SPORTS MEDICINE SPINE FRACTURES IN DRIVERS OF OPEN-WHEEL OPEN COCKPIT RACE CARS – Written by Terry Trammell and Kathy Flint, USA This paper is intended to explain the mechanisms responsible for production of spinal fracture in the driver of an open cockpit single seat, open-wheel racing car (Indy Car) and what can be done to lessen the risk of fracture. In a report of fractures in multiple racing • Seated angle (approximately 45°) • Lumbar spine flexed series drivers (Championship Auto Racing • Hips and knees flexed • Seated semi-reclining Cars [CART]/Champ cars, Toyota Atlantics, Indy Racing League [IRL], Indy Lights and Figure 1: Body alignment in the Indy Car. Formula 1 [F1]), full details of the crash and mechanism of injury were captured and analysed. This author was the treating physician in all cases from 1996 to 2011. All images, medical records, data available BASILAR SKULL FRACTURE Use of this specific safety feature from the Accident Data Recorder-2 (ADR), Following a fatal distractive basilar is compulsory in most professional crash video, specific on track information, skull fracture in 1999, the Head and Neck motorsport sanctions and has resulted in a post-accident investigation of damage and Support (HANS) device was introduced into dramatic reduction to near elimination of direction of major impact correlated with Indy Cars. Basilar skull fracture occurs when fatal basilar skull fractures. No basilar skull ADR-2 data were analysed. Results provided neck tension exceeds 3113.75 N forces. fractures have occurred in the IRL since the groundwork for understanding spine No data demonstrates that HANS introduction of the HANS and since 2006 fracture and forces applied to the driver in predisposes the wearer to other cervical there has been only one cervical fracture. an open-wheel open cockpit race car1. fracture. In a high G frontal impact, the The Indy Car requires drivers to be seated HANS yoke will cause bruising of the upper FRACTURES OF THE CERVICAL SPINE in a position such that the spine is out of its back and posterior aspects of the shoulders Some common perceptions exist normal contour. Spinal injuries typically and tenderness of the prominence of the C7 regarding the cause of fracture in the occur in impacts directed rearward (most spineous process (known as ‘HANS tattoo’ subaxial cervical spine. One is that common), frontward or vertically (the among racing physicians). These devices head impact loads the cervical spine in impact occurs on the bottom of the car after are now referred to as Frontal Head compression (similar to a diving accident being airborne). Basilar skull fractures are Restraints (FHR). Their primary design where the head impacts the bottom of the the most feared due to high incidence of couples the head to the torso with resulting pool). In a car, this is the same as the head mortality. They occur in all forms of racing reduction in distractive forces on the upper impacting the vehicle roof. Secondarily and were the first to be addressed. neck/skull junction. there are injurious motions or extremes 196 2 Without HANS® With HANS® 1120 lb. neck tension 210 lb. to neck tension (740 lb. injury threshold) (740 lb. injury threshold) 1350 lb. total neck load (700 lb. injury threshold) 107 62 head G’s head G’s 295 lb. total neck load (700 lb. injury threshold) 210 lb. neck shear (700 lb. injury threshold) 750 lb. neck shear (700 lb. injury threshold) 1.5 chest compression 54 G chest acceleration 0.8 chest compression 40 G chassis acceleration 64 G chest acceleration 40 G chassis acceleration Figure 2: HANS diagrams. 3 4 HANS=Head and Neck Support. Figure 3: First order buckling of the cervical spine. Flexion Flexion Figure 4: Second order buckling, CF, VC(3) CF, VC(3) resulting in both extension injury DE (2) DE (2) CE CE and flexion injury simultaneously. DE (2) DE (2) VC VC Extension Extension DE (3) DE (3) CE CE Extension ExtensionCE CE DE (2) DE (2) Flexion Flexion DE DE Flexion Flexion DF DF of flexion and extension. Unlike injuries The resulting neck fails as a column and mass, causing increased loads on the neck. seen in the general public2, this is seldom injuries due to bending moments (posterior Further, it shows that head motion does not seen in race drivers – signs of head impact element fractures, soft tissue injuries and contribute to cervical fracture. are usually absent and significant head facet fractures) are less common. Cervical fracture occurring in the injury associated with cervical fracture is Data derived from human and cadaveric absence of head impact is due to constraint uncommon. Head and neck motion (flexion testing and use of Anthropometric Test of the head which, depending on the versus extension) has no association with Dummies (ATD) has helped determine position of the cervical spine, results in the mechanism of injury3. timing of head and neck motion during first or second order buckling. Buckling However, constraint to head motion an injury