Partial median nerve entrapment in the distal arm because of an accessory bicipital aponeurosis

Causes, symptoms, and treatments of nerve entrapments around the elbow: Current concepts

The elbow is a joint extremely susceptible to stiffness, even after a trivial trauma. As for other joints, several factors can generate stiffness such as immobilisation, joint incongruity, heterotopic ossification, adhesions, or pain. Prolonged joint immobilisation, pursued to assure bony and ligamentous healing, represents the most acknowledged risk factor for joint stiffness. The elbow is a common site of nerve entrapment syndromes. The reasons are multifactorial, but peculiar elbow anatomy and biomechanics play a role. Passing from the arm into the forearm, the ulnar, median, and radial nerves run at the elbow in close rapport with the joint, fibrous arches and through narrow fibro-osseous tunnel. The elbow joint, in fact, has a large range of flexion which exposes nerves lying posterior to the axis of rotation to traction and those anterior to compression.

Anatomical considerations and clinical implications of bicipital aponeurosis: A magnetic resonance imaging study

The bicipital aponeurosis (BA) is the distal aponeurosis of the biceps brachii which usually covers the median nerve (MN), and the brachial artery (BrA) and sometimes causes compression of these structures. Since these situations are rarely reported in the literature, BA frequently does not come to mind as a cause of such compression. Therefore, the diagnosis may be delayed. In this study, we aimed to investigate the morphometry of BA and its relationship with the surrounding neurovascular structures and to draw attention to BA as a structure that can cause entrapment of the MN and rarely, the BrA. We examined the MRIs of the elbow of 279 patients (107 women, 172 men) aged between 18 and 72 years. We measured the thickness, length and width of BA, and investigated the anatomical relationship between BA, BrA, and MN. The respective median thickness, width, and length of BA were 0.7 (0.4-1.8 mm), 18.0 (6.0-34.0 mm), and 32.0 (18.0-50.0 mm), respectively. In all sections examined, the BA covered the BrA and MN, and was located immediately anterior to the BrA. In 225 (80.6%) of 279 MRIs, the BrA was located anterior to the MN and posterior to the BA. In the remaining 54 (19.4%) MRIs, the MN was located anterior to the BrA and posterior to the BA. The respective median thickness, width, and length of the BA were 0.7 mm, 18.0 mm, and 32.0 mm, respectively. It covered the BrA and MN and was located immediately anterior to the BrA. The BA sometimes causes compression syndromes of these structures, therefore, for physicians, it is important to understand the anatomy of the BA.

Experience With Proximal Median Nerve Entrapment by the Lacertus Fibrosus

BACKGROUND

Unconscious bias of the clinician favors the diagnosis of carpal tunnel syndrome (CTS) in patients with median paresthesia. We hypothesized that more patients in this cohort would be diagnosed with proximal median nerve entrapment (PMNE) by strengthening our cognitive awareness of this alternative diagnosis. We also hypothesized that patients with PMNE may be successfully treated with surgical release of the lacertus fibrosus (LF).

METHODS

In this retrospective study, cases of median nerve decompression at the carpal tunnel and in the proximal forearm for the 2-year periods before and after adopting strategies to mitigate cognitive bias for CTS were enumerated. Patients diagnosed with PMNE and treated by LF release under local anesthesia were evaluated to determine surgical outcome at minimum 2-year follow-up. Primary outcome measures were changes in preoperative median paresthesia and proximal median-innervated muscle strength.

RESULTS

There was a statistically significant increase in PMNE cases identified after our heightened surveillance was initiated (z = 3.433, P < .001). In 10 of 12 cases, the patient had previous ipsilateral open carpal tunnel release (CTR) but experienced recurrent median paresthesia. In 8 cases evaluated an average of 5 years after LF release, there was improvement in median paresthesia and resolution of median-innervated muscle weakness.

CONCLUSIONS

Owing to cognitive bias, some patients with PMNE may be misdiagnosed with CTS. All patients with median paresthesia, particularly those with persistent or recurrent symptoms after CTR, should be assessed for PMNE. Surgical release limited to the LF may be an effective treatment for PMNE.

