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The Effect of Dividing Muscles Superficial to the Transverse Carpal Ligament on Carpal Tunnel Release Outcomes
SCIENTIFIC ARTICLE
The Effect of Dividing Muscles Superficial to the Transverse Carpal Ligament on Carpal Tunnel Release Outcomes Hyun Sik Gong, MD, PhD, Joo Han Oh, MD, PhD, Woo Sung Kim, MD, Sae Hoon Kim, MD, Seung Hwan Rhee, MD, Goo Hyun Baek, MD, PhD
Purpose To test the hypothesis that division of muscle fibers lying over or within the transverse carpal ligament (TCL) in an open carpal tunnel release does not have an effect on outcomes in patients with carpal tunnel syndrome (CTS). Methods A total of 152 patients with a mean age of 57 years (range, 31– 83 y) diagnosed with CTS were enrolled for intraoperative observation of the muscles overlying or within the TCL as seen through a 3-cm incision. These muscles when present were incised layer by layer in line with division of the TCL. Patients were divided into 3 groups according to the extent of the muscles covering the TCL. We compared the 3 groups for outcomes of surgery at 6 months in terms of the Boston and Disabilities of the Arm, Shoulder, and Hand (DASH) scores, grip and pinch powers, and scar pain. Results Of the 152 patients, 75 had a purely ligamentous TCL (group 1), 52 had muscle fibers covering 50% or less of the incision length (group 2), and 25 had muscle fibers covering more than 50% of the incision length (group 3). There were no differences in the postoperative Boston symptom and function scores and the DASH scores among the groups. In addition, there were no differences in the grip and pinch strengths and scar pain. Conclusions Division of the muscles overlying or within the TCL in line with the third web space incision does not affect postoperative outcomes after carpal tunnel release in terms of the Boston and DASH scores, grip and pinch powers, and scar pain. (J Hand Surg 2011;36A: 1475–1481. Copyright © 2011 by the American Society for Surgery of the Hand. All rights reserved.) Type of study/level of evidence Prognostic I. Key words Carpal tunnel syndrome, muscles, outcomes, transverse carpal ligament. ARPAL TUNNEL SYNDROME (CTS) is the most common compressive neuropathy in the upper extremity, and the compression of the median nerve can occur by any condition that increases pressure in the carpal tunnel. The roof of the carpal tunnel is mainly composed of the transverse carpal ligament
C
From the Department of Orthopedic Surgery, Seoul National University Bundang Hospital, Seongnam, Korea. Received for publication December 9, 2010; accepted in revised form June 7, 2011. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
(TCL), which extends from the scaphoid tuberosity and trapezium to the pisiform and the hook of hamate. Several authors have reported the presence of muscle fibers lying superficial to or within the TCL.1–7 The exact nature of these muscle fibers is still uncertain, although several authors suggest their origin is thenar or Corresponding author: Hyun Sik Gong, MD, PhD, Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do 463707, Korea; e-mail: [email protected]. 0363-5023/11/36A09-0007$36.00/0 doi:10.1016/j.jhsa.2011.06.008
© ASSH 䉬 Published by Elsevier, Inc. All rights reserved. 䉬 1475
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hypothenar muscle in most cases.5–7 It has been suggested that these muscles have a role in the etiology of CTS.1– 4 Division of these muscle fibers has also been implicated in contributing to pillar pain.8 In addition, the relationship between muscle morphology and motor branch types has been highlighted recently.5–7 Rotman and Donovan9 recommended preserving the thin layer of the thenar muscle origin in the TCL to retain as much of the muscle attachment as possible. However, Lindley and Kleinert3 stated that trying to save too much muscle can lead to a more ulnar approach, which can injure the ulnar artery and nerve. Our practice includes routine use of the skin incision along the axis of the third web space and division of the muscle fibers over or within the TCL without dissecting them off the TCL, because these muscle fibers are difficult to manipulate during minimally invasive carpal tunnel release.4 The purpose of this study was to test the hypothesis that division of muscle fibers lying over or within the TCL in an open carpal tunnel release does not have an effect on outcomes in patients with CTS. MATERIALS AND METHODS Demographics We conducted this study after obtaining approval from our institutional review board. We included all patients treated at our center diagnosed with idiopathic CTS between October 2008 and April 2010, based on both the clinical symptoms and positive electrophysiologic findings. We excluded workers’ compensation cases and those with associated disease, such as cervical radiculopathy, cubital tunnel syndrome, diabetes mellitus, rheumatoid arthritis, and Buerger disease. Initially 206 patients (33 men and 173 women) met inclusion criteria. We enrolled 172 patients according to exclusion criteria; ultimately, 152 patients fulfilled full assessments at 6 months postoperatively. We analyzed these 152 patients. All patients were ethnic Koreans. In 37 patients with bilateral involvement, the hand with the more severe symptoms was included. Nine patients were men and 143 were women. Their age ranged from 31 to 83 years (mean, 57 y). The right hand was assessed in 81 of 152 patients, and the left in 71. Duration of symptoms ranged from 8 months to 40 years (mean, 2.6 y), and the mean follow-up period was 9 months (range, 6 –12 mo). We performed an electrophysiologic examination before all surgeries and graded the findings according to Bland’s classification.10 Three rehabilitation physicians performed the electrophysiologic examinations. Bland’s classification consists of 7 grades, from grade 0 (normal) to
grade 6 (extremely severe) based on conduction time and amplitude: grade 1 (very mild) is demonstrable only with the most sensitive tests; grade 2 (mild) shows slow sensory conduction and normal motor conduction; grade 3 (moderately severe) shows motor terminal latency greater than 4.5 milliseconds and less than 6.5 milliseconds with preserved sensory nerve action potential; grade 4 (severe) shows absent sensory nerve action potential and motor terminal latency less than 6.5 milliseconds; grade 5 (very severe) shows motor terminal latency greater than 6.5 milliseconds; and grade 6 (extremely severe) shows unrecordable surface motor potentials (⬍0.2 mV). A significant linear relationship between neurophysiological grading and clinical disease severity was reported.10 A single surgeon diagnosed thenar muscle atrophy on physical examination and considered it to be present if the bulk and contour of the thenar eminence was reduced markedly or if normal elastic consistency or muscle tone was absent during active opposition.11,12 Observation of muscles over or within the TCL During the carpal tunnel release surgery, a single surgeon observed and recorded the relationship of any muscle lying over or within the TCL. Under local anesthesia, a skin incision of 3 cm was made in line with the third web space from 1 cm distal to the wrist crease to Kaplan’s cardinal line while the wrist was in neutral radioulnar deviation and flexion-extension and the fingers in extension. In the subcutaneous plane, an effort was made to preserve the branches of the palmar cutaneous branch of the median nerve and the cutaneous branch of the ulnar nerve. After the superficial palmar fascia was divided in line with the skin incision, the TCL was exposed and inspected to determine whether any muscle fibers were attached to it. If no muscles were found, the patient was categorized as group 1 with a purely ligamentous TCL (Fig. 1). If any muscle fibers were identified at the TCL but their proximal-to-distal length (width) was less than or equal to 50% of the incision, the patient was categorized as group 2 (Fig. 2). If the width of the muscle fibers were more than 50% of the incision wound, the patient was categorized as group 3 (Fig. 3). This determination was estimated based on visual observation. The TCL and any overlying muscles were divided in line with the skin incision with special care not to injure the motor branch of the median nerve by dividing the muscle fibers layer by layer. However, no dissection of the median nerve was performed to identify the motor branch. We were ready to divide the muscles ulnarly if we had encountered the motor branch during division of the muscles. We did not perform neurolysis of the
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FIGURE 1: If no muscles were found in the wound, the patient was categorized as group 1 with a purely ligamentous TCL. The incision in line with the third web space is marked by a dotted line.
