Anatomical Structures Commonly Injected
The target matters. The same medication may have a different purpose and risk profile depending on whether it is placed in a joint, bursa, tendon sheath, or soft-tissue plane.
Joints
Joints are injected when pain arises from arthritis, synovitis, crystal disease, inflammatory disease, effusion, or other intra-articular pathology.
Commonly injected joints include the knee, hip, glenohumeral shoulder joint, acromioclavicular joint, elbow, wrist, thumb carpometacarpal joint, small hand joints, ankle, subtalar joint, midfoot joints, and first metatarsophalangeal joint.
Common diagnoses include osteoarthritis, inflammatory arthritis flares, post-traumatic arthritis, synovitis, crystal arthritis such as gout or pseudogout after infection has been excluded, adhesive capsulitis of the shoulder, painful effusion, and diagnostic evaluation of intra-articular pain.
Bursae
A bursa is a small fluid-filled structure that reduces friction between tendons, muscles, and bone. Bursae may become inflamed from overload, trauma, tendon disease, arthritis, or repetitive irritation.
Commonly injected bursae include the subacromial-subdeltoid bursa, greater trochanteric bursa or peritrochanteric space, pes anserine bursa, iliopsoas bursa, and selected superficial bursae such as the olecranon or prepatellar bursa. Superficial bursa injections require caution because of skin and infection concerns. Retrocalcaneal bursa injections also require caution because of the nearby Achilles tendon.
Tendons and tendon sheaths
Tendon injections require precision. Corticosteroid should generally not be injected directly into tendon substance because of potential tendon weakening. Depending on the diagnosis, the injection is usually placed around the tendon or into a tendon sheath.
Common targets include the long head of biceps tendon sheath, flexor tendon sheath in trigger finger, De Quervain's first dorsal extensor compartment, peroneal tendon sheath, posterior tibial tendon sheath, flexor hallucis longus tendon sheath, wrist extensor tendon compartments, common extensor or flexor origin at the elbow, patellar tendon region, Achilles tendon region, and plantar fascia origin.
Entheses
An enthesis is the site where a tendon, ligament, or fascia attaches to bone. Enthesis-related pain may occur with chronic tendinopathy, enthesopathy, calcific tendinopathy, plantar fasciitis, or greater trochanteric pain syndrome related to gluteal tendinopathy.
Common regions include the lateral epicondyle, medial epicondyle, greater trochanter gluteal tendon insertion region, patellar tendon origin or insertion region, Achilles insertion, and plantar fascia origin.
Ligaments, capsules, and periarticular soft tissues
Most ligament injuries are not treated primarily with injection. In selected situations, injections may be considered around capsular or ligamentous regions, such as the shoulder capsule in adhesive capsulitis or the acromioclavicular joint capsule.
Periarticular soft tissues may also be injected when the pain source is outside the joint. Examples include the trochanteric or peritrochanteric region, pes anserine region, iliotibial band friction region, subacromial space, periscapular bursae, and selected peripheral nerve entrapment regions in practices with appropriate expertise.