Practical anatomy of the carpal tunnel

The carpal tunnel is most narrow at the level of the hook of the hamate. The median nerve is the most superficial structure. It has specific relationships to surrounding structures within the carpal tunnel to the ulnar bursa, flexor tendons, and endoscopic devices placed inside the canal. The importance of the ring finger axis is stressed. Knowledge of topographical landmarks that mark the borders of the carpal tunnel, the hook of the hamate, superficial arch, and thenar branch of the median nerve ensure appropriate incision placement for endoscopic as well as open carpal tunnel release surgery. Anatomy of the transverse carpal ligament, its layers and relationships to adjacent structures including the fad pad, Guyon's canal, palmar fascia, and thenar muscles has been discussed. Fibers derived primarily from thenar muscle fascia with connections to the hypothenar muscle fascia and dorsal fascia of the palmaris brevis form a separate fascial layer directly palmar to the TCL and can be retained. This helps to preserve postoperative pinch strength. The fat pad in line with the ring finger axis overlaps the deep surface of the distal edge of the TCL and must be retracted in order to visualize the distal end of the ligament. Whereas the ulnar artery within Guyon's canal is frequently located radial to the hook of the hamate, injury to this structure has not been a problem during ECTR surgery. Variations of the median nerve and its branches, as well as the palmar cutaneous nerve distribution, have been reviewed. A rare ulnar-sided thenar branch from the median nerve, interconnecting branches between the ulnar and median nerves located just distal to the end of the TCL, and transverse ulnar-based cutaneous nerves can be injured during open or ECTR surgery. Anomalous muscles, tendons or interconnections, and the lumbricals during finger flexion may be seen within the carpal tunnel. These structures can be the cause of compression of the median nerve. The anatomy of the carpal tunnel and surrounding structures have been reviewed with emphasis on clinical applications to endoscopic and open carpal tunnel surgery. A thorough knowledge of the anatomy of the carpal tunnel is essential in order to avoid complications and to ensure optimal patient outcome. An understanding of the contents and their positions and relationships to each other allows the surgeon to perform a correct approach and accurately identify structures during procedures at or near the carpal tunnel.     

Endoscopic carpal tunnel release: an anatomic study of the two-incision method in human cadavers.

To determine the relationship of neurovascular structures to the sites of portal placement and transverse carpal ligament division during two-portal endoscopic carpal tunnel release, a study of 20 fresh cadaver specimens was carried out. Open dissection of the carpal tunnel after endoscopic surgery showed complete ligamentous release in 18 hands (90%). In 10 specimens, the procedure was performed as described by Chow. There was one partial transection of the superficial palmar arch (5%), and five specimens (50%) had complete divisions of the superficial palmar fascia with considerable pressure placed on the ulnar nerve at the wrist. A modified technique was used in 10 specimens in which the proximal incision was made in a more distal location and a distally based ligamentous flap was created. The superficial palmar arch and the distal edge of the transverse carpal ligament were visualized directly before passage of the trocar. No complications were noted with this method.     

Palmar uniportal extrabursal endoscopic carpal tunnel release

A new technique of endoscopic carpal tunnel release using a 1.5-cm longitudinal palmar incision was used in 280 cases. The incision allows identification of the superficial palmar arch as well as the median nerve and its branches. A new knife/sleeve device that attaches to a standard 4-mm endoscope was created to simplify the procedure. The flexor retinaculum is endoscopically divided proximally into the distal forearm; the “interthenar fascia” (fascia superficial to transverse carpal ligament) can be preserved. Early postoperative results include a mean overall return to work and full activity of 14 days. Postoperative pinch and grip strengths were near or at the preoperative level by weeks after surgery. One third of patients required no postoperative analgesics with minimal scar, ulnar pillar, and radial pillar tenderness.     

