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Thoracolumbar disc degeneration in young fast bowlers in cricket: a follow-up study
Clinrcd Biomec/mr~io Vol. 11. No. 6, pp. 305-310. 1996 Copyright 0 1996 Elsevier Science Limited. All rights rcsxved Printcd in Great Britain 0268-0033’96 $ I5 00 + 0.00
ELSEVIER
PII:SO268-0033(96)00007-l
Thoracolumbar disc degeneration fast bowlers in cricket: a follow-up
in young study
A F Burnett R N Marshall
D H Foster
M S Khangure FRCR~, B C Elliott Pm4, P H Hardcastle FRACS’
BPE’,
PhDl,
MEd3,
IDepartment of Human Movement, University of Western Australia; ‘Department of Radiology, Royal Perth Hospital, Western Australia; 3Kent County Cricket Club, UK; 4Division of Science and Technology, The University of Auckland, New Zealand
Abstract Objective. To determine the progression of thoracolumbar disc degeneration in young fast bowlers in cricket. Design. Prospective fast bowling technique and MRI follow-up study. Background. Previous studies on high-performance young fast bowlers have found that lumbar spine pathology was related to the mixed bowling technique. Methods. Nineteen young male fast bowlers (mean age 13.6 years) underwent MRI scans to detect the presence of intervertebral disc abnormalities. Subjects were also filmed laterally (200 Hz) and from directly above (100 Hz) whilst bowling two maximum velocity deliveries (session 1). Subjects were tested using an identical methodology 2.7 years later (session 2). Results. At session 1, the incidence of thoracolumbar disc degeneration was 21%; however, at session 2, the incidence significantly (P = 0.008) increased to 58%. Furthermore the increase in the incidence of back pain between session 1 and session 2 was also significant (P = 0.002). The progression of disc degeneration was found to be significantly (P = 0.015) related to the group of fast bowlers who utilized the mixed technique during both session 1 and 2 when compared to those who used this technique during one session only. Conclusions. Thoracolumbar disc degeneration and back pain increase significantly during the time period examined in this study. Further, bowlers who utilize the mixed bowling technique stand a greater chance of developing degenerative changes of the spine. Relevance Lumbar spine abnormalities in cricket have been related to the mixed bowling technique. Therefore an analysis of the progression of thoracolumbar disc degeneration and fast bowling technique in young fast bowlers is warranted. Copyright @ 1996 Elsevier Science Ltd. Key words:
Cricket, fast bowling,
Clin. Biomech.
disc degeneration,
Vol. 11, No. 6, 305-310,
magnetic
resonance
In the game of cricket, overuse injuries to the young fast bowler are extremely common. Elliott et al.’ found that in a group of high-performance young fast bowlers (mean age 17.9 years) the incidence of bony abnormalities (spondylolysis, spondylolisthesis and pedicle sclerosis) was 55%, while the prevalence of intervertebral disc abnormalities was 65%. Furthermore Elliott et al.* found that 21% of a group of male fast bowlers of mean age 13.7 years had at least one 16 August 1995; Accepfed:
Correspondence
and
reprint
21 December 1996 to: Professor Bruce Elliott, University of Western Australia,
requests
Department of Human Movement, Nedlands. Western Australia. 6907
injury
1996
Introduction
Received:
imaging,
degenerative disc. These two studies showed that during the adolescent growth period, fast bowlers seem to face a substantial risk of developing lumbar spine pathology. Foster et al.” postulated that the aetiology of the above-mentioned spinal pathologies was due to a combination of poor bowling technique, poor physical preparation and/or overuse; however, it is a common belief that the problem is predominantly a mechanical one. There exist three fast bowling techniques in which the fast bowler delivers the cricket ball: side-on, fronton, and mixed techniques3. These technique classifications are made by considering both the back foot angle at back foot impact and the alignment of the shoulders between back foot impact and front foot
306
Clin.
Biomech.
Vol.
7 1, No.
6, 1996
impact. It is the mixed fast bowling action (Figure la, b), which IS characterized by an increased degree of lumbar trunk axial rotation, extensioniflexion. and lateral bending when compared to the side-on and front-on fast bowling actions. that has been linked to an increased incidence of abnormal radiological features in the lumbar spine’ ‘. Therefore the aim of this study was to examine whether disc degeneration progressed in a group of young fast bowlers and if so. determine its relationship to iast bowling techniyue. Limitations of this study were that a suitably matched control group was not examined as this was a prospective follow-up study
examining the progression of disc degeneration in a group of fast bowlers only, and that the workload of the bowlers between the two testing sessions was not assessed, although all bowlers played both for school and for club teams. Methods Sampk
Nineteen male fast bowlers (mean age 13.6 years. 0.6: mean height 161.2 cm, SD 11.1; mean mass 51.2 kg. SD 7.5) were tested at the commencement of the 1991- 1992 cricket season (Session 1). After data from this session were analysed, all bowlers attended an educational clinic which outlined factors which were thought to be causative in the development of the abnormal radiological features in the lumbar spine’. All subjects from this original sample were later tested at the completion of the 1993- 1994 season (Session 2) (mean age 16.3 years. SD 0.6; mean height 180.2 cm, SD 7.1; mean mass 68.4 kg, SD 10.0). The sample consisted of subjects from five Western Australian schools who bowled competitively at school and club level and who showed potential as genuine fast bowlers. When the subjects presented at session 1, no bowler had any knowledge of any spinal abnormality and all were bowling completely freely, although at times some bowlers had complained of low back pain. SD
Data
collection
Filming procedures Prior to the collection of biomechanical data, subjects warmed up thoroughly and were then marked at selected anatomical landmarks as described below. Each subject, after as many practice trials as required, bowled two maximum-velocity trials at a wicket with their usual match approach, while being filmed by two l&mm Photosonics 1PL high-speed cameras loaded with Eastman 7251400 ASA daylight film. One camera operated at 200 Hz in an alignment perpendicular to the plane of motion (sagittal plane) and the other, positioned overhead, operated at 100 Hz (transverse plane). A large clock (to calculate film speed) and a calibration object of known length (to convert film measurements to real life size) were placed in both photographic fields.
