The Effect of Triple Pelvic Osteotomy on the Articular Contact Area of the Hip Joint in Dysplastic Dogs: An in Vitro Experimental Study

Objective —To investigate the effect of triple pelvic osteotomy (TPO) on articular contact area and acetabular coverage of dysplastic hip joints in dogs.
Study Design —Articular contact area and femoral head coverage by the acetabulum were computed in vitro in normal and dysplastic canine hips. The effect of TPO on articular contact and coverage was then analyzed in the dysplastic hips.
Sample Population—Five normal and six dysplastic canine cadaver specimens.
Methods —Contact area and coverage of loaded hips were computed using serial computed tomography scan images before and after TPO. Three angles of acetabular ventroversion (AVV) were studied (20°, 30°, and 40°). Using a custom-designed hinge plate, angles of spontaneous hip reduction in dysplastic hips were compared with previously recorded angles of reduction determined by the Ortolani test.
Results —Contact area significantly increased from 0° to 30° of AVV, then remained virtually unchanged. Coverage significantly increased from 0° to 20° of AVV. Both contact and coverage of normal hips were similar, yet significantly smaller than those of dysplastic hips once reduction had occurred. The experimental angles of reduction were significantly smaller and poorly correlated with the angles of reduction determined by the Ortolani test. Although coverage continued to increase with AVV, the actual joint contact area did not significantly vary after relocation of the femoral head.
Conclusions —This study suggests that increasing AVV beyond 20° does not significantly improve the beneficial effects of TPO and therefore should be carefully weighed against increased risks of postoperative complications associated with large angles of AVV.     

CT and gross pathology are comparable methods for detecting some degenerative sacroiliac joint lesions in dogs

Degenerative sacroiliac joint disease is a cause of lumbosacral pain in dogs; however, published information on cross‐sectional imaging characteristics is limited. Objectives of this retrospective, secondary analysis, methods‐comparison study were to test hypotheses that CT lesions reported in humans with degenerative sacroiliac joint disease are also present in dogs, and that CT is comparable to gross pathology for detecting these lesions. Matched CT and gross pathology slice images of 30 sacroiliac joints were retrieved from a previous prospective, canine cadaver study. A veterinary radiologist interpreted randomized CT images for each joint based on previously published CT characteristics of lesions in humans with degenerative sacroiliac joint disease. A veterinary pathologist independently interpreted randomized gross pathology images using the same criteria. All joints had at least one CT lesion consistent with degenerative sacroiliac joint disease. A new CT lesion was also identified and termed “subarticular cleft.” The CT and gross pathology methods agreed for detecting joints with subchondral sclerosis, subchondral erosion, and intra‐articular ankylosis lesions (P > .05, McNemar's test), but disagreed for detection of joints with subchondral cyst, para‐articular ankylosis, and subarticular cleft lesions (P ≤ .05). Using gross pathology as the reference standard, CT had 100% sensitivity for detection of subarticular cleft and subchondral cyst lesions, with 56% and 22% specificity, respectively. Para‐articular ankylosis lesions were detected by CT but not by gross pathology. Findings supported the hypothesis that CT lesions reported in humans with degenerative sacroiliac joint disease are also present in dogs, and partially supported the hypothesis that CT is comparable to gross pathology for detecting joints with these lesions.     

The pathogenesis of canine hip dysplasia.

Dogs with CHD are born with normal hips that subsequently undergo varying degrees of subluxation of the coxofemoral joint. Although the etiology of CHD is multifactorial, the pathogenesis or stages of change within the affected coxofemoral joint(s) are similar regardless of cause. With the onset of the disease, there are progressive structural changes including joint laxity and femoral head subluxation; swelling, stretching, fraying, and eventual rupture of the teres ligament; a shallow, flattened acetabulum, deformity of the head; erosion of articular cartilage, eburnation of subchondral bone, DJD; and periarticular osteophyte formation.     

The pathology of canine hip dysplasia.

Although the complete pathogenesis of cartilage damage in canine hip dysplasia has not been completely worked out, it appears that joint laxity with resultant excessive stresses upon articular cartilage is the initiating factor. Grossly, this damage is characterized by cartilage thinning with potential exposure of subchondral bone, osteophyte formation, and pannus formation. Microscopically, there is a marked variation in chondrocyte cellularity, with focal regions of hypocellularity and chondrocyte clusters and synovial lining cell hyperplasia and hypertrophy as well as a decrease in proteoglycan content. This latter change has been substantiated biomechanically. Ultrastructural studies indicate that there is extensive alteration of collagen organization within the cartilage.     

