Bone-based versus soft-tissue free flaps in lower extremity reconstruction.

BACKGROUND: Most lower extremity defects and minor bone defect wounds requiring a free flap are treatable with soft-tissue flaps, whereas large bone defect wounds are treated with bone-based flaps. This study aimed to compare bone-based and soft-tissue-free flaps in terms of operative procedures and postoperative complications, including long-term outcomes of lower extremity reconstruction. METHODS: This two-center retrospective cohort study collected data from all lower-extremity reconstructions with free flaps performed between March 2014 and February 2022; the level of evidence is considered to be therapeutic level III. We investigated the operative procedure and postoperative complications classified as being related to either bone-based or soft-tissue flaps. The data were further classified into the trauma and non-trauma groups and the long-term postoperative outcomes of patients who were followed up for ≥12 months were analyzed. RESULTS: A total of 122 free flaps were included: 29 bone-based flaps (1 scapular and 28 fibular flaps) and 93 soft-tissue flaps (22 muscle-based and 71 fasciocutaneous flaps). There was no significant difference in postoperative complications, including long-term outcomes, between the free flap types, regardless of etiology. Vein grafts were used more often for bone-based flaps than for soft-tissue flaps (20.7% vs. 7.5%; p = 0.045). The donor veins of bone-based flaps were more often anastomosed to superficial veins than were those of soft-tissue flaps (37.9% vs. 10.8%; p < 0.001). CONCLUSIONS: Using bone-based free flaps resulted in no significant differences in postoperative complications, including long-term outcomes, despite involving more complicated operative procedures than soft-tissue flaps. Thus, the use of vein grafts and anastomosis to the superficial venous system of the vascularized fibula graft may help avoid flap-related complications in bone-based free flaps.

Risk assessment in delayed free flap reconstruction for severe lower extremity trauma.

PURPOSE: This study aims to identify serum biomarkers that contribute to vascular thrombosis and complete flap failure in delayed reconstruction with free flaps, as well as to develop a scoring system of risk assessment including these biomarkers. METHODS: A retrospective review of the database was conducted for lower extremity open fractures reconstructed between 7 and 90 days from injury, from March 2014 to February 2022. We investigated changes in platelet count (PLT), D-dimer, creatine phosphokinase (CPK), and C-reactive protein (CRP) and then, developed a risk assessment system including these biomarkers as risk factors. RESULTS: A total of 62 free flaps were enrolled, and vascular thrombosis occurred in 14 flaps (22.6%), 9 of which (14.5%) developed complete flap failure. The risk assessment score was set to a maximum of 6 points for 6 items: age ≤ 40 years, time from injury to coverage ≥ 14 days, zone of injury from middle to distal leg, D-dimer on the day of injury ≥ 60 µg/mL, maximum value of CPK ≥ 10,000 U/L, and maximum value of CRP ≥ 25 mg/dL. The best cutoff score was 3 in the vascular thrombosis model (sensitivity: 0.79, specificity: 0.77) and 4 in the complete flap failure model (sensitivity: 0.78, specificity: 0.92). CONCLUSIONS: Our risk assessment system showed that the risk of vascular thrombosis was high at ≥ 3 points and that of complete flap failure was high at ≥ 4 points. Significantly, elevated levels of D-dimer, CPK, and CRP require more caution during reconstruction using free flaps.

Arthroscopic mobilization for metacarpophalangeal joint extension contracture.

