Approach to knee pain: Clinical sciences

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Introduction0:00–0:02

Introduction0:02–0:44

Knee pain is a common musculoskeletal symptom that can be caused by damage to any of the ligamentous, muscular, or bony structures comprising the joint.
Most often, knee pain is associated with trauma and conditions such as fractures and ligament or meniscus injuries. On the other hand, non-traumatic causes can be classified based on the presence of joint effusion.
No joint effusion is common in conditions, such as patellofemoral pain syndrome, prepatellar bursitis, and osteoarthritis; while joint effusion is typically seen in septic arthritis, crystal-induced arthropathy, and non-infectious inflammatory arthritis.If a patient presents with knee pain, the first step is to perform a focused history and physical examination.

History and physical exam0:44–0:57

Start by assessing the patient’s history of trauma preceding the onset of knee pain.If the patient reports trauma to the knee, consider traumatic causes of knee pain and assess their risk for fracture using the Ottawa knee rules.

Traumatic knee pain - Fracture0:57–1:45

Ottawa knee rules include the age of 55 or older, point tenderness at the fibular head, isolated point tenderness of the patella, inability to flex the knee to 90 degrees, or inability to bear weight on the affected knee.
If the patient does not have any of these characteristics, your patient has a low risk for fracture, so no further evaluation is needed.
On the flip side, if the patient meets any of the criteria, then they have a high risk of fracture, so you should order x-rays.
If an x-ray is performed, it may reveal a fracture, for example a fracture of the tibia, patella, or other surrounding bones.

ACL1:45–2:51

Let’s take a look when x-ray findings are normal. If the x-ray findings show no fracture, consider ligamentous or meniscal injury.
The mechanism of injury and physical exam can help distinguish between injuries of the anterior cruciate, posterior cruciate, and collateral ligaments.
First, let’s start with the anterior cruciate ligament injury or ACL injury for short. Let’s say the patient's knee pain developed after suddenly pivoting the knee with the foot firmly planted on the ground.
Also, the patient may report an audible pop during the injury, followed by knee instability and a rapidly developing effusion.
Additionally, the physical exam reveals a positive anterior drawer test. You can perform the anterior drawer test by having the patient lie supine with the affected knee flexed and the foot flat on the table.
Sit directly in front of the leg and try to draw the tibia forward. If the tibia can be pulled too far forward, the anterior drawer test is positive, which confirms the diagnosis of ACL injury.Ok, now let’s take a look at the posterior cruciate ligament injury or PCL injury for short.

PCL2:51–3:34

In this case, history typically reveals knee pain after a high-impact trauma to the anterior tibia, like during a motor vehicle accident, or after a hyperflexion injury; while the physical exam reveals a positive posterior drawer test.
You perform the posterior drawer test by having the patient lie supine with the knee flexed and the foot flat on the table.
Sit directly in front of the leg, and try to draw the tibia backward. If the tibia can be pushed too far back, you have a positive posterior drawer test, which confirms the PCL injury.Alright, moving on to collateral ligament injuries.

Collateral ligament injury3:34–4:17

Your patient will typically report a knee injury from a valgus or varus force as well as medial or lateral joint pain. Physical exam reveals point tenderness along the joint line and laxity or gapping with valgus or varus stress testing.
Perform valgus and varus stress testing by asking the patient to lie with the leg extended. Place one hand on the femur and one hand on the tibia, and apply oppositional pressure, moving the tibia medially and the femur laterally, and vice versa.
If there is excessive movement or laxity, that’s a positive test, which indicates lateral or medial collateral ligament injury.
Finally, don’t forget the meniscal tear as a cause of knee pain! History usually reveals knee pain that develops after a twisting injury, and the patient often experiences episodes in which the affected knee locks or gives way.

Meniscal injury4:17–5:10

Additionally, important physical exam findings include joint line tenderness and a positive McMurray test. Perform the McMurray test by having the patient lie supine with the affected knee flexed.
Place one hand across the knee joint line, hold the patient's foot with the other. Then, extend the patient’s knee while internally rotating the tibia and applying varus stress.
This motion tests the lateral meniscus. Next, extend the patient’s knee while externally rotating the tibia and applying valgus stress.
If the maneuver reproduces the patient's pain, or there’s locking or clicking in the joint, it’s a positive test, and indicates a meniscal injury.Now let’s go all the way back and take a look at individuals with no history of trauma preceding the knee pain.

Assess for effusion5:10–5:50

In these patients, you should consider non-traumatic causes and assess whether or not knee effusion is present. You can do this using the bulge or stroke test.
Perform the test by asking the patient to lie supine with the knee extended. Next, “milk” the knee by sweeping fluid from the medial aspect of the knee, over the top of the patella, and into the lateral compartment.
Then, apply pressure laterally. If the skin on the medial side of the knee bulges as fluid moves back into the medial compartment, then the test is positive for effusion.
But, if the test is negative and there is no effusion, assess the location of the patient’s knee pain. If the pain is in the anterior knee, you should consider patellofemoral pain syndrome and prepatellar bursitis.First, let’s focus on patellofemoral pain syndrome.