FIGURE 2: If any muscle fibers were identified at the TCL but their width was less than or equal to 50% of the incision, the patient was categorized as group 2.
median nerve in any case. The wound was closed and a short-arm splint was applied for 4 days. Patients did not receive formal hand therapy and were educated to massage the scar after the sutures were removed 2 weeks postoperatively.
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FIGURE 3: If the width of the muscle fibers were more than 50% of the incision wound, the patient was categorized as group 3. Muscle fibers are marked with an asterisk.
Outcome evaluation We divided patients into groups 1, 2, and 3 according to the existence and extent of the muscle fibers over the TCL, and prospectively compared these groups in terms of patient-based questionnaires regarding functional status, grip and pinch strength, and scar pain at the preoperative and 6-month postoperative visits. We obtained patients’ assessments of the symptoms and functional state based on the Boston carpal tunnel questionnaire and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire.13,14 The Boston carpal tunnel questionnaire consists of a symptom severity scale and functional scale, and each is scored from 1 (none) to 5 (most severe).13 The DASH questionnaire quantifies general disabilities related to the upper extremity and is scored between 0 and 100, with higher scores representing more upper extremity disability.14 We measured grip and key pinch strengths with a Jamar hand dynamometer and pinch gauge (Asimow Engineering, Los Angeles, CA) in a standardized manner: with the shoulder, elbow, forearm and wrist in neutral position, 3 consecutive attempts with 1-minute intervals were each measured in kilograms and the maximum value was recorded.15,16 We assessed scar pain around the incision. Pain intensity was measured using an 11-point pain numeric rating scale, which is a reliable and valid measure of pain intensity from 0 (no pain) to 10 (worst imaginable pain).17,18
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TABLE 1.
DIVISION OF MUSCLES SUPERFICIAL TO TCL
Baseline Patient Characteristics
Patients (n) Male:female Right:left:bilateral Age (y) (mean ⫾ SD) Symptom duration (y) (mean ⫾ SD)
Group 1
Group 2
Group 3
75
52
25
2:50
7:68
0:25
.17
33:25:17
24:18:10
6:9:10
.25
57.5 ⫾ 9.9
56.5 ⫾ 9.6
57.4 ⫾ 12.4
.85
2.7 ⫾ 4.5
2.5 ⫾ 3.0
2.8 ⫾ 3.8
.95
9
6
3
Electrophysiologic grade (n) 1 (18)
.93
2 (9)
5
2
2
3 (67)
30
26
11
4 (10)
6
4
0
5 (39)
20
11
8
5
3
1
13
12
6
6 (9) Thenar muscle atrophy
P Value
A single evaluator who was unaware of this study asked patients to fill out the questionnaires and check the pain scale, and evaluated grip and pinch strength. Data analysis To determine statistical power, the primary outcome variable was the DASH score. We designed the present study to determine a 10-point mean difference in the DASH score among 3 groups, with a standard deviation of 10 points (for an effect size of 1.0). A power analysis indicated that a sample size of 23 patients in each of the 3 groups would provide 90% statistical power to detect this effect size between the groups (␣ ⫽ 0.05,  ⫽ 0.10) with use of an analysis of variance test. To safeguard against loss to follow-up, we recruited patients until the number of patients in the smallest group reached 25. We compared the demographic parameters and evaluation scores among the 3 groups using analysis of variance and posthoc analyses. Postoperative improvement in the outcome scores in each group was analyzed using paired t-test. Significance was accepted at P ⬍ .05. RESULTS Variations in muscles over the TCL We categorized 75 patients as group 1 (a purely ligamentous TCL), 52 as group 2 (muscle fibers covering 50% or less of the incision length), and 25 as group 3 (muscle fibers covering more than 50% of the incision length).
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In the 37 patients who had bilateral operations, only 1 patient had different muscle morphologies, with 1 side belonging to group 2 and the other to group 3, and this patient was finally categorized as group 3 because we counted the side with more severe symptoms. There were no statistical differences among groups in terms of age, affected hand, symptom duration, preoperative electrophysiologic grades, and incidence of thenar muscle atrophy (Table 1). Outcomes after carpal tunnel release With respect to the variations of the muscle morphology over the TCL, there were no differences in the preoperative Boston symptom and function scores and the DASH scores among groups. The mean Boston symptom and function scores all improved significantly in all groups. The mean DASH scores improved significantly in all groups. In a comparison of the 3 groups, there were no differences in postoperative Boston symptom and function scores and the DASH scores (Table 2). The mean grip and lateral pinch strengths also significantly improved in all groups, and there were no significant differences in preoperative, postoperative, or changes in grip strength. There were no differences in scar pain numeric rating scale among the 3 groups. We observed no cases of injury to the recurrent motor branch of the median nerve because no patients experienced new-onset thenar atrophy or difficulty with thumb opposition. There were 3 cases of wound dehiscence without infection, 2 in group 1 and 1 in group 2.