BACKGROUND: As a first-line surgical treatment for treating metacarpophalangeal (MCP) joint extension contractures, mobilization surgery with open dorsal approach has been indicated. However, this procedure has the possibility to result in postoperative recurrence over the course of time because its invasive open dorsal approach has a negative impact on the postoperative gliding of the extensor mechanism. We report the preliminarily outcomes of patients who underwent a minimally invasive arthroscopic mobilization to alter and enhance their existing surgical strategy in place of MCP joint extension contractures. METHODS: This retrospective study included seven patients with 13 MCP joint extension contractures who had received an arthroscopic release of the bilateral collateral ligament and/or dorsal capsule of affected MCP joint. The extension contractures were caused by long-time immobilization with inadequate extended position of the MCP joint after either hand and wrist fractures, extensor tendon injury, or peripheral nerve palsy. All patients received sufficient exercise under the supervision of a physical therapist for more than 3 months before surgery. However, physical therapy did not improve the MCP joint extension contractures. We measured the active and passive flexion angles preoperatively at 1 and 6 months after surgery. The passive flexion angle was also measured after arthroscopic mobilization on the operation table. Surgery-related complications regarding nerve, vessel, skin, and tendon were also assessed. RESULTS: In all patients, significant improvements were observed in both the active and passive flexion angles 1 month after surgery, and continued to improve 6 months after surgery. Two out of 13 metacarpophalangeal joints developed blisters on the dorsal side of the joint, but conservatively recovered. CONCLUSIONS: Based on the positive improvements observed in our patients, we conclude that this minimally invasive arthroscopic technique has the potential to alter and enhance the surgical treatment strategy for MCP joint extension contractures.

Transcranial direct current stimulation reduces ischemia-induced sensory disturbance in the hands of healthy subjects.

INTRODUCTION/AIMS: The treatment of entrapment neuropathies, such as carpal tunnel syndrome or cubital tunnel syndrome, has significant challenges that have yet to be solved. To a large extent, the success of the treatment of peripheral nerve damage is dependent on brain plasticity during the recovery process. Recently, noninvasive brain stimulation procedures, such as transcranial direct current stimulation (tDCS), to modulate brain activity have been developed. This study aimed to determine whether tDCS can improve artificially induced ischemic sensory disturbances in the finger. METHODS: Ten right-handed, healthy volunteers, with an average age of 25.5 years, participated in this study. A rubber bandage at the base of the right index finger was used to induce a regional sensory disturbance for 30 minutes. An anodal tDCS was applied over their left M1 area 15 minutes into the session. The current perception threshold (CPT) in the index and little finger pad was evaluated using the PainVision system and used as a measure of the sensory threshold. RESULTS: In the index finger, the CPT increased significantly with time, a finding that was absent after tDCS application. DISCUSSION: It has been reported that anodal tDCS over M1 primarily modulates the functional connectivity of sensory networks, and our findings demonstrate that it improved ischemia-induced sensory disturbances. Modulating the central nervous system using tDCS represents a potential avenue for treating entrapment neuropathies.

Ultrasonographic digital blood flow measurement in professional baseball pitchers - A quantitative and comparative study with non-throwers.

BACKGROUND: Vascular disorders in throwing athletes can occur from the thoracic outlet to the fingertips. The occurrence of these disorders around the shoulder is well known, and treatment options have been established for them. However, the occurrence of vascular pathology in the digital arteries in elite baseball pitchers is unclear, and treatment options have not yet been established. We hypothesized that asymptomatic professional baseball pitchers often have existing pathological changes in their digital blood flow; therefore, we quantitatively measured the blood flow in the index finger using ultrasonography and compared the results to those of non-baseball players. METHODS: Seven asymptomatic professional baseball pitchers (pitcher group) and 11 healthy volunteers (control group) were included. The flow velocity, flow volume and vessel resistance index of the ulnar digital artery of the index finger were measured just distal to the proximal interphalangeal joint using pulsed wave Doppler in two positions: 1) with the proximal interphalangeal (PIP) joint relaxed (10-15° flexed) and 2) with the PIP joint passively extended (0-5°). RESULTS: The mean flow velocity and flow volume were lower in the extended position than in the relaxed position in both groups. In the dominant hand, which was the throwing hand in the pitcher group, the mean flow velocity and the flow volume in the relaxed position were significantly lower in the pitcher group than in the control group. The vessel resistance index in the relaxed position of the dominant hand was significantly higher in the pitcher group than in the control group. In the nondominant hand, there was no significant difference in any parameter between the two groups. CONCLUSIONS: Asymptomatic professional baseball pitchers may have a pathological change in digital blood flow in the throwing hand. As treatment options for this condition have not yet been established, it is of utmost importance to carry out periodic examination and prevention before the condition progresses to the symptomatic end stage.

