Evaluation of a contoured saw guide for tibial plateau leveling osteotomy in dogs

Abstract

Objective

To evaluate the effectiveness of a new contoured saw guide in tibial plateau leveling osteotomy (TPLO) by comparison with the conventional TPLO technique.

Study design

In vitro study using bone models and canine cadavers.

Sample population

Twenty epoxy‐resin bone models and 10 canine pelvic limbs from cadavers.

Methods

Tibial plateau leveling osteotomy procedures were performed on 20 bone models (10 using the contoured saw guide without a jig and 10 using the conventional jig‐assisted technique) and on 10 cadaveric limbs (five per group). Measurements included osteotomy angulation, medial cortical damage, eccentricity distance, postoperative tibial plateau angle, angular and torsional deformities, and surgical time. Data were obtained from specimen photographs and computed tomography images and then compared statistically.

Results

The contoured saw guide was related to improvements in bone models, with reduced osteotomy angle of inclination (0.97° vs. 3.4°, p = .038), osteotomy angle of torsion (257 vs. 2573 pixels, p < .001), and medial cortical damage (247 vs. 1866 pixels, p < .001). In cadaveric limbs, the contoured saw guide also demonstrated better performance, with reduced osteotomy angle of inclination (1.2° vs. 4.3°, p = .008) and osteotomy angle of torsion (2054 vs. 5039 pixels, p = .016).

Conclusion

Tibial plateau leveling osteotomy performed with the contoured saw guide achieved more precise osteotomy angulation and caused less medial cortical damage than the conventional jig‐assisted technique.

Clinical significance

The contoured saw guide may enhance osteotomy accuracy and minimize iatrogenic damage caused by the saw during TPLO but in this study it did not shorten surgical time.

Abbreviations

3D printer

3‐dimensional printer

ACO

actual centroid of the osteotomy

CCLR

cranial cruciate ligament repture

CT

computed tomography

DOE

distance of eccentricity

ICO

intended centroid of the osteotomy

mMPTA

medial mechanical proximal tibial angle

SLA

stereolithography apparatus

TC‐CnT

transcondylar and distal cranial tibial axes

TPLO

tibial plateau leveling osteotomy

1. INTRODUCTION

Cranial cruciate ligament rupture (CCLR) is one of the most common orthopedic conditions in dogs. ¹ , ² , ³ Complete or partial rupture of the cranial cruciate ligament causes cranial translation of the tibia, leading to instability, which can result in discomfort and potential complications. ⁴ Various surgical techniques have been developed to treat this condition. Tibial plateau leveling osteotomy (TPLO), introduced by Slocum, is among the most widely performed techniques. ⁵ , ⁶ It neutralizes cranial tibial thrust by rotating the tibial plateau via radial osteotomy of the proximal tibia. This procedure requires meticulous preoperative planning and precise execution to achieve optimal outcomes. ⁷

Inaccurate osteotomy angulation or orientation can lead to complications such as malalignment, inaccurate leveling, cortical damage, or tibial tuberosity fractures. ⁵ , ⁸ , ⁹ , ¹⁰ Precise osteotomy is therefore essential to improve TPLO success rates and minimize complications. However, it is particularly challenging to perform osteotomies on the curved medial surface of the tibia because this procedure requires proper alignment of the saw blade perpendicular to the long axis of the tibia. ¹¹

Jig techniques have been developed to assist with osteotomy during conventional TPLO. Prior to osteotomy, jig pins are inserted at the proximal and distal ends of the medial cortex, perpendicular to the long axis of the tibia. ⁶ The jig attaches to these pins to align the saw blade, ensuring perpendicular alignment with the long axis of the tibia. This approach helps maintain proper alignment of the tibial segments and reduces the risk of varus or valgus malalignment. ¹¹ , ¹² However, the advantages of using a jig during TPLO have not been proven definitively. One study demonstrated that osteotomies performed without a jig were positioned more accurately relative to those performed with a jig. ¹³ Another study showed no difference in limb malalignment between groups with and without a jig. ¹⁴ The use of a jig also introduces potential disadvantages such as increased surgical time or risk of jig pin placement within the joint. ¹⁵

This study aimed to evaluate the effectiveness of a new contoured saw guide in TPLO by comparing it with the conventional TPLO technique. We hypothesized that use of the contoured saw guide would improve osteotomy accuracy, reduce medial cortical damage, and shorten surgical time.

