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This prospective cohort study was conducted to identify the risk factors for acute knee injuries among male football players. A total of 508 players representing 31 amateur teams were tested during the 2004 preseason for potential risk factors for knee injury through a questionnaire on previous injury, Knee Osteoarthritis Outcome Score (KOOS) and a clinical examination. Generalized estimating equations were used in univariate analyses to identify candidate risk factors, and factors with a P-value o0.10 were then examined in a multivariate model. During the football season, 61 acute knee injuries, affecting 57 legs (53 players), were registered. Univariate analyses revealed the KOOS subscores ‘‘Pain’’ and ‘‘Function in daily living’’ (OR for a 10-point difference in score: 1.26, 95% CI 1.03– 1.55 and 1.35, 95% CI 0.98–1.85, respectively), any findings at clinical examination (OR: 2.62, 95% CI 1.03–6.68), flexion contraction in range of motion testing (OR: 0.96, 95% CI 0.93–1.00) and varus stress tests in full extension (OR: 8.50, 95% CI 1.85–39.0) and 301 flexion (OR: 5.69, 95% CI 1.73–18.8) as candidate factors. However, in a multivariate analysis, none of these factors were associated with an increased injury risk.

This prospective cohort study was conducted to identify risk factors for acute ankle injuries among male soccer players. A total of 508 players representing 31 amateur teams were tested during the 2004 pre-season through a questionnaire on previous injury and function score (foot and ankle outcome score; FAOS), functional tests (balance tests on the floor and a balance mat) and a clinical examination of the ankle. Generalized estimating equations were used in univariate analyses to identify candidate risk factors, and factors with a P-value

Elevated levels of the neurotransmitter glutamate and the presence of its receptor, N-methyl-d-aspartate receptor type 1 (NMDAR1), have been established in patients with tendinopathy, i.e. chronic tendon pain and degeneration. However, whether NMDAR1 is up- or down-regulated in tendinopathy and co-localized with glutamate is still unexplored. We hypothesize that an alteration in tissue expression and in the coexistence of NMDAR1 and glutamate occurs in tendinopathy and might play a role in nociception and possibly also progression of tendon degeneration (tendinosis). We therefore examined the tissue distribution and levels of NMDAR1 and glutamate in biopsies from patients with patellar tendinopathy (n=10) and from controls (n=8). The biopsies were single- and double-stained immunohistochemically for glutamate and NMDAR1 and assessed subjectively and semi-quantitatively. The chronic painful tendons exhibited a significant elevation of NMDAR1 (ninefold), which was independent of the observed increase in glutamate (10-fold). This up-regulation of NMDAR1 and glutamate was found to be co-localized on nerve fibers as well as on morphologically altered tenocytes and blood vessels. None of the controls exhibited neuronal coexistence of glutamate and NMDAR1. The neuronal coexistence of glutamate and NMDAR1, observed in painful tendinosis but not in controls, suggests a regulatory role in intensified pain signalling.

who did not [relative risk (RR) 5 1.53, P 5 0.22], nor was there a difference compared with the baseline data (RR 5 0.89, P 5 0.75). The incidence of hamstring strains was lower in teams who used the eccentric training program compared with teams that did not use the program (RR 5 0.43, P 5 0.01), as well as compared with baseline data for the same intervention teams (RR 5 0.42, P 5 0.009). Eccentric strength training with Nordic hamstring lowers combined with warm-up stretching appears to reduce the risk of hamstring strains, while no effect was detected from flexibility training alone. These results should be verified in randomized clinical trials.

All cruciate ligament injuries in the three upper divisions for men and women (3392 players) in Norwegian team handball in the 1989-90 and 1990-91 seasons were registered. A questionnaire was mailed to all injured players. Ninety-three cruciate ligament injuries were registered; 87 in the anterior cruciate ligament (ACL), and six in the posterior cruciate ligament (PCL). Among women, 1.8% were injured compared with 1.0% of the men. In the first division, the risk of being injured was considerably higher: 4.5% of the players had a cruciate ligament injury. There were 0.97 cruciate ligament injuries per 100 playing hours in the three divisions taken together. Seventy-five per cent of the injuries occurred during games. Ninety-five per cent involved no contact between players. Activities in which the friction between shoe and floor was significant caused 55% of the injuries. Injuries caused by running into another player contributed to only 5% of the injuries. No significant differences were observed in injury incidence during matches between different types of floors (parquet, Pulastic and other synthetic surfaces.)

