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Acute injuries in soccer, ice hockey, volleyball, basketball, judo, and karate: analysis of national registry data

^a Unit for Sports and Exercise Medicine, Institute of Biomedicine, University of Helsinki, Toolo Sports Hall, Mannerheimintie 17, FIN-00250 Helsinki, Finland, ^b Department of Public Health, University of Helsinki, FIN-00290, Helsinki, ^c Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, FIN-00260 Helsinki

Correspondence to: Dr Kujala.

Abstract

Objective: To determine the acute injury profile in each of six sports and compare the injury rates between the sports.
Design: Analysis of national sports injury insurance registry data.
Setting: Finland during 1987-91.
Subjects: 621691 person years of exposure among participants in soccer, ice hockey, volleyball, basketball, judo, or karate.
Main outcome measures: Acute sports injuries requiring medical treatment and reported to the insurance company on structured forms by the patients and their doctors.
Results: 54186 sports injuries were recorded. Injury rates were low in athletes aged under 15, while 20-24 year olds had the highest rates. Differences in injury rates between the sports were minor in this adult age group. Overall injury rates were higher in sports entailing more frequent and powerful body contact. Each sport had a specific injury profile. Fractures and dental injuries were most common in ice hockey and karate and least frequent in volleyball. Knee injuries were the most common cause of permanent disability.
Conclusions: Based on the defined injury profiles in the different sports it is recommended that sports specific preventive measures should be employed to decrease the number of violent contacts between athletes, including improved game rules supported by careful refereeing. To prevent dental injuries the wearing of mouth guards should be encouraged, especially in ice hockey, karate, and basketball.

Introduction

The growing popularity of sports and exercise is focusing attention on the injuries that may occur in addition to the health benefits.^{1 2 3 4 5 6} Treating sports injuries may be expensive, so preventive strategies and measures are required on economic as well as medical grounds.^{7 8 9} Several epidemiological surveys have outlined the frequency and types of injuries in various sports, but study comparisons are complicated by the different injury criteria used as well as by inconsistency in data collection and recording.¹⁰ The risk of acute injury varies enormously. Most endurance sports are extremely safe, whereas formula 1 car racing killed 69 of a small group of drivers between 1950 and 1994. Injury rates in popular team games such as soccer, volleyball, basketball, and ice hockey lie between these extremes.¹¹ Martial arts such as judo and karate are also becoming popular, and the associated risks may be greater than in most team games.^{11 12} Though endurance sports may cause the highest rates of stress injury, these rarely result in permanent disability.

Before embarking on a programme to prevent sports injuries we must first define the extent of the problem and identify the mechanisms and factors involved. Then we must introduce measures likely to reduce the risks and monitor their effects. Research shows that strategies to prevent sports injuries may be useful and that most interventions effective enough to measurably alter injury profiles in various sports entail changing rules or improving equipment.^{5 13 14} In soccer, safety interventions and improved treatment of injuries and rehabilitation may prevent future injury.^{15 16}

We analysed the types and severity of acute injuries in some common team games (soccer, ice hockey, volleyball, basketball) as well as in judo and karate and compared the apparent injury risks between these sports. This information is crucial for prioritising measures in sports injury prevention.

Subjects and methods

From 1987 to 1991 anyone in Finland intending to compete in soccer, ice hockey, volleyball, basketball, judo, or karate was obliged to obtain a licence from the appropriate sports association. During the study period all licences issued to soccer and ice hockey players as well as those issued to judo and karate competitors were linked to an insurance policy from a single company (Pohjola Insurance Company Ltd) covering acute onset sports injuries. Among basketball players the insurance was not compulsory. For volleyball players the insurance was compulsory from 1987 to 1990 but not during 1991. However, about two thirds of basketball and volleyball players had the insurance linked to their sports licence even when it was not compulsory. This study is therefore based on 621691 person years of exposure among athletes with a sports licence linked to insurance (see table 1). Exact data on age and sex of the insured athletes at the beginning of each person year of exposure were available for 1990 and 1991 in all the sports except basketball. Thus the analysis of injury rates by age and sex was limited to five sports and two years (23363 injuries during 250291 person years of exposure; see table 2).

