Hip dysplasia, a common orthopedic disease of medium- and large-breed dogs, includes subluxation of the hip joint, leading to osteoarthritis.1–4 Several of the surgical procedures used to manage hip dysplasia are aimed at decreasing or eliminating subluxation of the hip joint to prevent or slow the development of osteoarthritis.1,5 Juvenile pubic symphysiodesis surgically induces premature closure of the pubic portion of the ischiopubic symphysis without affecting growth of the caudal portion of the symphysis and the acetabula.6–8 When JPS is performed at an early age, it results in ventrolateral rotation of the acetabular rims, thereby increasing dorsal coverage of the femoral heads and potentially decreasing subluxation of the hip joint.6,7,9,10
The geometry of the pelvis and acetabula has an important role in the pathogenesis of osteoarthritis secondary to hip dysplasia in both dogs and human patients.2,6,11 Pelvic conformation has been evaluated radiographically and with cross-sectional imaging (eg, CT). The accuracy of those methods is negatively affected by variability in patient positioning and the imaging protocol used.2,6,9 For example, geometric analysis of the acetabula is particularly challenging when 2-D radiographic or CT images are used.2–4 Three-dimensional reconstruction of CT images eliminates the shortcomings of 2-D images and offers a more detailed and accurate representation of skeletal changes.2,4,12 In human medicine, 3-D reconstruction of the pelvis and acetabula has led to advances in the understanding of hip dysplasia in children, aided in the reconstruction of acetabular fractures, and improved preoperative planning for total hip arthroplasty.4,13–15
The purpose of the study reported here was to evaluate the 3-D geometry of canine pelves and to characterize JPS-induced geometric changes by comparing the pelvic configuration between littermates that did and did not undergo the procedure. We hypothesized that JPS would alter the HPAA, ALO, DARA, and size (area, width, and height) of the pelvic canal but would not alter acetabular inclination or retroversion.
Materials and Methods
Animals
The study protocol was reviewed and approved by the North Carolina State University Institutional Animal Care and Use Committee. Labrador Retriever, Golden Retriever, or Labrador Retriever–Golden Retriever crossbred dogs from 13 litters of puppies were evaluated for study enrollment. All dogs were intended to become service dogs and were owned by Canine Assistants in Milton, Ga, which provided signed consent for the dogs to be considered for and enrolled in the study. At approximately 16 weeks old (mean ± SD age, 16.3 ± 0.6 weeks), all potential study subjects underwent an orthopedic examination that included radiographic evaluation of the pelvis and hip joints and calculation of the DI by the PennHIP method,16 which was performed at the PennHIP Analysis Center. Only dogs with an initial DI ≥ 0.50 were included in the study; that DI threshold was selected on the basis of the anticipated risk of such dogs subsequently developing osteoarthritis of the hip joint reported in the scientific literature17,18 available at the time of study initiation.
Study design
Dogs that met the study enrollment criterion (DI ≥ 0.50) were randomly assigned to 1 of 3 groups (thermal JPS, mechanical JPS, or sham surgical procedure) by means of a sealed-envelope draw. Dogs underwent the assigned procedure at 16 to 18 weeks old. Briefly, each dog was routinely anesthetized and positioned in dorsal recumbency. The ventral abdomen was clipped and aseptically prepared for ovariohysterectomy or orchiectomy as well as a ventral midline approach to the pubic symphysis. All surgical procedures were performed by a board-certified veterinary surgeon (KGM). A standard ovariohysterectomy or closed orchiectomy was performed prior to the assigned procedure. Then, a 5-cm-long incision was made over the pubic symphysis directly on the ventral midline (female dogs) or just lateral to the prepuce (male dogs). A 2-cm incision was made in the linea alba immediately cranial to the pubic symphysis. For dogs that underwent the sham procedure (controls), the linea alba, subcutaneous tissues, and skin were closed in a routine manner with 2–0 polyglyconate, 3–0 polyglyconate, and tissue adhesive, respectively, and the dogs were allowed to recover from anesthesia. For dogs that underwent thermal JPS, a periosteal elevator was used to clear muscle from the most cranial 1.5 cm of the pubic symphysis. The surgeon inserted a finger through the incision in the linea alba and positioned it dorsal to the symphysis to protect the underlying soft tissue structures. A needle-point electrocautery probe was placed at 3 evenly spaced points 2.0 mm on either side of the midline and along the midline (ie, 9 points total), and electrocautery at 40 W was applied for 10 seconds at each point. Surrounding tissues were cooled with saline (0.9% NaCl) solution. For dogs that underwent mechanical JPS, the most cranial 1.5 cm of the pubic symphysis was cleared of muscle as described for the thermal JPS procedure. A Mayo needle holder was introduced in a cranial-to-caudal direction through the incision in the linea alba. The needle holder was then partially closed on the left and right medial pubic physes until deformation of each physis was observed. For dogs in both the thermal and mechanical JPS groups, closure of the surgical site was identical to that described for the control dogs. Following completion of all surgical procedures, each dog was allowed to recover from anesthesia and returned to the owner. All dogs were monitored for potential complications (eg, wound infection, dehiscence, or lameness) by a licensed veterinarian on a daily basis for 7 days after surgery.
