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.     

Carpal tunnel syndrome associated with long-term hemodialysis: case report

Since Warren and Otieno reported carpal tunnel syndrome in patients on intermittent hemodialysis in 1975, a number of related reports have been published. However, there are few reports associated with neurosurgery about carpal tunnel syndrome in patients on long term hemodialysis. We reviewed this disease and reported our case. We treated a patient who complained of bilateral hand numbness and atrophy of the right thenar muscle. He had been suffering from chronic renal failure and had been treated with hemodialysis for ten years. We diagnosed carpal tunnel syndrome based on the findings concerning Tinel's sign, Phalen test, and the conduction velocity of the median nerve. We performed decompression surgery of the median nerve. However, although there was no recovery from thenar muscle atrophy, there was improvement of hand numbness. Histologically, amyloid deposits within the hypertrophic transverse carpal ligament on the right side, could be found but on the left side where the internal shunt had been made amyloid deposits were absent. The reason why patients receiving long term hemodialysis develop carpal tunnel syndrome is controversial, but it seems that beta 2 microglobulin may play an important role in developing carpal tunnel syndrome in hemodialysis patients. This was reported by Gejyo in 1985. There may be uremic and/or diabetic neuropathy in these patients, and these neuropathies may be responsible for the more rapid deterioration and poorer surgical results in carpal tunnel syndrome associated with hemodialysis than in idiopathic cases. It is most important that carpal tunnel syndrome has to be diagnosed early and that surgical decompression is performed while the disease is in its early stage.     

Anatomic investigations of nerves at the wrist: I. Orientation of the motor fascicle of the median nerve in the carpal tunnel

The orientation of the motor fascicle of the median nerve in the carpal tunnel was investigated in dissections of 50 hands. Topographically, the motor branch was located on the radial-volar aspect of the median nerve in 60% of the hands, the central-volar aspect in 22%, and between these two locations in the remaining 18%. In 56% of the hands, the motor branch passed through a separate distinct fascial tunnel before entering the thenar muscles. Awareness of these patterns will facilitate appropriate surgical management of thenar muscle weakness or wasting associated with the carpal tunnel syndrome.     

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.     

Congenital carpal tunnel syndrome

A case of congenital carpal tunnel syndrome associated with melorheostosis is described. The symptoms were lack of use of the hand since birth, hypotrophy of the fingers innervated by the median nerve, and severe atrophy of the thenar muscles. The total degeneration of the nerve in the carpal tunnel was successfully treated with a sural nerve graft.     

Entrapment neuropathy of the palmar cutaneous branch of the median nerve by the fascia of flexor digitorum superficialis

A case of thenar numbness, with concomitant carpal tunnel syndrome is presented. Physical findings and the result of injection of a local anesthetic into two different sites of tenderness suggested coexistence of entrapment and/or compression of the palmar cutaneous branch of the median nerve and the main trunk of the median nerve at the carpal tunnel. At operation, constriction of the palmar cutaneous branch of the median nerve by the fascia of seemingly normal flexor digitorum superficialis was observed beneath the site of maximum tenderness. After decompression of this nerve, combined with carpal tunnel release, the patient lost all pain and numbness; there was no recurrence at 5 months follow-up.     

The history of carpal tunnel syndrome

Carpal tunnel syndrome is the most frequently diagnosed, best understood and most easily treated entrapment neuropathy. During the first half of the 20th century, however, most patients with carpal tunnel syndrome were diagnosed as having compression of either the brachial plexus or thenar nerve motor branch of the median nerve. As late as 1950, only twelve patients with operative release of the transverse carpal ligament for idiopathic carpal tunnel syndrome had been reported. The delay in accurate anatomical localization of this compressive neuropathy can be attributed both to the confusion caused by the diverse manifestations of median nerve compression in the carpal tunnel, and to some interesting developments that altered early investigations in this area.     

Thenar eminence quantitative sensory testing in the diagnosis of proximal median nerve compression.

