725375
research-article2017
HANXXX10.1177/1558944717725375HANDJurbala and Burbank
Surgery Article
A Sonographically Guided In-Plane Distal-to-Proximal Transligamentous Approach to Carpal Tunnel Injections
HAND 1–7 © The Author(s) 2017 Reprints and permissions: sagepub.com/journalsPermissions.nav https://doi.org/10.1177/1558944717725375 DOI: 10.1177/1558944717725375 hand.sagepub.com
Brian M. Jurbala1 and Troy A. Burbank1
Abstract Background: Several sonographically guided injection methods have been described to treat carpal tunnel syndrome. In most cases, the medication diffuses through the carpal tunnel to the site of maximum compression of the nerve after being injected proximally. In this article, we describe a novel method of sonographically guided carpal tunnel injection that utilizes a distal-to-proximal, in-plane, and transligamentous approach. This novel method may provide ergonomic as well as safety advantages to both clinicians and patients, and should be considered by those performing carpal tunnel injections. Methods: A distal-to-proximal transligamentous approach is taken, utilizing high-resolution ultrasound guidance. Once the median nerve is sonographically visualized longitudinally within the carpal tunnel, an ulnar shift is made with the transducer. With the median nerve out of view, the needle is inserted in-line and distal to the transducer on the palmar side of the hand, at the ulnar portion of Kaplan’s cardinal line. Following a trajectory that is nearly parallel to the median nerve, the needle is sonographically guided to the site of maximum nerve compression. Conclusions: This novel method provides an alternative to previous carpal tunnel injections. The use of ultrasound guidance allows the clinician to visualize and avoid the neurovascular structures near the median nerve and guide the needle to the site of maximum nerve compression. It is possible that this parallel trajectory with the median nerve will provide a lower risk of damage to the nerve. Keywords: carpal tunnel syndrome, corticosteroids, sonography, injection, wrist
Introduction Carpal tunnel syndrome (CTS) is the most common form of upper limb entrapment neuropathy in adults, affecting approximately between 3% and 6% of the population.2,8,18 Most often affecting the dominant hand, the condition is caused by a decreased volume inside the carpal tunnel, resulting in a compression of the median nerve.27 For mild cases, therapies such as neutral wrist splints and oral corticosteroids are sometimes used.8,12,16,18 Steroid injections are considered the most effective conservative treatment for the symptoms of CTS1,3,23,24 and can also be used as a diagnostic tool.8,9,16,22,28,29,32 For more severe or recurrent cases, decompressive surgery should be considered.16,18 Conservative treatments overall have yielded symptom resolution at 12 months as low as 11%.24 Injection-specific studies generally report better 12-month follow-ups with between 31% and 50% of patients requiring no additional treatment.3,23 These results drop at an 18-month follow-up, with studies reporting between 6% and 34% of patients requiring no additional treatment.1,31 Corticosteroid injections are more effective in patients with mild CTS most,
while those suffering from severe CTS rarely gain relief from injections.31 Since carpal tunnel injections were first reported in 1958,17,20 there have been many complications associated with the procedure, such as muscle atrophy, depigmentation of the skin, and intratendinous and intravascular injections. The most common and serious complication is injury to the median nerve by intraneural penetration or injection, which can cause severe pain and, occasionally, sensory loss.5,8,16,20 As a way to prevent these complications and thereby improve patient outcomes, sonographically guided carpal tunnel injections were developed. Sonography allows clinicians to view anatomic variations in the carpal tunnel and landmark features to more accurately guide needle placement to the point of intercarpal injection.15,26 1
Highland Center for Orthopaedics, Lakeland, FL, USA
Corresponding Author: Troy A. Burbank, Highland Center for Orthopaedics, 2161 CR 540A #286, Lakeland, FL 33813, USA. Email: [email protected]
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Several sonographically guided methods for injection of corticosteroids to treat CTS have been described in the past. These methods, which include the proximal-to-distal inplane approach4,30 and the ulnar in-plane approach,28 involve viewing the carpal tunnel from either a long or short axis approach palmarly on the wrist and inserting the needle and injecting proximal to the carpal tunnel under the transverse carpal ligament (TCL).19 In both of these methods, the steroid medication, which is infused proximal to the carpal canal, travels by diffusion and mechanical movement of the tendons into the site of maximum nerve compression under the midportion of the TCL.28 We wish to describe a novel method of in-plane distal-toproximal transligamentous ultrasound-guided injection of the carpal canal that may have the advantages of allowing medication to be injected directly underneath the midportion of the TCL at the site of maximum compression of the nerve, improving visualization of the needle tip, reducing the risk of inadvertent nerve puncture (and potential for intraneural injection), and creating an ergonomically more comfortable experience for both the patient and clinician.