2. MATERIALS AND METHODS

Twenty left tibia bone models derived from the computed tomography (CT) data of a patient without orthopedic diseases or deformities, and 10 pelvic limbs collected from skeletally mature cadavers with no orthopedic diseases, were utilized as models in this study. The cadavers were euthanized for reasons unrelated to this study, in a manner approved by the institutional animal care (Jeonbuk National University) and use committee (approval number JBNU 2023‐224). Each cadaver was evaluated based on medical history, radiographs, and CT scans to confirm the absence of pathological abnormalities.

Tibial plateau leveling osteotomy was performed by the primary author and an assistant. Digital radiographs of the pelvic limbs were obtained (HF‐525 Plus Veat; Ecoray, Seoul, Korea). Measurements were then reassessed using a 16‐slice helical CT scanner (Alexion, TSX‐034A; Toshiba Medical Systems, Tochigi, Japan). The scan settings were 120 kVp, 150 mAs, a 512 × 512 matrix, 0.75 s rotation time, and 1 mm slice thickness.

The TPLO procedure was performed using the method with TPLO plates (TPLO‐L/R, Able Inc., Jeonju, Korea) as described by Slocum. ⁶ Precise osteotomy was achieved by measuring and applying the distances D1, D2, and D3, as previously reported. ¹⁶ D1 was defined as the distance from the osteotomy line to the tibial tuberosity, represented by a line perpendicular to the cranial border of the tibia. D2 was defined as the distance from the most proximal point on the osteotomy line to the most cranio‐proximal point on the tibial tuberosity. D3 was defined as the distance from the most caudal point on the osteotomy line to the caudal margin of the tibial plateau.

2.1. Contoured saw guide design

The contoured TPLO saw guide was designed using computer‐aided design software (Fusion 360, Autodesk, San Rafael, California) and manufactured using an epoxy stereolithography apparatus (SLA) with a resin three‐dimensional (3D) printer (Pixel One; Zerone, Gyeonggi, Korea) and epoxy resin (ZMD‐1000B CLEAR‐SG; Zenith, Daejeon, Korea). The guide was tailored to fit each saw and exhibited a crescent‐shaped surface that contacted the saw blade, holes for fixation to the tibia using a 1.2 mm K‐wire, a handle for manipulation, and a hole for a stopper pin (Figure 1A,B). When positioned distally to the osteotomy line, the contoured saw guide prevented slippage by guiding the convex side of the radial saw along its concave surface. The fixation pins were placed at three distinct angles to minimize saw vibration during the osteotomy, either entering the bone perpendicularly or oriented at 3° in both the craniocaudal and caudocranial directions (Figure 1C). The guide incorporated multiple pointed pins with a central stopper (Figure 1D), which increased the contact area between the guide and the curved medial tibia when pressed. This design enhanced stability while securing the guide to the tibia. The pins moved perpendicularly within the guide and were held in place by the stopper. This is defined as the pinpoint system (Figure 1E). When applying the guide with this system, the guide was pressed against the bone to ensure contact between the stopper pins and the bone, thereby facilitating alignment assessment. After alignment had been confirmed, fixation pins were inserted through the bone to secure the guide in place (Figure 1E).

FIGURE 1.

