biomechanics of far cortex locking
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The document discusses the biomechanics of far cortical locking (FCL) screws, highlighting their advantages over standard locking compression plates (LCP) in treating femoral and tibial fractures. FCL screws provide flexible fixation, uniform load distribution, and promote callus formation, effectively reducing non-union rates while mimicking the biological activity of external fixators. The study concludes that FCL constructs significantly improve healing outcomes by enhancing interfragmentary motion and reducing stiffness compared to traditional methods.
![ FAR CORTEX LOCKING:
WHAT IT HAS: ( 4 KEY FUTURES)
1.Flexible fixation. ( reduces stiffness by 80- 88%)
actively promotes callus formation similar to external fixator.
2.Uniform load distribution – mitigate stress raisers.
3.Progressive stiffening – on increased loading.
4.Parallel inter-fragmentary motion – by ‘S’ shaped flexion.
[ FUNCTIONS AS EXTERNAL FIXATORS IN BIOMECHANICAL
BEHAVIOUR AND BIOLOGIC HEALING ]](https://image.slidesharecdn.com/farcortexlockingscrew-170113143300/85/biomechanics-of-far-cortex-locking-6-320.jpg)
![ Stiffness is reduced by screws – fixed in plate & far cortex,
while retaining a controlled motion envelope at near cortex.
thereby promoting interfragmentary motion
[ IDEAL: 0.2 – 1 mm ]
to produce secondary callus](https://image.slidesharecdn.com/farcortexlockingscrew-170113143300/85/biomechanics-of-far-cortex-locking-8-320.jpg)
![ FCL CONSTRUCT :
reduces the stiffness of,
FEMORAL DIAPHYSIS – 88% ,
FEMORAL METAPHYSIS – 80%
TIBIAL DIAPHYSIS – 84%
[ Bottlang et al 2009,2010 JBJS Am ]](https://image.slidesharecdn.com/farcortexlockingscrew-170113143300/85/biomechanics-of-far-cortex-locking-10-320.jpg)
![LCP
INCREASING MOTION ON FAR CORTEX
DUE TO, RIGID FIXATION – NEAR CORTEX
ASYMMETRIC GAP CLOSURE
ASYMMETRIC CALLUS FORMATION
[ LUJAN et al 2010 – J orthop trauma ]](https://image.slidesharecdn.com/farcortexlockingscrew-170113143300/85/biomechanics-of-far-cortex-locking-20-320.jpg)
biomechanics of far cortex locking
- 1. BIOMECHANICS OF FAR CORTICAL LOCKING Michael Bottlang & Florian Feist Journal of Orthopaedic trauma ,Feb 2011. Presentation by: RAM SUDHAN.S.
- 2. NEED FOR FAR CORTEX LOCKING SCREW: COMPLICATIONS OF LCP’s: SUPRACONDYLAR # FEMUR: Non union rate – 18 – 23 % BOULTON C et al (AAOS 2011 )– 23% HOFFMANN et al (J ortho surg Res 2013) – 18 % , incl’ 10% - hard ware failure.
- 3. STANDARD LCP : (bridge plating) depends on secondary bone healing rather than primary bone healing traditionally achieved by external fixation constructs more flexible inter fragmentary motion ( 10 times more than LCP / DCP) inherently produce rigid stabilisation - kubiak et al 2006 (JBJS Am)
- 4. can supresses interfragmentary motion ( HIGH STIFFNESS) BOTTLANG et al 2010 (JBJS Am), lujan et al 2010 ( J orthop trauma) insufficient for secondary # healing. 1. rigid locking screws - uneven stress distribution. stress shielding under the plate. bone resorption
- 5. To enable flexible fixation with LCP’s / to reduce the stiffness FAR CORTEX LOCKING SCREWS WERE DEVELOPED
- 6. FAR CORTEX LOCKING: WHAT IT HAS: ( 4 KEY FUTURES) 1.Flexible fixation. ( reduces stiffness by 80- 88%) actively promotes callus formation similar to external fixator. 2.Uniform load distribution – mitigate stress raisers. 3.Progressive stiffening – on increased loading. 4.Parallel inter-fragmentary motion – by ‘S’ shaped flexion. [ FUNCTIONS AS EXTERNAL FIXATORS IN BIOMECHANICAL BEHAVIOUR AND BIOLOGIC HEALING ]
- 7. FLEXIBLE FIXATION : Flexibility: directly proportional - working length of the screw.
