Bill Oxley Cranial closing wedge osteotomy (CCWO) was the first dynamic stabilization technique described for the treatment of cruciate disease by Barclay Slocum and Theresa Devine in 1984 [1]. The same authors described radial tibial plateau leveling osteotomy (TPLO) in 1993 [2], and subsequent studies of the originally reported techniques revealed radial TPLO to be associated with lower overall complication and reoperation rates [3–6]. However, more recently, key alterations to the original technique (including the use of locking TPLO plates and modified wedge geometry) have resulted in similar major complication rates of approximately 5–8% for both procedures [7]. Many surgeons prefer CCWO to TPLO in small dogs due to the larger size of the proximal osteotomy segment, although the procedure can be used in dogs of any size, and those with excessive tibial plateau angles (TPAs), without technical modification or adjunctive procedures [8, 9]. Additionally, CCWO can be easily adapted to concurrently manage medial patellar luxation and proximal tibial deformities. This chapter will describe CCWO preoperative planning and surgical technique, highlighting potential pitfalls that can lead to preventable complications. The recognition and management of postoperative complications will then be reviewed. The importance of accurate and thorough preoperative planning cannot be overemphasized in the context of avoidance of not only intraoperative but also many postoperative complications. Good planning not only reduces the risk of surgical errors but facilitates less tangible benefits such as minimized tissue handling and reduced surgical time which are equally important in the reduction of complication rates. Preoperative planning starts with appropriately positioned mediolateral and craniocaudal radiographs including the stifle, tibia, and talocrural joint. Criteria for optimal positioning are identical to those described in Chapter 10 for radial TPLO. The ability to accurately measure distances on the radiograph is essential and thus the use of a magnification marker and/or digital calibration is mandatory. Figure 9.1 Various CCWO wedge geometries. In all cases, the wedge angle is 30°. (a) Closing symmetrical (isosceles) wedge [7]. Note that the proximal (a) and distal (a’) osteotomies are the same length and meet at the caudal cortex. (b) Closing asymmetrical wedge [1, 10]. Note that a ≠ a’, and that the osteotomies meet at the caudal cortex. Since the wedge is asymmetrical, the osteotomy surfaces differ in length and either the cranial or caudal cortices may be aligned. Aligning the cranial cortices shifts the long axis as indicated by the vertical blue line. Note the similar axis shift between the isosceles wedge and the asymmetrical, cranial cortical aligned geometries. (c) Neutral/closing asymmetrical wedge [8, 11, 12]. Note that a = a’ but that the osteotomies meet cranial to the caudal cortex, but more caudal than the midpoint between the cortices. Again, since the wedge is asymmetrical, either the cranial or caudal cortices may be aligned. As with the original asymmetrical wedge, cranial cortical alignment with a caudal overhang is preferred to reduce long axis shift. (d) Neutral symmetrical (isosceles) wedge. Note that a = a’ and the osteotomies meet at the midpoint between the cortices. (e) Neutral asymmetrical wedge. Note that a ≠ a’ and the osteotomies meet at the midpoint between the cortices. Since the difference in length between a and a’ is small, the difference in long axis shift between the cranial and caudal cortical alignment options is also small. Various different CCWO osteotomy geometries have been described (Figure 9.1) [1, 7, 8,10–12]. The original technique employed a closing asymmetrical wedge with its base perpendicular to the long axis of the tibia [1, 10]. Since the wedge is asymmetrical, the osteotomy surfaces differ in length, and either the cranial or caudal cortices are aligned, causing an “overhang” at the opposite cortex (Figure 9.1b). Alignment of the cranial cortices minimizes tibial long axis shift. Reported modifications include a closing symmetrical (isosceles triangle) wedge [7], and several neutral/closing asymmetrical wedge variations [8, 11, 12]. While each of these variations has specific potential advantages, none has been shown to be definitively superior in terms of indication (normal and excessive TPA), biomechanics, complication rates or functional outcome. All CCWO variations will cause relative distalization of the patella in the trochlea, although this is rarely of clinical significance. It is important to note that the degree of patella baja induced is proportional to the overall angular correction rather than the cranial wedge length as has been suggested, and is thus the same for closing, neutral, and indeed opening wedges. Given the relative similarity of the various modified techniques, it is improbable that any one technique will prove to be definitively superior, and the choice will