Hello, Well, I don t think there is something called as an underdeveloped shoulder as terminology in medicine if it does exist I really don t know. First time listening something like this. Also, maybe the attending physician has meant, that there is a weakness of the muscles of one shoulder when compared to another, apart from that I do not understand what is an underdeveloped shoulder. Not when you mention the pain in the neck and shoulder, I think this should be related to the cervical radiculopathy. If you can take an MRI of the cervical spine we can understand some of the things better. Because the pain in the neck and shoulder can be due to two reasons, one it might be inflammation of the trapezius muscle or might be the nerve entrapment. I will advise you to take a neck collar and use it for a week or two, during this use hot water fermentation for the neck, upper back and shoulder - front and back region. See if you find any changes if any muscle inflammation is present than you might get relief of it and later you can do some slow strengthening exercises under a guided physiotherapist for both the neck and the shoulder muscles. Coming to the deformity of the thumb and index finger, if you put more details in front of me that I can understand and comment over it as, as of now it is little difficult with the so small statement about the thumb and index finger deformity. Hope I have answered your query. Let me know if I can assist you further. Regards, Jay Indravadan Patel, Physical Therapist or Physiotherapist