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--- plug_gait_lower_limb_modified [2025/09/29 17:14] – [Modifications Explained] wikisysop
+++ plug_gait_lower_limb_modified [2025/09/29 19:28] (current) – [Impact of Modifications] wikisysop
@@ Line 10: / Line 10: @@
 //Workstation// or //Nexus// users will be familiar with the Plug-In Gait variation as Vicon's implementation of the CGM.
-In this tutorial, we describe this implementation of [[http://www.vicon.com|Vicon's]] Plug-In Gait using Visual3D.
+In this tutorial, we describe this implementation of [[http://www.vicon.com|Vicon's]] Plug-In Gait using Visual3D, with the necessary modifications made for marker placement error specific to this dataset. The original tutorial without modifications can be accessed [[visual3d:tutorials:modeling:plug-in_gait_lower_limb|here]].
-==== Pose Estimation ====
+In some trials, clear errors in marker placement can be identified when viewing the model. Here we make the necessary adaptations to the model to compensate.
-Plug-In Gait uses a Direct (Non-Optimal) Pose Estimation for computing the position and orientation of each segment based on a set of 3 tracking markers.
+====Marker Placement Error====
-Visual3D uses either [[Visual3D:Documentation:Kinematics_and_Kinetics:Pose_Estimation|Segment Optimization or Global Optimization pose estimation algorithms]].
+The placement of markers during static and dynamic trials can significantly impact the accuracy of the data that is captured. In this static trial markers were only placed on the lateral sides of each leg, with some being nearly co-linear and some incorrectly aligned with anatomical features.
-The results of the implementation of the Plug-In Gait model in Visual3D will differ slightly from the Vicon PIG implementation, but the differences are sufficiently modest that there are no clinically significant differences.
+The closer markers are to being placed co-linearly the more difficult it is to define all six degrees of freedom, this can cause error to be amplified leading to an incorrect model.
-==== Conventional Gait Model Decisions ====
+In this trial, and many others, markers are only placed on the lateral side of each leg. This is done to avoid markers being knocked off during movement trials, however having markers on the lateral and medial side (at least for static trials) helps to improve model accuracy.
-Since there are variations of the conventional gait model, decisions must be made prior to marker placement and data collection. The diagram below lays out some of the decisions based on body segment. This is not comprehensive since many variations exist. The following sections describe the conventional gait model marker placement locations and challenges based on these options.
+The placement of the foot markers, especially the heel, in this trial made it challenging to properly define foot positioning. The Toe_Z landmark was added as a solution to this error.
+====Modifications Explained ====
-{{:Conventional_gait_model_decisions1.png?790}}
+**Shank Definition:** In this tutorial the RKNE marker was added as the lateral boundary for the right shank definition. This was added to improve alignment of the shank and correct excessive incorrect internal rotation of the tibia that was previously present. In the original tutorial there was a significant difference in alignment between the shank and thigh segments which is not typically present or anatomically possible, this change in definition was done to correct this error.
-In the case of the Plug-In Gait, the decisions have already been made for option 2%%(c)%%, 4(b) and 5(b). Using Visual3D, it is possible to opt for different model decisions if needed or relevant. This would however not be consistent with the Plug-In Gait's implementation per se.
+**Toe Landmark and Definition:** The R_Toe_Z landmark was introduced to align the anterior axis of the foot with that of the shank and thigh segments (assuming the subject is standing in alignment). It serves as the distal joint center and the posterior foot alignment. In the original model the foot was defined by the heel and toe markers, both of which were incorrectly placed causing clear error in foot positioning.
-==== Manual Metrics For Plug-In Gait ====
-**The following should be measured during the data collection:**
-  * Height (m)
-  * Weight (kg)
-  * Left and Right Knee width (m)
-  * Left and Right Ankle width (m)
-  * Marker Radius (m)
-**The following metrics can be collected manually, or estimated using equations (if estimated using equations, they do not need to be manually recorded):**\\
-  * Left and Right Leg length (m)
-    * This can be estimated by calculating the distance from the ASIS target to the lateral ankle target
-  * ASIS to greater trochanter distance (m)
-    * This can be calculated from a regression equation: 0.1288*Leg Length-0.04856
-**NOTE:** Plug-in Gait uses the average of the two values (left and right sides) to compute the joint centers.
