Carpal tunnel syndrome (CTS) is the most frequent. Minimally Invasive Ultrasound-Guided Carpal Tunnel Release: A Cadaver Study

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1 Minimally Invasive Ultrasound-Guided Carpal Tunnel Release: A Cadaver Study Javier de la Fuente, PhD, 1 Maria Isabel Miguel-Perez, PhD, 2 Ramon Balius, PhD, 3 Valentin Guerrero, MD, 1 Johann Michaud, David Bong, MD 5 1 Clínica Pakea de Mutualia, San Sebastián, Spain 2 Human Anatomy and Embryology Unit, Department of Experimental Pathology and Therapeutics, Faculty of Medicine, Bellvitge Campus, University of Barcelona, Barcelona, Spain 3 Consell Catala de l`esport, Generalitat de Catalunya, Clinica Diagonal, Barcelona, Spain 4 Physical Medicine and Rehabilitation Department, CHUM--Hospital Notre Dame, University of Montreal, Montreal, Quebec, Canada 5 Instituto Poal de Reumatologia, Barcelona, Spain Received 4 October 2011; accepted 16 July 2012 ABSTRACT: Background. Carpal tunnel syndrome is a common condition frequently requiring surgical intervention. We describe a new minimally invasive surgical technique for carpal tunnel release utilizing ultrasound (US) visualization. Methods. The technique was performed on 20 fresh frozen cadaver specimens. A surgical metallic probe with a U -shaped trough and upward curved distal tip was precisely positioned in the carpal tunnel with US guidance followed by division of the flexor retinaculum (FR) with a V -shaped scalpel. Results. Complete division of the FR was confirmed by US. Dissection performed on the specimens confirmed complete release of FR and absence of neurovascular injury. The distance from the division of the FR to these structures, the safety margins, was measured. Conclusions. This new technique for carpal tunnel release appears to combine the safety and efficacy of open carpal tunnel surgery with the advantages of the minimally invasive techniques. VC 2012 Wiley Periodicals, Inc. J Clin Ultrasound 41: , 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: /jcu Keywords: carpal tunnel syndrome; carpal tunnel surgery; musculoskeletal ultrasound; flexor retinaculum; cadaver Carpal tunnel syndrome (CTS) is the most frequent compressive neuropathy of the upper limb with a prevalence of 1.55%. 1 The initial Correspondence to: J. de la Fuente ' 2012 Wiley Periodicals, Inc. stages are treated conservatively but the more severe or refractory cases require decompression of the median nerve by surgically opening the carpal tunnel (CT). The three types of surgical techniques for carpal tunnel release (CTR) include open surgery (O-CTR), endoscopic surgery (E-CTR), and minimally invasive surgery (MI-CTR). The common goal of all three approaches is the division of the flexor retinaculum (FR), resulting in median nerve decompression. 1 6 The O-CTR is the most common approach. It is considered the gold standard for CTR with excellent clinical results and wide scientific acceptance. 5 7 The main complications of O-CTR are a painful or dysesthetic scar and a decrease in grip strength that could be secondary to division of the interthenar fascia. 8 In an attempt to reduce these complications, the other less invasive procedures (E-CTR and MI-CTR) decrease the length of the surgical incision. These new limited approaches are associated with decreased visualization of the median nerve and its terminal branches (thenar muscular branch and palmar branch), vascular structures (the superficial palmar arch), and anatomic variations, thereby increasing the risk of serious neurovascular injury during the procedure. 7,8 In recent years, high-frequency musculoskeletal ultrasound (US) has become increasingly important not only in the diagnosis but also in guiding of therapeutic interventions in many musculoskeletal pathologies. 9,10 Owing to their superficial location, most of the anatomic structures of the VOL. 41, NO. 2, FEBRUARY

2 wrist and hand, including the FR, are easily visible on US. Some authors have already described surgical procedures under direct US control. Rowe et al, in 2005, published a study of US-guided surgical CTR in six cadavers. 11 Nakamichi et al compared the results of two types of US-guided surgical procedures, mini open versus percutaneous CTR, both using a distal-to-proximal approach. 