Anatomical And Clinical Studies On Modified Posterior Approach Technique For Accessory-Suprascapular Nerve Transfer

In recent, the nerve transfer technique of accessory nerve to suprascapular nerve, which is widely used in clinical work, has been the routine method for restoration of the shoulder abduction in brachial plexus injury. The traditional approach through the transverse supraclavicular incision sacrificed the function of the upper part of trapezius muscle dominated by the accessory nerve to some extent. If the trapezius muscle was so paralyzed that the scapula bone cann't close to the thorax, the restoration of should abduction will be impeded. Therefore, the reservation of accessory nerve dominating the upper trapezius muscle has great significance for shoulder abduction and its shape.This research carried out the anatomical and histological studies on the accessory nerve and suprascapular nerve in the deep surface of the trapezius muscle, designed the modified posterior approach nerve transfer technique. Then we put it into the clinical work and received a preliminary curative effect. The study has certain theoretical and practical significance for shoulder abduction rehabilitation in the treatment of brachial plexus injury.Material and Methods8 adult cadavers fixed by 10% Formaldehyde were involved, in which 12 neck specimen were ultimately dissected.Each cadaver was placed in a prone position. Stripping and turning laterally the skin of posterior region of neck and back, then exposing the posterior cervical triangle and trapezius muscle. Splitting bluntly along the inferior margin and cutting the originating point of this muscle. In the process, we recorded the main course of the muscular branches of accessory nerve, observed project of body surface and its relationship with the cervical plexus. Then we selected acromial end and C7-spinous process as the anatomical landmarks, then incised the skin along the imaginary line between the two points. The accessory nerve was found in the deep surface of trapezius muscle and cut distally after the length of scatheless dissociation was examined. Pull upward the trapezius muscle along the muscle fiber vertically to explore the superior margin of the supraspinous, then find out the suprascapular notch so as to the suprascapular nerve. After recording the distance from accessory nerve to suprascapular notch, the nerve transfer technique was tested in the designed incision. At last, we took the nerve segments of 0.5cm from the two anastomotic stomas and the cross-point of scapular spine and the margo medialis scapulae. The segments were made into histological section and stained with H-E method. Cross sectional histologic pictures of the analyzed nerve were captured by using a light microscope connected to a digital camera. The number of myelinated axons was counted with a computer assisted method.The data analysis was performed using SPSS 10.0 statistical software. Result(A) Anatomical outcome of the accessory nerve :1. accessory nerve in the posterior cervical triangle:The accessory nerve exited from the posterior border of the sternoc- leidomastoid muscle at the upper 1/3 point, and passed through the posterior triangle, divided 1~2 branches to the upper trapezius muscle before entering into the deep fascle of the trapezius muscle.2. accessory nerve in the deep surface of the trapezius muscle: The accessory nerve divided 1~3 branches at a distance of (1.67±0.32) cm from the superior margin of the trapezius muscle. Its trunk then followed a constant course along the vertebral border of the scapula until it became terminal muscular branches. The project of the truck and branches of accessory nerve was in the medial 30%~50% of line between the acromial end and C7-spinous process. And the most lateral branch located in the 43% of the line.3. branches of cervical plexus innervation of trapezius muscleThe cervical composition entered the spinal accessory nerve in the deep of the trapezius muscle, or entered the muscle to innervate it directly. These branches can mostly track to anterior root of the spinous process.(B) Anatomical and histological results of the technique:1.anatomical results:The two mentioned nerves can both be find in this incision. The length of scatheless dissociation of accessory nerve is(2.74±0.34)cm,and the distance between the accessory nerve and suprascapular notch is (2.84±0.41)cm. Their equation is(0.11±0.46)cm, so only can the suprascapular nerve dissociation length reach to 0.4cm, it suffices the need for nerve anastomosis .In the modeling operation, the two nerve can be anastomosed without any tension.2. histological results:The mean number of myelinated axons of the spinal accessory nerve was(2120±207),which is significantly more than that in the cross point of the scapular spine and medial border of the scapular bone in the descended part(1340±120).And the suprascapular nerve possesses the myelinated axons of(3137±199). Discussion:1. The necessity of retaining muscular branches of upper trapezius :According to the biomechanics of shoulder joint, the motion of shoulder abduction is the result of synergism of articulatio humeri and acromioclavicular joint. The upper trapezius is the main dynamic muscle to complete the motion of acromioclavicular joint . Recent studies on the innervation of trapezius demonstrate that accessory nerve is mainly nerve dominated, and the position and proportion of cervical branches are both uncertain. Therefore, when the accessory nerve transfer to suprascapular nerve to restore shoulder abduction, it is necessary to retain the function of upper trapezius. The researchers now are focus on the topic about the location where to cut the accessory nerve restoration of shoulder abduction.2. The superiority of posterior approach to nerve transfer technique to the anterior one:a. It is difficult to explore the nerve and has side damage from anterior approach; While the location of the accessory nerve and suprascapular nerve is relatively fixed at posterior area.b. The way of cutting accessory nerve at lower lever can retain some upper branches. But its splitting technique is hard to cause injury of the nerve itself.c. The posterior approach technique has the advantage of shortening the distance of nerve regeneration.d. We anastomose the two nerves at the suprascapular notch, by which the spinoglenoid notch region can be examined thoroughly.e. The anterior approach has the disadvantage of causing long scar and unacceptable for the patients.3. Choice of incision for the accessory nerve transfer to suprascapular nerve:The new modified technique has the advantages to the traditional ones: In this study, we select the the acromial end and C7-spinous process as the landmark of body, which is easily found through palpitation or even inspection. Moreover, the line of these two landmark lies 3cm below the anterior margin for the different constitutional types. Above the lever, the accessory nerve gives off 1~3 muscular branches. That is to say, the innervation of the upper trapezius muscle could be retained at this lever. The study on the anatomy of accessory nerve also shows that the projection of the truck and its branches are between 30~50% of the line connected the acromial end and C7-spinous process, while the suprascapular nerve was located in the suprascapular notch ~3.3cm just medial to the conoid tubercle of the clavicle. Thus, the incision along line mentioned above could identify both nerves.Comparing to the posterior approach of the upper margin of the scapular spine, this technique has the following advantages:①.The incision goes along with the direction of the trapezius muscular fiber, not cuts down the ending point of trapezius. These steps reduce the side damage of operation and make it easy to carry out;②The donor nerve could provide adequate regenerating axons. But it preserves only a few branches of upper trapezius. Whether these branches could innervate the trapezius is uncertain and determined by the clinical application.