Low Back Pain and Injury in Athletes (Pathogenesis) Part 1


Low back pain is an extremely common entity in the general population. Athletes are no different in their affliction for suffering low back pain and injuries, particularly in sports that carry specific low back demands. Whilst traditionally low back pain in the non-athletic population has been thought of in terms of being acute or chronic in nature, recent long-term epidemiological studies have suggested there is a need to revise views regarding the natural history of low back pain. Low back pain is not simply either acute or chronic but fluctuates over time with frequent recurrences or exacerbations and should not be considered self-limiting. The natural history of low back pain in athletes is most probably no different. The very nature of athletic preparation requires mechanical overload. Athletic manoeuvres produce significant compressive forces directed at the lumbar spine. A tradeoff is likely to exist between athletic demands and injury, with greater duration of training, training intensity and a lack of relative rest occurring at the expense of tissue overload and ongoing injury. This may explain why some athletes tend to have more persistent, chronic and recurrent low back symptoms, frequently associated with early degenerative joint disease.

Although most low back pain in both the athletic and non-athletic population is non-specific and mechanical in nature, athletes are often at special risk of more serious causes of back pain that are often sport specific in their aetiology. This is a result of the repetitive mechanical loading and often specific and unique motion imposed on the spines of athletes through various sporting requirements in training and competition. Furthermore, the paediatric sporting population carries a special risk for injury given they have less musculoskeletal maturity and they may be at a heightened risk for more severe and permanent skeletal damage, structural abnormalities and chronic pain.

The initial differential diagnosis list for athletic low back pain should be broad. Diagnosis should include a thorough history excluding red flag conditions, examination and a focussed evidence based approach to imaging. Attention should be paid to the mechanism of injury or the inciting event to assist in predicting the potential injury, implementing preventative measures and in developing a management and rehabilitation program. Consideration of the athlete’s age and an understanding of the sports specific biomechanics of an athlete is required. It is unclear about the relevance of yellow flags in the development of low back injuries and chronic pain in athletic populations. A lack of research exists investigating the management of low back pain in athletic populations. Elite level competitors are likely more willing to train and compete with pain and injury as a result of the financial commitments they receive from competition as well as their drive for competitive success, making the management of athletes with low back injury a challenge for the sports clinician. It is likely that management should mirror published guidelines designed for the non-athletic population and incorporate a period of relative rest, avoiding aggravating activities, changes to training and technique along with appropriate rehabilitation therapy.

Prevalence of low back pain in sporting populations

The anatomical boundaries of the low back being a shaded area between the last ribs and the gluteal folds (Figure 1) has been found to be the most commonly used in a review of methodologically sound low back pain prevalence studies (Walker, 2000). The prevalence of low back pain in the general, non-sporting population has been well described with numerous well designed, long term epidemiological studies and systematic reviews existing in the published scientific literature databases (Lebouef-Yde & Lauritsen 1995, Walker 2000). Evidence from this literature has clearly documented that low back is a very common entity and is responsible for substantial economic burden to society (Druss et al., 2002). However, most low back pain that people experience is low-intensity and low-disability in nature (Walker et al., 2004). Figures documenting lifetime prevalence have been as high as 84% with a point-prevalence between 12% and 33% recorded in a systematic review (Walker, 2000).

The anatomical boundaries representing the low back

Fig. 1. The anatomical boundaries representing the low back

Despite the amount and quality of literature investigating low back pain in the general, non-athletic population, less interest has been afforded to investigating the prevalence, severity and epidemiology of low back pain in athletic populations. In particular there are very few large, long term epidemiological studies assessing low back pain amongst active competing athletes, especially at the elite and professional level of competition. Of the literature that exists, studies have documented that low back pain prevalence and severity can vary between sports, with, not surprisingly, an increase in pain noted in those sports that carry with them significant low back demands (Sward et al., 1990; Bahr et al., 2004). Noteworthy is the reported lack of significant difference in low back injury rates between contact and non-contact sports (Greene et al., 2001), suggesting that other factors may be more important in the development of most cases of low back pain and injury. However, the true prevalence, severity and natural history of low back pain in sporting populations remains unclear due to a lack of well designed, large-scale prospective and longitudinal scientific literature.

