Knee Replacement Alternatives

Anterior cruciate ligament (ACL) injuries are extremely common and debilitating. Prior to the 1970’s little was done to try to repair/replace the ligament but since then ACL surgery has become the norm. However, knee replacement alternatives are now being sought as ACL recovery today does not necessarily guarantee a return to high level sports and it is still unclear if ACL surgery leads to accelerated joint degeneration in the long term.

The ACL is one of the four major ligaments in the knee joint; its role is to stabilize the knee. It prevents the tibia (shin bone) sliding forwards in relation to the femur (thigh bone) and limits rotational movement. An ACL tear may be partial or complete which to a degree dictates knee replacement alternatives.

In the event of an ACL tear (partial or complete) regeneration is unlikely. The ACL has a poor capacity for healing this is largely because of its position within the knee joint and the fact that it has a relatively poor blood supply. Depending on the degree of injury; the ligament may be structurally intact but functionally incompetent. The integrity of the ACL must be restored in some way in order to assist in normal function of the knee joint.

It is possible to partially compensate for a deficient ACL with non-operative treatment, which would consist of physical therapy and rehabilitation to strengthen the muscles surrounding the knee joint and to optimize proprioception at the knee; this can be done with or without the additional use of a hinged knee brace.

As the first knee replacement alternative, non-operative treatment is most suited to those who have a partial tear and remain functionally stable or those with complete tears but minimal athletic/functional demands. Many people can function perfectly well without an intact ACL, however the long term effect that this has on the health of the knee joint is not clear, with the suggestion that non operative management could lead to accelerated joint degeneration.

Where non operative treatment is not appropriate or has proven to be unsuccessful, surgical reconstruction of the ACL is considered. Surgical reconstruction involves repairing the ACL with some form of graft. The functional outcomes following ACL reconstruction are very good. However, rehabilitation following surgery is both long and costly. It can be 6-9 months before vigorous cutting and pivoting activities can be resumed and the estimated annual cost of ACL reconstruction surgery in the United States alone is in the region of $4 billion. Despite good functional outcomes a return to high level sport cannot be guaranteed.

Techniques to repair the ACL have progressed rapidly in the last four decades. Prior to the 1970’s a torn ACL would simply have been removed. As more was learnt about the structure and function of the ACL and its importance in stabilizing the knee, surgeons recognized the need to reconstruct the ligament. The principles of contemporary ACL reconstruction were developed in the 1980’s where three options to either repair or replace the damaged ligament emerged:

o   Autograft (tissue transplanted from one part of a person’s body to another in the same individual)

o   Allograft (a transplant from one person to another)

o   Xenograft (a surgical graft of tissue from one species to another, usually bovine in the case of ACL repair)

The use of an autograft, taken either from the hamstring or the patella tendon is currently widely considered to be the ‘gold standard’ for surgical treatment as allografts and xenografts pose problems due to rejection of the foreign tissue, a lack of available donors and scar formation. Yet even autografts can cause complications. The harvesting of the graft essentially causes further injury and the patient must heal at the site where the graft was taken from as well as at the reconstruction site, this can often lead to complications in rehabilitation. As with non operative management it is unclear if grafting leads to accelerated joint degeneration in the long term.

In an attempt to resolve the deficits in the techniques currently available for ACL injury management, research continues into other knee replacement alternatives. The use of growth hormone, gene therapy and cell therapy are all being explored. The use of cell therapy in particular is a potential source of interest. Human bone marrow mesenchymal stem cells cultured on biomaterial scaffolds are being shown to be beneficial and the hope is that using this technique will facilitate a more complete recovery of the ACL tissue. Further research is necessary and the long term results of this surgery will not be clear for some time. But with such a high prevalence of ACL injury and our increasing demands for full recovery and athletic performance, the developing evidence on this topic is a source of much interest for patients and medical experts alike.