Figure 1. The mixed action a at back foot impact, where the back foot points directly down the wicket and the shoulders face obliquely across the pitch, and b in the delivery stride, where the shoulders have been counter-rotate&to produce a shoulder alignment more typical of the side-on bowler.
Radiographic procedures Magnetic resonance imaging (MRI) scans for al.l subjects were recorded prior to each session. At session 1 scans were performed using a PHILIPS 1.5T system A sagittal dual echo T2 (TR2,000, TE20:80) sequence was combined with axial Tl scans through the lower three discs, or any other abnormal areas. A surface coil was used with a field of view of 230 mm, 2X2 matrix, and 4-mm slice thickness. At session 2 similar scans were obtained on a PICKER 1T system (except that the field of view was 260 mm).
Burnett
Dutu reduction and management
et al: Disc degeneration
in fast bowlers
Table 1. Incidence session 2
and
of back
The treatment and analysis of data for each session was identical. This was done to minimize the inherent variablity in the data. Analysis of film data The trial with the higher ball velocity (as measured from film) was then chosen for analysis. The coordinates of selected surface markers on the back lower limb during the delivery stride (fifth metatarsal head, lateral malleolus of the fibula, superior surface of the lateral condyle of the tibia, greater trochanter of the femur), front lower limb (medial malleolus of the tibia, superior surface of the medial condyle of the tibia, greater trochanter of the femur), trunk (acromial processes of right and left scapula) and ball were digitized at 100 Hz using a Calcomp 648 digitizer and stored on an IBM PC. The digitized data were then smoothed using a second-order digital filter at a cut-off frequency of 6 Hz. For ease of interpretation all data from left hand bowlers were transferred such that angles were representative of a right handed bowler. Analysis of radiographic data After all biomechanical data were analysed for both sessions, one of the authors (MSK) blindly reviewed the MRI scans and reported the status of the lumbar discs at each session. Although MRI scans from session 1 had been already previously reviewed*, these scans were re-read blindly. It was found that the interpretations for the session 1 scans were identical. Similarly, the session 2 scans were also re-interpreted with identical results. A non-degenerative disc on MRI was represented by a well-preserved disc space without evidence of collapse, smooth borders of both annulus and nucleus pulposus, no evidence of disc herniation, and a clear white signal of the disc4. Statistical analysis Statistical analyses for the progression of disc degeneration and back pain status between sessions 1 and 2 were performed using McNemar’s tes?. The association between the progression of disc degeneration and the fast bowling technique utilized at each session was examined using Fisher’s exact test (SASTAT V6.08, SAS Institute Inc., USA). If a significant difference (P
pain
disc
in cricket
degeneration
307
at session
1 and
Disc degeneration Session Back Yes No Total
pain
Yes 1 3 4
No 0 15 15
Session
1 Total 1 18 19
Yes 6 5 llf
No 4 4 8
2 Total lo** 9 19
*Occurrence of disc degeneration at session 2 was significantly (P = 0.008) different when compared to session 1. **Incidence of back pain at session 2 was significantly (P = 0.002) different when compared to session 1.
