Bone defects pose a significant challenge in orthopedic surgery, particularly when the defect size surpasses the body’s inherent healing capacity. While bone defects <5 cm are typically managed with direct bone grafting, larger defects often lead to non-union due to insufficient regenerative potential ^[1]. For such critical-sized defects, current treatment modalities include stabilization with bone grafting, bone transport surgery, and vascularized fibula grafts. However, these approaches are not without their drawbacks, such as graft site morbidity and procedural bulkiness [2, 3]. In addition, graft resorption remains a notable challenge in the context of large bone defects. In the management of femoral defects ranging from 6 to 15 cm, favorable outcomes are often achieved due to the substantial muscle mass in the area. Conversely, smaller tibial defects, particularly those exceeding 1–2 cm in size and involving more than 50% of the cortical circumference, tend to result in poorer outcomes [4, 5]. Critical-size defects, defined as those greater than 1 cm in length and encompassing more than 50% of the cortical diameter, consistently present union challenges even after bone grafting ^[6]. Tibial defects of 2.5 cm or more are especially susceptible to non-union, with the risk exacerbated by infection and soft tissue damage ^[7]. Traditional gold standard treatments for large bone defects in weight-bearing bones generally rely on “bone-bone” fusion techniques, such as bone grafting and bone transport. Nonetheless, these methods are associated with several limitations, including the need for revision surgeries, graft site morbidity, and the bulkiness of the grafts, which can be inconvenient for patients [8, 9]. In this context, we present a case report of a patient with distal tibia non-union successfully treated using a 3D-printed titanium mesh implant. This innovative approach offers a promising alternative to conventional methods, potentially addressing some of the inherent limitations and improving patient outcomes.

A 38-year-old male presented to OPD with an inability to walk, non-weight-bearing. According to the history, the patient had a road traffic accident (RTA) 1 year prior, which resulted in fractures of the medial malleolus and distal tibia-fibula with a grade 3b open wound. This was managed by an external fixator and fibula plating 1 year prior. Open wound was treated with vacuum-assisted closure dressing. The external fixator was removed at the 5^th month post-operatively. Following this patient was kept under immobilization. On X-ray there was an atrophic non-union at the fracture site. Clinically patient had a 2.5 cm shortening on the affected limb (Fig. 1a and b). For treatment, the Ilizarov ring fixator and fibula strut graft option were considered. The patient notably had a version toward any type of external fixator. Due to the need for a minimum incision and early weight bearing; the decision was made to proceed with a titanium mesh implant with plate construct. The patient was informed about the nature of the implant and potential outcomes. The patient accepted the advantages of definitive fixation while being aware of backup plans involving a ring fixator or strut graft if needed.

During surgical planning, a bilateral lower limb CT scan was used to make an anatomically 3d-printed implant by mirroring the normal tibia at the anatomical site. In MIMICS software by Materialise, a CT DICOM was imported, and equivalent cuts were made on the normal tibia by measuring the location of defect from a proximal and distal end of the tibia and normal tibial segment was isolated which was then mirrored. This segment was put up in a lattice structure with mesh stacks in software. To reduce weight of the implant cylindrical cavity of diameter 8 mm was made inside the design. This implant design was supported with a dynamic compressive plate, which was also 3d-printed. Polymer models were printed and fitted with the patient’s printed tibia to check for reproducibility of design in practice (Fig. 2a-d). Pre-operatively, the patient was started with pre-rehabilitation achieving neutral to 20° plantar flexion. During surgery, a thick flap incision was made to minimize complications. After exposure, the fibular plate and medial malleolus screw were removed. Planned cuts were made on the tibia for placing the implant by using Jig. Proper positing of the implant was confirmed under C-arm and the Implant was fixed with corticocancellous screws (Fig. 3a and b). The distal fragment of the distal tibia was noted to be osteoporotic during surgery. A thorough wash was given and wound closure was done in layers. Wound healing was uneventful.

Post-operatively, the patient was followed up under non-weight-bearing for 1.5 months. The patient was kept on partial weight-bearing. At the end of 3^rd month, the patient achieved full weight-bearing and restored ambulation, repeat X-ray performed showed the implant in place without any sign of loosening (Fig. 3c). The patient was followed up closely and adequate physiotherapy was continued (Video 1).

At the end of the 1.5 year, a CT scan was performed to check for integration of the implant with bone. CT scan showed two patterns of union; bone bridging through the canal along and bridging callus at the proximal end and some bone growth at the distal end (Fig. 3d) (Video 2).

Current clinical methods to deal with bone losses primarily include bone transport, autograft, and allografts. Bone grafts exhibit important properties of osteoconductive and osteoinductive, but repeated availability can be limited due to multiple number of revision surgeries. They also pose risks, such as donor site morbidity, infection, inadequate integration of graft, devitalization, resorption, and leading to diminished mechanical stability [10, 11]. In recent years, implants printed by 3D-technology are gaining popularity in hip and knee arthroplasty. Parameters, such as pore size, density, and topological patterns can be precisely adjusted in newer generation 3D-printing machines, hence implant usability due to better biocomparability has increased [12, 13]. In materials used, Titanium (Ti) has the advantage of being light and strong when fabricated, hence it is commonly used ^[14]. In previous few cases, large cages have been used for bone loss cases in the distal tibia, but such cage was used for total ankle arthrodesis ^[15]. Varieties of pore diameter and their bone ingrowth capacity have been tested among them 3D-printed implants with pore diameter 700 um has shown more bone ingrowth compared to other sizes of 300 μm, 900 μm, or larger diameter. The concept of bone-to-implant fusion without putting any bone graft is based on the fusion optimum pore size, strut diameter, and porosity of implants [16, 17]. We used titanium alloy powder in the DMLS EOS M280 printer to stratify the implant as per specification. The use of a 3D-printed implant with an anatomic design offers another feasible option for addressing critical-size bone defects. This aligns with findings by Teng Zhang et al. who proposed a concept of bone-to-implant fusion without bone grafting ^[18]. The advantages of this method over the Masquelet technique can be taken as short time for weight bearing, no donor graft site morbidity, and immediate stable construct ^[19]. Looking at the only complication study involving 3D-printed implants in open wounds found that 10/39 required removal due to non-union, which is comparable to existing methods of fixation ^[20]. In our case, the Mesh plate construct allowed additional space for bony ingrowth through a canal of mesh implant. The stability of the bone implant construct was achieved partially by intraimplant bone bridging and mesh-plate construct. Based on the findings of our study, this technique may prove highly beneficial in places where there is a shortage of bone grafts, large bone defects, critical-sized bone defects as well as in weight-bearing limbs following bone resection. However, further high-quality randomized control trials are necessary to validate the results.

The low young, modulus of mesh implants serves to minimize the stress shielding around bone implant junction. Enough sturdiness of the implant allowed early weight bearing along with partial bone bridging. The pattern of bone ingrowth was along the mesh as well as inside the canal. This Method of fixation can be considered as one of the sustainable way to treat large bone gaps, instances where large bone grafts are not available may be due to repeated surgeries. Further research and longitudinal studies will be important for the long-term efficacy and reproducibility of this technique.

This case report shows the usability of metal 3D-printing and the importance of surface properties of mesh implants such as porous structures.