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Release of the Transverse Carpal Ligament Alone Is Associated With Elevated Pressure Beneath the Distal Volar Forearm Fascia in a Cadaver Model of Carpal Tunnel Syndrome
Release of the Transverse Carpal Ligament Alone Is Associated With Elevated Pressure Beneath the Distal Volar Forearm Fascia in a Cadaver Model of Carpal Tunnel Syndrome Kenneth R. Means Jr, MD, Brent G. Parks, MSc, Steve K. Lee, MD, Keith A. Segalman, MD From the Curtis National Hand Center, Union Memorial Hospital, Baltimore, MD; Division of Hand Surgery, NYU Hospital for Joint Diseases, New York, NY.
Purpose: The purpose of this study is to determine whether release of the distal volar forearm fascia (DVFF) is necessary at the time of median nerve decompression for carpal tunnel syndrome. Methods: Five fresh-frozen cadaver specimens were mounted vertically with the hand dependent and a 2.27-kg weight suspended from the fingers. A pressure sensor wire was used to measure pressures starting just distal to the transverse carpal ligament (TCL). The wire was withdrawn proximally in 5-mm increments and into the forearm until pressure was below 10 mm Hg. An incision in the forearm was extended distally until the pressure sensor was found. The distance from this point to the distal volar wrist crease was measured. The TCL was released, keeping the DVFF intact, and the experiment was repeated. Paired t-tests determined whether there were statistically significant differences between measurements before and after TCL release. Results: Average peak pressure under the intact TCL was 57.8 ⫾ 10.1 mm Hg. Average peak pressure under the DVFF with the TCL intact was 61.2 ⫾ 43.6 mm Hg. Following release of the TCL, average peak pressure beneath the TCL significantly decreased to 14.0 ⫾ 9.0 mm Hg, whereas average peak pressure at the intact DVFF increased to 64.8 ⫾ 48.7 mm Hg. Average locations where DVFF pressure became less than 10 mm Hg with an intact TCL and with released TCL were 4.30 ⫾ 1.8 cm and 4.00 ⫾ 1.8 cm proximal to the distal volar wrist crease, respectively. There was no significant difference between DVFF pressures before or after TCL release. Conclusions: In a cadaver model of carpal tunnel syndrome, release of the TCL alone is associated with persistent pressures ⬎30 mm Hg in the region of the DVFF. Release of the TCL did not significantly change the location of the pressure drop-off under the DVFF. (J Hand Surg 2007;32A:1533–1537. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Carpal canal pressure, carpal tunnel syndrome, distal volar forearm fascia, transverse carpal ligament, wrist distraction.
he palmar boundary of the carpal tunnel has been described as including, from proximal to distal, the distal volar forearm fascia (DVFF), the transverse carpal ligament (TCL), and the distal portion of the flexor retinaculum.1 Carpal tunnel release is often combined with a partial release of the DVFF. This is true whether the release is performed
T
using single-portal endoscopic, mini-open, or traditional open techniques.2,3 It has been suggested that division of the DVFF up to 3 cm proximal to the TCL is necessary but that release of the flexor retinaculum distal to the TCL is not, based on clinical pressure measurements.4 There is no accepted standard as to how much, if any, of the DVFF should be divided. The Journal of Hand Surgery
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Previous investigations have found that carpal tunnel pressures greater than 30 mm Hg are associated with carpal tunnel syndrome.5 Prior study has also shown that distraction across the wrist can consistently increase carpal tunnel pressures in a cadaver model to levels that may be pathologic in a clinical situation.6 Release of the transverse carpal ligament in the same cadaver model reliably returned carpal tunnel pressures to within the normal range for up to 4.54 kg of distraction. To our knowledge, there are no cadaver studies to determine whether the DVFF truly needs to be released in combination with release of the TCL and if it does need to be released, what the optimal amount of release is in order to ensure adequate decompression of the median nerve at the level of the wrist. The current study seeks to determine whether release of the DVFF is necessary at the time of median nerve decompression for carpal tunnel syndrome.
