Evaluation of the Marsh Deer Stifle Joint by Imaging Studies and Gross Anatomy

This study aimed to evaluate the stifle joint of marsh deer using imaging studies and in comparison with gross anatomy. Ten hindlimbs from 5 marsh deer (Blastocerus dichotomus) were used. Radiography, computed tomography (CT) and magnetic resonance imaging (MRI) were performed in each stifle joint. Two hindlimbs were dissected to describe stifle gross anatomy. The other limbs were sectioned in sagittal, dorsal or transverse planes. In the craniocaudal radiographic view, the lateral femoral condyle was broader than the medial femoral condyle. The femoral trochlea was asymmetrical. Subsequent multiplanar reconstruction revealed in the cranial view that the external surface of the patella was roughened, the medial trochlea ridge was larger than the lateral one, and the extensor fossa at the lateral condyle was next to the lateral ridge. The popliteal fossa was better visualized via the lateral view. Sagittal MRI images identified lateral and medial menisci, caudolateral and craniomedial bundles of cranial cruciate ligament, caudal cruciate ligament, patellar ligament and common extensor tendon. In conclusion, the marsh deer stifle presents some anatomical characteristics of the ovine stifle joint.     

ULTRASONOGRAPHIC ANATOMY OF THE NORMAL CANINE STIFLE

Ultrasonographic examination of the normal canine stifle joint was performed to characterize its normal anatomy. Stifles of four normal adult dogs were imaged in sagittal and transverse planes and each anatomic structure visualized was recorded. Normal anatomic structures consistently seen included the patellar tendon, medial and lateral menisci, the cranial cruciate ligament and femoral condyle cartilage. The caudal cruciate ligament was visualized in two dogs. Collateral ligaments and meniscal ligaments were not visualized. The dogs were then euthanized and each stifle was isolated. Following removal of superficial muscles and skin, each stifle was imaged in a water bath to definitively identify the structures that had previously been visualized on the live dogs. The ultrasonographic appearance of the isolated stifle specimens was similar to that found in live dogs. The results of this study indicate that ultrasound can be used to image the normal anatomy of the canine stifle. The echogenicity of the patellar ligament, cruciate ligaments, menisci and articular cartilage was similar to that previously reported in equine stifles and human knees.     

PREVALENCE,ASSOCIATION WITH STIFLE CONDITIONS,AND HISTOPATHOLOGIC CHARACTERISTICS OF TIBIAL TUBEROSITY RADIOLUCENCIES IN DOGS

A tibial tuberosity radiolucency is sometimes identified on lateral radiographs of canine stifle joints, however little is known about the cause or significance. The purpose of this study was to describe the prevalence, association with other stifle conditions, and histopathologic characteristics of tibial tuberosity radiolucencies in a group of dogs. Radiographs of all canine stifle joints over 5 years were evaluated. Presence or absence of a tibial tuberosity radiolucency was recorded by an observer who was unaware of clinical status. Patient signalment and presence of other stifle joint conditions were recorded from medical records. A tibial tuberosity radiolucency was found in 145/675 dogs (prevalence = 21.5%). Statistically significant associations were identified between tibial tuberosity radiolucency and stifle condition (P < 0.0001), breed size (P = 0.011), and younger age of presentation (P = 0.001), but not with gender (P = 0.513). Dogs with a tibial tuberosity radiolucency had higher odds of having a medial patellar luxation than dogs without (OR = 9.854, P < 0.0001, 95% CI 6.422–15.120). Dogs with a tibial tuberosity radiolucency had lower odds of having a cranial cruciate ligament rupture than dogs without (OR = 0.418, P < 0.0001, 95% CI 0.287–0.609). Four canine cadavers, two with normal stifles and two with tibial tuberosity radiolucencies, underwent radiographic, computed tomographic, and histologic examination of the stifles. Computed tomography revealed a hypoattenuating cortical defect in the lateral aspect of the proximal tibial tuberosity that corresponded histopathologically to a hyaline cartilage core. Findings indicated that the tibial tuberosity radiolucency may be due to a retained cartilage core and associated with medial patellar luxation in dogs.     

