Anconeus Research Articles

Presynaptic failure of neuromuscular transmission and synaptic remodeling in EA2.

To further investigate the basis of abnormal neuromuscular transmission in two patients with congenital myasthenic syndrome associated with episodic ataxia type 2 (EA2) using stimulated single fiber EMG (SFEMG) and in vitro microelectrode studies. Two patients with genetically characterized EA2 previously shown to have abnormal neuromuscular transmission by voluntary SFEMG were studied with stimulated SFEMG and anconeus muscle biopsy with microelectrode studies and electron microscopy of the neuromuscular junction. In vivo stimulated SFEMG showed signs of presynaptic failure, with jitter and blocking that improved with increased stimulation frequency. Additional evidence of presynaptic failure was provided by the in vitro microelectrode studies, which showed marked reduction of the end plate potential quantal content in both patients. Of note, the end plate potentials showed high sensitivity to N-type blockade with omega-conotoxin not seen in controls. The ultrastructural studies revealed some evidence of small nerve terminals apposed to normal or mildly overdeveloped postsynaptic membranes, suggesting an ongoing degenerative process. The authors demonstrated presynaptic failure of neurotransmission in patients with heterozygous nonsense mutations in CACNA1A. The contribution of non-P-type calcium channels to the process of neurotransmitter release in these patients likely represents a compensatory mechanism, which is insufficient to restore normal neuromuscular transmission.

Choline acetyltransferase mutations in myasthenic syndrome due to deficient acetylcholine resynthesis.

The myasthenic syndrome due to abnormal acetylcholine resynthesis is characterized by early onset, recessive inheritance, and recurrent episodes of potentially fatal apnea. Mutations in the gene encoding choline acetyltransferase (CHAT) have been found to account for this condition. We have identified five patients from three independent families with features of this disease including, in four patients, a paradoxical worsening of symptoms with cold temperatures. Electrodiagnostic studies demonstrated impaired neuromuscular transmission in all patients. In vitro microelectrode studies performed in the anconeus muscle biopsies of two patients showed moderate reduction of quantal release. Electron microscopy of the neuromuscular junction was normal in both patients. Each patient had two heterozygous CHAT mutations including L210P and P211A (family 1), V194L and V506L (family 2), and R548stop and S694C (family 3). Three of these mutations have previously been reported and suggest that, in this syndrome, some molecular defects may be more prevalent than others.

ANCONEUS ARTHROPLASTY

Management of posttraumatic radiocapitellar and/or proximal radioulnar joint dysfunction and pain is a challenging problem, often with more than one pathological feature, and to date there are no consistently reliable solutions. The unreliability of prosthetic replacement prompted us to develop an anconeus arthroplasty wherein the anconeus muscle is rotated into the radiocapitellar and/or proximal radioulnar joint. Three interposition options were assessed in our laboratory and were employed clinically: interposition at the radiocapitellar joint (Type I), interposition at the radiocapitellar and proximal radioulnar joints (Type II), and proximal radioulnar interposition (wrap) (Type III). The clinical outcomes in fourteen patients who had been treated with one of the three types of anconeus interposition arthroplasty were reviewed at least two years (mean, 6.1 years) postoperatively. Anatomic dissection of twenty-five specimens revealed that all three applications were possible. Of the fourteen patients, twelve (all six with a Type-I interposition, three of the five with a Type-II interposition, and all three with a Type-III interposition) had a satisfactory overall subjective result. The Mayo Elbow Performance Score averaged 63 points before the surgery and 89 points after it. Anconeus interpositional arthroplasty offers a reasonable likelihood of improved subjective and objective function in patients with the challenging problem of radiocapitellar and/or proximal radioulnar joint dysfunction and pain after trauma, even when there is Essex-Lopresti axial instability.

Surgical techniques for reconstruction of chronic insufficiency of the triceps. Rotation flap using anconeus and tendo achillis allograft.

Seven patients with chronic insufficiency of the triceps were treated by either a rotation flap using anconeus (4) or an allograft of tendo Achillis (3). The latter procedure was selected for patients with a large defect in whom the anconeus muscle had been devitalised. Five disruptions were in patients who had previously undergone an elbow replacement. The patients were assessed for subjective satisfaction, pain, range of movement and strength, and the results were graded using the Mayo Elbow Performance Score (MEPS). The mean follow-up was for 33 months (9 to 63). One rotation flap failed six months after operation. At the most recent follow-up, the remaining six patients had no or slight pain, restoration of a functional arc of movement and normal or slightly decreased power of extension. All six were satisfied with the outcome and were able to resume their daily activities with no limitations other than those imposed by the previous elbow replacement. The final MEPS was 100 points in five patients and 75 in one.