Effect of lacertus fibrosus release on perineural pressure of the median nerve at the elbow: a cadaveric study

PURPOSE

The lacertus fibrosus (or bicipital aponeurosis) is a potential site of proximal median neuropathy at the elbow. Lacertus syndrome with motor and/or sensory symptoms has been addressed with a minimally invasive surgical lacertus release. This study evaluates if a lacertus release alters the maximal perineural pressure (Pmax) of the median nerve at the level of the lacertus fibrosus during elbow flexion.

METHODS

Seven upper limbs from four fresh cadavers were included. Perineural pressure of the median nerve at the level of the lacertus fibrosus was measured continuously during automated elbow flexions by the biceps brachii muscle.

RESULTS

The mean Pmax before the lacertus release was significantly different than the mean Pmax after the lacertus release (669.15 mmHg vs 77.01 mmHg, p = 0.0180). The mean Pmax after the lacertus release decreased with an average 81.41%.

CONCLUSION

A simple surgical release of the lacertus fibrosus significantly decreases the maximal perineural pressure of the median nerve at the level of the lacertus fibrosus during elbow flexion.

Bicipital aponeurosis. Anatomical study and clinical implications

Objective

The aim of this study was to analyze the anatomic variations of the bicipital aponeurosis (BA) (lacertus fibrosus) and its implications for the compression of the median nerve, which is positioned medially to the brachial artery, passing under the bicipital aponeurosis.

Methods

Sixty upper limbs of 30 cadavers were dissected, 26 of which were male and four, female; of the total, 15 had been previously preserved in formalin and glycerine and 15 were dissected fresh in the Laboratory of Anatomy.

Results

In 55 limbs, short and long heads of the biceps muscle contributed to the formation of the BA, and the most significant contribution was always from the short head. In three limbs, only the short head contributed to the formation of the BA. In two limbs, the BA was absent. The length of the bicipital aponeurosis from its origin to its insertion ranged from 4.5 to 6.2 cm and its width, from 0.5 to 2.6 cm. In 42 limbs, the BA was thickened; of these, in 27 it was resting directly on the median nerve, and in 17 a high insertion of the humeral head of the pronator teres muscle was found, and the muscle was interposed between the BA and the median nerve.

Conclusion

These results suggest that a thickened BA may be a potential factor for nerve compression, by narrowing the space through which the median nerve passes.

Anatomical variations of pronator teres muscle: predispositional role for nerve entrapment

Objective

To assess the anatomical variations of the pronator teres muscle (PTM) and its implication in the compression of the median nerve, which passes through the humeral and ulnar heads of the PTM.

Methods

For the present study, 100 upper limbs from human cadavers from the anatomy laboratory were dissected. Forty-six specimens were male and four, female, whose aged ranged from 28 to 77 years; 27 were white and 23, non-white. A pilot study consisting of six hands from three fresh cadaver dissections was conducted to familiarize the authors with the local anatomy; these were not included in the present study.

Results

The humeral and ulnar heads of PTM were present in 86 limbs. In 72 out of the 86 limbs, the median nerve was positioned between the two heads of the PTM; in 11, it passed through the muscle belly of ulnar head of the PTM, and in three, posteriorly to both heads of the PTM. When both heads were present, the median nerve was not observed as passing through the muscle belly of the humeral head of PTM. In 14 out of the 100 dissected limbs, the ulnar head of the PTM was not observed; in this situation, the median nerve was positioned posteriorly to the humeral head in 11 limbs, and passed through the humeral head in three. In 17 limbs, the ulnar head of PTM was little developed, with a fibrous band originating from the ulnar coronoid process, associated with a distal muscle component near the union with the humeral head. In four limbs, the ulnar head of the MPR was represented by a fibrous band. In both limbs of one cadaver, a fibrous band was observed between the supinator muscle and the humeral head of the PTM, passing over median nerve.