Caudal cruciate ligament damage in dogs with cranial cruciate ligament rupture

Objective: To investigate the incidence of caudal cruciate ligament (CaCL) damage in dogs with cranial cruciate ligament rupture (CCLR). Study Design: Prospective clinical study. Animals: Dogs (n=24) admitted for surgical stabilization of the stifle after CCLR and 8 healthy dogs with intact cranial cruciate ligament (CCL) and CaCL studied as controls. Methods: Preoperative radiographs and stifle joint images (arthrotomy, 6; arthroscopy, 18) were collected from dogs with CCLR. Severity of arthritis, synovitis, CCL damage, and CaCL damage were assessed using numerical rating scales. The CaCL was probed to determine whether minor fraying or a full thickness defect in the ligament was present. Data collected from the study population were compared with the control population of dogs. Results: The CaCL was damaged in 21/24 (88%) of dogs with CCLR; 6/24 (25%) had a full thickness defect in the CaCL. Severity of stifle synovitis and severity of damage to the CaCL were positively correlated (P<.05). Conclusions: The CaCL is damaged in a high percentage of dogs with CCLR. A significant and positive correlation exists between the degree of synovitis present and the extent of CaCL damage. Clinical Relevance: In dogs with CCLR, cruciate ligament pathology typically involves both the CCL and CaCL. As the severity of synovitis and the extent of CaCL damage are related, this observation supports the hypothesis that stifle synovitis may contribute to CCL and CaCL degeneration and subsequent damage.     

Diagnostic accuracy of positive contrast computed tomography arthrography for the detection of injuries to the medial meniscus in dogs with naturally occurring cranial cruciate ligament insufficiency

O bjective : To assess the usefulness of computed tomography arthrography of the stifle in diagnosing meniscal tears in dogs with cranial cruciate ligament insufficiency.
M ethods : A prospective clinical study was performed. Dogs were included if they had evidence of cranial cruciate ligament insufficiency or persistent or recurrent lameness following surgery for cranial cruciate ligament insufficiency. Dogs were sedated for a computed tomography scan of the affected stifle, orientated in the dorsal plane. A survey computed tomography scan was followed by a computed tomography arthrogram. A stifle arthrotomy was performed, and the surgical findings were recorded. The computed tomography scans were reviewed by three blinded reviewers, and the results were compared to the surgical findings.
R esults : Twenty-one computed tomography arthrograms from 20 dogs were included. At surgery, damage to the medial meniscus was identified in 14 stifles. Initial interpretation of computed tomography arthrography images was 57 to 64 per cent sensitive and 71 to 100 per cent specific for diagnosing medial meniscal injuries. Interpretation of the images on retrospective analysis was 71 per cent sensitive and 100 per cent specific, with an accuracy of 0·857.
C linical S ignificance : The accuracy of stifle computed tomography arthrography for the diagnosis of tears to the medial meniscus was found to be good. It is a minimally invasive and repeatable technique, which does not require general anaesthesia or specialist training to obtain the images. The ability to reliably diagnose meniscal injury without the need for surgery may be advantageous, particularly in dogs which had previously had surgery for cranial cruciate ligament insufficiency.     

Influence of signalment on developing cranial cruciate rupture in dogs in the UK

Objectives : To investigate risk factors associated with cranial cruciate ligament rupture in dogs. Methods : Retrospective case‐control study: medical records of a first‐opinion veterinary practice were searched for dogs diagnosed with cranial cruciate ligament rupture (1995 to 2007). For each case, six unaffected dogs were randomly selected from all dogs presenting that day for comparison. Multi‐variable binary logistic regression was performed to assess the association of variables on likelihood of cruciate rupture. Results : Frequency of cranial cruciate ligament rupture was 1·19% [95% confidence interval (CI) 1·02 to 1.36%]. West Highland white terriers (n=17), Yorkshire terriers (n=14) and Rottweilers (n=11) were at significantly increased risk of cranial cruciate ligament rupture (P≤0·002). Rottweilers were at five times greater risk compared with other pure breeds (OR 5·12, 95% CI 2·281 to 11·494, P<0·001), obesity quadrupled the risk of cranial cruciate ligament rupture (OR 3·756, 95% CI 1·659 to 8·502, P=0·001) and females were twice as likely to suffer cranial cruciate ligament failure compared to males (OR 2·054, 95% CI 1·467 to 2·877, P<0·001). Dogs less than two years old were statistically less likely to sustain cranial cruciate ligament rupture than dogs older than eight years (OR 0·246, 95% CI 0·127 to 0·477, P<0·001). There was no significant difference in median weights (in kilograms) of neutered dogs, compared to their entire counterparts in either the case group (P=0·994) or in the control group (P=0·630). There was also no significant difference in body condition (‐underweight/normal weight/overweight/obese) of neutered versus entire dogs among the cases (P=0·243), or the controls (P=0·211). Clinical Significance : Cranial cruciate ligament rupture is more likely in Rottweilers and in female dogs, older dogs and obese dogs. Following multi‐variable analysis, it was established that neutering was not associated with increased risk of cranial cruciate ligament rupture.     