Table 1--Person years of exposure, numbers of injuries,
and injury rate in six sports in Finland (sports insurance
data 1987-91)
-------------------------------------------------------------------
                                                  Injury rate
               Person years        No of       (95% confidence
Sport          of exposure        injuries        interval)+
-------------------------------------------------------------------
Soccer            296646           26330         89 (88 to 90)
Ice hockey        179798           16836         94 (92 to 95)
Volleyball         87668            5235         60 (58 to 61)
Basketball         39541            3472         88 (85 to 91)
Judo               9936             1163        117 (111 to 123)
Karate             8102             1150        142 (134 to 150)
-------------------------------------------------------------------
+Injuries per 1000 person years of exposure.

Table 2--Injuries per person years of exposure and injury rates (plus 95% confidence intervals) by age and sex in soccer, ice hockey, volleyball, judo, and
karate among competitive athletes in Finland in 1990 and 1991
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                           No of injuries/years of exposure [injury rate+ (95% confidence interval)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sport              Age <15                     Age 15-19                       Age 20-24                       Age 25-34                     Age >34
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
Soccer     1591/63591 [25 (24 to 26)]   2474/26698 [93 (89 to 96)]    2837/11162 [254 (246 to 262)]   4344/22553 [193 (187 to 198)]   766/11946 [64 (60 to 69)]
 Males     1273/56623 [23 (21 to 24)]   2065/21788 [95 (91 to 99)]     2602/9830 [265 (256 to 273)]   4183/21464 [195 (190 to 200)]   761/11768 [65 (60 to 69)]
 Females     318/6968 [46 (41 to 51)]     409/4910 [83 (76 to 91)]      235/1332 [176 (156 to 197)]     161/1089 [148 (127 to 169)]      5/178 [28 (9 to 64)]
Ice hockey 1202/33393 [36 (34 to 38)]  2875/19688 [146 (141 to 151)]   1829/7048 [260 (249 to 270)]   1705/8576 [199 (190 to 207)]     235/6727 [35 (31 to 39)]
 Males     1186/32958 [36 (34 to 38)]  2823/19027 [148 (143 to 153)]   1796/6759 [266 (255 to 276)]   1685/8262 [204 (195 to 213)]     231/6576 [35 (31 to 40)]
 Females     16/435 [37 (21 to 59)]       52/661 [79 (59 to 102)]        33/289 [114 (78 to 151)]        20/314 [64 (39 to 97)]          4/151 [27 (7 to 67)]
Volleyball   94/8202 [12 (9 to 14)]      391/7688 [51 (46 to 56)]      593/2753 [215 (200 to 231)]    1154/7962 [145 (137 to 153)]     364/5171 [70 (63 to 77)]
 Males       25/3838 [6 (4 to 10)]       185/3571 [52 (45 to 60)]      345/1461 [236 (214 to 258)]     815/5255 [155 (145 to 165)]     254/3816 [67 (59 to 75)]
 Females    69/4364 [16 (12 to 20)]      206/4117 [50 (43 to 57)]      248/1292 [192 (170 to 213)]     339/2707 [125 (113 to 138)]     110/1355 [81 (67 to 97)]
Judo        34/1142 [30 (21 to 41)]     154/1524 [101 (86 to 116)]     128/601 [213 (180 to 246)]      108/684 [158 (131 to 185)]      25/289 [88 (58 to 128)]
 Males       21/969 [22 (14 to 33)]      111/1228 [90 (75 to 108)]      95/436 [218 (179 to 257)]       81/496 [163 (131 to 196)]      22/260 [85 (54 to 125)]
 Females    13/173 [75 (41 to 125)]      43/296 [145 (105 to 185)]      33/165 [200 (139 to 261)]       27/188 [144 (94 to 194)]        3/29 [103 (22 to 273)]
Karate       11/352 [31 (16 to 55)]      91/896 [102 (82 to 121)]      141/572 [247 (211 to 282)]      185/885 [209 (182 to 236)]      32/188 [170 (116 to 224)]
 Males       9/304 [30 (14 to 56)]        63/664 [95 (74 to 120)]      123/417 [295 (251 to 339)]      148/710 [208 (179 to 238)]      27/158 [171 (112 to 230)]
 Females      2/48 [42 (5 to 143)]       28/232 [121 (79 to 163)]       18/155 [116 (66 to 167)]        37/175 [211 (151 to 272)]        5/30 [167 (57 to 347)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
+Injuries per 1000 person years of exposure.

