Functional differences between anatomical regions of the anconeus muscle in humans

Altered anconeus muscle activation characteristics during isometric gripping in individuals with lateral elbow tendinopathy compared with age- and sex-matched control

BACKGROUND

Individuals with lateral epicondyle tendinopathy (LET) commonly experience gripping deficits, which are marked by pain and altered motor control of the forearm extensors and flexors. Although delayed activation of the anconeus muscle during rapid wrist extension has been observed in LET, its role during gripping is not well understood. This study aimed to investigate anconeus activation and its relation to forearm muscle activity during gripping in individuals with LET.

METHODS

Eleven participants with LET and 11 healthy, age-, sex-, and limb-matched controls performed steady-state isometric gripping at 15% and 30% of their maximum voluntary contraction (MVC). Surface electromyography was recorded from anconeus and 6 forearm muscles. Standard clinical assessments for LET were conducted to evaluate the severity of the condition.

RESULTS

Participants with LET exhibited increased relative activation of the anconeus compared with the forearm flexors, but not with the extensors, during both 15% and 30% MVC gripping. In addition, the LET group demonstrated an increased coactivation ratio between anconeus and extensor carpi radialis brevis, as well as the flexor digitorum superficialis, during 15% MVC. At 30% MVC, this increased coactivation was observed between anconeus and all 3 flexors (flexor digitorum superficialis, flexor carpi radialis, and flexor carpi ulnaris). Lower anconeus activation was associated with greater LET-related disability, whereas higher anconeus activation was associated with increased anconeus tenderness.

CONCLUSION

This study presents novel evidence of an adaptive motor pattern in LET, characterized by increased relative activation and coactivation of the anconeus muscle depending on grip force. Signs of maladaptive motor patterns emerge when grip force becomes painful. These findings enhance our understanding of anconeus dysfunction in LET and the gripping deficits that accompany it, offering new insights into potential management strategies for this condition.

Anconeus and pronation: a palpatory and ultrasonographic study

PURPOSE

Depending on its axis, pronation varies from the radius rotation around the steady ulna to the reciprocal adduction of the radius and abduction of the ulna. While there is no question that pronator teres is a central pronation agonist, anconeus's role is not settled. The current investigation comparing palpation and ultrasonography in these two muscles during pronation along the axis capitulum-second digit evolved from a serendipitous finding in a clinical anatomy seminar.

METHODS

Single-hand palpation and two-transducer ultrasonography over anconeus and pronator teres were used on ten normal subjects to investigate their contraction during pronation around the capitulum-second digit axis. These studies were done independently and blind to the results of the other. The statistical analysis between palpation and ultrasonography was performed with Cohen's kappa coefficient and the χ2 test.

RESULTS

On palpation, on resisted full pronation, anconeus contracted in 8/10 subjects and pronator teres in 10/10 subjects. Without resistance, the corresponding ratios were 5/10 and 9/10. On two-transducer ultrasonography, the comparable ratios were 7/10 and 10/10, and 3/10 and 10/10. A fair concordance (Cohen's kappa = 0.21) between palpation and ultrasonography in detecting the simultaneous status of anconeus and pronator teres during resisted full pronation. Anatomic dissection illustrated the elements involved.

CONCLUSIONS

Plain palpation confirmed by ultrasonography showed the simultaneous contraction of anconeus and pronator teres during resisted pronation in most of the studied subjects. The study suggests that palpation can be helpful in directly studying muscle activity during movement.

Anconeus Exertional Compartment Syndrome and Posterolateral Rotatory Elbow Instability: A Clinical Association and Rare Cause of Elbow Pain

Background

Anconeus compartment syndrome is a rarely reported compartment syndrome in the anconeus muscle compartment of the forearm. It has anatomic and pathophysiological associations with posterolateral rotatory instability (PLRI) of the elbow.

Purpose

To present the history, management, and outcomes of 4 patients with anconeus compartment syndrome. Secondary aims were to (1) establish normative anconeus pressures and (2) measure the volume of this compartment with and without PLRI in cadavers.

Study Design

Case series; Level of evidence, 4.

