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Acl graft fixation options
The document discusses graft fixation options in ACL reconstruction. It notes that fixation is the weakest link in the early postoperative period and that tibial fixation carries a greater risk of failure. Interference screws provide the gold standard for fixation but tunnel widening remains a concern. The ideal fixation is strong, stiff, and secure to avoid graft slippage and interference with healing while allowing revision. Aperture fixation and hybrid techniques may improve outcomes over suspensory fixation alone. Rehabilitation must also account for the biomechanical strengths and weaknesses of the fixation method used.
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Acl graft fixation options
- 1. Dr Rajesh Purushothaman AssociateProfessor Government Medical College, Kozhikode Graft Fixation Options in ACL Reconstruction
- 2. Goal Functional and anatomical restorationof ACL in symptomatic ACL deficiency
- 3. Most Important Factors UnderSurgeon's Control • Graft selection • Graft positioning • Graft fixation • Rehabilitation
- 4. Graft Healing BTB graftheal 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 rehabprotocol •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 tofailure 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 ofGraft Motion • Longitudinal motion called Bungee Cord Effect • Horizontal motion called Wind- wiper effect • Creep of graft tissue leading to elongation
- 9. What Does GraftTunnel Motion Do? • >3mm motion interferes with graft incorporation • May cause tunnel widening
- 10. Tunnel Widening • Dueto 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 • Strongenough 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 ApertureFixation At the joint level- Interference screws Suspensory Fixation • Cortical- Endobutton, staples, screw posts • Cancellous- Transfixion pins
- 15. Interference Screws Interference isdefined 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 ScrewFixation Length Size and geometry of screw Divergence of screw • Torque of screw insertion • BMD • Screw Material
- 18. Length • Longer screwprovide 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 shouldbe 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 softthreads 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 • Morethe 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 • Underream by 2mm • Next 2mm increase done using dilators • Compacts the bone than removing it
- 23. Divergence • Difference betweenthe 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 gm2associated 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- absorbsearly, hence loses fixation early • Crystalline polylactides take years to be absorbed
- 26. Attractions • No needfor implant removal • Does not interfere with MRI • Revision easier
- 27. But……. • May breakduring 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 •Titaniumgets covered by bone •Steel gets enveloped by fibrous tissue
- 30. Suspensory Fixation- Cortical Endobutton Tightrope Grafttunnel motion more May lead to tunnel widening Clinical outcome studies show no difference
- 31. Endobutton • First generationsuspensory 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 Femoraltunnel length – Desired graft insertion length = Loop length Insertion tunnel length should be 10mm more than desired graft insertion length
- 33. If the tunnellength 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 Looplength reduced after flipping by tightening the rope Allows full length filling of graft part of the femoral tunnel
- 35.
- 36. Fixation Options •Femoral • Boneplug 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 theearly 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 fixationtheoretically better • Interference screws are the gold standard • Tunnel dilation improves fixation • Hybrid fixation is becoming more popular
- 44. Thank You Dr RajeshPurushothaman Associate Professor of Orthopaedics Government Medical College, Kozhikode, Kerala, India drrajp@gmail.com