Background: Metastatic lesions in the periacetabular region can cause pain and immobility. Symptomatic patients are often treated surgically with a total hip replacement using various modified Harrington methods. These open surgical procedures confer inherent risks. Prolonged recovery and potential complications may delay adjuvant radiation and systemic therapy. Methods: We describe a novel technique for acetabular reconstruction. Three large-bore cannulated screws are placed percutaneously under fluoroscopy in a tripod configuration to reinforce the mechanical axes of the acetabulum. Increased stability improves pain control and permits weight-bearing. Results: Twenty consecutive patients with periacetabular metastases were treated using the tripod technique. Eighteen patients (90%) had Harrington class-III lesions, and 2 patients had Harrington class-II lesions. The mean surgical time was 2.3 hours. Sixteen patients (80%) were able to get out of bed on postoperative day 1. At 3 months postoperatively, there was significant improvement in pain as documented on their visual analog scale (p < 0.01) and in functionality as measured by the Eastern Cooperative Oncology Group score (p < 0.01). The mean follow-up time was 7 months (range, 0.6 to 20 months). At the most recent follow-up, only 3 among the 16 surviving patients were using opioids chronically for pain. Total hip arthroplasty was performed in 4 patients (20%) in a staged fashion using the previously placed screws as support for a cemented cup and obviating the need for a cage device. Of the 16 patients, 15 could walk either independently (6 patients) or using an ambulatory aid (9 patients). Eight patients with the primary tripod reconstruction survived >6 months postoperatively. They were found to have either new bone formation filling the defects or healing of the pathological fractures. There has been no implant loosening or failure. Conclusions: The tripod technique is a novel application to provide safe and effective pain relief in the context of periacetabular metastatic disease. It can be easily converted to support a cemented acetabular cup for a total hip replacement should disease progression occur. This technique provides an alternative to open surgery as currently practiced in these patients. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Background: The percutaneous screw reconstruction technique, known as the “Tripod Technique,” has demonstrated favorable clinical outcomes in the management of metastatic periacetabular lesions, as evidenced by our prior investigations and corroborated by independent studies. Nevertheless, there is a steep learning curve in handling this technique, with possible complications such as intraarticular screw placement.Methods: Preoperative pelvic CT scans were acquired before surgery and utilized for the guiding frame design. A convolutional neural network model was trained with annotated data to identify the starting point and trajectory of each potential screw. A model boundary intersection detection technology was used to determine the optimal diameter and length of each screw. A non-rigid registration technology was matched with a prefabricated model of the body surface to design personalized anchoring skin pads. Finally, a polylactic acid-based guiding frame for intraoperative was custom-made with a 3D printer.Results: 12 patients underwent a guiding frame-assisted Tripod procedure for treatment of periacetabular metastatic lesions. An intraoperative CT scan was performed in all cases to confirm screw trajectories. Among 36 screws that were implanted, 26 screws were implanted as designed. The remaining ten screws drifted, but all remained within the intra-osseous conduit without any complications. The mean surgical time was 1.22 h with the guiding frame compared with 2.3 h without the guiding frame. Following the surgical procedure, a noteworthy enhancement in pain management, as evidenced by a reduction in scores on the visual analog scale (p < 0.01), and an improvement in functional status, as assessed through the Eastern Cooperative Oncology Group score (p < 0.01), were observed when compared to the patient’s pre-operative condition.Conclusion: This proof-of-concept investigation demonstrates that the amalgamation of AI-assisted surgical planning and additive manufacturing can improve surgical accuracy and shorten surgical duration. While access to this technology is currently constrained during its early stages of development, it is anticipated that these limitations will diminish as the potential of AI and additive manufacturing in facilitating complex orthopedic procedures becomes more evident, leading to a surge in interest and adoption of this approach.

