Hinged external fixation of the knee: intrinsic factors influencing passive joint motion

J Orthop Trauma. 2004 Mar;18(3):163-9. doi: 10.1097/00005131-200403000-00007.


Objective: To measure changes in knee kinematics after the application of articulated external fixators along a previously described knee flexion/extension axis and 16 specific "off-axis" fixator hinge configurations.

Design: Cadaver, biomechanical study.

Setting: Biomechanics laboratory.

Participants: Nine fresh cadaver knee specimens.

Intervention: Each specimen was mounted on a custom-built frame that constrained the knee to move about a fixed flexion/extension axis. Passive knee motion was induced, and the resulting flexion moment was measured. Data were collected for the on-axis fixator position and 16 distinct rotational and translational off-axis positions. In addition, effects of tibial translation and rotation were investigated.

Main outcome: Range of motion (ROM) attainable within a moment envelope of +/-1 N-m and average energy required to impart movement.

Results: The average ROM for unconstrained knees was 122 degree. Constraining the knee to rotation around an on-axis aligned hinge significantly reduced the ROM by 35% to 79 degree. The 5-mm posterior translated hinge was the only alignment to show on average a slightly larger ROM (86 degree) than the on-axis hinge. All other hinge alignments showed decreased average ROM compared with the on-axis position. Tibiofemoral alignments significantly affected the obtainable ROM for the on-axis aligned hinge.

Conclusion: It was not possible to replicate precisely the complex kinematics of the knee using a single axis fixator over the entire ROM. Using the axis of rotation previously defined in the literature, however, it was possible to obtain a limited ROM of the knee without placing excessive forces on the periarticular structures.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Biomechanical Phenomena*
  • Cadaver
  • Confidence Intervals
  • External Fixators*
  • Female
  • Humans
  • Knee Joint / anatomy & histology
  • Knee Joint / physiology*
  • Male
  • Middle Aged
  • Probability
  • Range of Motion, Articular / physiology*
  • Reference Values
  • Rotation
  • Sensitivity and Specificity
  • Stress, Mechanical
  • Weight-Bearing