All dogs underwent service dog training until they were 75.6 to 130.0 weeks old and subsequently worked as service dogs. Ten years after the JPS or sham procedure, the individuals to whom the dogs were assigned voluntarily brought the dogs back to the training facility for reevaluation that included CT examination of the pelvic region with the subject sedated. Additional procedures (an orthopedic examination, functional assessment, evaluation of gait and objective kinematics, and acquisition of radiographic images of the pelvic region) were also performed during the reevaluation as part of a separate study and will not be discussed further in this report.
For the CT scan, each dog was sedated and positioned in ventral recumbency with the hip joints in flexion. All CT scans were acquired with a spiral CT scannera with voltage ranging from 120 to 130 kV, intensity ranging from 150 to 225 mA, a slice thickness of 1.0 mm, and a field of view ranging from 180 × 180 mm to 480 × 480 mm (median field of view, 400 × 400 mm). The caretakers of dogs and investigators who performed the reevaluations remained unaware of (ie, were blinded to) the treatment group assignment of each dog for the duration of the study.
Image analysis
The DICOM images obtained from the CT scans were imported into a modeling software program.b A Cartesian coordinate system of the pelvis was established. The plane of symmetry of the pelvis was drawn manually and optimized to maximize overlap of the hemipelves. The cross-sectional surface created by the plane of symmetry was selected and the fit inertia axes function was used to determine the long axis of the ischiopubic symphysis (x-axis) and its perpendicular line within a sagittal plane (z-axis). The y-axis was defined as the line perpendicular to the plane of symmetry of the pelvis (x-z plane). The origin of all axes was defined by the fit inertia axes function and therefore was approximately centered at the ischiopubic symphysis.
Geometric indicators used to assess the efficacy of the JPS methods included the left and right HPAA, acetabular ALO as determined by both plane (ALOplane; Figure 1) and line (ALOline) methods, DARA, and orientation of the medial acetabular wall. The orientation of the ventral portion of the medial acetabular wall in the transverse plane was defined as the angle between the z-axis and a line drawn to join points at 30% and 60% of acetabular height. The orientation of the dorsal portion of the medial acetabular wall was defined as the angle between the z-axis and a line drawn to join points at 60% and 90% of acetabular height. The overall orientation of the medial acetabular wall was defined as the angle between the z-axis and a line drawn to joint points at 30% and 90% of the acetabular height.
Illustrations of 3-D reconstructed bone models of the left hemipelvis of a dog provided to depict how the HPAA (A), DARA (B), and acetabular ALO as determined by the plane method (C) were measured in a study conducted to assess the effect of JPS on pelvic geometry. A—A best-fit acetabular sphere (not shown) was drawn, and the pelvis was sectioned in a transverse (y-z) plane through the center of the sphere. The HPAA was the angle between the z axis and the line joining the ventral and dorsal aspects of the acetabulum (dashed line); the HPAA is 42.2° in this image. The orientation of the ventral portion of the medial acetabular wall was the angle between the z-axis and a line drawn to join at 30% and 60% of acetabular height (solid line); that angle is 18.1° in this image. The orientation of the dorsal portion of the medial acetabular wall was the angle between the z-axis and a line drawn to join points at 60% and 90% of acetabular height (dotted line); that angle is 18.7° in this image. The overall orientation of the medial acetabular wall was the angle between the z-axis and a line drawn to joint points at 30% and 90% of the acetabular height (not shown). B—A sphere with a radius that was two-thirds the radius of the best-fit acetabular sphere (large sphere) was drawn such that its center was at the dorsal aspect (leftmost red dot) of the acetabulum. The DARA was the angle between the z-axis and the radius of the smaller sphere that best fit the dorsal acetabular rim (black line). C—A plane was drawn that included points (red dots) at the cranial, caudal, and ventral aspects of the acetabulum. The acetabular ALO (plane method; ALOplane) was the angle of the intersection between the drawn plane and the y-z plane as measured from the y-axis (31.7° in this image).