-==== Plug-In Gait Marker Sets ====
-You can place four targets on the pelvis (right/left anterior iliac spine, and right/left posterior iliac spine), or place three targets on the pelvis (right/left anterior iliac spine, and the mid point of the right/left posterior iliac spine). The images below display the four marker version of the pelvis.
-The typical Plug-In Gait marker set is displayed below:
-{{:PiG_MarkerSet_4Targ.png}}
-Some labs use a Knee Alignment device during the static trial, and then place the lateral knee target for the dynamic trials. The image below displays the marker set for the static trial when using the knee alignment device:\\
-{{:PiG_MarkerSet_KAD_4Targ.png}}
-----
-**Pelvis Marker Placement Considerations**
-The plane of the Pelvis is visualized as a triangle or plane that is formed by either the three markers: the Right and Left Anterior Superior Iliac Spines (RIAS and LIAS) and either a Sacrum marker (SACR marker) or the mid-point between the Posterior Superior Iliac Spines (SACR Landmark).\\ \\ Place the centers of the markers over both Anterior Superior Iliac Spines (ASIS's). The sacral marker (SACR) is placed over the mid-point of the Posterior Superior Iliac spines (RIPS and LIPS).\\ \\ The origin of the pelvis is at the mid-point of the ASIS markers and perpendicular to the line joining them regardless of the position of the PSIS markers. Since this is the case, medial/lateral position of the PSIS markers is not critical but care should be taken regarding the vertical position.
-----
-**Thigh Marker Placement Considerations (without using Knee Alignment Device)**
-The upper leg segment can be visualized as a triangle or plane formed by the Hip Joint Center (RIGH_HIP, LEFT_HIP), lateral thigh marker and lateral knee marker. Palpate lateral epicondyles to estimate the knee flexion/extension axis. Place a marker on the right and left Lateral Epicondyles (RKNE, LKNE) to approximate this axis. This should be done in the standing position with the subject passively flexing and extending the joint to confirm placement. **You are looking for a point that is fixed in the thigh and about which the lower leg appears to rotate.** Mark that location with eyeliner pencil or a pen.\\ \\ When not using a [[Visual3D:Documentation:Modeling:Segments:Knee_Alignment_Device|Knee Alignment Device]] (KAD) the placement of the thigh markers (RTHI, LTHI) or wands (stick on a base with an attached marker) is critical. This marker is used to define the frontal plane of the femur (knee flexion/extension axis location and orientation). The distal 1/3 of the thigh is the best location to decrease movement due to muscle bulk and swing of the hands. The vertical height is not critical but try not place the thigh marker too low on the thigh. The anterior/posterior position of this marker is critical and it is extremely difficult to visualize. Adjust the marker so that it is aligned in the plane that contains the hip and knee joint centers and the knee flexion/extension axis. Position this marker standing and observe knee flexion/extension to confirm.
-----
-**Knee Alignment Device Placement Considerations**
-The upper leg segment can be visualized as a triangle or plane formed by the Hip Joint Center (RIGHT_HIP, LEFT_HIP), lateral thigh marker and lateral knee marker. The difference in this variation is that a [[Visual3D:Documentation:Modeling:Segments:Knee_Alignment_Device|Knee Alignment Device]] (KAD) is used in the static trial to define the coronal plane for the knee. Palpate the lateral epicondyles to estimate the knee flexion/extension axis. Place the KAD over the epicondyles such that the device is in line with the visualized knee flexion/extension axis. This should be done in standing position.\\ \\ After the subject static calibration trial, remove the KAD and mark the KAD location on the lateral epicondyle with a eyeliner pencil or pen. Place a marker on that location (RKNE, LKNE). Placement of the thigh (RTHI, LTHI) markers or wands (stick on a base with an attached marker) is not critical in this case so it can be placed anywhere on the thigh.\\ \\ The KAD can be aligned improperly or can slip after placement. If this does occur, then the knee's frontal plane will be improperly defined. Care should be taken when using the KAD. As a safety measure, it may be best practice when using the KAD to align the thigh marker correctly or use medial knee markers (which is detailed in the next section) and collect a static trial with the KAD and one without the KAD. A choice can be made post data collection on whether to use the KAD alignment or the thigh or medial knee alignment.
