{
  "_id": ObjectId("54f44a657f8b9a1d318b4567"),
  // other fields
  "ligaments": [
    [
      {
        "data": "dia",
        "order": 0
      },
      {
        "data": "hub",
        "order": 1
      }
    ],
    [
      {
        "data": "pcd",
        "order": 0
      },
      {
        "data": "width",
        "order": 1
      }
    ]
  ]
}