Lower back injury risk in the fast bowling population

Studies invesitgating spinal pathologies have focussed primarily on the incidence of spondylolysis and disc degeneration; usually located at the L4/5 vertebra (Ranson et al. 2005; Ranson et al. 2010). Prevalence of bony abnormalities has been placed at between 24-55%; 74% of these abnormalities are accounted for by spondylolysis and 24% by

spondylolisthesis (calculated using weighted averages) (Elliott et al. 1992; Hardcastle et al. 1992; Stretch 1992; Engstrom and Walker, 2007). Hardcastle et al. (1992) placed disc degeneration prevalence of a sample of junior bowlers (16-18yrs) at 64%, with 36% displaying grade one degeneration; 21% grade two and 43% displaying grade three disc degeneration.

2.2.4.1 Spondylolysis prevalence

Spondylolysis has been defined as stress fractures located at the pars interarticularis, typically found at the lumbar vertebrae at L4 and L5 (Crewe et al. 2012). Fractures on the non-dominant side (non-bowling arm side) having a much higher prevalence than dominant side or bilateral fractures (Ranson et al. 2005; Morton et al. 2013). An example of spondylolysis can be seen in figure 2.2.2 (Hardcastle et al. 1992).

Figure 2.2.2. Reverse gantry CT scan showing spondylolysis (Hardcastle et al. 1992). Spondylolysis has been reported as having high prevalence among fast bowlers (Hardcastle, 1993). Prevalence of around 22% in the fast bowling population has been observed; significantly higher than the 6-7% prevalence reported in the general male population (Engstrom and Walker, 2007). However, prevalence as high as 67% has been reported in some studies using x-rays (Hardcastle et al., 1992). Research has highlighted that pain may not always be a symptom of spondylolysis, consequently,

some disparity in results may exist due to cases not being identified or differences in methods of reporting injury (as some studies use self-reporting injury criteria) (Millson et al. 2004). This may also highlight the issue of players not reporting pain as a result of selection pressures (Crewe et al. 2012). Whilst, pain in certain cases may not occur, spondylolysis remains a significant issue in regards to time loss from the game (Orchard et al. 2002). MRI scans have enabled more recent studies to be able to more effectively identify players that have developed this pathology and in earlier stages, thus decreasing time loss as a result of this injury (Crewe et al. 2012; Kountouris et al. 2012). Spondylolysis has been widley reported in the literature and as such, professional coaches and players are becoming more aware of the risk it poses to the fast bowling population, resulting in more tailored training sessions and match strategies to reduce this risk. This is evident in junior bowling restrictions discussed later (ECB, 2016b). 2.2.4.2 Spondylolisthesis prevalence

Spondylolisthesis is typically developed from spondylolysis and can be defined as the anterior translation of one vertebrae relative to another (Jacobsen et al. 2007). In the fast bowling population, prevelence has been placed at between 2-25% compared with a 3% prevalence in the general male population (Annear et al. 1992; Elliott et al. 1992; Hardcastle et al. 1992; Engstrom and Walker, 2007; Jacobsen et al. 2007). Spondylolithesis is usually also observed at the L4/5 vertebra. A radiograph of spondylolisthesis can be seen in figure 2.2.3 (Kornblum et al. 2004).

Research has highlighted the importance of effective screening methods for fast bowlers ‘playing through pain’ in order to reduce the prevalence of spondylolisthesis, as recovery time from this condition is much longer than spondylolysis (Crewe et al. 2012). However, this recommendation may be problematic, due to the dissociation between spondylolysis and pain (Millson et al. 2004). As a result, in many cases the only method of tracking injury status is regular scans, which may become costly as MRI scans are likely to be the only viable option for this volume of repeated screening (Patel, 2004). This emphasises the need for further guidelines to highlight ‘at risk’ groups within the fast bowling population, so more accurate and costly injury surveillence methods can focus on these groups to prevent the development of more serious pathologies such as spondylolisthesis.

2.2.4.3 Intervertebral disc degeneration

Research has analysed intervertebral disc degeneration, which although naturally occuring, it is more pronounced in fast bowlers (Elliott and Khangure, 2002). Intervertebral disc degeneration can be described as the progressive dehydration of a disc located between two vertebra (seen in figure 2.2.4) (Hadjipavlou et al. 2008). Imaging studies have placed prevalence of lumbar disc degeneration at between 14-65% in the fast bowling population (Elliott et al. 1992; Hardcastle et al. 1992; Elliot et al. 1993; Burnett et al. 1996; Ranson 2005; Crewe et al. 2012; Morton et al. 2013). In addition, Crewe and colleagues (2012) reported 75% of bolwers with intervertebral disc degeneration displayed a disc bulge and 17% of these participants also displayed an annular fissure (a breaking or separation of the outer layer of the intervertebral disc). Imaging studies have reported the most common sites of intervertebral disc abnormalities are at the L4-5 and L5-S1 discs, with 38% of individuals displaying disc degeneration at more than one site (Crewe et al. 2012).

Figure 2.2.3 Radiograph showing spondylolisthesis at the L4 vertebrae (Kornblum et al. 2004).

Figure 2.2.4. Intervertebral disc degeneration located at the L4-5 and L5-S1 discs (Hadjipavlou et al. 2008).

