Shrinking the ACL

Abstract & Commentary

Synopsis: Radiofrequency thermal shrinkage can weaken the ligament and predispose to rupture.

Source: Sekiya JK, et al. Autodigestion of a hamstring anterior cruciate ligament autograft following thermal shrinkage: A case report and sentinel of concern. J Bone Joint Surg Am 2000;82-A(10):1454-1457.

This case report by Sekiya and colleagues describes a 16-year-old female athlete who, five months after ACL reconstruction with semitendinosus-gracilis autograft, sustained a twisting injury to her knee. Clinical evaluation revealed laxity (2+ Lachman—i.e., 5-10 mm) consistent with a tear of the ACL graft as well as a probable medial meniscal tear. MRI imaging confirmed the medial meniscal tear but demonstrated the ACL graft to be intact. At the time of arthroscopy, a medial meniscal bucket-handle tear was resected, but since the ACL graft was intact, thermal shrinkage with the ORATEC device (ORATEC Interventions, Menlo Park, Calif.) was undertaken using 40 watts of energy and a temperature of 65°C as recommended by the manufacturer. Following shrinkage, the graft was probed and found to be intact with appropriate tension, and the Lachman test was comparable with the noninjured side.

Postoperatively, the patient underwent a rehabilitation program that emphasized graft protection for 12 weeks, after which the Lachman test was found to be 1+ and the pivot-shift test was negative. The athlete was released to full activity but sustained a non-contact reinjury to her knee one week later. Examination revealed significant laxity (3+ Lachman), and arthroscopy revealed no remnant of the previous hamstring autograft in the notch. An ACL revision procedure using bone-patella tendon-bone autograft was performed.

Comment by Letha Y. Griffin, MD, PhD

This article reminds us that monopolar or bipolar radiofrequency thermal energy is just that, thermal energy, and in addition to shrinking tissue it can also destroy it. In 1998, Thabit, using a monopolar device, reported excellent results in 23 of 25 patients after thermal shrinkage of the anterior portion of the patient’s lax ACL.1 He recommended that the device be used only on the anterior fibers so that the posterior portion of the ligament could serve as a source of revascularization. However, in this case reported by Sekiya et al, no mention is made of whether the entire graft was thermally treated or only the anterior portion. The ultimate outcome was destruction of the graft despite the radiofrequency being used at the recommended settings. One must ask why? Is this case merely an outlier or might this complication be more common than initially thought?

A study of 13 patients reported by Thomas Carter2 at the AOSSM summer meeting (Sun Valley 2000) using the monopolar ORATEC probe for shrinking lax, previously normal ACLs (6) or lax, reconstructed ACLs (7) followed for an average of 17.8 months, had a failure rate of 69%. Perry and Higgins3 reported a case of a 31-year-old who ruptured both the anterior and posterior cruciate ligaments following minor knee trauma (pushing children on a sled) 10 weeks after treatment of these ligaments with the bipolar Arthrocare thermal probe. The probe had been used to treat laxity found at the time of arthroscopy because of a one-year history of occasional swelling and posterior knee tightness. Perry and Higgins caution that the biomechanical characteristics of thermally treated tissues are still being defined. Recently, cautions have been issued regarding shoulder capsular shrinkage to avoid early mobilization, as this can stretch the heated tissue.4 Prolonged probe contact and high-energy settings also negatively influenced results. The ultimate power setting and duration of treatment is still yet to be determined, as are the long-term effects of the denaturation of the collagen microstructure caused by thermal energy. Until more is known, caution is recommended when using RF thermal energy to treat laxity, especially pathologic laxity of the cruciate ligaments.

References

1. Thabit G. The arthroscopic monopolar radiofrequency treatment of chronic anterior cruciate instability. Operative Techniques in Sports Medicine 1998;6: 157-160.

2. Rapp SM. Thermal shrinkage has limited use for ACL laxity. Orthopaedics Today 2000;11:25.

3. Perry JJ, Higgins LD. Anterior and posterior cruciate ligament rupture after thermal treatment. Arthroscopy 2000;16(7):732-736.

4. Hecht P, et al. Monopolar radiofrequency energy effects on joint capsular tissue: Potential treatment for joint instability. An invivo mechanical, morphological and biomechanical study using an ovine model. Am J Sports Med 1999;27:761-771.