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SplintER Series: Patellar Tendon Rupture

Karl Koivisto |

A 46-year-old female with a history of diabetes and morbid obesity presents to the emergency department (ED) with difficulty walking after she tripped on a curb and fell onto her right knee. You obtain X-rays (Figure 1). What is your suspected diagnosis? What is your initial workup in the ED? What is your management and disposition?

Figure 1. AP/lateral x-ray of the right knee. Author’s own images.

Patellar tendon rupture

  • Pearl: Patellar tendon ruptures are most frequently seen in men under 40 years of age. This is opposed to quadricep tendon ruptures, which are typically seen in older patients [1]. Common comorbidities include diabetes mellitus, chronic renal failure, and gout. Rupture usually occurs at the inferior pole of the patella.

There are three main mechanisms for a patellar tendon injury [2]:

  • Indirect low energy trauma, which usually occurs after eccentric contraction of the quadriceps muscle.
  • Indirect high energy trauma, which is usually associated with other ligamentous, bony, and cartilaginous injuries of the knee.
  • Direct injury to the tendon itself, e.g. penetrating injury.
  • Weakness or loss of active extension. About 20 degrees of extension can still be expected in complete rupture, as the patella only begins to engage the trochlea at this angle [3].
  • Anterior swelling of the knee inferior to the patella, which can be severe enough to mask the expected palpable tendon defect in complete rupture.
  • Superiorly displaced patella can be seen in complete rupture.

1. X-rays: Can show a superiorly displaced patella, known as patella alta (Figure 1), as well as avulsion fractures from the inferior pole of patella and, less frequently, the tibial tuberosity [2].

    • Pearl: Insall-Salvati ratio (ratio of patellar tendon length to diagonal length of patella) >1.2 suggests patellar tendon tear (Figure 2) [2,5]. See Figure 3 for the typical location of the patella on the lateral knee x-ray. For more on patella alta x-rays, please see the associated SplintER Series article.

Figure 2: Insall-Salvati index. Case courtesy of Dr Wael Nemattalla, Radiopaedia.org, rID: 10329.

Figure 3: Normal lateral knee radiograph demonstrating the typical location of the patella; case courtesy of Dr. Matt Skalski, Radiopaedia.org, rID: 30420.

2. Ultrasound: Useful, but operator dependent and has been associated with a false positive rate of up to 33.3% in one study [2,4].

3. MRI: The gold standard, but may not be feasible or necessary in the emergency department [2]. See Figure 4 below for an MRI demonstrating a rupture of the patellar tendon.

MRI showing a sagittal view of complete rupture of the patellar tendon. Author’s own images

Figure 4. MRI showing a sagittal view of complete rupture of the patellar tendon. Author’s own images.

All patients should be immobilized in a non-hinged knee immobilizer or posterior long leg splint, made non-weight bearing, and given crutches.

Orthopedic surgery does not typically need to be consulted in the emergency department. Patients should be seen by an orthopedic surgeon within two weeks of injury.

  • Pearl: Primary surgical repair for complete rupture should happen within two weeks for optimal outcomes [1,2,6].
  • Pearl: Partial tears may be managed conservatively with immobilization in extension. Chronic tears can be conservatively managed or with reconstructive surgical techniques.

Check out ALiEM’s Paucis Verbis cards to brush up on other can’t miss orthopedic injuries, and SplintER Series or EMrad for more knee injury cases.


  1. Nori S. Quadriceps tendon rupture. J Family Med Prim Care. 2018;7(1):257-260. doi:10.4103/jfmpc.jfmpc_341_16. PMID: 29915772
  2. Tandogan RN, Terzi E, Gomez-Barrena E, Violante B, Kayaalp A. Extensor mechanism ruptures. EFORT Open Rev. 2022;7(6):384-395. Published 2022 May 31. doi:10.1530/EOR-22-0021. PMID 35638613
  3. Hsu H, Siwiec RM. Patellar Tendon Rupture. In: StatPearls. Treasure Island (FL): StatPearls Publishing; April 30, 2022.
  4. Swamy GN, Nanjayan SK, Yallappa S, Bishnoi A, Pickering SA. Is ultrasound diagnosis reliable in acute extensor tendon injuries of the knee?. Acta Orthop Belg. 2012;78(6):764-770. PMID: 23409573
  5. Bartalena T, Rinaldi MF, De Luca C, Rimondi E. Patellar tendon rupture: radiologic and ultrasonographic findings. West J Emerg Med. 2010;11(1):90-91. PMID: 20411086
  6. Matava MJ. Patellar Tendon Ruptures. J Am Acad Orthop Surg. 1996;4(6):287-296. doi:10.5435/00124635-199611000-00001. PMID: 10797196

Author information

Karl Koivisto

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