Abstract

BACKGROUND: Metal-on-metal hip surface arthroplasty has improved the abradability for hip joint prosthesis and has the characteristics of normal biological stress transfer.

OBJECTIVE: To observe the long-term state of hip-joint function of patients who underwent metal-on-metal hip surface arthroplasty.

DESIGN: Follow-up study for cases.

SETTING: Department of Orthopaedics, Jiangsu Provincial Corps Hospital of the Chinese People's Armed Police Force; Department of Orthopaedics, Affiliated Hospital of Nantong University.

PARTICIPANTS: Eighteen cases (23 hips) who underwent a metal-on-metal hip surface arthroplasty procedure in the Department of Orthopaedics, Jiangsu Provincial Corps Hospital of the Chinese People's Armed Police Force, and Department of Orthopaedics, Affiliated Hospital of Nantong University between September 2004 and July 2005 were recruited in this study. All cases, aged 28 to 54 years, include 11 males and 7 females. According to the classification of etiology, there were 13 cases of osteonecrosis(16 hips),3 cases of osteoarthritis( 4 hips ),1 case of congenital hip dysplasia (2 hips) and 1 case of posterior trauma arthritis(1 hip ). All cases applied the Conserve Plus resurfacing prosthesis (manufactured by Wright Medical Technology, USA), of which the pattern number of acetabular cup (press-fit depth: 1-2 mm) ranged from 38 mm to 56 mm in the inner diameter and from 44 mm to 62 mm in the outer diameter and that of femoral head cup ranged from 38 mm to 56 mm in the outer diameter. Preoperatively all patients signed the informed consent for the surgery, and the application of this technique also gave the approval of the Ethics Committee of the hospital.

METHODS: ①After the epidural and lumbar combination anesthesia was satisfactory, the coxacava was exposed at first and the suitable size acetabular cup coated by hydroxyapatite ceramic was selected to be implanted, to be tightened and to be fixed by press-fit referring to the anatomical position. Subsequently to install the femoral head prosthesis, femoral cup was laid on the ready caput femoris and impacted by the presser to make the metal cup paste close-up with sclerotin when the concocted bone cement was overlaid on the prefabricated caput femoris surface and internal surface of prosthesis. Further, short-term of femoral cup should be kept the conformity with axial ray of the femoral neck. ②Patients were allowed to make the function exercise such as initiative stretch and contract of quadriceps muscle of thigh, passive motion of the knee joint and initiative motion of the knee joint under the non-weight loading on bed. Then they were encouraged to walk with two walking sticks two weeks after operation, progressing to get out of the two walking sticks six weeks postoperatively. All affected extremities were fixated with T-shaped tabula shoes in the abduction position after operation. ③All patients were reviewed with taking the anteroposterior radiographs of pelvis, evaluation of the clinically curative effect on the procedure of metal-on-metal hip surface arthroplasty and biocompatibility between the prosthesis and the host one year and two years after operation. Moreover, Harris score was assessed for all affected hips preoperatively, one year and two years postoperatively.

MAIN OUTCOME MEASURES: ①The clinically curative effect on metal on metal hip surface arthroplasty; ②Biocompatibility;③The Harris score for the affected hips; ④The pain status of hip after operation.

RESULTS: Eighteen cases were all brought into the outcome analysis at last.①The curative effect on the metal-on-metal hip surface arthroplasty: The femoral component of one case had a varus deformation of 10°six weeks after operation, but such complications as component loosening and femoral neck fractures, etc. did not occur during the coming follow-up. The locations of rest prosthesis were satisfactory. Substantial radiolucencies were found at the rim of acetabular component (1 and 2 zone) in two hips, respectively one and two years after operation. But there was no evidence of radiolucencies around the short-stem of femoral component.②Biocompatibility: No patients were found to have obvious reactions including renal toxicity, pyretogen and rejection. No radiograph showed signs of loosening, dislocation, heterotopic bone formation, femoral neck narrowing, femoral head necrosis and prosthesis fixation failure, etc.③Harris score for the affected hips: The Harris score of all disease hips was improved from the mean 46 preoperatively to 85 one year after operation to 93 two years postoperatively. Of these,15 hips were excellent(> 90),6 hips good (80-89), and 2 hips fair（70–79）.④The pain status of hip after operation: Two patients complained of slight pain, one patient of moderate pain, and no cases of severe pain happened.