Methods

Four patients with clinical signs of anconeus compartment syndrome (2 gymnasts, 1 swimmer, and 1 footballer/weightlifter) were identified over a 3-year period (2015-2017 inclusive). Patient history, sporting activity, physical examination, anconeus compartment pressures, and treatment outcomes were recorded. Manometry of the anconeus compartment in 2 healthy male controls was performed to establish normative compartment pressures. Anconeus volumetric anatomy and the effect of creating PLRI on compartment volume was investigated in 4 cadaveric elbows.

Results

All 4 patients had microtraumatic PLRI, and 2 patients had anconeus hypertrophy. Anconeus compartment pressures at rest and at 2-minutes postexercise were median 28.0 and 67.5 mm Hg, respectively, in the patients and mean 16.5 and 18 mm Hg, respectively, in the controls. Simultaneous fasciotomy and PLRI reconstructive procedures were performed in 2 patients, with outcomes showing full return to competition. Fasciotomy alone was performed in 2 patients to allow return to competition, with both requiring later reconstruction to address PLRI. Cadaver dissection revealed that the anconeus compartment was extremely small and that creation of PLRI reduced the direct volume of the compartment and increased the distance between the anconeus origin and insertion.

Conclusion

Our case series demonstrated that anconeus compartment syndrome can occur in upper limb-dominant athletes in the presence of PLRI and anconeus hypertrophy. Pain is relieved by fasciotomy, but definitive treatment of the underlying instability prevents further symptomatology.

Elbow Extensor Muscles in Humans and Chimpanzees: Adaptations to Different Uses of the Upper Extremity in Hominoid Primates

Simple Summary

Chimpanzees and humans are both species of hominoid primates that are closely related phylogenetically. One of the key differences between these two species is their use of their upper extremities. Humans use this limb mainly in manipulative tasks, while chimpanzees also use it during locomotion. In this study, we have analyzed the muscle architecture and the expression of the myosin heavy chain isoforms in the two elbow extensor muscles, the triceps brachii and the anconeus, in humans and chimpanzees, in order to find differences that could be related to the different uses of the upper extremities in these species. We have found that the triceps brachii of chimpanzees is more prepared for strength and power as an adaptation to locomotion, while the same muscle in humans is more prepared for speed and resistance to fatigue as an adaptation to manipulative activities. Our results increase the knowledge we have of the musculoskeletal system of chimpanzees and can be applied in various fields, such as comparative anatomy, evolutionary anatomy or anthropology.

Abstract

The anatomical and functional characteristics of the elbow extensor muscles (triceps brachii and anconeus) have not been widely studied in non-human hominoid primates, despite their great functional importance. In the present study, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms in the elbow extensors in humans and chimpanzees. Our main objective was to identify differences in these muscles that could be related to the different uses of the upper extremity in the two species. In five humans and five chimpanzees, we have analyzed muscle mass (MM), muscle fascicle length (MFL), and the physiological cross-sectional area (PCSA). In addition, we have assessed the expression of the MHC isoforms by RT-PCR. We have found high MM and PCSA values and higher expression of the MHC-IIx isoform in the triceps brachii of chimpanzees, while in humans, the triceps brachii has high MFL values and a higher expression of the MHC-I and MHC-IIa isoforms. In contrast, there were no significant differences between humans and chimpanzees in any of the values for the anconeus. These findings could be related to the participation of the triceps brachii in the locomotion of chimpanzees and to the use of the upper extremity in manipulative functions in humans. The results obtained in the anconeus support its primary function as a stabilizer of the elbow joint in the two species.

Comparison of Regional Hamstrings Activation During Resistance Exercises in Females With Prior Athletic Experience

CONTEXT

Within each hamstring muscle, there are segments with separate nerve innervation. However, a better understanding of activation levels within these regions during resistance exercise could lead to region-specific training for improved performance and injury prevention.

OBJECTIVE

To compare muscle activation levels within regions of the hamstrings during various resistance exercises.

DESIGN

Within-subjects repeated measures.

SETTING

Biomechanics laboratory.

PARTICIPANTS

Eighteen young adult females with previous competitive sport participation and resistance training experience.

INTERVENTION

One set of 3 repetitions with an 8RM load on the bilateral squat, modified single-leg squat, stiff-legged dead lift, and leg curl (LC).