Citation: American Journal of Veterinary Research 79, 11; 10.2460/ajvr.79.11.1217
Geometric indicators used to assess the safety of the JPS methods included the pelvic canal height, width, and area; diameters of the right and left acetabula; and distance between the centers of the right and left acetabula (pelvic width). To obtain pelvic canal measurements, the pelvis was oriented perpendicular to the x-z plane and was rotated around the y-axis to find the minimal pelvic canal area. A cross-sectional image of the pelvis was created at that level. The area of the pelvic canal was measured by use of the modeling software program. Measurement of the maximal pelvic canal width required identification of the most abaxial point on the left and right side of the canal. Parallel lines tangential to the most abaxial points were drawn within the cross-sectional plane, and the maximal pelvic canal width was defined as the distance between those tangential lines. Minimal pelvic canal height was similarly measured. Two parallel lines were drawn within the cross-section plane; one was drawn tangential to the most ventral aspect of the sacrum, and the other was drawn tangential to the most dorsal aspect of the pubis. The minimal pelvic canal height was defined as the distance between those 2 parallel lines. The effect of JPS on the acetabular orientation beyond its potential influence on dorsal coverage of the femoral head, ALO, and dorsal acetabular rim health was evaluated by comparison of the acetabular version (and retroversion) and inclination as determined by both the plane and line methods between dogs that underwent a JPS procedure and control dogs. Acetabular version was defined as the orientation of the acetabulum relative to the ischiopubic symphysis, measured from the symphysis. Anteversion referred to an acetabulum oriented forward, and retroversion referred to an acetabulum oriented backward. When measured by the plane method, acetabular retroversion was defined as the angle at the intersection between a plane drawn to include the most cranial, caudal, and ventral points of the acetabulum (ALO plane) and the dorsal (x-y) plane as measured from the x-axis, and acetabular inclination was defined as the angle at the intersection of the ALO plane and the sagittal (x-z) plane (Figure 2). When measured by the line method, acetabular retroversion was defined as the angle between the x-axis and the projection of a line joining the cranial and caudal aspects of the acetabulum in the dorsal plane, and acetabular inclination was defined as the angle between the x-axis and the projection of a line joining the cranial and caudal aspects of the acetabulum in the sagittal plane.
Illustrations of 3-D reconstructed bone models of the left hemipelvis of a dog provided to depict how acetabular retroversion (A) and inclination (B) as determined by the plane method were measured in a study conducted to assess the effect of JPS on pelvic geometry. A—A plane was drawn that included points at the cranial, caudal, and ventral aspects of the acetabulum (ALO plane; red-shaded area), and acetabular retroversion was the angle of the intersection of that plane with the dorsal (x-y) plane as measured from the x-axis. B—Acetabular inclination was the angle of the intersection of the ALO plane (red-shaded area) with the sagittal (x-z) plane as measured from the x-axis.
Citation: American Journal of Veterinary Research 79, 11; 10.2460/ajvr.79.11.1217
The effect of JPS on the length of the pubis was evaluated by measurement of the height of the left and right acetabula, with the knowledge that a decrease in pubis length was consistent with a decrease in the distance between the pubic symphysis and center of the acetabulum. The effect of JPS on the orientation of the wing of the ilium relative to the pubic symphysis was evaluated by comparison of the pelvic inclination between dogs that underwent a JPS procedure and control dogs.
Statistical analysis
The distribution of data for all measured variables was assessed for normality by means of the Shapiro-Wilk test. All variables were found to be normally distributed. Variables were compared among the 3 treatment groups (mechanical JPS, thermal JPS, and control) as well as between the 2 JPS groups combined and the control group. The DI and body weight was compared between groups by use of t tests. The Pearson correlation coefficient (r) was calculated to assess the relationship between measurements determined by the plane method and the corresponding measurements determined by the line method. Geometric indicators of JPS efficacy (left and right HPAA, ALO, and DARA) and safety (pelvic canal height, width, and area; diameter of the left and right acetabula; and distance between the centers of the left and right acetabula [pelvic width]) and other geometric pelvic measurements (left and right acetabular inclination and retroversion, pubic length, and pelvic inclination) were individually compared among the treatment groups by means of multivariate ANOVA. Litter information was not considered in the analyses. When necessary, F tests were used for pairwise comparisons. Tests were not adjusted for multiplicity. For all analyses, values of P < 0.05 were considered significant.
