Patellar apprehension could identify patients with patella alta and trochlear dysplasia
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Patellar apprehension in knee flexion of greater than 60° could identify patients with patella alta, severe trochlear dysplasia and increased tibial tubercle-trochlear groove distance, according to recently presented study results.
“Patellar apprehension is a common physical exam test used to identify patellar instability; however, it can likely provide us much more than ‘yes/no’ information,” said Robert A. Magnussen, MD, MPH, an orthopedic surgeon specializing in sports medicine at The Ohio State University, who presented findings of his systematic review on patellar apprehension at the American Orthopaedic Society for Sports Medicine Annual Meeting. The meeting was held as a virtual meeting.
“We identified 76 patients prospectively with recurring patellar instability,” Magnussen said in the presentation. “We utilized a goniometer to measure the angle at which apprehension disappeared. Patients were grouped as those in whom apprehension resolved before 60° of flexion - which was 55 patients - and those in whom apprehension persisted beyond 60° of flexion – 21 patients.”
Magnussen and colleagues compared plain films, MRI data, patellar height (measured with the Caton-Deschamps index), tibial tubercle-trochlear groove (TT-TG) distance, sulcus angle and trochlear depth between the two groups.
“Patients with persistent apprehension had a larger Caton-Deschamps index on average, were more likely to have more severe trochlear dysplasia (of Dejour B, C or D), had a higher sulcus angle, shallower trochlear depth and increased TT-TG distance,” Magnussen said. “Most importantly, the negative predictive value of all these tests is quite high, particularly for detecting patella alta and high-grade trochlear dysplasia,” he added.
Of the 21 patients who had persistent apprehension beyond 60°, 18 had patella alta and/or severe trochlear dysplasia, and TT-TG distance was never the only risk factor present, Magnussen said.
“Ninety percent of patients with significant patella alta and the majority of patients with high-grade trochlear dysplasia demonstrated patellar apprehension,” he said. “Further work is needed to evaluate the utility of this exam finding to inform surgical decision-making in this population,” Magnussen concluded.
Perspective
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Jack Farr, MD
During the virtual meeting of AOSSM this month, Robert Magnussen presented an interesting study he and his colleagues conducted at The Ohio State University on factors effecting patellar apprehension in patients with recurrent instability (RPI). The treatment of RPI continues to evolve from the didactics of the 1970 and ‘80s to the “a la carte” approach popularized by David Dejour; that is, outline all the patient’s contributing risk factors for RPI and then plan treatment to address each factor as needed. However, as each risk factor treatment carries potential risk and morbidity, the goal is to perform the fewest interventions that results in a stable and pain-free patella. Magnussen and colleagues pointed out that their prior systematic review demonstrated only a 1% risk of subsequent patellar instability after “isolated MPFL reconstruction.” Can we do better?
To further refine selecting specific surgery for a specific patient, all data points are helpful when deciding when to add tibial tubercle medialization, distalization, lateral lengthening and trochleoplasty. While imaging gives us useful guidance a specific number in a specific patient, it does not dictate surgery. For example, a Caton of 1.4 does not dictate tubercle distalization nor does a Caton of 1.2 prohibit it. Magnusson and colleagues are able to differentiate patients with greater bony patho-anatomy: in this case, whether apprehension resolved before or after 60° of flexion. This elegant concept has promise to be quite useful as it ties together tubercle position, patellar height, trochlear height, patella trochlear engagement and trochlea dysplasia. In these patients with apprehension persisting past 60°, it is imperative to preoperatively investigate if, in fact, other risk factors should be addressed at the time of MPFL reconstruction.
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Magnussen RA, et al. Presentation 15. Presented at: American Orthopaedic Society for Sports Medicine Annual Meeting; July 8-9, 2020 (virtual meeting).
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