Synovitis in dogs with stable stifle joints and incipient cranial cruciate ligament rupture: a cross-sectional study

Objective: To evaluate stifle joints of dogs for synovitis, before development of joint instability and cranial cruciate ligament rupture (CrCLR). Study Design: Cross‐sectional study. Animals: Dogs (n=16) with CrCLR and stable contralateral stifles; 10 control dogs with intact CrCL. Methods: Arthritis and tibial translation were graded radiographically. Synovitis severity and cruciate pathology were assessed arthroscopically. Presence of inflammatory cells in synovial membrane biopsies was scored histologically. CrCLR stifle pairs and control stifles were compared. Results: Radiographic evidence of arthritis, cranial tibial translation, and arthroscopic synovitis were increased in unstable stifles, when compared with stable contralateral stifles in CrCLR dogs (P<.05). Arthroscopic synovitis in both joints of CrCLR dogs was increased compared with controls, was correlated with radiographic arthritis (S_R=0.71, P<.05), and was present in all stable contralateral stifles. Arthroscopically, 75% of stable stifle joints had CrCL fiber disruption, which correlated with severity of synovitis (S_R=0.56, P<.05). Histologic evidence of synovitis was identified in all CrCLR dogs, but was only significantly correlated with arthroscopic observations in stable stifles (r²=0.57, P<.005). Conclusion: Synovitis is an early feature of the CrCLR arthropathy in dogs before development of joint instability clinically. Severity of synovitis is correlated with radiographic arthritis in joints with minimal to no clinically detectable CrCL damage.     

Partial rupture of the cranial cruciate ligament of the stifle in dogs: 25 cases (1982-1988)

Partial rupture of the cranial cruciate ligament was diagnosed in 25 dogs. In all dogs, the primary problem at the time of physical examination was hind limb lameness. The mean time from initial onset of lameness to diagnosis at exploratory surgery was 17 weeks. A cranial drawer sign was detected in 13 of the 25 dogs; in 9, the cranial drawer sign was evident only when the stifle was positioned in flexion. Of the 25 dogs, 12 had no detectable cranial drawer sign in response to manipulation of the involved stifle. In all dogs, lateral stifle arthrotomy was performed in routine manner, and the cranial cruciate ligament was found to be incompletely torn. Lesions identified during arthrotomy were rupture of the craniomedial band (n = 20 dogs), interstitial tear (n = 4 dogs), and rupture of the caudolateral band (n = 1 dog).     

Canine stifle positive contrast computed tomography arthrography for assessment of caudal horn meniscal injury: a cadaver study

Objective— To investigate the use of computed tomography (CT) arthrography in cadaveric canine stifles with particular emphasis on the diagnosis of meniscal injury.
Study Design— Prospective cadaver study.
Sample Population— Pelvic limbs from adult Beagles (n=10).
Methods— After survey CT scan of each stifle oriented in the dorsal plane, positive contrast stifle CT arthrogram (CTA) was performed using the same slice orientation. Each stifle was then randomly allocated into 1 of 2 treatment groups: group A—arthrotomy, cranial cruciate ligament (CCL) transection and simulated injury to the caudal horn of the medial meniscus; group B—arthrotomy and CCL transection only. CT scan was repeated as before and post-arthrotomy images were interpreted by a radiologist unaware of treatment grouping.
Results— The cranial and caudal cruciate ligaments, medial and lateral menisci, menisco-femoral ligament, and long digital extensor tendon were all identifiable on CTA images. CTA was 90% sensitive and 100% specific for diagnosing simulated caudal horn meniscal injury.
Conclusions— Stifle CTA enables identification of intra-articular structures within the stifle and is a reliable method for identifying simulated meniscal injuries in a cadaver model.
Clinical Relevance— CTA imaging of the canine stifle has potential clinical value for detection of meniscal injury.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE NORMAL CANINE STIFLE

