Paul H. Marks, B.Sc., M.D., FRCSC, D.I.P. Sports Medicine (CASM)
Orthopaedic and Arthritic Institute
Sunnybrook and Woman's College Hospital Science Centre
University of Toronto
Toronto, ON

As one initiates the discussion of graft selection for Anterior Cruciate Ligament (ACL) reconstruction, one usually begins with a certain bias or philosophy. Indeed, one of the products of studying philosophy is an awareness that the most apparently simple questions cannot be answered simply. Philosophy may provide a theoretical underpinning for our most cherished beliefs, but it equally may show us how little we know. The Delphic Oracle deemed Socrates the wisest man in Athens, which came as a surprise to him, as he felt that he didn't know anything for certain. But, through his questioning of those who were confident that they knew what they were talking about, Socrates came to realize that the Oracle was right. His wisdom lay in knowing the limits of his knowledge, whereas others dogmatically asserted indefensible opinions.  

As a resident, I once asked my mentor Dr. Peter J. Fowler what the gold standard operation was for ACL reconstruction. He replied, "the gold standard is the normal knee, and no surgeon is that good". For practical purposes, this debate distills down to surgical preference of Hamstring or Bone Tendon Bone (BTB) grafts.

The next critical issue becomes the method used to measure success or clinical outcome. Is a success a: 1) KT-1000 stable knee? 2) A good hop test? 3) Return to previous level of sport? 4) An improvement on generic and disease-specific quality of life measures? 5) Normal radiographs at long-term follow-up? 6) An Olympic medal?

Perhaps the most important question has not been answered thus far. Does ACL reconstruction prevent articular degeneration? The natural history of the ACL-deficient knee has yet to be completely elucidated, as much debate exists regarding the relationship between osteoarthritis and the ACL-deficient knee. Approximately 44% of patients with ACL deficiency develop osteoarthritis if the injury is left unrepaired. A publication by Fritchy and Daniel, however, showed that reconstructing the ligament, rendering the knee KT-1000 stable, does not necessarily reduce the risk of developing degenerative change.

The conventional view of post-traumatic arthritis of the knee proposes that instability leads to cartilage wear and arthritic change. It may be that multiple risk factors are implicated in the development of osteoarthritis. These may include concomitant meniscal pathology, osteochondral pathology, impaired proprioception, and biochemical mediators (i.e., cytokines), MRI bone bruises, amongst others. In an effort to aid in the evaluation of risk of post-traumatic OA after ACL rupture, we have proposed that the ACL Risk Equation be developed. This proposed equation would be a function of all the pertinent risk factors. To properly generate the ACL Risk Equation, a multi-variate analysis investigating the degree of interaction among these risk factors is necessary. In addition, novel therapeutic strategies may be developed, such as gene therapy, in order to counteract or neutralize the relevant factors and thus protect the ACL-insufficient knee from degenerative changes.

We now turn back to the subject of debate. What is the best choice of graft tissue for use in ACL reconstruction? Freedman et al. (2003) published a meta-analysis comparing patellar tendon and hamstring tendon autografts for ACL reconstruction. A Medline search identified articles from January 1966 to May 2000 describing arthroscopic ACL reconstruction with either patellar tendon or hamstring autograft and with a minimum patient follow-up of 24 months. Patellar tendon autografts had a significantly lower rate of graft failure and resulted in better static knee stability and increased patient satisfaction compared with hamstring tendon autografts. However, patellar tendon autograft reconstructions resulted in an increased rate of anterior knee pain.

The debate then really centres on the "apparent" increased rate of anterior knee pain with patellar tendon grafts. Since the meta-analysis endpoint of 2000, there have been ten prospective randomized studies comparing hamstring to Bone Tendon Bone graft techniques. Nine of the ten publications have shown no difference in anterior knee pain amongst their patients. It is interesting to note that some patients having undergone hamstring grafting continue with anterior knee pain. This cannot be explained on the basis of graft site morbidity. Perhaps these patients have some residual laxity causing anteroposterior translation and overload of the patellofemoral articulation. In fact, we may not be asking the anterior knee pain question properly. Bynum et al. (1995) published a randomized study comparing open versus closed chain kinetic exercises after ACL reconstruction. Embedded in the results was a most interesting finding. In a group of 100 patients who had undergone arthroscopic ACL reconstruction with Bone Tendon Bone graft, postop follow-up showed an actual decrease in anterior knee pain. The study group had described 41% anterior knee pain preop and only 21% postop. The BTB surgery apparently decreased the anterior knee pain complaint by 50%. Was this related to diminishing the AP translation in the joint?

If the Bone Tendon Bone provides lower graft failure, better static knee stability, increased patient satisfaction when compared to hamstring tendon, and apparent decrease in overall anterior knee pain, why perform any other procedure?

There may be reasons for use of the hamstring graft. These may include: lower demand patients, significant extensor mechanism issues, religious demands (i.e., kneeling) and significant associated chronic degeneration where over constraint of the joint may accelerate arthritis.

It would appear that, currently, most high-level professional athletes in North America (NBA, NFL, NHL) are treated with Bone Tendon Bone grafting. Techniques for minimizing potential donor site morbidity with BTB include careful preservation of the peritenon, avoiding impact while taking the patellar bone block, taking a small patellar bone block, bone grafting the defects, and postop rehabilitation (i.e., patellar mobilizations).

In future, the ACL Risk Equation will help to define variables that may predict those individuals who are at risk of developing degenerative change and osteoarthritis. The ultimate goal is full restoration of the injured knee to pre-injury status: "the normal knee". Possibilities may exist in the distant future through genetic manipulation, resorbable stents, incorporation of bioactive growth factors, improved fixation techniques, robotic surgical techniques for graft placement, control of muscle atrophy, enhancing cerebellar-proprioceptive rehabilitation, and functional retraining.

As with Socrates, our wisdom will lie in knowing the limits of our knowledge, and in avoiding dogmatic assertions of indefensible opinions.

References

1. Bynum et al.: Open versus closed chain kinetic exercise after anterior cruciate ligament reconstruction. AJSM, Vol 23, No 4, 1995.
   
   
2. Craig, Edward (ed.), Routledge Encyclopedia of Philosophy, London and New York: Routledge, 1998.
   
   
3. Daniel et al.: Fate of the ACL-injured patient. AJSM Vol 22, 1994.
   
   
4. Dye, S.F.: The future of anterior cruciate restoration. CORR, 325, 1996.
   
   
5. Freedman et al.: Arthroscopic anterior cruciate reconstruction: A metaanalysis comparing patellar tendon and hamstring tendon autografts. AJSM Vol 31, No 1, 2003.
   
   
6. Marks et al.: The ACL Risk Equation: Does ACL Reconstruction prevent articular degeneration. Sports Injuries of the Knee. Oxford University Press, Oxford, United Kingdom 2003 (In Press).