Xray is done while lying down or standing?

Based on the X-ray, your mother has degenerative changes (osteoarthritis) in the left knee, more likely affecting the joint surfaces, which is common at her age and weight. The sudden sound while stretching was likely due to cartilage roughness or a meniscal strain, which can trigger acute pain without a fracture. Pain while getting up from a chair and walking initial steps is very typical of knee osteoarthritis with acute inflammation. For quick pain relief, she should rest the knee, avoid squatting and stairs, use ice or warm fomentation, apply a topical anti-inflammatory gel, and take short-term pain medication as prescribed. If pain does not improve in a few days, a knee injection or further evaluation (MRI if locking persists) may be needed; this is painful but not an emergency condition.

Severe knee arthritis