Cycling is often considered a leisurely activity with minimal potential for severe or chronic injury. Acute head and spinal trauma can be devastating and can predominantly contribute to all-cause mortality in injuries attributed to cycling. Chronic overuse injuries primarily affecting the ulnar, median, and pudendal nerves are also a cause of significant morbidity for the cyclist.
Bicycling is one of the most popular means of transportation, recreation, fitness, and sport among millions of people of all ages. The bicycle has undergone extensive refinements since its initial beginnings as the velocipede in 1817 by Karl von Drais, remaining a readily available form of aerobic nonimpact exercise with established beneficial cardiovascular effects. Bicycling also continues to be a popular means of city transport, especially within Asian and European countries. Commercial interests, such as the postal service and law enforcement, continue to use cycling for transportation. Additionally, in the past, bicycles were an effective vehicle for mobilizing soldiers and supplies to combat zones during World Wars I and II.
Cycling was part of the inaugural first modern Olympic Games in 1896. Since this time, the International Olympic Committee has recognized the popularity of various forms of cycling and included mountain biking in the 1996 games in Atlanta with plans to incorporate bicycle motocross (BMX) in the 2008 games in Beijing. Bicycle sales have steadily increased in each decade, with mountain bikes currently accounting for 62% of new bicycle sales in the United States. The increasing attractiveness is not limited to the adult population, however. In 1994, the Centers for Disease Control and Prevention estimated that 73% of children aged 5 to 14 years ride bicycles.
Cycling is not generally considered a high-risk activity. Given the increased number of people riding bicycles and the development of “extreme forms” of the activity, such as mountain biking, however, there has been a continued increase in injury incidence. Generally, bike-related injuries can be classified into acute physical trauma or chronic overuse patterns. The annual incidence of bicycle deaths has been reported as 900, with 23,000 hospital admissions, 580,000 emergency department visits, and greater than 1.2 million physician consults per year. Bicycle crashes rank second only to riding animals as a sports- or recreation-associated cause of serious injury. Although injuries to mountain bikers of all ages account for only 3.7% of bike injuries overall, up to 51% of recreational and 85% of competitive mountain bikers sustain injuries each year. The peak incidence of bike-related injuries and fatalities is within the group aged 9 to 15 years, whereas 20- to 39-year-old riders comprise the group incurring the most mountain bike injuries. Mortality and morbidity rates attributable to bicycle accidents remain highest in older individuals, male cyclists, and cyclists involved in collisions with motor vehicles.
Most bicycle-related injuries involve superficial trauma, such as abrasions, contusions, and lacerations. Significant trauma to the upper and lower extremities and to the head, face, abdomen, and thorax are also commonly seen. Neurologic involvement, unfortunately, may represent a large proportion of the more severe injury patterns. Head injuries, in particular, often involve collision with a motor vehicle and are responsible for more than 60% of all bicycle-related deaths and most long-term disabilities.
Central nervous system injuries
Head Injuries
Off-road cyclists seem to have a lower incidence of head, facial, and dental injuries compared with on-road cyclists. This is presumably attributable to physical segregation from vehicular traffic and the tendency to more frequent helmet use. A recent report analyzed severe cycling injuries over a 10-year period and found that 18% involved a head injury with 10% spinal involvement. Principal risk factors for head injury include not wearing a helmet, crashes involving motor vehicles, an unsafe riding environment, and male gender. The effect of rider errors, such as losing control, performing stunts, inexperience, or bike mechanical failure, remains unclear. Elevated riding speeds do seem to be linked to more severe head injury, however.
Severe head injuries, such as intracranial hemorrhage and contusions, generally have a low incidence among cyclists but do remain the top culprit contributing to mortality. Intracranial hemorrhage and contusions, if present, typically involve the cerebral cortex, followed by the cerebellum and brain stem. Conversely, the most common head injury is a closed head injury without an overt structural lesion, presenting as a brief loss of consciousness. Given the relative infrequent nature of structural closed head injuries, it is not unexpected that only 1.5% of all cases require operative intervention.
