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Median and ulnar nerve injuries in cyclists: A narrative review

Cycling is popular internationally as a mode of transport and sport. Cyclists often report sensory and motor changes in the hands during rides. In the past, assessment of these symptoms was based on clinical history, physical examination and neurophysiology. The aim of this narrative review was to evaluate existing publications and determine if there are areas for further improvement in the clinical setting. Methods Searches were undertaken in accordance with the PRISMA guidelines using four online databases: PUBMED, OVID, CINAHL and WEB OF SCIENCE. Articles were evaluated using adapted versions of guidelines for case and cohort studies. Results 2630 articles were found and 13 were included in the review. 2 considered median, 9 considered ulnar and 2 assessed both nerves. 11 were case and 2 were cohort studies. 7 discussed neurophysiology and 1 mentioned ultrasound as a modality of investigation. Interventions were described in 3 articles. Conclusion The quality of evidence is generally low when considering this problem. Clinical assessment and neurophysiology are commonly regarded as the method for assessing nerve symptoms amongst cyclists. Advances in musculoskeletal ultrasound add to our early investigative repertoire and may help expedite management and limit future disability. In addition, further research is required into screening and preventative measures amongst cyclists.


Introduction
P eripheral nerve injuries are common in athletes, occurring anywhere in the body and usually due to direct nerve trauma, sudden traction [1], or a compressive force [2]. Cycling is an increasingly popular activity that people have adopted as transportation, a pastime, or sport. It is estimated that over 7 million people cycle in the United Kingdom weekly [3], while there are nearly 800,000 commuter cyclists daily in the United States [4]. In Singapore, a government survey estimated that 125,000 people cycle regularly [5]. A variety of subcategories (including road, mountain, cyclo-cross, BMX, or track) cater to individual preferences, each with a unique environment [6,7] and associated physical challenges, yet the mechanics and biomechanics remain constant [8]. Primarily intended for directional change and guiding the bicycle, the rider controls the front of the frame via the handlebars. The seat and pedals are rear contact points that carry the rider and produce propulsion [9]. The rider must effectively manage all these intrinsic aspects and also navigate various environmental obstacles.
While cycling is an excellent way of keeping fit and healthy [10e12], it can lead to various injuries from an acute incident or chronic exposure to riding. Common areas where symptoms develop include the back, knees, and shoulders, particularly if the bicycle has not been correctly adjusted to the rider [13]. Cycling may also cause nerve injuries, leading to impotence in male riders [14]. However, the hands are more commonly affected, with injury to the median and ulnar nerves (M&UN), resulting in sensory alterations such as numbness (paresthesia), pain, and muscle atrophy. Dubbed "cyclist's palsy" [15], this condition can occur acutely, following a single prolonged episode of cycling or after repeated exposure with excessive pressure on the handlebars from a wrong frame size, poor positioning, or overall conditioning of the rider [16]. Often dismissed by cyclists as "part of the ride," the increasing popularity of this activity will likely mean that cyclist's palsy will be a more frequent pathology in the future. It is important that rehabilitation specialists, sports physicians, and hand surgeons who encounter riders with these symptoms be aware of the problem and treat it accordingly.
This review aims to summarize existing clinical knowledge of cyclist's palsy, including investigations that confirm the changes and appropriate treatments to limit the functional impact on the individual.

Methods
A literature search of the medical databases PubMed, Ovid, CINAHL, and Web of Science was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [17]. The following MeSH terms (bicyclist, median nerve, ulnar nerve, median neuropathy, and ulnar neuropathy) were incorporated with additional synonyms (Cyclist, Cycling, and Bicycling) ( Table 1) and executed using a Boolean search (Cyclist OR Bicyclist OR Cycling OR Bicycling) AND (Median nerve OR Ulnar nerve OR Median neuropathy OR Ulnar neuropathy).

Review process
Articles were imported into Endnote X9.3.3 (Clarivate Analytics, Philadelphia, PA, USA), duplicates were eliminated, and two study members (DS and SS) examined titles and abstracts for suitability. Full texts identified in the screening were then evaluated before disagreements were resolved by consensus. Authors IL and VR further evaluated the screened articles. References of relevant papers were checked for additional studies.

