White Matter Changes Related to Subconcussive Impact Frequency during a Single Season of High School Football.

BACKGROUND AND PURPOSE: The effect of exposing the developing brain of a high school football player to subconcussive impacts during a single season is unknown. The purpose of this pilot study was to use diffusion tensor imaging to assess white matter changes during a single high school football season, and to correlate these changes with impacts measured by helmet accelerometer data and neurocognitive test scores collected during the same period. MATERIALS AND METHODS: Seventeen male athletes (mean age, 16 ± 0.73 years) underwent MR imaging before and after the season. Changes in fractional anisotropy across the white matter skeleton were assessed with Tract-Based Spatial Statistics and ROI analysis. RESULTS: The mean number of impacts over a 10-g threshold sustained was 414 ± 291. Voxelwise analysis failed to show significant changes in fractional anisotropy across the season or a correlation with impact frequency, after correcting for multiple comparisons. ROI analysis showed significant (P < .05, corrected) decreases in fractional anisotropy in the fornix-stria terminalis and cingulum hippocampus, which were related to impact frequency. The effects were strongest in the fornix-stria terminalis, where decreases in fractional anisotropy correlated with worsening visual memory. CONCLUSIONS: Our findings suggest that subclinical neurotrauma related to participation in American football may result in white matter injury and that alterations in white matter tracts within the limbic system may be detectable after only 1 season of play at the high school level.

Contributions of neuroimaging, balance testing, electrophysiology and blood markers to the assessment of sport-related concussion.

OBJECTIVE: To review the diagnostic tests and investigations used in the management of sports concussion, in the adult and paediatric populations, to (a) monitor the severity of symptoms and deficits, (b) track recovery and (c) advance knowledge relating to the natural history and neurobiology of the injury. DESIGN: Qualitative literature review of the neuroimaging, balance testing, electrophysiology, blood marker and concussion literature. INTERVENTION: PubMed and Medline databases were reviewed for investigations used in the management of adult and paediatric concussion, including structural imaging (computerised tomography, magnetic resonance imaging, diffusion tensor imaging), functional imaging (single photon emission computerised tomography, positron emission tomography, functional magnetic resonance imaging), spectroscopy (magnetic resonance spectroscopy, near infrared spectroscopy), balance testing (Balance Error Scoring System, Sensory Organization Test, gait testing, virtual reality), electrophysiological tests (electroencephalography, evoked potentials, event related potentials, magnetoencephalography, heart rate variability), genetics (apolipoprotein E4, channelopathies) and blood markers (S100, neuron-specific enolase, cleaved Tau protein, glutamate). RESULTS: For the adult and paediatric populations, each test has been classified as being: (1) clinically useful, (2) a research tool only or (3) not useful in sports-related concussion. CONCLUSIONS: The current status of the diagnostic tests and investigations is analysed, and potential directions for future research are provided. Currently, all tests and investigations, with the exception of clinical balance testing, remain experimental. There is accumulating research, however, that shows promise for the future clinical application of functional magnetic resonance imaging in sport concussion assessment and management.

Detecting altered postural control after cerebral concussion in athletes with normal postural stability.

OBJECTIVE: To determine if approximate entropy (ApEn), a regularity statistic from non-linear dynamics, could detect changes in postural control during quiet standing in athletes with normal postural stability after cerebral concussion. METHODS: The study was a retrospective, case series analysis of centre of pressure (COP) data collected during the Sensory Organization Test (SOT) from NCAA Division I (USA) athletes prior to and within 48 h after injury. Subjects were 21 male and six female athletes from a variety of sports who sustained a cerebral concussion between 1997 and 2003. After injury, athletes displayed normal postural stability equivalent to preseason levels. For comparison, COP data also were collected from 15 male and 15 female healthy non-athletes on two occasions. ApEn values were calculated for COP anterior-posterior (AP) and medial-lateral (ML) time series. RESULTS: Compared to healthy subjects, COP oscillations among athletes generally became more regular (lower ApEn value) after injury despite the absence of postural instability. For AP time series, declines in ApEn values were much larger in SOT conditions 1 and 2 (approximately three times as large as the standard error of the mean) than for all other conditions. For ML time series, ApEn values declined after injury in all sensory conditions (F(1,55) = 6.36, p = 0.02). CONCLUSIONS: Athletes who demonstrated normal postural stability after concussion nonetheless displayed subtle changes in postural control. Changes in ApEn may have represented a clinically abnormal finding. ApEn analysis of COP oscillations may be a valuable supplement to existing concussion assessment protocols for athletes.

