Low-Profile Modifications of the Losee Pivot Shift Test for Assessment of an ACL-Deficient Knee in the Awake Patient

Abstract

Background:

Pivot shift test results have demonstrated widely inconsistent sensitivities when used on awake clinic patients. We believe the painful valgus force applied during traditional pivot shift techniques is the primary culprit and can be circumvented with our novel examination technique.

Indications:

The reason for publishing this examination technique is to maximize the sensitivity and accuracy of the pivot shift examination in the awake patient.

Technique Description:

Four major modifications of Ronald Losee’s original valgus-based examination technique are introduced. These are the 4 general modifications: minimizing the sagittal plane arc of motion, avoiding applying valgus force to the knee, application of gentle anteriorly directed force to the lateral tibia, and performing the examination on the patient’s noninjured knee first. We also provide detailed description of the hand placement during the Albright-Losee pivot shift test. (1) Once the patient is relaxed, the examiner’s hands are placed as follows: (1) the ulnar side of the examiner’s thumb is applied to the posterior aspect of the fibular head. The fingers are placed above the patella on the distal femur as shown in the video. (2) With the examiner’s hands in the correct position, the knee is flexed to 20° to 30°. One-to-3 pounds of anterior translatory force is then applied by the side of the thumb to the fibular head while the knee is taken slowly toward extension. Pathological anterior tibial translation can be expected to begin in a 20° to 30° range short of the patient’s complete knee extension. The examiner must be conscious not to provide any valgus or additional internal or external rotation of the leg.

Results:

This examination is useful for reproducing the subluxation phenomenon in anterior cruciate ligament (ACL)-deficient knees. Our work has shown that these modifications yield an accuracy of 95.51% and a sensitivity of 94.7% in 353 knees examined by 71 clinicians.

Discussion/Conclusion:

The Albright-Losee pivot shift test is an easy to perform, highly sensitive, and highly specific test. In our recently submitted American Journal of Sports Medicine manuscript, the Albright-Losee pivot shift test suggested to be of greater value than Lachman test.

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

The title of our presentation is Low-Profile Modifications of the Losee Pivot Shift Test for Assessment of an ACL-Deficient Knee in the Awake Patient.

My name is Brandon Bates, and I will be narrating this video. Our authors have no pertinent disclosures.

During this presentation, we will discuss the following: The background of the pivot shift and the purpose of this study. A description of the modifications for the Albright-Losee pivot shift test, and potential complications of the Albright-Losee pivot shift test. This video is to be used in conjunction with our recently submitted American Journal of Sports Medicine manuscript validating the sensitivity, specificity, and biomechanics of our novel modifications to a classic examination technique.

Documentation of pivot-shift test results are often required for acceptance of anterior cruciate ligament (ACL) disruption research submitted to today’s highest impact orthopedic journals. Ironically, there is no single, universally accepted pivot shift technique for use in the clinic setting. Most of the published pivot shift techniques appear to be of greatest success while the patient is under anesthesia. The failure of the adequacy of these tests in the office setting is evident in demonstrations of inconsistent sensitivities ranging from 6% to 93%.

Many of the pivot shift test variations rely on application of valgus stress. One of these is the late Ron Losee’s classic pivot shift technique. His examination method was previously used for several decades at our institution. The angular force applied to the lateral knee used to produce the pivot shift is commonly painful. This pain is classically proportional to the amount of valgus force applied. Even a patient’s anticipation of pain can yield low test sensitivity given the protective role of the hamstrings in hiding a positive anterolateral rotational pivot shift subluxation.

In this first video, we demonstrate the classic Losee pivot shift test on a patient and knee model. The examiner stands at the side of the knee being examined. The examiner’s left hand supports the patient’s left foot while the leg is internally rotated. The examiner then flexes the knee while internally rotating the foot and leg while also applying a valgus force. This complex movement yields the impressive, but painful “clunk or pivot” at around 30° short of terminal extension.

The overall purpose of adding 4 low profile modifications to Ronald Losee’s original technique (LP-LPST) was to maximize the sensitivity and accuracy of the pivot shift phenomenon in the awake patient. This is accomplished by performing the examination in a way that optimizes patient relaxation.

Now, we will compare the classic Losee pivot shift test with our alterations done in collaboration with Dr Losee. The Albright-Losee pivot shift test is performed with the 4 following modifications: (1) Minimizing the sagittal plane arc of motion by starting the examination just short of the anticipated subluxation target. This limits the knee’s motion from 30° of flexion to the patient’s terminal extension. (2) The examiner consciously avoids applying any valgus force to the patient’s knee. (3) The examiner gently applies anteriorly directed force to the lateral tibia by pressure of the ulnar side of the examiner’s thumb to the posterior aspect of the fibular head during knee extension. (4) The examiner should always first perform the examination on the patient’s non-injured knee.

We always recommend performing the motions of the Albright-Losee pivot shift test on the unaffected knee. This will allow the patient to become at ease with what to expect in the testing of the injured knee. In addition, doing this will demonstrate how important it is to relax and allow the hamstrings to remain quiet during the passive extension.

It also allows for sophisticated knowledge about the refined axial plane rotations that occur in the sagittal plane near full extension. The patient can observe the external rotation of the leg that occurs in the terminal “screw home” phase of knee extension when compared with their pathological knee.

