The Study Of Anatomical Variations In The Innervation Of The First Dorsal Interosseous Mucscle And Clinical Significances

Background Info.In the general population, the first dorsal interosseous muscle is innervated by the deep branch of the ulnar nerve. It is hard to discover the variant innervation of it. On the other hand, the symptom of muscular atrophy could be seen in the patients with nerve compression. The nerve could recover and reinnerve after the injury. We can see the phenomena of the compensation of nerve, especially in the sensory nerve. It confirms that the role of the injury nerve could be replaced by the normal nerve around it after the injury. Besides, there are many anatomical variations in the nerve path. If one effector which is regularly charged by one nerve is innerved by some more nerve, the abnormal clinical manifestations could be found when the injury happened in the regular one or the variant one. So it is clear that corresponding manifestations could be seen in the first dorsal interosseous muscle if the injury happens in the anatomical variant nerve which innerves the first dorsal interosseous muscle.PurposeTo find the possibility of the anatomical nerve variance in the first dorsal interosseous muscle via anatomy study. To use the electrophysiology study to observe this possibility clinically. To analyze the correlation of the findings in the anatomy and in the clinic. to discover the significances to the diagnosis.Materials and MethodsWe collected the qualified patients who had nerve injury which needed to have the surgery in our department from Oct.2012 to Feb.2014. The patients were divided into three groups:the cubital tunnel syndrome group, the carpal tunnel syndrome group and the control group. Several examinations were proceed under the consent of the patients before and after operation, including the physical examination of motor on the upper limb, the electromyogram of the median nerve and the ulnar nerve. All the data were processed through STATA 11.2., with the statistical methos of descriptive statistical analysis, chi-square test, logistic regression and ROC regression, etc.ResultsIn the total 57 anatomy sample of hand, there were 3 hand discovered the muscular branch from the median nerve to innerve the first dorsal interosseous muscle, including two left and one right. One sample came from the common palmar digital nerve of thumb and index finger, two samples came from the ulnar part of the median nerve at the wrist.The results of the electromyogram test for the patients showed that there were two cases that the median nerve controlled the first dorsal interosseous muscle among the 128 cases of the carpal tunnel syndrome group. Eighteen cases were found in total 59 cases in the cubital tunnel syndrome group. And two cases in the 24 cases of the control group. Among all the 211 cases, there were 12 cases in the 109 left cases and 10 cases in the right. There were seventeen cases found in all the 46 cases in the cubital tunnel syndrome group whose age was equal or under 60, and only 1 case was found in 13 cases whose age was older than 60 in the cubital tunnel syndrome group.By using the chi-square test, there was statistical significance in the differences between the cubital tunnel syndrome and the carpal tunnel syndrome, the cubital tunnel syndrome and the control group, the patients more than 60-year-old and under 60-year-old in the cubital syndrome. There was no statistical significance in the differences between left and right hand, the carpal tunnel syndrome and the control group. The study compared the ratio of the grip strength of the thumb and index finger between the affected arm and unaffected arm in 58 cases of the cubital tunnel syndrome group. By using Mann-Whitney U test, it showed that there was statistical significance between the positive cases which the first dorsal interosseous muscle was innervated by the median nerve and the negative cases which were not. According to this result, we made a logistic regression over the the ratio of the grip strength of the thumb and index finger, and provided predictive calculation that can be applied to clinics.ConclusionWe confirm the anatomical variance that the first dorsal interosseous muscle could be innervated by the median nerve by both anatomy study and electrophysiology study. What’s more, it happens more frequently in the patients with cubital tunnel syndrome. It means that the median nerve gives the compensation to the first dorsal interosseous muscle after the injury of the ulnar nerve. Moreover, the phenomenon shows some correlation with the age. Meanwhile, when the ratio of the grip strength between the thumb and index finger was more than 0.32 in a cubital tunnel syndrome patient, it is highly possibility that there may be an anatomical variance of the median nerve to innerve the first dorsal interosseous muscle.