Conclusion

The results suggest that these anatomical variations in relationship median nerve and PTM are potential factors for median nerve compression, as they narrow the space through which the median nerve passes.

Brachialis syndrome: a rare consequence of patient positioning causing postoperative median neuropathy

BACKGROUND

Poor positioning of patients can result in devastating permanent neurologic deficits. We describe a previously unreported cause of median nerve compression that we have termed the brachialis syndrome, associated with patient positioning that results in permanent median nerve damage.

METHODS

We identified this condition affecting 6 median nerves. All patients underwent surgical decompression of the proximal median nerve at the level of the antecubital fossa.

RESULTS

Five patients presented with symptoms of median nerve compression; 6 affected median nerves manifested brachialis syndrome after a lengthy index surgery. Every patient had a similar presentation characterized by a mixed sensory and motor deficit. Average time to symptom presentation postoperatively was 1 hour. Two patients had delayed time to decompression, one of 25 days and one of 92 days. In the additional patients, the average time to decompression was 19.7 hours. At median nerve decompression, the brachialis was found to have varying degrees of muscle necrosis. In the patients whose decompression was delayed, there was only partial neurologic recovery at follow-up to 1 year. In the patients expeditiously decompressed, full neurologic recovery occurred in 1 to 14 days.

CONCLUSIONS

This is the first description of the brachialis syndrome. During surgery, arms were placed into full extension, compressing the brachialis against the trochlea. The brachialis reliably developed necrosis, resulting in swelling, compressing the median nerve against the lacertus fibrosus. Two patients with delayed decompression had poor neurologic outcomes. This supports modification of patient positioning, postoperative vigilance, and timely surgical management of brachialis syndrome.

A Perplexing Presentation of Entrapment of the Brachial Artery

A 45-year-old male being otherwise healthy presented acute onset of right upper extremity ischemia. On physical examination, axillary artery could be palpated whereas the brachial artery could not be palpated below the level of the antecubital fossa, including radial and ulnar artery pulses. Pulses were also inaudible with pocket-ultrasound below the level of the brachial artery bifurcation. The patient was initially diagnosed to have acute thromboembolic occlusion and given 5000 IU intravenous heparin. The patient was taken to the operating room. We noticed that the ischemic symptoms disappeared within a couple of minutes just before we began the operation. However, ischemic symptoms reappeared six hours later and computed tomography angiography showed lack of enhancement below the elbow crease. We were taking the patient to the operating room for the second time when the symptoms recovered in a few minutes, again. The operation was not canceled anymore. In the operation, the brachial artery was found anomalously perforating and it was entrapped by the bicipital aponeurosis. The artery was relieved by resecting the aponeurosis and there was no need for any other intervention. The patient had no more recurrence of symptoms postoperatively.

Compression and entrapment neuropathies

Peripheral nerve entrapments are frequent. They usually appear in anatomical tunnels such as the carpal tunnel. Nerve compressions may be due to external pressure such as the fibular nerve at the fibular head. Malignant or benign tumors may also damage the nerve. For each nerve from the upper and lower limbs, detailed clinical, electrophysiological, imaging, and therapeutic aspects are described. In the upper limbs, carpal tunnel syndrome and ulnar neuropathy at the elbow are the most frequent manifestations; the radial nerve is less frequently involved. Other nerves may occasionally be damaged and these are described also. In the lower limbs, the fibular nerve is most frequently involved, usually at the fibular head by external compression. Other nerves may also be involved and are therefore described. The clinical and electrophysiological examination are very important for the diagnosis, but imaging is also of great use. Treatments available for each nerve disease are discussed.

Endoscopically assisted decompression for pronator syndrome

PURPOSE

Traditional surgical management for pronator syndrome results in a relatively long and possibly disfiguring scar across the antecubital fossa. The purposes of this study were to present an endoscopic technique that facilitates the decompression of the proximal median nerve without extensile incisions, and to evaluate whether this minimally invasive procedure could adequately and safely treat the condition to improve outcome scores.

