2022 — Lumbar Bone Stress Injuries and Risk Factors in Adolescent Fast Bowlers

Research theme

How often do teenage fast bowlers actually get lumbar bone stress injuries, and what marks out the ones who will? Previous injury statistics came from bowlers who reported pain — so silent, asymptomatic injuries were invisible. This study MRI-screened every bowler at baseline and again a year or two later, whether they had symptoms or not.

Method: 40 asymptomatic male fast bowlers aged 14–17, recruited from professional academies and strong school/club programmes. Baseline pre-season lumbar spine (L3–L5) MRI (3.0T, three sequences) plus DXA, then annual DXA and an exit MRI after one or two years — 22 bowlers completed follow-up (mean 1.31 ± 0.05 and 2.26 ± 0.03 years after baseline). Scans read by a musculoskeletal radiologist experienced in cricket LBSI. Skeletal age assessed from a DXA hand scan (Tanner-Whitehouse 3). Bowling workload self-recorded via online questionnaire (balls per day). A physiotherapy musculoskeletal flexibility screen performed annually on both legs. Injured vs uninjured compared by t-test (Mann-Whitney where non-parametric) with Hedges’ g effect sizes.

Note: this is NOT a biomechanics study. There is no motion capture and no technique measurement at all. It is epidemiology plus off-field screening.

What they measured

• Whether the bowler had a lumbar bone stress injury (MRI, asymptomatic screening — stress reaction = bone marrow oedema without fracture line; lumbar stress fracture = incomplete or complete fracture line).
• How old they are, and how old their skeleton is (chronological age; skeletal age from hand DXA; maturity rating — delayed / average / advanced / complete).
• How dense and how big the low back vertebrae are (contralateral-side BMD at L3 and L4; L3 and L4 vertebral area; total-body fat-free mass).
• How much they bowled (total balls in the season; bowling days per week; peak 7-day “acute” workload; peak 90-day “medium-term” workload).
• How flexible they are, off the field, on both legs (passive hip internal and external rotation; bent knee fallout; passive straight leg raise; sit and reach; weight-bearing ankle dorsiflexion “knee to wall”). Screening protocol reproducibility ICC ≥ 0.946.

Findings

1. One in five teenage fast bowlers already has a lumbar bone stress injury — with no symptoms. At baseline, 20.5% of the cohort (aged 14.2–17.3) had radiological evidence of acute or chronic LBSI. Half had chronic lesions, half active bone stress. Bowlers as young as 14 were affected.

2. Annual incidence is roughly ten times the senior professional figure.

• 27.3 ± 18.6 LBSI per 100 players per year (mean ± 95% CI).
• Incomplete lumbar stress fracture specifically: 22.7 ± 17.3 per 100 players per year.
• For comparison, symptomatic presentations in elite senior English fast bowlers: 2.5 per 100 bowlers per year (Alway et al., 2019a). The gap is largely because senior figures count only bowlers who report pain; this study screened everyone.

3. Injury pattern in teenagers mirrors adults, except it sits lower in the spine.

• 92.3% of unilateral injuries were contralateral to the bowling arm (adults: 93%).
• All 8 prospective injuries were at the pars interarticularis, all contralateral.
• L5 accounted for 52.6% of injuries — versus 32.0% in adults. The authors attribute this to the relatively delayed development of the iliolumbar ligament which stabilises L5, potentially permitting increased extension at the lumbopelvic joint — the joint the 2021 Alway paper implicated in adult LBSI.
• Prospective severity: 2 bone stress, 6 incomplete stress fracture.

4. Age was the only statistically significant risk factor — and every injury happened at 17 or 18.

• Injured bowlers were 16.8 (95% CI 16.2–17.5) years old at the start of the season preceding injury; uninjured 15.6 (15.1–16.0). Mean difference 1.3 years, P = 0.006, Hedges’ g = 1.396 (large).
• Prospective injury rate by age: 14 = 0, 15 = 0, 16 = 0, 17 = 25 per 100 bowlers/year, 18 = 80 per 100 bowlers/year.
• Yet skeletal age barely differed (15.9 vs 15.6 years, g = 0.274, P = 0.278) and maturity rating did not differ significantly (g = 0.611, P = 0.363). So it is chronological age, not biological maturity, that tracks the injuries — which points at what happens to a bowler at 17–18 (promotion to senior cricket, workload step-up), not at what their skeleton is doing.
• One maturity signal worth noting: 33% of the injured bowlers had delayed maturation vs only 13% of the uninjured.