The design of the contoured saw guide for a tibial plateau‐leveling osteotomy (TPLO). The guide consists of a crescent‐shaped surface that contacts the saw blade, holes for fixation to the tibia with 1.2 K‐wire, a handle for manipulation, and holes for stopper pins (A). It comprises two parts connected by two screws (arrows) (B). The fixation pins have three trajectories. The hole for the fixation pin (yellow dashed‐and‐dotted line) is oriented perpendicular to the long axis. The cranial fixation pins (red solid line) are oriented approximately 3° in the craniocaudal direction. The caudal fixation pins (green dashed line) are oriented approximately 3° in the caudocranial direction (A, C). The center of the pin includes a stopper (arrowhead) larger than the diameter of the guide hole, and the tip of the pin is pointed (D). When compressed against the curved medial tibia, the pinpoint system increases the contact area between the guide and the bone, ensuring perpendicular alignment (E).

2.2. Part 1: TPLO performed on bone models

Twenty left tibial bone models were utilized in this study. Conventional TPLO using a jig and TPLO using a contoured saw guide without a jig were each applied to 10 models. The bone models were designed using computer‐aided design software (Fusion 360; Autodesk) based on CT data and manufactured using an epoxy stereolithography apparatus (SLA) with a resin 3D printer (A1; Sindoh, Seoul, Korea) and epoxy resin (Harpiks White; Zenith, Daejeon, Korea).

The bone canal of the 3D‐modeled tibia was aligned with the long axis, and holes crossing this axis were created. Both the jig and osteotomy procedures were performed perpendicular to the long axis. Additional holes were created perpendicular to the long axis and the sagittal plane in the distal diaphysis. A 3.0 mm K‐wire and a 1.0 mm K‐wire were inserted into these holes to serve as the long axis and reference points for photographic documentation of the frontal and sagittal positions of the bone models (Figure 2).

FIGURE 2.

The three‐dimensional‐ (3D)‐printed bone model. The bone canal of the 3D‐modeled tibia was defined along the long axis; hole crossing this axis was created (arrow). Hole perpendicular to the long axis and sagittal plane was created in the distal diaphysis (arrowhead). During data collection, a 3.0 K‐wire (A) was inserted into the long axis, and a 1.0 K‐wire (B) was inserted into the transverse hole, respectively, with the 1.0 K‐wire acting as a reference point.

2.2.1. Conventional TPLO with a jig on bone models

The jig pin was inserted prior to TPLO. The proximal jig pin was positioned approximately 3 mm distal to the articular surface and perpendicular to the long axis. The osteotomy was performed parallel to the jig. A distal jig pin was placed in the center of the diaphysis. ⁷ After the jig had been mounted, the TPLO procedure was conducted as described by Slocum. ⁶

2.2.2. Tibial plateau leveling osteotomy with a contoured saw guide on bone models

The TPLO procedure was performed using a contoured saw guide without a jig (Figure 3). The guide was positioned perpendicular to the medial side of the tibia and aligned based on the measured D1, D2, and D3 values. After the guide was pressed parallel to the tibia to ensure proper alignment, it was fixed to the bone using a 1.2 mm K‐wire. Osteotomy was then performed with a saw, guided by the secured contoured saw guide.

FIGURE 3.

The contoured saw guide applied to the bone model.

2.2.3. Measurements on bone models

Bone models were mounted so that the long axis, defined by a K‐wire inserted along the bone canal, was perpendicular to the table. The segment of the K‐wire in the diaphysis was aligned parallel to the table and the osteotomy line was assessed for perpendicularity to the long axis. Digital photographs of the caudal part of the bone models were taken; the resulting images were analyzed using imaging software (Desktop Ruler v3.8.6498; AVPSoft, Moscow, Russia). The angle of inclination was defined as the angle of osteotomy toward the proximal side from the medial side of the tibia (positive value), whereas the angle of declination was defined as the angle of osteotomy toward the distal side from the medial side of the tibia (negative value) (Figure 4A).

FIGURE 4.

