Pain that occurs after total hip surgery is a very complex problem. It can be caused by a variety of reasons, such as implant-related, intra-articular, peri-articular, and distal nerve-related. Orthopedic surgeons who perform total hip revisions face many technical challenges in patients who are often older and weaker, with a combination of incomplete tissues and inadequate metabolic reserves. There may be many issues that must be addressed, such as postoperative pain, loosening of the prosthesis, instability, unequal length of the lower extremity, periprosthetic fracture, infection, loss of bone mass, or significant bone loss. Pain is the primary indication for total hip revision, but not all pain requires revision surgery. A portion of patients, despite the absence of severe pain, sometimes have lesions that need revision in the short term as detected by clinical examination and X-ray, and delaying surgery will make future treatment more difficult, and also require revision surgery, but this is only a minority of cases. It is important to analyze the cause of the pain and determine whether the pain is due to failure of the total hip replacement, and then consider the need for revision surgery to address the cause. If it is caused by other factors, such as intervertebral disc pathology, spinal arthritis, spinal stenosis, metastatic or primary tumor, vascular obstruction, stress fracture or reflex sympathetic dystrophy, etc., then it is not a surgical indication for total hip revision. I. Evaluation of painful artificial total hip Pain after total hip replacement can be categorized into acute pain and chronic pain according to the duration. Acute pain often has an obvious trigger and has a certain time limit. Chronic pain is defined as more than one month and usually exceeds the usual self-healing time for pain. There is a chronic course with persistent or intermittent episodes. The causes of pain are usually categorized into skeletal-muscular pain and neuropathic pain. Most pain after total hip replacement falls into the former category. Pain is the main symptom in revision patients. However, almost all joint replacement patients who begin walking activities after prolonged sitting experience some pain and stiffness. Follow-up of 333 cemented Charnley total hip replacements performed at Mayo Hospital in the United States found that 25% of patients had hip pain and discomfort at one year postoperatively, and 20% of patients had hip pain and discomfort at 5, 10, and 15 years postoperatively. In some patients, the pain can be so mild that it has no effect on daily activities, while in others it can be so severe as to be disabling. For example, patients with artificial joint loosening will have pain that lasts for a longer period of time and will not be able to walk long distances. The pain of acetabular cup loosening is mostly confined to the groin, and the pain of femoral stem loosening is mostly in the thigh and can also radiate to the knee. The pain is usually noticeable with weight bearing and is alleviated or relieved by rest. The pain is aggravated by rotational movements of the hip, and a Trendelenburg’s syndrome or painful gait may be present, sometimes voluntarily shortening the limb and turning it to the outside. The onset of pain soon after arthroplasty is of great concern and suggests that an infection may be present or that the prosthesis has not gained Initial Stability, or that extra-acetabular factors may be responsible for the involvement of the hip. If there is separation of the prosthesis, abnormal rattling may occur. Pain can also be caused by conditions such as mucous bursitis, tendonitis, lumbar spine disease, abscesses and hernias. Evaluation of painful artificial total hip includes: 1. Medical history The medical history is very important in determining the source of postoperative pain after total hip surgery, and the patient’s history should be pursued and analyzed in detail, including the location of the pain, the time of pain, the severity of the pain, and the characteristics of the attack that may suggest a diagnosis, and is especially helpful in the differential diagnosis. For example, a history of tumor or nocturnal pain suggests the presence of neoplastic disease, a history of manipulation that can lead to bacteremia suggests the possibility of a bacterial infection, and a history of low back pain may suggest that spinal disease may be the cause of hip pain. Metabolic bone disease problems or severe osteoporosis can alert the physician to the patient’s risk of stress fractures. Peripheral circulatory disorders can also sometimes manifest as discomfort in the hip or thigh area. In addition, the patient’s complaints can suggest various characteristics such as the degree, location, and timing of the onset of pain after hip replacement, making