October 18, 2020
extensor tendon injuries of the knee cover

Extensor Tendon Injuries of the Knee

This week we’re going to review injuries to the extensor mechanism of the knee. To begin, we should review the anatomy of the knee. The quadriceps muscle is composed of the rectus femoris, vastus lateralis, intermedius and medialis which all coalesce to form the quadriceps tendon. The quad tendon (QT) inserts into the patella which in turn attaches to the proximal patellar tendon (PT) which ultimately attaches at the tibial tuberosity. Extensor tendon injuries are generally characterized as either quad tendon or patellar tendon ruptures.

Case Question

A 30 year old male presents to the clinic several days after developing acute right knee pain while playing basketball. He states he came down from a rebound and as he was landing he felt a pop in his knee. He was unable to continue playing. On exam, he has a moderate sized joint effusion and tenderness at the insertion of the tibial tubercle. He is unable to actively extend his knee. You obtain radiographs of the affected knee. Which of the following is most likely to be seen on radiographs?

A) Tibial Plateau fracture
B) Patella fracture
C) Patella Alta
D) Patella Baja

Body

The overall prevalence in a british study was 1.37 (QT) and 0.6 (PT) per 100,000 person years (Clayton 2008). QT ruptures are more common in patients older than 40 and typically associated with degenerative tears. They also occur at a rate approximately 6 times more frequently than PT ruptures (Saragaglia 2013). PT ruptures are more commonly seen in patients under 40 years of age and are associated with either direct trauma or some consider it to be the end stage of patellar tendinopathy (Kannus 1991).

The pathophysiology is the result of sudden contraction of the knee in a flexed position. Most commonly this is an eccentric contraction. Examples would include jump and land mechanism, a sudden change in direction and less commonly direct trauma. The ruptures typically occur at the musculotendinous junction or osseotendinous junction while mid-substance tears are uncommon. In some cases, avulsion fractures do occur at the patellar or tibial tubercle.
Commonly accepted risk factors include age, obesity, ESRD, Diabetes, Rheumatoid Arthritis, Gout and Hyperparathyroidism. Orthopedic history of patellar tendonitis, ACL repair or total knee arthroplasty are also risk factors. Certain medications increase the risk of tendon rupture including fluoroquinolones, statins and a history of oral or intra-articular corticosteroid use.
The clinical features include acute pain with a popping or tearing sensation. The pain will be suprapatellar in QT tears and infrapatellar in PT tears. They will be unable to bear weight. They will have tenderness and a palpable defect in complete tears, while partial tears may be more subtle. A joint effusion is often present. Most notably, they will be unable to extend their leg. In partial tears, they may have weak extension or extension lag which suggest incomplete disruption.
patella baja patella alta illustration
IMAGE 1. ILLUSTRATION OF NORMAL, PATELLA BAJA AND PATELLA ALTA (ADOPTED FROM BRACEABILITY.COM)
quadriceps rupture ultrasound knee pain
IMAGE 2. COMPLETE TEAR OF QUADRICEPS TENDON ABOVE PATELLA SHOWN IN LONG AXIS. NOTE THE TENDON DEFECT AND ASSOCIATED HEMATOMA. (ADOPTED FROM RADIOPAEDIA.ORG)
Standard radiographs of the knee may demonstrate patella alta (PT) or patella baja (QT). Ultrasound can easily identify complete and partial tendon ruptures by evaluating for hypoechoic areas within the tendon fibers. MRI can help distinguish between them as well and can evaluate for other injuries. 
For complete ruptures, surgical management is indicated. Most studies report good or excellent outcomes following surgical repair (Boudissa 2014, Lee 2013). Post surgical rehab involves a hinged knee brace locked in full extension with slow progression to increasing range of motion in the first few weeks. Isometric strengthening starts immediately with active knee extension around 6 weeks. Ambulation with crutches typically begins around 6 weeks, braces can usually be discontinued around 12 weeks. The most common complications are pain, stiffness, extensor weakness and extensor leg. Athletes have a favorable return to play prognosis even in elite athletes such as the NFL (Boublik 2011) and NBA (Nguyen 2018).

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Case Answer

Answer is C, patella alta. This patient has a history and exam highly suspicious for a patellar tendon rupture. When this occurs, the quadriceps tendon has unopposed tension pulling the patella proximal resulting in patella alta on radiographs. Quadriceps tendon has the opposite effect, the unopposed tension of the patella tendon pulls the patella inferiorly resulting in patella baja. The patient may have a patella fracture, however the mechanism is not consistent with this injury and he is not tender along the patella. Tibial plateau fracture is also possible however far less likely given the mechanism and the patients pain would typically be along the medial or lateral plateau with an intact extensor mechanism.

 

Rauh M, Parker R. Patellar and quadriceps tendinopathies and ruptures. In: DeLee JC, ed. DeLee and Drez’s Orthopaedic Sports Medicine. Philadelphia, PA: Saunders; 2009:1513–1577.

References

1. Clayton RAE, Court-Brown CM. The epidemiology of musculoskeletal tendinous and ligamentous injuries. Injury. 2008;39:1338–44.
2. Saragaglia, D., A. Pison, and B. Rubens-Duval. “Acute and old ruptures of the extensor apparatus of the knee in adults (excluding knee replacement).” Orthopaedics & Traumatology: Surgery & Research 99.1 (2013): S67-S76.
3. Kannus P, Józsa L. Histopathological changes preceding spontaneous rupture of a tendon. A controlled study of 891 patients. J Bone Joint Surg Am 1991; 73 (10) 1507-1525
4. Boudissa, M., et al. “Acute quadriceps tendon ruptures: a series of 50 knees with an average follow-up of more than 6 years.” Orthopaedics & Traumatology: Surgery & Research 100.2 (2014): 217-22
5. Lee, Dennis, Daniel Stinner, and Hassan Mir. “Quadriceps and patellar tendon ruptures.” The journal of knee surgery 26.05 (2013): 301-30
6. Boublik M, Schlegel T, Koonce R, Genuario J, Lind C, Hamming D. Patellar Tendon Ruptures in National Football League Players. The American Journal of Sports Medicine. 2011;39(11):2436-2440.
7. Nguyen, Michael V., et al. “A comprehensive return-to-play analysis of national basketball association players with operative patellar tendon tears.” Orthopaedic journal of sports medicine 6.10 (2018): 2325967118800479.

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