Pes Anserinus Pathology

The same topic at 4 depths

Each tier deepens the one below it and never repeats it. Choose the level you want.

Pes Anserinus Pathology

Choose a depth

Student MRCS FRCS Fellow

For Medical Students

What It Tests

The pes anserinus is the conjoined insertion of the medial hamstring tendons on the upper medial tibia, with a bursa beneath it. 4.16.6 covers the tendons.

Examining it tests for tenderness at that insertion, which presents as medial knee pain and is frequently attributed to the joint or the meniscus. 4.6.4 covers joint line tenderness.

It matters because the site is a short distance below the medial joint line, and that distance is the whole diagnosis. 4.12.7 covers a related separation.

How It Is Performed

Lay the patient supine with the knee slightly flexed and the medial side exposed.

Find the medial joint line with a finger and then move distally and slightly posteriorly onto the upper medial tibia, which is where the insertion sits. 4.6.1 covers systematic palpation.

Palpate for focal tenderness and for a boggy swelling, which indicates a bursitis rather than an insertional problem alone.

Compare the tenderness there with the tenderness at the joint line itself, and record which is greater, because that comparison is the finding. 4.6.4 covers the joint line.

Ask the patient to flex the knee against resistance and note whether that reproduces the pain, which implicates the hamstring insertion. 4.16.6 covers that test.

Perform the medial ligament and meniscal assessments, since the alternatives have to be excluded rather than assumed away. 4.12.1 covers valgus stress testing.

What a Positive Means

Focal tenderness below the medial joint line with a normal joint line, a normal valgus examination and a normal meniscal examination indicates a pes problem.

A boggy swelling at that site indicates a bursitis, which is the version that responds to local treatment.

Pain reproduced by resisted flexion supports the hamstring insertion as the source. 4.16.6 covers it.

Tenderness at both the pes and the joint line means two possible sources, which is common in a degenerative knee and should be recorded as both. 4.18.3 covers the varus arthritic knee.

A normal pes with medial joint line tenderness points at the meniscus or the deep medial ligament instead. 4.12.7 covers that separation.

Key Learning Points

The pes is the conjoined medial hamstring insertion, with a bursa beneath it.
It sits a short distance below and behind the medial joint line, and that distance is the diagnosis.
A boggy swelling there indicates a bursitis.
Pain reproduced by resisted flexion supports the hamstring insertion.
Tenderness at both sites means two possible sources, which is common in a degenerative knee.

MRCS Level

How It Is Performed

In a viva this is the answer when asked for an extra-articular cause of medial knee pain, and the anatomical localisation is the mark.

The expected points are finding the joint line first, moving distally and posteriorly, the comparison of the two tenderness sites, the resisted flexion, and the exclusion of the joint causes.

Say that you would find the joint line before palpating the pes, since the diagnosis depends on knowing where the joint line is. 4.6.4 covers it.

Say that the condition coexists with medial compartment arthritis often enough that finding it does not exclude the joint. 4.18.3 covers that knee.

Say that you would examine the hamstrings, since the pes is their insertion and the problem may be proximal to it. 4.16.6 covers them.

What a Positive Means

The reasoning expected is that the medial hamstring tendons converge on a small area of the upper medial tibia, so the stress there is concentrated and the bursa beneath reduces friction. 2.9.5 covers the semimembranosus.

Overload or a degenerate knee's altered mechanics increases that stress, which is why the condition appears both in athletes and in older patients with medial compartment change. 3.5.3 covers load distribution.

The bursa inflames in response, which is why a boggy swelling is part of the picture in some patients and absent in others.

The site is below the joint line because the insertion is, and that is why the examination's localisation to within a short distance is diagnostic. 4.6.4 covers the joint line.

How Good It Is

The examination is specific when the tenderness is focal, below the joint line and reproduced by resisted flexion, which makes this one of the better localising diagnoses in the section.

It is non specific when the whole medial side is tender, which is common in a degenerative knee. 4.18.3 covers that knee.

It cannot separate an insertional tendinopathy from a bursitis reliably, and ultrasound does, although the distinction changes the treatment modestly. 4.1.6 covers that relationship.