No acute changes in postural control after soccer heading.

BACKGROUND: Soccer heading has been proposed as a potential cause of cerebral dysfunction. OBJECTIVE: To examine the acute effects of two types of soccer heading on postural control. METHODS: Collegiate soccer players were randomly assigned to one of four groups: control, linear heading, simulated rotational heading, or rotational heading. Each subject completed a baseline postural stability assessment on day 1. On day 2 the same assessment was completed for the control subjects. The simulated rotational heading group completed a simulated heading drill before postural stability testing. The linear and rotational heading groups performed a heading drill with 20 balls at 88.71 km/h (55 mph), before postural stability testing. Separate one between (group), three within (surface, eyes, and day), mixed model, repeated measures analyses of variance were conducted on values for total sway and mean centre of pressure. RESULTS: The mixed model analysis of variance of results showed no significant differences (p>0.05) for the interactions of interest for either variable. Results suggest no acute changes in measures of postural control in soccer players completing either a linear or rotational soccer heading drill of 20 balls at a fixed speed. CONCLUSION: Non-significant interactions between surface, eyes, day, and group indicate that sensory interaction of the balance mechanism components are not be compromised by the heading drill. This research supports previous studies suggesting that there are no acute risks associated with routine soccer heading. A direct comparison between these findings and those suggesting long term chronic deficits, however, cannot be made. Other studies that report chronic cerebral deficits in soccer players may have resulted from factors other than soccer heading and warrant further examination.

Augmented feedback reduces jump landing forces.

STUDY DESIGN: Randomized, experimental design using a 1-way ANCOVA to determine the influence of various forms of feedback on jump landing forces. OBJECTIVE: To investigate the effects of augmented feedback versus sensory feedback on the reduction of jump landing forces. BACKGROUND: Several investigators have reported an increased risk of lower extremity injury associated with landing from a jump. METHODS AND MEASURES: Nonimpaired college students (N=63) were randomly assigned to 1 of 4 feedback groups. Subjects were instructed to perform maximal vertical jumps onto a force plate for 3 testing sessions (baseline, 2-minute post-test, and 1-week post-test). Three feedback groups (augmented, sensory, and control I) were tested during all 3 testing sessions, while a fourth feedback group (control II) was evaluated at only 2 sessions (baseline and 1-week post-test). Subjects in the augmented feedback condition were provided information via video and verbal analysis of how to land softer. Subjects in the sensory feedback condition were asked to use the experience of their baseline jumps to document how they could land softer. Subjects in each of the control groups were not provided any extraneous feedback. Peak vertical ground reaction force data were collected for analysis. RESULTS: The subjects in the augmented feedback group significantly reduced their peak vertical ground reaction force in both post-test conditions (2-minute post-test reduction, 0.85+/-0.62; 1-week post-test reduction, 0.74+/-0.58) as compared to the sensory, control I, and control II feedback groups. CONCLUSIONS: High impact landing forces may be reduced by the implementation of augmented feedback information instructing individuals about how to land properly. The reduction of jump landing forces with the use of augmented feedback may prove beneficial in the creation of instructional landing programs.

Postural stability assessment following concussion: one piece of the puzzle.

Clinicians regularly assess concussion according to the symptoms that an athlete manifests at the time of injury, as well as during subsequent evaluations. The subjectivity involved with symptom assessment, however, often leaves the clinician without a clear picture of the athlete's true mental status. Neuropsychologic testing has become very popular in the sports medicine community for assessing the cognitive domain of neurologic functioning, and postural stability testing is gaining credence for assessing the motor domain. The objective of this review was to determine the efficacy of postural stability testing as an adjunct to concussion assessment of athletes. Multiple studies, using both sophisticated force plate technology, as well as those using less sophisticated clinical balance tests, have identified postural stability deficits lasting several days following sport-related concussion. It appears that postural stability testing provides a useful tool for objectively assessing the motor domain of neurologic functioning, and should be considered a reliable and valid adjunct to the assessment of athletes suffering from concussion. Although symptom severity, neurocognitive function, and postural stability are often affected initially following concussion, they are not necessarily related or even affected to the same degree.

Epidemiology of concussion in collegiate and high school football players.

