament during dynamic activities.

TECHNIQUE

An athlete, who had characteristics of high anterior cruciate ligament injury risk, was chosen. A motion capture system (Optotrak Certus; Northern Digital, Waterloo, ON, Canada) was used to record dynamic trials during drop-landing activity of this subject with and without the knee brace being worn. A musculoskeletal model was used to estimate the muscle forces during this activity. A dynamic knee simulator then applied kinematics and muscle forces on a cadaver knee with and without the brace mounted on it. The anterior cruciate ligament strain was measured.

DISCUSSION

The peak strain in the anterior cruciate ligament was substantially lower for the braced (7%) versus unbraced (20%) conditions. Functional knee braces could decrease the strain in the anterior cruciate ligament during dynamic activities in a high-risk subject. However, the reduction seems to be a result of altered muscle firing pattern due to the brace.

CLINICAL RELEVANCE

Prophylactic knee brace could reduce the strain in the anterior cruciate ligament of high-risk subjects during drop-landing through altered muscle firing pattern associated with brace wear. This could help reduce the anterior cruciate ligament injury risk.

Sports Specialization, Part II: Alternative Solutions to Early Sport Specialization in Youth Athletes

Context:

Many coaches, parents, and children believe that the best way to develop elite athletes is for them to participate in only 1 sport from an early age and to play it year-round. However, emerging evidence to the contrary indicates that efforts to specialize in 1 sport may reduce opportunities for all children to participate in a diverse year-round sports season and can lead to lost development of lifetime sports skills. Early sports specialization may also reduce motor skill development and ongoing participation in games and sports as a lifestyle choice. The purpose of this review is to employ the current literature to provide evidence-based alternative strategies that may help to optimize opportunities for all aspiring young athletes to maximize their health, fitness, and sports performance.

Evidence Acquisition:

Nonsystematic review with critical appraisal of existing literature.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Conclusion:

Based on the current evidence, parents and educators should help provide opportunities for free unstructured play to improve motor skill development and youth should be encouraged to participate in a variety of sports during their growing years to influence the development of diverse motor skills. For those children who do choose to specialize in a single sport, periods of intense training and specialized sport activities should be closely monitored for indicators of burnout, overuse injury, or potential decrements in performance due to overtraining. Last, the evidence indicates that all youth should be involved in periodized strength and conditioning (eg, integrative neuromuscular training) to help them prepare for the demands of competitive sport participation, and youth who specialize in a single sport should plan periods of isolated and focused integrative neuromuscular training to enhance diverse motor skill development and reduce injury risk factors.

Strength of Recommendation Taxonomy (SORT):

B.

What is the best material for molding casts in children?

BACKGROUND

Casts are used to treat clubfeet, developmental dysplasia of the hip (DDH), forearm fractures, and femur fractures. The ability of a cast to maintain a desired shape is termed moldability. Clinicians use plaster, fiberglass, and soft casts. To our knowledge the biomechanical molding characteristics of these 3 materials have never been reported. We hypothesized that moldability of plaster would be better than fiberglass and fiberglass would be better than soft cast.

METHODS

We compared 12.7 cm wide casts of plaster, fiberglass, and soft cast. Casts were 5 layers thick, prepared in 40°C water, and placed over 2 layers of cotton padding on 5.1 cm and 15.2 cm diameter foam cylinders. A loading device simulated loads applied by clinicians when molding casts for 4 conditions: clubfoot (thumb-shaped 50 N load on 5.1 cm model), DDH (thumb-shaped 100 N load on 15.2 cm model), forearm fracture (palm-shaped 50 N load on 5.1 cm model), and femur fracture (palm-shaped 100 N load on 15.2 cm model). The loading device applied molding for 7 minutes. Five casts of each material were made for each model. Casts were removed, photographed, and the area of maximal deformation was compared with an unmolded cast. A large area of maximal deformation meant that the deformation was spread out over a large area, less precise molding.

