Partial meniscectomy of tears in the avascular zone remains one of the most common orthopedic procedures. While results of partial meniscectomy in younger patients have excellent short- to medium-term results, the long-term clinical outcomes are often less favorable.1-3 Repair in the avascular “white-white” zone has resulted in lower patient satisfaction scores and higher revision surgery rates.4-7 Consequently, most tears in this region have been treated with partial meniscectomy.
The inability to repair rather than resect menisci with avascular tears has led to extensive research. Techniques such as trephination and rasping to initiate an angiogenic response have had inconsistent and unreliable results when applied to the white-white zone.8-13 In contrast, Tasto and colleagues14 have shown that radiofrequency (RF) applied to hypovascular tissue can not only stimulate tissue vascularity, but also increase organization of fibroblastic cells. In addition, Tasto and colleagues15,16 have shown that RF application can significantly improve histologic healing and clinical outcomes in refractory cases of Achilles tendinopathy and lateral epicondylitis. In Japanese white rabbit menisci, Higuchi and coauthors17 applied monopolar RF at 60°C and 40W to avascular zone tears to fuse the tissue. They found a significant increase in fibroblast proliferation and fusion of collagen fibers at 2, 4, and 12 weeks after surgery. They also found significant acellular zones of meniscus tissue and attributed these findings to fibrochondrocyte death because of thermal treatment.
This body of research led to the present study, which evaluates the effect of low-temperature, bipolar RF stimulation, in conjunction with suture repair, on the healing of tears in the avascular white-white zone of the meniscus both in vivo and ex vivo. We performed gross and histologic analyses of the treatment groups for the in vivo aspect of the study and biochemical analyses to study the ex vivo effects of RF treatment. 3H-thymidine incorporation has been shown to be a reliable indicator of cellular proliferation in several studies, and this was measured in our treatment groups.18-21 In addition, the response of mitogenic growth factors (IGF-1, bFGF) and angiogenic markers (VEGF, αV) to RF treatment was studied.22 We hypothesized that bipolar RF application would show increased gross, histologic, and biochemical healing when combined with suture repair of longitudinal avascular zone meniscus tears.
Materials and Methods
Creation of Meniscal Tears
Fifty-four healthy, skeletally mature male and female adult New Zealand white rabbits aged 7 to 18 months were used for the study. All procedures conformed to the guidelines of our university’s institutional animal care and use committee and the American Association for Accreditation of Laboratory Animal Care. All rabbits underwent a surgical procedure in which a longitudinal tear was created in the avascular white-white zone of the medial meniscus. Using sterile technique and instrumentation, a medial parapatellar incision was made on the left knee of each rabbit. The patella was retracted laterally, exposing the medial meniscus. The tibia was then externally rotated to sublux the anterior horn of the medial meniscus anteriorly. A longitudinal full-thickness meniscal tear (3-4 mm in length) was created in the avascular zone (inner third) of the anterior horn of the medial meniscus using an 11-blade scalpel (Figures 1A, 1B). The location of the tear was grossly performed in the same location in each meniscus. The rabbits were randomly divided into 3 treatment groups: 1, 2, and 3 (Table 1). Group 1 (n = 6) served as a control with no repair or RF treatment applied. Group 2 (n = 15) underwent suture repair only of the meniscal tear using 5-0 nylon suture in a horizontal mattress pattern (Figure 2A). Group 3 (n = 33) underwent suture repair after RF stimulation was applied to both sides of the meniscus tear (Figures 2B, 2C). RF was applied using a 0.8-mm TOPAZ MicroDebrider (ArthroCare, Sunnyvale, California) set at level 4 (175 V-RMS) for 500 milliseconds. Lactated ringer’s solution was continuously infused through the probe via sterile tubing to prevent overheating.
After meniscal treatment, hemostasis of the surrounding surgical dissection was achieved to prevent hematoma formation, and the wounds were irrigated. The patellae were relocated and the arthrotomies were closed with a running 2-0 vicryl suture. Fascial and subcutaneous layers were closed with a running 3-0 vicryl suture, and skin was closed with subcuticular 4‑0 vicryl sutures. The rabbit limbs were allowed weight-bearing with unrestricted range of motion within 2x2x2-ft cages.
For all groups, menisci were explanted at 28 and 84 days for gross and histologic analysis. For biochemical assessments, menisci were explanted at 9, 28, and 84 days (Table 1).