Canine Hip Dysplasia

Diagnostic Imaging

a, b
J. Ryan Butler, DVM, MS *, Jennifer Gambino, DVM

KEYWORDS
 Hip-extended radiographs  Distraction radiography  Hip osteoarthritis
 Norberg angle  Computed tomography  MRI

KEY POINTS
 A properly positioned hip-extended radiograph is useful as a screening tool for hip
dysplasia and for detection of osteoarthritis but may not adequately represent the degree
of hip laxity.
 The caudal curvilinear osteophyte (Morgan line) and circumferential femoral head osteo-
phyte represent 2 of the earliest signs of coxofemoral osteoarthritis.
 A PennHip distraction index of 0.3 in dogs 16 weeks of age is generally considered to
indicate an increased risk of future osteoarthritis development.
 MRI modalities such as T2 mapping and dGEMRIC imaging allow for a more sensitive
assessment of cartilage health.

INTRODUCTION

Imaging of the canine pelvis couple with physical exam findings are the principle
methods used to screen for and diagnose canine hip dysplasia, especially when
evaluating juvenile patients in the early course of the disease. Once the disease
has progressed to a state of severe osteoarthritis, the ability to diagnose the condi-
tion becomes less complicated because the radiographic changes are more readily
apparent. Many imaging modalities such as radiography, computed tomography
(CT), ultrasound, and MRI can be used in the assessment of canine patients with
hip dysplasia. These imaging modalities are used for the preliminary diagnosis of
hip dysplasia as well as in the surveillance of disease progression and the evaluation
of the success of treatment interventions. Each imaging modality has inherent

Disclosure Statement: The authors have nothing to disclose.

a
Small Animal Surgery, Department of Clinical Sciences, College of Veterinary Medicine, Mis-
sissippi State University, PO Box 6100, Mississippi State, MS 39762, USA; b Diagnostic Imaging,
Department of Clinical Sciences, College of Veterinary Medicine, Mississippi State University,
PO Box 6100, Mississippi State, MS 39762, USA
* Corresponding author.
E-mail address: ryan.butler@msstate.edu

Vet Clin Small Anim 47 (2017) 777–793

http://dx.doi.org/10.1016/j.cvsm.2017.02.002 vetsmall.theclinics.com
0195-5616/17/ª 2017 Elsevier Inc. All rights reserved.
778 Butler & Gambino

advantages, disadvantages, and limitations. This article discusses the various imag-
ing modalities and their utility with regard to canine hip dysplasia.

RADIOGRAPHY

Hip dysplasia is defined as radiographic evidence of joint laxity or signs of osteoar-

thritis, with hip laxity being the primary risk factor for osteoarthritis development.1 Ra-
diographs have been used for diagnosing hip dysplasia since the condition was first
reported in 1935.2 Numerous radiographic projections can be used to evaluate and
screen patients. The most commonly reported techniques include hip-extended radi-
ography, Norberg angle, distraction-stress radiographs, and the dorsal acetabular rim
(DAR) view.

Hip-Extended Radiography
The ventrodorsal, hip-extended radiograph is the most commonly used radiographic
projection for evaluating canine hips. Proper positioning for this view often requires
heavy sedation and/or general anesthesia and is achieved by placing the animal in
dorsal recumbency, extending the hind limbs caudally, and slightly internally rotating
the femurs. A properly positioned radiograph should include a symmetric pelvis, par-
allel and fully extended femurs, and patellas that are centered within the femoral
trochlea (Fig. 1A).3 This radiographic position is the one most often used by screening
organizations such as the Orthopedic Foundation for Animals (OFA), Fédération Cyn-
ologique Internationale, and the British Veterinary Association/Kennel Club. Common