Materials and Methods The patient should be in a supine position, with the forearm supinated and the wrist positioned over a folded towel in 25° to 35° of dorsiflexion. Using a high-frequency linear transducer, a diagnostic scan of the wrist is performed to confirm the diagnosis of CTS based on a median nerve cross-sectional area larger than 1 cm2 just proximal to the level of the pisiform.7 A diagnostic scan should also be used to evaluate for secondary causes of nerve compression such as a tumor, cyst, or an aberrant muscle belly within the carpal canal. The nerve is scanned distally along the TCL until the superficial palmar arch at the level of Kaplan’s cardinal line (Figure 1) has been reached, and this line is noted with a marking pen. The transducer should then be translated 1 cm proximal to Kaplan’s cardinal line along the median nerve (Figure 2). In this view, the TCL, median nerve, and flexor tendons will appear to be traveling from proximal to distal obliquely and away from the transducer face (Figure 3). The transducer should then be translated ulnarly approximately 0.5 cm (Figure 4) until the median nerve is no longer visualized (Figure 5). Holding the transducer in place, an alcohol swab is used to clean the area on the palm in which the needle will be inserted. A 3-mL syringe should be prepared with 2.5 mL of a 1% lidocaine HCl solution (with or without epinephrine) and 0.5 mL of betamethasone sodium phosphate and betamethasone acetate 6 mg/mL injectable solution. A 27-gauge 1.5-in hypodermic needle should be used on the syringe. The needle is then inserted into the skin at or just distal to Kaplan’s line parallel to the transducer face (Figures 6). Patients should be told in advance that after the initial needle prick in the skin, they will feel very little pain. The needle is then
Figure 1. Kaplan’s cardinal line. Defined by Kaplan as “a line drawn from the apex of the interdigital fold between the thumb and index fingers toward the ulnar side of the hand, parallel with the middle crease of the hand.”14
Figure 2. Transducer starting point when scanning for the median nerve.
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Figure 3. Longitudinal view of the median nerve.
the midportion of the TCL. The angle bevel of the needle should be directed such that it matches the obliquity of the TCL. Resistance caused by the thickness of ligament will be felt if this is done slowly. After the needle reaches the ligament, pressure is then applied to the plunger on the syringe. Because of the density of the ligamentous tissue, very little fluid will be able to be injected. The needle is slowly advanced while simultaneously pressing the needle plunger. As soon as the needle passes from the ligament tissue into the carpal canal, there will be a sudden loss of resistance at the syringe plunger, and further passage of the needle should be stopped. A hypoechoic bolus of fluid will be seen as it fills the carpal canal and displaces any tendons or nerve tissue directly in opposition to the undersurface of the TCL (Figures 7 and 8). In some instances, hyperechoic crystalline components of the steroid medication can be visualized in the superior portion of the hypoechoic bolus below the ligament. Once the full volume of medication is injected, the needle can then be withdrawn from the patient. If there is any blood at the injection site, it should be wiped clean and a band-aid applied to the injection site. Figure 4. Ulnar translation of the transducer adjusts the median nerve out of view. The transducer is now parallel with the needle trajectory.
advanced and should be seen clearly as it passes through the space above the TCL until it starts to pass obliquely across
Discussion Although there have been case reports of median nerve injury with blind corticosteroid injections of the carpal tunnel,8,16,20,29 the exact incidence of this complication is largely unknown. However, what we do know is that intraneural injection of steroid medication is extremely neurotoxic
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Figure 5. Longitudinal view of the needle trajectory—superficial to flexor tendons (a) but deep to the transverse carpal ligament (b).
