The left arm pain and weakness may be related to cervical spine lesion, shoulder joint lesion, elbow joint lesion, wrist joint lesion and so on. 1. Cervical spine lesions: such as cervical disc herniation, due to local nerve compression, the left upper arm pain and weakness may occur. 2. Shoulder joint lesions: common causes include frozen shoulder, rotator cuff injury, etc. Clinically, it mainly manifests as weakness and pain in the left upper limb. 3. Elbow joint lesions: if the elbow joint undergoes degenerative changes or is deformed after trauma, the ulnar nerve of the elbow will be compressed, and then there will be abnormal sensation in the left forearm or even the whole left hand, such as soreness and weakness. 4. Carpal joint lesion: If it is caused by carpal joint lesion, it is mostly related to the compression of the median nerve on the palm side of the wrist, resulting in limb pain and weakness, or accompanied by activity disorder. In short, when the left arm pain, weakness, do not self-correction, it is recommended to the regular hospital orthopedic consultation, a clear diagnosis and timely treatment to avoid aggravation of the condition.