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During any examination in an OSCE it is important to understand the pathology and reasoning behind each of the signs and symptoms elicited. This applies even if the patient being examined is ‘normal’. This article explains how to perform a knee examination and the key findings you should look for, showing you what each sign means and what conditions it may indicate.
The knee examination follows the standard musculoskeletal structure of look, feel and move, finishing with a set of special tests. These stress individual structures: the cruciate ligaments (the crossed pair inside the joint), the collateral ligaments (on either side of the joint) and the menisci (the two cartilage pads between the femur and tibia). Throughout, always compare the affected knee with the contralateral side. The other knee shows what is normal for this patient, unless both knees are affected.
Contents
- Introduction
- General Inspection
- Gait Assessment
- Look (Standing)
- Look (Lying)
- Knee Anatomy
- Feel (Temperature and Palpation)
- Feel (Effusion Tests)
- Move (Range of Movement)
- Patellofemoral Assessment
- Special Tests – Cruciate Ligaments
- Special Tests – Collateral Ligaments
- Special Tests – Menisci
- Completing the Examination
- Quiz
Introduction
Wash your hands and put on personal protective equipment (PPE, such as gloves or an apron) if appropriate.
Introduce yourself to the patient and say your grade, for example third-year medical student, junior doctor or consultant, whichever applies to you.
Confirm the patient’s details, usually using three points of identification: full name, date of birth and NHS or hospital number.
Briefly explain the examination and gain consent, for example: “I’d like to examine your knees today. This will involve looking at and feeling both knees, moving them, and doing some specific tests. Is that alright?”
Ask the patient if they have any pain anywhere before you begin, and reassure them you will stop if they become uncomfortable. This is both courteous and clinically important, as pain often localises the underlying pathology.
Adequately expose both lower limbs from the groin down so that the knees, thighs and lower legs can be compared directly. The patient should ideally be in shorts. Begin with the patient standing so you can assess alignment and gait (the way the patient walks).
General Inspection
Take a moment to look at the patient as a whole and at the area around the bed. Look for mobility aids such as walking sticks, crutches, a frame or a wheelchair, which suggest reduced weight-bearing ability or instability. Note any knee braces, splints or supports, and look for prescriptions or analgesia (painkillers) that hint at chronic pain.
Assess whether the patient appears comfortable or in distress, and whether they look systemically well. Note the patient’s body habitus (build): a raised body weight loads the knee heavily and is an important risk factor for both osteoarthritis (wear-and-tear arthritis of a joint) and slower recovery from injury. Generalised features such as a rheumatoid hand deformity (from rheumatoid arthritis, an autoimmune joint disease) or a psoriatic rash (the scaly rash of psoriasis) may point towards an inflammatory arthropathy (inflammatory joint disease) affecting the knee.
Gait Assessment
Ask the patient to walk a short distance, turn, and walk back, while you observe the whole gait cycle. The normal cycle moves through heel strike (the heel meets the ground), foot flat, mid-stance (body weight passes over the planted foot), heel off and toe off (the foot leaves the ground); pain or weakness disrupts these phases.
An antalgic gait is the classic finding of a painful knee, for example in osteoarthritis or following injury. The patient spends as little time as possible bearing weight on the painful leg (a shortened stance phase). Look also for an unstable or ‘giving way’ gait, which suggests ligament injury or quadriceps weakness. Look too for a stiff knee that the patient swings out to the side (circumduction) because they cannot flex it.
Note any leg-length discrepancy, which may be either the cause or the consequence of knee pathology. Watch how confidently the patient turns, as turning slowly often reflects pain or instability.
Glance at the patient’s footwear as well. Uneven sole wear can betray an abnormal gait pattern or chronic deformity. Orthotic insoles (shoe inserts) suggest an attempt to correct alignment or to take weight off a painful compartment (one part of the knee joint).
Look (Standing)
With the patient still standing, inspect both knees from the front, the side and behind, always comparing one side with the other.
