Variations in innervation of the flexor digitorum profundus muscle

The 3D muscle morphology and intramuscular innervation of the digital bellies of flexor digitorum profundus: Clinical implications for botulinum toxin injection sites

Spasticity of flexor digitorum profundus is frequently managed with botulinum toxin injections. Knowledge of the 3D morphology and intramuscular innervation of the digital bellies of flexor digitorum profundus is necessary to optimize the injections. The purpose of this study was to digitize and model in 3D the contractile and connective tissue elements of flexor digitorum profundus to determine muscle morphology, model and map the intramuscular innervation and propose sites for botulinum toxin injection. Fiber bundles (FBs)/aponeuroses and intramuscular nerve branches were dissected and digitized in 12 formalin embalmed cadaveric specimens. Cartesian coordinate data were reconstructed into 3D models as in situ to visualize and compare the muscle morphology and intramuscular innervation patterns of the bellies of flexor digitorum profundus. The 3rd, 4th and 5th digital bellies were superficial to the 2nd digital belly and located adjacent to each other in all specimens. Each digital belly had distinct intramuscular innervation patterns. The 2nd digital belly received intramuscular branches from the anterior interosseus nerve (AIN). The superior half of the 3rd digital belly was innervated intramuscularly by the ulnar nerve (n = 4) or by both the anterior interosseus and ulnar nerves (n = 1). The inferior half of the belly received dual innervation from the anterior interosseus and ulnar nerves in 2 specimens, or exclusively from the AIN (n = 2) or the ulnar nerve (n = 1). The 4th digital belly was innervated by intramuscular branches of the ulnar nerve. One main branch, after coursing through the 4th digital belly, entered the lateral aspect of the 5th digital belly and arborized intramuscularly. The morphology of the FBs, aponeuroses and intramuscular innervation of the digital bellies of FDP were mapped and modelled volumetrically in 3D as in situ. Previous studies were not volumetric nor identified the course of the intramuscular nerve branches within each digital belly. Based on the intramuscular innervation of each of the digital bellies, one possible optimized botulinum toxin injection location was proposed. This injection location, at the junction of the superior and middle thirds of the forearm, would be located in dense nerve terminal zones of the anterior interosseus and ulnar nerves. Future anatomical and clinical investigations are necessary to evaluate the efficacy of these anatomical findings in the management of spasticity.

MR elastography-based slip interface imaging (SII) for functional assessment of myofascial interfaces: A feasibility study

PURPOSE

Abnormal adherence at functional myofascial interfaces is hypothesized as an important phenomenon in myofascial pain syndrome. This study aimed to investigate the feasibility of MR elastography (MRE)-based slip interface imaging (SII) to visualize and assess myofascial mobility in healthy volunteers.

METHODS

SII was used to assess local shear strain at functional myofascial interfaces in the flexor digitorum profundus (FDP) and thighs. In the FDP, MRE was performed at 90 Hz vibration to each index, middle, ring, and little finger. Two thigh MRE scans were performed at 40 Hz with knees flexed and extended. The normalized octahedral shear strain (NOSS) maps were calculated to visualize myofascial slip interfaces. The entropy of the probability distribution of the gradient NOSS was computed for the two knee positions at the intermuscular interface between vastus lateralis and vastus intermedius, around rectus femoris, and between vastus intermedius and vastus medialis.

RESULTS

NOSS map depicted distinct functional slip interfaces in the FDP for each finger. Compared to knee flexion, clearer slip interfaces and larger gradient NOSS entropy at the vastus lateralis-vastus intermedius interface were observed during knee extension, where the quadriceps are not passively stretched. This suggests the optimal position for using SII to visualize myofascial slip interface in skeletal muscles is when muscles are not subjected to any additional force.

CONCLUSION

The study demonstrated that MRE-based SII can visualize and assess myofascial interface mobility in extremities. The results provide a foundation for investigating the hypothesis that myofascial pain syndrome is characterized by changes in the mobility of myofascial interfaces.

Cadaveric study of flexor digitorum profundus and superficialis and flexor pollicis longus innervation patterns for application in selective neurectomy

PURPOSE

Spasticity management in finger flexors (flexor digitorum profundus and superficialis and flexor pollicis longus) is a challenge. Recent studies demonstrated the short- and long-term efficacy of selective and hyperselective neurectomy for the spastic upper limb. However, hyperselective neurectomy of flexor digitorum profundus and flexor digitorum superficialis branches was incomplete, without impairing their muscular body and function. This cadaveric study describes a novel medial approach in the forearm, to reach all the muscular branches: flexor digitorum superficialis and profundus and flexor pollicis longus.

