Overview of Knee Assessment

Original Editor - Rachael Lowe based on the course by Shala Cunningham

Top Contributors - Jess Bell, Admin, Naomi O'Reilly, Rachael Lowe, Laura Ritchie, Kim Jackson, Wanda van Niekerk, Ben Kasehagen, 127.0.0.1, Tarina van der Stockt, Evan Thomas, Michelle Lee, Kai A. Sigel, Vidya Acharya, Rucha Gadgil and Samuel Winter

Introduction

Knee pain is a common issue globally, accounting for around 5% of visits to primary care providers. While many acute and chronic knee conditions respond favourably to rehabilitation, successful outcomes depend on accurate assessment. Rehabilitation professionals must be able to develop systematic evaluation skills to effectively distinguish between conditions suitable for rehabilitation and those requiring onward referral. This article provides an overview of the subjective and objective knee assessment for rehabilitation professionals.

Subjective History

The L-M-N-O-P-Q-R-S-T mnemonic outlines the essential aspects to cover when taking a patient’s history.

L: location of symptoms and level of functional impairment

We want to establish the exact location of a patient’s pain to help formulate a potential diagnosis. Like any part of the body, it is important to establish if pain is referred from the back or another joint.

For knee-specific presentations, anterior knee pain could be caused by a range of conditions, including patellofemoral pain syndrome, patellar tendinopathy and patellofemoral joint instability. Osgood-Schlatter disease is another cause of anterior knee pain in adolescents. Medial knee pain might suggest a medial collateral ligament injury, a medial meniscus tear, or osteoarthritis, among other conditions. Lateral knee pain might indicate conditions such as lateral collateral ligament injury, lateral meniscus tear, iliotibial band syndrome or lateral compartment osteoarthritis. Posterior knee pain could indicate distal hamstring tendinopathy, a meniscus injury of the posterior horn or a Baker’s cyst. Please note that this list of conditions is not exhaustive.

M: medical factors (medications) and mechanism of injury

We need to find out what medications the patient is taking (including supplements and those prescribed by physicians or other healthcare providers) and what comorbidities they may have.

We also want to determine when and how the injury occurred. The following table highlights a few mechanisms of injury to consider and which structure could be affected. Again, this list is not exhaustive.

Table 1. Mechanisms of injury for common knee conditions.

Mechanism	Potential structure affected
Jumping, twisting or changing direction with the foot planted	Anterior cruciate ligament, patellar subluxation, meniscus
Posterior force applied through the tibia	Posterior cruciate ligament
Varus force applied to the knee	Lateral collateral ligament
Valgus force applied to the knee	Medial collateral ligament
Anterior force applied to the knee	Anterior cruciate ligament
Hyperextension (e.g. foot is fixed and body travels over the foot)	Anterior cruciate ligament, posterior capsule
Hyperflexion injury (e.g. a fall onto a flexed knee or forced flexion)	Posterior cruciate ligament injury

It’s also important to find out if the patient could walk away after their injury / continue with their activity. If patients can’t walk away after an injury, a more serious injury is indicated, such as a fracture or an anterior cruciate ligament (ACL) tear. High-energy impacts (e.g. road traffic accidents) are more likely to result in a fracture.

Red flags: sudden onset of severe pain without an incident / accident AND neurological symptoms following a trauma.

N: Neurological symptoms

Neurological symptoms include numbness, tingling, burning, and electric-shock-like sensations. When neurological symptoms are present, we need to determine if they are constant or intermittent and if they follow a dermatomal or peripheral nerve pattern. A key nerve to consider in patients with knee injuries is the peroneal (fibular) nerve.

Red flag: glove-like numbness.

O: Occupation including limitations

Are there any work- or activity-related factors that are relevant?

P: What palliates or provokes symptoms?

Find out from the patient exactly what makes their symptoms better or worse. It is important to determine how long it takes for symptoms to decrease.

Red flag: symptoms that are constant and unrelenting.

