Current research on Pelvic Asymmetry in Racehorses
Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse. Lameness is one of the main reasons for wastage in the racehorse industry, and was the reported cause of 68% of total horse days lost to training in a study of racehorses in England (Rossdale et al. 1985).
This study also suggested that 10% of all diagnosed lameness cases were caused by tendon injury. Overstrain injuries to the superficial digital flexor tendon (SDFT) are amongst the most common injuries observed in the athletic horse (Goodship, 1993). It is therefore important to determine all possible causative factors of SDFT injury so that methods for preventing injury can be implemented as part of a training programme.
The hindquarters of the horse provide the propulsion, and the forelimbs support 60% of the horse’s weight. Problems affecting the pelvic structure in the horse can lead not only to poor performance, but also to an unlevel gait and to lameness of the hindlimb. There are to date very few scientific reports on the frequency of hindquarter asymmetries in the horse, although Bathe (2002) found that most hard working horses were likely to have some degree of pelvic asymmetry.
This factor may not always affect performance, as many successful horses have been found to have asymmetry of the pelvis. Dalin et al. (1985) investigated the hindquarter asymmetry in Standardbred Trotters for any correlation with poor performance. He measured differences in height between the left and right tuber sacrale when the horse was standing square. Of the 500 horses measured 39 of them showed marked hindquarter asymmetry. In 30 horses the tuber sacrale was lower on the left, and in 9 horses it was lower on the right. The asymmetric horses had significantly inferior performance (measured by total earnings) compared to the symmetrical horses.
All the horses were trained and raced in Sweden on a left handed track. The asymmetrical horses were also of significantly larger body size than the symmetrical horses. In a recent study undertaken by Stubbs et al. (2006) in conjunction with the Hong Kong Jockey Club, a number of racehorses were presented for euthanasia (for injury and/or lameness). Racing and training details were examined in detail, and a clinical examination was carried out before the horses were euthanased. Following post mortem the thoracolumbar spine and pelvis were dissected out and examined. Although not part of the study it was noted that asymmetry of the pelvis was prevalent in many of the horses that had been dissected, the reason probably being due to a natural torsion of the pelvis as a result of training and racing on right handed tracks only.
It is suggested that asymmetrical loads on the pelvic structure caused by external factors (such as racetrack), and by internal factors (such as locomotor apparatus pain) may lead to a higher stress being placed on one hindlimb, and as a result lead to the development of pelvic asymmetry which may be apparent as pelvic rotation. Improper movement patterns of the hindquarters, due to pain caused by overuse or from fatigue, may also result in abnormal alignment of the pelvic structure.
This in turn may then cause overloading on the forelimbs (by off loading the hindquarters) and therefore predisposing the forelimbs to injury. If this can be proved then surely this would emphasise the importance of correcting pelvic misalignments using manipulation techniques such as chiropractic, osteopathic and myofascial release approaches. There is some unpublished material available to support the use of McTimoney manipulation methods and other soft tissue manipulation in the correction of pelvic rotation. Hindquarter asymmetry is often associated with sacroiliac joint lesions or with chronic hindlimb lameness.
The tuber sacrale can appear asymmetrical in clinically normal horses as well as in horses with misalignment of the sacroiliac joint (Dyson, 2004). Horses with longstanding poor performance attributed to chronic sacroiliac damage were investigated by Jeffcott et al. (1985). The majority of these horses showed some asymmetry of the hindquarters with the tuber coxae and tuber sacrale lower on the same side that the animal was lame on. Hindquarter asymmetry may be due to some tilting or rotation of the pelvis in addition to muscle wastage of one quarter, usually the side the horse is lame on.
ABNORMAL ALIGNMENT OF THE PELVIS
Pelvic rotation or abnormal alignment of the pelvis to the thoracolumbar spine can be measured by the level of the tuber coxae to the ground. If the horse is unable to produce the propulsion from its hindquarters due to discomfort in the pelvic region, then the forelimbs may be required to provide more horizontal propulsion. The horse will in effect be pulling himself forward with his forelimbs, rather than pushing from his hindquarters. This may result in over development of the shoulder muscles, thereby reducing the efficiency of the forelimb movement by adding unnecessary weight. Unpublished data has suggested a positive relationship between injury to the forelimb stay apparatus and pelvic asymmetry, particularly where the presence of functional asymmetry in the hindquarters was found to be due to pelvic rotation, and not as a result of differences in individual bone lengths of the hindlimb.
LAMENESS AND COMPENSATORY MOVEMENT PATTERNS
The compensatory mechanisms of horses with lameness have been extensively researched and reported. The potential for secondary injuries resulting from a horse’s attempt to compensate for lameness by altering its gait pattern are still unclear. Clayton (2001) found that when a lame limb is supporting body weight, the horse minimises pain by decreasing the load on that limb, resulting in a compensatory increase in the vertical forces in other limbs. The compensating limbs are therefore subjected to abnormally high forces, and these may lead to lameness in the compensating limbs. Uhlir et al. (1997) found that in all cases of diagnosed hindlimb lameness that true lameness of the left hind caused a compensatory lameness of the left fore, and that true stance phase lameness of the left fore caused a compensatory lameness in the right hind. TENDON INJURY The SDFT is the most frequently injured tendon in horses. In a recent study of steeplechase horses diagnosed with tendon and ligament injuries sustained during training, 89% occurred in the SDFT (Ely et al. 2005). It has been suggested that an optimum level of exercise is required at an early age for tendon adaptation to training, but with increasing age accumulation of microdamage and localised fatigue, failure to the tendon will occur with increasing exercise (Smith et al. 1999). The induction of injury to the SDFT occurs when loading overcomes the resistive strength of the tendon. Factors which increase the peak loading of the SDFT, such as weight of rider, ground surface, shoeing, conformation, incoordination, jumping, and speed will act not only to increase the rate of degeneration, but will also increase the risk of the onset of SDFT strain (Smith, 2006). Therefore the prevention of tendon strain-induced injuries by reducing some of the risk factors that increase loading on the tendon may provide the most satisfactory answer.
ANIMAL MANIPULATION TECHNIQUES
McTimoney Animal Manipulation aims to improve asymmetries through manipulation. There has been much anecdotal evidence for the benefits of McTimoney Manipulation Techniques on animals (Andrews and Courtney, 1999). There is anecdotal evidence to suggest that McTimoney and other manipulative therapies can make a difference where veterinary medication has failed (Green, 2006), although the application of manipulation techniques in veterinary medicine may be dependent of further research into the clinical effects of manipulation. Manipulation techniques are thought to cause muscle relaxation and to correct abnormal motor patterns which may be the result of muscular imbalances and restricted joint motion or altered joint mobility (Haussler, 1999). There is some unpublished material to support that there are significant changes in the symmetry of the pelvis after the application of McTimoney manipulation techniques, and that there is continued improvement one month after initial treatment.
CURRENT RESEARCH INTO PELVIC ALIGNMENT
In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method. Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs. Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides. Various data was collected on each horse, regarding race history, how many races run, whether “bumper” (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history. The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime. Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right.
This could have been due to training methods or gallops used, and certainly warrants further research. There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses. Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury. The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age. Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.
FUTURE STUDIES INTO PELVIC ASYMMETRY
The preliminary investigation as described above has formed the basis for further research into abnormal pelvic alignment in racehorses, and whether or not there is any association between side of misalignment and side of forelimb injury. Further research is due to be carried out with a larger sample of horses, and from different yards, to investigate whether there is any prevalence as to the side of misalignment, or if pelvic alignment is affected by training methods and the use of different gallops.