Word count: 2532



Word count: 2532

Knee: Acute Knee Ligament Injuries;

Incidence In Sports

Markku Jarvinen, Antero Natri, and Pekka Kannus

Section of Orthopaedics, Department of Surgery,

University Hospital,

Tampere, Finland, and

Tampere Research Station of Sports Medicine and Accident &

Trauma Research Center

The UKK Institute for Health Promotion Research,

Tampere, Finland

Injuries of the knee are extremely common and their incidence has apparently been rising during the past few decades. In sports, knee injuries represent 15-30% of all injuries. However, only a few studies have been published on the incidence of knee injuries. Epidemiological studies are important when planning prevention programs for sports injuries. Different sports habits in various countries mean that national injury trends as well as injury mechanisms will vary from one nation to another.

We found an annual rate of knee injuries to be about 1.1 % in a rural population of Finland (15). Half of these were sports injuries and 43% knee ligament injuries. About 10% of all visits to the general practitioner due to knee injury led to a surgical consultation. The most common reasons for referring the patient for such evaluation were meniscus tears (40%), acute traumatic hemarthrosis (22%), knee ligament injuries (18%) and a loose bodies (10%).

In Denmark, in the city of Aarhus, the knee injury rate was about 1.2%, with 6% of all injuries involving the knee joint. The rate of anterior cruciate ligament (ACL) injury was 30 per 100,000 inhabitants per year (22). In Sweden, of 600 sports injuries which led to permanent impairment and disability, 50% were knee injuries (5). ACL injury was found in 85% of these knee injuries and 50% were sustained in soccer. Thus, the rupture of ACL seems is the most common serious knee ligament injury sustained in sports.

The frequency of various knee injuries in sports have been calculated in patients with acute injuries who sought medical attention at a hospital, in patients presenting with a hemarthrosis of the knee, and patients undergoing knee surgery. Sports injuries were the most common cause (50 to 93%) of traumatic hemarthrosis of the knee joint involving serious ligament injury.

Only few studies have examined the incidence of knee ligament injuries in the general population. Hirshman et al. (7) have analyzed the knee ligament injuries from the population of 280,000 inhabitants in San Diego, California, area from 1985-1988. They found 1833 acute knee injuries and 819 (45%) of those injuries were knee ligament injuries. This represents an injury rate of 98 per 100000 population per year. Three hundred and nineteen of these had isolated grade I collateral ligament injuries (306 medial and 13 lateral). Ligament injuries with pathologic motion (i.e., Grade II or III) were diagnosed in 500 patients, presenting a ligament injury rate of 60 per 100,000 population per year. Three hundred fifty-eight (72%) of these patients were male and 142 (28%) were females.

We have analyzed the injury rate for a similar group of patients who were treated for knee ligament injuries in our hospital. From 1975 to 1981, 317 patients sustained knee ligament injuries, which represented 13 per 100,000. Of these patients, 221 were treated conservatively and 96 operatively. Between 1985-1988, 251 patients were treated in our hospital for rupture to the ACL representing an injury rate of 16 per 100,000. This increased incidence of injury is probably due to the improved diagnosis of ACL rupture as well as an increase of these injuries. From 1975 to 1981 a medial collateral ligament (MCL) injury was found in about three fourths of the knees, while ACL injuries were found in only 50%. In these cases the diagnosis was solely based on clinical examination. Two thirds of our patients were treated conservatively.

At Tampere University hospital, between 1980 and 1989, 450 anterior cruciate ligament injuries were treated. In all cases, the diagnosis was made clinically as well as surgically (operation or arthroscopy). Isolated ACL injury was found in 167 cases (37%) and combined ACL-MCL injury was found in 161 (36%) patients. In an other Finnish study with 350 consecutive acute hemarthrosis, an isolated ACL rupture was found in about 38% of cases (6). Meniscus injuries are often accompanied by ACL injuries. In 270 ACL injuries meniscus injury was found in 60% of cases, the rupture occurring more often in lateral than medial meniscus.

The combination ligamentous injuries together with the ACL rupture represent more than half of all ACL injuries. The medial collateral ligament (MCL) is the most often injured ligament with the ACL rupture. In our study of 450 ACL injuries 167 (37%) were isolated and 130 (29%) were ACL-MCL injuries. "Unhappy triad" ( ACL, MCL and medial meniscus injuries) was found in 31 patients (7%).

In the San Diego study, 61% of acute knee ligament injuries with pathological motion were sustained in sports activities (7) (Table 2). In this study the majority of ACL injuries sustained in sports occurred in soccer, skiing, football, baseball and basketball. Apparently all the skiing injuries in this study occurred in downhill skiing. In our patients in Tampere, Finland, soccer was also the principle sport where ACL injuries most often. This was the case if the ACL injuries sustained in downhill and cross-country skiing were estimated separately.

