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The accuracy of distal posterior interosseous and anterior interosseous nerve injection
The Accuracy of Distal Posterior Interosseous and Anterior Interosseous Nerve Injection Paul W. Grutter, MD, Gregory L. DeSilva, MD, Robert E. Meehan, MD, Stephen P. DeSilva, MD, Detroit, MI
Purpose: To standardize a technique of delivering a local anesthetic to the posterior interosseous nerve (PIN) and anterior interosseous nerve (AIN) by using the anatomic landmarks of the wrist and to evaluate the accuracy of the technique in a cadaver model. Methods: Techniques for PIN and AIN injection and for PIN injection alone are described. Techniques were tested in a fresh frozen cadaver model by using methylene blue injections. Stained nerves were dissected under loupe magnification. Digital photographic images were taken of each nerve. Staining was quantified by calculating the mean density and area stained. Results: For both techniques methylene blue was delivered accurately to the PIN in 100% of the samples. Methylene blue was delivered accurately to the AIN in 100% of samples in which it was injected. Conclusions: These techniques saturated successfully the PIN and AIN and may be useful as diagnostic and therapeutic tools for chronic wrist pain and in evaluating presurgically the effectiveness of partial wrist denervation. (J Hand Surg 2004;29A:865– 870. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Denervation, injection, interosseous, nerve, wrist.
Complete or partial wrist denervation has been advocated as a useful palliative procedure when reconstructive procedures for chronic wrist pain are not feasible or desired.1– 8 The innervation of the wrist has been studied both histologically and with microdissection9,10 and techniques for wrist denervation have been well described.1–5 Initial attempts at wrist From the Department of Orthopaedic Surgery, Wayne State University, Detroit, MI. Received for publication September 30, 2002; accepted in revised form May 10, 2004. No benefits in any form have been received or will be received by a commercial party related directly or indirectly to the subject of this article. Reprint requests: Gregory L. DeSilva, MD, Department of Orthopaedic Surgery, Wayne State University, 4201 St Antoine, UHC, 7C, Detroit, MI 48201. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A05-0013$30.00/0 doi:10.1016/j.jhsa.2004.05.012
denervation sought to provide complete denervation and required multiple incisions. The ulnar nerve (dorsal branch and main trunk), radial nerve (dorsal branch and posterior interosseous nerve), lateral antebrachial cutaneous nerve, medial antebrachial cutaneous nerve, and median nerve (palmar cutaneous branch and anterior interosseous nerve) have all been shown to contribute branches to the wrist. More recent descriptions have shown similar results with posterior interosseous nerve (PIN) resection with or without anterior interosseous nerve (AIN) resection, which can be done via a single incision.5,8 Posterior interosseous nerve resection alone has been advocated as a useful secondary procedure for patients having many elective wrist procedures such as arthrodesis and resection/implant arthroplasty.8 The branches of the PIN have been described thoroughly.11 The fifth branch of the PIN divides into a radial and ulnar branch at a mean distance of 12.8 The Journal of Hand Surgery
865
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The Journal of Hand Surgery / Vol. 29A No. 5 September 2004
Figure 1. Injection sites. X indicates the 2 injection sites used. Group 1, 1 cm ulnar and 3 cm proximal to Lister’s tubercle; group 2, 1 cm proximal to Lister’s tubercle.
