Reconstruction of bone defects after oncological resection with Free Fibula Flap supported with Decellularized Bone Scaffold

Introduction and Aim The musculoskeletal system is the main system that provides mobility to the human body. Reconstruction of defects after oncological resection of bone tumors or soft tissue tumors with bone invasion is a current and multidimensional concept. The evolution of treatment process, which started with amputation for tumors located in the extremities, turned into limb-sparing surgery with the use of biological (bone grafts, bone flaps and materials that can integrate with bone) or non-biological (endoprosthesis, internal fixator, etc.) materials, improvements in neoadjuvant and adjuvant therapies (chemotherapy, radiotherapy, immunotherapy). Although endoprosthesis are favored for their ease of reconstruction and allografts for their speed of reconstruction and low additional comorbidities, bone flaps and especially fibula bone flaps are advantageous due their ability to be used with different modifications (double-barrel, end-to-end, with bone graft, with bone scaffold), to address simultaneous muscle and skin defects and to enable physiological bone healing process increasing survival and functionality of bone flap due to preservation of vascularization. One of the most important factors in ensuring homeostasis of long bones is the mechanical stress placed on the bone (Wolff's law) in addition to the hormonal factors. It has been shown in many studies that the fibula bone flap shows this homeostatic adaptation and undergo hypertrophy when placed under mechanical stress after its transfer to the recipient site. For this reason, the fibula bone flap can be used for reconstruction purposes even in cases where it differs in diameter from the recipient bone. Hypertrophic adaptation of the fibula flap is a long-lasting process that develops over time. It has been reported to continue for 3 years. In order to ensure early functional recovery of patients after reconstructive surgeries and their adaptation to social life, Capanna et al. described the combined use of allografts and fibula flap. In this technique, bone allografts are processed to prevent disease transmission and then placed around the fibula flap to reconstruct the defect, aiming to accelerate functional recovery and reduce the risk of early fibula flap fracture. However, the technique did not popularize due to transportation difficulties, additional costs and low mechanical load carrying capacities. Yamamato et al. reported that bone tumors treated with liquid nitrogen devitalized and decellularized over time, losing their proliferative potential. Using this technique, tumor tissue removed from the patient can be used in reconstructive surgeries as decellularized bone scaffold with liquid nitrogen application. The aim of this study is to evaluate the oncological safety, radiological and functional results of the combined use of bone scaffold obtained by decellularizing the resected tumor bone tissue with liquid nitrogen and fibula flap in bone defects formed after oncological resections, by comparing them with patients who had similar defects repaired with fibula flaps and the literature. Material and Methods This study was carried out with the approval of Bezmialem Vakıf University Non-Interventional Research Ethics Committee dated 09.08.2023 and numbered 2023/239. A retrospective analysis of patients treated by Bezmialem Vakıf University Faculty of Medicine Hospital, Department of Plastic, Reconstructive and Aesthetic Surgery and Department of Orthopedics and Traumatology, between 1 June 2010 and 1 June 2022, for oncological defects of femur and tibia and reconstructed with a fibula flap (F) alone or a fibula flap supported by a bone scaffold (FS) and completed a 12-month follow-up period. The patients' ages, gender, comorbidities, and medical history were recorded. The pathological types, localizations, sizes of the tumors the patients had, and details of neoadjuvant chemotherapy or radiotherapy treatment before surgery were investigated. The surgical technique applied, the size of the bone defect formed in the surgery, the leg from which the fibula flap was taken, whether bilateral fibula was used, whether it was used in combination with bone scaffold, whether a double barrel was used or not were investigated from the surgery notes and digital archive records. Postoperative adjuvant chemotherapy and radiotherapy treatment status, early and late term complications were examined. In order to evaluate the functional recovery of the patients, MSTS scores evaluated at the 3rd, 6th and 12th months after surgery were noted. Percent union scores were calculated using the modification of RUST scores on anteroposterior and lateral direct radiographs taken at the 3rd, 6th and 12th months after surgery. In addition, bone hypertrophies were evaluated using the formula defined by de Boer and Wood on standardized direct radiographs taken from the same angle in the early postoperative period and at the first year. The information of the patients in the study was recorded and tabulated using the Statistical Package for the Social Sciences version 23 (SPSS Inc, Chicago, IL) program. Means and distributions were found with descriptive methods. Independent samples t-test was used to compare nominal data. Categorical data were compared using the chi-squared test. Results with p<0.05 and a confidence interval of 95% were considered significant. Results 34 patients suitable for the study were found according to the inclusion and exclusion criteria and their data were examined. Of the 34 patients, 18 were men and 16 were women. The average age of the patients was 30.9±17.6 years. The youngest patient was 7 years old and the oldest patient was 65 years old. The ages of the patients showed a bimodal distribution, peaking at 10-20 years old and around 50 years old. The defects