The stifle joint is a complex structure composed of the femorotibial (FT), femoropatellar (FP), and tibiofibular joints. The role of the FT joint is to support weight and the FP joint contributes to the extensor mechanism of the stifle joint (20,34). There are at least 15 ligaments in the stifle joint. The cranial cruciate ligament (CrCL), one of the most important stifle ligaments, is the main stabilizer during walking. The functions of the CrCL are to resist cranial tibial thrust, to limit excessive internal rotation of the tibia, and to prevent hyperextension of the stifle joint (5). Cruciate ligament disease is a common cause of pelvic limb lameness in dogs (8,32). Partial or complete rupture of the CrCL increases instability of the stifle joint, causes secondary osteoarthritis, meniscal injury, synovitis, and lameness, and alters the kinematics of the stifle joint (10,18). Cranial tibial wedge osteotomy (CTWO) and tibial plateau leveling osteotomy (TPLO) are both corrective osteotomies used to treat cranial cruciate ligament rupture (CCLR). The aim of both surgeries is to neutralize cranial tibial thrust, eliminate displacement of the tibia cranially in the stance phase, restore the stifle joint kinetics, and delay osteoarthritis (2,36). Theoretically, cranial tibial thrust depends on the tibial plateau angle (TPA) and the compressive force during walking (23). CTWO, the first corrective osteotomy designed by Slocum and Devine in 1984, achieves stabilization through changing the dynamics of the tibia by wedge osteotomy (35). By decreasing the TPA, the tibia does not displace cranially when weight-bearing (2). TPLO was developed by Slocum and has the same biomechanical principles as CTWO in terms of reducing the TPA (38). However, unlike CTWO, TPLO reduces the TPA through biradial osteotomy of the tibia. The selection of an appropriate surgical method is made based on the patient’s size and activity (13). After treating the CCLR by CTWO or TPLO, similar clinical outcomes were obtained (4,10) and no significant difference was identified in the degree of osteoarthritis prevention in previous studies (28). However, recently, TPLO has replaced CTWO as a common way to treat CCLR (38). When compared to CTWO, TPLO had the advantage of restoring limb function more similarly to a normal limb with lower complication rates (2,10,24). In addition, dogs that underwent CTWO revealed hyperextended gait patterns during the swing phase (27). Thus, for better understanding of those methods to apply them appropriately to the dogs with CCLR, the purpose of this study was to compare CTWO and TPLO through radiographic evaluation.

Experimental design

Five cadaver dogs euthanized for reasons unrelated to this study were used after they were donated by the owner. The dogs consisted of German Shepherd (n = 3), Belgian Malinois (n = 1), and mixed breed (n = 1), ranging in weight from 26.5 to 37.0 kg (mean weight [± SD], 32.9 ± 4.1 kg). There were three males and two females and their ages ranged from three to eight years (mean age [± SD], 6 ± 2 years). The right and left limb were assigned to the CTWO group and the TPLO group, respectively. The CrCL was transected by a minimally invasive approach using a scalpel blade before surgery. CTWO and TPLO were performed by the standard surgical methods. The CTWO on the right limb was performed with a 6° target TPA. After indicating the line for wedge osteotomy, an oscillating saw was used to cut the bone and the resected wedge was removed. A 3.5 mm dynamic compression plate was used to reduce the gap after osteotomy. The TPLO on the left limb was done to achieve 5° of the target TPA. Before the osteotomy, a jig was placed to stabilize the osteotomy. Then, biradial osteotomy was performed using a 2.4 mm TPLO saw blade, and a 3.5 mm locking TPLO plate was used for fracture reduction. A tibial compression test was performed after each operation. Pre- and postoperative radiographs were taken and analyzed using a digital image measurement program (eFilm Workstation 4.1, Merge Healthcare, Hartland, WI). The flexion and the extension of the stifle joint were determined by measuring the angle between lines parallel to the caudal cortical bone of the diaphysis at the femur and tibia (11,26). The TPA was evaluated by measuring the angle between the line connecting the center of the talus and the center of the intercondylar eminence of the tibia and the slope of the tibial plateau (Fig. 1A) (31). The anatomical mechanical axis angle (AMA-angle) was evaluated by measuring the angle between the anatomical axis and the mechanical axis of the tibia. The anatomical axis was defined as the line connecting the center of one-half and three-fourths of the tibial shaft. The mechanical axis was defined as the line extending from the center of the talus to the center of the intercondylar eminence of the tibia (Fig. 1B) (15). Changes in the AMA-angle generally reflect caudal angulation and transposition of the functional weight-bearing axis of the tibia against the anatomical axis. The tibial length was measured as the length from the middle of the distal ridge of the tibia to the center of the intercondylar tubercle (Fig. 1C) (38). Lateral radiographs of the stifle joint flexed to 90° were used to measure the patellar height according to the Labelle-Laurin method. The patellar height was evaluated by comparing the proximal pole of the patella with the tangent of the cranial cortical line of the femur (Fig. 1D) (1,33). The mechanical medial proximal tibial angle (mMPTA) and mechanical medial distal tibial angle (mMDTA) were measured on craniocaudal view radiographs (14). The frontal plane alignment (FPA) was defined as the summation of the mMPTA and the mMDTA, minus 180° from the result (Fig. 1E) (12,14).

