Key quality assessment findings and methodological considerations

Six high-quality studies evaluating factors associated with LBP were identified, with four of these possessing elements of a prospective design.12 ,25–27 Therefore, owing to the paucity of high-quality prospective findings at present, there is limited information about risk factors for LBP in cricketers. All five intervention studies were low quality, with only one being a randomised control trial,34 and the remaining studies possessing inadequate control groups.35–38 Therefore, conclusions that could be drawn from currently available research on interventions are somewhat limited.

Sample sizes in all the studies were generally small as might be expected given the difficulty in accessing large cohorts, with most studies containing sample sizes of less than 30—often from only one squad or team—and with no power calculation reported.11 ,13 ,25 ,27–31 35–38 Confounding variables were neither fully described for any studies, nor were they adjusted for (appendix table 2). Only one study considered that the cricketers included played other competitive sports, which is important as other sports are known to be strongly associated with trunk injuries.12 ,39 Little information was provided on LBP history and other injuries. Additionally no intervention studies evaluated potential adverse effects caused by the intervention (eg, other injuries).34–38 This is a vital consideration for coaches and medical staff before choosing to implement any new intervention programme and must be addressed in future research. Control groups were either absent or insufficient for the intervention being investigated. Outcome measures were often described but with no indication of their reliability, somewhat reducing the confidence in conclusions drawn from the data.13 ,25 ,28–33 Nevertheless, significant findings were observed within the studies.

Risk factors for LBP in cricketers

One risk factor identified from prospective data was the presence of acute bone stress on MRI, indicating the potential of MRI as a screening tool. Specifically, 11 of 15 players demonstrating signs of bone stress, classified using the Hollenberg et al40 scale, developed a partial or complete spinal stress fracture within an average of 10 weeks of MRI, and four asymptomatic adolescent fast bowlers with radiological evidence of bone stress at baseline in Kountouris et al's26 recent study all went on to develop a symptomatic bone stress injury during the cricket season. Additionally, conference proceedings published in 2008 by Ranson et al41 showed that 70% of the asymptomatic bowlers who had acute stress changes on MRI went on to suffer an acute lumbar stress injury within one season. These findings should be considered when screening or assessing the meaning of MRI scans in young cricketers and particular attention should be paid to early bone stress signs by responsible clinicians. Importantly, the four players who did not develop a stress fracture in Hollenberg et al's40 study only bowled two to four more weeks and then had a 6–12 weeks rest period, suggesting time off may be an effective preventive strategy.

There is conflicting evidence shown in figure 4.4 on the effect increased QL asymmetry has on the development of lumbar bone stress injuries. Engstrom et al12 showed that QL asymmetry was associated with an L4 lesion whereas Kountouris et al26 did not. It may be that the different criteria resulted in the differences noted, as Engstrom included results over four seasons compared to Kountouris including results after only one season.12 ,26 However, conference proceedings by Ranson et al41 also showed no link between QL asymmetry and lumbar spine injury. Interestingly, a recent observational study by Crewe et al examining both biomechanics and QL asymmsetry suggests that those bowlers who experience large lumbopelvic lateral flexion loads during bowling may develop greater QL asymmetry. This position is also associated with an increased risk of lumbar spondylolysis and therefore identifying asymmetry on MRI may be a warning of an increased risk of injury rather than a risk factor itself.42 Further research is needed in this area.

Increased shoulder counter rotation appears to be associated with both disc degeneration and stress fracture development, known to be associated with a mixed bowling action.8 In addition, Burnett et al's25 study indicated an OR of 16 for greater disc degeneration prevalence when a mixed bowling action continued over a period of 3 years. Theoretically, large shoulder counter-rotation, along with increased range of lateral flexion of the thorax in relation to the pelvis during the delivery stride is likely to increase spinal stress,43 leading to disc herniation and/or pars interarticularis failure.8 Consideration of shoulder counter rotation as a covariate in prospective analyses of risk factors for LBP would be useful.

Increased stride length to height ratio, and relative knee extension at ball release were found to be present in cricketers with trunk injuries. It is suggested that both factors may impair the dissipation of impact forces.33 Specifically, if the knee is more flexed there will also be a decreased release height which is seen in non-injured bowlers; it may well be that by bending the knee more at ball release, the ground reaction forces are dissipated better through the body resulting in less impact through the spine.33 Considering this, coaching bowlers to reduce stride length during their run up and increasing knee flexion at ball release may provide potential treatment and prevention strategies for LBP in cricketers. Further research to evaluate this possibility is needed. Posture also requires further study, given the strong association seen between increased head displacement from vertical and the decreased prevalence of spondylolysis. These factors could be studied further using simple video analysis in coaching and or sports medicine consultations.