Monitoring Vascular Compromise Using Ultrasound After Free Tissue Transfer.

OBJECTIVES: To report the clinical utility of high-resolution ultrasound (US) for monitoring vascular compromise after free tissue transfer. METHODS: Fifty-two tissue transfers in the extremities were included in this study. Blood flow around the anastomotic pedicle and subcutaneous tissue of the grafted flap was monitored with pulsed color and power Doppler US whenever the conventional monitoring method, comprising the bedside assessment of the temperature, capillary refill, and flap color, showed abnormalities until 1 week after reconstruction. RESULTS: All flaps were indicated for US monitoring, with 44 flaps showing Doppler signals in each position, even though conventional flap monitoring showed an abnormality. Forty of the 44 flaps showed no flap failure, whereas the remaining 4 flaps developed partial necrosis. Abnormal US findings were noted in 8 of the 52 flaps. Ultrasound revealed interruption of venous blood flow around the anastomotic pedicle in 6 of 8 flaps. Emergent exploration revealed venous occlusion at the anastomotic pedicle, similar to the US finding. In 2 of the 8 flaps, US showed no blood flow to either the anastomotic pedicle or subcutaneous tissue. Emergent exploration revealed arterial occlusion at the anastomotic pedicle. Seven of the 8 reexplored flaps were salvaged after revision surgery with complete flap survival. Partial flap survival was noted in 1 case, but complete flap failure was avoided. CONCLUSIONS: Ultrasound is a useful adjunct that enables a direct assessment of perfusion in grafted tissues, which may reduce unnecessary exploration when conventional flap monitoring shows an abnormality.

Virtual reality-based action observation facilitates the acquisition of body-powered prosthetic control skills.

BACKGROUND: Regular body-powered (BP) prosthesis training facilitates the acquisition of skills through repeated practice but requires adequate time and motivation. Therefore, auxiliary tools such as indirect training may improve the training experience and speed of skill acquisition. In this study, we examined the effects of action observation (AO) using virtual reality (VR) as an auxiliary tool. We used two modalities during AO: three-dimensional (3D) VR and two-dimensional (2D) computer tablet devices (Tablet). Each modality was tested from first- and third-person perspectives. METHODS: We studied 40 healthy right-handed participants wearing a BP prosthesis simulator on their non-dominant hands. The participants were divided into five groups based on combinations of the different modalities and perspectives: first-person perspective on VR (VR1), third-person perspective on VR (VR3), first-person perspective on a tablet (Tablet1), third-person perspective on a tablet (Tablet3), and a control group (Control). The intervention groups observed and imitated the video image of prosthesis operation for 10 min in each of two sessions. We evaluated the level of immersion during AO using the visual analogue scale. Prosthetic control skills were evaluated using the Box and Block Test (BBT) and a bowknot task (BKT). RESULTS: In the BBT, there were no significant differences in the amount of change in the skills between the five groups. In contrast, the relative changes in the BKT prosthetic control skills in VR1 (p < 0.001, d = 3.09) and VR3 (p < 0.001, d = 2.16) were significantly higher than those in the control group. Additionally, the immersion scores of VR1 (p < 0.05, d = 1.45) and VR3 (p < 0.05, d = 1.18) were higher than those of Tablet3. There was a significant negative correlation between the immersion scores and the relative change in the BKT scores (Spearman's rs = - 0.47, p < 0.01). CONCLUSIONS: Using the BKT of bilateral manual dexterity, VR-based AO significantly improved short-term prosthetic control acquisition. Additionally, it appeared that the higher the immersion score was, the shorter the execution time of the BKT task. Our findings suggest that VR-based AO training may be effective in acquiring bilateral BP prosthetic control, which requires more 3D-based operation.