Materials and Methods Five fresh-frozen cadaver specimens amputated at the mid-humeral level or proximal were used. There was no history of upper extremity trauma and no surgical or traumatic scars for any of the limbs. The samples were placed in an impervious plastic bag and thawed in warm water prior to testing. An incision was made at the mid-forearm level on the radial border of the forearm. Dissection was carried down to the radius. Two holes were predrilled in the radius, across the interosseous space, and into the ulna with the forearm and wrist held in a neutral position of rotation. Two 3.5-mm external fixator half-pins were placed in the predrilled holes to transfix the radius and ulna as described in a prior study.6 A small, palmar, longitudinal incision was made in line with the radial border of the ring finger at the level of Kaplan’s cardinal line so as to be just distal to the transverse carpal ligament. Dissection was carried down through palmar fascia. The distal edge of the TCL was identified and left intact. Hollow plastic tubing was inserted deep to the distal edge of the TCL (Fig. 1). The tubing was passed proximally until it was palpated subcutaneously in the midforearm. An incision was made in the skin and fascia at this level, and the tubing was retrieved, while leaving enough tubing distally so that some remained distal to the TCL. Thus, the tubing was deep to the entire TCL as well as the DVFF. We used a pressure sensor wire (WaveWire Pressure Guide Wire; Volcano Corporation, Rancho Cordova, CA) that was used in another carpal tunnel pressure study (Ikeda
Figure 1. Hollow plastic tubing was inserted deep to the distal edge of the TCL.
K, Katsuro T, Naoki O. Segmental carpal canal pressure in patients with carpal tunnel syndrome. ASSH Annual Meeting, Scientific Abstracts Presentation, 2005 September, San Antonio, TX). The guide wire was placed into the hollow plastic tubing in a proximal to distal direction with the pressure sensor portion of the wire facing distally. The plastic tubing was then removed distally. The surgeons used direct visualization to leave the guide wire in place such that the pressure sensor was located just distal to the distal edge of the TCL. The guide wire was attached to the real-time pressure monitor display. Each specimen was mounted to a table vise using the external fixator pins. The samples were mounted vertically such that the hand was in the most dependent position and the wrist was in slight extension. A 2.27-kg weight was suspended from the index and middle fingers (Fig. 2). This degree of extension and weight distraction was chosen based on prior study showing that these values most consistently caused an elevation in carpal canal pressure.6 Each cadaver trial consisted of two runs. In the first run, the guide wire was withdrawn in a distal to proximal direction in 5-mm increments, with pressure readings being recorded at each increment. Thus, pressures deep to the TCL and the DVFF with the wrist distracted were established. The measurements continued into the distal forearm until a pressure ⬍10 mm Hg was encountered. The skin and the fascia were incised in a proximal to distal direction to determine the exact location of the wire. The distance from this point to the distal volar wrist crease (DVWC) was measured. For the second run, the TCL was first released by extending the palmar skin incision proximally and
Means et al / Elevated Pressure After Carpal Tunnel Release
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fascia incision was then extended distally until the pressure sensor portion of the wire was found. The distance from this point to the DVWC was again measured. Several trial runs were performed initially to determine the final protocol as outlined earlier, as well as to gather preliminary data for a power analysis. Average peak pressures were obtained below the TCL (46.5 ⫾ 8.2 mm Hg) and the DVFF (36.1 ⫾ 12.5 mm Hg) in the early trials and were used for sample size determinations. We assumed that nonpathologic pressure should be, at most, 10 mm Hg, based on previous studies.7 Setting p-value to 0.05 and seeking power of 0.80, we determined that 3 specimens would be necessary to detect the expected difference in pressure at the TCL, whereas 5 samples were required for the DVFF. For this reason we chose to test a total of 5 cadaver arms. Averages and standard deviations for peak pressures and distances were determined for the 5 specimens run using the final protocol. A paired t-test was used to determine whether there were statistically significant differences between measurements before and after TCL release.
