Tibial Plateau Angles in Small- and Large-Breed Dogs with Cranial Cruciate Ligament Rupture: A Retrospective Study of 132 Cases

Abstract

Objective

Cranial cruciate ligament rupture (CrCLR) is a common orthopaedic condition in dogs, with tibial plateau angle (TPA) considered a potential predisposing factor. This study compared TPA, age and signalment between CrCLR and intact cranial cruciate ligament dogs in small- and large-breed groups.

Study Design

Medical records from 171 client-owned dogs (222 tibiae) diagnosed at the Veterinary Teaching Hospital, Khon Kaen University, between February 2020 and December 2024, were analysed.

Results

Dogs in the CrCLR group (132 dogs) had a significantly higher TPA (25.28 ± 4.65 degrees) than those in the intact cranial cruciate ligament group (21.49 ± 4.15 degrees, p < 0.001). Among CrCLR dogs, small-breed dogs exhibited a higher TPA (26.04 ± 4.74 degrees) compared with large-breed dogs (24.25 ± 4.33 degrees, p < 0.05). Receiver operating characteristic analysis indicated a moderate predictive value of TPA in diagnosing CrCLR, with higher accuracy in small-breed dogs (area under the curve: 0.76, optimal cut-point: 21.65 degrees) compared with large-breed dogs (area under the curve: 0.66, optimal cut-point: 23.95 degrees).

Conclusion

Although TPA was higher in CrCLR dogs, it is not an individual determinant of the condition. Further research is required to explore additional contributing factors and enhance predictive models.

Keywords

CrCLR - ROC - stifle - TPA - CCLD

Introduction

The cranial cruciate ligament (CrCL) is located within the stifle joint and is responsible for limiting hyperextension, tibial internal rotation, and craniocaudal translation of the tibia relative to the femur. During weight-bearing, mechanical forces generate a cranial shearing force known as cranial tibial thrust, caused by the craniocaudal inclination of the tibial plateau.[1] The magnitude of cranial tibial thrust increases with the inclination of the tibial plateau. The CrCL counteracts the cranial tibial thrust force through passive stabilization.[1] [2]

Cranial cruciate ligament rupture (CrCLR) is the most common orthopaedic condition in dogs, with a higher prevalence in large breeds.[1] [3] [4] [5] [6] The condition arises from a combination of biological and biomechanical factors. Biological factors include breed, body weight, age, sex, neuter status and genetics. Biomechanical factors involve stifle joint conformation, bone alignment, stance position, muscle strength, narrowed intercondylar notch and an elevated tibial plateau angle (TPA).[3] [5] [6] [7] [8] [9] [10] [11]

Caudal angulation of the proximal tibia results in an elevated TPA. Studies indicate that a higher TPA increases the incidence of CrCLR.[4] [12] TPA is measured on a mediolateral radiographic view of the tibia, stifle joint and femur. It is defined as the angle between tibial plateau axis intersecting with a line perpendicular to the mechanical axis of the tibia.[13] In intact CrCL small-breed dogs, TPA ranges from 20.21 to 32.00 degrees, while in large-breed dogs, it ranges from 18.10 to 27.97 degrees.[4] [5] [6] [12] [14] [15] In dogs with CrCLR, TPA range from 27.12 to 32.40 degrees in small breeds and from 23.80 to 28.20 degrees in large breeds.[3] [5] [12] [14] [15] [16]

Further investigation is needed to clarify the risk factors for CrCLR, with TPA considered a potential contributor. However, more evidence is required to establish TPA as a primary predisposing factor. The aim of this study was to evaluate TPA in dogs with CrCLR, categorized into small-breed and large-breed groups, compared with intact CrCL dogs. Additionally, it examined the relationship between TPA and gender as well as the association between neuter status and the occurrence of CrCLR. We hypothesized that dogs in the CrCLR group would exhibit a higher TPA than those in the intact CrCL group based on radiographic evaluation.

Materials and Methods

Animals

The data obtained from the medical records of the Veterinary Teaching Hospital, Khon Kaen University (VTHKKU), between February 2020 and December 2024, were reviewed. The small-breed dogs were classified as those with a projected adult body weight of less than 15 kg, and large-breed dogs with over 15 kg.[3] Information recorded included age, sex, breed, body weight, neuter status, side of the effect limb and TPA of each limb.