RESULTS

In the clubfoot model, plaster was more precise than fiberglass (P=0.002) and soft cast (P<0.0001). In the DDH model, plaster was more precise than fiberglass (P<0.0001) and soft cast (P<0.0001) and fiberglass was more precise than soft cast (P<0.0001).In the femur fracture model, plaster was more precise than fiberglass (P=0.001) and soft cast (P=0.001).

CONCLUSIONS

The moldability of plaster is better than fiberglass and soft cast and fiberglass is better than soft cast.

CLINICAL RELEVANCE

If precise molding is required, plaster has the best moldability. In cases not requiring precise molding, fiberglass and soft cast are lightweight, waterproof, and available in child-friendly colors.

Anterior cruciate ligament bracing: evidence in providing stability and preventing injury or graft re-rupture

Ligamentous knee injuries are common and costly, both in financial terms and time missed from work and recreational activities. Furthermore, ligamentous injuries appear to predispose patients to future osteoarthritis and other morbidities. Therefore, prevention strategies are important in limiting the potential impact of these injuries. Knee braces are one of the most often prescribed devices in the billion-dollar orthotic industry. Despite widespread use of prophylactic and functional knee braces, the evidence supporting their efficacy in reducing and/or preventing injury remains limited. Knee braces have been shown to be more effective in preventing medial collateral ligament injuries than anterior cruciate ligament injuries in both cadaveric and clinical studies. The use of functional braces after anterior cruciate ligament reconstruction has been supported and refuted in both postoperative and long-term studies.

The effect of prophylactic knee bracing on performance: balance, proprioception, coordination, and muscular power

PURPOSE

Prophylactic knee braces are largely used in the prevention of ligament injuries, but their effectiveness on performance are still controversial. The aim of this study was to determine which brace was the most effective on functional performance.

METHOD

Twenty-four healthy subjects (14 men and 10 women), between the age of 18 and 22 with no prior history of lower limb injury and brace use, voluntarily participated in this study. Five different prophylactic knee braces were used. The test protocol consisted of dynamic balance, jumping performance, proprioception, coordination, and maximal force. Balance was assessed by the Y balance test; jumping performance was assessed by vertical jump and one-leg hop tests; maximal force, proprioception, and coordination were assessed by using functional squat testing. Proprioceptive test was performed by using the functional squat system machine that the participants were instructed to keep the crosshair on the line, even after the visual aid had disappeared. The subjects without a brace and with the brace by using 5 different braces (DonJoy-USA) were evaluated by five different therapists.

RESULTS

Hinged "H" buttress for the support of the knee brace was found to be more effective than the others in terms of balance. Drytex economy hinged knee brace had the best result in terms of proprioception and maximal force. There were no significant differences in vertical jump and one-leg hop tests (n.s.).

CONCLUSION

In conclusion, the hinged "H" buttress for support of the knee brace and Drytex economy hinged knee brace produced the best results on the performance parameters. The other three braces demonstrated more variable and less optimal results. Prophylactic knee braces can be used for both healthy subjects and athletes to enhance proprioception, coordination, maximal force, and balance, but it is important to choose the best proper brace to the individuals according to their fitness level.

LEVEL OF EVIDENCE

(Economic and decision analysis-developing an economic or decision model), Level II.

Knee injuries and the use of prophylactic knee bracing in off-road motorcycling: results of a large-scale epidemiological study

BACKGROUND

The effectiveness of prophylactic knee bracing in preventing knee injuries during sports has been evaluated; however, because of the variability in study conclusions, the topic remains controversial. Despite a paucity of data, the authors believe that prophylactic knee bracing is frequently used in off-road motorcycling.

HYPOTHESIS

No statistically significant difference exists in the frequency and types of knee injuries incurred between braced and nonbraced riders using commercially available knee braces in off-road motorcycling.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

Data from 2115 off-road motorcycle riders was obtained using an Internet-based survey over a 1-year period. Participants were grouped by use or nonuse of prophylactic knee bracing, and an incidence rate ratio was used for injury rate comparison.

