Possible causes of hard nodules at the finger joints include tendon sheath cysts, bone tumors, skin-like diseases, osteophytes, and soft tissue tumors. 1. Tendon sheath cysts: chronic inflammatory changes formed due to repeated wear and tear of the tendon sheath of the finger joints. If the volume is small and does not affect normal function, it is temporarily observed. If the cyst increases in size and becomes painful during the process, closed treatment or surgical resection is recommended. 2. Bone tumor: Bone tumor invading surrounding tissues may form hard nodules in the finger joints. It is recommended to improve imaging examination such as CT or MRI to clarify the size and scope of the tumor, and perform surgical resection as early as possible, combined with radiotherapy if necessary. 3. Skin diseases: warts caused by viral infection may also form nodules, and dermatology consultation is recommended. 4. Bone hyperplasia: with age, bones will undergo aging and degenerative changes, resulting in bone hyperplasia, which may also form nodules. 5. Soft tissue tumors: Fibroids may also cause nodule formation. It is recommended to go to the local hospital as soon as possible to get a clear diagnosis and follow the doctor’s instructions for treatment.