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TABLE 2.
Outcomes After Carpal Tunnel Release Group 1
Group 2
Group 3
P Value
Boston symptom score (mean ⫾ SD) Preoperative
2.8 ⫾ 0.5
2.9 ⫾ 0.5
3.0 ⫾ 0.6
.38
6 mo
1.5 ⫾ 0.3
1.6 ⫾ 0.3
1.6 ⫾ 0.3
.61
Change
1.1 ⫾ 0.7
1.2 ⫾ 0.7
1.3 ⫾ 0.7
.42
Boston function score (mean ⫾ SD) Preoperative
2.9 ⫾ 0.5
2.8 ⫾ 0.5
2.9 ⫾ 0.5
.76
6 mo
1.5 ⫾ 0.3
1.6 ⫾ 0.3
1.6 ⫾ 0.3
.58
Change
1.3 ⫾ 0.6
1.2 ⫾ 0.7
1.2 ⫾ 0.7
.80
DASH score (mean ⫾ SD) Preoperative
43 ⫾ 10
42 ⫾ 10
41 ⫾ 9
.66
6 mo
23 ⫾ 8
24 ⫾ 8
24 ⫾ 11
.48
Change
20 ⫾ 11
18 ⫾ 8
16 ⫾ 10
.19
Grip strength (kg) (mean ⫾ SD) Preoperative
22.7 ⫾ 10.9
23.1 ⫾ 10.8
25.1 ⫾ 11.2
.66
6 mo
25.9 ⫾ 10.3
25.8 ⫾ 10.0
28.8 ⫾ 11.4
.45
3.2 ⫾ 2.1
2.7 ⫾ 2.3
3.1 ⫾ 2.3
.18
Change Lateral pinch strength (kg) (mean ⫾ SD) Preoperative
6.5 ⫾ 3.0
6.1 ⫾ 2.9
7.1 ⫾ 3.4
.46
6 mo
7.4 ⫾ 2.9
6.9 ⫾ 2.5
8.1 ⫾ 2.9
.17
Change Scar pain numeric rating scale at 6 mo (mean ⫾ SD)
0.9 ⫾ 0.7
0.7 ⫾ 0.8
1.0 ⫾ 1.0
.12
1.1 ⫾ 1.3
1.5 ⫾ 1.4
1.2 ⫾ 1.1
.23
No complex regional pain syndrome or recurrence of nerve compression symptoms occurred during the study period. DISCUSSION This study demonstrated that the presence and division of the muscles overlying or within the TCL in line with the third web space had no effect on outcomes of open carpal tunnel release in terms of Boston and DASH scores, grip and pinch powers, and scar pain. To date, the true identity of the muscles overlying or within the TCL is not definite. Mannerfelt and Hybbinette19 suggested these muscles were aberrant palmaris brevis and flexor pollicis brevis muscles, but Shrewsbury et al20 reported that the palmaris brevis muscle never extended past the ulnar margin of the palmar aponeurosis. Jonson and Shrewsbury21 noted that the flexor pollicis brevis and flexor digiti quinti blended into the TCL. However, Green and Morgan5 noted that in some cases the muscles overlying the TCL had no apparent connection with the normal thenar or the hypothenar muscles. Ragoowansi et al2 thought these muscles belonged to a separate muscle named the transverse carpal muscle or musculus transverses carpi. We
did not dissect the muscles and thus were unable to verify what these muscles were, although in most cases they appeared to be the thenar muscles, judging from the direction of the fibers. We expected that if the muscle fibers are the thenar muscles, division of them would cause some loss of power, but our data demonstrated no differences in grip or pinch power between groups. We also expected that patients with muscle fibers might have more scar pain because of scar formation within the divided muscles. Also, patients with thenar muscles originating more from the TCL than from the carpals might experience a direct effect of muscle relaxation after carpal tunnel release that might result in more pillar pain of muscular origin.8 However, there was no difference in the rated pain between groups. This study also demonstrated that there are no associations between the muscle morphology and preoperative severity of nerve compression in terms of patient-based scores, electrophysiologic grades, or incidence of thenar muscle atrophy. Iob et al1 suggested that contraction of these muscles may reduce the diameter of the carpal canal. However, Hollevoet et al6 found no difference in the
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incidence and types of these muscles between patients with CTS and cadavers with no known medical history. They concluded that the muscle fibers do not cause CTS. In the current study, we had no motor branch injuries. Previous studies have shown that the existence of muscles over the TCL is associated with certain thenar motor branch types. Green and Morgan5 noted that special care should be taken to identify and protect the motor branches when muscle fibers are encountered over the TCL, because an anomalous motor branch was found in 93% of hands in those cases. They recommended not proceeding with transection of the TCL until the motor branch has been identified and protected. Al-Qattan7 reported that transligamentous and preligamentous types are associated with the presence of hypertrophic muscles over the TCL, and incision of this muscle should be done carefully and on the ulnar side to avoid injury. In our series, although we did not attempt to identify motor branch types and divided the muscles bit by bit in line with the third web space, we have not had occasion to encounter the motor branch within the muscle fibers. Al-Qattan stated that dissection of the hypertrophic muscle over the radial side of the TCL is unnecessary and that the thenar motor branch is expected to be within the radial side of the hypertrophic muscle because the branch almost always arises from the radial side of the median nerve. However, there have been reports of the motor branch branching from the medial side of the median nerve.22 Thus, a careful layer-by-layer incision of the muscle is still necessary. In the current study performed in Koreans, 49% of patients had a purely ligamentous TCL, whereas 34% had muscle fibers covering 50% or less of the incision length and 16% had muscle fibers covering more than 50% of the incision length. Thus, 51% had some muscle fibers over or within the TCL. These results are comparable to those of Hollevoet et al,6 who investigated muscle fibers in 143 ethnic Caucasians. They found that muscle fibers crossing the line of incision were absent in 50%, 2 to 10 mm wide in 39%, and more than 10 mm in 11% of the operated hands, and 50%, 35%, and 15% respectively in the cadaveric hands. Because our incision was 3 cm and we categorized the muscles according to whether their length was more or less than 50% of the incision length, we probably have categorized some patients with muscle fibers of more than 10 mm length into group 2 rather than group 3. Other studies reported lower incidences of the muscle fibers over the TCL. Al-Qattan7 reported that in 100 Middle East-
