The PIVOT App: A User Guide

Abstract

Background:

While the pivot shift examination is often regarded as the gold standard test for diagnosis of anterior cruciate ligament (ACL) injury, one of the pitfalls of the pivot shift test is that it lacks standardization among physicians. The PIVOT App is a validated application to quantify the amount of tibial translation during the pivot shift maneuver and improve standardization of clinical measurement.

Indications:

The PIVOT App can be used in both clinic and operating room settings for patients who sustained injury to the ACL. The PIVOT App may assist in identifying the amount of rotatory knee laxity in patients with ACL deficiency or following ACL reconstruction.

Technique Description:

The PIVOT App works by quantifying the amount of translation in the lateral tibia relative to a marker on the lateral femoral epicondyle. To use the PIVOT App, 3 yellow circle stickers are placed on the bony prominences of the lateral knee: the lateral epicondyle, Gerdy’s tubercle, and the “pivot point” 3 cm posterior to Gerdy’s tubercle parallel to the joint line. Once placed, the pivot shift flexion maneuver can be recorded in the PIVOT App and analyzed to identify both the distance of spontaneous tibial reduction during the pivot shift maneuver and the time of reduction in seconds. The most common problems encountered while using the application include (1) improper marker placement, (2) interference of marker tracking with yellow color in the background, (3) interference of marker tracking with overhead lighting, and (4) extraneous data collection before and after pivot shift flexion.

Results:

Previous studies have validated the PIVOT App to accurately distinguish normal, low-grade, and high-grade pivot shifts with resultant increasing tibial translation in the lateral compartment of the knee. The PIVOT App has been used at institutions worldwide to quantify and standardize measurement of the pivot shift.

Conclusion:

The PIVOT App is a validated application to quantify the amount of lateral tibial translation and reduction during the pivot shift maneuver. Proper use and avoidance of complications while using the application can aid clinicians in accurate diagnosis of rotatory knee laxity in patients following ACL injury.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

This is a presentation on “The PIVOT App: A User Guide” by Sahil Dadoo, Liane Miller, Gabrielle Fatora, Robert Tisherman, and Volker Musahl from the University of Pittsburgh and UPMC Freddie Fu Sports Medicine Center. These are our disclosures. This presentation will discuss the background of the PIVOT App, how the PIVOT App works to quantify the pivot shift examination, a case demonstration using the PIVOT App, and possible complications while using the app and how to avoid them. The timings relevant to the possible complications are included here for ease of access.

The pivot shift test is often regarded as the gold standard test for diagnosis of anterior cruciate ligament (ACL) injury. However, one of the pitfalls of the pivot shift test is that it lacks standardization among physicians, making it difficult to grade and use clinically. ² There are 2 phases of the pivot shift test: anterior subluxation of the lateral tibial plateau during internal rotation and spontaneous reduction of the lateral tibial plateau during flexion of the knee. ¹ Due to the variability in pivot shift maneuvers and grading, it is thought that quantitative measurement of the pivot shift can improve repeatability and reliability.

The PIVOT App was developed at the University of Pittsburgh in an attempt to quantify tibial translation during the pivot shift. The P.I.V.O.T. Trial was an International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine (ISAKOS)/Orthopaedic Research and Education Foundation (OREF)–funded multicenter trial at 4 institutions worldwide, aimed at validating quantitative measurement of the pivot shift maneuver. Previous studies have validated the PIVOT App to distinguish normal, low-grade, and high-grade pivot shifts with resultant increasing tibial translation in the lateral compartment of the knee. ⁴ The PIVOT App works by quantifying the amount of translation in the lateral tibia relative to a marker on the lateral femoral epicondyle. ³ The app works in 2 planes to quantify this translation.

This is the typical output provided by the PIVOT App. In the top right corner of the screen, the amount of tibial reduction during the pivot shift can be identified and recorded in millimeters, along with the reduction time in seconds. The amount of tibial reduction can also be seen as the vertical distance between the 2 yellow points on the resultant graph. The Y axis indicates the position of the lateral femoral epicondyle relative to Gerdy’s tubercle and corresponds to distance in millimeters, whereas the X axis corresponds to time in seconds. It is important to understand the typical curve output in order to identify when problems may have occurred during testing.

To use the PIVOT App, 3 yellow circle stickers are placed on the bony prominences of the lateral knee. The first marker is placed on Gerdy’s tubercle, and the second marker is placed 3 cm posterior to marker one along the axis parallel to the joint line. The second marker is referred to as the “pivot point” and is used to identify the plane in which tibial reduction will occur. The third marker is placed on the lateral femoral epicondyle and is used to triangulate with the previous 2 markers.