RESULTS

Participants recorded 39 611 riding hours over the study period. A total of 57 riders (2.7%) sustained at least 1 knee injury, for a total of 89 injuries. The most common injuries involved the anterior cruciate ligament, menisci, and medial collateral ligament. There was a significantly higher rate of overall injuries in the nonbraced group versus the braced group (3.675 vs 1.587 per 1000 rider hours, P < .001). Significantly higher incidence rates of anterior cruciate ligament rupture (1.518 vs 0.701 per 1000 rider hours, P = .0274) and medial collateral ligament injury (0.799 vs 0.111 per 1000 rider hours, P = .002) were found among nonbraced riders compared with braced riders.

CONCLUSION

The most common knee injuries in off-road motorcycling involve the anterior cruciate ligament, menisci, and medial collateral ligament. The use of prophylactic knee bracing appears to have a beneficial effect in preventing medial collateral ligament and anterior cruciate ligament injuries as well as overall knee injury occurrence. These findings may be applicable to other sports that involve similar forces and mechanics.

A systematic review of prophylactic braces in the prevention of knee ligament injuries in collegiate football players

OBJECTIVE

To determine the relative risk reduction associated with prophylactic knee braces in the prevention of knee injuries in collegiate football players.

DATA SOURCES

An exhaustive search for original research was performed using the PubMed, SportDiscus, and CINAHL databases from 1970 through November 2006, with the search terms knee brace, knee braces, knee bracing and football, prophylactic brace, and prophylactic knee braces.

STUDY SELECTION

Seven studies comparing knee injuries among braced and non-braced collegiate football players were included. Study methods were assessed using the Physiotherapy Evidence Database (PEDro) scale. PEDro scores ranged from 2 to 5.

DATA EXTRACTION

The number of participants and frequency of knee injuries were used to calculate the relative risk reduction or increase.

DATA SYNTHESIS

We found a relative risk reduction for 3 studies with point estimates of 10% (36% to -26%), 58% (25% to 76%), and 56% (13% to 77%). Four studies demonstrated an increased risk of injury, with point estimates of 17% (19% to -71%), 49% (-31% to -69%), 114% (23% to -492%), and 42% (-18% to -70%).

CONCLUSIONS

Data from existing research are inconsistent. Based on a Strength of Recommendation Taxonomy level of evidence of 2 with a grade B recommendation, we cannot conclusively advocate or discourage the use of prophylactic knee braces in the prevention of knee injuries in collegiate football players.

The use of knee braces, part 1: Prophylactic knee braces in contact sports

Surrogate knee model biomechanical studies have indicated that off-the-shelf braces provide 20% to 30% greater resistance to a lateral blow when the knee is in full extension. Custom functional braces doubled the protective effects and proved effective with the knee in some flexion. Although functional performance studies are not consistent, preventive knee braces may slow straight-ahead sprint speed, cause early fatigue, and increase muscular relaxation pressures, energy expenditure, blood lactate levels, maximal torque output, oxygen consumption, and heart rate. Two epidemiologic studies have been performed. At West Point, a randomized control study of 71 injuries in 1396 cadets indicated knee brace effectiveness with a statistically higher rate of injury in the control group (3.4/1000 exposures) than in the braced group (1.5/1000 exposures), with the most significance for medial collateral ligament sprains in defensive players. The Big Ten Conference conducted a descriptive study of 100 medial collateral ligament sprains among 987 players in different positions, strings, and types of session. Brace-wear tendency varied directly with the unbraced player counterpart's risk of medial collateral ligament sprain, with the nonplayer linemen experiencing both the greatest risk of unbraced practice session injury (0.0801 injuries/1000 exposures) and the highest incidence of brace wear (85%). During practices, there was a nonsignificant but very consistent reduction in injury rate for braced players in every position and string. During games, there was also a reduced rate for linemen and the linebacker/tight end group. The study concluded that although the issue is not closed, preventive knee braces appear to offer some protection to the medial collateral ligament from a contact injury involving a valgus blow, but there may be negative effects on performance level, leg cramping, and fatigue symptoms.