Despite evolutionary changes in protective equipment, head injury remains common in football. We investigated concussion in football and associated epidemiologic issues such as 1) incidence of injury, 2) common signs and symptoms, and 3) patterns in making return-to-play decisions. We received 242 of 392 surveys (62%) that were sent to high school and collegiate certified athletic trainers at the beginning of three football seasons. Of the 17,549 football players represented, 888 (5.1%) sustained at least one concussion, and 131 (14.7% of the 888) sustained a second injury during the same season. The greatest incidence of concussion was found at the high school (5.6%) and collegiate division III (5.5%) levels, suggesting that there is an association between level of play and the proportion of players injured. Players who sustained one concussion in a season were three times more likely to sustain a second concussion in the same season compared with uninjured players. Contact with artificial turf appears to be associated with a more serious concussion than contact with natural grass. Only 8.9% of all injuries involved loss of consciousness, while 86% involved a headache. Overall, 30.8% of all players sustaining a concussion returned to participation on the same day of injury.

Effects of mild head injury on postural stability as measured through clinical balance testing.

OBJECTIVE: Although force-platform measures of postural stability provide objective information concerning mild head injury (MHI) resolution, their application has remained limited due to the high costs and impracticality for sideline use. Therefore, we investigated the efficacy of a clinical balance testing procedure for the detection of acute postural stability disruptions after MHI. DESIGN AND SETTING: We used a posttest control group design with repeated measures. Postural stability was tested at 3 postinjury time intervals (days 1, 3, and 5) using 2 procedures in a sports medicine laboratory: 1) a clinical balance battery consisting of 3 stances (double leg, single leg, and tandem) on 2 surfaces (firm and foam), and 2) the Sensory Organization Test using a sophisticated force-platform system. SUBJECTS: Sixteen MHI and 16 matched control subjects participated in this study. MEASUREMENTS: We measured performance with the Balance Error Scoring System for each of the clinical balance tests and the NeuroCom Smart Balance Master for Sensory Organization Testing. RESULTS: We found significantly higher postural instability in the MHI subjects revealed through the clinical test battery, with the 3 stances on the foam surface eliciting significant differences through day 3 postinjury. Results of the Sensory Organization Test revealed significant group differences on day 1 postinjury. CONCLUSIONS: Our results revealed that the Balance Error Scoring System may be a useful clinical procedure to assist clinicians in making return-to-play decisions in athletes with MHI in the absence of force-platform equipment.

A comparison of sideline versus clinical cognitive test performance in collegiate athletes.

OBJECTIVE: To test whether performance on 5 cognitive tests administered in a controlled clinical environment differed compared with administration in an uncontrolled sideline environment. Additionally, we investigated the effect of testing environment order on the learning effect for each cognitive test. DESIGN AND SETTING: Athletes were assessed on 2 test occasions (8 +/- 2 days apart), once in a sports medicine research laboratory and once on a lacrosse practice field site. SUBJECTS: A total of 59 Division I collegiate student-athletes participated in this study. MEASUREMENTS: Normative data were collected on 5 cognitive tests (Stroop Test, Trail-Making Test part A, Trail-Making Test part B, Wechsler Digit-Span Forward Test, and Digit-Span Backward Test). RESULTS: An independent-samples t test for environment difference on test day 1 revealed no significant differences between tests performed in the controlled environment and those performed in the uncontrolled environment. A repeated- measures analysis of variance test revealed a significant learning effect for all 5 tests, as subjects tended to improve approximately 11 points on the Stroop Test, 3 seconds on the Trail-Making A Test, 7 seconds on the Trail-Making B Test, and 1 point each on the Wechsler Digit Span Forward and Backward Tests. A paired-samples t test using delta scores (first test minus second test), sorted by order of testing environment, revealed a significant difference for the Stroop Test, but not for the remaining cognitive tests. CONCLUSIONS: There appears to be no difference in cognitive testing performance completed in a controlled clinical environment versus that performed in an uncontrolled sideline environment. This finding suggests that clinicians can administer cognitive tests to athletes with mild head injuries in uncontrolled sideline environments and expect valid results. Thus, clinicians can more thoroughly evaluate mildly head-injured athletes during the most crucial period after injury so that a safe return-to-play decision can be based on quantifiable, objective data.

Stress fracture of the eighth rib in a female collegiate rower: a case report.