CONCLUSION: The long-term outcome for hip disease patients who undergo metal-on-metal hip surface arthroplasty is satisfactory.

INTRODUCTION

Hip arthroplasty in the younger and more activities patients remains a challenge for the orthopaedic community. The excellent results achieved in an elderly and inactive population are generally not replicated in the younger group. In addition, the expectations of a younger arthritic population have changed over the past decades such that modern prosthetic design must address both the low demand requirements of an elder patient and the work and leisure aspirations of the younger patient. Resurfacing of the hip has promised to offer a solution for several decades. The proposed advantages of the metal on metal hip resurfacing when compared to conventional THR include the initial preservation of the head and neck bone and of the femoral canal, maintaining normal femoral loading and stresses, leaving more options for future revisions, and decreasing the risk for dislocation, etc. However, such problems as its design, fixation and bearing performance, etc. have usually led to fixation failure [1]. After several pilot studies, it
became clear by 1996 that a metal on metal device with a hybrid fixation could produce acceptable results. The current design is a high-carbon cast chrome-cobalt device with a stemmed spherical component designed for cemented fixation and a hydroxyapatite porous-coated acetabular component for non-cemented press-fix fixation [2]. There have been some recent reports of good early results of resurfacing arthroplasty. This paper reported the long-term outcomes of a consecutive series of hip resurfacing using Conserve Plus (manufactured by Wright Medical Technology) that have now reached a minimum two years after implantation so as to direct the reasonable application clinically.

SUBJECTS AND METHODS

Subjects
Eighteen cases (23 hips) who underwent a metal-on-metal hip surface arthroplasty procedure in the Department of Orthopaedics, Jiangsu Provincial Corps Hospital of the Chinese People's Armed Police Force, and Department of Orthopaedics, Affiliated Hospital of Nantong University between September 2004 and July 2005 were recruited in this study. According to the classification of etiology, there were 13 cases of osteonecrosis(16 hips),3 cases of osteoarthritis( 4 hips ),1 case of congenital hip dysplasia (2 hips) and 1 case of posterior trauma arthritis(1 hip ). All cases include 11 males and 7 females; The mean age at operation was 43 years old, ranging from 28 to 54 years, the mean height was 175.25 cm, ranging from 155 to 180.25 cm, and the mean body weight was 84.8 kg, ranging from 51.7 to 144.7 kg. All of hip resurfacing used hybrid metal-on-metal hip resurfacing prosthesis（Conserve Plus, Wright, USA）which were comprised by acetabular cup of type non-bone-cement and femoral cup of type bone cement. Preoperatively, all patients signed the informed consent for the surgery, and the application of this technique also gave the approval of the Ethics Committee of the hospital. The general state of all cases is summarized in Table 1.