⫾ 2.2 cm proximal to Lister’s tubercle.11 The ulnar branch supplies the extensor pollicis longus and extensor indicis proprius. The radial branch supplies the extensor pollicis longus and extensor pollicis brevis before passing deep to the level of the interosseous membrane where it courses before innervating the dorsal wrist capsule. This terminal branch of the PIN has been shown to be the main articular branch to the dorsal aspect of the wrist capsule.9,12 The terminal branch of the PIN runs along the dorsal surface of the interosseous membrane and has a length between 5 and 10 cm.12 In the distal forearm near the wrist the terminal branch of the PIN is located in the radial deep aspect of the fourth dorsal compartment. It is based in the fascial layer ulnar to Lister’s tubercle and superficial to the periosteum of the radius. Resection of this terminal branch anywhere along its length provides denervation to the main portion of the dorsal aspect of the wrist capsule. Although there is no main articular branch on the palmar aspect of the wrist such as the PIN on the dorsal aspect the AIN has been shown to provide partial innervation to the palmar radiocarpal joint.9 In the distal forearm the AIN runs along the volar surface of the interosseous membrane. This location makes the AIN easily amendable to resection along with the PIN when performing partial wrist denervation through a dorsal incision.5 Local anesthetic injections are advocated as a key to the presurgical evaluation in patients with chronic wrist pain to determine which patients will benefit from partial wrist denervation.2–5,13,14 Isolated PIN injection or combined PIN/AIN injections can be performed. In an initial office visit the PIN can be injected and monitored with a pain diary. In a subsequent office visit the PIN and AIN can be injected and the results used to determine the appropriate procedure. Posterior interosseous nerve injection
alone is useful during presurgical evaluation of other procedures such as proximal row carpectomy and total wrist arthrodesis to evaluate whether denervation may be a useful adjunct to these procedures. Other than Weinstein and Berger,5 researchers fail to provide a detailed description of how to perform a PIN and AIN blockade using anatomic landmarks. The accuracy of local anesthetic techniques for PIN and AIN blockade has not been studied or validated. We sought to standardize techniques of delivering a local anesthetic to the PIN and AIN or the PIN alone using the anatomic landmarks of the wrist and to evaluate their accuracy using modern digital imaging techniques.
Materials and Methods Based on the previously described anatomy of the PIN and AIN9,12 multiple injection sites were pilottested in embalmed cadavers. Lister’s tubercle was used as the reference point. By using these preliminary observations, 2 injection sites were selected as shown in Figure 1. For group 1, AIN and PIN injection, a site 1 cm ulnar and 3 cm proximal to Lister’s tubercle was used. For group 2, PIN injection alone, an injection site 1 cm ulnar to the proximal aspect of Lister’s tubercle was evaluated. For group 1 injections a 3.8-cm 25-gauge needle was advanced from dorsal to volar beginning 1 cm ulnar and 3 cm proximal to Lister’s tubercle. The needle was advanced until the slight resistance of the interosseous membrane was encountered. This is similar to the increased resistance felt just before the needle “pops” through the dura into the subarachnoid space when doing a lumbar puncture. Once the interosseous membrane was encountered the needle was withdrawn minimally and 1 mL of a 0.5% methylene blue solution was
Figure 2. Forearm cross section of group 1 injection for PIN and AIN blockade.
Grutter et al / PIN and AIN Injection Technique
Figure 3. Wrist cross section of group 2 injections for PIN blockade.
injected just dorsal to the interosseous membrane to simulate PIN blockade as shown in Figure 2. The needle was then advanced just past the interosseous membrane and an additional 1 mL of methylene blue solution was injected to attempt blockade of the AIN. This technique was evaluated in 11 fresh frozen cadavers. For group 2 injections the needle was inserted 1 cm ulnar to the proximal aspect of Lister’s tubercle. Advancing the needle from dorsal to volar until the distal radius is encountered places the tip of the needle in the floor of the fourth extensor compartment where the distal sensory branch of the PIN is located as shown in Figure 3. Because the fourth
867
extensor compartment is a much more confined space group 2 injections consisted of 0.5 mL of 0.5% methylene blue. Five fresh frozen cadavers were injected. After injection the PIN and AIN (group 1) or the PIN alone (group 2) were dissected out using 2.5⫻ loupe magnification. Posterior interosseous nerve dissections were done through a 7- to 9-cm longitudinal incision made dorsally between the distal radius and ulna. The deep antebrachial fascia and extensor retinculum were incised longitudinally exposing the extensor compartment. The extensor tendons and muscles were retracted exposing the PIN on the dorsal surface of the interosseous membrane. An approximately 8-cm section of the PIN was resected from its terminal insertion into the dorsal wrist capsule proximally. Anterior interosseous nerve dissections were done through a separate 5- to 7-cm longitudinal incision made volarly between the distal radius and ulna. The flexor muscles and tendons were retracted in a similar fashion exposing the AIN running along the interosseous membrane before it passes deep to and innervates the pronator quadratus (Fig. 4). The pronator quadratus was then split in its midline exposing the terminal branches of the AIN (Fig. 5). Approximately 8 cm of the AIN was then resected from its terminal insertion into the volar wrist capsule proximally.