ern patients, 36 had hypertrophic muscles over the TCL. Green and Morgan5 reported that 28% of 1,400 CTS patients in the United States had some muscle fibers overlying the TCL. There are several limitations to the study. First, the grouping of the muscles overlying the TCL was not validated for reliability. We estimated rather than measured the percentage of muscle fibers over the TCL. However, a single surgeon who was unaware of the major outcome variables at the time of the operation performed all classifications. Second, we did not have a control group that had overlying muscles that were not divided during carpal tunnel release, because it was practically difficult to avoid dividing the overlying muscles in an open carpal tunnel release. However, to determine whether dividing the muscle over the TCL has an effect on outcomes in patients with CTS, it would have been necessary to divide the muscle in some patients and not divide them in a control group. Therefore, we do not know whether those who had preserved muscles would have better outcomes than those who did not, although it is unlikely because there were no differences in preoperative or postoperative functional status between groups. At least we can say that outcomes of carpal tunnel release with concomitant division of the overlying muscles are similar to those of carpal tunnel release in patients without the muscles in the first place (purely ligamentous type). Third, our measurement might not have been sensitive enough to detect small differences between groups that have a wide range of symptom severity. A study of groups with more controlled variables, or isolation of the variable of presence or absence of overlying muscle, might have definitely revealed anything of importance that could be attributed to the presence or absence of the muscle and its division. Finally, because the patients were mostly women, the results may not represent the general population with CTS. REFERENCES 1. Iob I, Battaggia C, Rossetto L, Ermani M. The carpal tunnel syndrome. Anatomo-clinical correlations. Neurochirurgie 2000;46:355– 357. 2. Ragoowansi R, Adeniran A, Moss AL. Anomalous muscle of the wrist. Clin Anat 2002;15:363–365. 3. Lindley SG, Kleinert JM. Prevalence of anatomic variations encountered in elective carpal tunnel release. J Hand Surg 2003;28A:849 – 855. 4. Tuncali D, Barutcu AY, Terzioglu A, Aslan G. Transverse carpal muscle in association with carpal tunnel syndrome: report of three cases. Clin Anat 2005;18:308 –312. 5. Green DP, Morgan JP. Correlation between muscle morphology of the transverse carpal ligament and branching pattern of the motor branch of median nerve. J Hand Surg 2008;33A:1501511.
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6. Hollevoet N, Barbaix E, D’herde K, Vanhove W, Verdonk R. Muscle fibres crossing the line of incision used in carpal tunnel decompression. J Hand Surg 2010;35B:115–119. 7. Al-Qattan MM. Variations in the course of the thenar motor branch of the median nerve and their relationship to the hypertrophic muscle overlying the transverse carpal ligament. J Hand Surg 2010;35A: 1820 –1824. 8. Ludlow KS, Merla JL, Cox JA, Hurst LN. Pillar pain as a postoperative complication of carpal tunnel release: a review of the literature. J Hand Ther 1997;10:277–282. 9. Rotman MB, Donovan JP. Practical anatomy of the carpal tunnel. Hand Clin 2002;18:219 –230. 10. Bland JD. A neurophysiological grading scale for carpal tunnel syndrome. Muscle Nerve 2000;23:1280 –1283. 11. Gong HS, Oh JH, Bin SW, Kim WS, Chung MS, Baek GH. Clinical features influencing the patient-based outcome after carpal tunnel release. J Hand Surg 2008;33A:1512–1517. 12. Mallette P, Zhao M, Zurakowski D, Ring D. Muscle atrophy at diagnosis of carpal and cubital tunnel syndrome. J Hand Surg 2007; 32A:855– 858. 13. Levine DW, Simmons BP, Koris MJ, Daltroy LH, Hohl GG, Fossel AH, et al. A self-administered questionnaire for the assessment of severity of symptoms and functional status in carpal tunnel syndrome. J Bone Joint Surg 1993;75A:1585–1592.
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14. Hudak PL, Amadio PC, Bombardier C. Development of an upper extremity outcome measure: the DASH (disabilities of the arm, shoulder and hand) [corrected]. The Upper Extremity Collaborative Group (UECG). Am J Ind Med 1996;29:602– 608. 15. Günther CM, Bürger A, Rickert M, Crispin A, Schulz CU. Grip strength in healthy caucasian adults: reference values. J Hand Surg 2008;33A:558 –565. 16. Günther CM, Bürger A, Rickert M, Schulz CU. Key pinch in healthy adults: normative values. J Hand Surg 2008;33E:144 –148. 17. Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain 1986;27:117–126. 18. Williamson A, Hoggart B. Pain: a review of three commonly used pain rating scales. J Clin Nurs 2005;14:798 – 804. 19. Mannerfelt L, Hybbinette CH. Important anomaly of the thenar motor branch of the median nerve. A clinical and anatomical report. Bull Hosp Joint Dis 1972;33:15–21. 20. Shrewsbury MM, Johnson RK, Ousterhout DK. The palmaris brevis—a reconsideration of its anatomy and possible function. J Bone Joint Surg 1972;54A:344 –348. 21. Johnson RK, Shrewsbury MM. Anatomical course of the thenar branch of the median nerve— usually in a separate tunnel through the transverse carpal ligament. J Bone Joint Surg 1970A;52:269 –273. 22. Lanz U. Anatomical variations of the median nerve in the carpal tunnel. J Hand Surg 1977;2A:44 –53.
