Document Title: Carter-AJSM-Mar02
Article Title: Radiofrequency electrothermal shrinkage of the anterior cruciate ligament
Authors: Thomas R Carter, David S Bailie, Samantha Edinger.
Publication: The American Journal of Sports Medicine
ISSN: 03635465
Date: March-April 2002
(Figures included. Reference-denoting numbers appear in the same point size as document text.)
Volume: 30
Issue: 2
Pages: 221-226
Key Words: Knee, ACL, thermal shrinkage, radiofrequency.

Comments: In this carefully-done study, Carter et al. find that thermal shrinkage does not bring good results for ACLs. They conclude that the procedure is inappropriate for treating chronically lax or previously reconstructed ACLs. The mean follow-up period in this study was 20.5 months (excepting cases in which failure occurred sooner). At the time this article was submitted for printing, thermal shrinkage had failed in 11 of 18 patients, hence an aggregate failure rate of 61% overall. This translates into a staggering 86% failure rate for the people who had previously undergone reconstruction on the ACL, and a nonetheless-worrisome 45% failure rate with the patients for whom the thermal shrinkage was used as a first-time treatment (e.g. for partial ACL tearing). A major reason for the understandably disappointing performance of ACL thermal shrinkage is embodied in the enormously long lever arms of the tibia and femur, which make it impossible to completely shield the treated ACL from physiological loadings during the rehab period (even if a full-leg cast is used). Also notable is the thermal damage done to the highly biomechanically optimized helical-parallel-aligned collagen tensile-fibre structure of the ACL, along with heat-related (searing) damage to the ligament cells in general. Clearly, thermal shrinkage has no place in the realm of knee-ligament treatment. Doctors who are still using this procedure for ACLs might do well to think of the old adage: "when all you have is a hammer, everything starts to look like a nail".

It should be kept in mind that, in general, stretching seems to occur more commonly with reconstructed ACLs (as compared to with original ACLs), whereas partial rending seems more common with original ACLs than with reconstructed ones; however, both stretching and tearing modes of injury occur in both original and reconstructed ACLs. (Carter found that the type of ACL damage [i.e. stretching versus tearing] did not correlate to the thermal-shrinkage failure rate.) Also, note that partial tearing in particular brings a weakening of the ligament, in accordance with the fact that tensile stress is defined as force divided by cross-sectional area...and so a halving of a ligament (i.e. 50% partial tear) immediately brings a doubling of stress in the remaining intact portion. The fact that thermal shrinkage does absolutely nothing to alleviate this unfavourable state of affairs means that the procedure is inherently just as worthless for people with nonreconstructed partly-torn ACLs as it is for people with reconstructed-but-stretched ACLs. Finally, note that the use of ACL thermal shrinkage, if it manages to bring a fleeting reduction in ACL laxity, may encourage the person to return to knee-demanding sports...whereupon the ACL can be expected to fail catastrophically, thereby resulting in almost-certain damage to the menisci and articular cartilage. So, the false hope of ACL thermal shrinkage could best be described as a bitter disappointment. For severely partly-torn ACLs (herein defined as being badly torn to the extent that the knee is rendered unstable or has manifested itself as unstable during the initial tearing event, and assuming that conservative treatment is infeasible), the best solution is standard tendon-graft reconstruction. (For first-time ACL reconstructions, the failure rates of patellar-tendon and hamstring autografting are 5% and 10%, respectively.) For unsuccessfully-grafted ACLs (i.e. the graft has failed to revascularize and reinnervate, or it has failed via stretching-out or tearing), the best solution clearly remains revision reconstruction (for which the failure rate is roughly 25%).

The efficacy of electrothermal collagen shrinkage in the treatment of patients with anterior cruciate ligament laxity was evaluated. Eighteen patients who had continuity of the anterior cruciate ligament but had symptomatic laxity were treated with arthroscopic electrothermal shrinkage of the anterior cruciate ligament using a monopolar radiofrequency probe. The mean length of follow-up in patients whose stability was maintained was 20.5 months. Seven of the patients had undergone previous reconstruction, four with patellar tendon graft and three with quadrupled hamstring tendon graft. Laxity was chronic in nine patients and acute in nine. The KT-1000 arthrometer results at one month postoperatively revealed decreased anterior excursion, with an average side-to-side difference of 1.9 mm. However, eleven patients had a failed result at an average 4.0 months. Of the seven patients with successful results, six had native ligaments and had been treated for acute laxity and one had a patellar tendon graft and had been treated for chronic laxity. Even with the short-term follow-up in our study, it is evident that thermal shrinkage using radiofrequency technology has limited application for patients with anterior cruciate ligament laxity. Although it may be useful in treating patients with an acutely injured native anterior cruciate ligament, further study is needed to see if the ligament stretches out over time or is at increased risk of reinjury.

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