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Weight-bearing Merchant radiograph reliable for assessment of patellar tracking in TKA
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The weight bearing Merchant radiographic view compared with the routinely used standard radiographic view may offer additional information, is easy to perform and is reliable for the assessment of patellar tracking, according to a recently published study.
Researchers randomly selected 120 patients who were to undergo TKA to receive either an inset round, onlay round or onlay ova patellar implant with a single TKA prosthesis. At 6 months postoperatively, patients were assessed with both the non-weight bearing standard radiographic views and weight-bearing Merchant views. Improvements in KOOS, WOMAC and Kujala scores were associated with indicators of patellar tracking. Two readers evaluated radiographs for reliability assessment.
Results showed the weight bearing Merchant view, compared with the standard view, reduced the percentage of outliers of tracking indices. Investigators noted with the weight bearing Merchant view there was an increase in the lateral contact state. There was a constant and statistically significant correlation between the state of the lateral contact and the improvement in KOOS, WOMAC and Kujala scores. Good reliability and accepted variability were seen with all radiographic indices. – by Monica Jaramillo
Disclosures: The researchers report no relevant financial disclosures.
Perspective
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William R. Post, MD
The authors sought to gain insight into the cause of anterior knee pain after total knee replacement comparing three groups with different patellar prostheses with the same femoral and tibial components. Patellar axial (Merchant views) with and without weight-bearing (WB) were obtained 6 months post operatively to evaluate “patellar tracking” and compared to KOOS, WOMAC and Kujala scores. They concluded that the WB Merchant view offered improved assessment of patellar tracking, more closely reflecting in vivo kinematics.
It is important to realize that a single patellar axial image whether weight bearing or not weight bearing is only one of many factors in the origin of knee pain before or after surgery. Slightly different measurements resulted from the weight bearing views. A single image does not define “tracking” which is a term applied to the path of the patella relative to the trochlea throughout the full range of motion. The WB view is another tool to consider using in evaluation, but this study does not clearly define its usefulness in clinical decision making.
Morgantown, West Virginia
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