Cranial Cruciate Ligament Rupture Diagnosis and Tibial Plateau Angle Measurement

Cranial cruciate ligament rupture was diagnosed based on physical examination and confirmed by a positive cranial drawer sign and tibial compression test. Additionally, CrCLR was confirmed through stifle arthrotomy before applying osteotomy or extracapsular stabilization techniques.

The mediolateral radiographic views were retrieved from the radiograph database, the Picture Archiving and Communication System and reviewed on a 32-inch 4K monitor (Dell UP3216Q, Dell Inc., TX) at VTHKKU, the stifle and tarsal joint were positioned at a 90-degree angle to the tibia, ensuring adequate superimposition (<4-mm overlap) of the intercondylar eminence of the proximal tibia. Tibial plateau angle evaluation was conducted using a software tool (Vue Motion, version 12, Phillips Medical Systems Nederland B.V., Best, Netherlands). Tibial plateau angle measurement involved three lines: (1) A straight line drawn from the intercondylar eminence of the proximal tibia to the center of the talus, representing the mechanical axis of the tibia (line a); (2) a line connecting the cranial and caudal edges of the medial tibial condyle, defining the tibial plateau axis (line b); (3) a perpendicular line to the tibial mechanical axis intersecting the tibial plateau slope line (line c). The TPA was measured as the angle formed by the intersection of lines b and c ([Fig. 1]).[5] [15]

Fig. 1 Measurement of tibial plateau angle. A line from the intercondylar eminence to the center of the talus represents the mechanical axis of the tibia (line, a). A line connecting the cranial and caudal edges of the medial tibial condyle, defining the tibial plateau axis (line, b). A line perpendicular to the tibial mechanical axis and intersected with the tibial plateau slope (line, c). The tibial plateau angle was measured at the angle formed by the intersection of lines b and c.

The CrCLR diagnosis was made by a veterinary surgeon with 17 years of experience (S.H.), while TPA measurements were performed by a veterinary surgeon with 8 years of experience (P.K.), with an average of two measurements per dog. Dogs over 6 years of age, presented for routine health check-up programs and radiograph evaluation of hip and stifle joint, without any evidence of stifle disease, were selected as representatives of the intact CrCL group in this study.

Statistical Analysis

Descriptive statistics were used to summarize data on TPA, age and body weight, expressed as means and standard deviations. Comparisons of TPA and age between small- and large-breed dogs, as well as between CrCLR and intact CrCL groups, were conducted using independent t-tests. Categorical variables, including breed, gender, and affected limb side, were analysed with Pearson's chi-square test. Receiver operating characteristic (ROC) analysis was performed to determine the cut-point values of TPA for distinguishing between intact CrCL and CrCLR groups. The ROC curves yielded the appropriate sensitivity and specificity of cut-point TPA for screening CrCLR in small- and large-breed dogs, and the area under the curve (AUC) was calculated to evaluate predictive performance. A p-value of <0.05 was considered significant. All analyses were conducted using STATA statistical software version 14.1 (StataCorp LLC, TX).

Results

A total of 171 client-owned dogs (n = 222 tibiae) were included in this study, consisting of 132 dogs (n = 172 tibiae) in the CrCLR group and 39 dogs (n = 50 tibiae) in the intact CrCL group. The CrCLR group comprised 73 females and 59 males, with a mean TPA of 25.28 ± 4.65 degrees (range: 16.00–49.91 degrees) and an average age of 6.86 ± 3.35 years (range: 1–14 years). In the intact CrCL group, the mean TPA was 21.49 ± 4.15 degrees (range: 13.45–29.15 degrees), which was significantly lower than in the CrCLR group (mean difference: 3.79 degrees, p < 0.001).

No significant association was found between TPA and gender in either the CrCLR group (p = 0.35) or the intact CrCL group (p = 0.44). Similarly, neutered dogs showed no significant relationship in males (chi-square test, p = 0.15) or females (chi-square test, p = 0.90) when compared with intact CrCL dogs. Furthermore, gender distribution did not significantly differ between the CrCLR and intact CrCL groups (chi-square test, p = 0.25).