Methods
Operation procedure: A standardized pre- and post-operative regimen was used for all patients. Using the scaled X-ray templates provided, the approximate size of component was firstly assessed on the AP pelvis and true lateral. The surgery was performed in a clean-air laminar-flow environment under the epidural and lumbar combination anesthesia and the patients were in lateral positon with an anterior pelvic stabilizer pressed against the pubis. After routine sterilization and paving scarf, a posterior- lateral approach incision was made which was a hockey stick commencing about 6-8 centimeters distal to the top of the trochanter over the center the shaft extending proximally just above the tip of the greater trochanter and angling sharply posteriorly for about 4-6 centimeters. The skin, subcutaneous tissue and fasia lateralis were bluntly dissected. The gluteus maximus fibers were bluntly separated, and the tendon of which was completely sectioned as it was inserted into the linea aspera. The short rotators including piriformis, short rotators tendons and quadratus femourus muscule fibers, were divided to release the superior capsule. A Hoffmann retractor was placed under the abductor muscles. Hip was dislocated by flexion, adduction and internal rotation and then the entire capsule was released so that the pin-centering guide (PCG) can be placed around the neck with the mobile arm inferiorly. The neck diameter was then measured in order to determine the size of the components to be used. Then the guide was aligned with a goniometer so that the direction of the pin was superior to the central axis of the neck at a 140°pin shaft angle. The accuracy of pin alignment was assessed relative to the central axis of the neck by using the cylindrical reamer or cylindrical reamer gauge (CRG) for the anticipated final size. Femoral head was reamed with a cylindrical reamer and head was cut roughly within a size of final templated size until after the acetabulum component insertion being finished. The acetabulum was then reamed with hemispherical reamers in 2 mm increment usually starting with a 42 mm reamer and continued to within 2 mm of the desired size to remove soft tissue and cartilage from the floor of the cotyloid foramen, exposing some cancellous bone. Content of cyst was evacuated with curetts and a high-speed burr and then grafted. After using the translucent acetabular gauges to assess the size, roundness and depth of the reamed cavity, the suitably sized acetabular cup coated by hydroxyapatite ceramic was selected to be implanted, to be tightened and to be fixed by press-fit referring to 42°lateral and 15°anteverted until fully seated. Subsequently, a cylindrical reaming of femoral neck was conducted by reinserting the pin through the last cylindrical reamer used and proceed with downsizing. After the saw cutoff guide was positioned and stabilized, the dome of the femoral head was then resected with a saber. A starter drill was used to initiate an accurate entry and chamfer guide was inserted into the head to guide the appropriately sized chamfer reamer to obtain the final shape. Additionally, fixation holes were made using a 3.5 mm drill into the reactive dense sclerotic bone in the dome and chamfered areas. After removing all bone fragments and soft tissue and drying the cancellous bone and surface, the femoral component containing the doughy cement was pressed into the prepared femoral surface fully seated and hold until the bone cement had cured. At last, the hip was reduced and range of motion was checked. When there was no impingement during the motion in every direction, the wound was then closed with one drain after gluteus maximus tendon was reattached and short rotators were repaired with sutures.
Postoperative processing and evaluation of curative effects: Patients were allowed to make the function exercise such as initiative stretch and contract of quadriceps muscle of thigh, passive motion of knee joint and initiative motion of knee joint under the non-weight loading two days after operation in bed. Then they were encouraged to walk with two walking sticks 2 weeks after operation, progressing to get out of the two walking sticks 6 weeks postoperatively. All affected extremities were fixated with T-shaped tabula shoes in the abduction position after operation. We began the first follow-up 2 months postoperatively, which was made once every year afterward. Main observation index included the function condition of the affected hips, pre- and post-operative hip Harris score（excellent: > 90; good: 80–89; fair:70–79; poor:< 70）,the pain status of hip after operation（slight, moderate and severe）and X-ray analysis, etc.

RESULTS

Quantitative analysis of the participants
Eighteen cases were involved in the final analysis.

Radiological characteristics about prothesis and peripheral sclerotin
The femoral component of one patient had a varus deformation of 10°six weeks after operation, but such complications as component loosening and femoral neck fractures did not occurr during the coming follow-up. The locations of rest prosthesis were satisfactory. X-radiolucent rays were found at the rim of acetabular component (1 and 2 zone) in 2 hips, respectively one and two years after operation. But there was no evidence of radiolucencies around the short-stem of femoral component. No radiograph showed signs of loosening, dislocation, heterotopic bone formation, femoral neck narrowing, femoral head necrosis and prosthesis fixation failure, etc (Table 2). A typical case is shown in Figure 1.

Harris hip score and status of pain after operation
The Harris score of all diseased hips was improved from the mean 46 preoperatively to 85 one year after operation to 93 two years postoperatively. Of these,15 hips were excellent (> 90), 6 hips good (80–89), and 2 hips fair（70–79）. Two patients had the complaint of slight pain, one patient had that of moderate pain, and no cases of severe pain happened. Status of pain and score results of all cases two years after operation are summarized in detail in Table 2.
Radiological characteristics: Cases1-5: abduction angle and anteversion angle of acetabular cup were suitable and handle-stem angle and anteversion angle of femoral component were satisfactory.No signs such as osteolysis around the prosthesis, notch of femoral neck, heterotopic ossification（HO）, etc. had been seen. Case 6: The femoral component of one patient had a varus deformation of 10°(handle-stem angle of femoral component was less than 135 °) and the contain degree of articulation was dissatisfactory, but such complications as component loosening and femoral neck fractures had not been found in the coming follow-up. Case 7: Substantial radiolucencies were found at the rim of acetabular component (1 and 2 zone), but there was no evidence of component loosening and displace. Cases 8–14: As case 1–5. Case 15:Substantial radiolucencies were found at the rim of acetabular component (1 and 2 zone), but there was no evidence of radiolucencies around the short-stem of femoral component. Cases 16–18:As cases 1–5.