Surgical techniques for reconstruction of chronic insufficiency of the triceps

Seven patients with chronic insufficiency of the triceps were treated by either a rotation flap using anconeus (4) or an allograft of tendo Achillis (3). The latter procedure was selected for patients with a large defect in whom the anconeus muscle had been devitalised. Five disruptions were in patients who had previously undergone an elbow replacement. The patients were assessed for subjective satisfaction, pain, range of movement and strength, and the results were graded using the Mayo Elbow Performance Score (MEPS). The mean follow-up was for 33 months (9 to 63). One rotation flap failed six months after operation. At the most recent follow-up, the remaining six patients had no or slight pain, restoration of a functional arc of movement and normal or slightly decreased power of extension. All six were satisfied with the outcome and were able to resume their daily activities with no limitations other than those imposed by the previous elbow replacement. The final MEPS was 100 points in five patients and 75 in one.

Novel delta subunit mutation in slow-channel syndrome causes severe weakness by novel mechanisms.

We investigated the basis for a novel form of the slow-channel congenital myasthenic syndrome presenting in infancy in a single individual as progressive weakness and impaired neuromuscular transmission without overt degeneration of the motor endplate. Prolonged low-amplitude synaptic currents in biopsied anconeus muscle at 9 years of age suggested a kinetic disorder of the muscle acetylcholine receptor. Ultrastructural studies at 16 months, at 9 years, and at 15 years of age showed none of the typical degenerative changes of the endplate associated with the slow-channel congenital myasthenic syndrome, and acetylcholine receptor numbers were not significantly reduced. We identified a novel C-to-T substitution in exon 8 of the delta-subunit that results in a serine to phenylalanine mutation in the region encoding the second transmembrane domain that lines the ion channel. Using Xenopus oocyte in vitro expression studies we confirmed that the deltaS268F mutation, as with other slow-channel congenital myasthenic syndrome mutations, causes delayed closure of acetylcholine receptor ion channels. In addition, unlike other mutations in slow-channel congenital myasthenic syndrome, this mutation also causes delayed opening of the channel, a finding that readily explains the marked congenital weakness in the absence of endplate degeneration. Finally, we used serial morphometric analysis of electron micrographs to explore the basis for the progressive weakness and decline of amplitude of endplate currents over a period of 14 years. We demonstrated a progressive widening and accumulation of debris in the synaptic cleft, resulting in loss of efficacy of released neurotransmitter and reduced safety factor. These studies demonstrate the role of previously unrecognized mechanisms of impairment of synaptic transmission caused by a novel mutation and show the importance of serial in vitro studies to elucidate novel disease mechanisms.

Presynaptic congenital myasthenic syndrome due to quantal release deficiency.

To provide clinical, electrophysiologic, and ultrastructural findings in three patients with a presynaptic congenital myasthenic syndrome (CMS). Familial infantile myasthenia and paucity of synaptic vesicles are the only two fully characterized CMS. We are describing here three patients with another form of presynaptic CMS characterized by deficiency of the action potential-dependent release without reduction of the spontaneous release of neurotransmitter from the nerve terminal. The authors performed electromyography and anconeus muscle biopsies that included intracellular recordings and electron microscopy of the neuromuscular junction in three patients with presynaptic CMS. They also sequenced part of the P/Q-calcium alpha(1)-subunit gene (CACNA1A) and the acetylcholine receptor subunit (AChR) genes in these patients. In these patients there were additional neurologic findings including nystagmus and ataxia. In all three patients the end-plate potential quantal content (m) was markedly reduced but neither the amplitudes nor the frequencies of miniature end-plate potentials were diminished. Ultrastructurally, postsynaptic end-plate folds, nerve terminal size, and synaptic vesicle number were normal but double-membrane-bound sacs containing synaptic vesicles were present in the nerve terminal of all three patients. The screening of reported pathogenic mutations in the CACNA1A and a mutational analysis of AChR subunit genes were negative. This form of CMS appears to result only from a deficiency of the quantal release of neurotransmitter that may be due to an abnormal calcium mechanism or impaired endocytosis and recycling of synaptic vesicles.