Images used for data collection from the tibial bone model. To assess the angle of osteotomy inclination, photographic images were captured using a reference pin parallel to the table at a consistent distance from the caudal aspect. (A) Photographs of the medial and lateral cortices of the bone model were taken from a consistent distance to evaluate osteotomy angulation for torsion (B), medial cortical damage from the saw blade (C), and osteotomy position. The angle of osteotomy torsion was measured by creating a line that bisected the width at the most distal level of the osteotomy line, and measuring the section in which the osteotomy plane was visible cranially to this line. The osteotomy position was measured by overlaying photographs of the bone model taken from the same distance before and after osteotomy. A circle of the same size as the saw used in the surgery was formed to determine the actual centroid of the osteotomy (ACO) (orange dot with a solid line) and intended centroid of the osteotomy (ICO) (reddish dot with a dashed line), and the distance between them was subsequently measured (D).

Photographs of the medial and lateral cortices were also captured at a consistent distance to evaluate the osteotomy angulation for torsion, medial cortical damage caused by the saw blade, and osteotomy position. These parameters were analyzed using the previously described imaging software (Desktop ruler v3.8.6498, AVPSoft). Positive torsion was defined as the caudal angulation of the osteotomy from the medial side of the tibia (positive value), and negative torsion was defined as cranial angulation (negative value) (Figure 4B). Medial cortical damage in multiple areas of the bone models was observed due to saw blade slippage, defined as unintentional movement of the saw blade leading to iatrogenic medial cortical damage in the bone models (Figure 4C). The osteotomy position was determined by overlaying photographs of the bone models taken from a consistent distance before and after the osteotomy. The actual centroid of the osteotomy (ACO) and the intended centroid of the osteotomy (ICO) were identified, and the distance between them was measured. This measurement was defined as the distance of eccentricity (DOE) (Figure 4D). ¹⁷

2.3. Part 2: TPLO performed on cadavers

Ten pelvic limbs from five dogs were utilized in this study. Five limbs were randomly assigned to conventional TPLO with a jig and five to TPLO with the contoured TPLO saw guide. The limbs were disarticulated and stored at −21°C, then thawed at room temperature for 48 hours before the procedures. The postoperative tibial plateau angle (TPA) was planned to be 6°. ² , ¹⁸ After preoperative planning, the D1, D2, and D3 measurements were confirmed; the jig pins and contoured TPLO saw guide were mounted, as described in the bone model study. The saw size, the D1, D2, and D3 measurements, and the rotation distance of the proximal segment were confirmed preoperatively using a commercial radiographic planning tool (vPOP PRO; VetSOS Education Ltd. of Column House, Llangollen, UK).

2.3.1. Conventional TPLO with a jig performed on cadavers

Conventional TPLO was performed according to the method described by Slocum—the jig was applied in a manner consistent with its use in the bone model study. ⁶ After the completion of osteotomy the jig was removed and gauze packing was placed between the proximal segment and the tibia. A CT scan was performed before continuing with the remainder of the procedure.

2.3.2. Tibial plateau leveling osteotomy with a contoured saw guide on cadavers

Tibial plateau‐leveling osteotomy using the contoured saw guide was performed with a guide produced using 3D printing (Figure 5). Before the procedure, the D1, D2, and D3 measurements were marked on the tibia. The guide was placed over these marks and compressed to conform to its shape. A 1.2 mm K‐wire was inserted perpendicular to the sagittal plane to secure the guide to the bone. To ensure additional stability at least two additional pins were inserted at different trajectories through the two types of pinholes before the osteotomy. After osteotomy, the guide was removed and gauze was placed between the proximal segment and the tibia. A CT scan was then performed and a plate was placed to complete the procedure.

FIGURE 5.

The contoured saw guide applied to cadavers.