the next step in the examination relevant. Among the things to be noted are: (1) temporal characteristics of the pain. It is necessary to determine whether the pain is related to the surgery. The possibilities that should be considered in the event of more than expected pain shortly after surgery are acute infection, hematoma, heterotopic ossification, tissue entrapment, impingement of the prosthesis, and failure or instability of the initial fixation. When hip pain develops after a period of pain-free hip arthroplasty, the causes to consider are: loosening of the prosthesis, chronic infection, biological stress response, soft tissue problems such as tendonitis or bursitis, and prosthesis instability. The reaction of UHMW wear particles caused by prolonged use of the prosthesis can lead to periprosthetic osteolysis, causing loosening of the prosthesis. Synovitis due to wear particles can also cause pain in the hip joint. (2) Characterization of the site of pain. Loosening of the acetabular cup often leads to pain in the hip or groin area, unipolar or bipolar artificial femoral head prosthesis can occur after the use of limb overgrowth, excessive pressure on the head and socket appearing acetabular cartilage wear, the femoral head subsidence, and the pain that occurs is also often in the groin area. If the femoral stem prosthesis loosens, it usually presents as thigh pain. Once a femoral stem prosthesis fails, especially a long-stemmed prosthesis, pain can manifest in the knee area in some patients. With a stable, uncemented femoral stem prosthesis, if pain is present, it is often in the thigh area (thigh pain). Pain in the lateral hip or lateral thigh should be considered as a possibility of bursitis of the greater trochanter. Pain located in the groin can also be secondary to iliopsoas tendonitis or iliopubic bursitis. (3) Characteristics of pain episodes. Pain caused by a sudden change in position, such as standing up after sitting for a period of time, or the first few steps when walking (“onset pain”), is usually associated with loosening of the prosthesis. The pain can be located in the groin area, buttocks, or thighs and is related to the components of the loosened prosthesis. The pain of loosening is often associated with activity and worsens after walking a certain distance. However, the same pain can also occur in patients with well-fixed prostheses, such as thigh pain, and is especially common in patients with high activity and labor intensity. Active pain can also be caused by excessive limb length, excessive pressure on the acetabulum, and wear and tear of the acetabular cartilage after artificial femoral head replacement. Hip pain due to hip instability or subluxation often occurs when the hip is in a certain position. Patients may or may not report experiencing a subluxation, but instead report pain in the groin or buttocks, which can lead to inflammation of the joint capsule or soft-tissue inflammation if this occurs frequently. Persistent pain that occurs at rest or at night should be considered more often in relation to infection or tumor. Although primary tumors or metastatic tumors in the pelvis, femur and spine are not common causes. The presence of the same pain after surgery as before should also be considered as to whether there is an extra-articular cause. If there is radiating pain, numbness, tingling or burning below the knee, lumbar spine disease should be considered as a possible cause. Neurogenic diseases, spinal stenosis, neurogenic diseases, and mechanical lower back pain require differential diagnosis. (4) Thigh pain in patients with well-fixed prostheses. A common cause of thigh pain is loosening of the femoral stem prosthesis. However, thigh pain occurs not only in patients with loosened prosthesis, but also in patients with well-fixed prosthesis and some well-fixed bone growing-in prosthesis. Often, thigh pain in patients with well-fixed prostheses has been interpreted as being related to the stiffness of the femoral prosthesis stem. In the past published literature, thigh pain was more prevalent in uncemented than in cemented femoral stem prostheses. The incidence of persistent postoperative thigh pain has been variably reported, but there is up to 30% incidence of postoperative thigh pain 2–4 years after surgery.Heekin reported that for patients with microporous anatomic total hip arthroplasty (porous–coated anatomic, PCA), the incidence of postoperative pain Heekin reported that the incidence of postoperative pain in patients with microporous anatomic total hip arthroplasty (PCA) was 15-26% at 5-7 years of follow-up. The majority of these patients presented with postoperative pain in the form of thigh pain. xenos et al. found a 12% incidence of thigh pain in the same series of patients with at least 10 years of