Evaluation of a method for experimental induction of osteoarthritis of the hip joints in dogs

OBJECTIVE: To evaluate a method for experimental induction of osteoarthritis in the hip joints of dogs. ANIMALS: 12 mixed-breed dogs. PROCEDURE: A unilateral triple pelvic osteotomy was performed. In 6 dogs, the iliac osteotomy was repaired with 45 degrees of internal rotation, reducing coverage of the femoral head by the acetabulum. In the other 6 dogs, the fragments were repaired in anatomic alignment. Radiography, force plate evaluations, and subjective lameness evaluations were performed before and after surgery. Dogs were euthanatized 7 months after surgery, and samples of cartilage and joint capsule were examined histologically. RESULTS: Subjective lameness scores, radiographic appearance of the hip joints, and Norberg angles were not significantly different between groups; however, force plate evaluations did reveal significant differences in vertical ground reaction forces. Femoral head coverage was significantly decreased with rotation of the acetabulum. Mild inflammatory changes were discernible in the joint capsule and articular cartilage of some dogs in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that 45 degrees internal rotation of the acetabulum does not consistently induce biologically important osteoarthritic changes in the hip joints of dogs.     

The Innervation of Canine Hip Joint Capsule: An Anatomic Study

To clarify the contributions of the nerves supplying the canine hip joint capsule for clinical application, cadaver study of six healthy mongrel dogs was performed. The pelvises and hindlimbs of cadavers were dissected and fixed in formaldehyde. Innervation of the joint capsule was investigated with the aid of an operative microscope. As a result, the canine hip joint capsule receives multiple innervations from articular branches of four nerves. They are articular nerve fibres of femoral, obturator, cranial gluteal and sciatic nerves from the cranioventral, caudoventral, craniolateral and dorsolateral directions of the joint, respectively. No branch originating from the caudal gluteal nerve was observed innervating the hip joint capsule. Our data provides useful information for research on the canine hip joint, including pain analysis with hip disorders and surgical nerve blockade to relieve pain.     

Influence of intensity and changes of physical activity on bone mineral density of immature equine subchondral bone

Reasons for performing study: Subchondral bone provides structural support to overlying articular cartilage and plays an important biomechanical role in osteochondral diseases. Mechanical features of bone correlate strongly with bone mineral density, which is directed by the loading conditions to which the tissue is subjected. Objective: To investigate the influence of physical activity levels on subchondral bone mineral density (sBMD) in foals during early development. Methods: Three groups of foals were subjected to different physical activity levels from birth until age 5 months. A proportion of these foals were subjected to euthanasia at 5 months while remaining foals were subjected to similar physical activity levels for 6 months until euthanasia at 11 months. Osteochondral specimens were collected for measurement of sBMD with peripheral quantitative computed tomography at 2 differently loaded anatomical sites of the proximal phalangeal bone at 1, 2, 3, 4 and 5 mm depth from the osteochondral junction. Results: Growth significantly increased sBMD but by a different amount depending on anatomical location and physical activity level. Significantly higher sBMD was found at the habitually loaded central area in comparison to the intermittently peak loaded marginal site. Exercise increased sBMD throughout the whole depth of analysed tissue, but changes were generally more obvious at a depth of 2 mm. Interestingly, foals subjected to additional sprint training preserved the exercise‐induced sBMD increase at the habitually loaded central area during the 6 months of the second phase of the study. Conclusions: Habitual low‐intensity loading elicits a greater response in sBMD in quantitative terms than high‐intensity low‐frequency loading at the sites investigated in this study. Future sBMD may be influenced by means of well‐tailored exercise regimens at young age. Potential relevance: Specific physical activity levels during early development may potentially reduce the prevalence of osteochondral injury later in life.     

