Periarticular Injections in Knee and Hip Arthroplasty: Where and What to Inject.

BACKGROUND: Periarticular injections have become a valuable adjunct to multimodal pain control regimens after knee and hip arthroplasties. Injection techniques vary greatly among surgeons with little standardization of practice. METHODS: We performed an extensive literature search to determine where nociceptive pain fibers are located in the hip and the knee and also to explore the pharmacology of periarticular cocktail ingredients. RESULTS: Large concentrations of nociceptors are present throughout the various tissues of the knee joint with elevated concentrations in the infrapatellar fat pad, fibrous capsule, ligament insertions, periosteum, subchondral bone, and lateral retinaculum. Less empiric evidence is available on nociceptor locations in the hip joint, but they are known to be located diffusely throughout the hip capsule with elevated concentrations at the labral base and central ligamentum teres. Local anesthetics are the base ingredient in most injection cocktails and function by blocking voltage-gated sodium channels. Liposomal anesthetics may offer longer duration of action over traditional anesthetics. Nonsteroidal anti-inflammatory agents and corticosteroids block peripheral production of inflammatory mediators and may desensitize nociceptors. Opioid receptors are present in lower densities peripherally as compared with the central nervous system, but their inclusion in injections can lead to pain relief. Sympathetic drugs can provide adjunct effects to periarticular cocktails to increase duration of action and effectiveness of medications. CONCLUSION: Targeting specific sites of nociceptors may help to further decrease pain after knee and hip arthroplasties. Altering periarticular cocktail ingredients may aid in multimodal pain control with injections.