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THE SPINAL ACCESSORY NERVE DISTAL TO THE POSTERIOR TRIANGLE
THE SPINAL ACCESSORY NERVE DISTAL TO THE POSTERIOR TRIANGLE M. T. PEREIRA and W. W. WILLIAMS From Broomfield Hospital, Chelmsford, UK
Thirty cadaver necks were dissected to determine the course of the accessory nerve distal to the posterior triangle. The nerve was found to have a constant course on the deep surface of the trapezius muscle. This has clinical implications for surgery in the region. Journal of Hand Surgery (British and European Volume, 1999) 24B: 3: 368–369 The course of the accessory nerve has been well described in its intracranial portion and its course across the posterior triangle (Williams et al., 1995). However, the course of the nerve after it leaves the posterior triangle is poorly described, and in order to establish this, 30 cadaver shoulders were dissected.
the accessory nerve received a branch from the cervical plexus. This branch ran obliquely across the lower part of the posterior triangle of the neck, under the trapezius muscle to divide into three or four branches, which entered the trapezius or joined the accessory nerve. This point was at a mean distance of 5.6 cm from the acromioclavicular joint (range, 3.5–7.5 cms) There was also a small plexus of veins adjacent to or overlying this
MATERIALS AND METHODS Thirty cadaver neck dissections were carried out. The accessory nerve was identified at its entry into the posterior triangle as it emerged from the sternocleidomastoid muscle. It was followed across the posterior triangle and on to the deep surface of the trapezius muscle. From there it was carefully followed until it became intramuscular at the level of the lower part of the scapula. The attachment of the trapezius to the clavicle and scapular spine was elevated to display the nerve. The findings were recorded by drawings and photographs. In 18 dissections the distances from the cervical contribution to the accessory nerve to the point of exit of the nerve from the posterior triangle and to the acromioclavicular joint respectively were measured. In six dissections a needle was inserted at the apex of the superior angle of the scapula as a reference point before displaying the nerve. RESULTS The accessory nerve followed a constant course on the deep surface of the trapezius muscle after it left the posterior triangle of the neck. At the anterior border of the trapezius it pierced the fascia covering the deep surface of the muscle. For the remainder of its course it ran between the muscle and the fascia. After piercing the fascia of the muscle it ran caudally parallel to, and about 2 cm from, the anterior border of the muscle. After a variable distance, it turned medially and inferiorly and ran parallel to, and about 4 cm from, the insertion of the muscle on to the spine of the scapula. At the medial end of the spine of the scapula the nerve turned caudally and ran parallel to the medial border of the scapula. At a distance of approximately 7 cm below the scapular spine it divided into terminal muscular branches. All along its course it gave off muscular branches which gradually reduced in size more distally. At a point approximately 3 cm (range, 0.9–5.3 cm) from the entry of the nerve into the fascia of the muscle,
Fig. 1 368
Dissection of the spinal accessory nerve.
SPINAL ACCESSORY NERVE
junction. The plexus of veins was seen in all cases, but the branch from the cervical plexus was absent in six dissections. Proximal to its entry into the fascia of the trapezius the accessory nerve lay loosely in fat with plenty of slack allowing the nerve to move when the neck and shoulder are moved. Beyond this point, however, the nerve was tethered down to the fascia and it was not mobile. Deep to the trapezius the course of the nerve was in the form of a question mark (?) with the arm adducted. When the arm is elevated the scapula rotates and protracts and the course of the nerve would be straighter. The reference needle that had been inserted at the superior angle of the scapula prior to dissection was found to lie within a 1.5 cm radius of the nerve. DISCUSSION The course of the proximal accessory nerve is well described (Caliot et al., 1989; Williams et al., 1995). Our dissections have shown that the nerve continues in a constant course for a long distance on the undersurface of the trapezius, until it terminates in muscular branches over the lower part of the scapula. The entry point of the branch from the cervical plexus is a distinct landmark in the distal part of the nerve. Injury to the nerve proximally can result in paralysis of the trapezius, with pain, drooping of the shoulder, and
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loss of shoulder movement (Williams et al., 1996). Distally the nerve can be used in the reconstructive surgery of brachial plexus injuries for neurotization of the suprascapular nerve, without risk of denervation of the upper trapezius (Alnot et al., 1996). Therefore the entry point of the branch from the cervical plexus serves as a useful surgical landmark to identify the distal part of the nerve. This nerve can be absent (6/30 in our study). However, the constant venous plexus at this point can be used as an additional guide at operation. References Alnot J-Y, Oberlin C (1996). Nerves available for neurotization: the spinal accessory nerve. In: Alnot J-Y, Narakas A (Eds) Traumatic brachial plexus injuries. Paris, Expansion Scientifique Francaise, 1996: 33–38. Caliot P, Bosquet V, Midy D, Cabanié P (1989). A contribution to the study of the accessory nerve: surgical implications. Surgical and Radiologic Anatomy, 11: 11–15. Williams PL, Bannister LH, Berry MM, et al. (Eds) Gray’s Anatomy, 38th edn. Edinburgh, Churchill Livingstone, 1995: 1253–1255. Williams WW, Donell ST, Twyman RS, Birch R (1996). The posterior triangle and the painful shoulder: spinal accessory nerve injury. Annals of the Royal College of Surgeons of England, 78: 521–525.
