Page 28 - Slipped Capital Femoral Epiphysis Pathogenetic and Clinical aspects

Chapter 2
Generally, the recommendation for treatment of unstable slips is gentle reduction, decompression and internal fixation within 24 hours of aggravation of the complaint [73, 74].
Despite this, no statistical differences was found in a meta-analysis study by Lowndes et al. [74]. They found 4 studies regarding reducing or not reducing unstable slips and 5 studies regarding a time window of 24 hours. Their advice was that reduction should be undertaken with great caution and probably within 24 hours. Bonescintigraphy is a sensitive predictor for development of AVN in unstable SCFE. This can be used preoperatively to diagnose AVN, before any treatment has been carried out, which will worsen the prognosis of the slip [113].
Screw position and amount of screws.
For a more accurate position and length of the percutaneous cannulated screw, biplanar fluoroscopy [148] or the use of an intraoperative arthrogram [157] has been advised. Senthi [124] recommends a CT scan if there is any doubt about the position of the screw. Intraoperative radiographs overestimate the distance between screw tip and the subchondral bone of the femoral head. A suggestion is to keep the screw tip at least 6 mm away from the subchondral bone of the femoral head during fluoroscopy on the AP plane and 4 mm away from the subchondral bone of the femoral head in the lateral plane intra-operatively. Fully and partially threaded screws for fixation were tested for stability. No biomechanical benefit was found between fully and partially threaded screws in this in vitro model with porcine femurs. However they mentioned that it may differ after bone healing, with fully threaded screws eventually providing greater stability [84]. Whether to use one or two screws is debatable. In a porcine model, one and two screws were tested in a displaced and nondisplaced model. The conclusion was that the in situ fixation with one screw is sufficient in a nondisplaced SCFE, while two screws might optimize a displaced slip [123]. Currently, the recommended entree-point for the percutaneous cannulated screw is anterior to cross the physis perpendicularly and to position the screw point in the middle of the femoral head. Merz et al. [79] compared anterior and lateral entree-points for the percutaneous screw in 22 paired porcine femurs and found no statistically significant difference in load to failure and stiffness of their model. However, Hagiwara et al. [41] showed a 53% slip progression after a percutaneous screw fixation. Multiple regression analysis showed that a lateral entree-point for a cannulated screw insertion prevented postoperative slip progression.
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