Computed tomographic (CT) imaging of eight normal cadaveric canine stifles was performed before and after intra-articular administration of iodinated contrast medium. Transverse CT images were reconstructed in dorsal, parasagittal, and oblique planes. The following ligamentous structures were identified on transverse CT images in all stifles: cranial cruciate ligament, caudal cruciate ligament, medial meniscus, lateral meniscus, and the medial and lateral collateral ligaments. The following ligamentous structures were identified on transverse computed tomographic arthrography (CTA) images in all stifles: cranial cruciate ligament, caudal cruciate ligament, medial meniscus, lateral meniscus, meniscofemoral ligament, cranial meniscotibial ligaments, caudal meniscotibial ligaments, intermeniscal (transverse) ligament, and the medial and lateral collateral ligaments. The patellar tendon was identified on transverse and reconstructed dorsal and sagittal CT and CTA images in all stifles. Multiplanar reconstructions enabled further evaluation of the continuity of the cranial and caudal cruciate ligaments and menisci. The medial and lateral collateral ligaments were not clearly identified on CT or CTA multiplanar reconstructed images.     

前十字韧带断裂犬胫骨平台角的X线和CT测量

为探究胫骨平台角（tibial plateau angle,TPA）在犬前十字韧带断裂（cranial cruciate ligament rupture,CCLR）中的临床意义及为犬CCLR的整体发病规律与风险、诊断和治疗方案提供参考,本研究选用2018年6月至2019年1月在中国农业大学动物医院确诊为CCLR的共15只患犬的30个膝关节,使用X线和CT测量TPA （R-TPA和CT-TPA）并比较X线和CT测量TPA的一致性及优缺点。结果显示,R-TPA大小与年龄、体重、胖瘦、性别及绝育/去势与否均无关（P>0.05）,前十字韧带是否断裂亦与TPA大小无关（P>0.05）。经CT测量所得30个CT-TPA的平均值为26.93°（范围：19.03°~32.67°）;左侧膝关节的CT-TPA的平均值为26.82°,右侧为27.04°。R-TPA与CT-TPA值具高度相关性（r>0.75,P>0.05）;21个膝关节（70%）可在CT图像中观察到骨赘生成,其CT图像比X线图像能更清楚地辨识出骨赘与骨皮质的分界。结果表明,TPA与CCLR患犬的临床病理因素无关,X线与CT在测量犬TPA方面具有一致性,CT测量在测量图像的采集上较X线拍摄更方便、快捷与全面,并在骨关节炎病例中的测量精度更高。     

Clinical Results of Surgical Correction of Medial Luxation of the Patella in Dogs

Thirty-four dogs that had surgical correction of medial patellar luxation (MPL) in 52 stifle joints were examined after a minimum follow-up period of 1 year (median, 3.6 years). The dogs were divided into the following three groups depending on their age at the time of surgery: group 1, 3 to 6 months; group 2, 8 to 20 months; and group 3, 2.2 to 12 years. Two of the dogs in group 3 had ruptured their cranial cruciate ligament in addition to having MPL. The results were based on a clinical assessment of the animal's gait, and physical and radiographic examination of the stifle joints. Six of seven stifle joints evaluated in group 1 had radiographic evidence of moderate to severe degenerative joint disease of the patellofemoral joint, and in two of the joints recurrence of MPL was observed. Failure to maintain reduction of the patellofemoral joint was also observed in 11 of 22 (50%) and 12 of 23 (52%) of the stifle joints in groups 2 and 3, respectively. In the latter groups, mild degenerative joint disease was evident radiographically in stifle joint that had not maintained reduction. Four of the 34 dogs were consistently (n = 2) or intermittently (n = 2) lame; the two dogs that were consistently lame had cranial instability of the stifle consistent with rupture of the cranial cruciate ligament. In the latter two dogs, the cranial cruciate ligament had been intact at the time of surgery for correction of MPL.     

Radiographic measurement of craniocaudal instability in stifle joints of clinically normal dogs and dogs with injury of a cranial cruciate ligament