of disc degeneration at session 2 (58%) when compared to session 1 (21%). It should also be noted that one subject who reported back pain, but showed no degeneration of the thoracolumbar spine, was later diagnosed (using reverse gantry computed tomography (CT)) as having a fracture of the pars interarticularis on the side contralateral to the bowling arm. For the purpose of the analysis this subject was included in the radiological abnormalities group for session 2. Furthermore the increase in the incidence of back pain between session 1 (5%) and session 2 (53%) was also significant (P = 0.002). At session 1, four bowlers showed signs of disc degeneration and a total of five discs were degenerative. Degeneration was most commonly seen at L5/S1 (3 discs), while degeneration was also seen at L2/L3 (1) and L4/L5 (1). At Session 2, 11 bowlers showed disc degeneration and 19 discs were degenerative (plus a unilateral pars fracture at Ls). Five of these abnormal discs were seen at L5/S1, four at TIJL1 and L1/L2, three at L,/L3, two at L4/L5, and one at L3/L4. The association between back pain and disc degeneration was not examined statistically because of lack of an appropriate statistical test; however, from an examination of Table 1, 84% of bowlers showed a positive relationship (presence of disc degeneration and back pain or absence of disc degeneration and back pain) between disc degeneration and back pain at session 1, but only 53% showed the same relationship a session 2. To examine the association between fast bowling technique and progression of disc degeneration of the thoracolumbar spine, both sets of data were classified into groups. The classification of fast bowling technique, modified from Elliott et a1.2,determined at back foot impact was performed using the following criteria: Side-on. Shoulder alignment of 200” or less and a back foot angle of 290” or less, where the right hand horizontal is a line drawn through the leading shoulder parallel with the pitch. Front-on. Shoulder alignment greater than 200” agd a back foot angle greater than 290”. Mixed. Shoulder alignment greater than 200” and a back foot angle less than 290”, or a counter-rotation of the shoulders greater than 20”. This classification system resulted in there being two side-on, two front-on, and fifteen mixed bowlers at session 1. At session 2 there were five side-on, two
308
C!in. Bmmech.
Vol.
11, No. 6, 1996
degeneration (and pars fracture) and fast bowling technique are presented in Table 2. A significant difference (P~0.05) was found for the 3 x 2 contingency table (2-tail), indicating that at least two distributions were different. Later pairwise comparisons of the three 2 x 2 contingency tables, showed that the group of bowlers who bowled with the mixed bowling technique at each session were more likely to show progressive degeneration of the discs in the thoracolumbar spine when compared to the group who bowled with a mixed action at one session only (P = 0.015). Table 3 demonstrates that no relationship was evident between the level of disc degeneration and bowling technique at either session 1 or session 2. The mixed technique bowlers at session 2. however.
Figure2 Subject with mixed bowlingtechnique imaged at session one. Thefourconsecutive images of a sagittal T2 sequence (TR2000 TE80: 230.mm field of view) extend from left (top) to right (bottom) of midline. images on the right are midline and just right of midline. The discs and endplates are all normal in appearance
front-on and twelve mixed bowlers. The bowlers were then categorized into groups which represented the actions utilized for each of these two sessions. They were as follovvs. Side-c)rr-~rorIr-o,llside-on-front-on. The bowlers who used either the side-on or front-on technique at both sessions nert pooled as both these actions have previously been shown to be related to a decreased presence of abnormal radiological features in the lumbar spine. .Tldr-on-froni-oninzix-Ed. Those players who bowled with a mixed technique at one session. As it was unknown exactly when players who used the mixed technique changed to either a front-on or side-on action and Liw :~ersa, it was necessary to combine these group< Mixed/mixed. Those players who bowled with a mixed technique at both sessions The classification of disc degeneration was performed as follows: ‘vo progression. No evidence of disc degeneration (or pars fracture) at either session, or no further degeneration from session 1 Progression. Evidence of progression from session 1 to session 2 (Figures 2 and 3). The frequencies concerning the progression of disc
Figure 3. Same subject as in Figure 2, imaged at session 2. Sagittal section ofT, study (TR2000TE80: 260-mm field of view1 left of midline (top) and right of midline (bottom) demonstrate loss of signal in the lower four discs caused by disc degeneration, and loss of signal at the level of the apophysis (arrows) because of intrabody disc herniation with resultant sclerosis.
Burnett Table2. progression
Observed frequency of disc degeneration
table
for
No
fast
bowling
progression
technique
and
Progression
Side-on-Front-on1 Side-on-Front-on
1
1
Side-on-Front-on/ Mixed
6
1
Mixed/* Mixed *Indicates significantly mixed distribution.
