Trauma can breach the integrity of the joint capsule and result in infection, long-term arthritis, and other serious potentially permanent morbidity. Any breach of the joint capsule can introduce contaminants and risk septic inoculation of the joint. Synovial joint fluid provides nutrition to the articular cartilage. Loss of this fluid without prompt joint capsule closure can lead to cartilage wasting and arthritis. The injection of joints with methylene blue provides a rapid and definitive way to assess joint capsule integrity in cases of periarticular trauma where the clinical examination is inconclusive.
ANATOMY AND PATHOPHYSIOLOGY
Synovial joints (e.g., the fingers, wrist, shoulder, and knee) consist of a fibrous capsule that overlies a thin and delicate synovial membrane (Figure 98-1). The synovial membrane is a highly vascular structure and the site of synovial fluid production. The synovial fluid provides nutritional support to the relatively avascular articular cartilage. Joint capsules contain varying volumes of fluid that can be greatly expanded under conditions of inflammation or injection.
The anatomy of the knee joint.
Methylene blue is a relatively safe and stable deep blue dye used in both chemistry and medicine. It is frequently used to treat methemoglobinemia and for marking skin and lymphatic tracts for oncologic surgery. The proposed basis for its vasoconstrictive effects is its ability to be readily oxidized.1 Undiluted methylene blue can cause direct tissue necrosis without prior immune sensitization.2
The literature regarding the safety of methylene blue supports its use, even during direct intradermal injection. When used for lymph node mapping by direct intradermal and intraparenchymal injection, there is consistent evidence of local inflammatory reactions ranging from local wheal and flare in 0.5% of patients to focal erythema with induration in 5% of patients.3,4 Superficial tissue toxicity occurred in only 1.25% of patients.4 These reactions were proportional to the concentration of methylene blue ranging from a dilution of 1:1 to 1:7 and the superficiality of the injection.4 Emergency Physicians (EP) need to be aware of the potential complications of methylene blue. The tissue toxic effects are believed to be much less for intraarticular injections than direct intradermal injection.
The primary indication for injecting a joint with methylene blue is to assess the integrity of the articular joint capsule (Figure 98-2). This includes any of the following injuries in proximity to a joint: skin laceration, a visible joint capsule through a wound, an open fracture, extravasation of serous or serosanguineous fluid from a wound, or a traumatic loading of the joint with evidence of a deformity or an acute effusion. The finger, wrist, elbow, shoulder, toe, ankle, knee, and hip joints can all be injected with methylene blue.