Q: Quality of symptoms / pain

For knee pain, consider if the pain is sharp, dull, stabbing, aching or electric-shock-like. Is there any numbness or tingling? It is also essential to ask if the patient is experiencing any giving way, clicking, locking or popping. Popping is common in ACL injuries. Clicking or locking may be seen with meniscus injuries. Giving way can be associated with instability (e.g. an ACL injury) or meniscal tears and patellofemoral pain.

Giving way: it is important to distinguish between pseudo-giving way and true giving way. True giving way, where the knee collapses, usually suggests ligamentous injury. Pseudo-giving way is a sense that the knee may give way rather than actually giving way. Pseudo-giving way is associated with poor dynamic control (e.g. from quadriceps weakness or pain inhibition).

Locking: similarly, we need to distinguish between pseudo-locking and true locking. True locking requires immediate referral to an orthopaedic surgeon. In true locking, a person is unable to actively or passively extend their knee. This indicates that there is an intra-articular loose body or bucket-handle meniscus tear. Pseudo-locking is when a person cannot extend or flex their knee because of stiffness or pain inhibition.

R: Radiation of symptoms

Questions to consider for radiating symptoms are:

• Where do the symptoms radiate to?
• Are radiating symptoms provoked by activities or position?
• How long do symptoms last?

Red flag: radiating symptoms down multiple dermatomes (ruling out peripheral nerve distributions first).

S: Severity of symptoms

It can be helpful to use scales such as the Visual Analogue Scale or the Numeric Pain Rating Scale, but also to consider how symptoms affect function and activities. Is the patient having to stop or adapt activities because of their pain?

Red flag: sudden onset of severe pain without incident or accident.

T: Timing of symptoms

Consider the sequence of symptoms and the progression of symptoms throughout the day.

Red flag: pain that interrupts sleep or is worse at night (this pain isn’t related to sleeping position) OR constant pain.

The following optional video provides an overview of the subjective knee evaluation:

Additional Red Flags

Always remember to check for additional red flags, or constitutional symptoms (symptoms or health issues that affect the entire body rather than a specific part), including:

• progressive symptoms
• weight loss
• night pain
• systemically unwell (fever / chills)
• night sweats

If you would like to learn more, please see: An Introduction to Red Flags in Serious Pathology.

Self-Assessment Questionnaires for Knee Pain

The following self-assessment questionnaires can be useful for people with knee pain:

• Lower Extremity Functional Scale (LEFS)
• Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)

Objective Assessment

The objective examination gives you quantifiable measures to rule out what structures may be involved in a person's knee pain. Objective measures can also determine changes over time or after treatment.

Observation

You can observe a patient’s knee in sitting, standing, supine and during gait. When observing the knee, look for any bony deformity that would suggest trauma, as well as signs of inflammation, bruising, swelling, heat, redness or changes in muscle bulk (hypertrophy or atrophy).

If there is swelling, it is important to find out about the timing of the swelling.

Immediate swelling/haemarthrosis (0-2 hours post-injury) indicates there may be a fracture or ACL rupture. Please note that effusion is not common with patellofemoral pain and infrapatellar swelling can indicate that the fat pad is involved.

Observation in Standing

When the patient is standing, it is important to observe their whole leg, not just the knee.

Looking from the front, determine if the patient is placing equal weight through their lower extremities. Starting at the foot, check to see if their foot is pronated or supinated. At the knee, check if there is any valgus or varus. Look also at the position of the patella and the quadriceps (Q) angle (see below).

From the side, you can check the degree of knee extension in standing—is there any hyperextension or is the patient keeping their knee slightly flexed? From behind, look for posterior swelling and compare muscle bulk across sides.

Q angle: the Q angle describes the vector pull of the quadriceps on the patella. While a number of studies have found that Q angle measurements are unreliable, Merchant et al. suggest that using a standard protocol could “restore the Q angle to a reliable, accurate measurement”. This is relevant as it is a quick and easy test to include in a physical examination. The normative Q angle values vary in the literature, but the following values were given by Merchant et al.:

• 13.5 degrees of valgus for males
• 15.9 degrees for females

If you would like to learn more about the Q angle and how to measure it, please watch the following video:

Gait Analysis

A full gait assessment is discussed in detail here. During a gait assessment, you can look at temporal variables, such as stride and step time, and distance variables, such as stride length, step length and step width. Other variables include cadence and gait speed / velocity.