Background: Methods for analyzing the mechanisms of injuries in sports from video sequences of injury situations are so far limited to a simple visual inspection, which has shown poor accuracy. Purpose: To investigate whether a new model-based image-matching technique could successfully be applied to estimate kinematic characteristics of three typical anterior cruciate ligament (ACL) injury situations. Methods: A four-camera basketballvideo, a three-camera European team handball video and a single-camera downhill skiing video were imported into the program Poser® 4, where a skeleton model and a model of the surroundings were matched to the background image frame by frame. When the match was considered satisfactory, joint angles as well as velocity and acceleration of the center of mass were calculated using Matlab®. Results: In the basketball and handball matchings, the skeleton and surrounding models were successfully matched to the background through all frames in all camera angles. Detailed time courses for joint kinematics and ground reaction force were obtained, while less information could be acquired from the single-view skiing accident. Conclusion: The model-based image matching technique can be used to extract kinematic characteristics from videotapes of actual ACL injuries, and may provide valuable information on the mechanisms for ACL injuries in sports.

The purpose of this study was to examine the injury incidence and pattern of injuries in youth female and male team handball players using two different prospective registration methods; match reports (90 teams, 1080 players) and coach reports (34 teams, 428 players). A total of 118 injuries were recorded by the coach report, of which 93 (79%) were acute injuries (incidence training: 0.9+/-0.16 injuries/1000 player hours; matches: 9.9+/-1.26; rate ratio vs training: 10.8 [95% confidence interval (CI) 7.0-16.6]; P

We study nonBoolean PCPs that have perfect completeness and read three positions from the proof. For the case when the proof consists of values from a domain of size d for some integer constant d/spl ges/2, we construct a nonadaptive PCP with perfect completeness and soundness d/sup -1/+d/sup -2/+/spl epsiv/, for any constant /spl epsiv/>0, and an adaptive PCP with perfect completeness and soundness d/sup -1/+/spl epsiv/, for any constant /spl epsiv/>0. The latter PCP can be converted into a nonadaptive PCP with perfect completeness and soundness d/sup -1/+/spl epsiv/, for any constant /spl epsiv/>0, where four positions are read from the proof. These results match the best known constructions for the case d=2 and our proofs also show that the particular predicates we use in our PCPs are nonapproximable beyond the random assignment threshold.

By the breakthrough work of Hastad [J ACM 48(4) (2001), 798–859], several constraint satisfaction problems are now known to have the following approximation resistance property: Satisfying more clauses than what picking a random assignment would achieve is NP-hard. This is the case for example for Max E3-Sat, Max E3-Lin, and Max E4-Set Splitting. A notable exception to this extreme hardness is constraint satisfaction over two variables (2-CSP); as a corollary of the celebrated Goemans-Williamson algorithm [J ACM 42(6) (1995), 1115–1145], we know that every Boolean 2-CSP has a nontrivial approximation algorithm whose performance ratio is better than that obtained by picking a random assignment to the variables. An intriguing question then is whether this is also the case for 2-CSPs over larger, non-Boolean domains. This question is still open, and is equivalent to whether the generalization of Max 2-SAT to domains of size d, can be approximated to a factor better than (1 − 1/d2). In an attempt to make progress towards this question, in this paper we prove, first, that a slight restriction of this problem, namely, a generalization of linear inequations with two variables per constraint, is not approximation resistant, and, second, that the Not-All-Equal Sat problem over domain size d with three variables per constraint, is approximation resistant, for every d ≥ 3. In the Boolean case, Not-All-Equal Sat with three variables per constraint is equivalent to Max 2-SAT and thus has a nontrivial approximation algorithm; for larger domain sizes, Max 2-SAT can be reduced to Not-All-Equal Sat with three variables per constraint. Our approximation algorithm implies that a wide class of 2-CSPs called regular 2-CSPs can all be approximated beyond their random assignment threshold. © 2004 Wiley Periodicals, Inc. Random Struct. Alg. 2004

The purpose of this study was to compare the ACL injury rate between two different floor types - wooden floors (parquet, generally having lower friction) and artificial floors (generally having higher friction). ACL injuries have been recorded prospectively from the three top divisions for men and women in Norwegian team handball during seven seasons (1989-2000). A total of 174 ACL injuries have been recorded, and of these 53 occurred in regular league games. The floor types for all regular games from the same seasons have been determined retrospectively based on match schedules. The matches were divided into two groups: those played on wooden floors and those played on artificial floors. A total of nine injuries occurred among men (incidence: 0.24+/-0.09 injuries per 1000 player hours) and 44 among women (0.77+/-0.04 injuries 1000 h(-1); OR vs. men: 3.21 (1.56-6.58); P=0.001). Among men, four injuries occurred on wooden floors (0.32+/-0.13 injuries 1000 h(-1)) and five injuries occurred on artificial floors (0.20+/-0.12 injuries 1000 h(-1); OR vs. wooden floors: 0.63 (0.17-2.37); ns). Among women, eight injuries occurred on wooden floors (0.41+/-0.09 injuries 1000 h(-1); OR vs. men: 1.29 (0.39-4.28); ns) and 36 on artificial floors (0.96+/-0.04 injuries 1000 h(-1); OR vs. wooden floors: 2.35 (1.09-5.07); P=0.03; OR vs. men: 4.77 (1.87-12.18); P=0.001). These results indicate that the risk of ACL injury for women is higher on artificial floors than on wooden floors.