2.3.3. Measurements on cadavers

All procedures were completed and postoperative CT scans were obtained to produce three sets of data: preoperative, postosteotomy, and postoperative. Three‐dimensional reconstructions of the osteotomized tibia were generated using computer‐aided design software (Fusion 360). As in the bone model analysis, the ACO and ICO were measured from these reconstructions and the DOE was calculated. Osteotomy angulations in the dorsal plane (inclination) and transverse plane (torsion) were measured using postosteotomy 3D reconstructions and imaging software. Additional postoperative evaluations included TPA, deviation of the medial mechanical proximal tibial angle (mMPTA), and transcondylar and distal cranial tibial axes (TC‐CnT), ¹⁹ all of which were measured using postoperative 3D reconstructions. The times required for device attachment and osteotomy were also compared. Device attachment time was defined as the period from the start of jig pin insertion or pin insertion for guide application to immediately before the osteotomy. Osteotomy time was defined as the period from osteotomy initiation until its completion.

2.4. Statistical analysis

Statistical analyses were conducted using Prism software (GraphPad, San Diego, California). The Kolmogorov–Smirnov test was used to confirm the normality of data distributions. Depending on the data distribution, independent t‐tests (parametric tests) or Mann–Whitney U‐tests (nonparametric tests) were performed to compare the outcomes of the contoured TPLO saw guide and conventional TPLO with a jig. For parametric data, means, 95% confidence intervals (95% CIs), and standard deviations were calculated; medians and ranges were calculated for nonparametric data. The significance level was p < .05.

3. RESULTS

3.1. Part 1: TPLO performed on bone models

3.1.1. Angle of the osteotomy (inclination)

The angles of inclination were 0.97 ± 0.69° (95% CI, 0.48, 1.47) for the contoured saw guide and 3.4 ± 3.14° (95% CI, 1.16, 5.65) for the conventional TPLO with a jig, indicating a difference between groups (p = .038). In the dorsal plane, osteotomies performed with the contoured saw guide were closer to perpendicular than were osteotomies performed with the conventional TPLO technique (Figure 6A).

FIGURE 6.

Box plots of measurements after tibial plateau leveling osteotomy (TPLO) in the two groups of bone models. Angle of osteotomy inclination (A). Osteotomy torsion angle measured by the number of pixels (B). Medial cortical damage measured by the number of pixels (C). Distance from eccentricity (DOE) (D).

3.1.2. Angle of the osteotomy (torsion)

The number of pixels, indicating the angle of torsion, ² , ¹¹ were 257 ± 1064 (95% CI, −504, 1019) for the contoured saw guide and 2573 ± 976 (95% CI, 1874, 3271) for the conventional TPLO with a jig, indicating a difference between groups (p < .001). In the transverse plane, osteotomies performed with the contoured saw guide were more perpendicular than were osteotomies performed using the conventional TPLO with a jig (Figure 6B).

3.1.3. Medial cortical damage

The mean numbers of pixels indicating iatrogenic damage to the medial cortex ² , ¹¹ due to the blade were 247 ± 141 (95% CI, 146, 348) for the contoured saw guide and 1866 ± 554 (95% CI, 1470, 2263) for the conventional TPLO with a jig, indicating a difference between groups (p < .001). Osteotomies performed with the contoured saw guide resulted in less iatrogenic damage to the medial cortex relative to osteotomies performed using the conventional TPLO with a jig (Figure 6C).

3.1.4. Distance of eccentricity

The mean DOE, defined as the distance between the ACO and ICO, was 1.32 mm (range, 0.36–1.73) for the contoured saw guide and 1.6 mm (range, 0.61–2.64) for the conventional TPLO with a jig, with no differences between the two groups (p = .32) (Figures 6D, 7).

FIGURE 7.

Direction and distance of eccentricity (DOE) for osteotomies performed on tibial bone models using the contoured saw guide (triangle) and using traditional tibial plateau leveling osteotomy (TPLO) with a jig (square). Positive values on the x‐axis indicated cranial, while positive values on the y‐axis indicated proximal, with the intersection point (0, 0) indicating the intended centroid of the osteotomy (ICO). Each data point represents an actual centroid of the osteotomy (ACO).

