Valgus high tibial osteotomy (HTO) results in changes in the frontal as well as sagittal planes. Our hypothesis suggests that patellar height increases and posterior tibial inclination decreases after closed wedge (cw) HTO, whereas patellar height decreases and tibial slope increases after open wedge (ow) HTO. Lateral radiographs of 100 knees were assessed for patellar height (PH) using Insall-Salvati (ISI), Caton-De Champ (CDI) and Blackburne-Peel indices (BPI) as well as posterior tibial slope. Measurements were done before HTO (50 cw and 50 ow), direct postoperatively and before hardware removal. In the cw-group all three PH indices increased direct postoperatively and at removal of the hardware with changes in CDI and BPI being significant (P 0.05). Posterior tibial slope showed a significant decrease of 3.1 ± 3.4° after closed wedge HTO and a significant increase of 2.1 ± 3.6° after ow HTO direct postoperatively. In cw-HTO the correlations between frontal plane correction and PH changes were moderate (CDI: r = 0.57; BPI: r = 0.64). In ow-HTO these correlations were weak (CDI: r = 0.44; BPI: r = 0.46). According to ISI there was no correlation (cw: r = 0.11; ow: r =0.16). There was no correlation between PH changes according to CDI and slope changes. The incidence of patella infera increases after open wedge HTO, whereas the incidence of patella alta increases after closed wedge HTO. We recommend considering the PH and tibial slope before planning for HTO or TKR after HTO, also performing cw-HTO or ow-HTO with the tuberosity left at the proximal tibia in cases of patellofemoral complaint or patella infera.

Patellar height and posterior tibial slope after open and closed wedge high tibial osteotomy

Background:
Sacroiliac (SI) screw fixation is a demanding technique, with a high rate of screw malposition due to the complex pelvic anatomy. TiRobot™ is an orthopedic surgery robot which can be used for SI screw fixation. This study aimed to evaluate the accuracy of robot-assisted placement of SI screws compared with a freehand technique.


Methods:
Thirty patients requiring posterior pelvic ring stabilization were randomized to receive freehand or robot-assisted SI screw fixation, between January 2016 and June 2016 at Beijing Jishuitan Hospital. Forty-five screws were placed at levels S1 and S2. In both methods, the primary end point screw position was assessed and classified using postoperative computed tomography. Fisher’s exact probability test was used to analyze the screws’ positions. Secondary end points, such as duration of trajectory planning, surgical time after reduction of the pelvis, insertion time for guide wire, number of guide wire attempts, and radiation exposure without pelvic reduction, were also assessed.


Results:
Twenty-three screws were placed in the robot-assisted group and 22 screws in the freehand group; no postoperative complications or revisions were reported. The excellent and good rate of screw placement was 100% in the robot-assisted group and 95% in the freehand group. The P value (0.009) showed the same superiority in screw distribution. The fluoroscopy time after pelvic reduction in the robot-assisted group was significantly shorter than that in the freehand group (median [Q1, Q3]: 6.0 [6.0, 9.0] s vs. median [Q1, Q3]: 36.0 [21.5, 48.0] s; χ2 = 13.590, respectively, P < 0.001); no difference in operation time after reduction of the pelvis was noted (χ2 = 1.990, P = 0.158). Time for guide wire insertion was significantly shorter for the robot-assisted group than that for the freehand group (median [Q1, Q3]: 2.0 [2.0, 2.7] min vs. median [Q1, Q3]: 19.0 [15.5, 45.0] min; χ2 = 20.952, respectively, P < 0.001). The number of guide wire attempts in the robot-assisted group was significantly less than that in the freehand group (median [Q1, Q3]: 1.0 [1.0,1.0] time vs. median [Q1, Q3]: 7.0 [1.0, 9.0] times; χ2 = 15.771, respectively, P < 0.001). The instrumented SI levels did not differ between both groups (from S1 to S2, χ2 = 4.760, P = 0.093).


Conclusions:
Accuracy of the robot-assisted technique was superior to that of the freehand technique. Robot-assisted navigation is safe for unstable posterior pelvic ring stabilization, especially in S1, but also in S2. SI screw insertion with robot-assisted navigation is clinically feasible.


Key words: 
Computer-Assisted; Pelvic Injuries; Percutaneous Screw Placement; Robotics; Sacroiliac Screw; Surgery

Percutaneous Sacroiliac Screw Placement: A Prospective Randomized Comparison of Robot-assisted Navigation Procedures with a Conventional Technique.

Biomechanical analysis of the fixation systems for anterior column and posterior hemi-transverse acetabular fractures.

Finite element analysis is a common tool that has been used for the past few decades to predict the mechanical behavior of bone. However, to our knowledge, there are no round-robin finite element a...

A round-robin finite element analysis of human femur mechanics between seven participating laboratories with experimental validation.