Increase in medial meniscal extrusion in the weight-bearing position observed on ultrasonography correlates with lateral thrust in early-stage knee osteoarthritis.

BACKGROUND: Lateral thrust is known to be risk factors for knee osteoarthritis progression. Medial meniscus extrusion is also known to be risk factors for knee osteoarthritis progression; moreover, the amount of change in medial meniscus extrusion from non-weight bearing to weight bearing is an important factor for the progression of knee osteoarthritis. This study aimed to investigate the correlation between lateral thrust and the change in medial meniscus extrusion. METHODS: In total, 44 knees from 44 patients (mean age, 68.9 years) with knee osteoarthritis were divided into two groups according to the Kellgren-Lawrence grade: early-stage osteoarthritis (Kellgren-Lawrence = 2) and severe osteoarthritis (Kellgren-Lawrence = 3 or 4). The lateral thrust during gait, represented as the lateral acceleration peak immediately after heel strike, was recorded by an inertial sensor. The amount of change in medial meniscus extrusion, which was the difference between weight-bearing (unipedal standing) and non-weight-bearing (supine) conditions, was evaluated using ultrasonography. RESULTS: The mean value of the lateral acceleration peak in the severe osteoarthritis group was higher than that of the early-stage osteoarthritis group (p < 0.05). The non-weight-bearing and weight-bearing medial meniscus extrusion in the severe OA group were significantly higher than those of the early-stage osteoarthritis group (p < 0.001). However, the amount of change in medial meniscus extrusion in severe osteoarthritis group was significantly lower than in the early-stage osteoarthritis group (p < 0.05). The amount of change in medial meniscus extrusion showed a significant correlation with the lateral acceleration peak in the early-stage osteoarthritis group (r = 0.56, p < 0.001). On the other hand, there was no significant correlation in the severe osteoarthritis group. CONCLUSION: The lateral thrust shows a positive correlation with the amount of change in medial meniscus extrusion by weight bearing in patients with early-stage knee osteoarthritis.

Correlation between spinal and pelvic movements during gait and aggravation of low back pain by gait loading in lumbar spinal stenosis patients.

BACKGROUND: Lumbar alignment of posterior or anterior tilts affects the exacerbation and remission of symptoms of lumbar spinal stenosis patients. This study aimed to clarify the correlation between spinal and pelvic movements during gait and the aggravation of low back pain after gait loading in lumbar spinal stenosis patients. METHODS: A total of 29 patients with lumbar spinal stenosis completed leg and low back pain assessments and gait analysis before and after gait loading tests. Patients were divided into leg and low back pain change (n = 8), leg pain only change (n = 12), and non-change (n = 9) groups based on the differences of leg and low back pain between before and after the tests. Peak kinematic values of the anterior tilts of the trunk, thoracic spine, lumbar spine, and pelvis during the stance phase were obtained via three-dimensional gait analysis. RESULTS: In the leg and low back pain change group, the anterior lumbar and pelvic tilts were larger after than before the tests; however, in the leg pain only change and non-change groups, only the anterior lumbar tilt was larger after than before the tests. Anterior lumbar tilt before and after the tests negatively correlated with the aggravation of low back pain, and an increase in the anterior pelvic tilt positively correlated with the aggravation of low back pain. CONCLUSIONS: In lumbar spinal stenosis patients, smaller anterior lumbar tilt and larger anterior pelvic tilt during gait loading may affect the aggravation of low back pain by gait loading. Increasing in lumbar lordosis during gait might be one of the factors leading to low back pain in lumbar spinal stenosis patients.

Joint distraction and early mobilization using a new dynamic external finger fixator for the treatment of fracture-dislocations of the proximal interphalangeal joint.

