We have all been tempted when faced with a lameness in a small patient, to simply radiograph the entire animal if it fits on the film and then try to make a diagnosis. This session focuses on practical ways to get the most diagnostic value out of our orthopedic radiographs. Critical evaluation of positioning and interpretation of the more common joints and conditions encountered will also be discussed with case examples. The main key take home points are highlighted below.
Localize the Lameness
Similar to other diagnostic tests, radiographs should be utilized to add additional information to help rule in or out differential diagnoses based on gait evaluation and our orthopedic exam. Even if a case presents with a previous proposed diagnosis and radiographs, I try not to read the medical record or view the radiographs until after my history and orthopedic exam, so I can then see if my findings were consistent with the historic ones. It is ideal to localize the lameness to 1–2 joints or bones of the affected leg and grade the severity of the lameness to see if the clinical findings fit with the radiographic interpretation.
More Is Not Always Better
If the regions of interest are the pelvis and the stifles, even if both regions can fit on one radiographic film, it is best to take a separate set of radiographs for each region that is centered on the joint/bone of interest. This will allow optimal positioning and subsequent interpretation of each region.
When in a rush it is easy to forget to follow the radiation safety principles of ALARA (as low as reasonably achievable). Use of personal protective equipment, collimation, and sedation of the patient as needed. Proper positioning of many orthopedic radiographs often requires at least light to moderately heavy sedation. A common protocol used at CSU in an otherwise healthy patient is a combination of butorphanol (0.1–0.3 mg/kg IV/IM/SQ), and dexmedetomidine (2–5 mcg/kg IV/IM/SQ) that is reversed with atipamezole once the procedure is complete. The sedation can be helpful not only to allow for a less stressful and painful positioning of the patient, but also may allow for more thorough palpation and manipulation of the injured region.
Anytime you take a radiograph of a bone or joint, place a radio-dense object of known size as close to and at the same height as the targeted bone or joint. Positioning of the object in this way allows it to be under the same influence of magnification as it is the same distance from the radiographic beam. This has become increasingly important with wider spread use of digital radiography. Calibration allows important measurements to be made for pre-operative implant and technique planning. Even if you are not the clinician that is going to be performing the definitive surgery, the surgeon and client will be very happy that repeat radiographs are not needed if there are well positioned and calibrated radiographs that arrive with the patient.
Don’t Forget the Opposite Leg
When a bone is fractured or if an unusual bone lesion is seen, it is a great idea to take a set of calibrated radiographs of the ipsilateral “normal” limb. The normal side can be an invaluable reference for the true shape/size and unique “normal” anatomic variants for that patient.
Critically Evaluate Your Positioning
The number one reason that orthopedic radiographic misdiagnoses are made is poor positioning. Poorly centered and positioned radiographs are more difficult to interpret, can create “artificial lesions,” and may hide true pathology. Before the patient has left the radiology table (and before it is re-positioned for the next view if you have digital radiography), critically evaluate if the projection is truly what you aimed to achieve, and learn how to adjust the positioning of the patient or the radiographic beam if it is not quite right.
Stifle Joint Radiographs
The lateral projection is most commonly used for interpretation. Useful positioning tools and tips and critical evaluation of positioning will be covered using clinical case examples. Dogs with cranial cruciate ligament disease will frequently have varying degrees of effusion and secondary osteoarthritis. Case examples will be used to illustrate how to be more objective about evaluation of these changes and how to differentiate these findings from more aggressive disease such as septic arthritis or neoplasia. This session will also overview how to measure the tibial plateau angle (TPA), and why this is an important step to take in our CrCL patients even if we are only performing extracapsular stabilization or conservative management.
Hip Joint Radiographs
The ventro-dorsal (VD) hip extended pelvic view (OFA-like positioning) is the most useful for interpretation of hip dysplasia. Useful positioning tools and tips and critical evaluation of positioning will be covered using clinical case examples. Dogs with hip dysplasia will have varying degrees of dysplasia secondary osteoarthritis depending on the phase of their disease. Case examples will be used to illustrate how to be more objective about evaluation of these changes.
Elbow Joint Radiographs
Three views are necessary to evaluate all regions of the elbow. Critical evaluation of positioning and interpretation will be covered using clinical case examples. The most common orthopedic condition affecting the elbow in dogs is elbow dysplasia due to medial coronoid disease. This condition is very difficult to evaluate using radiographs and the author’s preference is instead to utilize CT to evaluate such cases.
Carpal and Tarsal Radiographs
It is not uncommon to have traumatic ligamentous injury to these lower joints. Knowledge of the degree of instability and joint level affected is critical in the treatment decision making process. This information can only be obtained by careful palpation of the joints under sedation and the use of stress-views.