In vivo evidence of lumbricals incursion into the carpal tunnel in healthy hands: An ultrasonographic cross sectional study

Motion mapping and positioning of lumbrical muscles in the carpal tunnel-a cadaveric study

Aims and objectives

Dynamic incursion of lumbrical muscle proximal to the distal edge of transverse carpal ligament (TCL) has been long debated for its role in causing median nerve compression in the carpal tunnel. This study aims to evaluate the pattern of lumbrical incursion into the carpal tunnel in various finger positions and determine their extent of presence and relationship with respect to the TCL and to each other in the carpal tunnel.

Materials & methods

Dissection of 30 fresh frozen cadaveric hands was done to map the lumbrical muscles. The distance from each lumbrical muscle's proximal origin to the TCL's distal edge was measured using a Vernier caliper in three finger positions namely full extension, lumbrical, and full flexion position. Statistical tests like paired t-test, ANOVA and Chi-Square test were used to evaluate the mean changes in lumbrical incursion, percentage of incursion, relative positions and the proportion of hands showing lumbrical origins proximal to the TCL.

Results

The second lumbrical exhibited the highest mean incursion in all finger positions, followed by the third. Significant increases in incursion were observed from full extension to lumbrical position and from lumbrical position to full flexion in all lumbricals. The number of hands with lumbrical origins proximal to the TCL increased significantly from complete extension to complete flexion.

Conclusions

Lumbrical incursion significantly increases the content within the carpal tunnel with various finger positions. In full flexion, there is significant pressure of lumbricals within the tunnel. Hence, along with the tendons and median nerve, the lumbricals should be considered a dynamic content of the carpal tunnel. These muscles could 1significantly contribute to idiopathic Carpal tunnel syndrome in the backdrop of alteration in tunnel size or content. The second lumbrical, due to its proximal-most origin, is pivotal in this process.

Level of evidence

Level V.

The Elias University Hospital Approach: A Visual Guide to Ultrasound-Guided Botulinum Toxin Injection in Spasticity: Part I-Distal Upper Limb Muscles

Post-stroke spasticity significantly impairs upper limb function and quality of life. Ultrasound-guided botulinum toxin-A (BoNT-A) injections have become a cornerstone of management, enhancing precision and safety. This paper offers a comprehensive guide for clinicians on ultrasound-guided BoNT-A injections for distal upper limb muscles. Each muscle is detailed in terms of its role in spasticity management, ultrasound identification with key anatomical landmarks, clinical relevance, and injection strategies. Motor points, traditionally identified through anatomical studies or electromyography (EMG), are precisely localized using a musculoskeletal ultrasound by targeting the point of maximum muscle thickness, often corresponding to the motor point. The authors present their clinical method, developed at Elias University Hospital (EUH), to refine BoNT-A injection practices. This approach enhances efficacy, reduces dosage requirements, and improves patient outcomes. The paper also explores unique ultrasound characteristics of spastic muscles, such as their relationship with peripheral nerves, adjacent vascular and muscular structures, and intra- and intermuscular fascia, to guide clinicians in targeting functional muscle tissue. This guide is illustrated with representative ultrasound images and clinical diagrams and provides practical insights into anatomical relationships and injection techniques. Part I focuses on distal upper limb muscles, with Part II addressing proximal upper limb muscles.

Association Between Thenar Musculature and Carpal Tunnel Syndrome

Background: Dynamic forces acting on the transverse carpal ligament (TCL) may influence the mechanics of the carpal tunnel (CT), thus affecting the occurrence of CT syndrome (CTS). Previous studies demonstrated an association between muscle overlying the CT and the diagnosis of CTS. Understanding the location of insertion/origin of the thenar musculature will allow mechanical analysis of the forces applied to the TCL during performance of individual tasks. Our purpose was to determine the location of muscle overlying the CT on magnetic resonance imaging (MRI) in CTS and controls. Methods: Case-control study of 21 normal adult wrist MRI scans. MRI measurements were performed on an axial cut at the level of the hook-of-hamate. Median nerve cross-sectional area (CSA), median nerve shape and increased signal intensity within the CT were associated with CTS. The amount and length of muscle crossing the midline and the CT on the same cut was measured and the association with the occurrence of CTS was analysed. Results: We found an inverse relationship between the amount of muscle crossing the midline and the size of the CT, and a direct relationship with occurrence of CTS p less than 0.01, but no differences regarding length of muscle crossing the midline. Conclusions: This study supports an association between the thenar musculature location relative to the CT and the predictors of CTS on MRI. Since the location of muscle origin/insertion is variable, their effect may differ accordingly, therefore, further study is needed to describe the exact location of origin/insertion and its differential dynamic or static effect on the pathogenesis of CTS. Level of Evidence: Level IV (Diagnostic).

Ultrasound of the palmar aspect of the hand: normal anatomy and clinical applications of intrinsic muscles imaging

Intrinsic hand muscles play a fundamental role in tuning the fine motricity of the hand and may be affected by several pathologic conditions, including traumatic injuries, atrophic changes induced by denervation, and space-occupying masses. Modern hand surgery techniques allow to target several hand muscle pathologies and, as a direct consequence, requests for hand imaging now carry increasingly complex diagnostic questions. The progressive refinement of ultrasound technology and the current availability of high and ultra-high frequency linear transducers that allow the investigation of intrinsic hand muscles and tendons with incomparable resolution have made this modality an essential tool for the evaluation of pathological processes involving these tiny structures. Indeed, intrinsic hand muscles lie in a superficial position and are amenable to investigation by means of transducers with frequency bands superior to 20 MHz, offering clear advantages in terms of resolution and costs compared to magnetic resonance imaging. In addition, ultrasound allows to perform dynamic maneuvers that can critically enhance its diagnostic power, by examining the questioned structure during stress tests that simulate the conditions eliciting clinical symptoms. The present article aims to review the anatomy, the ultrasound scanning technique, and the clinical application of thenar, hypothenar, lumbricals and interossei muscles imaging, also showing some examples of pathology involving these structures.