Patellar Ligament [Quadriceps Tendon]
The quadriceps tendon extends to the patella and consists of pieces from all four quadriceps muscles. The appearance is made up of three layers:
- Superficial layer: rectus femoris
- Middle layer: vastus medialis, vastus lateralis
- Deep layer: vastus intermedius1
Patellar Ligament: Injury
Forced flexion of the knee, or direct impact, are typically the cause of quadricep rupture.
Patellar Ligament: Injury Location
At the superior pole of the patella, the osseotendinous junction is the most common location for ruptures.4
Patellar Ligament: Pathology
Predisposing illnesses include:
- Connective tissue disorders
- Systemic lupus erythematosus
- Rheumatoid arthritis
- Renal impairment
- Corticosteroid use
- Macrolide antibiotics (e.g. ciprofloxacin, azithromycin, etc.)
Quadriceps tendon ruptures are more common than patellar tendon ruptures, but less common than patellar fractures.4
Patellar Ligament: Pearls
Quadriceps tendon components:
- Rectus femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius
Patellar tendon features:
- Normal patellar tendon length should approximate patellar bone length. When the tendon is inordinately long compared to the patella, it’s called patella alta, and an inordinately short tendon is called patella baja.
- Tendinitis often a precursor of tendon rupture
- Avulsion at patellar insertion more common than midsubstance tear
- Anisotropic rotation or magic angle [55° artifact] phenomenon produces false intratendinous increased signal which disappears on long echo-time (Te) T2 sequences. “Magic angle” signal is ill-defined, linear, and corresponds to foci of tendon angulation or “waviness”.
- Complete rupture is associated with tendon discontiguity
- Tendinopathy may be associated with a hypertrophic or enlarged tendon with intermediate T1 and hyperintense T2 fat-sat or PD SPIR / STIR. “Magic angle” has normal sized tendon and normal peritendinous fat.
- Lamellated appearance to the tendon consisting of alternating bright and dark signal on T1 imaging is related to interposition of fat between layers of the quadriceps tendon [layers of bright T1 signal may be 1, 2, 3 or 4 in number]
- Suprapatellar rupture is more common in patients > 40 years old and may be associated with traction enthesopathy, spurs, gout, calcium pyrophosphate dihydrate deposition (CPPD) disease, autoimmune disease, macrolide antibiotic administration, and renal insufficiency.
- Infrapatellar rupture is more common in patients < 40 years old, and is usually a sports-related injury2. Focal signal at the infrapatellar teno-osseous junction without rupture is known as "jumper's knee" and is seen in volleyball (especially middle blockers) and basketball players. Infrapatellar bony hypertrophy predisposes. Enlarged or detached infrapatellar tubercles associated with Sinding-Larsen-Johansson syndrome predisposes to patellar tendon disorders.
Patellar Ligament [Quadriceps Tendon]: Example
Click here to launch this case
Click here to watch a Case Review with Dr. Pomeranz
56-year-old female with right medial and anterior knee pain, instability, weakness and stiffness x5 days. No injury. Limited range of motion, unable to lift or bend. Evaluate for quadriceps tendon rupture. No history of surgery.
Image 1 - Coronal T2 FS Image 2 - Axial PD FS
Image 3 - Sagittal T2 FS Image 4 - Sagittal T2 FS
CLICK EACH IMAGE TO EXPAND
Lateral retinaculum and medial patellofemoral ligament (MPFL) are normal. Lateral tilt of the patella, with dysplastic appearance; short medial facet and long lateral facet, with peripheral spurring of the lateral facet. Shallow trochlea. Moderate to severe chondral thinning of the lateral patellar facet, patellar apex and lateral trochlea, without penetrating osteoedema.
Full-thickness tear of the vastus medialis insertion at the patella, and high-grade partial-thickness tear of the vastus lateralis insertion. Severe tendinopathy and interstitial delamination tear of the midline distal quadriceps tendon. Early separation at the proximal patellar plate. Patellar tendon and flexor mechanism are unremarkable.
No traumatic tear or injury of the ACL, PCL, MCL or lateral collateral complex.
No acute active or traumatic medial or lateral meniscus tear.
Large joint effusion, with synovial hypertrophy. Diffuse, moderate to severe, soft tissue swelling. No intra-articular bodies.
Generalized mild chondral thinning of the medial and lateral femorotibial weightbearing surfaces, without penetration of the subchondral plate. No acute or chronic bony injury.
Diffuse, generalized, moderate muscle atrophy. Marrow signal is normal. No posterior soft tissue mass or bursal cyst. The neurovascular bundle is intact.
1 - Full-thickness tear of the vastus medialis (image 1, green arrow) insertion at the patella, and high-grade partial-thickness tear of the vastus lateralis (images 2 and 3, green arrow) insertion.
2 - Severe tendinopathy of the distal quadriceps tendon, with interstitial delamination tear at midline. Early separation of the proximal pre-patellar plate (image 4, green arrow).
