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.)     

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.     

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     

Safety of carpal tunnel release with a short incision. A cadaver study

The standard long incision technique for carpal tunnel release causes inevitable damage to skin sensation, the inter-thenar plexus and especially the distal branches of the palmar cutaneous branch of the median nerve (PCM), and may cause long-term disabling pain and scar tenderness. There are many variations in the distal branches of the median nerve at the wrist. Anatomic studies of this region also have important clinical implications to prevent injury to important anatomic structures. The purpose of this study was to evaluate the short-incision carpal tunnel release in cadavers. Several important anatomic structures, with possible anatomic variations, pass through the carpal tunnel, and blind percutaneous transection of the transverse ligament seems to be a high risk procedure. Sixty hands from 40 fresh cadavers were evaluated. Both the transverse ligament and the distal third of the deep forearm fascia were released using a Smillie knife. At the end of each procedure, the hand was explored for injury to tendinous and neurovascular structures of the wrist. In all cases the release of the carpal tunnel and the distal third of the forearm fascia was found to be complete. The superficial palmar arterial arch, flexor tendons, ulnar nerve and vessels, digital nerves, median nerve and its recurrent accessory branches, the flexor tendons, and even the subcutaneous tissue over the transverse ligament were damaged in no instance. Guyon's canal was entered in 6 (10%) hands without damage to its components. The distal branches from the ulnar side of the palmar cutaneous branch of the median nerve (PCM) were injured in 8 (13.6%) hands, an injury that is almost unavoidable with the classic open technique.     

Anmerkungen zur endoskopischen Karpaltunneloperation

Complication rates both of endoscopic and of open carpal tunnel release are higher than commonly recognized. Either technique must be performed with due consideration for the anatomical details, such as the exact course of the palmar branch of the median nerve, the oblique position of the flexor retinaculum between thenar and hypothenar, and the course of the ulnar artery at the distal edge of the flexor retinaculum. Even in the case of endoscopic carpal tunnel release, the more important first part is the correct positioning of the endoscope, which requires open dissection. The differences between open and endoscopic techniques may therefore be of minor importance.     

Iatrogene Nervenverletzungen

BACKGROUND: The objective of this study was to evaluate the causes of failed endoscopic carpal tunnel release (CTR) in order to detect potentially hazardous operative steps. The intraoperative findings of 10 microsurgically revised cases were retrospectively analyzed. RESULTS: From January 1999 to October 2001, ten patients underwent open revision surgery after being referred because of failed endoscopic carpal tunnel release (CTR). The median nerve had been injured in five cases, necessitating autologous sural nerve grafting in four. Two other patients underwent extensive (external and internal) neurolysis. The lesions were located twice in the main nerve trunk, three times in the recurrent motor branch, three times in a digital nerve, and once in the sensory palmar branch. The transverse carpal ligament (TCL) had not been sectioned in four cases and was incomplete in two. In another two cases, previously sectioned TCLs were closed again by firm fibrous tissue. In three cases, postoperative hematomas after the initial release were described and possibly contributed to symptoms. CONCLUSION: Endoscopic CTR in the hand of the inexperienced bears major risks for iatrogenic neurovascular injury.     

The surgical anatomy of ulnar and median nerve communications in the palmar surface of the hand

OBJECT: Sensation in the palmar surface of the digits is supplied by the median and ulnar nerves, with the boundary classically being the midline of the ring finger. Overlap and variations of this division exist, and a communicating branch between the ulnar and median nerve could potentially explain further variations in digital sensory innervations. The aim of this study was to examine the origin and distribution of the communicating branch between the ulnar and median nerves and to apply such findings to the risk involved in surgical procedures in the hand. METHODS: The authors grossly and endoscopically examined 200 formalin-fixed adult human hands obtained in 100 cadavers, and a communicating branch was found to be present in 170 hands (85%). Of the specimens with communicating branches, the authors were able to identify four notable types representing different points of connections of the branches. The most common, Type I (143 hands, 84.1%), featured a communicating branch that originated proximally from the ulnar nerve and proceeded distally to join the median nerve. Type II (12 hands, 7.1%) designated a communicating branch that originated proximally from the median nerve and proceeded distally to join the ulnar nerve. Type III (six hands, 3.5%) designated a communicating branch that traversed perpendicularly between the median and ulnar nerves in such a way that it was not possible to determine which nerve served as the point of origin. Type IV (nine hands, 5.3%) designated a mixed type in which multiple communicating branches existed, arising from both ulnar and median nerves. CONCLUSIONS: According to the origin and distribution of these branching patterns, the investigators were able to define a risk area in which the communicating branch(es) may be subject to iatrogenic injury during common hand procedures.     