Results Figure 2. The specimen was mounted vertically with the hand dependent and a 2.27-kg weight suspended from the index and middle fingers.
dividing the palmar fascia and the TCL only. The DVFF remained intact. Again, the plastic tubing was inserted in a distal to proximal direction and retrieved proximally. The guide wire was placed in a proximal to distal direction, and the plastic tubing was removed, leaving the guide wire in place, distal to the distal edge of the transected TCL. The skin was allowed to close over the released TCL and palmar fascia. The wire was again withdrawn in 5-mm increments, with pressure readings being recorded under the now divided TCL and under the intact DVFF. Again, measurements continued into the forearm until a pressure ⬍10 mm Hg was noted. The forearm
Table 1 shows the average results for the 5 specimens. Figures 3A and 3B present representative graphs for one of the specimens before and after TCL release. In this case, the drop below 10 mm Hg occurred at 70 mm proximal to the distal edge of the TCL, which, after dissection to find the pressure sensor, correlated with a distance of 2.5 cm proximal to the DVWC. The average peak pressure under the intact TCL with 2.27 kg of distraction was 57.0 mm Hg ⫾10.1. The peak pressure under the released TCL was 14 mm Hg ⫾ 8.9. This difference was statistically significant (p ⫽ .0003). There was not a statistically significant difference between the pressures beneath the DVFF before and after TCL release (p ⫽ .69) nor between the average location where the DVFF pressure became less than 10 mm Hg whether the TCL was intact or released (p ⫽ .37). During the open dissections, a thickening of the DVFF was observed, as described by previous au-
Table 1. Comparison of Biometric Measurements Before and After TCL Release TCL (mm Hg) DVFF (mm Hg) Distance to DVWC (cm)
Before TCL Release
After TCL Release
p Value
57.0 ⫾ 10.1 61.0 ⫾ 43.6 4.3 ⫾ 1.8
14.0 ⫾ 8.9 64.0 ⫾ 48.7 4.0 ⫾ 1.8
⬍0.003 0.69 0.37
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Figure 3. (A) Representative specimen graph before TCL release. (B) Representative specimen graph after TCL release.
thors.1 This thickening typically extended 2 cm to 4 cm proximal to the DVWC.
Discussion This study shows that, in a cadaver model of carpal tunnel syndrome, release of the TCL alone is associated with persistent pressures ⬎30 mm Hg in the region of the DVFF. Pressures this high are known to damage nerves secondary to compression or ischemia.5,8,9 We were able to reproduce pressures under the TCL with this model that are similar to those seen in other carpal tunnel syndrome studies, both clinical and biomechanical.5–7,9 Furthermore, these elevated pressures at the TCL were associated with significantly elevated pressures under the DVFF proximal to the DVWC. Also, release of the TCL did not significantly change the location of the pressure drop below pathologic levels under the DVFF. Incomplete carpal tunnel release is a potential cause for persistent or recurrent symptoms following endoscopic and open techniques. The recurrence rate of carpal tunnel syndrome following release has been reported as being from 0% to 10% with all techniques, whether open, mini-open, or endoscopic, falling on both the low and the high end of that range in different studies and reviews.10 –16 The literature we reviewed did not discuss how much DVFF was released at the time of the carpal tunnel release for most techniques. Revision carpal tunnel releases are routinely performed in an open fashion. There is also usually considerably more dissection and exploration around the median nerve to ensure complete decompression and to rule out any prior injuries. This dissection typically includes further release of the forearm fascia proximally. Some authors have suggested that release of the thickened portion of the distal forearm fascia at the index procedure could lower the recurrence rate.17