Anatomy of the ulnar artery as it relates to the transverse carpal ligament

The anatomic relationship between the ulnar artery and transverse carpal ligament (TCL) as an aid in planning for minimally invasive carpal tunnel surgery was investigated. The anatomic course of the ulnar artery and its branches toward the TCL and the location of the median nerve were determined in 24 fresh cadaver hands perfused with a silicone compound. The ulnar artery coursed from 7 mm ulnar to 2 mm radial to the hook of hamate. The average distance between the superficial palmar arch and the distal margin of the TCL was 12 mm as measured along the flexor tendon of the ring finger. The location of the median nerve extended an average of 11 mm radial to the hook of hamate. A small arterial branch (average diameter, 0.7 mm) from the ulnar artery ran transversely just over the TCL in 6 of the 24 specimens. This branch was consistently located within 15 mm proximal to the TCL distal margin. These and other microscopic observations indicated that transecting the ligament at approximately 5 mm radial to the radial margin of the hook of hamate may minimize postoperative bleeding and avoid iatrogenic vascular and neural injury. (J Hand Surg 2002;27A:101-104. Copyright © 2002 by the American Society for Surgery of the Hand.)     

The anatomy of the Berrettini branch: implications for carpal tunnel release

OBJECT: Dissections were performed in 100 fresh cadaver palms to determine the frequency with which superficial palmar communication between the median and ulnar nerves occurs and to what extent it might incur iatrogenic injury during endoscopic carpal tunnel release. METHODS: Superficial palmar communication between the median and ulnar nerves was present in 81% of the dissected hands. Superficial palmar communication, also known as the Berrettini branch, has been classified into four distinct types by Ferrari and Gilbert. Twelve hands were classified as Group 1 (communication in an oblique course from the ulnar to the median nerve originating >4 mm above the distal margin of the transverse carpal ligament [TCL]), 16 hands were classified as Group 2 (communication parallel to the distal margin of the TCL), and 53 hands were classified as Group 3 (communication in an oblique course from the ulnar nerve to the third common digital nerve, originating below the distal margin of the TCL). No hand fit the Group 4 classification (atypical communication). CONCLUSIONS: The Berrettini branch can be considered a normal anatomical finding. In 28% of the hands in this study, the branch was proximal to the edge of the distal ligament and, therefore, prone to iatrogenic injury in both one-portal and two-portal endoscopic surgery.     

小切口治疗腕管综合征14例报告

Objective　To introduce the technique of carpal tunnel release by small incision,and evaluate its outcome in the treatment of carpal tunnel syndrome.Methods　This method was applied in the operations of 14 cases of carpal tunnel syndrome.An incision 1.5 cm in length was made at the level of the proximal transverse wrist crease ulnar to the palmaris longus tendon.The proximal margin of the transverse carpal ligament was visualized and the ligament was cut subcutaneously under direct vision.The flexor digitorum tendons were retracted and the edematous synovium excised.Results　Follow - up of the patients 2 weeks postoperatively showed that the symptoms of numbess and pain disappeared in all 14 cases.Normal 2 - PD in the pulp of the thumb,index finger and long finger was ＜ 4 mm.One year after the operation,muscle atrophy in 5 patients who sustained preoperative thenar muscle atrophy was greatly improved with recovery of normal opponens function of the thumb.No pillar pain and injury of the ulnar nerve and superficial palmar arch was found.Conclusion　Carpal tunnel release under direct vision through a small incision is a new and effective surgical procedure.     

Anomalous palmar cutaneous branch of the median nerve in the distal forearm: case report

Variations exist in the anatomy of the palmar cutaneous branch of the median nerve about the wrist. We report an anatomic variation in the course of the palmar cutaneous branch of the median nerve identified in a 17-year-old girl undergoing surgery for a scaphoid nonunion. Instead of coursing ulnar to the flexor carpi radialis tendon, deep to the antebrachial fascia between the tendons of the flexor carpi radialis and palmaris longus, the palmar cutaneous branch of the median nerve was noted to cross volar to the distal aspect of the flexor carpi radialis to lie on its radial aspect. Knowledge of the anatomic variant described in this report should encourage surgeons to dissect carefully as they expose the flexor carpi radialis during the exposure of the distal radius or scaphoid.     

The use of topographical landmarks to improve the outcome of agee endoscopic carpal tunnel release

A modified approach to endoscopic carpal tunnel release has been developed and tested in 60 cadaveric specimens by three surgeons using the Agee endoscopic carpal tunnel release system. The modified approach, which includes specific localization of the hook of the hamate, flexor retinaculum, and the superficial palmar arch utilizing topographical landmarks, avoids entry into Guyon's canal and injury to the ulnar artery and nerve, median nerve, and common digital nerves. Use of the anatomic approach resulted in significantly superior results. There were fewer incomplete releases, and fewer surgical passes were required, for the inexperienced surgeons. When these anatomic considerations were not included, the learning curve was much steeper. For surgeons planning endoscopie surgical release of the transverse carpal ligament, the described topographical approach improves the technical competence with the procedure and reduces the number of complications and learning curve associated with new procedures. We recommend the use of topographical landmarks and other anatomic considerations during endoscopic carpal tunnel release.     