of 19 patients (56%) were repaired with fibula flap alone (F) and the defects of 15 patients (44%) were repaired with fibula flap supported by decellularized bone scaffold (FS). When the pathological diagnoses of the patients were examined, 13 patients with Ewing's sarcoma, 6 patients with chondrosarcoma, 6 patients with osteosarcoma, 3 patients with malignant mesenchymal tumor (MMT) subtypes (liposarcoma, pleomorphic MMT, undifferentiated MMT), 3 patients with adamantinoma, 2 patients with giant cell bone tumor in and 1 patient with synovial sarcoma was found. It was found that 76% (n = 26) of the patients received neoadjuvant chemotherapy, 38% (n = 13) received neoadjuvant radiotherapy, 62% (n = 23) received adjuvant chemotherapy and 15% (n = 5) received adjuvant radiotherapy. When the anatomical regions with bone defects were examined, 6 patients had right femur defects, 12 patients had left femur defects (total femur n=18), 11 patients had right tibia defects, 5 patients had left tibia defects (total tibia n=16). Fibula flap supported by bone scaffold was used in 6 (33%) of the patients with femoral defects and 9 (56%) of the patients with tibial defects. Osteocutaneous fibula flap was used in 47% of the patients (n=16) for repair of skin defects or as a monitor. Osteocutaneous flap use comprised 46.7% (n=7) of the FS group and 47.4% (n=9) of the F group. Pedicled fibula flap was used in 4 patients (11.8%), and combined repair with bone scaffold was achieved in 3 of these patients. In 2 patients (5.9%), repair was achieved in a double-barreled manner (osteotomized single fibula flap in 1 patient and bilateral fibula flap in 1 patient) without the use of scaffold. When the bone defect lengths of the patients were examined, the average length of the defect was 15.4±5.9 cm. The average defect size in patients using fibula flap alone was 12.8±4.5 cm, and in the fibula flap supported with bone scaffold group, the average defect size was 18.6±6.0 cm. The difference was statistically significant (p<0.05). When all patients were examined, the average length of the fibula flaps used was found to be 19.7±7.6 cm. When the groups were examined separately, the average fibula flap length was 17.9±8.2 cm in the F group and 21.9±6.5 cm in the FS group. In the statistical comparison made by excluding two cases with double-barreled repair, it was found statistically significant that the fibula flaps were longer than the defect and the FS group flaps were longer than the F group flaps (p<0.05). Postoperatively, 65% of the patients were hospitalized in the intensive care unit (ICU). These patients stayed in the ICU for an average of 3.5±2.1 days. When all patients were examined, the average number of days spent in the ICU was 2.2±2.4. When the groups are examined, average ICU stay was 2.0±2.3 days in the F group and 2.5±2.5 days in the FS group. The difference between groups was not statistically significant (p=0.52). The average total hospital stay of the patients after surgery was 10.0±5.5 days. When the groups were examined separately, the F group stayed in the hospital for an average of 10.4±5.8 days, and the FS group stayed in the hospital for an average of 9.5±5.3 days. The difference between groups was not statistically significant (p=0.65). In the evaluation made with the MSTS scoring system at the follow-up visits of the patients, the mean MSTS scores at the 3rd month were 55.5±5.8% (F:53.7%±6.0, FS:57.8%±5.0), and the mean MSTS scores at the 6th month was 71.0±6.8% (F:68.3±6.8%, FS:74.4±5.3%) and 12th month mean MSTS was 85.3±7.4% (F:%85.1±8.2, FS:85.6±6.6%). The difference between MSTS scores between groups was statistically significant at 3 and 6 months after surgery (p<0.05). When MSTS values were analyzed at the 12th month follow-up after surgery, the difference was not statistically significant between the groups (p=0.86). The average time to start adjuvant chemotherapy treatment after surgery (n=23) was 35.1±11.9 days. When the groups were examined separately, the F group (n=14) started chemotherapy after an average of 33.9±14.0 days, and the FS group (n=9) started chemotherapy after an average of 37.0±8.2 days. The difference was not statistically significant (p=0.55). Early complications (wound infection) were observed in 7 patients (21%) and late complications (contracture, short limbs, union problems, implant failure) were observed in 9 patients (26%). Including all complications, the difference of complication rate between the fibula flap supported by bone scaffold (FS) and fibula flap alone (F) groups was not statistically significant (p=0.58). When complications are examined separately, wound infection rates (p=0.37), need for debridement (p=0.43), contracture risk (p=0.45) and union problems (p=0.43) were not statistically different between the groups. During long-term follow-up, distant metastases were observed in 6 patients (17.7%). No amputation or local recurrence was observed. The RUST scores calculated by evaluating the patients' direct radiographs taken at the 3rd, 6th and 12th month follow-ups were 56.3±9.3%, 75.5±8.8% and 92.9±9.8%, respectively. When the groups' mean RUST scores are examined separately, at the 3rd month, the F group's mean score 54.4±8.9% and the FS group's mean score was 58.6±9.5%, and at the 6th month, the F group's mean score was 73.7±8.1% and the FS group's mean score was 77.8±9.3%. At 12 months, the F group had mean RUST scores of 92.5±9.4% and the FS group had 93.3±10.7%. In follow-ups, the difference between groups was not statistically significant (p=0.19/p=0.18/p=0.82). Bone hypertrophy values calculated using standardized radiographs with the same angle were 15.50±5.94% on average at the 12th month. When the groups were examined separately, the F group's mean bone hypertrophy was 15.97±3.93% and the FS group's mean bone hypertrophy was 14.89±7.91%. The difference between groups was not statistically