Arthroscopic surgery is the current standard of care for human knee surgery. Arthroscopy is becoming more widely accepted in the veterinary community for evaluation of the canine stifle joint. Arthroscopic examination provides a minimally invasive means of visualizing the intra-articular structures of the stifle, such as the cranial and caudal cruciate ligaments, medial and lateral meniscus, cartilage surface and synovium. The structures within the joint are highly illuminated and greatly magnified, which allows improved visualization over traditional arthrotomy and better sensitivity at diagnosis of meniscal injury.
Rupture of the cranial cruciate ligament (CCL) is one of the most common causes of pelvic limb lameness in dogs. Partial and complete CCL tears cause instability of the stifle joint. This instability results in inflammation, cartilage damage, meniscal injuries and subsequent osteoarthritis. In dogs, CCL rupture is most often a result of degeneration. Meniscal injury is often found as a result of the instability, which occurs with cranial cruciate disease. Shearing forces on the caudal horn of the medial meniscus caused by cranial subluxation and internal rotation of the tibia during loading may predispose to these tears. Most of the meniscal tears involving the caudal horn of the medial meniscus likely occur as a result of its firm attachment to the tibial plateau. The most common form of medial meniscal tear is a vertical longitudinal tear (otherwise known as a bucket handle tear), which can account for about 57% of medial meniscal tears.
During any surgery for cranial cruciate disease, the first step is evaluating the joint and diagnosing the severity of the cruciate tear and any meniscal injury. This joint exploration can either be performed with arthrotomy or arthroscopy. Arthrotomy involves a full-thickness incision through the joint capsule and reflecting the patella laterally so that instruments can be placed to open the joint space. Arthroscopy involves placing two small portals and an egress cannula (each a few millimeters wide) to allow fluid to enter and exit the joint. This technique allows for enhanced visualization, and the camera allows for magnification of the joint structures. With arthroscopy, there is less disruption of the joint fibers, which subjectively may lead to less pain, swelling and bruising, and may help with a faster recovery postoperatively. During arthroscopy, we remove any torn ends of cruciate ligament with a shaver. If the CCL is partially torn, we leave the intact portion alone, as that may help with stability. Both the medial and lateral meniscus are thoroughly probed to see if there are any visible tears or fraying. If the meniscus looks healthy, it can be left intact to allow continued prevention of bone-on-bone contact. Though primary meniscal repair has been described in dogs, it is not commonly performed, and most tears are treated with partial meniscectomy. If there is a meniscal tear, that is removed with specialized meniscal instrumentation through the small arthroscopic portals. The most common type of meniscal tear is a bucket handle tear, which is removed via caudal pole partial meniscectomy.
The prevalence of meniscal tears found during CCL surgery is between 20 to 77% overall. Concurrent meniscal tears were diagnosed in 83% of stifles assessed by arthroscopy and 44% of stifles assessed by arthrotomy. Overall, concurrent tears were 1.9 times more likely to be diagnosed by arthroscopy than arthrotomy. Studies have found that the sensitivity and specificity for finding meniscal tears is best with probing of the meniscus during arthroscopy compared with arthrotomy. Probing during arthroscopy made the correct diagnosis of meniscal tear 8 times more likely during arthroscopy. Dogs with a complete CCL tear have been found to have a higher incidence of meniscal tear than dogs with a partial meniscal tear. One paper showed that meniscal tears were seen more often in stifles with a full CCL tear as compared with a partial CCL tear at a ratio of 11:1.
Subsequent medial meniscal injury has been noted to be a late complication of surgical management of dogs with cruciate rupture. The incidence of subsequent meniscal tears has been reported to be about 10.5% after tibial plateau leveling osteotomy (TPLO), 21.7% after tibial tuberosity advancement (TTA) and 16.5% after extracapsular repair. Arthroscopy of the stifle for a subsequent meniscal tear is the perfect tool for a minimally invasive diagnosis and treatment of this process. Once the meniscal tear is identified with probing, the torn portion is removed via arthroscopy. This allows for a rapid recovery with the least amount of pain and incisional swelling compared with a full arthrotomy for a subsequent meniscal tear.
Meniscal release can also be performed during the stifle arthroscopy without having to convert to an open arthrotomy. This is a controversial procedure among surgeons, as there is some belief that performing meniscal release may change the biomechanics within the joint and therefore affect contact pressure on cartilage and potentially worsen osteoarthritis. However, performing a meniscal release has been shown to decrease the chances of a subsequent meniscal tear. Cases treated with meniscal release did not have subsequent meniscal tears, whereas dogs not treated with meniscal release had a subsequent meniscal tear rate of 11% in one study. Cases diagnosed and treated for concurrent meniscal tears were 1.3 times more likely to have a successful long-term outcome. In one study, medial meniscal tears after TPLO were 4 times more likely after arthrotomy with no medial meniscal release than after arthroscopy without medial meniscal release.
Once the stifle exploration is completed via arthroscopy, the stifle is stabilized with the surgeon’s technique of choice. Both the TPLO and TTA are designed to stabilize the joint and carry an excellent outcome for returning to weight-bearing activities and improving lameness/pain. Arthroscopy, when combined with TPLO or TTA, is the most definitive and least invasive way to diagnose and treat canine cranial cruciate ligament and meniscal disease. Arthroscopy is the standard of care for human stifle disease and is now readily available for our canine patients as well.
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