Referred Pain

For Medical Students

What It Tests

Asking about referred pain tests whether the knee is the source of the symptom or only the site of it.

The knee is a frequent destination for referred pain, and a patient with knee pain and a normal knee examination has a cause somewhere else.

The two sources that matter most are the hip and the lumbar spine, and both are missable if the knee is examined in isolation. 4.1.5 covers the pitfall.

How It Is Performed

Ask whether the pain is only in the knee or whether it extends into the thigh, the groin or the calf.

Ask about the hip directly: groin pain, pain on putting shoes and socks on, and difficulty getting in and out of a car.

Ask about the back: back pain, pain radiating below the knee, pins and needles, numbness and weakness.

Ask whether anything in the back or hip provokes the knee pain.

Then examine the hip and perform a neurological assessment, because the history selects who needs it and the examination settles it.

What a Positive Means

Anterior thigh and knee pain with groin pain and restricted hip rotation is hip disease referring to the knee, and this is the classic missed diagnosis.

Pain radiating from the back below the knee, with altered sensation, is a radicular cause.

Knee pain in a child or adolescent with a limp and a normal knee is a hip problem until the hip is imaged, and this is the highest-stakes version. 4.19.1 covers paediatric assessment.

Pain in the calf with swelling is a vascular question rather than a knee one.

Posterior knee pain with no joint findings may be a cyst, a hamstring origin or a vascular cause. 4.6.10 covers the popliteal fossa.

MRCS Level

What a Positive Means

The reasoning expected is anatomical: the knee shares innervation with the hip through the obturator and femoral nerves, which is why hip disease refers there.

Pain from the hip typically reaches the anterior thigh and knee and does not reach below the knee.

Radicular pain follows a dermatome and frequently continues below the knee, with sensory or motor signs.

A knee examination that is entirely normal in a patient with convincing knee pain is a positive finding, and the next step is the hip and the spine rather than a knee scan.

Referred pain can coexist with knee pathology, and a degenerate knee with a degenerate hip is common in older patients, where deciding which is symptomatic is the clinical problem.

How Good It Is

The history performs well for identifying who needs the hip and spine examined and poorly for deciding which of two abnormal joints is responsible.

The distribution of pain is the most useful feature: above the knee only suggests hip, below the knee suggests spine.

Provocation is the second: pain reproduced by hip rotation rather than by knee movement settles a great deal, and that is an examination finding the history should prompt.

Where both joints are abnormal the history alone will not decide, and a diagnostic injection is often what resolves it.

FRCS Level

How Good It Is

At decision level the cost of missing referred pain is an operation on the wrong joint, and that is a recognised and avoidable event.

The patient most at risk is the older patient with radiographic change in both the hip and the knee, where either could plausibly be blamed and the knee is the one being complained about.

The history feature that most often resolves it is what the patient cannot do: difficulty with shoes, socks and car entry points to the hip, while stairs and walking distance point to either.

A knee arthroplasty in a patient whose pain was coming from the hip is the clearest example in this chapter of a technically successful operation that helped nobody.

Where It Misleads

The commonest error is a knee-only consultation, which is a structural failure of the assessment rather than an oversight.

The second is accepting that a previous hip examination was normal, when the hip was not the reason the patient attended and the examination may have been cursory. 4.1.5 covers the inherited normal.

The third is in the post-arthroplasty patient with persistent pain, where referral from the spine or hip is a recognised cause of a painful but well-functioning replacement. 4.20.8 covers the assessment.

And a patient with knee pain and a known spinal problem may have both, so attributing everything to the spine is the same error in reverse.

Fellowship Level

Where It Misleads

In referred practice the patient with an unexplained painful knee after surgery needs referred causes revisited, because they were frequently excluded before the operation and not since.

A spinal cause can develop after a knee operation and will be attributed to the operation by everybody including the patient.

Complex regional pain and neuropathic pain after knee surgery are distinct from referred pain and are also distinct from a mechanical cause, and the history is where all three are separated. 4.23.5 covers revision patients.

Infrapatellar branch neuroma after arthroscopy or reconstruction is a specific, recognisable and frequently missed cause of anterior knee pain, and the history is localised numbness or hypersensitivity in a defined area rather than joint pain.

The honest limit is that the history can raise all of these and cannot confirm any, and no figure here supports which features discriminate, under decision 023.