For specific deviations caused by knee pain, please see: Gait Deviations Associated with Pelvis and Knee Pain Syndromes.

Functional Screen

It’s important to include functional tasks, such as a single-leg stance, squat, single-leg squat or lunge. If your patient cannot tolerate a squat, you can instead assess their sit to stand or a partial squat.

Neurological Screen

If you suspect neurological deficits or referral from the lumbar spine, you should perform a neurological assessment. The full neurological screen is discussed here. The neurological screen should include myotome testing, sensory testing, reflex testing and neurodynamic tests.

Lower limb reflexes to test are the patellar (L3/4) and Achilles (S1/2) tendon reflexes. The lower limb dermatomes are L1-S4/5. Key myotomes are:

• L2: hip flexion
• L3: knee extension
• L4: dorsiflexion
• L5: big toe extension
• S1: plantar flexion

Useful lower limb neurodynamic tests are the straight leg raise and the femoral nerve test. These are particularly relevant if the patient has pain that radiates past their knee. Other neurological tests you might include are the Babinski sign and the clonus sign.

Please watch the following video if you would like to see a quick demonstration of a neurovascular assessment in supine.

Palpation

Key structures to palpate at the knee are the:

• patellofemoral joint
• quadriceps and patellar tendons
• medial and lateral collateral ligaments
• joint line (medial and lateral)
• tibial tuberosity

Palpate for pain, swelling or warmth around the knee joint and surrounding tissues.

Warmth around the knee suggests an inflammatory process. It is important to link objective findings back to the subjective assessment. Does this inflammation link to an injury or an inflammatory state (i.e. osteoarthritis or a systemic inflammatory issue)?

In prone, you can palpate the hamstring tendons and the origins of gastrocnemius. Posterior swelling could indicate a Baker’s cyst.

The Ballottement test can be useful for patients with a knee effusion.

When considered together, self-detected swelling and a positive Ballottement test have diagnostic value. Kastelein et al. found the following likelihood ratios:

• positive likelihood ratio for self-noticed swelling = 1.5
• positive likelihood ratio for the ballottement test = 1.6
• positive likelihood ratio for the two combined = 3.6

The following optional videos show how to palpate the knee:

Range of Motion

As with any joint, it's important to assess a patient’s active and passive range of motion at their knee joint. The main movements at the knee are flexion and extension. You can also assess tibial rotation.

Check for the presence of pain or guarding, quality of movement and end feel. Knee flexion typically has a soft end feel, and extension has a firm end feel. Knee flexion range is around 130 degrees, and knee extension is 0 degrees. However, always consider what is usual for each person and compare sides.

The following optional videos show how to assess active range of motion at the knee:

The following optional video shows how to assess passive range of motion at the knee:

Accessory Joint Mobility

If your patient has limited active and / or passive range of motion, it is useful to assess their accessory joint mobility:

• an anterior glide of the tibia on the femur influences extension
• a posterior glide of the tibia on the femur influences flexion
• external rotation of the tibia on the femur tends to be associated with extension
• internal rotation of the tibia on the femur tends to be associated with flexion

Muscle Length

Muscle length is also an important consideration. Key muscles to assess are the hamstrings, quadriceps, gastrocnemius and soleus. The tensor fascia lata and gluteus maximus are also relevant as they influence the knee through their connection to the iliotibial band. As always, compare sides and consider what is usual for each person.

The following muscle length tests might be included in a knee assessment:

• Active knee extension test: assesses hamstring length
• Sit and reach test: assesses hamstring length
• Modified Thomas test or Thomas test: assesses hip flexor length
• Ely's test: assesses rectus femoris length
• Silfverskiold test: distinguishes between gastrocnemius and soleus muscle tightness
• Ober's test: assesses for tightness of the tensor fascia lata and / or the iliotibial band

To learn more, please see: Assessing Muscle Length and Muscle Length Assessment and Treatment Related to Patellofemoral Pain.