The injury criteria remained similar throughout. The sports insurance covered all traumatic acute injuries during competitions and training. The injury criteria also included all injuries of sudden onset, such as those that usually have no clear external accidental cause--for example, muscular strains.

The insurance company paid the medical costs of treatment after the injured athlete completed the injury report and the treating physician the medical accident report. Data on each injury, based on the two reports, were entered into a computer database by means of a structured format. Before paying the medical costs the insurance company checked the two reports for agreement. In cases of disagreement or incomplete information the insurance company sought clarification. This increased the validity of the data. The structured format of each injury report included age at the time of injury, type of sports event, circumstance of injury (training or competition), type of injury and mechanism, and injured body part. Data on payments made as death benefits or permanent disability benefits after sports injuries were also recorded. The insurance company and the sports associations consented to our using the data (without personal identification codes).

Statistical analyses--For each sport we calculated injury rates per 1000 person years of exposure (plus 95% confidence intervals) by age and sex as well as by types of injuries, anatomical locations of the injuries, and circumstances of the injuries.

Results

A total of 54186 acute sports injuries (48256 in males, 5930 in females) were recorded during the five years of the study. Karate and judo had the highest injury rates, followed by ice hockey, soccer, and basketball. Volleyball had the lowest injury rate (table 1). In the team games 46-59% of the injuries occurred during competitions, whereas in judo and karate around 70% occurred in training (figure). From the data for 1990 and 1991 the injury rates were clearly highest among 20-24 year old athletes (table 2). Sex differences in injury rates were less obvious, though among 20-24 year olds men had a higher injury rate than women in each sport.

View larger version (49K): [in this window] [in a new window]   Proportions of injuries occurring in competitions (dark areas) and training sessions (light areas) in different sports

Most injuries were to the lower limbs in soccer (66.8%), volleyball (57.4%), and basketball (56.0%), whereas upper limb injuries were most common in judo (37.6%). Sites other than limbs, including the teeth, were injured most often in karate and ice hockey (table 3). Sprains, strains, and bruises were the most common types of injury (table 4). Non-dental fractures accounted for 4.0-10.8% of injuries overall, occurring most often in karate, judo, and ice hockey and least often in volleyball (table 4). Dislocations were proportionally more frequent in judo and karate (table 4).

