Double entrapment neuropathy of the ulnar nerve at the elbow and the wrist : double crush syndrome?

BACKGROUND

Double crush syndrome refers to a nerve in the proximal region being compressed, affecting its proximal segment. Instances of this syndrome involving ulnar and cubital canals during ulnar neuropathy are rare. Diagnosis solely through clinical examination is challenging. Although electromyography (EMG) and nerve conduction studies (NCS) can confirm neuropathy, they do not incorporate inching tests at the wrist, hindering diagnosis confirmation. We recently encountered eight cases of suspected double compression of ulnar nerve, reporting these cases along with a literature review.

METHODS

The study included 5 males and 2 females, averaging 45.6 years old. Among them, 4 had trauma history, and preoperative McGowan stages varied. Ulnar neuropathy was confirmed in 7 cases at both cubital and ulnar canal locations. Surgery was performed for 4 cases, while conservative treatment continued for 3 cases.

RESULTS

In 4 cases with wrist involvement, 2 showed ulnar nerve compression by a fibrous band, and 1 had nodular hyperplasia. Another case displayed ulnar nerve swelling with muscle covering. Among the 4 surgery cases, 2 improved from preoperative McGowan stage IIB to postoperative stage 0, with significant improvement in subjective satisfaction. The remaining 2 cases improved from stage IIB to IIA, respectively, with moderate improvement in subjective satisfaction. In the 3 cases receiving conservative treatment, satisfaction was significant in 1 case and moderate in 2 cases. Overall, there was improvement in hand function across all 7 cases.

CONCLUSION

Typical outpatient examinations make it difficult to clearly differentiate the two sites, and EMG tests may not confirm diagnosis. Therefore, if a surgeon lacks suspicion of this condition, diagnosis becomes even more challenging. In cases with less than expected postoperative improvement in clinical symptoms of cubital tunnel syndrome, consideration of double crush syndrome is warranted. Additional tests and detailed EMG tests, including inching tests at the wrist, may be necessary. We aim to raise awareness double crush syndrome with ulnar nerve, reporting a total of 7 cases to support this concept.

Systematic review of nerves at risk at the wrist in common surgical approaches to the forearm: Anatomical variations and surgical implications

Three commonly used approaches to the forearm in orthopedic surgery are Henry's, Thompson's, and the ulnar approach, each of which has the potential to cause injury to nerves around the wrist. Preserving these nerves is important to prevent complications such as neuroma formation and motor and sensory changes to the hand. We conducted a review of the literature to assess the nerves at risk and whether 'safe zones' exist to avoid these nerves. An independent reviewer conducted searches in Embase and MEDLINE of the literature from 2010 to 2020. A total of 68 papers were identified, with 18 articles being included in the review. Multiple nerves were identified as being at risk for each of the approaches described. In the anterior approach, the palmar cutaneous branch of the median nerve (PCBMN) is most at risk of injury. An incision immediately radial to the flexor carpi radialis (FCR) or directly over the FCR is most likely to avoid injury to both superficial branch of the radial nerve (SBRN) and PCBMN. With Thompson's approach, the safest zone for an incision is directly over or slightly radial to Lister's tubercle to avoid injury to SBRN and lateral cutaneous nerve of the forearm. For the ulnar approach, a safe zone was shown to be on the ulnar side of the wrist around the ulnar styloid (US) when the forearm was in supination or a neutral position to avoid injury to the dorsal branch of the ulna nerve (DBUN). Care must be taken around the US due to the density of nerves and the proximity of the last motor branch of the posterior interosseous nerve to the ulnar head. This review highlighted the proximity of nerves to the three most common surgical incisions used to access the forearm. In addition, anatomical variations may exist, and each of the nerves identified as being at risk has multiple branches. Both factors increase the potential of intraoperative damage if the anatomy is not properly understood. The surgeon must adhere carefully to the established approaches to the wrist and distal forearm to minimize damage to nerves and optimize surgical outcomes for the patient.