Figure 7. Superficial to the flexor tendons (a), the bolus of medication (b) is injected through the needle tip (arrow c) and into the carpal tunnel.
Figure 6. Position of the transducer at needle insertion.
and should be avoided.21 To improve accuracy and avoid the potential complication of intraneural injection, sonographically guided injections have been described,19,28,30
although the best method has yet to be determined. The distal-to-proximal approach to sonographically guided carpal tunnel injections may offer several advantages over the ulnar and proximal-to-distal approach.4,28,30 First, it enables the clinician to place the needle more parallel to the transducer face by way of wrist positioning. This can allow for better needle visualization throughout the procedure. Second, although the most effective location for corticosteroid injection in the carpal tunnel has yet to be determined,5 this method may provide better results due to delivery of steroid
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Figure 8. With the transducer held transversely on the wrist, the needle tip (arrow a) can be seen injecting the medication (b) superior and ulnarly to the median nerve (c), and just deep to the transverse carpal ligament (d).
medication that is closer to the site of maximum compression of the nerve at the midportion of the TCL.13 Third, this approach allows the needle and its bevel to be placed ulnarly and parallel to the median nerve at a tangential angle. By advancing the needle in this way under direct ultrasound guidance, there is likely a reduced risk of inadvertent penetration of the nerve or tendons resulting in intraneural or intratendinous injection and potential associated complications. Fourth, pushing the plunger on the syringe as the needle is slowly advanced through the ligament allows for immediate release of a leading bolus of fluid. As the fluid is released, any structures (including the median nerve) directly adherent to the undersurface of the TCL tend to be displaced palmarly and radially with the fluid bolus, potentially further reducing the risk of inadvertent penetration of the nerve or tendons. Finally, this approach allows the patient to position the hand comfortably in the supine position and for the clinician to comfortably and steadily rest his or her hand containing the needle on the table (and/or the patient’s hand), which may make the procedure ergonomically more appealing to both. Habib et al described similar ergonomic benefits to the surgeon with a blind distal-to-proximal approach10; however, the approach was not sonographically guided. Nevertheless, using this approach, many patients experienced decreased pain severity and neural improvement.25 Although median nerve damage may be less likely with this method than other blind methods,6 the method is likely more dangerous without
ultrasound guidance, because the location of the median nerve would be uncertain throughout the procedure. For this reason, it is likely that there is a higher risk of intraneural, intratendinous, or intravascular injection using a blind technique than with ultrasound guidance. Smith et al described an ulnar approach for carpal tunnel injections28 that offered the safety advantages of being sonographically guided. However, the method may be technically and ergonomically more challenging to execute than the distal-to-proximal method we describe. Furthermore, the needle trajectory taken with the ulnar approach may involve a higher risk of inadvertent penetration to the neurovascular structures, such as the ulnar artery and ulnar nerve, which have to be traversed with the needle during the approach. In addition, there is an increased risk of median nerve injection because the needle is directly toward and not parallel and tangential to it. Lee et al reported 3 variations of carpal tunnel injection techniques, one of which bears some similarity to our technique.19 Although that approach was sonographically guided and used a distal-to-proximal approach, the ultrasound transducer was orientated along the short axis of the median nerve, thus making the needle approach out-ofplane. Therefore, the technique described by Lee et al provides the benefits of ultrasound guidance, but the visibility of the needle tip is decreased because it is out-of-plane with respect to the ultrasound transducer axis. Likewise, the sonographically guided proximal-to-distal approach
6 described by Üstün et al shares some of the benefits of the currently described technique. However, the approach is out-of-plane with respect to the needle approach, which may be regarded as unsafe, due to a lack of sufficient needle visualization during the procedure.30 The closest match to the technique currently described in this technical note can be found in the study by Hong et al.11 The approach described there is sonographically guided, distal-to-proximal, and in-plane. However, the major difference is that with the technique of Hong et al, the needle is guided toward the median nerve, which may represent a serious safety issue. On the contrary, with the current technique, the median nerve is found using the ultrasound transducer along the long axis. The probe is then translated just ulnar, in order that the approach is in the interval between the median nerve and ulnar artery. Importantly, with this approach, needle insertion runs parallel to the median nerve and not toward it. In summary, we have found that performing sonographically guided carpal tunnel injections using the distal-toproximal approach is well tolerated by patients, with very little pain reported by patients. Although further studies are necessary to confirm our preliminary experience, this injection method appears to be safe and effective, and may be ergonomically more appealing for both the clinician and the patient. This procedure may lead to better results and fewer complications than previously described methods, although, certainly, further studies are necessary to validate this hypothesis. Ethical Approval This study was approved by our institutional review board.