Figure 4. Example of AIN dissection after injection using group 1 injection technique. Retraction of flexor muscles and tendons shows the AIN running along the interosseous membrane before passing beneath the pronator quadratus (PQ) on its way to innervate the volar wrist capsule.
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Figure 5. Example of AIN dissection after injection. The same specimen as shown in Figure 4 is shown after the pronator quadratus has been split in its midline showing intense staining of the terminal branches of the AIN.
A concentration gradient of methylene blue saturation was also created as a quantification standard. Ten 0.5-cm sections of the proximal aspect of the PIN in 1 specimen were dipped in serial dilutions of methylene blue from 0.5% to 0.0% methylene blue to create a gradient of blue color correlating to the concentration of stain uptake. Digital photographic images of each resected nerve and the concentration gradient were taken as
shown in Figure 6. Images were taken at the camera’s highest resolution (2048 ⫻ 1536 pixels). A rule was included in each image for calibration purposes. The images were analyzed using image analysis software (Image Pro Plus, Media Cybernetics Silver Spring, MD) to quantify staining. The image analysis software package provides sophisticated image acquisition, processing, measurement, and analysis options. The software calculates the mean density (in-
Figure 6. Dissected PIN and AIN after injection.
Grutter et al / PIN and AIN Injection Technique
tensity) in an area and converts to integrated optical density (IOD), which normalizes any nonspecific errors among specimens. It also provides the total stained area based on the color spectrum. The 0.5% methylene blue specimen from the concentration gradient was used for color selection. The mean IOD of each specimen in the concentration gradient was plotted using graphical analysis software (SigmaPlot 8.0 Statistical Solutions, Saugus, MA) and the correspondence of mean IOD measurements with methylene blue saturation was validated. Specimens with a mean IOD of 43.37 or lower were saturated visually with methylene blue and considered successful injections. Lower values of mean IOD corresponded to increased methylene blue saturation. For each PIN and AIN specimen the mean IOD of a 100 pixel2 maximally stained area was measured to determine its saturation of methylene blue.
Results Methylene blue was delivered accurately to the PIN in 100% of the samples using both techniques. Methylene blue was delivered accurately to the AIN in 100% of samples in group 1. For group 1 the average mean densities of staining for the PIN and AIN were 15.96 and 22.70, respectively. For group 2 the average mean density of staining for the PIN was 15.93. The difference in PIN injections was not statistically significant (p⫽.37). The average areas of staining for the PIN and AIN in group 1 injections were 83.97m2 and 82.87m2, respectively. The average area stained in group 2 PIN injections was 33.41m2. The difference in PIN area stained was statistically significant (p ⬍ .05) between groups 1 and 2.