Medial and lateral collateral injuries: prognosis and treatment

This article presents a comprehensive review of medial and lateral knee ligament injuries. It reviews the basic anatomy, physical examination, imaging techniques, and current treatment of medial and lateral knee injuries. It includes a step-by-step guide to proper physical examination of the knee as well as MRI images. Current treatment of medial and lateral knee injuries is extensively reviewed to aid the primary care physician in diagnosis and provision of care.

The influence of functional knee bracing on the anterior cruciate ligament strain biomechanics in weightbearing and nonweightbearing knees

Functional knee braces are commonly prescribed after anterior cruciate ligament injury or reconstruction; however, their ability to protect the ligament, or graft, remains unclear. Our objective was to evaluate the anterior cruciate ligament strain response in braced and unbraced knees during weightbearing and nonweightbearing in combination with three externally applied loads: 1) anterior-posterior shear forces, 2) internal-external torques, and 3) varus-valgus moments. The Legend brace was tested. All external loads were applied to the tibia with the knee flexed to 20 degrees. Reproducible data were obtained from 11 subjects. For anterior shear loads up to 130 N, the brace significantly reduced strain values compared with the unbraced knee during nonweightbearing and weightbearing conditions. For internal torques of the tibia (up to 9 N x m), strain in the braced knee was significantly less than in the unbraced knee when the knee was nonweightbearing only. The brace did not reduce strain values when the knee was subjected to external torques (9 N x m) or varus-valgus moments (10 N x m) in weightbearing and nonweightbearing knees. These data indicate that a functional knee brace can protect the anterior cruciate ligament during anterior-posterior shear loading in the nonweightbearing and weightbearing knee and during internal torques in the nonweightbearing knee.

Effects of protective knee bracing on speed and agility

We evaluated the effects of prophylactic knee braces on athlete speed and agility, as well as brace tendency to migrate. Thirty college football players in full gear ran a 40-yard dash and a four-cone agility drill wearing braces on both knees or no brace (control). Braces included the DonJoy Legend, Breg Tradition, OMNI-AKS 101W, McDavid Knee Guard, and models 1 and 2 of the Air Armor Knee and Thigh Protection System. Brace migration and subjective measures were recorded after each trial. In the 40-yard dash, times using Air Armor 1 and OMNI did not differ significantly from control. Times with other braces were significantly slower. In the four-cone drill, only the Breg times were significantly slower than control. The Air Armor 1 and McDavid braces showed significantly less superior/inferior migration in the 40-yard dash than other braces. In the four-cone drill, the Air Armor 1 and 2 showed significantly less superior/inferior migration than other braces. These findings indicate that selected knee braces do not significantly reduce speed or agility. Braces showed a variable tendency to migrate, which could affect their protective function and athlete performance. This information will help athletes and coaches decide about knee-brace use during sports; studies are needed regarding whether braces protect against knee injury. This study does not constitute an endorsement of knee-brace use or efficacy.

Cruciate injury patterns in knee hyperextension: a cadaveric model

We created an experimental model to evaluate the effects of strain rate on the mechanism of combined cruciate ligament injuries in knee hyperextension. Using straight knee hyperextension to rupture the anterior and posterior cruciates, two strain rates (approximately 100% per second and 5400% per second) were applied to reproduce two clinical injury patterns of the knee: low energy (sporting) and high energy (pedestrian-motor vehicle accident). Ten pairs of fresh-frozen cadaveric knees were injured to 45 degrees of hyperextension. Strain rate sensitivity of the posterior cruciate ligament was shown in this model, with midsubstance tears occuring in specimens tested at a low rate and avulsion "stripping" injuries from the femoral side occuring at a high rate. A variable pattern of anterior cruciate ligament tears at both high and low rates suggests that the specific injury mechanism may also involve other factors including notch morphology. We present a simplified mathematic model used to estimate posterior cruciate ligament strain during knee hyperextension.

