Computational simulation study on ilio-sacral screw fixations for pelvic ring injuries and implications in Asian sacrum.

OBJECTIVES: Despite a high possibility of technique-related complications, ilio-sacral (IS) screw fixation is the mainstay of operative management in posterior pelvic ring injuries. We aimed to make IS screw trajectory with fully intraosseous path that was optimal and consistent, and confirm the possibility of transiliac-transsacral (TITS) screw fixation in Asian sacrum. METHODS: Eighty-two cadaveric sacra (42 males and 40 females) were enrolled and underwent continuous 1.0-mm slice computed tomography (CT) scans. CT images were imported into Mimics® software to reconstruct three-dimensional model of the pelvis. To simulate IS screws, we inserted 7.0-mm-sized TITS cylinder for first (S1) and second (S2) sacral segment and 7.0-mm oblique cylinder for S1. TITS cylinder could not be inserted into S1 of 14 models (sacral variation models) but could be inserted into the S2 of all models. The actual length of virtual IS screws was measured, and anatomic features of safe zone (SZS2) including the area, horizontal distance (HDS2), and vertical distance (VDS2) were evaluated by the possibility of TITS screw fixation in the S1. RESULTS: When the oblique cylinder was directed toward the opposite upper corner of S1 at the level of the first foramen, there was no cortical violation regardless of sacral variation. The average length of TITS cylinder was 152.3 mm (range 127.9-178.2 mm) in S1 and 136.0 mm (range 97.8-164.1 mm) in S2, and for oblique cylinder it was 99.2 mm (range 82.4-132.2 mm). The average VDS2, HDS2, and the area of SZS2 were 15.5 mm (range 8.7-24.4 mm), 18.3 mm (range 12.7-26.6 mm), and 221.1 mm2 (range 91.1-386.7 mm2), respectively. The VDS2 and SZS2 of sacral variation were significantly higher than those of normal (both p = 0.001). CONCLUSIONS: Considering the high variability of the S1, it is better to direct the IS screw trajectory toward the opposite upper corner of the S1 at the level of first sacral foramen. If a TITS screw is needed, the transverse fixation for the S2 could be performed alternatively due to its sufficient osseous site even in Asian sacrum.

Computational simulation of cephalomedullary nailing in the osteoporotic Asian femur and clinical implications.

PURPOSE: To assess the conformity of PFNA-II® and introduce clinical implications of new cephalomedullary nail (CMN) by analyzing three-dimensional (3D) modeling with virtual implantation at the actual size. MATERIALS AND METHODS: Thirty-four patients (average age; 79 years, range 68-94 years) who sustained the intertrochanteric fracture of the femur were enrolled in the present study. After importing into Mimics® software, the intact femurs on the opposite side were selected as cropping areas to reconstruct the 3D femur model with the medullary canal. PFNA-II® and new CMNs (lateral angle 0° and 2°, CCD angle 130°; CMN0° and CMN2°) were processed at the actual size and ideally placed in the proximal femur using Mimics® software. The virtual entry point (EP), nail conformity, and anatomical relationships with the adjacent structures were assessed. RESULTS: The virtual EP of PFNA-II® was placed along the cervico-trochanteric (CT) junction in the posterior half around trochanteric fossa and always medial to the tip of greater trochanter (GT). There were six abutments in PFNA-II® models, one impingement in CMN 0°, and no impingement in CMN 2°. All the models with cortical abutment showed increased anterior and lateral bowing of the proximal shaft owing to age-dependent changes. Compared with PFNA-II®, with a decreasing tendency on the mediolateral angle of new CMNs, the virtual EP shifted to the medial and anterior side towards the CT junction. By simulating the intentional positioning in the media-to-lateral direction, the abutments in the PFNA-II® model could not be avoided. Furthermore, the lag screw of CMN 0° was placed ideally at the center or inferior side of the femoral head < 10 mm in any direction without a cortical abutment. CONCLUSION: To avoid cortical abutment of CMN in the Asian geriatric femur, the virtual EP would be technically placed in the medial to the GT tip, and the implant design should be changed to decrease the mediolateral angle.

Elastic Modulus of Osteoporotic Mouse Femur Based on Femoral Head Compression Test.