A cut throat: a case of C5-C8 brachial plexus root transection providing evidence of T1 innervation of thumb and finger extensors

The T1 nerve root is not routinely thought of as innervating the extensors of the thumb and fingers. Work by Bertelli and Ghizoni proposed that the pattern of brachial plexus paralysis with intact hand function and thumb and finger extensors traditionally attributed to C5/6/7 root injury is in fact a C5/6/7/8 injury, with only T1 remaining intact - a 'T1 hand'. This case presents a 19-year-old male who was stabbed in the neck; exploratory surgery determined complete transection of the brachial plexus, with only the T1 nerve root remaining intact. Clinical examination demonstrated grade M4 pronation (with pronator quadratus), wrist extension (with extensor carpi ulnaris), thumb and finger extension (with extensor policis longus and brevis, extensor digitorum communis and extensor index proprius), wrist flexion (with palmaris longus), finger flexion (with flexor digitorum superficialis and profundus), thumb flexion (with flexor policis longus), and thenar and hypothenar muscles. Extensor carpi radialis longus and brevis, flexor carpi radialis and flexor carpi ulnaris were paralyzed. Triceps scored M2. This case provides unequivocal evidence that the T1 root provides significant innervation to the extrinsic thumb and finger extensors.

Hand and Wrist Injuries Associated With Application of Physical Restraints: A Systematic Review

While handcuffs and zip ties are common methods of physical restraint used by law enforcement, they have been noted to damage soft tissue and bony structures of the hand and wrist. This paper seeks to characterize the safety of physical restraints by summarizing its effects on hand and wrist function and disability. Relevant studies were gathered through an independent double selection and extraction process using 3 electronic databases (EMBASE, MEDLINE, and CINAHL) from database inception to June 19, 2020. A total of 16 studies involving 807 participants were included. Lesion to the superficial branch of the radial nerve was the most commonly reported injury noted in 82% (42/55) of hands examined. A total of 6% (5/77) of examined hands had bony injury, including 3 radial styloid fractures and 2 scaphoid fractures. Both studies on zip ties noted presence of handcuff neuropathy, with 1 case report documenting severe rapidly progressing ischemic monomelic neuropathy. Overall, the use of handcuffs and zip ties is associated with entrapment neuropathies and bony injury to the hand and wrist. Further studies of higher quality evidence are necessary to understand the effects of physical restraint on hand function and disability.

Wrist Arthroscopy Using the 2R Portal: Is It Safer Than the 1,2 Portal?

BACKGROUD

The purpose of this study was to compare the 1,2 with a novel 2R portal in terms of proximity to critical structures.

METHODS

Wrist arthroscopy was performed on 8 fresh frozen cadavers via the 1,2 and 2R portals. External anatomy was then dissected under loupe magnification. The closest distance between the portals and surrounding anatomical structures was measured in millimeters using digital calipers.

RESULTS

The 1,2 portal was significantly closer to radial artery and first extensor compartment tendons than the 2R portal. The radial artery was on average 1.32 mm from the 1-2 portal and 14.25 mm from the 2R portal. The 2R portal was significantly closer to the second and third extensor compartment tendons. The closest branch of the superficial branch of the radial nerve (SBRN) was on average 2.04 mm from the 1-2 portal and 7.59 mm from the 2R portal, but this was not statistically significant.

CONCLUSIONS

We advocate using the 2R portal preferentially to the 1,2 portal when treating radial sided wrist pathology to decrease the risk of iatrogenic radial artery and SBRN injury.

Analysis of Mechanoreceptors and Free Nerve Endings of the Transverse Carpal Ligament

Background: The treatment of carpal tunnel syndrome (CTS) by sectioning the transverse carpal ligament (TCL) is not exempt from complications. Some nerve branches may be damaged by the incision. The aim of this study is to identify and map the TCL nerve endings, serving as a guide for sectioning this structure in a zone with less nerve ending density. Methods: Ten TCLs were obtained from fresh frozen cadavers. The TCLs were measured, divided into 3 equal bands (radial, central, and ulnar), and submitted to cryostat sectioning. The sections were subjected to immunofluorescence with the protein gene product (PGP) 9.5 and confocal microscopy analysis. Results: All the specimens contained type I and type IV mechanoreceptors. Neural elements occupied 0.695 ± 0.056% of the ligament area. The density of the neural elements was greater in the radial, followed by the ulnar and central bands, with 0.730 ± 0.083%, 0.686 ± 0.009%, and 0.669 ± 0.031%, respectively. Conclusion: The present findings suggest that the region with the least potential for neural element injury during TCL release is the central third near the transition with the ulnar third. When performed distally to proximally with a slight inclination from the radial to the ulnar, this release compromises the lowest nerve element density. Topographically, the proximal limit of the release is the distal wrist crease, while the distal limit is the intersection of Kaplan cardinal line and the axis of the third webspace.

