What Is Your Diagnosis?

Michelle E. Matusicky from the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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 DVM, MPH
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Jonathan Dyce from the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

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 MA, VetMB

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History

A 12-month-old 60-kg (132-lb) sexually intact male Caucasian Shepherd Dog was referred for examination because of a 4-month history of progressive lameness in the right hind limb. The dog had no history of related trauma, and treatment with firocoxib (4 mg/kg [1.8 mg/lb], PO, q 24 h) prescribed by the referring veterinarian ameliorated but did not resolve the lameness.

On physical examination, the dog had moderate to severe weight-bearing lameness in the right hind limb that worsened at paces faster than a walk. There was dorsal displacement of the right greater trochanter, palpable laxity of the right hip joint, and substantial atrophy of the right pelvic and crural muscles. Range of motion in the right hip joint was restricted, particularly in extension and abduction, and extremes of motion elicited signs of pain. The dog also had bilateral hyperextension but no collateral instability of the talocrural joints. The remainder of findings on general physical examination and results of a CBC and serum biochemical analyses were unremarkable. The dog was sedated with dexmedetomidine (2.9 mg/kg [1.3 mg/lb], IV) and butorphanol (0.13 mg/kg [0.06 mg/lb], IV) and underwent pelvic and hind limb radiography (Figure 1).

Figure 1
Figure 1

Pelvic (ventrodorsal [A] and right lateral [B]) and right femoral (true mediolateral [C] and true craniocaudal [D]) radiographic images of a 12-month-old 60-kg (132-lb) sexually intact male Caucasian Shepherd Dog examined because of a 4-month duration of progressive lameness in the right hind limb and no history of related trauma.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.455

Diagnostic Imaging Findings and Interpretation

Compared with the dog's vertebral column, the dog's pubic symphysis was markedly deviated toward the right and rotated counterclockwise, with the cranial aspect toward the right and the caudal aspect toward the left (Figure 2). Only the caudal 2 sacral vertebrae were fused, and L7 was asymmetric with an unremarkable left transverse process and a massively expanded right transverse process that mimicked a sacral wing. There was dorsal luxation of the right hip joint, and the right acetabulum was shallow and had attrition of the dorsal acetabular rim.

Figure 2
Figure 2

Same images as in Figure 1 (A through D) and a schematic of the right femur from the proximal perspective (E). A and B—The dog's pubic symphysis (arrowhead) is markedly deviated to the right and rotated with the cranial aspect toward the right and the caudal aspect toward the left. Asymmetry of L7 is evident with an unremarkable left transverse process and a massively expanded right transverse process (large solid arrow) that mimics a sacral wing. The right acetabulum is shallow and has attrition of the dorsal acetabular rim (dotted arrow). There is dorsal luxation of the right hip joint, and the right femoral head (asterisks) is flattened and has circumferential osteophytosis (small solid arrows). C through E—The images show the long axis of the right femur (yellow line [C and D] or dot [E]), long axis of the femoral neck (white line; D and E), center of the femoral head (center of the blue circle), and lines that on true mediolateral (C) and craniocaudal (D) projections connect the center of the femoral head to the long axis of the femur perpendicularly (fuchsia [C and E] and orange [D and E], respectively). D—The angle between the long axis of the femur and the long axis of the femoral neck is 145° of inclination and is classified as coxa valga of the femur. E—The right triangle created by lines established in the radiographic images are used to determine the angle of anteversion of the femoral neck, which in this dog is 66°.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.455

On the true mediolateral and craniocaudal radiographic images of the right femur, reference lines and points were drawn, including the long axis of the femoral neck, long axis of the femur, and center of the femoral head, along with lines that connected the center of the femoral head to the long axis of the femur perpendicularly. The angle between the long axis of the femur and the long axis of the femoral neck was 145° of inclination (reference range, 141° to 157°) and was classified as mild coxa valga of the femur.1,2 Additionally, when the drawn references were considered from the proximal perspective of the right femur, the resulting right triangle was used to determine the angle of version of the femoral neck with the formula tanθ = opposite/adjacent, where tanθ is the tangent of the angle of version, opposite is the length of the line (that on the true mediolateral projection connected the center of the femoral head to the long axis of the femur perpendicularly) opposite the angle of version, and adjacent is the length of the line (that on the true craniocaudal projection connected the center of the femoral head to the long axis of the femur perpendicularly) adjacent to the angle of version. The result was 66° (reference range, 10° to 20°), which was considered moderate anteversion1 of the femoral neck.