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The Effect of Dividing Muscles Superficial to the Transverse Carpal Ligament on Carpal Tunnel Release Outcomes Hyun Sik Gong, MD, PhD, Joo Han Oh, MD, PhD, Woo Sung Kim, MD, Sae Hoon Kim, MD, Seung Hwan Rhee, MD, Goo Hyun Baek, MD, PhD
Purpose To test the hypothesis that division of muscle fibers lying over or within the transverse carpal ligament (TCL) in an open carpal tunnel release does not have an effect on outcomes in patients with carpal tunnel syndrome (CTS). Methods A total of 152 patients with a mean age of 57 years (range, 31– 83 y) diagnosed with CTS were enrolled for intraoperative observation of the muscles overlying or within the TCL as seen through a 3-cm incision. These muscles when present were incised layer by layer in line with division of the TCL. Patients were divided into 3 groups according to the extent of the muscles covering the TCL. We compared the 3 groups for outcomes of surgery at 6 months in terms of the Boston and Disabilities of the Arm, Shoulder, and Hand (DASH) scores, grip and pinch powers, and scar pain. Results Of the 152 patients, 75 had a purely ligamentous TCL (group 1), 52 had muscle fibers covering 50% or less of the incision length (group 2), and 25 had muscle fibers covering more than 50% of the incision length (group 3). There were no differences in the postoperative Boston symptom and function scores and the DASH scores among the groups. In addition, there were no differences in the grip and pinch strengths and scar pain. Conclusions Division of the muscles overlying or within the TCL in line with the third web space incision does not affect postoperative outcomes after carpal tunnel release in terms of the Boston and DASH scores, grip and pinch powers, and scar pain. (J Hand Surg 2011;36A: 1475–1481. Copyright © 2011 by the American Society for Surgery of the Hand. All rights reserved.) Type of study/level of evidence Prognostic I. Key words Carpal tunnel syndrome, muscles, outcomes, transverse carpal ligament. ARPAL TUNNEL SYNDROME (CTS) is the most common compressive neuropathy in the upper extremity, and the compression of the median nerve can occur by any condition that increases pressure in the carpal tunnel. The roof of the carpal tunnel is mainly composed of the transverse carpal ligament
C
From the Department of Orthopedic Surgery, Seoul National University Bundang Hospital, Seongnam, Korea. Received for publication December 9, 2010; accepted in revised form June 7, 2011. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
(TCL), which extends from the scaphoid tuberosity and trapezium to the pisiform and the hook of hamate. Several authors have reported the presence of muscle fibers lying superficial to or within the TCL.1–7 The exact nature of these muscle fibers is still uncertain, although several authors suggest their origin is thenar or Corresponding author: Hyun Sik Gong, MD, PhD, Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do 463707, Korea; e-mail: [email protected]. 0363-5023/11/36A09-0007$36.00/0 doi:10.1016/j.jhsa.2011.06.008
© ASSH 䉬 Published by Elsevier, Inc. All rights reserved. 䉬 1475
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hypothenar muscle in most cases.5–7 It has been suggested that these muscles have a role in the etiology of CTS.1– 4 Division of these muscle fibers has also been implicated in contributing to pillar pain.8 In addition, the relationship between muscle morphology and motor branch types has been highlighted recently.5–7 Rotman and Donovan9 recommended preserving the thin layer of the thenar muscle origin in the TCL to retain as much of the muscle attachment as possible. However, Lindley and Kleinert3 stated that trying to save too much muscle can lead to a more ulnar approach, which can injure the ulnar artery and nerve. Our practice includes routine use of the skin incision along the axis of the third web space and division of the muscle fibers over or within the TCL without dissecting them off the TCL, because these muscle fibers are difficult to manipulate during minimally invasive carpal tunnel release.4 The purpose of this study was to test the hypothesis that division of muscle fibers lying over or within the TCL in an open carpal tunnel release does not have an effect on outcomes in patients with CTS. MATERIALS AND METHODS Demographics We conducted this study after obtaining approval from our institutional review board. We included all patients treated at our center diagnosed with idiopathic CTS between October 2008 and April 2010, based on both the clinical symptoms and positive electrophysiologic findings. We excluded workers’ compensation cases and those with associated disease, such as cervical radiculopathy, cubital tunnel syndrome, diabetes mellitus, rheumatoid arthritis, and Buerger disease. Initially 206 patients (33 men and 173 women) met inclusion criteria. We enrolled 172 patients according to exclusion criteria; ultimately, 152 patients fulfilled full assessments at 6 months postoperatively. We analyzed these 152 patients. All patients were ethnic Koreans. In 37 patients with bilateral involvement, the hand with the more severe symptoms was included. Nine patients were men and 143 were women. Their age ranged from 31 to 83 years (mean, 57 y). The right hand was assessed in 81 of 152 patients, and the left in 71. Duration of symptoms ranged from 8 months to 40 years (mean, 2.6 y), and the mean follow-up period was 9 months (range, 6 –12 mo). We performed an electrophysiologic examination before all surgeries and graded the findings according to Bland’s classification.10 Three rehabilitation physicians performed the electrophysiologic examinations. Bland’s classification consists of 7 grades, from grade 0 (normal) to
grade 6 (extremely severe) based on conduction time and amplitude: grade 1 (very mild) is demonstrable only with the most sensitive tests; grade 2 (mild) shows slow sensory conduction and normal motor conduction; grade 3 (moderately severe) shows motor terminal latency greater than 4.5 milliseconds and less than 6.5 milliseconds with preserved sensory nerve action potential; grade 4 (severe) shows absent sensory nerve action potential and motor terminal latency less than 6.5 milliseconds; grade 5 (very severe) shows motor terminal latency greater than 6.5 milliseconds; and grade 6 (extremely severe) shows unrecordable surface motor potentials (⬍0.2 mV). A significant linear relationship between neurophysiological grading and clinical disease severity was reported.10 A single surgeon diagnosed thenar muscle atrophy on physical examination and considered it to be present if the bulk and contour of the thenar eminence was reduced markedly or if normal elastic consistency or muscle tone was absent during active opposition.11,12 Observation of muscles over or within the TCL During the carpal tunnel release surgery, a single surgeon observed and recorded the relationship of any muscle lying over or within the TCL. Under local anesthesia, a skin incision of 3 cm was made in line with the third web space from 1 cm distal to the wrist crease to Kaplan’s cardinal line while the wrist was in neutral radioulnar deviation and flexion-extension and the fingers in extension. In the subcutaneous plane, an effort was made to preserve the branches of the palmar cutaneous branch of the median nerve and the cutaneous branch of the ulnar nerve. After the superficial palmar fascia was divided in line with the skin incision, the TCL was exposed and inspected to determine whether any muscle fibers were attached to it. If no muscles were found, the patient was categorized as group 1 with a purely ligamentous TCL (Fig. 1). If any muscle fibers were identified at the TCL but their proximal-to-distal length (width) was less than or equal to 50% of the incision, the patient was categorized as group 2 (Fig. 2). If the width of the muscle fibers were more than 50% of the incision wound, the patient was categorized as group 3 (Fig. 3). This determination was estimated based on visual observation. The TCL and any overlying muscles were divided in line with the skin incision with special care not to injure the motor branch of the median nerve by dividing the muscle fibers layer by layer. However, no dissection of the median nerve was performed to identify the motor branch. We were ready to divide the muscles ulnarly if we had encountered the motor branch during division of the muscles. We did not perform neurolysis of the
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FIGURE 1: If no muscles were found in the wound, the patient was categorized as group 1 with a purely ligamentous TCL. The incision in line with the third web space is marked by a dotted line.