Penetration of the posterior interosseous nerve fibers into the dorsal capsule of the wrist - a new perspective on wrist innervation

The dorsal capsule of the wrist and the DCSS may play a significant role in the conduction of nerve signals transmitted from proprioceptors present in SL to PIN, which is located above the dorsal capsule. Hence, this study aimed to determine if nerve fibers of PIN penetrate inside the dorsal capsule. The dorsal capsules of the wrist were dissected from both sides from 15 cadavers. Eventually, 30 dorsal capsules were dissected. It can be concluded that the PIN nerve fibers penetrate the dorsal capsule of the wrist, as the penetration was noticeable in every part evaluated. The present study proves that afferent fibers from the mechanoreceptors of the SLIL potentially pass through the DCSS and subsequently through the dorsal capsule of the wrist to the PIN. This knowledge can surely be of great use for hand surgeons that perform procedures on the dorsal wrist.

The Window Test: a simple bedside method to detect radial deviation of the wrist commonly seen in posterior interosseous nerve palsy

BACKGROUND

Posterior interosseous nerve palsy (PINP) is a disorder caused by damage to the posterior interosseous nerve, resulting in weak extension of the wrist and fingers as well as radial deviation of the wrist.

METHODS

In this study, a new type of evaluation for PINP was analyzed in hopes of increasing ease of diagnosis and earlier detection of the disorder. The "Window Test" is performed by the examiner laying hands on the ulnar aspect of the patient's pronated forearm while the latter is trying to extend the wrist. A positive test is observed when a gap (window) appears between the examiner's forearm and the patient's hand. Lay people, medical students, residents, and practicing providers were assessed prospectively on their ability to correctly diagnose PINP by observing one hand, both hands, and by using the Window Test.

RESULTS

The Window Test was consistently found to be the most effective method of evaluation as it increased the accuracy of diagnoses in all groups surveyed. Additionally, case studies were performed using the Window Test on patients, further demonstrating the efficacy of the test by confirming wrist radial deviation.

CONCLUSION

The Window Test introduces a reference frame, making it easier to assess wrist radial deviation and offering a simple evaluation that can be administered by virtually anyone. These findings indicate that the implementation of the Window Test will increase the accuracy and effectiveness of PINP diagnosis, thus allowing early diagnosis and better management.

The Neurophysiological Severity of Carpal Tunnel Syndrome Cannot Be Predicted by Median Nerve Cross-Sectional Area and Wrist-to-Forearm Ratio

PURPOSE

The median nerve cross-sectional area at the wrist (CSA) and the wrist-to-forearm ratio of the cross-sectional areas (WFR) are ultrasound parameters used in the diagnosis and grading of carpal tunnel syndrome. This study aimed to determine the diagnostic accuracy of the CSA and WFR as well as to compare their diagnostic value.

METHODS

A retrospective evaluation was conducted of a cohort of 218 patients who had undergone nerve conduction studies (NCSs) and an ultrasound of the median nerve. The examined wrists were classified into an NCS negative and three NCS positive (mild, moderate, and severe) categories. The CSA and WFR were compared across the categories.

RESULTS

The CSA and WFR were significantly smaller in the NCS negative category than in the NCS positive categories. The WFR was significantly smaller in the mild category than in the moderate category. The CSA could not be used to differentiate across the NCS positive categories.

CONCLUSIONS

The CSA and WFR are satisfactorily reliable in detecting carpal tunnel syndrome, but they cannot be considered as surrogate indicators of electrophysiological severity.

Marinacci anastomosis (reverse Martin-Gruber anastomosis): A case report

RATIONALE

The incidence of Martin-Gruber anastomosis ranges from 5% to 34%, which is characterized by crossing over from the median to the ulnar nerve and innervating the first dorsal interosseous, thenar or hypothenar muscles. However, the reverse Martin-Gruber anastomosis, or Marinacci anastomosis, is far less discussed and appears in recent literature.