BACKGROUND: Dynamic external fixation is a useful treatment option for unstable fracture-dislocations of the proximal interphalangeal (PIP) joint, because it simultaneously reduces axial pressure load on the joint surface, maintains congruent joint reduction, and permits early joint motion. However, most current devices are large, hindering finger movement, and unstable. To address these problems, we developed a dynamic external finger fixator, named the Micro Ortho Fixator®. The purpose of this study was to review the results of using the new external finger fixator to treat unstable fracture-dislocations of the PIP joint. MATERIALS AND METHODS: Nine patients who sustained unstable fracture-dislocation injuries of the PIP joint were treated with the Micro Ortho Fixator®. Seven fractures were accompanied by depressed bony fragments at the base of the middle phalanx. All patients were evaluated for pain and range of PIP motion at the final follow-up. Radiographs of the affected fingers were evaluated for PIP congruity and reduction. The mean follow-up duration was 11.1 months (range: 6-33 months). RESULTS: At the final follow-up, pain averaged 0.3 (range: 0-2) on the Numeric Pain Rating Scale, and the total arc of motion at the PIP joint averaged 91.2° (range: 50-110°). All fractures had healed, and the intra-articular step-off improved from 1.9 mm (SD: 1.0) before surgery to 0.2 mm (SD: 0.4) at the final follow-up. The patients who sustained sports injuries returned to competition after an average of 3.5 months (range: 2.5-4 months). CONCLUSION: The external fixator is compact and facilitates range-of-motion (ROM) exercises, has high stability, and achieves good joint congruity and an ROM equivalent to the healthy joint of the patient. STUDY DESIGN/LEVEL OF EVIDENCE: Therapeutic/IV.

Comparison of sonography and MRI in the evaluation of stability of capitellar osteochondritis dissecans.

PURPOSE: To compare the diagnostic accuracies of ultrasonography (US) and magnetic resonance imaging (MRI) with intraoperative capitellar osteochondritis dissecans (COCD) fragment stability findings. METHODS: Patients whose International Cartilage Repair Society (ICRS) osteochondritis dissecans (OCD) classifications were I/II (stable) or III (unstable) were included. Patients underwent preoperative US and MRI. On US, lesions were evaluated as unstable when irregular contours of the chondral surface were observed. On MRI, lesions were evaluated as unstable when articular bone irregularity, a T2 high signal intensity interface, or a high signal intensity line through the articular cartilage was observed. Using the surgical assessment as the gold standard, accuracies of fragment stability diagnoses were calculated for US and MRI. RESULTS: Thirty-four patients with OCD classifications of I/II (stable) or III (unstable) were included. Twenty-four patients (stable: 12, unstable: 12) underwent preoperative US; 22 (stable: 11, unstable: 11) underwent preoperative MRI. Preoperative US and MRI stability assessments correctly matched intraoperative fragment findings in 23 of 24 patients and 16 of 22 patients, respectively. US criteria in this study achieved superior accuracy compared with MRI criteria (96% vs. 73%; P < .05). CONCLUSION: US was a useful tool for evaluating fragment instability in COCD.

Correlation between "hourglass-like fascicular constriction" and idiopathic anterior interosseous nerve palsy.

INTRODUCTION: In recent operative cases of anterior interosseous nerve palsy (AINP), hourglass-like fascicular constrictions have been reported. We prospectively investigated the ultrasonographic history of these lesions to better understand the role of this lesion in AINP. METHODS: Seven patients who were diagnosed with idiopathic AINP based on classic clinical findings and had hourglass-like fascicular constrictions found on ultrasonography were included. All but 1 patient selected surgery, and we followed up all patients clinically and with ultrasonography. RESULTS: In the 5 patients treated surgically in whom paralysis recovered to a level greater than M4, postoperative ultrasonography revealed less constriction. The other patient experienced little recovery after surgery, and the severe constriction remained. In a conservatively treated patient, the paralysis recovered completely, and upon ultrasonography, the constriction had lessened. CONCLUSIONS: Although the mechanism is still unknown, hourglass-like fascicular constriction lessened with relief of motor weakness both in operatively and conservatively treated patients. Muscle Nerve 55: 508-512, 2017.

