Lumbar MRI abnormalities and muscle morphology, trunk kinematics and lower back injury in professional fast bowlers in cricket
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Lower back injury remains the most important injury problem in professional cricket with lumbar stress fractures in fast bowlers accounting for the most lost playing time. Previous research has associated workload, paraspinal muscle asymmetry and technique factors with lower back injury in fast bowlers, however, preventative strategies such as workload directives and coaching guidelines have not reduced the incidence and prevalence of these injuries. Recent developments in medical imaging technology have improved diagnosis of pathologies such as lumbar posterior bony element (partes interarticulares and pedicles) stress fractures and intervertebral disc degeneration in athletes whilst also allowing quantification of other, potentially associated factors such as paraspinal muscle asymmetry. However, there is very little published research regarding the use of modalities such as magnetic resonance imaging (MRI) in the identification and prognosis of these types of injuries in fast bowlers. Similarly, advances in three-dimensional (3D) motion analysis has aided technique evaluation in a variety of sports, however, little remains known about the pathomechanics of lower back injury in fast bowling. Therefore, the aim of this doctoral research was to investigate relationships between lower back injury and; the MRI appearance of the lumbar posterior bony elements and intervertebral discs, MRI-derived lumbar muscle morphology and the three-dimensional (3D) trunk kinematics of professional fast bowlers in cricket. This was examined in a series of five studies. The first study undertaken was an investigation of the MRI appearance of the lumbar spines of 36 asymptomatic professional fast bowlers and 17 active controls.It was identified that the fast bowlers had a high prevalence of multi-level, predominantly non-dominant side, acute and chronic stress changes in the posterior bony elements of the lumbar spine. Multiple level disc degeneration was also more advanced in the fast bowlers compared with the control - iv - participants. However, disc degeneration appeared not to be associated with lumbar stress injury. The second study investigated the reliability and accuracy of using MRI to determine the FCSA of the lumbar paraspinal muscles (psoas, quadratus lumborum, erector spinae and multifidus). The novel methodology developed in this study was determined to be both valid and highly reliable. In the third study, this technique was then used to describe the functional crosssectional area (FCSA) morphology of the paraspinal muscles in a group of 46 professional fast bowlers and the 17 control participants scanned in the first study. It reinforced that there was a higher prevalence of lumbar muscle asymmetry in the fast bowler group. Paraspinal muscle asymmetry, consistent with hypertrophy of the dominant side muscle, was most prevalent in the quadratus lumborum of fast bowlers, and was also evident in the lumbar multifidus in both groups of subjects. The aims of the fourth study of the thesis were to quantify the proportion of lower trunk motion utilised during the delivery stride of fast bowling and to investigate the relationship between the most accepted fast bowling action classification system and potentially injurious kinematics of the lower trunk. 3D kinematic data were collected from 50 male professional fast bowlers during fast bowling trials and these were normalised to each bowler’s standing lower trunk range of motion. A high percentage of the fast bowlers used a mixed bowling action attributable to having shoulder counter-rotation greater than 30°.The greatest proportion of lower trunk extension (26%), contralateral side-flexion (129%) and ipsilateral rotation (79%) was utilised during the front foot contact phase of the fast bowling delivery stride. There was no significant difference between mixed and non-mixed bowlers in the range of motion used during fast bowling. It was concluded that fast bowling action characteristics currently used to identify potentially dangerous action types may not be directly related to the likely pathomechanics of contralateral side lumbar stress injuries. It is proposed that coupled lower trunk extension, ipsilateral rotation in addition to extreme contralateral side-flexion, during the early part of the front foot contact phase of the bowling action may be an important mechanical factor in the aetiology of this type of injury. In the final study, a combination of the factors described in earlier studies i.e. the lumbar MRI appearance of the partes interarticulares and intervertebral discs, paraspinal muscle asymmetry and selected bowling action and delivery stride trunk kinematic variables, were examined. Therefore, the aim of this study was to examine the relationship between fast bowler lower back injury occurrence (one season either side of testing) and the aforementioned factors that were measured when participants were asymptomatic and bowling competitively. The results of this study indicated that a high percentage of professional fast bowlers in the United Kingdom continue to sustain a high number of acute lumbar stress injuries and these result a significant amount of lost playing and training time. Fast bowling action classification and lower trunk kinematic variables were not conclusively linked to acute lumbar stress injury occurrence. However, further investigation of the effect of coupled lower trunk motion on nondominant side lumbar bone stress is indicated.The presence of acute MRI stress changes (particularly acute stress changes such as bone marrow oedema, periostitis and acute fracture lines) in the non-dominant side lumbar posterior elements seem to have a relationship with acute stress injury occurrence. Regular lumbar MRI scanning may assist in identifying early acute stress changes prior to the onset of symptoms. Intervertebral disc degeneration was less prevalent amongst professional fast bowlers who suffered acute stress injuries than those who had no significant lower back injury. Finally, although fast bowlers have a high prevalence of quadratus lumborum and lumbar multifidus asymmetry (larger on the dominant side), there was no observed relationship between acute lumbar stress injury and these findings.
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