In vitro evaluation of metacarpophalangeal joint loading during simulated walk

Reasons for performing study: Insight into the loading pattern of the articular cartilage surface during the complete stride is important as biomechanical factors play a pivotal role in the pathogenesis of joint trauma and osteoarthritis (OA). Objectives: To determine the loading pattern in the equine MCP articulation in vitro during simulated walk. Methods: Eight cadaveric limbs from mature Dutch Warmblood horses were loaded in a pneumatic loading device in 6 different positions (A1‐A6). The pressure distribution on the articular surface of the proximal phalanx (P1) was measured at 7 sites (S1‐7) using intra‐articularly placed pressure sensitive films, which were analysed by scanning and densitometry. Results: Pressures recorded after mid‐stance (A4, 5, 6) were significantly (P<0.05) higher than those before (A1, 2, 3) and showed the biphasic loading pattern of the walk at all sites, except for the site halfway along the sagittal groove (S7). At S7, there was a linear increase in pressure during the progress of the stance phase of the stride in most horses. Medially (S4, 5, 6) the pressure was significantly higher than laterally (S1, 2, 3) (P<0.05). Conclusions and potential relevance: The heavier medial loading coincides with the location where articular cartilage degeneration in the process of OA in the equine MCP joint is known to start. The discrepancy between the loading of the central groove and the other parts of the joint may result in large stress differences at the end of the stance phase, which might be related to the pathogenesis of stress fractures in the first phalanx and distal third metacarpal bone.     

10 years experience with denervation of the hip joint capsule for treatment of canine hip joint dysplasia and arthrosis

Denervation of the canine hip joint capsule is described as a surgical therapy method in the treatment of canine hip joint dysplasia and arthrosis. The goal of this operation is a removal of the pain immediately and a reactivation of the dynamic active component of the hip joint in moving the body forward. Simple removal of the periosteum of the craniolateral acetabulum edge destroys the rami articulares of the cranial glutaeal nerve and the rami articulares dorsalis of the sciatic nerve. Within 10 years now we performed the denervation of the canine hip joint capsule. Evaluation of the post operative clinical course in 269 cases revealed an impressive improvement of lameness due to pain relief in almost 92% of the cases.     

Evaluation of increased subchondral bone density in areas of contact in the metacarpophalangeal joint during joint loading in horses

OBJECTIVE: To quantitatively evaluate contact area under 2 loads and subjectively compare contact areas with subchondral bone (SCB) density patterns in intact metacarpophalangeal joints of horses. SAMPLE POPULATION: 6 forelimbs from horses without musculoskeletal disease. PROCEDURES: Computed tomographic scans of intact metacarpophalangeal joints were analyzed to obtain SCB density measurements. Each limb was loaded on a materials testing system to 150 degrees and 120 degrees extension in the metacarpophalangeal joint, and the joint was stained via intra-articular injection with safranin-O or toluidine blue, respectively. Each joint was disarticulated, and the surface area was digitized. Total articular surface area, contact area, and percentage contact area at each angle were calculated for the distal third metacarpal condyles, the proximal phalanx, and the proximal sesamoid bones. RESULTS: Contact area on the third metacarpal condyles, proximal sesamoid bones, and the proximal phalanx significantly increased with increased load. Areas of contact subjectively appeared to have a higher density on computed tomographic scans. CONCLUSIONS AND CLINICAL RELEVANCE: Areas consistently in contact under higher load were associated with increased SCB density. This supports the idea that the SCB adapts to the load applied to it. As load increased, contact area also increased, suggesting that areas not normally loaded may have a high degree of stress during impact loading. Quantifying how contact in the joint changes under different loading conditions and the adaptation of the bone to this change in normal and abnormal joints may provide insight into the pathogenesis of osteochondral disease.     

DEVELOPING A TECHNIQUE FOR ULTRASOUND‐GUIDED INJECTION OF THE ADULT CANINE HIP

An accurate method for guiding injections into the canine hip would facilitate diagnostic localization of lameness and targeted treatments. Ultrasound‐guided hip injections are commonly used in humans and large animals. Aims of this prospective study were to describe ultrasound (US) anatomy of the adult canine hip and determine the feasibility and accuracy of intra‐articular placement of injectate using US‐guidance. Seven adult dogs were used to describe US anatomy, five dog cadavers were used to assess the feasibility of the injection technique and 11 dog cadavers were used to assess accuracy of injections. For the accuracy test, 22 joints were injected with iodinated contrast medium by three operators with different experience. With dogs in lateral recumbency, the hyperechoic femoral head surface was identified by following the femoral neck from the greater trochanter or the acetabular rim was localized by following caudally the ilium from the iliac wing.  An anechoic gap between the femoral head and acetabular surface represented the joint. The capsule was visible as a triangular echoic structure and the femoral head articular cartilage appeared as an anechoic band. The needle was inserted axial to the greater trochanter and directed in a dorsolateral–ventromedial direction toward the joint space and then pushed through the capsule. Based on postinjection radiography, accuracy was 81.8% at first attempt and 100% at second attempt. This study indicated that US‐guided injection is a feasible and accurate technique for injecting the adult canine hip. Future studies in live dogs are needed to assess safety and efficacy.     