OBJECTIVE: To determine craniocaudal laxity of the stifle joint of dogs when joints were positioned in tibial compression or neutral position. SAMPLE POPULATION: 19 normal stifle joints in 10 clinically normal dogs, 29 stifle joints with varying injury to the cranial cruciate ligament (10 complete ruptures alone, 10 complete ruptures with concomitant damage to the medial meniscus, 6 partial ruptures alone, and 3 partial ruptures with concomitant meniscal tearing), and 19 unaffected contralateral stifle joints in those 29 dogs. PROCEDURE: Relative displacement of bony landmarks was measured on paired lateral radiographs (neutral and tibial compression positions). Two measuring techniques were customized for use in dogs. RESULTS: The first technique failed to distinguish results in normal stifle joints from those in stifle joints with partial deficiency of cranial cruciate ligaments. Significant differences were found for joints with complete rupture, compared with stifle joints in clinically normal dogs. The second technique detected differences between normal stifle joints and injured joints with partial or complete rupture of the cranial cruciate ligament. Significant differences were not detected between joints with partial versus complete rupture. Adjusting data to account for size of dog did not improve results. CONCLUSIONS AND CLINICAL RELEVANCE: A wide range in measurements of laxity was found for stifle joints with intact cranial cruciate ligaments. Differences in degree of damage to the ligament and medial meniscus cannot be deduced from the amount of relative displacement measured on radiographs. Pathologic changes to the cranial cruciate ligament will not necessarily induce detectable changes in laxity of stifle joints in dogs.     

Determination of Pelvic Limb Alignment in the Large‐Breed Dog: A Cadaveric Radiographic Study in the Frontal Plane

Objectives— To report a method for radiographic determination of the mechanical axis of the canine pelvic limb and its relationship to the joints and bone axes. To report reference ranges for the relationships between the axes of the pelvic limb and for joint position relative to the pelvic limb axis. Study Design— Cadaveric radiographic anatomic study. Animals— Pelvic limbs (n=101) from normal midsized to large breed dogs; tibiae (n=105) from dogs with cranial cruciate ligament disease (previous study). Methods— Extended full‐limb radiography was performed and images analyzed to determine: mechanical joint reference angles (femur, tibia), pelvic limb axis, tibiofemoral and metatarsotibial angle, mechanical axis—femur/metatarsus angle, and mechanical axis deviation (MAD) of the stifle/tarsus. Results— Mean mechanical angles were: lateral proximal femoral (103.7°±5.4°), lateral distal femoral (98.6°±2.5°), medial proximal tibial (92.2°±1.8°), medial distal tibial (95.9°±2.2°), tibiofemoral (9.1° varus ±2.8°), metatarsotibial (0.6° valgus ±2.1°). Mean mechanical axis—femur and—metatarsus angles were 5.6° (±1.7°) and 2.9° (±1.5°), respectively. Mean MAD of the stifle and tarsus were 3.6% (±1.1%) and 1.2% (±0.6%), respectively. Tibial angles were not different between dogs with and without cranial cruciate ligament disease. Conclusions— Mechanical axes of the canine pelvic limb and their relationship to the joints can be determined by full‐limb radiography. Clinical Relevance— Techniques and reference ranges may be useful for diagnosis, surgical planning, and postoperative assessment of pelvic limb deformities.     

The Intercondylar Fossa of the Normal Canine Stifle: An Anatomic and Radiographic Study

The intercondylar fossa (ICF) in dogs consists of a cranial outlet, intercondylar shelf, caudal arch, caudal outlet, a medial wall, and a lateral wall. The normal cranial outlet is bell-shape and, in mixed-breed dogs (mean body weight 19.2 kg, N = 21), measured 5.8 mm cranially, 8.1 mm centrally, and 10.3 mm caudally. The ICF is oriented 12° from the dorsal plane of the femoral diaphysis and obliqued 7°, proximolateral to distomedial, in the sagittal plane. To adjust for dog size, a fossa width index (FWI) was calculated by dividing the cranial outlet width by the distance between epicondyles. The normal FWI as determined in this study was 0.18 cranially, 0.25 centrally, and 0.32 caudally. The fossa height index was 0.31. Contact between the ICF and the cranial cruciate ligament began at about 115° of extension. The contact area moved cranially in the intercondylar fossa as the stifle was extended. Evaluation of the ICF can be performed radiographically but positioning is critical.     

