The shoulder block: a new alternative to interscalene brachial plexus blockade for the control of postoperative shoulder pain.
This report describes the development of the shoulder block, an alternative to interscalene brachial plexus blockade for the control of postoperative pain following shoulder surgery. Included is a review of the relevant anatomy of the shoulder joint and its associated structures Two nerves provide the bulk of the innervation to this area: the suprascapular nerve and the axillary (circumflex) nerve The shoulder block technique involves selective blockade of both of these nerves instead of general blockade of the entire brachial plexus via the interscalene route The technique of Meter is used to block the supragcapular nerve in the supra6 pinaus fossa. No descriptions of axillary nerve block were available in the literature, so a technique for blocking this nerve as it travels across the posterior surface of the humerus was developed and is described along with a discussion of the author's initial clinical experience
Key Words: axillary nerve, interscalene nerve block, shoulder surgery, suprascapular nerve
Postoperative pain following shoulder surgery in many patients is severe (1). Traditionally, this has been controlled by the application of local anaesthetic to the proximal brachial plexus, via the interscalene approach. The interscalene block is effective in the control of postoperative pain, but is associated with significant side-effects and complications (2,5). There may however, be an alternative approach for the control of postoperative shoulder pain, using specific blockade of the two major peripheral nerves supplying the shoulder joint, the suprascapular and axillary (circumflex) nerves.
This paper describes a new technique for specific blockade of the major nerves supplying the shoulder joint and describes the author's initial experience with this technique.
Any attempt to achieve regional anaesthesia of the shoulder joint requires an understanding of the relevant anatomy (1,6,7). Effective control of post-surgical shoulder pain generally requires local anaesthetic blockade of the nerve supply to the synovium, capsule, articular surfaces, periosteum, ligaments and muscles of the shoulder joint (1). These structures receive sensory innervation from the nerves that supply the muscles working across the glenohumeral articulation. The bulk of the posterior, medial and superior supply to the joint is via the suprascapular nerve, a branch of the superior trunk (Figures 1 and 2). There is also a contribution from the lateral pectoral nerve, a branch of the lateral cord. The suprascapular nerve also supplies the supraspinatus and infraspinatus muscle of the rotator cuff, with some branches to teres minor (1,7,8). The inferior, lateral and anterior structures of the shoulder joint are supplied primarily by the axillary nerve, a branch of the posterior cord, which also supplies the deltoid and has fibres to teres minor. There is a contribution from the subscapular nerve, a branch of the posterior cord, and small contributions from the musculocutaneous nerve, the continuation of the lateral cord (1,8).
The axillary nerve is formed as a terminal branch of the posterior cord at the lateral border of subscapularis, as it winds towards the posterior aspect of the surgical neck of the humerus (6,7,9,10) (Figures 1 and 2). It runs beneath the shoulder joint, passing 12 mm below the inferior aspect of the glenoid, but only 2 to 3 mm below the inferior capsule (9,10). In association with the posterior humeral circumflex artery the nerve passes back through the quadrilateral space, a small opening formed by teres minor above, teres major below, long head of biceps medially and the proximal humerus laterally (6,7). Upon traversing the quadrilateral space the nerve immediately forms an anterior and a posterior branch (9,10). The posterior branch courses posteriorly 10 mm before dividing into two terminal nerves, the nerve to teres minor and the superior-lateral brachial cutaneous nerve. The latter branch is purely sensory and becomes superficial by coursing around the medial border of the deltoid (9). A muscular branch to the posterior aspect of the deltoid also arises from the posterior branch.
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The anterior branch passes forward around the humerus on the posterior aspect of the deltoid, to which it supplies motor innervation, lying just 3 to 5 cm below the anterior acromial edge (11). It has traditionally been possible to block all the relevant nerves supplying the shoulder joint via an interscalene approach to the upper roots of the brachial plexus. This approach permits blockade of the superior cord prior to the suprascapular nerve branching from it (1,8). However, individual blockade of both the suprascapular nerve and the axillary nerve should provide analgesia to a significant proportion of the joint. The techniques employed for achieving this will now be detailed below.
