Walks normally, but feels weak in the knees when climbing upstairs.

Generally, normal walking but difficulty exerting strength in the knees when climbing stairs may be caused by meniscus injury, osteoporosis, lower extremity varicose veins, or other reasons. It is recommended to visit a hospital for diagnosis to identify the specific cause. Detailed analysis is as follows:

1. Meniscus Injury

Degeneration of the knee meniscus reduces its tolerance to friction and load, making it susceptible to damage even from minor compression. During the chronic phase of this condition, individuals may experience leg weakness or buckling. Treatment options include arthroscopic meniscus repair or partial meniscectomy performed by a qualified physician to correct the damaged meniscus and alleviate symptoms.

2. Osteoporosis

Inadequate nutritional intake, lack of physical activity, or insufficient sun exposure may lead to loss of bone matrix, resulting in osteoporosis and causing leg soreness, weakness, and fatigue. It is recommended to undergo treatments such as extracorporeal shockwave therapy or ultraviolet radiation under the guidance of a medical professional to improve bone density and relieve symptoms.

3. Lower Extremity Varicose Veins

Prolonged standing or engaging in heavy physical labor may impair venous valve function, leading to abnormal blood flow and the development of varicose veins in the legs. This can cause abnormal sensations in the lower limbs, including pain, tenderness, and numbness. It is advisable to rest more, avoid prolonged standing or sitting, and wear medical compression stockings as directed by a physician.

In addition, patellar chondromalacia may also cause similar symptoms. A detailed examination at a hospital is recommended to determine the exact cause and initiate appropriate treatment promptly.