MATERIAL AND METHODS

Fourteen cadaveric fresh frozen upper limbs were used. The feasibility of the medial surgical approach was studied, as well as the number, length and point of emergence of the muscular branches from the median and ulnar nerves to the flexor pollicis longus, flexor digitorum profundus and flexor digitorum superficialis.

RESULTS

The medial approach to the forearm gave access to all the muscular branches from the median and ulnar nerves to the flexor pollicis longus, flexor digitorum superficialis and flexor digitorum profundus, in all cases. A Martin Gruber communicating branch was found in 7 cases out of 14.

CONCLUSION

The medial approach to the forearm gave access to all the muscular branches from the median and ulnar nerve to the flexor pollicis longus, flexor digitorum superficialis and flexor digitorum profundus, without extensive transmuscular dissection of the pronator teres or flexor digitorum superficialis muscles. This approach opens the way for selective neurectomy of the flexor pollicis longus, flexor digitorum profundus and flexor digitorum superficialis muscles.

LEVEL OF EVIDENCE

IV.

Challenges in evaluating forearm muscle activity based on the compound muscle action potential of the flexors of the whole forearm

Objective

Muscle strength, which correlates with the compound muscle action potential (CMAP), can also be estimated by measuring the CMAP. Therefore, we evaluated the CMAP of the flexor muscles of the whole forearm to identify their muscle strength.

Methods

Fourteen healthy volunteers were enrolled. The elbow was determined to be the stimulation point, and the recording site for the flexor muscles of the whole forearm was set at approximately 8 cm distal to the elbow. We prospectively evaluated the baseline-to-peak amplitude of the CMAP of the whole forearm flexor muscles (WFFM), including that obtained from the median nerve stimulation (WFFMm), ulnar nerve stimulation (WFFMu), and their sum (WFFMsum). Additionally, we analyzed the relationships between WFFMm and WFFMu amplitudes with other quantitative parameters, including grip strength and routine CMAP amplitudes.

Results

The CMAP's test-retest analysis revealed high reliability. Grip power was significantly correlated with WFFMm and WFFMsum and mildly correlated with WFFMu. Tip-pinch strength with WFFMm and flexor pollicis longus (FPL) measurements correlated significantly. Lateral-pinch strength was significantly correlated with the first dorsal interosseous muscle (FDI) measurements but not with WFFM. The abductor digiti minimi (ADM) and abductor pollicis brevis (APB) were not correlated with grip power or pinch strength.

Conclusions

By electrophysiology examination, this study demonstrated that WFFMm is involved in grip power and other pinch strengths. This method may serve as a novel tool for measurement of distal muscle strengths.

Significance

This is the first study to attempt to evaluate the muscle strength of forearm flexor muscles by measuring the CMAP.

Safe Approach for Flexor Digitorum Profundus I and II Using the Palmaris Longus Tendon

OBJECTIVE

To investigate a safe and accurate approach to achieve needle insertion for electromyography (EMG) of the flexor digitorum profundus (FDP) I and II muscles by identifying the anatomic relationship between the palmaris longus (PL) tendon, FDP muscle, and neurovascular bundle using ultrasonography.

DESIGN

Descriptive study SETTING: Department of physical medicine and rehabilitation.

PARTICIPANTS

Healthy individuals (age, 20-70y) without any diseases (N=29; 15 men, 14 women; 58 forearms).

INTERVENTIONS

Ultrasonography.

MAIN OUTCOME MEASURES

The FDP I and II muscles were transversely scanned on the volar aspect of the forearm at the junction of the middle and distal third between the medial epicondyle and ulnar styloid process. The distances and angles from the medial border of the PL tendon to FDP I, FDP II, and median nerve were measured.

RESULTS

The probability of damage to the neurovascular structures and the accuracy of entering the FDP I and II muscles were calculated for 3 imaginary needle insertion angles (61.7°, 100.6°, and 90°). When the needle was inserted at an angle of 61.7°, it reached FDP I with an accuracy of 91.4%. Upon needle insertions at 90° and 100.6°, the needle reached FDP II with accuracies of 90% and 89.6%, respectively. In all 3 cases (61.7°, 90°, and 100.6°), there was no chance of penetrating the blood vessels or nerves.

CONCLUSION

EMG of FDP I and II can be performed precisely and safely with the anterior approach at the distal one-third between the medial epicondyle and ulnar styloid process using the PL tendon.