When comparing the literature that exists, it is not entirely clear whether competing athletes are at a risk of a higher prevalence or increased severity of low back pain compared with the non-athletic population. This is largely due to a lack of homogeneity in study design and methodology. It also has not been investigated whether low back pain prevalence or severity varies at different levels of athletic competition. Evidence suggests that sporting participation in the general population, regardless of activity, contributes to less frequent low back pain (Jacob et al., 2004). However, once low back pain is established, participation in sporting activities may indirectly contribute to increased severity of pain (Jacob et al., 2004). Bahr et al. analysed low back pain prevalence between elite athletes competing in endurance based sports: cross-country skiing (n=257), rowing (n=199), orienteering (n=278) as well as a non-athletic group (n=197) (Bahr et al., 2004). Low back pain lifetime (51-65%), year (48-63%) and seven day prevalence (20-25%) was similar between groups although lower in non-athletes. As far as the author is aware, despite smaller studies existing (Sward et al., 1991; Kujala et al., 1996), no other large study has used homogeneity in study design and methodology to make direct comparisons between active athletes and non-athletes. One difficultly in measuring low back pain in an athletic population is the lack of validated questionnaires to quantify the functional disability associated with low back pain. Whilst the validated questionnaires measuring pain severity and quality are likely to be useful, the validated questionnaires in use asking about functional limitations are unlikely to be useful as the parameters asked about are not created for sporting populations and questions asked are likely to be irrelevant to the high functional demands of athletes. The development of a validated sports specific, functional low back pain questionnaire is encouraged.

Much of the current sporting literature on low back pain and injury has tended to focus on sports with specific low back demands such as rowing (O’Kane et al., 2003; Teitz et al., 2003; Bahr et al., 2004), skiing (Mahlamaki et al., 1988; Eriksson et al., 1996; Ogon et al., 2001; Bahr et al., 2004), gymnastics (Sward et al., 1990; Hutchinson, 1999; Cupisti et al., 2004), diving (Baranto et al., 2006), wrestling (Lundin et al., 2001; Iwai et al., 2004), golf (McHardy & Pollard, 2005), cricket fast bowling (Elliott & Khangure, 2002; Ranson et al., 2010), tennis (Lundin et al., 2001) and American football (Iwamoto et al., 2004). Elite sporting activity is these sports is known to produce significant compressive forces directed at the lumbar spine (Hosea et al., 1989). The repetitive mechanical loading on the spines of athletes in these sports, often in positions involving end range of motion and the increased volume of training required for elite athletic performance is likely to result in tissue overload and subsequent injury. This, combined with a lack of full recovery between episodes of pain and injury due to many athletes not wanting to miss time off training or competition, may explain why athletes may have more persistent, chronic and recurrent low back symptoms, frequently associated with degenerative joint disease (Ong et al., 2003).

The knowledge surrounding the prevalence and magnitude of low back pain in sports that are not known for having specific low back demands, including the various highly popular football codes, remains largely unknown. Research has tended not to focus on low back pain as an area of interest in these sport, likely for a variety of reasons. Firstly, there are other well known more common and more serious injuries that tend to impact the functional demands of these athletes, resulting in loss of competition match play. Secondly, unlike other injuries that athletes experience, it is uncommon that low back pain is severe enough to prevent a professional footballer from competing or from relinquishing his place in team selection. This is particularly true when medical management frequently incorporates epidural steroid injections (Bono, 2004) and local anaesthetic agents (Orchard, 2004a), considered ‘part of the game’ in professional football (Orchard, 2001). Despite this, injury surveillances have documented that low back injury if present can be severe and have high recurrence rates. In one study on elite soccer, low back pain was reported as the most common overuse injury (Walden et al., 2005). In elite rugby league, ‘back injuries’ have been shown to have the highest rates of recurrence for all injuries (Orchard, 2004b), whilst in retired elite rugby league players, chronic low back pain has been the third most common complaint, reported by 39 % (Meir et al., 1997). In elite Australian Rules football, the Australian Football League’s (AFL) long running injury surveillance has documented that five per cent of all players will miss a match each season with a ‘lumbar or thoracic spine’ injury, causing them to miss on average four weeks or matches per injury (Orchard & Seward, 2002). In amateur Australian Rules football players, 27% of player report a long term or recurrent back problem (McManus et al., 2004). In school children playing rugby union, low back pain has been shown to afflict over 40% of participants (Iwamoto et al., 2005).