In a clinical study of endoscopic carpal tunnel release (ECTR), Okutsu et al3 showed that release of the forearm fascia did not produce a notable decrease in carpal canal pressures when compared to TCL release alone. In that study, however, there was no measurement of the pressure beneath the forearm fascia itself. Ikeda et al (Ikeda K, Katsuro T, Naoki O. Segmental carpal canal pressure in patients with carpal tunnel syndrome. ASSH Annual Meeting, Scientific Abstracts Presentation, 2005 September, San Antonio, TX) found in 9 clinical cases that there were some patients with significant pressure elevations 1 cm proximal to the DVWC, although their pressure measurements (7.3 ⫾ 10.6 mm Hg) were not as high as those found in our study. They recommended release of up to 1 cm of DVFF to ensure complete decompression, although they did not evaluate the pressure under the DVFF following TCL release. In 2005, Morimoto et al performed a crosssectional MRI study of the carpal canal.18 They found that there was no significant increase in crosssectional area proximal to the DVWC for 21 mm to 25 mm. They proposed that antebrachial fascia release may be necessary to fully decompress the median nerve, given this relatively constricted area proximal to the DVWC, although they did not note a specific focal area of volume reduction to establish the exact extent of release needed. This narrowing, which corresponds to the thickened portion of the DVFF, likely explains the elevated pressures that we observed in our cadaver measurements. There are several limitations that must be considered with our study. Although the 5-mm markings on the guide wire allowed fairly accurate estimates as to the position of the pressure sensor relative to the distal edge of the TCL, because the guidewire was withdrawn in a “blind” fashion with the skin and deeper structures intact, the only distance that was
Means et al / Elevated Pressure After Carpal Tunnel Release
able to be directly measured was that between the pressure sensor and the DVWC after the distal forearm skin and fascia had been dissected after the pressure dropped below 10 mm Hg. It is likely that the distances recorded for pressure changes relative to the distal edge of the TCL are not exact. Fortunately, because we were studying the contribution of the DVFF to median nerve compression, the DVFF was the only area where we were interested in having an exact distance measurement to determine where the pressure dropped relative to the DVWC. It is likely that there is considerable anatomic variation between patients with regard to thickness and length of the DVFF, and this may explain the relatively wide range we experienced in our recordings between specimens. Even in the seminal paper by Gelberman et al5 in 1981, the authors observed a fairly wide range in pressure readings beneath the TCL in the neutral, flexed, and extended positions. Clinical recommendations as to how much DVFF should be released in addition to the TCL are difficult to make based on this study alone. For example, the surgeon may choose to release proximal to the average peak pressure region at the DVFF, release to the area where the average pressure is ⬍30 mm Hg, or release to the point at which the average pressure is ⬍10 mm Hg. Based on this study, the latter decision would require release of the DVFF 4 cm proximal to the DVWC. The consequence of even this degree of release is, however, uncertain. Perhaps a lesser release of the fascia proximal to the DVWC would sufficiently decrease the pressure proximally. The two former decision possibilities were unable to be assessed with the current study. Rather, this study suggests that, in a cadaver carpal tunnel syndrome model, at least some amount of DVFF release proximal to the DVWC is necessary in order to decrease pressures below a pathologic level. We suggest that the next step in researching this topic should be a cadaver study of sequential release of the DVFF in a distal to proximal direction to determine how much release is necessary to decrease the pressure to nonpathologic levels. Alternatively, a clinical study of patients with and without DVFF release in addition to their TCL release and examining recurrence rates and postoperative improvement would be useful. Received for publication May 15, 2007; accepted in revised form August 27, 2007. This study was supported by the Raymond M. Curtis Research Foundation. Corresponding author: Ken Means c/o Anne Rupert Mattson, Editor, Curtis National Hand Center, Union Memorial Hospital, 3333 N. Calvert Street, #400, Baltimore, MD 21218; e-mail: [email protected].
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Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A10-0005$32.00/0 doi:10.1016/j.jhsa.2007.08.020