Helmets are known to reduce the risk for head injuries by 69% to 85% and are strongly advocated by various preventative health and government agencies. It has been estimated that although nearly 50% of children have helmets, only 15% to 25% wear them consistently or correctly. Proposed barriers to helmet use include poor fit, cost, discomfort, and negative pressure from peers, particularly among school-aged children. Helmet legislation has been shown to be effective for increasing helmet use and for decreasing the frequency of head injuries. Strong community-based programs designed to provide free or subsidized helmets are also effective for promoting helmet use among children. Most cycling organizations now mandate bicycle helmet use, and many state jurisdictions in the United States have added mandatory use legislation, but with restrictions only applied to children.
Further preventative measures have aimed to educate riders to anticipate the errors of motorists and to become familiar with the risks of different road surfaces and weather conditions. Younger children are encouraged to avoid riding in the vicinity of traffic. Environmental solutions have centered around separating cyclists from road traffic by the use of designated cycle lanes on streets. Furthermore, the design of bike pathways has included the use of smoother surfaces, avoidance of obstacles, and discouraging “wrong-way” riding. The impact of these design strategies so far has been unclear. Recently, Aultman-Hall and Kaltenecker have indicated that riding on sidewalks and dedicated bicycle paths may actually be more detrimental than riding on roads, presumably because of less adherence to “road safety rules.”
Spinal Cord Injuries
Like head injuries, spinal cord injuries are, fortunately, less common compared with acute musculoskeletal or chronic overuse injuries. Kim and colleagues found a 12% incidence rate of spinal injuries occurring in a population of patients experiencing cycling injuries. The cervical cord was the most frequently involved spinal region. Typically, severe cervical injury results from being propelled over the handlebars after loss of control or collision with an obstacle. Injuries can range from simple vertebral fracture patterns to more severe injuries, such as central cord injury and overt cord disruption. Cord injury leading to para- or quadriplegia is not infrequent. Unlike head injuries, the severity of cord involvement in cycling injuries frequently necessitates immediate operative intervention.
Peripheral nervous system injuries
Upper Extremity
Ulnar nerve
Anatomy
The ulnar nerve arises from the medial cord of the brachial plexus and is composed of fibers from the anterior rami of C8 and T1. In the upper arm, the ulnar nerve is posteromedial to the brachial artery, posterior to the intermuscular septum, and anterior to the medial head of the triceps. The ulnar nerve passes posterior to the medial epicondyle of the humerus and medial to the olecranon before entering the cubital tunnel at the elbow. Once through the cubital tunnel, the ulnar nerve travels deep into the forearm immediately innervating flexor carpi ulnaris and flexor digitorum profundus to the ring and small fingers. It then descends the forearm along the ulnar side of the ulnar artery to pass through Guyon’s canal. Guyon’s canal is formed by the pisiform bone ulnarly, the volar carpal ligament radially and superficially, and the transverse carpal ligament as its deep surface. Once exiting Guyon’s canal, the ulnar nerve divides into superficial and deep branches. The superficial branch provides sensation to the small finger and the ulnar half of the ring finger, whereas the deep branch supplies motor fibers to the hypothenar muscles, the third and fourth lumbricals, the dorsal and volar interossei, the deep head of flexor pollicis brevis, and the adductor pollicis.
Etiology
Common sites of ulnar nerve compression attributable to trauma, anomalous muscles, or overt masses include the thoracic outlet, the medial intermuscular septum in the arm, the cubital tunnel, and Guyon’s canal. Compression in Guyon’s canal is typically seen after repetititive trauma, such as with prolonged grip pressures on bicycle handlebars or as a result of the unique position of the wrists during cycling, often leading to “cyclist’s palsy”.