Inclusion and exclusion criteria
Seminal articles that included the search criteria were chosen and formed the foundation for other papers that cited them. Since this was a narrative review, any studies that described M&UN injury, involvement, or neuropathy with cycling were included. All non-cycling-related nerve articles were excluded.
Inclusion criteria were studies with human subjects over 18 years, articles focused on assessing median or ulnar nerve pathologies in cyclists, and articles published in English in peer-reviewed journals. Non-peer-reviewed journals and review articles, anatomical studies, and studies that do not focus on median or ulnar nerve symptoms, did not perform research in cyclists, or had no abstract or English translation were excluded.

Study analysis
Articles were analyzed according to which nerve (median, ulnar, or both) was considered, the type of riding of the subjects, if any inciting event had precipitated the symptoms, the assessments or investigations undertook, interventions that were required, and the key findings from the study. The level of evidence for each article was graded according to the Oxford CEBM Levels of Evidence [18].

Quality assessment
A quality assessment of included articles was undertaken using an adapted form of the National Heart, Lung, and Blood Institute (NHLBI) guidelines for cohort and case studies/series [19].

Results
A total of 2630 articles were found in the initial search; 2301 articles were screened based on title and abstract, from which 51 full texts were obtained. A final list of 13 articles was included in the review [16,20e31] (Fig. 1).

Median nerve (Table 2, Section 1)
Isolated median nerve (MN) injuries were infrequently described in the literature. Two case studies reported bilateral symptoms in men following longdistance rides [26,30]. One patient underwent an ultrasound and neurophysiology assessment, while the other did not undergo an initial assessment; however, both received cortisone injections as part of their management.

Ulnar nerve (Table 2, Section 2)
Nine studies described ulnar nerve (UN) injuries. These comprised 4 case reports [20,22,27,31] and 5  [20,23,24], whereas the others described unilateral cases [21e25, 27,28,31]. Only two reported hand dominance [21,22]. Eight papers reported the precipitating event before the onset of symptoms; six described single long-distance rides of varying distances [20e23, 25,28], of which one included a downhill ride [28]. One article reported multiple long-distance rides [24], and one documented that symptoms developed following a 3-to 4-h bicycle lesson [31]. The mechanism of injury was not described in one study [27]. In six out of nine studies, nerve conduction studies were used as an assessment [20e22, 24,28,31], and no other modalities were described. One case series reported hand therapy as a mode of treatment [27]; again, no other intervention was described in the other cases.

Median and UN (Table 2, Section 3)
Two cohort studies evaluated M&UN symptoms in cyclists [16,29]. The first studied 25 riders, randomly selected out of 1800 who participated in a 600-mile cycling event [16]. Undertaking a mixture of strength and sensory assessments, the researchers found that up to 22% of mountain bikers and 25% of those riding road bikes had a reduction in grip strength. However, there were also concurrent UN symptoms with weakness in pincer strength in many of these cases. Only four subjects (16%) reported sensory changes in an MN distribution, but three had concurrent changes in a UN distribution. No further assessments (imaging or neurophysiology studies) were performed. A subsequent investigation was performed among 14 riders who participated in a week-long ride where   70 miles were covered daily [29]. Using an electrophysiological assessment of the hands, they found that three subjects had changes consistent with carpal tunnel syndrome pre-ride, which worsened after their participation. One rider developed these changes de novo following the event.

Quality assessment
Based on the NHLBI [19] guidelines, each of the case studies/series included in the review scored 8/ 12 (Table 3), while the cohort studies scored 7/11 ( Table 4).