From the front, assess the coronal alignment of the legs. Genu varum (‘bow legs’) describes knees that bow outwards and is commonly seen in medial compartment osteoarthritis (wear of the inner half of the knee joint), where loss of medial cartilage collapses the joint into varus. Genu valgum (‘knock knees’) describes knees that angle inwards and is more typical of lateral compartment disease (the outer half of the joint) or rheumatoid arthritis.
From the side, look for genu recurvatum (hyperextension of the knee), which may reflect ligament laxity (looseness). From behind, inspect the popliteal fossa (the hollow at the back of the knee) for any swelling, in particular a Baker’s cyst. This is a fluid-filled distension of a bursa (a small fluid-filled sac that cushions tissues) behind the knee. It communicates with the joint and is associated with effusions (extra fluid in the joint) and osteoarthritis.
Throughout, look for scars (suggesting previous surgery such as arthroscopy (keyhole surgery of a joint) or joint replacement), swelling, muscle wasting and redness.
Look (Lying)
Ask the patient to lie on the couch with their legs straight and re-inspect the knees up close.
Look for an effusion, seen as a loss of the normal dimples either side of the patella and a generally ‘full’ appearance to the joint. An effusion is extra fluid within the joint. It may be synovial fluid, the lubricating fluid inside a joint (in osteoarthritis or inflammatory arthritis); blood, called a haemarthrosis, which follows an acute rupture of the anterior cruciate ligament (ACL) or a fracture inside the joint; or pus (septic arthritis, an infection inside the joint).
Assess the quadriceps, particularly the vastus medialis (the inner part of the quadriceps), for wasting. Because the quadriceps rapidly atrophies with disuse, wasting is a useful sign of chronic knee pathology or pain that has limited activity.
Look again for scars, erythema (redness, which may indicate infection or active inflammation) and any obvious deformity.
Knee Anatomy
A quick recap of the relevant anatomy makes the special tests much easier to understand. The knee is stabilised by four key ligaments. The anterior cruciate ligament (ACL) prevents anterior translation (forward sliding) of the tibia on the femur. The posterior cruciate ligament (PCL) prevents posterior translation (backward sliding). The medial collateral ligament (MCL) resists valgus (inward-angulating) force, and the lateral (fibular) collateral ligament (LCL) resists varus (outward-angulating) force. The two menisci are C-shaped discs of fibrocartilage (tough, rubbery cartilage) that cushion and distribute load across the joint.
Image - Anatomy of the right knee showing the cruciate ligaments, collateral ligaments and menisci. Understanding these structures explains the logic behind each special test.
Source: Mysid, via Wikimedia Commons (public domain)
Image - The knee joint viewed from behind, demonstrating the cruciate and collateral ligaments that the special tests are designed to isolate.
Source: Henry Vandyke Carter, via Wikimedia Commons (public domain)
Feel (Temperature and Palpation)
Before palpating, ask again about pain and watch the patient’s face throughout.
Using the back of your hand, assess and compare the temperature over both knees and the thigh above. An increased temperature over the joint suggests an active inflammatory or infective process such as septic arthritis, gout (joint inflammation caused by urate crystals) or a flare of inflammatory arthritis. The back of the hand is used because it is more temperature-sensitive than the palm.
Measure and compare quadriceps bulk by measuring the thigh circumference a fixed distance (e.g. 15 cm) above the tibial tuberosity (the bony bump below the kneecap) on each side; a difference between the thighs suggests quadriceps wasting. The tape also measures the fat under the skin, so the figure may not reflect the muscle alone.
With the knee extended, palpate systematically for tenderness over the borders of the patella, the quadriceps and patellar tendons, the tibial tuberosity and the joint lines. Joint-line tenderness is an important sign of meniscal injury or osteoarthritis. Tenderness at the tibial tuberosity in an adolescent suggests Osgood–Schlatter disease (growth-related pain and swelling over the bony bump below the kneecap, most often at ages 10 to 15).