Limited evidence suggests a strong association between reduced lateral slide of the anterior abdominal fascia and LBP.11 Anterior abdominal slide occurs during concentric contraction of the transversus abdominis muscle bilaterally in a ‘drawing-in’ action of the abdominal wall in normal pain-free elite cricketers.44 Therefore, reduced lateral anterior abdominal slide seen in cricketers with LBP may reflect an inability to draw in the transversus abdominis muscle appropriately, which is known to be related to lumbopelvic pain.44 Importantly, improved ability to ‘draw-in’ the transversus abdominis muscle and increase anterior abdominal slide has been reported to reduce and maintain reduction of LBP in the general population.45

Consistent with studies on the general adolescent population,46 findings from Elliot et al13 suggest that as age increases the prevalence of spondylolysis and disc degeneration also increases in adolescent cricketers. However, it seems that cricketers are starting at a higher prevalence level than other sportsmen at comparable performance levels. For example, when compared to adolescent swimmers, young fast bowlers show an increased prevalence, indicating skills required in the game (eg, bowling) may accelerate the normal aging process of disc degeneration.4–6 Future research could therefore address whether this process is accelerated and whether the increased prevalence seen in adolescence continues for an adult cricketing population.

Interventions for LBP in cricketers

As noted above, reduced anterior abdominal fascia lateral slide is associated with LBP.11 ,12 Two studies investigated a 13-week abdominal stabilisation training programme to improve anterior abdominal fascia slide and decrease asymmetry of the multifidus muscles.35 ,36 Unfortunately, it is difficult to draw conclusions from these studies as they included both very low participant numbers (6–7) and no control groups. However, graphically there is some indication from effect size calculations that LBP may be reduced as a result of the programme (appendix figure 6.1).35 Additionally, the stabilisation programme was also found to increase in anterior abdominal fascia slide, a factor found to be reduced in cricketers with LBP.11 ,35 ,36 Importantly, similar programmes in high-risk sporting populations, such as golf and gymnastics, have indicated improvements in LBP.39 ,47 ,48 For example, a study in 51 top level young gymnasts (age 11–16) reported a 12-week training programme based on specific segmental muscles of the lumbar spine reduced the number of days on which LBP was reported.48 These findings encourage larger randomised controlled trials following CONSORT guidelines to evaluate the effectiveness of stabilisation training in cricketers with LBP to enable clear clinical recommendations to be made.49 It must also be considered that results from these stabilisation studies may be confounded by cointervention.11 ,12 Specifically, the stabilisation training programme involved the removal of weights training for 6 weeks and then gradual reintroduction for 7 weeks. It may be that a lack of weights training decreased LBP rather than the stabilisation programme, a factor that should be considered in the design of any follow-up study.36

Three intervention studies evaluated forms of coaching to encourage bowlers not to use the mixed bowling action and move towards a safer bowling action, such as a more side-on technique, to prevent LBP developing.34 ,37 ,38 Findings indicate limited evidence that shoulder counter rotation can be decreased by coaching, and that a ‘safe’ action results in reduced lumbar disc degeneration.38 Considering the link between increased shoulder counter rotation and LBP in cricketers, these findings indicate that retraining programmes may be effective in the treatment or prevention of LBP. Further research is needed to establish if such changes can prevent or effectively treat LBP. Importantly, studies involving coaching over a 2-year to 3-year period showed a reduction in the use of a mixed bowling action;37 ,38 however, the study that provided 8 weeks of coaching did not.34 This highlights that effective retraining may take a long period of time, although the optimal time period still needs to be established. Additionally, moderate evidence also indicates that the use of a bowling harness may not assist bowling action changes.34

Clinical implications and key areas for future research

Current interventions evaluated, including core strengthening and bowling retraining, appear promising and should be considered in clinical practice as a means to both prevent and treat LBP. However, further evaluation is needed before their importance in the development of injury prevention and treatment programmes for cricketers with LBP can be established. Additionally, the review suggests that relative knee extension at FFC during bowling is associated with an increased prevalence of trunk injuries, suggesting that increasing knee flexion during the bowling action could prevent trunk injuries. Interestingly, however, in Ranson et al's37 study, players were coached towards less back and front foot knee flexion, possibly because of the suggestion that a straight front leg will increase ball speed owing to more efficient transfer of kinetic energy.32 ,50 Therefore, in this case, injury risk may be over-ruled by performance. Further research to identify if relative knee extension is a true risk factor for LBP development is needed to improve coaching guidelines.

The potential for MRI as a screening tool to prevent the occurrence, or worsening, of LBP, and specifically highly debilitating stress fractures is highlighted.5 Importantly, a scan in the middle of season and appropriate response (eg, rest) may prevent months of lost playing time. This may be especially important in international cricketers as the ‘off-season’ grows ever shorter with autumn, winter and spring tours. However, the expensive nature of completing MRI scans must be considered, particularly for amateur cricketers. In fact, the high cost of completing an MRI scan highlights the need to identify more clinically applicable risk factor screening tests in future research.

Another area requiring strong consideration in future research is the age which cricketers should begin to receive intervention for treatment or prevention of LBP, especially considering the high prevalence of lumbar spine injuries in adolescence.4 ,34–38 Additionally, directives and guidelines currently in place, such as “Bowling Prehab”, ECB coaches’ safety pack and ECB under 19 guidelines, require scientific validation, especially, as they appear to be often ignored.15–18