X-knee

Indication/Technique

X-rays of the knee joint are requested frequently, particularly at the Emergency Assistance department. They are used primarily to confirm/exclude a fracture, or to assess the level of osteoarthritis in the knee joints (= gonarthrosis).

Technique 

To establish the presence of a fracture, as in each conventional X-ray, the knee should be imaged in at least two directions.
A standard examination includes an anterior-posterior image and a lateral image. Additional directions may be added when indicated.
The most commonly used examinations are explained below.

AP/PA image

The front-to-back or anterior-posterior knee image can be made in both supine and standing positions (fig.  1 & 2). In supine position, the X-rays pass through the knee from anterior to posterior (= AP image). An alternative to the supine position is the standing AP image. The knee is fully extended and imaged in the craniocaudal direction under a 10° angle. 
Additionally, a standing posterior-anterior image (= PA image) may be opted for, also known as the Rosenberg method. In the Rosenberg method, knees should be flexed at 45° (fig. 2).
Standing images have the advantage over supine images that by the additional load on the knee joint they more reliably detect reduced joint space caused by meniscus and cartilage disorders (see also the Pathology section).

Figure 1. Technique for supine anterior-posterior (AP) image.

Figure 2. Technique for standing posterior-anterior (PA) image and standing anterior-posterior (AP) image.

Lateral image

Lateral images are made in the supine position with the knee flexed to 30°. The X-rays pass through the knee joint from medial to lateral (fig. 3).

Figure 3. Technique for lateral image of the right knee (mediolateral projection).

In a good lateral image, the medial and lateral femoral condyles project over each other and the patellofemoral joint is projected free.
Where necessary, oblique images can be obtained by exorotation of the knee from the neutral supine position (= lateral oblique image) or endorotation (= medial oblique image).
In a trauma setting, an image using a horizontal x-ray beam may be preferred over the standard lateral image in order to establish lipohemarthrosis (see Pathology section). The knee is fully extended and the X-rays pass through the knee from lateral to medial (fig. 4).

Figure 4. Technique for lateral knee image using a horizontal X-ray beam.

Axial image

The axial image is also termed the sunrise image and provides information on the patellofemoral joint.  Additionally, patellar pathology (fracture & subluxation/luxation in particular) can be identified.
There are several techniques to make an axial image of the patella. One commonly used technique is the inferosuperior projection.  The patient is in the supine position and flexes the knee to 40-45° using knee support (fig. 5).

Figure 5. Technique for axial image (inferosuperior projection). The patient holds the X-ray plate.

Tunnel view

In a tunnel view, the intercondylar fossa is projected free. 
It is used primarily to identify a free body or osteochondral defect (see Pathology section). 
There are various techniques to make a tunnel image. One commonly used technique is the axial projection. The patient is in the supine position and flexes the knee to 40-45° using knee support (fig. 6).
X-rays pass through the knee from anterior to posterior at a 90° angle to the lower leg.

Figure 6. Technique for tunnel view (axial projection).

Normal anatomy

AP/PA image

The knee joint is formed by the femorotibial joint (femur - tibia articulation) and the patellofemoral joint (patella - femur articulation). The femorotibial joint is subdivided into the medial compartment and the lateral compartment. 
Despite the fact that the three above articulations are regularly described as separate joints, they share a common articular capsule.  
The femoral condyles and tibial plateau are visible on an AP/PA image (fig. 7). The lucent spaces at the level of the medial & lateral compartments of the femorotibial joint are the same in a normal knee. This space is indicative for the joint space.  An asymmetric joint space may suggest meniscus disorders and/or cartilage loss (note: cartilage is not visible on X-ray) and/or ligament laxity. 
The medial & lateral tibial plateau are separated by a minor elevation; the tibial intercondylar eminence. 

Figure 7. Standing AP image of the left knee. Normal anatomy.

Measurement of AP/PA image:

  • Tibiofemoral alignment: on an AP/PA image, draw a vertical line along the lateral femoral condyle.  Be alert for a lateral tibial plateau fracture if the line is more than 5 mm lateral of the lateral tibial plateau (fig. 8).

Figure 8. Standing AP image of the left knee. Normal tibiofemoral alignment.

Lateral Image

The lateral image produces a better image of the patellofemoral joint than the AP image.
In addition to bone, we can also assess soft tissue. The knee has three fat pads (fig. 9):

  1. Infrapatellar fat pad, also termed Hoffa's fat pad.
  2. Posterior suprapatellar fat pad (= prefemoral fat).
  3. Anterior suprapatellar fat pad.