3.2. Part 2: TPLO performed on cadavers

This part of the study involved 10 hind limbs from five dogs. The cadavers had an average age of 3.2 years (range, 3–4 years) and an average weight of 8.7 kg (range, 8.36–9.2 kg). In the contoured saw guide group, three left hind limbs and two right hind limbs were used; in the conventional TPLO with a jig group, two left hind limbs and three right hind limbs were used. All limbs were randomly assigned to the groups. Blades of 15 and 18 mm were selected based on preoperative planning, leading to the design of two types of contoured saw guides tailored for use in this study.

3.2.1. Angle of the osteotomy (inclination)

The mean angles of inclination were 1.2° (range, 0.9–3.4) with the contoured saw guide and 4.3° (range, 3.95–6.6) with the conventional TPLO with a jig, indicating a difference between groups (p = .008). In the dorsal plane, osteotomies performed with the contoured saw guide were closer to perpendicular than were osteotomies performed using the conventional TPLO with a jig (Figure 8A).

FIGURE 8.

Box plots of measurements after traditional tibial plateau leveling osteotomy (TPLO) on cadavers in the two groups. Angle of osteotomy inclination (A). Osteotomy torsion angle measured by the number of pixels (B). Postoperative tibial plateau angle (TPA) (C). Distance of eccentricity (DOE) (D). Deviation of angular deformity (mMPTA) (E). Deviation of torsional deformity (TC‐CnT) (F). Device application time (G). Osteotomy time (H).

3.2.2. Angle of the osteotomy (torsion)

The mean torsional angles, represented in pixels, ² , ¹¹ were 2054 (range, −2203–3113) for the contoured saw guide and 5039 (range, 2959–8494) for the conventional TPLO with a jig, indicating a difference between groups (p = .016). In the transverse plane, osteotomies performed with the contoured saw guide were closer to perpendicular than were osteotomies performed using the conventional TPLO with a jig (Figure 8B).

3.2.3. Postoperative tibial plateau angle

The mean preoperative TPA for all cadavers was 26.5° (range, 24.5–28.6). Rotations were performed with the goal of achieving a postoperative TPA of 6°. The actual postoperative TPA values were 6.4° (range, 5.3–8.1) for the contoured saw guide group and 7.6° (range, 6.4–8.3) for the conventional TPLO with a jig. No difference in postoperative TPA was observed between the two groups (p = .15) (Figure 8C).

3.2.4. Distance of eccentricity (DOE)

The DOE, defined as the distance between the ACO and ICO, was 1.38 mm (range, 0.37–2.54) for the contoured saw guide and 2.5 mm (range, 0.43–4.1) for the conventional TPLO with a jig. No difference was observed between the two groups (p = .31) (Figures 8D and 9).

FIGURE 9.

Direction and distance of eccentricity (DOE) for osteotomies performed on cadavers using a contoured saw guide (triangle) and traditional tibial plateau leveling osteotomy (TPLO) with a jig (square). Positive values on the x‐axis indicated cranial, while positive values on the y‐axis indicated proximal, with the intersection point (0, 0) indicating the intended centroid of the osteotomy (ICO). Each data point represents an actual centroid of the osteotomy (ACO).

3.2.5. Deviation of mMPTA

Postoperatively, the median deviations of the mMPTA of the tibia were 3.26° (range, 0.3–5.4) for the contoured saw guide group and 5.62° (range, 3.6–7.5) for the conventional TPLO with a jig group. There was no difference between the groups (p = .17) (Figure 8E). In all cases, the postoperative mMPTA increased, resulting in proximal tibial valgus.

3.2.6. Deviation of torsional deformity

Postoperatively, the median torsional deformities of the tibia were 2.8° (range, 1.5–3.8) for the contoured saw guide group and 3.34° (range, 2–5.5) for the conventional TPLO with a jig group, indicating no difference between groups (p = .65) (Figure 8F).

