Orthopedics

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Sports Medicine Update 

Injuries in Men’s Lacrosse

Bernard R. Bach, Jr., MD; Patrick C. McCulloch, MD

As participation in lacrosse expands into new geographic areas, orthopedic surgeons who are unfamiliar with the sport will be called on to treat these patients. Familiarity with the game and its unique injury patterns is essential.

Lacrosse is the most rapidly growing team sport in the United States.1 It also is the oldest team sport in North America, with roots in Native American tradition. One of the original purposes of the game was to keep men fit and prepared for war.2

Since 2003, there has been an overall growth of 41% in the number of players participating in lacrosse nationwide. The number of youth and high school programs is increasing dramatically.

While the sport has a long tradition on the East Coast of the United States and in Canada, it has gained increasing popularity nationwide. Since 1995, the number of US varsity high school programs has grown nearly 200% to >2332 teams. There are >360,000 active players in the United States, with a projected growth of >20% annually.1,3,4 Despite these high participation levels, relatively few recent sport-specific publications exist on lacrosse injuries.

Game Description

Men’s lacrosse is a team field sport played with 10 players per side on a field 110 yards long. Players attempt to gain possession of the ball in their sticks and advance it down the field either by running or passing in an effort to shoot the ball into the opposing team’s goal. The ball is held in the webbing of the stick, or “crosse,” at the end of a metal shaft. Offensive players use sticks that are 40 inches (1 m) in length, while defensemen may use a stick that is up to 6 feet (1.8 m) in length.

Body checking and stick checking are used to defend the goal and attempt to regain possession of the ball. A player may be body checked from the front or side whenever he possesses or is within 5 yards of the ball. Stick checks may be used to the arms or hands in an attempt to dislodge the ball. In this respect, the men’s game differs from the women’s game, which has a distinctly different set of rules intended to limit player-to-player and stick-to-player contact. The result is a fast-paced, continuous action game combining elements of soccer, basketball, and ice hockey. The specific injury patterns reflect these different elements.

Protective Equipment

Both US Lacrosse and the NCAA have set regulations that require the use of protective equipment designed mainly to protect the head and upper extremities. This includes a circumferential helmet (similar to a hockey helmet) with full facemask, mouth guard, and four-point chin strap. Non-cantilevered shoulder pads, arm pads (which typically cover mid-arm to mid-forearm), and padded gloves that cover the wrist are also required. Groin protection is strongly recommended. No protection is required on the back, chest, ribs, abdomen, hips, or lower extremities (Figure 1).

NCAA Injury Rates

Men’s lacrosse is sometimes perceived to be a violent sport, but injury statistics do not support this claim. For the past 20 years, the National Collegiate Athletic Association (NCAA) has maintained prospective injury surveillance data on inter-collegiate lacrosse programs. Injury rates have been defined for players per 1000 athletic exposures. An athletic exposure refers either to a practice session or game.

While it is listed by the NCAA as a “collision sport,” in the same category with football and ice hockey, lacrosse has lower reported injury rates. For the 2004 season, the overall injury rate for men’s lacrosse was 4.7 per 1000 athletic exposures and 11.5 for games.5,6 Compared to other NCAA sports, lacrosse ranks seventh in game injury rate (Figure 2).6 Recent prospective studies have described the epidemiology of lacrosse injuries in high school boys’ and girls’ lacrosse, and in women’s collegiate lacrosse.7,8 Together with the NCAA data, these studies have begun to shed light on the specific injury patterns and injury rates for lacrosse.

Reviewing the available literature, certain trends have consistently been observed. Most injuries above the waist occur from direct trauma. These occur either from a collision with another player, or as a result of impact from a stick check or thrown ball. In contrast, lower extremity injuries often occur from non-contact mechanisms, such as pivoting or twisting. Approximately 40% of lacrosse injuries are non-contact.5,9,10

According to the NCAA, the body parts most frequently injured were the ankle, upper leg, and knee, which combined accounted for 48% of the injuries (Table 1).3

The injury rate in games is significantly higher than that in practice.6,11 For the past 10 years, game injury rates have been 3 to 5 times higher than practice injury rates, which suggests the need for medical coverage during games as is common for football.6