Diagnosis of proximal median nerve compression (PMNC) remains a clinical challenge. The authors hypothesized that measurement of the sensibility of the thenar eminence might identify PMNC by demonstrating abnormal function in the palmar cutaneous branch of the median nerve. This hypothesis was evaluated by means of quantitative sensory testing of the thenar eminence in 33 healthy volunteers, 14 patients with carpal tunnel syndrome, and 35 patients with PMNC. The cutaneous pressure thresholds for one-point static touch (1PS) and two-point static touch (2PS) were measured with the Pressure-specified Sensory Device (Sensory Management Services, Baltimore, Maryland). There was no significant difference in thenar eminence sensibility between the healthy volunteers and the patients with carpal tunnel syndrome. In contrast, patients with PMNC had higher cutaneous pressure thresholds for 1PS (p<0.001), 2PS-pressure (p<0.001), and 2PS-distance (p<0.001) than did patients with carpal tunnel syndrome. The p values were less than 0.001 for each of these three comparisons between the healthy volunteers and the patients with PMNC. For the diagnosis of PMNC, quantitative sensory testing of the thenar eminence has a sensitivity of 90.3%, a specificity of 83.3%, and a positive predictive value of 87.5%.     

Median nerve compression by a radially inserted palmaris longus tendon after release of the antebrachial fascia: A complication of carpal tunnel release

We describe a case that had recurrent median nerve compression after release of the antebrachial fascia in carpal tunnel release. The nerve was compressed by a palmaris longus tendon that was inserted radially into the thenar fascia. After decompression (detachment of the tendon) the patient had symptom relief. Release of the antebrachial fascia in the presence of this tendon variant carries a risk of median nerve compression by the tendon.     

Internal neurolysis fails to improve the results of primary carpal tunnel decompression

This prospective, randomized study compares two treatment methods in patients with primary carpal tunnel syndrome. Decompression of the transverse carpal ligament was done in thirty-two hands (thirty patients) and decompression of the transverse carpal ligament with the addition of an internal neurolysis of the median nerve was done in thirty-one hands (twenty-nine patients). Relief of symptoms was described in eighty-eight percent of the patients with carpal ligament release and eighty-one percent of patients with carpal ligament release plus internal neurolysis. Improvement in hand sensibility testing, in thenar muscle strength, and atrophy was noted in both treatment groups with no statistical difference between groups. The addition of an internal neurolysis to division of the transverse carpal ligament does not add significant improvement in the sensory or motor outcome of patients with primary carpal tunnel syndrome.     

Median innervated hypothenar muscle: anomalous branch of median nerve in the carpal tunnel

A hypothenar motor branch of the median nerve in the carpal tunnel was observed and its motor function was documented by direct intraoperative nerve stimulation in two patients having carpal tunnel releases. The hypothenar branch left the median nerve at the midcarpal tunnel area. It crossed the tunnel superficial to the flexor tendons and penetrated the transverse carpal ligament ulnarly to innervate the abductor digiti quinti. Such branching of the median nerve at this level has not been reported previously. Good visualization of the carpal tunnel and careful dissection of its content even in the so called safe zone ulnar to long axis of palmaris longus tendon is recommended.     

Recurrent carpal tunnel syndrome--caused by an inadequate surgical technique?

The carpal tunnel syndrome (CTS) is a common disease, and the decompression of the median nerve is one of the most often performed procedures in surgery. Within our patients from the 1. 12. 1987 to the 1. 12. 1988 we found 16 cases of recurrent CTS. Intraoperatively in more than 60% of the cases we could detect some sort of subluxation or even luxation of the median nerve and severe scarring involving the median nerve and the regenerated transverse carpal ligament in all cases. Considering the anatomy of the transverse carpal ligament, to guide the median nerve and the flexor tendon within the carpal tunnel, as well as serving as origin for the thenar musculature, especially for the opposition, one concludes that the simple dissection of the carpal ligament should be avoided. For the past 4 years we therefore have been performing a widening Z-plasty and reconstruction of the transverse carpal ligament, for the primary CTS as well as for revisions. The favorable postoperative results seem to confirm our theory. We discuss our operative technique as well as the results in CTS revision cases.     

