There are two kinds of diagnoses: symptom-based and pathology-based. The medical diagnosis your mother was given is an example of a symptom-based diagnosis. When it comes to joint pain, back pain, or neck pain, the underlying cause is often unknown.
For the older adult. aging and degeneration cause the symptoms listed. Treatment is often the same no matter what the cause is anyway. Patients are more likely to get a specific diagnosis based on more advanced testing (lab work, X-rays, MRIs) if they don't get better with conservative care.
Patients who are hospitalized are also more likely to be given a pathology-based diagnosis. If no pathology can be determined, then the physician once again relies on a symptom-based diagnosis.
Medical researchers are very busy trying to find ways to better classify or group patients with neck or back pain. These type of groupings is called a taxonomy. Improving taxonomy for painful musculoskeletal conditions could help direct research and ultimately find better treatment for each condition.