title: Three dimensional measurement of minimum joint space width in the knee from stereo radiographs using statistical shape models.
abstract: OBJECTIVE
  An important measure for the diagnosis and monitoring of knee osteoarthritis is the minimum joint space width (mJSW). This requires accurate alignment of the x-ray beam with the tibial plateau, which may not be accomplished in practice. We investigate the feasibility of a new mJSW measurement method from stereo radiographs using 3D statistical shape models (SSM) and evaluate its sensitivity to changes in the mJSW and its robustness to variations in patient positioning and bone geometry.
  
  
  METHODS
  A validation study was performed using five cadaver specimens. The actual mJSW was varied and images were acquired with variation in the cadaver positioning. For comparison purposes, the mJSW was also assessed from plain radiographs. To study the influence of SSM model accuracy, the 3D mJSW measurement was repeated with models from the actual bones, obtained from CT scans.
  
  
  RESULTS
  The SSM-based measurement method was more robust (consistent output for a wide range of input data/consistent output under varying measurement circumstances) than the conventional 2D method, showing that the 3D reconstruction indeed reduces the influence of patient positioning. However, the SSM-based method showed comparable sensitivity to changes in the mJSW with respect to the conventional method. The CT-based measurement was more accurate than the SSM-based measurement (smallest detectable differences 0.55 mm versus 0. 82 mm, respectively).
  
  
  CONCLUSIONS
  The proposed measurement method is not a substitute for the conventional 2D measurement due to limitations in the SSM model accuracy. However, further improvement of the model accuracy and optimisation technique can be obtained. Combined with the promising options for applications using quantitative information on bone morphology, SSM based 3D reconstructions of natural knees are attractive for further development.Cite this article: E. A. van IJsseldijk, E. R. Valstar, B. C. Stoel, R. G. H. H. Nelissen, N. Baka, R. van't Klooster, B. L. Kaptein. Three dimensional measurement of minimum joint space width in the knee from stereo radiographs using statistical shape models. Bone Joint Res 2016;320-327. DOI: 10.1302/2046-3758.58.2000626.
authors: Department of Orthopaedics, Leiden University Medical Center, Biomechanics and Imaging Group, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: E A
authors: EA
authors: van IJsseldijk
authors: Department of Orthopaedics, Leiden University Medical Center, Biomechanics and Imaging Group, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: E R
authors: ER
authors: Valstar
authors: Department of Radiology, Leiden University Medical Center, Division of Image Processing, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: B C
authors: BC
authors: Stoel
authors: Department of Orthopaedics, Leiden University Medical Center, Biomechanics and Imaging Group, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: R G H H
authors: RG
authors: Nelissen
authors: Department of Orthopaedics, Leiden University Medical Center, Biomechanics and Imaging Group, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: N
authors: N
authors: Baka
authors: Department of Radiology, Leiden University Medical Center, Division of Image Processing, PO 9600, 2300 RC, Leiden, The Netherlands.
authors: R
authors: R
authors: Van't Klooster
authors: Department of Orthopaedics, Leiden University Medical Center, Biomechanics and Imaging Group, PO 9600, 2300 RC, Leiden, The Netherlands B.L.Kaptein@lumc.nl.
authors: B L
authors: BL
authors: Kaptein
keywords: Knee; Roentgen stereophotogrammetric analysis; Statistical shape model; mJSW measurement