Shrinking the ACL
Shrinking the ACL
Abstract & Commentary
Synopsis: Eleven of 18 patients failed electrothermal shrinkage of the ACL at an average of 4 months due to rupture. Of the 7 with successful results, 6 were acute injuries in native ligaments. Use of electrothermal shrinkage is cautioned in partial ACL tears and probably contraindicated for ACL grafts or chronic laxity.
Source: Carter TR, et al. Am J Sports Med. 2002;30:221-226.
Radiofrequency, or electrothermal energy, has enjoyed rapid acceptance and widespread applications despite a major lack of scientific studies supporting its clinical use for specific indications. The ability to shrink collagen is visually impressive. And it is to be expected that it would be used to try to address partial ACL injuries or lax ACL grafts after reconstruction.
Dr. Tom Carter and colleagues in Arizona critically evaluated the success of this treatment in 18 persons, including 7 with previous reconstructions and 11 with native ligaments. Half of the group had acute and half had chronic (> 3 months) laxity. All patients were demonstrated on arthroscopy to have loose ligaments which were in continuity, and KT-1000 differences > 5 mm with loose Lachman exams but a firm end point. Patients were treated with monopolar radiofrequency (Oretec device, Menlo, Calif) at 67° and 40 watts of power by painting the ligament on 3 sides until tight. They were immobilized in extension for 4 weeks then gradually rehabbed with level running held until 3 months and return to sport not until 4 months. They were evaluated on a monthly basis, including KT-1000 arthrometry.
All patients initially demonstrated tighter knees after shrinkage with improvement of KT values basically to the normal range. Unfortunately, at a mean of 4 months, 11 of 18 patients suffered a clinical failure, with increased laxity on exam and by KT compared to preoperative values. Examining the failures more closely revealed that only 1 of 9 with chronic laxity had a favorable outcome. Six of 8 patients with acute laxity had stable knees. Only 1 of 7 ACL reconstructions had a favorable outcome after shrinkage. These reconstructions were basically half patellar tendon and half hamstring autografts. All 11 patients who failed went on to reconstruction due to symptomatic laxity. Histology of failed ligaments revealed disorganized collagen and poor vascularity, in contrast to a biopsy of a successful second-look biopsy at 15 months.
Comment by David R. Diduch, MS, MD
Heat kills. We have seen it before and, unfortunately, we will see it again. Surgeons must be extremely cautious when using radiofrequency energy to shrink tissues as the initial results do not portend to final outcome in all cases. The temperature zone for safe shrinkage without necrosis is quite narrow at 65-75°C, but necrosis can occur even at low temperatures with excessive exposure time. The results of heat shrinkage are to disrupt collagen crosslinkages and unwind the triple helix, allowing the collagen to contract. At this point, fibroblasts must make new collagen on this shortened lattice framework before the collagen is stretched out again. This takes at least 3 months, with the tissue quite vulnerable in the interim.
The big issue, however, is vascularity. Shrinkage kills fibroblasts in the area, and without adequate blood supply, new fibroblasts cannot come in to repopulate the area and create healthy, healing tissue. Dr. Carter saw a distinct difference in outcomes for patients with native ligament partial tears treated acutely, when there would be an acute inflammatory response with associated increased vascularity. They conclude that this may be the only proper indication for this treatment but should be used with caution even then. Clearly, further studies are needed. Although most failures occurred by 4 months, longer follow-up may reveal these early successes are at risk to rupture over time. And clearly, this treatment should not be used on existing ACL grafts or chronic partial tears where the vascular supply is marginal.
This study was carefully constructed and carried out, and Carter et al are to be congratulated for an honest presentation of unfavorable results from which we can all learn. The differences in outcome from the only other published paper on the same topic by Thabit are difficult to explain,1 although the present study was more rigorous and complete. Again, this further supports the need for more studies before adapting this technology into clinical practice.
Reference
1. Thabit G 3rd. Operative Techniques in Sports Medicine. 1998;6:157-160.
Dr. Diduch, Associate Professor, Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA,is Editor of Sports Medicine Reports.
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