The Forearm Sensory Dominate Region Of The Ulnar Nerve:Clinical And Anatomical Study

Background Info.The art of clinical assessment involves an accurate determination of the causes of a patient’s symptoms. Hypoesthesia presented in the medial forearm was considered very useful diagnostic information for people who suffered ulnar neuropathy. The sensory of medial forearm was generally dominated by the medial antejjrachial cutaneous nerve(MACN), which originated from the medial cord of the brachial plexus, then went down medial to the ulnar nerve, superficially outside the cubital tunnel at the elbow, and ended into the ulnar side skin of the forearm. Therefore, numbness or stabbing pain in this region indicated MACN injury coexisting with the ulnar lesion. Clinically, in this situation doctors should further consider about thoracic outlet syndrome (TOS) of the lower trunk rather than the cubital tunnel syndrome (CuTS), in which cases those two nerves compressed by the abnormal structures of the thoracic outlet at the same time. However, some of the CuTS patients who had excluded MACN abnormality still had the symptoms of forearm hypoesthesia; and a former anatomical study reported a little cutaneous branch originated from the ulnar nerve and dominate the distal medial side of skin in the forearm. We try to observe and evaluate the incidence rate of this cutaneous branch under high resonance sonography in the volunteers; meanwhile, we also collect the cases of CuTS patients with special hypoesthesia skin area in forearm and conclude the features of this region.PurposeTo observe the occurrence rate of regional forearm numbness in the patients diagnosed cubical tunnel syndrome in our hospital, recording their hypoesthesia skin region distribution. To observe the anatomical characteristics of this unreported forearm cutaneous branch of the ulnar nerve under ultrasound. To provide more valid statistical diagnostic data of the CuTS patients.MethodsWe collected the qualified patients diagnosed with CuTS both in the out-patient and in-patient department of our hospital from Feb.2012to March2013. Several examinations were proceed under the consent of the patients before operation, including the physical examination of motor and sensory on the upper limb, the electromyogram of the branchial plexus, the ulnar nerve and the medial antebrachial cutaneous nerve, the high-resonance ultrasonography of the forearm and the ulnar nerve block anesthesia inside the cubital tunnel. We investigated the origin point of this observed forearm cutaneous branches from the ulnar nerve as well as the entry points to the skin. The patient with forearm numbness and the diagnostic examinations were all recorded in details. All the data were processed through STATA10.0., with the statistical methods of descriptive statistical analysis, T test, Pearson correlation, logistic regression and ROC regression, etc.ResultsIn the sample, there were5people reported presenting sensory loss in the medial forearm skin. The physical examinations of sensory showed significant difference. The ultrasound traced back a tiny cutaneous nerve branch dominated this skin area, originating from the ulnar nerve in the forearm. We preceded bilateral ultrasonography to all the objects, and managed to observe more similar anatomical structure of this forearm ulnar nerve branch by ultrasound in sample patients. The dominate area of this cutaneous branch were the distal ulnar one-third of the forearm skin.Observation by means of high-resonance ultrasound in124arms revealed a40.32%incidence rate of this forearm cutaneous branch of ulnar nerve. The pathway of nerve bundles origins at middle of the forearm, of which the distance to the carpi transversum was averagely47.13%±14.92%of the length of the forearm length. And the nerve branch ended at about1/3of the forearm distally, of which the distance to the carpi transversum was averagely28.41%±10.88%of the forearm length. The length of this nerve was measured on average4.84±2.27cm。According to the diagnostic information, we made a logistic regression over the maximum cross-sectional area (CSA) of the ulnar nerve at the cubital tunnel, the nerve conduction velocity, muscle atrophy degree, and age in order to conclude their correlation and provide predictive calculation that can be applied to clinics.ConclusionWe report a cutaneous branch of ulnar nerve in the forearm, proven by anatomy and clinical manifestation, of which the cutaneous branch dominates the distal ulnar one-third of the forearm skin. The clinical significance of this overlooked cutaneous nerve lies in its inspiration on the locating of the injury level. Therefore, we should no more contribute all the causes of sensory loss on the medial forearm to medial antebrachial cutaneous nerve lesion, further exams to discriminate whether it was CuTS or TOS were recommended.