Tendons are impressively strong structures that link muscles to bone. They function to transmit the force of muscular contraction to a bone, thereby moving a joint or helping to immobilize a body part. Their microscopic organization is thoroughly described elsewhere.
The organizational unit in a tendon is the collagen fibril, which collectively forms fascicles, which as a group compose the tendon itself. Some tendons, especially long ones, are guided and lubricated along their paths by sheaths ( Fig. 12-1 ) (e.g., biceps brachii, ( Fig. 12-2 ) extensor pollicis brevis, and abductor pollicis longus).
A prototypical muscle consists of the muscle belly centrally, two musculotendinous junctions, and tendinous insertions into bone at the points of anatomic origin and insertion. Some muscles, such as the extensor carpi radialis longus and brevis at the elbow, attach directly into bone ( Figs. 12-3 ), an arrangement that may be more susceptible to injury.
Much is known about a tendon’s response to laceration and operative repair, although this clinical situation is not frequently encountered. Less is understood about the more common and clinically relevant overuse tendinitis. A tendon and its sheath (if present) will undergo a typical inflammatory response to acute or chronic overuse injury, followed by a regenerative repair process. The distinction between an overload type of acute injury and a chronic overuse mechanism will aid in successful rehabilitation of tendinitis.
Cortisone and its derivatives are known to reduce or prevent inflammation. Numerous corticosteroid preparations are available for local injection (see Chapter 2 on medications). The injectable corticosteroids are suspensions of insoluble particles, and therefore, the antiinflammatory effect is profound only where the material is deposited. The ability of corticosteroids to control inflammation makes them a valuable adjunct in treating tendon injuries because they do not alter the underlying process that leads to inflammation.
As with many other physical medicine treatment modalities, well-designed scientific studies regarding the usefulness of corticosteroid injections are rare. These injections should be considered when, in the practitioner’s judgment, the recognized antiinflammatory effect of local corticosteroid placement may be beneficial for the conditions of tendinitis, enthesitis, or tenosynovitis, and no harm will likely result.
McWhorter and colleagues injected hydrocortisone acetate into rat Achilles peritenons that had been previously injured. There were no deleterious effects of one, three, or even five injections, measured biomechanically (tension to failure) or histologically (light microscopy), compared to controls. This finding should reassure physicians that they are not doing harm with properly placed steroid injections. A 30-year literature review identified eight prospective, placebo-controlled studies of steroid injection treatment for sports-related tendinitis. Three of the studies showed beneficial effects of injections at clinical follow-up. A meta-analysis of properly designed investigations of steroid injection for Achilles tendinitis found no beneficial effects, although very few studies qualified as rigorous. Adverse side effects occurred with a 1% incidence. No “proof” of the usefulness or uselessness of this treatment modality exists.
Contraindications, Complications, and Side Effects
The lack of a specific diagnosis is the single largest contraindication to a local corticosteroid injection. If the diagnosis is clear and the antiinflammatory effect of a corticosteroid may facilitate the rehabilitation process, injection can be considered.
Repeated injections to the same area must be avoided, particularly into joints. Alterations in articular cartilage have been documented with repeated administration, possibly resulting in joint damage and weakened ligaments. A widely recognized complication of steroid injection is tendon rupture, a negative outcome that appears to be decreasing in frequency because it is now well understood. Achilles and other tendon ruptures have been reported, and deposition of injected material directly into any tendon substance is contraindicated. One report links the effect of repeated steroid injections to rupture of the plantar fascia.
Some experimental findings have suggested that corticosteroid administration led to smaller, weaker tendons as a side effect. A more common side effect is subcutaneous atrophy, especially at the knee and lateral elbow and more frequently with the use of triamcinolone. Theoretically, atrophy of the specialized fat pads of the heel following steroid injection for plantar fasciitis may lead to a significant disability in an athlete, due to the loss of cushioning effect.
Alternatives to Corticosteroids
In recent years alternatives to corticosteroids have emerged for the treatment of chronic localized musculotendinous pain. These treatments include percutaneous tenotomies and platelet rich plasma (PRP) injections.