Evaluation of subchondral bone mineral density associated with articular cartilage structure and integrity in healthy equine joints with different functional demands

OBJECTIVE: To determine and correlate subchondral bone mineral density and overlying cartilage structure and tensile integrity in mature healthy equine stifle (low magnitude loading) and metacarpophalangeal (high magnitude loading) joints. ANIMALS: 8 healthy horses, 2 to 3 years of age. PROCEDURE: Osteochondral samples were acquired from the medial femoral condyle (FC) and medial trochlear ridge (TR) of the stifle joint and from the dorsal (MC3D) and palmar (MC3P) aspects of the distal medial third metacarpal condyles of the metacarpophalangeal joint. Articular cartilage surface fibrillation (evaluated via India ink staining) and tensile biomechanical properties were determined. The volumetric bone mineral density (vBMD) of the underlying subchondral plate was assessed via dual-energy x-ray absorptiometry. RESULTS: Cartilage staining (fibrillation), tensile moduli, tensile strength, and vBMD were greater in the MC3D and MC3P locations, compared with the FC and TR locations, whereas tensile strain at failure was less in MC3D and MC3P locations than FC and TR locations. Cartilage tensile moduli correlated positively with vBMD, whereas cartilage staining and tensile strain at failure correlated negatively with vBMD. CONCLUSIONS AND CLINICAL RELEVANCE: In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way.     

High field (4.7 T) magnetic resonance imaging of feline hip joints

Magnetic resonance imaging (MRI) is a non-invasive technique widely used to investigate degenerative joint disease (DJD). In this study, we obtained magnetic resonance images of feline hip joints, using a high magnetic field MRI unit (4.7 tesla) with proton density (PD)-weighted and T2-weighted fast spin-echo (FSE). PD-weighted FSE provided detailed anatomical images of feline hip joints with superb depiction of subchondral bones of the femoral head and acetabulum. Articular cartilage (AC) was also visualized with PD-weighted and T2-weighted FSE; however, mild AC lesions noted on gross examination were not detectable with these sequences.     

Comparison of trochlear block recession and trochlear wedge recession for canine patellar luxation using a cadaver model

OBJECTIVE: To compare trochlear block recession (TBR) to trochlear wedge recession (TWR) with regards to patellar depth (percentage of patellar volume under the trochlear ridges), patellar articular contact, percentage of recessed trochlear surface area, and resistance to patellar luxation. STUDY DESIGN: In vitro computed tomography (CT) and biomechanical evaluation using a cadaver model. SAMPLE POPULATION: Twelve normal, large-breed canine cadavers. METHODS: Bilateral pelvic limb specimens with intact stifle joints were mounted on a positioning device. The femoral trochlear ridges were reduced to provide a standard shallow trochlea. TBR or TWR was performed to a standard depth randomly on paired specimens. CT and biomechanical evaluations were performed pre- and postoperatively in both an extended (148 degrees ) and flexed (113 degrees ) stifle position. CT images were digitized and measurements made using an image-analysis software program. Biomechanical testing consisted of applying 40 degrees of internal tibial rotation and documenting patellar luxation. RESULTS: The change in trochlear depth (depth of recession) was not significantly different between groups. In the extended stifle position (patella in the proximal trochlea), patellar depth and patellar articular contact with the recessed trochlea were significantly greater after TBR compared with TWR. The percentage of recessed trochlear surface area was significantly greater after TBR compared with TWR. In the extended position, a smaller percentage of the patellae luxated within 40 degrees of internal tibial rotation after TBR compared with TWR. CONCLUSIONS: TBR increases proximal patellar depth, increases patellar articular contact with the recessed proximal trochlea, recesses a larger percentage of trochlear surface area, and results in a greater resistance to patellar luxation in an extended position as compared with TWR. CLINICAL RELEVANCE: TBR may help limit the development of stifle DJD in dogs treated for canine patellar luxation.     