Electrodiagnosis in Martin-Gruber anastomosis

An anomalous median-ulnar nerve communication in the forearm (Martin-Gruber anastomosis) is not rare. Knowledge of this crossover is of crucial importance in the clinical evaluation of nerve injuries of median and ulnar nerves as well as in accurate interpretation of nerve conduction velocity of these nerves especially in association with carpal tunnel syndrome. The aim of this study was to describe a simple electrophysiological method to detect the anomalous communication innervating hypothenar and thenar muscles. A crossover was detected in 83 (14%) of 600 unselected subjects or 116 (9.7%) of 1,200 limbs. The anomaly was bilateral in 33 (40%) of the subjects and unilateral in 50 (60%), thirty-three on the right and seventeen on the left. Since the crossing fibers are likely to supply primarily the 1st dorsal interosseus muscle, recording of this muscle is essential to disclose the anomaly in addition to routine median and ulnar motor studies of hypothenar and thenar muscles. The anomaly may represent a phylogenetic variant.     

Results of treatment of severe carpal tunnel syndrome

A retrospective study was undertaken to determine the efficacy of carpal tunnel decompression in patients with advanced carpal tunnel syndrome. The criteria for inclusion in this study were unobtainable median sensory-evoked response and absent or prolonged median motor distal latency. Fifteen hands in 13 patients met these criteria. All patients had symptoms, including pain, weakness, or decreased sensation. Postoperative follow-up averaged 27 months. Symptomatic improvement was obtained in 14 of the 15 hands, and sensory-evoked response improved in 13 hands. Preoperative thenar atrophy was present in 10 of the 15 hands and was completely resolved in 2 of the 10 patients. These results indicate that carpal tunnel decompression is of benefit to patients with severe carpal tunnel syndrome. Long-standing symptoms, thenar atrophy, virtual anesthesia, and the absence of demonstrable sensory and motor-evoked responses are not contraindications to surgery.     

内镜下两点单侧钩切法治疗腕管综合征的临床应用

目的：探讨应用内镜的两点单侧钩切法切断腕横韧带,解除正中神经压迫的手术方法和疗效。方法：临床治疗原发性11例13侧（左侧3例,右侧6例,双侧2例）43～68岁女性腕管综合征患者。全部患者均有桡侧3个半指的指端刺痛觉减退,腕部正中神经Tinel征阳性,11例大鱼际肌萎缩,同时4例存在拇指对掌功能减弱。术中局部麻醉,分别采取近侧腕横纹线处,掌长肌腱与桡侧屈腕肌腱之间1cm皮肤横切口（入口）和患者拇指最大桡侧外展位,拇指尺侧平行线与中环指间的长轴线交叉点向尺侧1cm处呈45°切口（出口）。预制隧道后入口处置入腕关节镜,由出口插入钩刀。钩刀钩住腕横韧带近段后,内镜随钩刀移动而远行,全程镜视下由近及远切断腕横韧带。结果：患者经随访4～20个月全部疗效满意,捏握功能明显改善。术后3个月时恢复至S3＋M3以上。无血管、神经或屈肌腱损伤等并发症。结论：两点单侧钩切法操作步骤简单,是一种有效的手术方法。     

Division of the median nerve at the carpal tunnel caused by a high-pressure injection injury of the hand: a case report

We describe a patient who was injected water into the palm of his left hand. He injured the median nerve at the carpal tunnel. The injected water did not cause serious damage to the soft tissue, but caused the division of the median nerve brought about serious pain and sensory and motor disturbance. The patient was taken to the operating room to undergo a nerve graft operation on the same day. Two years after the injury, numbness was reduced his index, middle, and ring fingers up to the distal interphalangeal joint. Except for thumb abduction, we did not observe contracture of the joints of his left hand. The strength of his grip was 47?kg in the right hand and 42?kg in the left hand. His ability to make a perfect O improved from the previous year. His thenar muscle remained slightly atrophied. He still could not support anything with his left hand, but he no longer felt hindered in his work since he was accustomed to his work.     

