Abstract and Introduction
Abstract
Orthopaedic surgeons frequently use aspirations and injections to both diagnose and treat disorders of the lower extremity. Comprehensive knowledge of regional anatomy, procedural indications, and appropriate techniques are essential. Clinicians must be well versed in a range of musculoskeletal aspiration and injection techniques, including patient positioning, equipment needs, injectable solutions, aspirate analysis, and potential complications. Safe and effective aspiration and injection techniques for the lower extremity, including the hip, knee, foot, and ankle, are reviewed. Image guidance modalities include fluoroscopy, ultrasonography, CT, and MRI.
Introduction
Intra-articular and soft-tissue aspirations and injections are common procedures used by orthopaedic surgeons and other providers to assist in the diagnosis and management of lower extremity injuries and disorders. Successful outcomes rely on the clinician's knowledge of pertinent local anatomy, appropriate indications, and awareness of evidence-based techniques that optimize accuracy and outcomes.
Arthrocentesis, or aspiration of synovial joint fluid, is indicated primarily for diagnostic purposes in the setting of acute synovitis, suspected infection, and chronic arthropathy. Repeated aspiration may be used in certain settings, such as with chronic, noninfectious effusions. Aspiration should always be performed before injection when clinical suspicion for septic arthritis exists. Aspirated synovial fluid should be analyzed for cell count with differential, Gram stain, microbiologic culture, and the presence of crystals.[1] A preexisting diagnosis of rheumatoid arthritis, gout, or pseudogout does not exclude the possibility of concomitant infection.[2] Therapeutic aspiration may be indicated in the setting of noninfectious effusions that limit range of motion or cause substantial pain. Such aspiration also may be indicated to drain a hemarthrosis or to drain a septic joint in patients with medical comorbidities that preclude surgical irrigation and drainage.
Joint or soft-tissue injections may be helpful for both the diagnosis and treatment of several musculoskeletal conditions. Injections are frequently used for targeted delivery of medication into joints, bursa, and tendon sheaths. Important contraindications exist. Injection and aspiration through cellulitic-appearing skin should be avoided when possible to minimize bacterial dissemination into the adjacent soft tissues or joint space.[3] In addition, corticosteroids should not be injected into a joint until infection has been excluded. Injections in patients on anticoagulation or with a known coagulation disorder (ie, a relative contraindication) may be considered; however, a small-gauge needle should be used along with the application of appropriate manual pressure after the procedure. Furthermore, safe aspiration or injection can be performed on fully anticoagulated patients by using lidocaine with epinephrine as a local anesthetic. Complications are rare, and when they occur, they are often minor in severity (Table 1).
Sterile technique is critical to avoid infection and ensure accurate fluid analysis. At minimum, the injection site should be prepared with an alcohol- or iodine-based skin preparation solution. A sterile drape may also be used at the discretion of the clinician. If ultrasonography (US) guidance is performed, a sterile probe cover should be used, followed by cleaning the probe with antiseptic wipes after each injection and before use on subsequent patients. Sterile gloves should be worn by the clinician for all injections, including both palpation and image guided. The patient position varies by the intended target (Table 2). The needle gauge depends on the joint; large joints such as the knee may necessitate use of an 18- to 21-gauge needle, particularly if aspiration is planned, whereas smaller joints may be entered with a 20- to 25-gauge needle (Table 2). A spinal needle is often used with hips and deep shoulders. The syringe size varies based on the joint and effusion size, if present (range, 5 to 50 mL).
For certain injections, a growing body of evidence has demonstrated that image guidance may enhance accuracy and outcomes.[4–11] Multiple modalities are available, including fluoroscopy, US, CT, and MRI. Fluoroscopy with the use of intra-articular contrast has traditionally been used for therapeutic injections and aspirations of deep joints, such as the hip. With this technique, a small amount of iodinated contrast may be administered to confirm an intra-articular position of the needle. For the purposes of this review, the use of US will be emphasized, given its growing utility to provide image guidance in an office setting. US uses high-frequency sound waves to image soft tissues and bony structures and, because of advances in resolution capabilities, can, in most circumstances, detail tendons, nerves, ligaments, joint capsules, and muscles.[12] Practitioners may perform both static and dynamic US imaging, depending on the clinical indication. Static US involves precise localization of structures, with the underlying tissue in a relaxed position, whereas dynamic US is performed during provocative testing and/or with the assistance of the patient moving a joint or contracting a muscle (eg, to evaluate tendon subluxation).[12] The advantages of US over other imaging modalities include the absence of radiation and the ability to provide real-time guidance for interventional procedures in the office setting.[12]
In patients with obesity, the soft-tissue envelope may be larger, especially with more central joints such as the hip. Targeted structures may, therefore, be deeper and anatomic landmarks less distinct, posing a challenge with regard to accurate needle placement. In our experience, the following measures are helpful in patients with obesity. First, a longer 3.5-inch spinal needle should be considered. Second, the provider should have a lower threshold for the use of image guidance. US imaging may be optimized with use of a lower frequency, curvilinear probe as well as optimizing the focal zone to target deeper structures. If image quality remains poor after US optimization, fluoroscopy or CT guidance should be considered as an alternative. Finally, immediate pain relief with the use of a local anesthetic in the injection solution may help confirm the accuracy of needle placement.
J Am Acad Orthop Surg. 2018;26(15):e313-e320. © 2018 American Academy of Orthopaedic Surgeons