Statement of Human and Animal Rights This article does not contain any studies with human or animal subjects.
Statement of Informed Consent Informed consent was not obtained for this study, as no patient information or identifying factors were used.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
References 1. Armstrong T, Devor W, Borschel L, Contreras R. Intracarpal steroid injection is safe and effective for short-term management of carpal tunnel syndrome. Muscle Nerve. 2004;29(1): 82-88.
HAND 00(0) 2. Azami A, Maleki N, Anari H, Iranparvar Alamdari M, Kalantarhormozi M, Tavosi Z. The diagnostic value of ultrasound compared with nerve conduction velocity in carpal tunnel syndrome. Int J Rheum Dis. 2014;17(6):612-620. 3. Blazar PE, Floyd WE, Han CH, Rozental TD, Earp BE. Prognostic indicators for recurrent symptoms after a single corticosteroid injection for carpal tunnel syndrome. J Bone Joint Surg Am. 2015;97(19):1563-1570. 4. Cartwright MS, White DL, DeMar S, et al. Median nerve changes following steroid injection for carpal tunnel syndrome. Muscle Nerve. 2011;44(1):25-29. 5. Dubert T, Racasan O. A reliable technique for avoiding the median nerve during carpal tunnel injections. Joint Bone Spine. 2006(73):77-79. 6. EL-Badaway MAA-F. Electrophysiological and clinical comparison of local steroid injection by means of proximal versus distal approach in patients with mild and moderate carpal tunnel syndrome. Egypt Rheumatol Rehabil. 2015;42:120-127. 7. Fowler JR, Munsch M, Tosti R, Hagberg WC, Imbriglia JE. Comparison of ultrasound and electrodiagnostic testing for diagnosis of carpal tunnel syndrome. J Bone Joint Surg Am. 2014;96(148):1-4. 8. Frederick H, Carter P, Littler J. Injection injuries to the median and ulnar nerves at the wrist. J Hand Surg Am. 1992;17(4):645-647. 9. Green DP. Diagnostic and therapeutic value of carpal tunnel injection. The Journal of Hand Surgery. 1984;9(6):850-854. 10. Habib GS, Badarney S, Rawashdeh H. A novel approach of local corticosteroid injection for the treatment of carpal tunnel syndrome. Clin Rheumatol. 2005;25:338-340. 11. Hong J-P, Lew HL, Lee C-H, Tang SF. Ultrasound-guided injection for the treatment of carpal tunnel syndrome. Am J Phys Med Rehabil. 2015;94(12):e119-e120. 12. Hui ACF, Wong S, Leung CH, et al. A randomized controlled trial of surgery vs steroid injection for carpal tunnel syndrome. Neurology. 2005;64(12):2074-2078. 13. Ikeda K, Osamura N, Tomita K. Segmental carpal canal pressure in patients with carpal tunnel syndrome. J Hand Surg Am. 2006;31A(6):925-929. 14. Kaplan E. Surface anatomy of the hand and wrist. In: Spinner E, ed. Functional and Surgical Anatomy of the Hand. Philadelphia, PA: J.B. Lippincott; 1953:227-231. 15. Kim DH, Jang JE, Park BK. Anatomical basis of ulnar approach in carpal tunnel injection. Pain Physician. 2013;16:191-198. 16. Kim H, Park S. Median nerve injuries caused by carpal tunnel injections. Korean J Pain. 2014;27(2):112-117. 17. Kopell HP. Carpal tunnel compression median neuropathy treated nonsurgically. N Y State J Med. 1958;58(5):744-745. 18. Leblanc K, Cestia W. Carpal tunnel syndrome. Am Fam Physician. 2011;83(8):952-958. 19. Lee JY, Park Y, Park KD, et al. Effectiveness of ultrasoundguided carpal tunnel injection using in-plane ulnar approach: a prospective, randomized, single-blind study. Medicine (Baltimore). 2014;93(29):e350 20. Linskey M, Segal R. Median nerve injury from local steroid injection in carpal tunnel syndrome. Neurosurgery. 1990;26(3):512-515. 21. Mackinnon SE, Hudson AR, Gentili F, Kline DG, Hunger D. Peripheral nerve injection injury with steroid agents. Plast Reconstr Surg. 1982;69(3):482-490.
