With the advancement of chemotherapy drugs and artificial manufacturing system, joint-sparing limb salvage surgery (JSLSS) has been the standard treatment for children with osteosarcoma in order to maintain normal joint function and protect the epiphyseal plate. Biological reconstruction with vascularized fibular graft, treated autologous bone[10-11], allograft combined fibula allograft and segmental transport would be acceptable techniques for this kind of patients. But, these reconstruction techniques would be usually associated with frequent complications, such as graft resorption, nonunion, pathological fractures and insufficient demand of weight-bearing. Three-dimensional-printed segmental prosthesis with the advantages of high shape compatibility and osteointegration capacity of the porous surface has gradually been popular for the JSLSS. Recently, Lu et al reported the good postoperative functional outcome of a patient with 3D-printed prosthesis to reconstruct the defect of the proximal tibia bone tumor defect. Besides, Liu et al reported excellent functional results and oncological status for the patients with bone tumors in femur or tibia by 3D‐printed intercalary. The 3D-printed prosthesis for the patients in our study were designed by ourselves. According to previous research, aseptic loosening would be the most common complication for the patients with prosthesis replacement in distal femur[16-17]. So, the proximal femoral medullary stalk of the prosthesis and the lateral auxiliary plate would be biological fixation type by 3D-printed technology to promote the bone union and prevent the prosthesis from loosening and rotation. Also, since the main force between the prosthesis and epiphysis would be longitudinal gravity, lateral placement of four locking screws could ensure stability of the implant to a large extent. As a result, all patients in our research had good function without aseptic loosening during the follow-up. Also, compared to other reconstruction method, after the operation for the patients with reconstruction by our 3D-printed prosthesis, the child could carry out the weight-bearing activities and rehabilitation exercises early which would be very important for the function of knee.
The main objective treatment for the surgery of osteosarcoma should be the complete resection of tumor with a safe surgical margin. Luis et al reported that the safe surgical margin should be at least 1 cm with the accurate evaluation by MRI, which could confirm the epiphyseal extension of osteosarcoma successfully[19-20]. With the assistance of surgical guide (Patient-Specific Instruments), Bellanova et al. reported 4 cases about resection of tumors with histologically negative margins for pediatric tibial bone sarcoma. Based on these findings, in our opinion, if the tumors do not invade the epiphyseal plate according to the evaluation by MRI after the first cycle of chemotherapy, the epiphyseal plate could be preserved completely with the assistance of 3D-printed guide plate even though the surgical margin would be less than 1 cm. Although, there was one patient of local recurrence in remaining bony epiphysis during the follow-up in our research, we thought it would be strongly associated with the insensitivity of preoperative chemotherapy with necrosis rate less than 90%. Actually, the key factor that would impact the local recurrence rates and overall survival rates would be the tumor sensitivity to chemotherapy when adequate margins would be achieved for all patients as reported[22-23].
For the patients with metaphyseal osteosarcoma, resection of the growth plate could cause limb-length discrepancy(LLD). In 1994, Canadell report the technique of physeal distraction to solve this problem, which permits limb-sparing reconstruction without compromising oncological principles. But, the physeal distraction would be painful and need to take very long time. The expandable prosthesis has been design to avoid limb-length inequality. However, the high rate of complications, including breakage and aseptic loosening of the prosthesis, would have a great influence on the application of this technology. Besides, the length of extension would be limited and the function of the lower extremity could not be as well as expected.So, another problem is whether the latitudinal growth would be arrested after epiphyseal-preservation surgery with our dependent design 3D-printed prothesis. The LLD would also be happened for the patients with epiphysis preservation for the patients in our study, but the shortened distance would be similar compared to reconstruction of expandable prosthesis which could be corrected by the assistance of insole and the incidence of complications would be much lower[15,26-28] (Table 4). Besides, Takeuchi et al reviewed 12 patients with osteosarcoma who underwent epiphysis preserving tumor excision and found out that epiphysis transverse growth would not be diminished after epiphyseal-preservation surgery in their small series of childhood osteosarcoma around the knee which would be very important to maintain the stability of the knee. Also, according to our research, there was absence of epiphyseal collapse after the surgery and all the patients who underwent JSLSS, achieved similar results for ROMs in 6DOF during gait compared with normal data of Chinese knees.
This is the first study that report the surgical technique and outcome of joint-sparing limb salvage surgery for children with osteosarcoma in distal femur with our dependent designed 3D-printed prothesis. We recognize that our research still have some limitations. First, the sample size of the research would be too small and the the follow-up time would be not long enough for some complications to be detected. Second, because of the study’s retrospective nature and lack of a control group, it would be difficult to draw a convincing conclusion. Third, our research only focus on the osteosarcoma in the distal femur for the children, future research about different sites and different types of bone tumors with randomized controlled study need to be conducted.
In conclusion, as long as the tumor does not invade the epiphyseal plate for the patients with osteosarcoma in distal femur, the epiphyseal plate could be preserved completely with acute epiphyseal osteotomy by the assistance of 3D-printed guide plate. Also, joint-sparing limb salvage surgery with our dependent design of 3D-printed prosthesis would be a good choice for the children with osteosarcoma in distal femur.