follow-up. vresilovic et al. found that in patients with a stable shank, thigh pain was associated with a larger shank diameter. They suggested that in some patients, inconsistency in the modulus of elasticity between the prosthesis and the surrounding bone was the source of thigh pain. In a recent report in the literature, Barrack et al. examined the incidence of thigh pain in a controlled study of uncemented all-stemmed microporous (AML), uncemented proximal microporous versus cemented femoral shank fixation, and found that patients with proximally-fixed uncemented femoral shank prostheses had a thigh pain incidence 2 times that of patients with all-stemmed fixed uncemented femoral shank prostheses or patients with cemented femoral shank prostheses, with a p-value of less than 0.5. 2 times, with a P value of less than 0.01, showing a significant difference. There was no significant difference in the incidence of thigh pain between all-dry fixation of uncemented femoral stems and cemented femoral stems. Most of the thigh pain occurred within one year after surgery, and with the passage of time, thigh pain disappeared on its own in some patients. The pain level of thigh pain was not severe. Calculating the severity by visual inspection 0-10, the average thigh pain in the three groups was between 3-3.5. 2. Physical examination The patient’s pain can be duplicated in most cases by physical examination. Physical examination should include observation of gait, and gait observation helps to recognize the specific manifestations of hip disease. Determine whether there is claudication and the type of claudication, such as whether there is Trendelenburg’s sign, paralyzed gait, shortening of the lower limbs, etc., as well as whether there are neurological symptoms, such as foot drop and Parkinson’s disease tremor. Some patients with uncemented total hip replacements may be found to have limited full hip extension on gait observation, which can be seen with micromobility or unstable fiber fixation of the uncemented femoral stem prosthesis, as well as residual hip flexion contracture. On examination of hip motion, pain at the poles of flexion or extension may be due to total hip loosening, whereas pain throughout the full range of motion of the hip may indicate the presence of an acute infection. A push-pull maneuver at 90 degrees of hip flexion may be helpful in detecting subluxation and may confirm the presence or absence of instability. The examination should also include palpation of the hands, including the hip joint, nearby bursae, and tendon stops. If a patient with bursitis of the greater trochanter is reluctant to lie on the affected side, there is tenderness in the greater trochanter, and the pain is exacerbated by tension in the gluteus maximus muscle when the hip is internally rotated, compressing the bursa. Pressure pain in the pubic ramus suggests the possibility of a stress fracture. Limited tenderness in the thigh is common with loosening of the femoral stem prosthesis and may also be an indication of a stress concentration. Because pain in the buttocks and thighs may be secondary to disease of the lumbar spine, examination of the low back and lower extremity nerves can help identify the source of the pain. Tenderness along the spine or sacroiliac joints can suggest pathologic changes in these areas, and tenderness at the greater trochanter, the beginning of the N cord muscle of the sciatic bone, the gluteus maximus stop, and the region of the pyriformis muscle can suggest localized pain due to soft tissue inflammation in these areas. Examination of the nerves should include the femoral, sciatic, and obturator nerves. Spinal stenosis can be present prior to total hip replacement, but neurologic symptoms may not be evident because the hip lesion limits the patient’s mobility. After total hip surgery, long-distance walking becomes possible, and the symptoms of spinal stenosis can become noticeable enough to be brought to the patient’s attention. Acute pain after total hip surgery may be caused by a postoperative hematoma. Severe hematomas may lead to paralysis of the sciatic nerve. Excessive use of anticoagulants postoperatively increases the risk of hematoma. Acute pain associated with dislocations, fractures, or other traumatic injuries is usually characterized by a significant history of association, findings on physical examination, and radiographic demonstration. Joint infections are usually characterized by localized erythema, elevated skin temperature, and protective spasm. II.IMAGING EVALUATION OF PAINFUL ARTIFICIAL TOTAL HIP The standard radiographs include orthopantomograms of the pelvis of the involved hip joint and different types of upper segment femoral radiographs. A series of orthopantomograms, lateral radiographs, and oblique radiographs are very