Jurbala and Burbank 22. Makhlouf T, Emil N, Sibbitt W, Fields RA, Bankhurst AD. Outcomes and cost-effectiveness of carpal tunnel injections using sonographic needle guidance. Clin Rheumatol. 2014;33(6):849-858. 23. McDonagh C, Alexander M, Kane D. The role of ultrasound in the diagnosis and management of carpal tunnel syndrome: a new paradigm. Rheumatology. 2015;54:9-19 24. Miranda GV, Fernandes CH, Raduan Neto J, et al. Corticoid injection as a predictive factor of results of carpal tunnel release. Acta Ortop Bras. 2015;23(2):76-80. 25. Özdemir G, Demir R, Özel L, Ulvi H. The effect of steroid injection by novel method in carpal tunnel syndrome on pain severity and electrophysiological findings. Dicle Medical Journal. 2014;41(2):277-281. 26. Propeck T, Quinn TJ, Jacobson JA, et al. Sonography and MR imaging of bifid median nerve with anatomic and histologic correlation. AJR Am J Roentgenol. 2000;175(6): 1721-1725.
7 27. Saint-Lary O, Rébois A, Mediouni Z, Descatha A. Carpal tunnel syndrome: primary care and occupational factors. Front Med. 2015;2(28):1-4. 28. Smith J, Wisniewski SJ, Finnoff JT, Payne JM. Sonographically guided carpal tunnel injections: the ulnar approach. J Ultrasound Med. 2008;27(10):1485-1490. 29. Tavares SP, Giddins GEB. Nerve injury following ste roid injection for carpal tunnel syndrome. J Hand Surg. 1995;21B(2):208-209. 30. Üstün N, Tok F, Yagiz AE, et al. Ultrasound-guided versus blind steroid injections in carpal tunnel syndrome. Am J Phys Med Rehabil. 2013;92(11):999-1004. 31. Visser LH, Ngo Q, Groeneweg SJM, Brekelmans G. Longterm effect of local corticosteroid injection for carpal tunnel syndrome: a relation with electrodiagnostic severity. Clin Neurophysiol. 2012;123(4):838-841. 32. Wood MR. Hydrocortisone injections for carpal tunnel syndrome. Hand. 1980;12(1):62-64.
