Aims

To devise a method to quantify and optimize tightness when inserting cortical screws, based on bone characterization and screw geometry.

Introduction: Conventional cancellous screws have proven purchase in healthy bone, but may be prone to loosening in osteoporotic bone. Locking screws have become a popular choice to combat loosening. A new screw design has optimized thread form to gain better purchase into poor quality bone. The purpose of this study was to evaluate the maximum stripping torque and pull-out strength of the PERI-LOCTM 5.0mm Osteopenia Bone Screw using an osteopenic model. Methods: Stripping Torque: PERI-LOCTM 5.0mm Osteopenia Bone Screws were inserted through a One-Third Tubular B-plate into a pre-drilled pilot hole to a depth of 20mm. Rotational loading was applied manually using a hex driver until torque reached a peak value. The maximum torque value due to screw head contact with the plate was measured using a torque-meter and denoted as the stripping torque. This same procedure was used for TC-100TM 4.0mm Cancellous Bone Screws, which were inserted through a TC-100TM Standard Tubular Plate. Pull-Out Strength: PERI-LOCTM 5.0mm Osteopenia Bone Screws were inserted to a depth of 20 mm into an osteopenic model. Axial pull-out was then conducted on a MTS testing frame by applying a tensile load along its longitudinal axis at a rate of 0.2 in/min. The maximum pull-out force was recorded. This same procedure was used for TC-100TM 4.0mm Cancellous Bone Screws. The test set-up is shown in Figure 1. Discussion: The PERI-LOCTM 5.0mm Osteopenia Bone Screws showed a 34% increase in stripping torque and a 40% increase in pull-out strength (p < < 0.01 at á = 0.05 in both instances) as compared to clinically successful bone screws. Conclusions: When tested in an osteopenic bone model, the PERI-LOCTM 5.0mm Osteopenia Bone Screw provided superior stripping torque and pull-out strength as compared to conventional cancellous bone screws. The increased torque generation during insertion of PERI-LOCTM 5.0mm Osteopenia Bone Screws provides better fracture reduction, as compared to conventional screws. These findings indicate that the use of the improved thread design is advantageous in poor quality bone

Introduction. Conventional screws achieve sufficient insertion torque in healthy bone. In poor bone screw stripping can occur prior to sufficient torque generation. It was hypothesized that a screw with a larger major/minor diameter ratio would provide improved purchase in poor bone as compared to conventional screws. We evaluated the mechanical characteristics of such a screw using multiple poor bone quality models. Methods. Testing groups included: conventional screws, osteopenia screws used in bail-out manner (ie, larger major/minor diameter screws inserted into a hole stripped by a conventional screw), and osteopenia screws used in a preemptive manner (ie, no screw stripping occurrence). Stripping Torque: Screws were inserted through standard straight plates into a low density block of foam with a predrilled hole. Stripping torque was defined as maximum insertion torque reached by the screw before the screw began to spin freely in the foam. Pullout. Pullout tests were conducted on screws inserted into the same test media. Axial pull-out testing was then conducted by applying a tensile load to the screws. Compression. Screws were inserted through standard straight plates by hand while the amount of compression achieved between plate and bone was measured using a pressure sensor. The same foam test media was utilized in addition to osteoporotic fresh-frozen femoral diaphyseal cadaver (bone mineral density<0.60 g/cm2). The screws were tightened across a range of possible insertion torques with pressure measurements taken at multiple intervals. Results. The osteopenia bone screws showed a 67% increase in torque before stripping occurred (p<0.01) when compared to the conventional screw. The osteopenia screw used in a bail-out manner showed a 57% increase in stripping torque (p<0.01) and a 76% increase in pullout strength (p<0.01) when compared to the conventional screw. Additionally, the bail-out screw showed a minimal decrease in both stripping torque (6%, p = 0.45) and pullout strength (11%, p<0.01) when compared to the osteopenia screw tested in preemptive manner. There was a linear relationship between applied torque and compressive force generation for both osteopenia and conventional screws. The osteopenia screws were able to gain greater compression against bone across a range of insertion values as compared to conventional bone screws. Discussion. The osteopenia screw achieved superior stripping torque, pullout strength, and compressive forces when compared to conventional screws in simulated poor quality bone and osteoporotic cadaver bone. When used as a bail-out screw, it also achieved superior stripping torque and pullout strength. The results of this study indicate that a screw of larger major/minor diameter ratio could be an effective bail-out option for screw stripping associated with osteopenic fracture fixation

Introduction. Osteosynthesis with open reduction techniques in comminuted subtrochanteric femoral fractures can further devitalise fragments and lead to increased rate of non-union, infection, and implant failure. Therefore, these fractures require indirect reduction techniques that do not further damage the vascular supply or soft tissue attachments of the fragments. Dynamic condylar screw (DCS) using indirect reduction and minimally invasive technique may be a good alternative to avoid these complications in such fractures. Material & methods. Forty-three patients with comminuted subtrochanteric fractures underwent indirect reduction and biological internal fixation with DCS. Mean age was 43.9 (range 25–65) years. There were six Seinsheimer type III, 15 type IV and 22 type V fractures. Results. All fractures united without bone grafting at average union time of 16.16 weeks (range, 13–22) weeks. There were no cases of non-union or implant failure at mean follow-up of 25.13 months. We observed technical difficulties in six patients such as: inaccurate placement of guide pin in two patients, difficulty in sliding the plate due to obesity in one patient, difficulty in gliding barrel plate over condylar screw in one patient and technical failure in a further two patients. Seven patients had mean limb length discrepancy of 1.48 cm (range, 1–2). Mean Harris hip score was 88.2 (range 80–90) points. Two patients had coxa vara and persistent limp. Discussion. Stripping of the soft tissues to the lateral cortex is kept to a minimum in indirect reduction. The vitality of the medial fragments is not further compromised since they are not exposed. Viable bone rapidly unites by callus formation. Conclusions. Osteosynthesis of comminuted subtrochanteric fractures is desirable using indirect reduction and minimally invasive technique. Dynamic condylar screw can be used based on these principles; however, proper planning and execution of the technique is required to achieve good functional outcome and to avoid complications