Assessment of knee injury

Common

Patellofemoral joint injuries

see our comprehensive coverage of Patellofemoral pain syndrome

History	Exam	1st test	Other tests
pain over the anterior aspect of knee; subluxation or dislocation episodes; anterior knee pain with squatting, sitting, or getting up from a chair; difficulty with ascending or descending stairs and with performing knee extension exercises; crepitation with active knee ROM; may experience "catching" or "locking" [9]	pain on palpation of inferior pole of patella (patellar tendinopathy), superior pole of the patella, prepatellar bursae, deep infrapatellar bursa, pes anserine bursa, fibular collateral ligament (FCL)-biceps bursa, medial suprapatellar plica, retropatellar fat pad, and semimembranosus bursa; increase in lateral translation during lateral patellar apprehension test performed at 45° of knee flexion; increased medial subluxation of patella in first 0° to 40° of knee flexion; [14] retropatellar crepitation with translation of patella in trochlear groove	patellar sunrise x-ray: medial or lateral patellofemoral joint space narrowing, patellar tilt, or subluxation; a bipartite patella (present in 2% of the population, it involves the superolateral aspect of the patella) and small avulsion fractures of the medial patellofemoral ligament off the medial aspect of the patella or osteophyte formation of their patellofemoral, medial, or lateral compartment of the kneeMore patellar sunrise x-ray The most standard position to obtain an axial patellar x-ray is at 45° of knee flexion. lateral x-ray: assessment of patellar height (and compared to the contralateral side) to look for patella alta or patella baja (when the patella rides too low down the femur); osteophyte formation of the patellofemoral jointMore lateral x-ray The lateral x-ray should be taken at approximately 30° of knee flexion, with the patient standing.	MRI: injuries to medial patellofemoral ligament, lateral retinacular structures, and articular cartilage of the patella and trochlear groove can be assessed; the articular cartilage of the patella and trochlear groove can also be observed on the sagittal views or any tears of the quadriceps tendon or patellar tendonMore MRI Best test to diagnose medial patellofemoral ligament tears. The axial cuts are most useful to assess for injuries to the patellofemoral joint.

Anterior cruciate ligament (ACL) injury

see our comprehensive coverage of Anterior cruciate ligament injury

History	Exam	1st test	Other tests
subluxation on twisting, turning, or pivoting; some patients can feel it coming on, other patients are not able to feel it and may experience frequent falls due to their injury	increase in anterior translation during Lachman's test and the anterior drawer test compared to the contralateral knee; [15] positive anterior drawer test in external rotation; positive pivot shift test	standing AP x-ray: rules out fractures or any significant arthritis or joint subluxationMore standing AP x-ray Useful to look for small lateral capsule avulsion fractures (Segond fractures). This can be an important secondary finding in an ACL tear. lateral x-ray: potential joint space narrowing of anterior and posterior aspects of the knee, and potential anterior subluxation of the tibia on the femur (for a chronic ACL injury); assessment of potential impaction fractures of the anterior lateral femoral condyle or posterior lateral tibial plateauMore lateral x-ray The lateral x-ray should be taken at approximately 30° of knee flexion, with the patient standing.	arthroscopy: direct visualisation of the ACL injury; assessment of meniscal tearsMore arthroscopy Can be used to confirm a diagnosis and for treatment. MRI: ACL tear; concurrent meniscal tears or bone bruisingMore MRI Most accurate test. A non-orthogonal sagittal view is the most useful to look for an ACL tear. KT-1000 or KT-2000: increase of anterior tibial translation >3 mm is usually indicative of an ACL tear; KT values 0-3 mm usually an indication of an intact ACL or ACL reconstruction graftMore KT-1000 or KT-2000 The KT-1000 and KT-2000 are instrumental measurement tests, usually performed by a physiotherapist, which measure the amount of increased anterior tibial translation of the injured knee compared to the normal contralateral knee.

Medial collateral ligament (MCL) injury and associated valgus instability

see our comprehensive coverage of Medial collateral ligament injury: diagnosis and treatment

