Because the kidney is located at the waist, people often think that there is something wrong with the kidney when they feel discomfort or pain in the waist. In fact, the tissue structure of the waist is more complicated, and there are many reasons for low back pain. The common causes of low back pain can be divided into two categories:

(1) There are no nociceptive nerves in renal parenchyma, but there are abundant nociceptive nerves in renal capsule. Therefore, only when the renal capsule is involved, pain will occur, and its pain nature can be divided into:

① Kidney swelling: it is the swelling or dull pain caused by kidney disease pulling the renal capsule, or the swelling or dull pain caused by pathological changes invading local nerves, which often presents a persistent internal heavy feeling, often aggravated after standing or fatigue, without nausea and vomiting. Common in acute nephritis, renal cyst, pyelonephritis, obstructive nephropathy, nephrotic syndrome, renal vein thrombosis, nephroblastoma and so on.

② Perirenal inflammation: It is severe pain caused by acute ischemia, rupture, suppurative inflammation or trauma of renal parenchyma or perirenal. It is persistent, but unlike renal colic, the waist pain is aggravated, so patients often take a lying position. Check the muscle spasm of the affected part, and there is obvious tenderness at the rib ridge angle. It is common in inflammation or abscess of perirenal tissue, rupture of renal cyst, hemorrhage or necrosis of renal tumor, renal infarction (thrombotic arterial occlusion, arteriosclerosis, renal artery occlusion, polyarteritis, renal vein occlusion) and trauma.

③ Obstructive colic: Most of them are sudden, intermittent or persistent colic, which is aggravated during the attack. The site of colic is often related to the site of urinary tract obstruction. For example, at the junction of renal pelvis and ureter or the upper ureter is blocked, colic begins in the lateral abdomen and can radiate to the upper abdomen, waist or lower abdomen, and even the pudendal part and the inner thigh. If the obstruction is under the ureter 1/3, colic usually begins in the anterior abdomen, groin or ipsilateral testis or vulva, and can also occur in the lateral abdomen. The duration of the attack varies, and patients often feel restless in painful dramas, accompanied by vomiting, sweating, cold hands and feet and even a drop in blood pressure. After the attack, the pain suddenly stopped, frequent urination and hematuria. If there is no infection, there will be no chills and fever. The common causes are renal tuberculosis, renal tumor, stones or blood clots falling off when renal papilla is necrotic, or necrotic tissue blocks, which are blocked in renal calices, renal pelvis outlets or ureters, causing strong peristalsis, contraction and spasm of renal calices, renal pelvis and ureters. It can also be seen in nephroptosis or wandering kidney. Because of the change of position, the blood vessels and ureters at the renal pedicle are distorted, leading to acute blood flow disorder or hydronephrosis. When the renal arteriovenous trunk and its main branches are infarcted to form thrombus, the acute blood circulation disorder of the kidney can cause severe pain similar to renal colic, but the pain is mostly persistent. Patients with vesicoureteral reflux occasionally have brief colic when urinating.

(2) Extrarenal diseases, such as lumbar muscle diseases, spinal diseases, pancreatitis, fibrous tissue hyperplasia of abdominal posterior wall or tumor, abdominal aortic aneurysm, etc. , can also cause low back pain, but they all have symptoms of corresponding diseases.