In clinical practice, the learning curve associated with surgery is an essential consideration when advising patients about the possible treatment options and their expected efficacy. Besides, after the safety and effectiveness of a new surgical technique have been verified, this technique's promotion and popularization also need to consider the learning curve. MISS is a safe and effective surgical technique, the current optimal treatment for spinal metastases [6,7,8,9,10,11,12]. However, the learning curve for this technique has not been analyzed. This study described the learning curve of MISS, and analyzed and compared preoperative, intraoperative and postoperative objective factors related to this surgical technique's learning curve.
In this series of patients with spinal metastases, the operative time-based learning curve of MISS showed that the operative time decreased gradually with the number of surgical cases increasing and became stabilized after the 20th patient. Based on this, this series of cases were divided into the early phase group and the later phase group. There was no statistical difference in demographic characteristics and preoperative characteristics between the two groups. Under this premise, we analyzed and compared the surgical data and clinical efficacy of the two groups of patients. The mean operative time was significantly shorter in the later phase group than that in the early group, about 39 min shorter on average. It demonstrated that after the appropriate number of surgical cases, the surgeon can quickly reach the technical steady period, and the operative time is stable within a certain range. Crucially, shorter operative time in the later phase group did not affect operative data. There were no statistically significant differences between the two groups in intraoperative blood loss, the incidence of massive blood loss, postoperative drainage volume, the retention time of drainage tube, postoperative hospital stay, and incidence of perioperative complications. Moreover, it is worth noting that both groups of patients obtained good postoperative outcomes, and there was no statistical difference in surgical treatment effect between the two groups. In both groups, neurological function improved to varying degrees or remained stable in most patients.
With the progress of comprehensive treatment of tumors, the number of patients with spinal metastases is increasing. Therefore, it is necessary to promote and popularize the MISS technique. Although many cancer centers have developed this technique successively, many surgeons are still concerned that the small incision of MISS will increase the difficulty of the operation and that it is difficult to stop intraoperative tumor bleeding through a small incision, etc. These worries may be caused by the fact that the learning curve of MISS was not clearly defined and analyzed before this study. By defining and analyzing the learning curve of MISS, this study shows that this surgical technique's learning curve is not steep, and surgeons could reach the technical proficiency period after receiving formal training and an appropriate number of surgical cases. Although the initial operative time is longer than that in the latter stage, the surgical treatment effect is comparable to that of the latter cases, and the effect is satisfactory. Therefore, we believe that after the training of minimally invasive separation procedures, surgeons can gradually carry out this surgical technique so that more patients with spinal metastases can benefit from this minimally invasive technique.
According to Selafani's systematic review, for most minimally invasive spinal surgery techniques, continuous completion of 20–30 procedures can overcome the learning curve marked by operative time and incidence of complications [19]. Therefore, a beginner must pay attention to the prevention of complications when developing new technology and find some regular experience in literature study and attending academic conferences to go through the learning curve smoothly. For MISS, our recommendations to surgeons who are performing this technique in the early stages are as follows. Firstly, before carrying out this operation, it is necessary to have a specific basis in spinal surgery and bone oncology and to receive surgical skill training from a professional department. Otherwise, the probability of spinal cord or nerve root injury during the operation may increase. Secondly, for metastatic spinal lesions with a rich blood supply (such as kidney cancer, thyroid cancer, liver cancer, etc.) [20, 21], preoperative embolization can be considered to reduce intraoperative bleeding. Thirdly, when the spinal cord or nerve root decompression is performed, it is better to carry out electrophysiological nerve monitoring. After returning to the ward after surgery, it is necessary to ensure that the drainage tube is patency and closely observe the changes in nerve function. If problems are found, timely treatment should be carried out.
The study is not without limitations. Firstly, this was a retrospective study, not a prospective one, making it difficult to avoid the cofounder bias, although the early and late group cohorts seemed to match well. Secondly, long-term QOL was not assessed due to the short follow-up time.