Introduction. Porous scaffolds for bone ingrowth have numerous applications, including correcting deformities in the foot and ankle. Various materials and shapes may be selected for bridging an osteotomy in a corrective procedure. This research explores the performance of commercially pure Titanium (CPTi) and Tantalum (Ta) porous scaffold materials for use in foot and ankle applications under simplified compression loading. Methods. Finite element analysis was performed to evaluate von Mises stress in 3 porous implant designs: 1) a CPTi foot and ankle implant (Fig 1) 2) a similar Ta implant (wedge angle = 5°) and 3) a similar Ta implant with an increased wedge angle of 20°. Properties were assigned per reported material and density specifications. Clinically relevant axial compressive load of 2.5X BW (2154 N) was applied through fixtures which conform to ASTM F2077–11. Compressive yield and fatigue strength was evaluated per ASTM F2077–11 to compare CPTi performance in design 1 to the Ta performance of design 3. Results. FEA results indicate peak stresses at fixture contact locations. Similar designs (CPTi design 1 and Ta design 2) resulted in similar von Mises stresses (Fig 1). Increasing the wedge angle (Ta design 3) increased stress by 15%. The static compressive yield strength of CPTi design 1 (20,560 N) was similar to the Ta design 3 (20,902 N), with yield manifesting as barreling and crushing of the components (Fig 2a). However, the fatigue strength of CPTi (6,000 N) was 40% lower than the Ta design 3 (9,500 N) (Fig 3). In both cases fracture initiated from regions of highest stress predicted in FEA. Fracture progression was not instantaneous and was characterized by an accumulation of damage (Fig 2b–c) leading to gross component fracture and loss of implant integrity. Discussion. FEA is a useful tool to determine stress variations and can be used to identify worst case within a material: in this case, a larger implant wedge angle leads to higher stresses. Additionally, FEA accurately predicted fracture initiation location. However, material selection plays a large role in porous implant performance: although FEA predicted higher stresses in a Ta component with a greater wedge angle than a similar sized CPTi component, static compressive strengths were nearly identical, and the Ta component had 58% higher fatigue strength. When selecting a material or geometry for an implant application, both FEA and static testing allow for rapid evaluation of designs. However, caution should be used in interpreting the results: the ultimate performance of an implant in-vivo will depend on its ability to maintain integrity over a long period of time, and should be characterized by dynamic testing

High tibial osteotomy (HTO) is a common surgical procedure for treatment of patients with varus mal-alignment. The success rate of the procedure is strongly dependent on the quality of the correction. Thus, an accurate pre-planning is essential to ensure that the precise amount of alignment is achieved postoperatively. The purpose of this study was to simulate the HTO in a patient with varus deformity in order to explore the interactions between the wedge angle, the mechanical axis, and the knee joint configuration. A finite element model of the knee joint of a patient with varus deformity was developed. The geometry was obtained using the whole limb CT scans the knee MR images. The bones were assumed as rigid bodies, the articular cartilage and the meniscus as elastic solids, and the ligaments as nonlinear springs. A 600N force was applied at the femoral head in the line of the mechanical axis and the resulting knee configuration was studied. The HTO was simulated assuming insertion of wedges with different angles beneath the tibial plate and applying the resulting alteration of the loading axis to the model. The results indicated that the actual change of the mechanical axes was always smaller than what predicted by a geometric pre-planning approach that does not consider the post-operative change of the knee joint configuration. It was suggested that subject-specific models are needed to simulate the HTO in patients before surgery and determine the appropriate wedge angle that locates the mechanical axis in the middle of the knee

Eight consecutive patients with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation. The osteotomy was fixed with locking plates and screws. Post-operative assessment included planar X-rays, CT-scan and full leg standing X-rays. One three-planar, three bi-planar and four single-plane osteotomies were performed. Maximum weightbearing mechanical femoro-tibial coronal malalignment varied between 7° varus and 14° valgus (mean 7.6°, SD 3.1). Corrective angles varied from 7°–15°(coronal), 0°–13°(sagittal) and 0°–23°(horizontal). The maximum deviation between the planned pre-operative wedge angle and the executed post-operative wedge angle was 1° in the coronal, sagittal and horizontal plane. The desired mechanical femorotibial axis on full-leg standing X-rays was achieved in 6 patients. Two patients were undercorrected by 1° and 2° respectively. Conclusion. 3D planning and guided correction of multi-planar deformity of femur or tibia is a feasible and accurate novel technique