We will now observe the low-profile modifications in the following videos. The patients in these videos possess magnetic resonance imaging (MRI)-confirmed ACL disruption of their left and right knees, respectively. Before applying the actual pivot test, the examiner re-enforces the importance of hamstring muscle relaxation by initially moving the knee passively from 20° to 30° of flexion toward extension. This short arc of motion minimizes the activation of the hamstrings that hides any slipping sensation of the pivot.

Once the patient is relaxed, the examiner’s hands are placed as follows: The ulnar side of the examiner’s thumb is applied to the posterior aspect of the fibular head. The fingers are placed above the patella on the distal femur as shown in the video.

With the examiner’s hands in the correct position, the knee is flexed to 20° to 30°. One to 3 pounds of anterior translatory force is then applied by the side of the thumb to the fibular head while the knee is taken slowly toward extension. This allows for an anterior force to be applied to the lateral tibial plateau. Pathological anterior tibial translation or merely subtle excessive internal rotation of the lateral tibial plateau can be expected to begin in a 20° to 30° range short of the patient’s complete knee extension. The examiner must be conscious not to provide any valgus or additional internal or external rotation of the leg.

Here you can see the same low-profile modifications applied from a different vantage point, as well as a knee model demonstrating the minor movements. At the end of this video, note the examiner’s 5th finger ensuring that there is no hamstring activation.

Recognition of abnormal translational slipping is key to documenting a positive test. When the examiner feels the subluxation beginning to occur, the motion is stopped, and the patient is asked if they feel that their knee is “out of place” compared with the sensation experienced on the normal side. Acknowledgment of the subluxed tibial position by both the clinician and patient is required for recording a positive pivot-shift.

Next, we will discuss potential technical hitches with this examination technique. Knee swelling with pain is a hallmark feature of acute ACL rupture. In our few patients with a gross degree of knee swelling to the point of great discomfort, the Albright-Losee pivot shift test still yielded a sensitivity of 62.26%. For initially inconclusive results in this patient population, we found re-examination of value once swelling subsided at a second clinical visit.

It is important to anticipate that there is a significant group of ACL-deficient patients who have established, sophisticated levels of dynamic hamstring motor control that is sufficient to effectively stabilize their knees during examination. This group of patients are referred to as “copers.” A study by Engebretsen et al showed that up to 50% of children with this type of control in ACL-deficient knees progressed to adulthood without the need for operative repair. The ability of these copers to stabilize their knee despite well done examinations likely contributes to the Albright-Losee pivot shift test’s lower negative predictive value of 89% found in our referenced study. Furthermore, work by Banovetz et al has even been able to grade a patient’s level of hamstring control. They describe this ability as “none, partial, and complete” voluntary motor control. They further described a category of reflexive or “autonomic” control where the laxity will only be demonstrable when completely paralyzed under anesthesia.

A simple way a clinician can assess a patient’s hamstring control is to manually palpate the hamstring muscle tension. This is accomplished by assessing the subtle tautness of the biceps femorus muscle-tendon unit. Another option would be to examine the side-to-side difference in the patient’s ability to relax any detected resistance to the passive extension during the Albright-Losee pivot shift test.

Here you can see a video of this voluntary hamstring control in an awake clinic patient. This patient was an elite high school tennis athlete who continues to compete with a torn right ACL. In the first video, she is relaxing her hamstring musculature to showcase the pivot phenomenon. In the second video clip, she was asked to use her hamstrings to subtly prevent the pivot. She can hide pivot even during rapid examination testing. We recommend against trying the rapid examination movement at home, but this demonstrates how good of control this patient had. Her case emphasizes the importance of the clinician being aware of this possibility and actively paying attention to the biceps femorus muscle-tendon unit throughout the examination.

As we previously mentioned, a positive examination result is achieved only when both the patient and the examiner note the abnormal positioning of the knee. There is a small group of patients whose proprioception is so poor that they will be unable to recognize the subluxation of the knee with this test. In this scenario, the examiner can recognize the positional abnormality while the patient states their knee feels normal. One additional step can be taken to help work through this problem. The examiner can maintain the knee in the potentially subluxed position and slowly apply 2-to-5 lbs of light valgus isokinetic force. This light amount of force will alter the sensation in a way that the patient should be able to recognize a truly subluxed knee and confirm a positive Albright-Losee pivot shift test.

In conclusion, the Albright-Losee pivot shift test is an easy to perform, highly sensitive, and highly specific test. It is well tolerated by a high percentage of awake patients with an ACL-deficient knee. This examination is useful for reproducing the subluxation phenomenon in ACL-deficient knees. Our work has shown that these modifications yield an accuracy of 95.51% and a sensitivity of 94.7% in 353 knees examined by 71 clinicians. In addition, the Albright-Losee pivot shift test proved significantly better than the Lachman test. This examination can be easily implemented in a variety of clinical settings, including acute on the sideline examination prior to the onset of gross pain and swelling. However, to date, we have limited our validation efforts to evaluating patients in the office setting. We have plans to formally examine the utility of this examination on the sideline in future studies.

I would like to acknowledge all who have helped in establishing this examination technique and creating this video.

Thank you very much.