Fig. 1. (A) Properly positioned hip-extended radiographic view should include a symmetric
pelvis, parallel and fully extended femurs, and patellas that are centered within the femoral
trochlea. (B) Common errors in positioning include failure to fully extend and internally
rotate the femurs.
 Diagnostic Imaging 779

errors in positioning include failure to fully extend the limbs and inadequate internal
rotation of the femurs (Fig. 1B).
One of the main advantages of the hip-extended radiograph is the ability to evaluate
the joint for signs of osteoarthritis. Radiographic evidence of osteoarthritis of the cox-
ofemoral joint includes femoral periarticular osteophyte formation, subchondral scle-
rosis of the craniodorsal acetabulum, osteophytes along the acetabular margin, and
joint remodeling (Fig. 2).4 The caudal curvilinear osteophyte (CCO, or Morgan line)
and circumferential femoral head osteophyte (CFHO) (Fig. 3) represent 2 radiographic

Fig. 2. (A) Moderate radiographic evidence of osteoarthritis of the coxofemoral joint

including periarticular osteophyte formation and subchondral sclerosis of the craniodorsal
acetabulum. (B) More severe cases include substantial thickening of the femoral neck. (C)
Extreme cases can present with substantial joint remodeling and periarticular osteophytosis.
780 Butler & Gambino

Fig. 3. Early radiographic signs of osteophytosis (as indicated by the arrows) include the CFHO
(A) and the caudocurvilinear osteophyte (more specifically, an enthesophyte, also called a Mor-
gan line) (B). Note the progression of periarticular osteophyte formation along the femoral
neck and the increased opacity of the Morgan line. The puppy line (arrows) (C) is located in a
similar location to the Morgan line and is typically seen in dogs less than 18 months of age. How-
ever, the puppy line is more diffuse and subtle when compared with the Morgan line and is of
no clinical significance. (From Smith GK, Karba GT, Angello KA, et al. Pathogenesis, diagnosis,
and control of canine hip dysplasia. In: Tobais KM, Johnson SA, editors. Veterinary surgery: small
animal, vol. 1. 1st edition. St Louis (MO): Saunders/Elsevier; 2012. p. 836, with permission; and
[A] Szabo SD, Biery DN, Lawler DF, et al. Evaluation of a circumferential femoral head osteo-
phyte as an early indicator of osteoarthritis characteristic of canine hip dysplasia in dogs.
J Am Vet Med Assoc 2007;231(6):890, with permission.)

features that have been reported to represent early osteophyte formation that predict
later development of more characteristic signs of osteoarthritis.5–9 However, the CCO
and CFHO radiographic signs are not yet adopted by the screening organizations. The
puppy line is a more subtle opacification of the femoral neck seen in the area of the
CCO in young dogs (see Fig. 3C).5,7,8 It is important to differentiate between the puppy
line and the CCO because the puppy line represents an incidental finding that is often
gone by 18 months of age and has no correlation with later development of
osteoarthritis.8
 Diagnostic Imaging 781

Although radiographic evidence of osteoarthritis occurs in most cases of hip

dysplasia, this clinical feature occurs later in the disease process.3,10 In the absence
of radiographic signs of osteoarthritis, joint subluxation on the hip-extended radio-
graph is considered diagnostic for hip dysplasia (Fig. 4).11,12 The degree of subluxa-
tion can be subjectively evaluated or objectively quantified using methods such as the
Norberg angle and femoral overlap (% coverage), which are discussed separately.
However, the hip-extended radiograph may mask joint subluxation by tightening the
joint capsule as the limbs are extended and forcing the femoral heads to sit more
deeply with the acetabula. The joint capsule tightening can make dysplastic hips
appear normal and may be a factor contributing to a high rate of false-negative radio-
graphic evaluations.13,14
The relatively low interobserver and intraobserver agreement seen when used as a
screening tool further complicates the incidence of false negative evaluations.3,15–17
Even when specific radiographic markers of osteoarthritis such as the CFHO and
CCO are evaluated, the reliability within and between experienced observers is low,
which increases errors in the screening process and surgical decision making.18
Norberg Angle and Femoral Overlap
The Norberg angle and femoral overlap (otherwise known as % coverage) represent 2
means to objectively quantify the degree of femoral subluxation seen on hip-extended
radiographs. The Norberg angle is calculated by measuring the angle between a line
that connects the center of the femoral head between the left and right hips and a line

