Investigation of factors affecting the optimal pathway for first sacrum (S1) pedicle screw in orthopaedic surgical operation

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Investigation of factors affecting the optimal pathway for first sacrum (S1) pedicle screw in orthopaedic surgical operation


Author: Ng, Tat-ming
Title: Investigation of factors affecting the optimal pathway for first sacrum (S1) pedicle screw in orthopaedic surgical operation
Degree: M.Sc.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Cervical vertebrae -- Surgery
Department: Dept. of Health Technology and Informatics
Pages: xiii, 56 leaves : ill. (some col.) ; 30 cm.
Abstract: Background: Pedicle screws instrumentation of the spine was first described in the 1970s. Technically, the placement of pedicle screw into first sacrum (S1) was a difficult surgical procedure because of the unique anatomy of the first sacral vertebra. Most previous studies employed the pedicle width (PW) as a parameter for pedicle screw pathway in S1. There were interference and risk factors which influence the pedicle screw pathway and antero-medial insertion angle in real intra-operative situation. After applying the affected factors, a new pedicle screw pathway named 'Safe Zone Width' (SZW) was created. Objectives: This study aims to find out how the change of pedicle screw pathway and antero-medial insertion angle in S1 is influenced by the affected factors such as iliac crest, sacral canal, vital nerve and vessels, screw driver head etc. Moreover, the study also aims to compare the variation among the genders both in the change of pedicle screw pathway and antero-medial insertion angle in S1 respectively. The result of this study would give a patient's gender alert and more information to orthopaedic surgeons in surgical planning and preparation. Methodology: A retrospective study of 108 patients who had computed tomography (CT) lumbar sacral (LS) examination performed were selected randomly with close to equal split of gender. PW and SZW were measured in both sexes. This study also finds out how the affected factors influence the antero-medial insertion angle of PW (β) and SZW (θ) in both sexes. Angle β and θ was measured between a line perpendicular the central axis of PW and SZW with the sagittal vertebral plane respectively. Moreover, the parameter of posterior border height (PB) was measured to find out correlation with PW and SZW. The other parameters such as sacral canal width (SCW) and posterior iliac crests width (PICW) were also measured in order to find out any correlation with SZW and angle θ in both genders.
Results: The mean PW and SZW were found to 18.23±2.49mm and 13.66±2.64mm respectively and both showed statistically significant difference (ρ<0.05). Mean PW in male was found wider than that in female. The mean PW in male was 18.68±2.8mm and was wider in female which was 17.70±1.96mm. However, it was surprisingly found that female have a wider mean SZW than male subjects with the mean SZW in male and female subjects measured 13.02±2.98mm and 14.40±1.95mm respectively. Average insertion angle (β) was measured 57.52±4.20º which is more obtuse than the insertion angle (θ) which was measured 16.35±6.63º after applied the affected factors. The mean insertion angle (β) in male and female were 56.85±4.36º and 58.31±3.91º respectively and both showed no statistically significant difference (p>0.05). However, the mean angle θ in male and female were 13.79±5.58º and 19.32±6.56º respectively and both showed statistical significant difference (p<0.05). Moreover, it was found that the mean PICW in female was wider than that in male but for the mean SCW this was vice versa. Both PICW and SCW had correlated relationship with the mean SZW and angle θ. The SZW and angle θ also had correlation. The mean PB was 23.0±2.22mm and showed statistically significant difference with PW. Moreover, PB also had correlation with PW but not with SZW. Conclusion: The mean SZW is narrow than the mean PW and mean insertion angle β is much more obtuse than that in angle θ after applying the interference and risk factors. The mean SZW in female is wider than that in male. The mean angle θ is more obtuse than that in male after applying the affected factors. Both the mean SZW and angle θ in both sexes are closely correlated to the mean PICW and SCW. Moreover, the SZW and angle θ also closely correlated. In this study, a new concept of SZW contributes to orthopaedic surgeons in choosing the diameter of pedicle screw among the genders. Moreover, pre-operative computed tomography (CT) assessment of S1 morphology would be very helpful in selecting optimal screw placement.

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