Laminar configuration of the transverse carpal ligament

We investigated the laminar configuration of the transverse carpal ligament, using 77 hands from 44 donated cadavers. According to the running directions and attachments of the fiber bundles composing the ligament, we identified four basic bundle patterns: proximal transverse, distal transverse, radial oblique, and ulnar oblique. Although these patterns often coexisted and the bundles were somewhat intermingled, a specific pattern was very evident in several laminae. Laminae with the distal transverse bundle pattern were the thickest and were reinforced by additional fibers which originated from the palmar aponeurosis and were deeply inserted into the lamina. Based on the laminar configurations of the superficial and deep layers and their composite fiber bundles, we classified the ligaments into four types. Type I, in which distal transverse and ulnar oblique laminae predominated in every layer, was the most common (44.2%), while another large group (41.6%) exhibited type II ligaments, comprising distal transverse and ulnar oblique laminae in the superficial layer and proximal transverse and radial oblique laminae in the deep layer. Thus, in almost half of the patients (type II), the strong distal transverse lamina is likely to be excised during the final step of endoscopic carpal tunnel release because of its superficial localization. This could be a major reason for the frequent occurrence of incomplete release. Moreover, the almost universal superficial ulnar oblique bundle pattern (observed in type I, II, and III ligaments), predisposes to scarring, which may cause radial shifting of the ulnar neurovascular bundle and may affect the palmar branch of the median nerve. We conclude that the interindividual variability seen in the results of endoscopic carpal tunnel release, including minor complications, depends partly on configurational variations in the laminar arrangement of the transverse carpal ligament. Received: June 4, 2001 / Accepted: September 9, 2001     

Mini-open carpal tunnel decompression

Carpal tunnel syndrome is the most common entrapment neuropathy, and it is caused by compression of the median nerve at the wrist. The authors describe the mini-open carpal tunnel technique for surgical release of the transverse carpal ligament. The success of the procedure depends on meticulous technique with attention to certain important anatomic details and careful avoidance of injury to the palmar cutaneous nerve and the recurrent motor branch.     

Anatomical study of the pre-retinacular fat pad of the wrist: application to a new surgical approach to the carpal tunnel

INTRODUCTION: Decompression of the median nerve in the carpal tunnel by section of the flexor retinaculum is the generally accepted treatment for carpal tunnel syndrome and is usually effective in relieving the symptoms. Following postoperative observations we proposed the hypothesis that incisional pain following open carpal tunnel release could be partly explained by injury to the fat pad situated between the palmar carpal ligament and the flexor retinaculum. METHOD: We performed an anatomical study on 20 fresh adult latex injected upper limbs. RESULTS: The sus-retinacularis fat pad is a real anatomical structure, clearly delineated and located inside a defined fibrous space with its own innervation from the ulnar nerve. It lies in the path of the normal carpal tunnel approach. DISCUSSION: Although most postoperative scar tenderness is attributed to neuroma formation because of injury to transverse branches of the palmar cutaneous nerves, we nevertheless consider that injury to the preretinacular fat pad also plays a part. We propose a modified approach to the carpal tunnel. This is a safe and simple method which respects the integrity of the sus-retinacularis fat pad so as to minimise the extent of scar tenderness.     

Prevalence of anatomic variations encountered in elective carpal tunnel release

PURPOSE: To determine the prevalence of aberrant or unexpected anatomic structures within one surgeon's elective experience of carpal tunnel releases and their association with pathologic compression. METHODS: A total of 31 anomalies of median nerve, muscle, and tendon, median artery persistence, and ulnar nerve were documented in 30 hands during the course of 526 elective carpal tunnel releases in one surgeon's practice. The data collected were reviewed retrospectively. All carpal tunnel releases were performed open, exposing the median nerve from the palmar arch to the proximal wrist crease. Anomalies were categorized into those involving the median nerve and its motor and sensory branches, the ulnar nerve, a persistent median artery, and anomalies of muscle/tendon units traversing the carpal tunnel area. RESULTS: Seven hands were noted to have aberrant muscle/tendon variations within the carpal tunnel region (1.3%). Anomalies of the median nerve or its palmar cutaneous or motor branches were observed in 5 hands (1.0%). An anomaly of the ulnar nerve with an aberrant branch crossing the carpal tunnel incision occurred in one hand. A persistent median artery (>or=1 mm) was noted in 18 hands (3.4%). One hand had 2 anomalies present. One anomaly was high bifurcation of the median nerve and the second anomaly was an anomalous muscle to the long finger superficialis. CONCLUSIONS: The specific anatomic variations described may be anticipated and more readily recognized by hand surgeons during such open surgery, thus increasing the efficacy and safety of this common procedure.     