References 1. Cobb TK, Dalley BK, Posteraro RH, Lewis RC. Anatomy of the flexor retinaculum. J Hand Surg 1993;18A:91–99. 2. Lee WP, Plancher KD, Strickland JW. Carpal tunnel release with a small palmar incision. Hand Clin 1996;12:271–284. 3. Okutsu I, Hamanaka I, Tanabe T, Takatori Y, Ninomiya S. Complete endoscopic carpal canal decompression. Am J Orthop 1996;25:365–368. 4. Megele R, de VU, Hinderer G. Intraoperative pressure measurement at the median nerve in carpal tunnel syndrome and its surgical significance. Handchir Mikrochir Plast Chir 1991;23:327–333. 5. Gelberman RH, Hergenroeder PT, Hargens AR, Lundborg GN, Akeson WH. The carpal tunnel syndrome. A study of carpal canal pressures. J Bone Joint Surg 1981;63A:380 – 383. 6. Baechler MF, Means KR, Jr., Parks BG, Nguyen A, Segalman KA. Carpal canal pressure of the distracted wrist. J Hand Surg 2004;29A:858 – 864. 7. Schuind F. Canal pressures before, during, and after endoscopic release for idiopathic carpal tunnel syndrome. J Hand Surg 2002;27A:1019 –1025. 8. Lundborg G, Gelberman RH, Minteer-Convery M, Lee YF, Hargens AR. Median nerve compression in the carpal tunnel—functional response to experimentally induced controlled pressure. J Hand Surg 1982;7A:252–259. 9. Hargens AR, Romine JS, Sipe JC, Evans KL, Mubarak SJ, Akeson WH. Peripheral nerve-conduction block by high muscle-compartment pressure. J Bone Joint Surg 1979;61A: 192–200. 10. Kulick MI, Gordillo G, Javidi T, Kilgore ES, Jr., Newmayer WL, III. Long-term analysis of patients having surgical treatment for carpal tunnel syndrome. J Hand Surg 1986; 11A:59 – 66. 11. Langloh ND, Linscheid RL. Recurrent and unrelieved carpal-tunnel syndrome. Clin Orthop Relat Res 1972;83:41– 47. 12. Botte MJ, von Schroeder HP, Abrams RA, Gellman H. Recurrent carpal tunnel syndrome. Hand Clin 1996;12:731– 743. 13. Cellocco P, Rossi C, Bizzarri F, Patrizio L, Costanzo G. Mini-open blind procedure versus limited open technique for carpal tunnel release: a 30-month follow-up study. J Hand Surg 2005;30A:493– 499. 14. Lindau T, Karlsson MK. Complications and outcome in open carpal tunnel release. A 6-year follow-up in 92 patients. Chir Main 1999;18:115–121. 15. Chow JC, Hantes ME. Endoscopic carpal tunnel release: thirteen years’ experience with the Chow technique. J Hand Surg 2002;27A:1011–1018. 16. Concannon MJ, Brownfield ML, Puckett CL. The incidence of recurrence after endoscopic carpal tunnel release. Plast Reconstr Surg 2000;105:1662–1665. 17. Brooks JJ, Schiller JR, Allen SD, Akelman E. Biomechanical and anatomical consequences of carpal tunnel release. Clin Biomech (Bristol, Avon) 2003;18:685– 693. 18. Morimoto KW, Budoff JE, Haddad J, Gabel GT. Crosssectional area of the carpal canal proximal and distal to the wrist flexion crease. J Hand Surg 2005;30A:487– 492.
Purpose: The purpose of this study is to determine whether release of the distal volar forearm fascia (DVFF) is necessary at the time of median nerve decompression for carpal tunnel syndrome. Methods: Five fresh-frozen cadaver specimens were mounted vertically with the hand dependent and a 2.27-kg weight suspended from the fingers. A pressure sensor wire was used to measure pressures starting just distal to the transverse carpal ligament (TCL). The wire was withdrawn proximally in 5-mm increments and into the forearm until pressure was below 10 mm Hg. An incision in the forearm was extended distally until the pressure sensor was found. The distance from this point to the distal volar wrist crease was measured. The TCL was released, keeping the DVFF intact, and the experiment was repeated. Paired t-tests determined whether there were statistically significant differences between measurements before and after TCL release. Results: Average peak pressure under the intact TCL was 57.8 ⫾ 10.1 mm Hg. Average peak pressure under the DVFF with the TCL intact was 61.2 ⫾ 43.6 mm Hg. Following release of the TCL, average peak pressure beneath the TCL significantly decreased to 14.0 ⫾ 9.0 mm Hg, whereas average peak pressure at the intact DVFF increased to 64.8 ⫾ 48.7 mm Hg. Average locations where DVFF pressure became less than 10 mm Hg with an intact TCL and with released TCL were 4.30 ⫾ 1.8 cm and 4.00 ⫾ 1.8 cm proximal to the distal volar wrist crease, respectively. There was no significant difference between DVFF pressures before or after TCL release. Conclusions: In a cadaver model of carpal tunnel syndrome, release of the TCL alone is associated with persistent pressures ⬎30 mm Hg in the region of the DVFF. Release of the TCL did not significantly change the location of the pressure drop-off under the DVFF. (J Hand Surg 2007;32A:1533–1537. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Carpal canal pressure, carpal tunnel syndrome, distal volar forearm fascia, transverse carpal ligament, wrist distraction.
