Distal locking screw fixation, in intramedullary nail (IMN) fixation, remains the most technically demanding and problematic portion of the procedure being responsible for as much as one-half of the exposure of the surgeon‘s hands to radiation. This biomechanical study was undertaken to compare the effectiveness of using one distal locking cross screw instead of two cross screws in femoral fractures fixed with IMN system. A composite model made from a stainless steel IMN (12mm×1mm), was axially loaded to 2kN (3 times body weight) to reproduce the forces experienced during weight bearing, or until a maximum displacement of 1 mm was reached. The distal locking end of the intramedullary nail was attached to the centre of the cylinder, representing different parts of the distal femur, with a dedicated single or two rods (5mm diameter), made from stainless steel and titanium, to represent the distal locking cross screw. In the 50mm×5mm cylinder (diaphyseal femur), the mean stability of fracture model using either single or two screws were similar. But in the 75mm×5mm and 100mm×3mm cylinders (metaphyseal and distal femur), the mean stability of the fracture model significantly decreased (50%) with single distal locking cross screw fixation when compared to two distal locking cross screws fixation. Similarly, stainless steel alloy provided more stability compared to titanium alloy cross screws in 75mm×5mm and 100mm×3mm cylinders. However there was no difference between the cross screws performance for 50mm×5mm when comparing both the alloys. As shown in this experiment, femoral shaft (diaphyseal) fractures fixed with shorter IMN had the same stability for one or two distal locking cross screws. However fractures fixed with longer IMNs, to fix diaphyseo-metaphyseal junction fractures and extreme distal femoral fractures, single distal locking cross screw fixation provide poorer fracture stability compared to two distal locking cross screws fixation.
Suture anchors are widely used to secure tendons and ligaments to bone during both arthroscopic and open surgery. However, single stage insertion suture anchors, i.e. anchors that could be inserted without predrilling of the bone, are not currently available. We aimed to record the impact needed for insertion of the new design single stage suture anchors, and to compare their pull out strength with another range of commercially available suture anchors. The force required to insert the new design of suture anchors was investigated using an impact hammer capable of recording the number and force of each of the hits. The anchors were inserted in a consistent manner into animal (porcine) bone at sites analogous to common anchor sites used in clinical practice. Pull out strength was assessed using a digital force gauge after tying the suture to create a secure loop. Thereafter, force was applied steadily until either the anchor or the suture failed and compared with a popular range of commercially available suture anchors (Mitek). Our initial investigations using prototype designs for small, medium and large anchors compared favourably with the Mini-mitek, GII, and Superanchor range of Mitek anchors. Essentially the most common point of failure for each of the suture anchor families was the suture itself with both suture anchor systems performing similarly. In addition, similar pull out strengths were demonstrated for both the Mitek and new design of suture anchors when loaded parallel, or at 90°, to the line of anchor insertion. The new design single stage suture anchors have an equivalent pull out strength compared with a popular commercially available family of suture anchors, but in addition have the significant advantage of being suitable for single stage insertion in many clinical settings.