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.     

Anatomic variations in sensory innervation of the hand and digits

Anatomic dissections under microscopic magnification were performed on 30 fresh cadaveric hands to depict the course and interconnections of the sensory nerves to the digits. The dissections included the median nerve, the ulnar nerve, the superficial branch of the radial nerve, the dorsal branch of the ulnar nerve, and the dorsal branch of the proper digital nerve. The communicating branches between the median and ulnar nerves in the palm were found in 20 of the 30 (67%) specimens. The dorsal branch of the proper digital nerve was found to arise at or proximal to the A1 pulley zone in 62% of the long digits, more proximally than previously reported. The dorsal sensory nerves (the terminal branch of radial or ulnar sensory nerves) extending to the nail bed area were found in 46% of the digits, thus confirming that sensory supply to the dorsum of the distal phalanx and nail bed also arises from the dorsal sensory nerves. Four types of palmar-dorsal interconnections, located in the middle of the proximal phalanx, were found in the digits but not in the thumb. The presence of these branches indicates dual innervation of the dorsal and palmar side of the distal areas of the digits. These anatomic findings may help hand surgeons interpret discrepancies in sensory loss after either dorsal or palmar injuries.     

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.     

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.     

Endoscopic management of carpal tunnel syndrome

This article describes a subcutaneous endoscopic operative procedure for carpal tunnel syndrome and analyzes its effectiveness using electrophysiological data. Subcutaneous transverse carpal ligament release under universal subcutaneous endoscope (USE) was performed using local anesthesia without pneumotourniquet in 54 hands of 45 patients since June 1986. The mean follow-up period was 13.8 months. Sensory disturbances began to subside immediately after the operation and disappeared within 2 months in all cases. After the disappearance of sensory disturbances, we performed postoperative electrophysiological studies in 27 patients (33 hands). Postoperative electrophysiological data were significantly improved in all cases. Patients did not suffer from any serious complications such as motor branch injuries of the median nerve, hypesthesia of the palm, or injuries of the superficial palmar arch. From these results, we conclude that the transverse carpal ligament can be safely incised by this procedure.     

A rare anatomical variant of the thenar branch discovered during open decompression of the median nerve

Abstract

We describe a rare anatomical variant of the thenar branch of the median nerve during open release of the carpal tunnel. The thenar branch originated from the ulnar side of the median nerve and traversed supraligamentously close to the top of the transverse ligament. A high resolution clinical photograph shows the relation between the anatomical structures when the thenar variant is present in the carpal tunnel. This is one of the dangers faced by surgeons when doing open or endoscopic release of the carpal tunnel.     

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.     

Bipartite median nerve with a double compartment within the transverse carpal canal

An anomaly of the median nerve in which there is a division into two branches at the level of the distal third of the forearm is reported. This case was unique in that the ulnar branch of the median nerve passed through a separate compartment within the transverse carpal ligament. It was necessary to decompress both branches of the nerve when releasing the carpal canal. Received: 26 April 1999     