In vitro force mapping of normal canine humeroradial and humeroulnar joints

OBJECTIVE: To determine the distribution of force between the articular surfaces of the humerus and radius and between the humerus and ulna in normal canine forelimbs. SAMPLE POPULATION: 12 cadaveric canine right forelimbs. PROCEDURE: Transarticular force maps were created by placing a tactile array pressure sensor into the elbow joint cavity and loading cadaveric forelimbs in a materials testing system. Mean joint forces were determined at loads of 50, 100, 150, and 200 N. RESULTS: All tests produced 2 distinct areas of high load that corresponded with the proximal articular surfaces of the radius and ulna. Mean forces for the radial proximal articular surface were slightly but significantly greater than for the ulna, averaging 51% to 52% of total force for all applied loads. CONCLUSIONS AND CLINICAL RELEVANCE: The proximal articular surface of the ulna contributes substantially to load transfer through the canine elbow joint. Abnormalities, which increase this load, might contribute to canine elbow joint dysplasia, specifically fragmentation of the medial coronoid process and osteochondritis dissecans of the medial aspect of the humeral condyle. In the treatment of these conditions, the normal force distribution within the canine elbow joint should be taken into consideration.     

Biomechanical Evaluation of Acetabular Cup Implantation in Cementless Total Hip Arthroplasty

Objective: To report biomechanical properties of the Biologic Fixation System (BFX) acetabular cup impacted into a normal canine pelvis and to compare the effect of implant positioned to and beyond the medial acetabular wall. Study Design: In vitro cadaveric study. Animals: Hemipelves of mature, large‐breed dogs (n=6). Methods: For each dog, 1 hemipelvis was reamed to the depth of the acetabular wall (group A) and 1 was reamed an additional 6 mm after penetration of the medial cortex of the acetabulum (group B). The hemipelves were implanted with acetabular cups and loaded in compression through a matching femoral prosthetic component until failure. Specimen stiffness, and failure displacement, load, and energy were determined from load and displacement data and results between groups compared with a paired t‐test. Results: Mean failure load was greater in group A (3812 ± 391 N) than group B (2924 ± 316 N; P<.014). No other differences (P>.05) were observed between groups. Bone fracture (n=5) and cup displacement (1) occurred in group A whereas in group B there were 3 fractures and 3 cup displacements. Conclusions: Although medial placement of the BFX cup affected compressive failure loads, failure loads for both groups exceeded normal physiologic loads. Clinical Relevance: Medial positioning of the acetabular cup does not appear to compromise acetabular implant‐pelvic stability under normal physiologic loads. Because arthroplasty candidates often have abnormal acetabular architecture, mechanical properties of the cup placed in acetabula without a dorsal rim should be investigated.     

Computed tomographic evaluation of growth-related changes in the hip joints of young dogs

OBJECTIVE: To evaluate changes in canine hip joint characteristics during growth via computed tomography (CT) and compare CT features of hip joints with and without laxity in young dogs placed in 2 imaging positions. ANIMALS: 21 dogs (42 hip joints). PROCEDURES: From 2 to 12 months after birth, CT examinations of the acetabulum of each hip joint in simulated normal standing and simulated weight-bearing positions were performed monthly for all dogs. Acetabular angle, dorsal acetabular rim angle (DARA), and femoral head diameter (FHd) were analyzed as skeletal variables; the lateral center edge angle (LCEA), dorsolateral subluxation (DLS) score, and center distance (CD) index were analyzed as joint laxity variables. At 12 months, all dogs underwent the Ortolani test to as-sess hip joint laxity. RESULTS: Hip joint laxity was detected in 5 dogs (10 joints) at 12 months of age; from 2 months, the acetabular angle and FHd increased and DARA decreased significantly until 5 months and the LCEA and DLS score increased significantly until 6 months. In nonlax hip joints in both positions, the CD index decreased significantly until 4 months of age and be-came stable thereafter. In lax hip joints, the CD index increased from 4 through 12 months; between 8 and 12 months, these changes were significantly greater in the weight-bearing position than in the standing position. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that CT-detected abnormalities in the DARA and CD index during body weight loading might be useful indicators of hip dysplasia in 2- to 6-month-old dogs.     

Biochemical development of subchondral bone from birth until age eleven months and the influence of physical activity