Patellofemoral pain syndrome & prepatellar bursitis5:50–6:50

Patellofermoral pain syndrome is typically associated with pain that worsens with flexion during weight-bearing activities like climbing stairs, or after getting up from prolonged sitting.
The individual may have a history of overuse, such as long-distance running, or they may report a recent increase in physical activity.
Physical exam reveals pain reproducible with squatting. These findings are consistent with patellofemoral pain syndrome.
On the other hand, let’s say the patient has anterior knee pain and a history of frequent kneeling; while the physical exam reveals a tender swelling anterior to the patella.
In this case, the patient likely has prepatellar bursitis.Now let’s take a look at a patient that presents with medial knee pain.

Pes anserine bursitis6:50–7:18

In this case, history most commonly reveals pain that worsens with climbing stairs or rising from a seated position. Additionally, they may have risk factors like being a biological female and obesity.
On exam, there might be tenderness over the upper medial tibia. These findings are consistent with pes anserine bursitis.

Iliotibial band syndrome7:18–7:44

Ok, let’s say a person presents with lateral knee pain. This person will usually have a history of overuse and report that the pain is worse during knee extension, like when they push down on the pedal of a bicycle or when their foot strikes the ground while running.
Physical exam may reveal tenderness over the lateral femoral epicondyle. These findings are highly suggestive of iliotibial band syndrome.

Bakers cyst7:44–8:04

Next up is posterior knee pain! If an individual has posterior knee pain that worsens with prolonged standing or hyperflexion of the knee, and physical exam shows tenderness and swelling of the popliteal fossa, then the patient likely has a Baker cyst.

Osteoarthritis8:04–8:41

Finally, knee pain can be diffuse! In this case, history usually includes joint stiffness, and pain that worsens with physical activity.
They may have risk factors such as older age or a prior joint injury. Physical exam may reveal crepitus, as well as bony deformity of the joint.
In this case, consider osteoarthritis and order a weight-bearing x-ray of the knee. If the x-ray shows joint space narrowing, osteophytes, and subchondral sclerosis, then you can diagnose osteoarthritis.Alright, now that we are done with causes associated with no joint effusion, let’s go back and take a look at individuals that present with joint effusion.

Effusion present8:41–9:02

In this case, perform an arthrocentesis and send synovial fluid for analysis, including cell count and differential, crystals, and gram stain and culture.First, let’s focus on septic arthritis!

Septic arthritis9:02–9:50

These patients typically present with a history of abrupt onset of knee pain, warmth, swelling, and restricted movement; as well as systemic symptoms like fever, which is present in most patients, but keep in mind that older patients might be afebrile.
History may also reveal risk factors like immunosuppression or pre-existing joint disease. On the other hand, physical exam might reveal an ill-appearing patient with erythema and warmth of the skin overlying the affected knee, and limited range of motion in the affected joint.
If the synovial fluid is cloudy and purulent with a white blood cell count over 50,000, and positive gram stain and cultures, you can diagnose septic arthritis.
Next up is crystal-induced arthropathy. Ok, let’s say a patient has episodes of joint pain, swelling, and warmth.

Crystal-induced arthropathy9:50–10:35

They may have a history of medications such as diuretics, alcohol use, or a high-purine diet. The exam shows tenderness to joint palpation and limited range of motion; while the synovial fluid is positive for either monosodium urate crystals or calcium pyrophosphate or CCPD crystals.
White blood cell count is between 2,000 and 50,000, and gram stain and cultures are negative. These findings are consistent with crystal-induced arthropathy, like gout or calcium pyrophosphate deposition disease.

Non-infectious Inflammatory arthritis10:35–11:41

Now, switching gears and moving on to non-infectious inflammatory arthritis. Consider this condition in a patient with pain and swelling in multiple joints, and prolonged morning stiffness.
Physical examination usually reveals oligo- or polyarthritis, and synovial thickening. Synovial fluid analysis reveals negative crystals, white blood cell count between 2,000 and 50,000 and negative gram stain and cultures.
This is consistent with non-infectious inflammatory arthritis, such as psoriatic arthritis or systemic lupus erythematosus.
Here’s one clinical pearl to keep in mind! On rare occasions, non-inflammatory arthritis can cause mild effusion as well, but in this case, the synovial fluid shows a white blood count of less than 2,000 and a negative gram stain and cultures.
This is common in conditions such as osteoarthritis or chronic meniscal injury. Although these conditions are primarily non-inflammatory, patients can experience flares of worsening pain and mild joint effusion.
Alright, as a quick recap… When a patient presents with knee pain, first assess for a history of trauma. Some important causes of knee pain associated with trauma include fractures, as well as ligament and meniscal injuries.

Review11:41–12:20

If you rule out trauma, you should assess the patient’s knee for effusion. If no effusion is present, think of conditions, such as patellofemoral syndrome, prepatellar bursitis, and osteoarthritis.
On the flip side, if there’s effusion, you should consider septic arthritis, crystal-induced arthropathy, non-infectious inflammatory arthritis and non-inflammatory arthritis.