Discussion
This review yielded two case studies focusing on the MN [26,30], nine case studies/series on the UN [20e25, 27,28,31], and two cohort studies [16,29] focused on the M&UN. In both articles considering the MN, preexisting pathologies were suspected, and due to protracted symptoms following presentation that were not solved with conservative management, a cortisone injection was required.
The two cohort studies investigating M&UN injuries examined the prevalence in road and mountain bikers [16,29]. The first considered neurophysiological changes in cyclists' hands and found that conduction was impaired in the first dorsal interossei (FDI) and the abductor digiti minimi (ADM) after the ride. At the same time, several subjects had MN changes.
Although neurophysiology was reported in most articles, ultrasound was used to evaluate the nerves more comprehensively [32e34]. Indeed, only one case report documented the use of ultrasound imaging when assessing the MN [30], leading to the suspicion that chronic changes, in keeping with carpal tunnel syndrome, had been present for some time. Typically, when nerves are examined, they can be assessed at the site of compression, for flattening or pinching of the nerve, and more proximally, where there is swelling suggestive of nerve compression [35]. In the hand, the UN can be traced from Guyon's canal to its deep and superficial divisions. Measurements and typical pathological changes such as the "notch sign" can help assess and monitor the nerve [36]. As ultrasound imaging resolution improves, it may be possible to assess the nerve glide in a longitudinal plane to identify tethering areas from the compression pathology. Presently, ultrasound is more commonly used to guide treatments around nerves that have been compressed and are causing pain [37]. Thus, ultrasound can improve symptoms and allow subjects to return to normal activities, as in case reports of isolated MN compression [26,30]. However, ultrasound may have a role in screening and tracking the progression of nerve changes in cyclists to identify if and when further assessment is needed. Such progression tracking has been effective in other nerverelated [38] and muscle-related pathologies [39].
The classical description of a "handlebar palsy" [40] involves the UN and its deep branches distal to Guyon's canal [41]. It is associated with sensory, motor, and coordination aberrations in the hand that can manifest during or several days after the ride. Most studies of this phenomenon were case reports [20,22,27,31] or case series [21,23e25,28]. The subjects mostly presented motor weakness in the FDI or ADM following prolonged compression during riding. Most of the subjects were experienced road-bike riders, with only two articles reporting this phenomenon in mountain bikers [25,28] and one in a novice cyclist [31]. Two articles also described this injury in semi-professional or competitive cyclists [22,28]. Rauch et al. (2016) [42] examined the UN in relation to the hamate in various riding positions using magnetic resonance imaging. They found that with the wrist extended or in ulnar deviation, the nerve was closer to the hamate, representing the common handlebar position adopted by riders. However, owing to the non-dynamic nature of MRI scanning and the cost for the patient, this would not be considered a first-line tool and might only be required with atypical symptoms.
During the ride, pressure on the hands to support the rider's body weight and subsequent compression of the nerves appears to be the underlying trigger in most cases, particularly during a long ride. Indeed, compression is recognized as a risk factor for acute and chronic neuropathies [43] and has also been reported in occupationally induced nerve injuries such as carpal tunnel syndrome [44,45]. The typical forward riding position, particularly in road cycling, means that handlebar compression can vary according to the gripping style of the cyclist and whether they use gloves. While road cyclists appear to be most commonly affected at the wrist, triathletes who place the load on the forearms suffer compression neuropathies at the elbow [46]. Therefore, two interventions are proposed to support the cycling community. The first is incorporating neural protection and preservation among cyclists through education and training to alleviate potential problems in the future. As part of this process, it is important to undertake further research with experts in bicycle biomechanics to investigate different grip types [47], handlebar Table 3. Case study quality assessment using the NHLBI guidelines for cohort and case studies/series [19]. design, seat height [48], stem length [9], and the use of gloves [47,49], all of which influence weight distribution on the hands. Equally, cycling ergonomics and core muscle training [50] to ensure maintenance of posture should be included more widely in educational resources.

Author
As a further intervention, a screening program for cyclists is proposed, incorporating self-administered questionnaires like the Boston Carpal Tunnel Questionnaire [51], which has been investigated as a potential screening tool for carpal tunnel syndrome in a potentially high-risk cohort [52]. Should symptoms be identified, referral to a specialist for further assessment and study can be recommended.

Conclusion
Given the rising popularity of cycling internationally, healthcare professionals and cyclists must work together to raise awareness of median and ulnar neuropathies among this active population. Preventive measures, prompt diagnosis, and treatment can potentially limit the morbidity associated with these pathologies. This evaluation highlights the need for further work, particularly when screening cyclists. Hopefully, this work will enable positive symptoms to be identified early rather than attributed to being part of the cycling experience.