Patellar morphology highly variable among knees with and without patella instability
Published results showed knees with and without patellar instability had highly variable patellar morphology, as well as minimal association between measurements of patellar morphology and trochlear dysplasia.
Andrew E. Jimenez, MD, J. Lee Pace, MD, and colleagues analyzed and compared MRI scans of 97 patients with patella instability and 100 control patients with ACL tears but no patella instability. Researchers collected radiologic measurements of trochlear morphology and 15 measurements of patellar morphology and performed regression analysis to determine associations between the measurements.
Variability in patella shape
Results showed patients in the patellar instability group had significantly smaller medial facet angles of cartilage at the distal level compared with the control group, but no statistically significant differences between medial facet angles of cartilage at the proximal and middle levels. Researchers also found statistically significantly smaller medial facet angles of bone at the proximal level, middle level and distal level among patients with patellar instability.
Researchers noted significantly larger patellar width at the middle level vs. the proximal and distal levels, as well as significantly larger medial facet angle of bone at the proximal and middle levels vs. the distal level among patients with patellar instability. Patients in the control group had significantly larger patellar width at the middle level vs. the proximal level, significantly smaller medial facet angle of bone at the distal level vs. the proximal level and significantly larger lateral facet angle of bone at the middle level vs. the distal level, according to results.
Although regression analysis showed a statistically significant association between medial facet angle of bone and measures of increasing severity of trochlear dysplasia, researchers found these differences to be small. Results showed an association between decreasing sulcus angle and lateral facet angle of cartilage, lateral facet angle of bone and medial facet angle of cartilage.
Treatments for patella instability
According to Pace, results of this study showed variability in the shape of the patella whether it is unstable, with no clear or consistent patellar shape that occurs in patients with patellar instability. Pace noted there is no evidence that the shape of the patella is associated with the development of patellar instability, as well as no evidence that a patella may develop a dysplastic pattern that would match a dysplastic trochlea.
“This work is important because it allows us to focus our treatments for patellar instability on the various patho-anatomic risk factors that have previously been identified: trochlear dysplasia, patella alta, etc.” Pace told Healio Orthopedics. “Further, none of our treatment options for these anatomic risk factors need to be (except in a few rare exceptions) weighed against the shape of the patella when determining surgical options for patients with patellar instability.”
Perspective
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The authors found “patients in the patellar instability group had significantly smaller medial facet angles of cartilage at the distal level compared with the control group.” They also state “regression analysis showed a statistically significant association between medial facet angle of bone and measures of increasing severity of trochlear dysplasia.” They also found “an association between decreasing sulcus angle and lateral facet angle of cartilage, lateral facet angle of bone and medial facet angle of cartilage.”
Nonetheless, the authors conclude “no differences between control and dysplastic patellae that would affect treatment options.” They also state “no evidence that a patella may develop a dysplastic pattern that would match a dysplastic trochlea.”
Our research with 3D prints of patella instability patients at Yale University shows that, as expected and as Drs. Jimenez and Pace found with statistical significance, there are structural changes in patellae that are congruous with dysplastic trochleas. This is important because this suggests trochleoplasty will create incongruity. So, my conclusions after looking at their findings are different than those of the authors.
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Is a dysplastic trochlea always associated with a dysplastic or dysmorphic patella? In an Orthopaedic Journal of Sports Medicine article, investigators from Connecticut Children’s Medical Center recently analyzed 100 controls and 97 patellofemoral instability patients in an attempt to answer that question. They concluded that there were no significant differences in the majority of the patella morphology measurements between the control and the patella instability groups.
The authors conclude that their data fail to support a role of patella osseous morphology in patella instability patients, leading them to speculate that there should be little theoretical concern about development of a trochlea patella mismatch if a sulcus-deepening trochleoplasty was performed.
However, data in the manuscript do demonstrate a significant association between the patella medial facet angle of bone and measurements of trochlea dysplasia.
This is an important topic, and I am hopeful that this manuscript will stimulate further research to help patella femoral surgeons answer the question, “Is trochlea dysplasia associated with a dysplastic patella?”
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