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Ultrasound-guided percutaneous injection, hydrodissection, and fenestration for carpal tunnel syndrome: description of a new technique.


Carpal tunnel syndrome, involving compression of the median nerve deep to the flexor retinaculum, is one of the most common nerve compression syndromes encountered in musculoskeletal medical practice, and has a variety of causes and disease associations. (1-3) Most patients are initially treated with conservative measures using some combination of removing the offending or causative activity, treatingyhe underlying disease, physical therapy, occupational therapy, and/or splinting. When conservative measures fail, interventional techniques are considered the next step.

Many studies have appeared comparing open surgical flexor retinaculum release to blind injections of corticosteroids into the carpal tunnel, but there is no agreement on which is preferable. This is due in part because outcomes from both techniques vary depending on a variety of factors. (4) Advantages of injection are: lower level of invasiveness, faster recovery, and ease of the technique. The main disadvantage is that symptom relief is often short-lived, it may not provide a permanent solution, and some patients ultimately need surgical release. (4,9) Occasional failures and complications occur with all treatment methods, including surgery, and to a great degree, outcomes depend on the severity of the compression, the duration of symptoms, and the degree of irreversible nerve damage. (4,10-12)

We have been using an ultrasound-guided procedure of mobilizing the nerve away from the deep surface of the flexor retinaculum by percutaneous hydrodissection, followed by fenestration and splitting the laminar layers of the flexor retinaculum. The intent is to lower the pressure exerted by the flexor retinaculum on the median nerve, potentially offering a longer-lasting solution than simple blind injection. We have found our method to be safe, effective, minimally invasive, far cheaper than open surgical release, and relatively easy to learn and perform. Recovery time is measured in hours instead of days or weeks, and the technique can be repeated if necessary. Herein we report our series of 44 consecutive procedures, with outcomes at times ranging from 3 to 96 weeks.


Patients were included in this series in the order they presented to the rheumatology practices of two of the authors (NW and DGM), rheumatologists experienced in ultrasound-guided interventional musculoskeletal procedures. The Internal Review Board of the University of Wisconsin designated this retrospective review to be a quality assurance project and found it in compliance with the IRB's standard, and to present no ethical concerns. Patients were included provided that they had symptoms typical for carpal tunnel for at least 4 months, eg, pain and numbness in the median nerve sensory distribution, nocturnal worsening of symptoms, worsening of symptoms while driving, holding a telephone hand set, or gripping.


All patients had EMG/NCV confirmation of that condition. None of the patients had previously had open carpal tunnel release, and two patients had had previous blind carpal tunnel injection without fenestration or hydrodissection. Patients were instructed that carpal tunnel steroid injections are standard therapy when conservative measures fail. In addition, the entire procedure was described and patients were shown how our technique differs from blind carpal tunnel steroid injection, ie, that hydrodissection (using the jet of injected isotonic fluid from the needle tip) is used to separate the median nerve from the deep surface of the flexor retinaculum along nearly its entire course within the carpal tunnel, which is a series of perforations of the flexor retinaculum is done along the long axis of the forearm from the distal to the proximal borders of the carpal tunnel. All of the above is done under direct visualization in real time using ultrasonographic guidance, to avoid damaging the nerves and blood vessels. The palmar sensory branch of the median nerve, which can be damaged in open procedures as well as in blind injections of the carpal tunnel, can be avoided, since it is visible under ultrasound along its course on the ulnar aspect of the flexor carpi radialis tendon and distally in a more ulnar position. (13)

Both wrists were done in 10 patients and one wrist was done in each of the remaining 24 patients. The technique used was as follows: Using a General Electric LogiQ e ultrasound system with a 10-12 mHz linear array probe, the proximal border of the procedure area was defined by visualizing the radiolunate joint with the probe in the anatomical sagittal plane, and drawing a line on the volar forearm skin along the intersection of the anatomic axial plane at the radiolunate joint, with the skin (line PR, Figure 1). Then the distal end of the procedure area was defined in the same manner, at about 1 cm distal to the distal wrist crease, at the distal end of the capitate bone, where a second line, parallel to the first, was drawn (line DI).


The probe was then oriented to visualize the middle of the median nerve in its longitudinal axis (ie, in the anatomic sagittal plane). A line was drawn on the skin of the volar forearm along the intersection of the skin and the anatomic sagittal plane containing the middle of the median nerve, (line MN), and another line, parallel to line MN, was drawn along the intersection of the anatomic sagittal plane 2-3 mm radial to the median nerve, and the skin (line OP). The operator can choose to place line OP 2-3 mm ulnar to the median nerve, instead of radial to it, to further minimize the chance of damaging the palmar cutaneous branch of the median nerve. The intersection of line OP and line DI was the entry point of the needle. The skin in the entire area was then sterilized with 2% chlorhexidine solution in 70% isopropyl alcohol (Chloraprep[R]).