The posterior and anterior suprapatellar fat pads are separated by the suprapatellar recess. The suprapatellar recess is also termed the suprapatellar bursa and is connected to the femorotibial joint.  In joint effusion, the recess may be distended, this is explained in more detail in the Pathology section. A normal knee has little fluid in the suprapatellar recess (anterioposterior thickness <5 mm).

Figure 9. Lateral image (mediolateral projection) of the left knee. Normal anatomy.

Importantly, it is more difficult to assess joint effusion as knee flexion increases (fig. 10). Explanatory note: under flexion > 30°, the patella moves downward and the suprapatellar recess and surrounding soft tissues may be compressed/deformed. Consequently, small amounts of fluid stay unnoticed in the suprapatellar recess.

Figure 10. Effect of knee flexion on suprapatellar recess. At flexion > 30°, fluid assessment in the suprapatellar recess is less reliable.

Additionally, the contours of the quadriceps tendon and the patellar tendon are visible on a lateral image (fig. 9). They have a denser (= whiter) aspect than the fat. Remember, fat has a more hypodense aspect (= blacker) because fat absorbs fewer X-rays than muscles/tendons. See class X-ray/CT technique for more information on X-ray densities.
On a normal knee image, the femoral condyles are superimposed, but seeing the lateral condyle is smaller than the medial, a good lateral image will show that the front of the medial condyle projects before the front of the lateral condyle. By minor asymmetries in the femoral condyles, it may be possible to distinguish between medial and lateral on a lateral image.
Tip (fig. 11):

  • The lateral femoral condyle has a small superficial notch / lateral femoral notch (= transition of range of movement of femorotibial & patellofemoral joint). Note: the medial femoral condyle also has a femoral notch, however it is located more anteriorly and is often not easily seen.
  • Directly proximal to the posterior side of the medial femoral condyle is a bony elevation; the adductor tubercle. This is where the adductor magnus muscle inserts.

Figure 11. Lateral image of the left knee. As a result of the slight oblique projection, the femoral condyles are not fully superimposed.  Using the adductor tubercle and the lateral femoral notch, the medial and femoral lateral condyles can be distinguished.

Patellar measurements in lateral image:

  • The length of the tibial tubercle - patellar lower pole is about the same as the length of the patella, with a variation of 20%.
  • The Insall-Salvati ratio is a commonly used measurement; it is the ratio between the length of the patellar tendon length and that of the patella (fig. 12). Ideally, the measurement is performed with the knee flexed at 30°. In a normal knee, the ratio is between 0.8 - 1.2 (mean value = 1). If the ratio is < 0.8, the patella lies low (= patella baja); if the ratio is > 1.2, the patella lies high (= patella alta). It should be noted here that another proposal has been made in the literature for the normal value, a ratio between 0.74 - 1.5.
  • In the more recently developed modified Insall-Salvati ratio, the same measurement is performed, but the patellar tendon is measured up to the lower pole of the articulating portion of the patella (fig. 12). The patellar length includes the articulating portion of the patella. The mean normal value ratio is 1.25 and a ratio > 2.0 is considered diagnostic for patella alta.

Figure 12. Lateral image (mediolateral projection) of the left knee. The yellow and blue arrows are used for the Insall-Salvati and the Modified Insall-Salvati ratios respectively.

Axial Image

An axial (sunrise) image provides information on the patella and the patellofemoral joint. 
During flexion/extension, the patella slides in the trochlea (notch) and is located in the middle of the trochlea.
The patellofemoral joint has a medial facet and a lateral facet (with the crista in between), where the lateral facet is longer than the medial facet. Rule of thumb: the longest facet is the lateral side.  
The contours are smooth everywhere and the joint space is symmetric at the medial and lateral sides.

Figure 13. Axial (sunrise) image of the left knee. Normal anatomy.

Tunnel view

In a tunnel view, the intercondylar fossa (= separation between the femoral condyles) is projected free. In a normal knee, there are no osteochondral defects or intra-articular bodies (see Pathology section). The medial joint compartment has a slightly smaller joint space on the tunnel view than the lateral joint compartment. This is a normal finding. Explanatory note: the cartilage is slightly thinner on the contact point of the medial femoral condyle and the medial tibial plateau when the knee is flexed at 40-45° (= physiologic).

