Rupture of the CCL is a frequent cause of hind limb lameness in dogs. The CCL undergoes a degenerative process, which results in partial and later complete rupture, for reasons that are still not completely understood.1,2,a Age, body weight, breed, sex, diet, immune-mediated disease, and conformation abnormalities are related to CCLD.3–9
The influence of the TPA in the pathogenesis of CCLD is continuously debated. Results of 1 study10 indicate that a greater TPA predisposes to CCL rupture. In other studies,11–13 no significant association was found between an increase in TPA and CCLD. In another study,14 no difference in the TPA was found between dogs affected and unaffected with CCLD and unaffected wolves. One study12 evaluated and compared TPAs between Greyhounds and Labrador Retrievers with and without CCLD. Those investigators evaluated not only traditional TPA measurements obtained from mediolateral radiographic views of the stifle joint, but also, in athletically sound dogs, the TPA in a normal standing position. Unaffected Labrador Retrievers had the larger traditional TPA measurements, followed by Labrador Retrievers with CCLD. Greyhounds had the smallest traditional TPA measurements. No differences were found between standing TPA measurements of sound Labrador Retrievers and Greyhounds.
In 2 recent studies,15,16 the angle between the tibial plateau and the patellar ligament was evaluated and compared between dogs with unaffected stifle joints and dogs with surgically confirmed partial CCL rupture. It was determined that the angle between the patellar ligament and tibial plateau is larger in dogs with CCLD than the same angle in dogs with unaffected stifle joints. Because the angle between the patellar ligament and tibial plateau is larger in dogs with CCLD, the CCL is loaded with greater force during the weight-bearing phase of the stride, which may contribute to the degenerative process.15–17
The relationship between skeletal configuration of the knee joint and the development of clinical signs after rupture of the anterior cruciate ligament in humans has been investigated.18 On evaluation of mediolateral radiographic views of human knee joints affected by anterior cruciate ligament rupture, it was determined that people with spherical femoral condyles have more difficulty in recovering after an anterior cruciate rupture than people with a caudal projection of the femoral condyles.18 The shape of the proximal portion of the tibia has also been studied in humans.19 Variation in the convexity of the lateral tibial condyle seems to be associated with signs of instability and the pivot shift phenomenon at examination of patients affected with anterior cruciate ligament rupture.19 Basset Hounds and Dachshund are some of the breeds with the lowest prevalence of CCLD.4 These chondrodystrophic breeds have a greater caudal projection of the femoral condyles than other breeds of dogs.20
To our knowledge, no morphometric study evaluating the relationship between femoral condyle conformation and risk of CCLD has been performed in dogs. The purpose of the study reported here was to evaluate mediolateral radiographic views of canine stifle joints to identify conformational differences between athletically sound dogs and dogs with CCLD. We hypothesized that dogs with less caudal projection of the femoral condyles or dogs with a less developed tibia tuberosity would have more CCL lesions.
Materials and Methods
Data collection—Preoperative radiographs of 50 stifle joints of 43 client-owned dogs (representing 15 large breeds) with surgically confirmed partial CCL rupture (CCLD group dogs) and 50 stifle joints of 38 client-owned dogs (representing 20 large breeds) without clinical signs of stifle joint disease (control group dogs) were evaluated. In CCLD group dogs, surgical confirmation of partial CCL rupture was accomplished arthroscopically or by means of a medial arthrotomy of the stifle joint. Data from dogs with radiographic signs of severe degenerative joint disease, in which adequate identification of radiographic landmarks was difficult, were not included in this study. This study was performed in compliance with institutional guidelines of the Clinic for Small Animal Surgery of the University of Zurich. All owners signed a consent form allowing all documentation regarding their dog to be used for scientific research and publication.
