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
â˘Early weight bearing
â˘Early return to full ROM
â˘Neuromuscular coordination
â˘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;66:344â352.
7. Biomechanics
â˘Ultimate load to failure is about 3000N for BPTB
and 4000N for QSTGG
â˘This far exceeds the usual forces of 150-500N
â˘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
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 ďŹxation with soft tissue interference screws: inďŹuence 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 ďŹxation:
inďŹuence 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
inďŹuence of screw geometry on hamstring tendon interference ďŹt
ďŹxation. 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 ďŹxation: inďŹuence 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 ďŹxation 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.
26. Attractions
⢠No need for implant
removal
⢠Does not interfere with
MRI
⢠Revision easier
27. ButâŚâŚ.
⢠May break during insertion. Use
with special screw driver only
⢠Tissue reaction in some
⢠Fixation lost after partial
degradation
28. AndâŚ
â˘By 6 weeks, 80% loss of strength and
60% loss of stiffness
â˘Incidence of effusion is more
â˘Tunnel widening more
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 â
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
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