significant (p=0.53). However, when the distributions were examined, the F group had a normal distribution, while the FS group had a bimodal distribution concentrated at 8% and 22%. Discussion In order for a new surgical technique to enter clinical practice and gain a foothold, it must be compared with existing techniques using quantitative and qualitative methods, and its reliability and long-term results must be demonstrated. The parameters that should be considered for a technique to be used in the reconstruction of oncological bone defects should include the demonstration of its oncological safety (recurrence, time until the start of adjuvant treatment, etc.), comparative analysis of complication rates, and comparative analysis of radiological and functional improvements. No local recurrence was observed in any of the patients included in this study at their 12-month follow-up. Patients who would receive adjuvant treatment (n=23, 68%) first started chemotherapy treatment after surgery. Patients in the fibula flap (FS) group supported by bone scaffold (n=9) waited an average of 37.0±8.2 days, and patients in the fibula flap alone (F) group (n=14) waited an average of 33.9±14.0 days to start adjuvant treatments. The fact that there is no statistically significant difference between the two groups and that there is no recurrence in the patients is important in terms of showing the oncological reliability of the techniques and providing post-surgical treatments without delay. After surgery, early wound complications were observed in 7 patients and late complications (contracture, short limbs, union problems, implant breakage) were observed in 9 patients. Wound complications were staged according to need and managed with medical treatment and regional wound care, debridement or secondary flaps after debridement, and no limb loss or flap loss was observed. Statistical analysis of wound infection rates (F:26.3%, FS:13.3%), post-debridement flap requirement (F:15.8%, FS:6.7%) and union problems (F:5.3%, FS:13.3%) revealed no statistical difference. The results were found to be consistent with the bone union problems and revision surgeries reported in the fibula flap combined with allograft (Capanna technique) and with autograft treated with liquid nitrogen studies in the literature. In radiological evaluations, direct radiographs taken during the follow-up examinations of the patients were used, and 3rd month, 6th month and 12th month bone union scores and 12th month hypertrophy rates of fibula flaps were used. No significant difference was found between groups. In the modification of the RUST scoring system designed for bone flap repair, bone union scores were lower at 3 months (F: 54.4%, FS: 58.6%) and at 6 months (F: 73.7%, FS: 77.8%). and similar results were seen at the 12th month (F: 92.5%, FS: 93.3%). Standardized angles were used to calculate bone hypertrophy rates. It was found that hypertrophy occurred at a rate of 15.97±3.93% in the F group and 14.89±7.91% in the FS group. In order to ensure bone hypertrophy, it is important to fixate the fibula flaps with the load-sharing technique and to harvest flaps longer than the existing bone defects. While the average bone defect was 15.4±5.9 cm (F:12.8±4.5 cm, FS:18.6±6.0 cm), the average fibula flap length was 19.7±7.6 cm. It was found statistically significant that fibula flaps supported with bone scaffold were preferred in longer defects and that the fibula flaps used were longer than the existing defects (p<0.05). It has been shown in various studies that hypertrophy after bone union continues until the 3rd year, but when the demonstration of early bone hypertrophy is evaluated together with bone union scores, the fibula flap combined with bone scaffold is not statistically significant in the early period compared to the fibula flap alone. It shows that it provides better union and does not have worse results than the fibula flap alone at 12 months. Functional results can be considered the most important outcome for the patient, next to oncological safety. In the analysis of the MSTS scores at the patients' follow-up visits, the difference between groups' mean MSTS scores at the 3rd month (F: 53.7%±6.0, FS: 57.8%±5.0) and 6th month (F:%68.3±6.8, FS:74.4±5.3%) after surgery was found to be statistically significant (p<0.05). The difference is not significant at 12 months after surgery (F: 85.1%±8.2, FS: 85.6%±6.6), but is consistent with the 12th month MSTS scores commonly reported in the literature. The primary purpose of supporting the fibula flap with a bone scaffold is to prevent early fibula flap fractures and provide early functional recovery for patients. Therefore, they can be expected to have similar scores at 12 months after surgery. Conclusion In the studies of fibula flap combined with allograft and fibula flap combined with autograft treated with liquid nitrogen in the literature, comparisons were generally made with allograft/bone scaffold alone. In this study, the combined use of bone scaffold and fibula flap obtained after processing the tumor-bearing bone segment with liquid nitrogen was compared with the use of fibula flap and with the literature on oncological, radiological and functional parameters, and it was shown that it had results that were not worse than fibula flap alone. In post-operative functional evaluations, its superiority over reconstructions performed with fibula flap alone in the early period has been demonstrated. A more in-depth analysis will be possible by extending the follow-up period and increasing the number of patients. In addition, the development of techniques that will enable the evaluation of bone integration and volumetric bone volume instead of bone hypertrophy will make it possible to better evaluate bone healing. Keywords: Autograft; Bone Reconstruction; Bone Scaffold; Capanna Technique; Fibula Flap; Oncoplastic Surgery; Vascularized Fibula Graft