12,13 The goal of our cadaveric study was to demonstrate the effectiveness and safety of surgical FR release under US guidance using a new minimally invasive technique that has significant modifications in comparison to the previously described techniques. We paid particular attention to possible complications by assessing the safety margins, ie, proximity to important neurovascular structures, in this new procedure. DE LA FUENTE ET AL METHODS Twenty wrists from 10 fresh cadavers (six men and four women) with no sign of local lesions or previous surgery were included. The division of the FR in the 20 wrists was performed using the technique described below by two of the authors, who have more than 20 years of experience in either hand surgery or musculoskeletal US. We utilized a GE Voluson ir 3D/4D Portable Ultrasound System (GE Healthcare, Milwaukee, WI) with a linear broadband multifrequency probe ( MHz) for the evaluation and identification of the anatomic structures of the volar wrist, for the skin marking of the anatomic landmarks, and for the direct US visualization of the probe positioning and confirmation of complete division of the FR. A detailed dissectionofeachwristwasthenperformedbyour anatomist. The specimen was evaluated for the completeness of the division of the FR. The palmar aponeurosis was examined and the specimens were also inspected for the presence of associated lesions of the median nerve and its terminal branches (the thenar muscular branch and the palmar branch), the superficial palmar arch, the structures within Guyon s canal, and, finally, the presence of anatomic variants (Figures 1 and 2). The following measurements were made during the dissection: (1) the length (proximal to distal) of the FR; (2) the safety margins, that is, the distance between the area of FR division and the thenar muscular branch of the median nerve, the palmar branch of median nerve, and the superficial palmar arch (Figure 3). Surgical Technique The main bony landmarks of the CT are identified by palmar wrist US exploration (scaphoid tubercle, FIGURE 1. Neurovascular structures at risk in carpal tunnel surgery: median nerve (arrow), thenar muscular branch of the median nerve (left arrowhead), and the superficial palmar arch (right arrowhead). pisiform, trapezium, and hamulus of the hamate). Then a line defining the distal border of the FR is drawn on the skin between the trapezium and the hamulus (hook) of the hamate. The median nerve is then identified by ultrasound and a line is drawn over the skin marking its course (Figure 4B). A transverse incision of 1.5 cm is made at the level of the most distal skin fold of the wrist, starting at the palmaris longus tendon and incising in an ulnar direction (Figure 4C). An opening through the deep antebrachial fascia (palmaris longus fascia) is then made, deep and ulnar to the tendon of the palmaris longus. A metallic probe (BN012, Nelaton Probe Curved; Aesculap Surgical Instruments, Center Valley, PA) with a U -shaped trough is inserted (Figure 4D) just below the deep surface of the FR until the tip of the probe passes the distal borderofthefr(thelinedrawnbetweenthehook ofthehamateandthetubercleofthetrapezium). Thedistalpartoftheprobehasagentleupward curve that allows palpation of the undersurface of the FR and identification of the distal border of FR as a loss of resistance on the tip of the probe (Figure 5). Probe positioning is controlled and confirmed by real-time US imaging. The probe is always located on the ulnar side of the median nerve and gentle ulnar and radial movement of 102 JOURNAL OF CLINICAL ULTRASOUND

3 MINIMALLY INVASIVE ULTRASOUND-GUIDED CARPAL TUNNEL RELEASE the probe is used to confirm that it is in direct contact with the undersurface of the FR (Figure 6A with the probe * below the FR -arrowheads-) and not deep to the median nerve (Figure 6B with the probe * below the median nerve -m- and arrowheads marking the FR). When the final positioning of the probe is confirmed, the FR is divided with a scalpel ( V -shaped meniscotome, Atlantech-ArthroCare Corporation, Austin, TX), which has a V -shaped blade with 5-mm distance between the two points of the blade. To achieve the division, the scalpel is vertically oriented and introduced into the U -shaped trough of the probe with its inferior horn in contact with the bottom of the trough (Figure 5D). This results in 2 mm of the scalpel in the trough of the probe and 3 mm above it, thus reaching the superior border of the FR. The FR is then divided by sliding the scalpel in the trough from proximal to distal until there is a loss of resistance just beyond the line marking the distal border of the FR. Further distal movement of the scalpel is stopped by the distal upward curve of the probe. This protects the distally located distal vascular arch. During the actual division of the FR, a characteristic sandpaper sound is heard. Complete division of the FR is confirmed by US visualization of displacement of the probe completely out of the CT space when gentle upward pressure is applied to the probe (Figure 6C showing the probe * outside the FR-arrowheads). FIGURE 2. Layers of the roof of the carpal tunnel in a left hand: dissection demonstrating the flexor retinaculum (arrows) and the overlying palmar aponeurosis (arrowheads), which has been reflected away. RESULTS The complete section of the FR was confirmed in all of the cadaveric wrists. In one case, the FR di- FIGURE 3. Measurements at dissection in right hands. (A) Dissection demonstrating the proximal to distal length of the divided flexor retinaculum (arrows). (B) Measurement of distance from FR division (arrows) to thenar muscular branch of the median nerve (arrowhead). (C) Measurement of distance from FR division (arrows) to the superficial palmar arch (arrowhead). VOL. 41, NO. 2, FEBRUARY