Malgaigne fractures are the most common and widespread pelvic injuries resulting from the shear forces the action mechanism of which has not been explained in the literature yet. Military accidents with improvised explosive devices (IED) perfectly reflect this type of pelvic fracture. The finite element (FE) model of lumbar-pelvic complex (LPC) was developed based on computed tomography (CT) scans with the seat including steel frame, padding and soft tissue. The correlation coefficients of both low (100 N) and high (500 N) loads were greater than that currently obtained in the literature due to the presence of muscle force, pubic symphysis and joint cartilage. The dynamic analysis was performed to determine the influence of varying kinds of foam materials i.e. polyurethane, aluminium honeycomb structured and polyurethane auxetic foam on the stress/strain distribution in LPC under vertical impact load with the velocity of 7 m/s. Performed analysis showed the first fracture occurred in the L5 vertebrae resulting in the sacroiliac ligaments disruption and stress concentration in the pelvic ring causing further fractures of the wing of ilium, pubis and ischium bones. This results clearly explain the inconclusive findings about the second fracture that occurs in the pelvic area under a vertical impact load. The applied seat padding foam significantly reduced the stresses transmitted to the anatomical structures, thereby avoiding the risk of pelvic fracture. The analysis has proven that the auxetic polyurethane foam can be used as a good energy absorber.

Influence of energy absorbers on Malgaigne fracture mechanism in lumbar-pelvic system under vertical impact load.

Objective To observe the effects of boundary conditions and connect conditions on biomechanics predictions in finite element (FE) pelvic models. Methods Three FE pelvic models were constructed to analyze the effect of boundary conditions and connect conditions in the hip joint: an intact pelvic model assumed contact of the hip joint on both sides (Model I); and a pelvic model assumed the hip joint connecting surfaces fused together with (Model II) or without proximal femurs (Model III). The model was validated by bone surface strains obtained from strain gauges in an in vitro pelvic experiment. Vertical load was applied to the pelvic specimen, and the same load was simulated in the FE model. Results There was a strong correlation between the FE analysis results of Model I and the experimental results (R 2 = 0.979); meanwhile, the correlation coefficient and the linear regression function increased slightly with increasing load force. Comparing the three models, the stress values in the point near the pubic symphysis in Model III were 48.52 and 39.1% lower, respectively, in comparison with Models I and II. Furthermore, the stress values on the dome region of the acetabulum in Models II and III were 103.61 and 390.53% less than those of Model I. Besides, the posterior acetabular wall stress values of Model II were 197.15 and 305.17% higher than those of Models I and III, respectively. Conclusions These findings suggest that the effect of the connect condition in the hip joint should not be neglected, especially in studies related to clinical applications.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/os.12315

Influence of Different Boundary Conditions in Finite Element Analysis on Pelvic Biomechanical Load Transmission.

To compare the stability of sacroiliac joint disruption fixed with three kinds of internal fixation using both biomechanical test and finite element analysis. Five embalmed specimens of an adult were used. The symphysis pubis rupture and left sacroiliac joint disruption were created. The symphysis pubis was stabilized with a five-hole plate. The sacroiliac joint disruption was fixed with three kinds of internal fixation in a randomized design. Displacements of the whole specimen and shifts in the gap were recorded. Three-dimensional finite element models of the pelvis, the pelvis with symphysis pubis rupture and left sacroiliac joint disruption, and three kinds of internal fixation techniques were created and analyzed. Under the vertical load, the displacements and shifts in the gap of the pelvis fixed with minimally invasive adjustable plate (MIAP) combined with one iliosacral (IS) screw were the smallest, and the average displacements of the pelvis fixed with an anterior plate were the largest one. The differences among them were significant. In finite element analysis and MIAP combined with one IS screw fixation showed relatively best fixation stability and lowest risks of implant failure than two IS screws fixation and anterior plate fixation. The stability of sacroiliac joint disruption fixed with MIAP combined with one IS screw is better than that fixed with two IS screws and anterior plate under vertical load.

/pdf/biomechanical-study-of-three-kinds-of-internal-fixation-for-ypelfj6vzc.pdf

Biomechanical study of three kinds of internal fixation for the treatment of sacroiliac joint disruption using biomechanical test and finite element analysis.

Limited information exists on the incidence of postoperative deep venous thromboembolism (DVT) in patients with isolated patella fractures. The objective of this study was to investigate the postoperative incidence and locations of deep venous thrombosis (DVT) of the lower extremity in patients who underwent isolated patella fractures and identify the associated risk factors. Medical data of 716 hospitalized patients was collected. The patients had acute isolated patella fractures and were admitted at the 3rd Hospital of Hebei Medical University between January 1, 2016, and February 31, 2019. All patients met the inclusion criteria. Medical data was collected using the inpatient record system, which included the patient demographics, patient’s bad hobbies, comorbidities, past medical history, fracture and surgery-related factors, hematological biomarkers, total hospital stay, and preoperative stay. Doppler examination was conducted for the diagnosis of DVT. Univariate analyses and multivariate logistic regression analyses were used to identify the independent risk factors. Among the 716 patients, DVT was confirmed in 29 cases, indicating an incidence of 4.1%. DVT involved bilateral limbs (injured and uninjured) in one patient (3.4%). DVT involved superficial femoral common vein in 1 case (3.4%), popliteal vein in 6 cases (20.7%), posterior tibial vein in 11 cases (37.9%), and peroneal vein in 11 cases (37.9%). The median of the interval between surgery and diagnosis of DVT was 4.0 days (range, 1.0-8.0 days). Six variables were identified to be independent risk factors for DVT which included age category (> 65 years old), OR, 4.44 (1.34-14.71); arrhythmia, OR, 4.41 (1.20-16.15); intra-operative blood loss, OR, 1.01 (1.00-1.02); preoperative stay (delay of each day), OR, 1.43 (1.15-1.78); surgical duration, OR, 1.04 (1.03-1.06); LDL-C (> 3.37 mmol/L), OR, 2.98 (1.14-7.76). Incidence of postoperative DVT in patients with isolated patella fractures is substantial. More attentions should be paid on postoperative DVT prophylaxis in patients with isolated patella fractures. Identification of associated risk factors can help clinicians recognize the risk population, assess the risk of DVT, and develop personalized prophylaxis strategies.

