Suspected back pain or dysfunction is a common cause for owners to seek veterinary advice. Cases presenting with perceived back pain are often challenging due to the large number of possible underlying causes (Jeffcott 1980). Back pain may be the primary complaint or could be part of a broader poor performance issue. In order to reach a diagnosis, it is important to have a systematic approach to the diagnostic process, often aiming to systematically rule out common causes of back pain before arriving at the correct diagnosis. Successful treatment requires identifying the underlying problem as well as considering other contributing factors such as lameness, sacroiliac or neck pain, saddle fit and the exercise regime. The main problem encountered when investigating back pain is the lack of a ‘gold standard’ test.
Investigating back pain
Horses exhibiting signs such as rearing, kicking out, bucking or hypersensitivity to grooming or palpation of the back, frequently prompt further investigations into a potential back problem.
The clinical examination is a vital part of investigating horses with suspected back pain. The physical examination should follow a systematic approach and is the same as any other orthopaedic case. It is important to palpate the limbs as well as the head and neck in order to identify possible contributing factors. Horses presenting with back pain sometimes have a strong aversive reaction to back palpation. It is, therefore, advised to leave the thorough palpation of the back until last. Clinical signs of back pain may include reduced mobility, swelling or heat. Pain may be elicited by spinal mobilisation or by pressure applied to the dorsal spinous process and the epaxial musculature. The horse’s back should be approached carefully. Sudden, firm pressure could cause the horse to react with aggression or anxiety, even in absence of back pain, which frequently leads to misinterpretations. Depending on the patient’s temperament, the interpretation of findings during the physical examination can be challenging.
Following the physical examination the horse should be assessed dynamically, ideally both on the lunge and under the saddle. Any asymmetry of the gait should be investigated, as back pain and concurrent lameness is common (Zimmermann et al, 2011). Horses deemed to be unsafe to ride, due to exhibiting dangerous behaviours, can be assessed with tack on the lunge or with a weighted surcingle. The majority of clinical signs associated with back pain have not been measured yet and, therefore, the investigation is primarily subjective.
The ‘gold standard’ for the objective assessment of back movement is 'optical motion capture'. This technique is highly accurate but restricted to the gait laboratory or treadmills and is not applicable for the use in the field. Alternatively, wireless inertial sensors can be used to collect kinematic data. This technique can also be used to assess for gait asymmetries and evaluate interactions between horse and rider (Pfau et al, 2007, 2009). When compared to optical motion capture, inertial sensor data showed a good level of consistency and an acceptable accuracy for back movement (Warner et al. 2010).
Back pain and lameness
Horses compensate hindlimb lameness by adapting spinal movement, which becomes evident as a reduction of range of motion at the lumbosacral junction and extension of the thoracolumbar region (Buchner et al 1996; Alvarez et al 2008). By abolishing the hindlimb lameness with diagnostic local anaesthesia, these asymmetries and reduced range of motion can be reversed (Greve et al 2017).
Saddle slip was observed in a large proportion of horses with hindlimb lameness, probably partly due to asymmetrical epaxial muscling (Greve et al 2013). Furthermore, saddle slip could be corrected by abolishing hindlimb lameness, suggesting that asymmetrical thoracolumbar movement in lame horses is the cause. A study assessing back dimensions of sport horses over time showed that lame horses had a reduced ability to develop normal epaxial musculature (Greve et al 2015).