Strength Testing

Assessing muscle strength is essential when evaluating knee conditions. Look out for differences in strength between sides and any pain during testing. If you would like to learn more about the strength assessment, please see: Assessing Muscle Strength.

Key muscles to assess for patients with knee pain include the quadriceps, hamstrings, hip abductors (gluteus medius), hip external rotators (gluteus medius, gluteus maximus) and gastrocnemius / soleus.

Please watch the following optional video if you would like to see how an orthopaedic surgeon assesses the knee:

Common Knee Conditions

The following sections discuss several common knee conditions and identify clinical signs, special tests and diagnostic clusters that can be useful in your assessment.

Please remember that special tests vary in terms of their specificity and sensitivity, but when used together, they are an important part of your assessment. To find out more about these special tests, including their validity, reliability, sensitivity and specificity, please see the linked pages. The tests listed in these sections are not exhaustive.

Knee Osteoarthritis

Knee osteoarthritis is a common cause of knee pain, stiffness, reduced mobility and functional limitations, particularly in adults aged over 45 years. More information on osteoarthritis is available here. If you would like more information on diagnosing knee osteoarthritis and other clinical classification criteria, please see here.

Décary et al. proposed a diagnostic cluster that can rule knee osteoarthritis in and out (see Table 2). They found that these clusters were able to accurately classify 64% of all cases and 71% of all “non-cases”.

Table 1. Clusters to rule symptomatic knee osteoarthritis in or out.

Clusters to rule symptomatic knee osteoarthritis IN	Clusters to rule symptomatic knee osteoarthritis OUT
Cluster 1: Age 50-58 years AND body mass index (BMI) is greater than 30 kg/m2 AND valgus or varus knee misalignment OR reduced passive knee extension range	Cluster 1: Aged less than 40 years
Cluster 2: Aged over 58 years AND palpable crepitus in any knee compartment	Cluster 2: Aged 40-50 years AND no palpable crepitus in any knee compartment AND BMI is less than 35 kg/m2
These two clusters have a positive likelihood ratio of 13.6	Cluster 3: Aged between 40 and 58 years AND has palpable crepitus in any knee compartment AND BMI is less than 26 kg/m2
	These three clusters have a negative likelihood ratio of 0.11

Anterior Cruciate Ligament

The anterior cruciate ligament (ACL) helps to provide knee stability, preventing anterior tibial translation and internal tibial rotation relative to the femur. Most ACL injuries are non-contact injuries and are often associated with changes in velocity or multidirectional force generated across the knee during weight bearing. They are also associated with jumping, twisting and pivoting movements.

Acute ACL injuries often occur alongside other injuries, including meniscus, articular cartilage, posterior cruciate ligament, lateral collateral and medial collateral ligament injuries. Patients might describe hearing or feeling a sudden "pop" and may experience a deep knee pain. The majority (around 70%) experience immediate swelling (haemarthrosis). Other reported symptoms include giving way, difficulty walking and reduced knee range of motion.

Various special tests have been proposed to assess the integrity of the ACL. Like most special tests, they should not be used in isolation, but as part of a broader assessment.

Please see the linked pages for more information on these tests:

• Lever sign or Lelli’s test
• Lachman test
• Anterior drawer test
• Pivot shift test

Posterior Cruciate Ligament

The posterior cruciate ligament (PCL) is an important knee stabiliser, preventing excessive posterior translation of the tibia on the femur and external rotation. The PCL isn't often injured in isolation. Injuries typically result from hyperflexion, a significant posterior force to the proximal tibia when the knee is flexed (e.g., dashboard injury) or from falling onto a flexed knee. Individuals with PCL injuries might present with posterior knee pain, stiffness, and swelling. As with ACL injuries, various special tests can be used to help identify PCL injuries, including:

• Posterior sag sign
• Posterior drawer test
• Quadriceps active test

Medial Collateral Ligament

Medial collateral ligament injuries are commonly caused by sudden turning, cutting or twisting movements. They can also be caused by a direct impact on the lateral side of the knee, resulting in a valgus stress. MCL injuries can occur in isolation or with other structures (e.g. medial meniscus, ACL, etc.).