FIGURE 2: If any muscle fibers were identified at the TCL but their width was less than or equal to 50% of the incision, the patient was categorized as group 2.
median nerve in any case. The wound was closed and a short-arm splint was applied for 4 days. Patients did not receive formal hand therapy and were educated to massage the scar after the sutures were removed 2 weeks postoperatively.
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FIGURE 3: If the width of the muscle fibers were more than 50% of the incision wound, the patient was categorized as group 3. Muscle fibers are marked with an asterisk.
Outcome evaluation We divided patients into groups 1, 2, and 3 according to the existence and extent of the muscle fibers over the TCL, and prospectively compared these groups in terms of patient-based questionnaires regarding functional status, grip and pinch strength, and scar pain at the preoperative and 6-month postoperative visits. We obtained patients’ assessments of the symptoms and functional state based on the Boston carpal tunnel questionnaire and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire.13,14 The Boston carpal tunnel questionnaire consists of a symptom severity scale and functional scale, and each is scored from 1 (none) to 5 (most severe).13 The DASH questionnaire quantifies general disabilities related to the upper extremity and is scored between 0 and 100, with higher scores representing more upper extremity disability.14 We measured grip and key pinch strengths with a Jamar hand dynamometer and pinch gauge (Asimow Engineering, Los Angeles, CA) in a standardized manner: with the shoulder, elbow, forearm and wrist in neutral position, 3 consecutive attempts with 1-minute intervals were each measured in kilograms and the maximum value was recorded.15,16 We assessed scar pain around the incision. Pain intensity was measured using an 11-point pain numeric rating scale, which is a reliable and valid measure of pain intensity from 0 (no pain) to 10 (worst imaginable pain).17,18
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TABLE 1.
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Baseline Patient Characteristics
Patients (n) Male:female Right:left:bilateral Age (y) (mean ⫾ SD) Symptom duration (y) (mean ⫾ SD)
Group 1
Group 2
Group 3
75
52
25
2:50
7:68
0:25
.17
33:25:17
24:18:10
6:9:10
.25
57.5 ⫾ 9.9
56.5 ⫾ 9.6
57.4 ⫾ 12.4
.85
2.7 ⫾ 4.5
2.5 ⫾ 3.0
2.8 ⫾ 3.8
.95
9
6
3
Electrophysiologic grade (n) 1 (18)
.93
2 (9)
5
2
2
3 (67)
30
26
11
4 (10)
6
4
0
5 (39)
20
11
8
5
3
1
13
12
6
6 (9) Thenar muscle atrophy
P Value
A single evaluator who was unaware of this study asked patients to fill out the questionnaires and check the pain scale, and evaluated grip and pinch strength. Data analysis To determine statistical power, the primary outcome variable was the DASH score. We designed the present study to determine a 10-point mean difference in the DASH score among 3 groups, with a standard deviation of 10 points (for an effect size of 1.0). A power analysis indicated that a sample size of 23 patients in each of the 3 groups would provide 90% statistical power to detect this effect size between the groups (␣ ⫽ 0.05,  ⫽ 0.10) with use of an analysis of variance test. To safeguard against loss to follow-up, we recruited patients until the number of patients in the smallest group reached 25. We compared the demographic parameters and evaluation scores among the 3 groups using analysis of variance and posthoc analyses. Postoperative improvement in the outcome scores in each group was analyzed using paired t-test. Significance was accepted at P ⬍ .05. RESULTS Variations in muscles over the TCL We categorized 75 patients as group 1 (a purely ligamentous TCL), 52 as group 2 (muscle fibers covering 50% or less of the incision length), and 25 as group 3 (muscle fibers covering more than 50% of the incision length).
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In the 37 patients who had bilateral operations, only 1 patient had different muscle morphologies, with 1 side belonging to group 2 and the other to group 3, and this patient was finally categorized as group 3 because we counted the side with more severe symptoms. There were no statistical differences among groups in terms of age, affected hand, symptom duration, preoperative electrophysiologic grades, and incidence of thenar muscle atrophy (Table 1). Outcomes after carpal tunnel release With respect to the variations of the muscle morphology over the TCL, there were no differences in the preoperative Boston symptom and function scores and the DASH scores among groups. The mean Boston symptom and function scores all improved significantly in all groups. The mean DASH scores improved significantly in all groups. In a comparison of the 3 groups, there were no differences in postoperative Boston symptom and function scores and the DASH scores (Table 2). The mean grip and lateral pinch strengths also significantly improved in all groups, and there were no significant differences in preoperative, postoperative, or changes in grip strength. There were no differences in scar pain numeric rating scale among the 3 groups. We observed no cases of injury to the recurrent motor branch of the median nerve because no patients experienced new-onset thenar atrophy or difficulty with thumb opposition. There were 3 cases of wound dehiscence without infection, 2 in group 1 and 1 in group 2.