PATIENT CONCERNS

A 56-year-old man presented to the clinic of a university hospital because of left neck soreness with numbness radiating to the left lateral shoulder. The neck discomfort was aggravated while the neck rotated or tilted to the right.

DIAGNOSIS

Higher compound muscle action potential over the abductor pollicis brevis on elbow stimulation than on the wrist was found during upper limb nerve conduction velocity study. Ulnar to median anastomosis was identified.

INTERVENTION

We performed cervical spine X-ray and electrophysiological examinations and monitored the patient.

OUTCOMES

We identified that this patient had left C5 and C6 subacute radiculopathy with active denervation and left subclinical ulnar sensory neuropathy, and verified the existence of ulnar-to-median anastomosis.

LESSONS

We demonstrated a pure motor ulnar-to-median anastomosis without sensory correspondence and higher CMAP over the abductor pollicis brevis on elbow stimulation of the ulnar nerve than on the wrist. The prevalence might be underestimated in a Chinese population-based published study.

Efficacy of Hyalase Hydrodissection in the Treatment of Carpal Tunnel Syndrome: A Randomized, Double-Blind, Controlled, Clinical Trial

BACKGROUND

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, which results from median nerve compression. A lot of nonsurgical modalities are available for the management of mild to moderate situations. Local Hyalase hydrodissection (HD) of the entrapped median nerve could offer a desirable sustained symptom alleviation.

OBJECTIVES

To evaluate the clinical efficacy of Hyalase/saline solution carpal tunnel HD on pain, functional status, and nerve conduction in patients with CTS.

STUDY DESIGN

A randomized, double-blinded trial.

SETTING

Anesthesia, pain, and rheumatology clinics in a university hospital.

METHODS

Patients: 60 patients with CTS (> 6 months' duration).

INTERVENTION

patients were allocated equally into either group 1 (HD with Hyalase + 10 mL saline solution injection), or group 2 (HD with 10 mL saline solution only).

MEASUREMENTS

assessment of pain using Visual Analog Scale (VAS), functional disability (FD) score, and nerve conduction studies before injection, and over 6 months after injection. Nerve conduction parameters before injection and postinjection by the end of 3 and 6 months were evaluated as well.

RESULTS

Statistically significant lower postinjection values of VAS (1 ± 1.8, 2 ± 1.1, 2 ± 1.2, 2 ± 1.1) in group 1 versus (2 ± 1.2, 3 ± 1.7, 4 ± 1.5, 5 ± 2.6) in group 2 by the end of the first week, and the first, third, and sixth months, and significantly lower FD scores (15.3 ± 1.2, 13 ± 1.3, 10.2 ± 1.3, 10.2 ± 1.3) in group 1 versus (17.5 ± 1.8, 16.6 ± 2.8, 19.4 ± 3.2, 21.2 ± 2.5) in group 2 during the same time intervals. Nerve conduction study parameters have shown significantly higher velocity and lower latency in the Hyalase group than in the saline solution group by the 3 and 6 month follow-up.

LIMITATION

We suggest a longer period could be reasonable.

CONCLUSIONS

Carpal tunnel HD with Hyalase with saline solution is considered as an efficient technique offering a rapid onset of pain relief and functional improvements, and better median nerve conduction in patients with CTS over 6 months follow-up duration.

KEY WORDS

Carpal tunnel syndrome, Hyalase, median nerve hydrodissection.

Accuracy of Carpal Tunnel Injection: A Prospective Evaluation of 756 Patients

Background: Corticosteroid injection into the carpal tunnel is both a diagnostic test and a therapeutic modality in the treatment of carpal tunnel syndrome. Many injection techniques are described in the literature. Improper placement of injection may result in damage to neurovascular structures in the carpal canal or decrease efficacy of the test and/or therapy. The purpose of this study is to determine if carpal tunnel injection using anatomic landmarks is reproducible and safe. A review of the senior author's injection technique is presented. Methods: Over 8 years, there were 756 attempted placements of a 25-gauge needle into the carpal tunnel in a simulated carpal tunnel injection prior to open carpal tunnel release. The needle was inserted at the wrist crease, just ulnar to palmaris longus. Open carpal tunnel release was subsequently performed, and position of the needle was recorded. Results: In 572 patients (75.7%), the needle was found to be in the carpal tunnel without penetration of contents. The needle was in the carpal tunnel but piercing the median nerve in 66 attempts (8.7%). The carpal tunnel was missed in 118 attempts (15.6%). Conclusions: This is the largest study looking at accuracy of carpal tunnel injection using anatomic landmarks. Our injection accuracy (75.7%) is less than reported in previous studies, which note 82% to 100% accuracy using the same injection technique. This may indicate that carpal tunnel injection is less reliable than previously thought. Safety of carpal tunnel injection remains an important concern. The median nerve was penetrated in 8.7% of attempts.