Suprascapular nerve block Several descriptions of suprascapular nerve block were found in the literature, associated with use of the block in the control of both acute and chronic shoulder pain (l2--20). The ideal approach to the nerve would ensure blockade of the more proximal branches to the acromium and the subacromial region. Blockade of the nerve in the suprascapular notch does achieve this, but is associated with a small risk of pneumothorax (8,19,20). The technique chosen was that described by Meier, which allows blockade of the suprascapular nerve during its passage from the suprascapular notch to the spinoglenoid notch, as it lies in the lateral supraspinous grooves (19,20). It also allows a large volume of local anaesthetic to be injected beneath the supraspinatus muscle, as well as the option of inserting a catheter.
Figures 3 and 4 illustrate the technique of Meier (19,20),the patient is in the sitting position with the arm in full adduction. A line connecting the lateral part of the acromion and the medial end of the spine of the scapula is identified. The insertion point is located 2 cm medial and 2 cm cephalad to the midpoint of this line. A 22-gauge, 100 mm Stimuplex block needle (B. Braun Medical Inc., Bethlehem, PA, U.S.A.) was inserted 4 to 6 cm lateralocaudally (45[degrees] in the coronal plane), with a ventral inclination of about 30[degrees], while connected to a peripheral nerve stimulator (B. Braun Medical Inc., Bethlehem, PA, U.S.A.). If stimulation of the infraspinatus muscle was observed, or the patient reported a pain-free 'knocking' sensation in the shoulder, 15 ml of 0.75% ropivacaine was injected (19,20). After three passes, if no twitches were elicited, ropivacaine 0.75% 15 ml was injected along the bony surface of the lateral supraspinous groove, as described by Meier (l9,20).
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Axillary nerve block
A Medline search for axillary nerve block and circumflex nerve block revealed no description of this procedure. One paper describes blocking the articular branches of this nerve, but in association with a suprascapular nerve block for the control of chronic paints. An approach to the axillary nerve was developed over time following a literature review of the anatomy (6,7,9-11) and examination of the bony components of the shoulder joint. Cadaver dissection of the posterior shoulder region gave insight into the surrounding soft tissue structures and orientations, while a review of MRI films of the shoulder joint allowed accurate measurement of the position the axillary nerve in a number of cases. The initial approach was subsequently refined clinically into a low risk, reliable technique (Figures 2, 5 and 6).
Peer review during development of the axillarynerve block consisted of informal discussion with colleagues experienced in the area of shoulder surgery. Three upper limb orthopaedic surgeons were consulted as to any potential hazards they could see performing axillary nerve block in this setting, all three observing placement of the block. Three experienced regional anaesthetists in the author's hospital department were also consulted at every stage of development of the block, including the first time it was performed.
The safest and most consistent point at which to block the axillary nerve is immediately following the nerve's passage through the quadrilateral space to lie posterior to the humerus. This guarantees blockade of the four terminal nerves and any articular branches that may arise along its course. It avoids injection more proximally where the nerve lies only 2 to 3 mm below the inferior capsule, carrying a risk of entering the joint with the block needle. The technique relies on bony landmarks that are easily palpated in almost all patients and are consistent between patients. As for the suprascapular nerve block, the patient is seated with the arm in full adduction.
Both the anterior aspect of the acromion and the inferior angle of the scapula are palpated. A line directly joining these two landmarks points is drawn across the skin (Figure 5). The midway point along this line is identified and marked with a horizontal line. The quadrilateral space lies at the level of this horizontal plane (Figure 2 and 6).
The postero-lateral aspect of the acromion is palpated and from this point a vertical line is traced down, directly behind the humerus (Figure 5). This represents a vertical plane through which the axillary nerve passes laterally, at the level of the horizontal plane. The point on the skin at which the vertical plane and the horizontal plane intersect designates the needle puncture point (Figure 2 and 6).
With the patient in a seated position, a 22-gauge, 100 mm Stimuplex block needle (B. Braun Medical Inc., Bethlehem, PA, U.S.A.) attached to a nerve stimulator (B. Braun Medical Inc., Bethlehem, PA, U.S.A.) is passed directly anterior from this intersection towards the posterior aspect of the humerus, in line with both the horizontal and the vertical planes. Twitches in the posterior deltoid may occur after 2 to 3 cm due to direct stimulation as the needle passes through that muscle. Muscular twitches involving the anterior deltoid at a depth of 6 to 8 cm indicate the axillary nerve has been located. The current is reduced to 0.5 mA or less with the twitches maintained, then 10 to 15 ml of 0.75% ropivacaine is injected.
