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Background The pronator quadratus (PQ) is a flat muscle located in the distal forearm, between the radius and ulna, primarily responsible for forearm pronation. Given its frequent involvement in volar surgical approaches to the distal radius and its use in reconstructive procedures, such as flap transfers, a detailed understanding of its anatomy is clinically significant. This study aims to analyze the morphometric properties of the PQ, determine its distances from key osseous landmarks, and assess gender-based anatomical differences to inform surgical planning and minimize iatrogenic complications. Materials and methods A total of 27 formalin-fixed cadaveric forearms (18 male, 9 female), with no prior surgical history, were dissected. The forearms were positioned in supination, and anatomical landmarks were marked with needles. ImageJ software was used to measure the PQ’s surface area and the anterior surface area of ​​the radius distal to the pronator quadratus, devoid of muscle fibers (muscle-free radius area-MRA). Morphometric measurements of the PQ muscle were also performed. In addition, the anatomical relationships of the PQ muscle and the anterior interosseous nerve (AIN) with adjacent bony landmarks were evaluated. Right-left and male-female comparisons were conducted. Results The PQ was present in all specimens, originating from the medial border of the distal third of the ulna and inserting into the distal third of the radius. It was innervated by the anterior interosseous nerve (AIN) and primarily supplied by the anterior interosseous artery (AIA), with additional branches from the radial artery in six cases. Gender comparisons showed that PQ’s proximal and distal widths were greater in men, but muscle area showed no significant difference. However, the muscle-free radius area on the anterior radius was significantly larger in males. The AIN was positioned farther from the radius and ulna in men. No right-left differences were observed for AIN, though the PQ’s distance to the lunate fossa was longer on the right side. Conclusions This study could provide valuable biometric data for surgical procedures involving the distal forearm by detailing the anatomy of the PQ. In particular, measurements based on fixed bone landmarks may serve as a guide for determining reliable areas for plate and screw placement in distal radius fractures. In addition, awareness of possible anatomical variations in this region may contribute to safer and more individualized surgical planning.

The median nerve (MN) is frequently targeted in invasive procedures. Accurately locating its depth is essential to minimize complications. This study aimed to develop predictive models of MN depth based on anthropometric features. Design: cross-sectional observational study. Fifty-three healthy adults (Men: 53%; Age range: 18-60 years) were evaluated. Sociodemographic (age and sex) and anthropometric data (height, weight, BMI, and proximal/mid-forearm circumference) were ascertained. Ultrasound was used to measure the depth of the MN relative to the skin and brachial artery at the elbow and mid-forearm. Hierarchical linear regression was applied to identify significant predictors of nerve depth. Men were significantly taller, heavier, and had a higher forearm circumference than women (p < 0.05 for all). Proximal forearm circumference strongly correlated with BMI and nerve depth. Regression analysis revealed it as a significant predictor of MN depth, explaining 49.4% (proximal) and 95.2% (mid-forearm) of the variance. The model for nerve-to-artery distance showed limited explanatory power (R2 = 0.164). The mid-forearm circumference is a strong and accessible predictor of MN depth. The proposed models can support clinicians in estimating appropriate needle depth in ultrasound-guided procedures, potentially reducing the risk of nerve injury.

Fluctuating asymmetry, the non-directional deviation from bilateral symmetry resulting from developmental instability, can indicate early-life environmental stress. While fluctuating asymmetry can affect individual survival and reproductive success, its effect on fitness differs between species. Here, we analyzed up to 27 years of mark-recapture data from 894 RFID tagged individuals of three forest-living bat species in southern Germany to investigate the degree of fluctuating asymmetry in forearm length. In Bechstein’s bats, Myotis bechsteinii , the species with the highest sample size, we furthermore investigated if fluctuating asymmetry has become more frequent over the study period, a time when juvenile bats have grown larger forearms in response to warmer summers. We also investigated whether fluctuating asymmetry affects individual lifespan and lifetime reproductive success in female Myotis bechsteinii . The degree of fluctuating asymmetry clearly exceeding the measurement error estimated on recaptured individuals was similar in all three species (1.8%). In female Myotis bechsteinii , the frequency of fluctuating asymmetry did not increase over the course of the study and even strong asymmetry had no effect on individual reproductive success and life expectancy. Our data suggest that fluctuating asymmetry is a poor predictor of fitness in the female Myotis bechsteinii studied, and is so far unaffected by the warming environment which is leading to larger individuals in our study population.

