, and meetings of the American Economic Association, Association for Public Policy Analysis and Management, and National Bureau of Economic Research for helpful comments. All opinions are of course our own and do not necessarily represent the views of the Federal Reserve Board of Governors or its staff. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

Background: The use of artificial turf in American football continues to grow in popularity, and the effect of these playing surfaces on athletic injuries remains controversial. Knee injuries account for a significant portion of injuries in the National Collegiate Athletic Association (NCAA) football league; however, the effect of artificial surfaces on knee injuries remains ill-defined. Hypothesis: There is no difference in the rate or mechanism of knee ligament and meniscal injuries during NCAA football events on natural grass and artificial turf playing surfaces. Study Design: Descriptive epidemiology study. Methods: The NCAA Injury Surveillance System Men’s Football Injury and Exposure Data Sets for the 2004-2005 through 2013-2014 seasons were analyzed to determine the incidence of anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), medial meniscus, and lateral meniscal tear injuries. Injury rates were calculated per 10,000 athlete exposures, and rate ratios (RRs) were used to compare injury rates during practices and competitions on natural grass and artificial turf in NCAA football as a whole and by competition level (Divisions I, Divisions II and III). Mechanisms of injury were calculated for each injury on natural grass and artificial turf surfaces. Results: A total of 3,009,205 athlete exposures and 2460 knee injuries were reported from 2004 to 2014: 1389 MCL, 522 ACL, 269 lateral meniscal, 164 medial meniscal, and 116 PCL. Athletes experienced all knee injuries at a significantly higher rate when participating in competitions as compared with practices. Athletes participating in competitions on artificial turf experienced PCL injuries at 2.94 times the rate as those playing on grass (RR = 2.94; 95% CI, 1.61-5.68). When stratified by competition level, Division I athletes participating in competitions on artificial turf experienced PCL injuries at 2.99 times the rate as those playing on grass (RR = 2.99; 95% CI, 1.39-6.99), and athletes in lower NCAA divisions (II and III) experienced ACL injuries at 1.63 times the rate (RR = 1.63; 95% CI, 1.10-2.45) and PCL injuries at 3.13 times the rate (RR = 3.13; 95% CI, 1.14-10.69) on artificial turf as compared with grass. There was no statistically significant difference in the rate of MCL, medial meniscal, or lateral meniscal injuries on artificial turf versus grass when stratified by event type or level of NCAA competition. No difference was found in the mechanisms of knee injuries on natural grass and artificial turf. Conclusion: Artificial turf is an important risk factor for specific knee ligament injuries in NCAA football. Injury rates for PCL tears were significantly increased during competitions played on artificial turf as compared with natural grass. Lower NCAA divisions (II and III) also showed higher rates of ACL injuries during competitions on artificial turf versus natural grass.

No abstract

Purpose To compare gap displacement at various intervals of cyclic testing and biomechanical load to failure of a Krackow patellar tendon repair augmented with high-strength suture tape versus the standard Krackow transosseous technique for inferior pole patellar tendon rupture. Methods Twelve matched pairs of cadaveric knees were used (8 males and 4 females; mean age 79.6 years, range 57 to 96). An inferior pole patellar tendon rupture was simulated after random assignment of specimens in each pair to the standard or augmented Krackow technique. Each specimen was then repetitively cycled from 90° to 5° for 1,000 cycles. A differential variable reluctance transducer was used to measure gap displacement. After cyclic loading, load to failure was determined by pulling the tendon at a rate of 15 mm/s until a sudden decrease in load occurred. Results Compared with the control repair, specimens with augmented repair demonstrated significantly less displacement at all testing intervals up to 1,000 cycles ( P < .05). Two patellar tendons failed before the end of cyclic loading, and 4 specimens had inadequate tendon length for loading. Among the 18 remaining specimens, no significant difference in load to failure was observed between the experimental group (n = 11) and the control group (n = 7) (1,006.5 ± 332.1 versus 932.8 ± 229.1 N, respectively; P = .567). Conclusions Significantly greater gap displacement was observed in the standard Krackow repair group compared with the augmented Krackow group at all cyclic loading intervals. This suggests that the Krackow transosseous procedure augmented with high-strength suture tape is biomechanically viable for inferior pole patellar tendon repair. Clinical Relevance This biomechanical study supports the use of high-strength suture tape augmentation of Krackow transosseous repair for inferior pole patellar tendon rupture.

No abstract