Table 3--Anatomical locations of injuries by sports and injury rates (plus 95% confidence intervals) (sports insurance data 1987-91)
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                    %+ (No) [injury rate++ (95% confidence interval)]
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Injury location                            Soccer                      Ice hockey                       Volleyball                    Basketball                       Judo                        Karate
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Lower limb                      66.8 (17577) [59 (58 to 60)]    35.8 (6031) [34 (33 to 34)]    57.4 (3005) [34 (33 to 36)]   56.0 (1945) [49 (47 to 51)]   38.6 (449) [45 (41 to 49)]    37.3 (429) [53 (48 to 58)]
 Thigh                            10.6 (2803) [9 (9 to 10)]       6.1 (1031) [6 (5 to 6)]         2.3 (118) [1 (1 to 2)]        2.5 (87) [2 (2 to 3)]        1.9 (22) [2 (1 to 3)]         4.3 (49) [6 (4 to 8)]
 Knee                            21.5 (5657) [19 (19 to 20)]    17.2 (2888) [16 (16 to 17)]     19.0 (993) [11 (11 to 12)]    15.8 (547) [14 (13 to 15)]   20.2 (235) [24 (21 to 27)]    11.0 (127) [16 (13 to 18)]
 Legsection                        5.9 (1557) [5 (5 to 6)]        1.9 (325) [2 (2 to 2)]          1.8 (94) [1 (1 to 1)]         2.0 (68) [2 (1 to 2)]        2.0 (23) [2 (1 to 3)]         3.3 (38) [5 (3 to 6)]
 Ankle                           20.5 (5397) [18 (18 to 19)]      7.9 (1325) [7 (7 to 8)]      31.1 (1626) [19 (18 to 19)]   31.4 (1090) [28 (26 to 29)]    8.3 (97) [10 (8 to 12)]       7.7 (88) [11 (9 to 13)]
 Foot                              7.7 (2015) [7 (7 to 7)]        2.4 (404) [2 (2 to 2)]          2.9 (153) [2 (1 to 2)]       4.0 (138) [3 (3 to 4)]        6.0 (70) [7 (5 to 9)]       10.7 (123) [15 (13 to 18)]
 Lower limb, other@                 0.6 (148) [0 (0 to 1)]         0.3 (58) [0 (0 to 0)]          0.4 (21) [0 (0 to 0)]         0.4 (15) [0 (0 to 1)]         0.2 (2) [0 (0 to 0)]          0.3 (4) [0 (0 to 1)]
Upper limb                       12.1 (3189) [11 (10 to 11)]    31.5 (5306) [30 (29 to 30)]    22.4 (1174) [13 (13 to 14)]    19.3 (670) [17 (16 to 18)]   37.6 (437) [44 (40 to 48)]    26.3 (303) [37 (33 to 42)]
 Upper arm and shoulder             3.0 (800) [3 (3 to 3)]      10.2 (1724) [10 (9 to 10)]        9.3 (489) [6 (5 to 6)]        2.6 (92) [2 (2 to 3)]      20.0 (233) [24 (21 to 26)]      6.1 (70) [9 (7 to 11)]
 Forearm and elbow                  1.3 (334) [1 (1 to 1)]        4.6 (771) [4 (4 to 5)]          1.6 (84) [1 (1 to 1)]         1.3 (46) [1 (1 to 2)]        7.7 (90) [9 (7 to 11)]        3.8 (44) [5 (4 to 7)]