Body part reported injured in NCAA men’s lacrosse

Type of injury reported in NCAA men’s lacrosse

In games, the most frequently injured body parts are the shoulder, knee, and upper leg.5,6,10 These accounted for 40% of the in-game injuries.6 The top three injury types are sprains, strains, and contusions (Table 2).5,6,10 While the pattern is similar, the overall injury rates for high school players are only one-third those of collegiate players.7

Despite the fact that injuries are fairly common, they generally are minor and rarely require surgical intervention. The University of Virginia reported that for one season, although 85% of players reported an injury, only 20% of these injuries resulted in any missed practice or games.11 The NCAA data shows that 37% of the reported injuries caused a loss of 2 practice sessions.5 The rate of injuries requiring surgery was 0.3 per 1000 athletic exposures, which corresponds to approximately 6% of all injuries.5,12

Head/Neck

Protective helmets with full facemasks and mouth guards are required. Lacrosse helmets must meet National Operating Committee Standards for Athletic Equipment standards for safety, as do football and hockey helmets.13,14 Despite this fact, cerebral concussion injuries are still common. Diamond and Gale15 reported on head injuries in lacrosse and found that the most common mechanism was collision with another player. This was twice as common as sustaining a concussion from being struck in the head by an illegal stick check or a ball. National Collegiate Athletic Association data shows that head injuries represented 9% of all injuries.6 Over 90% of these were classified as grade 1 injuries.5,10

Formerly, players often were cleared for return to play in a game following a minor concussion. However, a new consensus statement on concussion in sports was published following the Prague 2004 Symposium. It recommends that no player should return to play in a game or practice in which he has sustained any degree of concussion.16 They recommended an evaluation by a physician, and gradual step-wise return to play. Recurrent or more complex injuries also may benefit from neuropsychological testing.17

Neck injuries are uncommon. A direct blow to the shoulder may result in a “burner,” or transient traction injury to the brachial plexus resulting in parasthesias and pain. This injury occurs less commonly than is seen in football.

Body checking should be performed with the head up to prevent cervical spine injury, as can occur with spearing in football. In an injured athlete, a high suspicion for cervical spine injury should be maintained. Studies have supported the practice of in-line stabilization with the lacrosse helmet left in place.18 As in football, access to the airway should achieved by removing the facemask with a screwdriver or bolt cutter.

Chest/Ribs/Back

While shoulder pads are required by rule, the currently used models sit directly atop the shoulders and do not provide adequate coverage of the chest and ribs. Rib fractures and contusions are not uncommon.9,11 These areas can be protected with the use of a hanging rib pads; however, some players believe that this prohibitively restricts their mobility. Interestingly, abdominal injuries appear to be exceedingly rare. There are isolated case reports of pancreatitis from a direct blow and splenic rupture from a stick check.19,20

The goalie is the only player required to wear an anterior chest protector. While it remains an exceedingly rare injury, there have been several reported cases of commotio cordis.21-24 This may result in sudden death when a player is struck in the sternum while defending a shot. It is believed to be caused by an impact occurring during a specific phase of cardiac repolarization resulting in the usually fatal arrhythmia.21 This occurs more commonly in the adolescent age group. It can occur from even a low-velocity impact, and has been reported in both field players and goalies (who are wearing chest protectors).

It is not clear whether the modification of the shoulder pads to include sternal protection is likely to decrease incidence of this rare occurrence. Currently available chest protection is inadequate, and research efforts are now underway by US Lacrosse to address this issue and potentially modify protective equipment. Furthermore, the NCAA Sports Medicine Handbook recently has added early access to an automated external defibrillator to its guidelines.25 Recent surveys of NCAA Division I programs revealed that >90% of schools are equipped with this potentially lifesaving device.26

The back is largely unpadded and contusions from errant checks occur. However, most back injuries are muscle strains from collisions and falls. Open field play often involves twisting and bending as players attempt to pick up ground balls and dodge oncoming defensemen. Midfielders and attackmen are more likely to experience back strains than defensemen.11 According to a recent study in collegiate athletes, the overall incidence of low-back pain was not significantly greater for contact than non-contact sports. The factor most predictive of in-season back reports was a history of previous back injury.27