Figure 1. Measurement of the TPA (A), AMA-angle (B), tibial length (C), patellar height (D), and mMPTA and mMDTA (E) by lateral radiographs of the stifle joint flexed to 90°. TPA, tibial plateau angle; AMA-angle, anatomical mechanical axis angle; mMPTA, mechanical medial proximal tibial angle; mMDTA, mechanical medial distal tibial angle.

Statistical analysis

The data were analyzed by Wilcoxon signed ranks test to compare the differences between the pre- and postoperative measurements. Analyses were performed using SPSS for Windows version 12.0 and a p-value of <0.05 was considered significant. All data are expressed as the mean ± SD.

The mean preoperative TPA was 28.8° ± 1.8° and 29.2° ± 1.3° in the CTWO group and the TPLO group, respectively, and decreased by 9.0° ± 2.9° and 5.4° ± 1.3° after surgery (Fig. 2). The flexion angle of the stifle joint was significantly increased in both groups (from 16.0° ± 4.6° to 29.8° ± 6.0° in the CTWO group and from 12.4° ± 5.9° to 28.4° ± 14.0° in the TPLO group). The extension angle of the stifle joint was significantly increased from 143.2° ± 6.4° to 149.8° ± 3.4° only in the CTWO group. No significant difference was measured in the TPLO group (from 141.6° ± 6.2° to 139.8° ± 6.1°). The mean AMA-angle was significantly decreased from 2.8° ± 0.8° to –2.4° ± 0.9° in the CTWO group and from 2.8° ± 0.5° to 1.8° ± 0.5° in the TPLO group. The mean preoperative tibial length was 19.8 ± 0.7 cm and 19.9 ± 0.8 cm in the CTWO group and the TPLO group, respectively, and decreased significantly by 19.2 ± 0.9 cm and 19.6 ± 0.8 cm postoperatively. The mean patellar height measured by the Labelle-Laurin method was significantly decreased from 0.3 ± 0.1 cm to –0.2 ± 0.2 cm in the CTWO group and no significant difference was identified in the TPLO group (from 0.4 ± 0.1 cm to 0.3 ± 0.2 cm). The mean preoperative mMPTA, mMDTA, and FPA were 95.0° ± 3.2°, 95.2° ± 6.7°, and 10.2° ± 3.9° in the CTWO group and 94.6° ± 2.7°, 97.2° ± 3.8°, and 11.8° ± 5.4° in the TPLO group, respectively. The mean postoperative mMPTA, mMDTA, and FPA were 90.8° ± 4.2°, 97.0° ± 3.2°, and 7.8° ± 5.1° in the CTWO group and 94.0° ± 2.2°, 95.4° ± 2.5°, and 9.4° ± 2.5° in the TPLO group, respectively. No significant pre- and postoperative differences were found in either group (Table 1).

Table 1 . Radiographic evaluation of the CTWO and TPLO groups (Mean ± SD).

	CTWO		TPLO
	Pre-OP	Post-OP	Pre-OP	Post-OP
Flexion angle (°)	16.0 ± 4.6	29.8 ± 6.0*	12.4 ± 5.9	28.4 ± 14.0*
Extension angle (°)	143.2 ± 6.4	149.8 ± 3.4*	141.6 ± 6.2	139.8 ± 6.1
TPA (°)	28.8 ± 1.8	9.0 ± 2.9*	29.2 ± 1.3	5.4 ± 1.3*
AMA-angle (°)	2.8 ± 0.8	–2.4 ± 0.9*	2.8 ± 0.5	1.8 ± 0.5*
Tibial length (cm)	19.8 ± 0.7	19.2 ± 0.9*	19.9 ± 0.8	19.6 ± 0.8*
Patellar height (cm)	0.3 ± 0.1	–0.2 ± 0.2*	0.4 ± 0.1	0.3 ± 0.2
mMPTA (°)	95.0 ± 3.2	90.8 ± 4.2	94.6 ± 2.7	94.0 ± 2.2
mMDTA (°)	95.2 ± 6.7	97.0 ± 3.2	97.2 ± 3.8	95.4 ± 2.5
FPA (°)	10.2 ± 3.9	7.8 ± 5.1	11.8 ± 5.4	9.4 ± 2.5

*p < 0.05 compared to preoperative value..

