Experimental And Clinical Studies On The Mechanism Of Contralateral C7 Transfer

Brachial plexus injuries have always been trials for neurosurgeons.Despite many surgical procedures exploited before the advent of contralateral C7 transfer,they just couldn't provide adequate motor fibers to restore a totally injured brachial plexus.In that context,contralateral C7 transfer was initiated by Gu to solve the problem, especially for the management of lower trunk reconstruction after brachial plexus avulsion.Contralateral C7 spinal nerve contains 18,000～40,000 motor fibers while the sum of those were about 20,000 in previous donor nerves.No sooner had contralateral C7 transfer become an international focus than the morbidity of its donor site attracted the attention of neurosurgeons all around the world.It is generally considered that the C7 domain is also cross innervated by adjacent spinal nerves, resulting in the functional compensation of the donor site after transection of C7 for transfer.But up to date,such a hypothesis has nerve been proved by any concrete experimental or clinical study.How C7 fiber distribute in an upper extremity? How to get maximal number of motor fibers at cost of minimal morbidity of the donor site? These questions need further investigations.Methods in microanatomy,histology and electrophysiology combined with long term follow-ups were used in this study,the results of which might lead to a further comprehension of the mechanism of contralateral C7 transfer. Part 1 Rat model for precise orientation of nerves or muscles to the spinal root segmentsObjectiveAs traditional rat model is unsuitable for precise orientation of nerves or muscles to the spinal root segments,we set about initiating a new one and testing it in precise orientation of the brachialis branch of musculocutaneous nerve(BBMCN).Materials and methodsAfter general anaesthesia,the BBMCNs of SD rats were exposed.An incision along the clavicle was also made to expose brachial plexus.After transection of adjacent roots and preservation of one root of study,BBMCN was dipped into retrograde tracer true blue(TB).Traditional rat model was also used for results comparison.ResultsBBMCN was precisely oriented to C5,6,7 spinal root segments by using the new rat model,While to C4,5,6,7,8 spinal cord segments by the traditional one.But the sum of the neurons innervating BBMCN in 2 groups showed no statistical difference.ConclusionThe new rat model averts the deficits of the traditional one,for after the transection of adjacent roots and preservation of one root of study,retrograde tracer transport was limited to axons from the preserved spinal root.And if the spinal cord had been taken long enough,all those labeled neurons should be counted despite their diffusion.So the validity of the new model is self-evident. Part 2 Precise orientation of muscles in anterior limb to the spinal root segmentsObjectiveTo obtain precise orientation of muscles in anterior limb to the spinal root segments using the rat model introduced in part 1 and study the distribution of C7 domain,so as to investigate the mechanism of contralateral C7 transfer.Materials and methodsTrue blue was injected into deltoid,biceps,triceps,brachialis,flexor carpi radialis(FCR),extensor digitorium communis(EDC),flexor digitorum profundus (FDP),intrinsic muscles to obtain precise orientation of these muscles,using the same methods shown in part 1.ResultsIn rat,deltoid is mainly innervated by C5 spinal root(52.78%),biceps by C5,6 (48.36%&42.62%),triceps by C7,8(35.65%&56.52%),brachialis by C5,6 (37.83%&49.24%),flexor carpi radialis(FCR) by C5,6(55.13%&9.74%),extensor digitorium communis(EDC) by C6,7(27.12%&33.9%),flexor disitorum profundus (FDP) by CS,T1(56.25%&35.94%),intrinsic muscles by C8,T1(43.14%&49.02%).All 8 muscles studied were innervated by C7 spinal root and the innervating ratio of C7 to each muscle is to deltoid 6.94%,to biceps 7.38%,to brachialis 12.93%, to triceps 35.65%,to flexor carpi radialis 5.13%,to extensor digitorium communis 33.90%,to flexor digitorum profundus 7.81%,to intrinsic muscle 7.84%.ConclusionC7 domain is rather dispersed and all 8 muscles studied were partially innervated by C7 motor fibers.The upmost innervating ratio of C7 was less than 40%in triceps and EDC,while that of other spinal roots were over 50%.These results might help to explain the mechanism of contralateral C7 transfer,that is,the cross innervation of C7 and its adjacent spinal roots resulted in the disperse distribution of C7 domain,leading to a functional compensation after C7 