Many NP-hard languages can be "decided" in subexponential time if the definition of "decide" is relaxed only slightly. Rubinfeld and Sudan introduced the notion of property testers, probabilistic algorithms that can decide, with high probability, if a function has a certain property or if it is far from any function having this property. Goldreich, Goldwasser, and Ron constructed property testers with constant query complexity for dense instances of a large class of graph problems. Since many graph problems can be viewed as special cases of the Constraint Satisfaction Problem on Boolean domains, it is natural to try to construct property testers for more general cases of the Constraint Satisfaction Problem. In this paper, we give explicit constructions of property testers using a constant number of queries for dense instances of Constraint Satisfaction Problems where the constraints have constant arity and the variables assume values in some domain of finite size.

We present a retrospective study of the number of arthroscopically verified total meniscus and cruciate ligament tears seen in our Emergency department one year before, and one year after introducing magnetic resonance imaging (MRI) as a diagnostic tool. The number of total ruptures of the anterior cruciate ligament increased from 34 (1.7% of total 2003 patients) to 67 (2.9% of total 2277). The number of ruptures of the medial meniscus increased from 42 (2.1%) to 87 (3.8%). The number of ruptures of the lateral meniscus remained unchanged. In the first 12 months after introducing MRI we ordered 513 (23%) scans of the total number of 2277 patients with an acute knee condition. Thirty-nine (8%) of these were described with no pathology, 227 (44%) showed total meniscus or cruciate ligament tears. The remaining 247 (48%) were mainly degenerative or partial injuries. The cost per additional new diagnosis was approximately USD 800. The introduction of MRI has enabled us to identify a larger number of patients with meniscus and cruciate ligament injuries.

Patellar tendinitis is a condition that occurs in patients who are involved in repetitive use of the extension mechanism. The most common symptoms are pain at the inferior pole of the patella, and radiographic changes may also occur. This case report demonstrates an extreme example of elongation of the inferior pole of the patellar tendon. The ossification caused the patient pain, which was resolved with surgical removal of the bone.

We evaluated retrospectively the 5-year outcome of 13 patients with an initially undiagnosed and thus untreated anterior cruciate ligament rupture. At follow-up, these patients experienced decreased knee function and moderate to severe knee instability. They had attempted to reduce their discomfort by decreasing their activity level during the follow-up period. Immediately after the 5-year examination, 6 of the patients decided to have a late reconstruction of the ruptured anterior cruciate ligament. These results agree with previous reports of the natural course of anterior cruciate ligament ruptures.

In order to determine the appropriate load history for optimal remodeling of an anterior cruciate ligament graft, methods for establishing and measuring graft forces in vivo are required. Our objectives with this study were to (a) develop a method in which the graft force due to an external load could be set to a preselected value in a living animal, (b) show that this force could be maintained after fixation, and (c) determine what happens to the forces after the animal has functioned for as long as 2 weeks postoperatively, when differing levels of load sharing between the segments had been set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a bone-patellar tendon-bone graft and a synthetic augmentation device. The forces in the graft segments were established, at the time of surgical fixation, with use of a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force; in the remaining seven animals, the augmentation segment was set to share 90% of the total graft force. Graft forces were measured, with the use of buckle transducers mounted extra-articularly over the anterior tibia, under a 67 N anterior tibial load at 60° of knee flexion before and after fixation and at 2 weeks postoperatively. When the tendon was the high force-carrying member, the force in the tendon decreased by an average of 25% during the 2 weeks after surgical fixation, while the force in the augmentation segment showed a significant increase of 111%. When the augmentation segment was the high force-carrying segment, the force in that segment decreased by an average of 10% during the 2 weeks and the tendon force increased by 47%. These data suggest that when the tendon was set to carry high force, it may have stretched, due to biological changes in the tissue, and that the augmentation segment was not as greatly affected over the 2 postoperative weeks when it was set to carry most of the total load. Because of the frictional effects of the graft segments passing around the osseous contours of the anterior tibia and the fact that the calibrations of the buckle transducer from surgery were used to reduce the data on force at 2 weeks postoperatively, there are uncertainties related to the measured graft segment forces in this study. However, if the animals had been killed and the buckle transducers calibrated immediately after the test at 2 weeks, these uncertainties would not exist.

