Screws in orthopedics

Screws in orthopedics

1. SCREWS DR. PRATIK DHABALIA JUNIOR RESIDENT

2. OVERVIEW HISTORY Father of screw - Archimedes of Syracuse Used for irrigation

3. By the late 18th century, European and American craftsmen had developed and patented effective screw-cutting lathes

4. In 1850, French surgeons Cucel and Rigaud performed the first internal fixation procedure by reducing an olecranon fracture with 2 transcutaneous screws fastened by string. Perhaps more famously, German surgeon Carl Hansmann performed the first internal plate fixation using a removable steel plate and nickel-plated screws in 1886.

5. Danis was able to achieve precise anatomical fracture reductions with rigid fixation. Maurice Müller, himself one of Danis ’ students. Arbeitsgemeinschaft für Osteosynthesefragen  (AO)—German for the Association for the Study of Internal Fixation. Introduction of stainless steel in 1926 to the testing of titanium alloys in the 1970s. Biomechanical qualities of screw features, such as cannulation, tread depth, pitch, and single- vs double-lead threads.

6. SCREW - INTRODUCTION A device used to convert small applied rotational force into large compressive force. Helps in Holding plate or other prosthesis to the bone Fixing fracture fragments Achieving compression at fracture fragments.

7. ANATOMY OF SCREW Four main parts: Head Shank/shaft Thread Tip

8. 1. HEAD Serves two functions – Provides the means for applying torque to the screw. It acts as a stop – translation force converts to compressive force. Recess – for firm purchase of screwdriver on the head for insertion and removal.

9. OTHER TYPES

10. 2. COUNTERSINK Undersurface of the head. Either conical or hemispherical Conical – inserted centered or perpendicular to the hole in the plate. Hemispherical – allows the screw to be angulated Hemispherical threaded – used in locking plates.

11. 3. SHAFT Link between head and thread. Non existent in standard cortical screw. Long shaft in lag screws – smooth shaft has no purchase.

12. 4. RUN OUT Transitional area between shaft and thread. Represents location of significant stress because of changes in diameter and sharp corners. Typically breaks with spiral configuration. More chances in fully threaded than in partially threaded.

13. 5. THREAD Converts torque into compressive force. Standard screw – single threaded Double threaded – advances more faster but requires more torque. 6. CORE DIAMETER Inner or root diameter Narrowest diameter Determines minimum cross section area of screw Smaller diameter has more tendency to shear off

14. 7. OUTER DIAMETER Diameter across maximum thread width. Affects the pull out strength More in cancellous screws. 8. PITCH Distance between two adjacent threads Determines rate of advance Small pitch – advances less, more compression, cortical bone. Typically – 1.75mm/40.5tpi Lead is the distance it travels on one complete turn.

15. 9. TIP Self tapping Non self tapping Corkscrew Trocar tip Self drilling self tapping tip

16. CORTICAL CANCELLOUS TIP Tapered Non tapering PITCH Small Large CORE DIAMETER Larger than shaft Smaller than shaft HOLD More Less PULL OUT STRENGTH Less More LAG SCREW No Yes PILOT HOLE Pre tapping No Pre tapping CANNULATION Absent Present

17. SPECIAL SCREWS Herbert screw Lag screw Dhs screw

18. HERBERT SCREW Interfragmentary compression Differential pitch Headless

19. DYNAMIC HIP SCREW

20. LAG SCREW