Arthroscopy of the Stifle. Traditional & Nontraditional Portal Sites
Traditional Portal Sites and Technique
The arthroscope portal is located lateral to the patella tendon approximately midway between the tibial tubercle and the inferior pole of the patella. The instrument port is placed at the same proximodistal level but medial to the patella tendon. The egress port is placed superior and medial to the patella. Once the egress port is established, a scope port is made and the arthroscope inserted. A systematic examination of the supra-patella compartment and trochlear ridges is performed. As the joint is flexed, the arthroscope is positioned lateral to the intercondylar notch. Further examination of the joint is limited by the presence of the fat pad. The latter structure is generally inflamed and obscures visualization of the cruciate ligaments and menisci. A viewing window through the fat pad must be made before thorough examination of the ligaments and menisci is possible. Use of a motorized shaver is the best method to remove inflamed fat pad. The arthroscope is positioned to view the intercondylar notch and top of the fat pad. An instrument port is established as described above and the shaver blade inserted. The shaver blade is visualized and the shaver window positioned away from the lens of the arthroscope. Tissue is removed by the suction and cutting action of the shaver blade. As a viewing window is established through removal of fat pad, the cruciate ligaments (often remnants of the CCL) are examined. Remnants of a torn CCL can be removed with the motorized shaver. Both the lateral and medial menisci are examined for the presence of fraying or classical bucket handle tears. The medial meniscus is most commonly injured (bucket handle tear, radial tears, or fraying). Observation of the posteromedial compartment (medial meniscus) is performed by placing a Hohmann retractor through a superior portal. Small hand instruments such as a grasper or probe are used to hold a torn section of meniscus; the damaged meniscus is then removed with hand instruments or a motorized shaver.
Non-traditional Portal Sites
One alternate approach is to use a 1.9mm or 2.3mm arthroscope placed into the joint through a superior portal. The joint is distended with LRS; a 3mm incision is made with a number 11 blade through the skin and soft tissue but does not enter the joint. The arthroscope enters the joint medial to the patella tendon just distal to the inferior pole of the patella. The conical blunt obturator and arthroscope sheath are pushed through the soft tissue into the joint. The tip of the obturator is directed toward the intercondylar notch medial to the fat pad. Egress is established with an 18 gage needle. From this point, the camera and light post are adjusted to view the medial and lateral compartments. If needed, a second portal is made lateral to the patella tendon just distal to the inferior pole of the patella. A small Hohmann retractor can be placed to distract and open the medial compartment. An instrument portal can be established medially at the standard position.
The advantage of the superior portal technique is that the surgeon is able to explore the medial and lateral compartments without the need to create a viewing window. The disadvantages of this technique are the small field of view available through the smaller arthroscopes. The close proximity view with proliferative synovia and fat pad can make treatment of meniscal injuries difficult.
The Posteromedial Arthroscope Portal
A posteromedial portal can be established to view the intra-articular structures in the posterior medial compartment. Joint capsule, articular surface of the fabella, posterior cruciate ligament, posterior meniscocapsular ligament, posterior articular surface of the femoral condyle are readily examined through this portal. The arthroscope enters the joint just distal to the inferior pole of the medial fabella. A 2.3mm or 2.7mm arthroscope is used for this technique. The inferior pole of the medial fabella is palpated; a 3-4mm skin incision is made and the arthroscope sheath with blunt conical obturator pushed into the joint. Egress is established with an 18 gage needle placed into the anterior medial compartment. The camera head and light post are positioned to examine the posterior cruciate ligament, posterior meniscocapsular ligament, and articular margins of the femoral condyle and fabella.
Indications for this arthroscope site include suspected isolated posterior cruciate ligament injuries, isolated medial meniscal injury, and other suspected posteromedial pathology. Limitations include small working space for establishing a working instrument portal.
Lateral meniscal tears: The majority of meniscal injuries involve the medial meniscus. The medial meniscus is firmly attachment to the tibial plateau and moves with the plateau during the abnormal AP translation associated with a torn CCL. As the medial tibial plateau and medial meniscus translate cranially in the CCL deficient stifle, the medial femoral condyle compresses the body of the medial meniscus. The result is the classical bucket handle tear. The lateral meniscus is loosely attached to the tibial plateau rendering it more mobile; the lateral meniscus is able to move with the lateral femoral condyle during abnormal AP translation rendering it less prone to injury. Nevertheless, lateral meniscal injury does occur and in some cases results in serious lateral compartment degeneration. Lateral meniscal injury occurs in conjunction with cranial cruciate ligament injury, following ACL treatment, or as an isolated injury. Small radial tears arising from the inner free edge of the lateral meniscus are a common arthroscopic finding with long standing ACL injury. They are considered non-clinical and no treatment is necessary. However, large radial tears and bucket handle tears of the central or caudal body of the lateral meniscus are occasionally noted with ACL tears. These are managed by excision of damaged meniscus.
Previous studies have shown the incidence of postliminary meniscal tears following treatment of CCL injury to range from 5%-15% depending upon technique. Slocum indicated that latent meniscal tears associated with the TPLO procedure could be as high as 40%. The overwhelming majority of postliminary meniscal tears are medial meniscal tears but lateral meniscal tears do occur. These have generally been bucket handle tears in the author's experience and are managed with excision of damaged meniscus. One should not do a complete lateral meniscectomy or a meniscal release of the lateral meniscus. Loss of a functional lateral meniscus may lead to severe lateral compartmental OA.
Osteoarthritis (OA) of the stifle joint is a leading cause of rear limb dysfunction in the dog. Non-inflammatory OA is often secondary to an underlying problem; the most frequent presentation being that of a partial tear of the cranial cruciate ligament. At times, no palpable instability is detected and the diagnosis of partial CCL injury is based on the radiographic presence of OA. Surgical intervention in these cases ordinarily confirms the presence of CCL injury. In a small percentage of cases, open arthrotomy or arthroscopy cannot confirm injury of the CCL. In these cases, an isolated lateral meniscal tear is suspected. Surgical findings are comparable in all cases: 1. moderate synovitis and osteophyte formation, intact cranial and caudal cruciate ligaments, intact medial meniscus, complete transverse or oblique radial tear of the posterior horn of the lateral meniscus. Long standing cases will develop erosive eburnation of the femoral condyle and tibial plateau.
Articular cartilage lesionsof the medial or lateral femoral condyle associated with TPLO. TPLO is an accepted method for treatment of the CCL deficient stifle. Although a very successful technique complications are reported to be as high as 28%. The majority of complications are self-limiting and rarely require surgical intervention. The author has seen five cases where the osteotomy has healed but the dog has not returned to normal function. No abnormal physical or radiographic findings are apparent in these cases. Second look arthroscopy has shown erosion of articular cartilage of the medial femoral condyle in each case. Assessment was that the femoral condyle was displaced forward and articulating with hardened cranial horn of the medial meniscus. Treatment consisted of motorized shaving of the soft tissue and microfracture of the abraded lesion bed.