Fig. 4. Hip-extended radiograph of an immature dog with bilateral joint subluxation consis-
tent with a diagnosis of hip dysplasia.
782 Butler & Gambino

that connects the center of the femoral head with the lateral tip of the cranial acetab-
ular rim (Fig. 5A).11 A larger angle indicates a deeper acetabulum and more congruent
hips, whereas smaller angles are consistent with increasing degrees of subluxation. A
Norberg angle of greater than 105 is generally considered to be normal.19 Norberg
angles less than 105 are consistent with hip laxity. Femoral overlap is also a measure-
ment of femoral displacement from the acetabulum. Normal joint overlap is consid-
ered to be 50% with values less than this being consistent with joint incongruity
(Fig. 5B).20 The percentage of femoral overlap is commonly used to determine the
postoperative success of the triple pelvic osteotomy (TPO) procedure.21
Disadvantages of using either the Norberg angle or percentage of femoral overlap
include the significant effect of pelvic positioning on the measurement and, as previ-
ously discussed, the possible effect of hip extension on joint laxity.22 Slight rotation of
the pelvis on the radiograph will substantially affect both the Norberg angle and the
femoral overlap, causing the congruency of one hip joint to be overestimated, with un-
derestimation of the contralateral hip joint.22 Furthermore, the use of a strict reference
value for the Norberg angle is not appropriate because a value consistent with
dysplastic hips can vary between breeds.23

Distraction-Stress Radiographs
Distraction-stress radiography techniques are used to better estimate the degree of
passive laxity of the coxofemoral articulation. Ideally, the techniques would determine
the degree of laxity present during ambulation, otherwise known as functional laxity.
However, a method that accurately determines functional laxity is not currently

Fig. 5. Joint subluxation can be quantified with either the Norberg angle (A) or % Femoral
Overlap (% Coverage) (B).
 Diagnostic Imaging 783

available. The distraction stress radiography methods most commonly used include
the University of Pennsylvania Hip Improvement Program (PennHip), Dorsolateral
Subluxation Measurement (DLS), and the Flückiger Subluxation Index.20
The PennHip method of radiography is performed in a heavily sedated or anesthe-
tized animal. Three radiographic projections are obtained: a standard hip-extended
radiograph, a neutral stance-phase compression radiograph, and a neutral stance-
phase distraction radiograph (Fig. 6).14 For the distraction radiograph, an acrylic
fulcrum device is placed between the proximal femurs, and an adduction force results
in hip subluxation in abnormal dogs. From the distraction radiograph, a distraction in-
dex (DI) can be calculated as the degree of femoral head subluxation from the

Fig. 6. The PennHip radiographic method includes 3 radiographic views: standard hip-
extended radiograph (A), compression radiograph (B), and a distraction radiograph (C).
The hip-extended radiograph is used to evaluate the joint for signs of osteoarthrosis; the
compression radiograph is used to determine joint congruency (compression index), and
the distraction radiograph is used to determine the degree of passive laxity (DI).
784 Butler & Gambino

acetabulum. A DI score of 0 equates to no subluxation, whereas a DI score of 1 equa-