OBJECTIVE: To present the case of a stress fracture of the eighth rib in a female collegiate rower. BACKGROUND: A female collegiate rower experienced severe pain in her chest, increasing with movement, deep breathing, and erect posture. No acute mechanism of injury was apparent. The team physician diagnosed a rib stress reaction based on clinical examination. The athlete rested for 2 days and then was able to resume rowing workouts. Five months later, she experienced the same sharp pain, with the diagnosis and treatment being the same. The athlete was able to compete in the championships 3 weeks later. At the end of the season, a bone scan revealed a stress fracture of the eighth rib. The athlete rested for 3 weeks and then returned to activity. DIFFERENTIAL DIAGNOSIS: Intercostal muscle strain, serratus anterior muscle strain. TREATMENT: Active rest, involving pain-free cardiovascular workouts and weight training, cessation of rowing until the athlete was asymptomatic, strengthening of dynamic support structures, and analgesic modalities. UNIQUENESS: Most stress fractures occur in the lower extremity. Those that do occur in the rib cage most often involve the first rib. A limited number of published works have addressed stress fractures to the remaining ribs; of these, posterior and posterolateral fracture sites are most often reported. This case is unique in that the fracture site was on the anterolateral aspect of the eighth rib. CONCLUSIONS: Stress fractures are thought to result from a variety of causes, including muscular fatigue, sudden changes in training intensity or duration, and microtrauma to bone at the muscular origin and insertion sites ("wear-and- tear" theory). In addition, hormonal factors in women can predispose an athlete with amenorrhea to a decrease in bone mineral content. Athletic trainers should be aware of these potential causes and focus on the prevention of stress fractures.

Comparison of 3 methods of external support for management of acute lateral ankle sprains.

OBJECTIVE: To examine the efficacy of 3 different types of injury support systems (standard elastic wrap with horseshoe, Aircast Sport Stirrup, and Omni Multiphase orthosis) used in treating acute inversion ankle sprains. SUBJECTS: We recruited 30 physically active college-aged subjects who had sustained a grade 1 + or 2 lateral ankle sprain within the previous 24 hours for the study. DESIGN AND SETTING: Subjects were randomly placed into one of 3 groups, the first treated with standard elastic wrap with horseshoe, the second with an Aircast Sport Stirrup, and the third with an Omni Multiphase orthosis. Subjects reported to the athletic training room on days 1, 2, 3, 5, and 7 postinjury. MEASUREMENTS: We assessed subjects for ankle volume, functional performance, and self-perception of symptoms during the 5 postinjury assessments. RESULTS: We found no significant differences among the 3 groups on measures of volume, level of function, and self-perception of symptoms. CONCLUSIONS: Our results suggest that none of these methods is superior to the others for reducing swelling, restoring function, or relieving symptoms during the acute management of lateral ankle sprains.

Syncope and atypical chest pain in an intercollegiate wrestler: a case report.

OBJECTIVE: To present the case of a 20-year-old collegiate wrestler who suffered from atypical chest pains and syncope after rigorous exercise, dehydration, and ingestion of a metabolic stimulant. BACKGROUND: As a result of pressure to obtain a lower body weight for competition, wrestlers often pursue practices to lose a substantial amount of weight in a short period of time. These practices include rigorous exercise, starvation, dehydration, laxatives, diuretics, and over-the-counter stimulants. Our case involves an athlete who ingested a metabolic stimulant containing ma huang (ephedrine) and suffered from syncope and atypical chest pains during a bout of rigorous exercise and dehydration to lose weight for competition. DIFFERENTIAL DIAGNOSIS: Hypertrophic cardiomyopathy, electrolyte imbalance, drug overdose, traumatic head injury, myocardial infarction, syncope. TREATMENT: The emergency medical services transported the athlete to the emergency room, and he was hospitalized for 2 days. After discharge, the team physician counseled the athlete in the dangers of metabolic stimulants and excessive weight-loss techniques. UNIQUENESS: This case is unique because it presents an athlete who ingested an over-the-counter stimulant to lose weight and suffered from syncope and atypical chest pains during a bout of rigorous exercise and dehydration. CONCLUSIONS: Athletic trainers must understand not only the dangers of excessive weight loss, but also the dangers of using unregulated ephedrine-containing stimulants to aid in weight loss.

Proprioception and neuromuscular control of the shoulder after muscle fatigue.