Its main value is excluding the joint as the source, which prevents a pointless arthroscopy in a patient whose problem is on the surface. 4.9.11 covers that error's commonest version.

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

Key Learning Points

The medial hamstring tendons converge on a small area, so the stress there is concentrated.
A degenerate knee's altered mechanics increases that stress, which is why older patients get it.
The bursa inflames in response, which is why a boggy swelling appears in some patients.
It is specific when focal and below the joint line, and non specific when the whole side is tender.
Its main value is excluding the joint as the source.

FRCS Level

How Good It Is

At decision level this is a non surgical diagnosis whose value is preventing an operation on the joint.

A patient with focal pes tenderness, a normal joint line and normal ligament and meniscal examinations has an extra-articular problem managed locally and by load. 4.6.4 covers the joint line.

A patient with both pes tenderness and medial compartment change has two sources, and treating the compartment leaves part of the complaint, which is worth saying before an operation rather than after. 4.18.3 covers that knee.

A patient with pes tenderness after a hamstring graft harvest has donor site symptoms at the insertion, and the history separates them. 4.20.1 covers that assessment.

A patient with tenderness at several insertions and systemic features has an enthesopathy, which moves the specialty. 4.2.14 covers inflammatory pain.

Where It Misleads

The commonest error is attributing the tenderness to the joint line without finding the joint line first.

The second is treating the pes finding as an exclusion of medial compartment disease, when the two coexist.

The third is omitting the resisted flexion test, which is the localising step.

The fourth is missing a hamstring problem proximal to the insertion. 4.16.6 covers it.

The fifth is injecting or treating locally without excluding the joint causes.

Key Learning Points

The value of this diagnosis is preventing an operation on the joint.
Pes tenderness with medial compartment change means two sources and a partial result.
Donor site symptoms after a hamstring harvest sit at this insertion.
Several tender insertions with systemic features is an enthesopathy.
Finding the joint line first is what makes the localisation mean anything.

Fellowship Level

Where It Misleads

In referred practice the pes is the finding that explains medial knee pain in a patient whose joint has been investigated and found acceptable.

A patient with a normal arthroscopy and persisting medial pain, tender below the joint line, had an extra-articular problem available at the first examination. 4.6.4 covers the joint line.

A patient with a hamstring graft harvest and medial pain at the insertion has donor site symptoms, which are common and under recognised. 4.20.1 covers that assessment.

A patient with medial compartment arthritis and a prominent pes component has a complaint that an osteotomy or an arthroplasty will only partly address, and saying so before the operation protects the expectation. 4.18.3 covers that knee.

A patient with a previous medial reconstruction and tenderness at the pes may have a problem at a fixation point rather than at the insertion, and the operation note separates them. 4.12.8 covers that assessment.

In medicolegal work this is an overload or degenerative condition and is difficult to attribute to a single event. 4.23.7 covers that setting.

Key Learning Points

The pes explains medial pain in a patient whose joint has been found acceptable.
Donor site symptoms after a hamstring harvest sit here and are under recognised.
With medial compartment arthritis, an operation on the joint only partly addresses the complaint.
After a medial reconstruction the tenderness may be at a fixation point.
As an overload condition it is hard to attribute to a single event.

Explore Further

Where this topic came from and where it goes next in the spiral.

References

No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. This page carries no diagnostic accuracy figure, which is decision 023 rather than an omission. The comparative standing of these tests is standard teaching and a specific sensitivity written from memory is the same class of claim as an invented citation, so ACC-001 refuses the number and the page states the comparison. A reviewer with the literature can add the figures into How Good It Is without restructuring the page, and chapter 3.17 lists the studies the figures would come from. Any measurement here, including a flexion angle, is written from standard teaching, has not been checked, and is registered under decision 006 in pipeline/config/figures with a verification state of UNVERIFIED_FROM_MEMORY.

Safety. KneeSchool is educational and does not give individual medical advice. Seek urgent assessment for a knee that cannot bear weight after an injury, a hot swollen knee with a fever, or new numbness, weakness or coldness in the leg or foot.