2 different
(P - 0.015) when
the
8 compared
to the side-on-front-on/
displayed a fairly even distribution of degenerative discs througout the thoracolumbar spine. Discussion
MRI is a non-invasive and radiation free method of detecting intervertebral disc abnormalitie&‘. X-ray and CT involves the use of ionizing radiation and may only reveal disc degeneration by a reduction of disc height; therefore MRI is not only more ethically viable for screening young bowlers, but it is also a superior imaging modality in detecting disc degeneration, as disc height reduction is a relatively late sign of disc degeneration”. Disc degeneration is known to start during the second decade of life and is known to increase with age“‘-i3. This follow-up MRI study showed that there was a significant increase (P = 0.008) in the number of subjects (mean age 16.3 years) showing disc degeneration at session 2 (58%) when compared to session 1 (21%) (mean age 13.6 years). The causal role of disc degeneration in low back pain has been controversial. There have been reports indicating that subjects with disc degeneration are symptomatic’4-17 or asymptomatic’8~‘“. In this study, there seemed to be a strong relationship between the presence of disc degeneration and back pain at session 1; however, at session 2, although there was significant increase in the incidence of back pain, no relationship appeared to exist between these two variables. From previous studies’.20 it was apparent that pars defects were a more likely cause of back pain in fast bowlers under the age of 21 years. These defects, however, are poorly shown on MRI, and as CT scanning involves ionizing radiation, such screening could not be performed on these subjects. It was found that the group of bowlers who utilized the mixed technique at both sessions were more likely to show progression of thoracolumbar disc degeneration when compared to those who bowled with the mixed technique during one session only (Table 2). The reason for this finding could be twofold. Firstly, the mixed bowling technique has been related to an increased incidence of stress fractures in the lower lumbar spine” and an increase in the occurrence of abnormal radiological features in the lumbar spine’. An explanation of this finding could be that the increased degree of trunk rotation in the three anatomical planes possibly associated with the mixed
et al: Disc degeneration
in fast bowlers
in cricket
309
technique, may in turn subject the spinal structures to greater mechanical loadings. Secondly, those subjects who bowled with the mixed technique at both sessions (and therefore are assumed to have used this technique during the intermittent period), are more likely to show accelerated disc degeneration, as they are bowling with poor technique over a long period. Although a significant probability was not obtained between the group of bowlers who utilized either a side-on or fronton and mixed technique at both sessions, this was due to there being a small sample in the former group. Therefore, it should be stated that either of these two techniques are still preferable to the mixed action. At each level of the spine, there exists the two facet joints and the intervertebral disc which constitute the ‘three joint complex’4. It therefore seems that the intervertebral disc should play an important role in the mechanics of the spine, as changes in one joint will cause changes in the remaining two joints4,2’. In an analytical model study22 it was shown that simulated changes in volume of the nucleus pulposus led to increased contact loads on the facets joints. Further, it was found by Dunlop et a1.23in an experimental study on isolated motion segments that the peak pressure across the facet joints was significantly increased in extension when disc height was reduced. It could therefore be possible that if the subjects who bowled with a mixed action at both sessionscontinue to bowl with this action, they may eventually show more serious degenerative changes such as a pars interarticularis defect. The progressive degeneration of the intervertebral discs in the thoracolumbar spine shown in this study is therefore of great concern. A relationship between bowling technique (and therefore possibly movements of the trunk) and the level of degeneration in the thoracolumbar spine could only be feasibly examined for the mixed technique group at session 2 because of the small number of degenerative discs in the remaining categories (Table 3). It is tempting to speculate that there could be different types of shearing and compression forces in specific areas of the thoracolumbar spine as a result of differences in bowling technique; however, no such association could be supported. Conclusions
The incidence of disc degeneration in a group of young fast bowlers was found to be significantly higher when Table 3. Level of disc and session 2
degeneration
Session SO
for
each
bowling
action
at session
Session
1
FO
M
SO
M 3 3 3 1 2 3*
TV&
0
0
0
0
1
LA L/L3 LL UL LJSI
0 0 0 0 0
0 0 0 0 0
0 1 0 1 3
1 0 0 0 1
0 0 0 0 1
pars fracture
at Lg.
*Plus
a unilateral
2
FO
1
310
Clin. Biomech.
Vol. 11, No. 6, 1996
these bowlers were examined 2.7 years later, and the rate of disc degeneration at session 2 was similar to values previously reported for fast bowlers of a similar age’.“. Furthermore there was an increased incidence of hack pain in this period. The progression of disc degeneration was found to be related, to those bowlers who used a mixed action during both sessions as opposed to using this technique during one session only. It is therefore recommended that bowlers who use a mixed action should be supervised over a protracted period of time to ensure they bowl with either a side-on or front-on action.
References 1 Elliott BC, Hardcastle PH. Burnett AF. Foster DH. The influence of fast bowling and physical factors on radiologic features in high performance young fast bowlers. Sports Med Trclin Rehahil1992;
3: 113.-30
2 Elliott BC, Davis JW, Khangure MS et al. Disc degeneration and the young fast bowler in cricket. Clin Biomech 1993;8:227-33
3 Foster DH, John D, Elliott BC et al. Back injuries to young fast bowlers in cricket: A prospective study. Br J Sports Mrd 1989; 23: 150 4