helpful in the evaluation of painful total hips.The radiographs must be of good quality in order to allow for the evaluation of bone mass and the examination of any minor radiographic changes that occur, such as periosteal reactions and translucent bands between the cement and the bone, between the cement and the prosthesis, and between the prosthesis and the bone. Depending on the position of the femoral head relative to the acetabular rim, it is possible to quantify the extent of polyethylene wear. If possible, current radiographs should be compared with previous radiographs, as this demonstrates the presence or absence of displacement of the acetabular or femoral prosthesis; displacement is evidence of loosening of the prosthesis. Progressive translucent bands between bone and cement, translucent bands between prosthesis and cement, or cement fractures are disturbing findings, usually associated with initiation pain and weight-bearing pain, and can be diagnostic of symptomatic loosening of the prosthesis. Subtractive hip radiographs can be helpful in confirming the diagnosis; reports have shown that plain radiographs are more sensitive and easy to detect femoral stem prosthesis loosening than acetabular cup prosthesis loosening, and subtractive hip radiographs are more accurate for both femoral stem and acetabular cup loosening.Lyons et al. reported that plain radiographs are approximately 69% accurate in diagnosing acetabular cup prosthesis loosening, femoral stem prosthesis loosening is approximately 84% accurate, and subtractive hip radiography is accurate in both sides of the hip. The accuracy of subtraction hip radiographs for bilateral prosthesis loosening is about 96%. The most commonly used radiograph is the plain radiograph, where the translucent bands produced by the loosening of the prosthesis often have reactive sclerotic lines at the margins, which can be distinguished from the normal translucent bands of the adjacent cancellous bone. A number of other signs are also clearly suggestive of loosening of the cemented prosthesis, including cement fracture, the presence of an x-ray translucency band between the prosthesis and the cemented wall, and fracture of the femoral stem and/or acetabular polyethylene. X-rays should be carefully observed regarding separation of bone growing into the surface, osteolysis, or fracture of the prosthesis. Osteolysis can progress significantly after many years without obvious signs and symptoms. It is recommended that radiographs be obtained every other year for well-functioning prostheses to evaluate for progressive osteolysis, wear of the acetabular liner, and other problems, despite the lack of clinical symptoms. Other helpful radiographs are Judet radiographs of the pelvis to evaluate the amount of bone in the anterior and posterior columns of the pelvis. Lateral films are useful for assessment of the amount of residual bone in the posterior column and for localization of the acetabulum relative to the pelvis. Computed tomography (CT) scans of the pelvis and femur are useful in visualizing the amount of residual bone despite distracting interference with imaging from the metal prosthesis.CT scans combined with endovascular angiography can show the major blood vessels surrounding the loose prosthesis. Magnetic resonance imaging (MRI) is of limited use but is helpful in the evaluation of the periarticular soft tissues, especially when looking for causes of pain unrelated to the prosthesis. Sensitivity of skeletal scanning for prosthesis loosening using technetium-99 nuclide is high but accuracy needs to be improved, Lyons et al. reported about 77% on the acetabular side and 89% on the femoral side. Labeled leukocyte skeletal nuclide scans are helpful in differentiating aseptic loosening from infection. 1.Cemented total hip replacement (1) Plain radiographs Studies have shown that 100% of migrated acetabular prostheses have loosening, and 94% of acetabular prostheses with a continuous translucent band (regardless of the width of the band) have loosening. In contrast, only 5% of acetabulars with no acetabular migration, no radiographic translucency bands, or translucency bands only in acetabular zone I were found to have intraoperative loosening of the prosthesis. When translucent bands were present in both acetabular zones I and II, 79% of the acetabular prostheses were found to be loose. However, there are many patients who still cannot be diagnosed on plain radiographs alone. The significance of the translucent band between the femoral stem prosthesis and the bone cement is controversial. Berry et al. concluded that this translucent band is not necessarily associated with hip pain in femoral stem loosening, and their study of 297 non-elective Charnley total hip arthroplasties over a period of at least 20 years or up to