Radiographic measurements—All measurements were performed on radiographs of mediolateral views that were centered on the stifle joint with exact superposition of the femoral condyles and included the entire tibia. The femur was imaged to a variable extent on radiographs, but at least up to the mid diaphysis. Long axes of the femur and tibia were defined from radiographs in the same way as described in a previous study16 by use of similar templates. Angle j was measured between these 2 long axes to determine the degree of stifle joint flexion represented on each radiograph. Three circles were drawn on the radiographs. Circles 1 and 2 were drawn as reported in a previous study16; circle 1 represented the joint surface of the femoral condyles, and circle 2 represented the area of contact on the tibial plateau. Circle 3 was drawn to outline the groove of the femoral trochlea. The long axis of the femoral condyles was defined by a line starting at the long axis of the femur and passing over the midpoints of circles 1 and 3 to the articular surface of the femoral condyles. Angle d was measured between the long axes of the femur and femoral condyles. Line K was drawn between the midpoint of circles 1 and 2. Line G was drawn between the midpoint of circle 2 and the most cranial aspect of the tibial tuberosity. Two other lines were drawn perpendicular to the patellar ligament. Line L was drawn from the cranial edge of the patellar ligament to the midpoint of circle 1, and line H was drawn from the cranial edge of the patellar ligament to the point in which line K was tangential to the tibiofemoral contact area. Lengths of these segments, the distance between the midpoints of circles 1 to 3 (line E), and radii of circles 1 (line B), 2 (line F), and 3 (line C) were measured. The length of the tibia (line I) was measured between the points in which line K crossed the tibiofemoral area to the center of the tibial cochlea. Angle m was measured between lines G and I (Figure 1).
Mediolateral radiographic view of the left stifle region of a dog without clinical signs of stifle joint disease. The degree of flexion of the stifle joint (angle j) is measured between the long axes of the femur (af) and the tibia (at). The ac is the long axis of the femoral condyles. Angle d is between af and ac. Circles 1, 2, and 3 represent the joint surface of the femoral condyles (1), the area of contact on the tibial plateau (2), and the femoral trochlea (3). Lines B, F, and C are, respectively, the radii of circles 1, 2, and 3. Line K represents the distances between the midpoints of circles 1 and 2. Line E is the distance between centers of circle 1 to circle 3. Line G is the distance between the midpoint of circle 2 and the most cranial aspect of the tibial tuberosity. Line I is the length of the tibia. Angle m is between lines G and I. Line L is a line perpendicular to the cranial border of the patellar ligament (pl) to the center of circle 1. Line H is a line perpendicular to the pl from its cranial border to the point in which K cross the tibiofemoral contact area.
Citation: American Journal of Veterinary Research 68, 12; 10.2460/ajvr.68.12.1332
Statistical analysis—To evaluate differences in conformation of the distal portion of the femur that could lead to CCLD, quotients of the long axis of the femoral condyles and lengths of lines B, C, E, H, I, K, and L were obtained and compared between dog groups. Angle d was an absolute variable and therefore was compared directly between dog groups. Lengths of lines K, L, and H may change on the basis of the degree of stifle joint flexion. When these variables were evaluated by use of a factorial ANOVA, angle j was used as a covariant (Appendix). The proximal portion of the tibia was investigated with quotients created between the lengths of lines G, F, H, I, K, and L. Angle m, as an absolute variable, was compared between dog groups without the use of quotients. Data were analyzed by use of a software program.b The Bonferroni test was used as a post hoc test. Values of P < 0.05 were considered significant.
Results
One hundred radiographs of the mediolateral view of canine stifle joints were evaluated. Fifty radiographs were of 43 CCLD group dogs, and 50 radiographs were of 38 control group dogs.