 Palm and wrist                     3.6 (948) [3 (3 to 3)]        8.2 (1382) [8 (7 to 8)]         2.1 (111) [1 (1 to 2)]       3.8 (131) [3 (3 to 4)]        3.4 (40) [4 (3 to 5)]         6.0 (69) [9 (7 to 11)]
 Fingers                            3.7 (978) [3 (3 to 4)]        6.4 (1074) [6 (6 to 6)]         9.1 (477) [5 (5 to 6)]      11.1 (386) [10 (9 to 11)]      4.5 (52) [5 (4 to 7)]        9.3 (107) [13 (11 to 16)]
 Upper limb, other@                 0.5 (129) [0 (0 to 1)]         2.1 (355) [2 (2 to 2)]         0.2 (13) [0 (0 to 0)]         0.4 (15) [0 (0 to 1)]        1.9 (22) [2 (1 to 3)]          1.1 (13) [2 (1 to 2)]
Other sites                      21.1 (5564) [19 (18 to 19)]    32.7 (5499) [31 (30 to 31)]    20.2 (1056) [12 (11 to 13)]   24.7 (857) [22 (20 to 23)]    23.8 (277) [28 (25 to 31)]    36.3 (418) [52 (47 to 56)]
 Teeth                              2.8 (737) [2 (2 to 3)]        7.1 (1196) [7 (6 to 7)]         2.0 (106) [1 (1 to 1)]       5.2 (182) [5 (4 to 5)]        2.7 (31) [3 (2 to 4)]         6.4 (74) [9 (7 to 11)]
 Eye                                0.9 (245) [0 (0 to 1)]         1.2 (202) [1 (1 to 2)]         1.9 (101) [1 (1 to 1)]       3.0 (103) [3 (2 to 3)]        0.9 (11) [1 (0 to 2)]          2.1 (24) [3 (2 to 4)]
 Head and neck, other sites        4.9 (1282) [4 (4 to 5)]        8.6 (1448) [8 (8 to 8)]         5.6 (291) [3 (3 to 4)]       7.4 (256) [6 (6 to 7)]        6.3 (73) [7 (6 to 9)]       10.9 (125) [15 (13 to 18)]
 Thorax and abdomen                 2.6 (693) [2 (2 to 3)]         3.8 (632) [4 (3 to 4)]          0.9 (47) [1 (0 to 1)]        1.5 (52) [1 (1 to 2)]        4.2 (49) [5 (4 to 6)]          4.7 (54) [7 (5 to 8)]
 Back                              5.8 (1531) [5 (5 to 5)]        7.2 (1220) [7 (6 to 7)]         8.7 (458) [5 (5 to 6)]       5.4 (187) [5 (4 to 5)]        7.9 (92) [9 (7 to 11)]       9.7 (111) [14 (11 to 16)]
 Pelvis and hip                     2.5 (665) [2 (2 to 2)]         2.7 (447) [2 (2 to 3)]          0.5 (28) [0 (0 to 0)]         0.9 (3) [1 (0 to 1)]         0.7 (8) [1 (0 to 1)]           1.5 (17) [2 (1 to 3)]
 Multiple sites or unknown          1.6 (411) [1 (1 to 2)]         2.1 (354) [2 (2 to 2)]          0.5 (25) [0 (0 to 0)]        1.4 (47) [1 (1 to 2)]        1.1 (13) [1 (1 to 2)]          1.1 (13) [2 (1 to 2)]
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+Percentage of injuries in sports studied.                                                         sectionLeg refers to anatomical area between knee and ankle.
++Injuries per 1000 person years of exposure.                                                      @Other or multiple sites: this category of upper limb includes clavicle injuries.

