Does increased acetabular depth affect safe infra-acetabular screw placement in acetabular fracture fixation?

BACKGROUND Infra-acetabular screws enhance the fixation strength in acetabular fractures with separation of both columns. Placement without iatrogenic femoral head violation is challenging. PURPOSE To assess the impact of the acetabular configuration, the patients' age and gender on safe infra-acetabulum screw insertion. METHODS In 112 patients (69 females; mean age: 34 years, range 17-88; n = 200 hips), the lateral center-edge angle (LCE) was measured on radiographs. Using corresponding axial CT scans the residual distance from (the lateral border) of the screw to (the medial border of) the femoral head ("Screw-to-Femoral Head distance"; "RD_SFH") was determined. Statistical analysis was carried out using linear regression, multiple linear regression and normal distribution estimation. RESULTS The mean (range) LCE angle was 30° (7°-51°) and the mean (range) "RD_SFH" was 5 mm (1-14 mm). The linear regression model shows a significant linear relation between LCE and "RD_SFH" with a slope parameter of - 0.15 (p value < 0.0001), the Pearson correlation between LCE and "RD_SFH" is - 0.56 (CI [- 0.71, [- 0.40]). Age did not have a significant impact on the relation between LCE and "RD_SFH" (p value 0.85). Compared to male patients, in females, the intercept is 4.62 mm (p value 0.0005) less, the slope parameter is 0.09 (p value 0.029) larger. CONCLUSION The virtual possibility to place an infra-acetabular screw was given in all patients. An increasing depth of the acetabulum correlated with a decrease in residual distances. As hip joint cartilage thickness was not considered in measurements, intraoperative rule-out of screw mispositioning especially in deep acetabular sockets and females is still of utmost importance

Secure Screw Placement in Management of Acetabular Fractures Using the Suprapectineal Quadrilateral Buttress Plate.

Acetabular fractures involving predominantly the anterior column associated with a disruption of the quadrilateral surface can be treated with instrumentation implementing the stabilization of the quadrilateral surface. The recently introduced suprapectineal quadrilateral buttress plate is specifically designed to prevent secondary medial subluxation of the femoral head, especially in elderly patients with reduced ability for partial weight bearing. Whereas there are guidelines available for safe screw fixation for the anterior and posterior columns, there might be a concern for intra-articular placement of screws placed through the infrapectineal part of the quadrilateral buttress plate. Within this report we analyzed retrospectively screw placement in 30 plates in postoperative CT scans using algorithms for metal artifact reduction. None of the screws of the buttress plate penetrated the hip joint. We describe the placement, length, and spatial orientation of the screws used for fracture fixation and suggest that the use of intraoperative image intensifiers with a combined inlet-obturator view of 30-45° best projects the screws and the hip joint. Preoperative knowledge of approximate screw placement and information for accurate intraoperative imaging may contribute to safe acetabular fracture fixation and may reduce operating time and limit radiation exposure to the patient and the personnel. This trial is registered with KEK-BE: 266/2014

Conditional and unconditional errors of geostatistical predictions - silivicultural case studies

Bei der Interpolation räumlicher Prozesse werden meist unbedingte Prognosefehler angegeben, da die durch die Meßwerte bedingten Randverteilungen und damit die bedingten Prognosefehler nur für räumliche Gaußprozesse mit bekannter Erwartungswertfunktion bekannt sind. Für den Spezialfall eines räumlichen Gaußprozesses mit unbekannter aber konstanter Erwartungswertfunktion wird die Differenz zwischem unbedingtem und bedingtem Prognosefehler des Gewöhnlichen Krigings hergeleitet. Es wird gezeigt, daß die Differenz einer Chi-Quadrat-Verteilung mit einem Freiheitsgrad folgt und der bedingte Fehler somit mit einer Wahrscheinlichkeit von etwa 68% kleiner als sein Erwartungswert, der unbedingte Fehler ist. In einer Fallstudie die Breiten der aus diesen beiden Fehlern abgeleiteten Konfidenzintervalle für den wahren Wert betrachtet: Sie unterscheiden sich nur wenig. Zur Approximation der bedingten Randverteilungen eignen sich Gewöhnliches Kriging unter Annahme eines Gaußprozesses (Polfeldt-Ansatz), Indikator- und Disjunktives Kriging. In zwei weiteren Fallstudien werden die drei Methoden anhand von Realdaten und simulierten Daten verglichen, der Polfeldt-Ansatz erweist sich als stabiler als die nichtlinearen Verfahren bei der Approximation von bedingten Randverteilungen mit extremen Erwartungswerten

Consensus models weighted by AUC for multiple class responses

This vignette shows how to build a consensus model for the fgl data (see [Venables and Ripley, 2002] or?MASS::fgl). We will follow the modelling process shown in [Marmion et˜al., 2009, Figure 1] restricting ourselves to only two ’Single-models’: a classification tree and a multinomial log-linear model usin

Surgical exposures and options for instrumentation in acetabular fracture fixation: Pararectus approach versus the modified Stoppa.