Subchondral bone provides structural support to the overlying articular cartilage, and plays an important role in osteochondral diseases. There is growing insight that the mechanical features of bone are related to the biochemistry of the collagen network and the mineral content. In the present study, part of the normal developmental process and the influence of physical activity on biochemical composition of subchondral bone was studied. Water content, calcium content and characteristics of the collagen network (collagen, hydroxylysine, lysylpyridinoline (LP) and hydroxylysylpyridinoline (HP) crosslinking) of subchondral bone were measured in newborn foals, 5-month-old foals (pasture-grown and box-confined) and 11-month-old foals at 2 differently loaded sites of the proximal articular surface of the first phalanx. During the first 5 months postpartum, water and hydroxylysine content decreased significantly while calcium and collagen content and the amount of HP and LP crosslinks increased significantly. The withholding of physical activity during this developmental phase affected the biochemical characteristics of subchondral bone only at the site that is loaded during physical exercise. At this site, calcium content and both HP and LP crosslink levels increased significantly less than in pasture-raised animals. During development from 5-11 months, measured parameters remained essentially constant, except for water content, which decreased further. It is concluded that substantial changes, presumed to be largely exercise-driven, take place during the normal process of development in the biochemical composition of equine subchondral bone. Normal development of subchondral bone is presumably important for the normal functional adaptation of this bone to the loading conditions it is subjected to and therefore essential to resist the future biomechanical challenges the horse will encounter during its athletic career. The findings from this study and the assumed important role of subchondral bone quality in the pathogenesis of osteochondral disease merit more attention to the role of the collagen network in subchondral bone.     

Study of cartilage and bone layers of the bearing surface of the equine metacarpophalangeal joint relative to different timescales of maturation

REASONS FOR PERFORMING STUDY: A detailed and comprehensive insight into the normal maturation process of the different tissues that make up functional units of the locomotor system such as joints is necessary to understand the influence of early training on musculoskeletal tissues. OBJECTIVES: To study simultaneously the maturation process in the entire composite structure that makes up the bearing surface of a joint (cartilage, subchondral and trabecular bone) in terms of biochemical changes in the tissues of juvenile horses at 2 differently loaded sites of the metacarpophalangeal joint, compared to a group of mature horses. HYPOTHESIS: In all the structures described above developmental changes may follow a different timescale. METHODS: Age-related changes in biochemical characteristics of the collagen part of the extracellular matrix (hydroxylysine, hydroxyproline, hydroxypyridinum crosslinks) of articular cartilage and of the underlying subchondral and trabecular bone were determined in a group of juvenile horses (n = 13) (Group 1, age 6 months-4 years) and compared to a group of mature horses (n = 30) (Group 2, >4 years). In both bony layers, bone mineral density, ash content and levels of individual minerals were determined. RESULTS: In cartilage, subchondral bone and trabecular bone, virtually all collagen parameters in juvenile horses were already at a similar (stable) level as in mature horses. In both bony layers, bone mineral density, ash- and calcium content were also stable in the mature horses, but continued to increase in the juvenile group. For magnesium there was a decrease in the juvenile animals, followed by a steady state in the mature horses. CONCLUSIONS: In horses age 6 months-4 years, the collagen network of all 3 layers within the joint has already attained a mature biochemical composition, but the mineral composition of both subchondral and trabecular bone continues to develop until approximately age 4 years. POTENTIAL RELEVANCE: The disparity in maturation of the various extracellular matrix components of a joint can be assumed to have consequences for the capacity to sustain load and should hence be taken into account when training or racing young animals.     

Comparison of measurements of dorsolateral subluxation of the femoral head and maximal passive laxity for evaluation of the coxofemoral joint in dogs

OBJECTIVE: To determine whether dorsolateral subluxation (DLS) of the femoral head reflects osseous conformation of the coxofemoral (hip) joint and represents a property distinct from maximum passive laxity of the hip joint in dogs. ANIMALS: 14 Labrador Retrievers, 16 Greyhounds, 58 Greyhound-Labrador Retriever mixed-breed dogs, and 1 Rottweiler. PROCEDURES: DLS of the femoral head (DLS score) and passive laxity of the hip joint (distraction index) were determined radiographically in 3 groups of dogs: not treated (167 joints of 84 dogs); before and after injecting 2 ml of hyaluronan into 25 hip joints of 13 dogs; and before and after unilateral triple pelvic osteotomy in 5 dogs. Results of the 2 methods were compared for each group. RESULTS: In untreated dogs, the correlation coefficient (r) of DLS score versus distraction index was -0.73 and -0.69 for 84 left and 83 right hip joints, respectively. Mean coefficient of determination (r2) for both hips was 0.5. Mean DLS score did not differ before and after intra-articular injection of hyaluronan into either hip joint, whereas mean distraction index increased significantly after intra-articular injection. Unilateral triple pelvic osteotomy resulted in a significant increase in DLS score, compared with values obtained before surgery. However, distraction index before and after surgery did not differ significantly. CONCLUSIONS AND CLINICAL RELEVANCE: The DLS test assesses the congruity of the acetabulum and the femoral head in a canine hip joint and thus represents a characteristic distinct from maximum passive laxity. The DLS score and the distraction index evaluate different components of hip joint stability.