Association between three-dimensional motion analysis of the thumb and clinical parameters in patients with carpal tunnel syndrome.

We analysed the relationship between motor dysfunction of the thumb and the clinical parameters of carpal tunnel syndrome using three-dimensional motion analysis. This single-centred, prospective study included 65 hands in 51 patients with idiopathic carpal tunnel syndrome and 30 healthy hands. Three-dimensional thumb kinematics were acquired using a motion capture system with a retroreflective surface-based marker method. The trajectory area of thumb tip, adduction and abduction of the trapeziometacarpal joints and metacarpophalangeal joints were correlated with the clinical parameters. There was no significant correlation between the results of motion analysis values and patient-reported outcomes measures. Thumb movement disorder associated with carpal tunnel syndrome affected specific activities of daily living based on the pinching movements, such as 'writing' and 'buttoning clothes' among the patient-reported outcome measure items.Level of evidence: III.

Three-dimensional motion analysis of pre- and postoperative thumb movement in trapeziometacarpal joint osteoarthritis-Comparison of arthrodesis and trapeziectomy with suspensionplasty.

Trapeziometacarpal osteoarthritis (TMC-OA) reduces the range of motion (ROM) of the thumb. However, the kinematic change achieved through surgical treatment remains unclear. Therefore, to quantify the kinematic change following TMC-OA surgery, we performed a three-dimensional motion analysis of the thumb using an optical motion capture system preoperatively and 1 year postoperatively in 23 patients with TMC-OA scheduled for arthrodesis (AD) or trapeziectomy with suspensionplasty (TS). Eighteen hands of nine healthy volunteers were also included as controls. Both procedures improved postoperative pain and Disability of the Arm, Shoulder and Hand scores, and AD increased pinch strength. The ROM of the base of the thumb was preserved in AD, which was thought to be due to the appearance of compensatory movements of adjacent joints even if the ROM of the TMC joint was lost. TS did not improve ROM. Quantifying thumb kinematic changes following TMC-OA surgery can improve our understanding of TMC-OA treatment and help select surgical procedures and postoperative assessment.

Effect of lateral wedge insole on medial meniscus extrusion and its association with knee osteoarthritis progression.

BACKGROUND: Medial meniscus extrusion (MME) is associated with knee osteoarthritis (OA) progression because of increased loading stress in the medial compartment of the knee. Using a lateral wedge insole (LWI) decreases loading stress and immediately reduces MME. OBJECTIVE: To investigate whether the wearing duration of LWI affects the midterm response to MME and is associated with knee OA progression. STUDY DESIGN: Cohort study. METHODS: Twenty-three patients with knee OA who were conservatively treated with LWI were classified according to the duration of the LWI wear per day: less than 5 h (short-duration group) or over 5 h (long-duration group). MME was evaluated in the single-leg standing position by ultrasound. Knee OA progression and limb alignment were evaluated radiographically. These evaluations were performed thrice: at the initial office visit as a baseline without LWI (time 0), with LWI (LWI-time 0), and 1 year after intervention with LWI (LWI-1 year). RESULTS: In both groups, the MMEs at LWI time 0 were significantly decreased compared with those at time 0. In the long-duration group, this reduction in MME was maintained 1 year after the intervention compared with time 0 (time 0: 3.9 ± 0.9, LWI-1 year: 2.6 ± 1.1), but this improvement was not observed in the short-duration group (time 0: 3.8 ± 1.7, LWI-1 year: 3.6 ± 1.7). In addition, three of four patients demonstrated OA progression, and varus alignment had significantly progressed compared with that at time 0 in the short-duration group. However, the long-duration group showed OA progression only in one patient and maintained limb alignment. CONCLUSIONS: The duration of wearing LWI affects the midterm reduction of MME and knee OA progression while maintaining limb alignment.

Somatosensory mechanical response and digit somatotopy within cortical areas of the postcentral gyrus in humans: an MEG study.