4 DE LA FUENTE ET AL FIGURE 4. US-guided technique. (A) Ultrasound image of the FR (arrowheads) between trapezium (T) and hamulus (H) with the median nerve (arrow). (B) Skin marks of the four bony landmarks (arrows), lines marking the distal border of the FR, and the course of the median nerve with the skin incision (arrowhead). (C) Size and location of the skin incision (between arrows) in relation to the palmaris longus tendon (arrowhead). (D) Positioning of the probe below the FR under US control through the antebrachial fascia. FIGURE 5. Surgical equipment. (A) Lateral view of the probe demonstrating upward curved tip. (B) Top view of the V- shaped scalpel. (C) Top of the probe demonstrating U -shaped trough. (D) Lateral view of scalpel demonstrating its positioning in the trough of the probe. vision was incomplete after the first pass of the scalpel. In this case, probe displacement out of the CT was not noted on US when gentle upward pressure was applied and a second pass of the scalpel was needed to complete the division of the most distal fibers of the FR. In all cases, the subsequent dissection did not show any evidence of injury to the neurovascular structures. The measurement of the length (proximal to distal) of the FR was performed. The average length of the 104 JOURNAL OF CLINICAL ULTRASOUND

5 FR in our study was 31.4 mm (Figure 3A). The average distance from the site of division of the FR to the thenar muscular branch of the median nerve (Figure 3B) was 4.5 mm (range, 3 13 mm). The average distance from the division site of the FR to the palmar branch of the median nerve was 8.2 mm (range, 7 11 mm). Average distance from the division site of the FR to the superficial palmar arch (Figure 3C) was 14.4 m (range, mm). DISCUSSION MINIMALLY INVASIVE ULTRASOUND-GUIDED CARPAL TUNNEL RELEASE FIGURE 6. Transverse sonograms of the carpal tunnel with different positions of the metallic probe. (A) Probe (*) below the FR (arrowheads) on the ulnar side of the median nerve (m). (B) Probe (*) positioned immediately below the median nerve (m). (C) US after section of the FR (arrowheads) with the probe (*) out of the carpal tunnel confirming complete section. T, trapezium; H, hamulus. The long-term results of the various surgical techniques of CTR (O-CTR, E-CTR, and MI-CTR) are similar. 2,14,15 The O-CTR, made through an interthenar longitudinal incision, is considered the gold standard as it allows optimal visualization. Possible drawbacks of the O-CTR are a painful or dysesthetic scar, a decrease in grip strength, and a longer healing time. One study suggests that postsurgical pain is more frequent when the subcutaneous tissue is incised. 16 To reduce these potential complications, less aggressive surgical interventions by means of minimal longitudinal or transverse incisions, including techniques under endoscopic control, have been developed. 2,17 The E-CTR causes less tissue trauma with its smaller scar and less postoperative pain and faster healing time along with conservation of grip strength Nevertheless, the cost of the equipment, the cost of the procedure itself, and the prolonged learning curve necessary to master this technique are limitations to its use. Incomplete FR division has been described in both patient and cadaver studies with an incidence of incomplete section of 38% noted in one cadaver study. 6,21 23 The MI-CTR technique has the same advantages of the E-CTR by creating a smaller incision through which the FR division is made. Unlike E- CTR, MI-CTR does not allow direct visualization. It utilizes a luminous scalpel and special retractors. 16,24,25 MI-CTR, which is considered a blind technique, requires the precise identification of the anatomic landmarks to insure greater safety. 26 MI-CTR does not allow the identification of anatomic variations (aberrant positions of the palmar branch and thenar muscular branch of the median nerve, presence of a bifid median nerve, persistent median artery, or variations of the ulnar artery) that can influence the surgical result. E-CTR and MI-CTR have a greater risk of injury to neurovascular structures. There are reports in the literature of partial and complete median nerve laceration with the Indiana Tome (BiometOrthopedics, Warsaw, IN) and injury to the superficial palmar arch using KnifeLight (Stryker, Kalamazoo, MI) in MI-CTR Our main goal was to develop a surgical technique that allowed not only the use of a small incision but also direct visualization of all the key anatomic structures including anatomic variants, thereby combining the advantages of the limited visibility techniques with the safety and efficacy of the open technique. The use of US enabled us to accomplish these goals. In our cadaver study, we were able to divide the FR using a small incision at the wrist while monitoring the intervention at the distal blind area with ultrasound. VOL. 41, NO. 2, FEBRUARY