Osteotomies around the knee are traditionally templated on 2D plain X-rays. Results are often inaccurate and inconsistent and multiplanar osteotomies are hard to perform. The aim of this study is to evaluate the feasibility and accuracy of virtual three-dimensional CT-based planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates. Eight consecutive patients with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation. The osteotomy was fixed with locking plates and screws. Post-operative assessment included planar X-rays, CT-scan and full leg standing X-rays. One three-planar, three bi-planar and four single-plane osteotomies were performed. Maximum weightbearing mechanical femoro-tibial coronal malalignment varied between 7° varus and 14° valgus (mean 7.6°, SD 3.1). Corrective angles varied from 7°–15° (coronal), 0°–13° (sagittal) and 0°–23° (horizontal). The maximum deviation between the planned pre-operative wedge angle and the executed post-operative wedge angle was 1° in the coronal, sagittal and horizontal plane. The desired mechanical femorotibial axis on full-leg standing X-rays was achieved in 6 patients. Two patients were undercorrected by 1° and 2° respectively. Conclusion. 3D planning and guided correction of multi-planar deformity of femur or tibia is a feasible and accurate novel technique

Introduction. Osteotomies around the knee are traditionally templated on 2D plain X-rays. Results are often inaccurate and inconsistent and multiplanar ostetomies are hard to perform. The aim of this study is to evaluate the feasibility and accuracy of virtual three-dimensional CT-based planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates. Methods. Eight consecutive patients with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation. The osteotomy was fixed with locking plates and screws. Post-operative assessment included planar X-rays, CT-scan and full leg standing X-rays. Results. One three-planar, three bi-planar and four single-plane osteotomies were performed. Maximum weightbearing mechanical femoro-tibial coronal malalignment varied between 7° varus and 14° valgus (mean 7.6°, SD 3.1). Corrective angles varied from 7°-15°(coronal), 0°–13°(sagittal) and 0°–23°(horizontal). The maximum deviation between the planned pre-operative wedge angle and the executed post-operative wedge angle was 1° in the coronal, sagittal and horizontal plane. The desired mechanical femorotibial axis on full-leg standing X-rays was achieved in 6 patients. Two patients were undercorrected by 1° and 2° respectively. Conclusion. 3D planning and guided correction of multi-planar deformity of femur or tibia is a feasible and accurate novel technique

Background. Osteotomies around the knee have been used to correct lower limb mal-alignment for over 50 years. The procedure is technically demanding and carries specific risks of neurovascular injury, incorrect planning and execution, and insufficient fixation. In recent years, with the advent of locking plates, fixation techniques have improved significantly but the correct planning and execution of the operation remains difficult. Despite the availability of CT and MRI 3D imaging, surgical planning is still traditionally performed on 2D plain X-rays [1]. Especially with multi-planar deformities, this technique is prone to error. The aim of this clinical pilot study is to evaluate the feasibility of virtual pre-operative three-dimensional planning and correct execution of osteotomies around the knee with the aid of patient specific surgical guides and locking plates. Patients and methods. Eight consecutive patients, presenting with significant malalignment of the lower limb were included in the study. Pre-operative CT scans of the affected limb and the normal contra-lateral side were obtained and 3D models of the patient's anatomy were created, using dedicated software (Mimics® 3-matic®, Materialise, Leuven Belgium) [2]. These models were used to evaluate the required surgical correction. The healthy contralateral limb was mirrored and geometrically matched to the distal femur or proximal tibia of the healthy side. A virtual opening wedge correction of the affected bone was used to match the geometry of the healthy contralateral bone. Standard lower limb axes measurements confirmed correction of the alignment [3]. Based on the virtual plan, surgical guides were designed to perform the planar osteotomy and achieve the planned wedge opening and hinge axis orientation (see figure 1). Apart from guiding the osteotomy, the patient specific surgical guide also guided drilling of the planned screw holes. Post-operative assessment of the correction was obtained through planar X-rays, CT-scan and full leg standing X-ray. Results. One three-planar, three bi-planar and four single-plane osteotomies were performed. All guides could be used during surgery and served accurate guidance of the osteotomy plane and screwholes. The guides matched the bone very well in all cases without remaining toggle. The maximum deviation between the planned pre-operative wedge angle and the executed post-operative wedge angle was 1° in the coronal, sagittal and horizontal plane. The desired mechanical femorotibial axis on full-leg standing X-rays was achieved in 6 patients. Two patients were undercorrected by 1° and 2° respectively. No significant peri-operative complications occurred. Conclusion. 3D planning and guided correction of multi-planar deformity of femur or tibia is a feasible and accurate novel technique