Physical Examination for Patellofemoral Instability

Abstract

Background:

We use 2 patient cases to demonstrate relevant physical examination findings when evaluating patients with patellofemoral instability.

Indications:

Case 1 is a 19-year-old female college soccer player with multiple recurrent instability events. Case 2 is a young man in the military service, who is also 19 years old, who began having recurrent instability after a hard landing while skydiving.

Technique Description:

Normal patellar glide is 2 quadrants laterally and 1 quadrant medially; greater than 3 laterally indicates hypermobility. The moving apprehension test is performed with stepwise flexion to determine when the patellar engages the trochlea and no longer shifts laterally. It is important to ensure the quadriceps is relaxed. This test can help distinguish patellar instability from pain-related buckling. The jumping J sign is seen when the patella is completely disengaged from any bony restraint when going from flexion to extension of the knee.

Results:

On physical examination, both patients had positive effusion, tenderness, apprehension, and patellar tilt. Case 1 had an apprehension test positive to 80° of flexion, patellar mobility with a 2-quadrant shift laterally, and a soft J-sign. Case 2 instability was more prominent on examination with a moving apprehension test to 90°, a 4-quadrant shift laterally, and the prominent jumping “J” sign.

Discussion/Conclusion:

The physical examination, in addition to imaging, is essential for operative planning. For case 1, we proceeded with right knee tibial tubercle osteotomy, medial patellofemoral ligament reconstruction, lateral retinacular lengthening, and loose body removal. For case 2, we proceeded with right knee trochleoplasty, tibial tubercle osteotomy, medial patellofemoral ligament reconstruction, and lateral retinacular release.

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

In this video, we go over the physical examination findings in patellofemoral instability and how they can impact your management of patients.

Here are our disclosures.

Background

We highlight the physical examination findings to look out for using 2 case presentations in this video.

We use 2 patient cases to demonstrate relevant physical examination findings when evaluating patients with patellofemoral instability. Case 1 is a 19-year-old female college soccer player with multiple recurrent instability events. These were noncontact injuries during soccer. Case 2 is a young man in the military service, who is also 19 years old, who began having recurrent instability after a hard landing while skydiving. They both had conservative treatment that did not resolve their symptoms.

Physical Exam and Imaging

On physical examination, both patients had positive effusion, tenderness, apprehension, and patellar tilt. Case 1 had an apprehension test positive to 80° of flexion, patellar mobility with a 2-quadrant shift laterally, and a soft J-sign. Case 2 had instability that was more prominent on examination with a moving apprehension test to 90°, a 4-quadrant shift laterally, and the prominent jumping “J” sign.

This slide highlights the importance of considering trochlear dysplasia when evaluating patients with instability, as it significantly increases the likelihood of recurrence. Dejour type B and D dysplasia that has trochlear spurs can produce the jumping J sign, and these types of dysplasia can be amenable to trochleoplasty.^1,2

Normal patellar glide is 2 quadrants laterally and 1 quadrant medially, which is found on examination in this patient. Greater than 3 laterally indicates hypermobility. The moving apprehension test is performed with stepwise flexion to determine when the patellar engages the trochlea and no longer shifts laterally. It is important to ensure the quadriceps are relaxed. This test can help distinguish patellar instability from pain-related buckling. In this patient, it was positive until 80°. Normal is typically around 20° to 30° of flexion.

Case 2 has a more prominent examination finding with the jumping J sign. This is seen when the knee goes from flexion to extension as the patella leaves the bony constraint of the trochlea due to trochlear dysplasia or patella alta. In this case, it is due to the prominent trochlear spur that we will review on imaging. The contralateral left knee in this patient has a normal reference for the apprehension test at 25°. The right knee had a hypermobile patella with a 4-quadrant shift and a positive moving apprehension test to 90° of flexion.

Additionally observed on examination is lateral patellar tilt. Standing alignment for both patients was neutral, but it is important to look out for valgus knee alignment, as an increased Q angle makes patients more susceptible to lateral subluxation. To quantify the degree of genu valgum, you should obtain long-leg alignment films on each patient, as it can be difficult to assess on physical examination alone.