Pseudo-Anterior Interosseus Nerve Syndrome: A Case Report and a Review of Clinical Signs, Pathology and Functional Anatomy of the Precision Grip

Precision grip, a prehensile function of humans, is exacted through the action of the median nerve and its main tributary, the anterior interosseus nerve (AIN). In the forearm, the AIN can be subject to nerve entrapment by tendinous and fibrous arches or accessory and variant muscles. It is also vulnerable to trauma of the upper arm and forearm. To the neurologist, an isolated neuritis or an immune-mediated medial cord or lower trunk brachial plexopathy (Parsonage-Turner syndrome) is the usual mode of presentation. When the spread of muscle weakness is beyond the territory of the AIN, the syndrome is referred to as a pseudo-AIN. The AIN is grouped into fascicles that are compartmentalized separately from the median nerve proper, and trauma in the upper arm may selectively involve the AIN. We present a case of pseudo-AIN following elbow arthroscopic surgery and outline the pathology, clinical signs, and functional anatomy of the AIN and the precision grip.

Median Nerve Injury After Removal of Subdermal Implantable Contraceptive

Background: Subdermal implantable contraceptives are highly effective, approved in over 60 countries, and used by millions of women. Due to simple insertion and removal protocols, these procedures are often performed in the outpatient clinic setting, and procedural complications are rare. However, given the location of the implant in the medial antebrachial interval, there is a risk of neurovascular injury, especially with malpositioned or deeply placed implants. Methods: We present a case of proximal median nerve injury leading to severe neuropathy after attempted removal of a subdermal implantable contraceptive requiring neurolysis and tendon transfers. Results: At 6 months post surgery, the patient regained flexion of the index interphalangeal joints and protective sensation in the thumb and index fingers. Conclusions: Subdermal implant retrieval can lead to nerve injury, despite the relative simplicity of the procedure. If difficulty is encountered, imaging or open retrieval should be considered. Improvement in function can be gained through operative interventions including neurolysis and tendon transfers in the setting of severe neuropathy.

Magnetic resonance imaging patterns of mononeuropathic denervation in muscles with dual innervation

Magnetic resonance imaging (MRI) of mononeuropathy in muscles with dual innervation depicts geographic denervation corresponding to the affected nerve. Knowledge of the normal distribution of a muscle's neural supply is clinically relevant as partial muscle denervation represents a potential imaging pitfall that can be confused with other pathology, such as muscle strain. This article reviews the normal innervation pattern of extremity muscles with dual supply, providing illustrative examples of mononeuropathy affecting such muscles.

Innervation of the Flexor Digitorum Profundus: A Systematic Review

Purpose

The aim of this study was to review the innervation of the flexor digitorum profundus (FDP).

Methods

In PubMed and Scopus, terms (Flexor digitorum profundus OR FDP) AND (innervation OR nerve) were used, resulting in 233 and 281 papers, respectively. After excluding 142 duplicates, 73 abstracts were reviewed. Forty-seven abstracts were excluded, 26 full papers were reviewed, and 17 papers were analyzed.

Results

In most cases (97.6%), the index FDP was innervated by the anterior interosseous nerve (AIN). Dual innervation from the AIN and ulnar nerve (UN) was observed in 2.4% of papers. In majority (76.8%), the middle FDP received dual innervation from the AIN and the UN. The rest was innervated by the AIN only (22.0%) or the UN only (1.2%). In most cases (85.4%), the ring FDP was innervated by the UN only. The rest (14.6%) received dual innervation from the AIN and the UN. In majority of cases (64.6%), the little FDP was innervated by the UN only. The rest (35.4%) received dual innervation from the AIN and the UN. The AIN entered the FDP at 107.63 (8.80) mm from the elbow, corresponding to 26.75% (2.17%) of the forearm length, measured proximally. The average number of AIN branches to the FDP was 2.27 (1.33). The average number of UN branches to the FDP was 1.37 (0.94). In 8.8% of limbs, a communicating branch supplied the FDP. Among the limbs with a communicating branch, 32.3% had branches supplying the FDP.

Conclusion

The results of this study may be useful in managing nerve injury patients.

Low Median Nerve Transfers (Opponensplasty)

Opposition is the placement of the thumb opposite the fingers into a position from which it can work. This motion requires thumb palmar abduction, flexion, and pronation, which are provided by the abductor pollicis brevis, flexor pollicis brevis (FPB), and opponens pollicis. In the setting of a median nerve palsy, this function is typically lost, although anatomic variations and the dual innervation of the FPB may prevent complete loss at times. There are multiple well described and accepted tendon transfers to restore opposition, none of which have been proven to be superior to the others.