Somatosensory evoked fields in response to compression (termed as Co) and decompression (termed as De) of glabrous skin (D1, thumb; D2, index finger; D5, little finger) were recorded. Although estimated equivalent current dipoles (ECDs) following stimulation of D1 and D5 were larger, but not significantly larger, in decompression than in compression, those of D2 were significantly larger (P = 0.035). The ECDs were located in the postcentral gyrus in the order of D5De, D2De, and D1De medially, posteriorly, and superiorly in decompression but not in compression (z-value, F = 2.692, P = 0.031). The average distance of ECDs between D1 and D5 was longer in decompression (12.8 ± 1.6 mm) than in compression (9.1 ± 1.6 mm). Our data suggest that the cortical response for the commonly used digit D2 is functionally different from those for other digits (D1 and D5) that the somatotopic variability is greater in compression.

Effects of metacarpophalangeal joint position and finger joint movement speed on lumbrical muscle activity.

OBJECTIVES: The effect of metacarpophalangeal joint position and finger joint movement speed on lumbrical muscle activity remains unproven and was examined in this study. MATERIAL AND METHODS: Twenty-four healthy adults performed flexion-extension movements of the index finger in different metacarpophalangeal joint positions (extension or flexion) and movement speeds (60, 120, 240, and 360 beats per minute). The activities of the first lumbrical, first dorsal interosseous, and extensor digitorum muscles were evaluated using surface electromyography, and compared with those during finger joint extension. RESULTS: The metacarpophalangeal joint positions affected only lumbrical muscle activity, which was greater during extension. Further, finger movement speed affected the lumbrical and extensor digitorum muscle activities, which increased with increasing movement speeds. CONCLUSION: The present study suggests that position and movement speed can influence the lumbrical muscle activity during metacarpophalangeal joint extension. These findings may help expound lumbrical function and develop suitable strategies for inducing lumbrical muscle activity.

Effect of extension of the ulnar fingers on force control and muscle activity of the hand during a precision pinch.

Some individuals extend the three ulnar fingers when performing a precision pinch. The aim of the present study was to investigate the mechanisms and effect of the extension of the ulnar fingers during a pinch. When performing a pulp pinch task with the ulnar fingers in two positions (extension and flexion), 27 participants maintained 5% of their maximum force. The mean pinch force, force variability and time taken to reach the targeted force (reaching time) were calculated. Muscle activity was simultaneously measured, using surface electromyography, for nine muscles: the flexor pollicis brevis; abductor pollicis brevis; flexor pollicis longus; first lumbrical; first dorsal interosseous; flexor digitorum superficialis of the index finger; extensor indicis; and extensor digitorum of the index and ring fingers. No significant differences in the mean pinch force or force variability were found. However, the reaching time was significantly shorter (approximately 20% reduction) in the extension position and the activities in the flexor pollicis brevis, first lumbrical, extensor indicis and extensor digitorum of the ring finger were significantly higher. These findings suggest that extending the ulnar fingers during pinching enhances the activity of key muscles involved in the movement and allows for more rapid force exertion.

Measurement of the lumbrical muscle activity of the hand using electromyography supported by the ultrasound imaging technique with string navigation.

Although placing surface electrodes on small muscles by palpation is difficult, ultrasound guidance may enable electrode placement on the small muscles. This study aimed to examine whether ultrasound guidance is helpful for placement of electrodes on a small muscle, such as the hand lumbrical muscle. Twelve dominant hands of 12 healthy right-handed adults were included in this study. The first lumbrical muscle belly of the hands was identified using ultrasound guidance with a string navigation technique for placing surface electrodes. This technique was designed to identify the location of the center of the muscle belly under ultrasound imaging using a string. After the electrodes were placed on the muscle belly using this technique, the surface electromyographic signals of the first lumbrical, first dorsal interosseous, and adductor pollicis muscles were recorded. The activity of the lumbrical muscle could be separately measured of the first dorsal interosseous and adductor pollicis muscles. This technique has the potential to enable surface electromyography of small muscles for which placement of surface electrodes by palpation is challenging.