Injection Tests

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The injection of a short-acting local anesthetic provides an excellent litmus test of one's clinical examination. The presumption is that if a local anesthetic is specifically placed in an area causing pain, that pain will be temporarily and nearly completely relieved. As important, the converse is true, making injection tests sensitive and specific. Performing a successful injection test has several important principles including the accurate placement of the anesthetic, time for this to take effect, re-examination for the elimination of the various provocative maneuvers, and subjective assessment of the patient's relief.

Accurate placement of the anesthetic takes time and experience to achieve consistency. One study has shown that attempts

Figure 16-21 A and B, Scapular stabilization test.

Figure 16-21 A and B, Scapular stabilization test.

at subacromial injection can be unsuccessful in 17% of shoulders, and attempts at AC injections can be unsuccessful 33% of the time.33 Therefore, meticulous attention must be paid to technique. A second pitfall to the successful employment of the injection test is a failure to give the anesthetic time to take effect. With today's emphasis on the 10-minute office visit, the importance of providing this time is often put aside, and the outcome of the injection test is postponed for a future visit. Asking the patient to recall the immediate response to the injection several weeks after the fact may be inaccurate and misleading. Finally, accuracy of interpretation of the injection test demands that the patient be re-examined during the same office visit. Particular diagnostic maneuvers that were specific to the patient's symptoms are repeated. The patient is asked what percentage of the symptoms were relieved by the injection, and the agreed-on level is recorded in the note. In our experience, 80% to 100% relief should be obtained by the injection test. If significantly less relief is gained, the examiner should reconsider the diagnosis and consider an additional injection.

Subacromial Injection

We normally perform this injection from the back using the posterior lateral angle of the acromion as a landmark, although an anterior approach was originally described by Neer (Fig. 1622). The area is prepped sterilely, and 5 mL of 1% lidocaine and 5 mL of 0.25% Marcaine are placed in the subacromial space by advancing the needle directly under the acromion anteriorly and slightly medially. Care must be taken in the exceptionally large individual that the needle be long enough to reach the anterior one third of the subacromial area since the pathology exists anteriorly. Alternatively, lateral and anterior injections can be placed in the subacromial space. Once an adequate amount of time has passed (usually 5 minutes), re-examination of the patient is performed. We inquire about any resting relief that the patient experiences with the injection. Next, we ask the patient to move the arm into positions that caused pain before the injection to see whether he or she obtained relief. This generally includes reassessment of Neer and Hawkins signs and painful abduction arc tests, as well as palpation over the greater tuberosity (Codman's point). The patient is asked to grade the relief as less than 25%, 25% to 75%, or greater than 75% relief. Rotator cuff strength testing is also repeated. Weakness in these tests when there is no pain is highly suggestive of rotator cuff tear and is often met with a more aggressive treatment plan.

Figure 16-23 Acromioclavicular joint injection. Acromioclavicular Joint Injection

Injection of the AC joint is performed by palpating the end of the clavicle, prepping the area sterilely, and attempting to inject 3 mL lidocaine into the joint (Fig. 16-23). This can be a tricky joint to inject because there may be considerable degenerative spurring or an abnormal angle of entry. Plain radiographs of the area will help direct the angle of injection. In addition, if in the joint, one should be able to perform a "refill test." This is done by allowing the increased intra-articular pressure created by the injection to refill the syringe when pressure is taken away from the piston. This test is positive whenever a closed space is entered and distended and is a routine part of any closed-space injection that we perform. The AC joint is variable in its volume, and enough local anesthetic should be used to meet firm resistance with a 20-gauge needle. This injection test is among the most dramatic in the office when positive and, when steroid is added, often provides dramatic lasting relief.

Biceps Tendon Sheath Injection

As previously mentioned, the biceps tendon is very difficult to feel in all but the thinnest individuals. However, the position of the tendon and its groove have been shown to be reproducibly located directly anterior on the shoulder, 2 cm distal to the anterolateral corner of the acromion, when the arm is held in 10 degrees of internal rotation.20 Injection is accomplished by sterilely prepping the area, and placing a 20-gauge needle down to bone, then drawing back until resistance is released (Fig. 1624). This step is important as it is not desirable to inject directly

Figure 16-22 Subacromial injection.

Figure 16-24 Biceps tendon sheath injection.

into the tendon, and the release of tension during injection should signify the needle moving out of the tendon and into the surrounding area. We have seen several tendons rupture after this injection, and although this is of concern if the patient has not given consent properly, it often provides lasting relief.