Background: The pelvis is one of the most common locations for metastatic bone disease. While many of the publications that describe surgical treatments focus on periacetabular lesions (Enneking zone II), there is a lack of investigation into lesions in the non-periacetabular areas (zones I, III, and IV). We recently described a minimally invasive percutaneous screw application for metastatic zone-II lesions with excellent results. In the present study, we aimed to extend this approach to the other pelvic areas. Methods: Twenty-two consecutive patients with painful non-periacetabular pelvic metastatic cancer were included based on retrospective chart review. There were 16 women and 6 men with an average age of 60 years (range, 36 to 81 years). The most common primary cancers were multiple myeloma (7 cases) and breast (5 cases). The most common locations were the sacrum and the ilium. A pathologic fracture was identified in 15 patients. Most of the lesions were treated with multiple large-diameter screws, except for the isolated zone-III lesions. All of the procedures were completed in a standard operating room without the need for special instruments. Radiation therapy was given to 19 patients; the average dose was 15 Gy. The studied outcomes were pain and functionality as assessed by a visual analog scale (VAS) score and the Eastern Cooperative Oncology Group score (ECOG), respectively. Results: There were no surgical complications and no need for blood transfusion. The average follow-up time was 7 months (range, 0.3 to 34.0 months). Two patients died within 4 weeks of surgery due to COVID-19 infection. There was significant improvement in the postoperative VAS pain score (p < 0.0001) and the ECOG score (p < 0.05) when compared with the preoperative scores. There was no implant failure or revision surgery. Local bone-healing was observed in 12 of 14 patients (86%) who survived for >3 months after surgery. Conclusions: Percutaneous screw application is safe and effective in the treatment of metastatic non-periacetabular pelvic lesions. Given the simplicity of the technique and the instrumentation and the tolerance for concomitant treatments, this approach is worthy of broader consideration. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Osteosarcoma is an aggressive bone malignancy with a poor prognosis. One putative proto-oncogene in osteosarcoma is SKP2, encoding a substrate recognition factor of the SCF E3 ubiquitin ligase. We previously demonstrated that Skp2 knockout in murine osteosarcoma improved survival and delayed tumorigenesis. Here, we performed RNA sequencing (RNA-seq) on tumors from a transgenic osteosarcoma mouse model with conditional Trp53 and Rb1 knockouts in the osteoblast lineage (“DKO”: Osx1-Cre;Rb1lox/lox;p53lox/lox) and a triple-knockout model with additional Skp2 germline knockout (“TKO”: Osx1-Cre;Rb1lox/lox;p53lox/lox;Skp2−/−), followed by qPCR and immunohistochemistry validation. To investigate the clinical implications of our results, we analyzed a human osteosarcoma patient cohort (“NCI-TARGET OS”) with RNA-seq and clinical data. We found large differences in gene expression after SKP2 knockout. Surprisingly, we observed increased expression of genes related to immune microenvironment infiltration in TKO tumors, especially the signature genes for macrophages and to a lesser extent, T cells, B cells, and vascular cells. We also uncovered a set of relevant transcription factors that may mediate these changes. In osteosarcoma patient cohorts, high expression of genes upregulated in TKO was correlated with favorable overall survival, which was largely explained by the macrophage gene signatures. This relationship was further supported by our finding that SKP2 expression was negatively correlated with macrophage infiltration in the NCI-TARGET osteosarcoma and the TCGA Sarcoma cohorts. Overall, our findings indicate that SKP2 may mediate immune exclusion from the osteosarcoma tumor microenvironment, suggesting that SKP2 modulation in osteosarcoma may induce antitumor immune activation.

The blood supply, metabolism, and composition of bone are known to be altered in a variety of pathologies of the skeletal system including osteoporosis, diabetes, anemias, and some forms of arthritis.^1,2 Likewise, sarcomas, malignant tumors of bone and connective tissue are known to have substantially altered blood supply at the tumor site, often with hypoxia and necrosis.^3,4 The quantitative measurement of bony regions of the body could assist in diagnosis, prognosis, and basic understanding of the pathophysiology of these diseases.