This study was undertaken to determine how accurately total graft force and load-sharing between graft segments could be set and maintained during augmented anterior cruciate ligament (ACL) reconstruction in the goat knee. Special procedures were developed to reduce the effect of tissue creep and to overcome difficulties in the setting of graft force. Five knees from goat cadavers were reconstructed using a bone-tendon-bone graft (PT) and a synthetic augmentation device (LAD). Prescribed levels of total graft force and load-sharing between the autograft and LAD were set under a standardized external joint load. Immediately after fixation, the set force declined an average of 9 and 3% in the LAD and PT, respectively. After three subsequent exercise sequences, the set forces fell from their initial level by an average of 25% for the LAD and 28% for the PT. An analysis of variance did not show the loss of force with exercise to be statistically significant. We conclude from this in vitro study that our method can be used to set forces in an ACL reconstruction with reasonable maintenance of load-sharing but that losses of approximately 30% of total graft force after exercise of the reconstructed joint are to be expected.

List of Contributors, vi Foreword, viii Preface, ix 1 Why is injury prevention in sports important? 1 Lars Engebretsen and Roald Bahr 2 A systematic approach to sports injury prevention 7 Willem Meeuwisse and Roald Bahr 3 Developing and managing an injury prevention program within the team 17 Andrew McIntosh and Roald Bahr 4 Preventing ankle injuries 30 Jon Karlsson, Evert Verhagen, Bruce D. Beynnon and Annunziato Amendola 5 Preventing knee injuries 49 Timothy E. Hewett, Bruce D. Beynnon, Tron Krosshaug and Grethe Myklebust 6 Preventing hamstring injuries 72 Geoffrey M. Verrall and Arni Arnason, Kim Bennell 7 Preventing groin injuries 91 Per Holmich, Lorrie Maffey and Carolyn Emery 8 Preventing low back pain 114 Adad Baranto, Tor Inge Andersen and Leif Sward 9 Preventing shoulder injuries 134 Michael R. Krogsgaard, Marc R. Safran, Peter Rheinlaender and Emilie Cheung 10 Preventing elbow injuries 153 Mark R. Hutchinson and James R. Andrews 11 Preventing injuries to the head and cervical spine 175 Paul McCrory, Michael Turner and Andrew McIntosh 12 Preventing tendon overuse injuries 187 Jill Cook, Mads Kongsgaard, Karim Khan and Michael Kjaer 13 Implementing large-scale injury prevention programs 197 Randall W. Dick, Claude Goulet and Simon Gianotti 14 Planning for major events 212 Michael Turner and Jiri Dvorak Index, 228

The objective of this study was to develop a method for obtaining a controllable and reproducible immediate postoperative mechanical state in a knee with an anterior cruciate ligament (ACL) reconstruction. This method, called the force-setting technique, was demonstrated using a composite graft consisting of the middle third of the patellar tendon with bone blocks (PT) and the ligament augmentation device (LAD). The total graft force was set to match the force in the intact ACL at 30° flexion with the knee under the same standardized external load, while at the same time the load sharing between the biologic and augmentation components was controlled. The total graft force was set to match the ACL force three separate times in each knee, with ratios of load sharing set at the following levels: 50% PT-50% LAD, 25% PT-75% LAD, and 75% PT-25% LAD. ACL, PT, LAD, and collateral forces were measured using buckle transducers, and three-dimensional knee motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to eigth specimens at 0°, 30°, 60°, and 90° flexion with an intact ACL, an excised ACL, and the three load-sharing reconstruction states. The total graft force could be consistently set to within an average of 2% of the intact ACL force at 30° flexion, and load sharing between the graft segments could be set to within an average of 5.1% of the desired ratio at 30°. The load sharing was maintained at the other flexion angles except 90° when the PT was to have carried 25 and 50% of the total graft force, and extension when the PT was to have carried 75% of the graft force. When averaged over all specimens and flexion angles, the total graft force was 15% greater than the force in the ACL, and this was not statistically significant.

The effect of the maximum unloaded graft length (Lo) and femoral fixation hole location on graft force with the knee under anteriorly directed tibial loads was measured in five fresh cadaver knees with a reconstruction of the anterior cruciate ligament (ACL). The reconstruction was performed using a composite graft consisting of the semitendinosus and gracilis tendons augmented with the Kennedy ligament augmentation device (LAD). Buckle transducers were used to measure ligament and graft forces. The total graft force was adjusted to match the intact ACL at 30 degrees flexion using a force-setting method so that a standardized reference configuration could be repeatedly obtained. The graft force was highly sensitive to Lo, typically changing by 50% with a change in Lo of 3 mm. Variation in femoral hole location of 5 mm anterior, posterior, proximal, and distal to the anatomic position produced changes in graft force, particularly at 60 degrees and 90 degrees flexion; however, these changes were not statistically significant. The effect of femoral hole location varied considerably between knees. This variability makes predicting proper hole placement difficult, and suggests the need to adjust each knee at surgery to account for this variable femoral hole position sensitivity.