3.2.7. Device application time

The median device application times were 195 s (range, 145–285) for the contoured saw guide group and 230 s (range, 186–311) for the conventional TPLO with a jig group, indicating no difference between groups (p = .55) (Figure 8G).

3.2.8. Osteotomy time

The median osteotomy times were 160 s (range, 127–209) for the contoured saw guide group and 159 s (range, 122–192) for the conventional TPLO with a jig group, demonstrating no difference between groups (p = .69) (Figure 8H).

4. DISCUSSION

The accuracy of osteotomy during TPLO is a key factor influencing surgical outcomes. ¹¹ , ¹³ , ¹⁷ , ²⁰ To manage this factor, various assistive devices have been developed for proximal tibial osteotomies. This study demonstrates several potential advantages of the contoured TPLO saw guide compared with conventional jig‐based osteotomies. The results indicate that the contoured saw guide produces more precise osteotomy angulation for inclination and torsion with less medial cortical damage. However, no differences were observed between the two groups regarding postoperative TPA, deviation of deformity, DOE, or surgical time.

In this ex vivo study, the osteotomy group using the contoured saw guide achieved more accurate osteotomies in terms of angulation for inclination relative to the conventional TPLO with a jig (p < .05). Similarly, the osteotomy angulation for torsion was more precise in the group using the contoured saw guide than in the conventional TPLO with a jig group (p < .05). Accurate osteotomy angles offer several clinical benefits. An osteotomy that is orthogonal and perpendicular to the long axis facilitates rotation of the tibial proximal segment because the medial and lateral cortices remain equidistant from the intercondylar eminence. ²⁰ The performance of an osteotomy with excessive positive inclination or torsion may also require the plate to be placed more proximally or caudally than planned to prevent screws from crossing the osteotomy line, and this could result in intra‐articular screw placement. ¹¹ Moreover, an inaccurate osteotomy can shift the intercondylar eminences after tibial plateau rotation, causing a tibial long‐axis deviation that may affect the postoperative TPA. ²⁰ , ²¹ Inaccurate osteotomies can also lead to deformities in the proximal tibia. ¹⁸

A previous study of crescent guides, designed to improve osteotomy precision by providing a reference bar aligned along the tibial axes, failed to demonstrate improved accuracy. ¹² Based on the authors' experience, secure fixation of such guides is challenging, especially when the guide does not make complete contact with the curved medial surface of the tibia. To address this limitation, the contoured saw guide used in this study incorporated a pinpoint system. This system included multiple pins, each equipped with stoppers that moved perpendicularly, allowing the guide to provide stable support on irregular surfaces. This configuration is expected to increase the contact area between the guide and the curved surface of the tibia, thus improving the stability of the guide's fixation. However, this aspect was not evaluated in our study and further research is necessary. The use of multiple pins also facilitated intuitive assessment of perpendicularity to the long axis. Previous studies have emphasized that precise osteotomies depend on the ability to determine when an alignment device is correctly positioned. ¹² In this study, we suspected that the multiple pins in the contoured saw guide would be useful for assessing perpendicularity between the axis and the guide; however, this was not evaluated explicitly.

In the assessment of medial cortical damage using a bone model, the contoured saw guide group demonstrated less damage relative to the conventional TPLO with a jig group. Due to its morphological characteristics, the radial blade tends to “walk” along the curved surface of the tibia at the start of the osteotomy. The shape of the proximal tibia often directs this walking, cranially and distally. ¹¹ , ¹⁷ Consistent with previous reports, we observed distal walking of the blade in the jig group. The contoured saw guide mitigates medial cortical damage by positioning the osteotomy line distally and preventing the radial blade from walking in a distal direction.