Results
Dogs
Twenty-nine dogs from 13 litters were eligible for study inclusion and underwent 1 of the 3 surgical procedures (mechanical JPS, thermal JPS, or sham [control] procedure). The caretakers of 5 of those dogs were either unwilling or unable to bring the dogs back to the training facility for reevaluation 10 years later; therefore, only 24 dogs were reevaluated. Of the 24 dogs that were reevaluated, 12 were males and 12 were females. Nine (5 male and 4 female) dogs had undergone thermal JPS, 8 (5 male and 3 female) had undergone mechanical JPS, and 7 (2 male and 5 female) had undergone the control procedure. The mean ± SD body weight at the time of the assigned surgery did not differ significantly among the thermal JPS (12.3 ± 2.5 kg), mechanical JPS (11.3 ± 1.6 kg), and control (14.2 ± 5.0 kg) groups. Likewise, the mean ± SD DI at the time of the assigned surgery did not differ significantly among the thermal JPS (0.55 ± 0.04), mechanical JPS (0.60 ± 0.11), and control (0.55 ± 0.11) groups. No postoperative complications were recorded for any of the dogs reevaluated. The mean ± SD duration between the assigned surgery and reevaluation was 10.3 ± 0.5 years.
Pelvic geometry
Measurements of pelves that underwent thermal JPS did not differ significantly from those that underwent mechanical JPS, with the exception of the orientation of the ventral portion of the left and right medial acetabular wall and the overall orientation of left and right medial acetabular wall. Pelvic measurements for all 3 treatment groups as well as the 2 JPS groups combined were summarized (Table 1).
Mean ± SD pelvic measurements for 10-year-old Labrador Retriever-Golden Retriever crossbred service dogs that underwent mechanical (n = 7) or thermal (9) JPS or a sham (control) surgical procedure at approximately 16 weeks old.
| Measurement | Side | Control | Mechanical JPS | Thermal JPS | Both JPS groups combined |
|---|---|---|---|---|---|
| JPS efficacy | |||||
| HPAA (°) | Left | 38.9 ± 3.0 | 42.3 ± 1.8* | 44.8 ± 4.2* | 43.7 ± 3.5* |
| Right | 38.5 ± 3.0 | 40.7 ± 2.9 | 43.8 ± 3.4* | 42.4 ± 3.5* | |
| Acetabular ALOplane (°) | Left | 50.7 ± 3.4 | 55.0 ± 2.2* | 57.0 ± 4.7* | 56.1 ± 3.8* |
| Right | 51.2 ± 4.0 | 53.8 ± 3.1 | 58.0 ± 5.8* | 56.2 ± 5.1* | |
| Acetabular ALOline (°) | Left | 32.0 ± 4.7 | 37.1 ± 11.3 | 34.5 ± 8.3 | 35.6 ± 9.5 |
| Right | 30.9 ± 3.3 | 37.9 ± 12.7 | 34.7 ± 5.5 | 36.1 ± 9.1 | |
| DARA (°) | Left | 86.1 ± 3.4 | 84.1 ± 4.1 | 85.9 ± 8.6 | 85.1 ± 6.8 |
