Abstract
Patellofemoral pain (PFP) is commonly caused by abnormal pressure on the knee due to excessive load while standing, squatting, or going up or down stairs. To better understand the pathophysiology of PFP, we conducted a noninvasive patellar tracking study using a C-arm computed tomography (CT) scanner to assess the non-weight-bearing condition at 0° knee flexion (NWB0°) in supine, weight-bearing at 0° (WB0°) when upright, and at 30° (WB30°) in a squat. Three-dimensional (3D) CT images were obtained from patients with PFP (12 women, 6 men; mean age, 31 ± 9 years; mean weight, 68 ± 9 kg) and control subjects (8 women, 10 men; mean age, 39 ± 15 years; mean weight, 71 ± 13 kg). Six 3D-landmarks on the patella and femur were used to establish a joint coordinate system (JCS) and kinematic degrees of freedom (DoF) values on the JCS were obtained: patellar tilt (PT, °), patellar flexion (PF, °), patellar rotation (PR, °), patellar lateral-medial shift (PTx, mm), patellar proximal-distal shift (PTy, mm), and patellar anterior-posterior shift (PTz, mm). Tests for statistical significance (p < 0.05) showed that the PF during WB30°, the PTy during NWB0°, and the PTz during NWB0°, WB0°, and WB30° showed clear differences between the patients with PFP and healthy controls. In particular, the PF during WB30° (17.62°, extension) and the PTz during WB0° (72.50 mm, posterior) had the largest rotational and translational differences (JCS Δ = patients with PFP—controls), respectively. The JCS coordinates with statistically significant difference can serve as key biomarkers of patellar motion when evaluating a patient suspected of having PFP. The proposed method could reveal diagnostic biomarkers for accurately identifying PFP patients and be an effective addition to clinical diagnosis before surgery and to help plan rehabilitation strategies.
Highlights
25% of patients presenting with knee pain to musculoskeletal clinics are diagnosed with patellofemoral pain (PFP) [1]
The statistically significant joint coordinate system (JCS) coordinates included patellar anterior-posterior shift under all three loading conditions, patellar proximal-distal shift under non-weight-bearing condition at 0 ̊ knee flexion (NWB0 ̊), and patellar flexion under WB30 ̊
Our results showed that the largest differences in degrees of freedom (DoF) values between the PFP and control group was observed in patella flexion (PF) during WB30 ̊ (− E: − 17.62 ̊) (p < 0.01) and PTz during weight-bearing at 0 ̊ (WB0 ̊) (− P2: − 72.50 mm) (p < 0.01), which suggests that the PFP group presumably adapted to avoid knee pain
Summary
This study was approved by Stanford Institutional Review Board (IRB file #20144). Under the IRB-approved protocol, the study cohort included two groups: a PFP group consisting of 12 females and 6 males (mean age, 31 ± 9 years; mean weight, 68 ± 9 kg) who were treated for more than 6 months, but achieved no symptom improvement, and a control group consisting of 8 females and 10 males (mean age, 39 ± 15 years; mean weight, 71 ± 13 kg) with no symptoms of PFP. Included subjects in the PFP group suffered persistent anterior knee pain for at least three months up to 11 years and reported reproducible pain during at least two of the following physical activities: squatting, stair ascent/descent, kneeling, prolonged sitting, or isometric quadriceps contraction. All study participants received an explanation of the study aims and agreed to participate
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