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Upper thoracic pedicle screws loss of fixation causing spinal cord injury.

To the Editor: We read with interest the article entitled: “Upper thoracic pedicle screws loss of fixation causing spinal cord injury: a review of the literature and multicenter case series” by Skaggs et al, in the January 2013 issue of the Journal of Pediatric Orthopaedics. We would like to congratulate the authors for this interesting report, about the risk associated with upper thoracic pedicle screws when associated with precarious biomechanical situations. We realize how difficult is to assess patients who are treated by others, and with an incomplete imaging study; however, there are some suggestions that the screws were not placed properly in the first instance. In cases 1 and 3 the postoperative radiographs are highly suggestive that the screws were not into the pedicle initially, besides none of the posterior image studies show evidence of pedicle fracture, or lysis of the bone around the pedicle, that would be expected if the screw were initially in the right location, finally the findings of a “split” in the spinal cord may be difficult to imagine just by plowing of the screw. Undoubtedly, the precarious biomechanical situation of the screws increase the risk of further displacement, but not only by the fact that too few screws were placed along, but also other factors may have played a role; all screws “migrated” were terminal screws, and therefore, submitted to more stresses, the terminal construct was asymmetric on 1 side (hook and screw, case 2), and the contralateral screws appears to be placed extrapedicular in some instances (cases 1 and 3), the length of the screw could also play its role (case 1). Finally it came into notice that the failing screw was always the top left screw in a right curve, and in case of curve progression, this will be undoubtedly the screw at risk, as the dural sac will drive towards the screw, especially when the screw is into the canal. A recent report of Mac-Thiong et al demonstrated that the tolerance of screws inside the canal is higher than expected, but that neurological damage may appear early or delayed. It also clearly proves that even when more screws are placed, if the terminal screws are into the canal, they have a serious risk of delayed damage. I think the authors should show evidence of proper placement of the screws, or if not, because of the lack of evidence, include these considerations into their discussion.