LUMBAR SPONDYLOLYSIS

POSSIBLE PREDISPOSING FACTORS

1) Biomechanical factors During fast bowling, the lumbar area is at greatest risk as a result of the high ground reaction forces occurring during the tran- sition from the run up phase to the deliv- ery stride. Elliott (7) as well as Foster et al (8) showed that the forces through the front leg during delivery can be anything from 3-9 times that of body weight verti- cally and two times body weight horizon- tally. These forces are transmitted through the leg to the lower back (9). During the delivery phase, the trunk hyperextends, stretches sideways and bends and twists in an attempt to achieve maximum speed and strength (10), with the body tissue and footwear helping to absorb the forces.

The fast bowling action can be divided into three or four different categories (see Figure 2). The three most commonly used classifications are ‘side on’, ‘front on’ and ‘mixed action’. It is accepted that the ‘mixed action’ is the one most likely to result in injury (11). It is felt that the greater the shoulder counter-rotation in the transverse plane away from the bats- man, the higher the risk of stress fractures to the lumbar spine (12). While Weatherley et al (13) found that a combi- nation of hyperextension, lateral flexion and rotation are to blame.

A bowler adopting the ‘mixed action’ would have increased hyperextension and lateral flexion as well as greater counter- rotation during the delivery stride thereby making themselves more susceptible to the stresses associated with fast bowling. This problem is compounded when adding in the overuse of having to bowl six balls in an over followed five minutes later by another six balls for as many as a 9 or 10 overs in a spell. This is particularly true with young bowlers (under 20 years) when the pars interarticularis is immature and the stresses in the bone exceed the fatigue strength (14), resulting in an overuse injury.

Elliott et al (15) suggested that a possible reason for the high incidence of injuries in young fast bowlers was that they were being forced to train longer, harder and earlier in life to excel in their chosen sport, and that the hours of repetitious practice may produce gradual deterioration in specific parts of the body. It would be

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AB C

Figures 2: Examples of fast bowling actions a) side-on

logical to suggest the possibility that as the young bowler fatigues from bowling a long spell, his bowling action may be affected, resulting in a potential increase in shoulder counter-rotation, increasing the stress on the pars interarticularis.

Despite various guidelines being intro- duced with regards to the fast bowling action and the number of overs that vari- ous age groups should bowl in a single spell and a single day, the incidence of lumbar spine spondylolysis does not seem to have decreased and it is as much a problem today as it was 15 years ago. This may suggest that there truly is a multifac- torial aetiology involved.

b) semi-open (mixed action)

c) front open

2) Physiological factors Noakes and Durandt (16) have suggested that the real stress of cricket results from damage caused by repeated eccentric muscle contractions that occur during fast bowling. This implies that the more the fast bowler is expected to bowl without a rest, the more damage would occur. As fast bowling is a ‘one-sided activity’ it is possible that muscle imbalances could develop in young adolescents. Engstrom et al (17) found a significant association between stress fractures of the pars inter- articularis and asymmetry of the quadra- tus lumborum muscle on the bowling arm side of the body, with the larger muscle volume appearing on the bowling arm side

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