tes to a fully luxated joint.20 The compression radiograph is used to evaluate joint con-
gruency, as inability to fully compress the joints and achieve complete congruity (a
compression index 0) may be an early estimator of osteoarthritis.24 The hip-
extended radiograph is used to evaluate the coxofemoral joints for standard evidence
of osteoarthritis.
The significance of the DI score has been thoroughly investigated, and its signifi-
cance in predicting the future development of osteoarthritis is reported.5,25–28 A major
advantage to the PennHip method is its ability to predict the future development of
osteoarthritis in younger animals. The method can be predictive for osteoarthritis
development in animals as young as 16 weeks of age.27,29,30 In addition, the PennHip
method allows researchers the ability to develop breed-specific DI profiles to provide
a better estimate of future breed-related osteoarthritis development.26,28 Although
there are breed differences, a DI of greater than 0.3 is generally accepted as the cutoff
value for osteoarthritis susceptibility.31 However, the passive laxity measured by DI
may not fully account for all forces acting across the joint in the awake and ambulatory
dog. For example, a heavily muscled dog may be more tolerant of a higher DI and be
less likely to develop osteoarthritis compared with a more petite dog of the same
breed with the same DI.32
Because of its ability to predict osteoarthritis development at an earlier age, the
PennHip method is often used for screening at-risk breeds before use for breeding,
to determine candidacy for preventative procedures such as the juvenile pelvic sym-
physiodesis, or to initiate preventative measures such as calorie restriction in “at-risk”
animals.33,34 A minor disadvantage to the PennHip method is the requirement for vet-
erinarians to attend a training course for certification in order to take and submit the
radiographs. Although this likely improves the quality of film submission and the clin-
ical relevance of the interpretations, it limits the availability of the program. It is impor-
tant to note that the PennHip program is not a pass/fail or certifying program: it is a
continuous scale that provides owners, breeders, and veterinarians information
regarding the susceptibility of a patient for osteoarthritis development. However,
definitive radiographic evidence of osteoarthritis will result in a designation of
“confirmed hip dysplasia.”20
The DLS is a distraction stress radiography technique that is similar in principle to
the PennHip method, but less rigorously investigated. Positioning for the test aims
to better simulate a weight-bearing position with the unrealistic goal of better esti-
mating functional laxity. To perform the test, the animal is anesthetized and placed
in sternal recumbency in a foam rubber mold with the hips flexed to a weight-
bearing angle, femurs adducted, and the stifles flexed (Fig. 7).20 In this position, the
femurs are forced to dorsolaterally subluxate, and the degree of subluxation is quan-
tified by determining the percentage of femoral overlap. A DLS score of 56% has been
reported to have similar clinical implications as a DI score of greater than 0.3.27,35,36
However, long-term studies in large populations of dogs are lacking. Furthermore,
as with the hip-extended method of radiography, the DLS score is highly dependent
on proper patient positioning and can be affected by arthritic changes within the
joint.20 Opponents of the technique also argue that the method does not truly place
the animal in a weight-bearing position because the hips are actually more extended
and adducted.20 Because of the lack of long-term studies and issues associated with
patient positioning, the clinical utility of this method is questionable.
The Flückiger Subluxation Index is similar in principle to the DLS method. However,
the animals are placed in dorsal recumbency with a lesser degree of hip adduction
(Fig. 8).37 A dorsally directed force is applied to the limbs, which results in dorsolateral
 Diagnostic Imaging 785

Fig. 7. To position a dog for the dorsolateral subluxation radiographic view, the patient is
placed in a rubber mold with the limbs adducted and the distal femurs slightly caudal to the
greater trochanters. (From Smith GK, Karba GT, Angello KA, et al. Pathogenesis, diagnosis,
and control of canine hip dysplasia. In: Tobais KM, Johnson SA, editors. Veterinary surgery:
small animal, vol. 1. 1st edition. St Louis (MO): Saunders/Elsevier; 2012. p. 840; with permission.)

