Unilateral anterior knee pain is associated with increased patellar lateral position after stressed lateral translation

Abstract

Purpose To objectively compare side‐to‐side patellar position and mobility in patients with idiopathic unilateral anterior knee pain (AKP) using a stress‐testing device concomitantly with magnetic resonance imaging. It is hypothesized that the painful knees present greater patellar mobility than the contralateral non‐painful knees. Methods From a total sample of 359 patients, 23 patients with idiopathic unilateral AKP (30.9 years, 23.4 kg/m2, 43% males) were included within the present study. Both knees of all the patients were examined by conventional imaging, including the measurement of trochlear sulcus angle, Caton‐Deschamps index, tibial tuberosity to trochlear groove distance, patellar tilt angle and patellar subluxation (both at rest and upon quadriceps contraction). Additionally, the same patients underwent stress testing (Porto Patella Testing Device); these measurements were taken with the patella at rest, after lateral patellar translation and after lateral patellar tilt. Clinical and functional outcomes were obtained using physical examination and the Kujala and Lysholm scores. Results Painful knees showed statistically significant higher patellar lateral position after stressed lateral translation than non‐painful knees (p = 0.028), 9.8 ± 3.6 mm and 7.1 ± 6.3 mm, respectively. The adjusted multivariate logistic model identified the patellar position after lateral displacement to be significantly associated with AKP (OR = 1.165) and the model (AUC = 0.807, p < 0.001) showed reasonable sensitivity (67%) and specificity (73%). Conclusion Patients with idiopathic unilateral AKP with morphologically equivalent knees showed statistically significant increased patellar lateral position after stressed lateral displacement in their painful knee. The greater lateral patellar mobility quantified by the PPTD testing brings more objectivity to the diagnosis. Level of evidence II.

Patients with different patellofemoral disorders display a distinct ligament stiffness pattern under instrumented stress testing

“…The examination included clinical history and patellofemoral physical exam. Physical examination comprised common patellofemoral testing for patellar pain, tracking and mobilisation that are routinely performed at our institution 27 28. All patients filled out the Kujala and Lysholm Scores 29 30…”

“…Two independent experienced musculoskeletal radiology technicians (blinded to the patient’s condition) performed all imaging procedures, including bilateral standard radiographs, standard MRI or CT, and combined them with instrumented assessment of stress using PPTD. Radiological and imaging protocols were performed as previously described 27 28. The PPTD (figure 1) is a stress instrumented device that is safe and compatible for use within MRI/CT systems.…”

“…The PPTD (figure 1) is a stress instrumented device that is safe and compatible for use within MRI/CT systems. This device is valid and reliable to objectively quantify the patellar position (PP) and displacement after stress testing, providing enhanced accuracy and precision, and less variability than physical examination 27 28…”

“…The PPTD procedures were performed as detailed in previous studies 27 28. Patients were positioned (with no stress) and a first scan was performed to record the initial patellar position (figure 2A).…”

“…One line crosses the deepest point of the TG and the other intersects the most posterior point of the patellar central ridge. The lateral patellar displacement (PP_LT-NS_diff) is measured by calculating the difference between the PP after lateral stress (PP_LT) and patella at rest (PP_NS) 27 28…”