Discussion Partial wrist denervation provides good results in patients with chronic wrist pain. The injection techniques outlined above show local anesthetic can be delivered effectively to the PIN and AIN and can be used to determine which patients may benefit from partial denervation. The group 1 injection technique is very similar to that described by Weinstein and Berger.5 In their technique the needle is placed 2 cm proximal to the distal radioulnar joint and advanced 5 mm. Two milliliters of local anesthetic is injected to block the PIN. The needle is then advanced an additional 5 mm, penetrating the interosseous membrane, and an additional 2 mL of anesthetic is injected to block the AIN. We used Lister’s tubercle as our reference point because we believe it is defined more easily and produces a more reproduc-
869
ible injection site. Also, because there is a great deal of anatomic variation and an increasingly obese population we believed that advancing the needle 5 mm in all patients potentially risks injection into subcutaneous fat alone, producing false negative results. In a patient of ideal body weight both the described technique and that described by Weinstein and Berger5 produce similar injection sites and would likely produce identical results. In group 1 the goal was to provide local anesthetic blockade of both the PIN and AIN. The efficacy of this injection site depends on the ability of the examiner to feel the interosseous membrane with a 25-gauge needle. Should the physician not feel the interosseous membrane the entire injection could be placed volar to the interosseous membrane (not providing blockade of the PIN) or volar to the pronator quadratus (not affecting either nerve). Although the group 1 injection technique was reproducible in the laboratory its efficacy in the clinical setting will be determined by the examiner’s ability to appreciate the interosseous membrane. The group 2 injection site, 1 cm ulnar to Lister’s tubercle, may be easier clinically because it is based on bony anatomy alone. In group 2 we evaluated an isolated PIN blockade, which is performed easily because it relies on bony anatomy alone. Isolated PIN blockade can serve also as a useful comparison between results for PIN resection alone or PIN and AIN resection if opposite injection techniques are used in subsequent clinic visits. Isolated PIN injection serves also as a useful presurgical evaluation of the contribution of PIN resection in combined procedures. The group 2 technique allows injection into a relatively confined area, the ring finger extensor compartment. This allows for small, localized injections with less concern for extravasation. Large-volume local anesthetic injections in undefined compartments cause concerns that the perceived analgesia may not be from the intended blockade but from extravasation and blockade elsewhere. Our study shows that distal PIN injection provided equivalent staining of the nerve but over a smaller area than proximal injection. This may be due to the larger injection volume used for proximal PIN injections (1 mL proximally and 0.5 mL distally) and the lack of a distinct compartment to inject into proximally with the resultant extravasation of dye. This study shows that local anesthetic can be delivered accurately and predictably to the PIN and AIN nerves. The PIN alone can be blocked reliably with an injection 1 cm ulnar to Lister’s tubercle with the needle
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The Journal of Hand Surgery / Vol. 29A No. 5 September 2004
just touching the radius and both the PIN and AIN can be anesthetized from a single injection site beginning 1 cm ulnar and 3 cm proximal to Lister’s tubercle. With a better understanding of the anatomy of the PIN and AIN based on superficial landmarks a blockade of the AIN and PIN may be easier to accomplish clinically. Local anesthetic injection of the PIN and AIN may help determine which patients will benefit from partial wrist denervation alone or as an adjunct to other procedures about the wrist. We thank Dr Shang-You Yang for his assistance with image analysis.
References 1. Wilhelm A. Gelenkdenervation und ihre anatomishcen Grundlagen. Ein neues Behandlungsprinzip in der Handechirurgie. [Articular denervation and its anatomical foundation. A new therapeutic principle in hand surgery. On the treatment of the later stages of lunatomalacia and navicular pseudarthrosis.] Hefte Unfallheilkd 1966;86:1–109. 2. Ferreres A, Foucher G, Suso S. Extensive denervation of the wrist. Techniques in Hand and Upper Extremity Surgery 2002;6:36 – 41. 3. Buck-Gramcko D. Denervation of the wrist joint. J Hand Surg 1977;2A:54 – 61. 4. Ferreres A, Suso S, Foucher G, Ordi J, Llusa M, Ruano D. Wrist denervation. Surgical considerations. J Hand Surg 1995; 20B:769 –772.
