Hemarthrosis implies bleeding into the joint space and may occur in a variety of conditions, but presence of hemophilia and trauma are the most most common causes. Pain and significant disability are clinical hallmarks and the diagnosis is made through MRI studies and joint aspiration. The therapeutic approach depends on the underlying cause, but either open surgery or arthroscopy are performed in most cases.
The clinical presentation of hemarthrosis is characterized by an acute and sudden onset of joint swelling and pain, regardless of the cause. Pain is often excruciating and renders patents unable to move the affected joint, leading to atrophy of the proximal muscles and significant disability . Joints that are most frequently involved are the ankles, knees and elbows, but virtually any joint may be affected .
A detailed patient history that includes information regarding recent trauma may be vital in determining the cause of joint injury. If spontaneous development of joint swelling and pain is seen in the pediatric population, a strong suspicion toward genetic coagulopathies should be made . A thorough physical examination is equally important in assessing the exact site of pain and can guide the physician to the diagnosis. MRI is considered as a first-line imaging study that can determine the extent of joint involvement and associated factors that may have provoked pooling of blood in the joint space . Plain radiography may also be a useful method in determining the presence of bone fractures and is often performed first due to its accessibility and low cost compared to MRI. In addition to imaging studies, a full coagulation panel should be drawn, in order to exclude coagulopathies as an underlying cause . To make a definite diagnosis, however, aspiration of synovial fluid is necessary. If blood is seen in the joint aspirate, hemarthrosis is confirmed. The presence of lipid particles in the fluid are highly suggestive of fracture, since bone marrow fat leaks into the synovial space.
Treatment principles comprise symptomatic measures to reduce pain and swelling, evacuation of blood from the synovial space and management of the underlying cause, if possible. Rest and cryotherapy are effective initial methods that reduce further swelling, whereas joint aspiration is frequently performed, with a goal to relieve joint pressure . If the diagnosis of hemophilia is made (or if it is already known), immediate administration of deficient factors (either VIII or IX) is necessary in order to prevent further bleeding . Although non-steroidal anti-inflammatory drugs (NSAIDs) are readily administered for analgesia, their use should be reconsidered, as they may further increase the risk of bleeding . Athroscopic surgery, however, is considered as a gold standard of managing hemarthrosis, but open synovectomy is frequently performed as well   . Guidelines for management of hemarthrosis are not solidified, leaving the choice of treatment to the physician. It is stated that the surgical approach depends on the age of the patient, severity of disability, as well as presence of additional lesions that may provide as an additional challenge for therapy. Open synovectomy is associated with a risk of post-operative reduced range of motion, which is why radiosynovectomy (using radioactive isotopes such as yttrium or phosphorus) has been recently introduced  . As a last resort, total joint replacement may be performed in patients with severe destruction .
The prognosis of patients who develop hemarthrosis depends on the time of diagnosis and severity of injury to adjacent structures, as disability created by swelling and pain may be permanent. If untreated, chronic hemophilic synovitis may lead to significant impairment of the quality of life, which is why an early diagnosis is detrimental in achieving better long-term outcomes.
Causes and factors that induce joint bleeding are the following  :
Exact rates of hemarthosis in the population are unknown. In patients with severe forms of hemophilia, isolated reports indicate that almost 50% develop hemarthrosis . In terms of risk factors, joint trauma and accompanying structural injury is considered to be the most prominent. Namely, hemarthrosis is observed in almost half of all individuals who develop ACL tears and a slight, but significant gender predilection toward males has also been noted in certain studies . Apart from long-term anticoagulant therapy, additional risk factors have not been established.
Depending on the underlying cause, different pathophysiological mechanisms may be observed. In the setting of trauma, blood vessel damage leads to extravasation of blood into the articular space. For example, the middle genicular artery that branches from the femoral artery supplies the anterior and posterior cruciate ligaments in the knee and both lateral and medial menisci, In the setting of trauma, this vessel is the principle source of blood in knee hemarthrosis. On the other hand, pathological features seen in hemophilia are more complex. Fragility of vessels that stems from insufficient capacity for coagulation results in a chronic tendency for bleeding . Once blood is introduced into the articular space, oxygen-mediated injury to chondrocytes and their apoptosis leads to damage of the cartilaginous structures and consequent degeneration . Hemodsiderin-induced synovial damage is another pathophysiological process that runs parallel with oxygen-induced injury . In severe forms, fibrosis and destruction of the joint may ensue , and the term hemophilic synovitis represents a severe form of hemarthrosis that is seen in hemophilic patients .
Because hemarthrosis is seen in almost 50% of patients with hemophilia, adequate treatment and long-term follow-up of patients could be considered as an adequate preventive strategy. Additionally, regular screening of patients who receive anticoagulation therapy may be beneficial in reducing the incidence of bleeding and hemarthrosis .