likely remain one of surgeon preference. A further variation on the original CCWO technique is to concurrently perform radial TPLO [13]. This technique has been recommended in cases with excessive TPA (>34°) since it permits plateau leveling without the very large proximal segment rotation necessary during radial TPLO or the large distalization of the patella during CCWO. However, the technique is technically challenging and associated with a high complication rate. More recently, CCWO as a stand‐alone alone technique has been reported with a much lower overall complication rate [8]. Although patella baja was not assessed in that study, no specific complications associated with patella position were reported and long‐term functional outcomes were very good. CCWO is therefore recommended in cases with excessive TPA; both the symmetrical isosceles and asymmetrical neutral variations can be used without additional technique modifications. The author is most familiar with the isosceles closing wedge technique which will be described here, but the general principles of planning and execution will apply equally to other variations. The osteotomy is templated by drawing an isosceles triangle‐shaped wedge as proximally as possible on the tibia while preserving sufficient bone stock for plate fixation and remaining an adequate distance distal to the tibial tuberosity. In dogs weighing more than 20 kg, a 10 mm distance is recommended, but in smaller dogs a minimum of 5 mm is acceptable (Figure 9.2). To achieve a tibial plateau angle of 5°, for starting TPAs of 20° or less the planned wedge angle should be the TPA −5°. To compensate for greater tibial long axis shift associated with larger starting TPAs, the planned wedge angle should be increased by 1° for each increase of 5° (Table 9.1). For example, a 31° wedge angle is recommended for a 33° starting TPA. Figure 9.2 Preoperative planning. An isosceles triangle wedge is templated with its proximal point on the cranial cortex located 5 mm distal to the proximal point of the tibial tuberosity in dogs weighing <20 kg, and 10 mm distal to that point in heavier dogs (distance ‘a’). Distance ‘b’ is then measured along the cranial cortex between the proximal and distal osteotomy lines. Table 9.1 Planned wedge angles based on preoperative tibial plateau angle (TPA). The sequence is continued for higher TPAs. Templating is performed to ensure that the proximal segment is large enough to accommodate the proximal portion of an appropriately sized plate; if necessary, the wedge can be replanned a few millimeters distally. In dogs weighing more than 50 kg, placement of a second, cranial plate should be considered. The increase in overall strength afforded by orthogonal plating is well established [14]; however, for stabilization of a CCWO osteotomy, a cranial plate is particularly well positioned to oppose “rock‐back” of the proximal osteotomy segment. As a secondary implant, even in very big dogs, a relatively small plate can be used (typically 2.4 mm). While placement of a single proximal locking screw may suffice, two screws are recommended; this will require distalization of the osteotomy by approximately 3–4 mm. If desired, the caudal point of the wedge where the equal length osteotomy lines intersect can be planned to be 1–2 mm cranial to the caudal cortex (Figure 9.3). Although not essential, if this caudal bridge of bone is preserved during the osteotomies, it will deform and act as a hinge as the ostectomy is closed, reducing the risk of torsional malalignment, enabling inspection of osteotomy plane parallelity before reduction, and facilitating maintenance of segment alignment for plating. Figure 9.3 The proximal and distal osteotomies meet at a point 1–2 mm cranial to the caudal cortex. Two distance measurements along the cranial tibial cortex are made and recorded for intraoperative reference. The first measurement is the distance between the proximal extent of the tibial tuberosity and the proximal osteotomy line, and the second is the length of the base of the isosceles triangle (Figure 9.2). The majority of potential complications that may occur during the surgical procedure are ultimately avoidable. Key principles include thorough preoperative planning, knowledge of the relevant anatomy, and careful attention to an appropriate surgical sequence which safely accomplishes the goals of surgery while minimizing tissue injury and surgical time. The surgical approach for CCWO is almost identical to that previously described for TPLO. If mini arthrotomy for meniscal inspection is to be performed, the medial incision is started at the level of the distal pole of the patella; if not, it is commenced slightly proximal to the tibial tuberosity. The distal extent of the incision is determined by the required exposure for placement of the planned plate. It is rarely necessary to expose the medial saphenous artery and vein which are typically just distal to the incision. An incision is made in the crural fascia