5. Weinstein LP, Berger RA. Analgesic benefit, functional outcome, and patient satisfaction after partial wrist denervation. J Hand Surg 2002;27A:833– 839. 6. Geldmacher J, Legal HR, Brug E. Results of denervation of the wrist and wrist joint by Wilhelm’s method. Hand 1972; 4:57–59. 7. Rostlund T, Somnier F, Axelsson R. Denervation of the wrist joint—an alternative in conditions of chronic pain. Acta Orthop Scand 1980;51:609 – 616. 8. Dellon AL. Partial dorsal wrist denervation: resection of the distal posterior interosseous nerve. J Hand Surg 1985;10A: 527–533. 9. Fukumoto K, Kojima T, Kinoshita Y, Koda M. An anatomic study of the innervation of the wrist joint and Wilhelm’s technique for denervation. J Hand Surg 1993;18A:484 – 489. 10. Ferreres A, Suso S, Ordi J, Llusa M, Ruano D. Wrist denervation. Anatomical considerations. J Hand Surg 1995; 20B:761–768. 11. Elgafy H, Ebraheim NA, Rezcallah AT, Yeasting RA. Posterior interosseous nerve terminal branches. Clin Orthop 2000; 376:242–251. 12. Waters PM, Schwartz JT. Posterior interosseous nerve: an anatomic study of potential nerve grafts. J Hand Surg 1993; 18A:743–745. 13. Lluch AL, Beasley RW. Treatment of dysesthesia of the sensory branch of the radial nerve by distal posterior interosseous neurectomy. J Hand Surg 1989;14A:121–124. 14. Loh YC, Stanley JK, Jari S, Trail IA. Neuroma of the distal posterior interosseous nerve. A cause of iatrogenic wrist pain. J Bone Joint Surg 1998;80B:629 – 630.
Purpose: To standardize a technique of delivering a local anesthetic to the posterior interosseous nerve (PIN) and anterior interosseous nerve (AIN) by using the anatomic landmarks of the wrist and to evaluate the accuracy of the technique in a cadaver model. Methods: Techniques for PIN and AIN injection and for PIN injection alone are described. Techniques were tested in a fresh frozen cadaver model by using methylene blue injections. Stained nerves were dissected under loupe magnification. Digital photographic images were taken of each nerve. Staining was quantified by calculating the mean density and area stained. Results: For both techniques methylene blue was delivered accurately to the PIN in 100% of the samples. Methylene blue was delivered accurately to the AIN in 100% of samples in which it was injected. Conclusions: These techniques saturated successfully the PIN and AIN and may be useful as diagnostic and therapeutic tools for chronic wrist pain and in evaluating presurgically the effectiveness of partial wrist denervation. (J Hand Surg 2004;29A:865– 870. Copyright © 2004 by the American Society for Surgery of the Hand.) Key words: Denervation, injection, interosseous, nerve, wrist.
Complete or partial wrist denervation has been advocated as a useful palliative procedure when reconstructive procedures for chronic wrist pain are not feasible or desired.1– 8 The innervation of the wrist has been studied both histologically and with microdissection9,10 and techniques for wrist denervation have been well described.1–5 Initial attempts at wrist From the Department of Orthopaedic Surgery, Wayne State University, Detroit, MI. Received for publication September 30, 2002; accepted in revised form May 10, 2004. No benefits in any form have been received or will be received by a commercial party related directly or indirectly to the subject of this article. Reprint requests: Gregory L. DeSilva, MD, Department of Orthopaedic Surgery, Wayne State University, 4201 St Antoine, UHC, 7C, Detroit, MI 48201. Copyright © 2004 by the American Society for Surgery of the Hand 0363-5023/04/29A05-0013$30.00/0 doi:10.1016/j.jhsa.2004.05.012
denervation sought to provide complete denervation and required multiple incisions. The ulnar nerve (dorsal branch and main trunk), radial nerve (dorsal branch and posterior interosseous nerve), lateral antebrachial cutaneous nerve, medial antebrachial cutaneous nerve, and median nerve (palmar cutaneous branch and anterior interosseous nerve) have all been shown to contribute branches to the wrist. More recent descriptions have shown similar results with posterior interosseous nerve (PIN) resection with or without anterior interosseous nerve (AIN) resection, which can be done via a single incision.5,8 Posterior interosseous nerve resection alone has been advocated as a useful secondary procedure for patients having many elective wrist procedures such as arthrodesis and resection/implant arthroplasty.8 The branches of the PIN have been described thoroughly.11 The fifth branch of the PIN divides into a radial and ulnar branch at a mean distance of 12.8 The Journal of Hand Surgery
865
866
The Journal of Hand Surgery / Vol. 29A No. 5 September 2004
Figure 1. Injection sites. X indicates the 2 injection sites used. Group 1, 1 cm ulnar and 3 cm proximal to Lister’s tubercle; group 2, 1 cm proximal to Lister’s tubercle.
