Lower limb gangrene refers to the swelling and ulceration of the thigh, shank, knee, and ankle. In ancient medical texts, this condition is recorded as bone-attaching carbuncle (suppurative osteomyelitis), shank gangrene, ankle-penetrating carbuncle, and in modern terms, lumbar vertebrae phlegm, crane's knee flowing phlegm (tuberculosis of bone and joint), and ankle-penetrating phlegm, all of which fall under the category of yin gangrene. These conditions mostly occur in the bones and joints of the lower limbs and are within the scope of discussion for this condition.

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1. Dampness-heat Damage︰It is commonly seen in children, with the tibia being the most frequent site of onset, followed by the femur. The disease begins abruptly, initially with general malaise, shivering, high fever, dry mouth, yellow urine, yellow and greasy tongue coating, and a slippery, rapid pulse. The affected area shows diffuse swelling without a defined head, and the skin color remains unchanged. Subsequently, the affected limb experiences severe bone-deep pain, followed by slight redness of the skin and mild fever. After the affected area ulcerates, pus is discharged, initially thick and gradually thinning, with continuous drainage of pus, making it difficult to heal and leading to the formation of a fistula disease. The affected area often exhibits palpable bone enlargement and irregularity, with necrotic bone fragments discharging from the ulcer. It is often caused by residual pathogens remaining unresolved after conditions such as boil and sore, cold-damage disease, or measles, leading to internal excess of dampness-heat, with toxins penetrating deeply and lingering in the bones and tendons, resulting in blocked meridians and disharmony of qi and blood. Alternatively, it may arise from external trauma, local bone damage, and subsequent infection with toxic pathogens, leading to stagnation transforming into heat, blocking the meridians, and congealing in the bones and tendons to produce this disease. Initially, the affected limb experiences severe bone-deep pain, and within one or two days, movement becomes impossible, followed by slight redness of the skin, mild fever, and obvious swelling and bone distension. Suppuration typically occurs in about a month. Treatment should focus on clearing heat and resolving dampness, dispelling stasis to unblock collaterals. The Immortal Formula Life-Saving Decoction combined with Five-Marvel Decoction can be modified, along with oral administration of Wake-Up Subsiding Pill.
2. Wind-cold Dampness Pathogen︰It commonly occurs in children, with the same affected areas as before. Initially, there is aversion to cold and fever (though a few cases may not present with chills or fever at the onset). The tongue coating is white and greasy, and the pulse is tight and rapid or slow and tight. The affected limb has a dull, aching pain in the bones and joints, without redness or heat. Later, the pain becomes sharp like a needle prick. If the skin turns red, it may ulcerate, and the tongue coating changes to yellow and greasy, with a slippery and rapid pulse. This condition often arises in individuals with a generally weak constitution, where the defensive qi is insufficient. It may also result from exposure to wind and cold while lying outdoors, or from being exposed to cold after bathing, allowing wind-cold-damp pathogens to invade and obstruct the bones and joints. This leads to stagnation of qi and congealing of yin-blood. Initially, the affected limb has a dull pain in the bones and joints, without redness or heat, and swelling or bone distension is not obvious. Later, the pain becomes sharp like a needle prick, and the limb cannot bend, stretch, or move. Suppuration typically takes about 1 to 3 months. For cases with an exterior pattern at the onset, treatment should focus on releasing the exterior and promoting sweating, such as with Schizonepeta and Saposhnikovia Toxin-Vanquishing Powder. For cases without an exterior pattern, the approach should involve warming the meridians and dissipating cold, dispelling wind, and resolving dampness, such as with Pubescent Angelica and Taxillus Decoction.
3. Kidney Essence Deficiency︰It commonly occurs in children and young adults, often with a history of pulmonary tuberculosis. Initially, there are no obvious external lesions, only a dull aching pain in the affected area. Later, joint movement becomes impaired. In the late stage [third stage], the swollen area ulcerates, discharging thin pus. Over time, the sore becomes sunken with purplish, swollen skin around it, forming a fistula disease tract that is difficult to heal, and the muscles of the affected limb atrophy. Prolonged illness may lead to systemic symptoms: those with dual deficiency of qi and blood experience gradual emaciation, listlessness, dull complexion, fear of cold, palpitations, insomnia, night sweats, a pale red tongue with thin white coating, and a thin or weak, large pulse; those with yin deficiency with effulgent fire exhibit afternoon tidal fever, dry mouth and throat, loss of appetite, or cough with bloody sputum, a red tongue with scant coating, and a thin, rapid pulse. The condition often arises from congenital insufficiency, coupled with the softness of children's bones or injury, leading to disharmony of qi and blood and the accumulation of turbid phlegm in the bones. In young adults, it is mostly caused by excessive sexual activity, leukorrhea, or seminal emission, resulting in kidney essence depletion. Although it mostly attaches to the bone, it frequently occurs in the joints. Key points for diagnosis: in the early stage, both local and systemic symptoms are mild. Suppuration is slower, taking about six months to over a year. After ulceration, the pus is thin and often mixed with tofu-like material. Initial treatment should focus on nourishing the liver and kidneys, tonifying qi and blood, warming the meridians and unblocking collaterals, and dispersing cold-transformed stasis. Yang-Harmonizing Decoction can be used. In the intermediate stage [second stage], treatment should aim to drain toxins by tonifying and replenishing, using Toli Powder. In the late stage [third stage], for those with dual deficiency of qi and blood, treatment should focus on tonifying and replenishing qi and blood, using Ginseng Nutrient-Nourishing Decoction or Ten Major Tonics Decoction. For those with yin deficiency with effulgent fire, treatment should aim to nourish yin and clear heat, using Major Yin-Tonifying Pill combined with Bone-Clearing Powder.

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1. Waike Dacheng．Thigh Section: "Bone-attaching carbuncle (suppurative osteomyelitis), occurring on the outer side of the thigh. Bone-attaching carbuncle (suppurative osteomyelitis), occurring on the inner side of the thigh. Swelling below and firmness, arising from the tendons, is a disease caused by pudendal coldness entering the bones."
2. Waike Zhengzong．Bone-attaching carbuncle (suppurative osteomyelitis): "Bone-attaching carbuncle (suppurative osteomyelitis) is caused by long-standing sores that fail to heal, resulting from the inability of qi and blood to circulate to this area, leading to a lack of nourishment to the bones. Fine bones are formed by the accumulation of toxic qi, while large bones are formed by the intertwining of essence and blood during conception, which will inevitably lead to this type of abscess in the future."
3. 《Sore and Ulcer Encyclopedia．Bone-attaching carbuncle (suppurative osteomyelitis) Section Main Discussion》: "Feng Luzhan said: All bone-attaching carbuncle (suppurative osteomyelitis) conditions originate from the kidney. The kidney governs the bones, and treatment should focus on warming and tonifying kidney yang. When the bones receive yang warmth, the swelling and hardness will naturally dissolve."
4. Waike Zhengzong．Ankle-piercing abscess: "Ankle-piercing abscess is caused by the downward flow and stagnation of dampness-heat in the three yin meridians of the foot... Those with a head are yang in nature and easy to rupture; those without a head are yin in nature and difficult to ulcerate."