research-article2017
HANXXX10.1177/1558944717725375HANDJurbala and Burbank
Surgery Article
A Sonographically Guided In-Plane Distal-to-Proximal Transligamentous Approach to Carpal Tunnel Injections
HAND 1–7 © The Author(s) 2017 Reprints and permissions: sagepub.com/journalsPermissions.nav https://doi.org/10.1177/1558944717725375 DOI: 10.1177/1558944717725375 hand.sagepub.com
Brian M. Jurbala1 and Troy A. Burbank1
Abstract Background: Several sonographically guided injection methods have been described to treat carpal tunnel syndrome. In most cases, the medication diffuses through the carpal tunnel to the site of maximum compression of the nerve after being injected proximally. In this article, we describe a novel method of sonographically guided carpal tunnel injection that utilizes a distal-to-proximal, in-plane, and transligamentous approach. This novel method may provide ergonomic as well as safety advantages to both clinicians and patients, and should be considered by those performing carpal tunnel injections. Methods: A distal-to-proximal transligamentous approach is taken, utilizing high-resolution ultrasound guidance. Once the median nerve is sonographically visualized longitudinally within the carpal tunnel, an ulnar shift is made with the transducer. With the median nerve out of view, the needle is inserted in-line and distal to the transducer on the palmar side of the hand, at the ulnar portion of Kaplan’s cardinal line. Following a trajectory that is nearly parallel to the median nerve, the needle is sonographically guided to the site of maximum nerve compression. Conclusions: This novel method provides an alternative to previous carpal tunnel injections. The use of ultrasound guidance allows the clinician to visualize and avoid the neurovascular structures near the median nerve and guide the needle to the site of maximum nerve compression. It is possible that this parallel trajectory with the median nerve will provide a lower risk of damage to the nerve. Keywords: carpal tunnel syndrome, corticosteroids, sonography, injection, wrist
Introduction Carpal tunnel syndrome (CTS) is the most common form of upper limb entrapment neuropathy in adults, affecting approximately between 3% and 6% of the population.2,8,18 Most often affecting the dominant hand, the condition is caused by a decreased volume inside the carpal tunnel, resulting in a compression of the median nerve.27 For mild cases, therapies such as neutral wrist splints and oral corticosteroids are sometimes used.8,12,16,18 Steroid injections are considered the most effective conservative treatment for the symptoms of CTS1,3,23,24 and can also be used as a diagnostic tool.8,9,16,22,28,29,32 For more severe or recurrent cases, decompressive surgery should be considered.16,18 Conservative treatments overall have yielded symptom resolution at 12 months as low as 11%.24 Injection-specific studies generally report better 12-month follow-ups with between 31% and 50% of patients requiring no additional treatment.3,23 These results drop at an 18-month follow-up, with studies reporting between 6% and 34% of patients requiring no additional treatment.1,31 Corticosteroid injections are more effective in patients with mild CTS most,
while those suffering from severe CTS rarely gain relief from injections.31 Since carpal tunnel injections were first reported in 1958,17,20 there have been many complications associated with the procedure, such as muscle atrophy, depigmentation of the skin, and intratendinous and intravascular injections. The most common and serious complication is injury to the median nerve by intraneural penetration or injection, which can cause severe pain and, occasionally, sensory loss.5,8,16,20 As a way to prevent these complications and thereby improve patient outcomes, sonographically guided carpal tunnel injections were developed. Sonography allows clinicians to view anatomic variations in the carpal tunnel and landmark features to more accurately guide needle placement to the point of intercarpal injection.15,26 1
Highland Center for Orthopaedics, Lakeland, FL, USA
Corresponding Author: Troy A. Burbank, Highland Center for Orthopaedics, 2161 CR 540A #286, Lakeland, FL 33813, USA. Email: [email protected]
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Several sonographically guided methods for injection of corticosteroids to treat CTS have been described in the past. These methods, which include the proximal-to-distal inplane approach4,30 and the ulnar in-plane approach,28 involve viewing the carpal tunnel from either a long or short axis approach palmarly on the wrist and inserting the needle and injecting proximal to the carpal tunnel under the transverse carpal ligament (TCL).19 In both of these methods, the steroid medication, which is infused proximal to the carpal canal, travels by diffusion and mechanical movement of the tendons into the site of maximum nerve compression under the midportion of the TCL.28 We wish to describe a novel method of in-plane distal-toproximal transligamentous ultrasound-guided injection of the carpal canal that may have the advantages of allowing medication to be injected directly underneath the midportion of the TCL at the site of maximum compression of the nerve, improving visualization of the needle tip, reducing the risk of inadvertent nerve puncture (and potential for intraneural injection), and creating an ergonomically more comfortable experience for both the patient and clinician.
