David L. Dycus and Don Hulse The center of rotation of angulation (CORA)‐based leveling osteotomy (CBLO) is a recently described osteotomy procedure to stabilize the cranial cruciate ligament (CCL)‐deficient stifle [1–3]. The concept of the CBLO is to modify the normal canine procurvatum to function with the normal recurvatum to eliminate cranial tibial thrust. The normal canine tibia has a proximal curvature (procurvatum) and as such a CORA exists. This means that the proximal anatomical longitudinal axis is not aligned with the distal longitudinal axis. It is the intersection of the proximal and distal anatomical lines (Figure 11.1) that defines the position of the CORA [3]. The angle formed at the intersection of the two lines will determine the magnitude of the CORA (Figure 11.2). As the angulation correction axis (ACA) is centered at the CORA, correction of the magnitude of the CORA will lead to the desired tibial plateau angle (TPA) and thus stabilization of cranial tibial subluxation through alignment of the proximal and distal longitudinal axes (Figure 11.3) [3]. Reported advantages of the CBLO include ample bone stock for fixation in both small/toy breeds and giant‐breed dogs, compression of the osteotomy resulting in stable/early healing [4], improved alignment, no secondary translation, near normal articular cartilage appearance on second‐look arthroscopy [5], facilitation of leveling in skeletally immature dogs with open proximal tibial physis [6], ease of procedure in dogs with an excessive TPA, facilitation of correction with concurrent patella luxation or patients with a compromised tibial crest, and allowing application of intraarticular auto/allografts. With any new procedure, the scientific evidence is emerging in regard to the advantages as well as the disadvantages. Currently, several aspects of the CBLO are being investigated, such as looking at the ease of the CBLO in patients with an excessive TPA, utilization of tibial tuberosity transposition with the CBLO in patients with patella luxation, and determination of the biomechanical strength of various fixations for the CBLO. Therefore, while some complications and prevention of complications have been identified, others may emerge in the future. An owner evaluation of the CBLO revealed that 77% of the dogs had full function, 19% had acceptable function, and 4% had unacceptable function. Figure 11.1 A lateral radiograph of the left stifle. Notice how the proximal anatomical longitudinal axis is not aligned with the distal longitudinal axis (green lines). The yellow arrow is the intersection of the proximal and distal longitudinal axis. This intersection is the location of the CORA. Complications were noted in 16% of the cases, and included incisional issues, late‐onset meniscal tear, and implant‐related complications [7]. The cases (3/11) that developed incisional issues were resolved with empirical antibiotic administration. In 8/11 cases that needed additional surgery, it was found that the majority (6/8) had late‐onset meniscal tears. The two remaining cases (2/8) that required additional surgery had implant‐related issues. In one of these cases the compression screw had become loose and was replaced without further incident. The other case was a juvenile dog that developed a tibial valgus secondary to screw malposition into the proximal tibial physis. The dog went on to undergo a tibial corrective surgery. All cases that required a second surgery returned to normal function [7]. Figure 11.2 The same lateral radiograph as in Figure 11.1; the angle formed at the intersection of the proximal and distal longitudinal axis is the magnitude of the CORA (white arrow). In this example it is 30.4°. Potential complications are suspected to be similar to other osteotomy procedures, including infection, patellar tendon thickening, postoperative meniscal tears, and pivot shift. These complications are covered elsewhere in this book and will not be discussed here. Complications identified to date specific to the CBLO include discomfort from utilizing a compression screw that is too long, impingement of the cranial distal tuberosity of the proximal segment with the cranial tibial cortex of the distal segment, opening of the cranial aspect of the osteotomy due to pull of the quadriceps, and induction of angulation and/or torsional proximal tibial changes. Figure 11.3 A lateral radiograph of the left stifle revealing preoperative planning of rotation of the proximal tibial segment to achieve the desired postoperative TPA (yellow arrow) and thus allowing alignment of the proximal and distal longitudinal axis. In this example the planned postoperative TPA is 8.0°. Given the pull of the quadriceps, it is recommended to use adjunctive fixation across the osteotomy in conjunction with the CBLO plate. This is commonly achieved with a compression or lag screw. This adjunctive fixation is placed before the addition of the CBLO plate. The goal is for the screw to begin at or just proximal to the patellar tendon insertion, cross the osteotomy in a perpendicular fashion and exit the caudal tibial cortex. Failure of the screw to cross the osteotomy perpendicular could result in loss of compression. Prior to placement of the compression screw, the length is measured using a standard depth gauge. It is important to remember that compression should occur across the osteotomy site so using a screw size that is equal to the depth gauge measurement will likely result in a screw that is 1–2 mm too long. If the popliteal muscle is elevated from the caudal tibial cortex then palpation or visualization of the screw can be seen. Once the screw has been placed and compression achieved, it should be noted how far caudally the screw penetrates the caudal tibial cortex. If a cannulated screw is used and noted to be too long, it should be cut flush with the caudal tibial cortex. If a noncannulated screw is used, then it can be backed out and a shorter one placed. Care should be taken not to damage the screw hole or allow movement of the osteotomy when replacing the compression screw. A compression screw that is too long (Figure 11.4) can irritate the gastrocnemius muscle, causing discomfort. Alternatively, if the screw is too long, it can cause pain while sitting due to the force of the screw into the gastrocnemius as the stifle if flexed.
11
Complications Associated with CORA‐Based Leveling Osteotomy
11.1 Introduction
11.2 Literature Review of Complications
11.3 Complications Specific to CORA‐Based Leveling Osteotomy
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