OBJECTIVE: To examine the effects of fatigue on proprioception and neuromuscular control of the shoulder. DESIGN AND SETTING: Subjects were randomly assigned to either an experimental group or control group. Subjects were tested using either the active angle-reproduction or the single- arm dynamic stability test. The subjects were then fatigued using a dynamometer performing continuous, concentric rotation exercises of the shoulder. Once fatigued, the subjects were posttested using the same test. One week later, the subjects returned and were pretested, fatigued, and posttested using the other test. SUBJECTS: Thirty-two college-age (18 to 25 years) subjects (16 males, 16 females) with no history of glenohumeral instability or upper extremity injury volunteered for this study. MEASUREMENTS: Absolute angular error was measured using an electrogoniometer present within the isokinetic dynamometer, while sway velocity was measured using a force-plate system. RESULTS: Repeated-measures analysis of variance revealed a significant difference between the pretest and posttest values for absolute angular error in the experimental group, whereas no significant difference was revealed between pretest and posttest sway velocity for either the control or experimental group. CONCLUSIONS: Fatigue of the internal and external rotators of the shoulder decreased proprioception of the shoulder, while having no significant effect on neuromuscular control.

Establishment of normative data on cognitive tests for comparison with athletes sustaining mild head injury.

OBJECTIVE: To provide normal data for comparison with objective measures of an athlete's cognitive ability after mild head injury (MHI). SUBJECTS: Seventy-two Division I college athletes. DESIGN AND SETTING: Athletes were assessed on three test dates (two days apart) in a sports medicine research laboratory. MEASUREMENTS: Normative data were collected on four cognitive tests (Hopkins Verbal Learning Test, Stroop Test, Reitan Trail-Making Tests, and Wechsler Digit Span Tests). RESULTS: A repeated-measures analysis of variance revealed significant learning effects on all tests except the Hopkins Verbal Learning Test. A high correlation was noted between the Stroop and the Trail-Making Tests. CONCLUSIONS: These normative data can be used as comparisions to provide an objective measure of an athlete's cognitive ability following MHI. By adding this test battery to the athlete's other physical and neurologic tests, the decision to return an athlete to competition after MHI can be made with greater confidence and with less risk of reinjury.

Alternative approaches to the assessment of mild head injury in athletes.

OBJECTIVES: Athletic trainers and team physicians are often faced with decisions concerning the severity and timing of an athletes return to play following mild head injury (MHI). These decisions can be the most difficult ones facing clinicians because of the limited amount of quantitative information indicating injury severity. Several authors have published guidelines for return to play following MHI, however these guidelines are based on limited scientific data. The purpose of this paper was to examine the effects of MHI on two objective measures, postural stability and cognitive function, to determine their usefulness in MHI assessment. The data gathered from these two measures has the potential to establish recovery curves based on objective data. METHODS: Eleven Division I collegiate athletes who sustained a MHI and eleven matched control subjects were assessed for postural stability and cognitive function at four intervals following injury. Postural stability was assessed using the Sensory Organization Test on the NeuroCom Smart Balance Master. Cognitive functioning was measured through the use of four neuropsychological tests: Stroop Test, Trail Making Test, Digits Span and Hopkins Verbal Learning Test. Separate mixed model repeated measures ANOVAs were calculated for the composite score and three ratio (vestibular, visual and somato-sensory) scores from the Sensory Organization Test and the scores from the neuropsychological test to reveal significant differences between groups and across days postinjury. RESULTS: A significant group by day interaction for overall postural stability (composite score) revealed that MHI athletes displayed increased postural instability for the first few days following MHI (p < .05). Analysis of the ratio scores revealed a significant interaction for the visual ratio. No significant group differences were revealed for any of the neuropsychological tests (p > .05), however significant day differences were revealed (p < .05). CONCLUSIONS: The results from this study indicate that athletes demonstrate decreased stability until 3 days postinjury. It appears this deficit is related to a sensory interaction problem, whereby the injured athlete fails to use their visual system effectively. These findings suggest that measures of postural stability may provide clinicians with a useful clinical tool for determining when an athlete may safely return to competition, although these findings need to be confirmed in larger groups of athletes.

Effect of mild head injury on postural stability in athletes.