⫾ 2.2 cm proximal to Lister’s tubercle.11 The ulnar branch supplies the extensor pollicis longus and extensor indicis proprius. The radial branch supplies the extensor pollicis longus and extensor pollicis brevis before passing deep to the level of the interosseous membrane where it courses before innervating the dorsal wrist capsule. This terminal branch of the PIN has been shown to be the main articular branch to the dorsal aspect of the wrist capsule.9,12 The terminal branch of the PIN runs along the dorsal surface of the interosseous membrane and has a length between 5 and 10 cm.12 In the distal forearm near the wrist the terminal branch of the PIN is located in the radial deep aspect of the fourth dorsal compartment. It is based in the fascial layer ulnar to Lister’s tubercle and superficial to the periosteum of the radius. Resection of this terminal branch anywhere along its length provides denervation to the main portion of the dorsal aspect of the wrist capsule. Although there is no main articular branch on the palmar aspect of the wrist such as the PIN on the dorsal aspect the AIN has been shown to provide partial innervation to the palmar radiocarpal joint.9 In the distal forearm the AIN runs along the volar surface of the interosseous membrane. This location makes the AIN easily amendable to resection along with the PIN when performing partial wrist denervation through a dorsal incision.5 Local anesthetic injections are advocated as a key to the presurgical evaluation in patients with chronic wrist pain to determine which patients will benefit from partial wrist denervation.2–5,13,14 Isolated PIN injection or combined PIN/AIN injections can be performed. In an initial office visit the PIN can be injected and monitored with a pain diary. In a subsequent office visit the PIN and AIN can be injected and the results used to determine the appropriate procedure. Posterior interosseous nerve injection
alone is useful during presurgical evaluation of other procedures such as proximal row carpectomy and total wrist arthrodesis to evaluate whether denervation may be a useful adjunct to these procedures. Other than Weinstein and Berger,5 researchers fail to provide a detailed description of how to perform a PIN and AIN blockade using anatomic landmarks. The accuracy of local anesthetic techniques for PIN and AIN blockade has not been studied or validated. We sought to standardize techniques of delivering a local anesthetic to the PIN and AIN or the PIN alone using the anatomic landmarks of the wrist and to evaluate their accuracy using modern digital imaging techniques.
Materials and Methods Based on the previously described anatomy of the PIN and AIN9,12 multiple injection sites were pilottested in embalmed cadavers. Lister’s tubercle was used as the reference point. By using these preliminary observations, 2 injection sites were selected as shown in Figure 1. For group 1, AIN and PIN injection, a site 1 cm ulnar and 3 cm proximal to Lister’s tubercle was used. For group 2, PIN injection alone, an injection site 1 cm ulnar to the proximal aspect of Lister’s tubercle was evaluated. For group 1 injections a 3.8-cm 25-gauge needle was advanced from dorsal to volar beginning 1 cm ulnar and 3 cm proximal to Lister’s tubercle. The needle was advanced until the slight resistance of the interosseous membrane was encountered. This is similar to the increased resistance felt just before the needle “pops” through the dura into the subarachnoid space when doing a lumbar puncture. Once the interosseous membrane was encountered the needle was withdrawn minimally and 1 mL of a 0.5% methylene blue solution was
Figure 2. Forearm cross section of group 1 injection for PIN and AIN blockade.
Grutter et al / PIN and AIN Injection Technique
Figure 3. Wrist cross section of group 2 injections for PIN blockade.