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TABLE 2.
Outcomes After Carpal Tunnel Release Group 1
Group 2
Group 3
P Value
Boston symptom score (mean ⫾ SD) Preoperative
2.8 ⫾ 0.5
2.9 ⫾ 0.5
3.0 ⫾ 0.6
.38
6 mo
1.5 ⫾ 0.3
1.6 ⫾ 0.3
1.6 ⫾ 0.3
.61
Change
1.1 ⫾ 0.7
1.2 ⫾ 0.7
1.3 ⫾ 0.7
.42
Boston function score (mean ⫾ SD) Preoperative
2.9 ⫾ 0.5
2.8 ⫾ 0.5
2.9 ⫾ 0.5
.76
6 mo
1.5 ⫾ 0.3
1.6 ⫾ 0.3
1.6 ⫾ 0.3
.58
Change
1.3 ⫾ 0.6
1.2 ⫾ 0.7
1.2 ⫾ 0.7
.80
DASH score (mean ⫾ SD) Preoperative
43 ⫾ 10
42 ⫾ 10
41 ⫾ 9
.66
6 mo
23 ⫾ 8
24 ⫾ 8
24 ⫾ 11
.48
Change
20 ⫾ 11
18 ⫾ 8
16 ⫾ 10
.19
Grip strength (kg) (mean ⫾ SD) Preoperative
22.7 ⫾ 10.9
23.1 ⫾ 10.8
25.1 ⫾ 11.2
.66
6 mo
25.9 ⫾ 10.3
25.8 ⫾ 10.0
28.8 ⫾ 11.4
.45
3.2 ⫾ 2.1
2.7 ⫾ 2.3
3.1 ⫾ 2.3
.18
Change Lateral pinch strength (kg) (mean ⫾ SD) Preoperative
6.5 ⫾ 3.0
6.1 ⫾ 2.9
7.1 ⫾ 3.4
.46
6 mo
7.4 ⫾ 2.9
6.9 ⫾ 2.5
8.1 ⫾ 2.9
.17
Change Scar pain numeric rating scale at 6 mo (mean ⫾ SD)
0.9 ⫾ 0.7
0.7 ⫾ 0.8
1.0 ⫾ 1.0
.12
1.1 ⫾ 1.3
1.5 ⫾ 1.4
1.2 ⫾ 1.1
.23
No complex regional pain syndrome or recurrence of nerve compression symptoms occurred during the study period. DISCUSSION This study demonstrated that the presence and division of the muscles overlying or within the TCL in line with the third web space had no effect on outcomes of open carpal tunnel release in terms of Boston and DASH scores, grip and pinch powers, and scar pain. To date, the true identity of the muscles overlying or within the TCL is not definite. Mannerfelt and Hybbinette19 suggested these muscles were aberrant palmaris brevis and flexor pollicis brevis muscles, but Shrewsbury et al20 reported that the palmaris brevis muscle never extended past the ulnar margin of the palmar aponeurosis. Jonson and Shrewsbury21 noted that the flexor pollicis brevis and flexor digiti quinti blended into the TCL. However, Green and Morgan5 noted that in some cases the muscles overlying the TCL had no apparent connection with the normal thenar or the hypothenar muscles. Ragoowansi et al2 thought these muscles belonged to a separate muscle named the transverse carpal muscle or musculus transverses carpi. We
did not dissect the muscles and thus were unable to verify what these muscles were, although in most cases they appeared to be the thenar muscles, judging from the direction of the fibers. We expected that if the muscle fibers are the thenar muscles, division of them would cause some loss of power, but our data demonstrated no differences in grip or pinch power between groups. We also expected that patients with muscle fibers might have more scar pain because of scar formation within the divided muscles. Also, patients with thenar muscles originating more from the TCL than from the carpals might experience a direct effect of muscle relaxation after carpal tunnel release that might result in more pillar pain of muscular origin.8 However, there was no difference in the rated pain between groups. This study also demonstrated that there are no associations between the muscle morphology and preoperative severity of nerve compression in terms of patient-based scores, electrophysiologic grades, or incidence of thenar muscle atrophy. Iob et al1 suggested that contraction of these muscles may reduce the diameter of the carpal canal. However, Hollevoet et al6 found no difference in the
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incidence and types of these muscles between patients with CTS and cadavers with no known medical history. They concluded that the muscle fibers do not cause CTS. In the current study, we had no motor branch injuries. Previous studies have shown that the existence of muscles over the TCL is associated with certain thenar motor branch types. Green and Morgan5 noted that special care should be taken to identify and protect the motor branches when muscle fibers are encountered over the TCL, because an anomalous motor branch was found in 93% of hands in those cases. They recommended not proceeding with transection of the TCL until the motor branch has been identified and protected. Al-Qattan7 reported that transligamentous and preligamentous types are associated with the presence of hypertrophic muscles over the TCL, and incision of this muscle should be done carefully and on the ulnar side to avoid injury. In our series, although we did not attempt to identify motor branch types and divided the muscles bit by bit in line with the third web space, we have not had occasion to encounter the motor branch within the muscle fibers. Al-Qattan stated that dissection of the hypertrophic muscle over the radial side of the TCL is unnecessary and that the thenar motor branch is expected to be within the radial side of the hypertrophic muscle because the branch almost always arises from the radial side of the median nerve. However, there have been reports of the motor branch branching from the medial side of the median nerve.22 Thus, a careful layer-by-layer incision of the muscle is still necessary. In the current study performed in Koreans, 49% of patients had a purely ligamentous TCL, whereas 34% had muscle fibers covering 50% or less of the incision length and 16% had muscle fibers covering more than 50% of the incision length. Thus, 51% had some muscle fibers over or within the TCL. These results are comparable to those of Hollevoet et al,6 who investigated muscle fibers in 143 ethnic Caucasians. They found that muscle fibers crossing the line of incision were absent in 50%, 2 to 10 mm wide in 39%, and more than 10 mm in 11% of the operated hands, and 50%, 35%, and 15% respectively in the cadaveric hands. Because our incision was 3 cm and we categorized the muscles according to whether their length was more or less than 50% of the incision length, we probably have categorized some patients with muscle fibers of more than 10 mm length into group 2 rather than group 3. Other studies reported lower incidences of the muscle fibers over the TCL. Al-Qattan7 reported that in 100 Middle East-
