Lameness in dogs due to musculotendinous and ligamentous injury is commonplace and although diagnosis of severe injury is relatively straightforward, diagnosis of more subtle injury can present a diagnostic challenge. There has been a recent increase in the popularity of canine sports such as agility and flyball, and also in the number of animals participating in competitive events. This has prompted an increase in demand for more advanced diagnostics and therapeutics as, at elite level, effective diagnosis and treatment of even very minor injuries is paramount to ensure optimal performance. This has led to increased awareness of the various types of injury that occur in dogs. Although the implications of injury may be different for competition animals compared to non-athletes, the principles involved in diagnosing and treating these soft tissue injuries are the same regardless.
Sprain or strain
The terms sprain, strain and “pulled muscle” are often used interchangeably to describe a suspected soft tissue injury.
Ligaments originate and insert on bones and typically span a joint. They provide joint stability, and specifically, sprain is the appropriate term for a ligamentous injury. Ligamentous injury usually occurs due to acute overstretching or twisting. Recurrent sprain injuries are common due to inadequate healing of an injured ligament. Even after optimal healing has occurred, a healed ligament is estimated to be only 75 percent as strong as the original ligament.
Tendons connect muscle to bone; their primary function is to transfer the force of muscular contraction to the skeleton, and specifically, strain is the appropriate term for injury involving the muscle-tendon unit. Concentric muscle contraction is when a muscle shortens during contraction. In isometric contraction the muscle length does not change during contraction, and in eccentric contraction the muscle elongates during contraction. An example of eccentric contraction is the lengthening of the quadriceps muscles as an animal braces landing from a height. Musculotendinous injury usually occurs due to overstretching during eccentric contraction and most commonly occurs at the musculotendinous junction. Contusions and lacerations can also occur, but are less common. Repetitive strain injury (RSI) is from overuse, as is commonly seen in iliopsoas injuries and supraspinatus tendinopathy.
Grade of injury
In basic terms, ligamentous and musculotendinous injuries are divided into three grades, based on the severity of injury. Grade 1 are minor injuries that involve damage to a small percentage of the fibres with minimal loss of architecture of the injured tissue, grade 3 injuries are complete ruptures and a grade 2 injury is typically anything in between grade 1 and grade 3. With the advent of advanced imaging, in humans this basic grading of severity has been largely replaced by classifications and subclassifications based on specific location, specific aetiology and mechanism of injury. These classifications can be helpful in prognosis and predicting outcomes, an important consideration in elite sport. This is not yet commonplace in animals.
In grade 1 injuries there may be a localised region of discomfort, but there is minimal heat or swelling, no palpable instability present and minimal lameness is present. Bruising is more common with musculotendinous injury than with ligamentous injury.
Diagnosis of a grade 2 or 3 injury can usually be made following a thorough physical examination as there is usually more obvious focal pain, with marked swelling present at the site of injury. With ligamentous injury, there is invariably a degree of joint instability present. Musculotendinous injuries are less common and can be more difficult to detect on clinical exam, but obvious focal pain and marked heat and swelling are usually present in grade 2 and grade 3 injuries. There is often spectacular bruising, and initially a physical defect is palpable at the site of injury. If left untreated large swellings can result as the large haematoma is replaced by fibrous tissue (Figure 1).
Plain radiography can be helpful in assessing for the presence of focal soft tissue swelling and “stressed” radiography can be helpful in documenting joint instability in cases with significant ligamentous injury (Figure 2).
Computed tomography (CT) provides significantly more information than plain radiographs, especially in chronic cases where regions of dystrophic mineralisation may have formed. CT is invaluable in acute trauma cases that may have sustained subtle avulsion injuries.
Ultrasonography has now become the initial modality of choice in the assessment of a variety of musculotendinous injuries. In broad terms, hypoechoic regions represent recent injury and show regions of haemorrhage and/or fluid, whereas hyperechoic regions represent regions of fibrosis and scar tissue more typical of chronic injury (Figure 3). Ultrasound can also provide additional information in real time whilst the tissue of interest is placed through varying ranges of motion.
