What Is A Muscle Contusion

A muscle contusion is a type of injury that occurs as a result of a high-impact blunt or non-penetrative trauma to muscle tissue. As skeletal muscle is widely distributed throughout the body and is nominally close to the outer boundary (skin) of the body, it is particularly prone to this type of injury as we interact with our external environment performing everyday activities.

A more common means by which a person can suffer a muscle contusion is via compression injuries, such as when the muscle is rapidly compressed between a solid object and bone, for example. These types of impact injuries occur frequently in contact sports. Indeed, muscle contusions are most frequently observed in the field of sports medicine but are also reported in orthopaedics and traumatology, where contusion injuries may result from an accident, for example.¹

Diagnosis and characterisation

The main hallmark of a muscle contusion is the formation of a bruise underneath unbroken skin. The severity of the injury, unsurprisingly, is dependent on a number of factors: the amount of force sustained by the trauma, patient age, the location and activation status of the muscle involved. These all culminate in the extent the muscle fibres rupture or tear on impact and the secondary injuries that are associated with the contusion.

The secondary injuries typically form the known symptoms of muscle contusion and, therefore, its diagnosis. These are inclusive of internal bleeding, which can form a localised haematoma (blood pool), swelling, loss of muscle function, pain, inflammation and fibrosis.^1,2

Clinical diagnosis of a muscle contusion is usually performed visually and at the physician's discretion. However, the use of more sophisticated imaging technologies such as magnetic resonance imaging (MRI) and ultrasonography are increasingly important in being able to accurately diagnose the extent and severity of an injury and guide recommendations for optimised treatment choices.

Complications from untreated or undiagnosed muscle contusions

The process of healing and regeneration of muscle tissue is broadly categorised into three phases.3 The first phase occurs on injury and is characterised by the degeneration and necrosis of damaged tissue. An inflammatory response triggers the migration of immune cells to the injury site. In addition to the inflammatory response, the physical hallmarks used to diagnose contusions, such as the formation of a haematoma, also occur.

The migration of macrophages and neutrophils to the injury site then initiates phagocytosis to eliminate damaged tissue, and cell signalling cascades trigger the activation and regulation of growth factors to induce muscle regeneration. Muscle satellite cells are recruited to the injury site and undergo proliferation and differentiation into mature myoblasts, which can then be assembled into new tissue.

In some severe cases, healing may involve the formation of scar tissue. Scar tissue possesses a different structural make-up from muscle tissue and, therefore, becomes an inferior replacement to the damaged tissue.

While this regeneration process often works smoothly for most cases of muscle contusion, more severe injuries can be prone to further complexities and complications on healing. Therefore, it is important to be able to diagnose the extent and severity of a muscle injury early on in order to prevent the onset of complications.

Early onset complications - acute compartment syndrome

Fascia compartments are groups of muscle and nerves that are separated by a dense network of connective tissue (fascia). Muscle contusions that result in haematoma or an oedema in an inextensible compartment subsequently causes a reduction in space that builds up pressure within the compartment. This pressure build can cause further tissue insult and in severe cases, tissue necrosis.  

Acute compartment syndrome occurs most frequently in the anterior fascia compartment of the leg, and common symptoms are a disproportionate amount of pain one would expect from the injury and an unresponsiveness to prescribed painkillers. Other symptoms can be swelling, decrease in motor function and loss of pulse .^4,5

Intermediate onset complications - myositis ossificans

Myositis ossificans, also referred to as post-traumatic ectopic calcification in muscle, is an abnormal formation of bone or cartilage on muscle tissue.⁴ The breakdown and necrosis of damaged muscle tissues create an environment for the migration and proliferation of stem cells into the injury space, and these cells go on to develop into abnormal bone or cartilage in place of muscle fibres. The growth, however, is characteristically benign and non-neoplastic, making it distinct from other tumours. While some patients with myositis ossificans experience pain, swelling or the formation of a palpable mass, others can be asymptomatic.