hip subluxation. From the radiographs, circular gauges are placed over the femoral
heads and acetabula for calculation of a subluxation index, which is similar to the
DI. No studies have been performed that report the sensitivity, specificity, or predict-
ability for osteoarthritis development for this diagnostic method.20
Dorsal Acetabular Rim View
The DAR view was first described by Slocum and Devine38 in 1990. This radiographic
view is used to evaluate the dorsal aspect of the acetabular rim, which is the area of
the acetabulum that receives much of the stress concentration with subluxation of the
femoral head during ambulation.12,39–41 The DAR view achieves an unobstructed view
of the dorsal acetabula from a cranial to caudal perspective. To obtain this radiograph,
the patient is anesthetized and placed in sternal recumbency, and the rear limbs are
pulled cranially and held close to the animal’s body (Fig. 9). A spacer can be placed
below the tarsi to provide additional pelvic rotation. Correct radiographic positioning
results in superimposition of the ilial wings, ilial body, acetabulum, and tuber ischii,
with an unobstructed view of the dorsal acetabula.38

Fig. 8. To perform the Flückiger stress technique, the patient is placed in dorsal recumbency
with the hips extended to approximately 60 from the table top. A dorsally directed force
(arrow) results in coxofemoral subluxation in dysplastic dogs. The laxity is quantified radio-
graphically in manner similar to the PennHip radiographic method.
786 Butler & Gambino

Fig. 9. To position for the DAR view (A), the patient is placed in sternal recumbency with the
hind limbs pulled forward. The limbs are held parallel with the body with tape and the tarsi
are slightly elevated with sandbags. (B) This view allows visualization of the DARs (arrows,
outlined in yellow) as demonstrated in this pelvis model.

The DAR view is reportedly useful to document the degree of joint damage as the
acetabular rim progresses from sharply pointed in the normal dog to more rounded
and blunted with joint damage.42 However, the portion of the acetabula evaluated
by the DAR view, the DAR point, has been shown be approximately 37 caudal to
the point of maximum wear in the standing animal and may underrepresent changes
to the DAR.43 Some surgeons also use this view to measure the dorsal acetabular
slope to determine the appropriate degree of pelvic rotation when performing a
TPO.38,42,44–47 However, the DAR radiographic view is not widely used because diag-
nostic quality images can be difficult to obtain, and there is limited clinical utility of the
study when compared with other diagnostic methods such as joint palpation or DI
calculations.32

ULTRASOUND

Ultrasound imaging of human neonates has been used since 1980 as a screening tool
for hip dysplasia in at-risk patients.48,49 A similar technique has also been described in
the dog to detect joint laxity with mixed results.50–53 Disadvantages of the technique
include inability to evaluate acetabular morphology after approximately 8 weeks of
age in dogs because of femoral head ossification, subjectivity of the evaluation and
scoring systems, and the lack of normal reference values.20
Ultrasound of the canine hip usually includes a subjective assessment of the acetab-
ular morphology, determination of the acetabular angle of inclination (a-angle), and
cartilage roof angle (b-angle). The a-angle is an indicator of the bony remodeling of
the acetabulum, and the b-angle is an indicator of acetabular cartilage remodeling
(Fig. 10). Dynamic sonographic techniques also attempt to determine joint laxity by
reporting a distraction value.51 Generally, lower a-angle values are consistent with a
shallow acetabulum, and higher b-angles are consistent with blunting of the cartilage
rim.50–53 However, these ultrasonographic variables in young animals had no correla-
tion with the diagnosis of hip dysplasia in the mature animals.51 Furthermore, the clinical
utility of the ultrasound is highly operator dependent. For these reasons, ultrasound is
not routinely used for diagnosing or screening canine patients for hip dysplasia.20

COMPUTED TOMOGRAPHY

CT, although becoming more readily available in veterinary medicine, is not used
routinely for the evaluation of canine hips and is seldom used in pediatric patients
 Diagnostic Imaging 787

