1 Introduction

Motocross is a form of motorcycle racing in an off- road area which is gaining an increasing popularity worldwide.¹,² The length of a Motocross route varies between 1000 m (m) and 4000 m, what is not as technically demanding as a Supercross route. The condition of a Motocross track, which can be hard-packed, soft, muddy, sandy, rutted or any combination thereof, depends on the weather.

Supercross is a variant of Motocross where off-road motorcycles are driven on a constructed indoor dirt track. It is characterized by steep jumps at high speeds over short distances and obstacles. Obstacles are combined and can have whoop sections where riders skim along at the tops of several bumps, rhythm sections with irregular series of jumps or triple jumps which can also be cleared with a single leap. A high concentration and a lot of skills are required for this. The tracks for Supercross events are specially prepared in large halls or stadiums and the ground condition is usually hard.

There are some guidelines for building a Supercross or Motocross track. The route includes various obstacles and challenges. Special sections are for example:a)Single jumps: a minimum distance between the hills is necessary (Fig. A1

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Fig. A Guidelines for building a Supercross trackA1 - Single jumps: a minimum distance between the hills is necessaryA2 - Multiple jumps: second and/or third hill is within the landing zone of the first hillA3 - “Washboard”: the “waves” have a maximum height difference of 1m and a maximum length from 8 to 10m, it's only for SupercrossA4 - “Table”: a jump with an ascent, middle section (plateau) and a descent A5 - Step up: the ascent is lower than the rest of the jump behind itA6 - Step down: the ascent is higher than the rest of the jump.

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The demands of these jump variations are adapted to the performance level.

Competitions are held in different classes, shown in Table 1.

Beside the main Supercross event, a special supporting program, typically filled with music and freestyle shows is performed. In freestyle Motocross (FMX) the driver tries to perform the best or most beautiful trick with his machine during the jump. FMX is an own subclassification. Because of the extremely high jumps and special, risky moves, this subcategory has a high risk of injuries, too.

Those Supercross events need good organization and a lot of qualified staff.

Furthermore, medical equipment and -staff is required. Needs depend on the route and the type of event.

To ensure a good and fast medical care, various positions at the track have to be filled with professional staff. In this study we want to analyse what severe injury patterns we can expect at a single Supercross event and to what extent the presence of medical personnel is required.

2 Methods

During the 17th International Supercross Event in Chemnitz (Germany; 29.- 30.11.2019) 93 participants started and all injuries were analyzed if clarification and treatment at the hospital (Medical Center of Chemnitz) was needed. A total of 5 classes started (Driver field SX: 1 (N = 29); 2 (N = 29); 125 (N = 11); 4 (N13); 5 (N = 12)). This Supercross event during 2 days is one of the largest international Supercross competitions and the only one in eastern Germany.

We supervised all participants and analyzed patients who needed clarification and treatment at the hospital. We only included patients in this study who had an accident during the event and were taken directly to the hospital by ambulance. Patients who were only treated at the site or who presented themselves to a hospital later on, were not included in this study.

We accompanied these patients from the track, through the emergency department and during hospital stay up to their dismission. The type and severity of injuries were analyzed.

3 Theory/calculation

Accidents in Motocross and especially Supercross can lead to various injuries which require a quick assessment at the scene of the accident in order to make the right decision for treatment. Because of that, it would be desirable to have further knowledge of the typical injury patterns. The patterns of injuries could also give an advice for planning medical equipment and staff as well as preventive measures.

4 Results

Overall 5 participants (Injury rate: 4.65%) had to be admitted to the clinic. Every patient was male, the age range was between 9 and 33 years (mean 25 years). One patient participated in group SX5 (Injury rate: 8.3%) and 4 patients started in group SX1 (Injury rate: 13.8%). A total of 16 injuries required 3 Operations. The mean length of hospital stay was 4.4 days (range: 0–10 days). No intensive care/intermediate care unit was needed.

The cases were as followed:

4.2

4.2 Foot and ankle trauma

A 22 year old athlete (SX1) crashed into the “washboard” between jump and landing. He suffered a contusion of his left foot. When he tried to continue participating in the race and bring the motorcycle back on track, he had to stop because of severe pain. He wasn't able to move and stopped competing. After a brief pause in the race to rescue the patient and the motorcycle, he was brought into the ambulance. Taking off the protective gear for foot, ankle and lower leg was very painful. The protective gear is very stiff and fits closely. Therefore, it is not easy to remove the gear without pain, so that sufficient analgesics are needed. The foot and ankle were swollen. The patient was transferred to the hospital where x-rays of the foot, ankle and knee were performed. Fractures of the metatarsal bones II (AO 87.2.2A1), III (AO 87.3.2A1) and IV (AO 87.4.2B2) were seen (Fig. B1,2). The athlete left the clinic on crutches on his own request after plastering. This patient needed orthopaedic follow-up in another fracture clinic.

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Fig. B X-ray of the left foot of a 22-year old man The d.p.-view (B1) and the oblique view (B2) shows a dislocated fracture of the metatarsal bones II (AO 87.2.2A1), III (AO 87.3.2A1) and a non-dislocated fracture of the metatarsal bones IV (AO 87.4.2B2).

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4.3

4.3 Multiple injuries

A 29 year old participant (SX1) fell after a 3 m jump on his back. The race was stopped immediately to rescue the patient from the track with spine board and stiff neck. After short unconsciousness, he suffered headache, back pain and dysaesthesia in his right leg for a moment. The body check showed a painful thorax and diffuse pain in the thoracic and lumbar spine. He was able to move all extremities. Peripheral blood circulation, motor skills and sensitivity were intact.