History	Exam	1st test	Other tests
sensation of side-to-side toggle with activities; difficulty with twisting or turning; difficulty with running or pivoting; joint thrusting in patients with medial compartment arthritis or medial compartment pseudolaxity	increased valgus opening in extension and in 30° flexion; important to differentiate true joint line opening from increased motion due to joint line collapse and pseudolaxity, which can be found in patients with medial compartment arthritis	standing AP x-rays: useful to look for avulsion fractures of the superficial MCL or evidence of heterotopic ossification (Pellegrini-Stieda disease is calcification from an old previous MCL injury)	valgus stress x-rays: increased medial joint space opening to an applied load; >3.2 mm medial compartment gapping correlates with a complete superficial medial collateral ligament tear; >9.8 mm of medial gapping correlates with a capular grade III medial knee injury [30] More valgus stress x-rays Useful in patients with open physes (growth plates) who appear to have an MCL or posterolateral corner injury as it helps to differentiate between a true ligamentous injury and a possible growth plate fracture. Usually obtained with the knee at 20° of knee flexion. Due to the variation of normal joint space narrowing caused by physiological laxity, it is important to obtain bilateral stress x-rays comparing the injured to the normal contralateral side. In this test, the examiner stabilises the thigh and applies a varus or valgus stress to the foot/ankle. It is important to have the patient relax as much as possible during these x-rays. Used to confirm diagnosis of chronic injuries. MRI : coronal view MRI scans are very useful to assess for both the location of an MCL tear (meniscofemoral or meniscotibial) or whether there is a partial or complete tear; can also reveal attachment avulsions or a midsubstance tear of the medial knee structures More MRI Used to confirm diagnosis of acute injuries.

Posterolateral knee injury and associated varus instability

History	Exam	1st test	Other tests
sensation of side-to-side toggle of knee with activity; weakness of foot and ankle that may be secondary to a concurrent common peroneal nerve neuropraxia or complete injury	increased varus opening in extension indicates combined posterolateral corner injury plus an anterior cruciate ligament and/or a posterior cruciate ligament injury; increased varus opening at 30° knee flexion indicates an isolated or combined posterolateral corner injury; positive posterolateral drawer test; 15° more external rotation compared to contralateral knee in dial test at 30° in knee flexion; positive reverse pivot shift test; dynamic thrusting of the knee with gait	standing AP x-rays: useful to exclude avulsion fractures of the femur, tibia (Segond fractures), or fibular head (arcuate fractures) lateral x-ray: useful to exclude fibular head (arcuate) fractures or tibial plateau fracturesMore lateral x-ray Alignment of femoral condyles should be ensured.	varus stress x-rays: increased lateral joint space opening to an applied load; >2.7 mm opening correlates with a fibular collateral ligament tear; >4.0 mm correlates with a grade III posterolateral knee injury [31] More varus stress x-rays Useful in patients with open physes (growth plates) who appear to have a posterolateral corner injury, to help differentiate between a true ligamentous injury and a possible growth plate fracture. Obtained with the knee at 20° of knee flexion. Due to the wide variation of normal joint space narrowing caused by physiological laxity of the lateral compartment of the knee, it is recommended to obtain bilateral stress x-rays that compare the injured to the normal contralateral side. In this test, the examiner stabilises the thigh and applies a varus stress to the foot/ankle. It is very important to have the patient relax as much as possible during these x-rays. MRI: coronal, coronal oblique, and sagittal views (1.5- or 3-tesla, thin slice to include entire fibular head) [32] More MRI Useful to identify injuries to the lateral (fibular) collateral ligament, popliteus tendon, popliteofibular ligament, iliotibial band, biceps femoris, and lateral capsule. However, low-field MRIs may not show sufficient detail of these structures. It is highly recommended to include the entire fibular head in the scans. [32] Fat suppression views visualise localized soft tissue oedema (to indicate injury) or bone bruises.

Posterior cruciate ligament (PCL) injury

History	Exam	1st test	Other tests
history of hyperextension mechanism or a blow to anterior aspect of knee; difficulty while going down inclines, descending stairs, or running down hills	increase in posterior translation compared to the contralateral knee in the posterior drawer test; posterior sag of the tibia on the femur (posterior sag sign); positive quadriceps active test	AP x-ray: bony avulsions of the posterior cruciate ligament off the tibia or concurrent fracturesMore AP x-ray In acute injuries, plain x-rays should be taken in all patients, consisting of an AP and lateral view. lateral x-ray: narrowing of joint space of the anterior and posterior aspects of the knee; posterior subluxation of the tibia on the femur; bony avulsion of the PCL off the tibiaMore lateral x-ray Taken at approximately 30° of knee flexion, with the patient standing.	kneeling PCL stress x-rays: amount of posterior translation difference seen between normal knees is 0-2 mm; partial posterior cruciate ligament tears have between 2-7 mm of increased posterior translation; complete PCL tears have between 8-11 mm of increased posterior translation, while combined (severe) PCL injuries have ≥12 mm increased posterior translation of their injured knee compared to the normal contralateral side indicative of a concurrent combined posterolateral and/or posteromedial knee injury [33] More kneeling PCL stress x-rays Quantification of the amount of posterior laxity of the knee in the face of a PCL or combined PCL and posterolateral corner or posteromedial corner injury is very difficult. Thus, kneeling stress x-rays are essential to determine the amount of instability seen with a PCL injury. [33] arthroscopy: direct visualisation of the PCL injury; assessment of concurrent meniscal tears or medial or lateral joint space gapping indicative of a combined ligament injuryMore arthroscopy Can be used to confirm a diagnosis and for treatment. MRI: T2 or proton-density MRI scans show oedema within the substance of the ligament and possible ligament stretching or disruption; concurrent injuries of the posterolateral structures or a medial meniscus root tearMore MRI In acute injuries, x-rays do not show any obvious bony avulsions of the PCL. MRI scans have been shown to be extremely sensitive and specific to diagnose acute PCL injuries. In chronic injuries, it is much more difficult to determine on the MRI scans if there is a PCL tear present because the PCL does have some inherent capability to heal. Thus, there may be significant laxity present in the knee and the PCL may look normal, or relatively normal, on the MRI scan. In these situations, the physical examination may be more useful than the MRI reading. For clinicians, in these type of circumstances, kneeling PCL stress x-rays, or stress x-rays using a Telos device, have been shown to be very accurate to assess for increases in posterior knee laxity. [33]