Shoulder/Elbow

Lacrosse is somewhat unique in that it is an overhead collision sport. Furthermore, the added length provided by the lacrosse stick creates a long lever arm potentially generating increased torque on the shoulder when a player falls or is struck with the arm away from the body (Figure 3). These factors combine to result in the relatively high rate of shoulder injuries. In fact, the shoulder is the most frequently injured body part during games.6

Shoulder instability is common in the young athletic population. Acute anterior subluxation or dislocation may occur when a player is struck or falls while holding the stick overhead or out to the side. Symptoms of instability may be noted when reaching back for a pass or during wind-up of a shot. These activities place the arm in an extended and externally rotated position, that may be exacerbated by the long lever arm of the stick. Restrictor braces that limit the range of motion in an attempt to avoid the position of dislocation are poorly tolerated by players as it interferes with the normal motions of reaching for a pass or wind-up of a shot. Excellent return to play rates can be expected with surgical repair, with recurrent dislocation rates similar to other contact sports.28

While anterior instability is by far the most common, posterior instability occurs. Warren has noted several cases of posterior Bankart lesions and believes that the mechanism is similar to that seen in football lineman.29,30 This may occur from a collision with another player or a fall to the ground with the arm in a forward flexed position.

Superior labral tears often are felt to occur due to compression of the glenohumeral joint in the abducted arm. This mechanism is re-created when a player is checked with the arms in an overhead position, such as when reaching for a pass or shooting. There is an increased recognition of this type of injury in young athletes in all throwing sports.31 Persistent posterior shoulder pain and weakness may warrant consideration of this diagnosis.

Despite the use of shoulder pads, bony and ligamentous injuries occur about the shoulder girdle from direct blows. The shoulder pads are relatively thin and lightweight when compared to those used in football and hockey. Furthermore, they are of a non-cantilever design that rests directly on the shoulders. Clavicle fractures and acromioclavicular injuries, “shoulder separations,” are common from collision with another player or fall onto the point of the shoulder.9,32-34

Unlike other overhead throwing sports, lacrosse appears to have a lower rate of over-use injuries. Shoulder impingement and elbow epicondylitis are not common.7,12 The same is true for valgus instability of the elbow. While it has been reported, the rates are insignificant when compared to baseball throwers.35 Despite the long lever arm, lacrosse players have been shown to have equivalent medial collateral ligament (MCL) laxity to other asymptomatic throwing athletes.36 While the stick extends above the head, the elbows are usually held at or below the level of the shoulders. Furthermore, passing and shooting is almost always performed with both hands on the shaft of the stick, which limits the extreme ranges of motion. These factors may account for the relatively rare incidence of elbow pathology.

Wrist/Hand/Fingers

Injuries to the wrist and hand nearly always occur from a direct blow. Although the gloves are padded, they are softer and more flexible than hockey gloves to allow for greater dexterity of the fingers. Phalangeal fractures are relatively common from the entrapment of the grasped fingers against the metal shaft of the player’s own stick.37,38 For field players, this usually occurs as a result of a stick check from an opposing player (Figure 4). A defenseman’s stick may be up to 6 feet in length and can therefore generate significant velocity and force. For goalies, these injuries usually result from being struck with a high velocity shot. Elite players can generate shot velocities near 100 mph. The thumb is the most frequently injured digit, and modifying the protective gloves to encap the end of the thumb has been recommended.38 While hand and clavicle fractures are the most common, fractures in general are approximately six times more common in football than in lacrosse.39

Hip/Knee/Leg

Hip injuries are relatively uncommon. Groin strains occur as in any running sport. Muscles that cross two joints, such as the hamstrings, quads, and gastrocnemius are most prone to strains. Hip contusions or “hip pointers” also may occur from collisions with another player or being struck with a shot.

Knee injuries are among the most commonly observed in the sport of lacrosse. They represent 10%-15% of all injuries.6 These include meniscal and ligamentous injuries. While the most common ligament injury is to the MCL, the most common season-ending injury is an acute rupture of the anterior cruciate ligament (ACL). For the 2003-2004 season, there were 11 ACL ruptures among 27 teams participating in injury reporting to the NCAA.5 These usually occurred from a noncontact mechanism while a player was attempting to cut or pivot.

