Patellofemoral OA

For Medical Students

What It Tests

Patellofemoral wear presents as pain on stairs, on rising from a chair and on kneeling, with stiffness after sitting and a grinding sensation at the front. 4.15.9 covers patellofemoral pain.

The examination is deciding whether the front of the knee is the source, whether the patella tracks normally, and whether the compartments are also involved. 4.15.1 covers patellar tracking.

It is examined separately from the tibiofemoral joint because the loads, the provoking activities and the findings all differ. 3.12.3 covers patellofemoral contact pressures.

How It Is Performed

Take the history: the stairs, the chair, the kneeling, the sitting, and whether the pain is at the front rather than at the sides. 4.2.11 covers aggravating factors.

Watch the patient rise from a chair and climb a step, since both load the patellofemoral joint and both are usually painful. 4.4.10 covers functional movement screening.

Look at the quadriceps and the patellar position with the knee extended and then flexed. 4.15.1 covers tracking.

Palpate the patellar facets with the knee relaxed, since facet tenderness localises the wear to the front. 4.6.5 covers patellar tenderness.

Feel for crepitus through the range with a hand on the patella, which is the sign patients describe as grinding. 4.15.10 covers patellofemoral arthritis.

Assess the range and specifically the painful arc, since patellofemoral wear hurts in the middle of the range rather than at the ends. 4.7.6 covers the arc.

Assess the compartments, because combined disease is common and the treatment depends on which joints are involved. 4.18.2 covers established disease.

What a Positive Means

Anterior pain on stairs and on rising, with facet tenderness and crepitus, is the characteristic picture.

Pain in the middle of the arc rather than at the extremes supports a patellofemoral source, since that is where the contact pressure peaks. 3.12.3 covers contact pressures.

Crepitus without pain is a common finding in a normal knee and is not diagnostic. 4.15.10 covers patellofemoral arthritis.

Facet tenderness with a normal joint line and a normal mechanical examination points to the front alone, which is the group with the clearest options. 4.6.4 covers joint line tenderness.

Anterior pain with compartment tenderness means combined disease, which changes the conversation. 4.18.2 covers it.

MRCS Level

How It Is Performed

In a viva this is the anterior knee pain station in an older patient and the expected answer separates the front from the compartments.

The expected points are the activity history, the functional tests, the tracking, the facet palpation, the crepitus, the painful arc, the compartments and the hip.

Say that you would use the stairs and the chair rather than the flat walk, because those are the loading activities. 4.4.10 covers functional movement screening.

Say that you would assess tracking and alignment, since maltracking and a high Q angle load the lateral facet. 3.12.6 covers the Q angle.

Say that you would not rely on the patellar grind as a diagnostic test, because it is uncomfortable in normal knees. 4.6.5 covers patellar tenderness.

What a Positive Means

The reasoning expected is that patellofemoral contact pressure rises steeply with flexion under load, which is why stairs and chairs provoke the pain and level walking does not. 3.12.3 covers contact pressures.

The lateral facet carries more load in a knee with a valgus vector, which is why maltracking and lateral facet wear go together. 3.12.6 covers the Q angle.

Pain on prolonged sitting comes from sustained compression at low flexion rather than from movement, which is why it eases on standing.

Crepitus reflects surface irregularity, so its presence indicates change and its severity does not indicate symptoms. 4.15.10 covers patellofemoral arthritis.

How Good It Is

The examination localises pain to the front reasonably well and cannot grade the wear.

Its best contribution is the activity pattern, because the stairs and chair history is more specific than any physical sign. 4.2.11 covers aggravating factors.

The individual signs are weak. Facet tenderness, crepitus and compression tests are all present in asymptomatic knees. 4.6.5 covers patellar tenderness.

Skyline and lateral radiographs show the joint, so the examination establishes the symptomatic pattern and the films establish the structure. 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 the question is whether the patellofemoral joint is the sole source, a contributor, or incidental, and the examination is the main instrument for answering it.

Isolated patellofemoral wear with normal compartments is a distinct group, and the examination identifies it by the localisation and the activity pattern. 4.20.7 covers the partial replacement assessment.

Patellofemoral wear alongside compartment disease moves the knee towards a different treatment, and the examination is what finds the combination. 4.18.2 covers established disease.

Maltracking and trochlear dysplasia underlying the wear change the plan, so tracking is assessed rather than assumed. 4.15.1 covers tracking.

Pain disproportionate to the findings at the front raises a non structural component, which is examined for rather than inferred. 4.2.10 covers severity.

Where It Misleads

The commonest error is omitting the patellofemoral examination in a knee with compartment disease, so the combination is missed. 4.18.2 covers it.

Crepitus is read as evidence of a symptomatic joint when it is also a normal finding. 4.15.10 covers patellofemoral arthritis.

A positive compression test is read as specific when it is uncomfortable in a high proportion of normal knees. 4.6.5 covers patellar tenderness.

Anterior pain from a worn compartment refers to the front and reproduces the pattern, so the joint line is palpated before the front is accepted. 4.6.4 covers the technique.

Hip disease and lumbar referral both produce anterior thigh and knee pain, and neither is excluded by the knee examination. 4.2.15 covers referred pain.

Fellowship Level

Where It Misleads

At fellowship level the difficulty is apportioning symptoms between the front and the compartments in a knee where both are worn, and the examination does not do this reliably.

The localisation of tenderness, the activity pattern and the arc all help and none is decisive, so the apportionment stays an estimate. 4.7.6 covers the arc.

A patellofemoral joint worn secondary to maltracking behaves differently from one worn primarily, and the examination finding that separates them is the tracking rather than the pain. 4.15.1 covers tracking.

Trochlear dysplasia underlying the wear is a structural finding the examination only infers, and the inference is often wrong. 4.15.8 covers trochlear dysplasia.

Pain on sitting and pain on stairs can arise from different parts of the same joint, and the examination does not distinguish them.

A previous realignment or a previous lateral release changes the examination baseline, so the findings are read against the surgical history rather than against normal. 4.20.6 covers the reconstructed restraint.