4 Butler D, Tratimow JH, Andersson GBJ et al. Discs degenerate before facets. Spine 1990; IS: 11l-13 5 Krauth J. Distribution+ee Statistics: An Applicationorientated Approach. Amsterdam: Elsevier, 1988 6 Gibson MJ, Buckley J, Mawhinney R et al. Magnetic resonance imaging and discography in the diagnosis of disc degeneration. .I Bone Joint Surg 1986; 68-B: 369-73 7 Medic MT. Masaryk TJ, Ross JS, Carter JR. Imaging of degenerative disk disease. Rudiology 1988; 168: 177-86 8 Tertti M, Paajanen H, Laato M et al. Disc degeneration in magnetic resonance imaging: a comparative biochemical. histologic, and radiologic study in cadaver spines. Spine 1991A; 16: 629-34 9 Sward L. The thoracolumbar spine in young elite athletes: current concepts on the effects of physical training. Sports Med 1992: 13: 357-64
10 Miller JAA, Schmatz C, Schultz AB. Lumbar disc degeneration: Correlation with age, sex and spine level in 600 autopsy specimens. Spine 19X8; 13: 173-8 11 Goldstein JD. Berger PE, Windler GE, Jackson DW. Spine injuries in gymnasts and swimmers: an epidemiologcal study. Am J Sports Med 1990; 19: 463-8 12 Parkkola R, Kormano M. Lumbar disc and back muscle degeneration on MRI: correlation to age and body mass. JSpinal Dis 1992; 5: 86-92 13 Videman T. Battie MC, Gill K et al. Magnetic resonance imaging findings and their relationships in the thoracic and lumbar spine: insights into the etiopathogenesis of spinal degeneration. Spine 1995; 20: 928-35 14 Tertti MO, Salminen JJ, Paajanen HEK et al. Low back pain and disk degeneration in children: a case-control MR imaging study. Radiology 1991B; 180: 503- 7 15 Torgerson WR, Dotter WE. Comparative roentgenographic study of the asymptomatic and symptomatic lumbar spine. J BoneJoint Surg 1976; 5% A: 850~-3 16 Biering-Sorenson F. Hansen FR, Schroll M, Runeborg 0. The relation of spinal X-ray to low back pain and physical activity among 60-year-old men and women. Spine 1985: 10: 44-51 17 Paajanen H, Erkintalo M, Kuusela T et al. Magnetic resonance study of disc degeneration in young low back pain patients. Spine 1989; 14: 982-S 18 Magord A, Schwartz A. Relation between the low back pain syndrome and X-ray findings. Stand J Rehahil Med 1976; 8: 115-2s 19 Witt I, Vestergaard A, Rosenkilt A. A comparative analysis of X-ray findings of the lumbar spine in patients with and without lumbar pain. Spine 1984; 9: 298-300 20 Hardcastle P, Annear P, Foster DH et al. Spinal abnormalities in young fast bowlers. J Bone Joint Surg 1992;74-B:421-5 21 Kim YE, Gael VK, Weinstein JN, Lim TH. Effect of disc
degeneration at one level on the adjacent level in axial mode. Spine 1991; 16: 331-5 22 Shirazi-Ad1 A. Finite clement simulation of changes in the fluid content of human lumbar discs: mechanical and clinical implications. Spine 1992; 17: 206- 12 23 Dunlop RB, Adams MA, Hutton WC. Disc space narrowing and the lumbar facet joints. J Bone Joint Surg 1984: 66-B: 706-10
ELSEVIER
PII:SO268-0033(96)00007-l
Thoracolumbar disc degeneration fast bowlers in cricket: a follow-up
in young study
A F Burnett R N Marshall
D H Foster
M S Khangure FRCR~, B C Elliott Pm4, P H Hardcastle FRACS’
BPE’,
PhDl,
MEd3,
IDepartment of Human Movement, University of Western Australia; ‘Department of Radiology, Royal Perth Hospital, Western Australia; 3Kent County Cricket Club, UK; 4Division of Science and Technology, The University of Auckland, New Zealand
Abstract Objective. To determine the progression of thoracolumbar disc degeneration in young fast bowlers in cricket. Design. Prospective fast bowling technique and MRI follow-up study. Background. Previous studies on high-performance young fast bowlers have found that lumbar spine pathology was related to the mixed bowling technique. Methods. Nineteen young male fast bowlers (mean age 13.6 years) underwent MRI scans to detect the presence of intervertebral disc abnormalities. Subjects were also filmed laterally (200 Hz) and from directly above (100 Hz) whilst bowling two maximum velocity deliveries (session 1). Subjects were tested using an identical methodology 2.7 years later (session 2). Results. At session 1, the incidence of thoracolumbar disc degeneration was 21%; however, at session 2, the incidence significantly (P = 0.008) increased to 58%. Furthermore the increase in the incidence of back pain between session 1 and session 2 was also significant (P = 0.002). The progression of disc degeneration was found to be significantly (P = 0.015) related to the group of fast bowlers who utilized the mixed technique during both session 1 and 2 when compared to those who used this technique during one session only. Conclusions. Thoracolumbar disc degeneration and back pain increase significantly during the time period examined in this study. Further, bowlers who utilize the mixed bowling technique stand a greater chance of developing degenerative changes of the spine. Relevance Lumbar spine abnormalities in cricket have been related to the mixed bowling technique. Therefore an analysis of the progression of thoracolumbar disc degeneration and fast bowling technique in young fast bowlers is warranted. Copyright @ 1996 Elsevier Science Ltd. Key words:
Cricket, fast bowling,
Clin. Biomech.
disc degeneration,
Vol. 11, No. 6, 305-310,
magnetic
resonance
In the game of cricket, overuse injuries to the young fast bowler are extremely common. Elliott et al.’ found that in a group of high-performance young fast bowlers (mean age 17.9 years) the incidence of bony abnormalities (spondylolysis, spondylolisthesis and pedicle sclerosis) was 55%, while the prevalence of intervertebral disc abnormalities was 65%. Furthermore Elliott et al.* found that 21% of a group of male fast bowlers of mean age 13.7 years had at least one 16 August 1995; Accepfed:
Correspondence
and
reprint
21 December 1996 to: Professor Bruce Elliott, University of Western Australia,
requests
Department of Human Movement, Nedlands. Western Australia. 6907
injury
1996
Introduction
Received:
imaging,
degenerative disc. These two studies showed that during the adolescent growth period, fast bowlers seem to face a substantial risk of developing lumbar spine pathology. Foster et al.” postulated that the aetiology of the above-mentioned spinal pathologies was due to a combination of poor bowling technique, poor physical preparation and/or overuse; however, it is a common belief that the problem is predominantly a mechanical one. There exist three fast bowling techniques in which the fast bowler delivers the cricket ball: side-on, fronton, and mixed techniques3. These technique classifications are made by considering both the back foot angle at back foot impact and the alignment of the shoulders between back foot impact and front foot
306
Clin.