A recent study examined the kinematics of the stance knee when performing cutting maneuvers while holding a lacrosse stick compared to having the arms free. Holding the lacrosse stick constrains the arm position when landing and cutting that resulted in increased valgus loading at the knee and the possibility of greater risk of ACL injury.40 This is the most common reason for operative intervention.

United States Lacrosse insurance data showed that 42% of all claims dollars were paid for knee injuries, and >50% of the claims were paid out to high school players.41 Despite the fact that men’s lacrosse is a collision sport and women’s lacrosse is not, men appear to have a slightly lower incidence of ACL rupture than women, a finding that has been observed in other sports such as soccer and basketball.5,10,42-44 Neuromuscular training programs that have been shown to decrease the incidence of ACL rupture in soccer players may be applicable to lacrosse.45 No data exists on return to play rates after ACL reconstruction for lacrosse.

Overuse injuries such as patellar tendonitis and iliotibial tendonitis frequently are seen. These injuries usually can be managed symptomatically, with periods of rest, ice, and stretching. Injections into these areas generally are not recommended.

Because no pads are worn on the lower extremities, leg injuries commonly occur. Abrasions and contusions are the most frequently reported. Sliding or falling on artificial turf may cause “turf burns” over the extensor surface of the leg and knee. Prepatellar bursitis also is not uncommon. Both of these injuries may be more common in players taking face-offs. These relatively minor injuries may account for the increased incidence of injuries observed on artificial versus natural grass playing surfaces.5,6,10

Shin splints (posterior medial stress syndrome), tibial stress fractures, and exercise-induced compartment syndrome may be a source of chronic leg pain in this running-intensive sport. Mid to lower leg pain that manifests shortly after the onset of running, but not with lower demand activities, should suggest such a diagnosis.

Ankle/Foot

Acute ankle ligament sprains are the most commonly observed injuries in men’s lacrosse. They generally fall into one of two categories: inversion injuries (low ankle sprains) and eversion injuries (high ankle sprains). Together, these injuries caused the greatest number of days lost due to injury.6 High ankle sprains are less common and may result from contact with another player while the foot is planted. Low ankle sprains often are non-contact injuries.

In a study of collegiate lacrosse players, first-time low ankle sprains occurred at rates similar to soccer and basketball.46 This is the most frequent injury observed during practice.6 One potential reason for this observation is that while one ball is used in a game, there often are multiple balls used during drills. Inversion injuries may occur from players inadvertently stepping on a ball resting on the practice surface, causing them to “roll the ankle.” Limiting the number of balls left on the playing surface may help decrease the incidence of this injury. Furthermore, evidence exists to support the use of proprioceptive board training to help decrease the incidence of these injuries and speed return to play.47,48

Summary/Recommendations

As participation in lacrosse continues to grow, increasing emphasis on sport-specific injury patterns will be essential to promote the safety and health of its players. Continued prospective data collection will allow for appropriate modifications to rules and protective equipment.

The higher rate of game injuries suggests the need for sideline coverage at the collegiate and professional levels.11,49 As the game spreads to new regions of the country, physicians not familiar with lacrosse will be asked to provide game coverage and care for injured players. Sports medicine physicians will need to have an understanding of the game of lacrosse and its physical demands to help guide decisions regarding treatment and return to play.