In skiing injuries, more injuries were sustained during the early 1980's (20 injuries) than during the last half of the decade (10 injuries). This pattern was reversed in downhill skiing, with 5 injuries during the first 5 years of the decade and 43 during the last five years. Hence, during the period 1980 to 1989 there was a marked decrease in ACL injuries sustained in cross-country skiing and a tremendous increase in ACL injuries sustained in down-hill skiing. One reason to this change was an increased participation in downhill skiing in Finland during these years.

In downhill skiing in the areas with a good reporting system for injuries (i.e., Sugarbush; Vermont), injuries below the knee have decreased dramatically during the last two decades. In the 1960s, the incidence of downhill skiing injuries was approximately 10 per 1000 skier-days. In the early 1980s, the injury rate was between 2 and 4 per 1000 skier-days. Presently the incidence in Scandinavian is even lower ( 0.5 to 1 per 1000).

Johnson et al (11) studied the trends of skiing injuries between 1972 and 1987 in Sugarbush ski area, Vermont. There was a 50% decline in the overall injury rate . Most of the decline could be attributed to a 60% reduction in the incidence of lower extremity injuries. In knee injuries, there was a moderate but only marginally significant decline (36%). Also the type and severity of knee sprains changed over time. There was a 72% improvement in mild and moderate knee sprains, but a 172% increase in severe, grade III sprains. Of these, complete tears of the anterior cruciate ligament (ACL) were most frequent. In the knee, the acute rupture of ACL is the greatest problem because binding designs do not adequately protect the ACL. This is no surprise because the principle factor dictating binding design has been the stress-strain relationship in the tibia.

As for the other ligaments, the lateral collateral and posterior cruciate ligaments are rarely injured in skiing. Skiing-associated injuries to the medial collateral ligament, which generally involve forced external rotation of the leg due to catching an inside edge of the ski, are very common but do not create any major therapeutic problems.

Mechanisms Of ACL Injury In Skiing

Johnson (13) has described that the primary cause of ACL sprains in skiing. They can be divided into three different injury mechanisms can be found: 1) valgus-external rotation; 2) "anterior drawer maneuver" mechanism and 3) flexion-internal rotation (Figs. 1, 2 and 3).

In the classic forward fall in which the medial edge of the anterior portion of the ski engages the snow, the skier is propelled forward by the momentum, and the lower leg rotates externally in relation to thigh. The ski accentuates this rotational force (in mechanical terms, the ski acts as a moment arm). Although in this accident the medial collateral ligament is the most commonly injured structure, in approximately 20% of cases the ACL also is injured.

ACL injury also occurs when the skier falls backwards or, in some cases, when the skier has a loss of balance backwards and momentarily loses control. The two mechanisms that produce these injuries have recently been identified: In the first, the ACL is damaged when the airborne skier comes off a bump and lands on one ski, slightly off balance with the upper body leaning backward, the involving knee is in almost full extension, and the contralateral arm thrown back in an attempt to regain balance. The tail of the ski hits the snow first, causing the ski to drive into the snow quickly and the stiff, high boot top to the drive the shaft of the tibia forward producing an " anterior drawer maneuver" that results in isolated disruption of the ACL.

In the second, the skier, who may still be in control, is positioned well back on the skis and then suddenly catches the inside edge of the tail of the ski, producing a sudden internal rotation of the hyperflexed knee, which again results in an apparent isolated ACL injury. In the both mechanisms, the design of the boot contributes directly to the injury. In the past when boot tops were more flexible and allowed plantar flexion of the ankle, such injury mechanisms were less likely. In 53 patients with ACL injuries sustained in skiing, valgus external rotation was the injury mechanism in 25 (47%) and flexion-internal rotation in 21 (40%) cases, The role of the other injury mechanisms was minimal.

To prevent knee ligament injuries in other sports, especially that of the ACL, it is important to determine the mechanism of injury. Tremendous decreases in injuries have occurred when attention has been focused on prevention of sports injuries, . In Sweden, for example, Ekstrand (3) found more than 50% decline in soccer injuries when attention was focused to the preventive aspects of sports injuries. Also in Sweden a marked decline in downhill skiing injuries occurred in 1970s, when a large campaign was conducted on TV, radio and in the press concerning the correct use of equipment, boots and bindings.

References:

1. Asikainen, P., P. Luthje, M. Jarvinen, V. Avikainen, and I. Koskinen. Downhill skiing injuries and their costs at a Finnish skiing area. Scand J Med & Sci Sports 1:228-231, 1991

2. Clancy, W.G. Jr. Knee ligamentous injury in sports: the past, present, and future. Med Sci Sports Exerc 15:9-14, 1983

3. Ekstrand, J. Soccer injuries and their prevention. Linkoping University Medical Dissertations. No 130, 1982

4. Eriksson, E. Ski injuries in Sweden: a one year survey. Orthop Clin North Am 7:3-9, 1976

5. Folksam: Sports Injuries 1976-1983. A report from Folksam Insurance Company, Stockholm, Sweden, 1985

6. Harilainen, A. The diagnosis and treatment of acute traumatic henarthrosis of the knee joint. A prospective study of 350 patients based on clinical, radiological, arthroscopic and operative findings. Thesis, University of Helsinki, p.1, 1990

7. Hirshman, P.H., D.M. Daniel, and K. Miyasaka:The fate of unoperated knee ligament injuries. In: Knee ligaments: Structure, function, injury and repair. Ed: D. Daniel, W. Akeson, J. O Connor, New York: Raven Press, 1990, p.481-503.