Dynamic impact response of human cadaveric forearms using a wrist brace

The purpose of this study was to compare the dynamic impact response of braced and unbraced cadaveric wrists using a commercially available wrist guard. Twelve arms were harvested from six cadavers. Each pair of forearms, one with and one without a brace, were impacted using a modified guillotine-type drop fixture placed over a force platform. Using a piece-wise linear regression analysis, we identified four phases of dynamic loading in the vertical force profile before fracture. These phases included an initial linear loading phase starting at impact, followed by a nonlinear phase, a second rapid linear loading phase, and a final nonlinear loading phase to failure. Three transition points were identified that defined the boundaries of the linear loading phases. Vertical force and impulse were significantly higher (P < 0.01) at each transition point and at failure in all braced specimens compared with unbraced specimens. However, the most noticeable differences were found during the initial two loading phases. Time to each transition point and to failure was not significantly different (P > 0.27) between the braced and unbraced wrists. The results of this study differ from those obtained under more quasistatic loading conditions. Dynamic impact testing suggests that wrist guards may have a prophylactic effect during low-energy dynamic impact situations.

External knee support in rugby union. Effectiveness of bracing and taping

Rugby football is associated with a number of biomechanical stresses which are frequently associated with knee injury. Consequently, there has been a significant interest within the game regarding the techniques of knee surgery and accelerated rehabilitation and the prophylactic use of external knee support. Knee bracing and strapping techniques are widely practised by rugby players but their results vary and there are mixed opinions over their usefulness. This article discusses the current trends in external knee support, draws on the experiences of other professional football codes and extrapolates these to the rugby union setting. Widespread opinion confirms that improper or incomplete rehabilitation is linked to re-injury. There is also a general acceptance that external support for the knee in sport should never be used to mask an injury. There is no evidence that the prophylactic taping of the knee joint provides any significant external stabilisation for more than the first few minutes of play. This lack of lasting stabilisation is due to the vigorous physical activity associated with rugby which results in a rapid loss of the custom fit of the external support to the profile of the joint. The taping the patella to reduce the pain associated with poor patellar alignment is considered to be effective; however, the correction of other biomechanical influences is also important. Adhesive tape, when applied correctly, will reposition the patella but this technique is limited by factors such as sweating and movement. A number of knee braces are currently available and these are classified according to their prophylactic, rehabilitative or functional design. In this article, their use in rugby applies to external support as an aid to rehabilitation rather than injury prevention.

Electromyographic activity in expert downhill skiers using functional knee braces after anterior cruciate ligament injuries

We studied six expert downhill skiers who had sustained anterior cruciate ligament injuries and had different degrees of knee instability. The aim was to measure possible changes in electromyographic activity recorded from lower extremity muscles during downhill skiing in a slalom course without and with a custom-made brace applied to the injured knee. Surface electrodes were used with an eight-channel telemetric electromyographic system to collect recordings from the vastus medialis, biceps femoris, semimembranosus, semitendinosus, and gastrocnemius medialis muscles from both legs. Without the brace, the electromyographic activity level of all muscles increased during knee flexion. The biceps femoris muscle was the most activated and reached 50% to 75% of the maximal peak amplitude. With the brace, the electromyographic activity increased in midphase during the upward push for the weight transfer and the peak activity occurred closer to knee flexion in midphase. Also, the uninjured knee was influenced by the brace on the injured leg, a decrease in electromyographic activity was seen in midphase. Spearman's rank correlation revealed a significant correlation between an increase in biceps femoris activity of the injured leg and increasing knee instability. We suggest that the brace caused an increased afferent input from proprioceptors, resulting in an adaptation of motor control patterns secondarily modifying electromyographic activity and timing.