Percutaneous tenotomies have been described for treatment of chronic lateral epicondylitis and plantar fasciitis. These injections are performed with large bore needles (18 or 20 gauge) under ultrasound guidance. The needle tip is used to repeatedly fenestrate the affected tissue under local anesthetic. The bony surface (i.e., epicondyle) can be abraded and calcifications may be fragmented. This technique is thought to be a safe and effective alternative to corticosteroid injections.
Platelet rich plasma injections use concentrated platelets from autologous blood to stimulate a healing response in damaged tissue. Blood is drawn from the patient and placed in a centrifuge. The concentrated platelets are removed and reinjected directly into the patient’s abnormal musculotendinous tissue or ligament usually under ultrasound guidance. These concentrated platelets produce growth factors that include platelet derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta (TGF-β). These compounds are instrumental in attracting cells that promote healing by stimulating neovascularization and cellular reproduction. The efficacy of PRP injections and appropriate clinical indications (when and where it should be used) are currently being researched and yet to be definitively determined. Initial results of clinical studies appear promising.
Methods of Injection
Tendon and tendon sheath injections are office procedures, typically performed under clean or sterile conditions. The corticosteroid of choice is often combined with a local anesthetic, the latter helping to confirm the proper location of the deposited material. Diagnostic ultrasound has been advocated to guide injections near the heel when guidance by palpation alone fails.
Immobilization of the treated structure usually is not needed following injection, although vigorous use of weight-bearing tendons (Achilles, patellar) should be avoided for 48 hours. Ice application may help when the local anesthesia fades, along with other physical medicine modalities as indicated by the particular condition present, usually starting after 48 hours.
If an initial corticosteroid injection proves useful, one or two repeat injections separated by a few weeks or more may be considered. Numerous injections over time should not be considered the sole or primary treatment.
Corticosteroid or local anesthetic injections should not be used routinely to arrive at diagnoses pertinent to the musculoskeletal system. The range of physical examination techniques used by the physician is described elsewhere and, in most cases, will suffice at pinpointing the specific cause of pain. The distinction between the conditions of subacromial bursitis and rotator cuff tendinitis can be clarified with injection, but even in this case the physical examination and subsequent rehabilitation program deservedly receive most of the attention.
In most instances, the literature supports an adjunctive, not primary, role for injections in the treatment of tendon and tendon sheath injuries. When the doctor and patient decide to proceed with injection, the control of inflammation that is obtained should be used to facilitate the prescribed rehabilitation program, rather than being the only treatment. The area of exception to this generalization is the wrist and hand (to be discussed in detail later).
Upper Extremity Injections
The literature supports the use of corticosteroid injections as a primary treatment for stenosing flexor tenosynovitis in the hand, known as trigger thumb or trigger digit. In this setting, injection has been shown to be as effective as operative release of the tendon sheath and to have fewer complications. Injection has been employed successfully into the hands of patients with diabetes mellitus and trigger digit, but the success rate may be reduced. Instillation of the material directly into the tendon sheath has no apparent benefit over subcutaneous placement. Multiple pulley rupture and flexor digitorum profundus and superficialis tendon rupture has been reported as a complication from this injection. As with other soft tissue injections, a physician treating trigger finger with instillation of corticosteroid needs to maintain expertise by performing this procedure at least several times yearly.
Stenosing tenosynovitis of the first dorsal wrist compartment also is known as de Quervain syndrome. This compartment typically transmits the tendons of both the abductor pollicis longus (APL) and extensor pollicis brevis (EPB). However, anatomic studies have demonstrated that multiple APL slips are common, as are two subcompartments. Interestingly, although one or more injections are usually successful in treating de Quervain syndrome nonoperatively, patients requiring subsequent operative release have been found to have two subcompartments in greater than expected frequency. Trigger digit and de Quervain syndrome, therefore, are usually treated successfully nonoperatively, and corticosteroid injection is the primary component of the management ( Fig. 12-4 ).