A total of 41 patients (70 hips) with ARCO stage II were included in this study, including 24 patients (48 hips) in the traditional surgery group and 17 patients (22 hips) in the robot-assisted group. The mean follow-up time was (14.6±4.8) months. To the last follow-up, a total of 13 patients (13 hips) suffered collapse of femoral head, including 11 cases (11 hips) in traditional surgery group, and 2 cases (2 hips) in robot-assisted group. The collapse rate of femoral head in traditional surgery group was in agreement with other previous reports(8), and the collapse rate of femoral head in robot-assisted group was significantly lower than that of other previous studies. In addition, robotic surgery was superior to traditional surgery in terms of operation time, number of intraoperative X-ray fluoroscopy and postoperative pain improvement. At the last follow-up, Harris hip score was better in both groups than before, but there was no significant difference between the traditional surgery group and the robot-assisted group.
There are many classification criteria for femoral head necrosis. In this study, the 2019 revised ARCO staging system was used to regularly classify the included patients. In the 2019 revision of the ARCO staging system, stage 0 was removed, and the location and size of necrotic lesions were not used as staging criteria(9). In this study, a total of 13 hips progressed to ARCO III with collapse at the last follow-up. After case summary of these 13 hips, it was found that the area of femoral head necrosis of 9 hips exceeded 30%, which was classified as ARCO IIc of 1994 edition. Eight patients received hormone therapy again during the follow-up period due to primary disease progression. For the hip joint which necrotic area of the femoral head exceeds 30%, the necrotic bone cannot be completely removed, which leaded to the lack of bone grafting through the core decompression canal. The size of necrotic area in the femoral head before operation and the amount of necrotic bone remaining during operation will affect the success rate of surgery. Landgraeber et al. suggested that a better surgical efficiency could be achieved when the postoperative residual dead bone was less than 1000mm3(10). Compared with traditional surgery, robot-assisted surgery can reach the necrotic area more accurately and remove the necrotic bone to the maximum extent. However, at present, the related instruments of robot-assisted surgery are still scarce, which cannot give full play to the advantages of precision of robots(11). In addition, for the hip joint with large necrosis area of the femoral head, a simple working path for decompression cannot completely remove the dead bone. In this case, robot-assisted decompression combined with arthroscopic removal of dead bone and bone grafting of the hip joint or open surgery are required to ensure better surgical results(12, 13).
In this study, the postoperative Harris score and VAS score of patients in the two groups were significantly improved compared with the preoperative score, while the VAS score was significantly different at the last follow-up between the two groups, and the Harris score was not significantly different. Patients with early necrosis of the femoral head usually present with pain in the hip joint without significant range of motion limitation. Therefore, for the evaluation of the treatment effect of early femoral head necrosis, the improvement of VAS is more significant. Among the 41 patients included in this study, a total of 29 patients underwent simultaneous surgical treatment for bilateral femoral head necrosis. For this part of patients, Harris score could not evaluate the function of a single hip joint very well, which affected the final results. The VAS score can be used to evaluate the unilateral hip joint without being affected by the contralateral hip joint. At present, there is a lack of independent comprehensive evaluation criteria for bilateral hip joint.
The robot used in this study is an orthopedic surgery robot made entirely in China, which is mainly used in trauma, spine and other fields. Till now, there is a lack of relevant research on decompression treatment of femoral head necrosis. As such robots has natural advantages for bone tissues, through a combination of preoperative CT data and intraoperative real-time X-ray image, the robot can help complete core decompression precisely and convenient with a more minimally invasive surgical incision. According to the follow-up data, robot-assisted operation can achieve superior outcome, and effectively reduce the number of intraoperative radiation exposure, intraoperative bleeding, reduce the operation time, and complications related to drilling. By fitting the preoperative CT-based reconstruction image with the intraoperative X-ray image, the robot system can realize the drilling point of femoral under the intraoperative three-dimensional field of vision. At the same time, for some necrotic areas that are difficult to reach, traditional surgery requires repeated puncture to determine the drilling path, which increases the risk of vessel and nerve damage and steel needle fracture. Traditional surgery usually requires a 5cm surgical incision below the greater trochanter and partial dissection of the gluteus medius, which may result in decreased hip abductor strength. The robot-assisted system has been proved to be able to perfectly avoid these complications in other clinical operations(14, 15), and no related complications occurred in this study.
Traditional core decompression combined with bone grafting is usually performed under direct vision or fluoroscopy with low grafting strength. The virtual wall technology of the robot can effectively and accurately implant the graft material into the necrotic decompression area, which will ensure the support strength and avoid iatrogenic collapse. In terms of implant material, we chose the commonly used nano-bone rod which had been introduced in our former research. This bone rod can provide excellent biocompatibility, mechanical compatibility and bioactivity to avoid the possible rejection of other endoplants in our previous study(16), while good ability of bone ingrowth is one of the important factors for successful hip preservation(17, 18). At the last follow-up, the collapse rate of the robot group was significantly lower than that of the traditional surgery group, suggesting that accurate removal of dead bones and high strength mechanical support can bring better clinical results. In this study, 2 patients with post-operative collapse chose hip replacement, during which a layer of fibrous tissue was found between the implanted rod and the bone, and no bone ingrowth occurred. How to induce better osteogenesis and bone ingrowsion is an important research direction for achieving better results of core decompression surgery(19, 20).
There are still some problems in this study. First of all, since the robot needs to use intraoperative X-ray and preoperative CT reconstruction data for fitting, even slight changes in posture will lead to deviation of the results after the X-ray image of hip joint is obtained. Secondly, there is still a lack of robotic core decompression equipment, which can not give full play to the characteristics of robotic surgery. Thirdly, the number of cases included in this study is still small, the follow-up time is not long, and the medium and long term results are still to be observed.