Control group dogs comprised 20 large-breed dogs with a mean body weight of 31.8 kg (range, 17 to 71 kg). Mean age of control group dogs was 6.29 years (range, 1 to 11 years). Mean ± SD length of the tibia for this group was 197.74 ± 24.4 mm (range, 137 to 250 mm). Control group dogs were considered free of stifle joint disease on the basis of no clinical signs of joint disease and no radiographic abnormalities in either stifle joint. Breeds represented in the control group were mixed breed (n = 13 stifle joints), German Shepherd Dog (4), Golden Retriever (4), Old English Sheepdog (4), Labrador Retriever (3), Boxer (2), Rottweiler (2), Flat-Coated Retriever (2), Bergamasker (2), Appenzeller Mountain Dog (2), Bernese Mountain Dog (2), Bouvier des Flandres (2), Cane Corso (1), Poodle (1), Staffordshire Bull Terrier (1), Dalmatian (1), Briard (1), Deutsche Wachtelhund (1), Greater Swiss Mountain Dog (1), and Belgian Sheepdog (1).
The CCLD group dogs comprised 15 large dog breeds with a mean body weight of 37.9 kg (range, 22 to 76 kg). Mean age of CCLD group dogs was 6.2 years (range, 2 to 11 years). Mean ± SD length of the tibia for this group was 197.96 ± 24.75 mm (range, 115 to 260 mm). Breeds represented in the CCLD group were mixed breed (n = 15 stifle joints), Golden Retriever (7), Rottweiler (5), German Shepherd Dog (4), Belgian Shepherd (4), Bernese Mountain Dog (3), Dalmatian (2), Boxer (2), Appenzeller Mountain Dog (2), Labrador Retriever (1), Flat-Coated Retriever (1), Greater Swiss Mountain Dog (1), Vizla (1), Great Dane (1), and Leonberger (1). No significant difference was found in age or weight between CCLD group dogs and control group dogs.
Except for the quotients between the lengths of lines G and F (ie, G/F) and between lines G and K (ie, G/K), no significant differences were found in all other angles and quotients between CCLD group dogs and control group dogs.c Angle d was 124.62 ± 9.23° (mean ± SD) and 123.50 ± 7.71° in CCLD group dogs and control group dogs, respectively. Angle j was 72.42 ± 26.41° and 71.56 ± 21.47° in CCLD group dogs and control group dogs, respectively. Angle m was 136.64 ± 11.10° and 134.00 ± 11.10° in CCLD group dogs and control group dogs, respectively.
Mean ± SD length of line F was 34.14 ± 6.82 mm and 32.80 ± 7.09 mm in CCLD group dogs and control group dogs, respectively. Length of line G was 25.76 ± 4.64 mm and 26.16 ± 5.21 mm in CCLD group dogs and control group dogs, respectively. A significant difference was found in the quotient created by the lengths of lines G and F (ie, G/F) between CCLD group dogs and control group dogs. Mean ± SD length of line K was 46.74 ± 8.05 mm and 45.24 ± 8.25 mm in CCLD group dogs and control group dogs, respectively. A significant difference was found in the quotient created by the lengths of lines G and K (ie, G/K) between CCLD group dogs and control group dogs. Angle j had no influence on the quotient of G/K.
Discussion
To compensate for the variety of dog sizes, all the values, except for angles d, j, and m, were evaluated as quotients in the study reported here. All variables obtained from the distal portion of the femur that would vary with dog size were related to each other and also with the length of the tibia. By creating quotients and making comparisons between the obtained data, we tried to identify morphologic differences in the femoral condyles between CCLD group dogs and control group dogs. A shorter axis of the femoral condyles; a larger radius of the circle representing the joint surface of the femoral condyles; less distance between the centers of circles 1 and 2; or less length of segments L or H in CCLD group dogs, compared with control group dogs, would help us to prove our hypothesis that round femoral condyles with less of a caudal projection may be a predisposing variable for CCLD. We also expected to find a larger difference in angle d between CCLD group dogs and control group dogs. However, no significant differences in the conformation of the distal portion of the femur were detected between CCLD group dogs and control group dogs.
Variables measured in the proximal portion of the tibia, with the exception of the angle m, were related to each other and also with the length of the tibia and segments L and H. A short length of G, H, or L may be indicative of a less developed tibial tuberosity. Angle m was investigated, and no significant difference was found between CCLD group dogs and control group dogs. The amplitude of the angle m varies not only with the development of the tibial tuberosity, but also with the inclination and diameter of the tibial plateau. An obtuse angle could be indicative of a less developed tibial tuberosity.