-----
-**Shank Marker Placement Considerations**
-The lower leg segment can be visualized as a triangle or plane formed by the Knee Joint Center and the Ankle Flexion/Extension axis (Transmalleolar axis). Palpate the medial and lateral malleoli and visualize an imaginary line that runs through the transmalleolar axis. Place a marker on the right and left Lateral Malleolus (RFAL, LFAL) along that line. Remember to mark that location with eyeliner pencil or a pen.\\ \\ As in the thigh, the placement of the shank markers (RSK, LSK) or wands (stick on a base with an attached marker) is critical. This marker is used to define the coronal plane of the tibia (ankle flexion/extension axis location and orientation). The distal 1/3 of the tibia is the best location to decrease movement due to muscle bulk. The vertical height is not critical but try not place the shank marker too low on the shank. The anterior/posterior position of this marker is critical and it is extremely difficult to visualize. An alignment reference device such as a ruler under the subject's heel can be used to visualize the placement. Adjust the marker so that it is aligned in the plane that contains the knee and ankle joint centers and the ankle flexion/extension axis. This marker can be placed in a seated position but should be checked when standing to confirm.
-----
-**Foot Marker Placement Considerations**
-The foot is visualized as a line along the long axis of the foot from the 2nd metatarsal heads and the ankle joint center projected onto the plantar surface of the foot.\\ \\ The forefoot (toe) marker (RTOE, LTOE) is placed on the dorsal aspect on the 2nd metatarsal heads proximal to the MP joint (on the mid-foot side of the equinus break between forefoot and midfoot). Care should be taken in feet with midfoot breakdown or collapse. The placement of this marker should be proximal to the deformity to avoid exaggerating dorsiflexion in stance.\\ \\ The heel marker (RHEE, LHEE) is placed on the calcaneous where the medial/lateral position is in line with the ankle joint center. In a plantargrade foot, the heel marker is at the same height above the plantar surface of the foot as the toe marker. For a non-plantargrade foot as well as shoe/brace conditions, the height of the heel marker must be placed so that the line from the heel to toe (when viewed from the sagittal plane) is parallel to the plantar surface of the foot.\\ \\ **Note that inversion/eversion of the foot cannot be measured reliably with any Conventional Gait Model without any enhancement to the foot marker set**\\ \\ See [[Visual3D:Tutorials:Modeling:Building_a_Conventional_Gait_Model#Enhancing_the_Foot_Segment|Enhancing the foot segment]] for more detail.
-----
 ==== Load Static Trial ====
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 ----
-====Left Side====
+====Left Side Model====
 To build the left side of the model start by copying and reflecting the appropriate landmarks that were created for the right side. Do the same for the thigh, shank and foot segments.
-====Modifications Explained ====
+====Impact of Modifications====
+The images below show the original model, before modifications, compared to the modified model. Significant errors in tibial rotation and foot orientation can be seen in the original that are corrected for in the updated model.
-**Shank Definition:** In this tutorial the RKNE marker was added as the lateral boundary for the right shank definition. This was added to improve alignment of the shank and correct excessive incorrect internal rotation of the tibia that was previously present.
-**Toe Landmark:** The R_Toe_Z landmark was introduced to align the anterior axis of the foot with that of the shank and thigh segments (assuming the subject is standing in alignment). It serves as the distal joint center and the posterior foot alignment.
-==== References ====
-**Bell AL, Pederson DR, and Brand RA** (1989) Prediction of hip joint center location from external landmarks. Human Movement Science. 8:3-16
-**Bell AL, Pedersen DR, Brand RA** (1990) A Comparison of the Accuracy of Several hip Center Location Prediction Methods. J Biomech. 23, 617-621.
-**Davis RB, Ounpuu S, Tyburski D, Gage JR.** (1991) "A Gait Analysis Data Collection and Reduction Technique." Human Movement Science 10: 575-587.
-**Kadaba MP, Ramakrishnan HK, Wootten ME** (1990) "Measurement of Lower Extremity Kinematics During Level Walking." J. Orthopedic Research8: 383-392.
-**Serge van Sint Jan** "Color Atlas of Skeletal Landmark Definitions: Guidelines for Reproducible Manual and Virtual Palpations" 2007 - Churchill Livingstone
-[[https://www.clinicalgaitanalysis.com/faq/sets/|Gait Models in Common Use]]
-\\
+**Original:**
+{{:without_mods.png?400|}}
+**Modified:**
+{{:with_mods.png?400|}}
+As a result of the modifications made in this tutorial the updated model shows improved alignment between the thigh, shank, and foot segments as well as a more neutral (less supinated) foot position.