Whilst there are many potential pain generators for low back pain, in reality most pain that both the general public and sporting population will experience, despite the use of advanced imaging techniques, can not be attributed to a tissue diagnosis and remain ‘nonspecific’ and mechanical in diagnosis. However, there are several examples of where it is apparent that certain sports and activities have a clear association between the development of certain injuries and the mechanical demands associated with these sports and activities. Examples of this include spondylolisthesis in cricket bowlers (Ranson et al., 2010) and gymnasts (Toueg et al., 2010), herniated discs in weight lifters (Mundt et al., 1993) and traumatic injuries in body contact sports (Tewes et al. 1995). This will be discussed in further detail later in the topic.

Prevalence of low back pain in adolescent sporting populations

There has been an increased awareness of low back pain in children and adolescents with several studies showing that low back pain is highly prevalent in the early years of life (Burton et al., 1996; Balague et al., 2003). Low back pain is known to increase with age during the first decades of life (Salminen et al., 1995), with prevalence increasing significantly following sexual maturity (LeResche et al., 2005). It has been theorized that low back pain in childhood may have important consequences for chronic low back pain in adulthood (Watson et al., 2002). This theory has more recently been validated with clear correlations now existing between low back pain in childhood and adolescence and in adulthood (Hestbaek et al., 2006). Hestbaek et al. in a large longitudinal study found low back pain in adolescence to be a significant risk factor for low back pain in adulthood with odds ratios as high as four (Hestbaek et al., 2006). A dose-response association was also demonstrated: the more days with low back pain the adolescent experienced, the higher the risk of future low back pain that they were more likely to experience. These findings are supported by other well conducted, long term research which has demonstrated that 90% of schoolchildren with low back pain will suffer from low back pain 25 years later (Harreby et al., 1996).

Questions have been raised regarding low back pain at the junior level of sporting competition, given that participation in adolescent sports has been found to be a risk factor for low back pain in one large, well conducted study (Kujala et al., 1997). Furthermore, sporting participation at an adolescent level has also been linked with higher low back pain prevalence than in adolescents who are non-athletes (Kujala et al., 1996). This is particularly true in the male sporting population (Burton et al., 1996). It is believed that adolescent athletes with less musculoskeletal maturity may be at a heightened risk for more severe and permanent skeletal damage and structural abnormalities, particularly when exposed to years of intense athletic training (Wojtys et al., 2000). However, there is a paucity of research documenting the true prevalence and severity of back pain in junior athletes and whether low back pain at a junior level predisposes increased prevalence of back pain later in a career. Like the adult literature, of the literature that does exist, it is extremely difficult to compare results due to a lack of homogeneity in study design. There is also a lack of literature comparing the prevalence and severity of back pain at varying levels of adolescent competition.

Risk factors for low back pain in sporting populations

Risk factors for the development of low back pain in the general population have been extensively researched in the published literature. Epidemiological studies into the prevalence of low back pain have identified that there are many individual, psychosocial and occupational risk factors for the onset of low back pain (Manek & MacGregor, 2005). A growing body of literature also exists implicating the role of genetic factors in back pain, in particular the development of disc injuries (Videman et al., 2005). Of the occupational factors there is evidence for a causal relationship between low back injuries and exposure to forceful exertions, awkward postures and vibration (Keyserling, 2000). Although not specifically targeted in research of athletic populations, it is probable that a combination of these ‘occupational’ factors is responsible for the development of most low back pain in athletic populations given many of the sports with low back demands are well known for their awkward posturing, forceful exertions and high mechanical loading of the lumbar spine (Hosea et al., 1989; Hosea & Boland, 1989; Cholewicki et al., 1991; Gatt et al., 1997).