scenario. When appropriate load is a term used to describe mechanical increases the likelihood of neck injury. This is applied, neck injury occurs within 2 to instability in which a structure deforming occurs because the head is a constraint 20 milliseconds, muscle contraction from primarily in compression suddenly changes due to its mass and, as such, increases 50 to 65 milliseconds, while head motion its deformation to a pattern of primary neck loads. Preflexion of the cervical actually occurs from 90 to 130 milliseconds. bending with compression2. This produces spine appears to alter the types of injuries Even if the event is anticipated it is not the extremes of motion and resultant produced, yielding a greater incidence possible to contract the neck muscles before loading within the cervical spine. Second of lower cervical compression and burst the event that results in fracture is over, and order buckling provides an explanation for fractures than a neutrally positioned spine. head motion does not occur until after the seeing an injury in flexion in one region of It increases the flexural rigidity of the spine, event is over. This supports evidence that the cervical spine and an extension injury thereby decreasing its propensity to buckle. the head acts as a constraint by virtue of its in another. 197 SPORTS MEDICINE Axial Forward (n) Rearward (n) (vertical) (n) Thoracic 2 7 3 Thoracolumbar 4 8 0 WHAT CAN WE LEARN FROM THIS? • Remove or neutralise anything that Lumbosacral 0 3 1 increases the head constraint. • Reducing the head restraint by use of a Table 1: Direction of impact and region of spinal fracture (1996 to 2005). head surround. • Provide adequate energy absorption. • Made with resilience and stiffness without cavitating or ‘grabbing’ Severity of Injury Scale the head. • The head is an inertial constraint. • Torso accelerates toward the head. Criteria Description • Mass of the head experiences Compression fracture Not initially present on plain X-ray and often not acceleration lag (cannot get out of 1 without deformity appreciated on CT. Evident on MRI T2 sequence and/ the way). or STIR sequence. Oedema and haemorrhage into the • Results in increased loading on vertebral body adjacent to the endplate. This fracture the neck. may settle until it meets Type 2 criteria • Head comfort pads should not be used. • Passenger cars and other types 2 Mild compression <10% compression (single endplate) ; <15° wedging of sedan comfort pad should be fracture hard and slick to reduce frictional Moderate >10% but <30% compression; >15°but <30° angulation constraint between it and the head 3 compression fracture so as not to cavitate. • The FHR should transition between the 4 Severe compression ≥30% compression ; ≥30° wedging seatback and the head surround. or burst fracture involving a single • A ‘tall HANS’ lessens the likelihood endplate that it will dig into the head surround thus reducing the constraint of the Type 4+ injury to the posterior ligamentous head and resultant neck loading. 5 complex (PLC) An unintended benefit of the combination of head surround, tall HANS 6 Fracture dislocation; burst fracture involving both and tuning of the head surround to prevent endplate; cord or other spinal neurological injury. cavitation has resulted in a reduced incidence of cervical fractures from 23.7% Table 2: Severity of Injury Scale. CT=computed tomography, MRI=magnetic resonance of spinal fractures to 6.7%. imaging, STIR=short TI inversion recovery, PLC=Posterior Ligamentous Complex. FRACTURES OF THE THORACIC, In order to quantitate the severity of car chassis modified to allow full-length THORACOLUMBAR, LUMBAR AND fractures we created a Severity of Injury spinal X-rays. X-rays of the spine were SACRAL SPINE Scale (Table 2). Analysis revealed that obtained and segmental angulation was When fractures of the thoracic, fractures occurring in a rearward directed measured as well as global lordosis and thoracolumbar and lumbosacral spine crash were more common (2 out of 3) than kyphosis. Individual drivers’ seats were were analysed and stratified based on those occurring in a frontal crash. However, scanned to determine the frequency of and direction of the major impact vector, the fractures occurring from a frontal impact variations in angulation and alignment majority resulted from rearward impacts. were more severe (4.5 to 5) than those from of the seatback. This showed that the Each was classified according to Gertzbein’s rearward (2.4 to 3.3). average inclination of the thoracolumbar Comprehensive Classification System4. All and lumbar spine was 45±5°. Individual of the thoracic, thoracolumbar and lumbar STUDYING THE MECHANISM OF INJURY drivers were also measured to obtain fractures resulting from a rearward directed We examined occupant kinematics and anthropometric data. This helped identify impact were classified as Type A fractures, its effect on production of injury utilising the average driver (1.72 m, 70 kg).