Clinical presentation
Cyclist’s palsy is classically described as numbness and paresthesias in the small finger and ulnar half of the ring finger, with motor findings like weakness on abduction or adduction of fingers or adduction of the thumb. Patterson and colleagues reported that 92% of long-distance cyclists experience motor or sensory symptoms, whereas 24% had both modalities involved. Furthermore, the incidence was independent of handlebar design. Despite the predominance of sensory symptoms in cyclist’s palsy, Capitani and Beer have reported cases of isolated motor palsy affecting the ulnar-innervated intrinsic muscles. Akuthota and colleagues found significantly increased distal motor latencies in the deep branch of the ulnar nerve after a long-distance cycling event, suggesting the possibility of acute trauma.
Treatment
Although decompression of Guyon’s canal directly or in combination with carpal tunnel release is a viable surgical option, it is rarely indicated. Typically, most cases resolve spontaneously after transient avoidance of cycling, albeit symptoms may not subside for several months. Additionally, the use of gloves, padded handlebars, and frequent changes in hand position have been advocated as measures to prevent or alleviate symptoms of cyclist’s palsy. The effectiveness of these preventative strategies remains to be substantiated, however.
Median nerve
Anatomy
The median nerve is formed from branches of the medial and lateral cords of the brachial plexus. It travels distally between the brachialis muscle and the medial intermuscular septum before passing through the antecubital fossa and under the bicipital aponeurosis. The nerve then travels into the forearm between the deep and superficial heads of pronator teres while providing innervation to the palmaris longus, flexor carpi radialis, and flexor digitorum superficialis. After exiting pronator teres, it gives off the anterior interosseous nerve, which supplies the flexor pollicis longus, flexor digitorum profundus to the index and long fingers, and pronator quadratus. The main branch of the median nerve descends vertically behind the flexor digitorum superficialis, and before passing through the carpal tunnel, gives off the palmar cutaneous branch to supply sensation to the thenar eminence. Once through the carpal tunnel, the median nerve divides into five branches: a recurrent motor branch to supply the thenar muscles and four digital branches to supply sensation to the thumb, index finger, long finger, and radial half of the ring finger. The second and third branches also give off motor branches to the first and second lumbricals.
Etiology
Typical sites of median nerve compression include at the medial intermuscular septum, where the nerve travels through pronator teres leading to pronator syndrome as well as to two clinical entities distally: anterior interosseous nerve entrapment and carpal tunnel syndrome at the wrist. Similar to ulnar nerve involvement, cycling has been implicated primarily in entrapment at the wrist, causing carpal tunnel syndrome. Although not as well documented as cyclist palsy, the presentation of median nerve compression at the wrist is analogous to the prototypical carpal tunnel syndrome.
Clinical presentation
Although rarely reported, the typical symptoms of carpal tunnel syndrome, such as numbness in the lateral digits after cycling, have been observed. Akuthota and colleagues did not demonstrate any significant electrophysiologic abnormality in median motor and sensory functions, however.
Treatment
Similar to ulnar nerve compression, median nerve symptoms seem to improve after a change in handlebar and riding position. Once again, if these measures fail to provide symptomatic relief, brief cessation from cycling or surgical decompression may be needed in some cases.
Lower Extremity
Pudendal nerve
Anatomy
The pudendal nerve arises from the sacral plexus (S2–S4) and comprises a mixed nerve transmitting somatosensory impulses from the genitalia and motor impulses to the perineal muscles, such as the ischiocavernosus and bulbocavernosus. The major trunk of the nerve passes caudally between the sacrospinal and sacrotuberous ligaments (“the clamp region”) near the ischial spine before penetrating the obturator muscle aponeurosis, often called Alcock’s canal. Subsequently, the nerve emerges below the pubic bone to innervate the perineum and genitalia.
Etiology
Three potential sites for pudendal nerve compression exist. Proximally, as the nerve crosses between the sacrospinal and sacrotuberous ligaments, it can be stretched repeatedly during pedaling. Additionally, increased friction within Alcock’s canal can arise as the result of increased perineal pressure during prolonged sitting on a hard bicycle saddle. Finally, once the nerve escapes the protection of the bony pelvis, it is prone to compression from direct pressure on the perineum and symphysis, such as from the nose of the riding saddle.
