The biomechanics of lateral knee bracing. Part II: Impact response of the braced knee

In Part I of our study on lateral knee bracing, we evaluated brace effectiveness using cadaveric knees and two commercially available braces (McDavid and Omni). The results indicated that for low-rate dynamic valgus loading, neither brace provided significant protection against MCL injury. Also, four potentially adverse effects were noted. The goals in Part II were to: 1) determine the clinical significance of brace induced MCL preload; 2) define the functional character of an "ideal" brace; 3) design and validate a surrogate knee model for testing brace effectiveness; and 4) determine brace performance under impact loading using the surrogate knee and six commercially available brace types (manufactured by DonJoy, McDavid, Mueller, Omni Scientific, Stromgren-Scott, and Tru-Fit). Knee braces, modified to measure varus/valgus bending force, were used to determine MCL preload effects in 13 human volunteers. An anatomically correct surrogate knee model, instrumented to measure ligament/tendon tension and medial joint opening, was developed and validated using information from our previous cadaver studies and results of analyses on the effects of high strain rates (100% versus 1000% strain/sec) on MCL failure. Over 500 impact tests were performed on the surrogate knee in unbraced versus braced conditions. Tests were conducted for three impactor masses, two flexion angles, and free or constrained limb positions. Impact safety factors (ISF) were calculated for each test condition and brace type. An ISF of 1.50 (MCL load reduction of 30%) was considered significant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Is valgus unloader bracing effective in normally aligned individuals: implications for post-surgical protocols following cartilage restoration procedures

Purpose

Utilizing valgus unloader braces to reduce medial compartment loading in patients undergoing cartilage restoration procedures may be an alternative to non-weightbearing post-operative protocols in these patients. It was hypothesized that valgus unloader braces will reduce knee adduction moment during the stance phase in healthy subjects with normal knee alignment.

Methods

Gait analysis was performed on twelve adult subjects with normal knee alignment and no history of knee pathology. Subjects were fitted with an off-the-shelf adjustable valgus unloader brace and tested under five conditions: one with no brace and four with increasing valgus force applied by the brace. Frontal and sagittal plane knee angles and external moments were calculated during stance via inverse dynamics. Analyses of variance were used to assess the effect of the brace conditions on frontal and sagittal plane joint angles and moments.

Results

With increasing tension in the brace, peak frontal plane knee angle during stance shifted from 1.6° ± 4.2° varus without the brace to 4.1° ± 3.6° valgus with maximum brace tension (P = 0.02 compared with the no brace condition). Peak knee adduction moment and knee adduction impulse decreased with increasing brace tension (main effect of brace, P < 0.001). Gait velocity and sagittal plane knee biomechanics were minimally affected.

Conclusion

The use of these braces following a cartilage restoration procedure may provide adequate protection of the repair site without limiting the patient’s mobility.

Level of evidence

Therapeutic prospective comparative study, Level II.     

In vitro assessment of prophylactic knee brace function

In an attempt to evaluate the effectiveness of prophylactic knee bracing and to determine the influence of brace design and material characteristics on the protection of knee ligaments, a series of biomechanical studies were completed. The first series of tests were preliminary parametric tests of brace function utilizing cadaver limbs to understand the failure biomechanics of the medial restraints during low- and high-rate valgus-producing knee trauma. Static and dynamic mechanical properties of the braces were also studied. Finally, a limited series of brace/cadaver knee low-rate loading response tests were performed. With the information obtained from preliminary testing, an instrumented surrogate knee was developed and validated for lateral impact responses. The surrogate allowed for the measurement of ligament force time response during a controlled impact. Special impact facilities were constructed to allow the measurement and control of impact momentum. The effectiveness of six different prophylactic braces in preventing MCL and ACL injury was evaluated using the surrogate and impact facility. Impact parameters of mass, velocity, knee flexion angle, and limb restraint were varied to simulate different direct lateral impact conditions of game play. Testing results were normalized and expressed as an impact safety factor to allow for comparison of braces. An ISF of 1.5 (representing a ligament force reduction of 30%) was arbitrarily chosen as the minimum standard for brace performance. The majority of prophylactic knee braces tested proved to be biomechanically inadequate for protecting the MCl from a direct lateral impact. A few, however, appear to protect the ACL preferentially. In the case of a controlled, direct lateral blow, all but a few braces tested provided some beneficial protection to the MCL and ACL, but performed well below the standard 1.5 ISF level. Therefore, based on the biomechanical research, it is our opinion that the concept of prophylactic lateral knee bracing can be effective. We recommend that prophylactic braces not be abandoned, but rather improved, biomechanically validated, and further evaluated through well-controlled prospective clinical studies.     