DISCUSSION

The proposed advantages of metal-on-metal hip resurfacing when compared to conventional THR include the initial preservation of the head and neck bone and of the femoral canal [3-5]. The procedure aims to preserve femoral bone, maintain normal femoral loadings and stresses, not to compromise future THR and to leave more options for future revisions [2, 5,6]. Because of low wear rates of metal-on-metal hip resurfacing, the implant may not be subject to dislocation and loosening and the procedure may be more durable than conventional THR in comparable patient groups, thus reducing the need for revisions. These advantages just solve such problems as the low survival rate and not easier revisions that the conventional THR has existed in treating the younger or greater activity amount patients of hip diseases. However, the survival rate of 5 years of the metal-on-metal hip resurfacing should be lower than the conventional THR if we do not apply it as specification. As followings, we should introduce some comprehensions that we have accumulated in its application of earlier period.
Reasonable patient selection: X-film examination should be made preoperatively and scope and extent of hip disease should be observed carefully. We have investigated the clinical outcomes of patients with osteonecrosis treated with metal-on-metal hip resurfacing (Conserve Plus,Wright Medical Technologies; n =16). Results indicated that hip with a greater scope of femoral changes and a more degree of acetabular changes (FicatIII and IV stage) had less satisfactory outcomes. Evaluation parameter included that preoperative and postoperative Harris hip score, occurrence of mild to moderate postoperative pain, preoperative and postoperative range of motion, preoperative and postoperative limb length discrepancy, etc. We think that the clinical outcomes are satisfactory for hips with a less scope of femoral changes (less than 30%).Some scholars reported that hip with a lesser degree of secondary arthritic changes that were classified as Grade A，B，C，D and F for four characteristics of proximal femur（bone density, shape, biomechanics, and focal bone defects）had a higher arthritic hip grade and better outcomes with total hip resurfacing.
The general experience indicates an increased risk for loosening of surface replacements associated with smaller component size and localized loss of bone greater than 1 cm in diameter [7, 8]. Amstutz et al [3] reported that the most important risk factors for femoral component loosening and substantial stem radiolucencies were femoral-head cysts, low body height, female gender, and smaller component size in male patients. In this series, the clinical outcomes of one patient (Charnley C group) complicated by hemiparalysis are not satisfactory for muscular atrophy. Furtherly, substantial radiolucencies were observed around 2 acetabular components postoperatively that were thought to be resulted from the higher degree of acetabular disease changes. Our experience indicates that more stringent patient selection can improve the survivorship of metal-on-metal hip resurfacing.
Femoral head preparation: When femoral head is reamed, we should make the remaining bone size larger than that of preoperative plan so as to prevent the reamed femoral head not to meet with the greater femoral component size once the acetabular bone need to be reamed. Moreover, on the selection of handle-stem angle of femoral component placement, we recommend using a gonimeter to ensure proper placement of the femoral component at proximately 135° to 140°because excessive valgus should be avoided in which notching of the femoral neck is more likely. Meanwhile, excessive varus (< 130°) also should be avoided in which excessive tension stresses on the superior aspect of the femoral neck cortex can possibly lead to premature fracture of the femoral neck or loosening of the component. Some scholars et al [9] reported that the risk coefficient of component failure in cases with handle-stem angle less than 130°was greater than that with handle-stem angle more than 130°. In this series，one case of femoral component placement was improper at less than 130°because of our excessive care of formation of the femoral neck notching. When femoral head is prepared, we also should clear out all the necrotic tissue and cyst in the superior to ensure femoral component supported by bone with enough strength. However, it has been reported that cut-off length of necrotic bone more than 1.5 cm is improper.
Femoral component fixation: There is a paucity of data on the optimal distribution of cement and optimal depth of penetration for lasting fixation of a femoral resurfacing component. It seems logical that one should use all of the available surface area for fixation and that a relatively uniform depth of penetration of cement into bone is desirable. Based on the aggregate clinical experience with cemented THRs and TKRs,a depth of penetration of 2 to 3 mm is sufficient for mechanical stability with negligiable damage to bone. Excessive penetration of cement may result in necrosis of bone secondary to the heat of polymerization [10-12]. Before the femoral component is fixed, pulsatile lavage should be used to remove bone debris (from reaming), blood, and fat from the cancellous spaces. The negative pressure generated by a suction cannula, most commonly inserted into the lesser trochanter ,can be effective in reducing or eliminating bleeding of the reamed femoral head as well as reducing embolic phenomena during insertion of the prosthesis. The suction may be left on until the cement cures to minimize bleeding into the cement-bone interface. Treacy et al [8,13-15] reported that one patient had such complication as avascular necrosis in the neck postoperatively confirmed by histology which was thought to be resulted from suction venting of the lesser trochanter not to be undertaken routinely at the time of implantation. We think that metaphyseal femoral stems should be cemented which may effectively prevent the occurrence of femoral component loosening. Amustutz et al [3, 14-16] reported that femoral radiolucencies were easier to be observed among the hips in which the metaphyseal femoral stems were non-cemented than cemented. Our experiences also have confirmed this view. In this series, all cases were not found to have such complications as femoral radiolucencies and the necrosis of femoral head which could be associated with our cemented femoral fixation and careful rinsing on-operation.
In conclusion, short-term outcomes for metal-on-metal hip resurfacing are very satisfactory, but its medium and long-term outcomes need still be researched further by accumulating the considerable review cases. We believe that the clinical outcomes for metal-on-metal hip resurfacing should be improved by proper selection of patients preoperatively, refined surgical technology intraoperatively and careful recovery exercises postoperatively. Further, the design for MOM articular surface now is gradually improved to reduce the wear rate of the prosthesis to effectively avoid such complication as the higher serum ion levels. As an alternative technology to conventional THR, metal-on-metal hip resurfacing should better meet with the younger patients or the elders of great activity, and could save more time for selecting the optimizing arthroplasty by continuously elevating the survival rate of prosthesis.

