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


METHODS
Cadaver, biomechanical study.


METHODS
Biomechanics laboratory.


METHODS
Nine fresh cadaver knee specimens.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Sommers
Mark B
MB
Biomechanics Laboratory, Legacy Clinical Research & Technology Center, Portland, OR 97232, USA.
Fitzpatrick
Daniel C
DC
Kahn
Kevin M
KM
Marsh
J Lawrence
JL
Bottlang
Michael
M
D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D016001:Confidence Intervals; D016267:External Fixators; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011336:Probability; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D012399:Rotation; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D016474:Weight-Bearing