Regardless of the sport in question, as Bono states, the low back is an important but under-recognized source of great dynamic power during a golf or baseball swing, a gymnast’s landing, a power lifter’s heavy squat, or a boxer’s knockout punch. In static mode, it functions to help maintain an infielder’s stand, a cyclist’s tuck, or a ballerina’s arabesque (Bono, 2006). These same sources of power and static control are likely to fail with fatigue, excess force and repetitive micro-trauma and result in low back injury. There are a few examples where a specific action or activity has been implicated in back injuries such as the fast bowling action in cricket, hyper-extension in gymnastics, prolonged flexion in skiing and cycling and repetitive lumbar flexion and loading in weight lifting pursuits. Despite this, there is a lack of literature investigating risk factors for the development of low back pain in athletic populations. Laboratory based studies exist demonstrating the high mechanical forces directed at the lumbar spine during a golfer’s swing (Hosea et al., 1989), the rowing action (Hosea & Boland, 1989), American football blocking (Gatt et al., 1997) and weight lifting (Cholewicki et al., 1991). Low back pain is also likely be related to the type, intensity, duration and/or amount of athletic activity performed. In endurance based sports with low back demands a dose response relationship appears to exist with low back pain (Bahr et al., 2004). Causes of low back injury have also received much discussion in the large body of literature documenting changes in lumbar-pelvic muscle activation and recruitment due to low back pain, producing altered neuromuscular control strategies (Hungerford et al. 2003). This will be discussed later in the topic.

What is less clear in athletic populations is the role that psychosocial factors have in both the development of low back injuries and also in the transition from acute to chronic pain. Multiple systematic reviews of the general population have shown that psychological factors have an important role in the transition from acute to chronic pain (Manek & MacGregor, 2005). In a recent systematic review of the literature, depression, psychological distress, passive coping strategies and fear-avoidance beliefs were sometimes found to be independently linked with poor outcome, whereas most social and socio-occupational factors were not (Ramond et al., 2011).

How this literature relates to athletic populations is unclear. Psychosocial factors may be more important for the professional and semi-professional athlete who has financial, contractual and performance concerns. These athletes generate a meaningful income and employment from their sporting endeavours. It has been suggested that a well motivated athlete may under-report pain in order to improve performance, their chances of team selection and for a positive mind frame (Lundin et al., 2001). Alternatively, pain may be over-reported as it may be provoked easily by intense training and competition requirements and hinder athletic performance (Lundin et al., 2001). The athlete may therefore place a greater impact on pain than may be appreciated. This situation is potentially more of a concern as exaggeration of self-reported low back pain and disability may be a predictor for low back pain chronicity (Gatchel et al., 1995). However, previous research on amateur athletes has found psychosocial issues such as level of satisfaction with coaches or team-mates not to be related to the development of low back pain (Greene et al., 2001). Despite this, it has been shown that low back pain in former elite athletes is predicted by psychosocial issues such as life dissatisfaction, neuroticism, hostility, extroversion and poor sleep quality (Videman et al., 1995). Future research is required to more broadly investigate psychosocial factors in athletes and their impact and relevance, if any, to the development of low back injuries and chronic pain during play and after a career has ended.

Risk factors for low back pain in adolescent sporting populations

As opposed to the adult population, literature investigating risk factors for the development of low back pain in adolescent populations is not as conclusive in it its findings. A recent systematic review of the literature included five studies (Hill & Keating, 2010). The included studies varied considerably in the methods used to gather data, definitions of low back pain, and recall periods for an episode of low back pain. Inconsistency in definitions of low back pain, pre-defined recall periods, and methods used to collect and analyse data limit conclusions that can be drawn about factors that identify children at risk of developing low back pain. As no risk factor has been validated in independent investigation, the authors concluded that there is no certainty that any factor places children at risk of developing low back pain (Hill & Keating, 2010).

Looking at studies investigating risk factors for low back pain in adolescent sporting populations, a large cross sectional survey has found that adolescents are at a greater risk of low back pain if they have low isometric muscle endurance in the back extensors, with no associations found for aerobic fitness, functional strength, flexibility, or physical activity level after adjustment for muscle endurance (Bo Anderson et al., 2006). It may be that the junior sporting population is initially protected from low back pain due to their increased physical fitness, but this could be lost following excessive spinal loading (Kujala et al., 1996) and high training duration (Kujala et al., 1992) that many become exposed to. This is more likely to be the case with the advanced professionalism and training commitments junior athletes face when they reach the transition to increased sporting specialization in elite junior and adult professional sporting competitions. This would be particularly the case if the athlete is allowed to progress with poor techniques that would predispose injury. Junior athletes at the elite level of competition also face pressure to play and train with low back pain (and other injuries) given non-participation or obvious injury history can affect future selection to professional adult level competition. This again makes management difficult.