Anatomic study of arborization patterns of the ulnar artery in Guyon's canal

PURPOSE: To show variations in arborization patterns of the ulnar artery in Guyon's canal and to investigate the relationship between the hypothenar muscles and the ulnar artery. METHODS: Thirty-five embalmed cadaveric hands were dissected and the existence and course of the superficial and deep palmar branches of the ulnar artery and the site of feeding branches to the hypothenar muscles were recorded. The anatomic relationship between the ulnar artery and the hypothenar muscle variations also was investigated. RESULTS: Four arborization patterns were identified. In type 1UA (n = 17 hands), an artery accompanying the deep branch of the ulnar nerve (AADBUN) formed a deep palmar arch (DPA). In type 2UA (n = 11 hands) the AADBUN continued to the feeding artery of the abductor digiti minimi and the distal deep palmar branch of the ulnar artery (DDPBUA) branched off distally. This arterial structure formed a DPA. In type 3UA (n = 6 hands) both the AADBUN and DDPBUA formed DPAs. In type 4UA(n = 1 hand), the AADBUN continued to the feeding artery of the abductor digiti minimi with no DDPBUA and therefore no DPA. A dorsal perforating artery of the ulnar artery also was found in 4 hands. This branch came from the AADBUN at the level of the distal edge of the pisiform and merged with the dorsal carpal arterial arch. We also investigated the relationship between the structural pattern of the hiatus for the deep branch of the ulnar nerve and ulnar artery variation but found no association. The most common pattern observed was a type 1 hiatus with a type 1UA arborization pattern. CONCLUSIONS: Our study confirmed considerable variations in the arborization pattern of the ulnar artery in Guyon's canal. To avoid injury to the arterial branches during surgery in this region care must be taken with respect to variations of the ulnar artery in Guyon's canal.     

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     

Endoscopic carpal tunnel release using the subligamentous two-portal technique

The surgical treatment for entrapment neuropathy of the median nerve in the carpal tunnel is varied. Recent publications have demonstrated a closed, endoscopic method for release of the carpal tunnel using a two-portal technique. In this report, a surgical technique for performing a subligamentous modification of this two-portal procedure is discussed, and the special tools used in this approach are demonstrated. In the early portion of this series of 75 symptomatic hands in 65 patients, 8% (6/75 hands) developed transient postoperative ulnar nerve neuropraxia. One patient experienced an iatrogenic laceration of the median nerve. Following the institution of the subligamentous approach, no postoperative nerve complications occurred. The majority of the patients experienced a significant decrease in their median nerve symptoms. This procedure has been found to be safe and is equally as effective as open surgical treatment of patients with carpal tunnel syndrome.     

Endoscopic carpal tunnel release and nerve conduction studies

We investigated the outcome of endoscopic carpal tunnel release (ECTR) for patients with carpal tunnel syndrome (CTS) in comparison with the results of preoperative nerve conduction studies. The compound muscle action potential (CMAP) of the abductor pollicis brevis muscle (APB) and the second lumbrical muscle (L2) was recorded following median nerve stimulation at the wrist. A total of 38 hands in 35 patients were classified into four categories. Hands with a similarly prolonged distal motor latency for the APB and L2 were classified as type I (n=25), while those with a more prolonged distal motor latency for the APB than for the L2 (>0.7 ms) were classified as type 2 (n=10). Hands with a CMAP for the APB, but not L2, were classified as type 3 (n=1), and hands with no CMAP for either the APB or L2 were classified as type 4 (n=2). After ECTR, all of the type 1 and 2 hands were improved. Patients with type 3 and type 4 hands did not show satisfactory improvement, which may have been due to anatomical variation of the recurrent motor branch of the median nerve.     

腕关节神经支配的解剖学研究

目的观察支配腕关节神经的来源、直径、数目及其行径;为去神经支配治疗腕关节疼痛提供解剖学资料。方法对10具20侧福马林固定的上肢标本,在手术显微镜下解剖并观察骨间后神经、前臂外侧皮神经、桡神经浅支、尺神经腕背支支配腕关节背侧的腕关节支;骨间前神经、正中神经掌皮支、尺神经深支及其主干支配腕关节掌侧的关节支。结果骨间后神经是支配腕关节背侧神经的主要来源;前臂外侧皮神经、桡神经浅支、尺神经腕背支也发支支配腕关节背侧。骨间前神经、正中神经掌皮支、尺神经深支发支参与支配腕关节的掌侧。结论用去神经支配的方法治疗腕关节顽固性疼痛主要适用于腕背侧的疼痛。