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Subtalar Joint Angle - Quintic Automatic Tracking

Q4E Case Study 23 – Using Quintic Biomechanics to calculate subtalar joint movement.

Intersection Angle Model

Proposed Subject usage:

Sports Science / Mathematics / Physics (A/AS level)
Sports Science / Physiotherapy/ Sports Injuries & Rehabilitation (Degree Yr 1/2/3)


Quintic have been able to optimize the Quintic Biomechanics Video analysis Software by integrating a novel method to measure the subtalar joint angle by using a 4 point calculation which measures the moving angle between two lines. (See Intersection Angle Model below). In the case of the subtalar joint, the bisection of the calcaneum and of the tibia. The difficulty in this observation is the changing angle between the bisection and the camera, in comparison with a sagittal plane analysing video (sagittal knee or ankle flexion-extension).

Intersection Angle Model:
Quintic uses specific digitisation templates to identify the point at which 2 separate lines that connect digitised points intersect. Upto 4 intersection angles can be created in this way, see diagram below.

Case Study 
The subject was a young football player with a history of left ankle instability and ankle inversion trauma. With literature showing that the highest incidence of injury occurs during ankle inversion at the initial contact phase of gait within football players, this area needs to be thoroughly understood and analysed.


The subjects subtalar joint is put into a neutral position and measured, reflective markers that can be automatically tracked by Quintic Biomechanics video analysis software are then applied to the subject. A two marker cluster is positioned on the tibia and another two marker positioned on the posterior aspect of the calcaneum fixed on the bisection of the tibia and calcaneum with the subtalar joint in his neutral position.

For the data analysis, high-speed Gig E cameras were configured to capture at 100fps focused horizontally on the sagital and transversal plane. The camera was positioned 1.5 m behind the treadmill. For the walking trial the treadmill was set at a speed of 4 km/h and for running (11 km/h). For each walking and running trial seven complete gait cycles were recorded for statistical analysis.

Illustration 1a: Marker position set-up for the barefoot trial.

Statistical Analysis
Kinematic data was collected using a high speed Gig E camera filming the subject from a rear view. Filming was conducted at 100fps and a shutter speed of 1/1000.  Reflective markers were attached to the subject at the subtalar joint. Marker placements were determined by joint palpation and identification of anatomical land marks.

A Hedler (1000w) lamp was positioned behind the camera to ensure the markers were clearly visible. The videos were opened in the Quintic Biomechanics software and heel strike and toe off were identified.  After calibration, the videos were then automatically digitized, due to Quintic’s accurate and quick automatic tracking system 700 frames (7 gait complete gait cycles) could be easily and accurately tracked.

Results: Barefoot Condition

Graph 1 : Quintic Biomechanics graph export of subtalar angular displacement
during seven complete gait cycles

Illustration 1 and Graph 2: Subtalar angle at point of contact (heel strike) from one gait cycle.
(Red line on graph indicates point of heel contact)

Illustration 2: Quintic multi image capture highlighting 18 specific points of the left foot
stance phase of one gait cycle.

Graph 3: Angular Displacement of the Subtalar angle during the stance phase of the left foot. (First red line indicates heel strike (foot contact) frame 109 in illustration 2, second red line indicates midstance, frame 141 in illustration 2 and the third red line indicates toe off (last contact) frame 173 in illustration 2

The data analysis as well illustration 1 and graph 2 reinforce  that there is significant subtalar inversion at heel strike, for each step. When looking at the complete stance phase graph 3 and illustration 2 illustrate that during the stance phase of the gait cycle the subtalar joint remains in an inverted position.


Results : Insole Condition
By recording the subjects walking and running gait using the Gig E cameras at 100fps in both sagittal and coronal planes and executing a full biomechanical analysis, (joint angles, stride lengths, stride frequencies, limb alignments etc,  insoles were prescribed. Once the insoles were fit into the subject’s daily footwear the same walking and running trials conditions were repeated from the barefoot condition (Walking at a speed of 4 km/h and running at a speed 11 km/h on the treadmill). The markers on the tibia stayed on the same place as the test before,  and the markers  placed on the rear heel of the shoe in the same position as the calcaneum markers has been placed in the barefoot trials.

Illustration 3a: Marker position set-up for the insole condition.



Results: Comparing Barefoot and Insole conditions

Illustration 3: Quintic multi image capture highlighting 18 specific points of the left foot stance phase of the gait cycle during the insole condition.

Graph 4: Comparison of walking subtalar angles, red line illustrates barefoot condition and blue line illustrates insole condition.

Graph 5: Comparison of running subtalar angles, red line illustrates barefoot condition and
blue line illustrates insole condition.

Graphs 4 and 5 illustrate that when the subject uses the insoles we can conclude that:

  • The subject experiences a normal inversion (functional varus) before heel strike (up to 6°)
  • An initial pronation through the subtalar neutral movement up to 7° (in a real pronation moment).

The new subtalar analysis function which is available with Quintic Biomechanics video analysis software allows the clinician to accurately and quickly identify and  diagnose subtalar joint problems, while also enabling detailed observation and control of an intervention/treatment in an objective way. With many anatomical joints not having a fixed axis of rotation, Quintic’s new intersection angular analysis method is a more accurate method of analysing body motion and is more accurate than fixing an artificial axis of rotation.

Subtalar joint angle calculation | Quintic Sports