he palmar boundary of the carpal tunnel has been described as including, from proximal to distal, the distal volar forearm fascia (DVFF), the transverse carpal ligament (TCL), and the distal portion of the flexor retinaculum.1 Carpal tunnel release is often combined with a partial release of the DVFF. This is true whether the release is performed
T
using single-portal endoscopic, mini-open, or traditional open techniques.2,3 It has been suggested that division of the DVFF up to 3 cm proximal to the TCL is necessary but that release of the flexor retinaculum distal to the TCL is not, based on clinical pressure measurements.4 There is no accepted standard as to how much, if any, of the DVFF should be divided. The Journal of Hand Surgery
1533
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The Journal of Hand Surgery / Vol. 32A No. 10 December 2007
Previous investigations have found that carpal tunnel pressures greater than 30 mm Hg are associated with carpal tunnel syndrome.5 Prior study has also shown that distraction across the wrist can consistently increase carpal tunnel pressures in a cadaver model to levels that may be pathologic in a clinical situation.6 Release of the transverse carpal ligament in the same cadaver model reliably returned carpal tunnel pressures to within the normal range for up to 4.54 kg of distraction. To our knowledge, there are no cadaver studies to determine whether the DVFF truly needs to be released in combination with release of the TCL and if it does need to be released, what the optimal amount of release is in order to ensure adequate decompression of the median nerve at the level of the wrist. The current study seeks to determine whether release of the DVFF is necessary at the time of median nerve decompression for carpal tunnel syndrome.
Materials and Methods Five fresh-frozen cadaver specimens amputated at the mid-humeral level or proximal were used. There was no history of upper extremity trauma and no surgical or traumatic scars for any of the limbs. The samples were placed in an impervious plastic bag and thawed in warm water prior to testing. An incision was made at the mid-forearm level on the radial border of the forearm. Dissection was carried down to the radius. Two holes were predrilled in the radius, across the interosseous space, and into the ulna with the forearm and wrist held in a neutral position of rotation. Two 3.5-mm external fixator half-pins were placed in the predrilled holes to transfix the radius and ulna as described in a prior study.6 A small, palmar, longitudinal incision was made in line with the radial border of the ring finger at the level of Kaplan’s cardinal line so as to be just distal to the transverse carpal ligament. Dissection was carried down through palmar fascia. The distal edge of the TCL was identified and left intact. Hollow plastic tubing was inserted deep to the distal edge of the TCL (Fig. 1). The tubing was passed proximally until it was palpated subcutaneously in the midforearm. An incision was made in the skin and fascia at this level, and the tubing was retrieved, while leaving enough tubing distally so that some remained distal to the TCL. Thus, the tubing was deep to the entire TCL as well as the DVFF. We used a pressure sensor wire (WaveWire Pressure Guide Wire; Volcano Corporation, Rancho Cordova, CA) that was used in another carpal tunnel pressure study (Ikeda
Figure 1. Hollow plastic tubing was inserted deep to the distal edge of the TCL.
K, Katsuro T, Naoki O. Segmental carpal canal pressure in patients with carpal tunnel syndrome. ASSH Annual Meeting, Scientific Abstracts Presentation, 2005 September, San Antonio, TX). The guide wire was placed into the hollow plastic tubing in a proximal to distal direction with the pressure sensor portion of the wire facing distally. The plastic tubing was then removed distally. The surgeons used direct visualization to leave the guide wire in place such that the pressure sensor was located just distal to the distal edge of the TCL. The guide wire was attached to the real-time pressure monitor display. Each specimen was mounted to a table vise using the external fixator pins. The samples were mounted vertically such that the hand was in the most dependent position and the wrist was in slight extension. A 2.27-kg weight was suspended from the index and middle fingers (Fig. 2). This degree of extension and weight distraction was chosen based on prior study showing that these values most consistently caused an elevation in carpal canal pressure.6 Each cadaver trial consisted of two runs. In the first run, the guide wire was withdrawn in a distal to proximal direction in 5-mm increments, with pressure readings being recorded at each increment. Thus, pressures deep to the TCL and the DVFF with the wrist distracted were established. The measurements continued into the distal forearm until a pressure ⬍10 mm Hg was encountered. The skin and the fascia were incised in a proximal to distal direction to determine the exact location of the wire. The distance from this point to the distal volar wrist crease (DVWC) was measured. For the second run, the TCL was first released by extending the palmar skin incision proximally and
Means et al / Elevated Pressure After Carpal Tunnel Release
1535
fascia incision was then extended distally until the pressure sensor portion of the wire was found. The distance from this point to the DVWC was again measured. Several trial runs were performed initially to determine the final protocol as outlined earlier, as well as to gather preliminary data for a power analysis. Average peak pressures were obtained below the TCL (46.5 ⫾ 8.2 mm Hg) and the DVFF (36.1 ⫾ 12.5 mm Hg) in the early trials and were used for sample size determinations. We assumed that nonpathologic pressure should be, at most, 10 mm Hg, based on previous studies.7 Setting p-value to 0.05 and seeking power of 0.80, we determined that 3 specimens would be necessary to detect the expected difference in pressure at the TCL, whereas 5 samples were required for the DVFF. For this reason we chose to test a total of 5 cadaver arms. Averages and standard deviations for peak pressures and distances were determined for the 5 specimens run using the final protocol. A paired t-test was used to determine whether there were statistically significant differences between measurements before and after TCL release.