REFERENCES

1 Harris WH. The problem is osteolysis. Clin Orthop Relat Res 1995; (311):46-53
2 Amstutz HC, Grigoris P, Dorey FJ. Evolution and future of surface replacement of the hip. J Orthop Sci 1998;3(3):169-186
3 Amstutz HC, Beaule PE, Dorey FJ, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am 2004;86-A (1):28-39
4 Schmalzried TP, Silva M, de la Rosa MA, et al. Optimizing patient selection and outcomes with total hip resurfacing. Clin Orthop Relat Res 2005;441:200-204
5 Blue Cross Blue Shield Association. Metal-on-metal total hip resurfacing. Technol Eval Cent Asses Program Exec Summ 2007;22 (3):1-4
6 Mai MT, Schmalzried TP, Dorey FJ, et al. The contribution of frictional torque to loosening at the cementbone interface in Tharies hip replacements. J Bone Joint Surg 1996;78A:505-511
7 Dong T, Sun J, Qu Y, et al. Resurfacing arthroplasty for treatment of avascular necrosis of femoral head in young and middle-aged patients. Zhongguo Xiufu Chongjian Waike Zazhi 2005;19(9):707-709
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9 Girard J,Lavigne M,Vendittoli PA, et al. Biomechanical reconstruction of the hip: a randomised study comparing total hip resurfacing and total hip arthroplasty. J Bone Joint Surg Br 2006;88(6):721-726
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11 Forrest N, Welch A, Murray AD, et al. Femoral head viability after Birmingham resurfacing hip arthroplasty: assessment with use of [18F] fluoride positron emission tomography. J Bone Joint Surg Am 2006; 88(Suppl 3):84-89
12 Moroni A, Cadossi M, Bellenghi C, et al. Resurrection of hip resurfacing: what is the evidence? Expert Rev Med Devices 2006;3 (6):755-762
13 Vail TP, Mina CA, Yergler JD, et al. Metal-on-metal hip resurfacing compares favorably with THA at 2 years followup. Clin Orthop Relat Res 2006;453:123-131
14 Vail TP, Mina CA, Yergler JD, et al. Failure mechanisms of total hip resurfacing: implications for the present. Clin Orthop Relat Res 2006; 453:110-114
15 dela Rosa MA, Silva M, Heisel C, et al. Range of motion after total hip resurfacing.Orthopedics 2007;30(5):352-357
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混合型金属对金属人工全髋表面置换术18例：2年随访★

