Abstract
Introduction and Aims: Compression hip screws are considered to be the gold standard for treatment of trochanteric proximal femoral fractures. Two implant designs exist; the ‘keyed’ and ‘non-keyed’ barrel profiles. Many biomechanical studies have been published on the performance of sliding hip screws, but most have used only static testing, and none to our knowledge have sought to compare the two-barrel profiles. This study aimed to compare the sliding characteristics of keyed and non-keyed systems in both static and dynamic loading conditions.
Method: Tests were performed on the implants using a multi axis servo-hydraulic testing machine. The machine possessed both linear and torsional actuators, such that hip flexion/extension could be simulated during testing. Load to initiate sliding in both implants was measured in a variety of testing conditions; screw engagement in barrel (20–38mm), angle of hip flexion (0–40 degrees), perpendicular loading force (50–190N), and cycle frequency (0–1 Hz).
Results: Results showed a tendency towards greater sliding in the non-keyed system, although these were significant only for the screw engagement testing (p< 0.001). However, load to initiate sliding in both implants was significantly higher in dynamic as compared to static testing (p< 0.001), and increased as torsional frequency increased. The non-keyed system did not demonstrate any tendency for screw rotation within the barrel during dynamic testing.
Conclusion: The non-keyed compression hip screw system does show a trend towards improved sliding characteristics, and does not display the tendency for screw rotation within the barrel under loading, often quoted as a misgiving of this implant. Also, since forces to initiate sliding are significantly higher when these implants are loaded dynamically (which mimics more closely the in vivo performance), future biomechanical studies should include dynamic testing for any hip fracture implant.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