Figure 14. Tunnel view (axial projection) of the left knee. Normal anatomy. Note the discrete narrowing of the medial joint compartment (= physiologic).

Normal Variations

A number of normal variations are explained below.

  • A fabella is a common sesamoid bone in the lateral head of the gastrocnemius muscle.  It is located posteriorly from the femorotibial joint and is not to be confused with a fracture. On an AP image, a fabella projects over the lateral femoral condyle (fig. 15).

Figure 15. Lateral image and AP image of the left knee. Fabella, normal variation. Note also the lateral femoral notch in order to distinguish the lateral & medial femoral condyles.

  • The patella may arise from various ossification centers. Sometimes these centers are not fused, which is termed a bipartite patella (fig. 16). Rarer is the tripartite patella (3 ossification centers). The unfused center is located for the most part at the superolateral side. The ossification center must always have a rounded and sclerotic border, otherwise a patella fracture may be present.

Figure 16. AP image of the right knee. Bipartite patella, normal variation. 

  • In children (particularly age 10 - 15 years), a cortical irregularity/lucency at the posteromedial side of the distal femur may be confused with an aggressive ossal lesion (fig.  17). This is the origin of the medial head of the gastrocnemius muscle (& insertion site of the adductor magnus muscle). The theory is that the irregularity is caused by traction of the above muscles. It is also termed a cortical desmoid.  A cortical desmoid may be associated with pain symptoms.  When in doubt about the presence of a cortical desmoid or possibly an ossal lesion, a radiologist should be consulted.

Figure 17. Lateral image (mediolateral projection) of the left knee. Cortical lucency at posteromedial side of the distal femur, consistent with a cortical desmoid.

Important: the above irregular lucency at adult age is not normal! Be alert for an ossal lesion (fig. 18). Again, when a lytic lesion is suspected, always consult the radiologist.

Figure 18. Patient with knee complaints. On the lateral image in particular, an irregular aspect and destruction of the cortex is visible. The lytic lesion (*) dorsally in the medial femoral condyle is a mammary carcinoma metastasis (mammary carcinoma was not known at the time of the knee X-ray). The MRI scan (sagittal T1 weighted image) shows extensive spread in soft tissue.

Checklist

The following points may be used as a guide to assess a knee X-ray.

General:

  1. Technique: has everything been imaged correctly; is it suitable for evaluation? Can the question be answered? 
  2. Soft tissues: swelling? Skin intact? Foreign body? Atherosclerosis?  
  3. Joint effusion? Lipohemarthrosis?
  4. Bone mineral density? Ossal lesions?
  5. Check the cortex; cortex interrupted? Cortex destruction? 
  6. Femorotibial joint: position? Osteoarthritis?  
  7. Patellofemoral joint: position of patella? Insall-Salvati ratio? Osteoarthritis? 
  8. Specific: free body? Osteochondral defects? 
  9. Accessory ossicles / normal variations? 
  10. Abnormalities outside the knee joint?  
  11. Changes versus previous examinations?

Pathology

  • Fracture  
  1. fracture general
  2. tibial plateau fracture
  3. patellar fracture
  • Avulsion fractures
  1. intercondylar eminence fracture
  2. Segond fracture 
  3. chronic: Osgood-Schlatter disease
  • Patellar instability
  • Osteochondritis dissecans/ osteochondral lesion
  • Osteoarthritis

Fracture General

Non-dislocated fractures (dislocation = displacement) may be very subtle.
A fracture is frequently associated with joint effusion.  The suprapatellar recess will fill with fluid/blood and the suprapatellar fat pads will expand (fig. 19).

Figure 19. Lateral image (mediolateral projection) with suprapatellar soft tissue density and obliteration of suprapatellar (SP) fat pads, consistent with hydrops.  Normal lateral image for comparison.

Be aware that hydrops may also occur in e.g. infection/inflammation and degenerative changes (clinical information is therefore essential!) 
In a trauma setting, a supine lateral image is recommended as this visualizes the fat-blood level; a lipohemarthrosis (fig.  20). Lipohemarthrosis is strongly associated with intra-articular fracture. It may occur also in a marked bony contusion or ligamentary lesion. In lipohemarthrosis, fat and blood are released into the joint from the bone marrow, creating a fat-blood level.