References

  1. US Lacrosse. 2005 Participation Survey. Available at: http://www.uslacrosse.org/pdf/05participation.pdf. Accessed February 17, 2006.
  2. Vennum T. The Creator’s Game: A Brief History of Native American Lacrosse. Baltimore, Md: US Lacrosse; 1994.
  3. US Lacrosse. 2004 Participation Survey. Available at: http://www.uslacrosse.org/pdf/ParticipationSurvey_04.pdf. Accessed February 17, 2006.
  4. Mees P. Lacrosse participation surges: exploring the medical issues. The Physician and Sportsmedicine. 2005; 33:15-18.
  5. National Collegiate Athletic Association. Injury Surveillance System: 2003-2004 Men’s Lacrosse. Indianapolis, Ind: NCAA; 2004.
  6. National Collegiate Athletic Association. Injury Surveillance System: Men’s Lacrosse Injury Summary 1983-2003. Indianapolis, Ind: NCAA; 2003.
  7. Hinton RY, Lincoln AE, Almquist JL, Douoquih WA, Sharma KM. Epidemiology of lacrosse injuries in high school-aged girls and boys: a 3-year prospective study. Am J Sports Med. 2005; 33:1305-1314.
  8. Matz SO, Nibbelink G. Injuries in intercollegiate women’s lacrosse. Am J Sports Med. 2004;32:608-611.
  9. Mueller FO, Blyth CS. A survey of 1981 college lacrosse injuries. The Physician and Sportsmedicine. 1982; 10:86-92.
  10. National Collegiate Athletic Association. Injury Surveillance System: 2002-2003 Men’s Lacrosse. Indianapolis, Ind: NCAA; 2003.
  11. Nelson WE, DePalma B, Gieck JH, et al. Intercollegiate lacrosse injuries. Phys Sports Med. 1981; 9:86-92.
  12. Casazza BA, Rossner K. Baseball/lacrosse injuries. Phys Med Rehabil Clin N Am. 1999; 10:141-157.
  13. Caswell SV, Deivert RG. Lacrosse helmet designs and the effects of impact forces. The Journal of Athletic Training. 2002; 37:164-171.
  14. Matthews LS, Hinton RY, Burke N. Lacrosse. In: Fu FH, Stone DA, eds. Sports Injuries: Mechanism, Prevention, Treatment. 2nd ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2001:568-582.
  15. Diamond PT, Gale SD. Head injuries in men’s and women’s lacrosse: a 10-year analysis of the NEISS database. National Electronic Injury Surveillance System. Brain Inj. 2001; 15:537-544.
  16. McCrory P, Johnston K, Meeuwisse W, et al. Summary and agreement statement of the 2nd International Conference on Concussion in Sport, Prague 2004. Clin J Sport Med. 2005; 15:48-55.
  17. Wojtys EM, Hovda D, Landry G, et al. Current concepts. Concussion in sports. Am J Sports Med. 1999; 27:676-687.
  18. Waninger KN, Richards JG, Pan WT, Shay AR, Shindle MK. An evaluation of head movement in backboard-immobilized helmeted football, lacrosse, and ice hockey players. Clin J Sport Med. 2001; 11:82-86.
  19. Attia MW, Russell J. Isolated first rib fracture in a high school lacrosse player. Pediatr Emerg Care. 2000; 16:31-32.
  20. Gangemi JJ, Binns OA, Young JS. Splenic injury after athletic trauma: a case report of splenic rupture induced by a lacrosse ball. J Trauma. 1999; 46:736-737.
  21. Maron BJ, Gohman TE, Kyle SB, Estes NA III, Link MS. Clinical profile and spectrum of commotio cordis. JAMA. 2002; 287:1142-1146.
  22. Edlich RF, Mayer NE, Fariss BL, et al. Commotio cordis in a lacrosse goalie. J Emerg Med. 1987; 5:181-184.
  23. Luckstead EF, Patel DR. Catastrophic pediatric sports injuries. Pediatr Clin North Am. 2002; 49:581-591.
  24. Rouzier P, Dexter W. Sudden death-lacrosse: clinical case. Med Sci Sports Exerc. 2001; 33(Supp1):S316.
  25. Lowenkron H. NCAA, Athletic trainers seek ways to stop fatal chest blows. Associated Press. Available at: www.USLacrosse.org/safety/news/ncaasummit05.phtml. Accessed August 1, 2005.
  26. Drezner JA. Practical guidelines for automated external defibrillators in the athletic setting. Clin J Sport Med. 2005; 15:367-369.
  27. Greene HS, Cholewicki J, Galloway MT, Nguyen CV, Radebold A. A history of low back injury is a risk factor for recurrent back injuries in varsity athletes. Am J Sports Med. 2001; 29:795-800.
  28. Uhorchak JM, Arciero RA, Huggard D, Taylor DC. Recurrent shoulder instability after open reconstruction in athletes involved in collision and contact sports. Am J Sports Med. 2000; 28:794-799.