Table 2.2.1. An overview of study results and methodology investigating incidence and prevalence of common fast bowling pathologies and lower back pain. Author Participants (n) Method of

Diagnosis LBP Spondylolysis Spondylolisthesis

Disc Degeneration Comments Kountouris et al. 2012 38 (mean age 15.5yrs) MRI 45% 21% Crewe et al. 2012 46 (13-18yrs) MRI 33% 4% 35% Engstrom &

Walker 2007 51 (aged 13-17yrs) MRI 24%

Dennis et al. 2005 44 (mean age 14.7yrs) Self/physiotherapist reported 52% 11% Ranson et al.

2005 36 (mean age 26yrs) MRI 0% 81% 61%

Free of LBP inclusion criteria Portus et al. 2004 30 (mean age 22.4yrs) Mixed (injury history reported) 30% Millson et al. 2004 10 (mean age 18.7yrs) CT Scan 90% 80%

Bowlers recruited with LBP

Gregory et al.

2004 39 (mean age 19.7) Self-reported 100% 67%

Bowlers recruited with LBP

Orchard et al.

2002 12 (No ages given) Mixed 33%

Burnett et al.

1996 19 (mean age 13.6) MRI 53% 58%

Elliott et al. 1993

24 (mean age

13.7yrs) MRI 21%

Annear et al.

1992 20 (mean age 48yrs)

X-ray, CT scan and

Hardcastle et al. 1992

22 (mean age

17.9yrs) CT scan and MRI 64% 36% 18% 14%

Foster et al. 1989

82 (mean age

16.8yrs) CT scan 11%

Mackay et al.

1988 72 (age 15-19yrs) X-ray 20%

Payne et al.

1987 12 X-ray 50%

2.2.4.4 Non-technique based risk factors of spondylolysis and spondylolithesis

Spondylolysis has been well reported in literature and consequently its risk is well know to researchers, players and coaches, however the factors that affect this risk are still poorly understood (Morton et al. 2013). Pathological studies have highlighted age as a significant risk factor, reporting adolescent fast bowlers at an increased risk of spondylolysis due to immature structures in the spine and typically, weaker stabilising muscles around the lower back (Crewe et al. 2013). Gray et al. (2000) examined the reported ages of fast bowlers with spondylolysis or spondylolithesis in previous research, stating that the mean age of these bowlers was under 18 years old in four out of five studies analysed (Payne et al. 1987; Mackay et al. 1988; Foster et al. 1989; Annear et al. 1992; Elliott et al. 1992; Hardcastle et al. 1992). Whilst these studies are dated, similar findings are reported in more recent studies; suggesting that whilst research may have increased the understanding of the problem to some degree, the underlying causes and how to reduce this risk remain unanswered (Johnson et al. 2012; Morton et al. 2013).

As well as age, workload has also been emphasised as having a strong correlation with increased risk of injury (Orchard et al. 2006). Fast bowling workload is generally determined from number of balls or overs bowled, or ‘days of bowling’. Research has suggested that bowling in excess of every 3.5 days significantly increases risk of injury (Dennis et al. 2005). Consequently, governing bodies have introduced restrictions on the number of overs adolescent fast bowlers can bowl and coach education at junior and senior level advises close monitoring of bowling workload in games and training in order to minimise risk. Table 2.2.2 shows recommendations set out by the England and Wales Cricket Board (ECB) for junior bowlers (ECB, 2016b). The ECB further recommends that no junior fast bowler should bowl more than 4 days in a week and no more than 2 consectutive days (ECB, 2016b).

Table 2.2.2. ECB fast bowling over limitations for junior fast bowlers Bowlers Age Max Overs Per Spell Max Overs Per Day

Under 13yrs 5 10

14-15yrs 6 12

16-17yrs 7 18

The relationship between risk of lumbar spine injury and quadratus lumborum (QL) asymmetry has also been explored, however research reports conflicting results between adult and junior fast bowlers (Engstrom and Walker 2007; Ranson et al. 2008; Kountouris et al. 2012). Larger dominant-side QL asymmetry was reported to increase risk of lumbar stress fractures in junior fast bowlers, however the same association between QL asymmetry and adult fast bowlers was not found (Engstrom and Walker 2007; Ranson et al. 2008). Consequently, it is still unclear as to whether QL symmetry is a significant risk factor, or if age and maturation have confounded reported results. Furthermore, it may be the case that QL asymmetry may be a result of injurous behaviours (such as spinal kinematics), but may not directly contribute to the mechanism of injury.

2.2.4.5 Non-technique based risk factors of disc degeneration

As with spondylolysis, young fast bowlers are placed at the highest risk of intervertebral disc abnormalities (Crewe et al. 2012). This may be due to increased elasticity in adolescent intervertebral discs, which do not resist shear forces (which have been reported to lead to increased disc degeneration) as effectively as matured, less elastic discs (Gray et al. 2000). Elliott and Khangure (2002) comment on an increase in prevelence of 44% (from 21%) between the ages of 13 to 18 years old. Due to it’s progressive nature, high levels of degeneration at a young age is likely to continue to affect fast bowlers later in their career and quality of life after retirement. Prevelences of 70% were observed in retired fast bowlers (Annear et al. 1992). Due to its progressive nature, high workload has been highlighted as one of the most significant risk factors to lumbar disc degeneration (Dennis et al. 2005). Findings show that repetitive impacts, causing microtraumas below the critical limit of the intervertebral discs, cause a degenerative effect over time (Hreljac, 2004). This effect is experienced in the fast bowling population due to very high workloads during the season, may result in a significantly faster degenerative effect, or a more severe injury response.