MAIN OUTCOME MEASURES

Normalized surface electromyography of 4 hamstring regions (proximal-medial, proximal-lateral, distal-medial, and distal-lateral).

RESULTS

For LC only, electromyography measures for the proximal-lateral location were significantly lower than for the distal-lateral, t18 = 5.6, P < .001, and proximal-medial, t18 = 2.4, P = .01 locations for concentric contractions. Similar results were observed for eccentric contractions. No other exercises revealed regional activation differences. When comparing the pooled proximal (medial and lateral) region across exercises, the LC demonstrated significantly greater activation than the modified single-leg squat, t18 = 5.20, P < .001, stiff-legged dead lift, t18 = 7.311, P < .001, and bilateral squat, F3,54 = 49.8, P < .001. Similar significantly greater levels were also found during the LC for the pooled distal, medial, and lateral regions. In addition, the modified single-leg squat electromyography was significantly greater at all regions in comparison with the stiff-legged dead lift and bilateral squat.

CONCLUSIONS

The data did not reveal consistent regional differences within the different exercises included in this study. However, the data indicate that the LC produces the highest hamstring activation in all regions across exercises. Inclusion of single-joint knee-flexion exercises would appear to be most beneficial for hamstrings development in a resistance-training program.

Role of the anconeus in the stability of a lateral ligament and common extensor origin-deficient elbow: an in vitro biomechanical study

BACKGROUND

The role of the anconeus in elbow stability has been a long-standing debate. Anatomic and electromyographic studies have suggested a potential role as a stabilizer. However, to our knowledge, no clinical or biomechanical studies have investigated its role in improving the stability of a combined lateral collateral ligament and common extensor origin (LCL + CEO)-deficient elbow.

METHODS

Seven cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An injured model was created by sectioning of the CEO and the LCL. The anconeus tendon and its aponeurosis were sutured in a Krackow fashion and tensioned to 10 N and 20 N using a transosseous tunnel. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated.

RESULTS

During active motion, the injured model resulted in a significant increase in varus angulation (P = .0001 for pronation; P = .001 for supination) and external rotation (P = .001 for pronation; P = .003 for supination) of the ulnohumeral articulation compared with the intact state. Tensioning of the anconeus significantly decreased the varus angulation (P = .006 for 10 N pronation; P = .0001 for 20 N pronation; P = .0001 for 10 N supination; P = .0001 for 20 N supination) and external rotation angle (P = .008 for 10 N pronation; P = .0001 for 20 N pronation; P = .0001 for 10 N supination; P = .0001 for 20 N supination) of the injured elbow.

CONCLUSIONS

In the highly unstable varus elbow orientation, anconeus tensioning restores the in vitro stability of a combined LCL + CEO-deficient elbow during simulated active motion with the forearm in both pronation and supination. These results may have several clinical implications in managing symptomatic lateral elbow instability.

ICA-based muscle-tendon units localization and activation analysis during dynamic motion tasks

This study proposed an independent component analysis (ICA)-based framework for localization and activation level analysis of muscle-tendon units (MTUs) within skeletal muscles during dynamic motion. The gastrocnemius muscle and extensor digitorum communis were selected as target muscles. High-density electrode arrays were used to record surface electromyographic (sEMG) data of the targeted muscles during dynamic motion tasks. First, the ICA algorithm was used to decompose multi-channel sEMG data into a weight coefficient matrix and a source matrix. Then, the source signal matrix was analyzed to determine EMG sources and noise sources. The weight coefficient vectors corresponding to the EMG sources were mapped to target muscles to find the location of the MTUs. Meanwhile, the activation level changes in MTUs during dynamic motion tasks were analyzed based on the corresponding EMG source signals. Eight subjects were recruited for this study, and the experimental results verified the feasibility and practicality of the proposed ICA-based method for the MTUs' localization and activation level analysis during dynamic motion. This study provided a new, in-depth way to analyze the functional state of MTUs during dynamic tasks and laid a solid foundation for MTU-based accurate muscle force estimation, muscle fatigue prediction, neuromuscular control characteristic analysis, etc.