High Median Nerve Injuries

The median nerve serves a crucial role in extrinsic and intrinsic motor and sensory function to the radial half of the hand. High median nerve injuries, defined as injuries proximal to the anterior interosseous nerve origin, therefore typically result in significant functional loss prompting aggressive surgical management. Even with appropriate recognition and contemporary nerve reconstruction, however, motor and sensory recovery may be inadequate. With isolated persistent high median nerve palsies, a variety of available tendon transfers can improve key motor functions and salvage acceptable use of the hand.

Vibration imaging for localization of functional compartments of the extrinsic flexor muscles of the hand

PURPOSE

To develop and test an MRI-based imaging technique for the localization of the functional compartments of the functionally finger-specific, yet anatomically indistinct, flexor muscles of the hand.

MATERIALS AND METHODS

A total of six normal healthy volunteers were involved in five studies in which individual fingers were vibrated with mechanical actuators and the resultant motion within the corresponding functional compartments of the flexor muscles, mechanically transferred through the structurally connected tendons, was imaged with a phase-contrast MR imaging technique that is highly sensitive to cyclic motion. The motion amplitude and relative phase relationship between the functional compartments of various muscles and fingers were obtained and analyzed from these images as a means to differentiate the various subcompartments.

RESULTS

The results show that this technique provides a detailed mapping of the regions of the complex flexor muscle compartments that correspond to each digit for both the flexor digitorum profundus and the flexor digitorum superficialis. The results also demonstrate the presence of mechanical interdependence between the flexor muscles.

CONCLUSION

It is concluded from the results that localization of the finger-specific subcompartments of the forearm flexor muscles can be performed with this technique.

Magnetic resonance elastography: a review

Magnetic resonance elastography (MRE) is a rapidly developing technology for quantitatively assessing the mechanical properties of tissue. The technology can be considered to be an imaging-based counterpart to palpation, commonly used by physicians to diagnose and characterize diseases. The success of palpation as a diagnostic method is based on the fact that the mechanical properties of tissues are often dramatically affected by the presence of disease processes, such as cancer, inflammation, and fibrosis. MRE obtains information about the stiffness of tissue by assessing the propagation of mechanical waves through the tissue with a special magnetic resonance imaging technique. The technique essentially involves three steps: (1) generating shear waves in the tissue, (2) acquiring MR images depicting the propagation of the induced shear waves, and (3) processing the images of the shear waves to generate quantitative maps of tissue stiffness, called elastograms. MRE is already being used clinically for the assessment of patients with chronic liver diseases and is emerging as a safe, reliable, and noninvasive alternative to liver biopsy for staging hepatic fibrosis. MRE is also being investigated for application to pathologies of other organs including the brain, breast, blood vessels, heart, kidneys, lungs, and skeletal muscle. The purpose of this review article is to introduce this technology to clinical anatomists and to summarize some of the current clinical applications that are being pursued.

Cyclic motion encoding for enhanced MR visualization of slip interfaces

PURPOSE

To develop and test a magnetic resonance imaging-based method for assessing the mechanical shear connectivity across tissue interfaces with phantom experiments and in vivo feasibility studies.

MATERIALS AND METHODS

External vibrations were applied to phantoms and tissue and the differential motion on either side of interfaces within the media was mapped onto the phase of the MR images using cyclic motion encoding gradients. The phase variations within the voxels of functional slip interfaces reduced the net magnitude signal in those regions, thus enhancing their visualization. A simple two-compartment model was developed to relate this signal loss to the intravoxel phase variations. In vivo studies of the abdomen and forearm were performed to visualize slip interfaces in healthy volunteers.

RESULTS

The phantom experiments demonstrated that the proposed technique can assess the functionality of shear slip interfaces and they provided experimental validation for the theoretical model developed. Studies of the abdomen showed that the slip interface between the small bowel and the peritoneal wall can be visualized. In the forearm, this technique was able to depict the slip interfaces between the functional compartments of the extrinsic forearm muscles.

CONCLUSION

Functional shear slip interfaces can be visualized sensitively using cyclic motion encoding of externally applied tissue vibrations.