Carpal tunnel changes and median nerve compression during wrist flexion and extension seen by magnetic resonance imaging

Magnetic resonance imaging was done on the wrists of 14 volunteer subjects with the wrists in the neutral position, then flexed and extended at 45 degrees. Computer enhanced cross-sectional areas were measured on each subject at the level of the hook of the hamate. In the neutral position the distance between confining structures around the median nerve is 2.0 +/- 0.2 mm in the anteroposterior direction, and the mean cross-sectional area of the carpal tunnel is 1.52 cm2. With the wrist in the extended position the distance available for the median nerve measures 2.2 +/- 0.4 mm and the cross-sectional area increases to 1.75 cm2. When the wrist is flexed, the distance available for the median nerve between the flexor tendons and transverse carpal ligament decreases to 1.1 +/- 0.4 mm, and the cross-sectional tunnel area decreases to 1.36 cm2. Flexion of the wrist and/or fingers both produces a palmar rearrangement of the flexor tendons creating potential compression of the median nerve. The nerve responds to these forces by becoming interposed in various positions between the superficial flexor tendons.     

Transverse carpal ligament reconstruction in surgery for carpal tunnel syndrome: a new technique

We present a two-year follow-up of a technique to reconstruct the transverse carpal ligament in surgery for carpal tunnel syndrome. The transverse carpal ligament is exposed through a four to five centimeter palmar incision in line with the axis of the ring finger. The ligament is divided in step-wise fashion, creating a distal radially-based flap and a proximal ulnarly-based flap. The apices of these flaps are approximated, lengthening the ligament six to ten millimeters. All seventy-three patients (one hundred-four hands) reported substantial improvement with 93% having complete resolution of symptoms. Ninety-seven percent returned to work (average disability, two months). There were no recurrences or significant operative complications. In those with unilateral reconstruction (60%), there was no diminution in grip strength (p less than 0.05). This technique of transverse carpal ligament reconstruction stabilizes the transverse carpal arch, provides protection to the median nerve, prevents bowstringing of the flexor tendons, and maximizes postoperative grip strength.     

Anomalous flexor digitorum superficialis muscle transposition for vascular coverage of the median nerve in recurrent carpal tunnel syndrome

Recurrent carpal tunnel syndrome is uncommon yet troublesome. Significant adhesions and scarring around the median nerve can render it relatively ischemic. A number of vascular flaps have been described to provide vascular coverage in attempts to decrease further cicatricial adhesions and to improve local blood supply around the median nerve. A rare case of an anomalous muscle in the distal forearm used as tissue to provide good vascularized coverage of the median nerve that was severely scarred in its bed is reported. The anomalous muscle was distal to the flexor digitorum superficialis tendon and inserted in the palmar fascia on the ulnar aspect of the hand. Referring branches from the ulnar artery provided vascular supply to the anomalous muscle. The muscle on these vascular pedicles was transposed over the median nerve, providing good, stable, unscarred coverage. The patient had an excellent result with resolution of the carpal tunnel symptoms. The redundant anomalous muscle provided a unique vascularized source for coverage of the median nerve in recurrent carpal tunnel syndrome.     