Biomech.
Vol.
7 1, No.
6, 1996
impact. It is the mixed fast bowling action (Figure la, b), which IS characterized by an increased degree of lumbar trunk axial rotation, extensioniflexion. and lateral bending when compared to the side-on and front-on fast bowling actions. that has been linked to an increased incidence of abnormal radiological features in the lumbar spine’ ‘. Therefore the aim of this study was to examine whether disc degeneration progressed in a group of young fast bowlers and if so. determine its relationship to iast bowling techniyue. Limitations of this study were that a suitably matched control group was not examined as this was a prospective follow-up study
examining the progression of disc degeneration in a group of fast bowlers only, and that the workload of the bowlers between the two testing sessions was not assessed, although all bowlers played both for school and for club teams. Methods Sampk
Nineteen male fast bowlers (mean age 13.6 years. 0.6: mean height 161.2 cm, SD 11.1; mean mass 51.2 kg. SD 7.5) were tested at the commencement of the 1991- 1992 cricket season (Session 1). After data from this session were analysed, all bowlers attended an educational clinic which outlined factors which were thought to be causative in the development of the abnormal radiological features in the lumbar spine’. All subjects from this original sample were later tested at the completion of the 1993- 1994 season (Session 2) (mean age 16.3 years. SD 0.6; mean height 180.2 cm, SD 7.1; mean mass 68.4 kg, SD 10.0). The sample consisted of subjects from five Western Australian schools who bowled competitively at school and club level and who showed potential as genuine fast bowlers. When the subjects presented at session 1, no bowler had any knowledge of any spinal abnormality and all were bowling completely freely, although at times some bowlers had complained of low back pain. SD
Data
collection
Filming procedures Prior to the collection of biomechanical data, subjects warmed up thoroughly and were then marked at selected anatomical landmarks as described below. Each subject, after as many practice trials as required, bowled two maximum-velocity trials at a wicket with their usual match approach, while being filmed by two l&mm Photosonics 1PL high-speed cameras loaded with Eastman 7251400 ASA daylight film. One camera operated at 200 Hz in an alignment perpendicular to the plane of motion (sagittal plane) and the other, positioned overhead, operated at 100 Hz (transverse plane). A large clock (to calculate film speed) and a calibration object of known length (to convert film measurements to real life size) were placed in both photographic fields.
Figure 1. The mixed action a at back foot impact, where the back foot points directly down the wicket and the shoulders face obliquely across the pitch, and b in the delivery stride, where the shoulders have been counter-rotate&to produce a shoulder alignment more typical of the side-on bowler.
Radiographic procedures Magnetic resonance imaging (MRI) scans for al.l subjects were recorded prior to each session. At session 1 scans were performed using a PHILIPS 1.5T system A sagittal dual echo T2 (TR2,000, TE20:80) sequence was combined with axial Tl scans through the lower three discs, or any other abnormal areas. A surface coil was used with a field of view of 230 mm, 2X2 matrix, and 4-mm slice thickness. At session 2 similar scans were obtained on a PICKER 1T system (except that the field of view was 260 mm).
Burnett
Dutu reduction and management
et al: Disc degeneration
in fast bowlers
Table 1. Incidence session 2
and
of back
The treatment and analysis of data for each session was identical. This was done to minimize the inherent variablity in the data. Analysis of film data The trial with the higher ball velocity (as measured from film) was then chosen for analysis. The coordinates of selected surface markers on the back lower limb during the delivery stride (fifth metatarsal head, lateral malleolus of the fibula, superior surface of the lateral condyle of the tibia, greater trochanter of the femur), front lower limb (medial malleolus of the tibia, superior surface of the medial condyle of the tibia, greater trochanter of the femur), trunk (acromial processes of right and left scapula) and ball were digitized at 100 Hz using a Calcomp 648 digitizer and stored on an IBM PC. The digitized data were then smoothed using a second-order digital filter at a cut-off frequency of 6 Hz. For ease of interpretation all data from left hand bowlers were transferred such that angles were representative of a right handed bowler. Analysis of radiographic data After all biomechanical data were analysed for both sessions, one of the authors (MSK) blindly reviewed the MRI scans and reported the status of the lumbar discs at each session. Although MRI scans from session 1 had been already previously reviewed*, these scans were re-read blindly. It was found that the interpretations for the session 1 scans were identical. Similarly, the session 2 scans were also re-interpreted with identical results. A non-degenerative disc on MRI was represented by a well-preserved disc space without evidence of collapse, smooth borders of both annulus and nucleus pulposus, no evidence of disc herniation, and a clear white signal of the disc4. Statistical analysis Statistical analyses for the progression of disc degeneration and back pain status between sessions 1 and 2 were performed using McNemar’s tes?. The association between the progression of disc degeneration and the fast bowling technique utilized at each session was examined using Fisher’s exact test (SASTAT V6.08, SAS Institute Inc., USA). If a significant difference (P
pain
disc
in cricket
degeneration
307
at session
1 and
Disc degeneration Session Back Yes No Total
pain
Yes 1 3 4
No 0 15 15
Session
1 Total 1 18 19
Yes 6 5 llf
No 4 4 8
2 Total lo** 9 19
*Occurrence of disc degeneration at session 2 was significantly (P = 0.008) different when compared to session 1. **Incidence of back pain at session 2 was significantly (P = 0.002) different when compared to session 1.