Radial shortening osteotomy reduces radiocapitellar contact pressures while preserving valgus stability of the elbow

PURPOSE

Shortening osteotomy of the proximal radius might represent a potential salvage procedure in symptomatic radiocapitellar osteoarthritis, which could decrease radiocapitellar load while preserving the native radial head. In an in-vitro biomechanical investigation, we sought to determine whether shortening osteotomy of the proximal radius (1) decreases the radiocapitellar joint pressure upon axial loading and (2) retains valgus stability of the elbow. In addition, the anatomic configuration of the lesser sigmoid notch was evaluated to assess possible contraindications.

METHODS

Axial loading (0-400 N) and valgus torque (7.5 N m) over the full range of motion were applied to 14 fresh-frozen specimens before and after shortening osteotomy of the proximal radius by 2.5 mm. Radiocapitellar and ulnohumeral load distribution during axial compression was evaluated using a digital pressure mapping sensor. Valgus displacement was analyzed with a 3D camera system. The inclination angle (α) of the lesser sigmoid notch was assessed via 50 CT scans.

RESULTS

Up to axial loading of 250 N, shortening osteotomy caused a significant decrease in radiocapitellar contact pressures (p < 0.041). Valgus stability of specimens did not differ before and after shortening osteotomy (n.s.). The mean inclination angle (α) of the lesser sigmoid notch was 11.3° ± 6.3°. 46% had an inclination angle of ≤ 10° (type I). 46% had an inclination angle of 11°-20° (type II). In 8%, the inclination angle was >20° (type III).

CONCLUSION

Shortening osteotomy of the proximal radius can decrease radiocapitellar contact pressures during axial loading of up to 250 N. Primary valgus stability is not relevantly influenced by this procedure. In few patients, shortening osteotomy may cause radioulnar impingement of the radial head at the distal edge of the lesser sigmoid notch due to an inclination angle of >20°. Shortening osteotomy might be a promising treatment option to decrease pain levels in case of isolated radiocapitellar osteoarthritis.

Muscle Activity during Rapid Wrist Extension in People with Lateral Epicondylalgia

BACKGROUND

Individuals with lateral epicondylalgia (LE) have delayed upper limb reaction time (RT); however, it is unknown if the mechanisms of this dysfunction are related to neural processing or the affected forearm muscles. The aim of this study was to examine the timing of processes that occur before and after forearm muscles are activated during the RT task.

METHODS

Eleven LE (42 ± 11 yr) and 11 healthy controls (42 ± 11 yr) performed rapid wrist extension in response to an audio cue. Intramuscular EMG was obtained from extensor carpi radialis brevis (ECRB), extensor digitorum communis (EDC), extensor carpi ulnaris (ECU), and anconeus. Premotor time (PMT) was the duration from an audio cue to the onset of muscle activity, and motor time (MT) was the onset of muscle activity to the onset of wrist extension. Standard clinical assessments of LE were also performed.

RESULTS

RT was significantly slower (33; 95% CI, 1-66 ms) in the LE group. There were no group differences in PMT and the order of muscle activation. Instead, the MT of ECRB (18; 95% CI, 6-31 ms), EDC (12; 95% CI, 1-23 ms), ECU (28; 95% CI, 9-46 ms), and anconeus (33; 95% CI, 11-56 ms) showed significant delay in LE group. Regression analyses revealed that the duration of LE could predict RT, ECRB, and anconeus PMT, whereas cold pain threshold predicted ECRB MT.

CONCLUSIONS

Delayed RT in LE was predominantly caused by deficits in ECRB and EDC MT. This study provides preliminary evidence that in the people with longer LE symptoms, duration appeared to have faster RT, although confirmation of this finding is required before firm conclusions can be drawn.

