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Subscapularis and sub-omohyoid plane blocks: an alternative to peripheral nerve blocks for shoulder analgesia.

Editor—The gold standard for shoulder analgesia is the interscalene block (ISB), but it has its own share of disadvantages. While some potential side-effects from ISB, such as phrenic nerve block, recurrent laryngeal nerve involvement and Horner’s syndrome, may lead to patient discomfort, others, such as neurological injury, intrathecal spread and systemic toxicity of local anaesthetic, can have serious consequences. Although studies of ISB have shown a reduction in the incidence in hemidiaphragmatic paralysis with low-volume ISB, the risk of phrenic paralysis is not completely eliminated. The majority of the shoulder is thought to be supplied by the axillary nerve and the suprascapular nerves, with minor contributions from subscapular and lateral pectoral nerves. The regional anaesthesia alternative techniques to the ISB include suprascapular or combined suprascapular and axillary nerve blocks. Although these blocks offer some analgesic benefits by themselves, the quality of analgesia has been shown to be inferior to the ISB. This difference in analgesic quality is likely to be attributable to the sparing of some of the shoulder innervation, and targeting all of the shoulder innervation may mitigate this problem. It is well known from anatomical studies that the innervation to the shoulder joint usually travels through various intermuscular planes before reaching the shoulder, and these intermuscular planes are easily identified by musculoskeletal ultrasonography. The suprascapular nerve leaves the superior trunk close to the supraclavicular fossa and travels in the posterior triangle of the neck parallel to the inferior belly of the omohyoid muscle to enter the suprascapular notch. The axillary nerve leaves the posterior cord in the infraclavicular fossa and bifurcates into anterior and posterior branches while traversing the subscapularis muscle before winding around the humerus to enter the quandrangular space. The subscapular nerves arising from the posterior cord are also present on the ventral surface of the subscapularis muscle. We describe below the selective targeting of shoulder innervation using intermuscular plane injections, which may be particularly useful in patients at high risk for respiratory morbidity from ISB. It is our practice to perform the subscapularis plane injection (with or without pectoral nerve block (PECS-1) block) before the sub-omohyoid block. The patient is placed in a semirecumbent/ supine position, with the arm adducted and externally rotated. The probe positions for both the sub-omohyoid block and the subscapularis plane block are shown in Fig. 1A. A linear high-frequency (6–13 MHz) ultrasound probe is placed in the coronal plane over the shoulder where the lesser and greater trochanters of the humerus are identified. The subscapularis muscle attachment to the lesser trochanter of the humerus is clearly evident once the arm is externally rotated (Fig. 1B). An in-plane medialto-lateral approach of the needle is used to deposit 15 ml of local anaesthetic over the subscapularis muscle, which blocks both axillary and subscapular nerves by dispersion of the injectate along the ventral surface of subscapularis muscle. In