There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.
An international faculty of orthopaedic surgeons
presented their work on the current challenges in hip surgery at
the London Hip Meeting which was attended by over
400 delegates. The topics covered included femoroacetabular impingement, thromboembolic
phenomena associated with hip surgery, bearing surfaces (including metal-on-metal
articulations), outcomes of hip replacement surgery and revision
hip replacement. We present a concise report of the current opinions
on hip surgery from this meeting with appropriate references to
the current literature.