of disc degeneration at session 2 (58%) when compared to session 1 (21%). It should also be noted that one subject who reported back pain, but showed no degeneration of the thoracolumbar spine, was later diagnosed (using reverse gantry computed tomography (CT)) as having a fracture of the pars interarticularis on the side contralateral to the bowling arm. For the purpose of the analysis this subject was included in the radiological abnormalities group for session 2. Furthermore the increase in the incidence of back pain between session 1 (5%) and session 2 (53%) was also significant (P = 0.002). At session 1, four bowlers showed signs of disc degeneration and a total of five discs were degenerative. Degeneration was most commonly seen at L5/S1 (3 discs), while degeneration was also seen at L2/L3 (1) and L4/L5 (1). At Session 2, 11 bowlers showed disc degeneration and 19 discs were degenerative (plus a unilateral pars fracture at Ls). Five of these abnormal discs were seen at L5/S1, four at TIJL1 and L1/L2, three at L,/L3, two at L4/L5, and one at L3/L4. The association between back pain and disc degeneration was not examined statistically because of lack of an appropriate statistical test; however, from an examination of Table 1, 84% of bowlers showed a positive relationship (presence of disc degeneration and back pain or absence of disc degeneration and back pain) between disc degeneration and back pain at session 1, but only 53% showed the same relationship a session 2. To examine the association between fast bowling technique and progression of disc degeneration of the thoracolumbar spine, both sets of data were classified into groups. The classification of fast bowling technique, modified from Elliott et a1.2,determined at back foot impact was performed using the following criteria: Side-on. Shoulder alignment of 200” or less and a back foot angle of 290” or less, where the right hand horizontal is a line drawn through the leading shoulder parallel with the pitch. Front-on. Shoulder alignment greater than 200” agd a back foot angle greater than 290”. Mixed. Shoulder alignment greater than 200” and a back foot angle less than 290”, or a counter-rotation of the shoulders greater than 20”. This classification system resulted in there being two side-on, two front-on, and fifteen mixed bowlers at session 1. At session 2 there were five side-on, two
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degeneration (and pars fracture) and fast bowling technique are presented in Table 2. A significant difference (P~0.05) was found for the 3 x 2 contingency table (2-tail), indicating that at least two distributions were different. Later pairwise comparisons of the three 2 x 2 contingency tables, showed that the group of bowlers who bowled with the mixed bowling technique at each session were more likely to show progressive degeneration of the discs in the thoracolumbar spine when compared to the group who bowled with a mixed action at one session only (P = 0.015). Table 3 demonstrates that no relationship was evident between the level of disc degeneration and bowling technique at either session 1 or session 2. The mixed technique bowlers at session 2. however.
Figure2 Subject with mixed bowlingtechnique imaged at session one. Thefourconsecutive images of a sagittal T2 sequence (TR2000 TE80: 230.mm field of view) extend from left (top) to right (bottom) of midline. images on the right are midline and just right of midline. The discs and endplates are all normal in appearance
front-on and twelve mixed bowlers. The bowlers were then categorized into groups which represented the actions utilized for each of these two sessions. They were as follovvs. Side-c)rr-~rorIr-o,llside-on-front-on. The bowlers who used either the side-on or front-on technique at both sessions nert pooled as both these actions have previously been shown to be related to a decreased presence of abnormal radiological features in the lumbar spine. .Tldr-on-froni-oninzix-Ed. Those players who bowled with a mixed technique at one session. As it was unknown exactly when players who used the mixed technique changed to either a front-on or side-on action and Liw :~ersa, it was necessary to combine these group< Mixed/mixed. Those players who bowled with a mixed technique at both sessions The classification of disc degeneration was performed as follows: ‘vo progression. No evidence of disc degeneration (or pars fracture) at either session, or no further degeneration from session 1 Progression. Evidence of progression from session 1 to session 2 (Figures 2 and 3). The frequencies concerning the progression of disc
Figure 3. Same subject as in Figure 2, imaged at session 2. Sagittal section ofT, study (TR2000TE80: 260-mm field of view1 left of midline (top) and right of midline (bottom) demonstrate loss of signal in the lower four discs caused by disc degeneration, and loss of signal at the level of the apophysis (arrows) because of intrabody disc herniation with resultant sclerosis.