the time of revision demonstrated that a thin, translucent band of prosthesis-bone-cement on the outer side of the femoral prosthesis, which is <2 mm in width, was not associated with hip pain in femoral stem loosening. that did not significantly correlate with distal loosening of the femoral stem prosthesis, nor did statistical analysis show an association with hip pain. It may be a fibrous layer formed after placement of the bone cement. This translucent band is more common in smooth, collarless, wedge-shaped cemented femoral stem prostheses without clinical symptoms or failure of the femoral stem prosthesis. However, there is a clear correlation with loosening of the femoral stem prosthesis if the width of the translucency band exceeds 2 mm, which is considered reliable evidence of loosening of the femoral stem prosthesis in the study by Lyons et al. 96% of patients with this translucency band had loosening of the femoral stem prosthesis at the time of revision surgery. Patients with progressive widening of the translucent band at the bone-cement interface are indicative of loosening of the cemented prosthesis. However, non-progressive mild subsidence of the femoral stem prosthesis does not indicate loosening of the prosthesis. The best way to assess the outcome after total hip surgery is to take serial radiographs. Progressive widening of the translucent band at the bone-cement junction is often suggestive of granulomatous membranous material, which correlates with loosening of the prosthesis as well as a debris reaction to wear. If the translucent zone changes rapidly, with rough edges and a periosteal reaction, the presence of joint infection should be highly suspected. (2) Arthrography Arthrography improves the detection rate of cemented acetabular loosening when compared with plain radiographs, but a proportion of the results are false positives. The most sensitive indicator for the diagnosis of acetabular loosening is the presence of continuous contrast around the entire acetabular prosthesis, all of which is more than 2 mm wide.Maus et al. reported a sensitivity of 97% and a specificity of only 68% for the diagnosis of acetabular loosening in 97 surgically confirmed arthrography cases. However, some authors have also concluded that arthrography is not of much value in the diagnosis of prosthetic loosening. For example, Miniaci et al. found that the detection rate of acetabular prosthesis loosening by arthrography was 68%, which was inferior to plain radiographs and nuclear scans. Arthrography improves the detection of cemented femoral stem loosening. If the contrast at the bone-cement interface extends to the interrotunda portion of the femoral stem prosthesis, it is indicative of prosthesis loosening with very high accuracy. The sensitivity increases from 84% on plain radiographs to 96%, and Maus et al. reported a sensitivity of 96% and specificity of 92% for the diagnosis of femoral stem prosthesis loosening on surgically confirmed arthrography. Thus, although most femoral stem loosening can be detected on plain radiographs and arthrography does not improve the overall sensitivity of the diagnosis, arthrography can occasionally detect cases that are missed on plain radiographs. Moreover, arthrography can be used to obtain joint fluid for smear and culture, and smear and culture of the puncture material is an important means of determining joint infection. (3) Bone scanning 99mTc bone scanning is performed in patients without pain symptoms after surgery, and the results may show normal uptake or a focal increase in uptake. Generally, at 6 months postoperatively, the somatic nuclide uptake of the small transducer and prosthesis returns to normal levels, and the nuclide uptake of the acetabulum, greater trochanter, and end of prosthesis does not roughly stabilize until about 2 years. However, Utz et al. found that nuclide concentrations at the end of the femoral stem prosthesis could persist for a longer period of time in nearly 10% of total hip replacement patients. A technetium 99 bone scan performed at 1 year postoperatively showed abnormal nuclide uptake in the acetabulum, greater trochanter, and distal femoral stem. Conventional technetium 99 scanning has good sensitivity but no specificity for the detection of prosthetic loosening after total hip surgery. Radionuclide concentrations around the femoral stem, usually located at the tip of the stem, are still seen 2 years after total hip replacement without complications. A progressive nuclide concentration enhancement on serial bone scans would indicate a pathologic response as a sign of loosening or infection.Jensen and Madsen found that technetium 99 bone scans were of no significant value in the assessment of pain in total hip replacement. They found that the sensitivity of the bone scan in