ern patients, 36 had hypertrophic muscles over the TCL. Green and Morgan5 reported that 28% of 1,400 CTS patients in the United States had some muscle fibers overlying the TCL. There are several limitations to the study. First, the grouping of the muscles overlying the TCL was not validated for reliability. We estimated rather than measured the percentage of muscle fibers over the TCL. However, a single surgeon who was unaware of the major outcome variables at the time of the operation performed all classifications. Second, we did not have a control group that had overlying muscles that were not divided during carpal tunnel release, because it was practically difficult to avoid dividing the overlying muscles in an open carpal tunnel release. However, to determine whether dividing the muscle over the TCL has an effect on outcomes in patients with CTS, it would have been necessary to divide the muscle in some patients and not divide them in a control group. Therefore, we do not know whether those who had preserved muscles would have better outcomes than those who did not, although it is unlikely because there were no differences in preoperative or postoperative functional status between groups. At least we can say that outcomes of carpal tunnel release with concomitant division of the overlying muscles are similar to those of carpal tunnel release in patients without the muscles in the first place (purely ligamentous type). Third, our measurement might not have been sensitive enough to detect small differences between groups that have a wide range of symptom severity. A study of groups with more controlled variables, or isolation of the variable of presence or absence of overlying muscle, might have definitely revealed anything of importance that could be attributed to the presence or absence of the muscle and its division. Finally, because the patients were mostly women, the results may not represent the general population with CTS. REFERENCES 1. Iob I, Battaggia C, Rossetto L, Ermani M. The carpal tunnel syndrome. Anatomo-clinical correlations. Neurochirurgie 2000;46:355– 357. 2. Ragoowansi R, Adeniran A, Moss AL. Anomalous muscle of the wrist. Clin Anat 2002;15:363–365. 3. Lindley SG, Kleinert JM. Prevalence of anatomic variations encountered in elective carpal tunnel release. J Hand Surg 2003;28A:849 – 855. 4. Tuncali D, Barutcu AY, Terzioglu A, Aslan G. Transverse carpal muscle in association with carpal tunnel syndrome: report of three cases. Clin Anat 2005;18:308 –312. 5. Green DP, Morgan JP. Correlation between muscle morphology of the transverse carpal ligament and branching pattern of the motor branch of median nerve. J Hand Surg 2008;33A:1501511.
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6. Hollevoet N, Barbaix E, D’herde K, Vanhove W, Verdonk R. Muscle fibres crossing the line of incision used in carpal tunnel decompression. J Hand Surg 2010;35B:115–119. 7. Al-Qattan MM. Variations in the course of the thenar motor branch of the median nerve and their relationship to the hypertrophic muscle overlying the transverse carpal ligament. J Hand Surg 2010;35A: 1820 –1824. 8. Ludlow KS, Merla JL, Cox JA, Hurst LN. Pillar pain as a postoperative complication of carpal tunnel release: a review of the literature. J Hand Ther 1997;10:277–282. 9. Rotman MB, Donovan JP. Practical anatomy of the carpal tunnel. Hand Clin 2002;18:219 –230. 10. Bland JD. A neurophysiological grading scale for carpal tunnel syndrome. Muscle Nerve 2000;23:1280 –1283. 11. Gong HS, Oh JH, Bin SW, Kim WS, Chung MS, Baek GH. Clinical features influencing the patient-based outcome after carpal tunnel release. J Hand Surg 2008;33A:1512–1517. 12. Mallette P, Zhao M, Zurakowski D, Ring D. Muscle atrophy at diagnosis of carpal and cubital tunnel syndrome. J Hand Surg 2007; 32A:855– 858. 13. Levine DW, Simmons BP, Koris MJ, Daltroy LH, Hohl GG, Fossel AH, et al. A self-administered questionnaire for the assessment of severity of symptoms and functional status in carpal tunnel syndrome. J Bone Joint Surg 1993;75A:1585–1592.
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14. Hudak PL, Amadio PC, Bombardier C. Development of an upper extremity outcome measure: the DASH (disabilities of the arm, shoulder and hand) [corrected]. The Upper Extremity Collaborative Group (UECG). Am J Ind Med 1996;29:602– 608. 15. Günther CM, Bürger A, Rickert M, Crispin A, Schulz CU. Grip strength in healthy caucasian adults: reference values. J Hand Surg 2008;33A:558 –565. 16. Günther CM, Bürger A, Rickert M, Schulz CU. Key pinch in healthy adults: normative values. J Hand Surg 2008;33E:144 –148. 17. Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain 1986;27:117–126. 18. Williamson A, Hoggart B. Pain: a review of three commonly used pain rating scales. J Clin Nurs 2005;14:798 – 804. 19. Mannerfelt L, Hybbinette CH. Important anomaly of the thenar motor branch of the median nerve. A clinical and anatomical report. Bull Hosp Joint Dis 1972;33:15–21. 20. Shrewsbury MM, Johnson RK, Ousterhout DK. The palmaris brevis—a reconsideration of its anatomy and possible function. J Bone Joint Surg 1972;54A:344 –348. 21. Johnson RK, Shrewsbury MM. Anatomical course of the thenar branch of the median nerve— usually in a separate tunnel through the transverse carpal ligament. J Bone Joint Surg 1970A;52:269 –273. 22. Lanz U. Anatomical variations of the median nerve in the carpal tunnel. J Hand Surg 1977;2A:44 –53.
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