• Specifications
• Registration

TableOfContents

Target Outcome

Prerequisites

Infrastructure

For more details see ["Infrastructure/ExperimentationMechanics"].

Previous Protocols

For more details see ["Specifications/Specimens"].

For more details see ["Specifications/ExperimentationJointMechanics"].

For more details see ["Specifications/ExperimentationAnatomicalImaging"]

For more details see ["Specifications/SpecimenPreparation"].

Protocols

Overview

Registration of the knee includes three main steps:

1. Register imaged (MRI) anatomical landmarks to MRI compatible registration markers. See ["Specifications/ExperimentationAnatomicalImaging"]
2. Register robot-controlled clinical coordinate system to MRI compatible registration markers
   1. Register digitized anatomical landmarks on each bone with respect to an optoelectronic sensor rigidly mounted on each bone
   2. Register digitized MRI compatible registration markers on each bone with respect to an optoelectronic sensor rigidly mounted on each bone
3. Register robot-controlled clinical coordinate system with respect to imaged (MRI) anatomical landmarks

Coordinate System Definition

In order to perform proper registration, the following coordinate systems (CS) must be identified and defined:

1. Tibia

Anchor(Tibia_MRI_CS)

1. Tibia MRI marker CS
   • [:Specifications/SpecimenPreparation#MRI_markers_prep: MRI Marker Preparation]
   • Consists of three spheres (positioned medial(S1), lateral (S2), posterior (S3))
   • Origin - S1
   • X-axis - unit vector S1 to S2
   • Z-axis - unit vector of X-axis cross vector of S1 to S3
   • Y-axis - Z-axis cross the X-axis

Anchor(Tibia_CS)

• Tibia digitized CS - transformation matrix between the Tibia CS (TIB) and mounted optoelectronic marker CS (TibWorld)

  • http://www.ncbi.nlm.nih.gov/pubmed/6865355

  • The tibia CS is defined for a right knee. It should be mirrored when used for a left knee.
  • Digitized points
    • T1. Medial tibial plateau
    • T2. Lateral tibial plateau
    • T3. Medial malleolus of the tibia
    • T4. Lateral malleolus of the fibula
  • Algorithm:
    1. TIB origin - center of tibial plateau: Otib = (T1+T2)/2
    2. TIB Z-axis to point superiorly: Ztib = normalize(Otib-(T3+T4);
    3. TIB Y-axis to point posteriorly: Ytib = normalize(Ztib,(T2-T1))
    4. TIB X-axis to point medially: Xtib = cross(Ytib,Ztib)

  • Store results in 4x4 matrix: T_TibWorld_TIB = [Xtib Ytib Ztib Otib; 0 0 0 1];

• Femur

Anchor(Femur_MRI_CS)

1. Femur MRI marker CS
   • [:Specifications/SpecimenPreparation#MRI_markers_prep: MRI Marker Preparation]
   • Consists of three spheres (positioned anterior(S1), medial (S2), lateral (S3))
   • Origin - S1
   • X-axis - unit vector S1 to S2
   • Z-axis - unit vector of X-axis cross vector of S1 to S3
   • Y-axis - Z-axis cross the X-axis

Anchor(Femur_CS)

• Femur digitized CS - transformation matrix between the Femur CS (FEM) and mounted optoelectronic marker CS (FemWorld)

  • http://www.ncbi.nlm.nih.gov/pubmed/6865355

  • The femur CS is defined for a right knee. It should be mirrored when used for a left knee.
  • Digitized points
    • F1. Lateral epicondyle of the femur
    • F2. Medial epicondyle of the femur
    • F3-F6. 4 points around the epiphyseal line of the femur
  • Algorithm:
    1. FEM origin - mid-epicondylar point: Ofem = (F1+F2)/2.
    2. FEM X-axis to point medially: Xfem = normalize(F2-F1)
    3. FEM Y-axis to point posteriorly: Yfem = normalize(cross(Ofem-(centroid(F3,F4,F5,F6),Xfem))
    4. FEM Z-axis to point superiorly: Zfem = cross(Xfem,Yfem)

  • Store results in 4x4 matrix T_FemWorld_FEM = [Xfem Yfem Zfem Ofem; 0 0 0 1]

Anchor(Patella_Registration)

• Patella Registration

Anchor(Patella_MRI_CS)

1. Patella MRI marker CS ["Specifications/SpecimenPreparation"]
   • [:Specifications/SpecimenPreparation#MRI_markers_prep: MRI Marker Preparation]
   • Consists of three spheres (positioned superior(S1), medial (S2), lateral (S3))
     • Origin - S1
     • X-axis - unit vector S1 to S2
     • Z-axis - unit vector of X-axis cross vector of S1 to S3
     • Y-axis - Z-axis cross the X-axis

Anchor(Patella_CS)

• Patella digitized CS - transformation matrix between the Patella CS (PAT) and mounted optoelectronic marker CS (PatWorld)

  • The Patella CS is defined for a right knee. It should be mirrored when used for a left knee.
  • Digitized points
    • P1. Most lateral point
    • P2. Most medial point
    • P3. Most superior point
    • P4. Most inferior point
  • Algorithm:
    1. PAT origin - Opat = (P1+P2)/2.
    2. PAT X-axis to point medially: Xpat = normalize(P2-P1)
    3. PAT Y-axis to point posteriorly: Ypat = normalize(cross((P3-P4),Xpat))
    4. PAT Z-axis to point superiorly: Zpat = cross(Xpat,Ypat)

  • Store results in 4x4 matrix T_PatWorld_PAT = [Xpat Ypat Zpat Opat; 0 0 0 1]