Patellar Tracking

For Medical Students

What It Tests

Patellar tracking is the path the patella follows as the knee flexes and extends, and assessing it tests whether that path is central or deviates.

It is an active phenomenon. The patella is pulled by the quadriceps and constrained by the trochlea, so a passive assessment of a relaxed patella describes its laxity rather than its track. 3.12.1 covers the mechanics.

The track matters most near extension, where the patella is least constrained by bone and most dependent on the soft tissues. 2.12.1 covers the trochlea.

How It Is Performed

Sit the patient on the edge of the couch with both knees flexed and the feet hanging free. 4.3.4 covers the sitting assessment.

Ask them to extend the knee slowly, and watch the patella from directly in front rather than from the side.

Note the path: whether the patella rises in the midline or deviates laterally, and at what point in the arc any deviation occurs.

Repeat with the patient actively flexing from full extension, since a deviation appearing on the way out and on the way back in is more convincing than one seen once.

Compare with the other knee, and note the knee's alignment and the foot position, since both change the track. 4.5.7 covers dynamic alignment.

What a Positive Means

A patella that deviates laterally in the last part of extension indicates a tracking abnormality, and the abrupt version of that is the J sign. 4.15.2 covers it.

A central track with anterior pain does not exclude a patellofemoral problem, since pain and maltracking are separate findings that often coexist. 4.15.9 covers patellofemoral pain.

A visible deviation in a patient with no complaint is a finding without a diagnosis, and it is common. 4.23.3 covers hypermobile patients.

A track that worsens when the patient is asked to extend against resistance suggests the deviation is dynamic rather than structural. 4.15.6 covers dynamic tracking.

A knee that falls into valgus as the patient extends has a proximal problem contributing to the track, and the hip is where that is addressed. 4.4.5 covers that pattern.

MRCS Level

How It Is Performed

In a viva the sitting position and the active movement are the two things that separate an assessment of tracking from an assessment of patellar mobility.

The expected points are the sitting position, the slow active extension watched from the front, the arc in which any deviation occurs, the repeat into flexion, and the comparison.

Say that tracking is active and that the glide and tilt tests assess something different, which is the distinction the question is probing. 4.15.4 covers the glide.

Say that you would assess the rotational alignment and the foot, since femoral anteversion and tibial torsion both alter the track without any patellofemoral abnormality. 4.5.6 covers rotational alignment.

Say that you would record the arc rather than the word maltracking, because the arc is what the next clinician can compare. 4.1.8 covers the record.

What a Positive Means

The reasoning expected is that the patella is held centrally by the trochlea through most of flexion and by the medial soft tissues near extension, so a deviation near extension implicates those soft tissues or the trochlea's proximal shape. 2.12.1 covers the trochlea.

The quadriceps pulls the patella slightly laterally because of the angle between the muscle and the patellar tendon, which the trochlea normally resists. 3.12.6 covers the Q angle.

Trochlear dysplasia removes the bony constraint, which is why a dysplastic knee tracks abnormally in a way soft tissue surgery alone does not correct. 4.15.8 covers that assessment.

Dynamic valgus adds to the lateral vector through the limb rather than at the knee, which is why hip control affects the track. 3.12.7 covers dynamic valgus.

How Good It Is

Clinical assessment of tracking identifies a gross abnormality reliably and a subtle one poorly, and it cannot distinguish the causes.

It is specific when the deviation is abrupt and reproducible and non specific when it is a slight lateral drift, which is common in people without complaints.

It is more informative than any passive patellar test for the question of what the patella does in use. 4.15.4 covers the passive tests.

Imaging in flexion and dynamic imaging measure what this estimates, and they are the reference where a plan depends on it. 4.1.6 covers that relationship.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level tracking contributes to whether a patellofemoral problem is treated at the soft tissue level, the bony level, or neither.

An abrupt deviation near extension in a patient with instability is a structural finding and contributes to the case for surgery. 4.15.2 covers the sign.

A smooth track in a patient with anterior pain moves the assessment away from instability and towards load, alignment and the extensor mechanism. 4.15.9 covers patellofemoral pain.

A maltracking knee with trochlear dysplasia is a different operation from one with a normal trochlea, and the examination raises the question that the imaging answers. 4.15.8 covers it.

Where dynamic valgus contributes, treating the proximal control is part of the treatment and sometimes all of it. 4.4.10 covers functional screening.

Where It Misleads

The commonest error is assessing tracking passively, which measures something else entirely.

The second is watching from the side.

The third is reading a lateral drift as a diagnosis in a patient whose complaint is pain rather than instability.

The fourth is attributing a track to the patella when the rotational alignment is the cause. 4.5.6 covers it.

The fifth is recording maltracking without the arc, which gives the next clinician nothing to compare.

Fellowship Level

Where It Misleads

In referred practice the track is usually being assessed after an operation, and the question is whether the operation changed it.

A patient with a reconstructed medial patellofemoral ligament and a persisting abrupt deviation has either a failed reconstruction or an unaddressed bony abnormality, and the two are separated by the dysplasia assessment. 4.15.7 covers the ligament.

A patient whose track is now central and whose pain is unchanged had a tracking problem and a pain problem, and only one was treated. 4.15.9 covers the second.

A patient with an over constrained reconstruction tracks medially and has medial facet pain, which is a complication that is under recognised because nobody looks for a medial deviation. 4.6.5 covers patellar tenderness.

In a knee with a tubercle osteotomy the track has been altered deliberately, so the comparison is with the intended result rather than with the other knee. 4.6.7 covers the tubercle.

In medicolegal work a recorded track is a weak observation unless the arc is described, since the word maltracking carries no information about what was seen. 4.23.7 covers that setting.