Table 4--Injury types by sports and injury rates (plus 95% confidence intervals) (sports insurance data 1987-91)
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                    %+ (No) [injury rate++ (95% confidence intervall)]
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Injury type                                Soccer                      Ice hockey                       Volleyball                   Basketball                       Judo                      Karate
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sprains and strainssection         56.1 (14769) [50 (49 to 51)] 36.9 (6213) [35 (34 to 35)]  74.6 (3905) [45 (43 to 46)]  61.3 (2128) [54 (52 to 56)]   59.8 (696) [70 (65 to 75)]  44.7 (514) [63 (58 to 69)]
 Knee                               16.4 (4321) [15 (14 to 15)] 11.2 (1886) [11 (10 to 11)]    15.4 (807) [9 (9 to 10)]    12.4 (432) [11 (10 to 12)]   15.3 (178) [18 (15 to 21)]   9.0 (104) [13 (10 to 15)]
 Ankle                              16.7 (4401) [15 (14 to 15)]    4.8 (812) [5 (4 to 5)]    29.2 (1527) [17 (17 to 18)]  29.5 (1023) [26 (24 to 27)]     6.5 (76) [8 (6 to 9)]       6.3 (72) [9 (7 to 11)]
Bruises and wounds                  31.1 (8184) [28 (27 to 28)] 42.0 (7069) [39 (38 to 40)]   16.3 (853) [10 (9 to 10)]    22.2 (773) [20 (18 to 21)]   23.1 (269) [27 (24 to 30)]  35.1 (404) [50 (45 to 55)]
Fractures                             9.6 (2515) [8 (8 to 9)]   17.1 (2885) [16 (16 to 17)]     5.9 (311) [4 (3 to 4)]     12.6 (436) [11 (10 to 12)]   11.3 (131) [13 (11 to 15)]  16.9 (194) [24 (21 to 27)]
 Fractures other than dental          7.0 (1844) [6 (6 to 7)]    10.6 (1785) [10 (9 to 10)]     4.0 (212) [2 (2 to 3)]       7.6 (265) [7 (6 to 8)]      8.8 (102) [10 (8 to 12)]   10.8 (124) [15 (13 to 18)]
   Foot and ankle@                    25.0 (461) [2 (1 to 2)]     11.3 (201) [1 (1 to 1)]       29.2 (62) [1 (1 to 1)]       18.5 (49) [1 (1 to 2)]      34.3 (35) [4 (2 to 5)]      21.0 (26) [3 (2 to 4)]
   Lower limb, proximal from ankle@   16.1 (297) [1 (1 to 1)]      6.8 (122) [1 (1 to 1)]        7.5 (16) [0 (0 to 0)]        3.8 (10) [0 (0 to 0)]        3.9 (4) [0 (0 to 1)]        4.0 (5) [1 (0 to 1)]
   Fingers, palm, and wrist@          35.5 (654) [2 (2 to 2)]     48.1 (858) [5 (4 to 5)]      53.8 (114) [1 (1 to 2)]      57.0 (151) [4 (3 to 4)]      18.6 (19) [2 (1 to 3)]      36.3 (45) [6 (4 to 7)]
   Upper limb proximal from wrist@     8.4 (154) [1 (0 to 1)]     21.6 (386) [2 (2 to 2)]         0.9 (2) [0 (0 to 0)]        4.2 (11) [0 (0 to 0)]      31.4 (32) [3 (2 to 3)]        5.6 (7) [1 (0 to 2)]
   Other, non-dental@                 15.1 (278) [1 (1 to 1)]     12.2 (218) [1 (1 to 1)]        8.5 (18) [0 (0 to 0)]       16.6 (44) [1 (1 to 1)]      11.8 (12) [1 (1 to 2)]      33.1 (41) [5 (4 to 7)]
 Dental fractures                      2.5 (671) [2 (2 to 2)]     6.5 (1100) [6 (6 to 6)]        1.9 (99) [1 (1 to 1)]        4.9 (17) [4 (4 to 5)]       2.5 (29) [3 (2 to 4)]      6.1 (70) [9 (6 to 11)]
Dislocations                           0.8 (215) [1 (1 to 1)]      1.1 (191) [1 (1 to 1)]        1.4 (73) [1 (1 to 1)]        1.7 (59) [1 (1 to 2)]       3.9 (45) [5 (3 to 6)]       1.1 (13) [2 (1 to 2)]
 Knee||                                 0.3 (76) [0 (0 to 0)]       0.2 (39) [0 (0 to 0)]        0.3 (17) [0 (0 to 0)]        0.5 (16) [0 (0 to 1)]       1.0 (12) [1 (1 to 2)]        0.1 (1) [0 (0 to 0)]
 Shoulder and elbow                     0.2 (52) [0 (0 to 0)]      0.7 (113) [1 (1 to 1)]        0.2 (11) [0 (0 to 0)]        0.3 (10) [0 (0 to 0)]       1.9 (22) [2 (1 to 3)]        0.3 (3) [0 (0 to 1)]
 Fingers                                0.1 (31) [0 (0 to 0)]       0.1 (13) [0 (0 to 0)]        0.5 (25) [0 (0 to 0)]        0.3 (12) [0 (0 to 0)]        0.3 (4) [0 (0 to 1)]        0.3 (3) [0 (0 to 1)]
Others or unknown                      2.5 (647) [2 (2 to 2)]      2.8 (478) [3 (2 to 3)]        1.8 (93) [1 (1 to 1)]        2.2 (76) [2 (1 to 2)]       1.9 (22) [2 (1 to 3)]       2.2 (25) [3 (2 to 4)]
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+Percentage of injuries in sport studied.                         sectionIncludes ligament, tendon, and muscle ruptures.                        ||Includes patellofemoral joint.
++Injuries per 1000 person years of exposure.                     @Percentages of non-dental fractures.