| Right | 86.4 ± 5.0 | 80.5 ± 7.3* | 85.7 ± 4.3 | 83.4 ± 6.2 | |
| Dorsal aspect of the medial acetabular wall (°) | Left | 9.1 ± 4.4 | 12.9 ± 1.9 | 16.7 ± 5.3* | 15.1 ± 4.5* |
| Right | 8.9 ± 2.5 | 11.7 ± 4.3 | 17.0 ± 6.1* | 14.7 ± 5.9* | |
| Ventral aspect of the medial acetabular wall (°) | Left | 12.7 ± 4.3 | 16.3 ± 4.8 | 20.8 ± 3.1*† | 18.8 ± 4.4* |
| Right | 13.4 ± 3.3 | 16.6 ± 4.7 | 21.0 ± 3.4*† | 19.0 ± 4.5* | |
| Overall medial acetabular wall (°) | Left | 10.9 ± 3.5 | 14.7 ± 3.0* | 18.8 ± 3.5*† | 17.0 ± 3.8* |
| Right | 11.2 ± 2.7 | 14.2 ± 3.9 | 19.0 ± 4.4*† | 16.9 ± 4.7* | |
| JPS safety | |||||
| Pelvic canal area (mm2) | NA | 3,132 ± 243 | 2,549 ± 314* | 2,350 ± 171* | 2,437 ± 256* |
| Pelvic canal width (mm) | NA | 55.3 ± 2.7 | 50.8 ± 2.6* | 49.4 ± 3.8* | 50.0 ± 3.3* |
| Pelvic canal height (mm) | NA | 65.5 ± 4.3 | 57.8 ± 5.5* | 55.7 ± 3.0* | 56.6 ± 4.2* |
| Acetabular diameter (mm) | Left | 11.0 ± 0.5 | 10.8 ± 0.4 | 11.1 ± 0.7 | 11.0 ± 0.6 |
| Right | 10.9 ± 0.6 | 10.9 ± 0.6 | 11.1 ± 0.8 | 11.0 ± 0.7 | |
| Pelvic width (mm) | NA | 81.9 ± 3.1 | 76.0 ± 2.7* | 72.7 ± 3.7* | 74.2 ± 3.6* |
| Other | |||||
| Acetabular retroversionplane (°) | Left | 16.5 ± 5.0 | 13.3 ± 8.5 | 17.9 ± 8.2 | 15.9 ± 8.4 |
| Right | 17.4 ± 3.4 | 10.2 ± 6.2* | 18.5 ± 7.7 | 14.9 ± 8.1 | |
| Acetabular retroversionline (°) | Left | 16.9 ± 2.2 | 14.9 ± 4.0 | 14.2 ± 4.6 | 14.5 ± 4.2* |
| Right | 16.0 ± 17 | 13.9 ± 4.9 | 14.1 ± 5.0 | 14.0 ± 4.8* | |
| Acetabular inclinationplane (°) | Left | 13.6 ± 3.9 | 9.4 ± 5.9 | 11.5 ± 4.7 | 10.6 ± 5.2 |
| Right | 14.2 ± 3.0 | 7.7 ± 5.4* | 11.3 ± 3.8* | 9.7 ± 4.7* | |
| Acetabular inclinationline (°) | Left | 26.1 ± 3.4 | 19.5 ± 3.8* | 20.3 ± 5.2* | 20.0 ± 4.5* |
| Right | 25.8 ± 4.1 | 17.5 ± 4.3* | 19.7 ± 5.1* | 18.8 ± 4.8* | |
| Acetabular height (mm) | Left | 17.6 ± 2.3 | 13.6 ± 2.6* | 12.6 ± 2.8* | 13.1 ± 2.6* |
| Right | 17.9 ± 2.3 | 14.1 ± 2.7* | 12.8 ± 2.7* | 13.4 ± 2.7* | |
| Pelvic inclination (°) | NA | 37.4 ± 2.3 | 32.7 ± 2.9 | 34.3 ± 4.6 | 33.5 ± 3.7 |
The mechanical JPS procedure involved the use of Mayo needle holders to physically deform the left and right medial pubic physes. The thermal JPS procedure involved the application of electrocautery at specific points 2.0 mm on either side of and along the pubic symphysis.
Value differs significantly (P < 0.05) from the corresponding value for the control group.
Value differs significantly from the corresponding value for the mechanical JPS group.
NA = Not applicable.
See Image analysis section for details about the pelvic measurements.