Here is a great demonstration of the jumping J sign from an arthroscopic point of view.

We review a few key measurements for instability. The Caton-Deschamps ratio is measure by having a ratio of the distal patellar articular surface to the tibial articular surface divided by the length of the patellar articular surface. Anything above 1.2 is considered patella alta. This is preferred over the Insall-Salvati ratio for elongated patellar poles and the Blackburne-Peel index for abnormal tibial slope.

To measure the PT-LTR (patellar tendon-lateral trochlear ridge distance), select the first axial slice distal to the patella with full PT width. ³ Similar to TT-TG (tibial tubercle-trochlear groove distance), you create a line perpendicular to the line connecting the posterior condyle, but you place this at the LTR. You then measure the length within the PT itself that is beyond the LTR line, seen here in yellow.

Surgical Indications and Technique

For case 1, no patella alta, increased TT-TG, a 5-mm trochlear spur, and the absence of a jumping J sign in this patient helped determine our operative plan. There is clear chondral damage present on magnetic resonance imaging (MRI) from recurrent subluxation events that would be addressed as well. This chondral lesion was on the lateral patella facet and subject to continued elevated load; this is partly what prompted the tibial tubercle osteotomy with borderline high TT-TG and PT-LTR numbers. It also influenced a steeper cut that further offloads the lateral facet.

We proceeded with right knee tibial tubercle osteotomy, medial patellofemoral ligament reconstruction, lateral retinacular lengthening, and loose body removal.

Case 2 axial MRI helps demonstrate how unstable the patellofemoral joint is in this patient. The increased TT-TG, a 10-mm supratrochlear spur, and prominent jumping J sign on physical examination helped to determine the operative plan.

We proceeded with right knee trochleoplasty, tibial tubercle osteotomy, medial patellofemoral ligament reconstruction, and lateral retinacular release.

This slide helps outline indications for trochleoplasty and when it can benefit patients. Key indicators for trochleoplasty include supratrochlear spur height and a jumping J sign on physical examination. ⁴ Another take-home point is that flatness is not the indication for trochleoplasty, as this can be addressed with medial patellofemoral ligament reconstruction alone.

For tibial tubercle osteotomies, the decision to medialize, distalize, or move anteriorly is based on the criteria above. Case 1 had a significant focal chondral lesion, and we therefore made a steep cut to move anterior when medializing the tibial tubercle.

This clip has highlights of the technique for trochleoplasty. Leaflet markings help guide all cuts moving forward. The thick shell technique by the senior author leaves 5-mm thick leaflets that are undercut utilizing the windshield wiper technique shown here. Bone tamp and a No. 20 blade complete the cuts for the leaflets. Knotless anchors with suture tails are then used to tie down the leaflets and deepen the trochlear groove.

In the top left image, you can see the 10-mm trochlear spur. In the top right image is our leaflet marking to help guide our cuts. Both bottom images show the leaflets tied down flush to the anterior cortex of the femur with deepening of the trochlear groove. With the trochlear spur now removed and the groove deepened, there will no longer be a jumping J sign on physical examination. Postoperatively, we encourage immediate motion with the following restrictions.

Discussion/Conclusion

The cases presented in this video highlight the importance of a thorough and specific patellofemoral physical examination when evaluating patients for patellofemoral instability. Specific findings, such as the jumping J sign, can help guide physicians toward the pathology of instability. The jumping J sign means the patella is completely disengaged from any bony restraint. It is kicked out laterally by a convex proximal trochlear prominence described as a “spur.” The convex prominence is key to decision-making to alter the trochlear anatomy. The J sign can also be produced with severe patella alta and an abnormal vector in the coronal plane, such as from genu valgum or a lateralized tibial tubercle. The physical examination, in addition to imaging, is essential for operative planning.

From the Department of Orthopaedics at the University of Virginia, we thank you for watching.