内窥镜下腕管松解术的应用解剖及临床应用

目的 从解剖及临床方面报告内窥境下腕管松解术的解剖人路及手术方法,旨在提高手术疗效、减少手术并发症。方法 以１８侧新鲜成人上肢标本及２６侧福尔马林液固定的成人上肢标本为对象,观察在内窥镜下碗管松解术入路的解剖结构,观察、测量及定周围相关组织结构。临床应用１９例２１侧,镜视下切断腕横韧带,手术在局麻、无止血带下进行。结果观测屈肌支持带、正中神经圾其分支和掌浅弓等结构。手术入口为腕横纹近端２～３ｃｍ、     

The Cup of Diogenes: a fixed anatomical landmark for carpal tunnel surgery

Purpose

Carpal tunnel syndrome is a common entrapment neuropathy. When conservative management fails to relieve symptoms, carpal tunnel surgery is indicated. The surgical exposure for this procedure is commonly based on variable anatomic landmarks. The purpose of this study was to describe a fixed, easily referenced anatomical landmark for the distal extension of the transverse carpal ligament, the “Cup of Diogenes.”

Materials and Methods

Topographical landmarks including Kaplan cardinal line, palmaris tendon, and distal palmer crease were marked on six fresh frozen cadaveric wrist and hand specimens. The apex of the Cup of Diogenes is determined to be the confluence of the thenar and hypothenar musculature of the palm. Wrists were dissected and the distance between these landmarks and the superficial palmar arch, median nerve, transverse carpal ligament, and ulnar nerve were measured.

Results

In all specimens, the ulnar nerve was ulnar to this the apex of the Cup of Diogenes, while the median nerve was radial. The apex was proximal in all specimens to the superficial palmar arch. The apex marked the distal extent of the transverse carpal ligament in all specimens.

Discussion

Based on our results, we feel the apex of the Cup of Diogenes is a consistent, fixed anatomical marker for the distal extent of the transverse carpal ligament, marking a safe zone in the palm for surgical planning of incisions.

Level of Evidence

Level V - Therapeutic     

Carpal tunnel syndrome secondary to wrist and finger flexor spasticity

Ten patients with spastic wrist flexion deformities secondary to traumatic brain injury were evaluated for carpal tunnel syndrome. The angle of wrist flexion deformity averaged 75 degrees (range, 58 to 115 degrees). Nerve conduction studies demonstrated prolonged median motor and/or sensory latencies in all patients. Preoperative wick catheter measurements of carpal tunnel pressures in eight patients averaged 11 mm Hg in the resting position, 21 mm Hg in maximal wrist flexion, and 15 mm Hg in maximal extension. Each patient had carpal tunnel release with simultaneous wrist and finger flexor tendon releases or lengthenings. At surgery nine of the median nerves were constricted at the proximal edge of the transverse carpal ligament. The presence of normal carpal tunnel pressures and impingement of the median nerve at the proximal edge of the transverse carpal ligament indicates that the chronically flexed posture of the wrist resulted in median nerve compression, and this condition may be aggravated by underlying pressure from the spastic finger flexors.     

Complications of surgical release for carpal tunnel syndrome

Review of a series of 186 operative cases of carpal tunnel release revealed 34 complications in 22 patients, for an incidence of 12%. Complications were grouped into seven categories: (1) inadequate section of the transverse carpal ligament (associated with both transverse and curved incisions), (2) symptoms related to damage to the palmar cutaneous branch of the median nerve, (3) reflex sympathetic dystrophy, (4) unsightly hypertrophic scar due to inappropriate incision, (5) damage to the superficial palmar arch following blind sectioning of the transverse carpal ligament, (6) bowstringing of the flexor tendons after excision of the transverse carpal ligament, and (7) adherence of the flexor tendons following excision of the mesotenon. Except for four of the complications, two each of bowstringing and reflex sympathetic dystrophy which occurred in our own practice, all of the complications were seen in patients referred for care. Most complications can be prevented by proper operative technique.     

内窥镜下松解腕管综合征的神经并发症

目的 报道内窥镜治疗腕管综合征时引起神经损伤的原因。方法 1997年至2003年，应用内窥镜治疗腕管综合征136例。对其中2例在内窥镜术后发生并发症的患者，在直视下再次进行手术探查，以明确神经损伤的部位及性质，并探讨引起神经损伤的原因。结果 1例正中神经在腕管内与腕横韧带粘连，在切断腕横韧带时同时损伤相连的正中神经外膜与部分束膜。经神经外膜松解后症状缓解。另1例正中神经掌皮支起始部发生变异，在内窥镜插入腕上切口处，直接损伤该皮支；经神经松解后症状缓解。结论 内窥镜治疗腕管综合征，通常是安全有效的。但在解剖变异及内窥镜下手术有困难时，易发生神经损伤，再次进行手术松解，症状缓解。