- Email: [email protected]
The strap muscles in thyroid surgery: To cut or not to cut?
THE STRAP MUSCLES IN THYROID SURGERY: TO CUT OR NOT TO CUT? ANTHONY E. YOUNG, MA, MCHIR, FRCS
Adequate access to the upper polar vessels and the thyroid hilum is crucial in thyroid surgery if safe vascular control and visualization of From St. Thomas' Hospital, London, England. Address reprint requests to Anthony E. Young, MA, MChir, FRCS, Consultant Surgeon, St. Thomas' Hospital, Lambeth Palace Rd, London SE1 7EH, England. Copyright © 1994 by W.B. Saunders Company 1043-1810/94/0502-0011 $05.00/0
the technique of surgery evolved and the thyroid glands coming to surgery were less heroic in proportion, division of the muscles was seen to be only infrequently necessary. The situation has evolved w h e r e b y m a n y surgical trainees believe that to divide the strap muscles reflects; poorly on their technical prowess. A logical view might also suppose that an inferior functional result could follow division, b u t this has rarely been tested.
the parathyroids, the recurrent laryngeal nerve, and the external branch of the superior laryngeal nerve is to be achieved. When a goiter or tumor is small, access is readily and safely achieved by vertical division between the two sternohyoid muscles followed by their mobilization and simple lateral retraction. In the traditional management of large goiters, the division of the sternohyoid and sternothyroid muscles transversely to facilitate access was normal; but as
Hyoid 11. Stemomastoid m. Crleothyroid m.
/
Omohyoid m.
Stemohyoid m.
m.
Thyroid
FIGURE 1. StTap muscles of the neck and sites for division. The sternohyoid and omohyoid muscles are not shown on the left side of the neck in this diagram. The thick dotted line marks the level for division of the muscles.
OPERATIVE TECHNIQUES IN OTOLARYNGOLOGY--HEAD AND NECK SURGERY, VOL 5, NO 2 (JUN), 1994: PP 129-131
129
Xll
Thyrohyoid m.
Omohyoid m.
C3
- Stemohyoid m. Stemothyroid m.
ARS8 1
cervicalis
FIGURE 2. Nerve supply to the right side strap muscles of the neck.
STRAP MUSCLE ANATOMY AND FUNCTION The infrahyoid strap muscles derive from the same ventral sheet of muscles as the rectus abdominus (Fig 1). The primitive muscle mass develops into two layers; the superficial, which forms the sternohyoid medially and the omohyoid laterally, and the deep, which attaches to the oblique line on the thyroid cartilage and forms the sternothyroid caudally and the thyrohyoid cranially. The nerve supply to the sternothyroid and sternohyoid enters the deep lateral surface of the muscle from the ansa cervicalis (Fig 2). The muscles, w h e n divided, are divided high to avoid damage to these nerves. This high division also avoids tethering of the skin incision to the muscle closure. The function of the strap muscles is primarily to stabilize the larynx and d r a w it d o w n after deglutition. They may have a less defined function as accessory muscles of respira-
130
tion and may also, in synergy with the cricothyroids, contribute to the control of vocal cord length. 1
A STUDY OF THE EFFECTS OF DIVIDING THE STRAP MUSCLES To determine whether there are any significant sequelae from muscle division, we assessed 30 consecutive patients at routine follow-up after thyroid surgery (27) or parathyroid surgery (7). They were assessed by questioning and clinical examination I month to 15 years after thyroid surgery by an assessor who had no knowledge of whether the strap muscles had been divided. In fact, 12 had had bilateral division, 11 had had unilateral divisions, and in 7 no division had been p e r f o r m e d . The patients w e r e questioned about their voice, swallowing, neck movements, and comfort. Objective assessments were
made of cosmetic appearance, muscle s t r e n g t h , a n d the s p e a k i n g voice. The results s h o w e d that there were no subjective complaints on direct questioning. Furthermore, there was no evidence in any patient of any objective defect of function or voice, nor was there any cosmetic defect. In particular, in 11 patients w h o had u n d e r g o n e unilateral strap muscle division, blind assessment failed to detect any difference in the size or function between the two sides, except for a slight lateral induration in 1 patient who had undergone surgery 4 w e e k s p r e v i o u s l y . We concluded that from a practical point of view, strap division does not result in any subjective or objective functional or cosmetic deficit. 2
DISCUSSION Few would dispute that the division of the strap muscle is unequivocally indicated in surgery for some large ANTHONY E. YOUNG
Omohyoid m. Sup. thyroid a.&v.~ m.