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.     

The effect of proprioceptive knee bracing on knee stability after anterior cruciate ligament reconstruction

BackgroundInjury to the anterior cruciate ligament (ACL) is common among young athletes and can impact knee stability and control. Wearing proprioceptive knee braces can improve knee control and may reduce the risk factors associated with injury and re-injury, although the effect of such braces after ACL reconstruction (ACLR) is unclear.Research questionThis study aimed to determine the effect of proprioceptive knee bracing on knee control and subjective rating of participants post ACLR during three dynamic tasks.MethodsFifteen participants 2–10 years post ACLR performed a slow step down, single leg drop jump, and pivot turn jump with and without a proprioceptive knee brace. Knee kinematics in the sagittal (flexion – extension), coronal (abduction – adduction), and transverse (internal – external rotation) planes were collected using a 3D infrared system. Paired t-tests were performed to explore differences in knee angles and angular velocities between the no brace and brace conditions during the three tasks. After each task, subjective ratings regarding ease of the task were recorded.ResultsThe brace reduced the peak knee external rotation angle and range of motion in the transverse plane during the pivot turn jump task, and significantly increased the maximum knee flexion angular velocity during the single leg drop jump task. The majority of participants reported that tasks were easier to perform with the proprioceptive brace than without.SignificanceThis study confirms that proprioceptive knee braces can significantly influence knee kinematics during dynamic tasks post ACLR. The observed effects were clinically relevant.     

Laboratory evaluation of prophylactic knee brace performance under dynamic valgus loading using a surrogate leg model

Because of contradictory data accumulating from on-field trials of prophylactic knee braces, benchtop laboratory studies of brace performance have become important. This study (1) describes design considerations for a mechanical leg surrogate developed for prophylactic brace testing, (2) validates surrogate performance under dynamic lateral loading, and (3) reports comparative performance data for eight commercial knee braces tested using this surrogate system.     

The effect of proprioceptive knee bracing on knee stability during three different sport related movement tasks in healthy subjects and the implications to the management of Anterior Cruciate Ligament (ACL) injuries

IntroductionProprioceptive knee braces have been shown to improve knee mechanics, however much of the work to date has focused on tasks such as slow step down tasks rather than more dynamic sporting tasks.ObjectiveThis study aimed to explore if such improvements in stability may be seen during faster sports specific tasks as well as slower tasks.MethodTwelve subjects performed a slow step down, single leg drop jump and pivot turn jump with and without a silicone web brace. 3D kinematics of the knee were collected using a ten camera Qualisys motion analysis system. Reflective markers were placed on the foot, shank, thigh and pelvis using the Calibrated Anatomical Systems Technique. A two way ANOVA with repeated measures was performed with post-hoc pairwise comparison to explore the differences between the two conditions and three tasks.ResultsSignificant differences were seen in the knee joint angles and angular velocities in the sagittal, coronal and transverse planes between the tasks. The brace showed a reduction in knee valgum and internal rotation across all tasks, with the most notable effect during the single leg drop jump and pivot turn jump. The transverse plane also showed a significant reduction in the external rotation knee angular velocity when wearing the brace.DiscussionThe brace influenced the knee joint kinematics in coronal and transverse planes which confirms that such braces can have a significant effect on knee control during dynamic tasks. Further studies are required exploring the efficacy of proprioceptive braces in athletic patient cohort.     

The effects of functional knee bracing on muscle function and performance.