The following is a case demonstration using the PIVOT App. The first step is to ensure the markers remain in frame throughout full knee range of motion. The pivot shift can be attempted prior to starting the iPad test to ensure the markers remain within frame. The next step is to align the camera angle in line with the markers during internal rotation of the tibia, to ensure that all 3 markers remain as full circles while being tracked in the app. Once confirmed, the iPad examiner will countdown from 3, after which the pivot shift flexion will occur. The pivot shift examiner will hold the knee in flexion until the iPad test is stopped.

This is the output of the case demonstration. A reduction of 2.7 mm can be appreciated and confirmed as the distance between the 2 yellow dots. The top left corner of the screen portrays the recorded video, which can be scrolled through to determine the specific time point of pivot shift reduction. The bottom left of the screen highlights the marker tracking and can be assessed to ensure that only the marker circles are being tracked. Any extraneous tracking will be identified in green in the bottom left of the screen.

The following slides will show the most common problems encountered while using the app:

1. The most common reason for incorrect data collection is when yellow objects are shown in the background, as the PIVOT App perceives any yellow color as data collection. Here, the strings of the scrub pants are yellow and can be identified by the app. This demonstrates the output when there is color interference with the markers. As can be identified, the graph appears abnormal and a reduction of 18 mm was identified, which is likely too large a value to occur clinically. On the right, the strings of the scrub pants can be seen and identified as white, indicating the app accidentally tracked the yellow strings as a marker. This can be confirmed on the bottom left of the screen, which shows the strings being tracked. The solution to this problem is to hold a blue sheet as a background for PIVOT App recording, which will eliminate any extraneous yellow in the background and increase the likelihood of a successful test.

2. Another common problem encountered while using the app is overhead light interference with the markers, as can be seen here. In this scenario, the operating room lights overhead are reflecting against the markers, impairing appropriate data collection from being recorded by the app. As you can see in the output when this problem occurs, the markers are not visible in the video or in the bottom left corner, as only one marker was captured and additional data collection beyond the markers occurred. Furthermore, a tibial reduction of 78 mm was recorded, which is unrealistic clinically and should be questioned for possible errors if found. The solution to this problem is to adjust the sensitivity setting of the app. As can be seen on the image of the Rubiks cube on the right, the app works by tracking all yellow markings. ³ The ideal sensitivity setting is when all yellow is being perfectly captured, as can be seen an image B, without any extraneous collection, such as in image D. The sensitivity can be adjusted on the home screen prior to recording, and can be decreased if too much light is present, or increased if not enough light is observed to adequately record all 3 markers. The ideal sensitivity is when all 3 markers are fully captured with no extra light.

3. A third problem that can occur is if the marker shape changes from a circle to an ellipse. This is a common problem in patients where significant tibial internal rotation is required to perform the pivot shift test. As can be seen here, the lateral epicondyle marker was inadequately recorded, and a reduction of 4.3 mm was identified in a patient with a clinically negative pivot shift. In this scenario, the marker shape was altered due to light reflection in the room, and therefore the test was repeated after adjusting the lighting, until all 3 markers were adequately tracked as full circles throughout all of flexion during the pivot shift.

4. The final problem discussed in this video occurs when recording both flexion and extension during the pivot shift test. While using the app, it is important to only record flexion and instruct the pivot shift examiner to hold the knee in flexion until the PIVOT App test is stopped. This is important to minimize extraneous data collection and ensure the app is only recording pertinent data relevant to tibial translation during pivot shift flexion. As can be seen in this resultant graph, significant data was collected before and after the tibial reduction phase of the pivot shift, which can impair video analysis by the app. The solution is to minimize time of recording prior to flexion and stop recording at the peak flexion point.

In summary, the most important tips for success include:

1. Placing the yellow markers appropriately on the lateral femoral epicondyle, Gerdy’s tubercle, and pivot point 3 cm posterior to Gerdy’s tubercle and parallel to the joint line.

2. Removing all yellow from the background and adjusting sensitivity to fully capture all 3 markers.

3. Minimizing data collection before and after the pivot shift to avoid improper analysis by the iPad app: This can be accomplished by having the iPad examiner countdown from 3 prior to starting the test and by the pivot shift examiner holding the knee in flexion until the test is stopped to avoid recording extension data as well.

4. Tibial reduction should be correlated clinically and reduction values greater than 15 mm should be questioned and re-testing should be considered.

Here are our references. Thank you for listening to our presentation on “The PIVOT App: A User Guide” and we hope you find this information helpful while using the app.