detecting loosening was only 77% (97% for radiographs) and the specificity was only 4 6% (70% for radiographs). False positives for technetium 99 bone scans were 23% (surgical exploration based on the results of 99mTc bone scans revealed no loosening).Leiberman et al. found that technetium 99 bone scans did not add to the basis for loosening relative to plain radiographs in a study of 54 patients. Of the 10 patients with a final diagnosis of prosthesis infection, 3 had normal bone images; of the 44 patients with femoral prosthesis loosening, 3 also had bone images that revealed no abnormality; and of the 43 cases of acetabular loosening, 4 revealed no abnormality. It is therefore proposed that technetium 99 bone scanning should only be used in patients in whom joint loosening is highly considered clinically but not demonstrated on radiographs. Leukocytes can be labeled with indium 111. Labeled leukocyte imaging is highly sensitive and specific in the setting of infection complicating total hip arthroplasty. Local uptake of leukocytes can be significantly increased following infection, either around the prosthesis, in the joint cavity or in adjacent tissue. However, labeled leukocytes can also be concentrated in aseptic inflammatory lesions, osteonecrosis tissue, rheumatoid arthritis and partially loosened prosthesis. 2, Uncemented Total Hip Replacement The porous, long-entry surface of a stable femoral prosthesis should have bone tissue growing into it with no translucent bands between them. Proximal thinning of cortical bone (stress masking) is uncommon. The welded area of the endosteal point is the bone concentration area that connects the endosteal surface to the bone long-in area; this phenomenon is most common at the distal end of the bone long-in, where it sometimes resembles small floating support jigs. The translucent zone is common around the distal end of the glossy shank, and it carries fewer consequences. Loosened femoral and acetabular prostheses may result in displacement of the prosthesis, but often a translucent band is present on the surface of the adjacent bone growth. After loosening occurs, the femoral prosthesis appears to sink, and a thick base of bone connecting the endosteal surfaces is often seen at the tip of the prosthesis. These bony tissues surrounding the loosened and displaced prosthesis can develop a significant bone remodeling shape after many years of formation. The widespread use of uncemented total hip replacements complicates the management of postoperative hip pain. The criteria for loosening of cemented prostheses do not apply to uncemented prostheses. Furthermore, the incidence of postoperative hip pain is higher with uncemented prostheses than with cemented prostheses, despite the fact that there is no radiographic basis for loosening. (1) Plain radiographs Progressive acetabular migration and changes in acetabular position indicate acetabular loosening. Fracture of the acetabular fixation screw also indicates acetabular loosening. Progressive detachment of the pearl surface from the microporous surface is consistent with acetabular migration and can be expected to result in acetabular loosening. Shank loosening correlates well with thigh pain and the incidence is higher than that of acetabular loosening.The criteria for determining shank loosening were developed by Engh et al. based on an extensive study of anatomic medullary locking (AML) prostheses. The basis for showing bone growth into and stability of the prosthesis are: a. No subsidence; and b. No increase in radiodensity on the surface of the bone and prosthesis micropores. (2) Arthrography Barrack et al. reported the results of arthrography after a number of uncemented total hip replacements; in 16 uncemented acetabulars, they found arthrography to be 29% sensitive, 89% specific , and 63% accurate. In femoral stem prostheses, they found a high proportion of both false-positive and false-negative cases, with an accuracy of 67% (3) Bone scans Bone scans of uncemented total hips showed increased uptake of nuclides in the delayed phase of the femoral stem in the majority of patients from the time of surgery to 2 years. Maniar et al. found that after 2 years, 20% of the patients still had an increase in nuclides, with a small number of patients having an increase in nuclides that extended to 4 years after the surgery. In three-phase bone imaging, Oswald et al. found that 76% of uncemented acetabular prostheses showed increased nuclide uptake in the delayed phase at 2 years or more after surgery. In noncemented femoral prostheses, 72% had abnormal technetium isotope uptake at the tip of the femoral stem at 2 years postoperatively. Thus, bone scans may have limited value for application in terms of complications in patients after noncemented total hip surgery. The significance