transection. Part 3 Precise orientation of muscles and dermal sensory areas to the spinal root segments in humanObjectiveTo obtain precise orientation of muscles and dermal sensory areas to the spinal root segments in human and study the distribution of C7 domain,so as to investigate the mechanism of contralateral C7 transfer.Materials and methodsAn intraoperative electrophysiological study was carried out in 6 cases during contralateral C7 transfer to record compound muscle action potentials(CMAP) of muscles in upper extremities while various roots of the brachial plexus were stimulated and sensory nerve action potential(SNAP) of various roots of the brachial plexus while different dermal sensory areas of hand in the healthy side were stimulated.The amplitude of CMAPs was analyzed to obtain precise orientation of muscles and the amplitude of SNAPs was analyzed to obtain precise orientation of dermal sensory areas to the spinal root segments in human.ResultsThe percentage of C7 motor fibers in deltoid,biceps,triceps,latissimus dorsi (LD),forearm flexors,forearm extensors,thenar muscles and hypothenar muscles were 9.39%,8.83%,58.42%,63.41%,17.17%,47.78%,5.92%and 4.70% respectively.In human,deltoid was mainly innervated by C5 spinal root(61.60%),biceps by C5,6(54.37%&36.80%),triceps by C7(58.42%),latissimus dorsi by C7(63.41%), flexors at forearm by C8,T1(55.39%),extensors at forearm by C7(47.78%),thenar muscles by C8,T1(94.08%),hypothenar muscles by C8,T1(95.30%).The percentage of C7 sensory fibers in 1-5 fingers,1^st web and ulnar dorsum of hand were 21.12%,61.63%,84.33%,27.36%,0.37%,44.69%and 0.00%.In human,dermal sensory fibers in thumb were mainly from C6(62.08%),index finger from C7(61.63%),middle finger from C7(84.33%),ring finger from C8,T1 (72.64%),little finger from C8,T1(99.63%),1^st web from C6,C7(42.95%&44.69%), ulnar dorsum of hand from C8,T1(100%). ConclusionC7 domain is rather dispersed which might be the mechanism of contralateral C7 transfer. Part 4 Predicting the morbidity of the donor limb after transection of contralateral C7 spinal rootObjectiveTo predict the morbidity of the donor limb after contralateral C7 transfer by intraoperative electrophysiological study.Materials and methods6 case of contralateral C7 transfer were followed up at 1^stday,3^rd day,7^th day,4^th week,8^th week,12^th week,24^th week after operation.Stimulated single fiber electromyography(SSFEMG) and muscle strength test were perform on deltoid, biceps,triceps,latissimus dorsi(LD),extensor digitorium communis(EDC), abductor pollicis brevis and abductor digiti minimi.Triceps reflex was also observed. 2 point discrimination and monofilament sensory evaluation were carried out at pulp and dorsum of 1-5 fingers,1^st web and ulnar dorsum of hand,thenar and hypothenar.Results4 of 6 cases finished the follow-up.The positive correlation coefficient between percentage of C7 fibers in hand dermal sensory areas and postoperative monofilament sensory evaluation was 0.9939.Percentage of C7 fibers in hand dermal sensory areas and hypoesthesia period were also correlated.The positive correlation coefficient between percentage of C7 fibers in LD,triceps,EDC and SSFEMG data was 0.9735. Percentage of C7 fibers in LD,triceps,EDC was also correlated with their muscle strength and triceps reflex recovering period.ConclusionIntraoperative electrophysiological study might be useful in predicting the morbidity of the donor limb after contralateral C7 transfer. SummaryMethods in microanatomy,histology and electrophysiology combined with long term follow-ups were used in this study.We initiated a novel rat model for precise orientation of nerves or muscles to the spinal root segments and then used it for precise orientation of main muscles in anterior limb to the spinal root segments in rat. The results showed that the C7 domain was rather dispersed,its upmost percentage of innervation in upper limb muscles was less than 40%,which might explain the functional compensation after transection of contralateral C7 spinal root.For the first time,standard methods have been utilized in precise orientation of muscles and dermal sensory areas to the spinal root segments in human and the results shows the cross innervation of C7 and its adjacent spinal roots is the practical mechanism of contralateral C7 transfer.By intraoperative electrophysiological study,we are the first to predict the morbidity of the donor limb after transection of contralateral C7 spinal root and establish a preliminary clinical standard to instruct contralateral C7 transection.