Dear Coley6

Thanks again for your updates,

ill try to give an explanation to what i think is going on however bear in mind that you are not being seen and what is being said here is in response to the information you have given so far therefore anything you get like you say is for your physician/doctor/consultant/physio to ultimately take charge of.

the trapezius muscle is mostly innervated motor wise by the spinal accessory nerve, this nerve runs underneath the trapezius muscle and can be injured in multiple cases of dislocation when there is excessive stretch to the trapezius (a kind of traction injury) or during compression when something pushes down on the trapezius muscle for prolonged periods. because you have a diagnosis for hypermobility which is a dysfunction of connective tissue, this is more likely to happen because the blood vessels are also affected.

nerves generally get damaged in three stages...ill summarize in simple terms.compression stage (gets better almost immediately the compression is taken off), mild post compression stage (some aspects of the nerve is damaged but it still conducts), and total compression or nerve snapping when the nerve is cut off... you might hear terms like neuropraxia, axonotmesis and neurotmesis to define these classifications.

howver prior to any of these stages, there is a stage that is not even noticed on a cellullar level...this has to do with the blood supply to the nerves, even a mild compression can cut of the blood supply thats starts the whole process...

because the spinal accessory is a motor nerve, you wont have any sensory perceptions i.e numbness, parasthesia, burning sensation etc in the beginning something that would cast your mind to a nerve issue....hence the only sign that you may notice is atrophy and weakness, so dont be surprised at how you didnt notice this until now

maybe the problem has been the trapezius muscle the entire time, giving the illusion of a serratus anterior weakness because both tend to couple in shoulder elevation tasks and a severe trapezius muscle weakness can give the illusion of serratus anterior weakness (scapular winging)

now muscles generally maintain their tone because of a trophic influence given to them by the nerves that supply them even when they are not active.

like a hose pipe that allows water flow through, if you block the hose slightly some water will pass but slowly , block it totally and no water passes at all. same thing happens with nerve transmission/conduction

headaches are quite a complex issue...ruling out other medical causes is necessary...however on a musculoskeletal level, there is an indirect relationship with trapezius muscle stress and headaches. often the headaches are one sided, are related to activity and usually present at the back of the head all the way to the eye level. this is usually muscles in the neck under tension working hard to maintain alignment in the light of deep flexor weakness.

MRI results are unremarkable and in the elderly radiological exams will show at best arthritic changes of the cervical vertebrae paticularly the facet joints of the superior ones.

the nerve conduction test will check to see if the nerves are the problem here and if they are how bad the situation is...only then can a good treatment plan be made...

shoulder shrugging is a good test but it has its own problems, the trapezius muscle is not the only muscle that carries out this action.

I guess on a clinical level, the challenge will be to see if the trapezius has any activity at all...the EMG is more accurate in answering this question. therefore if you dont want to go for this yet, your clinician may need to try different positions with and without gravity affecting with palpation to see if its active at all... if if it is, probably the site (and im assumming that it is a nerve issue now) of the nerve problem is within the trapezius muscle because thats where it becomes superficial...

neurodynamic tests may be necessary ( care to be taken not to stretch the nerve but to aim to glide instead), gentle massge may be necessary, keeping the trapezius in a shortened position without compression is neccessary...therefore any exercises that might stretch this should be avoided...

fixed postures that causes stretches of compression should be avoided....

it may be necessary to assess the neck too as the trapezius muscle has its origin from there....

not the most ideal situation, however a forearm sling cuff may be needed...the only downside to this is the risk of compressing the trapezius on the other side...

best of luck and keep us updated