In the CrCLR group, 74 small-breed dogs (n = 99 tibiae) had a mean TPA of 26.04 ± 4.74 degrees (range: 17.90–49.91 degrees) and an average age of 7.74 ± 2.88 years (range: 2–14 years) and a mean body weight of 7.68 ± 5.36 kg. In the intact CrCL group, which included 29 small-breed dogs (n = 33 tibiae), with a significantly lower mean TPA of 21.27 ± 4.48 degrees (range: 13.45–29.15 degrees; mean difference: 4.77 degrees, p < 0.001). Among large-breed dogs with CrCLR (58 dogs, 73 tibiae), the mean TPA was 24.25 ± 4.33 degrees (range: 16.00–33.00 degrees), with an average age of 5.67 ± 3.58 years (range: 1–14 years) and a mean body weight of 31.52 ± 9.64 kg. In the intact CrCL group, 11 large-breed dogs (n = 17 tibiae) had a mean TPA of 21.92 ± 3.52 degrees (range: 15.34–28.02 degrees), which was significantly lower than in large-breed dogs with CrCLR (mean difference: 2.33 degrees, p < 0.05).

Small-breed dogs with CrCLR revealed a significantly higher TPA than large-breed dogs (mean difference: 1.79 degrees, p < 0.05) and were significantly older on average (mean difference: 2.07 years, p < 0.001). There was no significant difference in TPA between unilateral and bilateral CrCLR cases (p = 0.90). Breed analysis showed Mixed Breed, Pomeranians and Chihuahuas were the most frequently affected by CrCLR, as shown in [Table 1]. Signalment and summary data are presented in [Table 2].

Table 1 Breed distribution and mean tibial plateau angle of cranial cruciate ligament rupture dogs

Breed (dogs, limbs)		Mean tibial plateau angle ± SD (degrees)	Mean age ± SD (years)	Mean weight ± SD (kg)
American Bully	(11, 14)	22.92 ± 4.61	4.57 ± 3.27	31.65 ± 4.42
Beagle	(2, 2)	28.12 ± 5.07	6.50 ± 4.95	24.20 ± 0.00
Border Collie	(1, 1)	27.00 ± 0.00	6.50 ± 0.00	17.20 ± 0.00
Chihuahua	(18, 25)	27.49 ± 5.54	8.04 ± 3.19	4.82 ± 1.43
Cocker Spaniel	(1, 2)	31.48 ± 1.67	12.00 ± 0.00	19.80 ± 0.00
Dobermann	(1, 1)	24.00 ± 0.00	2.00 ± 0.00	29.50 ± 0.00
Fila Brasileiro	(1, 1)	17.58 ± 0.00	11.00 ± 0.00	39.50 ± 0.00
French Bulldog	(1, 1)	29.58 ± 0.00	5.00 ± 0.00	14.20 ± 0.00
Golden Retriever	(5, 6)	23.27 ± 5.22	3.67 ± 1.03	36.12 ± 13.58
Great Pyrenees	(1, 1)	29.00 ± 0.00	11.00 ± 0.00	37.70 ± 0.00
Labrador Retriever	(10, 12)	23.67 ± 5.08	4.58 ± 3.68	39.18 ± 4.66
Mixed Breed	(29, 35)	25.82 ± 4.11	7.26 ± 3.43	23.95 ± 11.53
Pit Bull Terrier	(1, 2)	23.99 ± 0.01	5.00 ± 0.00	32.10 ± 0.00
Pomeranian	(22, 30)	23.14 ± 2.56	7.63 ± 2.24	5.35 ± 2.66
Poodle	(9, 15)	27.15 ± 5.59	7.93 ± 2.99	9.03 ± 4.07
Pug	(1, 1)	21.22 ± 0.00	12.00 ± 0.00	9.60 ± 0.00
Rottweiler	(2, 3)	23.18 ± 0.91	1.67 ± 1.15	37.60 ± 5.90
Shih Tzu	(4, 4)	29.60 ± 5.36	8.50 ± 3.70	8.98 ± 4.85
Siberian Husky	(3, 4)	25.24 ± 4.10	7.75 ± 2.06	30.50 ± 0.00
Thai Bang Kaew	(3, 3)	26.05 ± 3.34	5.33 ± 3.06	23.00 ± 10.89
Welsh Corgi	(3, 4)	24.35 ± 5.45	4.25 ± 1.50	16.96 ± 1.97
Yorkshire Terrier	(3, 5)	26.28 ± 1.99	7.80 ± 3.35	2.73 ± 0.71

Abbreviation: SD, standard deviation.