injected just dorsal to the interosseous membrane to simulate PIN blockade as shown in Figure 2. The needle was then advanced just past the interosseous membrane and an additional 1 mL of methylene blue solution was injected to attempt blockade of the AIN. This technique was evaluated in 11 fresh frozen cadavers. For group 2 injections the needle was inserted 1 cm ulnar to the proximal aspect of Lister’s tubercle. Advancing the needle from dorsal to volar until the distal radius is encountered places the tip of the needle in the floor of the fourth extensor compartment where the distal sensory branch of the PIN is located as shown in Figure 3. Because the fourth
867
extensor compartment is a much more confined space group 2 injections consisted of 0.5 mL of 0.5% methylene blue. Five fresh frozen cadavers were injected. After injection the PIN and AIN (group 1) or the PIN alone (group 2) were dissected out using 2.5⫻ loupe magnification. Posterior interosseous nerve dissections were done through a 7- to 9-cm longitudinal incision made dorsally between the distal radius and ulna. The deep antebrachial fascia and extensor retinculum were incised longitudinally exposing the extensor compartment. The extensor tendons and muscles were retracted exposing the PIN on the dorsal surface of the interosseous membrane. An approximately 8-cm section of the PIN was resected from its terminal insertion into the dorsal wrist capsule proximally. Anterior interosseous nerve dissections were done through a separate 5- to 7-cm longitudinal incision made volarly between the distal radius and ulna. The flexor muscles and tendons were retracted in a similar fashion exposing the AIN running along the interosseous membrane before it passes deep to and innervates the pronator quadratus (Fig. 4). The pronator quadratus was then split in its midline exposing the terminal branches of the AIN (Fig. 5). Approximately 8 cm of the AIN was then resected from its terminal insertion into the volar wrist capsule proximally.
Figure 4. Example of AIN dissection after injection using group 1 injection technique. Retraction of flexor muscles and tendons shows the AIN running along the interosseous membrane before passing beneath the pronator quadratus (PQ) on its way to innervate the volar wrist capsule.
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The Journal of Hand Surgery / Vol. 29A No. 5 September 2004
Figure 5. Example of AIN dissection after injection. The same specimen as shown in Figure 4 is shown after the pronator quadratus has been split in its midline showing intense staining of the terminal branches of the AIN.
A concentration gradient of methylene blue saturation was also created as a quantification standard. Ten 0.5-cm sections of the proximal aspect of the PIN in 1 specimen were dipped in serial dilutions of methylene blue from 0.5% to 0.0% methylene blue to create a gradient of blue color correlating to the concentration of stain uptake. Digital photographic images of each resected nerve and the concentration gradient were taken as
shown in Figure 6. Images were taken at the camera’s highest resolution (2048 ⫻ 1536 pixels). A rule was included in each image for calibration purposes. The images were analyzed using image analysis software (Image Pro Plus, Media Cybernetics Silver Spring, MD) to quantify staining. The image analysis software package provides sophisticated image acquisition, processing, measurement, and analysis options. The software calculates the mean density (in-
Figure 6. Dissected PIN and AIN after injection.
Grutter et al / PIN and AIN Injection Technique
tensity) in an area and converts to integrated optical density (IOD), which normalizes any nonspecific errors among specimens. It also provides the total stained area based on the color spectrum. The 0.5% methylene blue specimen from the concentration gradient was used for color selection. The mean IOD of each specimen in the concentration gradient was plotted using graphical analysis software (SigmaPlot 8.0 Statistical Solutions, Saugus, MA) and the correspondence of mean IOD measurements with methylene blue saturation was validated. Specimens with a mean IOD of 43.37 or lower were saturated visually with methylene blue and considered successful injections. Lower values of mean IOD corresponded to increased methylene blue saturation. For each PIN and AIN specimen the mean IOD of a 100 pixel2 maximally stained area was measured to determine its saturation of methylene blue.
Results Methylene blue was delivered accurately to the PIN in 100% of the samples using both techniques. Methylene blue was delivered accurately to the AIN in 100% of samples in group 1. For group 1 the average mean densities of staining for the PIN and AIN were 15.96 and 22.70, respectively. For group 2 the average mean density of staining for the PIN was 15.93. The difference in PIN injections was not statistically significant (p⫽.37). The average areas of staining for the PIN and AIN in group 1 injections were 83.97m2 and 82.87m2, respectively. The average area stained in group 2 PIN injections was 33.41m2. The difference in PIN area stained was statistically significant (p ⬍ .05) between groups 1 and 2.