Then flex the knee to 90° and palpate the joint lines again, along with the collateral ligaments, the head of the fibula and the popliteal fossa. A soft swelling in the popliteal fossa supports a Baker’s cyst.
Feel (Effusion Tests)
Two bedside manoeuvres help detect a knee effusion and give an idea of its size:
- The patellar tap (ballottement) test is used for a large effusion. Ballottement means bouncing the patella against the femur. Empty the suprapatellar pouch (the fluid pocket just above the kneecap) by sliding one hand down the thigh, then push the patella sharply backwards with a finger of the other hand. If fluid is present, the patella sinks, strikes the femur and bounces back with a palpable ‘tap’.
- The sweep (bulge) test is more sensitive for a small effusion. Empty the medial side of the joint by stroking upwards, then stroke down the lateral side; a positive test produces a visible bulge of fluid reappearing on the emptied medial side.
A confirmed effusion narrows the differential to the causes of joint fluid: degenerative, inflammatory, infective or traumatic. If infection is possible, for example a hot, tender, swollen knee with restricted movement, the patient needs urgent hospital assessment and joint aspiration (drawing fluid out of the joint with a needle) to exclude septic arthritis.
Move (Range of Movement)
Assess active movement first by asking the patient to move the knee themselves. Then assess passive movement by moving it for them, feeling for crepitus with a hand over the joint.
Normal flexion (bending) is up to about 135° and the knee should fully extend (straighten) to 0°. Reduced range, especially a fixed flexion deformity where the knee cannot fully straighten, is common in osteoarthritis. A difference between active and passive range suggests a muscular or tendon problem (e.g. a rupture of the extensor mechanism, the quadriceps, patella and patellar tendon that together straighten the knee) rather than a true joint restriction.
Crepitus is a grinding sensation through movement. It reflects roughened, worn articular (joint) surfaces and is typical of osteoarthritis. Always note whether movement reproduces the patient’s pain.
Patellofemoral Assessment
The patella deserves attention in its own right, as anterior knee pain and instability often arise from the patellofemoral joint (between the patella and the femur) rather than the tibiofemoral compartments (the joint between the femur and the tibia).
Assess patellar tracking by watching the patella as the patient slowly straightens and bends the knee through a small range. The patella should glide smoothly in the trochlear groove (the groove at the lower end of the femur). A sudden lateral deviation near full extension (a positive ‘J-sign’) suggests maltracking (the patella not following its normal path) and a tendency to subluxation (partial dislocation).
Check patellar mobility by gently pushing the patella medially and laterally with the knee relaxed in slight flexion. Reduced glide implies a tight or arthritic joint, whereas excessive lateral glide points to laxity (looseness) and risk of dislocation.
The patellar apprehension test screens for a history of recurrent lateral dislocation. With the knee almost straight, slowly push the patella laterally. The test is positive if the patient becomes visibly anxious, tenses the quadriceps or tries to stop you. They are anticipating the patella slipping out of joint as it has done before.
If anterior knee pain is the main complaint, you may also perform Clarke’s test (the patellar grind test). Press the patella distally into the trochlea and ask the patient to tense the quadriceps. Pain or grinding as the patella is pulled across the femur suggests patellofemoral pain or chondromalacia patellae (softening and wear of the cartilage under the kneecap). The test is uncomfortable even in normal knees, so interpret it cautiously.
Special Tests – Cruciate Ligaments
The cruciate ligament tests detect abnormal front-to-back movement of the tibia on the femur. Always compare with the other knee, as some baseline laxity is normal.
Begin by inspecting for a posterior sag sign. With both knees flexed to 90° and feet flat, look from the side; if the PCL is torn, the tibia sags backwards under gravity, so the upper shin looks displaced backwards compared with the other knee. Identifying a sag first is important because it can give a false-positive anterior drawer (you are simply pulling a sagged tibia back to neutral).