5. Four further large effect sizes, none statistically significant (n = 6 injured vs 16 uninjured — this study is badly underpowered):

Key numbers a coach can use, with the caveat that none reached significance:

• Hip internal rotation on the front (contralateral) leg was 7.2° tighter in the bowlers who got injured — 32.3° vs 39.5°.
• Peak 7-day workload was 64 balls (39%) higher in the injured group — 229 vs 165 balls in a week.
• Injured bowlers had MORE bone, not less — contralateral BMD was non-significantly higher at both L3 and L4, with large effect sizes.

6. Baseline cohort context. Age 15.5 ± 1.1 years; height 1.79 ± 0.07 m; weight 68.3 ± 10.6 kg; L1–L4 BMD Z-score +0.77 ± 1.10. Compared to senior elite bowlers: shorter (1.79 vs 1.88 m), less fat-free mass (56.48 vs 74.72 kg), lower L1–L4 BMD (1.20 vs 1.56 g/cm²) and lower Z-score (0.77 vs 2.45).

7. The authors’ interpretation. Injury clusters at 17–18 not because of age itself but because that is when bowlers step up to senior or elite cricket — more workload, higher bowling intensity, more strength & conditioning, greater muscle mass — “while their lumbar spine is immature, less robust, and not yet adapted to the demands imposed upon it.”

All of this is risk-factor identification: correlational, group comparison. No causal claim is made or supportable. With six injured bowlers, this study identifies signals worth chasing, not established causes.

What a coach should look for on video

This paper supports no video cue at all. There is no motion capture in it and no technique variable was measured.

That is worth saying explicitly, because the temptation is to read a “risk factor” paper as a technique paper. This one is about when injuries happen, how many there are, and what off-field measures differ. What it gives a coach is a screening and workload agenda, not a video one.

What it gives instead — four things a coach of teenagers should act on

1. Treat the step-up to senior cricket as the danger window, not a milestone. Every prospective injury in this study occurred at 17 or 18 years old — 25 per 100 bowlers/year at 17, 80 per 100 bowlers/year at 18, and zero at 14, 15 and 16. The authors’ recommendation is direct: “coaches and medical practitioners of adolescent fast bowlers who have made the step-up from junior to adult elite cricket need to manage their bowlers carefully and consider the use of rest weeks within their schedule to permit repair of bone microdamage.”

2. Watch the 7-day ball count, not the season total. The injured group’s peak acute (7-day) workload was 229 balls vs 165 — 39% higher, large effect size (g = 0.942), though not significant. Season totals (1608 vs 1237, g = 0.526) and bowling days per week (2 vs 2, g = 0.092) discriminated much less. Spikes, not volume, are the signal. The authors note an extra 64 balls in a week is roughly “an extra game a week or step-up in workload at a more senior level.”

3. Measure hip internal rotation on the front leg — this is the one off-field screen with a number attached.

• The measure: Passive hip internal rotation, contralateral leg (the front leg — opposite the bowling arm). Bowler lies prone, knees together and flexed to 90°, feet fall to the side, angle read from the medial tibia. ICC 0.94.
• What “good” looks like: Around 39.5° (uninjured group mean; 95% CI 36.3–42.7).
• What the concern looks like: Around 32.3° or less (injured group mean; 95% CI 25.7–39.0) — 7.2° tighter, Hedges’ g = 0.987 (large), though P = 0.115, not significant.
• Why it matters: The authors link reduced hip internal rotation to poor lumbo-pelvi-femoral control, which the 2021 Alway paper implicated in adult LBSI. The 2023 Felton ROM paper in this cluster then shows that reduced front-hip internal rotation correlates with exactly the technique faults that predict LBSI (see below). This is the closest thing in the cluster to a non-video intervention.
• Contradicting evidence exists: Dennis et al. (2008) found reduced ipsilateral hip internal rotation reduced musculoskeletal injury risk. The authors caution that Dennis’s study covered a wide age range and any back/trunk/lower-limb injury, most of which were not LBSI.

4. Do not screen for low bone density as your injury marker. The bowlers who got injured had more contralateral bone at L3 (1.625 vs 1.419 g/cm²) and L4 (1.667 vs 1.432), both with large effect sizes. The authors’ reading: even conditioned bone may be insufficient if workload rises faster than it can adapt — “bowling workload may be dependent on lumbar BMD to prevent LBSI,” i.e. the two must be matched, not one maximised.

One flexibility measure that did nothing

Sit and reach and straight leg raise were flat. Sit and reach: 19.0 vs 17.5 cm (g = 0.238). Straight leg raise contralateral: 68.0 vs 67.9° (g = 0.019). General hamstring/lower-back flexibility screening did not separate the groups. If you screen, screen hip rotation.

