Patients
The inclusion criteria of operation were: (1) giant cell tumor of distal femur according to histological evidence; (2) defect of distal articular surface of one side of femoral condyle caused by pathological fracture; (3) the follow-up time is more than 24 months and the follow-up data are complete. The exclusion criteria were (1) non-surgical treatment, (2) combined with cruciate ligament, meniscus, collateral ligament injury or serious joint degeneration, (3) bilateral condylar lesions or multiple articular surface defects, (4) preoperative treatment with denosumab. We retrospectively analyzed our database and identified 26 patients with articular surface defect caused by pathological fracture of GCT of distal femur treated from January 2012 to January 2018.
Data for age, sex, lesion site, Campanacci classification [13], operation time, blood loss, the Musculoskeletal Tumor Society (MSTS) scores[14], local recurrences and complications were collected (Table 1). In total, 12 patients were treated with three-dimension-printed custom-made prostheses ( 3D-printed group) (7 males, 5 females; mean age, 42.2 years, range 29-69 years), and 14 patients were treated with endoprosthesis replacement ( EPR group) (9 males, 5 females; mean age, 45.4 years, range 34-68 years). All surgeries were performed by the same medical team. This study was approved by the by the Ethics Committee of Qilu Hospital of Shandong University Medical Ethics Committee. All patients gave written informed consent to be included in scientific studies at the admission to the hospital.
The design and manufacturing of the 3D-printed custom-made prosthesis
All the patients were evaluated on preoperative imaging such as Fig. 1(a-d). Not only pre-operative plain radiography and magnetic resonance imaging (MRI) of the distal femur eroded by tumor were evaluated, but also the both distal femurs of the affected side and the healthy side were scanned with computerized tomography (CT, 1mm slice intervals). Then, the DICOM format data of CT were transferred to Mimics Medical 21.0 software (Materialise, Ann Arbor, MI). Masks of the both distal femurs were established using the Region Growing command. The 3D models of the both distal femurs were then obtained using the Calculate Part command. The 3D models of the affected side distal femurs before eroded by tumor were established using the mirror command from healthy side. Then, Boolean logic was used to model the defect articular surface from the models before and after pathological fracture. Geomagic studio 12 (Geomagic, Morrisville, NC) was used to help transform the defect articular surface model into a solid model which can be edited by Siemens NX 12.0 software (Siemens PLM Software, Plano, TX). Siemens NX 12.0 software was used to make the defect articular surface 0.5mm lower than the normal knee articular surface which is measured according to the MRI. In order to increase the stability of the defect articular surface, screws that pass through the defect articular surface of the prosthesis and an extra plate for fixation of the prosthesis were designed together with engineers using Siemens NX 12.0 software. (Fig. 2). A model of the lesion can be printed used to help understand the condition in more detail before surgery (Fig. 3a-b). Then, the final prosthesis was printed with the electron beam melting (EBM) technology of titanium powder, and the articular surface was highly polished (Fig. 3c-d). It took approximately two weeks for the design and manufacture of each personalized 3D-printed prosthesis (Shanghaishengshi Co., Shanghai, China).
Surgical procedure
3D-printed group: The surgery was performed under general anesthesia. The tumor was removed by curettage, which is performed through the window of the defect part of the articular surface. If the window of the defect part is not large enough to scrape away all the tumor, an additional window should be opened at the distal femur where was not covered by articular surface. After removing all visible tumor tissues, the tumor cavity is cauterized with electric knife, and then expanded with a high-speed burr (Fig. 3e). After the curettage was completed, anhydrous alcohol and distilled water pulse irrigation was used to rinse the cavity. Then the tumor cavity was filled with bone cement. The 3D-printed prosthesis should be installed before the bone cement sets. The installation process shall ensure the joint surfaces are in the proper position. (Fig. 3f-h).
EPR group: The surgery was performed under general anesthesia. A median incision in front of the knee joint was used and the distal femur was exposed outside the diseased bone or tumor mass. Osteotomy of the distal femur was performed according to preoperative measurements and A tibial osteotomy was performed in the same manner as a standard knee arthroplasty. A tumor type prosthesis (Beijingchunli Co., Beijing, China) was reconstructed by conventional methods after the resection of tumor.
Post-operative management
The postoperative management of the two groups was similar. Range of motion exercises of the knee were performed from postoperative day 1. The patient was allowed non-weight-bearing standing and walking with 7 days after surgery. Partial weight-bearing with crutches was encouraged from 2 weeks postoperatively, followed by gradual full weight-bearing. The patient was followed up every month for the first 3months, then every 3months thereafter. The oncology outcomes, and radiographs were assessed at each follow-up.
Statistical analysis
Continuous data are expressed as mean ± standard deviation. The independent sample t test were used to compare the age, operation time, bleeding volume, ROM and MSTS score of the two groups. The χ2 test was used to analyze the sex, tumor location, postoperative complications and recurrence rate of the two groups. A p-value of < 0.05 was considered to be significant. Statistical analysis was performed using the SPSS Statistics software version 22.0 (IBM, Armonk, NY, USA).