In a study18 on femoral condyle conformation in people, patients with spherical femoral condyles fail more frequently with conservative treatment for anterior cruciate ligament rupture and require reconstructive surgery more often than people with a longer sagittal projection of the femoral condyles. Those investigators hypothesized that a caudal projection of the femoral condyles would produce greater sliding motion during weight-bearing activities, allowing the patient to control the joint position in the absence of an anterior cruciate ligament. Round condyles would lead during the weight-bearing phase to a rapid jerk, principally against the convex lateral condyle of the tibia, increasing the difficulty in controlling joint position and the pivot shift phenomenon.
The cause of CCLD in dogs is still not clear and is probably multifactorial.3–9 A degenerative process takes place in the ligament before rupture.1,2,a We hypothesized that round femoral condyles could, like in humans,18 induce more instability against the lateral condyle of the tibia, increasing the internal rotation of the tibia during the weight-bearing phase of the gait, and it could result in overload of the CCL and subsequent degenerative changes. However, our data did not support this hypothesis.
In a study18 on human femoral condyles, the index between sagittal depth and axial height of the femoral condyle was evaluated from lateral radiographic views of the knee joint, with the most distal point of the cranial angle of Blumensaat's line (radiographic point representing the intersection of the trochlear groove with the roof of the intercondylar notch) as the main landmark for various measurements. Blumensaat's line on radiographs provides a consistent landmark for the evaluation of human knee joints that allows for reproducible measurements. To our knowledge, Blumensaat's line is not defined in dogs. Two circles, 1 representing the groove of the femoral trochlea and 1 the femoral condyles, were used in the study reported here as landmarks. Radiographs in which the femoral condyles were not perfectly superposed or that had signs indicative of severe degenerative joint disease, making identification of landmarks difficult, were not included in the study reported here.
To determine the conformation of the femoral condyles and to identify anatomic differences between CCLD group dogs and control group dogs that could predispose dogs to CCLD, angle d, quotients between a caudal projection of the femoral condyles and all other values, and quotients between various variables of the femoral condyles were evaluated and compared; no difference in these values was detected between groups. Radiographs from 23 various breeds of dogs were evaluated in the study reported here, many of them being mixed-breed dogs. It is possible that differences between breeds may have obscured morphologic differences.
By use of radiographic landmarks, the degree of flexion of the stifle joint was determined in the study reported here. Angle j was used as a covariant for all the quotients that could change with the degree of stifle joint flexion or extension; this allowed the use and comparison of radiographs that differed in the degree of flexion of the stifle joint.
A consistent correlation is found between dimensions of the knee joint and height of humans, but no correlation is found between knee joint dimensions and body weight.18 In the study reported here, tibial length was compared between CCLD group dogs and control group dogs as a means to avoid variations in body condition or absolute body weight. Dogs with greater-than-typical body condition are at increased risk of developing CCLD3; also, dogs with CCLD are prone to engage in less physical activity and therefore increase body weight. No significant difference in tibial length was found between CCLD group dogs and control group dogs in the study reported here.
To avoid false differences in measurements between CCLD group dogs and control group dogs, the CCLD group comprised only radiographs of dogs with surgically confirmed partial CCL rupture, as was done in a previous study.16 Subluxation of the tibia in respect to the femur occurs only in instances of extreme stifle joint flexion in dogs with partial CCL rupture. Avoiding the use of radiographs of the stifle joint in an extreme flexed position allows for comparable measurements between groups.1,21
One circle (circle 2) was drawn on the radiographs to evaluate conformation of the proximal portion of the tibia, signifying the area of contact on the tibial plateau; another circle was drawn to outline the femoral condyles (circle 1). The quotient (G/F) between the distance from the midpoint of circle 2 to the most cranial aspect of the tibial tuberosity (G) and the radius of this circle (F) was significantly smaller in CCLD group dogs than in control group dogs. The quotient (G/K) between the length of line G and the distance between the tangential points of both circles (line K) was also significantly smaller in CCLD group dogs than in control group dogs. Because the length of line K may be influenced by the degree of flexion of the stifle joint, angle j was used as a covariant and had no influence on the G/K quotient.