The mean left (P = 0.003) and right (P = 0.001) HPAA for the combined JPS group were 4.8° and 39° greater, respectively, compared with the mean left and right HPAA for the control group. The acetabular ALOplane and ALOline measurements were not significantly correlated (r = 0.19; P = 0.200). The mean left (P = 0.003) and right (P = 0.026) acetabular ALOplane for the combined JPS group were 5.4° and 5.0° greater, respectively, than the mean left and right acetabular ALOplane for the control group. The mean left (P = 0.303) and right (P = 0.128) acetabular ALOline and mean left (P = 0.684) and right (P = 0.179) DARA did not differ significantly between the combined JPS and control groups. Compared with the control procedure, the JPS procedure increased the mean angle of the ventral portion of the left (P = 0.003) and right (P = 0.004) medial acetabular wall in the transverse plane by 6.0° and 5.6°, respectively; increased the mean angle of the dorsal portion of the left (P = 0.005) and right (P = 0.013) medial acetabular wall in the transverse plane by 5.9° and 5.8°, respectively; and increased the mean angle of the overall left (P < 0.001) and right (P = 0.003) medial acetabular wall in the transverse plane by 3.9° and 3.8°, respectively. Conversely, the JPS procedure decreased the mean pelvic canal area by 22.2% (P < 0.001), width by 9.6% (P = 0.001), and height by 13.6% (P < 0.001; Figure 3) and decreased the mean pelvic width by 9.4% (P < 0.001) relative to the control procedure (Figure 4). The mean diameters of the left and right acetabula did not differ between the combined JPS and control groups.
Representative illustrations of 3-D reconstructed bone models of the pelves of 10-year-old Labrador Retriever–Golden Retriever crossbred service dogs that did (JPS dog; A) and did not (control; B) undergo a JPS procedure at approximately 16 weeks old obtained during a study to determine the effects of JPS on pelvic geometry. For each dog, DICOM images obtained from CT scans of the pelvic area were imported into a modeling software program, and a Cartesian coordinate system of the pelvis was established. To measure the dimensions of the pelvic canal, the pelvis was oriented perpendicular to the x-z plane and rotated around the y-axis until the smallest pelvic canal area was identified. A cross-sectional image of the pelvis was created at that level, and the maximal pelvic canal width was defined as the distance between the most abaxial points on the left and right sides of the canal, whereas the minimal pelvic canal height was defined as the distance between the most ventral aspect of the sacrum and the most dorsal aspect of the pubis. The pelvic canal height (73.2 mm) and width (55.4) for the control dog (B) were greater than the pelvic canal height (60.9 mm) and width (50.7 mm) for the JPS dog (A). A similar trend was observed for the entire study population; the mean pelvic canal height and width for control dogs (n = 8) were significantly greater than those of dogs that underwent a JPS procedure at 16 weeks old (16). Bar = 50 mm.
Citation: American Journal of Veterinary Research 79, 11; 10.2460/ajvr.79.11.1217
Representative illustrations of 3-D reconstructed bone models of the pelves in the cranial (A and B), dorsal (C and D), caudal (E and F), and lateral (G and H) planes for a control dog (A, C, E, and G) and JPS dog (B, D, F, and H) as described in Figure 3. Notice that there are subtle differences in the pelvic shape and acetabular orientation between the 2 dogs. The level of magnification is the same for all pelves. See Figure 3 for remainder of key.
Citation: American Journal of Veterinary Research 79, 11; 10.2460/ajvr.79.11.1217
The mean left (P = 0.161) and right (P = 0.293) acetabular retroversion as measured by the line method did not differ significantly among the 3 treatment groups (Table 1). When measured with the plane method, mean left acetabular retroversion did not differ significantly (P = 0.792) among the 3 treatment groups, but the mean right acetabular retroversion for the mechanical JPS group was significantly (P = 0.002) less than that for the control group. Acetabular version measurements determined by the plane method were not significantly (P = 0.813) correlated (r = −0.04) with those determined by the line method; however, there was a strong positive correlation (r = 0.80; P < 0.001) between acetabular inclination measurements determined by the plane method and those determined by the line method. The mean left acetabular inclination as determined by the plane method did not differ significantly (P = 0.779) among the 3 groups, whereas the mean right acetabular inclination as determined by the plane method for the JPS groups was significantly (P = 0.016) less than that for the control group. When measured by the line method, the mean left (P = 0.003) and right (P = 0.002) acetabular inclinations for the JPS groups were less than those for the control group. The mean heights of the left (P < 0.001) and right (P = 0.001) acetabula for both JPS groups were significantly less than those for control dogs, which indicated that the JPS procedure decreased the length of the pubis relative to the control procedure.
