Dejour classification may not accurately represent entire trochlear shape in patients with patellar instability
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Recent study results revealed that trochlear dysplasia types on an axial view based on Dejour classification are not representative of the entire trochlear geometry. Therefore, multiple axial planes should be used clinically to more accurately describe the entire shape of the trochlear.
Investigators assessed 90 knees from 81 patients with patellar instability and 15 knees from 10 healthy volunteers. They used MRIs to create 3D knee models. They defined femoral trochlear planes as virtual cross sections. The reference plane was the femoral trochlear plane 0 (FTP 0), which included the proximal edge of the femoral trochlea. Researchers assessed trochlear dysplasia types at every 10° of FTP 10 up to FTP 60. A normal trochlear had a sulcus angle less than 145°. Investigators assessed changes in trochlear type based on the FTPs and agreement with clinical classification.
They noted 86 knees in patients with patellar instability and 12 knees in healthy volunteers demonstrated changes in the trochlear types based on different FTPs. The patterns of change were different among patients with patellar instability and the healthy volunteers, which demonstrated morphological variation in the dysplastic trochleae. In patients with patellar instability, the agreement of trochlear type on each FTP with Dejour classification was 42% on FTP 10, 49% on FTP 20, 33% on FTP 30, 22% on FTP 40, 22% on FTP 50% and 22% on FTP 60. In healthy volunteers, the agreement of classification type was 20% at FTP 10, 80% at FTP 20 and 100% on FTP 30 through FTP 60.
These results showed trochlear type in the clinically used plane may not always match the trochlear types on planes that describe contact surface of the patella. – by Monica Jaramillo
Disclosure: The researchers report no relevant financial disclosures.
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James Bicos, MD
This study aimed to confirm whether or not the trochlear types on an axial view categorized by the Dejour classification represented the entire trochlear shape in patients with patellar instability (PI) and in healthy volunteers (HV) using 3D computer models.
The researchers looked at 81 patients with PI and 15 knees from 10 HV. They created 3D knee models from MRIs for each patient and looked at the femoral trochlear planes (defined as the virtual cross sections including the transepicondylar axis) from 0° to 60°.
They found that the clinical planes we typically use do not always match the ones on virtual cross sections where the patella actually contacts the surface of the trochlea. Although most patients with PI showed changes in their trochlear types on FTP, there were low rates of agreement between the trochlear type on each FTP and the classification obtained in the clinical setting in patients with PI.
What we continue to find when we scrutinize our understanding of the patellofemoral anatomy and try to correlate with our clinical findings in the office, is that we do not fully understand the complex interactions that control the patellofemoral kinematics in the knee. There are many schools of thought of just looking at distal anatomical variants (ie, tibial tubercle abnormalities), proximal patellar issues (ie, MPFL/MQTFL reconstructions), and even attributing patellofemoral related issues all to rotational issues in the lower extremities (ie, derotational osteotomies). The trochelar anatomy is complex and does play a significant role in patellofemoral stability. We need to continue to learn about the complex and diverse anatomy that the trochlea has and correlate that with how we can best serve our patients with PI.
William Beaumont Hospital, Royal Oak Michigan
Royal Oak, Michigan
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