When young patients experience an anterior cruciate ligament (ACL) rupture in the knee joint and do not undergo surgical treatment, they may face a series of long-term and severe consequences. The following is a brief analysis of these harmful effects:

1. Reduced Knee Joint Stability
        Main manifestation: The ACL is one of the crucial structures maintaining knee joint stability. After rupture, the stability of the knee joint significantly decreases. Patients will noticeably feel weakness and instability in the knee joint when walking, running, or performing other activities, and may even experience "giving way" of the knee.
        Consequences: Long-term reduced stability can lead to easier injury of the knee joint during movement, further aggravating the degree of knee joint damage.

2. Accelerated Wear of Articular Cartilage and Meniscus
        Cause: After the knee joint's stability decreases, the cartilage and meniscus within the joint are prone to wear when bearing abnormal stress.
        Consequences: The wear of cartilage and meniscus further exacerbates the instability of the knee joint, forming a vicious cycle. When wear is severe, it may lead to serious diseases such as bone hyperplasia and osteoarthritis, severely affecting the patient's daily life and athletic ability.

3. Muscle Atrophy
        Cause: Due to knee instability and pain, patients often reduce the activity of the affected limb, leading to insufficient exercise of the thigh muscles over an extended period, resulting in muscle atrophy.
        Consequences: Muscle atrophy not only affects the patient's appearance but also reduces their athletic ability and may even lead to disability.

4. Decreased Athletic Ability
        Manifestation: After ACL rupture, patients will noticeably feel inadequate in activities requiring rapid response and stable support from the knee joint, such as running, sudden stops, sharp turns, and single-leg jumps.
        Consequences: Long-term decrease in athletic ability can affect the patient's social life, work, and psychological health, reducing their quality of life.

5. Pain and Swelling
        Initial symptoms: After ACL rupture, patients often immediately feel pain and swelling in the knee joint. Although these symptoms may alleviate or disappear after some time, the internal damage to the knee joint has not been repaired.
        Long-term impact: Persistent internal damage to the knee joint can lead to continuous pain and swelling, severely affecting the patient's daily life and work.

6. Irreversible Joint Damage
        Cause: As time progresses, the internal damage to the knee joint gradually worsens, leading to severe wear and degeneration of structures such as articular cartilage, meniscus, and ligaments.
        Consequences: Once severe joint damage forms, it is often difficult to reverse, and even surgical treatment may not fully restore joint function.

    In conclusion, if young patients do not undergo surgical treatment after ACL rupture, they will face a series of long-term and severe consequences, including reduced knee joint stability, accelerated wear of articular cartilage and meniscus, muscle atrophy, decreased athletic ability, pain and swelling, and irreversible joint damage. Therefore, for young patients, once diagnosed with ACL rupture, early surgical treatment should be undertaken to restore the stability and function of the knee joint.