Diagnostic Sensitivity of Several Muscles in Repetitive Nerve Stimulation Test for Myasthenia Gravis

Background: This study was undertaken to evaluate the diagnostic sensitivity of several muscles in repetitive nerve stimulation test (RNST) for myasthenia gravis (MG) patients. Materials and Methods: The study population consisted of 39 MG patients classified by modified Ossermann's classification. Using Stalberg's method, RNST was systematically performed in facial (orbicularis oculi and nasalis) and upper extremity (flexor carpi ulnaris, abductor digiti quinti and anconeus) muscles. Results: The significant electrodecremental response of RNST were noted in orbicularis oculi(58.9%), nasalis (51.3%), flexor carpi ulnaris(42%), anconeus(41%) and abductor digiti quinti muscles(27%). Among the 3 muscles of upper extremity(abductor digiti quinti, flexor carpi ulnaris and anconeus), the positive electrodecremental response of anconeus muscles was significantly higher than other two muscles(p

Diagnostic ultrasonography of the ulnar nerve in cubital tunnel syndrome

Thirty-two elbows in 31 patients diagnosed as having cubital tunnel syndrome underwent ultrasonographic examination to assess morphological changes in the ulnar nerve and its surrounding tissues. On longitudinal images, the site of constriction due to the fibrous band and proximal swelling of the nerve were observed by ultrasonography and were confirmed intraoperatively. On axial images, the lengths of the major axis [7.2 (SD 1.6) mm] and the minor axis [3.7 (0.9) mm] of the nerve at the medial epicondyle were greater than those in normal subjects. There was a correlation between the stage of ulnar nerve palsy and the diameter of the major axis. Preoperatively, ganglia were detected by ultrasonography in the cubital tunnel in three cases and an anconeus epitrochlearis muscle in two.

Diagnostic Ultrasonography of the Ulnar Nerve in Cubital Tunnel Syndrome

Thirty-two elbows in 31 patients diagnosed as having cubital tunnel syndrome underwent ultrasonographic examination to assess morphological changes in the ulnar nerve and its surrounding tissues. On longitudinal images, the site of constriction due to the fibrous band and proximal swelling of the nerve were observed by ultrasonography and were confirmed intraoperatively. On axial images, the lengths of the major axis [7.2 (SD 1.6) mm] and the minor axis [3.7 (0.9) mm] of the nerve at the medial epicondyle were greater than those in normal subjects. There was a correlation between the stage of ulnar nerve palsy and the diameter of the major axis. Preoperatively, ganglia were detected by ultrasonography in the cubital tunnel in three cases and an anconeus epitrochlearis muscle in two.

Moment distribution among human elbow extensor muscles during isometric and submaximal extension

To understand better how the central nervous system (CNS) distributes a joint moment among muscles, moment distribution among the three heads of the triceps and the anconeus muscles during isometric elbow extension was quantified in vivo and noninvasively. Electrical stimulation was used to activate an individual muscle selectively at various contraction levels, and the relationship between the peak M-wave amplitude and peak elbow extension moment was established across various contraction levels for each muscle. The relationship was then used to calibrate the corresponding EMG signal and determine moment distribution among the muscles during voluntary isometric elbow extension. Results showed that moment distribution among muscles was not proportional to the muscles’ physiological cross-sectional areas (PCSA) and the CNS favored uniarticular muscles for the isometric task performed: the uniarticular lateral and medial heads of the triceps were dominant (contributing ∼70–90% of the total elbow extension moment) and the anconeus contributed significantly, especially at the lower levels of elbow extension moment (up to ∼15% of the extension moment). In contrast, the two-joint long head of the triceps contributed significantly less than the uniarticular heads of the triceps. While the absolute contributions of all the muscles increased with the total elbow extension moment, the relative contributions of the muscles may increase or decrease with the elbow extension moment. Cross-validation using fresh data (not used in determining the moment distribution) showed close match between the measured and predicted elbow extension moment except for trials in which fatigue became significant.

