need for far cortex locking - journal presentation. motion loc - zimmer, dynamic locking screw (DLS) - SYNTHES.

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…