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Effect of thread pitch on pull‐out strength of laparoscopic myoma screws
Author(s) -
Tintara Hatern,
Aiyarak Pattara,
Mitarnun Winyou,
Geater Alan
Publication year - 2006
Publication title -
journal of obstetrics and gynaecology research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 50
eISSN - 1447-0756
pISSN - 1341-8076
DOI - 10.1111/j.1447-0756.2006.00427.x
Subject(s) - thread (computing) , myoma , ultimate tensile strength , medicine , screw thread , buttress , orthodontics , composite material , materials science , structural engineering , computer science , mechanical engineering , uterus , engineering , operating system
Aim: The purpose of this study was to evaluate the effect of thread‐pitch on pull‐out strength and bending strength of buttress‐thread screws designed for laparoscopic myoma extraction. Methods: The ultimate failure load of four 5‐mm diameter buttress‐thread screws with 3‐, 4‐, 5‐, and 6‐mm thread pitch, 40 mm in thread‐length were examined on fresh myoma specimens. The myoma tissue at each traction site was evaluated histologically to determine its density. The critical minimal pull‐out strength based on moderate‐density myoma group was estimated. The bending strength was also determined for each screw. Results: A wide range of ultimate failure loads with a mean ± SE of 129.3 ± 5.5 N (range, 30.4–255.7 N) for all screws and tissue densities was recorded. In moderate‐density myomas, the mean ultimate failure loads decreased linearly with increasing thread‐pitch from 3 mm (148.0 ± 9.5 N) to 6 mm (119.8 ± 9.4 N) (test for trend: P < 0.05). Based on the criterion of a minimum pull‐out strength of at least 50 N in not less than 95% of tractions in medium‐density myomas, the 3‐mm and 5‐mm pitch screws were found to have acceptable properties. The 5‐mm pitch screw had less thread‐turn than the 3‐mm pitch for the same thread‐length and would need less application time. The bending strength also decreased with increasing thread pitch from 3 to 5 mm, then became stable at around 15 N. Conclusions: The pull‐out strength of soft tissue buttress‐thread screws decreased linearly with increasing thread‐pitch. Thread‐pitch should be considered when designing laparoscopic myoma‐screws.