Presentation on various graft fixation options in ACL Reconstruction

1. Dr Rajesh Purushothaman
Associate Professor
Government Medical College, Kozhikode
Graft Fixation Options in
ACL Reconstruction

2. Goal
Functional and anatomical
restoration of ACL in
symptomatic ACL deficiency

3. Most Important Factors
Under Surgeon's Control
• Graft selection
• Graft positioning
• Graft fixation
• Rehabilitation

4. Graft Healing
BTB graft heal by bone to bone
healing by 6 weeks
Soft tissue grafts incorporate by
Sharpey fibers by 12weeks
Allografts take longer
Till that time, fixation device should
secure the graft

5. Current Rehab
Accelerated rehab protocol
•Early weight bearing
•Early return to full ROM
•Neuromuscular coordination
•Strengthening

6. Biomechanics of Rehab
• Reconstructed ACL subjected to
150-500N forces by activities of
daily living and rehab
• Within the first 6 weeks, the graft
is subjected to 2,20,000 such
loading cycles
Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament
grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg (Am) 1984;66:344–352.

7. Biomechanics
•Ultimate load to failure is about 3000N for BPTB
and 4000N for QSTGG
•This far exceeds the usual forces of 150-500N
•Fixation has load to failure of about 500N
Fixation is the weakest link in the early
postoperative period

8. 3 Types of Graft Motion
• Longitudinal motion called
Bungee Cord Effect
• Horizontal motion called Wind-
wiper effect
• Creep of graft tissue leading to
elongation

9. What Does Graft Tunnel
Motion Do?
• >3mm motion interferes with graft
incorporation
• May cause tunnel widening

10. Tunnel Widening
• Due to biological and mechanical causes
• More with non-aperture fixation

11. Biomechanics of Fixation
• Strength - Ultimate load to failure
• Stiffness- Resistance to displacement under
load
• Slippage of graft- Change in initial position
under specific number of submaximal cycles

12. Ideal Fixation
• Strong enough to avoid
failure
• Stiff enough to restore
knee stability
• Secure enough to avoid
slippage

13. Ideal Graft Fixation
• Anatomic
• Biocompatible
• Safe and reproducible
• MRI compatible
• Allow easy revision

14. Types of Fixation
Aperture Fixation
At the joint level-
Interference screws
Suspensory Fixation
• Cortical- Endobutton,
staples, screw posts
• Cancellous- Transfixion
pins

15. Interference Screws
Interference is defined
as the amount by which
diameter of the screw
exceeds the gap
between graft and the
tunnel

16. Advantages of
Aperture Fixation
• Minimises Graft-
Tunnel motion
• Less femoral canal
widening
• Creep is less

17. Factors Influencing
Interference Screw Fixation
Length
Size and geometry of
screw
Divergence of screw
• Torque of screw
insertion
• BMD
• Screw Material

18. Length
• Longer screw provide
better fixation
• In BPTB engage only
the bone plug
Stadelmaier DM, Lowe WR, Elah OA, Noble PC, Kohl HW 3rd. Cyclic pull-out strength
of hamstring tendon graft fixation with soft tissue interference screws: influence of
screw length. Am J Sports Med 1999;27:778-83.

19. Size
Screw diameter should be 1mm more than tunnel
diameter for soft tissue grafts and same for bone
plug graft
Kohn D, Rose C. Primary stability of interference screw fixation:
influence of screw diameter and insertion torque. Am J Sports
Med 1994;22:334-8.

20. Geometry
• Use soft threads screw for soft
tissue fixation
• Use reverse threaded screw for left
side
Weiler A, Hoffmann RF, Siepe CJ, Kolbeck SF, Sudkamp NP. The
influence of screw geometry on hamstring tendon interference fit
fixation. Am J Sports Med 2000; 28:356-9.

21. Insertion Torque
• More the resistance better the
fixation
• More with metal screws
• Torque higher if screw diameter is
more
• Torque better if tunnel is prepared
by dilatation method than by
extraction drilling
Kohn D, Rose C. Primary stability of interference screw fixation: influence of screw
diameter and insertion torque. Am J Sports Med 1994;22:334-8.