3 - Large joint effusion with synovial hypertrophy. Diffuse, moderate to severe soft tissue swelling.
4 - Grade 3 chondromalacia of the lateral patellofemoral compartment, with moderate to severe chondral thinning but no penetrating chondromalacia.
5 - No traumatic meniscus or ligament tear.
Patellar Ligament [Quadriceps Tendon]: Appendix
Mechanism of injury
- Elderly patients descending stairs or jumping
- Abrupt deceleration in a highly trained athlete
Sites of involvement in order of frequency
- Muscle/tendon junction [powerlifters are especially prone to quadriceps rupture at the teno-osseous junction]
- Tendon / bone junction [above or below patella]
- Tibial tubercle insertion
- Systemic lupus erythematosus
- Diabetes mellitus
- Renal failure
- Macrolide antibiotics
Frequency of tears by age
- Intratendinous central anterior tear predisposed in elderly patients
- Patellar intratendinous tears predisposed in younger athletes
MR criteria for complete tear
- Complete transverse (horizontal) diastasis of tendon anatomy or tendon / osseous separation
- Retraction measured proximal to distal
- Depth is measured anteroposterior by:
- Percent penetration
MR Appearance of the Quadriceps Tendon
- [56%]: Three layers of alternating fat and tendon
- [30%]: Two layers of alternating fat and tendon
- [8%]: Poorly lamellated with appearance of one central tendon
- [6%]: Four lamellations of alternating fat and tendon
The layered configuration of the quadriceps tendon is related to fusion of the muscular layers of the vastus intermedius, vastus lateralis, vastus medialis and rectus femoris.
- Hamstring tightness
- Differentiate from artifactual tendon signal increase [anisotropism]
- Hoffa fat pad [10%] inflamed
- Young patients with teno-osseous partial tear or tendinitis is called “jumpers knee”
- Infrapatellar tendon
- Volleyball, basketball
Tendon Injuries about the Knee
- Suprapatellar: More common in patients under 40
- Infrapatellar: More common in patients over 40
- Rare unless there is severe internal derangement
- At the insertion site or associated with intramuscular hematoma formation; rupture may also be associated with compartment syndrome and Type III tibial stress syndrome
- This injury has a far better prognosis than that of gastrocnemius tendon rupture, although the two look alike clinically
- With plantaris rupture, the return to active physical duty and active sports is much quicker than with gastrocnemius rupture
- Plantaris rupture is easily diagnosed, since the length of involvement extends all the way from the knee down to the distal leg
- In contrast, gastrocnemius rupture and hematoma is localized to a few centimeters and is intramuscular within the confines of the gastrocnemius
- Large hematomas from plantaris rupture can produce secondary deep venous thrombosis (DVT)
- Jumpers cutting on rigid surfaces, teno-osseus separation
Magic Angle Versus Patellar Tendon Injury or Tendinitis
Tendon Injury or Tendinitis
Abrupt cut-off margins
Zones of transition are indistinct
Signal alterations occur at sites of signal angulation that are oriented 55° from the main magnetic field
Tendinitis and tendon injury signal is not dependent on tendon angulation
Occurs at sites of tendon undulation
Unrelated to tendon undulation
Less conspicuous on T2 long TE images
May persist on T2 or water weighted images
The tendon caliber is normal
Tendon caliber may be increased [rarely, decreased]
PATELLAR BURSITIS AND TENDINITIS BY LOCATION
- Hyperintense T2 signal, located between the skin and outer surface of the patella or upper half of the patellar tendon; known as housemaid's knee or lover's knee
Deep infrapatellar bursitis
- T2 signal hyperintensity located between the infrapatellar tendon and the tibia just above the tibial tubercle and within the caudal aspect of the Hoffa fat pad
Superficial infrapatellar bursitis
- T2 signal hyperintensity located just anterior to the inferior or tibial insertion of the patellar tendon; association with Osgood-Schlatter disease may be present
- Intermediate T1 and mild to moderately hyperintense T2 signal in the suprapatellar tendon
- Subpatellar: Called jumper's knee with intermediate T1 signal at the inferior patellotendinous attachment; may be associated with Larsen-Johansson disease
- Tibial insertion: Intermediate intratendinous T1 signal associated with acute injury in athletes or with Osgood- Schlatter disease2
Quadriceps Tendon: References
- Goel A., et-al. Quadriceps Tendon: Radiopaedia (sourced 17Jan2018): https://radiopaedia.org/articles/quadriceps-tendon
- Pomeranz SJ., Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
- Pomeranz SJ. Volume I: MRI of Entrapment Neuropathies, Saphenous Nerve Syndrome. P. 145 (2011).
- Yu JS, Petersilge C, Sartoris DJ et-al. MR imaging of injuries of the extensor mechanism of the knee. Radiographics. 1994;14 (3): 541-51.