Table 2 Comparison of mean tibial plateau angle, age, and signalment between cranial cruciate ligament rupture and intact cranial cruciate ligament dogs in small- (<15 kg) and large-breed dogs (≥15 kg)

	Small breed		Large breed
	Intact cranial cruciate ligament (n = 33 tibiae)	Cranial cruciate ligament rupture (n = 99 tibiae)	Intact cranial cruciate ligament (n = 17 tibiae)	Cranial cruciate ligament rupture (n = 73 tibiae)
Tibial plateau angle (degrees)
Mean ± SD (range)	21.27 ± 4.48[a] (13.45–29.15)	26.04 ± 4.74[a,b] (17.90–49.91)	21.92 ± 3.52[a] (15.34–28.02)	24.25 ± 4.33[a,b] (16.00–33.00)
Age (years)
Mean ± SD (range)	8.09 ± 2.32 (6.00–15.00)	7.74 ± 2.88b (2.00–14.00)	8.00 ± 1.84 (6.00–12.00)	5.67 ± 3.58b (1.00–14.00)
Sex (dogs)
Male  Female	12 16	32 42	9 2	27 31
Side of tibia (tibiae)
Left tibia  Right tibia	– –	54 45	– –	38 35
Cranial cruciate ligament rupture (dogs)
Unilateral  Bilateral	– –	49 25	– –	43 15

Abbreviation: SD, standard deviation.

^a,b Indicate a significant difference between the mean values of each group and breed size, respectively.

The ROC curve for TPA in small-breed dogs yielded an AUC of 0.76, with an optimal cut-point TPA of 21.65 degrees (sensitivity: 0.85, specificity: 0.55). Conversely, the ROC curve for TPA in large-breed dogs showed an AUC of 0.66, with an optimal cut-point TPA of 23.95 degrees (sensitivity: 0.58, specificity: 0.76; [Fig. 2]).

Fig. 2 The receiver operating characteristic curve for tibial plateau angle in small-breed dogs indicates the empirical optimal cut-point along the curve, with an area under the curve of 0.76 (A). The receiver operating characteristic curve for tibial plateau angle in large-breed dogs indicates the empirical optimal cut-point along the curve, with an area under the curve of 0.66 (B).

Discussion

In this study, we found that the average TPA in the CrCLR group was significantly higher than the TPA in dogs free of CrCLR, with a mean difference of 3.79 degrees. Among dogs with CrCLR, small-breed dogs had a significantly higher TPA compared with large-breed dogs, with a mean difference of 1.79 degrees. However, this difference was relatively small. In contrast, previous studies have reported a greater difference in mean TPA between small- and large-breed dogs, ranging from 3.1 to 4.9 degrees.[3] [15] Despite this variation, numerous studies have consistently demonstrated that dogs with CrCLR, regardless of breed size, exhibit higher TPA compared with intact CrCL dogs, aligning with our findings.[4] [5] [12] [15] [16] [17] [18]

Previous reports have suggested that early neutering may predispose dogs to excessive TPA development, particularly in large-breed dogs, as neutered dogs reportedly have a higher prevalence of CrCLR compared with intact CrCL dogs.[2] [3] [5] [15] [19] A systematic review further indicates that gonadectomy performed before 1 year of age in breeds like Golden Retrievers, German Shepherds, and Rottweilers increases the risk of CrCLR and obesity.[20] [21] Early neutering delays growth plate closure in long bones due to the role of reproductive hormones in maintaining ligament and muscle integrity.[19] [21] [22] Our study found no association between neutering status, gender and the occurrence of CrCLR; however, the age at neutering was not recorded in our data. Additionally, some studies have reported that the association between CrCLR and TPA remains unproven, as many dogs with a steep TPA do not develop CrCLR.[6] [23] [24] This suggests that while TPA may influence the condition, it is not likely a sole or definitive predisposing factor for CrCLR.