Clinical presentation
Because the pudendal nerve can be compressed at various locations along its course, its entrapment often leads to varying clinical presentations. The most common symptoms involve genital numbness and erectile dysfunction. Numbness may only involve the penis if the nerve is compressed distally or could present with mixed symptoms of penile, scrotal, or perianal anesthesia if compression is proximal within Alcock’s canal. Other symptoms may include difficulty in achieving orgasm and a reduced sensation of defecation. Through pressure mapping, Schrader and colleagues found that the pressures applied to the perineum of cyclists by the saddle are double the threshold value known to cause ischemic injury.
Sommer and colleagues reported genital numbness in 61% and erectile dysfunction in 24% of male cyclists whose weekly training program exceeded 400 km, with similar prevalence rates also found among amateur recreational cyclists. The Massachusetts Male Aging Study (MMAS) investigated the incidence of erectile dysfunction among cyclists from a variety of riding backgrounds and seemed to demonstrate a protective effect of moderate amounts of cycling on the occurrence of erectile dysfunction. A recent survey of 688 cyclists also did not find a significant correlation between erectile dysfunction and several cycling parameters. Despite these discrepant reports, an increased risk for erectile dysfunction and genital numbness has been linked to age older than 50 years, elevated body weight, more than 10 years of cycling history, and a high intensity of training.
Although most research into pudendal nerve involvement and cycling has been limited to the male population, women are equally affected. This is not surprising, because the anatomic course of the pudendal artery and nerve within Alcock’s canal is roughly homologous in men and women. Lasalle and colleagues reported that approximately one third of female members of a cycling club had experienced signs or symptoms of perineal trauma, such as numbness.
Treatment
Most cases require no treatment and resolve spontaneously after cessation of cycling for a brief period. Once again, preventative measures are the most effective strategy. Prevention aims to change the riding style and schedule but also modifies the design of the saddle and its positioning. The goal is to minimize the strain on the neurovascular structures in the perineum during vigorous cycling. The large variety of bicycle saddles on the market today are designed to shift the weight bearing from the perineum and to distribute the pressure over a wider area of the buttocks and the ischial tuberosities. Overall, the optimal saddle seems to be wide and heavily padded with a flexible or absent nose. Heavier riders seem to benefit the most from such wider saddles.
Positioning of the saddle also remains highly pertinent. A downward tilt of the nose of the saddle and a limited height difference between the seat and the top of the handlebar are crucial to avoid vigorous pressure directly on the perineum. Changes in riding styles, such as taking frequent breaks during long outings and regularly alternating between riding in sitting and standing positions, are also imperative.
Surgical options are rarely indicated. Pudendal nerve decompression, primarily of Alcock’s canal, was successful in reducing pain and incontinence recently in a female population. Three main surgical approaches for pudendal nerve decompression, including transgluteal, transischiorectal, and transperineal, have been proposed.
Other lower extremity peripheral nerves
Although most lower extremity peripheral nerves could potentially be hampered by means of direct trauma secondary to orthopedic involvement, there have only been a few documented cases of lesions other than that of the pudendal nerve associated with cycling. Kho and colleagues describe a lone case of meralgia paresthetica involving the lateral femoral cutaneous nerve after long-distance cycling. The patient described a painful sensation on the lateral aspect of the thigh, with an objective sensory deficit noted on clinical examination.
Related posts:
Spinal Injuries in Sports
Peripheral Nerve Injuries Attributable to Sport and Recreation
Concussion in the National Football League: An Overview for Neurologists
Sleep, Recovery, and Performance: The New Frontier in High-Performance Athletics
Neurologic Injuries from Scuba Diving
Peripheral Nerve Injuries in Baseball Players
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