Bracing is often recommended after anterior cruciate ligament reconstruction, in the interest of controlling range of motion and protecting the graft as it heals. However, few studies have scientifically examined this practice, and the available findings are conflicting.
By Laura Chachula, Kenneth L. Cameron, PhD, ATC, LTC Steven J. Svoboda, MD, and LTC Brett D. Owens, MD
The anterior cruciate ligament (ACL) controls motion at the tibiofemoral joint in the transverse plane.1,2 It aids in the passive stability of the joint by guiding the knee through internal and external rotation as well as abduction and adduction movements.3,4 Injury of the ACL, dependent on the degree of tear and nature of any subsequent injuries, can significantly alter the biomechanics of the knee through decreased stability, increased laxity of the joint, and diminished proprioception.3 With a deficient ligament, further damage can occur within the joint compartment, as instability often leads to meniscal and cartilage damage.3,5 For this reason, immobilization of the knee is frequently utilized in an effort to protect the joint and restore function by mimicking bilateral symmetry of the lower extremities—the ultimate goal of ACL rehabilitation.3
Surgical intervention and postoperative bracing
While some individuals are able to cope with a partial or complete ACL tear, many individuals who are either unable to regain normal function or are active in sports with frequent cutting, and large unpredictable forces placed on the knee, opt to undergo ACL reconstructive surgery.4 In this operation the deficient ligament is reconstructed with a tendon graft (typically hamstring or patellar tendon autograft, or allograft).4
Knee bracing is often suggested for one or two months following reconstructive surgery, as most surgeons are in agreement that a more extensive period of bracing can contribute to atrophy and associated losses in function and proprioception.3,6 Knee braces are thus used to help control range of motion, reduce anterior-posterior movement, shield against varus-valgus forces, and prevent quadriceps lag.3,7 In a study by Hiemstra et al, a sample of 65 surgeons, who performed more than 12 ACL reconstructions annually, was queried as to their preference and reasoning concerning post-operative bracing for the knee.6 The results indicated that 51.6% of the 31 doctors who use knee immobilizers following ACL reconstruction claimed their main motive in bracing patients is to reduce pain after surgery.6 Protection of the graft (38.7%), maintaining full extension (19.4%), and habit (12.9%) made up the remaining responses.6 Marx et al reported that 60% of surgeons surveyed recommended bracing post-ACL reconstruction (and 40% did not).8 Controversy exists as to whether immediate bracing post-ACL reconstruction is necessary, with some concern that it may even pose a risk of harm.5,6
Protecting the graft
Once the ACL graft is reconstructed, protecting the graft from excessive force in post operative period is of the utmost importance. In order to maintain a viable graft, the patient must protect the knee from undue forces that may disrupt the integrity or revascularization of the graft. Knee braces are often used with this goal in mind. Though braces might be effective in restraining anterior translations for minimal anterior shear forces, this does not carry over for larger, less predictable forces.9,10 Ramsey et al showed in a 3D kinematic analysis of functional bracing that while minor kinematic changes were evident with bracing, there was no consistency in reducing tibial translation during dynamic motion.9 This is a key point, as functional knee performance is not static, but dynamic in nature.4
Notably, while some functional braces have demonstrated protection from shear forces around 100N to 150 N, the maximal load of the ACL is approximately 2000 N.7 Even if bracing showed promising levels of protection sufficient to accommodate forces toward the upper end of this range, brace failure can still occur if the device is not properly fitted or worn correctly.2 For hinged braces especially, correct alignment of the hinges with the knee joint trumps all other brace criteria in regard to their stabilizing effects.11 However, because the knee lacks any fixed rotational center, even when worn properly, the hinged brace typically falls short of adequately replicating the kinematics of the knee joint.11
Whether knee braces are able to mechanically protect the reconstructed anterior cruciate ligament is unclear. In a study of ACL deficient subjects, Hinterwimmer et al found that with the loss of ACL function, increased tension is placed on collateral ligaments of the knee acting as secondary stabilizers.1 It was reported that the use of a mono-centric knee brace significantly decreased tension on both the medial and lateral collateral ligaments, bringing them to near-normal values and providing mechanical protection for these ligaments.1 Yet the idea that functional knee braces mechanically stabilize the knee is generally discounted. Instead, it is thought that the brace acts to alter motor patterns, thereby stabilizing the knee through increased symmetry and thus providing optimal conditions for recovery.2,3,12