A biomechanical test is a good evaluation method that describes the structural, functional, and pathological differences in the bones, such as osteoporosis and fracture. The tensile test, compression test, and bending test are generally performed to evaluate the elastic modulus of the bone using mice. In particular, the femoral head compression test is mainly used for verifying the osteoporosis change of the femoral neck. This study conducted bone mineral density analysis using in vivo microcomputed tomography (micro-CT) to observe changes in osteoporosis over time. It proposed a method of identifying the elastic modulus of the femur in the normal group (CON group) and the osteoporotic group (OVX group) through finite element analysis based on the femoral head compression test and also conducted a comparative analysis of the results. Through the femoral head compression test, it was verified that the CON group's ultimate and yield loads were significantly higher than those of the OVX group. It was considered that this result was caused by the fact that the bone mineral density change by osteoporosis occurred in the proximal end more often than in the femur diaphysis. However, the elastic modulus derived from the finite element analysis showed no significant difference between the two groups.

Implications of three-dimensional modeling of the proximal femur for cephalomedullary nailing: An Asian cadaver study.

PURPOSE: To determine the variability in the ideal entry point of cephalomedullary (CM) nail around the greater trochanter (GT) and the consequent conformity with the proximal femur by analyzing three-dimensional (3D) modeling and virtual implantation MATERIALS AND METHODS: A total of 105 cadaveric femurs (50 males and 55 females) underwent continuous 1.0mm slice computed tomography (CT) scans. CT images imported into Mimics® software to reconstruct the 3D model of the proximal femur and medullary canal. PFNA-II® was processed into a 3D model using a 3D-sensor at the actual size and optimally implanted in the proximal femur model using Mimics® software. The ideal entry point, nail conformity with the proximal femur, and the relationship between the entry point and adjacent structures were assessed. RESULTS: The ideal entry point was located a mean of 2.38mm (SD, 3.53mm) medial to the tip of GT. No lateral cortex impingement of the proximal femur occurred in the coronal plane based on the recommended point. However, a disparity in the sagittal plane between the proximal shaft and nail curvature was found in 47 models (44.8%). Rotation and magnification of the 3D model exposed all nails above the surface of the medial side of the GT. The proximal nail end was contained entirely within bone and circumferential endosteal cortical contact was present at the nail-bone interface.

Biomechanical analysis of operative methods in the treatment of extra-articular fracture of the proximal tibia.

BACKGROUND: To determine relative fixation strengths of a single lateral locking plate, a double construct of a locking plate, and a tibial nail used in treatment of proximal tibial extra-articular fractures. METHODS: Three groups of composite tibial synthetic bones consisting of 5 specimens per group were included: lateral plating (LP) using a locking compression plate-proximal lateral tibia (LCP-PLT), double plating (DP) using a LCP-PLT and a locking compression plate-medial proximal tibia, and intramedullary nailing (IN) using an expert tibial nail. To simulate a comminuted fracture model, a gap osteotomy measuring 1 cm was created 8 cm below the knee joint. For each tibia, a minimal preload of 100 N was applied before loading to failure. A vertical load was applied at 25 mm/min until tibial failure. RESULTS: Under axial loading, fixation strength of DP (14,387.3 N; standard deviation [SD], 1,852.1) was 17.5% greater than that of LP (12,249.3 N; SD, 1,371.6), and 60% less than that of IN (22,879.6 N; SD, 1,578.8; p < 0.001, Kruskal-Wallis test). For ultimate displacement under axial loading, similar results were observed for LP (5.74 mm; SD, 1.01) and DP (4.45 mm; SD, 0.96), with a larger displacement for IN (5.84 mm; SD, 0.99). The median stiffness values were 2,308.7 N/mm (range, 2,147.5 to 2,521.4 N/mm; SD, 165.42) for the LP group, 4,128.2 N/mm (range, 3,028.1 to 4,831.0 N/mm; SD, 832.88) for the DP group, and 5,517.5 N/mm (range, 3,933.1 to 7,078.2 N/mm; SD, 1,296.19) for the IN group. CONCLUSIONS: During biomechanical testing of a simulated comminuted proximal tibial fracture model, the DP proved to be stronger than the LP in terms of ultimate strength. IN proved to be the strongest; however, for minimally invasive osteosynthesis, which may be technically difficult to perform using a nail, the performance of the DP construct may lend credence to the additional use of a medial locking plate.