Management of radioulnar synostosis with mobilization, anconeus interposition, and a forearm rotation assist splint

Three cases of post-traumatic proximal radioulnar synostosis are presented. Each was treated with surgery with excision of the heterotrophic new bone and mobilization of the proximal radius. The anconeus muscle was mobilized as a vascularized pedicle graft and then interposed between the proximal radius and ulna. Two patients had postoperative radiotherapy. A forearm rotation assist splint was used to augment rehabilitation after surgery. This device consists of an inner sleeve that attaches to the hand and then rotates within a standard turnbuckle flexion/extension assist splint. The overall improvement in forearm rotation in each case was 100°, 140°, and 150°, respectively.

Anatomic and histologic studies of lateral collateral ligament complex of the elbow joint

We studied the gross and histologic anatomic characteristics of the lateral collateral ligament complex of the elbow joint from 15 cadavers to demonstrate its cross-sectional anatomy. The lateral ulnar collateral ligament adheres closely to the supinator, the extensor muscles, its intermuscular fascia, and the anconeus muscle and lies posterior to the radial collateral ligament. The lateral ulnar collateral ligament itself was identified with microscopy as a slender, poor structure consisting of the thick area of the posterolateral capsuloligamentous layer and a poorer structure than the anterior bundle of the medial collateral ligament as the primary stabilizer of the elbow joint. We believe that the lateral ulnar collateral ligament contributes to rather than is a major constraint to the posterolateral rotatory instability as part of the lateral collateral ligament complex with the surrounding tissues.

The anconeus muscle flap: its anatomy and clinical application.

The arterial anatomy, coverage area, and potential donor site morbidity of the anconeus muscle flap are described. Using 17 cadaveric upper extremities, we investigated the muscle's arterial anatomy in 12 specimens and defined the coverage area of the anconeus flap in 5 specimens. We also reviewed the records of 9 patients who underwent a pedicle anconeus muscle flap for elbow coverage to assess clinical results of the procedure. The anconeus muscle is supplied from 3 arterial pedicles: the recurrent posterior interosseus artery, the medial collateral artery, and the posterior branch of the radial collateral artery. The recurrent posterior interosseus artery and the medial collateral artery were present in all dissected cadavers and consistently anastomosed with each other underneath the anconeus muscle. By harvesting the muscle on the medial collateral artery, the anconeus muscle flap can be expected to cover a 7.3 cm2 defect over the radiocapitellar joint, a 6.1 cm2 defect over the distal triceps tendon, and a 7.2 cm2 defect over the olecranon. In this series, none of the patients experienced loss of elbow motion, stability, or extension strength. The results of this study indicate that the anconeus can be harvested with minimal risk of morbidity and provides effective coverage for soft tissue defects of the elbow.

Epicondylar resection with anconeus muscle transfer for chronic lateral epicondylitis

A retrospective evaluation of 61 patients surgically treated for persistent lateral epicondylitis, covering the 8-year period between 1982 and 1990, was conducted. The study compared a group of patients treated by limited surgical resection of the lateral extensor aponeurosis with a group of patients treated by wide surgical excision of the aponeurosis and coverage by a vascularized rotational pedicle flap of the anconeus muscle. This is a new procedure that uses the vascular pedicle of the anconeus muscle, rotating it into the defect created by the wide excision. Evaluation at an average of 48 months after surgery indicates that compared with the limited surgical resection group, a higher percentage of patients in the anconeus muscle transfer group were able to perform strenuous activities with complete or near-complete pain relief. A higher percentage also returned to work or to normal activities; 94% of the patients were satisfied with the results of the procedure. This study indicates that this is an effective primary operative treatment for lateral epicondylitis when conservative treatment has failed. It also is effective in patients who continue to have persistent pain and inability to perform normal activities after previous lateral epicondylar release or resection.

BILATERAL CHRONIC COMPARTMENT SYNDROME IN THE FOREARM AND THE HAND

We report two cases of bilateral chronic exertional compartment syndrome (CCS) in the forearm and hand. Measurement of the intramuscular pressure was useful for diagnosis. These two cases illustrate that bilateral CCS should be suspected in patients complaining of bilateral exercise-induced pain in the anconeus muscle, the forearms, the thenar and hypothenar regions and in the first dorsal interosseous muscle. Fasciotomy relieved the pain in both cases.