8. Jarvinen, M., P. Kannus, and R.J. Johnson. How to treat knee ligament injuries. Ann Chir Gynaecol 80:134-140, 1991

9. Jarvinen, M.and P. Kannus Clinical and radiological long-term results after primary knee ligament surgery. Arch Orthop Trauma Surg 104:1-6, 1985

10. Jarvinen, M. Sports traumatology expands the art of surgery. Ann Chir Gynaecol 80:79-80, 1991

11. Johnson RJ, C.F. Ettlinger, and J.E. Shealy. Skier injury trends. Skiing trauma and safety: Seventh international Symposium, ASTM STP 1022. Eds Robert J. Johnson, CD Mote Jr and Marc-Herve Binet, Philadelphia:American Society for testing and Materials, 1989, p.25-31.

12. Johnson, R.J. and M.H. Pope. Epidemiology and prevention of skiing injuries. Ann Chir Gynaecol 80:110-115, 1991

13. Johnson, R.J.Prevention of cruciate ligament injuries. In: The cruciate ligaments. Ed: JA Feagin Jr,New York: Churchill Livingstone, 1988, p.349-356.

14. Kannus, P. and M. Jarvinen. Long-term results of conservatively treated tears of the anterior cruciate ligament. Long term results. J Bone Joint Surg (Am) 69-A:1007-1012, 1987

15. Kannus, P. and M. Jarvinen. Incidence of knee injuries and the need for further care: a one-year prospective follow-up study. J Sports Med 29:321-325, 1989

16. Kannus P, Johnson RJ:Downhill skiing injuries: Trends to watch for this season. J Musculoskel Med 8:13-32, 1991

17. Kannus, P., H. Sievanen, M. Jarvinen, A. Heinonen, P. Oja, and I. Vuori. A cruciate ligament injury produces considerable, permanent osteoporosis in the affected knee. J Bone Miner Res 7:1429-1434, 1992

18. Kannus, P. Long-term results of conservatively treated medial collateral ligament injuries of the knee joint. Clin Orthop (Am) 226:103-112, 1988

19. Kannus, P. Nonoperative treatment of grade II and III sprains of the lateral ligament compartment of the knee. Am J Sports Med 17:83-91, 1988

20. Miyasaka, K., D. Daniel, M. Stone, and P. Mirshman. The incidence of knee ligament injuries in the general population. Am J Knee Surg 4:3-8, 1991

21. Natri, A., M. Jarvinen, P. Kannus, S. Niittymaki, J. Aarnio, and S. Lindholm. Changing injury pattern of acute ACL Tears in Tampere University Hospital in 1980s. In press: Scand J Med and Sci in Sports.

22. Nielsen, A.B. and J. Yde. Epidemiology of acute knee injuries: a prospective hospital investigation. J Trauma 31:1644-1648, 1991

Legends of figures

Figure 1: Valgus-external rotation knee injury mechanism in skiing

Figure 2 The so called anterior drawer maneuver" knee injury

Figure 3: Flexion-internal rotation knee injury mechanism in skiing.

Table 1.

Acute ligament injuries with pathologic motion. Comparison of the studies performed at San Diego Kaiser; n=500; and Tampere University Hospital; n= 317

Ligament Injurv

|ACL |MCL | PCL | LCL |San Diego |Tampere |

| | | | | | |

|X | | | |238(48%) |42 |

| |X | | |144 (29%) |126 |

| | |X | | 18 (4%) |3 |

| | | |X |10( 2%) |29 |

|X |X | | |64 (13%) |96 |

| |X |X | | 8 (2%) |7 |

|X | | |X | 6 ( 1%) | 3 |

| | |X |X |1 |- |

|X | |X | | 5(1%) |1 |

|X |X |X | |4( 1%) |10 |

|X | |X |X |1 | |

|X |X | |X |1 | |

Total

| |ACL |MCL |PCL |LCL | |

|San Diego |319 63%) |221 (44%) |37 (7%) |19 (4%) |n=500 |

|Tampere | 152 |239 | 21 |33 |n=317 |

Table 2.

Acute ACL injuries sustained in different sport events at San Diego, California and Tampere, Finland

| |San Diego |Tampere | |

| |N= 204 |N=243 | |

| | | | |

| | | | |

|Soccer |42 (21%) |Soccer |71 (29%) |

|Skiing |35 (17%) |Downhill skiing |48 (20%) |

|Football |33 (16%) |C-c skiing |30 (12%) |

|Baseball |26 (13%) |Volleyball |29 (12%) |

|Basketball |22 (11%) |Basketball |8 ( 4%) |

|Other sport |46 |Other sport | 57 |

| | | | |

| | | | |

|Total |204 |243 | |

C-c = Cross-country

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