of bone scanning of uncemented prostheses for assessing prosthesis stability is questionable. After uncemented total hip arthroplasty, patients can still experience increased uptake of indium 111-labeled leukocytes in their hips, even in the absence of complications. Studies have shown that when leukocyte-labeled indium 111 imaging is performed at two years postoperatively, increased uptake in the distal femoral stem or hip occurs in 50-80% of patients. Therefore, the use of labeled leukocyte imaging to check for the development of postoperative complications is not very reliable. Reflex Sympathetic Dystrophy and Its Treatment Reflex sympathetic dystrophy (RSD) should be considered in patients with unusual or unexplained lower extremity pain after total hip surgery. Reflex sympathetic dystrophy can be caused by any kind of trauma, and its incidence, severity, and course do not necessarily correlate with the severity of the injury or the size of the surgery. Earlier the syndrome was known by a number of names, and now the accurate professional name is Type I Complex Regional Pain Syndrome (CRPS). However, the widely accepted terminology is still Reflex Sympathetic Dystrophy (RSD). Reflex sympathetic dystrophy is a group of clinical manifestations characterized by limb pain, swelling, stiffness, skin discoloration, hyperhidrosis, and osteoporosis, caused by abnormalities and prolonged responses of the sympathetic nervous system. The etiology of reflex sympathetic dystrophy is not well understood. There are several theories, including a short-circuit effect in the area of injury, in which efferent sympathetic excitation stimulates sensory afferent fibers, periarteritis in the injured segment of the nerve, and abnormal feedback into the spinal cord contact centers. Clinical Presentation Reflex sympathetic dystrophy is a severe burning pain often described as accompanied by intolerable throbbing, knife-like rupture sensations, twinges, or squeezing pain. Patients may experience pain immediately after surgery or within a few weeks after surgery. The pain is usually not confined to the dermatomal distribution of a particular nerve and may be aggravated by emotional stimuli (e.g., shock, anger) or changes in the surrounding environment, most often in patients with severe reflex sympathetic dystrophy. Odd behaviors to relieve pain may also occur, such as certain patients' preference for wrapping the affected limb in a wet towel to relieve pain. They do not like the doctor to examine the localized pain area. Certain patients do not want to be tucked in at bedtime because the sheet also causes increased pain. In many cases, light touch, heat, or light movement of the trunk and limb can aggravate the existing pain. Often the pain is severe, with a burning, tearing pain that can worsen without a trigger and is not relieved by rest. The pain often begins at the distal end of the limb and progresses proximally over time. It is characterized by abnormal nociception, nociceptive hypersensitivity, sensory hypersensitivity and the presence of vasodilation and sweating abnormalities. In the early stages, there is often marked vasomotor instability and pain due to sympathetic hypersensitivity. Edema, congestion, elevated temperature, excessive sweating, and rigidity characterize this stage. There is frequent flushing, burning or cooling, pallor and pain in the extremities. The typical patient with early reflex sympathetic dystrophy has limb pain but no other abnormalities on clinical examination. There is often color asymmetry, or temperature asymmetry, or both, on both limbs. Nociceptive sensitization allows the patient to experience pain from even very light touch. Often the patient is reluctant to cover up while sleeping because the covers cause discomfort on the skin on the affected side. Painful symptoms and signs do not coincide with the peripheral nerve distribution area. Later the limb becomes pale and dry with increased stiffness as well as trophic changes in the skin. The patient may be more comfortable at rest, but the pain persists when it is time to exercise. In the later stages, this can lead to severe limb disability such as weakness, stiffness, coldness, muscle atrophy, and skin dystrophy can become apparent and can last for months or many years. The degree of pain is not constant. Manifestations of osteoporosis occur. There is no very satisfactory treatment for reflex sympathetic dystrophy. Early sympathetic block with physical therapy or oral medications is the widely recommended treatment. If the sympathetic block is effective, it can be continued for as long as the patient's symptoms resolve, usually for no more than 2 weeks at a time. For patients with mild symptoms who can tolerate and respond well to light active and active assisted activities, physical therapy