Local-to-distant development of the cerebrocerebellar sensorimotor network in the typically developing human brain: a functional and diffusion MRI study

Sensorimotor function is a fundamental brain function in humans, and the cerebrocerebellar circuit is essential to this function. In this study, we demonstrate how the cerebrocerebellar circuit develops both functionally and anatomically from childhood to adulthood in the typically developing human brain. We measured brain activity using functional magnetic resonance imaging while a total of 57 right-handed, blindfolded, healthy children (aged 8-11 years), adolescents (aged 12-15 years), and young adults (aged 18-23 years) (n = 19 per group) performed alternating extension-flexion movements of their right wrists in precise synchronization with 1-Hz audio tones. We also collected their diffusion MR images to examine the extent of fiber maturity in cerebrocerebellar afferent and efferent tracts by evaluating the anisotropy-sensitive index of hindrance modulated orientational anisotropy (HMOA). During the motor task, although the ipsilateral cerebellum and the contralateral primary sensorimotor cortices were consistently activated across all age groups, the functional connectivity between these two distant regions was stronger in adults than in children and adolescents, whereas connectivity within the local cerebellum was stronger in children and adolescents than in adults. The HMOA values in cerebrocerebellar afferent and efferent tracts were higher in adults than in children (some were also higher than in adolescents). The results indicate that adult-like cerebrocerebellar functional coupling is not completely achieved during childhood and adolescence, even for fundamental sensorimotor brain function, probably due to anatomical immaturity of cerebrocerebellar tracts. This study clearly demonstrated the principle of "local-to-distant" development of functional brain networks in the human cerebrocerebellar sensorimotor network.

Contralateral C7 to C7 nerve root transfer in reconstruction for treatment of total brachial plexus palsy: anatomical basis and preliminary clinical results

OBJECTIVEContralateral C7 (CC7) nerve root has been used as a donor nerve for targeted neurotization in the treatment of total brachial plexus palsy (TBPP). The authors aimed to study the contribution of C7 to the innervation of specific upper-limb muscles and to explore the utility of C7 nerve root as a recipient nerve in the management of TBPP.METHODSThis was a 2-part investigation. 1) Anatomical study: the C7 nerve root was dissected and its individual branches were traced to the muscles in 5 embalmed adult cadavers bilaterally. 2) Clinical series: 6 patients with TBPP underwent CC7 nerve transfer to the middle trunk of the injured side. Outcomes were evaluated with the modified Medical Research Council scale and electromyography studies.RESULTSIn the anatomical study there were consistent and predominantly C7-derived nerve fibers in the lateral pectoral, thoracodorsal, and radial nerves. There was a minor contribution from C7 to the long thoracic nerve. The average distance from the C7 nerve root to the lateral pectoral nerve entry point of the pectoralis major was the shortest, at 10.3 ± 1.4 cm. In the clinical series the patients had been followed for a mean time of 30.8 ± 5.3 months postoperatively. At the latest follow-up, 5 of 6 patients regained M3 or higher power for shoulder adduction and elbow extension. Two patients regained M3 wrist extension. All regained some wrist and finger extension, but muscle strength was poor. Compound muscle action potentials were recorded from the pectoralis major at a mean follow-up of 6.7 ± 0.8 months; from the latissimus dorsi at 9.3 ± 1.4 months; from the triceps at 11.5 ± 1.4 months; from the wrist extensors at 17.2 ± 1.5 months; from the flexor carpi radialis at 17.0 ± 1.1 months; and from the digital extensors at 22.8 ± 2.0 months. The average sensory recovery of the index finger was S2. Transient paresthesia in the hand on the donor side, which resolved within 6 months postoperatively, was reported by all patients.CONCLUSIONSThe C7 nerve root contributes consistently to the lateral pectoral nerve, the thoracodorsal nerve, and long head of the triceps branch of the radial nerve. CC7 to C7 nerve transfer is a reconstructive option in the overall management plan for TBPP. It was safe and effective in restoring shoulder adduction and elbow extension in this patient series. However, recoveries of wrist and finger extensions are poor.