An alternative very useful technique for marking the course or position of underlying structures (such as nerves, tendons, and vessels) with accurate skin lines was suggested by one of the authors (TBC), and was also employed in our procedures. To insure that the line drawn on the skin is exactly overlying any structure, that structure is visualized in short axis (ie, perpendicular to its course), and then a non-abrasive piece of straight thin wire, or a length of uncoiled smooth paper clip, is introduced with its long axis exactly perpendicular to the long axis footprint of the probe. This paper clip segment is interposed between the skin and the probe, in the gel layer, and casts an easily visible acoustic shadow onto the screen image. The paperclip is moved until the narrow acoustic shadow it casts encompasses the structure to be marked, all the while keeping the paper clip segment perpendicular to the probe long axis. Pressure is then exerted on the paper clip so as to indent the skin. The resulting small skin indentation is marked with a pen or permanent marker, and this mark therefore runs directly over the structure.


Under ultrasonographic guidance with the probe oriented in the transverse (anatomic axial) plane of the carpal tunnel, a 30 gm needle was introduced nearly perpendicular to the skin surface at the entry point defined previously, pointing slightly proximal along line OP, and 1% lidocaine was injected from the skin along a track ending at the deep surface of the flexor retinaculum. That needle was then withdrawn, and the procedural (20 gm) needle was then introduced along the anesthetized track, and was advanced to a position almost directly deep to the entry point, so as not to damage the nerve, viewed by ultrasound in short axis (Figure 2). Starting at this position, the injection of about 11 cc of hydrodissection fluid was begun, directly under, in the anatomic sagittal plane containing line OP, using the jet of fluid near the needle tip to carefully separate the median nerve from the deep surface of the retinaculum (figure 3), and was continued proximally along line OP until line PR was reached. The fluid consisted of 9 cc of normal saline, 1 cc of 1% lidocaine, and 1 cc of 40 mg/ml triamcinolone acetonide.

Next, using a superficial to deep pecking motion, starting with the needle almost completely perpendicular to the skin at the entry point, and with the needle bevel turned to be in the sagittal plane, taking care to keep the needle inserted at the entry point, a series of about 150 perforations of the flexor retinaculum was made using ultrasound to visualize the needle tip to insure that the tip perforated the retinaculum on each pass, and did not contact the median nerve. By gradually flattening the angle between the needle shaft and the skin, while keeping the needle inserted at the entry point, the perforations were done along the course of line OP, from the entry point proximally to line PR. Small volume additional fluid injections to keep the nerve away from the path of the fenestrating needle were also employed if needed. Some of the fluid was also used to separate the laminated layers of the flexor retinaculum along this same course. The needle was then withdrawn. Finally, the patient was asked to flex the wrist forcibly against resistance to further weaken pressure of the fenestrated retinaculum on the nerve.


During the procedure, after hydrodissecting the nerve from the retinaculum, we found it possible to position the needle tip virtually anywhere in the carpal tunnel; superficial to the nerve, to either the radial or medial side of the nerve, and, importantly, deep to the nerve , which allowed injection of fluid into the tenosynovium of the flexor tendon groups. The flexor tendon is commonly thickened, increasing the magnitude of nerve compression in carpal tunnel syndrome. (14) This resulted in the injected fluid completely surrounding the median nerve, and contacting the underlying flexor tendon tenosynovium (Figure 4)

Patients were contacted by telephone within 4 days following the procedure, and were asked about any complications such as bleeding, pain, return of symptoms, or infection.

Patients were again contacted twice in the next 24 months either by telephone, or in a subsequent clinic visit, (see Table 1) for followup, to determine one of the following three outcomes:

* Excellent-all symptoms resolved,

* Fair-some residual symptoms, or return of symptoms, but improved compared to prior to procedure,

* Failure-required open surgical release.

Initial follow-up periods after the procedure ranged from 3-60 weeks, averaging 32 weeks. Second follow up periods varied from 25-96 weeks post-procedure, averaging 63 weeks, not counting the patients who were failures.