Influence of tonic neck reflexes on the upper limb stretch reflex in man

This study was designed to test the influence of tonic neck reflexes (TNR) on the elbow extensor muscles. Surface electromyography (EMG) of triceps brachii (TB), anconeus (ANC) and biceps brachii (BB) muscles were recorded simultaneously with elbow acceleration. Stretch reflex responses from the elbow extensors were analysed in seven healthy subjects for three head positions, two positions of the eyes and two initial EMG levels. At the opposite of the short latency stretch component (M1), the occurrence of the long-latency stretch responses (M2-3) did not depend on the EMG level. The head position influenced the EMG activity only for the lowest initial EMG level: a rotated head position towards the stretched extensor muscles increased the tonic EMG level of these muscles and facilitated the M2-3 component. This influence was modulated by the position of the eyes and occurred in both anconeus and triceps brachii recordings. These results support the hypothesis that a low EMG activity is needed to express TNR. Changes in M2-3 with head position could result from the interaction of messages from limb afferents and neck afferents at a supraspinal level.

Ulnar nerve compression at the elbow caused by a prominent medial head of the triceps and an anconeus epitrochlearis muscle

A number of musculo-tendinous variations around the medial epicondyle have been alleged to cause ulnar nerve compression. Subluxation of the ulnar nerve, a "snapping" separate medial head of triceps, a prominent medial head of triceps covering the ulnar nerve, anconeus epitrochlearis, Osborne's band, and the ligament of Struthers have been implicated. We present a case of clearcut compression of the ulnar nerve at two levels just at and posterior to the epicondyle by a tightly applied prominent head of the triceps, and at a more distal level beneath an anconeus epitrochlearis muscle.

Changes in the electromyographic spectrum power distribution caused by a progressive increase in the force level

The purpose of the present study was to determine the specific changes occurring in the power spectrum with an increasing force level during isometric contractions. Surface electromyographic signals of the triceps brachii (TB) and the anconeus (AN) of 29 normal subjects were recorded during isometric ramp contractions performed from 0 to 100% of the maximum voluntary contraction (MVC) in a 5-s period. Power spectra were obtained at 10, 20, 30, 40, 50, 60, 70, 80 and 90% MVC. Changes in the shape of these spectra were evaluated visually and with the calculation of several statistical parameters related to the distribution of power along the frequency axis, such as median frequency and mean power frequency, standard deviation, skewness, first and third quartiles and half-power range. For the AN, the behaviour of the spectrum was relatively similar across subjects, presenting a shift toward higher frequencies without any major change in the shape of the spectrum. For the TB, subjects with a thin skinfold thickness presented similar behaviours. In subjects with a thicker skinfold, however, a loss of power in the high frequency region paralleled the increase in the force level. Significant correlations were obtained between the extent of the change in the value of higher order statistical parameters across force and the thickness of the skin. This points out the importance of the skinfold layer when recording with surface electrodes. Furthermore, the use of a combination of several parameters appears to provide a better appreciation of the changes occurring in the spectrum than any single parameter taken alone.

MR imaging of patients with lateral epicondylitis of the elbow (tennis elbow): importance of increased signal of the anconeus muscle.

The purpose of this study was to determine what changes might be detected on MR images of patients with chronic lateral epicondylitis (tennis elbow) that could explain why some cases are resistant to therapy. Seven consecutive patients with chronic lateral epicondylitis were included. The diagnosis was based on symptoms and signs characteristic of the disease, as determined by each patient's orthopedic surgeon. Three volunteers with normal elbows were control subjects. All patients had MR imaging of the involved elbow, and control subjects had MR imaging of the nondominant elbow. Short tau inversion-recovery (STIR) MR imaging was chosen because of its sensitivity to changes in the water content of muscle and its suppression of the fat signal. The images were analyzed visually and on an MR workstation to measure the signal intensity of the elbow muscles. In all seven patients, MR images showed increased signal intensity of the anconeus muscle. This increase in signal intensity was not observed in the control subjects, and to our knowledge it has not been reported previously. Increased signal intensity of the anconeus muscle on MR images in patients with chronic lateral epicondylitis suggests involvement of the muscle. Increased signal intensity is seen with edema, granulation tissue, and inflammation, which may explain the findings in this study. Our results are inconclusive as to whether this increased signal intensity contributes to the chronicity of patient symptomatology or is associated with abnormal elbow motion because of the symptoms.