Article Figures & Data
Figures
- Fig. 1
Posterior photo of specimen showing placement of strain gauge pads on lamina near facet joint. The pads contained 4 uniaxial gauges oriented parallel. The pads were aligned with gauge axes approximately parallel to the predicted primary direction of loading when the facets were compressed.
- Fig. 2
Specimen loading configurations. (A) Photo from a right-side perspective of a pure moment flexibility test. Strings and pulleys in conjunction with a standard servohydraulic test frame were used to induce flexion (shown), extension, axial rotation, and lateral bending. (B) Photo from a left-side perspective of a flexion-compression test. An electric motor connected to the upper fixture with a heavy-duty belt induced flexion or extension. Weights hung from the motor applied a constant compressive follower load of 70 N. Because of the orientation of the pulleys, the direction of the follower load stayed aligned with the axis of the specimen throughout movement.
- Fig. 3
Calibration of strain gauges required the specimen to be disarticulated after completion of testing. Then, test loads were applied with the MTS piston fitted with a plunger. Loads were applied to a series of points (shown marked with permanent ink) while output from each strain gauge was recorded. A neural network model used these test loads to establish the relationship between strain gauges and facet load. (A) In the first 6 specimens, a metal plunger with a small tip was used. (B) In the last 4 specimens, a rounded plastic plunger was used, which provided a surface mimicking the opposing facet better than the metal plunger.
- Fig. 4
Mean angular motion in each condition studied. Full bars represent ROM; the portion below the horizontal line represents LZ, and the portion above the horizontal line represents SZ. Error bars show standard deviation of ROM.
- Fig. 5
Angular coupled rotation per degree of primary rotation at C4-5 showing coupling pattern between lateral bending and axial rotation. Error bars show standard deviation.
- Fig. 6
Mean location of axis of rotation in sagittal plane during flexion to extension at index (C4-5) and adjacent (C3-4 and C5-6) levels. Error bars show standard deviation.
- Fig. 7
Mean facet loads during different conditions of specimen loading. Facet loads during flexion and extension are averages of right and left sides. Error bars show standard deviation. (Axl Rot'n, axial rotation; Lat Bend, lateral bending.)
Tables
Parameter and loading mode Normal (mean ± SD) (°) Arthroplasty (mean ± SD) (°) Plated (mean ± SD) (°) ROM Flexion 7.0 ± 1.6* 7.8 ± 1.9* 3.2 ± 2.3 Extension 6.9 ± 1.9* 6.7 ± 1.9* 2.9 ± 2.0 Lateral bending 5.4 ± 1.6* 3.8 ± 1.3*† 2.6 ± 1.5 Axial rotation 6.1 ± 1.4* 5.7 ± 1.6* 3.0 ± 1.4 LZ Flexion-extension 9.5 ± 2.8* 9.7 ± 3.6* 2.9 ± 3.2 Lateral bending 8.4 ± 2.9* 4.2 ± 2.0† 2.3 ± 2.1 Axial rotation 9.1 ± 2.2* 6.1 ± 2.4*† 2.5 ± 2.3 SZ Flexion 2.2 ± 0.5 2.9 ± 0.9* 1.7 ± 0.9 Extension 2.2 ± 0.6 1.9 ± 0.9 1.4 ± 0.6 Lateral bending 1.2 ± 0.2 1.7 ± 0.5† 1.4 ± 0.6 Axial rotation 1.5 ± 0.4 2.6 ± 0.8*† 1.7 ± 0.4 - Table 2
Summary of alterations relative to intact condition observed for arthroplasty-implanted and plated conditions
Parameter Arthroplasty Plated ROM Flexion No change Substantial decrease Extension No change Substantial decrease Lateral bending Mild decrease Substantial decrease Axial rotation No change Substantial decrease LZ Flexion-extension No change Substantial decrease Lateral bending Mild decrease Substantial decrease Axial rotation Mild decrease Substantial decrease SZ Flexion No change No change Extension No change No change Lateral bending Mild increase No change Axial rotation Mild increase No change Coupled axial rotation during lateral bending No change Substantial decrease Coupled lateral bending during axial rotation Substantial decrease Substantial decrease Anteroposterior position of axis of rotation No change Substantial increase Rostrocaudal position of axis of rotation Mild increase Substantial increase Facet load during flexion Mild decrease Mild decrease Facet load during other loading No change No change
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