Materials and Methods The patient should be in a supine position, with the forearm supinated and the wrist positioned over a folded towel in 25° to 35° of dorsiflexion. Using a high-frequency linear transducer, a diagnostic scan of the wrist is performed to confirm the diagnosis of CTS based on a median nerve cross-sectional area larger than 1 cm2 just proximal to the level of the pisiform.7 A diagnostic scan should also be used to evaluate for secondary causes of nerve compression such as a tumor, cyst, or an aberrant muscle belly within the carpal canal. The nerve is scanned distally along the TCL until the superficial palmar arch at the level of Kaplan’s cardinal line (Figure 1) has been reached, and this line is noted with a marking pen. The transducer should then be translated 1 cm proximal to Kaplan’s cardinal line along the median nerve (Figure 2). In this view, the TCL, median nerve, and flexor tendons will appear to be traveling from proximal to distal obliquely and away from the transducer face (Figure 3). The transducer should then be translated ulnarly approximately 0.5 cm (Figure 4) until the median nerve is no longer visualized (Figure 5). Holding the transducer in place, an alcohol swab is used to clean the area on the palm in which the needle will be inserted. A 3-mL syringe should be prepared with 2.5 mL of a 1% lidocaine HCl solution (with or without epinephrine) and 0.5 mL of betamethasone sodium phosphate and betamethasone acetate 6 mg/mL injectable solution. A 27-gauge 1.5-in hypodermic needle should be used on the syringe. The needle is then inserted into the skin at or just distal to Kaplan’s line parallel to the transducer face (Figures 6). Patients should be told in advance that after the initial needle prick in the skin, they will feel very little pain. The needle is then
Figure 1. Kaplan’s cardinal line. Defined by Kaplan as “a line drawn from the apex of the interdigital fold between the thumb and index fingers toward the ulnar side of the hand, parallel with the middle crease of the hand.”14
Figure 2. Transducer starting point when scanning for the median nerve.
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Figure 3. Longitudinal view of the median nerve.
the midportion of the TCL. The angle bevel of the needle should be directed such that it matches the obliquity of the TCL. Resistance caused by the thickness of ligament will be felt if this is done slowly. After the needle reaches the ligament, pressure is then applied to the plunger on the syringe. Because of the density of the ligamentous tissue, very little fluid will be able to be injected. The needle is slowly advanced while simultaneously pressing the needle plunger. As soon as the needle passes from the ligament tissue into the carpal canal, there will be a sudden loss of resistance at the syringe plunger, and further passage of the needle should be stopped. A hypoechoic bolus of fluid will be seen as it fills the carpal canal and displaces any tendons or nerve tissue directly in opposition to the undersurface of the TCL (Figures 7 and 8). In some instances, hyperechoic crystalline components of the steroid medication can be visualized in the superior portion of the hypoechoic bolus below the ligament. Once the full volume of medication is injected, the needle can then be withdrawn from the patient. If there is any blood at the injection site, it should be wiped clean and a band-aid applied to the injection site. Figure 4. Ulnar translation of the transducer adjusts the median nerve out of view. The transducer is now parallel with the needle trajectory.
advanced and should be seen clearly as it passes through the space above the TCL until it starts to pass obliquely across
Discussion Although there have been case reports of median nerve injury with blind corticosteroid injections of the carpal tunnel,8,16,20,29 the exact incidence of this complication is largely unknown. However, what we do know is that intraneural injection of steroid medication is extremely neurotoxic
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Figure 5. Longitudinal view of the needle trajectory—superficial to flexor tendons (a) but deep to the transverse carpal ligament (b).
Figure 7. Superficial to the flexor tendons (a), the bolus of medication (b) is injected through the needle tip (arrow c) and into the carpal tunnel.
Figure 6. Position of the transducer at needle insertion.
and should be avoided.21 To improve accuracy and avoid the potential complication of intraneural injection, sonographically guided injections have been described,19,28,30
although the best method has yet to be determined. The distal-to-proximal approach to sonographically guided carpal tunnel injections may offer several advantages over the ulnar and proximal-to-distal approach.4,28,30 First, it enables the clinician to place the needle more parallel to the transducer face by way of wrist positioning. This can allow for better needle visualization throughout the procedure. Second, although the most effective location for corticosteroid injection in the carpal tunnel has yet to be determined,5 this method may provide better results due to delivery of steroid
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Figure 8. With the transducer held transversely on the wrist, the needle tip (arrow a) can be seen injecting the medication (b) superior and ulnarly to the median nerve (c), and just deep to the transverse carpal ligament (d).