Fig. 10. Ultrasonographic measurement of hip congruity. The baseline (green) is parallel
with the ilial silhouette. The bony rimline (red) is drawn connecting the caudal edge of
the ilium in the acetabular fossa to the osseous convexity of the acetabular rim. The carti-
lage roof-line (blue) connects the osseous convexity of the bony acetabular rim to the carti-
lage roof triangle. The a-angle is the angle between the baseline and bony rimline. The
b-angle is the angle between the cartilage roof-line and the baseline. (From Fischer A, Flöck
A, Tellhelm B, et al. Static and dynamic ultrasonography for the early diagnosis of canine hip
dysplasia. J Small Anim Pract 2010;51:582; with permission.)

due to risks associated with ionizing radiation. Historically, the use of this modality in
people, and in canine research, supports the theory that the modality has merit in the
evaluation of dysplastic changes.20 CT provides accurate and easy evaluation of cox-
ofemoral joint indices while the animal is positioned in a weight-bearing position,
which may be a better indicator of the degree of functional laxity.54 Various CT hip
indices have been compared with PennHip and OFA conformation scores in an
attempt to predict hip microdamage and correlate findings with those seen on the
PennHip and OFA evaluations. Both the center edge angle (CEA) and dorsal acetab-
ular sector angle (DASA) were shown to correlate with the PennHip DI and joint micro-
damage at 30 months of age in a cohort of research dogs predisposed to coxofemoral
osteoarthritis (Fig. 11).55 Furthermore, the combined measures of CEA and DI and the
combined measures of DASA and Norberg Angle at 16 and 32 weeks of age, respec-
tively, were found to be predictive of future osteoarthritis development in the mature
animal.56 However, the normal reference ranges for these CT values and the ability
of these values to predict joint microdamage in a heterogeneous population of dogs
requires further investigation.

MRI

Conventional MRI is infrequently used for the evaluation of canine developmental

bone disorders in general. As an imaging modality, MRI exploits the hydrogen protons
of the water molecules within the patient and is an excellent modality for the evaluation
of soft tissues, ligamentous structures, joint capsule, and the proximal femoral physis.
MRI can provide a plethora of information regarding the health and integrity of the
788 Butler & Gambino

Fig. 11. Various hip indices can be determined from 2-dimensional CT images. Here the CEA
and DASA are shown. To determine these values, a line is drawn along the horizontal axis of
the pelvis to the center of the femoral head. A second line is drawn from the center of the
femoral head to the acetabular rim. The CEA (green) is the angle between the acetabular
rim and a line perpendicular to pelvic axis. The DASA (red) is the angle between the horizon-
tal pelvic axis and the acetabular rim.

subchondral bone with greater sensitivity than other modalities and is currently
considered the best noninvasive method for the assessment of articular cartilage.57
However, factors such as cost, time, required expertise, and need for general anes-
thesia likely preclude the frequency of the application of this modality with regard to
its use in juvenile canine patients for the evaluation of hip dysplasia.
Conventional MRI sequences such as short tau inversion recovery, T1-weighted
fast spoiled gradient echo, or T2* imaging are ideal for the evaluation of osseous struc-
tures, acetabular cup morphology, femoral head symmetry, and the proximal femoral
physes (Fig. 12). With proper positioning aids and foam padding, weight-bearing with
stress can be simulated within a large body coil with the dog positioned in sternal re-
cumbency. A stifle angle of approximately 135 and the pelvic axis at approximately
100 to 110 to the z-axis of the magnet can aid in this simulation.
Conventional magnetic resonance (MR) sequences do not provide a comprehensive
assessment of articular cartilage due to limitations related to spatial resolution and
biologic functional information.57 Two emerging MR methodologies that provide
high-resolution evaluation of the cartilage matrices and their physiologic properties
include delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 mapping.58
When used with gadolinium-based contrast agents in conjunction with T1-weighted
spin-echo inversion recovery pulse sequences, dGEMRIC is an advanced and more
sensitive protocol acquisition for the assessment of glycosaminoglycan (GAG) den-
sity. A loss of charge density within the articular cartilage is often associated with early
osteoarthrosis.58,59 With dGEMRIC imaging, an anionic gadolinium-based contrast
agent is given intravenously followed by 15 to 30 minutes of exercise. The MR images
are acquired approximately 2 hours later.60 The agent distributes within the cartilage
following active patient movement during the preimaging interim in a quantity that is
 Diagnostic Imaging 789