METHODS

We treated 13 patients (14 cases) with isolated pronator syndrome with endoscopically assisted decompression and retrospectively reviewed them. We excluded patients with concomitant carpal tunnel syndrome or other compression neuropathies. The average age of the patient at presentation was 41 years. Final follow-up averaged 22 months. We asked all patients to rate their preoperative and postoperative condition and functional capabilities using the validated Disabilities of the Shoulder, Arm, and Hand (DASH) scoring protocol.

RESULTS

All 13 patients improved symptomatically as reflected in the DASH score assessment. The preoperative scores averaged 56 and the postoperative scores were significantly reduced and averaged 6. There were 3 minor complications, which resolved spontaneously.

CONCLUSIONS

The endoscopically assisted, minimally invasive approach to treat pronator syndrome adequately and safely decompressed all anatomical points of compression and improved DASH scores. This may reduce morbidity and facilitate a quicker recovery compared with the traditional open incision techniques.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Anterior interosseous nerve compression syndrome: is there a role for endoscopy?

BACKGROUND

Anterior interosseous nerve syndrome is characterized by paralysis of the flexor digitorum profundus, the flexor pollicis longus and the pronator quadratus muscles without sensory loss. Extended exploration of the anterior interosseous nerve is the surgical treatment of choice. The present study evaluates the feasibility of an endoscopic approach for nerve decompression.

METHODS

Preparation of the anterior interosseous nerve was performed in ten human cadaver arms. Subsequently, one female patient suffering from anterior interosseous nerve syndrome was endoscopically operated on.

FINDINGS

A skin incision of 3-4 cm in the proximal direction was made at the forearm, and the median nerve was visualized between the pronator teres muscle and the flexor digitorum superficialis. Subsequently, the anterior interosseus nerve branch was identified, followed distally and decompressed under endoscopic view. The procedure could be accomplished in all cases under endoscopic view. Due to the very steep surgical angle, a branch of the anterior interosseus nerve was injured in one cadaver case. In all other cases, no adverse effects were observed. In the clinical case, the anterior interosseus nerve was endoscopically identified and decompressed, but a skin incision of 5 cm was required.

CONCLUSIONS

The results demonstrate that an endoscopic decompression of the anterior interosseus nerve is possible. Several difficulties occurred: Due to the depth of the surgical approach, especially in case of bulky muscles and very small skin incisions, the view is limited, harboring a higher risk of nerve injury. With more experience and specially designed endoscopes, application of this technique in anterior interosseus nerve compression syndrome might become more feasible.

Accessory muscles in the lower part of the anterior compartment of the arm that may entrap neurovascular elements

The aim of this study was to evaluate the incidence of abnormal muscular bands of the anterior compartment of the arm that may compress the median, the ulnar, and the medial antebrachial cutaneous nerve as well as the brachial artery and vein, thus causing entrapment at and above the elbow. A total of 56 adult cadavers were studied during routine dissections that occurred in our laboratory. In the 112 upper limbs studied, we found three variant muscles of the flexor compartment of the arm (2.68%) entrapping nerves and vessels. The first muscle was emerging from the tendon of long head of biceps brachii and coracobrachialis muscle insertion. The second muscle inserted partially into the belly of biceps brachii and should be considered as a supernumenary head of biceps brachii. The third muscle, in fact, represents an accessory fascicle of the brachialis muscle that is an embryonic remnant of that muscle. A number of structures cross anterior to the median, ulnar, and medial antebrachial cutaneous nerve as well as the brachial artery and vein. Compression of nerves and vessels may be caused by additional muscular bundles that pass anterior to these structures. These additional muscular bundles arise either from the brachialis, coracobrachialis, or biceps brachii muscle. Such variations have clinical implications and should be considered in patients, with a high median or ulnar or medial antebrachial cutaneous nerve paralysis with symptoms of lower brachial artery or brachial vein compression.