- 8. Stiffness is reduced by screws – fixed in plate & far cortex, while retaining a controlled motion envelope at near cortex. thereby promoting interfragmentary motion [ IDEAL: 0.2 – 1 mm ] to produce secondary callus
- 9. PARTS: 1. HEAD – locking thread 2. MOTION CONTROL COLLAR 3. FLEXIBLE SHAFT reduced diameter elastically deflect ( within - motion control collar of near cortex) 4. FAR CORTEX LOCKING THREADS resembling an monolateral external fixator
- 10. FCL CONSTRUCT : reduces the stiffness of, FEMORAL DIAPHYSIS – 88% , FEMORAL METAPHYSIS – 80% TIBIAL DIAPHYSIS – 84% [ Bottlang et al 2009,2010 JBJS Am ]
- 11. COMPARISON OF STIFFNESS: LCP- FCL – EX’FIX the FCL lowers - axial stiffness by 84% than standard LCP construct (4286N/mm) FCL --- APPROX’ EQUAL --- EXTERNAL FIXATOR (682N/mm) (488N/mm) produces inter fragmentary motion (0.6mm) Suitable for promoting callus formations
- 12. LOAD DISTRIBUTION: IN LCP: Transmits load thro’ fixed angle screws induce stress concentration at screw bone interface uneven load distribution esp: outermost locking screw (prox/dist) stress shielding in adjacent regions increases the # risk at the plate end 1. cortical porosis or 2. delayed bridging. FOCUSSED LOAD TRANSFER
- 13. IN FCL: strain Distributed equally to entire working length – all screws. supresses stress raisers at ends of plate Suitable in healthy bone Osteoporotic Diaphysis stress shielding & porosis focussed Adjacent to near cortex LCP Screw segment b/w near & far cortex Remains latent
- 15. PROGRESSIVE STIFFENING: ( similar- ilizorov fixator) SHOWS BIPHASIC STIFFNESS Normal loading elevated loading Low initial stiffness elastic flexion gains addition support at near cortex (All load – plate to far cortex) ( 6 fold increase in construct stiffness ) Thro’ flexible shaft SIMILAR TO LCP promotes inter fragmentary motion protects the bone from ( in early healing phase) excessive motion / loading
- 17. HOW IT DOES THAT: ( motion control collar) FCL screw DIA’ at near cortex is sufficiently large To confine the flexion within its elastic range Thus excessive flexion is prevented Thereby , screw fatigue – prevented.
- 18. MIMICKING THE FCL SCREW FUNCTION: overdrilling the near cortex with standard locking screws by 1 mm overloads the far cortex due to lack of flexibility of standard screw
- 19. PARALLEL INTERFRAGMENTARY MOTION: ON AXIAL LOADING Bridge plating constructs – plate flexion ( elastic plate bending) Coz’ plate – offset from cortex. Enables inter fragmentary motion BUT,
- 20. LCP INCREASING MOTION ON FAR CORTEX DUE TO, RIGID FIXATION – NEAR CORTEX ASYMMETRIC GAP CLOSURE ASYMMETRIC CALLUS FORMATION [ LUJAN et al 2010 – J orthop trauma ]
- 21. FCL PARALLEL interfragmentary motion Due to flexible shaft produces – ‘S’ SHAPED FLEXION THUS, symmetric callus – formed.
- 22. FCL: 1. SYMMETRIC HEALING 2. INCRESED BONE MINERAL DENSITY BY 44% 3. TOLERATES 156% MORE ENERGY TO FAILURE.
- 23. CONSTRUCT STRENGTH: LCP FCL AXIAL COMPRESSION 7% LOWER BENDING 24% HIGHER TORSION 54% HIGHER
- 24. CONCLUSION: FCL CONSTRUCT PROVIDES: FLEXIBILITY UNIFORM LOAD PROGRESSIVE PARALLEL DISTRIBUTION STIFFENING INTER FRAGMENTARY MOTION PROMOTES CALLUS FORMATION - PREVENTING PARTIAL NON UNION RESEMBLES internal fixation by construct but replicates the biomechanical function of external fixators.
- 25. THANK YOU…