Figure 20. Lateral knee X-ray with horizontal beam & AP image of the left knee. The lateral image shows lipohemarthrosis and a lateral tibial plateau fracture.  Note the abnormal tibiofemoral alignment (> 5 mm).

Tibial Plateau Fracture

A tibial plateau fracture is a common knee fracture. Subtle fractures may be missed in a knee X-ray. When in doubt, a CT scan should be made (e.g. for lipohemarthrosis without obvious fracture on knee X-ray).

The Schatzker classification is commonly used by surgeons/orthopedists and classifies tibial plateau fractures into 6 subtypes (fig. 21):

  • Type I: wedge-shaped fracture of lateral tibial plateau, with < 4 mm depression* or dislocation
  • Type II: split + compression fracture of lateral tibial plateau with > 4 mm depression (= type I with depression)
  • Type III: pure depression fracture of lateral tibial plateau
  • Type IV: medial tibial plateau fracture with split or compression component (poorest prognosis!)
  • Type V:  Fracture of medial & lateral tibial plateau
  • Type VI: transversal fracture through the metadiaphysis (involvement of medial/lateral tibial plateau is variable)

* depression is measured as the vertical distance between the lowest point of the intact medial tibial plateau and the lowest point of the lateral tibial plateau fragment.

Figure 21. Schatzker classification; type I-VI with corresponding frequencies in percentages.

Be aware that there is a reasonable chance that tibial plateau fractures will be underestimated on conventional images. CT scans are required for more reliable Schatzker classifications (fig. 22).

Figure 22. Lateral knee X-ray with a horizontal beam & AP of the left knee reveal lipohemarthrosis with a lateral tibial plateau fracture. There is depression (> 4 mm) of the lateral tibial plateau, therefore consistent with type II Schatzker. However, CT scan also reveals a fracture of the medial tibial plateau. Therefore, this is actually a type V Schatzker tibial plateau fracture.

Patellar Practure 

Most patellar fractures are easily recognized on lateral images (fig 23).

Figure 23. Lateral image with horizontal beam. Transversal patellar fracture with significant dislocation. Also note the lipohemarthrosis in the suprapatellar recess.

When a patellar fracture is suspected, an axial (sunrise) image should always be made. A vertical patellar fracture can be missed on the AP/PA image and the lateral image (fig. 24).
Be aware of bipartite patella as a normal variation. A fracture has an irregular cortex interruption (vs. smooth sclerotic contours in a bipartite patella) and will not be present on old images.

Figure 24. AP image, lateral image (mediolateral projection) and axial image. The vertical fracture is clearly visible on the axial image and subtly identifiable on the AP image.

  • Fracture
  1. fracture general
  2. tibial plateau fracture
  3. patellar fracture
  • Avulsion fractures
  1. intercondylar eminence fracture
  2. Segond fracture 
  3. chronic: Osgood-Schlatter disease
  • Patellar instability
  • Osteochondritis dissecans/ osteochondral lesion
  • Osteoarthritis

Intercondylar Eminence Fracture

The anterior cruciate ligament inserts on the medial tubercle (medial tibial spine) of the intercondylar eminence. 
The intercondylar eminence has not yet fully ossified in children. Following excessive stress, an avulsion fracture may develop on the anterior cruciate ligament (fig. 25). Think of e.g. forced hyperextension of the knee. An intercondylar eminence fracture may occur in the elderly also, particularly in the presence of osteoporosis. 
Concomitant meniscus and ligamentary damage may be present. However, this occurs more frequently in adults after high-energy trauma.

Figure 25. AP image and lateral image (mediolateral projection) of an intercondylar eminence fracture.

Segond Fracture

A segond fracture is an avulsion fracture on the outer side of the lateral tibial plateau and may develop following internal rotation in combination with varus stress (fig. 26). Debate continues on which structures are exactly involved in this type of avulsion fracture. It was originally held that an avulsion of the middle third part of the lateral joint capsule occurs. Others now believe it is a more complex avulsion that may also involve the iliotibial ligament and a portion of the lateral collateral ligament. 
A Segond fracture is highly associated with rupture of the anterior cruciate ligament.

Figure 26. AP image of the right knee. Segond fracture.