Acute compression of the median nerve at the elbow by the lacertus fibrosus

Chronic compression of the median nerve at the elbow has been described as resulting from a number of structures including the lacertus fibrosus. Symptoms of chronic compressive peripheral neuropathy consist predominantly of an achy feeling, paresthesias, numbness, and a sense of weakness or fatigue, with the onset being insidious and frequently without a precipitating cause. In this series, 7 consecutive cases of acute median nerve compression in the antecubital fossa resulted from an extremely forceful injury to the elbow. In all 7 cases, a sudden, severe attempt at elbow flexion was performed against a substantial counterforce, resulting in immediate severe pain radiating from the elbow down into the forearm. Pain was persistent and unremitting in all 7 until the time of diagnosis and treatment. Surgical decompression was performed in all cases. At the time of surgery, we found evidence of partial rupture of the myotendinous junction of the biceps brachii creating increased tension across the median nerve by a tethered lacertus fibrosus. Surgical decompression resulted in complete relief of symptoms in all 7 cases.

Pronator syndrome and other nerve compressions that mimic carpal tunnel syndrome

The purpose of this clinical commentary is to provide a comprehensive review of compressive neuropathies that may mimic carpal tunnel syndrome, provide the clinician with information to differentially diagnose these median nerve compression sites, and provide an evidence-based opinion regarding conservative intervention techniques for the various compression syndromes. While rare in comparison to carpal tunnel syndrome, pronator syndrome and anterior interosseous nerve syndrome are proximal median nerve compressions that may be suspected if a patient with carpal tunnel syndrome fails to respond to conservative or surgical intervention. Differential diagnosis is based largely on the symptoms, patterns of paresthesia, and specific patterns of muscle weakness. Due to the relative rarity of pronator syndrome and anterior interosseous nerve syndrome, few controlled studies exist to determine the most effective treatment techniques. Based on sound anatomical and biomechanical considerations, anecdotal experience, and available research, however, treatment strategies for pronator syndrome and anterior interosseous nerve syndrome compression neuropathies can be divided into 4 major categories: (1) rest/immobilization, (2) modalities, (3) nerve gliding, and (4) nonconservative treatment.

MR imaging of entrapment neuropathies at the elbow

MR imaging has a valuable role in the evaluation of compressive neuropathies at the elbow. Specific MR signs in association with clinical findings can supply an accurate diagnosis. A review of normal anatomy, clinical features, and MR assessment of nerve entrapment syndromes at the elbow is presented.

Peripheral nerve fascicles: Anatomy and clinical relevance

Within a peripheral nerve, the individual nerve fibers are grouped together in fascicles. Whether there is somatotopic organization within these fascicles has long been of interest, the subject of many investigations, and somewhat controversial. Evidence from diverse sources now points to important somatotopic clustering of nerve fibers within most of the length of the nerve. Information is lacking regarding proximal segments, particularly the plexus and spinal nerve root levels. As a result of this somatotopic arrangement, partial focal nerve lesions can produce restricted clinical deficits that defy the classic rules of localization. Examples of such restricted nerve lesions are provided in this review. Recognition of fascicle somatotopy is also important in the surgical approach to disorders of peripheral nerves.

Forearm arteries entrapment syndrome: a rare cause of recurrent angioaccess thrombosis

Entrapment syndrome below or just above the elbow is uncommon. These rare causes of neurologic or vascular entrapment are linked to anomalous anatomical structures. No case of entrapment syndrome has been reported in patients with angioaccess for hemodialysis. We report, for the first time, forearm arteries entrapment in two patients presenting with recurrent angioaccess for hemodialysis thrombosis. Anatomical, radiologic, and surgical features of these uncommon syndromes are discussed.

