title: Variability in Patellofemoral Alignment Measurements on MRI: Influence of Knee Position.
abstract: OBJECTIVE
  The purpose of this study was to determine the variability of distances between four distinct anatomic landmarks used for the evaluation of patellofemoral alignment while implementing controlled changes in patient positioning during MRI.
  
  
  METHODS
  Limited MRI was performed of 12 knees in healthy volunteers (10 men, two women; mean age, 28 years) with the knees in four different positions. The four landmarks used were TT (the most anterior point of the osseous tibial tubercle), TG (the nadir of the cartilaginous trochlear groove), PT (the center of the patellar tendon insertion on the tibia), and PCL (the medial border of the posterior cruciate ligament at its insertion along the posterior tibia). TT-TG, PT-TG, TT-PCL, and PT-PCL distances were measured on the MR images. Each distance was measured with the knee at maximum patient comfort (rest), full extension, 15° of flexion, and 30° of flexion. Linear mixed models with random intercepts were implemented to determine variability between measurements and knee position.
  
  
  RESULTS
  In general, measurements based on anatomic landmark and knee position varied greatly. The greatest variability in different knee positions was seen in mean TT-TG and PT-TG distances ± SD (TT-TG: rest, 18.1 ± 7.9 mm; full extension, 17.3 ± 5.3 mm; 15° of flexion, 11.4 ± 5.7 mm; 30° of flexion, 11.7 ± 6.0 mm; intraclass correlation coefficient [ICC] = 0.539; PT-TG: rest, 18.1 ± 6.3 mm; full extension, 17.9 ± 4.7 mm; 15° of flexion, 13.2 ± 5.2 mm; 30° of flexion, 11.8 ± 4.3 mm; ICC = 0.633). In contrast, knee position did not significantly affect distances for TT-PCL and PT-PCL (TT-PCL: rest, 23.5 ± 6.8 mm; full extension, 20.5 ± 5.5 mm; 15° of flexion, 22.8 ± 6.2 mm; 30° of flexion, 22.8 ± 6.7 mm; ICC = 0.484; PTPCL: rest, 23.4 ± 5.3 mm; full extension, 21.5 ± 4.5 mm; 15° of flexion, 22.3 ± 4.3 mm; 30° of flexion, 23.1 ± 4.8 mm; ICC = 0.509).
  
  
  CONCLUSIONS
  On MRI, TT-PCL and PT-PCL measurements have significantly less variability compared with TT-TG and PT-TG measurements, regardless of knee position. Although further studies are warranted, the use of TT-PCL and PT-PCL measurements may offer more reliable assessment of tibial tubercle lateralization and patellofemoral alignment.
authors.affiliation: 1 Department of Orthopedic Surgery, Wake Forest School of Medicine, Winston-Salem, NC.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Marquez-Lara
authors.affiliation: 1 Department of Orthopedic Surgery, Wake Forest School of Medicine, Winston-Salem, NC.
authors.forename: Jason
authors.initials: J
authors.lastname: Andersen
authors.affiliation: 2 Department of Radiology, Wake Forest School of Medicine, Winston-Salem, NC.
authors.forename: Leon
authors.initials: L
authors.lastname: Lenchik
authors.affiliation: 1 Department of Orthopedic Surgery, Wake Forest School of Medicine, Winston-Salem, NC.
authors.forename: Cristin M
authors.initials: CM
authors.lastname: Ferguson
authors.affiliation: 2 Department of Radiology, Wake Forest School of Medicine, Winston-Salem, NC.|3 Present address: Department of Radiology, Kadlec Regional Medical Center, 888 Swift Blvd, Richland, WA 99352.
authors.forename: Pushpender
authors.initials: P
authors.lastname: Gupta
mesh_terms: D000328:Adult; D059925:Anatomic Landmarks; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D057071:Patellofemoral Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D016059:Range of Motion, Articular
keywords: groove distance tibial tubercle–posterior cruciate ligament distance; patellar tendon–posterior cruciate ligament distance; patellar tendon–trochlear groove distance; patellofemoral alignment; tibial tubercle–trochlear