Osgood-Schlatter Disease

Repetitive microtrauma and traction of the patellar tendon at the level of the tibial tubercle may lead to Osgood-Schlatter disease. It is considered a chronic avulsion fracture of the proximal tibia and develops predominantly at age 10 - 14 years (boys > girls). Particularly jump & kick sports appear to increase the risk of Osgood-Schlatter disease.  
The clinical rationale and local pain symptoms are usually sufficient for diagnosis. A knee X-ray may appear entirely normal. The classical radiologic picture of Osgood-Schlatter disease is fragmentation of the tibial tubercle and local soft tissue swelling (fig. 27). There may also be obliteration of the caudal portion of Hoffa's fat pad (secondary to infrapatellar bursitis). Fragmentation of the tibial tubercle without soft tissue swelling may also occur as a normal variation (multiple ossification centers); patient symptoms determine presence/absence of Osgood-Schlatter disease.

Figure 27. Lateral image (mediolateral projection) of the right knee. The lead marking indicates patient's local pain symptoms.  Fragmentation of the tibial tubercle and local soft tissue swelling consistent with Osgood-Schlatter disease.

  • Fracture
  1. fracture general
  2. tibial plateau fracture
  3. patellar fracture
  • Avulsion fractures
  1. intercondylar eminence fracture
  2. Segond fracture
  3. chronic: Osgood-Schlatter disease
  • Patellar instability
  • Osteochondritis dissecans/ osteochondral lesion
  • Osteoarthritis

Patellar Instability

The patellofemoral joint is stabilized by the extensor muscles, the bone (trochlea) and ligaments (medial patellofemoral retinaculum/ligament). The patella may luxate towards lateral, frequently the result of a twisted leg; knee in flexion + internal rotation of the femur + fixated foot with a valgus component.  
 
A number of predisposing factors to patellofemoral instability: 

  • patella alta (patellar tendon too long) and patella baja (patella tendon too short)
  • abnormal shape of trochlea; trochlear dysplasia (fig. 28)
  • relatively weak vastus medialis muscle 
  • ligamentary laxity (including Ehlers-Danlos and Marfan syndrome)

Figure 28. Patient with habitual patella luxations. The axial image shows a subluxated position towards lateral. Markedly superficial trochlea, consistent with trochlear dysplasia.

Chronic instability of the patellofemoral joint may lead to progressive cartilage damage and eventually severe osteoarthritis.

  • Fracture
  1. fracture general
  2. tibial plateau fracture
  3. patellar fracture
  • Avulsion fractures
  1. intercondylar eminence fracture
  2. Segond fracture
  3. chronic: Osgood-Schlatter disease
  • Patellar instability
  • Osteochondritis dissecans/ osteochondral lesion
  • Osteoarthritis

Osteochondritis Dissecans/ Osteochondral Lesion

Osteochondritis dissecans (OCD) is an osteochondral disorder that is observed in children/teenagers with joint pain, swelling and/or locked joints. 
The exact etiology has not been elucidated.  It is likely a multifactorial process consisting of genetic factors, growth abnormalities and chronic subchondral stress. 
At adult age (= mature skeleton) the term osteochondral lesion is used rather than OCD.  
The disorder encompasses a spectrum starting at subchondral bone edema to subchondral fracture/fragmentation and eventually detachment of the osteochondral fragment (fig. 29).

Figure 29. Osteochondritis dissecans/ osteochondral lesion stages. The cartilage is still intact (stable) in A. B & C show a cartilage defect (unstable). Instability may lead to a free body (corpus liberum (D).

Figure 29. Osteochondritis dissecans/ osteochondral lesion stages. The cartilage is still intact (stable) in A. B & C show a cartilage defect (unstable). Instability may lead to a free body (corpus liberum (D).
The literature describes various laparoscopic and non-laparoscopic classifications (not addressed here). Irrespective what classification is used, MRI must be used to find out whether the OCD/osteochondral lesion is stable.  Intact cartilage suggests stability; a cartilage defect suggests instability. Cystic changes near the interface (see stage C & D in fig. 29) at adult age suggest instability, but are aspecific at a young age.

An OCD may develop in various joints (including ankle and elbow) but is most common in the knee joint.  The classical location for OCD in the knee is the lateral side of the medial femoral condyle. Rule of thumb: LAME, Lateral Aspect of the Medial femoral (Epi)condyle. 
The tunnel view image in particular provides good visualization of the osteochondral defects and free bodies (fig. 30).

Figure 30. AP image and tunnel view image of the right knee. OCD/osteochondral lesion at lateral side of the medial femoral condyle.  Despite the size of the free body, it is not visible on the AP image.