To assess the MCL, a valgus stress is applied. If you would like to learn more, please see: Valgus Stress Test.

Lateral Collateral Ligament

The lateral collateral ligament (LCL) is the knee's primary restraint to varus stress. LCL injuries are usually caused by a direct impact to the anteromedial knee, which results in a combination of hyperextension and extreme varus force. They can also be caused by non-contact hyperextension and varus forces. The LCL is rarely injured on its own (< 2% of injuries).

To assess this ligament, a varus stress is applied.

Logerstedt et al. note that a diagnosis of an LCL sprain can be made with a reasonable level of certainty if the following are present:

• varus trauma
• localised swelling over the LCL
• tenderness of the LCL and its attachments
• lateral knee pain with varus stress test at 0° and 30° of knee flexion
• laxity with varus stress test at 0° and 30° of knee flexion

Meniscus Injury

Meniscus injuries in younger people (i.e. less than 40 years) tend to be the result of trauma, while older people tend to have degenerative tears. Isolated meniscus injuries are often caused by rotational or shearing forces at the knee when there is increased axial load. These can occur during twisting or pivoting movements at the knee when the foot is planted.

Common tests include:

• Thessaly test
• McMurray's test
• Apley’s compression and distraction test
• Joint line tenderness

There are various test clusters to help rule meniscus tears in or out. Décary et al. proposed the following clusters to rule traumatic and degenerative meniscus tears IN (see Table 3).

Table 3. Clusters to rule traumatic and degenerative symptomatic meniscus tears IN.

Cluster to rule degenerative, symptomatic tear IN	Patient presents with progressive onset of knee pain and isolated medial knee pain AND mild to severe pain while pivoting on the knee during activities of daily living or sport OR at least one of the following: no knee varus or valgus misalignment OR full passive knee flexion
Cluster to rule traumatic, symptomatic meniscus tear IN	Patient presents with a complaint of knee pain related to trauma (either a direct force, twisting, running, etc.) AND they report at least one of either falling OR pivoting on the knee AND isolated medial or diffuse knee pain AND positive medial joint line tenderness

Patellofemoral Joint Pain

Patellofemoral joint pain (PFP) is an umbrella term used to describe pain arising from the patellofemoral joint or adjacent soft tissues. It causes generalised anterior knee pain that is aggravated by weight bearing and knee flexion. It is common in active adults and adolescents.

PFP is multifactorial and can be difficult to diagnose. Obtaining a detailed patient history is, therefore, key. Patients will tend to describe worsening pain with activities like squatting, prolonged sitting, climbing stairs, and running. Commonly used tests include the squat test, step test, palpation and patellar position and mobility.

Décary et al. proposed the following clusters to rule PFP in and out (see Table 4).

Table 4. Clusters to rule patellofemoral joint pain IN and OUT.

Clusters to help rule patellofemoral joint pain IN	Clusters to help rule patellofemoral joint pain OUT
Cluster 1: People aged less than 40 years who have isolated anterior knee pain or medial patellar facet tenderness	Cluster 1: People who are aged less than 58 years AND who have medial, lateral or posterior knee pain AND no medial or lateral patellar facet tenderness
Cluster 2: People aged 40-58 years who have isolated anterior or diffuse knee pain AND mild to moderate difficulty descending stairs AND medial patellar facet tenderness AND full passive knee extension	Cluster 2: People who are aged less than 58 years and who have diffuse or lateral knee pain AND medial or lateral patellar facet tenderness AND restricted passive knee extension
	Cluster 3: People aged more than 58 years

To find out more about PFP, including the objective assessment, please see: Patellofemoral Pain Syndrome.

Summary

Rehabilitation professionals often work with people who have knee pain. When assessing patients with knee pain, it is essential to take a detailed subjective history and conduct a thorough objective assessment. The L-M-N-O-P-Q-R-S-T framework can be used to guide the subjective assessment. The objective assessment should include observation, a gait analysis, functional screening, a neurological screen, palpation, range of motion testing, and muscle length and strength assessment. There are a number of special tests that can help identify specific knee conditions. Appropriate management depends on an accurate evaluation where all elements of the assessment are considered together.