The goal of this clinical trial is to learn if a single session of ultrasound-guided nerve hydrodissection can relieve symptoms of diabetic lower limb entrapment neuropathy, a condition caused by compressed nerves in the leg that leads to numbness, pain, or muscle weakness in people with diabetes. The main questions it aims to answer are whether nerve hydrodissection improves nerve function (measured by the Toronto Clinical Scoring System) one month after treatment, and whether it relieves pain and improves quality of life. Researchers will compare two groups: one will receive the actual nerve hydrodissection (injection of medicine around the compressed nerve), and the other will receive a sham procedure that involves injecting a small amount of fluid under the skin (not around the nerve). Participants will not know which group they are in, and the researchers who measure the results will also not know. Participants will have four in-person visits over about one month, complete questionnaires about their nerve symptoms, pain, and quality of life, undergo nerve ultrasound at the beginning and at follow-up visits (at 1 month after treatment), and receive either the nerve hydrodissection or the sham procedure at the second visit. All participants will continue their regular diabetes and nerve medication during the study.

Inclusion Criteria:

1. Age 18-85 years, male or female;
2. Diagnosis of DLLEN meeting the following criteria: ① Clinical diagnosis of DPN (presence of DPN clinical symptoms plus at least one positive physical sign, or absence of symptoms but presence of two or more positive physical signs), with other etiologies excluded; ② Presence of unilateral or bilateral lower limb symptoms suggestive of peripheral nerve entrapment, including hypoesthesia/paresthesia in a specific nerve distribution area, pain and/or motor dysfunction, or a positive Tinel sign at the corresponding site; ③ Physical examination findings such as decreased or absent skin sensation in the corresponding nerve distribution area, reduced or absent strength of ankle dorsiflexion or eversion, metatarsophalangeal joint movement disorder, foot drop, or foot inversion; ④ Electrophysiological study showing slowing or blockade of nerve conduction velocity at a specific site (across a narrowed segment); ⑤ Imaging study (nerve ultrasound) showing compression of the corresponding nerve (cross-sectional area at the entrapment site exceeding the upper limit of the reference range, decreased nerve echogenicity, or swelling of the nerve fascicles). Diagnosis requires fulfillment of ①, ②, and ③, plus either ④ or ⑤;
3. Inadequate response to adequate treatment with medications such as mecobalamin and α-lipoic acid;
4. Understanding of the entire study process and voluntary provision of written informed consent.

Exclusion Criteria:

1. Presence of another clearly identified etiology assessed by the investigator as the primary cause of the patient's current lower limb neurological symptoms, including but not limited to: cervical or lumbar spine disease (e.g., radicular symptoms or sciatica), lower extremity vascular disease, cerebral infarction, thyroid dysfunction, vitamin B12 deficiency, heavy alcohol use history, recent chemotherapy or radiotherapy, drug toxicity, or other non-diabetic causes of neuropathy (e.g., CIDP, cauda equina syndrome, subacute combined degeneration of the spinal cord, Guillain-Barré syndrome);
2. Concurrent malignancy, active systemic infection, or immune system disease;
3. Lower limb edema due to any cause;
4. Skin breakdown or infection at the treatment site below the knee;
5. Severe cardiac, hepatic, or renal insufficiency (eGFR <30 mL/min/1.73m², liver transaminases >2.5 times the upper limit of normal, or New York Heart Association functional class ≥II);
6. Cognitive impairment or severe mental illness;
7. Pregnancy or breastfeeding;
8. Participation in another interventional clinical trial within the past 3 months;
9. Poor compliance, assessed as unlikely to complete the study per protocol;
10. Any other condition assessed by the investigator as making the patient unsuitable to complete the trial.