Comparison of Convolutive Kernel Compensation and Non-Negative Matrix Factorization of Surface Electromyograms

We compared non-negative matrix factorization (NMF) and convolution kernel compensation techniques for high-density electromyogram decomposition. The experimental data were recorded from nine healthy persons during controlled single degree of freedom (DOF) wrist flexion-extension, supination-pronation, and ulnar-radial deviation movements. We assembled the identified motor units and NMF components into three groups. Those active mostly during the first and the second movement direction per DOF were placed in the G1 and G3 groups, respectively. The remaining components were nonspecific for movement direction and were placed in the G2 group. In ulnar and radial deviation, the relative energies of identified cumulative motor unit spike trains (CSTs) and NMF components were similarly distributed among the groups. In other two movement types, the energy of NMF components in the G2 group was significantly larger than the energy of CSTs. We further performed a coherence analysis between CSTs and sums of NMF components in each group. Both decompositions demonstrated a solid match, but only at frequencies <3 Hz. At higher frequencies, the coherence hardly exceeded the value of 0.5. Potential reasons for these discrepancies include the negative impact of motor unit action potential shapes and noise on NMF decomposition.

Anatomical variations of the median nerve and of the vascular-nervous structures at the wrist

Three cases of anatomical variation of the median nerve at the wrist found during our surgical activity led us to take the opportunity to expose anatomical variations by reviewing already published reviews. Consequently, on the basis of anatomical studies, clinical reports and imaging, as a result of careful examination of the published literature, it has been observed that the interventions in such anatomical area must take into account these variations. In particular, the most performed procedure is the lysis of the transverse carpal ligament (TCL), which is not free from complications. In our opinion it is therefore necessary, in order to avoid the complications of the nervous, vascular and tendinous sections, to use some specific technical procedures.

Variability in common synaptic input to motor neurons modulates both force steadiness and pegboard time in young and older adults

KEY POINTS

The fluctuations in force during a steady isometric contraction (force steadiness) are associated with oscillations in common synaptic input to the involved motor neurons. Decreases in force steadiness are associated with increases in pegboard times in older adults, although a mechanism for this link has not been established. We used a state-space model to estimate the variability in common synaptic input to motor neurons during steady, isometric contractions. The estimate of common synaptic input was derived from the discharge times of motor units as recorded with high-density surface electrodes. We found that the variability in common synaptic input to motor neurons modulates force steadiness for young and older adults, as well as pegboard time for older adults.

ABSTRACT

We investigated the associations between grooved pegboard times, force steadiness (coefficient of variation for force) and variability in an estimate of the common synaptic input to motor neurons innervating the wrist extensor muscles during steady contractions performed by young and older adults. The discharge times of motor units were derived from recordings obtained with high-density surface electrodes when participants performed steady isometric contractions at 10% and 20% of maximal voluntary contraction force. The steady contractions were performed with a pinch grip and wrist extension, both independently (single action) and concurrently (double action). The variance in common synaptic input to motor neurons was estimated with a state-space model of the latent common input dynamics. There was a statistically significant association between the coefficient of variation for force during the steady contractions and the estimated variance in common synaptic input in young (r2  = 0.31) and older (r2  = 0.39) adults, although not between either the mean or the coefficient of variation for interspike interval of single motor units with the coefficient of variation for force. Moreover, the estimated variance in common synaptic input during the double-action task with the wrist extensors at the 20% target was significantly associated with grooved pegboard time (r2  = 0.47) for older adults but not young adults. These findings indicate that longer pegboard times of older adults were associated with worse force steadiness and greater fluctuations in the estimated common synaptic input to motor neurons during steady contractions.