The jig serves several functions during TPLO but its usefulness has been questioned. ¹³ , ¹⁴ In response, the radial saw guide (Synthes TPLO Saw Guide, Synthes Inc., West Chester, Pennsylvania), which is fixed to a specialized jig, has been introduced to facilitate osteotomy positioning and ensure precise angulation from the medial aspect. ¹¹ However, retrospective studies have identified complications associated with jig use, including a 5.3% incidence of intra‐articular placement involving a proximal jig pin in 696 dogs. ¹⁵ Another study showed that in 70% of cases, the actual osteotomy position was located distally compared with the intended position. This finding was attributed to the influence of the proximal jig pin. ¹⁷ Despite these issues, radial saw guides must be mounted on specialized jigs, thus requiring placement of jig pins. To address this limitation, the contoured saw guide used in this study was designed to align the saw perpendicular to the tibial long axis, operating independently of a jig. Pins were applied to the distal tibia, eliminating the possibility of intra‐articular pin insertion.

The importance of osteotomy positioning has been emphasized in several studies. Clinically, osteotomy location can increase the risk of tibial tuberosity fractures or alter postoperative TPA due to shifts in the tibial long axis. ⁸ , ¹⁰ , ²⁰ , ²¹ Mathematical models evaluating osteotomy positions have indicated that positioning the osteotomy center cranially or distally could result in increased postoperative TPA. ²⁰ In the present study, we found that the osteotomy center was generally biased toward the distal side; postoperative TPA was higher than the planned TPA. Although various factors may influence postoperative TPA, our findings are consistent with those of previous studies. ²⁰

Both groups showed an increase in mMPTA, resulting in valgus. A previous study has emphasized that plateau rotation angle, osteotomy angle, and reduction technique influence deformity. ¹⁸ The deviation of the osteotomy angle was not significant in either group, and the mean preoperative TPA for all cadavers was 26.5°; however, valgus was still observed. We therefore speculate that valgus occurred due to the reduction technique, but this was not assessed in this study. Further study is needed to evaluate reduction techniques in TPLO using a guide.

Overall, we found no difference in device application time or osteotomy time between the two groups, which contradicts our hypothesis that surgical time would be reduced. This finding differs from results in previous studies involving novice surgeons. ¹² We initially assumed that jig pin placement might require more time due to the risks of intra‐articular penetration and the need for precise perpendicular alignment with the long axis. However, there was no significant difference in device application time between the two groups (p = .55). Several factors may explain this result. First, the jig pins were placed by an experienced surgeon, which likely reduced the time needed relative to previous studies. Second, during guide attachment, at least three pins were used to secure the guide to the bone. Additional pins were added after alignment assessment, extending the guide application time. As individual differences among surgeons can influence time variables, further studies are needed to understand this factor better.

This study had some limitations. First, a limited number of cadavers were used. Further prospective comparative studies are needed to evaluate the advantages of this guide. Second, although the procedures were performed by a single surgeon to minimize variability among surgeons, the sequential rather than simultaneous execution of surgeries may have influenced the results due to skill improvement over time. However, this factor was not formally assessed. The observer responsible for all measurements was also aware of the procedure details, which may have introduced subjective bias.

In conclusion, the contoured TPLO saw guide without a jig demonstrated improvement over conventional TPLO with a jig in performing accurate osteotomies and reducing iatrogenic damage caused by the saw. However, it did not reduce surgical time. Based on these findings, further clinical research involving contoured TPLO saw guides is warranted.

FUNDING INFORMATION

This research was supported by “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2023RIS‐008).

CONFLICT OF INTEREST

The authors declare no conflicts of interest related to this report.

Supporting information

Video S1. Pinpoint system. The guide includes multiple pointed pins with a stopper. The pins move perpendicularly within the guide and are secured in place by the stopper. This system is designed to improve contact between the guide and the bone when pressing the guide against the bone.

Jeong S, Yu Y, Heo S. Evaluation of a contoured saw guide for tibial plateau leveling osteotomy in dogs. Veterinary Surgery. 2025;54(7):1397‐1408. doi: 10.1111/vsu.14258