In the hospital the polytrauma- CT scan revealed a compression fracture of the thoracic vertebrae 4 and 5 (AO type A1) with undisplaced fractures of the 3rd left transverse process. Furthermore we diagnosed a minor head trauma. During the hospital stay the pain and headache decreased. We performed a MRI to exclude discoligamentous injuries. This showed contusions of the posterior spinous ligaments Th 4 and 5, the left musculus spinalis thoracis, the musculus multifidus and bone bruises in the thoracic vertebrae 6 and 7 (Fig. C1,2). The patient was mobilized by adapting the analgesic and physiotherapeutic therapy. Ten days after trauma we discharged the patient with this conservative treatment in a good condition for the return flight home.

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Fig. C MRI scan of a 29-year old man with spine injury Axial view (C1) and sagital view (C2) shows contusions of the posterior spinous ligaments Th 4 and 5, the left musculus spinalis thoracis, the musculus multifidus and bone bruises in the thoracic vertebrae 6 and 7.

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4.5

4.5 Multiple injuries

A 33 year old driver (SX1) crashed in a curve, fell on his left side and on the back. There were no signs for a head injury, limitations of movement or sensibility disorders of the extremities. The patient complained about pain in the area of the left clavicle and the lower lumbar spine. First-aid treatment took place on site and the patient was brought to the clinic. A burst fracture of the 2nd lumbar vertebra (Fig. D1,2) and a peri-implant fracture of the left clavicle (OTA type 15-B2) with a present plate osteosynthesis (Fig. E) were seen in the polytrauma scan. Operative treatment was necessary. Two days after trauma, open reduction and dorsal stabilisation of the spine from T 12, L1 to L3 was performed. Five days after trauma the removal of the present clavicle plate and reosteosynthesis with a LCDC plate was performed. Mobilisation and physiotherapeutic therapy started. After 10 days the patient was dismissed.

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Fig. D CT scan of a 33-year old man with spine injury Axial view (D1) and sagittal view (D2) shows a burst fracture of the 2nd lumbar vertebra.

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Fig. E X-ray of the left clavicle of a 33-year old man (same patient of Fig. D) A.p. view (E1) of the left clavicle with a peri-implant fracture (AO/OTA type 15.2A).

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5 Discussion

The present study aimed to evaluate the patterns of injuries and the extent of on-site medical care resources. The main findings were: the injuries were diverse with up to serious trauma with a severe injury rate of 4.65% where a clarification and treatment at the hospital was needed. There was no typical leading cause of accident regarding the trail.

In general, Motocross is one of the extreme sports and becomes more and more popular.¹ The literature shows several articles about Motocross, Freestyle Motocross (FMX), Bicycle Moto-Cross (BMX) or Bicycle Supercross. They are all classified as high-risk sports, but differ in speed and jump variation. Up to our knowledge there are no articles about injuries in Supercross.

Because of the high speed and steep jumps in Supercross, a good concentration as well as physical fitness is needed over a long time. One study measures the heart frequence and blood lactate concentration in Motocross athletes and shows the extremely physiological load.³ Also a very high concentration over a long period is needed. It is not surprising, that the pattern of injuries is a mixture between simple violation and polytrauma.

A retrospective study with FMX-athletes showed, that FMX is a high-risk sport. They found in 19 athletes over a period of 6 years 54 accidents resulting in 78 severe injuries. The most affected body regions were foot/ankle (20.5%), shoulder (12.8%), back (10.3%) and abdomen (9%). Because of that they recommended the best physical and mental condition of the athletes as well as the presence of medical staff at the track at all times.⁴ They also identified the landing to be the moment where accidents happen most often.

Colburn et al. showed an injury rate of 9.6% during a single Motocross event.⁵ In our Supercross event we found a severe injury rate of 4.65%. In the SX1 class, the injury rate was 13.8%. That could be due to the short distances at relatively high speeds. It seems that in the professional SX1 class, an athlete has to take high risks in order to win. The motorcycle has the highest performance in this category, which can lead to a higher risk of falling. Additionally the underground in Supercross is usually harder than in Motocross. Thus the probability of severe injuries is higher.

In our study from the patients that had to be admitted to hospital, 3 drivers crashed while landing, 1 collided with a passenger and 1 fell in a curve. This also shows that most accidents occur at jumps with unfortunate landings. Literature shows also that about 50% of injuries occur by being thrown over the handlebars.⁵ Comparing our patterns of injuries to the literature reveals that our batch is comparable to other reports. Out of the five patients with serious injuries, two (40%) suffered fractures of the spine. A high incidence of spine injuries with an increase in the spinal injury rate by almost 500% in the United States between 1997 and 2006 is reported.⁶ Literature shows that spinal injuries that occur during Motocross have significant capital connotations for regional spinal centers.⁷ This study also shows that a loco-regional hospital has to be aware if a Supercross event takes place, and has to take in account that there will be a higher patient volume in the emergency department.

The amount of treatments on site at the Supercross event shows that a high number of medical staff is really needed.

Further research is needed on a larger collective to describe typical fracture patterns.

6 Conclusion

Supercross is a popular variant of Motocross. It is undisputable that this is a high-risk- sport with a wide injury pattern. So the variety of injuries in a Supercross event can affect the head and face, the upper- and lower extremities, thoracal- and abdominal traumas and especially the spine. In general it seems to be, that in Supercross the injury rate could be higher than in Motocross. Maybe a softer underground, more padding and more space in the injury zone could be helpful.

Furthermore the presence of medical staff at the site and a good organisation with cooperation to loco- regional hospitals is necessary during a Supercross event. In addition, a special training concept in terms of preventive measures to prevent falls would be desirable.