Flat back syndrome is a degenerative condition of the lumbar spine or low back. The natural swayback position of the lumbar spine called lordosis flattens.
A decrease in lumbar lordosis causes other changes to occur in the spine. The mid-back (thoracic spine) becomes straighter without the slight kyphosis (forward curve) that is a more natural position.
Other changes occur in the soft tissue structures to compensate for the flat back position. The hips extend and the knees bend to help keep an erect posture. There is a natural tendency to hold the chest in an extended position. This helps the person keep the visual field centered ahead without focusing on the floor.
But muscle fatigue and eventual pain make it difficult to stay upright. A forward or stooped posture becomes inevitable. There is medical treatment available for this degenerative problem. But it may require surgery.
Not everyone is a good candidate for this operation. A medical evaluation is needed to find the right treatment for each patient. If your grandmother has not been examined by a medical doctor, your concern may help encourage her to do so.