If no twitches are elicited, the needle should continue to advance in the vertical plane until the posterior surface the humerus is contacted. The needle should then first be walked 2 to 3 cm inferiorly in the vertical plane (withdrawing 1 cm each time before advancing anteriorly again) looking for contact with the axillary nerve. If this is without success, the needle should be walked 1 cm above the initial entry point but no further, to avoid the needle perforating the shoulder capsule. If there is still no deltoid twitch, the needle should return to the initial insertion point, the needle directed down onto bone and 15 ml of local anaesthetic solution injected slowly. Contact with soft tissue when advancing onto the humerus indicates the needle tip is lying within the origin of the lateral head of triceps. The needle should be withdrawn 1 cm and walked superiorly in the vertical plane until free bone is contacted, or until deltoid twitch indicates the axillary nerve has been located. Fifteen ml of local anaesthetic is then injected slowly.
The direction of local anaesthetic spread during axillary nerve block is dramatically illustrated with the use of radio-opaque dye (Figures 7a and 7b). Immediately following injection (Figure 7a), a 15 ml ropivacaine 0.6% bolus containing 2 g of lohexol is seen to reside primarily in the space beneath the posterior deltoid, but also travels proximally into the quadrilateral space, seen as the medial cone-like projection in the figure. Thirty seconds later, the radio-opaque dye has spread medially to the anteromedial surface of the subscapularis muscle, via the quadrilateral space (Figure 7b).
The author has performed the combined suprascapular and axillary nerve in 70 instances up to the time of submission of this report. The first block was performed in June 2005 and the technique refined over the first 35 blocks, resulting in the above technique, which is easy to perform, as well as being the most reliable and easily replicated approach. The main indications were as an alternative to interscalene block in patients having predominantly arthroscopic shoulder surgery expected to result in more moderate pain postoperatively, including minor subacromial procedures (e.g. subacromial decompression) and intraarticular procedures (e.g. anterior stabilisations, SLAP lesion repairs). The technique was also employed for arthroscopic or open major subacromial surgery (e.g. rotator cuff repair) and total shoulder joint replacement where an interscalene block was contraindicated or where any of the side-effects may not be well tolerated clinically. This included phrenic nerve paralysis in morbid obesity and in a patient with severe restrictive lung disease and a ventriculoperitoneal shunt running through the ipsilateral side of the neck. The technique was also employed in instances of interscalene block failure postoperatively. All patients were consented to have the procedure, with the risks of postoperative nerve damage discussed in each case.
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All procedures had local anaesthetic infiltration of the wound edges pre-incision for arthroscopic cases and following completion of skin suturing for open cases. There was no local anaesthetic instilled into the subacromial or intra-articular spaces at any time. All patients were consented about the procedure being new and a modification of an established technique (lone suprascapular nerve block).
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Analysis of the first 40 cases recorded mean morphine consumption in PACU of 3 mg, with 57% of cases requiring no morphine in PACU. All patients received intraoperative morphine in case of block failure, averaging 5 mg for each case. Overnight morphine consumption until 0700 hours was 2 mg, with 83% of cases requiring no morphine overnight.
This report describes a new technique for local anaesthetic blockade of both the suprascapular nerve and the axillary nerve, which may provide effective relief of postoperative shoulder pain.
The use of a suprascapular nerve block alone for pain relief following arthroscopic shoulder surgery has been investigated by Singelyn and Lhotel (14,21). The technique was found to offer analgesia superior to intra-articular local anaesthetic administration at the end of surgery (14,21) and to no block at all (21), but inferior when compared to an interscalene block (14,21). The low rates of postoperative morphine dose reported following the author's first 40 cases could be due to augmentation of the suprascapular nerve block by axillary nerve blockade providing analgesia closer in quality to an interscalene block. However, the results of a small, retrospective, uncontrolled case series are not sufficient to draw conclusions as to the efficacy of this block for postoperative analgesia.