medication that is closer to the site of maximum compression of the nerve at the midportion of the TCL.13 Third, this approach allows the needle and its bevel to be placed ulnarly and parallel to the median nerve at a tangential angle. By advancing the needle in this way under direct ultrasound guidance, there is likely a reduced risk of inadvertent penetration of the nerve or tendons resulting in intraneural or intratendinous injection and potential associated complications. Fourth, pushing the plunger on the syringe as the needle is slowly advanced through the ligament allows for immediate release of a leading bolus of fluid. As the fluid is released, any structures (including the median nerve) directly adherent to the undersurface of the TCL tend to be displaced palmarly and radially with the fluid bolus, potentially further reducing the risk of inadvertent penetration of the nerve or tendons. Finally, this approach allows the patient to position the hand comfortably in the supine position and for the clinician to comfortably and steadily rest his or her hand containing the needle on the table (and/or the patient’s hand), which may make the procedure ergonomically more appealing to both. Habib et al described similar ergonomic benefits to the surgeon with a blind distal-to-proximal approach10; however, the approach was not sonographically guided. Nevertheless, using this approach, many patients experienced decreased pain severity and neural improvement.25 Although median nerve damage may be less likely with this method than other blind methods,6 the method is likely more dangerous without
ultrasound guidance, because the location of the median nerve would be uncertain throughout the procedure. For this reason, it is likely that there is a higher risk of intraneural, intratendinous, or intravascular injection using a blind technique than with ultrasound guidance. Smith et al described an ulnar approach for carpal tunnel injections28 that offered the safety advantages of being sonographically guided. However, the method may be technically and ergonomically more challenging to execute than the distal-to-proximal method we describe. Furthermore, the needle trajectory taken with the ulnar approach may involve a higher risk of inadvertent penetration to the neurovascular structures, such as the ulnar artery and ulnar nerve, which have to be traversed with the needle during the approach. In addition, there is an increased risk of median nerve injection because the needle is directly toward and not parallel and tangential to it. Lee et al reported 3 variations of carpal tunnel injection techniques, one of which bears some similarity to our technique.19 Although that approach was sonographically guided and used a distal-to-proximal approach, the ultrasound transducer was orientated along the short axis of the median nerve, thus making the needle approach out-ofplane. Therefore, the technique described by Lee et al provides the benefits of ultrasound guidance, but the visibility of the needle tip is decreased because it is out-of-plane with respect to the ultrasound transducer axis. Likewise, the sonographically guided proximal-to-distal approach
6 described by Üstün et al shares some of the benefits of the currently described technique. However, the approach is out-of-plane with respect to the needle approach, which may be regarded as unsafe, due to a lack of sufficient needle visualization during the procedure.30 The closest match to the technique currently described in this technical note can be found in the study by Hong et al.11 The approach described there is sonographically guided, distal-to-proximal, and in-plane. However, the major difference is that with the technique of Hong et al, the needle is guided toward the median nerve, which may represent a serious safety issue. On the contrary, with the current technique, the median nerve is found using the ultrasound transducer along the long axis. The probe is then translated just ulnar, in order that the approach is in the interval between the median nerve and ulnar artery. Importantly, with this approach, needle insertion runs parallel to the median nerve and not toward it. In summary, we have found that performing sonographically guided carpal tunnel injections using the distal-toproximal approach is well tolerated by patients, with very little pain reported by patients. Although further studies are necessary to confirm our preliminary experience, this injection method appears to be safe and effective, and may be ergonomically more appealing for both the clinician and the patient. This procedure may lead to better results and fewer complications than previously described methods, although, certainly, further studies are necessary to validate this hypothesis. Ethical Approval This study was approved by our institutional review board.
Statement of Human and Animal Rights This article does not contain any studies with human or animal subjects.
Statement of Informed Consent Informed consent was not obtained for this study, as no patient information or identifying factors were used.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
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