When applied, knee braces compress the soft tissues of the thigh and leg. External compression may abnormally elevate intramuscular pressure beneath the straps of the knee brace, decrease local muscle blood flow and muscular oxygenation, and induce premature muscle fatigue. Functional knee braces may give valuable support to athletes with unstable knees. They may also be a valuable rehabilitative tool in patients following surgery for knee joint instability. However, prophylactic and functional knee braces do not improve performance and may even inhibit performance in asymptomatic athletes. Athletes and coaches should be aware of the serious adverse effects of knee bracing.     

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.     

A historical perspective of PCL bracing

Purpose

Currently there are many functional knee braces but very few designed to treat the posterior cruciate ligament (PCL). No PCL braces have been biomechanically validated to demonstrate that they provide stability with proper force distribution to the PCL-deficient knee. The purpose of this review was to evaluate the history and current state of PCL bracing and to identify areas where further progress is required to improve patient outcomes and treatment options.

Methods

A PubMed search was conducted with the terms “posterior cruciate ligament”, “rehabilitation”, “history”, “knee”, and “brace”, and the relevant articles from 1967 to 2011 were analysed. A review of the current available PCL knee bracing options was performed.

Results

Little evidence exists from the eight relevant articles to support the biomechanical efficacy of nonoperative and postoperative PCL bracing protocols. Clinical outcomes reported improvements in reducing PCL laxity with anterior directed forces to the tibia during healing following PCL tears. Biomechanics research demonstrates that during knee flexion, the PCL experiences variable tensile forces. One knee brace has been specifically designed and clinically validated to improve stability in PCL-deficient knees during rehabilitation. While available PCL braces demonstrate beneficial patient outcomes, they lack evidence validating their biomechanical effectiveness.

Conclusions

There is limited information evaluating the specific effectiveness of PCL knee braces. A properly designed PCL brace should apply correct anatomic joint forces that vary with the knee flexion angle and also provide adjustability to satisfy the demands of various activities. No braces are currently available with biomechanical evidence that satisfies these requirements.

Level of evidence

IV.     

Effect of bracing on the prevention of anterior knee pain—a prospective randomized study

There have been numerous reports about the use of knee braces to prevent traumatic knee injuries. Despite the frequent use of braces, very few prospective studies have been performed to study the effect of knee braces for preventing anterior knee pain syndrome (AKPS). The purpose of this study was to assess the effectiveness of a dynamic patellofemoral brace (On-Track System, dj Orthopedics) in the prevention of AKPS. 167 military recruits without history of knee pain were randomized into two groups prior to the start of their 6-week basic military training (BMT) program. The first group (brace group) consisted of 54 recruits who wore the braces for all physical activities during these 6 weeks. 113 recruits served as a control group, and followed the same 6-week strenuous training program. Chi square statistics (Fisher exact test) were used to compare the number of AKPS patients in the brace group and in the non-brace group. Our results indicated that recruits in the brace group appeared to develop significantly less anterior knee pain compared to the recruits in the control group (p =0.020). Out of the 54 recruits in the brace group, ten (18.5%) developed anterior knee pain during this study. In the control group (n =113), 42 recruits (37%) developed anterior knee pain. We conclude that the result of the present study suggests that the use of a dynamic patellofemoral brace is an effective way to prevent the development of anterior knee pain in persons undergoing a strenuous training program.The views expressed in this article are those of the author and do not reflect the official policy or position of the Belgian Department of Defense     

The efficacy of a prophylactic knee brace to reduce knee injuries in football. A prospective, randomized study at West Point

The purpose of this prospective, randomized study was to determine the efficacy of a prophylactic knee brace to reduce the frequency and severity of acute knee injuries in football in an athletic environment in which the athletic shoe, playing surface, athlete-exposure, knee injury history, and brace assignment were either statistically or experimentally controlled. The participants in the study were 1396 cadets at the United States Military Academy, West Point, New York, who experienced a total of 21,570 athlete-exposures in the 1986 and 1987 fall intramural tackle football seasons. The use of prophylactic knee braces significantly reduced the frequency of knee injuries, both in the total number of subjects injured and in the total number of medial collateral ligament injuries incurred. However, the reduction in the frequency of knee injuries (total and medial collateral ligament) was dependent on player position. Defensive players who wore prophylactic knee braces had statistically fewer knee injuries than players who served as controls. This was not true of offensive players who served as controls; they had statistically no difference in the number of knee injuries from players who wore prophylactic knee braces. The severity of medical collateral ligament and anterior cruciate ligament knee injuries was not significantly reduced with the use of prophylactic knee braces.     