  29. Mair SD, Zarzour RH, Speer KP. Posterior labral injury in contact athletes. Am J Sports Med. 1998; 26:753-758.
  30. Williams RJ III, Strickland S, Cohen M, Altchek DW, Warren RF. Arthroscopic repair for traumatic posterior shoulder instability. Am J Sports Med. 2003; 31:203-209.
  31. Nam EK, Snyder SJ. Clinical sports medicine update: the diagnosis and treatment of superior labrum, anterior and posterior (SLAP) lesions. Am J Sports Med. 2003; 31:798-810.
  32. O’Neill PJ, Cosgarea AJ, McFarland EG. Unusual double clavicle fracture in a lacrosse player. Clin J Sport Med. 2000; 10:69-71.
  33. Gee, T. Sports science feature: shoulder injuries and rehabilitation in lacrosse. ACC Sports Sciences. Available at: http://theacc.collegesports.com/ot/sports-sciences.html. Accessed May 2005.
  34. Kulund DN, Schildwachter TL, McCue FC, et al. Lacrosse injuries. The Physician and Sportsmedicine. 1979; 7:83-90.
  35. Rohrbough JT, Altchek DW, Hyman J, Williams RJ III, Botts JD. Medial collateral ligament reconstruction of the elbow using the docking technique. Am J Sports Med. 2002; 30:541-548.
  36. Singh H, Osbahr DC, Wickham MQ, Kirkendall DT, Speer KP. Valgus laxity of the ulnar collateral ligament of the elbow in collegiate athletes. Am J Sports Med. 2001; 29:558-561.
  37. Livingston LA, Forbes SL. Lacrosse stick entrapment injury to the thumb. Br J Sports Med. 2003; 37:272-273.
  38. Elkousy HA, Janssen H, Ferraro BJ, Levin LS, Speer K. Lacrosse goalkeeper’s thumb. A preventable injury. Am J Sports Med. 2000; 28:317-321.
  39. Whiteside JA, Fleagle SB, Kalenak A. Fractures and refractures in intercollegiate athletes. An eleven-year experience. Am J Sports Med. 1981; 9:369-377.
  40. Chaudhari AM, Hearn BK, Andriacchi TP. Sport-dependent variations in arm position during single-limb landing influence knee loading: Implications for anterior cruciate ligament injury. Am J Sports Med. 2005; 33:824-830.
  41. Crispo LW. Insurance 101: accidental injuries in lacrosse. Lacrosse Magazine. June 2004:10-11.
  42. National Collegiate Athletic Association. Injury Surveillance System: 2003-2004 Women’s Lacrosse. Indianapolis, Ind: NCAA; 2004.
  43. National Collegiate Athletic Association. Injury Surveillance System: 2002-2003 Women’s Lacrosse. Indianapolis, Ind: NCAA; 2004.
  44. Arendt E, Dick R. Knee injury patterns among men and women in collegiate basketball and soccer: NCAA data and review of the literature. Am J Sports Med. 1995; 23:694-701.
  45. Griffin LY, Agel J, Albohm MJ, et al. Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 2000; 8:141-150.
  46. Beynnon BD, Vacek PM, Murphy D, et al. First-time inversion ankle ligament trauma: the effects of sex, level of competition, and sport on the incidence of injury. Am J Sports Med. 2005; 33:1-7.
  47. Thacker SB, Stroup DF, Branche CM, Gilchrist J, Goodman RA, Weitman EA. The prevention of ankle sprains in sports. A systematic review of the literature. Am J Sports Med. 1999; 27:753-760.
  48. Verhagen E, van der Beek A, Twisk J, Bouter L, Bahr R, Van Mechelen W. The effect of a proprioceptive balance board training program for the prevention of ankle sprains: a prospective controlled trial. Am J Sports Med. 2004; 32:1385-1393.
  49. Steiner ME, Quigley B, Wang F, Balint CR, Boland AL Jr. Team physicians in college athletics. Am J Sports Med. 2005; 33:1545-1551.

Authors

Dr McCulloch is from the Division of Sports Medicine, Department of Orthopedic Surgery, Baylor College of Medicine, Houston, Tex; and Dr Bach is from the Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Chicago, Ill.

The authors thank Randall Dick of the NCAA Injury Surveillance Program for access to the data.

Correspondence should be addressed to: Patrick C. McCulloch, MD, Baylor Sports Medicine, Baylor Clinic, 6620 Main St, Ste 1325, Houston, TX 77030.

10.3928/01477447-20070101-05

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