Subchondral Perfusion Mapping Using Indocyanin Green Laser

ICG has been FDA registered since 1959 and is a negatively charged, water-soluble, tricarbocyanine. It binds readily to plasma proteins after injection with almost exclusive bile excretion, and possesses an extremely low toxicity profile. In plasma, ICG has an absorption peak around 807 nm and an emission peak around 822 nm, both within the infrared range. ICG has a short half-life of 150-180 seconds, making multiple administrations possible intra-operatively. It is given intravenously during administration1-4. After it is given through an IV, it is rapidly distributed throughout the circulatory system. When a light of a specific wavelength interacts with the dye, the dye fluoresces in the near-infrared range, which can be acquired by a special camera.

In daily practice, both visualization and palpation are used to provide information about the health of articular cartilage, be it through arthroscopy or open treatment. However, real time assessment of cartilage viability and subchondral perfusion has not been available. Determination of the perfusion status of cartilage surfaces via intra-operative modalities may provide valuable information diagnostically, as well as guide therapeutic intervention. Some possible uses for this technology may be diagnosing and treating osteochondral defects, predicting future osteoarthritis, delineating or predicting areas of avascular necrosis, or use in oncologic surgery. It is currently thought that because this dye currently works extremely well in the soft tissue literature, this will directly translate to being able to accurately assess subchondral bone perfusion.

The incidence of symptomatic knee arthritis in the United States approaches 50% of the population by the time the patient turns 85 and has been shown to significantly impact a patient's quality of life. In 2003, the United States spent $128 billion on arthritis expenditures. Arthritis can be described as the degeneration, or absence of, healthy cartilage. The current way to intra-operatively assess cartilage viability is through inspection and palpation, although this is obviously not always indicative of the overall health of the cartilage. Although an MRI may be obtained pre-operatively showing similar information, this is costly and does not provide the same information that can be assessed intra-operatively. Furthermore, an MRI does not provide information on the perfusion status of the cartilage.

It is our belief that this imaging modality will provide valuable information diagnostically and be able to guide surgical decision making regarding treatments for patients. For example, prior to undergoing a unicompartmental knee replacement, if a patient is found to have degenerative changes of the other compartments, the surgeon may convert to a total knee arthroplasty. If a patient has an osteochondral defect, knowing the perfusion status may provide information on whether to reconstruct the defect with an allograft or drill the defect. A patient undergoing a cruciate retaining total knee arthroplasty may benefit from knowing if the posterior cruciate ligament is pathologic, leading to a posterior stabilized knee replacement. For a patient with avascular necrosis, valuable prognostic information on the viability of their cartilage may help determine if joint preserving surgery is possible. The use of intra-operative ICG may have an impact on intra-operative decision making as the perfusion observed may predict the overall health of structures we currently have no way of assessing in real-time.