Intraarticular bleeding (known as hemarthrosis) can develop in the setting of mechanical, functional and iatrogenic disorders. Various forms of trauma and diseases that alter normal coagulation, such as hemophilia and several other coagulation factor deficiencies are the two most important causes of hemarthosis . Additionally, joint bleeding has been reported in patients receiving fibrinolytic and anticoagulation therapy  , whereas post-operative development of hemarthosis after arthroplasty has been documented as well . The pathogenesis of hemarthosis varies depending on the underlying etiology. In patients with hemophilia, fragility of blood vessels and profuse bleeding into the joints eventually leads to synovitis . In fact, the term hemophilic arthropathy is often used to describe these changes, since it is considered to be one of the most common causes of morbidity in these patients . On the other hand, blood vessels and surrounding structures that are well-nourished, for ex. the anterior and posterior cruciate ligaments in the knee (ACL and PCL, respectively) can be damaged by contusion, fractures and joint dislocations, leading to vessel rupture and subsequent bleeding into the articular space . Recent history of trauma may be, in fact, the most important information when patients present with sudden onset of joint pain, which is usually the most prominent symptom. Pain may lead to significant disability, muscle atrophy and often limits the amount of physical activity . The knee, elbow, or ankle joint is most commonly affected , and the number of joints involved is also an important diagnostic sign. If these symptoms appear and recur in childhood, then the diagnosis shifts from trauma to genetic disorders of coagulation such as hemophilia . The initial diagnosis of hemarthrosis can be made through the use of imaging studies. Plain radiography may be performed first, but magnetic resonance imaging (MRI) is recommended in the evaluation of joint symptomatology . Joint aspiration and subsequent observation of blood in the synovial fluid confirms the diagnosis. Arthroscopy may be used in diagnostic purposes, as it provides a direct view into the affected joint, but it is also the recommended surgical method of choice . A standardized treatment protocol, however, is still not formed . Because hemarthrosis is often recurrent, open synovectomy is shown to be curative for many patients , but a risk of reduced range of motion exists when implementing this surgical method, which is why arthroscopy is favored. With appropriate therapy, the prognosis is good, but if the diagnosis is not made on time, significant damage to the joint may lead to severe arthropathy that can cause marked disability. Prophylaxis and appropriate management of disorders that interfere with coagulation is considered as one of the most important preventive strategies  .
Bleeding into the joint is medically termed hemarthrosis and can appear under various circumstances. Hemophilia is a genetic disease in which deficiency of some of the molecules that are involved in the process of coagulation occurs, leading to fragility of blood vessels and increased risk of bleeding. In fact, hemarthrosis is considered to be the most common clinical manifestation of this disorder. Trauma is an equally important cause of hemarthrosis, as injury of the joint structures (ligaments, tendons, bones and blood vessels) can cause blood leakage into the joint space. Joint surgery and use of anticoagulant drugs have also shown to be important risk factors. Any joint in the body can be affected, but the knees, ankles or elbows are targeted in most cases and depending on the underlying cause, one or more joints may be involved. The main symptom is pain that is severe or even excruciating and is accompanied with swelling and tenderness. Range of motion is significantly reduced and disability that impairs the quality of life is reported in many patients. A presumptive diagnosis can be made based on information obtained from a detailed patient history that may discover recent trauma or presence of diseases that alter normal blood coagulation, together with a careful physical examination. To confirm joint injury and intraarticular bleeding, magnetic resonance imaging (MRI) is recommended. Plain X-rays of the affected joint may be initially performed and can identify fractures that can turn out to be the underlying cause of bleeding. Aspiration of accumulated joint fluid that shows the presence of blood, however, is a definite diagnostic method. It is recommended to obtain a full coagulation panel in patients with hemarthrosis in order to exclude hemophilia and other coagulopathies (factor XIII deficiency, etc.). Initial management of patients includes rest, joint cooling by cryotherapy and rehabilitation, while pain management is a challenge, since non-steroidal anti-inflammatory drugs (NSAIDs) should not be used due to a risk for further bleeding, especially in the gastrointestinal tract. Surgery is the definite form of therapy and depending on patient age, degree of disability and additional findings, either arthroscopic or open surgery may be instated. The use of radioactive isotopes in treating joint disease (radiosynovectomy) has been recently introduced, whereas total joint replacement may be indicated for patients in whom severe destruction occurs. Joint damage in the setting of hemarthrosis can be significantly reduced through an early diagnosis, which is why this condition should be thought of in patients who experienced some form of trauma and developed sudden joint pain and swelling. A high index of suspicion is even more important in patients who are suffering from hemophilia, because severe degenerative arthritis (known as hemophilic arthropathy) may develop as a result of prolonged joint damage.