Discussion Partial wrist denervation provides good results in patients with chronic wrist pain. The injection techniques outlined above show local anesthetic can be delivered effectively to the PIN and AIN and can be used to determine which patients may benefit from partial denervation. The group 1 injection technique is very similar to that described by Weinstein and Berger.5 In their technique the needle is placed 2 cm proximal to the distal radioulnar joint and advanced 5 mm. Two milliliters of local anesthetic is injected to block the PIN. The needle is then advanced an additional 5 mm, penetrating the interosseous membrane, and an additional 2 mL of anesthetic is injected to block the AIN. We used Lister’s tubercle as our reference point because we believe it is defined more easily and produces a more reproduc-
869
ible injection site. Also, because there is a great deal of anatomic variation and an increasingly obese population we believed that advancing the needle 5 mm in all patients potentially risks injection into subcutaneous fat alone, producing false negative results. In a patient of ideal body weight both the described technique and that described by Weinstein and Berger5 produce similar injection sites and would likely produce identical results. In group 1 the goal was to provide local anesthetic blockade of both the PIN and AIN. The efficacy of this injection site depends on the ability of the examiner to feel the interosseous membrane with a 25-gauge needle. Should the physician not feel the interosseous membrane the entire injection could be placed volar to the interosseous membrane (not providing blockade of the PIN) or volar to the pronator quadratus (not affecting either nerve). Although the group 1 injection technique was reproducible in the laboratory its efficacy in the clinical setting will be determined by the examiner’s ability to appreciate the interosseous membrane. The group 2 injection site, 1 cm ulnar to Lister’s tubercle, may be easier clinically because it is based on bony anatomy alone. In group 2 we evaluated an isolated PIN blockade, which is performed easily because it relies on bony anatomy alone. Isolated PIN blockade can serve also as a useful comparison between results for PIN resection alone or PIN and AIN resection if opposite injection techniques are used in subsequent clinic visits. Isolated PIN injection serves also as a useful presurgical evaluation of the contribution of PIN resection in combined procedures. The group 2 technique allows injection into a relatively confined area, the ring finger extensor compartment. This allows for small, localized injections with less concern for extravasation. Large-volume local anesthetic injections in undefined compartments cause concerns that the perceived analgesia may not be from the intended blockade but from extravasation and blockade elsewhere. Our study shows that distal PIN injection provided equivalent staining of the nerve but over a smaller area than proximal injection. This may be due to the larger injection volume used for proximal PIN injections (1 mL proximally and 0.5 mL distally) and the lack of a distinct compartment to inject into proximally with the resultant extravasation of dye. This study shows that local anesthetic can be delivered accurately and predictably to the PIN and AIN nerves. The PIN alone can be blocked reliably with an injection 1 cm ulnar to Lister’s tubercle with the needle
870
The Journal of Hand Surgery / Vol. 29A No. 5 September 2004
just touching the radius and both the PIN and AIN can be anesthetized from a single injection site beginning 1 cm ulnar and 3 cm proximal to Lister’s tubercle. With a better understanding of the anatomy of the PIN and AIN based on superficial landmarks a blockade of the AIN and PIN may be easier to accomplish clinically. Local anesthetic injection of the PIN and AIN may help determine which patients will benefit from partial wrist denervation alone or as an adjunct to other procedures about the wrist. We thank Dr Shang-You Yang for his assistance with image analysis.
References 1. Wilhelm A. Gelenkdenervation und ihre anatomishcen Grundlagen. Ein neues Behandlungsprinzip in der Handechirurgie. [Articular denervation and its anatomical foundation. A new therapeutic principle in hand surgery. On the treatment of the later stages of lunatomalacia and navicular pseudarthrosis.] Hefte Unfallheilkd 1966;86:1–109. 2. Ferreres A, Foucher G, Suso S. Extensive denervation of the wrist. Techniques in Hand and Upper Extremity Surgery 2002;6:36 – 41. 3. Buck-Gramcko D. Denervation of the wrist joint. J Hand Surg 1977;2A:54 – 61. 4. Ferreres A, Suso S, Foucher G, Ordi J, Llusa M, Ruano D. Wrist denervation. Surgical considerations. J Hand Surg 1995; 20B:769 –772.
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