Reconstruction of massive bone defects after femoral tumor resection using two new-designed 3D-printed intercalary prostheses: a clinical analytic study with the cooperative utilization of multiple technologies

Abstract

Background: To reconstruct massive bone defects of the femoral diaphysis and proximal end with limited bilateral cortical bone after joint-preserving musculoskeletal tumor resections, two novel 3D-printed customized intercalary femoral prostheses were applied.

Methods: A series of nine patients with malignancies who received these novel 3D-printed prostheses were retrospectively studied between July 2018 and November 2021. The proximal and diaphyseal femur was divided into three regions of interest (ROIs) according to anatomic landmarks, and anatomic measurements were conducted on 50 computed tomography images showing normal femurs. Based on the individual implant-involved ROIs, osteotomy level, and anatomical and biomechanical features, two alternative 3D-printed prostheses were designed. In each patient, Hounsfield Unit (HU) value thresholding and finite element analysis were conducted to identify the bone trabecula and calcar femorale and to determine the stress distribution, respectively. We described the characteristics of each prosthesis and surgical procedure and recorded the intraoperative data. All patients underwent regular postoperative follow-up, in which the clinical, functional and radiographical outcomes were evaluated.

Results: With the ROI division and radiographic measurements, insufficient bilateral cortical bones for anchoring the traditional stem were verified in the normal proximal femur. Therefore, two 3D-printed intercalary endoprostheses, a Type A prosthesis with a proximal curved stem and a Type B prosthesis with a proximal anchorage-slot and corresponding locking screws, were designed. Based on HU value thresholding and finite element analysis, the 3D-printed proximal stems in all prostheses maximally preserved the trabecular bone and calcar femorale and optimized the biomechanical distribution, as did the proximal screws. With the 3D-printed osteotomy guide plates and reaming guide plates, all patients underwent the operation uneventfully with a satisfactory duration (325.00 ± 62.60 min) and bleeding volume (922.22 ± 222.36 ml). In the follow-up, Harris Hip and Musculoskeletal Tumor Society scores were ameliorated after surgery (P < 0.001 and P < 0.001, respectively), reliable bone ingrowth was observed, and no major complications occurred.

Conclusions: Two novel 3D-printed femoral intercalary prostheses, which achieved acceptable overall postoperative outcomes, were used as appropriate alternatives for oncologic patients with massive bone defects and limited residual bone and increased the opportunities for joint-preserving tumor resection. Several scientific methodologies utilized in this study may promote the clinical design proposals of 3D-printed implants.

Keywords: 3D printing; Bone tumor resection; Femur; Intercalary prosthesis; Joint-preserving surgery; Reconstruction.

Fig. 1

The division of the region of interest (ROI) and relevant radiographic measurements. A Graphical illustration of ROI-1, ROI-2 and ROI-3. B The radiographic identification of ROI-1, ROI-2 and ROI-3. C The measurements of the distance between the trochanteric fossa and the superior edge of the lesser trochanter (D1) expressed as a blue line, and the distance between the trochanteric fossa and the inferior edge of the lesser trochanter (D2) expressed as a red line. D Measurement of the calcar femorale (red dashed line). E Measurement of calcar femorale thickness (red line)

Fig. 2

Photographs and design proposals of new-designed 3D-printed prostheses. A The gross view of Type A prosthesis on design proposal showing the 3D-printed component (superior part) and LDK modular component (inferior part). B The gross view of Type B prosthesis on design proposal showing the 3D-printed component (superior part) and LDK modular component (inferior part). C The 3D-printed proximal stems in Type B prosthesis showing anchorage-slot structures (arrowheads) fixing the locking screw inserted into calcar femorale or spongy bone. D The finished 3D-printed curved stem and anchorage-slot stem. E 3D-printed osteotomy guide plate on design proposal and photograph of finished 3D-printed osteotomy guide plate and reaming guide plate. F A finished Type A prosthesis showing the 3D-printed proximal bone-implant interface, distal bone-implant interface, and curved stem. In this prosthesis, the patient-specific curve radius, stem diameter and length were 140°, 15 mm, and 69 mm, respectively. G The finished Type B prosthesis showing the 3D-printed proximal bone-implant interface, distal bone-implant interface, and anchorage-slot stem

Fig. 3

Illustration of HU value thresholding, FEA and intraoperative surgical techniques. A The identification of calcar femorale (arrowhead) and lateral cortical bone based on HU value thresholding. B The identification of trabecular bone based on HU value thresholding showing principle compressive trabecular bone (arrowhead), principle tensile trabecular bone (empty arrowhead) and Ward triangle (arrow). C The biomechanical distribution of the proximal femur analyzed by finite elements showing the direction and location of the applied loading force. D The lateral approach for the exposure of the proximal and middle thigh. E Intraoperative application of the 3D-printed osteotomy guide plate. F The resected tumor-involved segment

Fig. 4

Anatomic determination by HU value and biomechanical analysis by finite element in 3D-printed implants. A The preplanned position of the proximal curved stem in the Type A prosthesis, with the optimized preservation and abutment of the calcar femorale (thresholding by HU value). B The preplanned position of the proximal anchorage-slot stem in the Type B prosthesis, with the optimized locking screw insertion in the calcar femorale (thresholding by HU value). C The preplanned position of proximal screws in Type A prosthesis, with the optimized preservation of trabecular bone (thresholding by HU value). D The preplanned position of the proximal anchorage-slot stem and locking screws in Type B prostheses, with the optimized preservation of trabecular bone (thresholding by HU value). E The preplanned position of the proximal curved stem and screws in the Type A prosthesis obeying the stress distribution defined by FEA. F The preplanned position of the proximal anchorage-slot stem and locking screws in Type B prostheses obeying the stress distribution defined by FEA. Images (A, C, E) from Patient 1. Images (B, D, F) from Patient 3

Fig. 5

The successful placement of 3D-printed femoral prostheses. A The intraoperative implanted 3D-printed prosthesis of Patient 3. B The postoperative immediate X-ray of the left femur in Patient 1. C The postoperative immediate X-ray of the right femur in Patient 3

Fig. 6

The postoperative functional and radiographic outcomes in the follow-up. A and B The normal hip range of motion of abduction A and flexion B in Patient 9 at five months after surgery. C X-ray of the left femur at 99 days after surgery of Patient 1 showing reliable biological fixation. D X-ray of the right femur at 85 days after surgery of Patient 3 showing reliable biological fixation. E Bone ingrowth on the bone-implant interface of the 3D-printed stem and screw (Patient 6) or osteotomy plane (Patient 1) at six months after surgery on axial CT image. F Bone ingrowth on the bone-implant interface of the 3D-printed curved stem and screws at six months of Patient 1 after surgery on reconstructed sagittal CT image. G Bone ingrowth on the bone-implant interface of the 3D-printed anchorage-slot stem and screws at six months of Patient 6 after surgery on reconstructed coronal CT image