/pdf/incidence-and-risk-factors-for-deep-venous-thrombosis-of-4ho7lrilvl.pdf

Incidence and risk factors for deep venous thrombosis of lower extremity after surgical treatment of isolated patella fractures.

Objective To compare the biomechanical stability and compatibility of two iliosacral screws (ISS), a tension band plate (TBP), and a minimally invasive adjustable plate (MIAP) for treating Tile C pelvic fractures. Methods Three groups of finite element models of the intact pelvis, including the main ligament and the proximal one-third of both femurs, were developed to simulate vertical sacral fractures and treated with the three abovementioned internal fixation techniques. A 500 N vertical load, a 500 N vertical load plus a 10 Nm moment of forward sagittal direction, and 500 N vertical load plus a 10 Nm moment of right lateral direction were applied to the sacrum to simulate standing status, bending status, and flexion status, respectively. The maximum displacement value, the stress value, and the stress value of the fracture interface were compared among the three internal fixation techniques. Results The results showed that all three internal fixation techniques effectively restored the biomechanical transmission of the injured pelvis. The stress on the implants in the TBP model was 167.47% and 53.41% higher than that in the ISS model and the MIAP model, respectively, and the stress shielding phenomenon of the TBP model was more obvious than in the other two models. Meanwhile, the stress between the fracture interfaces in the TBP fixation models was apparently higher than that in the other two models. However, the vertical displacement of the MIAP model was not significantly different from that in the ISS and TBP model; therefore, strong fixation could be obtained in all three models. Conclusion Based on our results, we believe that the stability of Tile C pelvic fracture fixed with MIAP was similar to that of fractures fixed with ISS and TBP, but the stress shielding phenomenon and safety of implants in the TBP models were inferior to those in the MIAP and ISS fixation models. Meanwhile, MIAP and ISS fixation were more helpful to the healing processing than was TBP fixation, especially at the fracture interface of the second and third vertebral body levels.

Biomechanical Comparison of Three Internal Fixation Techniques for Stabilizing Posterior Pelvic Ring Disruption: A 3D Finite Element Analysis.

Background: Unstable pelvic fractures are complex and serious injuries. Selection of a fixation method for these fractures remains a challenging problem for orthopedic surgeons. This study aimed to compare the stability of Tile C pelvic fractures fixed with two iliosacral (IS) screws and minimally invasive adjustable plate (MIAP) combined with one IS screw. Methods: This study was a biomechanical experiment. Six embalmed specimens of the adult pelvis were used. The soft tissue was removed from the specimens, and the spines from the fourth lumbar vertebra to the proximal one-third of both femurs were retained. The pubic symphysis, bilateral sacroiliac joints and ligaments, bilateral hip joints, bilateral sacrotuberous ligaments, and bilateral sacrospinous ligaments were intact. Tile C pelvic fractures were made on the specimens. The symphysis pubis was fixed with a plate, and the fracture on the posterior pelvic ring was fixed with two kinds of internal fixation in turn. The specimens were placed in a biomechanical machine at a standing neutral posture. A cyclic vertical load of up to 500 N was applied, and displacement was recorded. Shifts in the fracture gap were measured by a grating displacement sensor. Statistical analysis used: Paired-samples t -test. Results: Under the vertical load of 100, 200, 300, 400, and 500 N, the average displacement of the specimens fixed with MIAP combined with one IS screw was 0.46, 0.735, 1.377, 1.823, and 2.215 mm, respectively, which was significantly lower than that of specimens fixed with two IS screws under corresponding load ( P P Conclusion: The stability of Tile C pelvic fractures fixed with MIAP combined with one IS screw was better than that fixed with two IS screws.

Xiaodong Cheng

Papers

Influence of Different Boundary Conditions in Finite Element Analysis on Pelvic Biomechanical Load Transmission.

Biomechanical study of three kinds of internal fixation for the treatment of sacroiliac joint disruption using biomechanical test and finite element analysis.

Incidence and risk factors for deep venous thrombosis of lower extremity after surgical treatment of isolated patella fractures.

Biomechanical Comparison of Three Internal Fixation Techniques for Stabilizing Posterior Pelvic Ring Disruption: A 3D Finite Element Analysis.

Biomechanical Comparison of Two Kinds of Internal Fixation in a Type C Zone II Pelvic Fracture Model