  • Fracture
  1. fracture general
  2. tibial plateau fracture
  3. patellar fracture
  • Avulsion fractures
  1. intercondylar eminence fracture
  2. Segond fracture
  3. chronic: Osgood-Schlatter disease
  • Patellar instability
  • Osteochondritis dissecans/ osteochondral lesion
  • Osteoarthritis

Osteoarthritis

Osteoarthritis is a complex disease characterized by synovitis, cartilage wear, meniscus abnormalities, reactive bone formation (osteophytes) and subchondral abnormalities. It is associated with a diversity of symptoms. Patients may complain about progressive load-dependent pain and/or reduced knee function. 
Osteoarthritis may develop in the knee (= gonarthrosis) in the femoral tibial joint and/or the patellofemoral joint. If femorotibial osteoarthritis develops in the medial joint compartment or the lateral joint compartment only, it is termed medial gonarthrosis and lateral gonarthrosis respectively. 
The osteoarthritis may be primary with no obvious identifiable cause.  Secondary osteoarthritis develops after e.g. a fracture.  
Radiological characteristics of osteoarthritis (fig 31):

  • Narrowing of the joint space secondary to meniscus pathology and to a lesser degree loss of cartilage 
  • Subchondral sclerosis (increased bone production secondary to increased pressure with cartilage loss)
  • Osteophyte formation (bone exostoses attempting to increase the joint surface)
  • Subchondral cysts (secondary to microfractures of the subchondral bone and pressure of the synovial fluid)
  • Synovitis

Figure 31. Standing AP image of the knees. The knees (left > right) are osteoarthritic. In particular, medial gonarthrosis can be seen.

Figure 31. Standing AP image of the knees. The knees (left > right) are osteoarthritic. In particular, medial gonarthrosis can be seen.  
One of the first characteristics of osteoarthritis is a narrowing of the joint space.  This can be subtle, always compare images with previous images.
AP/PA images in standing position have the advantage that the additional load on the knee joint makes them more suitable to detect subtle joint space narrowing. Therefore, when asked to confirm osteoarthritis, a standing AP/PA image is preferred. 

Patellofemoral osteoarthritis can be assessed on a lateral image and an axial image. 
Be aware that on lateral images, you will not always manage to project the joint space of the patellofemoral joint entirely free.  Consequently, joint space narrowing as a sign of osteoarthritis can frequently not be assessed adequately (fig. 32). An axial image, however, will allow more accurate assessment of the joint space narrowing (fig. 33).

Figure 32. Lateral image (mediolateral projection) of the knees. Patellofemoral (PF) osteoarthritis in the knees (left > right).

Figure 33. Axial image of the left knee. The lateral facet of the patellofemoral (PF) joint shows signs of osteoarthritis (other patient than fig. 32).

Sources

  • B.J. Manaster et al. The Requisites – Musculoskeletal Imaging. 2007
  • N. Raby et al. Accident & Emergency Radiology – A Survival Guide. 2005.
  • K.L. Bontrager, J.P. Lampignano. Textbook of Radiographic Positioning and Related Anatomy. 2014 (8th edition)
  • W. Fischer et al. MRI-essentials.com – An illustrated atlas of orthopedic MRI (2014)
  • B. Keegan Markhardt et al.Schatzker Classification of Tibial Plateau Fractures: Use of CT and MR Imaging Improves Assessment; RadioGraphics (2009)
  • N. Shabshin et al. MRI criteria for patella alta and baja; Skeletal Radiology (2004)
  • Ferris M. Hall, M.D. Radiographic Diagnosis and Accuracy in Knee Joint Effusions; Radiology (1975)
  • Duke G. Pao, MD. The Lateral Femoral Notch Sign; Radiology (2001)
  • C.J. Gottsegen et al. Avulsion Fractures of the Knee: Imaging Findings and Clinical Significance;  RadioGraphics (2008)
  • G. Diederichs et al. MR Imaging of Patellar Instability: Injury Patterns and Assessment of Risk Factors; RadioGraphics (2010)

 

Author

  • Annelies van der Plas, MSK radiologist Maastricht UMC+

  • Prof. dr. J.L. Bloem, radiologist LUMC

10/07/2016

Copyright
All the work (text, illustrations, visual elements) seen on this website is copyright by Annelies van der Plas.
It may not be used without written permission of Annelies van der Plas.

Test Yourself

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