Shoulder pain originating from the subacromial space has many etiologies, namely, glenohumeral stiffness or looseness, calcium deposits, rotator cuff tendinitis, rotator cuff tendon degeneration, rotator cuff tears, subacromial bursitis, and impingement syndrome. Because of these many etiologies, injection of the subacromial space is a common practice in the orthopaedic surgeon’s office. This well-designed Level-I study was performed to determine the effectiveness of injecting the subacromial bursa.
Previous literature on the subject has demonstrated a success rate of approximately 70% when the surgeon attempts to inject the subacromial space from either an anterior, lateral, or posterior approach1-3. These studies cannot be compared because they involved different approaches, different-length needles, and different patient populations. One study was from Japan1, another was from the Netherlands2, and the third was from the United States3. This paper presents the best data published on the success rate of injecting the subacromial bursa.
What does the paper tell us? What does the paper not tell us? What are some further questions that need to be answered?
First, the paper tells us that, in males, the accuracy of injection is approximately 90%, regardless of whether the injection is performed from an anterior, lateral, or posterior approach. Second, it tells us that, in females, the posterior approach is much less successful than the anterior or lateral approach.
What the paper does not tell us is the clinical efficacy of the intrabursal injection as some of the patients still had improvement even when the injection was extrabursal. We do not know the clinical diagnosis for the patients, so the three groups may not have had similar pathology, making the data on pain reduction questionable. The paper also does not tell us if the anatomic variability of the acromion really had an effect on the success rate of the injection route as the determination of the type of acromion and the slope of the acromion have been shown not to be accurate on radiographic analysis. The paper also does not give us details on the anatomy of the subacromial bursa and whether it is different in males and females. We know, from arthroscopic evaluation of the subacromial bursa, that there is a posterior veil, which limits the subacromial space primarily to the anterior two-thirds of the acromion both in men and women4.
What are the questions that need to be answered? The authors used a 5-cm, 21-gauge needle in this study. In most orthopaedic offices, only 1.5-in (approximately 3.8-cm) needles or spinal needles that are >3 in (>7.6 cm) long are available. Would the results have been the same if the authors had used a 1.5-in (3.8-cm) needle? Why are female patients less likely to have a successful injection from a posterior approach in the subacromial space? Do they have a smaller bursa? Perhaps the accuracy of the injection is really due to the body mass index (BMI). The authors concluded that the BMI did not influence the accuracy of the injection, but they did not provide data on BMI for the different sexes. As we know, heavy patients are not built the same. Some have more adipose tissue on the torso, which is more common in males, and some have more adipose tissue on the proximal extremities, which is more common in females. While the BMI may be the same, the difficulty of palpating the anatomy in a larger female may have led to the inaccuracy of injecting the subacromial bursa from a posterior approach.
In my opinion and based on the findings of the study, I think that using a conventional-length needle from an anterior or lateral approach would be the most successful technique for entering the subacromial bursa. The authors should be congratulated on this excellent Level-I study.