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1.  Mechanical Quantification of Local Bone Quality in the Humeral Head: A Feasibility Study 
Objectives:
Surgical treatment of proximal humerus fractures can be challenging due to osteoporosis. The weak bone stock makes stable implant anchorage difficult, which can result in low primary stability. Accordingly, significant failure rates, even with modern locking plates, are reported in the literature. Intraoperative knowledge of local bone quality could be helpful in improving results. This study evaluates the feasibility of local bone quality quantification using breakaway torque measurements.
Materials and Methods:
A torque measurement tool (DensiProbe™) was developed to determine local resistance to breakaway offered by the cancellous bone in the humeral head to quantify local bone quality. The tool was adapted to a standard locking plate (PHILOS, Synthes), allowing measurement in the positions of the six humeral head screws, as provided by the aiming device of the plate. Two hundred and seventy measurements were performed in 44 fresh cadaveric human humeri.
Results:
Handling of the tool was straight forward and provided reproducible results for the six different positions. The method allows discrimination between the respective positions with statistical significance, and thus provides reliable information on the local distribution of bone quality within the humeral head.
Discussion:
This study introduces a new method using breakaway torque to determine local bone quality within the humeral head in real time. Because DensiProbe is adapted to a standard locking plate, there is the potential for intraoperative application. The information provided could enable the surgeon to improve fixation of osteoporotic proximal humerus fractures.
doi:10.2174/1874325001307010172
PMCID: PMC3664459  PMID: 23730382
Bone quality; DensiProbe; fracture; osteoporosis; proximal humerus.
2.  Reinforcing the role of the conventional C-arm - a novel method for simplified distal interlocking 
Background
The common practice for insertion of distal locking screws of intramedullary nails is a freehand technique under fluoroscopic control. The process is technically demanding, time-consuming and afflicted to considerable radiation exposure of the patient and the surgical personnel. A new concept is introduced utilizing information from within conventional radiographic images to help accurately guide the surgeon to place the interlocking bolt into the interlocking hole. The newly developed technique was compared to conventional freehand in an operating room (OR) like setting on human cadaveric lower legs in terms of operating time and radiation exposure.
Methods
The proposed concept (guided freehand), generally based on the freehand gold standard, additionally guides the surgeon by means of visible landmarks projected into the C-arm image. A computer program plans the correct drilling trajectory by processing the lens-shaped hole projections of the interlocking holes from a single image. Holes can be drilled by visually aligning the drill to the planned trajectory. Besides a conventional C-arm, no additional tracking or navigation equipment is required.
Ten fresh frozen human below-knee specimens were instrumented with an Expert Tibial Nail (Synthes GmbH, Switzerland). The implants were distally locked by performing the newly proposed technique as well as the conventional freehand technique on each specimen. An orthopedic resident surgeon inserted four distal screws per procedure. Operating time, number of images and radiation time were recorded and statistically compared between interlocking techniques using non-parametric tests.
Results
A 58% reduction in number of taken images per screw was found for the guided freehand technique (7.4 ± 3.4) (mean ± SD) compared to the freehand technique (17.6 ± 10.3) (p < 0.001). Total radiation time (all 4 screws) was 55% lower for the guided freehand technique compared to conventional freehand (p = 0.001). Operating time per screw (from first shot to screw tightened) was on average 22% reduced by guided freehand (p = 0.018).
Conclusions
In an experimental setting, the newly developed guided freehand technique for distal interlocking has proven to markedly reduce radiation exposure when compared to the conventional freehand technique. The method utilizes established clinical workflows and does not require cost intensive add-on devices or extensive training. The underlying principle carries potential to assist implant positioning in numerous other applications within orthopedics and trauma from screw insertions to placement of plates, nails or prostheses.
doi:10.1186/1471-2474-13-8
PMCID: PMC3305668  PMID: 22276698
Distal interlocking; Distal targeting; Nailing; Free-hand locking; Computer aided surgery

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