BACKGROUND As an alternative to the modified Stoppa approach, the Pararectus approach is used clinically for treatment of acetabular fractures involving the anterior column. The current study assessed the surgical exposure and the options for instrumentation using both of these approaches. METHODS Surgical dissections were conducted on five human cadavers (all male, mean age 88 years (82-97)) using the modified Stoppa and the Pararectus approach, with the same skin incision length (10cm). Distal boundaries of the exposed bony surfaces were marked using a chisel. After removal of all soft-tissues, distances from the boundaries in the false and true pelvis were measured with reference to the pelvic brim. The exposed bone was coloured and calibrated digital images of each inner hemipelvis were taken. The amount of exposed surface using both approaches was assessed and represented as a percentage of the total bony surface of each hemipelvis. For instrumentation, a suprapectineal quadrilateral buttress plate was used. Screw lengths were documented, and three-dimensional CT reconstructions were performed to assess screw trajectories qualitatively. Wilcoxon's signed rank test for paired groups was used (level of significance: p<0.05). RESULTS After utilization of the Pararectus approach, the distances from the farthest boundaries of exposed bone towards the pelvic brim were significantly higher in the false but not the true pelvis, compared to the modified Stoppa approach. The percentage (mean±SD) of exposed bone accessible after utilizing the Pararectus approach was 42±8%, compared to 29±6% using the modified Stoppa (p=0.011). In cadavers exposed by the Pararectus approach, screws placed for posterior fixation and as a posterior column screw were longer by factor 1.8 and 2.1, respectively (p<0.05), and screws could be placed more posteromedial towards the posterior inferior iliac spine or in line with the posterior column directed towards the ischial tuberosity. CONCLUSION Compared to the modified Stoppa, the Pararectus approach facilitates a greater surgical access in the false pelvis, provides versatility for fracture fixation in the posterior pelvic ring and allows for the option to extend the approach without a new incision

Percutaneous screw fixation of the iliosacral joint: A case-based preoperative planning approach reduces operating time and radiation exposure.

INTRODUCTION A preoperative planning approach for percutaneous screw fixation of the iliosacral joint provides specific entry points (EPs) and aiming points (APs) of intraosseous screw pathways (as defined by CT scans) for lateral fluoroscopic projections used intraoperatively. The potential to achieve the recommended EPs and APs, to obtain an ideal screw position (perpendicular to the iliosacral joint), to avoid occurrence of extraosseous screw misplacement, to reduce the operating time and the radiation exposure by utilizing this planning approach have not been described yet. METHODS On preoperative CT scans of eight human cadaveric specimen individual EPs and APs were identified and transferred to the lateral fluoroscopic projection using a coordinate system with the zero-point in the center of the posterior cortex of the S1 vertebral body (x-axis parallel to upper S1 endplate). Distances were expressed in relation to the anteroposterior distance of the S1 upper endplate (in%). In each specimen on one side a screw was placed with provided EP and AP (New Technique) whereas at the contralateral side a screw was placed without given EP and AP (Conventional Technique). Both techniques were compared using postoperative CT scans to assess distances between predefined EPs and APs and the actually obtained EPs and APs, screw angulations in relation to the iliosacral joint in coronal and axial planes and the occurrence of any extraosseous screw misplacement. The "operating time (OT)" and the "time under fluoroscopy (TUF)" were recorded. Statistical analysis was performed by the Wilcoxon signed-rank test. RESULTS EPs were realized significantly more accurate using the new technique in vertical direction. The screw positions in relation to the iliosacral joint showed no significant difference between both techniques. Both techniques had one aberrantly placed screw outside the safe corridor. The (mean±SD) "OT" and the (mean±SD) "TUF" were significantly decreased using the new technique compared to the conventional technique (OT: 7.6±2min versus 13.1±5.8min, p=0.012; TUF: 1.5±0.8min versus 2.2±1.1min). CONCLUSION The presented preoperative planning approach increases the accuracy in percutaneous screw fixation of the iliosacral joint, reduces operating time and minimizes radiation exposure to patient and staff

The Pararectus approach provides secure access to the deep circumflex iliac vessel for harvest of a large sized and vascularized segment of the iliac crest.

BACKGROUND The feasibility of harvesting a vascularized iliac crest utilizing the Pararectus approach was assessed in cadavers and then this new technique was implemented in a clinical case. METHODS Bilaterally in five cadavers the branches of both external iliac arteries were injected with colored silicone to assess their position to each other and to harvest a bone graft vascularized by the deep circumflex iliac artery (DCIA) through the Pararectus approach. This technique was implemented in a 68-years-old female patient, initially admitted to a level-I-trauma center after sustaining multiple injuries by falling from great height. For definitive treatment of a severely contaminated medially open (Gustilo-Anderson Type 3A) calcaneal luxation fracture (Sanders type IIIBC) in this patient a vascularized iliac crest autograft harvest by the Pararectus approach was used for reconstructive surgery. RESULTS The DCIA and the deep inferior epigastric vessels (DIEV: vascularizing the rectus abdominis muscle and main pedicle of the inferiorly based rectus abdominis myocutaneous flap) are very close on the lateral and medial border of the external iliac artery, respectively. As a consequence, the retrograde dissection of the DIEV towards the DCIA through the Pararectus approach made the dissection of the vascularized iliac crest more amenable, preserving both the lateral femoral cutaneous and the genitofemoral nerves. Four months after the surgery the patient was able to fully weight-bear in orthopedic shoes. Radiographs and CT scans showed correct hind foot alignment and bony integration of the vascularized iliac crest graft into the residual calcaneal body. CONCLUSION The Pararectus approach allowed for secure collection of large vascularized iliac grafts. The presented technique was successful as a salvage procedure in a clinical case with substantial bone loss after an open calcaneal fracture