Results Figure 2. The specimen was mounted vertically with the hand dependent and a 2.27-kg weight suspended from the index and middle fingers.
dividing the palmar fascia and the TCL only. The DVFF remained intact. Again, the plastic tubing was inserted in a distal to proximal direction and retrieved proximally. The guide wire was placed in a proximal to distal direction, and the plastic tubing was removed, leaving the guide wire in place, distal to the distal edge of the transected TCL. The skin was allowed to close over the released TCL and palmar fascia. The wire was again withdrawn in 5-mm increments, with pressure readings being recorded under the now divided TCL and under the intact DVFF. Again, measurements continued into the forearm until a pressure ⬍10 mm Hg was noted. The forearm
Table 1 shows the average results for the 5 specimens. Figures 3A and 3B present representative graphs for one of the specimens before and after TCL release. In this case, the drop below 10 mm Hg occurred at 70 mm proximal to the distal edge of the TCL, which, after dissection to find the pressure sensor, correlated with a distance of 2.5 cm proximal to the DVWC. The average peak pressure under the intact TCL with 2.27 kg of distraction was 57.0 mm Hg ⫾10.1. The peak pressure under the released TCL was 14 mm Hg ⫾ 8.9. This difference was statistically significant (p ⫽ .0003). There was not a statistically significant difference between the pressures beneath the DVFF before and after TCL release (p ⫽ .69) nor between the average location where the DVFF pressure became less than 10 mm Hg whether the TCL was intact or released (p ⫽ .37). During the open dissections, a thickening of the DVFF was observed, as described by previous au-
Table 1. Comparison of Biometric Measurements Before and After TCL Release TCL (mm Hg) DVFF (mm Hg) Distance to DVWC (cm)
Before TCL Release
After TCL Release
p Value
57.0 ⫾ 10.1 61.0 ⫾ 43.6 4.3 ⫾ 1.8
14.0 ⫾ 8.9 64.0 ⫾ 48.7 4.0 ⫾ 1.8
⬍0.003 0.69 0.37
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Figure 3. (A) Representative specimen graph before TCL release. (B) Representative specimen graph after TCL release.
thors.1 This thickening typically extended 2 cm to 4 cm proximal to the DVWC.