tT•uYmrOid or"
Middle thyroid Stemothyroid m.
Re¢. laryng. Int.
i
Com. carotid a.
Inf. thyroid a. & v. or difficult thyroids, because of the quality of access it gives (Fig 3), and that it is not indicated in straightforward thyroid and parathyroid surgery. The q u e s t i o n at issue is whether the sequelae of division are significant e n o u g h to raise one's threshold of division of the muscle so that to do so becomes an infrequent rather than a common event. Our clinical data suggest that the side effects judged at follow-up are not severe enough to deter division of the strap muscles if it seems useful. Nevertheless, there are two elements to strap muscle division that we have not assessed. One is the effect on sophisticated vocal function such as singing. The second is postoperative pain. Sonninen I has made a detailed s t u d y of the contribution of the strap muscles to the function of the l a r y n x a n d has a s s e s s e d voice changes following bilateral, unilateral, or no division of the strap muscles during thyroid surgery. In 76 patients, he noted that those whose pretracheal muscles had been sectioned bilaterally could not achieve such high tones as those whose muscles h a d n o t b e e n d i v i d e d . Unilateral division produced intermediate results. Although Sonninen was aware of the potential con-
STRAP MUSCLES IN THYROID SURGERY
founding effects of damage to the external branch of the superior laryngeal nerve, in his study the contributory role of such a nerve injury was not specifically assessed. Nevertheless, his observations have been confirmed by others. 3'4 We have not yet completed our study of the severity of postoperative pain after strap muscle division. Analgesic requirements are consistently low after thyroidectomy and, as difference in pain levels on deglutition is likely to be the only significant difference, an objective assessment of differential pain levels with and without strap muscle division is difficult. Occasionally, division of the strap muscles, particularly in surgery for recurrent parathyroid or thyroid disease, can be avoided by a vertical split lateral to the s t e r n o h y o i d . This risks denervation of the muscles but avoids a difficult dissection freeing the strap muscles from the previous operative bed. Nevertheless, this approach is only rarely appropriate. One may conclude that with the exception of singers most patients may have division of the strap muscles w i t h o u t d e t r i m e n t , b u t it should be done high, and the sternohyoid, but not necessarily the
FIGURE 3. Improved access to the upper pole of the thyroid and to the hilum shown by cutting the pretracheal strap muscles and turning them back in clamps. sternothyroid, must be resutured carefully. It is not an appropriate maneuver for all thyroid surgery, b u t one t h a t m i g h t be r e c o m m e n d e d in the following circumstances: Large goiters Large tumors Reoperative surgery Toxic thyroids with large capsular vessels Malignant nodules with muscle involvement Cervical spinal disease preventing extension of the neck Large retrosternal tumors
REFERENCES 1. SonninenA: The role of the external laryngeal muscles in length adjustment of the vocal cords in singing. Acta Otolaryngol Suppl. 130, 1956 2. JaffeV, YoungAE: Strap Musclesin Thyroid Surgery. 1993;Ann R CollSurg Engl 75:118, 1993 3. Berendes J. Atmung und Stimme nach Lateralfixafioneiner Stimmlippe bei bedeiderseitiger Posticuslahmung. Arch Ohr usw Heilk u Z Hals-usw Heilk 159: 291, 1951 4. Michel R. Die Bedeuntung des Musclulus sternothyreoideus fur die Rahmenmodulation der rnenschlichen Stimme. Folia Phoniatre 6:65, 1954
131
Adequate access to the upper polar vessels and the thyroid hilum is crucial in thyroid surgery if safe vascular control and visualization of From St. Thomas' Hospital, London, England. Address reprint requests to Anthony E. Young, MA, MChir, FRCS, Consultant Surgeon, St. Thomas' Hospital, Lambeth Palace Rd, London SE1 7EH, England. Copyright © 1994 by W.B. Saunders Company 1043-1810/94/0502-0011 $05.00/0
the technique of surgery evolved and the thyroid glands coming to surgery were less heroic in proportion, division of the muscles was seen to be only infrequently necessary. The situation has evolved w h e r e b y m a n y surgical trainees believe that to divide the strap muscles reflects; poorly on their technical prowess. A logical view might also suppose that an inferior functional result could follow division, b u t this has rarely been tested.