Discussion
In the present study, approximately 16-week-old Labrador Retriever, Golden Retriever, and Labrador Retriever–Golden Retriever crossbred puppies considered at risk of developing osteoarthritis of the hip joints secondary to hip dysplasia (DI > 0.50) under went mechanical JPS, thermal JPS, or a sham (control) surgical procedure and then were reevaluated 10 years later to assess whether JPS affected pelvic geometry. Many littermates were included in the study population; therefore, genetic variation among the study subjects was believed to be minimal, and the observed differences were believed to be directly related to the assigned surgical procedure. On the basis of the observed results, we accepted (ie, failed to reject) our hypothesis that JPS alters the acetabular geometry and increases the HPAA and acetabular ALO. Compared with control dogs, dogs that underwent JPS had a mean increase of approximately 4° in HPAA, 5° in acetabular ALO, and 6° in orientation of the medial acetabular wall in the transverse plane. Although those 3 outcomes relied on different anatomic landmarks for measurement, they were consistent within each treatment group (coefficients of variation ranged from only 2% to 3%) and between the left and right hemipelves (angle differences were < 2°). Those indicators of consistency strengthen our confidence about the robustness of the methods used to assess the 3-D pelvic geometry of dogs in this study.
Both line and plane methods were used in the present study to measure acetabular ALO, retroversion, and inclination. The line method was consistent with 2-D measurement methods used for radiographic and cross-sectional CT images. The plane method was consistent with 3-D measurement methods. Interestingly, there was a strong positive correlation between the line and plane measurements for acetabular inclination, but the line and plane measurements for acetabular ALO and acetabular retroversion were not significantly correlated. Significant differences were identified among the 3 treatment groups when acetabular ALO was measured by the plane method but not when it was measured by the line method. That finding was most likely caused by the fact that the coefficient of variations for measurements obtained by the line method ranged from 7% to 9%, whereas those for measurements obtained by the plane method only ranged from 2% to 3%. Assessment of the acetabular ALO appeared to be less reproducible when measured by means of the line method than when measured by means of the plane method. The JPS-associated increase in mean HPAA (4°) observed for dogs of the present study was consistent with those (5° and 10°) determined by 2-D CT measurements for 6 and 5 dogs that underwent JPS at 15 weeks old in 2 other studies.6,19 The coefficients of variation for the 2-D measurements of HPAA in those 2 studies6,19 were 2- to 4-fold greater than the coefficients of variation for HPAA (7% to 8%) as determined by the 3-D methods used in the present study, which suggested that assessment of acetabular orientation is more precise on 3-D CT reconstructions than on 2-D CT images. Two-dimensional measurements are less accurate than 3-D measurements.20–23 Also, the larger coefficients of variation reported in those other studies6,19 relative to those of the present study might have resulted from the use of thicker CT slices (1.5 and 3.0 mm vs 1 mm in the present study), or the fact that CT scanning technology has improved markedly since those studies were performed.
To our knowledge, the present study was the first to evaluate the orientation of the medial acetabular wall in dogs that had undergone JPS. The orientation of the medial acetabular wall was measured at 3 regions (ventral aspect, dorsal aspect, and overall [whole] wall), and the measurements at each of those 3 regions were consistent (difference between left and right medial acetabular walls, < 1°; coefficient of variation, < 10%). Moreover, the mean angle of orientation for the medial acetabular wall was greater for dogs that underwent JPS than for control dogs at all 3 regions.
The present study was also, to our knowledge, the first to compare the relative efficacy between thermal and mechanical JPS. The means for 5 of 6 JPS efficacy indicators were numerically greater and 2 were significantly greater (orientation of the ventral aspect of the medial acetabular wall and orientation of the overall medial acetabular wall) for dogs that underwent thermal JPS, compared with dogs that underwent mechanical JPS. This suggested that thermal JPS might be more effective than mechanical JPS for prevention of hip joint osteoarthritis. However, the means for HPAA, DARA, and acetabular ALOplane did not differ significantly between dogs that underwent thermal JPS and those that underwent mechanical JPS. Collectively, these findings might indicate that the type (mechanical or thermal) of JPS had disparate effects on the medial acetabular wall and acetabulum or that medial acetabular wall measurements were more consistent than DARA and HPAA measurements. Our impression was that placement of only 1 point at the dorsal aspect of the acetabulum for measurement of the HPAA and DARA was somewhat subjective relative to the placement of multiple points for measurement of the orientation of the medial acetabular wall. Nevertheless, the coefficients of variation for both HPAA and DARA were low (2% to 3%), which suggested those 2 measurements were consistent. The repeatability of measurement point placement was not evaluated in the present study. In other studies, DARA was measured on radiographic7,10,24,25 or 2-D CT images6,9,10,12 and used to evaluate the orientation of the acetabulum. In the present study, the orientation of the acetabulum was indirectly measured on the basis of the orientation of the medial acetabular wall, which did not require placement of a measurement point on the dorsal acetabular rim. This was advantageous because the dorsal acetabular rim can be damaged as a result of hip subluxation, which may alter acetabular orientation measurements that are dependent on the dorsal acetabular rim.