Caveats and limits

• Tiny injured group: n = 6. Everything except age is non-significant, and with six cases the study cannot detect anything but very large effects. The authors say so.
• Heavy attrition: 40 recruited, only 22 followed up. 16 did not return, mostly due to Covid-19 apprehension or other commitments; 3 changed position or stopped high-level cricket; 1 had an unrelated operation. Whether the 18 lost differed systematically is unknown.
• Covid-19 disrupted the study. MRI follow-up was postponed four months, and bowling workload would have been reduced for around 10 weeks before follow-up. Non-cricket physical activity was not monitored during that period. LBSI incidence “may have been slightly affected.”
• Workload was self-reported, and only 11 of 22 bowlers reported it at all (5 of the 6 injured). Self-reporting in elite players has been validated (Warren et al. 2018) but 11 datasets is very thin for the workload conclusions.
• No Bonferroni correction, deliberately, to avoid Type 2 errors. The authors: “results should be considered with caution as significant results could be an artefact of multiple testing.” The one significant result — age — was tested alongside ~25 others.
• Sample: adolescent male bowlers only, aged 14–17, from English academies and strong club/school programmes.
• No technique data whatsoever. The authors explicitly name this gap in their own future-work section: “as well as the role bowling technique plays in LBSI development.”
• Baseline MRI covered L3–L5 only, so injuries above L3 at baseline would be missed (though the baseline table does record an L2 injury, presumably from a fuller sequence).
• “Injured” includes injuries found only on exit MRI with no symptomatic presentation — appropriate for the study’s purpose but not the same population as clinically-presenting injury.

Relationship to other Felton work

• Companion to the other 2022 Keylock paper (2022 Keylock — Lumbar Bone Mineral Adaptation in Adolescent Cricketers) — same research programme, overlapping adolescent cohort (39 vs 40 bowlers, near-identical baseline characteristics). That one measures technique against bone density cross-sectionally; this one tracks injury prospectively with no technique measurement.
• Cites the 2021 Alway MSSE paper (2021 Alway — Cricket Fast Bowling Technique and Lumbar Bone Stress Injury) as the adult technique model, and uses its lumbopelvic-extension finding to explain why L5 injuries dominate in teenagers (delayed iliolumbar ligament development permitting more lumbopelvic extension).
• Feeds directly into the 2023 Felton ROM paper (2023 Felton — Range of Motion and Key Performance and Injury Technique Characteristics), which uses this study’s musculoskeletal screening protocol verbatim and is co-authored by McCaig from this paper. That paper closes the loop: hip internal rotation restriction here → technique faults there → LBSI in the 2021 paper.
• Builds on Alway et al. 2019a (BMJ Open SEM) for adult LBSI epidemiology and Alway et al. 2019b (Bone) for lumbar bone asymmetry.

CONTRADICTION: Low bone density is not the risk factor it is assumed to be — the injured bowlers had MORE bone. Site-specific low BMD has been proposed as an LBSI risk factor (Alway et al., 2019b). Here, bowlers who subsequently sustained LBSI had non-significantly greater contralateral BMD at both L3 (1.625 vs 1.419 g/cm²) and L4 (1.667 vs 1.432), both with large effect sizes (g ≥ 0.812), plus greater vertebral area. The authors note this is “logical” to expect the opposite and concede it may reflect the injured group’s greater age. Either way, screening teenage bowlers for low lumbar BMD is not supported by this data.

CONTRADICTION: Skeletal maturity does not explain the age effect. The obvious hypothesis for “older bowlers get injured” is that something about maturation is at play. But chronological age differed hugely (16.8 vs 15.6, P = 0.006, g = 1.396) while skeletal age barely differed at all (15.9 vs 15.6, P = 0.278, g = 0.274) and maturity rating was non-significant. The injury clustering at 17–18 therefore looks like an environmental effect — the step-up in workload and intensity that comes with senior cricket — rather than a biological one.

CONTRADICTION (with Dennis et al., 2008): This study found reduced contralateral (front leg) hip internal rotation in the injured group (32.3° vs 39.5°, g = 0.987). Dennis et al. found that reduced ipsilateral hip internal rotation reduced musculoskeletal injury risk. Different leg, opposite direction. The authors flag the conflict and note Dennis covered a broad age range and all back/trunk/lower-limb injuries, most of which were not LBSI: “it is clear that further investigation is required.”

TENSION: Adolescent LBSI incidence (27.3 per 100 players/year) is roughly ten times the senior elite figure (2.5 per 100/year). Most of this gap is methodological — this study MRI-screened asymptomatic bowlers, the senior figure counts symptomatic presentations — but not all of it. Comparable asymptomatic-screening studies in adolescents found 22.0% (Engstrom & Walker, 2007) and 23.0% (Kountouris et al., 2018). The plain reading for a coach is that a large fraction of teenage fast bowlers are carrying bone stress injuries no one knows about.