22. Tunnel Dilatation
• Under ream by 2mm
• Next 2mm increase done
using dilators
• Compacts the bone than
removing it

23. Divergence
• Difference between the
angle of tunnel and
screw direction
• More with transtibial
technique of femoral
tunnel preparation
• >20 degree
compromises stability
Schroeder FJ. Reduction of femoral interference screw divergence during endoscopic anterior
cruciate ligament reconstruction. Arthroscopy 1999;15:41-8.

24. BMD
• <0.6 gm2 associated
with less pull out
strength
• Use hybrid technique
Brand JC Jr, Pienkowski D, Steenlage E, et al. Interference screw fixation strength of a quadrupled
hamstring tendon graft is directly related to bone mineral density and insertion torque. Am J Sports Med
2000;28:705-10.

25. Bioabsorbable screws
• Polyglycolide-
absorbs early, hence
loses fixation early
• Crystalline
polylactides take
years to be absorbed

26. Attractions
• No need for implant
removal
• Does not interfere with
MRI
• Revision easier

27. But…….
• May break during insertion. Use
with special screw driver only
• Tissue reaction in some
• Fixation lost after partial
degradation

28. And…
•By 6 weeks, 80% loss of strength and
60% loss of stiffness
•Incidence of effusion is more
•Tunnel widening more

29. Titanium Or Steel
•Titanium gets covered by bone
•Steel gets enveloped by fibrous
tissue

30. Suspensory Fixation- Cortical
Endobutton
Tightrope
Graft tunnel
motion more
May lead to tunnel
widening
Clinical outcome
studies show no
difference

31. Endobutton
• First generation suspensory
fixation
• Femoral tunnel has 2 parts-
Insertion & Connection parts
• Insertion part drilled to the
diameter of graft
• Connection part is of 4.5mm
diameter

32. Maths of Endobutton
Femoral tunnel length –
Desired graft insertion
length = Loop length
Insertion tunnel length
should be 10mm more
than desired graft
insertion length

33. If the tunnel length is 60mm, desired
insertion length is 40mm then the loop
length should be 20mm and the insertion
tunnel should be 50mm long

34. Tightrope
Second generation
suspensory fixation
Loop length reduced
after flipping by
tightening the rope
Allows full length filling
of graft part of the
femoral tunnel

35. Tightrope

36. Fixation Options
•Femoral
• Bone plug fixation
• Soft tissue fixation
•Tibial
• Bone plug fixation
• Soft tissue fixation

37. Bone Plug Fixation-
Femur
• Interference screws-
Gold standard
• Suspension type-
Endobutton BTB,
• Transfixation type-
Transfix

38. Bone Plug Fixation
Tibia
• Staples with or without
sutures
• Screws as screw
posts
• Interference screws

39. Soft Tissue Fixation
Femur
• Interference screws
• Suspension type like
Endobutton, Tightrope
• Transfixation type
Interference screw fixation
especially with bioscrews
needs slower rehabilitation

40. Soft Tissue Fixation
Tibia
• Staples singly or with two staples
using belt buckle technique
• Screws as posts or with spiked
washers
• Interference screws
Interference screw fixation especially with
bioscrews needs slower rehabilitation.
Hybrid fixation preferrable

41. Tibial Vs Femoral
Fixation
• Tibial fixation is less
secure
• Reduced bone density
• Angle of forces in line
with the graft
• Bone strength falls
rapidly away from the
joint line

42. Conclusions
• In the early postoperative period fixation is the
weakest link
• Tibial fixation is at greater risk of failure
• Clinical results of various methods are
comparable
• Tunnel widening is a growing concern

43. Conclusions
• Aperture fixation theoretically better
• Interference screws are the gold standard
• Tunnel dilation improves fixation
• Hybrid fixation is becoming more popular

44. Thank You
Dr Rajesh Purushothaman
Associate Professor of Orthopaedics
Government Medical College,
Kozhikode, Kerala, India
drrajp@gmail.com