a few millimeters caudal to the cranial border of the medial tibia. This incision is therefore caudal to the patella tendon insertion which should be clearly visible. Working from cranial to caudal, the fibrous pes ancerinus (the combined insertion of the sartorius, gracilis, and semitendinosus muscles) is elevated from the bone, taking care to preserve the medial collateral ligament which inserts at the caudal border of the cortex (Figure 9.4a). At this point, the entire pes ancerinus can be reflected caudally; this may be facilitated by a limited proximal extension of the fascial incision along the cranial border of the sartorius muscle. Figure 9.4 (a) The position of the proximal osteotomy on the cranial cortex is identified by measuring the preplanned distance distally from the point of insertion of the patellar tendon. In the image, a TPLO rotation gauge of the appropriate length is shown, but a ruler or calipers could be used. Note the change in color indicating the insertion of the patellar tendon at the proximal corner of the gauge. The bone is marked using any suitable method. The blue arrow indicates the medial collateral ligament; note the typical location of the proximal osteotomy a few millimeters distal to this. The green arrow indicates the position of the popliteal muscle elevation; note the limited proximal–distal extent. (b) The position of the distal osteotomy is measured from the proximal osteotomy position. Note that the proximal osteotomy position has been scored with the oscillating saw blade, and the gauge placed so as to include the kerf width. In this image, the distal position has been marked using diathermy. Opinions differ as to the necessity during radial TPLO of partial popliteal muscle elevation for swab placement for protection of the cranial tibial artery, but this step is strongly recommended during CCWO. This is due to the caudolateral angulation of the oscillating saw blade which is helpful to complete the caudal corticotomy. A periosteal elevator should be introduced between the cortex and the muscle at the level of the planned apex of the wedge (typically a few millimeters distal to the base of the collateral ligament insertion) (Figure 9.4a). The aponeurotic attachment to the bone is often quite fibrous and particular attention is warranted to ensure correct placement of the elevator to prevent unnecessary injury to the muscle or indeed the artery itself. The tip of the elevator is advanced caudally in contact with the cortex until it is felt to pass over the caudal border of the bone, often meeting some slight resistance halfway. The elevator is then moved proximally and distally a short distance, creating a space for insertion of a moist swab. This available space is small and need only be gently packed; a whole standard swab is generally far too large, and the excess is folded caudally or cut off. Correct positioning of the wedge ostectomy is a key step as an incorrect location could increase the risk of tibial tuberosity or other proximal segment fracture and could also hamper plate application. The planned positions of both osteotomies are identified with reference to the insertion point of the patellar tendon. This point is identified by the generally well‐demarcated transition line between the white striated appearance of the tendon and the cortical bone distally (Figure 9.4a). The planned distance distally from this point to the exit point of the proximal osteotomy is measured and the cortex marked (Figure 9.4a). This is easier if the tightly adherent fascia is elevated for a length a few millimeters more than the wedge base. The further distance distally to the exit point of the distal osteotomy is then measured and marked (Figure 9.4b). In very small patients, the doubled width of the kerf of the saw blade can represent a significant proportion of the length of the base of the wedge (Figure 9.5). This can lead to removal of a larger wedge than planned and thus an excessively low final TPA. To avoid this, care is taken that the blade is positioned distal to the proximal measured cortical mark and vice versa. Next, the equal length “legs” of the wedge are measured from their origins on the cranial cortex to intersect either at the caudal cortex or 1–2 mm cranial to this if planned. The intersection point can be found using a wedge osteotomy gauge (commercially available isosceles triangle gauges of various angles), an orthopedic ruler, or with experience by eye. The osteotomy positions are marked on the cortex, and if wished can be scored with the oscillating saw blade (Figure 9.6a).
9
Complications Associated with Cranial Closing Wedge Osteotomy
9.1 Introduction
9.2 Preoperative Planning
9.2.1 Isosceles Modified Cranial Closing Wedge Osteotomy (mCCWO) Planning
TPA
Wedge angle
≤20°
TPA − 5°
21–25°
TPA − 4°
26–30°
TPA − 3°
31–35°
TPA − 2°
36–40°
TPA − 1°
9.3 Intraoperative Complications
9.3.1 The Surgical Approach
9.3.2 Ostectomy Position
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