* Excellent at first followup, lost to second followup--two wrists, too little time to judge. Second followup--one wrist

* Excellent at first followup and second followup--19 wrists

* Excellent at first followup, fair at second followup--9 wrists

* Fair at first followup and second followup--five wrists

* Fair at first followup, lost to second followup--one wrist

* Fair at first followup, too little time to judge second followup-two wrists

* Failure--5 wrists

Outcome data are shown in Table 1. Data for the second followup were not available on threee patients because too little time had elapsed since the first post-procedure evaluation to make a second evaluation meaningful, and three patients were lost to followup after the first evaluation. Patients who were evaluated as failures at the first evaluation were not recontacted for a second evaluation.

Patients reported that they did not experience discomfort during the procedure except for the initial anesthesia, which was considered very minor and brief. A few patients reported soreness around the entry point for two days after the procedure, but in none did this require analgesics or other treatment. Two patients reported a small painless ecchymosis near the entry point that did not require treatment. No patient reported worsening of carpal tunnel symptoms. There were no infections.


We have described our technique, and report our experience using a carpal tunnel injection hydrodissection and fenestration procedure to relieve symptoms of carpal tunnel syndrome. Our technique, in essence, is an extension of the commonly performed blind carpal tunnel steroid injection, and has the advantages of safety, accuracy of medication placement, effectiveness, noninvasiveness, ease of performance, and lower cost than open surgical release. To current blind injection, our technique adds direct visual guidance under ultrasound, actual separation of the median nerve from the compressing flexor retinaculum throughout the carpal tunnel by hydrodissection, and mechanical partial disruption of the retinaculum to decrease wall tension-generated compression on the nerve. This method does not result in complete section of the retinaculum such as is accomplished in open procedures, but complete sectioning may not be necessary, especially in less severe cases. (4,10-12) Our procedure can be considered a viable intermediate treatment modality between conservative measures and open release. The magnitude of its advantage over other surgical and non-surgical treatment modalities can only be determined by a controlled comparative study, which was not the purpose of this mostly descriptive report.

We include hydrodissection to separate the median nerve from the retinaculum, separation of the several laminar layers of the retinaculum, and fenestration of the retinaculum, because pressure on the median nerve exerted by this structure within the carpal tunnel is what causes nerve malfunction and symptoms. Thus, any technique resulting in reduction of that pressure could be expected to be effective in treating this common entrapment syndrome. From a mechanical standpoint, decreasing the tension in a constricting cover such as the flexor retinaculum theoretically lowers the pressure exerted on structures deep to it. The degree and duration of this tension decrease was not determined in this study and awaits more detailed investigation. In a separate smaller study, we performed with a different set of patients, we did see functional improvement in patients undergoing this identical procedure. (15)

It has been observed that the tenosynovium of the flexor tendons underlying the median nerve is often edematous and inflamed in patients with carpal tunnel syndrome, and contributes to the increased pressure within the carpal tunnel. (14) Injection of this tissue, when swelling and inflammation are present, is recommended by some to help in reducing symptoms. (16) In performing our procedure, we did not use the separate ulnar toward radial approach described by Smith et al (16) to treat the flexor tendon tenosynovium, because we were able to create fluid spaces that completely surround the median nerve, within which the needle tip can be moved to virtually any position relative to the median nerve, including deep to it, so that flexor tendon tenosynovium can be accessed for injection of the glucocorticoid-containing hydrodissection fluid (Figure 4).

It is important to emphasize that this technique and others like it (16) must be performed with ultrasound guidance in real time, and should not be attempted unless experience and competence in ultrasound-guided procedures has been accomplished. It is now relatively convenient to obtain such training,17 which provides expertise that is likely to become standard and state-of-the-art in many types of musculoskeletal practice in the near future.


(1.) Stevens JC, Sun S, Beard CM, O'Fallon WM, Kurland LT. Carpal tunnel syndrome in Rochester, Minnesota, 196] to 1980. Neurology. 1988:38:134-138.

(2.) Marshall S. Carpal tunnel syndrome. Clin Enid. 2001;5:717-728.

(3.) Spinner RJ, Bachman JW, Amadio PC. The many faces of carpal tunnel syndrome. Mavo Clin Proc. 1989:64:829-836.

(4.) Katz JN, Simmons BP. Clinical practice. Car pal tunnel syndrome. N Engl J Med. 2002 Jun 6;346(23): 1807-12.

(5.) Marshall S, Tardif G, Ashworth N. Local corticosteroid injection for carpal tunnel syndrome. Cochrane Database Syst Rev. 2002; CD001544.

(6.) Girlanda P, Daltola R, Venulo C, Mangiapane R, Nicolosi C, Messina C. Local steroid treatment in idiopathic carpal tunnel syndrome: short- and long term efficacy. J Neurol 1993;240:187-90.

