Increased torsional stability by a novel femoral neck locking plate. The role of plate design and pin configuration in a synthetic bone block model, Brattgjerd et al. Clin. Biomech (2018) in press, accepted manuscript.
In undisplaced femoral neck fractures, internal fixation remains the main treatment, with mechanical failure as a frequent complication. As torsional stable fixation promotes femoral neck fracture healing, the Hansson Pinloc® System with a plate interlocking pins, was developed from the original hook pins. Since its effect on torsional stability is undocumented the novel implant was compared with the original configurations.
Forty-two proximal femur models custom made of two blocks of polyurethane foam were tested. The medial block simulated the cancellous head, while the lateral was laminated with a glass fiber filled epoxy sheet simulating trochanteric cortical bone. Two hollow metal cylinders with a circumferential ball bearing in between mimicked the neck, with a perpendicular fracture in the middle. Fractures were fixated by two or three independent pins or by five configurations involving the interlocking plate (two pins with an optional peg in a small plate, or three pins in a small, medium or large plate). Six torsional tests were performed on each configuration to calculate torsional stiffness, torque at failure and failure energy.
The novel configurations improved parameters up to an average of 12.0 (stiffness), 19.3 (torque) and 19.9 (energy) times higher than the original two pins (P < 0.001). The plate, its size and its triangular configuration improved all parameters (P = 0.03), the plate being most effective, also preventing permanent failure (P < 0.001).
The novel plate design with its pin configuration enhanced torsional stability.
To reveal clinical relevance a clinical study is planned.
The Hansson Pinloc® system increased torsional parameters with a factor of up to 20.
The plate per se, its size and its triangular configuration improved all parameters.
The plate itself was the most effective novel component of the fixation.
Torsional failure by twisting of the pins was prevented by the plate itself.
Distal locking is a challenging subtask of intramedullary nailing fracture fixation due to the nail deformation that makes the proximally mounted targeting systems ineffective. A patient specific finite element model was developed, based on the QCT data of a cadaveric femur, to predict the position of the distal hole of the nail postoperatively. The mechanical interactions of femur and nail (of two sizes) during nail insertion was simulated using ABAQUS in two steps of dynamic pushing and static equilibrium, for the intact and distally fractured bone. Experiments were also performed on the same specimen to validate the simulation results. A good agreement was found between the model predictions and the experimental observations. There was a three-point contact pattern between the nail and medullary canal, only on the proximal fragment of the fractured bone. The nail deflection was much larger in the sagittal plane and increased for the larger diameter nail, as well as for more distally fractured or intact femur. The altered position of the distal hole was predicted by the model with an acceptable error (mean: 0.95; max: 1.5 mm, in different tests) to be used as the compensatory information for fine tuning of proximally mounted targeting systems.
There is a three-point contact pattern between the intramedullary nail and medullary canal, only on the proximal fragment of the fractured bone.
Nail deflection during intramedullary nailing occurs mainly in sagittal plane.
Patient specific modeling can predict the nail deflection with a reasonably good accuracy.
Patent specific modeling can be used to provide the compensatory information for fine tuning of proximally mounted targeting systems during intramedullary nailing.
The use, timing, and priority of angioembolization in the management of bleeding pelvic fractures remain ambiguous. The most common vessels for angioembolization are, in decreasing order, the internal iliac artery and its branches, the superior gluteal artery, the obturator artery, and the internal pudendal artery. Technical success rates for this treatment option range from 74% to 100%. The fracture patterns most commonly requiring angioembolization are the Young and Burgess lateral compression and anterior-posterior compression types and Tile type C. Mortality rates after angioembolization of 16% to 50% have been reported, but deaths are usually related to concomitant injuries. The sensitivity and specificity of contrast-enhanced CT in detecting the need for angioembolization range from 60% to 90% and 92% to 100%, respectively. Angioembolization can be effective in the management of bleeding pelvic fractures, but as with any treatment, the risks of complications must be considered. Availability of angioembolization and institutional expertise/preference for the alternative strategy of pelvic packing influence its use.