茹江英1，刘 璠2，胡玉华1，胡传亮1，王长峰1
1武装警察部队江苏省总队医院骨科，江苏省扬州市 225003；2 南通大学附属医院骨科，江苏省南通市 226001
茹江英★, 男，1976年生，山西省晋城人，汉族，2006年南通大学医学院毕业，硕士,主治医师,主要从事创伤与关节外科研究。
摘要
背景：金属对金属人工髋关节提高了髋关节假体的耐磨性能，具有符合正常生物学应力传递的特点。
目的：观察混合型金属对金属人工全髋表面置换患者髋关节功能的远期状况。
设计：病例随访。
单位：武装警察部队江苏省总队医院骨科和南通大学附属医院骨科。
对象：选择2004-09/2005-07在武装警察部队江苏省总队医院骨科和南通大学附属医院骨科接受人工全髋表面置换术治疗的髋关节病变18例（23髋）患者。男11 例,女7例，年龄28~54岁。按病因学分类：股骨头坏死13例（16髋）、骨性关节炎3例（4髋）、先天性髋关节发育不良1例（2髋）和创伤后骨性关节炎1例（1髋）。混合型金属对金属人工全髋表面关节假体由Wright公司提供，髋臼杯型号:38~56 mm （内径）/44~62 mm （外径）；股骨头假体型号：38~56 mm （外径）；髋臼杯压配深度1~2 mm。术前患者签署手术知情同意书，该术式的临床应用经过医院伦理委员会批准许可。
方法：①硬腰联合麻醉后，暴露髋臼,选择大小合适的具有羟基磷灰石涂层的金属髋臼帽按解剖位置安放冲紧、压配固定。安装股骨头假体,用调制好的骨水泥涂摸在预制好的股骨头及股骨假体内表面，将金属杯套于准备好的股骨头上，用加压器压紧，使金属杯与骨质紧密相贴，并使金属杯的短柄与股骨颈的轴线保持一致。②术后2 d允许患者进行不负重的关节活动、被动关节活动及股四头肌主动等长舒缩功能锻炼，2 周后允许下床扶拐不负重行走，术后6周可逐渐过渡至完全脱拐行走。术后对所有患者予以患肢 “T”字横板鞋外展位固定。③术后1，2年行X 射线分析全髋表面置换效果及与宿主的生物相容性；术前及术后1，2年进行患髋Harris评分并观察患者髋关节情况。
主要观察指标：①全髋表面置换效果。②生物相容性。③患髋Harris得分。④术后髋关节疼痛情况。
结果：纳入患者18例均进入结果分析。①全髋表面置换效果：1例患者1个股骨假体内翻成10°角，未出现假体松动和股骨颈骨折的并发症, 其余表面置换假体位置满意。2例患者分别于术后1年和2年发现髋臼假体边缘1、2区有X线透亮线, 而在股骨短柄周围1、2和3区未发现有X线透亮线。②生物相容性：所有病例均无明显肾毒性、热原性及排斥反应，未发现有髋关节脱位、异位骨化、股骨颈狭窄、股骨头坏死及假体固定失败等并发症。③患髋Harris得分：术前患者平均46分，术后1年为85分，术后2年为93分，其中15个为优, 6个为良, 2个为中。④术后疼痛情况：2例患者术后轻微疼痛, 1例中度疼痛, 无严重疼痛者。
结论：应用混合型金属对金属人工全髋表面假体置换髋关节疾病患者后远期疗效满意。　
关键词：金属对金属髋关节；假体置入；生物材料
中图分类号: R318 文献标识码: A 文章编号: 1673-8225(2008)04-00770-05
茹江英，刘璠，胡玉华，胡传亮，王长峰.混合型金属对金属人工全髋表面置换术18例：2年随访[J].中国组织工程研究与临床康复，2008，12(4):770-774
[www.zglckf.com/zglckf/ejournal/upfiles/08-4/4k-770(ps).pdf]
(Edited by Zhu XQ/Song LP/Wang L)