Gonadectomy at an early age has been associated with delayed physeal closure in dogs and cats; however, a direct causal relationship between delayed physeal closure and the development of other orthopedic conditions, such as hip dysplasia or cranial cruciate ligament rupture, has not been documented.26 The lack of definitive causal evidence for the development of musculoskeletal problems, combined with the perceived benefit of preventing transmission of the excessive hip laxity phenotype to future generations of service dogs, was the reason we chose to gonadectomize the dogs of the present study at 16 weeks old.
On the basis of the results of the present study, we also failed to reject our hypothesis that JPS alters the pelvic canal shape. Compared with the control surgical procedure, the thermal and mechanical JPS procedures decreased the width and height of the pelvic canal by approximately 10%, the mean area of the pelvic canal by approximately 20%, and the width of the pelvis by approximately 10%. Similar changes in mean pelvic canal size have been reported between dogs that underwent JPS and control dogs of other studies.6,9 Although negative consequences associated with a decrease in pelvic width and pelvic canal size have not been reported, such decreases could theoretically lead to dystocia in sexually intact females and to colonic disease and obstipation in all dogs.27,28 The fact that JPS decreases the size of the pelvic canal, and thereby might increase the risk for dystocia, provides additional justification for performing a gonadectomy at the time of JPS. None of the dogs that underwent JPS in the present study developed adverse clinical consequences related to a decrease in pelvic canal size during the 10-year post-surgical observation period.
Thermal and mechanical JPS altered the acetabular cup inclination (ie, its orientation within a sagittal plane) by approximately 6%. Therefore, we rejected our hypothesis that JPS would not alter acetabular cup version or inclination. Prior to the present study, the effect of JPS on acetabular cup orientation in a sagittal plane had not been evaluated. Changes in inclination could alter hip joint motion or predispose dogs to femoroacetabular impingement.29 Mechanical JPS decreased acetabular retroversion. A decrease in acetabular retroversion could also increase the likelihood of femoroacetabular impingement. In children with hip dysplasia, acetabular anteversion is believed to contribute to the development of femoroacetabular impingement because the risk of impingement during extension and external rotation of the hip joint increases as the acetabulum is anteverted.30 Although femoroacetabular impingement has not been described in dogs with unaltered hip joints, it has been described in dogs that have undergone hip joint replacement surgery.31
The present study had a few limitations. The number of dogs included in each treatment group was small, which may have affected our ability to detect small intergroup differences. After the dogs completed their training and left the training facility, their activity level, diet, and body condition were not controlled, and any or all of those factors could have affected our findings. Novel 3-D analytic methods were used to evaluate the shape of the pelvis, and the intraobserver repeatability of those methods and their relationship to conventional 2-D cross-sectional CT or radiographic measurements are unknown. The severity of osteoarthritis and the potential influence of osteoarthritis on the repeatability of the 3-D measurements were also not evaluated. The fact that JPS appeared to alter the geometry of the pelvis cannot be construed as proof of its clinical effectiveness for prevention of hip dysplasia and hip joint osteoarthritis.
The present study assessed the effect of thermal and mechanical JPS on the 3-D pelvic geometry of dogs. It did not assess the effect of JPS on hip joint stability, development of osteoarthritis in the hip joint, or functional performance. Both procedures resulted in a moderate increase in femoral head coverage and decrease in pelvic size and altered acetabular cup retroversion and inclination. These findings may help guide future studies of alternatives for optimizing canine pelvic anatomy to minimize hip dysplasia and associated osteoarthritis.
Acknowledgments
Computed tomography was performed at the Blue Pearl Specialty & Emergency Pet Hospital in Sandy Springs, Ga.
ABBREVIATIONS
| ALO | Angle of lateral opening |
| DARA | Dorsal acetabular rim angle |
| DI | Distraction index |
| HPAA | Hemipelvis acetabular angle |
| JPS | Juvenile pubic symphysiodesis |
Footnotes
Luminys 2000s CT scanner, Picker International Inc, Cleveland, Ohio.
3-matic, research version 10.0, Materialise, Plymouth, Mich.
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