Meniscal tear

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History	Exam	1st test	Other tests
joint line pain along affected side, [9] pain with maximal knee flexion or with deep squatting of the knees when symptomatic posterior horn meniscal tears are present; difficulty with twisting and turning or kicking an object	lack of full flexion and extension; joint line crepitation and pain directly over the joint line; [9] positive assessment for meniscal tears; pain with maximal knee flexion	standing AP x-ray: decrease in the joint space may indicate some underlying arthritic changes; calcification of the meniscus consistent with chondrocalcinosis lateral knee x-ray: anterior or posterior joint line osteophytes may indicate some underlying arthritic process; calcification of the meniscus consistent with chondrocalcinosis	MRI: sagittal views: anterior and posterior meniscal tears; coronal view: far medial and far lateral meniscal tears and flap tearsMore MRI Used to confirm the diagnosis. Not all meniscal tears may be well visualised on normal MRI scans. In the case of previous surgery, such as a meniscal repair, it may be necessary to obtain MRI with intra-articular gadolinium contrast agent to leak into the area of the tear to best differentiate it, as normal scans may not show this. 45° patella sunrise (axial) x-ray: osteophytes along affected medial or lateral femoral condyle may indicate arthritic changes 45° PA standing (Rosenberg) x-ray: joint space narrowing in a patient who has had a previous partial meniscectomy or subtotal meniscectomyMore 45° PA standing (Rosenberg) x-ray In this instance, the anterior aspect of the joint articular cartilage will be preserved and a standing x-ray may not show any associated joint space narrowing. When the examiner flexes the knee to 45°, there may be significant joint space narrowing as the area of the arthritis in the more posterior aspect of the femoral condyle comes into contact with the more posterior aspect of the tibial plateau. These x-rays are particularly useful in patients who have had previous partial meniscectomies. arthroscopy: torn meniscal cartilage or meniscal root attachmentsMore arthroscopy Can be used to confirm a diagnosis and for treatment.

Open fracture

History	Exam	1st test	Other tests
laceration extends down to associated fracture, any laceration around the knee with an underlying fracture has to be considered an open fracture until proven otherwise	deformities and lacerations around the injured knee; pulses may be absent or diminished if vascular injury present; sensation or motor function may be decreased or absent if associated nerve injury	AP and lateral x-rays: fracture or dislocation	CT scan: complex fracture of the femur, tibia, or patellaMore CT scan Used to evaluate for complex fractures of the femur or tibia. Also useful if the patient has severe injuries and obtaining different views by x-ray is difficult.

Referred pain to knee

History	Exam	1st test	Other tests
often presents as anterior knee pain; history of previous hip injuries/pathologies; older patients; slipped capital femoral epiphysis in overweight adolescents	decreased motion, groin pain (true hip pain), or pain referred to the knee (hip flexion and rotation) during assessment of hip range of motion; in adolescents assess for the presence of a slipped capital femoral epiphysis using the log rolling test	AP pelvic x-ray: in osteoarthritis there will be evidence of osteophytes, joint space narrowing, and subchondral sclerosis; in slipped capital femoral epiphysis there will be evidence of posterior displacement or widening of epiphysis; for femoroacetabular impingement there will be evidence of bony prominence of the superior femoral neck	frog-leg lateral hip x-ray : in osteoarthritis there will be evidence of osteophytes, joint space narrowing, and subchondral sclerosis; in slipped capital femoral epiphysis there will be evidence of posterior displacement or widening of epiphysis; for femoroacetabular impingement there will be an increased bony prominence along the superior femoral neckMore frog-leg lateral hip x-ray Recommended test for slipped capital femoral epiphysis. MRI of hip: will show evidence of a subtle epiphyseal slip not evident on x-ray; also useful to demonstrate stress fractures or acetabular tearsMore MRI of hip Necessary when diagnosis is unclear.