Discussion This study shows that, in a cadaver model of carpal tunnel syndrome, release of the TCL alone is associated with persistent pressures ⬎30 mm Hg in the region of the DVFF. Pressures this high are known to damage nerves secondary to compression or ischemia.5,8,9 We were able to reproduce pressures under the TCL with this model that are similar to those seen in other carpal tunnel syndrome studies, both clinical and biomechanical.5–7,9 Furthermore, these elevated pressures at the TCL were associated with significantly elevated pressures under the DVFF proximal to the DVWC. Also, release of the TCL did not significantly change the location of the pressure drop below pathologic levels under the DVFF. Incomplete carpal tunnel release is a potential cause for persistent or recurrent symptoms following endoscopic and open techniques. The recurrence rate of carpal tunnel syndrome following release has been reported as being from 0% to 10% with all techniques, whether open, mini-open, or endoscopic, falling on both the low and the high end of that range in different studies and reviews.10 –16 The literature we reviewed did not discuss how much DVFF was released at the time of the carpal tunnel release for most techniques. Revision carpal tunnel releases are routinely performed in an open fashion. There is also usually considerably more dissection and exploration around the median nerve to ensure complete decompression and to rule out any prior injuries. This dissection typically includes further release of the forearm fascia proximally. Some authors have suggested that release of the thickened portion of the distal forearm fascia at the index procedure could lower the recurrence rate.17
In a clinical study of endoscopic carpal tunnel release (ECTR), Okutsu et al3 showed that release of the forearm fascia did not produce a notable decrease in carpal canal pressures when compared to TCL release alone. In that study, however, there was no measurement of the pressure beneath the forearm fascia itself. Ikeda et al (Ikeda K, Katsuro T, Naoki O. Segmental carpal canal pressure in patients with carpal tunnel syndrome. ASSH Annual Meeting, Scientific Abstracts Presentation, 2005 September, San Antonio, TX) found in 9 clinical cases that there were some patients with significant pressure elevations 1 cm proximal to the DVWC, although their pressure measurements (7.3 ⫾ 10.6 mm Hg) were not as high as those found in our study. They recommended release of up to 1 cm of DVFF to ensure complete decompression, although they did not evaluate the pressure under the DVFF following TCL release. In 2005, Morimoto et al performed a crosssectional MRI study of the carpal canal.18 They found that there was no significant increase in crosssectional area proximal to the DVWC for 21 mm to 25 mm. They proposed that antebrachial fascia release may be necessary to fully decompress the median nerve, given this relatively constricted area proximal to the DVWC, although they did not note a specific focal area of volume reduction to establish the exact extent of release needed. This narrowing, which corresponds to the thickened portion of the DVFF, likely explains the elevated pressures that we observed in our cadaver measurements. There are several limitations that must be considered with our study. Although the 5-mm markings on the guide wire allowed fairly accurate estimates as to the position of the pressure sensor relative to the distal edge of the TCL, because the guidewire was withdrawn in a “blind” fashion with the skin and deeper structures intact, the only distance that was
Means et al / Elevated Pressure After Carpal Tunnel Release
able to be directly measured was that between the pressure sensor and the DVWC after the distal forearm skin and fascia had been dissected after the pressure dropped below 10 mm Hg. It is likely that the distances recorded for pressure changes relative to the distal edge of the TCL are not exact. Fortunately, because we were studying the contribution of the DVFF to median nerve compression, the DVFF was the only area where we were interested in having an exact distance measurement to determine where the pressure dropped relative to the DVWC. It is likely that there is considerable anatomic variation between patients with regard to thickness and length of the DVFF, and this may explain the relatively wide range we experienced in our recordings between specimens. Even in the seminal paper by Gelberman et al5 in 1981, the authors observed a fairly wide range in pressure readings beneath the TCL in the neutral, flexed, and extended positions. Clinical recommendations as to how much DVFF should be released in addition to the TCL are difficult to make based on this study alone. For example, the surgeon may choose to release proximal to the average peak pressure region at the DVFF, release to the area where the average pressure is ⬍30 mm Hg, or release to the point at which the average pressure is ⬍10 mm Hg. Based on this study, the latter decision would require release of the DVFF 4 cm proximal to the DVWC. The consequence of even this degree of release is, however, uncertain. Perhaps a lesser release of the fascia proximal to the DVWC would sufficiently decrease the pressure proximally. The two former decision possibilities were unable to be assessed with the current study. Rather, this study suggests that, in a cadaver carpal tunnel syndrome model, at least some amount of DVFF release proximal to the DVWC is necessary in order to decrease pressures below a pathologic level. We suggest that the next step in researching this topic should be a cadaver study of sequential release of the DVFF in a distal to proximal direction to determine how much release is necessary to decrease the pressure to nonpathologic levels. Alternatively, a clinical study of patients with and without DVFF release in addition to their TCL release and examining recurrence rates and postoperative improvement would be useful. Received for publication May 15, 2007; accepted in revised form August 27, 2007. This study was supported by the Raymond M. Curtis Research Foundation. Corresponding author: Ken Means c/o Anne Rupert Mattson, Editor, Curtis National Hand Center, Union Memorial Hospital, 3333 N. Calvert Street, #400, Baltimore, MD 21218; e-mail: [email protected].
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Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A10-0005$32.00/0 doi:10.1016/j.jhsa.2007.08.020
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