Received: 28 August 1998 Accepted after revision: 8 February 1999 W. W. Williams FRCS(Orth), 132 Broomfield Road, Chelmsford, Essex CM1 1RN. E-mail: [email protected] © 1999 The British Society for Surgery of the Hand Article no. jhsb.1999.0158
Thirty cadaver necks were dissected to determine the course of the accessory nerve distal to the posterior triangle. The nerve was found to have a constant course on the deep surface of the trapezius muscle. This has clinical implications for surgery in the region. Journal of Hand Surgery (British and European Volume, 1999) 24B: 3: 368–369 The course of the accessory nerve has been well described in its intracranial portion and its course across the posterior triangle (Williams et al., 1995). However, the course of the nerve after it leaves the posterior triangle is poorly described, and in order to establish this, 30 cadaver shoulders were dissected.
the accessory nerve received a branch from the cervical plexus. This branch ran obliquely across the lower part of the posterior triangle of the neck, under the trapezius muscle to divide into three or four branches, which entered the trapezius or joined the accessory nerve. This point was at a mean distance of 5.6 cm from the acromioclavicular joint (range, 3.5–7.5 cms) There was also a small plexus of veins adjacent to or overlying this
MATERIALS AND METHODS Thirty cadaver neck dissections were carried out. The accessory nerve was identified at its entry into the posterior triangle as it emerged from the sternocleidomastoid muscle. It was followed across the posterior triangle and on to the deep surface of the trapezius muscle. From there it was carefully followed until it became intramuscular at the level of the lower part of the scapula. The attachment of the trapezius to the clavicle and scapular spine was elevated to display the nerve. The findings were recorded by drawings and photographs. In 18 dissections the distances from the cervical contribution to the accessory nerve to the point of exit of the nerve from the posterior triangle and to the acromioclavicular joint respectively were measured. In six dissections a needle was inserted at the apex of the superior angle of the scapula as a reference point before displaying the nerve. RESULTS The accessory nerve followed a constant course on the deep surface of the trapezius muscle after it left the posterior triangle of the neck. At the anterior border of the trapezius it pierced the fascia covering the deep surface of the muscle. For the remainder of its course it ran between the muscle and the fascia. After piercing the fascia of the muscle it ran caudally parallel to, and about 2 cm from, the anterior border of the muscle. After a variable distance, it turned medially and inferiorly and ran parallel to, and about 4 cm from, the insertion of the muscle on to the spine of the scapula. At the medial end of the spine of the scapula the nerve turned caudally and ran parallel to the medial border of the scapula. At a distance of approximately 7 cm below the scapular spine it divided into terminal muscular branches. All along its course it gave off muscular branches which gradually reduced in size more distally. At a point approximately 3 cm (range, 0.9–5.3 cm) from the entry of the nerve into the fascia of the muscle,
Fig. 1 368
Dissection of the spinal accessory nerve.
SPINAL ACCESSORY NERVE
junction. The plexus of veins was seen in all cases, but the branch from the cervical plexus was absent in six dissections. Proximal to its entry into the fascia of the trapezius the accessory nerve lay loosely in fat with plenty of slack allowing the nerve to move when the neck and shoulder are moved. Beyond this point, however, the nerve was tethered down to the fascia and it was not mobile. Deep to the trapezius the course of the nerve was in the form of a question mark (?) with the arm adducted. When the arm is elevated the scapula rotates and protracts and the course of the nerve would be straighter. The reference needle that had been inserted at the superior angle of the scapula prior to dissection was found to lie within a 1.5 cm radius of the nerve. DISCUSSION The course of the proximal accessory nerve is well described (Caliot et al., 1989; Williams et al., 1995). Our dissections have shown that the nerve continues in a constant course for a long distance on the undersurface of the trapezius, until it terminates in muscular branches over the lower part of the scapula. The entry point of the branch from the cervical plexus is a distinct landmark in the distal part of the nerve. Injury to the nerve proximally can result in paralysis of the trapezius, with pain, drooping of the shoulder, and
369
loss of shoulder movement (Williams et al., 1996). Distally the nerve can be used in the reconstructive surgery of brachial plexus injuries for neurotization of the suprascapular nerve, without risk of denervation of the upper trapezius (Alnot et al., 1996). Therefore the entry point of the branch from the cervical plexus serves as a useful surgical landmark to identify the distal part of the nerve. This nerve can be absent (6/30 in our study). However, the constant venous plexus at this point can be used as an additional guide at operation. References Alnot J-Y, Oberlin C (1996). Nerves available for neurotization: the spinal accessory nerve. In: Alnot J-Y, Narakas A (Eds) Traumatic brachial plexus injuries. Paris, Expansion Scientifique Francaise, 1996: 33–38. Caliot P, Bosquet V, Midy D, Cabanié P (1989). A contribution to the study of the accessory nerve: surgical implications. Surgical and Radiologic Anatomy, 11: 11–15. Williams PL, Bannister LH, Berry MM, et al. (Eds) Gray’s Anatomy, 38th edn. Edinburgh, Churchill Livingstone, 1995: 1253–1255. Williams WW, Donell ST, Twyman RS, Birch R (1996). The posterior triangle and the painful shoulder: spinal accessory nerve injury. Annals of the Royal College of Surgeons of England, 78: 521–525.
Received: 28 August 1998 Accepted after revision: 8 February 1999 W. W. Williams FRCS(Orth), 132 Broomfield Road, Chelmsford, Essex CM1 1RN. E-mail: [email protected] © 1999 The British Society for Surgery of the Hand Article no. jhsb.1999.0158