Somatotopic Mapping of the Developing Sensorimotor Cortex in the Preterm Human Brain

In the mature mammalian brain, the primary somatosensory and motor cortices are known to be spatially organized such that neural activity relating to specific body parts can be somatopically mapped onto an anatomical "homunculus". This organization creates an internal body representation which is fundamental for precise motor control, spatial awareness and social interaction. Although it is unknown when this organization develops in humans, animal studies suggest that it may emerge even before the time of normal birth. We therefore characterized the somatotopic organization of the primary sensorimotor cortices using functional MRI and a set of custom-made robotic tools in 35 healthy preterm infants aged from 31 + 6 to 36 + 3 weeks postmenstrual age. Functional responses induced by somatosensory stimulation of the wrists, ankles, and mouth had a distinct spatial organization as seen in the characteristic mature homunculus map. In comparison to the ankle, activation related to wrist stimulation was significantly larger and more commonly involved additional areas including the supplementary motor area and ipsilateral sensorimotor cortex. These results are in keeping with early intrinsic determination of a somatotopic map within the primary sensorimotor cortices. This may explain why acquired brain injury in this region during the preterm period cannot be compensated for by cortical reorganization and therefore can lead to long-lasting motor and sensory impairment.

Task- and domain-specific modulation of functional connectivity in the ventral and dorsal object-processing pathways

A whole-brain network of regions collectively supports the ability to recognize and use objects-the Tool Processing Network. Little is known about how functional interactions within the Tool Processing Network are modulated in a task-dependent manner. We designed an fMRI experiment in which participants were required to either generate object pantomimes or to carry out a picture matching task over the same images of tools, while holding all aspects of stimulus presentation constant across the tasks. The Tool Processing Network was defined with an independent functional localizer, and functional connectivity within the network was measured during the pantomime and picture matching tasks. Relative to tool picture matching, tool pantomiming led to an increase in functional connectivity between ventral stream regions and left parietal and frontal-motor areas; in contrast, the matching task was associated with an increase in functional connectivity among regions in ventral temporo-occipital cortex, and between ventral temporal regions and the left inferior parietal lobule. Graph-theory analyses over the functional connectivity data indicated that the left premotor cortex and left lateral occipital complex were hub-like (exhibited high betweenness centrality) during tool pantomiming, while ventral stream regions (left medial fusiform gyrus and left posterior middle temporal gyrus) were hub-like during the picture matching task. These results demonstrate task-specific modulation of functional interactions among a common set of regions, and indicate dynamic coupling of anatomically remote regions in task-dependent manner.

Movement-related beta oscillations show high intra-individual reliability

Oscillatory activity in the beta frequency range (15-30Hz) recorded from human sensorimotor cortex is of increasing interest as a putative biomarker of motor system function and dysfunction. Despite its increasing use in basic and clinical research, surprisingly little is known about the test-retest reliability of spectral power and peak frequency measures of beta oscillatory signals from sensorimotor cortex. Establishing that these beta measures are stable over time in healthy populations is a necessary precursor to their use in the clinic. Here, we used scalp electroencephalography (EEG) to evaluate intra-individual reliability of beta-band oscillations over six sessions, focusing on changes in beta activity during movement (Movement-Related Beta Desynchronization, MRBD) and after movement termination (Post-Movement Beta Rebound, PMBR). Subjects performed visually-cued unimanual wrist flexion and extension. We assessed Intraclass Correlation Coefficients (ICC) and between-session correlations for spectral power and peak frequency measures of movement-related and resting beta activity. Movement-related and resting beta power from both sensorimotor cortices was highly reliable across sessions. Resting beta power yielded highest reliability (average ICC=0.903), followed by MRBD (average ICC=0.886) and PMBR (average ICC=0.663). Notably, peak frequency measures yielded lower ICC values compared to the assessment of spectral power, particularly for movement-related beta activity (ICC=0.386-0.402). Our data highlight that power measures of movement-related beta oscillations are highly reliable, while corresponding peak frequency measures show greater intra-individual variability across sessions. Importantly, our finding that beta power estimates show high intra-individual reliability over time serves to validate the notion that these measures reflect meaningful individual differences that can be utilised in basic research and clinical studies.