Effect of Anconeus Muscle Blocking on Elbow Kinematics: Electromyographic, Inertial Sensors and Finite Element Study

The specific contribution of the anconeus muscle to elbow function is still uncertain. This study aimed to investigate the effect on elbow kinematics and kinetics of blocking anconeus using lidocaine. Ten healthy volunteers performed experimental trials involving flexion–extension and supination–pronation movements in horizontal and sagittal planes. Inertial sensors and surface electromyography were used to record elbow kinematics and kinetics and electrical activity from the anconeus, biceps and triceps brachii before and after blocking anconeus. Moreover, a finite element model of the elbow was created to further investigate the contribution of anconeus to elbow kinematics. The electrical activity results from the trials before blocking clearly indicated that activity of anconeus was increased during extension, suggesting that it behaves as an extensor. However, blocking anconeus had no effect on the elbow kinematics and kinetics, including the angular velocity, net torque and power of the joint. The electrical activity of the biceps and triceps brachii did not alter significantly following anconeus blocking. These results suggest that anconeus is a weak extensor, and the relative small contribution of anconeus to extension before blocking was compensated by triceps brachii. The finite element results indicated that anconeus does not contribute significantly to elbow kinematics.

Functional anatomy of the lateral collateral ligament of the elbow

INTRODUCTION

The aim of this study was to analyze the functional anatomy of the lateral collateral ligament complex (LCLC) and the surrounding forearm extensors.

MATERIALS AND METHODS

Using 81 human cadaveric upper extremities, the anatomy of the forearm extensors-especially the anconeus, supinator and extensor carpi ulnaris (ECU)-was analyzed. After removal of aforementioned extensors the functional anatomy of the LCLC was analyzed. The origin of the LCLC was evaluated for isometry. The insertion types of the lateral ulnar collateral ligament (LUCL) were analyzed and classified.

RESULTS

The ECU runs parallel to the RCL to dynamically preserve varus stability. The supinator and anconeus muscle fibers coalesce with the LCLC and lengthen during pronation. The anconeus fibers run parallel to the LUCL in full flexion. The LCLC consists of the annular ligament (AL) and the isometric radial collateral ligament (RCL). During elbow flexion, its posterior branches (LUCL) tighten while the anterior branches loosen. When performing a pivot shift test, the loosened LUCL fibers do not fully tighten in full extension. The LUCL inserts along with the AL at the supinator crest. Three different insertion types could be observed.

CONCLUSIONS

The LUCL represents the posterior branch of the RCL rather than a distinct ligament. It is non-isometric and lengthens during elbow flexion. The RCL was found to be of vital importance for neutralization of posterolateral rotatory forces. Pronation of the forearm actively stabilizes the elbow joint as the supinator, anconeus and biceps muscle work in unison to increase posterolateral rotatory stability.

In vivo measurement of fascicle length and pennation of the human anconeus muscle at several elbow joint angles

Ultrasound imaging has facilitated the reliable measure of the architectural variables fascicle length (LF ) and pennation angle (PA), at rest and during static and dynamic contractions in many human skeletal muscles in vivo. Despite its small size and very modest contribution to elbow extension torque, the anconeus muscle has proven a useful model for the study of neuromuscular function in health and disease. Recent single motor unit (MU) studies in the anconeus have reported discrete and identifiable individual trains of MU potentials from intramuscular electromyography (EMG) recordings during dynamic elbow extensions. It is unknown whether the anconeus has unique architectural features related to alterations in LF and PA throughout the elbow joint range of motion that may help explain these high-quality recordings. Previous anatomical studies have investigated this muscle in cadavers and at mainly one elbow joint angle. The purpose of this study was to measure in vivo PA and LF of the anconeus muscle in a relaxed state at different degrees of elbow flexion using ultrasonography. Ultrasound images were collected from 10 healthy males (25 ± 3 years) at 135°, 120°, 90°, 45°, and 0° of elbow flexion. Average values of LF decreased by 6 mm (10%), 6 mm (12%), and 4 mm (9%) from 135-120°, 120-90°, and 90-45° of elbow flexion, respectively, whereas average PA values increased by 1° (9%), 1° (8%), and 2° (14%) from 135-120°, 120-90°, and 45-0°, respectively. The results indicate that anconeus muscle architecture is dynamic, undergoing moderate changes with elbow joint excursion that are similar to other limb muscles reported elsewhere. The data obtained here are more comprehensive and representative of architectural changes at various elbow joint positions than those data reported in cadaveric studies. Furthermore, the results of this study indicate that despite experiencing similar relative changes in muscle architecture to other skeletal muscles about the elbow joint, the minimal absolute changes in LF of the anconeus likely contribute to the clarity of intramuscular EMG previously reported in this muscle.