PurposeThe aim of this cadaveric study was to further describe the vascular supply of the radial, posterior interosseous and superficial radial nerves.Methods11 cadaveric upper limbs, injected with colored latex, were dissected. Vascular afferents to the radial nerve, superficial radial nerve (SRN) and posterior interosseous nerve (PIN) were described and located. Their origin was identified and its distance to interepicondylar line was measured.ResultsThe radial nerve had an average of 3 vascular afferents (1–5), of septomuscular origin in 54% of cases. 46% came from adjacent arteries. The PIN had an average of 8 vascular afferents (6–14), arising from septomuscular branches in 82% of cases. The PIN was vascularized in 100% of cases by a large arterial plexus originating from the supinator muscle between its two heads. The SRN had an average of 4 vascular afferents (3–7). Before crossing the septum of the brachioradialis, vascularization was predominantly septomuscular; after crossing the septum, the nerve was exclusively vascularized by septocutaneous arteries.ConclusionThis is the first study to describe the vascularization of the radial nerve and its terminal branches along their entire length. Our results are in line with the data available in the literature. An arterial plexus between the two heads of the supinator was surrounding the PIN in all cases. This vascular plexus might be involved in dynamic compression of the posterior interosseous nerve.

PurposeThe brachioradialis muscle (BRM) belongs to the lateral group of forearm muscles and contributes to the elbow flexion. Accessory brachioradialis muscle (ABRM) or “brachioradialis accessorius” represents an uncommon BRM variant, not been enough studied. The present study investigates the prevalence of the ABRM, along with its origin, insertion, and innervation.MaterialsEighty-three upper limbs were meticulously dissected at the arm, forearm, and cubital fossa to investigate the ABRM presence. When the variant muscle was identified, morphometric measurements were obtained.ResultsThe ABRM was identified in two upper limbs (2/83, 2.4%), in a male cadaver, bilaterally. Its origin was located along with the typical BRM, and its insertion was identified into the anterior surface of the radius (proximal third). The ABRM was innervated by the radial nerve, coursing posteriorly (deeply).ConclusionsIn the current study, the variant muscle was observed in 2.4%. Radial nerve compression, at the forearm, is not an uncommon entrapment neuropathy. The relationship between the radial nerve and the ABRM could precipitate radial neuropathy.

The study of hand and finger movement is an important topic with applications in prosthetics, rehabilitation, and ergonomics. Surface electromyography (sEMG) is the gold standard for the analysis of muscle activation. Previous studies investigated the optimal electrode number and positioning on the forearm to obtain information representative of muscle activation and robust to movements. However, the sEMG spatial distribution on the forearm during hand and finger movements and its changes due to different hand positions has never been quantified. The aim of this work is to quantify 1) the spatial localization of surface EMG activity of distinct forearm muscles during dynamic free movements of wrist and single fingers and 2) the effect of hand position on sEMG activity distribution. The subjects performed cyclic dynamic tasks involving the wrist and the fingers. The wrist tasks and the hand opening/closing task were performed with the hand in prone and neutral positions. A sensorized glove was used for kinematics recording. sEMG signals were acquired from the forearm muscles using a grid of 112 electrodes integrated into a stretchable textile sleeve. The areas of sEMG activity have been identified by a segmentation technique after a data dimensionality reduction step based on Non Negative Matrix Factorization applied to the EMG envelopes. The results show that 1) it is possible to identify distinct areas of sEMG activity on the forearm for different fingers; 2) hand position influences sEMG activity level and spatial distribution. This work gives new quantitative information about sEMG activity distribution on the forearm in healthy subjects and provides a basis for future works on the identification of optimal electrode configuration for sEMG based control of prostheses, exoskeletons, or orthoses. An example of use of this information for the optimization of the detection system for the estimation of joint kinematics from sEMG is reported.

This study aimed to reveal the distribution pattern of antebrachial cutaneous nerves and provide a morphological basis for sensory reconstruction during flap transplantation. Forearm specimens containing skin and subcutaneous fat were obtained from 24 upper extremities of 12 adult cadavers. Cutaneous nerves were visualized using modified Sihler's staining. Then the data was used to show the distribution pattern and innervation area of the forearm cutaneous nerve. The anterior branch of lateral antebrachial cutaneous nerve innervates 26% of the medial anterior forearm; the posterior branch innervates 38.21% of the lateral anterior forearm and 24.46% of the lateral posterior forearm. The anterior branch of medial antebrachial cutaneous nerve innervates the medial aspect of the forearm covering 27.67% of the anterior region; the posterior branch the lateral part of the forearm covering 7.67% and 34.75% of the anterior and posterior regions, respectively. The posterior antebrachial cutaneous nerve covers 41.04% of the posterior forearm. Coaptations were found between the branches of these cutaneous nerves. The relatively dense secondary nerve branches were found in the middle 1/3 of the lateral anterior forearm and the middle 1/3 of the medial posterior forearm. The relatively dense tertiary nerve branches were the middle 1/3 and lower 1/3 of the medial anterior forearm. The intradermal nerve branches were the relatively dense in the middle 1/3 of the medial anterior and lateral posterior forearm. The middle 1/3 of the medial and lateral forearm had the relatively dense total nerve branches. These results can be used sensory matching while designing forearm flaps for reconstruction surgeries to obtain improved recovery of sensory.