CTWO, cranial tibial wedge osteotomy; TPLO, tibial plateau leveling osteotomy; OP, operative; TPA, tibial plateau angle; AMA-angle, anatomical mechanical axis angle; mMPTA, mechanical medial proximal tibial angle; mMDTA, mechanical medial distal tibial angle; FPA, frontal plane alignment..

Figure 2. Pre- and postoperative craniocaudal (A, C) and mediolateral (a, c) images of the cranial tibial wedge osteotomy group and pre- and postoperative craniocaudal (B, D) and mediolateral (b, d) images of the tibial plateau leveling osteotomy group.

In a previous study, the kinematic analysis showed relatively hyperextended gait patterns in the swing phase after treatment by CTWO compared to TPLO (27). Changes in extension or flexion angles can lead to clinical lameness (18). These changes can be related to muscles, fibroconnective tissues, ligaments, or osseous deformities (9,22,30). In terms of osseous deformity, since the principle of CTWO and TPLO is to neutralize cranial thrust through deformation of the tibia (10,23), several factors were evaluated in this study. Although both groups showed significantly increased flexion angles, significantly increased extension angle was identified only in the CTWO group. The extension angle may be associated with swing phase gait as previous study noted that the leg that received CTWO became hyperextended during the swing phase (27). The AMA-angle, the angle difference between the mechanical and anatomical axis of the tibia, may be considered a predisposing factor for CCLR (15). The mechanical axis is a static weight-bearing axis, which is often used to evaluate the tibia (17). In this study, both groups showed significantly decreased postoperative AMA-angles. Compared to the TPLO group, the mechanical axis of the CTWO group moved cranially against the anatomical axis, thus becoming the tibial recurvatum (16,37). Osseous genu recurvatum, one of the osseous deformities of the knee joint, is hyperextension of the knee. As it is related to knee pain, weakness, loss of the range of motion, and abnormal gait, surgical repair is required before the deformity gets worse (6,22,29). Thus, tibial recurvatum as a result of CTWO needs to be considered when planning surgery. When evaluating the angle from the frontal plane of the tibia, the FPA obtained from mMPTA and mMDTA indicates the degree of angular deformity (14). The pre- and postoperative mMPTA, mMDTA, and FPA were not significantly different in both groups in this study. In terms of the FP joint, changes in FP alignment may be associated with patellar tendonitis (34). Whether congenital or acquired, patella baja is related to a decreased range of motion, knee pain, and rupture of the tendon of patella or quadriceps muscles in humans (7). In human studies, the measurement of patellar height is largely divided into direct (the relationship between the position of the patella and the femur) and indirect (the relationship between the position of the patella and the tibia) method and various methods have been reported (33). The Insall-Salvati method, an indirect method using the ratio of the patellar ligament length to the patella length, was described in normal dogs in a previous study (19). However, this method was not suitable in the present study as the ratio was not affected by both CTWO and TPLO, and secondary shortening of the patellar tendon (7) was also excluded because this study was done by cadavers. To compare pre- and postoperative changes in patellar height, the Labelle-Laurin method (33) was applied. As it was designed to diagnose only patella alta, the distance between the proximal pole of the patella and the tangent of the cranial cortical line of the femur was evaluated according to a previous study (1). Unlike TPLO, significantly decreased patellar height was identified after CTWO. It was presumed to be due to limb shortening after the wedge removal in CTWO (32). Further clinical evaluation is needed for postoperative patella baja. Finally, the postoperative TPA was relatively less close to the target TPA in the CTWO group compared to the TPLO group. Previous studies described that CTWO showed a cranial tibial long-axis shift due to the mechanical change from the removal of the bone fragment, causing the postoperative TPA to be further from the target TPA (3,21,25). In conclusion, more changes were identified in the CTWO group than the TPLO group in the radiographic comparison. From a mechanical point of view, the TPLO rather than the CTWO is recommended as a surgical procedure for large breed dogs with CCLR. Although further studies with larger numbers of dogs are needed, AMA-angle and patellar height measurement using the Labelle-Laurin method can be considered potential factors for comparing pre- and postoperative differences in radiographic evaluation.

The authors have no conflicting interests.