Burnett Table2. progression
Observed frequency of disc degeneration
table
for
No
fast
bowling
progression
technique
and
Progression
Side-on-Front-on1 Side-on-Front-on
1
1
Side-on-Front-on/ Mixed
6
1
Mixed/* Mixed *Indicates significantly mixed distribution.
2 different
(P - 0.015) when
the
8 compared
to the side-on-front-on/
displayed a fairly even distribution of degenerative discs througout the thoracolumbar spine. Discussion
MRI is a non-invasive and radiation free method of detecting intervertebral disc abnormalitie&‘. X-ray and CT involves the use of ionizing radiation and may only reveal disc degeneration by a reduction of disc height; therefore MRI is not only more ethically viable for screening young bowlers, but it is also a superior imaging modality in detecting disc degeneration, as disc height reduction is a relatively late sign of disc degeneration”. Disc degeneration is known to start during the second decade of life and is known to increase with age“‘-i3. This follow-up MRI study showed that there was a significant increase (P = 0.008) in the number of subjects (mean age 16.3 years) showing disc degeneration at session 2 (58%) when compared to session 1 (21%) (mean age 13.6 years). The causal role of disc degeneration in low back pain has been controversial. There have been reports indicating that subjects with disc degeneration are symptomatic’4-17 or asymptomatic’8~‘“. In this study, there seemed to be a strong relationship between the presence of disc degeneration and back pain at session 1; however, at session 2, although there was significant increase in the incidence of back pain, no relationship appeared to exist between these two variables. From previous studies’.20 it was apparent that pars defects were a more likely cause of back pain in fast bowlers under the age of 21 years. These defects, however, are poorly shown on MRI, and as CT scanning involves ionizing radiation, such screening could not be performed on these subjects. It was found that the group of bowlers who utilized the mixed technique at both sessions were more likely to show progression of thoracolumbar disc degeneration when compared to those who bowled with the mixed technique during one session only (Table 2). The reason for this finding could be twofold. Firstly, the mixed bowling technique has been related to an increased incidence of stress fractures in the lower lumbar spine” and an increase in the occurrence of abnormal radiological features in the lumbar spine’. An explanation of this finding could be that the increased degree of trunk rotation in the three anatomical planes possibly associated with the mixed
et al: Disc degeneration
in fast bowlers
in cricket
309
technique, may in turn subject the spinal structures to greater mechanical loadings. Secondly, those subjects who bowled with the mixed technique at both sessions (and therefore are assumed to have used this technique during the intermittent period), are more likely to show accelerated disc degeneration, as they are bowling with poor technique over a long period. Although a significant probability was not obtained between the group of bowlers who utilized either a side-on or fronton and mixed technique at both sessions, this was due to there being a small sample in the former group. Therefore, it should be stated that either of these two techniques are still preferable to the mixed action. At each level of the spine, there exists the two facet joints and the intervertebral disc which constitute the ‘three joint complex’4. It therefore seems that the intervertebral disc should play an important role in the mechanics of the spine, as changes in one joint will cause changes in the remaining two joints4,2’. In an analytical model study22 it was shown that simulated changes in volume of the nucleus pulposus led to increased contact loads on the facets joints. Further, it was found by Dunlop et a1.23in an experimental study on isolated motion segments that the peak pressure across the facet joints was significantly increased in extension when disc height was reduced. It could therefore be possible that if the subjects who bowled with a mixed action at both sessionscontinue to bowl with this action, they may eventually show more serious degenerative changes such as a pars interarticularis defect. The progressive degeneration of the intervertebral discs in the thoracolumbar spine shown in this study is therefore of great concern. A relationship between bowling technique (and therefore possibly movements of the trunk) and the level of degeneration in the thoracolumbar spine could only be feasibly examined for the mixed technique group at session 2 because of the small number of degenerative discs in the remaining categories (Table 3). It is tempting to speculate that there could be different types of shearing and compression forces in specific areas of the thoracolumbar spine as a result of differences in bowling technique; however, no such association could be supported. Conclusions
The incidence of disc degeneration in a group of young fast bowlers was found to be significantly higher when Table 3. Level of disc and session 2
degeneration
Session SO
for
each
bowling
action
at session
Session
1
FO
M
SO
M 3 3 3 1 2 3*
TV&
0
0
0
0
1
LA L/L3 LL UL LJSI
0 0 0 0 0
0 0 0 0 0
0 1 0 1 3
1 0 0 0 1
0 0 0 0 1
pars fracture
at Lg.
*Plus
a unilateral
2
FO
1
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these bowlers were examined 2.7 years later, and the rate of disc degeneration at session 2 was similar to values previously reported for fast bowlers of a similar age’.“. Furthermore there was an increased incidence of hack pain in this period. The progression of disc degeneration was found to be related, to those bowlers who used a mixed action during both sessions as opposed to using this technique during one session only. It is therefore recommended that bowlers who use a mixed action should be supervised over a protracted period of time to ensure they bowl with either a side-on or front-on action.
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3: 113.-30
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