Proprioception and muscle recruitment
Changes in muscle recruitment are the result of proprioceptive mechanisms that are sent via neural impulses to the brain.9 Joint proprioception is crucial to knee joint function and stabilization, as mechanoreceptors, muscle and tendon receptors all send afferent messages to the central nervous system, which in turn modifies neuromuscular activity.10
After an ACL tear, muscles act synergistically to stabilize the affected joint, leading to changes in muscle recruitment as shown in a modified EMG response; however, with bracing this synergistic activity is further altered by both quadriceps and hamstring groups.10 Not surprisingly, these muscle groups have unbalanced modifications of EMG activity when the knee is braced, giving credence to the idea that prolonged bracing can negatively affect synergistic muscle function and even lead to significant hamstring atrophy.10 Lu et al showed that bracing reconstructed patients resulted in increased peak moments and impulses of abductors and extensors, in addition to reduced bilateral kinetic asymmetry.3
The use of a functional knee brace was originally thought to correlate to neuromuscular performance enhancement; however Birmingham et al found that improvements in proprioception due to bracing, as tested through a battery of stabilization and hop tests, although statistically significant, were only of minimal clinical significance.10,12 In the study, subjects wearing custom-fit ACL functional knee braces (at least six months post reconstruction) showed improved balance for a standing single-limb balance test, yet these gains were not repeated when subjects were asked to perform more difficult balancing tasks.12 Their study suggests that feedback from joint, skin and muscle receptors increases with task difficulty to the degree that any benefits provided by the brace may be rendered insignificant in the face of increased sensory motor activity.12 Furthermore, with regards to the testing timeframe, it is possible that the increased receptor communication due to brace-skin-bone contact is limited only to the initial postoperative stages after surgery, suggesting the possibility of gaps between studies.5
Joint laxity and functional outcomes
One of the main concerns of postoperative bracing is increased joint stiffness, which can hinder a patient’s return to normal physical activities.13 Joint laxity is an important indicator of functional outcome post-ACL surgery as it affects joint range of motion (ROM) as well as bilateral symmetry of the lower extremities. Despite these concerns, however, patients are often immobilized at full extension following surgery in order to help maintain full extension and also to allow for proper ROM through the duration of rehabilitation.14 Flexed immobilization has been found to lead to a loss of extension after ACL reconstruction, in a well-designed randomized control trial (RCT).11 In this study by Melegati et al, two groups of subjects underwent ACL reconstructive surgery with grafts harvested from the same site (bone-tendon-bone) and subjects adhered to identical physical rehabilitation methods.11 One group remained braced in full extension for the week following surgery, while the second group remained locked from 0° to 90°.5 The patients locked in full extension for one week were better able to restore complete knee extension over an eight week period than the group allowed immediate 0° to 90° range of motion.11 This is a critical finding as extension deficits are a common complication following ACL reconstruction.
In another well-designed multicenter RCT of young athletes following ACL reconstruction, two subject groups were immobilized at full extension for three weeks post-operatively prior to enacting experimental conditions.14 From the third to sixth week, one group began using a hinged side-bar brace (limiting subjects at 10° of maximal patient flexion), while the second group went without a brace for the remainder of the study.14 Unlike the previously described study by Melegati, both groups were able to benefit from the period of immobilization in full extension, as little variation was shown between the two groups in terms of either subjective or objective outcomes.14 The results of these two studies suggest that a brief period of immobilization (one to three weeks) following ACL reconstruction may be beneficial in limiting extension deficits; however, immobilization past three weeks may prove unnecessary.