The anterior drawer test assesses the ACL. Flex the knee to 90°, sit gently on the foot to fix it, and pull the tibia forwards. Excessive anterior translation indicates an ACL tear. A tear classically follows a sudden twisting or pivoting injury, and the joint then fills with blood (haemarthrosis).
The posterior drawer test uses the same position, but the tibia is pushed backwards. Excessive posterior movement indicates a PCL injury, often caused by a ‘dashboard’ force driving the tibia backwards.
The Lachman test is the most accurate bedside test for the ACL, although it can miss partial tears. With the knee flexed to about 20–30°, stabilise the femur with one hand and pull the tibia forwards with the other. Increased anterior glide with a soft or absent end-point (the tibia slides forward without a firm stop) indicates an ACL rupture. At this smaller flexion angle the hamstrings (the muscles at the back of the thigh) cannot hold the tibia back protectively, which makes the test more reliable than the anterior drawer.
Special Tests – Collateral Ligaments
The collateral ligament tests detect abnormal side-to-side opening of the joint.
For the valgus stress test, hold the ankle and place your other hand on the lateral side of the knee. Push the knee inwards (applying a valgus force) while the leg is held in slight flexion. Excessive opening of the medial joint line, or pain there, indicates a medial collateral ligament (MCL) injury, as the MCL is the structure that normally resists this force.
For the varus stress test, reverse the hands: place one hand on the medial side and push the knee outwards (a varus force). Excessive opening of the lateral joint line indicates a lateral (fibular) collateral ligament (LCL) injury.
Testing in slight flexion (around 30°) isolates the collateral ligaments. Testing in full extension also involves the cruciate ligaments and the joint capsule (the fibrous sleeve around the joint), so marked laxity (looseness) in extension implies a more severe, multi-ligament injury.
Special Tests – Menisci
The menisci can tear with a twisting injury on a loaded, flexed knee, typically producing joint-line tenderness, locking (the knee gets stuck and will not fully straighten) or a sensation of the knee giving way.
McMurray’s test is used to assess for a meniscal tear. With the patient supine, fully flex the knee, then rotate the tibia and slowly extend the knee while feeling along the joint line. External rotation with extension stresses the medial meniscus, and internal rotation stresses the lateral meniscus. A palpable click or reproduction of the patient’s pain suggests a tear, as the displaced meniscal fragment is being trapped and released between the joint surfaces.
Two alternatives may also be mentioned. Apley’s grind test is done with the patient prone and the knee flexed to 90°. Pressing the tibia downwards while rotating it loads and grinds the menisci, so reproduced pain points to a meniscal tear. Pain on distraction (pulling the tibia up while rotating) points instead to a ligament problem. The Thessaly test asks the standing patient to rotate the body over a knee flexed to 20° while you support their hands. Joint-line pain or locking is a positive result. How accurate this weight-bearing test is compared with the others is debated.
Because these tests are uncomfortable and none is accurate enough to rely on alone, findings should always be interpreted alongside the history and joint-line tenderness, and confirmed where necessary on MRI.
Completing the Examination
Thank the patient and allow them to redress, then wash your hands.
Summarise your findings and offer a sensible differential diagnosis.
To complete the examination, state that you would assess the joints above and below, namely the hip and the ankle and foot. Pathology in these joints can refer pain to the knee. You would also perform a neurovascular examination (of the nerves and blood supply) of both lower limbs, checking pulses, sensation and power.
Finally, suggest relevant investigations guided by your findings, such as plain radiographs (X-rays) of the knee. Request these after an injury if a fracture is suspected (the Ottawa knee rules help decide this), and in suspected osteoarthritis only if the picture is atypical, because osteoarthritis is usually diagnosed clinically. Other examples are an MRI scan (for suspected ligament or meniscal injury) and joint aspiration with fluid microscopy and culture (looking at the fluid under a microscope and growing any bacteria) if septic arthritis or crystal arthropathy (crystal joint disease such as gout) is suspected.
Quiz
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