Supine non-weight-bearing arrangement. The view can also be done in a standing (weight-bearing) position, which will give more accurate information about malalignment.
Normally the patella lies centrally within the groove.
Supine non-weight-bearing arrangement. The view can also be done in a standing (weight-bearing) position, which will give more accurate information about malalignment.Normally the patella lies centrally within the groove.
What is the value of the Merchant view of the knee?
The Merchant view x-ray is also commonly referred to as the skyline view or the sunrise view. It is a highly valuable view, but the need for the special cassette means that it is often omitted in routine knee X-rays.
Its 45 degree angle gives information about -
- how congruent the back of the patella is with the underlying groove, and whether there is trochlear dysplasia
- whether there is any patellar tilt
- whether or not the patella is abnormally displaced to one side, ie the TT-TG distance
Quote from peer-reviewed paper:
"....a sulcus angle measuring more than 145° in a Merchant view knee radiograph with the knee in 45° knee flexion and the beam at 30° inclination caudal down the patellar femoral joint is characteristic of trochlear dysplasia"
Citation: Kazley JM, Banerjee S. Classifications in Brief: The Dejour Classification of Trochlear Dysplasia. Clin Orthop Relat Res. 2019 Oct;477(10):2380-2386. doi: 10.1097/CORR.0000000000000886. PMID: 31393338; PMCID: PMC6999944.
How does a Merchant view compare to a weight-bearing X-ray?
In the Merchant view the patient lies at rest and any distortion of the anatomy that might be contributed from bearing weight is not appreciated.
So evaluation of any closure of the joint space from osteoarthritis or meniscal degeneration would need a weight-bearing view, such as the Rosenberg view.
Quick linksCan the TT-TG distance be measured on a Merchant view?
Usually a CT or MRI scan is ordered to measure the TT-TG distance, or how out of alignment the patellar tendon is, but in a large number of cases a Merchant view will allow an easier and more affordable way of making this measurement.
Peer-reviewed papersQuote from peer-reviewed paper:
"The tibial tubercle could be identified on Merchant radiograph in...81.7%....Merchant TT-TG strongly correlates with MRI TT-TG but measured 5-8 mm smaller...."
Citation: Bernholt D, Lamplot JD, Eutsler E, Nepple JJ. Utility of Merchant View Radiographs for Assessment of TT-TG: A Comparison to MRI. Orthop J Sports Med. 2018 Jul 27;6(7 suppl4):2325967118S00075. doi: 10.1177/2325967118S00075. PMCID: PMC6083762.