In a less conservative study, both braced and non-braced individuals were subject to early weight bearing rehabilitation.7 In reviewing joint laxity, functional performance levels, and ROM, among other factors, the study concluded that subjects using postoperative braces failed to exhibit any benefits from bracing compared to the non-braced test population at any follow-up stage over a two-year period.7 In fact, in following patients after surgery, the non-braced group actually showed higher levels of physical activity than their braced counterparts at six months out, though in the long-term such group disparities became less apparent.7 A randomized clinical trial conducted by Brandsson et al also showed no long term differences in functional outcomes two years following ACL reconstruction between subjects who wore a knee brace during the three weeks following surgery and those who did not wear a brace.15 However, Brandsson et al did observe decreased pain scores in the braced group during the first two weeks following surgery. They also observed fewer complications in the braced group during the first two weeks postoperatively (e.g., swelling, haemarthrosis, wound leakage), although these differences were not statistically significant.
These data help illustrate a common trend in the current literature related to bracing following ACL reconstruction, which suggests that postoperative bracing has limited value in terms of long term knee functionality, laxity, and activity levels following ACL reconstruction.13 Furthermore, the short term benefits of bracing reported by Brandsson et al should be interpreted with caution, as patients and outcome evaluators were not blinded to group assignment, which may have influenced the results related to these subjective measures.
Patient compliance with bracing protocol
Regardless of whether bracing provides any benefits or not, these benefits are irrelevant if the patient does not comply with treatment guidelines. While some patients might request to use a brace post operatively due to perceived benefits and increased security, others might choose to forego a bracing protocol altogether citing brace slippage, pressure sores and decreased range of motion as primary concerns.5,14
In comparing a soft water-filled brace with a commonly prescribed hard brace, Mayr et al. found that the softer brace led to decreased extension deficit and swelling while maintaining similar levels of thigh atrophy and ROM as the hard brace.5 Though providing slight comfort advantages over rigid braces, soft braces such as the neoprene sleeve unexpectedly correlate with decreased patient confidence in knee functionality.16 Muellner et al reported that a neoprene bandage resulted in significantly better ROM and functional performance on a one-leg hop test during the first 24 weeks following ACL reconstruction when compared to a group wearing a traditional hinged brace; however, no between-group differences remained at one year post surgery.17 Still, as shown by both Birmingham et al16 and Muellner et al,17 no excess strain or graft elongation occurred in either hard or soft brace groups, despite some patients’ inclinations for use.16 Whether increased feelings of security associated with a rigid brace provides the patient with a false perception of one’s knee capabilities, leading to increased risk of injury, is left for future research to consider.16
Although a soft brace might offer an alternative for patient comfort, the compression of any brace has the potential to decrease circulation and cause undue muscle fatigue, exacerbating patient discomfort.7 It is crucial to ensure a proper fit and level of comfort as subjects are less likely to properly use an ACL brace if slippage or discomfort persists.2,5 Looking past the possible negative reception of bracing by ACL reconstruction patients, in one study of a young, athletic population 50% of 38 survey respondents (despite expressing some of the aforementioned complaints) said they would request similar postoperative bracing if given the option in the future.14
The use of postoperative braces following ACL reconstruction remains controversial. The literature supports improvements in proprioception as well as mechanical protection from some of the forces that the graft is subjected to. Many current rehabilitation protocols employ brace use during the initial three to six weeks following reconstruction. While this early postoperative brace use is supported by the literature, longer term brace use beyond three weeks has not been shown to have a positive effect on patient outcomes or reduce post surgical complications in randomized clinical trials.
Laura Chachula is a cadet majoring in Kinesiology at the United States Military Academy, West Point, NY. Kenneth L. Cameron, PhD, ATC, CSCS is director of orthopaedic research and LTC Steven J. Svoboda, MD, is director of the John A. Feagin, Jr. Sports Medicine Fellowship at Keller Army Hospital, also in West Point, NY. LTC Brett D. Owens, MD, is chief of orthopaedic surgery at Keller Army Hospital.
Disclosure: The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or United States government. The authors are employees of the U.S. government.
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16. Birmingham TB, Bryant DM, Giffin JR, et al. A randomized controlled trial comparing the effectiveness of functional knee brace and neoprene sleeve use after anterior cruciate ligament reconstruction. Am J Sports Med 2008;36(4):648-655.
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