the parathyroids, the recurrent laryngeal nerve, and the external branch of the superior laryngeal nerve is to be achieved. When a goiter or tumor is small, access is readily and safely achieved by vertical division between the two sternohyoid muscles followed by their mobilization and simple lateral retraction. In the traditional management of large goiters, the division of the sternohyoid and sternothyroid muscles transversely to facilitate access was normal; but as
Hyoid 11. Stemomastoid m. Crleothyroid m.
/
Omohyoid m.
Stemohyoid m.
m.
Thyroid
FIGURE 1. StTap muscles of the neck and sites for division. The sternohyoid and omohyoid muscles are not shown on the left side of the neck in this diagram. The thick dotted line marks the level for division of the muscles.
OPERATIVE TECHNIQUES IN OTOLARYNGOLOGY--HEAD AND NECK SURGERY, VOL 5, NO 2 (JUN), 1994: PP 129-131
129
Xll
Thyrohyoid m.
Omohyoid m.
C3
- Stemohyoid m. Stemothyroid m.
ARS8 1
cervicalis
FIGURE 2. Nerve supply to the right side strap muscles of the neck.
STRAP MUSCLE ANATOMY AND FUNCTION The infrahyoid strap muscles derive from the same ventral sheet of muscles as the rectus abdominus (Fig 1). The primitive muscle mass develops into two layers; the superficial, which forms the sternohyoid medially and the omohyoid laterally, and the deep, which attaches to the oblique line on the thyroid cartilage and forms the sternothyroid caudally and the thyrohyoid cranially. The nerve supply to the sternothyroid and sternohyoid enters the deep lateral surface of the muscle from the ansa cervicalis (Fig 2). The muscles, w h e n divided, are divided high to avoid damage to these nerves. This high division also avoids tethering of the skin incision to the muscle closure. The function of the strap muscles is primarily to stabilize the larynx and d r a w it d o w n after deglutition. They may have a less defined function as accessory muscles of respira-
130
tion and may also, in synergy with the cricothyroids, contribute to the control of vocal cord length. 1
A STUDY OF THE EFFECTS OF DIVIDING THE STRAP MUSCLES To determine whether there are any significant sequelae from muscle division, we assessed 30 consecutive patients at routine follow-up after thyroid surgery (27) or parathyroid surgery (7). They were assessed by questioning and clinical examination I month to 15 years after thyroid surgery by an assessor who had no knowledge of whether the strap muscles had been divided. In fact, 12 had had bilateral division, 11 had had unilateral divisions, and in 7 no division had been p e r f o r m e d . The patients w e r e questioned about their voice, swallowing, neck movements, and comfort. Objective assessments were
made of cosmetic appearance, muscle s t r e n g t h , a n d the s p e a k i n g voice. The results s h o w e d that there were no subjective complaints on direct questioning. Furthermore, there was no evidence in any patient of any objective defect of function or voice, nor was there any cosmetic defect. In particular, in 11 patients w h o had u n d e r g o n e unilateral strap muscle division, blind assessment failed to detect any difference in the size or function between the two sides, except for a slight lateral induration in 1 patient who had undergone surgery 4 w e e k s p r e v i o u s l y . We concluded that from a practical point of view, strap division does not result in any subjective or objective functional or cosmetic deficit. 2
DISCUSSION Few would dispute that the division of the strap muscle is unequivocally indicated in surgery for some large ANTHONY E. YOUNG
Omohyoid m. Sup. thyroid a.&v.~ m.
tT•uYmrOid or"
Middle thyroid Stemothyroid m.
