Established OA

For Medical Students

What It Tests

Established osteoarthritis presents as pain at rest and at night, a deformity that is visible standing, a reduced range, and a walking distance the patient can quote. 4.2.11 covers aggravating factors.

The examination at this stage is no longer deciding the diagnosis. It is recording the deformity, the range, the stability and the function, because those are what the treatment decision uses. 4.18.7 covers that assessment.

It is a systematic examination rather than a set of special tests, and the findings are usually obvious.

How It Is Performed

Take the history: the rest pain, the night pain, the walking distance, the stairs, and what the patient has stopped doing. 4.18.6 covers functional limitation.

Watch the gait for a thrust, a shortened stance and the use of a stick, since all three grade the disease better than any single sign. 4.4.2 covers the antalgic gait.

Assess the alignment standing from the front and from the side, recording varus, valgus and any fixed flexion. 4.3.3 covers standing alignment.

Measure the range, recording the fixed flexion deficit first and the flexion second, since the deficit is the one that limits function. 4.5.4 covers the flexion deformity.

Palpate for joint line tenderness, osteophyte and an effusion, which together confirm the compartment and the activity. 4.6.4 covers joint line tenderness.

Assess the collateral ligaments, because the worn compartment shortens its own side and the opposite ligament may have stretched. 4.12.1 covers valgus stress testing.

Assess the patellofemoral joint, since it is involved in a large proportion of worn knees and is often not examined. 4.18.5 covers that examination.

What a Positive Means

A fixed deformity with a reduced range, joint line tenderness on the concave side and a thrust on walking is the established picture.

A deformity that corrects passively means the bone loss is limited and the soft tissues are not contracted, and that changes the options. 4.3.10 covers the deformity.

A fixed flexion deficit indicates posterior capsular contracture and osteophyte, and it is the finding patients notice most. 4.5.4 covers it.

Opposite side laxity in a worn compartment means the deformity has become structural rather than positional. 4.12.5 covers the posterior oblique ligament.

Night pain and rest pain mark a stage where activity modification has stopped working.

MRCS Level

How It Is Performed

In a viva this is the arthritic knee station and the expected answer is a systematic record rather than a diagnostic hunt.

The expected points are the gait, the standing alignment in both planes, the range with the fixed flexion stated separately, the joint lines, the collaterals, the patellofemoral joint, and the hip.

Say that you would examine the hip before concluding, because the hip and the knee refer to each other and the hip is the cheaper miss. 4.2.15 covers referred pain.

Say that you would record the walking distance and the stairs, since the functional record is what the decision is made against. 4.18.6 covers it.

Say that you would assess the neurovascular status, which is part of the preoperative record rather than the diagnosis. 4.3.9 covers it.

What a Positive Means

The reasoning expected is that the worn compartment loses height, so the limb angulates towards it and the opposite ligament lengthens. 3.5.2 covers contact pressures.

Once the opposite ligament has lengthened, correcting the alignment alone leaves the knee unbalanced, which is why the laxity is recorded. 4.12.5 covers the posterior oblique ligament.

Posterior capsular contracture and posterior osteophyte both block extension, so a fixed flexion deficit has a soft tissue and a bony component. 4.5.4 covers it.

Rest and night pain reflect subchondral and synovial involvement rather than load, which is why they do not respond to activity change.

How Good It Is

The examination at this stage is reliable, because the findings are large and reproducible.

Its contribution is the record of deformity, range and stability that the treatment plan is built from, and no imaging substitutes for it. 4.18.7 covers the assessment.

It is poor at predicting how much of the deformity will correct at operation, which is a different question. 4.3.10 covers the deformity.

Weightbearing and long leg radiographs quantify the deformity, so the examination establishes the clinical state and the films establish the geometry. 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 examination sorts the worn knee into the groups that different treatments serve, and the sorting is done by deformity, correctability, range and compartment involvement.

A single worn compartment with a correctable deformity, intact ligaments and a good range is one group, and the examination is what identifies it. 4.20.7 covers the partial replacement assessment.

A fixed deformity with opposite side laxity, lost range or multiple compartments is another, and again the examination defines it. 4.20.8 covers the total replacement assessment.

Patellofemoral involvement alongside compartment disease moves the knee between those groups, so it is examined deliberately. 4.18.5 covers it.

A worn knee with a flexion range below what the patient needs for their daily activity is a functional finding, not a structural one, and it is recorded separately. 4.18.6 covers functional limitation.

Where It Misleads

The commonest error is recording the alignment supine, where the deformity looks smaller than it is under load. 4.3.3 covers standing alignment.

A deformity that corrects under an examining hand can be read as correctable when the contracture is simply being stretched, and the distinction is one of degree. 4.3.10 covers the deformity.

Lateral joint line tenderness in a varus knee is often attributed to the medial disease and can represent real lateral compartment involvement. 4.6.4 covers the technique.

Hip disease reproduces the groin and thigh component of the pain closely, and the knee examination will be abnormal anyway in a worn knee. 4.2.15 covers referred pain.

Collateral laxity measured in a knee with a fixed flexion deficit is unreliable, because the position changes what the ligament resists. 4.12.3 covers the assessment in flexion.

Fellowship Level

Where It Misleads

At fellowship level the examination is a preoperative record, and its errors become operative surprises.

The deformity recorded clinically and the deformity measured on a long leg film can differ, and the film governs the geometry while the examination governs the soft tissues. 4.5.1 covers the mechanical axis.

A varus knee with a correctable deformity and medial laxity is an unusual combination that deserves rechecking, since it changes the balance the operation has to achieve. 4.12.5 covers the posterior oblique ligament.

A fixed flexion deficit of the same size can come mostly from posterior osteophyte or mostly from capsule, and the clinical end feel is the only clue before operation. 4.7.5 covers the end feel.

Rotational deformity and torsional malalignment sit outside the varus and valgus description and are not captured by it. 4.19.7 covers torsional assessment.

The examination cannot tell how much of the pain is coming from the patellofemoral joint when both joints are worn, and that uncertainty persists into the decision. 4.18.5 covers it.