Functional knee braces increase intramuscular pressures in the anterior compartment of the leg.

The effect of three different functional knee braces on intramuscular pressures in the anterior compartment of the leg was investigated in 8 healthy subjects. Pressures were recorded with the microcapillary infusion technique while the subjects were either supine, sitting, or standing. Pressures at rest in the anterior tibial muscle increased significantly following application of each of the three knee braces regardless of posture. Similarly, muscle relaxation pressure during exercise also increased significantly on brace application. A pressure of 40 mm Hg was exceeded in 9 of 18 intramuscular pressure measurements with the subject standing. The tested functional knee braces increased muscle pressures at rest and muscle relaxation pressure during exercise to levels that, according to other studies, might decrease muscle blood flow significantly. External compression from a knee brace on leg muscles might, therefore, induce premature muscle fatigue because of local insufficient perfusion of the working muscle.     

Post-operative use of knee brace in bone-tendon-bone patellar tendon anterior cruciate ligament reconstruction: 5-year follow-up results of a randomized prospective study

Sixty patients were prospectively randomized to brace and no-brace groups after bone-tendon-bone patellar tendon anterior cruciate ligament (ACL) reconstruction. The brace group wore a rehabilitation knee brace for 12 weeks post-operatively, while the no-brace group was mobilized immediately, and crutches were discarded 2 weeks post-operatively. The groups were comparable with respect to age, gender, time from injury to surgery and concomitant injuries. There were no differences either pre-operatively or 5 years post-operatively (80% of patients reviewed) between the groups in terms of the knee score (Lysholm), activity level (Tegner), degree of laxity or isokinetic peak muscle torque. Thus it appears that knee braces are not needed in the post-operative rehabilitation after ACL reconstruction with the patellar tendon graft.     

Prophylactic knee bracing in college football

We report on the number of knee injuries sustained by a major college football team during 2 full years when all players were required to wear laterally placed prophylactic knee braces during all practice sessions and all games. We found that the incidence rates of knee injuries were higher when the braces were worn compared to a similar period when the braces were not worn. There was also an increased number of ACL injuries during the brace period. Several indices characterizing the nature of the injuries were analyzed and were found not to be altered significantly when the prophylactic braces were used. These facts lead us to question the efficacy of prophylactic knee braces in preventing knee injuries in college football. The use of the braces was associated with increased episodes of muscle cramping in the triceps surae muscle group, required the constant attention of coaches and trainers to remind the players to wear the braces and to apply them correctly, and was costly. These findings indicate the need for other carefully controlled clinical and biomechanical studies of these devices before their routine use can be advocated.     

Evaluation of knee braces in Swedish ice hockey players.

In this retrospective investigation we have determined the rate and types of knee injuries among Swedish ice hockey players, and related these data to the use of knee braces. Thirty-seven of the originally selected 50 hockey teams (74%) of elite or first division calibre took part in the study, and 600 players answered a questionnaire. A total of 254 previous knee injuries sustained while playing hockey were reported by 243 players; tears of the medical collateral ligament (60%), meniscus (15%) or anterior cruciate ligament (12%) were the most commonly reported injuries. Prophylactic knee braces were worn by 138 (23%) of the players. Of these, 122 (88%) had earlier sustained a knee injury, and 16 had not. A total of 17 knee injuries had occurred while the players were wearing a brace. Six of these players had previously uninjured knees while 11 had repeat injury in a brace despite earlier successful rehabilitation or operation. The most common injury in braced knees was a tear of the medial collateral ligament. We conclude that the number of knee injuries is high among Swedish ice hockey players, and that the efficacy of functional knee braces to reduce knee injuries is questionable.     