The gold standard modality for assessing soft tissue injury is magnetic resonance imaging (MRI), which is performed routinely in humans. This is becoming more commonplace in animals and will continue to do so as experience in this field continues to grow (Figure 4).
The majority of minor grade 1 sprains and strains can be successfully managed merely by resting the patient until lameness resolves. In athletic animals, owners are more likely to employ the widely accepted PRICE (protect, rest, ice, compress, elevate) treatment plan used in human sports medicine. These basic techniques reduce the risk of further injury and reduce swelling and inflammation. The primary objective is to prevent the formation of disorganised scar tissue which is relatively inelastic and can predispose to a recurrence of injury as activity is resumed.
Ligamentous injury resulting in joint instability necessitates stabilisation which invariably involves surgical stabilisation by primary repair and/or augmentation. A period of immobilisation is then required to allow strengthening of newly formed collagen. For optimal outcomes, early controlled mobilisation is required to encourage subsequent remodelling of the new collagen fibres parallel to lines of stress. Ligaments have a relatively poor blood supply and thus healing times can be very protracted. Ideally a specific rehabilitation programme should be employed under the guidance of an experienced physiotherapist.
Management of muscle and tendon injuries follows the same principle in that the primary objective is the avoidance of scar tissue. If a significant gap defect is present then surgical apposition is recommended to reduce the propensity for scar formation, and again early, controlled mobilisation is critical to success. Therapeutic ultrasound was previously used to treat a variety of musculotendinous disorders; this has largely been replaced by adjunctive laser therapy to expedite the healing process.
Iliopsoas injuries are probably the most common underdiagnosed cause of unilateral hindlimb lameness in athletic dogs. Lameness is usually non-responsive to rest and NSAIDs, and lameness is usually exacerbated with a period of strenuous exercise. The iliopsoas muscle comprises two muscles, the psoas major and the iliacus. The psoas major arises from the transverse processes of the lumbar vertebrae of the lower spinal column at L2 and L3 and the bodies of L4-7, and the iliacus arises from the ventral or lower surface of the ilium. The muscles join together at the level of the ilium and insert as a common tendon on the lesser trochanter of the femur. The iliopsoas flexes the hip and flexes the vertebral column. The majority of injuries are thought to be due to repetitive injury, but acute injuries do occur. As in most cases of musculotendinous injuries the most common site of injury is at the musculotendinous junction, but muscle belly injuries are also seen. Diagnosis can usually be made by ultrasound; however, MRI is the gold standard modality for diagnosis as this allows detailed assessment of the entire muscle and can delineate even very minor abnormalities. Pain on hip extension and internal rotation is common but not specific and pain on digital pressure is more reliable. The femoral nerve runs in close proximity and some dogs can have a marked nerve root signature. Treatment in acute injury is aimed at preventing scar tissue formation, but in many cases, the situation is chronic. The use of extracorporeal shockwave therapy is the author’s treatment of choice to break down regions of fibrosis in combination with a structured rehabilitation programme.
Pain associated with the supraspinatus tendon of insertion (again most commonly at the musculotendinous junction) is a likely common cause of undiagnosed thoracic limb lameness, especially in athletic dogs. Similar to iliopsoas injury in the pelvic limb, lameness is often non-responsive to rest and NSAIDs and is worse after heavy exercise. The supraspinous originates from the supraspinatus fossa of the scapula and inserts on the greater tubercle of the humerus. It produces extension of the shoulder and advancement of the limb and injury is thought to be caused by a repetitive injury. It is seen commonly in flyball dogs who repeatedly hit the box with an outstretched limb. Clinically affected dogs usually have discomfort on firm digital palpation of the greater tubercle at the site of injury with the shoulder held flexed. Radiography and CT can reveal mineralisation within the tendon (Figure 5); however, this is often incidental and usually only causes pain by causing impingement on the adjacent tendon of insertion of the biceps muscle (Figure 6). Excision of the mineralised portion is advised by many, but the mineralisation often recurs and the optimal management is debated. The author’s preferred technique is a combination of extracorporeal shockwave treatment and intralesional injections of concentrated platelet-rich plasma, but these treatment techniques fall beyond the scope of this article and will be discussed in a future article.