Uncommon

Patella fracture

History	Exam	1st test	Other tests
direct trauma to the anterior aspect of the knee, e.g., onto a dashboard in a car accident; fall onto a knee in the semi-flexed position causing forceful contraction of the quadriceps	joint deformity or shortening; swelling from effusion or haemarthrosis and/or bruising; severe pain on movement; limited knee extension; pulses may be absent or diminished if vascular injury present; sensation or motor function may be decreased or absent if associated nerve injury	AP and lateral x-rays: patella fracture patellar sunrise x-ray: patella fracture; bipartite patella (present in 2% of the population, it involves the superolateral aspect of the patella)	CT scan: complex fracture of the femur, tibia, or patellaMore CT scan Used to evaluate for complex fractures of the femur, tibia, or patella.

Femoral condyle fracture

History	Exam	1st test	Other tests
fall onto a flexed knee; fall from a height; vertical loading onto existing valgus or varus knee deformity; existing osteoporosis	joint deformity or shortening; swelling from effusion or haemarthrosis and/or bruising; severe pain on movement; soft tissue damage; pulses may be absent or diminished if vascular injury present; sensation or motor function may be decreased or absent if associated nerve injury	AP and lateral x-rays: femoral condyle fracture	oblique view x-ray: femoral condyle fracture; may show an obliquely oriented fracture CT scan: complex fractures that may also involve the tibia and fibula; concurrent bony avulsions of ligaments or meniscal attachmentsMore CT scan Used for evaluation of complex fractures that may also involve the tibia and fibula.

Tibial plateau fracture

History	Exam	1st test	Other tests
injury mechanism involving valgus force (e.g., hit by a car bumper), compression (e.g., from parachuting), or both; may be unable to bear weight	joint deformity or shortening; swelling from effusion or haemarthrosis and/or bruising; soft tissue damage; there may be severe pain on movement; pulses may be absent or diminished if vascular injury present; sensation or motor function may be decreased or absent if associated nerve injury	AP and lateral x-rays: tibial plateau fracture or joint subluxationMore AP and lateral x-rays Tibial plateau fractures can be missed on a plain x-ray film and, therefore, CT scan is advised if there is uncertainty about the diagnosis. oblique view x-ray: tibial plateau fracture and joint space displacementMore oblique view x-ray Internal oblique will show lateral plateau fractures and external oblique will show medial plateau fractures.	CT scan: tibial plateau fracture or complex fracture

Dislocation

see our comprehensive coverage of Joint dislocation

History	Exam	1st test	Other tests
high-velocity knee injuries with gross instability; fracture dislocations	deformity of the tibiofemoral alignment; associated lacerations may indicate an open fracture or dislocation; decreased posterior tibial and dorsalis pedis pulses; decreased light touch sensation at the lower extremity needs to be assessed for the distribution of the tibial and common peroneal nerves; abnormal motor examination of the common peroneal and tibial nerves' motor functions needs to be assessed to rule out nerve injury	AP and lateral x-rays: fracture or dislocation; bony avulsions of ligament or meniscal attachmentsMore AP and lateral x-rays Many knee dislocations spontaneously reduce.	MRI: ligamentous disruption or other injury of the knee; assessment of associated meniscal or articular cartilage injuryMore MRI Definitive test. arteriogram or CT angiogram: disruption of integrity of the popliteal artery around the knee in concomitant vascular injury; visualisation of intimal flaps of the popliteal arteryMore arteriogram or CT angiogram Should be performed with decreased pulses and compared to the normal contralateral side, especially for high-velocity knee injuries.

Infection

see our comprehensive coverage of Septic arthritis

History	Exam	1st test	Other tests
significant pain, redness, warmth, and swelling around the knee; hx of recent surgery, recent open fractures or lacerations with increased pain, warmth, or swelling	redness or swelling and increased warmth	AP and lateral x-rays: normal	ESR: elevated significantly above “normal” valueMore ESR Can also be elevated for recent injury, surgery, gout, or pseudogout. CRP: elevated FBC with differential: elevated, especially with a left shift (increased neutrophils) on the differential aspiration (cell count, cell differential, Gram stain, aerobic/anaerobic cultures): WBC >50,000/microlitre; left shift on the WBC differential indicates possible infection; Gram stains and aerobic/anaerobic culture can show evidence of bacterial infection