Myositis ossificans can be tricky to diagnose as it does not present until 3 or 4 weeks post-injury. It is more likely to occur following the recurrent injury of a previously injured muscle. Myositis ossificans also have a shared pathophysiology with similar conditions, such as neurogenic heterotopic ossification and myositis ossificans progressive. The former of which includes paralysis as a symptom, and the latter is an inherited skeletal ossification condition.⁴

Infections

Blunt force trauma leading to muscle contusion often creates areas within or around the injury site that are particularly vulnerable and, therefore, highly susceptible to bacterial infiltration. In patients with muscle contusion injuries in large muscle groups (e.g., thigh muscle), there is an increased risk of developing pyomyositis, which is predominantly caused by infection of staphylococcus aureus into or adjacent to the injury site. Patients often experience a high fever, muscle pain and the development of an abscess at the injection site.

Delayed onset complications - post-traumatic fibrosis

While most muscle injuries will heal through tissue regeneration or the creation of new muscle fibres, in severe trauma cases, the damaged tissue is replaced with fibrotic or scar tissue.⁶ In vivo, the healing process often occurs via both pathways; tissue regeneration and scar tissue formation, in a competitive manner and at the same time. However, through mechanisms that are not fully understood, the balance can often shift to favour one mechanism over the other. A possible trigger for the formation of scar tissue over muscle fibre is the presence of a haematoma, which is converted into a blood clot that recruits fibroblasts to the injury site instead of non-differentiated satellite cells. The fibroblasts deposit type I collagen, which forms a strong bridging structure or scaffold for tissue reconstruction. Albeit, over time, this construction of scar tissue undergoes reduction; however, its presence and volume cause alteration in the innate tertiary structure of the affected muscle. This subsequently impedes the muscle's mechanics and overall functionality.⁶

Treatment approaches

Research and insights into the mechanisms and healing of muscle contusions are well-documented and exhaustive. A caveat to this is that most of our understanding and knowledge is from in vivo animal models, which may not always necessarily translate into a human model. In addition, research using animal models is conducted in a highly controlled environment, which differs greatly from a contusion that is sustained under real events (e.g., accidents), which are often far more complicated.

Most muscle contusions are treated with analgesics or non-steroidal anti-inflammatory drugs (NSAIDs) to manage the pain and swelling. And with minimised stress on the injury and rest, patients make a full recovery fairly quickly. The general approach for treating and managing a muscle contusion is known as the RICE protocol:

Rest – to reduce muscle activity of the injured site and ensure that it is protected from any further external injury or stress.

Ice – the use of an ice pack against the injury for approximately 20 minutes several times a day is particularly effective in relieving pain and controlling swelling.

Compression – the use of an appropriately fitted compression bandage is also recommended to keep the muscle in a gentle stretch and resist swelling

Elevation – when possible, elevating the injured area also helps to alleviate swelling, and this is often done concomitantly with applying an ice pack.

The RICE protocol is the first port of call when treating contusion and is usually not kept in place for more than the first 72 hours of treatment. It is recommended that your doctor be sought out if the swelling and pain persist for longer than this timeframe so that any potential complications can be diagnosed and treated as early as possible.

It is important that the injured muscle is not stressed prematurely, and as such, rehabilitation exercises and physical therapy play an important role in regaining muscle strength and function proportionately with the time it takes to heal. Secondary conditions associated with muscle contusions like haematomas, oedemas and myositis ossificans, dependent on their severity, can be relieved or removed with surgical intervention.  

Summary

Muscle contusion is a common injury that occurs due to blunt force trauma. It is rampant in contact sports and comes second only to muscle strain injury.⁷ Characterised by bruising, pain, stiffness and swelling, most muscle contusions are self-healing due to the exceptional regenerative properties of muscle tissue. Treatment options and management comprise the use of analgesics or corticosteroids for pain management and enacting the RICE protocol to facilitate the natural healing process. Secondary injuries like haematomas can cause complications to the innate healing process, and therefore, early diagnosis and assessment of injury severity is important to prevent the need for surgical interventions.