Use of knee braces in sport. Current recommendations

This article provides a review of the progress that has been made on the biomechanical, functional performance and epidemiological investigations into the effectiveness of prophylactic knee braces (PKBs) since the position statement against their use was issued in 1987 by the American Academy of Orthopaedics and a review of this subject was last published in Sports Medicine in 1989 by Montgomery and Korziris. The evolution of the salient design features of three surrogate knee models are reviewed along with the results of PKB effectiveness and safety factor testing. While still too limited in scope to be totally realistic, major advances have been made in the sophistication of the present biomechanics laboratory testing conditions. The on-the-field functional performance effects of wearing a knee brace are not always manifest in all individuals. The efficacy of PKBs remains in question but recent studies have taught us enough to put their use into perspective. While they may play some role, PKBs probably represent the least important factor in influencing the likelihood that a medial collateral ligament (MCL) sprain will occur. On the other hand, there is no evidence that such braces put added valgus pressure on some knees, or that wearing a brace is associated with an increased frequency or severity of knee or ankle injury. All else being equal, from the biomechanical studies, we know that whilst some braces are better than others, currently available PKBs can provide 20 to 30% greater resistance to a lateral blow, with the possibility that the anterior cruciate ligament (ACL) is given even greater protection than the MCL. This appears to be true when the lateral blow is of sufficient magnitude to cause significant medial joint line opening, but is not as great at the very lowest levels of impact. Regardless of the material they are made of, the most effective PKBs are those sufficiently stiff to prevent an external blow at the joint line from causing brace hinge contact with the knee tissues. Based on the superior results of the custom-fit functional braces, the most important future design feature appears to be the sizing and fitting of the thigh and tibial cuffs. On the negative side, the presence of a brace may slow an athlete's straight-ahead sprint speed and cause early fatigue to its wearer. This effect appears to vary from one brace to another according to its weight, design features, and pressure from the leg and thigh straps. However, it appears that knee braces do have the potential to restrict performance of the athlete for high-speed running but the effect is related to several factors. The weight of the brace resultant friction of the hinges, completeness of fit, and tightness of straps appear to be important. The most measurable effects include: increased muscular relaxation pressures; increased energy expenditure; and a related increase in blood lactate levels, maximal torque output, oxygen consumption and heart rate. On the other hand, experienced brace wearers and larger, stronger individuals displayed fewer, or no effects of donning a brace. Improvements in the protectiveness of the PKB are likely to accompany improvements in the ability to contour the braces to fit each individual's leg in the equipment room without the added expense of the cast-moulding process. Further improvement may be realised by friction-free polycentric joints, as well as an attachment system that minimises thigh and calf soft tissue compression perhaps by incorporating the braces into the trousers of the uniform to provide suspension from the waist.

Dynamic elongation behavior in the medial collateral and anterior cruciate ligaments during lateral impact loading

The objectives of this experimental study were to determine (a) how quickly the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) elongate when a lateral impact force is imparted to the knee and if a person can react rapidly enough to provide protective muscle forces in the case of such an impact, (b) if the MCL and the ACL elongate simultaneously during a lateral impact, and (c) if resection of the ACL affects elongation of the MCL during a lateral impact. Eight whole-leg cadaver specimens were used. Each leg was mounted vertically in a testing-frame with the knee in 0 and 30 degrees of flexion. A submaximal impact was delivered from the lateral side by a pendulum instrumented with a force transducer. Elongation of the midsubstance of the MCL and the ACL was measured with Hall-effect displacement transducers. The ACL was resected and the entire test sequence was repeated. Following a lateral impact, elongation of the MCL and ACL reached peak values by 70 ms. This study indicated that contraction of the leg musculature would not protect the MCL and ACL from injury when a lateral impact load is applied to the knee. The MCL and the ACL never elongated simultaneously during a lateral impact. After lateral impact loading, the time required to reach maximum elongation (peak delay) averaged 52 ms in the anterior MCL fibers and 61 ms in the ACL when the knee was in 0 degrees of flexion. At 30 degrees of flexion, the peak delay averaged 38 ms in the anterior MCL fibers and 22 ms in the ACL.(ABSTRACT TRUNCATED AT 250 WORDS)