Results of another study16 revealed that the angle between the tibial plateau and patellar ligament is larger in dogs with CCLD than in clinically normal dogs. This angle is influenced by the inclination of the tibial plateau and the development of the tibial tuberosity. Unfortunately, the TPA was not measured in that study.16 Results of a biomechanical study22 of the human knee indicate that women have a smaller patellar ligament moment arm and therefore larger joint forces affecting the knee joint than men. Women are also more often affected by degenerative changes in their knee joints than men.22
In the study reported here, the G/F quotient was significantly different between CCLD group dogs and control group dogs. These results indicated that an interaction between G and F existed proportionally, thereby eliminating dog size as affecting the development of CCLD. Therefore, dogs with radiographic findings of a short G line relative to a long F line may have a higher risk for CCLD.
If the distance from the center of circle 2 to the most cranial aspect of the tibial tuberosity is shorter in CCLD group dogs than in control group dogs, it may indicate that the tibial tuberosity is less developed in dogs with CCLD. The angle between tibial plateau and patellar ligament would then be larger, as was determined in a previous study,16 and the moment arm of the patellar ligament would be smaller. Shear forces in the stifle joint are larger when the tibial tuberosity is less developed in dogs with CCLD.17 In this situation, the CCL may be overcharged, which could contribute to the degenerative process.17
Use of magnetic resonance imaging to evaluate the lateral tibial condyle revealed that an increase in the convexity of the lateral condyle increases the signs of instability and the pivot shift phenomenon in human patients with anterior cruciate rupture.19 According to our results, even when line F was not significantly larger in CCLD group dogs than control group dogs, the G/F quotient was significantly different between CCLD group dogs and control group dogs, indicating that the tibial plateau could be, in discrepancy with findings for human patients, less convex in dogs with CCLD. Unlike findings for humans,18 no anatomic differences were detected in the study reported here in the distal portion of the femur between dogs with and without CCLD. In the study reported here, it could be that breed acted as a confounder. Results of the study reported here indicated that the development of the tibial tuberosity appeared to be relevant in the pathogenesis of CCLD. Further studies to evaluate anatomic differences and related forces among dogs are necessary.
ABBREVIATIONS
| CCL | Cranial cruciate ligament |
| CCLD | Cranial cruciate ligament disease |
| TPA | Tibial plateau angle |
Geyer H. Die Behandlung der Kreuzbandrisse beim Hund: Vergleichende Untersuchungen. Doctoral thesis, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland, 1966.
Stat-View, version 5.1, SAS Institute Inc, Wanger bei Dübendorf, Switzerland.
Raw data, results, and tables concerning the statistical work are available on request from the corresponding author.
References
- 1.
Vasseur PB. Stifle joint. In: Slatter D, ed. Textbook of small animal surgery. 3rd ed. Philadelphia: WB Saunders Co, 2003;2090–2133.
- 2.
Vasseur PB, Pool RR, Arnoczky SP, et al. Correlative biomechanical and histologic study of the cranial cruciate ligament in dogs. Am J Vet Res 1985;46:1842–1854.
- 3.↑
Lampman TJ, Lund EM, Lipowitz AJ. Cranial cruciate disease: current status of diagnosis, surgery, and risk for disease. Vet Comp Orthop Traumatol 2003;163:122–126.
- 4.↑
Withehair JG, Vasseur PB, Willits NH. Epidemiology of cranial cruciate ligament rupture in dogs. J Am Vet Med Assoc 1993;203:1016–1019.
- 5.