The dog underwent general anesthesia for CT to define the degree of pelvic rotation and the conformation of the right acetabulum. The pelvis deviated toward the right, and the degree of pelvic axial rotation from sagittal midline through the body of L7 was 18° (Figure 3) and increased to 25° caudally at the level of the ischial tuberosity (not shown), elevating the right hip joint relative to the body of L7. Findings on CT for the right hip joint also included a shallow acetabulum, deformity of the acetabular notch, and sclerosis and blunting of the dorsal acetabular rim. With 3-D rendering of CT images, rotation of the pelvis and conformation of the hip joints and femurs were better illustrated (Figure 4). Findings were consistent with asymmetric lumbosacral transitional vertebra (ALSTV) of L7. Other differential diagnoses for pelvic rotation (eg, pelvic fracture malunion [traumatic or associated with metabolic bone disease], sacroiliac fracture or luxation, and developmental malformation secondary to trauma of the pelvis [eg, hip joint luxation]) were considered less likely because the dog had no history of related trauma and no evidence of metabolic bone disease.

Figure 3
Figure 3

Transverse pelvic CT image obtained at the level of L7 and the left femoral head of the dog described in Figure 1 showing the measurement of pelvic axial rotation (18°), which is the angle between a line (white) that represents true sagittal midline and bisects the vertebral body of L7 and a line (yellow) that passes through the pubic symphysis and transects L7 on the sagittal midline at the dorsal aspect of the vertebral foramen. The image is in a bone window (window width, 2,500 HU; window level, 250 HU; slice thickness, 1.25 mm), with dorsal toward the top and the dog's right toward the left of the image.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.455

Figure 4
Figure 4

Craniocaudal transverse (A) and ventrodorsal (B) 3-D CT images of the dog described in Figure 1 showing rightward deviation and clockwise rotation of the pubic symphysis (arrowhead) relative to the sagittal midline (white line) bisecting the body of L7. There is asymmetry of L7 with an unremarkable left transverse process and a massively expanded right transverse process (large solid arrow) that mimics a sacral wing, attrition of the right dorsal acetabular rim (dotted arrow), dorsal luxation of the right hip joint, and a flattened right femoral head that has circumferential osteophytosis (small solid arrows). The dog's right is to the left in each image.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.455

Treatment and Outcome

The dog underwent hybrid total right hip joint replacement with a cementless acetabular cupa and cemented femoral stem,b with a particular focus on the orientation of the acetabular cup. On recheck examination 8 weeks after surgery, the dog had improved muscle mass in the right hind limb and good range of motion in the treated hip joint. Radiographically, the acetabular component of the implant was osseointegrated, both stem and cup components of the implant were stable, and there was no evidence of abnormal bone response.

Comments

A transitional vertebra can occur between any 2 vertebral groupings and has features of both groups. In addition, an ALSTV may alter the attachment of the pelvis to the sacrum, as observed in the dog of the present report. The degree of malformation is highly variable; thus, clinical signs also vary. For instance, ALSTV may cause no signs and be incidental in some animals, whereas it may be associated with conditions such as cauda equina syndrome, vertebral instability, or lateralized hip joint dysplasia in others.3,4 The true prevalence of ALSTV is likely unknown because of misdiagnosis (confusion for osteophytosis4 or prior trauma), various definitions of ALSTV, and dismissal as an incidental finding. Studies show that ALSTV occurred in approximately 2.9% (143/5,000)3 to 3.5% (138/4,000)5 of dogs, with German Shepherd Dogs and Labrador Retrievers identified most frequently. Furthermore, a study6 of diagnostic images of German Shepherd Dogs evaluated with a broad definition of ALSTV shows that 92 of the 228 (40%) dogs had ALSTV.

For the dog of the present report, CT was helpful to characterize the axial rotation of the pelvis. Abnormal lumbosacral attachments can create potential malalignment in multiple planes,3 and such cannot be fully appreciated on radiographic images. The rotational anomaly seen in this dog not only affected the lumbosacral junction, but also affected the hip joints in that the pelvic rotation altered the dorsal acetabular coverage of the femoral heads, leaving this dog's right femoral head insufficiently covered and the left femoral head well covered. Surgical treatment, such as total hip joint replacement performed in the dog of the present report, must be well planned with consideration for this altered conformation.

Although radiography generally allows for appropriate preoperative planning for total hip joint replacement, radiographic images sufficient for hip joint evaluation in accordance with the screening procedures of the Orthopedic Foundation for Animals7 may not be obtainable for patients with substantial hip joint subluxation secondary to pelvic rotation, and use of isolated craniocaudal and true lateral femoral radiographic images greatly enhances the accuracy of assessment for hip joint deformities. With the use of 3-D CT images of the dog of the present report, ATLSV and the extent of pelvic axial rotation were more clearly evident, and findings on CT were extremely helpful in planning the surgical treatment and mitigating potential complications.

Footnotes

a.

BFX, BioMedtrix LLC, Whippany, NJ.

b.

CFX, BioMedtrix LLC, Whippany, NJ.

References

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    Orthopedic Foundation for Animals. The hip screening procedures page. Available at: ofa.org/diseases/hip-dysplasia/hip-screening-procedures. Accessed May 4, 2020.

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