Another potential reason for an increased incidence of low back pain in elite level adolescent athletes includes the likely increased prevalence of weight lifting training into the typical training programs of most athletes. The effects of the mechanical loading that weight lifting may have on the developing spine, particularly when poor lifting techniques and sub-optimal training programs focusing on body building exercises rather than more functional exercises, combined with the effects of increased loading and training volume has been discussed by other authors (Wotjys et al., 2000).

Consequences of low back injury

The development of low back injury when occurring in athletes has several potential consequences. This includes the development of future, recurrent and repeated episodes of low back pain and injury which may be related to the neuro-physiological changes to lumbar-pelvic stability that is known to occur secondary to low back pain, issues associated with current and future playing performance, potential associations with the occurrence of other injuries and pain and disability to the player in the post career stage.

Recurrent pain and neuro-physiological changes of back pain

Without a doubt the biggest risk factor for future occurrences of low back pain in athletes are a previous or a current history of low back pain (Greene et al., 2001; O’Kane et al., 2003). It may be reasonable to conjecture that regardless of the aetiology of the initial low back pain, that once an athlete has experienced significant low back injury, that they remain susceptible to future pain and aggravation or exacerbation of pain. This fits with the natural history of low back pain in the non-athletic population (Hestbaek et al., 2006).

Low back pain is known to result in clinical instability of the lumbar-pelvic spine (Kaigle et al., 1995). Panjabi states that clinical instability occurs when segmental control around the physiological neutral zone cannot be accomplished (Panjabi 1992a). It results in a loss of the normal pattern of spinal motion as the neural control system alters the timing of muscular contraction patterns and reflex responses (Panjabi, 1992b; O’Sullivan et al. 1997a). With this loss of segmental stability, there is evidence to support the concept of increased compensatory substitution of the global system (Edgerton et al. 1996; O’Sullivan et al., 1997b), including earlier activation of various muscles involved with lumbar-pelvic motor control (Hungerford et al., 2003).

The lumbar-pelvic spine is preferably supported by an intricate arrangement of deep local muscles, including the multifidus and transversus abdominus, which provide a stabilising base on which the global muscles can act. The local muscles support the individual spinal segments during continuous full-body movements and allow the powerful activation of more global muscles acting across larger joints without spinal injury occurring (Wilke et al., 1995). Coordination of local muscle contraction to provide ongoing spinal stability and prevent injury is a complicated neurological process. Proprioceptive sensory feedback is necessary to permit the correct series, quantity and timing of muscular contraction (O’Sullivan et al., 1997a, Panjabi, 2003), a property lost with lumbar-pelvic pain and dysfunction (O’Sullivan et al., 1997b).

Several authors have suggested that of the local lumbar-pelvic stabilisation muscles, the multifidus and transversus abdominus are key stabilisers (Wilke et al., 1995, Hodges & Richardson, 1996). The multifidus muscles are the deepest of the posterior stabilising muscles having predominantly vertebrae-vertebrae attachments, attaching to the zygapophyseal joint capsules and being segmentally innervated (Macintosh et al., 1986). They function to finely control lumbar vertebral movements about the neutral zone, with their anatomical arrangement, joint attachments and neurological innervation making them the principal muscle for this function (McGill, 1991; Wilke et al., 1995). The transversus abdominus is the deepest of the abdominal muscles. It has extensive attachments to the thoracolumbar fascia and with its advantageous line of attachment, is the most capable of all muscles in tensioning the thoracolumbar fascia, thereby having a major effect on lumbar-pelvic stability by restricting vertebral displacement (Hodges & Richardson, 1996) and controlling rotational and lateral stability of the spine via the thoracolumbar fascia (Cresswell, 1993). In normal participants both the multifidus and transversus abdominus have a large cross sectional area of type one, or slow twitch muscle fibres, which allows them to provide a tonic contraction to assist with their responsibility of providing constant lumbar-pelvic stability (Jorgensen et al., 1993). Activity of the multifidus and transversus abdominus should occur in advance of the muscles required to provide body movement and action in a feed forward mechanism (Hodges & Richardson, 1996). This occurs regardless of the direction of reactive forces (Hodges & Richardson, 1996).

