CASE

A 25-year-old male with no past medical history presented to the Emergency Department with left knee pain after playing basketball. The patient reported that he was struck in the knee while jumping upwards and then twisted his knee as he landed. He complained of significant superior lateral knee pain and swelling, as well as difficulty moving his leg due to pain. On exam, he had notable swelling and tenderness of the left knee, particularly along the superior aspect of the patella. After controlling his pain with intravenous medications, he was able to flex at the hip but was unable to extend his lower leg at the knee or to perform a straight leg raise. He was otherwise neurovascularly intact.

A point of care ultrasound (POCUS) of the knee was performed which obtained a diagnosis prior to x-rays.

DIAGNOSIs

Patellar Tendon Rupture.

The POCUS of the left knee shown below demonstrates a complete tear of the left patellar tendon with surrounding edema (Figure 1). The patient’s atraumatic right patellar tendon was also viewed at the bedside and shown for comparison (Figure 2). Both the right and left patellar tendons are shown in sagittal and transverse planes below.

DISCUSSION

The classic clinical presentation of a complete patellar tendon rupture consists of sudden pain, knee swelling, inability to actively extend the leg at the knee and a high-riding patella on exam or on x-ray. [1] However, significant pain and swelling that limit physical exam can make this diagnosis more difficult at the bedside. POCUS is a rapid, low-cost diagnostic which enables evaluation of the soft tissue structures of the knee, especially the superficial structures, including the patellar tendon. [2] A ruptured tendon appears hypoechoic and with discontinuity of the tendinous fibers, often times with additional hypoechoic edema or hematoma. Partial patellar tendon tears, in contrast, show anechoic or hypoechoic clefts rather than total fiber disruption. [3] Viewing the contralateral, atraumatic knee at the time of point of care ultrasound can aid in the diagnosis of tendon rupture or injury, similar to the case above. For example, measuring the width of the tendon compared to the uninjured, contralateral side will demonstrate a larger width in the retracted full thickness patellar tendon tears, increased diffraction shadowing, and a wavy appearance compared to a thin, linear and hyperechoic appearance of the normal tendon. [3] In a prospective study of tendon injuries across multiple anatomical sites, bedside ultrasound was found to be more sensitive and specific than physical examination for detecting tendon injuries and led to a faster time to diagnosis than MRI or local wound exploration. [4]

CASE RESOLUTION

The case and ultrasound findings were discussed with the orthopedics team who agreed the patient could be discharged home with outpatient follow up. The patient was sent home in a knee immobilizer with weight bearing as tolerated and was seen the following week in the orthopedics office. He had a second ultrasound as an outpatient with radiology to evaluate the injury pre-operatively and then underwent surgical repair of the left patellar tendon 10 days following his initial injury. 

TAKE AWAYS

• Patellar tendon injuries, among other soft tissue knee injuries, can be accurately and rapidly evaluated with POCUS by emergency medicine physicians 

• Patellar tendon ruptures cause hypoechoic edema or total disruption of the tendinous fibers which can be identified with POCUS

• To examine a patellar tendon, use a linear probe for high resolution imaging and consider using the contralateral knee as a control

KEY WORDS: Knee exam, patellar tendon rupture, point of care ultrasound

AUTHOR: Katherine Stewart, MD is a second-year Emergency Medicine resident at Brown University/Rhode Island Hospital.

FACULTY REVIEWER: Kristin Dwyer, MD is the Director of Ultrasound Division of Brown Emergency Medicine

References

1. Phillips K, Costantino TG. Diagnosis of patellar tendon rupture by emergency ultrasound. J Emerg Med. 2014;47(2):204-206. doi:10.1016/j.jemermed.2014.02.012

2. Ogle K, Mandoorah S, Fellin M, Shokoohi H, Probasco W, Boniface K. Point-of-care Ultrasound Diagnosis of Bilateral Patellar Tendon Rupture. Clin Pract Cases Emerg Med. 2020;4(1):29-31.

3. Berg K, Peck J, Boulger C, Bahner DP. Patellar tendon rupture: an ultrasound case report. BMJ Case Rep. 2013;2013:bcr2012008189. 

4. Wu TS, Roque PJ, Green J, et al. Bedside ultrasound evaluation of tendon injuries. Am J Emerg Med. 2012;30(8):1617-1621.