No death benefit for an accidental sports injury was awarded during the study. There was one neck fracture in an ice hockey player leading to tetraplegia. Benefit in respect of various degrees of permanent disability (that is, at least 5% disability) was awarded in 102 cases. Fifty nine of these occurred in soccer (0.22% of all soccer injuries), 24 in ice hockey (0.14%), 11 in volleyball (0.21%), four in basketball (0.11%), two in judo (0.17%), and two in karate (0.17%); 92 occurred in males and 68 during competitions. The most common injury was a sprain or strain (66 cases), while 16 injuries were fractures. The knee was the most common location for injuries resulting in permanent disability (64 cases).

Discussion

We have defined the acute injury profiles in six sports on the basis of 54186 injuries examined by physicians and reported to a national sports insurance company. However, not all treated injuries are reported to the insurance company and many minor injuries that are self treated also go unreported. Thus our data underestimate the true injury rates in each sport.

The overall sex difference in injury risk was small but the age difference was clear. Athletes aged 20-24 years had the highest risk, probably because training and competition are most intense at this age. We did not have records on exact hours of exposure and so could not calculate the exact injury risk per hour of training or competition. Our findings agree with earlier reports that injuries in young team players are less frequent than in adults.^{17 18 19} In judo the reason for the unexpectedly high injury rate among young girls was probably that as a minority group in many clubs they often have to train with boys and men. In adult team games entailing various types of bodily contact between athletes men probably train more but tend to have a rougher style than women. This also may partly explain the sex difference in injury risk.

Athletes usually spend far more time training than competing. About half of the injuries to team game athletes occurred in competitions. Hence competitions plainly entail a higher risk of injury per hour than training.

When the analysis of injury rates was restricted to 20-24 year old athletes only small differences were found between sports. The overall injury risk was lowest in volleyball and highest in ice hockey, judo, and karate. Our findings agree with other reports that violent bodily contact between athletes increases the risk of injury^{20 21} but that use of protective equipment may reduce the difference in injury outcomes between sports. Comparison of injury rates with those in other studies is complicated by methodological differences. The ranking of injury risks in different sports may also vary with local circumstances in the study area, such as the age distribution and level of the teams playing. De Loes and Goldie reported that soccer players had a clearly higher injury risk than ice hockey players in one municipality in south west Sweden.¹¹ But our finding that the overall injury rate was higher in ice hockey players than footballers in Finland agrees with national data from Sweden.²² In our study the differences in overall injury rates between the sports were partly explained by the differing age distributions of the athletes.

All the sports studied had higher acute injury rates than reported among endurance athletes.²³ During the study period participants in motor sports had similar compulsory national sports licence insurance. In 1990 and 1991 among male participants in various competitive motor sports the injury rate per 1000 person years of exposure was 182 (95% confidence interval 171 to 194) and was highest in the youngest age groups--278 (223 to 333) among participants aged under 15 and 245 (220 to 269) among 15-19 year olds. From 1987 to 1991 fractures other than dental accounted for 29% of all injuries to motor sports participants. These data confirm that the relative safety of junior sports is not extended to all types of motor sports.

The types and anatomical distribution of injuries, as well as the rarity of severe injuries, corresponded with earlier findings.²⁴ As expected, the most common injuries were sprains, strains, and bruises. As found in earlier studies, knee injury was the most common cause of permanent disability,⁹ defined simply as an impairment of optimal function. Fractures seldom resulted in permanent disability, though the number of fractures (highest in ice hockey, judo, and karate) highlight the risk for high energy injuries.

High puck velocities, aggressive stick use, and body checking (collisions) account for most ice hockey injuries.²⁵ Catastrophic ice hockey injuries seem to be less frequent in Finland than North America,²⁶ possibly because of the larger rinks and less aggressive style in Europe. To avoid these injuries as far as possible, aggressive checking--particularly from behind the player and near the rink boards--should be minimised by game rules and strict refereeing.²⁵ Aggressive stick use may partly account for the high number of hand and wrist fractures in our study. Though facial injuries are common, they have declined with the more routine use of helmets and facemasks.²⁵ In ice hockey and many other sports mouth guards would substantially reduce dental injuries and should be designed according to the characteristics of each sport.

The injury profiles of the sports differed widely. To avoid injuries preventive measures should be specific to each sport. In general there should be greater focus on diminishing rough and violent contact between athletes.

Funding: Finnish Ministry of Education.

Conflict of interest: None.

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