In those with low back pain, significant changes to the multifidus and transversus abdominus have been recognised to occur which changes lumbar-pelvic stabilisation strategies (Biedermann et al., 1991; Hides et al., 1996; Hodges & Richardson, 1998; Hodges et al., 2003). This, in addition to the compensatory action of the global system, may produce altered muscle response patterns required for lumbar-pelvic stabilisation during sudden trunk loading in athletes following their clinical recovery from low back pain (Cholewicki et al., 2002). After the first episode of low back pain, selective atrophy of the multifidus can occur rapidly within days of pain occurrence, which can be as high as 31% in 24 hours (Hides et al., 1996), a temporal pattern suggestive of a neurogenic mechanism. This atrophy may not be restored following pain remission, which has been linked to a high rate of recurrent low back pain (Hides et al., 1996). In biomechanical research models, loss of even one segment of multifidus muscular control has been shown to significantly reduce the overall stability of the spine, particularly in controlling buckling when load on the spine is increased (Crisco & Panjabi, 1991). Multifidus also shows less endurance and greater fatigability after pain syndromes (Biedermann et al., 1991). This loss in endurance has enabled significant identification of athletes with existing low back pain (Roy et al., 1990). Changes to the internal structure of the type one fibres of the multifidus including a decrease in fibres can also occur following the onset of low back pain (Ford et al., 1983). This may result in reduction of neuromuscular control in fatigue situations and subsequent lumbar-pelvic clinical instability, as the multifidus cannot hold the contraction or the repetitive nature of contractions for the required time frame.

Low back pain is known to increase the threshold of transversus abdominus activation and cause a loss of its tonic activity so that it becomes phasic (Hodges et al., 2003). This suggests that the background stabilisation property provided by transversus abdominus is lost. In participants with a chronic history of low back pain, whilst in remission of pain, a delay in the activity of transversus abdominus has been found, regardless of the direction of imposed force (Hodges & Richardson, 1998). Importantly, this demonstrates that even with the absence of pain, there are alterations to the coordinated firing pattern, which predisposes injury. A lack of feed forward activation will have joints unprepared to take load at the point of loading so there is a higher risk of injury. Importantly this can occur in the absence of pain and may be related to performance deficit in the athlete. Other research has shown that imbalanced patterns of erector spinae activity and reduced trunk extension strength which results from low back pain remains present if low back pain does not resolve (Renkawitz et al., 2006).

Although likely to be multi-factorial, one explanation for recurrent low back pain in athletes could be that athletes who demonstrate neuromuscular control alterations to sudden trunk loading have an increased risk of sustaining a low back injury (Cholewicki et al., 2005). Previously it has been shown that athletes with a recent acute low back injury exhibit altered neuromuscular control strategies for sudden trunk loading (Cholewicki et al., 2002). These findings are relevant to the unexpected and expected contact nature of sports such as the various body contact football codes and related other sports but also for the agility, change of direction and sudden stop-start nature of many running based ball sports.

Lumbar muscle activity during gait functions to control trunk movements (Carlson et al., 1988). In a non-athletic population, low back pain has been shown to produce poorly coordinated activity of the lumbar muscles during gait (Lamonth et al., 2005). This situation occurring in athletes in running based sports may lead to forces being directed at unprotected spinal structures producing subsequent mechanical stress and injury. Greater and more frequent mechanical spinal loading could contribute to both injury and delayed healing response. Similar to the non-athletic population, a situation may exist where low back pain fluctuates over time with recurrences or exacerbations and temporary remissions (Hestbaek et al., 2003; van Tulder et al., 2002). In support of this mechanism for repetitive and recurrent injury, Green et al. documented that athletes with a history of low back injury with current low back pain have a six times greater risk for future injury (Greene et al., 2001). For athletes with a previous history of low back injury who are now asymptomatic, approximately a three times greater risk of injury exists (Greene et al., 2001; Cholewicki et al., 2005).

Next post:

Previous post: