Pedicel screws are employed in stabilizing the spine in cases of degeneration an

Question

Pedicel screws are employed in stabilizing the spine in cases of degeneration and deformity. The development of novel features associated with these screws continues to be a source of great competition as over 600,000 spinal surgeries are performed annually in the United States alone. The manufacturer believes that the screw thread may lay the largest role in overall performance. To that end they have designed three screws in which all of the features are identical with the exception of the thread design. Below is a table that indicated the toggle deformation of each screw (while in the bone) at given cycle number. Determine which screw thread design (1, 2, 3) is most likely to dislodge over time.

Explanation / Answer

The Screw 1 has the deformation at various cycle as -0.06, -0.11, -0.17, - 0.23, -0.29, -0.34

The Screw 2 has the deformation at various cycle as -0.04, -0.07, -0.12, - 0.16, -0.20, -0.23

The Screw 3 has the deformation at various cycle as -0.10, -0.21, -0.32, - 0.42, -0.52, -0.62

From, the observed values, it is seen that the maximum deformation is in Screw. Statistically speaking, the Mean of Screw 1 is -0.2, the mean of Screw 2 is -0.13667 and that of Screw 3 is -0.365 with their respective Stdev are 0.107, 0.074 and 0.194. Most probable rejection lies at Screw 3.   

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