patella alta

A 27-year-old female presents with left knee pain after a low-speed motor vehicle collision in which her knee hit the dashboard. She is tender over the patella without significant effusion and has an intact extensor mechanism. The above x-ray was obtained (Image 1. X-ray left knee. Case courtesy of Dr. M. Mourits, Radiopaedia.org, rID: 14476). 

 

 

Patella alta, which in this case is a congenital/developmental abnormality not caused by the recent trauma.

  • Pearl: Patella alta is diagnosed using the Insall-Salvati ratio, which compares the length of the patellar tendon to the pole-to-pole length of the patella (Image 2). A normal ratio (Tendon/Patella) is 0.8-1.2, with anything greater indicating patella alta and anything less patella baja.

Image 2. Insall-Salvatti ratio. Case courtesy of Dr. Wael Nemattalla, Radiopaedia.org, rID: 10329

A patellar tendon rupture can present with the same finding, as the ruptured tendon allows the patella to move proximally (Image 3).

Patella tendon rupture

Image 3. Ruptured patellar tendon – note the avulsed fragments at the inferior pole of the patella. Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 7514

  • Pearl: To verify tendon integrity, an intact extensor mechanism, exhibited by a straight leg raise, and/or ultrasound can be used (Image 4).

Image 4. Intact patellar tendon, courtesy of Joy English, MD

Due to its abnormal positioning, patients with patella alta are at an increased risk for recurrent dislocation, joint effusions, patellofemoral pain, and patellofemoral osteoarthritis [1,2].
Given an intact extensor mechanism and no other findings on exam, this patient likely suffered a contusion and can be made weight-bearing as tolerated and discharged with follow-up as needed. Surgical treatment is generally reserved for patients with severe symptoms.

 

Resources & References:

Don’t forget to brush up on these other can’t miss adult knee injuries

  1. Insall J, Goldberg V, Salvati E. Recurrent dislocation and the high-riding patella. Clin Orthop Relat Res. 1972;88:67-9. PMID: 5086583.
  2. Stefanik JJ, Zhu Y, Zumwalt AC, Gross KD, Clancy M, Lynch JA, Frey Law LA, Lewis CE, Roemer FW, Powers CM, Guermazi A, Felson DT. Association between patella alta and the prevalence and worsening of structural features of patellofemoral joint osteoarthritis: the multicenter osteoarthritis study. Arthritis Care Res (Hoboken). 2010 Sep;62(9):1258-65. PMID: 20506169.
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Mark Hopkins, MD

Mark Hopkins, MD

Loma Linda University Health
Mark Hopkins, MD

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Alexander J. Tomesch, MD

Alexander J. Tomesch, MD

Primary Care Sports Medicine Fellow
Department of Orthopedic and Sports Medicine
University of Arizona - Tucson
Alexander J. Tomesch, MD

@DocTomesch

Emergency Medicine physician, Primary Care Sports Medicine Fellow, Father, Husband, Sports Enthusiast, Craft Beer Lover!
Alexander J. Tomesch, MD

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William Denq, MD CAQ-SM

William Denq, MD CAQ-SM

Assistant Professor
Department of Emergency Medicine
University of Arizona
William Denq, MD CAQ-SM

@willdenq

Clinical Assistant Professor Emergency Medicine and Sports Medicine University of Arizona George Washington University '18 University of Pittsburgh '14 and '10
William Denq, MD CAQ-SM

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