Innervation of the Flexor Digitorum Profundus: A Systematic Review

Compound muscle action potential of whole-forearm flexors: A clinical biomarker for inclusion body myositis

Objective

This study aimed to investigate the potential of whole-forearm flexor muscle (WFFM) compound muscle action potential (CMAP) as a quantitative biomarker for inclusion body myositis (IBM) pathology.

Methods

We prospectively enrolled 14 consecutive patients (10 men and 4 women) diagnosed with IBM based on muscle biopsies. We evaluated the baseline-to-peak amplitude of the WFFM CMAP and other quantitative parameters, including grip and pinch strength, Inclusion Body Myositis Functional Rating Scale (IBMFRS) score, and other routine muscle CMAP amplitudes.

Results

The WFFM CMAP was strongly correlated with disease duration and the IBMFRS score. The WFFM CMAP on the more affected side was lower than that on the less affected side. Furthermore, grip power was strongly correlated with the WFFM CMAP, whereas lateral pinch strength was strongly correlated with the WFFM and first dorsal interosseous CMAPs. The 3-point pinch strength was also correlated with the WFFM CMAP.

Conclusions

This study demonstrates that the WFFM CMAP may serve as a biomarker of severity in IBM.

Significance

Identification of this biomarker can support drug development, diagnosis, prognosis, and treatment options for patients with IBM.

Ultrasonographic examination of the safe zone for medial needle approach towards the median-innervated flexor digitorum profundus muscle: Effect of changes in position of the forearm

The flexor digitorum profundus (FDP) is a forearm flexor muscle. Certain cases require the needle to be inserted accurately and safely into the deep, lateral portion of the FDP, which is innervated by the anterior interosseous nerve. In this study, we compared 2 techniques for approaching the median-innervated FDP (MFDP) medially, each according to the position of the forearm, supinated or pronated. The forearms of healthy volunteers without any musculoskeletal problems of the upper extremities were examined. Using high-resolution ultrasonography, the medial aspects of the forearms were scanned with elbows flexed at 90°. Using the images obtained, several parameters for distance and angle were measured in 2 different positions: forearm-supinated and forearm-pronated. Thirty-seven forearms from the volunteers were subject to examination. The angle α, which is the valid angle of insertion when approaching with the needle towards the deeply located MFDP, slightly increased from 22.89° to 23.41° when the forearm was pronated from the supinated position; however, this increase was not statistically significant. In contrast, the angle β, which is the safe angle of insertion when approaching with the needle towards the MFDP without contacting the ulnar nerve, was significantly increased from 41.40° to 46.80° upon forearm pronation. Because the safe angle of insertion of the needle medially into the MFDP increases with forearm pronation, the forearm-pronated position is recommended, instead of the forearm-supinated position, when inserting a needle into the MFDP in the medial aspect of the forearm.

High Median Nerve Paralysis: Is the Hand of Benediction or Preacher's Hand A Correct Sign?

High median nerve injuries are commonly presented in textbooks as adopting the typical posture of hand of benediction or preacher's hand. This study aimed to show that the hand of benediction or preacher's hand is incorrectly associated with a high median nerve paralysis.

METHODS

A retrospective review of four cases with a high median nerve injury is presented. Diagnosis of a high median nerve injury was performed by means of intraoperative findings, electrodiagnostic studies, or ultrasound imaging. None of the patients presented in this study had a hand of benediction on physical examination despite the presence of a high median nerve lesion.

RESULTS

All four patients with high median nerve injuries showed a similar hand posture when attempting to make a fist. Firstly, the index finger still flexed at the metacarpophalangeal joint because of the ulnar innervated interossei muscles. Secondly the thumb is completely abducted at the carpometocarpal joint and extended at the interphalangeal joint. Lastly, middle finger flexion is possible due to dual innervation of its flexor digitorum profundus by the ulnar nerve as well as due to the quadriga phenomenon.

CONCLUSIONS

The clinical appearance of a high median nerve palsy is different from the classical hand of benediction or preacher's hand posture pointing finger. We have shown that this incorrect association can result in delayed referral of patients with high median nerve injuries.

The muscular branching patterns of the ulnar nerve in fetal forearms

OBJECTIVE

We aimed to present our findings systematically by examining the muscular branching patterns of the ulnar nerve (UN) in the forearms of fetuses.

METHODS

This study was conducted on the 52 forearms of 26 formalin-fixed fetal cadavers with gestational ages varying between 19 and 37 weeks. The anatomical dissection was performed by using stereomicroscope with × 8 magnification. The numbers of muscular branches leaving UN and their order of leaving main nerve were noted down. The findings were classified according to the muscles they reached, and branching typing was done.

RESULTS

It was found that a total of 2-6 muscular branches left UN to reach flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP). UN was classified by separating into five main types according to the number of muscular branches, and these types were classified into 16 different branching patterns according to the order of branches leaving from the main trunk and going to FCU and FDP. The pattern where two branches left UN was classified as Type I (n = 6), three branches left was classified as Type II (n = 18), four branches left was classified as Type III (n = 24), five branches left was classified as Type IV (n = 3), and six branches left was classified as Type V (n = 1). Martin-Gruber connection occurred in 17 (32.7%) fetal forearms.

CONCLUSION

We believe that the information that UN can demonstrate different branching patterns on the forearm can help the surgeons to prevent complications that may develop in potential nerve injury during the selection and transfer of relevant branch.

Anatomy of the nerves, vessels, and muscular compartments of the forearm, as revealed by high-resolution ultrasound. Part 1: overall structure and forearm compartments

In recent decades, high-resolution ultrasound (HRUS) has revolutionized the morphological and structural evaluation of peripheral nerves and muscles, revealing details of the internal structure of the neural fascicles and muscle architecture. Applications range from diagnostics to interventional procedures. The anatomy of the forearm region is complex, with several muscles and an extensive network of vessels and nerves. To guarantee the success of the evaluation by HRUS, knowledge of the normal anatomy of the region is essential. The aim of these two companion articles is to present the normal anatomy of the nerves and compartments of the forearm, as revealed by HRUS, as well as the relationships between the main vessels and nerves of the region. Part 1 aims to review the overall structure of nerves, muscles and tendons, as seen on HRUS, and that of the forearm compartments. We present a practical approach, with general guidelines and tips on how best to perform the study. Part 2 is a pictorial essay about compartment vascularization and cutaneous innervation. Knowledge of the normal anatomy of the forearm improves the technical quality of the examinations, contributing to better diagnoses, as well as improving the performance and safety of interventional procedures.

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.