Effect of signalment on the presentation of canine patients suffering from cranial cruciate ligament disease

Objective : To determine the effect of signalment on the incidence and presentation of patients suffering from cranial cruciate ligament disease. Methods : Data relating to 426 dogs (44 breeds) that met specific selection criteria were obtained from the hospital archive (2002 to 2008). Cases were followed up for 2 years. Results : The breeds most commonly presented with cranial cruciate ligament disease were Labrador retriever (16%), Rottweiler (15%), golden retriever (12%) and boxer (9%). Rottweilers were significantly more likely (69%; P=0·05) to develop and present with (50%; P=0·03) bilateral cranial cruciate ligament disease. Rottweilers presenting with cranial cruciate ligament disease were significantly younger (median 977 days; P<0·0001) than other breeds; golden retrievers being significantly older at presentation (median 1994 days; P=0·004). Neither sex nor neutered status significantly affected the incidence of developing (P=0·77 and P=0·30, respectively) or presenting with (P=0·62 and P=0·35, respectively) bilateral cranial cruciate ligament disease. Entire dogs were significantly younger than neutered dogs at presentation (P=0·0004). Entire female dogs presented significantly younger than neutered females (P=0·0002), entire males (P=0·01) and neutered males (P=0·0001). Clinical Significance : Breed affects the incidence of developing and presenting with bilateral cranial cruciate ligament disease. Breed and sex both affect the age that patients present with cranial cruciate ligament disease.     

ULTRASONOGRAPHIC EVALUATION OF CRANIAL CRUCIATE LIGAMENT RUPTURE VIA DYNAMIC INTRA-ARTICULAR SALINE INJECTION

Ultrasonographic examination of both stifle joints of five clinically and radiographically normal adult dogs was performed before and after surgical transection of the cranial cruciate ligament (CrCL). At pre- and postsurgery, the hyperechoic patellar ligament and the infrapatellar fat interfered with sonographic visualization of the CrCL. When the stifle joint, however, was imaged via dynamic intra-articular saline injection, the hyperechoic ligament was visualized because of the separation of the infrapatellar fat and the CrCL and the contrasting effect of anechoic saline. When the stifle joint was imaged by real-time scanning after the transection of the CrCL, flutter of the ligament and an anechoic area between the bone and the CrCL were identified. The increased diameter of the ligament and the increased thickness of the joint space were identified as well. Ultrasonographic examination via dynamic saline injection into the joint space has potential as a diagnostic tool for assessing CrCL rupture.     

Popliteal Tendon Transposition for Stabilization of the Cranial Cruciate Ligament Deficient Stifle Joint in Dogs: An Experimental Study

Popliteal tendon transposition was performed in five dogs with surgically induced cranial cruciate ligament rupture. After a lateral approach to the stifle joint, the popliteal tendon was severed distal to the sesamoid bone and transposed cranially onto the tibial crest to mimic the sagittal orientation of the cranial cruciate ligament. The origin of the popliteal tendon on the lateral femoral condyle was preserved. Lameness was not clinically detectable 2 months after surgery. At 6 months postoperatively, there was minimal radiographic and histopathologic evidence of degenerative joint disease in the stifle joints that had underwent surgery. There was no gross or microscopic evidence of meniscal damage found at necropsy 6 months after surgery. Biome-chanical studies are warranted before recommending the procedure.     

Correlative biomechanical and histologic study of the cranial cruciate ligament in dogs

The mechanical properties of the cranial cruciate ligament were determined, using unilateral bone-ligament-bone preparations from 65 dogs of various ages and body sizes. Tensile loading of the cranial cruciate ligament from 1 of each pair of stifle joints demonstrated a decrease in material properties (modulus, maximum stress, strain energy) with aging. The decreases in maximum stress and strain energy with age were significantly less (P less than 0.05 and P less than 0.05, respectively) in the cranial cruciate ligament from dogs weighing less than 15 kg, compared with those weighing 15 kg or more. The cranial cruciate ligament and remaining femorotibial ligaments were collected from the opposite stifle joints and examined microscopically. By 5 years of age, the cranial cruciate ligaments of dogs weighing greater than 15 kg consistently had microscopic evidence of degenerative disease (loss of ligamentocytes, metaplasia of surviving ligamentocytes to chondrocytes, and failure to maintain collagen fibers and primary collagen bundles) which progressed in severity with age. The caudal cruciate ligaments were similarly affected, although the degenerative changes were rarely as severe as in the cranial cruciate ligament. The collateral ligaments underwent minimal degeneration. Sex differences had no bearing on degeneration. The cranial cruciate ligaments in dogs weighing less than 15 kg generally had less severe alterations than those in heavier dogs, and the onset of the degenerative process was delayed by several years. Cranial cruciate ligaments removed from dogs after ligament failure not only had degenerative disease, but also had undergone unsuccessful attempts at repair. In contrast, fibrous repair was rarely present in intact ligaments of asymptomatic dogs with degenerative disease of the cranial cruciate ligament.