Peripheral nerve injuries of the pediatric hand: issues in diagnosis and management

Peripheral nerve injuries resulting in significant neural disruption frequently present complex management challenges. Typically the product of fracture, dislocation, or crush injuries, pediatric peripheral nerve injuries may be difficult to accurately characterize. Thorough clinical examination coupled with electromyogram and neurophysiologic studies are extremely useful. When possible, primary repair should be attempted. If, however, defect size precludes primary reanastomosis, use of a nerve graft may be advantageous. Alternatively, nerve conduits, such as veins, pseudosheaths, and bioabsorbable tubes, are also effective facilitators of nerve regeneration. Although nerve injuries of the pediatric hand often present complex challenges, a thorough knowledge of diagnostic methods and advances in surgical interventions offers better outcomes.

Location of nerve entry points of flexor digitorum profundus

The aim of this study was to elucidate the anatomical location of nerve entry points of Flexor digitorum profundus (FDP) and its implications for non-surgical neurolysis. A total of 21 amputated forearms of 11 Korean fresh cadavers were dissected. Two transverse x-axes joined the medial and lateral epicondyles and the radial and ulnar styloid processes. The longitudinal y-axis joined the midpoints of the proximal and distal transverse x-axes. The locations of the points were marked relative to the forearm length (x) and forearm width (y). The number of nerve entry points from median nerve and ulnar nerve were average 3.91 +/- 0.62 (range 3-5, median 4) and 2.14 +/- 0.65 (range 1-3, median 2) respectively. Most (82.9%) nerve entry points of FDP from the median nerve were within two circles, with 15 mm diameter. The two circles were on medial 1/10 of forearm width from the y-axis, and on proximal 1/3 (1:2) and 2/5 (2:3) of forearm length on x-axis. Most (80.0%) nerve entry points of the ulnar nerve innervating FDP were within a 15 x 30 mm rectangle. Its center was located at +26.5% on x-axis and -36.0% on y-axis. The nerve entry points used to be selected in performing non-surgical neurolysis with either ethyl alcohol (50%) or phenol (5-12%).

Innervation of the levator ani muscles: description of the nerve branches to the pubococcygeus, iliococcygeus, and puborectalis muscles

We described the innervation of the levator ani muscles (LAM) in human female cadavers. Detailed pelvic dissections of the pubococcygeus (PCM), iliococcygeus (ICM), and puborectalis muscles (PRM) were performed on 17 formaldehyde-fixed cadavers. The pudendal nerve and the sacral nerves entering the pelvis were traced thoroughly, and nerve branches innervating the LAM were documented. Histological analysis of nerve branches entering the LAM confirmed myelinated nerve tissue. LAM were innervated by the pudendal nerve branches, perineal nerve, and inferior rectal nerve (IRN) in 15 (88.2%) and 6 (35.3%) cadavers, respectively, and by the direct sacral nerves S3 and/or S4 in 12 cadavers (70.6%). A variant IRN, independent of the pudendal nerve, was found to innervate the LAM in seven (41.2%) cadavers. The PCM and the PRM were both primarily innervated by the pudendal nerve branches in 13 cadavers (76.5%) each. The ICM was primarily innervated by the direct sacral nerves S3 and/or S4 in 11 cadavers (64.7%).

Incomplete functional subdivision of the human multitendoned finger muscle flexor digitorum profundus: an electromyographic study

The human flexor digitorum profundus (FDP) sends tendons to all 4 fingers. One might assume that this multitendoned muscle consists of 4 discrete neuromuscular compartments each acting on a different finger, but recent anatomical and physiological studies raise the possibility that the human FDP is incompletely subdivided. To investigate the functional organization of the human FDP, we recorded electromyographic (EMG) activity by bipolar fine-wire electrodes simultaneously from 2 or 4 separate intramuscular sites as normal human subjects performed isometric, individuated flexion, and extension of each left-hand digit. Some recordings showed EMG activity during flexion of only one of the 4 fingers, indicating that the human FDP has highly selective core regions that act on single fingers. The majority of recordings, however, showed a large amount of EMG activity during flexion of one finger and lower levels of EMG activity during flexion of an adjacent finger. This lesser EMG activity during flexion of adjacent fingers was unlikely to have resulted from recording motor units in neighboring neuromuscular compartments, and instead suggests incomplete functional subdivision of the human FDP. In addition to the greatest agonist EMG activity during flexion of a given finger, most recordings also showed EMG activity during extension of adjacent fingers, apparently serving to stabilize the given finger against unwanted extension. Paradoxically, the functional organization of the human FDP-with both incomplete functional subdivision and highly selective core regions-may contribute simultaneously to the inability of humans to produce completely independent finger movements, and to the greater ability of humans (compared with macaques) to individuate finger movements.