Duval JM, Budsberg SC, Flo GL, et al. Breed, sex and body-weight as risk factors for rupture of the cranial cruciate ligament in young dogs. J Am Vet Med Assoc 1999;215:811–814.
- 6.
Aiken SW, Kass PH, Toombs JP. Intercondylar notch widths in dogs with and without cranial cruciate ligament injuries. Vet Comp Orthop Traumatol 1995;8:128–132.
- 7.
Selmi AL, Padilha Filho JG. Rupture of the cranial cruciate ligament associated with deformity of the proximal tibia in five dogs. J Small Anim Pract 1995;42:390–393.
- 8.
Macias WM, McKee WM, May C. Caudal proximal tibial deformity and cranial cruciate ligament rupture in small-breed dogs. J Small Anim Pract 2002;43:433–438.
- 9.
Read RA, Robins GM. Deformity of the proximal tibia in dogs. Vet Rec 1982;111:295–298.
- 10.↑
Morris E, Lipowitz AJ. Comparison of tibial plateau angles in dogs with and without cranial cruciate ligament injuries. J Am Vet Med Assoc 2001;218:363–366.
- 11.
Zeltzman PA, Pare B, Johnson GM, et al. Relationship between age and tibial plateau angle in dogs with cranial cruciate rupture. J Am Anim Hosp Assoc 2005;41:117–120.
- 12.↑
Wilke VL, Conzemius MG, Besancon MF, et al. Comparison of tibial plateau angle between clinically normal Greyhounds and Labrador Retrievers with and without rupture of the cranial cruciate ligament. J Am Vet Med Assoc 2002;221:1426–1429.
- 13.
Reif U, Probst CW. Comparison of tibial plateau angles in normal and cranial cruciate deficient stifles of labrador retrievers. Vet Surg 2003;32:385–389.
- 14.↑
Venzin C, Howard J, Rytz U, et al. Tibial plateau angles with and without cranial cruciate ligament rupture—comparison between different dog populations and a wolf population. Vet Comp Orthop Traumatol 2004;17:232–236.
- 15.
Dennler R, Kipfer N, Tepic S, et al. Inclination of the patellar ligament in relation to flexion angle in stifle joints of dogs without degenerative joint disease. Am J Vet Res 2006;67:1849–1854.
- 16.↑
Schwandt CS, Bohorquez-Vanelli A, Tepic S, et al. Angle between the patellar ligament and tibial plateau in dogs with partial rupture of the cranial cruciate ligament. Am J Vet Res 2006;67:1855–1860.
- 17.↑
Tepic S, Damur D, Montavon PM. Biomechanics of the stifle joint, in Proceedings. 1st World Orthop Vet Congr ESVOT-VOS 2002;189–190.
- 18.↑
Friden T, Jonsson A, Erlandsson T, et al. Effect of femoral condyle configuration on disability after an anterior cruciate ligament rupture. 100 patients followed for 5 years. Acta Orthop Scand 1993;64:571–574.
- 19.↑
Kujula UM, Nelimarkka O, Koskinen SK. Relationship between the pivot shift and the configuration of the lateral tibial plateau. Arch Orthop Trauma Surg 1992;111:228–229.
- 20.↑
Simpson DJ, Lewis DD. Fractures of the femur. In: Slatter D, ed. Textbook of small animal surgery. 3rd ed. Philadelphia: WB Saunders Co, 2003;2059–2089.
- 21.
Moore KW, Read RA. Rupture of the cranial cruciate ligament in dogs. Diagnosis and management. Compend Contin Educ Pract Vet 1996;18:381–405.
- 22.↑
Nissel R. Mechanics of the knee: a study of joint and muscle load with clinical applications. Acta Orthop Scand Suppl 1985;216:1–42.
Appendix
Calculated quotients of lengths of the long axis of the femoral condyles and lines created to evaluate differences in conformations of the distal portion of the femur and proximal portion of the tibia between CCLD group dogs and control group dogs (See Figure 1 to view radiographic landmarks).
