The placement of percutaneous pedicle screws
The human spine is a biomechanical masterpiece that when it works properly is a testament to the evolutionary wisdom of nature. However when it starts to go wrong then all bets are off and the various structures will begin to collapse in a concertined fashion that leads to pain and disability. The involvement of the intervertebral discs occurs eraly in the degenerative cascade and commences with the appearance of radial tears in the annnulus fibrosus through which the nucleus pulposus dissects towards the exiting nerve roots. The disc begins to collapse with continued movement and at some point in the degeneration, after all conservative measures have been exhausted, the patient is referred for a lumbar fusion. This surgical intervention is only indicated after aprovocative discogram has been performed and the pain producing discs have been identified.
The fusion of two intervertebral bodies requires the remonbval of the diseased disc which can now be performed in aminimally invasive fashion through a 9 mm portal. The empyt space is then filled with a supportive cage/device and some boen either of the autologous or allogenic variety for the purposes of causing a fusion between the bony bodies. The question of whether or not to place titanium screws in the bony pedicles has been a source of debate within the spine community due to the fact that the screw placement has a degree of risk associated with it , including p[rincipally damage to nerve roots. The arguments for the insertion of screws in cases performed using wide aggressive dissections with significant muscle dissection and bone resection was that the removal of the body's natural stabilisers had to be replaced with internal devices that would restore some stability and foster the fusion. However that argument , with the advent and now routine implementation of minimally invasive spine surgery, does not carry as much weight as the natural body stabilisers have been left intact and ther is therefore no biomechanical requirement to place the pedicle screws. The advantage of not inserting screws is that the procedure is made a lot safer with a lower risk profile and a much reduced incidence of nerve injury.
The other non clinical factor to consider is the high cost associated with the placement of pedicle screws which in third world countries is often impossible. As the movement towards improving percutaneous techniques continues it is very likely that the routine use of pedicle screws in the surgical mangement of degenerative cases will disappear just as the corsets used to treat polio victims vanished when advanced technology stepped in.