6 DE LA FUENTE ET AL In our technique, the fundamental protective device is the probe with its U -shaped trough and an upward curved tip. The probe is easily identified on US, allowing precise positioning of the probe on the ulnar side on the median nerve and, also, confirming positioning directly in contact with the undersurface of the FR. The curved tip of the probe enables us to feel the loss of resistance that marks the distal edge of the FR, confirming that the tip of the probe is beyond the distal border of FR. Once the probe is positioned correctly and the median nerve is identified, we proceed to the FR division with a V -shaped scalpel from proximal to distal. The complete division is usually accomplished with one pass of the scalpel. One of the main problems of any technique with limited visibility is the confirmation of complete division of the most distal fibers of the FR. The technique we describe accomplishes the division by placing the tip of the probe beyond the line drawn marking the distal border of the CT and by feeling the loss in resistance during the procedure. We also utilize US to confirm the complete division of the FR by assuring upward displacement of the probe out of the CT immediately after sectioning. In one case, the section of the FR was incomplete after the first pass of the scalpel and we immediately performed a second pass with successful sectioning the distal fibers of the FR. There is some debate about the exact definition of the flexor retinaculum and the true limits of the carpal tunnel. 30,31 Three parts of the roof of the CT have been described: a proximal part made of the thickened antebrachial fascia, a central portion formed by the FR containing thick ligamentous fibers with bony insertions, and a more distal and superficial portion of the carpal tunnel formed by the palmar aponeurosis. 30,31 The release of the CT implies dividing of the most rigid part of the roof of the CT, the ligamentous FR. In our study, division of the FR and the thickened part of the antebrachial fascia resulted in complete opening of the carpal tunnel in all cases with preservation of the palmar aponeurosis and the interthenar fascia. With respect to postoperative morbidity, the painful scar could be related to the sectioning of small terminal unmyelinated fibers of the palmer branch of the median nerve that are located superficial to the FR at the level of the interthenar skinfold. 32 By sectioning only the FR and avoiding the more superficial structures, we may avoid injury to those small nerve fibers and so potentially avoid microscopic neuroma formation that could explain postoperative pain after O-CTR. 33 In this study, our surgical technique resulted in complete section of the FR in all cases. This technique maintained adequate safety margins by keeping the scalpel away from important neurovascular structures. The mean distance from FR division to the palmar arch was 14.4 mm (range, mm), to the palmar branch of the median nerve 8.2 mm (range, 7 11 mm), and to the thenar motor branch 4.5 mm (range, 3 13 mm). Our technique maintained the probe on the ulnar side of the median nerve in line with the third interdigital space at all times, thereby decreasing the risk of nerve lesion. Finally, direct visualization of the carpal tunnel content with US overcomes one of the main drawbacks of the blind techniques by determining the presence of neurovascular anatomic variations that could greatly jeopardize a successful surgical result if unidentified. In conclusion, we have described a minimally invasive surgical technique using US for precise positioning of an upward curved metallic probe with a U -shaped trough that guides the division of the FR. In all cases, our cadaver study resulted in the complete section of the FR without neurovascular injury. We have also demonstrated that the safety margins, especially regarding proximity of the thenar motor branch of the median nerve, are quite limited. However, with US guidance and the described probe, this technique combines the advantages of the limited visualization techniques with the safety and efficacy of the open technique. The technique is straightforward and reproducible but does require a knowledge of hand surgical anatomy and technique along with ultrasound. Further studies involving patients are needed to compare this new technique with the traditional surgical approaches for CTR in terms of clinical results, functional assessment, time of recovery, and complications. REFERENCES 1. Nordstrom DL, Vierkant RA, DeStefano F, et al. Risk factors for carpal tunnel syndrome in a general population. Occup Environ Med 1997;54: Cellocco P, Rossi C, Bizzarri F, et al. Mini-open blind procedure versus limited open technique for carpal tunnel release: a 30-month follow-up study. J Hand Surg Am 2005;30: Jacobsen MB, Rahme H. 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