may be used initially, and some patients may also find pain relief. Early detection and treatment may have an impact on the prognosis. Sympathectomy can be performed for patients who fail to respond to conservative treatment. The indications for sympathectomy are: those who can get temporary symptomatic relief with local sympathetic blockade, but without lasting effect. The use of preganglionic sympathectomy, which does away with the sympathetic ganglion and sympathetic chain, generally relieves the pain of reflex sympathetic dystrophy. IV.LABORATORY EXAMINATIONS Laboratory tests are helpful in the diagnosis of infection, but they do not confirm the diagnosis. In the presence of a deep infection, the patient's peripheral blood white blood cell count is often normal, but the sedimentation rate and C-reactive protein are often elevated. Normally, most patients with total hip replacement will return to a hematocrit of 20 mm/hour 6 months after surgery. Single or transient elevations of sedimentation have no clear significance and are usually due to other factors, so they should be checked several times or at regular intervals. Low-toxicity infections are a common cause of pain after total hip replacement. When the cause of pain cannot be determined after a thorough evaluation of the hip pain, a diagnostic puncture of the hip joint and a puncture fluid smear and culture are performed under fluoroscopic guidance. The most effective method for diagnosing infection after total hip replacement is arthrocentesis, and the cell count of the puncture fluid should be noted. If the white blood cell count exceeds 25,000/mm3 and is predominantly polymorphonuclear, prosthetic infection is likely. Gram staining is helpful, and if a sufficient amount of bacteria is present, Gram staining can confirm the bacterial species. If infection is still suspected at the time of revision surgery, intraoperative frozen sections should be done. More than l0 leukocytes per high power view strongly suggests the possibility of acute infection. If frozen sections combined with intraoperative findings are suggestive of infection, it is prudent to take multiple soft tissue cultures intraoperatively, as well as a large number of tissues for histologic examination, and not reinsert a new prosthesis until the patient's condition is identified. It is wise to take tissue specimens from multiple sites for bacterial cultures; if the cultures come back with the usual contaminants, it is more difficult to determine whether an infection can be diagnosed; if the bacterial cultures have only one strain, it remains uncertain whether the hip is actually infected. Elevated alkaline phosphatase (AKP) suggests that active heterotopic ossification may be present, and a positive finding on a tumor marker test may suggest the presence of a primary or metastatic tumor causing pain. V. TREATMENT OF PAINFUL ARTIFICIAL TOTAL HIP After obtaining detailed information about the patient with a painful artificial total hip, the focal issue is the management of the painful total hip or associated pain syndromes. In terms of the patient's history, the following points should be noted: the time and character of the onset of pain, the location of the pain, the duration of the pain, the circumstances under which the pain is aggravated or relieved, the presence or absence of radiating pain, the corresponding abnormal findings, and most importantly, the severity of the pain. These are very helpful in the differential diagnosis of pain. The key to pain management is a clear diagnosis and treatment of the cause of the pain. In patients with no obvious specific test findings, the usual medications available are nonsteroidal anti-inflammatory medications (NSAIDs). It is recommended to follow the World Health Organization's pain laddering program, which starts with mild pain medications and then progresses to stronger pain medications if they are not effective. Mild or moderate pain can be treated with NSAIDs, aspirin, or acetaminophen alone or with other complementary medications. Mild morphine analgesics may be added if pain relief is not apparent with their use, and strong morphine analgesics may be used if they are ineffective. Some authors have also advocated local intra-articular injection of bupivacaine for painful total hip replacements. Patients with intra-articular infections should be treated with anti-inflammatory therapy, lesion debridement and high-dose saline intra-articular irrigation containing antibiotics. If necessary, the prosthesis should be removed and the joint should be left open or filled with antibiotic-containing bone cement. Infection control is followed by a second-stage arthroplasty (usually takes about 3-6 months). For pain due to loosening of the prosthesis, total hip revision surgery should be performed.