Some level of morphine consumption postoperatively following the shoulder block would be predicted, due to a predominantly anterior but variable component of the nerve supply to the shoulder remaining unblocked. And consistent with the applied anatomy, the author has found pain following repair of the subscapularis muscle (supplied by neither the suprascapular or axillary nerve) during rotator cuff repair to be inadequately covered by the use of the shoulder block.
In addition to effective pain relief, the shoulder block may offer a reduction in both the rate of side-effects and the risk of severe complications when compared to an interscalene block. Potential complications of the shoulder block would include the risk of pneumothorax with suprascapular nerve blockade, but this should be much reduced with Meier's technique (19,20). There is also a risk of intraarticular puncture with both the suprascapular and axillary nerve blocks, but this may have low morbidity, especially in the arthroscopic surgical setting. In addition, the shoulder block would carry a theoretical risk of postoperative neuropathy and intravascular injection inherent in all peripheral nerve blocks.
In comparison, the interscalene approach is associated with infrequent but potentially major complications. These maybe the result of inadvertent injection of local anaesthetic into cerebrospinal fluid, the epidural space or the vertebral artery. Its associated side-effects are more common due to the unpredictable spread of local anaesthetic to important adjacent neural structures such as the phrenic and vagus nerves and the stellate ganglion (2,3,5). Interscalene blocks are also associated with a significant incidence of transient postoperative neurological complications, an incidence of 14% at 10 days reported by Borgeat (4). The same study found a rate of severe long-term complications of 0.4% (4).
The interscalene block also results in motor blockade of muscles supplied by terminal nerves of the brachial plexus. This will result in paralysis of the entire shoulder girdle and the upper arm and may even extend to the forearm and hand. Extensive paralysis of the upper limb is regarded as the sign of an effective interscalene block by anaesthetists, but for many patients it is a common yet significant cause of discomfort, especially in the ambulatory setting, despite the quality of analgesia it provides (3,14). In comparison, motor blockade associated with the shoulder block is limited to the three posterior rotator cuff muscles (supraspinatus, infraspinatus and teres minor) and the deltoid. The other shoulder girdle muscles such as latissimus dorsi and the pectoral muscles are preserved, along with the muscles of the upper arm, forearm and hand.
Two incidents of radial nerve blockade postoperatively were noted in the author's first 70 cases (both female), indicating that local anaesthetic had spread sufficiently proximal to reach the posterior cord. It may be that an axillary nerve block volume of 15 ml is more likely to reach the posterior cord in smaller patients and may need to be reduced if the incidence is too high. Sensory blockade of the shoulder block is limited to the cutaneous distribution of the axillary nerve over the deltoid region. Thus the technique offers potential preservation of the patient's functional capacity in addition to the analgesia provided. In comparison, the intense level of analgesia seen with an interscalene block will come at the cost of a higher rate of side-effects and complications, and may not actually improve patient satisfaction with their pain relief.
In conclusion, a new technique for specific blockade of the major nerves supplying the shoulder joint has been described and its anatomical basis has been justified. The initial data from the author's uncontrolled, retrospective case series in 70 patients suggest that satisfactory analgesia can be obtained. While that data is encouraging, further randomised controlled trials comparing single shot interscalene block to combined suprascapular and axillary nerve block are required to determine whether this approach offers comparable analgesia without any compromise in patient satisfaction or safety.
The author would like to thank Best Practice and Research Clinical Anaesthesiology for the use of the images appearing in Figures 1 and 2. The author would also like to thank Mr Gary Boxall, Anaesthetic Technician, North Shore Hospital, for his work producing the figures.
Accepted for publication on March 2, 2007.
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D. J. PRICE
Department of Anaesthesiology and Perioperative Medicinq North Shore Hospital, Takapuna, Auckland, New Zealand
* F.A.N.Z.C.A., Specialist Anaesthetist.
Address for reprints: Dr D. J. Price, Specialist Anaesthetist, Department of Anaesthesiology and Perioperative Medicine, North Shore Hospital, PO Box 93503, Takapuna, Auckland, New Zealand.