Re¢. laryng. Int.
i
Com. carotid a.
Inf. thyroid a. & v. or difficult thyroids, because of the quality of access it gives (Fig 3), and that it is not indicated in straightforward thyroid and parathyroid surgery. The q u e s t i o n at issue is whether the sequelae of division are significant e n o u g h to raise one's threshold of division of the muscle so that to do so becomes an infrequent rather than a common event. Our clinical data suggest that the side effects judged at follow-up are not severe enough to deter division of the strap muscles if it seems useful. Nevertheless, there are two elements to strap muscle division that we have not assessed. One is the effect on sophisticated vocal function such as singing. The second is postoperative pain. Sonninen I has made a detailed s t u d y of the contribution of the strap muscles to the function of the l a r y n x a n d has a s s e s s e d voice changes following bilateral, unilateral, or no division of the strap muscles during thyroid surgery. In 76 patients, he noted that those whose pretracheal muscles had been sectioned bilaterally could not achieve such high tones as those whose muscles h a d n o t b e e n d i v i d e d . Unilateral division produced intermediate results. Although Sonninen was aware of the potential con-
STRAP MUSCLES IN THYROID SURGERY
founding effects of damage to the external branch of the superior laryngeal nerve, in his study the contributory role of such a nerve injury was not specifically assessed. Nevertheless, his observations have been confirmed by others. 3'4 We have not yet completed our study of the severity of postoperative pain after strap muscle division. Analgesic requirements are consistently low after thyroidectomy and, as difference in pain levels on deglutition is likely to be the only significant difference, an objective assessment of differential pain levels with and without strap muscle division is difficult. Occasionally, division of the strap muscles, particularly in surgery for recurrent parathyroid or thyroid disease, can be avoided by a vertical split lateral to the s t e r n o h y o i d . This risks denervation of the muscles but avoids a difficult dissection freeing the strap muscles from the previous operative bed. Nevertheless, this approach is only rarely appropriate. One may conclude that with the exception of singers most patients may have division of the strap muscles w i t h o u t d e t r i m e n t , b u t it should be done high, and the sternohyoid, but not necessarily the
FIGURE 3. Improved access to the upper pole of the thyroid and to the hilum shown by cutting the pretracheal strap muscles and turning them back in clamps. sternothyroid, must be resutured carefully. It is not an appropriate maneuver for all thyroid surgery, b u t one t h a t m i g h t be r e c o m m e n d e d in the following circumstances: Large goiters Large tumors Reoperative surgery Toxic thyroids with large capsular vessels Malignant nodules with muscle involvement Cervical spinal disease preventing extension of the neck Large retrosternal tumors
REFERENCES 1. SonninenA: The role of the external laryngeal muscles in length adjustment of the vocal cords in singing. Acta Otolaryngol Suppl. 130, 1956 2. JaffeV, YoungAE: Strap Musclesin Thyroid Surgery. 1993;Ann R CollSurg Engl 75:118, 1993 3. Berendes J. Atmung und Stimme nach Lateralfixafioneiner Stimmlippe bei bedeiderseitiger Posticuslahmung. Arch Ohr usw Heilk u Z Hals-usw Heilk 159: 291, 1951 4. Michel R. Die Bedeuntung des Musclulus sternothyreoideus fur die Rahmenmodulation der rnenschlichen Stimme. Folia Phoniatre 6:65, 1954
131