Can a post-operative brace in slight hyperextension prevent extension deficit after anterior cruciate ligament reconstruction?

It has been our observation that post-operative anterior cruciate ligament (ACL) braces together with the post-operative bandages do not always allow the knee to reach full extension. In ten uninjured knees with known hyperextension, the knees were bandaged in the same way as after an ACL-reconstruction. The knees were then studied radiologically in a Hypex brace set at 0°, –5° and –10° of knee extension. Not a single knee was found to be straight in the brace set at 0°. At –5° most of the knees were straight or in slight hyperextension. It took –10° to get all knees straight or in hyperextension. In a prospective randomised study 44 patients who underwent an arthroscopic ACL-reconstruction with a bone patellar tendon bone graft were randomised to use either a brace set at –5° or a straight brace (0°) for at least the first three postoperative weeks. Before and three months after surgery range of motion was determined, using a goniometer with long arms, and sagittal knee laxity was measured with a KT-2000 arthrometer at manual max. Pre- and post-operative pain was evaluated with the Visual Analogue Scale (VAS). The same examiner (blindfolded to what type of brace was used) performed all the measurements. At three months, two of the 22 patients with the brace set at –5° and twelve of the 22 patients with the straight brace had a loss of full extension of 2° or more (p<0.001). No significant differences were found between the groups in terms of knee flexion, sagittal knee laxity or post-operative pain. Although extension deficit after ACL-reconstruction can be prevented also in other ways, a Hypex brace set at –5° seems to be an easy way of ensuring full knee extension.     

The effect of bracing on extension strength in patients with ACL insufficneicy

One of the problems following an anterior cruciate ligament (ACL) injury is to regain strength. We tested 11 patients (5 men, 6 women), mean age 28.4 years, with unilateral ACL insufficiency, with two braces (Donjoy Legend, and Bledsoe Brace Force III) versus a placebo brace. The patients were tested on a Biodex Dynamometer at 60 and 180 deg/s in an isokinetic mode. The experiment was designed as a comparative study in a crossover design with the stable knee as the patient's own control. We found no statistically significant effect of the two braces compared to a placebo brace under the test conditions, and no correlation between knee laxity and the effect of bracing.     

The forces in a knee brace as a function of hinge design and placement

Customized knee braces for three normal subjects were instrumented to monitor the forces and moments across the hinges as the subjects performed various activities. The forces and moments were taken to represent a mismatch between actual knee motion and the motion the brace sought to impose. The different hinge designs studied were fixed axis, gear-on-gear, rack-and-pinion, and natural 3-D; they showed only moderate differences in forces. Much larger differences were seen if the hinges were offset 12 mm from the ideal placement. Posterior placement resulted in the least force and anterior placement the highest. The mismatch of knee motion to brace motion would probably lead to abnormal ligament lengths and tensions and other internal mechanical changes, as well as to pistoning and discomfort. The results of this study have implications on brace design, selection, and placement.     

The biomechanics of lateral knee bracing. Part I: Response of the valgus restraints to loading

To better understand the role of preventive knee braces in injury prevention, a biomechanical study using fresh frozen cadaveric knees (N = 18) was conducted. Ligament tensions and joint displacements were measured at static, nondestructive valgus forces as well as low-rate destructive forces. After quantifying and establishing individual ligament contributions to valgus restraining function, knees were then braced with two different laterally applied preventive braces, the McDavid Knee Guard and the Omni Anderson Knee Stabler. The effects of lateral bracing were analyzed according to valgus force, joint line opening, and ligament tensions. Valgus applied forces, with or without braces, consistently produced medial collateral ligament (MCL) disruptions at ligament tensions surprisingly higher than the anterior cruciate ligament (ACL) and higher than or equal to the posterior cruciate ligament (PCL). Although large joint displacements were necessary for complete ligament failure, bundle disruption in the MCL, ACL, and PCL was noted at much smaller joint openings. In Part I of this study, no significant protection could be documented with the two preventive braces used. Also, four potentially adverse effects were noted: MCL preload, center axis shift, premature joint line contact, and brace slippage.