OBJECTIVE: Athletic trainers and team physicians are often faced with the dilemma of when to return athletes to participation following mild head injury. Unfortunately, clinicians rarely have quantitative information on which to base their decisions. The purpose of this investigation was to identify postural stability changes in athletes with acute mild head injury. DESIGN AND SETTING: High school and college male athletes were prescreened for postural stability before the start of their season. Subjects suffering injury during the season returned for testing on days 1, 3, 5, and 10 following injury, and 1 month postseason. Control subjects were selected for comparisons. SUBJECTS: Ten prescreened subjects (age = 17.4 +/- 2.2 yr; ht = 183.8 + 8.1 cm; wt = 87.7 + 17.3 kg) returned for testing following an injury. Ten matched control subjects (age = 18.6 +/- 2.6 yr; ht = 185.7 +/- 6.7 cm; wt = 84.5 +/- 19.5 kg) were selected for comparisons. Additionally, nine subjects (eight male and one female) (age = 19.9 +/- 4.2 yr; ht = 182.3 + 10.9 cm; wt = 89.6 +/- 25.2 kg) who had sustained a mild head injury from other varsity sports teams were recruited. Nine matched controls (age = 22.1 +/- 3.3 yr; ht = 181.0 +/- 9.9 cm; wt = 84.9 +/- 25.6 kg) were again utilized. MEASUREMENTS: Sway index and center of balance were measured using the Chattecx Balance System during three eye conditions and three surface conditions for all subjects. RESULTS: Repeated measures analyses of variance (ANOVA) for each prescreened subject's sway index revealed significant differences between injured subjects and control subjects on day 1 postinjury as compared with the prescreening and/or subsequent tests. The analysis for sway index and center of balance inclusive of all 19 subjects with mild head injury and all 19 control subjects demonstrated increased postural sway compared with control subjects on day 1 postinjury during all plafform conditions, and on day 3 during the foam platform condition. The analysis for center of balance using the same subjects revealed that injured subjects maintained their center of balance farther away on day 1 postinjury compared with subsequent tests (p < .05). CONCLUSIONS: These findings suggest that computerized dynamic posturography is a useful tool in objectively assessing postural stability in subjects with mild head injuries. Subjects with mild head injury appear to demonstrate impaired postural stability 1 to 3 days following injury. This information should aid clinicians in determining when an athlete can safely return to participation.

Effect of orthotics on postural sway following inversion ankle sprain.

Orthotic devices have been shown to successfully modify selected aspects of lower extremity mechanics and enhance foot stability during the support phase of running. It was hypothesized that orthotic intervention would relieve excessive strain on the ankle ligaments and reduce postural sway, especially in subjects with acute ankle sprains. The primary purpose of this study was to determine if orthotics would reduce postural sway in injured and uninjured subjects. Thirteen subjects with acute inversion ankle sprain and 12 uninjured subjects were assessed for postural sway on the Balance System under two treatment conditions (orthotic and nonorthotic) and four platform movements. A three-factor repeated measures analysis of variance revealed a significant group X treatment interaction, suggesting that postural sway with orthotic intervention improved significantly more in injured subjects than in uninjured subjects. A significant platform movement X treatment interaction, furthermore, revealed that postural sway for the four movement conditions was dependent upon treatment (orthotic vs. no orthotic). Tukey post hoc analysis revealed that orthotic intervention significantly reduced postural sway when the platform moved in the medial/lateral plane and inversion/eversion plane. This research suggests that custom-fit orthotics may restrict undesirable motion at the foot and ankle and enhance joint mechanoreceptors to detect perturbations and provide structural support for detecting and controlling postural sway in ankle-injured subjects.

Effect of ACL Reconstruction and Tibial Rotation on Anterior Knee Laxity.

The anterior cruciate ligament (ACL) is the primary restraint to anterior translation of the tibia on the femur. Research suggests that resistance to anterior translation changes as the tibia is rotated internally and externally. This study assessed the degree to which ACL reconstruction and tibial rotation affects anterior knee laxity. Nine subjects with ACL lesions and functional instabilities participated in the study. Subjects were measured 1 to 10 days before surgery and 6 to 8 months after ACL reconstruction using the KT-1000 knee arthrometer. A mechanical leg stabilizer was used to assess anterior translation at 20 degrees of knee flexion in three positions: internal rotation of 15 degrees , neutral, and external rotation of 15 degrees . Subjects were measured at 89 and 67 N of anterior force. Data were analyzed with a three-factor (test x position x force) repeated measures ANOVA. Following surgery, reduction in laxity (mm) for the three positions (internal rotation, neutral, and external rotation) was 1.9, 2.8, and 3.4, respectively, at 89 N and 1.5, 2.0, and 2.6, respectively, at 67 N. The degree of reduction in laxity (presurgery to postsurgery) was dependent upon rotation and force, and was greatest in external rotation and least in internal rotation pre- to postsurgery. We concluded that ACL reconstruction using a patellar tendon graft significantly decreased anterior tibial translation at all three positions, but a greater amount of reduction was observed postsurgically at the externally rotated position. This supports the theory that mechanical blocks and secondary restraints such as a taut mid-third of the iliotibial tract may interfere with clinical laxity tests in some positions of tibial rotation. Fixing the tibia in an externally rotated position may decrease the effect of secondary restraints and improve sensitivity in testing for ACL laxity.