Bifid median nerve and carpal tunnel syndrome: an uncommon anatomical variation

Dear sir, one of the most common entrapment neuropathy syndromes in clinical practice is "Entrapment of median nerve in carpal tunnel" also called "Carpal tunnel syndrome (CTS)" (Aydin et al., 2007; Huisstede et al., 2010). This syndrome is caused by entrapment of the median nerve in the wrist (Preston and Shapiro, 2005) when the pressure increases in the carpal tunnel. A high division of the median nerve proximal to the carpal tunnel, also known as a bifid median nerve, is a rare anatomic variation that may be associated with CTS and with persistent median vessels (Lanz, 1977). This anatomic variation has an incidence of 0,8% to 2,3% in patients with CTS. Lanz (1977) has characterized this anatomic condition of the median nerve in the carpal tunnel. These anatomic variants have been classified into four groups: - Group 0: extraligamentous thenar branch (standard anatomy); - Group 1: variations of the course of the thenar branch; - Group 2: accessory branches at the distal portion of the carpal tunnel; - Group 3: divided or duplicated median nerve inside the carpal tunnel; - Group 4: accessory branches proximal to the carpal tunnel. During dissection of the wrist performed for the treatment of a CTS under local anesthesia, we found an anatomical variation of the median nerve that was divided in two branches inside the carpal tunnel (Group 3 of Lanz Classification) and in which its radial branch passed through its own compartment. The two parts of the nerve seems to be unequal in size (Fig. 1). Moreover the nerve passed in carpal tunnel associated with a median artery, so we classified this variation in the group 3b of Lanz Classification (Fig. 2). The persistence of median artery coexisting with a bifid median nerve has been widely reported in surgical literature (Lanz, 1977; Barbe et al., 2005). Before surgical intervention clinical evaluation of patient and electrophysiological examination showed no differences compared to a non bifid median nerve entrapment syndrome. In conclusion the bifid median nerve may facilitate compression of median nerve in the carpal tunnel because of its increased cross sectional area even if it has no electrophysiological or clinical differential diagnosis in case of CTS. The aim of this letter is aware the physicians in order to borne in mind the possible presence of a median nerve variation during dissection of carpal tunnel in order to avoid the damage of this non common anatomical structures.

Wrist denervation of the posterior interosseous nerve through a volar approach: a new technique with anatomical considerations

PURPOSE

Full or selective wrist denervation is an effective treatment for chronic wrist pain. In this cadaveric study, a volar approach for prophylactic denervation of the posterior interosseous nerve (PIN) and the anterior interosseous nerve (AIN) was assessed, which can simultaneously be performed during volar approaches for distal radius fracture fixation or in combination with metalwork removal.

MATERIALS AND METHODS

In total 40 adult upper limbs, embalmed using Thiel's method, were investigated. Group 1 included 20 limbs of which the distances between AIN and PIN to the ulnar margin of radius were measured at levels 6, 8 and 10 cm proximal to the styloid process and the distance radial styloid process to proximal border of pronator quadratus which might be useful as an intraoperative landmark. Subsequently further additional 20 adult limbs (group 2) were used. Transection of the PIN via this volar approach at the evaluated best level of step 1 was performed and evaluated by dissection via a dorsal approach.

RESULTS

In group 1, the PIN runs within the interosseous membrane, from the ulnar border of the radius, 6.4 mm (SD 2.66) at 6 cm, 8.4 mm (SD 2.28) at 8 cm and 3.75 mm (SD 5.46) at 10 cm proximal to the radial styloid. The AIN runs within the interosseous membrane, from the ulna edge of the radius, 7.5 mm (SD 2.4) at 6 cm, 7.3 mm (SD 1.95) at 8 cm and 2.35 mm (3.42) at 10 cm proximal to the radial styloid. AIN and PIN were in close proximity at the 8-cm level which equals a 1-cm distance proximal to the pronator quadratus border. Group 2 showed a successful transection of the PIN through a single volar surgical approach in additional 18 out of 20 adult upper limbs.

CONCLUSIONS

This study shows the local anatomy of the PIN, allowing denervation via a volar approach.

Radical Wrist Denervation and Preliminary Results

Denervation is a well recognized procedure to treat degenerative or posttraumatic joint conditions, especially in cases where pain is a significant impediment to function even in the presence of stable and supple joint. However, this procedure currently is not as widely used for wrist surgeries as it merits. Denervation procedure obeys all-or-none phenomenon and we believe that even a few residual intact sensory fibers are able to transmit severe pain sensation and therefore every attempt should be made to target all the sensory supply to the wrist joint. In the present article a modified and radical technique using a single dorsal incision is proposed to address the hypothetical pitfalls of leaving undivided sensitive branches. Preliminary results of 21 cases operated on by this method are presented.