Prophylactic Knee Braces

The efficacy of prophylactic knee bracing has been refuted with regard to reducing the incidence and/or severity of injuries to the knee joint. This is thought to be a result of the prophylactic knee brace's ineffectiveness in protecting the knee joint from valgus loads. Furthermore, discrepancies exist regarding the prophylactic knee brace's detrimental effect on functional performance. The purpose of this study was to measure the effect of the prophylactic knee brace on selected isokinetic muscular characteristics andforward sprint speed. Twenty physically active, healthy, male college students with no prior history of brace use participated in this study. The subjects were randomly tested both with and without the prophylactic knee brace worn on various performance parameters. The dependent measures Paul A. Borsa is a doctoral student in the Exercise Physiology/Athletic Training Program at the University of Pittsburgh in Pittsburgh, PA 15261. Scott M. Lephart is Director of Sports Medicine/Athletic Training, an assistant professor in the School of Education, and an assistant professor in the School of Medicine, Department of Orthopedics, at the University of Pittsburgh. Freddie H. Fu is a Blue Cross/Blue Shield of Western Pennsylvania Professor of Orthopedic Surgery, and Team Physician at the University of Pittsburgh. assessed included peak torque (PT) and torque acceleration energy (TAE) at 60 and 240°/s. A 40-yard forward sprint was selected to assess sprint speed. A paired t-test analysis revealed mean values which were significantly lessfor PT at 60°/s (p < .05), 240°/s (p < .01), and TAE at 240°/s (p < .05) with the prophylactic knee brace applied during knee extension. Analysis also revealed slower times for sprint speed (p < .01), while the subjects were wearing the prophylactic knee brace. Muscular strength (PT) and power (TAE) scores were not correlated (p > .05) with sprint speed. This study suggests that wearing the prophylactic knee brace may consequently inhibit muscular and functional performance of the athlete, but that specific population has yet to be studied. E a pidemiological studies have recognized that knee joint injuries are the most common disabling injuries in athletics.24'28 Consequently, the use of prophylactic lateral knee braces in football has increased in an attempt to reduce the incidence and/or severity of injuries to the knee joint. 1012,14,2731 The efficacy of such knee braces has been refuted by researchers regarding prevention of laterally applied valgus loads that may induce ligamentous injuries to the knee joint. 1,2,6,21,22 The discrepancies in the efficacy of the prophylactic benefits of the prophylactic knee brace have led to inconsistencies among clinicians recommending their use. Inconsistencies in the available literature have elicited further scrutiny regarding the effects and possible decrements in functional performance while wearing the prophylactic knee brace. The prophylactic knee brace may inhibit leg muscle function and sprint speed, both of which are essential to athletic performance.7"13'25 Thus, the term "functional" as used in this manuscript implies dynamic muscular activity objectively measured for comparative analysis. The purpose of this study was to address these discrepancies in the literature by objectively measuring selected isokinetic muscular characteristics and sprint speed under the braced and nonbraced conditions. We hypothesized that the isokinetic muscular test scores would be significantly decreased and forward sprint times would be significantly slower in the braced condition, suggesting functional inhibition. Furthermore, there has been some debate suggesting that sprint speed is related to muscular strength and power.'5 Since these three performance parameters were measured in this study, we also hypothesized that strength measured as peak torque (PT), power measured as torque acceleration energy (TAE), and sprint speed would be positively correlated all during the nonbraced condition. Methods Twenty physically active, healthy, male college students (age = 21.3 + 3.6yr,ht=68+2.4 in, wt= 167 ±7.2 lb) with no prior history of brace use voluntarily participated in this study. Exclusion criteria included any previous knee pathology requiring surgical intervention, anterior cruciate ligament deficiency, and/or patellofemoral dysfunction. Informed consent approved by the Institutional Review Board at the University of Pittsburgh were reviewed and signed by each subject prior to testing. The subject acted as his own control and was tested on two separate sessions for both conditions (braced versus nonbraced). 336 Volume 28 * Number 4 * 1993 The test conditions (brace or nonbrace) were randomized, thus preventing the occurrence of any learning effects. The subjects attire consisted of a t-shirt, gym shorts, and athletic shoes. Two commercially available prophylactic knee braces were used according to the manufacturer's specifications. They were selected due to their popular use among intercollegiate football players. The McDavid Knee Guard (MKG) (M-155; McDavid Knee Guard Inc, Clarendon Hills, Ill) has a single-hinge design, while the Omni (Omni Scientific Inc, Lafayette, Ill) has a double or polyaxial design (Fig 1). The two prophylactic knee braces were randomly assigned to subjects with 11 wearing the MKG and 9 the Omni. The prophylactic knee brace was worn unilaterally on the dominant leg for the isokinetic tests (Fig 2), and bilaterally for testing sprint speed (Fig 3). Subjects were tested with identical protocols on two separate days, and the sessions were separated by 48 hours to allow for proper recovery. Test protocol consisted of testing for strength and power on the Cybex unit and sprint speed on an indoor track. Isokinetic muscular testing was computed using the Cybex H isokinetic testing device (Lumex, Inc, Ronkonkoma, NY). Subjects completFig 1.-The McDavid Knee Guard (top) is a single-hinge design, while the Omni (bottom) is a doubleor poly-hinge design. Fig 2.-During isokinetic testing, the prophylactic knee brace was worn unilaterally. ed a 5-minute warm-up on a Monarch stationary bicycle at a preset cadence (70 rpm) and resistance (.04 kg) relative to the subject's body weight (eg, 60 kg X .04 = 2.4 kp). Cybex testing was conducted in an isolated, thermoneutral environment. The parameters selected for testing included PT and TAE measured at two angular velocities (60 and 2400/s). Peak torque is defined and measured as the greatest torque produced during a given set of contractions, while TAE is defined and measured as the amount of work performed in the first one eighth of a second of torque production.5 Peak torque is recorded as a strength measure, and TAE is recorded as an anaerobic power output measure in this study.17'23 Each subject was tested using gravity correction, and standard stabilization was employed at the chest, waist, and distal thigh.3'4 The Cybex was calibrated prior to testing of the subjects. Each subject received verbal instructions prior to testing, followed by five pretrial submaximal repetitions at 600/s in order to accommodate to the test speed. After a 30second recovery, subjects completed four maximal repetitions and the highest value was recorded as PT. A 1minute recovery was given before continuing at the next test speed. Ten submaximal repetitions were used as a pretrial for testing at 2400/s in order for the subject to accommodate with the faster test speed. After a 30-second recovery, subjects completed four maximal repetitions and the highest values were recorded as TAE and PT. For testing sprint speed, the subjects went through a warm-up consisting of light jogging for 800 meters and large muscle group flexibility exercises. Each subject familiarized himself with the sprint distance by completing two submaximal trial runs. The 40-yard forward sprint was selected, due to its reproducibility and relevance to college football. The sprint was performed at maximal speed with the mean time (seconds) of three trials recorded as the criterion measure. A 1minute recovery period was given between trials. Sprint times were recorded by the same investigator using a hand-held stopwatch measured to the nearest tenth of a second. Analysis of variance (ANOVA) was used to identify significant (p < .05) differences between the two prophylactic knee brace designs on the various testing parameters. The selected isokinetic and sprint speed tests were treated as four separate tests and paired t-test analyses (p < .05) were used to compare the braced and the nonbraced (control) conditions for the