Fibrolipomatous hamartoma of the median nerve: A cause of acute bilateral carpal tunnel syndrome in a three-year-old child: A case report and comprehensive literature review

A three-year-old boy was investigated for inexplicable incessant crying. On examination, his left wrist was mildly swollen (three to four months) and sensitive. Exploration and carpal tunnel decompression of the left wrist with incisional biopsy was performed for the presence of a fusiform swelling intimately associated with the median nerve. Histopathology revealed the presence of enlarged nerve bundles admixed with mature fat cells and diffuse fibroblastic proliferation. Three months later, he underwent urgent contralateral carpal tunnel decompression for a similar presentation. The final diagnosis was bilateral fibrolipomatous hamartoma (FLH) of the median nerves causing acute bilateral compression neuropathy.FLH of the median nerve is an extremely unusual cause of acute bilateral carpal tunnel syndrome in a young child presenting with ‘incessant crying’. A comprehensive review of FLH including epidemiology, etiology, clinical presentation, differential diagnosis, imaging, pathology, treatment and prognosis is discussed.     

Measurement of median nerve blood flow during carpal tunnel release with laser Doppler flowmetry.

Eight consecutive median nerves in eight patients with clinical carpal tunnel syndrome were prospectively examined by non-contact laser Doppler flowmetry before and after undergoing carpal tunnel release. Before performing carpal tunnel release, the difference in the median nerve blood flow between the values at the distal and proximal portions to the transverse carpal ligament was statistically significant (p = 0.021). After carpal tunnel release, the median nerve blood flow both distal and proximal to the transverse carpal ligament increased by 1.5 and 1.3 times, respectively, compared to the flow prior to carpal tunnel release, however, only the difference at the distal portion to the transverse carpal ligament was statistically significant (p = 0.015). In this study, we directly measured the median nerve blood flow using non-contact laser Doppler flowmetry and thus demonstrated a significant difference in the median nerve blood flow between the values at the distal and proximal portions to the transverse carpal ligament before carpal tunnel release and a significant increase in the nerve blood flow only at the distal portion to the transverse carpal ligament after surgery. This technique is thus considered to be an easy and reproducible way to intraoperatively evaluate the nerve blood flow in real time during the release of entrapment neuropathies.     

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.     

Lipofibromatous hamartoma of the median nerve in patients with macrodactyly: diagnosis and treatment of a rare disease causing carpal tunnel syndrome

Lipofibromatous hamartoma is a very rare benign peripheral nerve tumour. It is mostly encountered in the proximal extremities of young adults, involving the median nerve in the majority of cases. We present two patients with macrodactyly and carpal tunnel syndrome caused by lipofibromatous hamartoma of the median nerve and discuss diagnosis and treatment of the disease. A 10-year-old girl with a congenital progressive macrodactyly of her right index finger presented with a slowly growing mass in her right palm and pain and numbness, along with motor and sensory deficits in the median nerve distribution. Treatment consisted of carpal tunnel release, epineurolysis and partial excision of the fibrofatty tissue. The second patient, a 25-year-old man presented with a swelling in his left palm and findings compatible with carpal tunnel syndrome. Intraoperatively, the lesion presented as sausage-shaped enlargement of the median nerve by fibrofatty tissue. After carpal tunnel release, a partial excision of the mass with epineurolysis was performed. In both patients, histology showed nerve bundles separated by abundant fibrofatty tissue. In the girl, a proliferation of dysplastic perineurial cells could be observed. The suspected diagnosis for patients with macrodactyly and clinical signs of carpal tunnel syndrome should be lipofibromatous hamartoma. A carefully taken history, physical examination, X-ray, and MRI are important for its correct diagnosis. The surgical management remains controversial. Treatment should include decompression of the median nerve at points of compression, partial excision of the fibrofatty tissue, and debulking of soft tissue. In some cases, an epineurolysis can be additionally performed.