Dynamic ultrasound evaluation of median nerve mobility at the wrist: implications for surgical safety

Forearm position–dependent variations in the carpal tunnel safe zone: an ultrasonographic anatomical rationale for a pronation-based injection concept

Forearm Supination Increases the Safety Corridor and Target Exposure for Ultrasound-Guided Flexor Pollicis Longus Injection: A Prospective Study in Healthy Adults

Background/Objectives: Ultrasound-guided flexor pollicis longus (FPL) injection is limited by the muscle’s deep location and its proximity to the cephalic vein (CV) and superficial branch of the radial nerve (SBRN). We aimed to identify the wrist and forearm posture producing the largest measured corridor width and target exposure. Methods: This prospective single-center study evaluated 51 forearms from 27 healthy adult volunteers with full range of motion, using transverse ultrasound of the distal volar forearm in six standardized positions. Two corridors were measured: CV-to-SBRN (L1, Approach A) and CV-to-radial-cortex apex (L2, Approach B), with FPL exposure height (F). Results: L2 was present in all limbs and was wider with forearm supination than in neutral (supination [SUP], +2.36 mm; flexion plus supination [F+SUP], +2.05 mm; extension plus supination [E+SUP], +2.66 mm; each p < 0.001), an ~40% increase; the three supination postures did not differ. F increased across the same postures and was greatest in E+SUP (+2.32 mm), which did not differ from SUP. L1 was absent in 12–28% of limbs and, where present, was narrower with supination (both p < 0.001). Conclusions: In healthy adults, forearm supination widened the safety corridor and increased target exposure. Applicability to spasticity requires confirmation.

[Effects of wrist dorsiflexion and palmar flexion on median nerve displacement and cross-sectional area in patients with carpal tunnel syndrome].

Localizing the course of the radial nerve based on anatomical landmarks: A cadaveric study.

Background Surgeons treating humeral shaft fractures must be able to reliably locate the radial nerve in the posterior arm to limit iatrogenic injury. This study aims to improve the understanding of radial nerve anatomy by increasing the sample size, comparing bilateral upper extremities, and analyzing the impact of sex on its location. Methods Twenty-five pairs (n = 50) of fresh cadaveric upper extremities were studied with the cadaver in the lateral position. The shoulder was abducted and internally rotated and the elbow flexed to 90° and supported, as done intraoperatively. A triceps-splitting approach was performed and the radial nerve was identified in situ. Distances were recorded, using an electromagnetic digitizer, taken from the medial epicondyle to the proximal and distal edges of where the radial nerve crossed the posteromedial border of the humerus. Two measurements were taken on the ipsilateral extremity using the lateral epicondyle and posterolateral border of the humerus as reference points. The contralateral extremity was measured using the same protocol. A midpoint between the proximal and distal edges of the radial nerve was then calculated for its crossing on both the medial and lateral borders of the humerus. Results The radial nerve, on average, crosses the posterior humerus 17.1 cm and 12.5 cm proximal to the medial and lateral epicondyles, respectively. There was no difference when matched pairs were compared bilaterally. The radial nerve was between 0.93 cm and 1.06 cm closer to the epicondyles in females than males, a statistically significant difference. Conclusions The increase in sample size and comparison between sexes provides a more reliable location for where to expect the radial nerve in the posterior arm. This improved understanding may help surgeons better anticipate the location of the radial nerve during operative repair of adjacent injured structures, thereby reducing the risk of iatrogenic nerve injury. Level of evidence V.

Nerve Transfers to Rebalance the Spastic Wrist: An Anatomical Feasibility Study.

PURPOSE Spastic wrist flexion deformities result from an imbalance between spastic wrist flexors and weak or paralyzed wrist extensors. Nerve transfers offer the potential to restore this balance by combining neurotomy of the spastic donor nerve with reinnervation of the paralyzed recipient muscle. This study evaluated the anatomic feasibility of addressing the spastic wrist flexion deformity by transferring a motor branch from the flexor carpi ulnaris (FCU) to the extensor carpi radialis brevis (ECRB) and/or longus extensor carpi radialis (ECRL). METHODS Ten fresh-frozen cadaveric upper-extremity specimens were dissected. Motor branches to the FCU were identified through an incision between its two heads. The radial nerve branches to the ECRL and ECRB were exposed via a separate curvilinear incision within the antecubital fossa. The number of motor branches, muscle entry points, and length available for nerve transfer was recorded for each motor branch relative to the interepicondylar line (IEL). RESULTS The ECRL received one to three motor branches, entering the muscle at a median distance 1.6 cm distal to the IEL (range: 4 cm proximal to 6.4 cm distal). The median branch length available for transfer was 3.8 cm (range: 1.5-7.0 cm). The ECRB received one to three motor branches, entering the muscle at a median of 2.7 cm distal to the IEL (range: 1.7-8.0 cm distal). The median maximal branch length was 5.5 cm (range: 4.0-9.0 cm). The FCU had two to three motor branches, median muscle entry point 2.5 cm distal to the IEL (range 0 to 8.0 cm distal), and median maximal branch length of 3.3 cm (range: 1.6-5.2 cm). Direct, tension-free coaptation of the FCU to ECRB motor nerve was feasible in 90% specimens and the FCU to ECRL motor nerve in 50% of specimens. CONCLUSIONS FCU to ECRB nerve transfer was anatomically feasible in the majority specimens and may offer a possible surgical option to rebalance resting wrist posture and function in patients with spastic wrist flexion deformities. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic, IV.

Diagnostic Musculoskeletal Ultrasound in the Evaluation of the Carpal Tunnel and Median Nerve

The carpal tunnel is a fibro-osseous canal at the wrist that is formed by the retinaculum and bony structures. The superficial border is composed of the flexor retinaculum, the floor of the tunnel is formed by the carpal bones, the medial (ulnar) border by the hamate, and the lateral (radial) border by the trapezium. Contents that originate in the forearm and run distally through the carpal tunnel include the finger and thumb flexors and the median nerve. Carpal tunnel syndrome, when the median nerve becomes compressed or entrapped, occurs due to various issues that will be discussed in this paper. Diagnostic musculoskeletal ultrasound (MSKUS) offers a portable, real-time, and cost-effective alternative that is gaining traction in rehabilitation and sports medicine settings. MSKUS has emerged as a valuable, non-invasive imaging modality for evaluating the size of the carpal tunnel and median nerve at the level of the wrist. MSKUS is excellent at detecting changes in carpal tunnel size, median nerve composition, thickness, and continuity. This manuscript will review the utility of MSKUS in evaluating carpal tunnel syndrome, including anatomy, common injury mechanisms, sonographic techniques, and clinical implications for those in the rehabilitation profession. Due to the confined area within the carpal tunnel and the number of structures that traverse through it, it is a very common site of pathology and symptoms. With a proper medical history and clinical examination, diagnosis is straightforward for this pathology. By integrating MSKUS into clinical practice, providers can improve the accuracy of diagnosis, enhance diagnostic confidence, monitor healing progression, and guide rehabilitation strategies to optimal patient outcomes for those with carpal tunnel overuse or injury.