(7.) Dammers JWHH, Veering MM, Vermeulen M. Injection with melhylprednisolone proximal to the carpal lunncl: randomised double blind trial. BMJ 1999;319:884-6.

(8.) Gelberman R1I, Aronson D, Weisman Mil. Carpal tunnel syndrome: results of a prospective trial of steroid injection and splinting. J Bone Joint Surg Am 1980;62:1181-4.

(9.) Jarvik JG, Comstock BA, Kliot M, Turner JA, Chan L, Heagerty PJ, Hollingworth W, Kerrigan CL, Deyo RA Surgery versus non-surgical therapy for carpal tunnel syndrome: a randomised parallel-group trial. Lancet. 2009: 374(9695): 1074-81.

(10.) Light T American Society for Surgery of the Hand: Hand surgery Update 2. Rosement, 111: American Academy of Orthopedic Surgeons; 1999.

(11.) DeStefano F. Nordstrom DL, Vierkant RA. Long-term symptom outcomes of carpal tunnel syndrome and its treatment. J Hand Surg [Am]. 1997;22:200-210.

(12.) Rosen B, Lundborg G, Abrahamsson SO, Hagberg L, Rosen I. Sensory function after median nerve decompression in carpal tunnel syndrome. Preoperative vs postoperative findings. J Hand Surg. 1997;22:602-606.

(13.) Matloub HS, Yan JG, Mink Van Der Molen AB, Zhang LL, Sanger JR. The detailed anatomy of the palmar cutaneous nerves and its clinical implications. J Hand Surg [Br] 1998;23:373-379.

(14.) Oh S, Belohlavek M, Zhao C. et al. Detection of differential gliding characteristics of the flexor digitorum superficialis tendon and subsynovial connective tissue using color Doppler sonographic imaging. J Ultrasound Med 2007; 26:149-155.

(15.) Beck J, Malone DG. Ultrasound guided tenotomy and hydro-dissection of the flexor retinaculum in the treatment of carpal tunnel syndrome: Outcome analysis of the Brigham and Woman's carpal tunnel questionnaire. Submitted for publication

(16.) Smith J, Wisniewski SJ, Finnoff JT, Payne JM. Sonographically guided carpal tunnel injections: the ulnar approach. J Ultrasound Med. 2008 Oct; 27(10):1485-90.

(17.); meetings/mus.index.asp

Daniel G. Malone, MD [1] Thomas B. Clark, DC, RVT [2] Nathan Wei, MD [3]

[1] corresponding author. Department of Medicine, Section of Rheumatology, University of Wisconsin, Madison. WI

[2] MSKUS, Vista, CA

[3] Arthritis & Osteoporosis Center of Maryland, Frederick, MD
Table 1

          ISTEVAL-                2ND EVAL-

1         03 Ex                   25 Ex
2         06 Ex                   too little time
3         06 Ex                   29 Ex
4         09 Ex                   lost to follow-up
5         12 Ex                   52 Ex
6         13 Ex                   lost to follow-up
7         23 Ex                   45 Ex
8         27 Ex                   48 Ex
9         39 Ex                   84 Ex
10        42 Ex                   S2 Ex
11        42 Ex                   82 Ex
12        44 Ex                   42 Ex
13        44 Ex                   66 Ex
14        45 Ex                   63 Ex
15        47 Ex                   70 Ex
16        48 Ex                   71 Ex
17        54 Ex                   76 Ex
18        54 Ex                   76 Ex
19        54 Ex                   92 Ex
20        56 Ex                   96 Ex
21        60 Ex                   81 Ex
22        60 Ex                   81 Ex
23        01 Ex                   27 Fair
24        08 Ex                   52 Fair
25        OS Ex                   52 Fair
26        16 Ex                   38 Fair
27        17 Ex                   39 Fair
28        38 Ex                   64 Fair
29        58 Ex                   79 Fair
30        58 Ex                   79 Fair
31        60 Ex                   77 Fair
32        12 Fair                 52 Fair
33        14 Fair                 too little time
34        14 Fair                 too little time
35        30 Fair                 70 Fair
36        30 Fair                 70 Fair
37        30 Fair                 70 Fair
38        38 Fair                 lost to follow-up
39        43 Fair                 65 Fair
40        06 Failure
41        09 Failure
42        21 Failure
43        54 Failure
44        58 Failure
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Author:Malone, Daniel G.; Clark, Thomas B.; Wei, Nathan
Publication:Journal of Applied Research
Geographic Code:1USA
Date:Mar 1, 2011
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