Regarding age, small-breed dogs with CrCLR tended to be older than large-breed dogs at the time of diagnosis. This aligns with findings from several studies reporting the average age of small-breed dogs range from 5.4 to 9.8 years, while large-breed dogs are typically affected between 4.3 and 5.7 years of age.[3] [4] [15] [16] [18] [25] However, one study of 200 large-breed CrCLR dogs showed no correlation between TPA and age at the time of CrCLR.[26]

Although the etiopathogenesis of CrCLR remains unclear, it is widely accepted that rupture often occurs spontaneously due to osteoarthritic changes in the stifle joint during normal physiologic loading. These changes result from collagen degradation and are considered a key feature of cranial cruciate ligament disease (CCLD).[1] [2] Cranial cruciate ligament rupture typically affects dogs between 2 and 10 years of age. In younger dogs under 4 years, the condition may occasionally be of traumatic origin, while in dogs aged 5 to 7 years, spontaneous rupture is more commonly caused by degenerative changes, ultimately leading to CCLD.[1] [21]

Our study identified several cases of CrCLR in large-breed dogs, particularly in Labrador Retrievers and Golden Retrievers. This aligns with previous reports highlighting breeds with a high prevalence of CrCLR, including the Labrador Retriever, Rottweiler, Newfoundland, Chow-Chow, Akita, Saint Bernard, Bulldog, Boxer and American Staffordshire Terrier.[1] [3] [12] [15] [27] [28] These breeds are predisposed to CrCLR partly due to abnormalities in the hyperextended position of the pelvic limb, often associated with hip dysplasia, which tends to correlate with a higher incidence of CrCLR.[29] [30] Additionally, increased body weight has been confirmed as a predisposing factor for CrCLR in young large-breed dogs.[2] [23]

Cranial cruciate ligament rupture is considered to have a strong breed-related predisposition.[31] Furthermore, genetic studies have identified several chromosomal regions associated with CrCLR, particularly in breeds, Labrador Retriever, Rottweiler and Newfoundland.[27] [31] [32]

Our study found a higher incidence of CrCLR in small-breed dogs, particularly in Pomeranians, Chihuahuas and Poodles. Other notably affected breeds included Bichon Frise, Yorkshire Terriers, West Highland White Terriers, Miniature and Toy Poodles.[4] [5] [15] In small-breed dogs, excessive stress on the ligament caused by tibial instability often accompanies patellar luxation.[33] However, CrCLR lesions in these dogs typically develop at an older age due to degenerative changes in the ligament, as their lower weight reduces strain on the ligament's elastic and mechanical strength.[1] Histological studies have shown a significant correlation between inflammatory and degenerative changes in the stifle synovium and in factors such as age and body weight.[2] [34] This finding aligns with the observation that small-breed dogs generally have a longer lifespan compared with large-breed dogs.[35] [36]

The ROC analysis demonstrated that TPA is a moderately effective predictor for CrCLR in small- and large-breed dogs, with small-breed dogs showing a somewhat higher predictive accuracy (AUC: 0.76) compared with large-breed dogs (AUC: 0.66). The optimal cut-point TPA was 21.65 degrees for small-breed dogs, while it was 23.95 degrees for large-breed dogs. These findings suggest breed-specific differences in the predictive utility of TPA, with small-breed dogs showing greater sensitivity to CrCLR identification at a lower TPA threshold.

A limitation of this study is its reliance on data from medical records at a single institution, which may not fully reflect the broader population of small- and large-breed dogs in the reporting region. Furthermore, while the ROC analysis offers valuable insights, the moderate AUC values suggest that TPA alone is not a good predictor of CrCLR. Lastly, grouping dogs solely by weight categories (small- and large-breed dogs) may oversimplify breed-specific anatomical and biomechanical variations.

Conclusion

In conclusion, this study found that dogs with CrCLR have higher TPA compared with dogs not affected by CCLD, with small-breed dogs exhibiting higher TPA than large-breed dogs. ROC analysis demonstrates that TPA is a fair predictor for CrCLR, especially in small-breed dogs (AUC: 0.76), confirming that TPA is only one of the risk factors for CCLD, some explored and others still unknown.

Conflict of Interest

None declared.

Acknowledgements

We would like to express our sincere gratitude to the Veterinary Teaching Hospital, Khon Kaen University, for their assistance with data collection and their dedication to patient care. Finally, we would like to acknowledge the pet owners for their trust and cooperation in allowing their pets to be part of this study.

Authors' Contributions

P.K., S.H., S.S. and N.K. designed the study and conducted the study. P.K., S.H. and N.K. performed the data collection and acquisition, revised the manuscript, and provided input on the study design. S.S. and P.K. performed the statistical analysis. P.K. prepared the manuscript. All authors have read, reviewed, and approved the final manuscript.

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Publication History

Received: 28 January 2025

Accepted: 17 April 2025

Article published online:
29 May 2025