Innervation of the medial epicondylar muscles: an anatomic study in 50 cases

The median nerve is classically distributed to the medial epicondylar muscles by two branches (superior and inferior) for the pronator teres muscle, a common trunk for the flexor carpi radialis and palmaris longus muscles, and a branch for the flexor digitorum superficialis muscle. The 50 dissections were made by two workers on 30 upper limbs of formalized cadavers and 20 limbs from fresh-frozen cadavers. The innervation of the pronator teres m. was classical in only 26% of cases, and the "normal" pattern for the flexor carpi radialis and palmaris longus mm. was found in only 40% of cases. The innervation of the flexor digitorum superficialis m. was the least subject to variations, a single branch being observed in 68% of cases. We found a solitary medio-ulnar anastomosis of Martin-Gruber to the flexor carpi ulnaris muscle. This study confirmed the great variability of the branches of the median nerve at the elbow, and the importance of identifying them in surgical procedures for transposition of the medial epicondyle.

Proximal median neuropathies

Proximal median neuropathies are uncommon. They are usually caused by overuse of the forearm, anatomic variations, or both. Forearm pain, weakness of muscles supplied by the affected nerves, and sensory loss, including the thenar eminence, are common clinical findings. Nerve conduction studies and needle electromyography are helpful in the diagnosis of these syndromes. Treatment is avoidance of overuse and release of mechanical compression. Prognosis is generally good.

Magnetic resonance imaging of the musculoskeletal system: Part 3. The elbow

Magnetic resonance imaging provides clinically useful information in assessing the elbow joint. Superior depiction of muscles, ligaments, and tendons as well as the ability to directly visualize nerves, bone marrow, and hyaline cartilage are advantages of magnetic resonance imaging relative to conventional imaging techniques. Ongoing improvements in surface coil design and newer pulse sequences have resulted in higher quality magnetic resonance images of the elbow. Traumatic and degenerative disorders of the elbow are well seen with MR imaging. The sequelae of medial traction and lateral compression from valgus stress include medial collateral ligament injury, common flexor tendon pathology, medial traction spurs, ulnar neuropathy, and osteochondritis dissecans. These conditions as well as lateral collateral ligament injury and lateral epicondylitis may be characterized with magnetic resonance imaging. Posttraumatic osseous abnormalities well seen by magnetic resonance imaging include radiographically occult fractures, stress fractures, bone contusions, and apophyseal avulsions. Magnetic resonance imaging also can be used to assess cartilaginous extension of fractures in children. Intraarticular loose bodies can be identified with magnetic resonance imaging, especially if fluid or contrast material is present within the elbow joint. Biceps and triceps tendon injuries can be diagnosed and characterized. Magnetic resonance imaging also can provide additional information regarding entrapment neuropathies about the elbow. Magnetic resonance imaging is perhaps most useful when patients have not responded to conservative therapy and therefore surgery and additional diagnoses are being considered.

Musculus comitans nervi mediani (M. palmaris profundus)

Palmaris profundus muscles were found in two cadavers during routine dissection of the upper limb. This rare muscle was found in two forms. In the first case, the muscle resembled a diminutive palmaris longus with the belly arising from the common flexor tendon. In the second case however, a reversed muscle with the belly emerging from beneath the transverse carpal ligament and its long thin tendon extended to and inserted in the common flexor tendon. The similarity therefore of these muscles to variable forms of palmaris longus is remarkable but they differed in one very important aspect from palmaris longus. The muscles are of special interest because, in both cases, the muscles were found enclosed in a common fascial sheath with the median nerve. These unusual muscles, in spite of mimicking palmaris longus, may perhaps, be better named "musculus comitans nervi mediani" to denote their very important relationship to the median nerve, that of being the intimate traveling companion of the median nerve through the forearm and into the hand by way of the carpal canal beneath the transverse carpal ligament. In one case, a well developed median artery was also found which also entered the carpal canal along with the median nerve and its muscular companion.

Spontaneous bilateral median nerve compressions in the distal arm

A case of bilateral median nerve compressions in the distal arm is described. The patient was seen initially with the spontaneous onset of paresis of the anterior interosseous nerve innervated muscles, as well as more proximal median nerve innervated muscles. There was no shoulder-girdle weakness or sensory abnormality. No systemic symptoms were identified. Surgical exploration in each extremity revealed enlarged communicating veins directly compressing the median nerve in the distal arms. Clinical improvement began 6 months after operation and was complete by 18 months.