PurposeThis study shows the danger zone and the safety corridor in the lateral approach with bridge plating by measuring the distance between the lateral side of the plate positioned on the lateral aspect of the humerus and the radial nerve after it pierces the lateral intermuscular septum, in the different forearm positions.MethodsForty arms of 20 human cadavers were used, the radial nerve was identified and marked on the lateral surface the radial nerve at the exit of the lateral intermuscular septum and anteriorisation of the nerve in relation to the humeral shaft and the lateral epicondyle was also marked. The distances were measured with a digital caliper. A submuscular extraperiosteal corridor was created, proximally between the biceps brachialis and deltoid muscle and distally between the triceps and brachioradialis muscle, followed by the positioning of the low contact large fragments contoured plate with 14 combined holes (fixed and cortical angle), inserted from distal to proximal. Measurements were performed in four positions (elbow flexion with forearm pronation, elbow flexion with forearm supination, elbow extension with forearm pronation and elbow extension with forearm supination).ResultsSignificant statistical differences occurred with the different positions, and the elbow flexion with forearm supination was shown to be the position that provides the safest submuscular extraperiosteal corridor in a lateral approach of the humerus.ConclusionThe danger zone of radial nerve is an area that extends from 15 cm to 5 cm proximal to the lateral epicondyle and the safest way to create a submuscular and extraperiosteal corridor in the lateral region of the humerus is with the elbow in flexion and the forearm in supination.

Background: The Posterior Interosseous Artery Flap (PIA) is widely used in soft tissue reconstruction of the wrist and hand due to its consistent vascularity, long pedicle, and favorable donor site. However, anatomical variations in the vascular pedicle, perforator distribution, and flap dimensions remain limitations for clinical use. Objective: This study aims to provide a detailed anatomical evaluation of the PIA flap in adult Vietnamese cadavers to support surgical planning. Methods: A observational study was conducted on 30 forearm specimens from 15 adult Vietnamese cadavers. Methylene blue was injected into the PIA to evaluate its origin, perforator distribution, pedicle length, and perfused skin territory. Measurements were made using anatomical landmarks, and data were analyzed with SPSS 26.0. Results: The PIA originated from the common interosseous artery in 93.3% (28/30) and from the ulnar artery in 6.7% (2/30). The reverse-flow pedicle length averaged 12.8 ± 1.6 cm. Perforators were concentrated in intervals 4–8, especially intervals 5 and 8. Pattern II was the most prevalent of the three identified perforator patterns, accounting for 70% of specimens. The methylene blue-stained skin territory measured 20.6 ± 2.0 cm in length, 8.4 ± 1.4 cm in width, and 175.9 ± 41.8 cm² in area. The stained area was located 1.9 ± 1.2 cm from the distal ulna (A1), 2.9 ± 1.2 cm from the anterior midline (A2), 0.8 ± 0.9 cm below the lateral epicondyle (A3), and 0.03 ± 0.18 cm from the posterior ulnar border (A4). Conclusion: The PIA flap demonstrates a reliable vascular supply and a wide perfusion range. It should be designed > 2 cm distal to the ulna, ≥ 3 cm lateral to the anterior midline, ~1 cm below the lateral epicondyle, and not extend beyond the posterior ulnar border.

It is still challenging to achieve a complex grasp or fine finger control by using surface functional electrical stimulation (FES), which usually requires a precise electrode configuration under laboratory or clinical settings. The goals of this study are as follows: 1) to study the possibility of selectively activating individual fingers; 2) to investigate whether the current activation threshold and selective range of individual fingers are affected by two factors: changes in the electrode position and forearm rotation (pronation, neutral and supination); and 3) to explore a theoretical model for guidance of the electrode placement used for selective activation of individual fingers. A coordinate system with more than 400 grid points was established over the forearm skin surface. A searching procedure was used to traverse all grid points to identify the stimulation points for finger extension/flexion by applying monophasic stimulation pulses. Some of the stimulation points for finger extension and flexion were selected and tested in their respective two different forearm postures according to the number and the type of the activated fingers and the strength of finger action response to the electrical stimulation at the stimulation point. The activation thresholds and current ranges of the selectively activated finger at each stimulation point were determined by visual analysis. The stimulation points were divided into three groups (\"Low\", \"Medium\" and \"High\") according to the thresholds of the 1st activated fingers. The angles produced by the selectively activated finger within selective current ranges were measured and analyzed. Selective stimulation of extension/flexion is possible for most fingers. Small changes in electrode position and forearm rotation have no significant effect on the threshold amplitude and the current range for the selective activation of most fingers (p > 0.05). The current range is the largest (more than 2 mA) for selective activation of the thumb, followed by those for the index, ring, middle and little fingers. The stimulation points in the \"Low\" group for all five fingers lead to noticeable finger angles at low current intensity, especially for the index, middle, and ring fingers. The slopes of the finger angle variation in the \"Low\" group for digits 2~4 are inversely proportional to the current intensity, whereas the slopes of the finger angle variation in other groups and in all groups for the thumb and little finger are proportional to the current intensity. It is possible to selectively activate the extension/flexion of most fingers by stimulating the forearm muscles. The physiological characteristics of each finger should be considered when placing the negative electrode for selective stimulation of individual fingers. The electrode placement used for the selective activation of individual fingers should not be confined to the location with the lowest activation threshold.