Fig. 12. Unenhanced, T1-weighted fast spoiled gradient echo, transverse (A) and sagittal (B)
images of a normal, juvenile, purpose-bred hound. Although not routinely used for evalu-
ating the canine pelvis for dysplastic changes, this modality can provide anatomic and phys-
iologic information regarding the subchondral bone and periarticular margins. Note the
discernible, isointense (to muscle), proximal femoral physis. (C) Enhanced, 3D, reconstruct-
able, dorsal, T1-weighted fast spoiled gradient echo image of an 8-year-old, mixed breed
dog with moderate, bilateral coxofemoral osteoarthrosis. Note the angular, periarticular os-
teophytic proliferation along the femoral head. These findings are not uncommonly
encountered in patients undergoing MR imaging of the lumbosacral junction or the peri-
neal region.

inversely proportional to the GAG content of the interrogated cartilage. The distribu-
tion of contrast is high in degraded cartilage void of GAGs, and conversely, low in
healthy cartilage where GAGs are abundant.58,60 Special software is needed for the
generation of T1 color maps that reflect the GAG quantification. In people, color-
coded T1 mapping has been shown to be useful for determining cartilage health
and can be a positive predictor of surgical outcome following periacetabular osteot-
omy compared with radiography.61
T2-weighted imaging is highly sensitive to water content and tissue hydration.58
Organized type II collagen fibers are associated with healthy cartilage and water con-
tent. Disruption of the cartilaginous matrices and anisotropy of these fibers leads to an
increase in water molecule content and interaction, which increase the T2-weighted
relaxation times.57 These T2 relaxation times increase linearly with cartilage damage.
Therefore, T2 mapping increases the T2 sensitivity for detecting cartilage damage.57
The use of both T2 mapping and dGEMRIC studies may enhance future studies of
cartilage degeneration associated with canine hip dysplasia and aid in the selection
of surgical candidates for juvenile surgical interventions such as the TPO.

ARTHROSCOPY

Although more invasive than diagnostic imaging techniques, arthroscopy can be used
to evaluate the coxofemoral joint with the advantage of being able to detect joint and
cartilage damage before the onset of radiographic sings of osteoarthritis.20 Holsworth
and colleagues10 demonstrated that approximately 50% of dogs without radiographic
signs of osteoarthritis had moderate to severe cartilage lesions seen arthroscopically.
Many surgeons agree that the presence of cartilage damage represents a contraindi-
cation for performing corrective osteotomies when treating hip dysplasia (such as with
the TPO procedure). Therefore, arthroscopy is often used as a diagnostic tool for
improved assessment of the surface of the articular cartilage before surgical
790 Butler & Gambino

interventions. (Please see Francisco Guevara and Samuel P. Franklin’s article, “Triple
Pelvic Osteotomy and Double Pelvic Osteotomy,” in this issue for examples of arthro-
scopic images of the hip.)

SUMMARY

Diagnostic imaging is a principal method used to diagnose canine hip dysplasia. As

evident by the myriad of methods available, no test is perfect, and practitioners
must understand the limitations of the modality they are using. Traditional hip-
extended radiographs remain the most used method for evaluation and are useful
as a screening tool and for detection of radiographic signs of osteoarthritis. However,
additional diagnostic methods such as PennHip distraction radiography have been
shown to improve sensitivity of laxity detection, allow for more objective means of
evaluation, and further aid in prediction of future osteoarthritis development in younger
animals. Future studies using more advanced techniques such as CT and MRI may
further improve the ability to diagnose and treat hip dysplasia patients, improve the
understanding of the disease process, and potentially aid in decreasing the preva-
lence of the disease through improved selective breeding.

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