Suprascapular Nerve Injection

This is a rarely used injection because it serves to diagnose a very rare condition—a suprascapular nerve compression that presents as pain. Although primarily a motor supplier, the suprascapular nerve does contain sensory and pain fibers that go to the sub-acromial bursa. Thus, in a patient who presents with posterior shoulder pain or what seems like subacromial pain that does not respond to subacromial injection and one has ruled out other causes, consideration may be given to compression of the supra-scapular nerve as the source of the pain.29 The diagnostic injection to confirm this is performed by palpation of the AC joint and injecting 5 mL of 1% lidocaine beginning at a point just posterior to this joint with the needle directed 2 cm medially and 2 cm inferiorly. Weakness of the spinatii confirms infiltration of the nerve, and temporary resolution of symptoms confirms the diagnosis of entrapment.

Intra-articular Glenohumeral Joint Injection

This injection can be very effective in isolating the source of pain to an intra-articular location. Internal impingement, SLAP and other labral tears, and chondral lesions will all show relief with an intra-articular injection. This injection can be difficult for the inexperienced clinician because the joint is deep and the injection is uncomfortable for the patient. We stress the importance of intra-articular placement of the local anesthetic by injecting 10 to 20 mL of fluid into the joint and allowing the refill test to confirm this placement.

We approach this injection anteriorly. The coracoid process and the anterolateral corner of the acromion are identified and sterilely prepped. With the forearm in neutral rotation, a point halfway between the coracoid and the acromion is identified and infiltrated with 5 mL lidocaine in the skin along the path of the needle. An 18-gauge needle is then introduced and directed posteriorly perpendicular to the plane of the body. If a bony stop is encountered, it is likely the humeral head and the arm is internally rotated allowing the needle to "fall" into the glenohumeral joint. This technique is the same as that used to establish an anterior portal for shoulder arthroscopy and has been demonstrated to be the most accurate method for entering the gleno-humeral joint without fluoroscopic assistance.

The glenohumeral joint may also be injected from a posterior approach, although this has demonstrated far less accuracy when compared to an anterior approach. The posterolateral corner of the acromion is identified and sterilely prepped. Next, a point 2 cm inferior and 1 cm medial to this point is identified and infiltrated with 5 mL lidocaine in the skin and along the path of the needle. An 18-gauge spinal needle is then introduced and directed anteriorly, aiming for the coracoid process. Often, the needle will hit a bony stop, and it must be determined whether this is the humerus or the glenoid. This can be determined by rotating the arm slightly internally and externally. If the needle moves with this rotation, the path must be redirected more medially to avoid the humerus. If it does not, it signifies that the needle is in the glenoid and must be directed more laterally. This is the same technique that we use to establish a posterior portal for shoulder arthroscopy.

Our choice of an 18-gauge needle is important for several reasons. First, a smaller gauge needle may not be stout enough to maintain its shape as it traverses through the posterior muscle mass and can be bent along its course. Second, an 18-gauge needle is large enough that once in the joint, intra-articular dis-tention will provide enough pressure to refill the syringe, where a smaller gauge needle often will provide too much resistance to do this. Because the intra-articular placement of the needle is so critical, its position must be confirmed by this maneuver. Again it is critical to allow time for the local anesthetic to set up in the shoulder and then to re-examine the patient, especially those maneuvers that reproduced the patient's symptoms prior to the injection. If those provocative tests have been eliminated by the injection, one can be quite confident that the source of the pain is intra-articular. Given the high incidence of so-called pathologic findings on MRI of asymptomatic individuals, such injections can differentiate between variations of anatomy and symptomatic pathology. Such differentiation is the key to the clinical evaluation.

It must be remembered that if an abnormal connection exists between two distinct anatomic spaces, an injection in one may relieve pain in another, leading to confusion in the interpretation of the injection test. An example of this is in the patient with a full-thickness rotator cuff tear who receives a subacro-mial injection. The tear will allow infiltration not only in the sub-acromial space, but also in the shoulder joint proper. Thus, it is incumbent on the examiner to interpret the result of an injection in light of these possibilities.

Subscapular Injection

In patients who present with posterior scapular pain with or without an associated "snapping scapula" (see "Chief Complaint: Noise"), subscapular bursitis may be considered. This condition may produce impressive popping and may have associated pain. Five milliliters of 1% lidocaine can be directed into the more common superomedial or less common inferior angle bursa. This is done by palpating the medial border of the scapula and inserting the needle 1 cm medial to this. The goal is to hit the most anterior portion of the scapula and slide just anterior to this for medication infiltration. Care should be taken not to direct the needle too anteriorly, as penetration of the thoracic cavity is an undesired consequence. The patient should wait several minutes and attempt to reproduce the pain and noise from the shoulder. Relief of pain helps to confirm a subscapular source.

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