Painful Os Peroneum Syndrome (POPS)

Acute Onset Lateral Foot Pain • Xray of the Week

63 y.o. male presented with 1 hour of aching pain on the lateral aspect of the right midfoot after he felt a pop while climbing stairs. He had no loss of sensation, stiffness, or swelling, but pain limited his range of motion. Initial x-rays of the right foot and ankle were taken with a follow up right foot MRI. What is the diagnosis?

Figure 1. Prior oblique (A), current oblique (B) and current frontal (C) radiographs of the right foot.

Figure 2. Prior oblique (A), current oblique (B) and current frontal (C) radiographs of the right foot demonstrate interval migration of an os peroneum from its expected position at the calcaneocuboid joint to the lateral aspect of the calcaneus (red arrows).

Figure 3. Prior (A) and current (B) lateral radiographs of the right foot demonstrate interval posterior migration of an os peroneum from its expected position at the calcaneocuboid joint to the lateral anterior aspect of the calcaneus (red arrows).

Figure 4. Illustration of the normal peroneus longus tendon viewed from the lateral plantar aspect of the foot. The os peroneum is a small ossicle located within the substance of the peroneus longus tendon at the inferolateral aspect of the base of the cuboid. The peroneus longus tendon passes posterior to the lateral malleolus, then curves anteriorly and obliquely down the lateral side of the foot where it curves forward under the fibular trochlea of the calcaneus. The os Peroneum is present in the substance of the The peroneus longus tendon proximal to cuboid tuberosity/tunnel. The peroneus longus tendon then extends under the foot to insert on the inferolateral aspect of the base of the first metatarsal and the distal end of the medial cuneiform. Illustration by Raf Ratinam, MBBS.

Figure 5. Illustration of the ruptured peroneus longus tendon viewed from the lateral plantar aspect of the foot. The os peroneum is retracted due to a complete tear of the peroneus longus tendon at the inferolateral aspect of the base of the cuboid. Illustration by Raf Ratinam, MBBS.

Figure 6: GIF. Axial PD MR images of the right foot demonstrating a complete tear of the peroneus longus tendon (red arrow) with approximately 2 cm gap. The os peroneum (labeled) is retracted to the inferior peroneal retinaculum. Note the distal peroneus longus tendon (yellow arrow) continuing through its anatomical course to the first metatarsal base.

Figure 7: GIF. Sagittal T1 MR images of the right foot demonstrating a complete tear of the peroneus longus tendon (red arrow) with approximately 2 cm gap. The os peroneum (labeled) is retracted to the inferior peroneal retinaculum. Note the distal peroneus longus tendon (yellow arrow) continuing through its anatomical course to the first metatarsal base.

Figure 8: Sagittal T1 MR images of the right foot demonstrating a complete tear of the peroneus longus tendon (red arrow) with approximately 2 cm gap. The os peroneum (labeled) is retracted to the inferior peroneal retinaculum.

Discussion

The os peroneum is an accessory ossicle found within the substance of the peroneus longus tendon. Normally seen in up to 30% of people, the os peroneum is bipartite approximately 30% of the time, and unilaterally ossified approximately 40% of the time [1-2]. Painful Os Peroneum Syndrome (POPS) is a general term to describe pain that results in an array of conditions, including fracture of the ossicle, partial or complete rupture of the peroneus longus tendon [Figs. 5-7], or diastasis of the bipartite ossicle. Primary tenosynovitis or peroneus longus tendinosis can also be a source of pain in this region[2]. POPS should be considered in patients with pain in the lateral midfoot. Palpation over the ossicle will often elicit pain, although physical exam is frequently variable. POPS may be secondary to trauma in an acute setting; however, the initial injury is often missed and the patient can present with chronic pain[1].

Plain radiographs, MRI, and increasingly ultrasound are useful in the diagnosis of POPS. Os peroneum fragment separation of ≥6mm, or proximal displacement of the proximal fragment by ≥10mm from the calcaneocuboid joint on lateral radiograph has 100% concordance with full thickness peroneus longus tendon tear demonstrated by MRI [Figs. 5-7] [3]. Fragment separation of 2 mm or less, or proximal displacement of 8 mm or less is associated with normal tendons, partial thickness tear, or only tendinosis [3]. As seen in this case prior to the peroneus longus tendon rupture, the normal os peroneum location ranges between 7 mm proximal and 8 mm distal to the calcaneocuboid joint [Fig. 3A][3].

The peroneus longus is a powerful evertor of the foot, thus surgical intervention is often necessary to repair a fully torn tendon. Since POPS may arise from a wide spectrum of conditions, the treatment is based upon the specific pathology [4]. Radiologists play an essential role in the diagnosis of POPS, and should be familiar with the appearance of both the normal os peroneum, and the various pathologic processes which may affect this accessory ossicle.

References: 1. Ghagas-Neto FA, Caracas de Souza, BN, Nogueira-Barbosa MH. Painful Os Peroneum Syndrome: Underdiagnosed Condition in the Lateral Midfoot Pain. Case Reports in Radiology 8739362 (2016): 1-4.

2. Oh SJ, Kim YH, Kim SK, et al. Painful Os Peroneum Syndrome Presenting as Lateral Plantar Foot Pain. Annals of Rehabilitation Medicine 36.1 (2012): 163-66.

3. Brigido MK, Fessell DP, Jacobson JA, et al. Radiography and US of os peroneum fractures and associated peroneal tendon injuries: initial experience. Radiology. 2005;237 (1): 235-41.

4. Malhotra R, et al. Peroneal Tendon Pathology Treatment & Management. Medscape, 10 May 2016. Web. 13 Feb. 2017

Jesse Chen, MD

Radiology Resident - Northwell/Staten Island University Hospital

Dr. Chen is a radiology resident (class of 2020) at Staten Island University Hospital. He started residency as a general surgeon at Medstar Washington Hospital Center in DC, but transferred to radiology after 2 years. He graduated Magna Cum Laude from the University of Pennsylvania and then attended medical school at Georgetown University. Dr. Chen is currently the secretary/treasurer of the New York State Radiological Society (NYSRS) Residents and Fellows Section.

Shirley Hanna, MD

Section Chief, Division of Musculoskeletal Imaging - Northwell/Staten Island University Hospital

Certified by the American Board of Radiology in 2011, Dr. Shirley Hanna joined the Northwell/Staten Island University Hospital faculty in 2012 after completing her fellowship in musculoskeletal and breast imaging at Yale-New Haven Hospital. Dr. Hanna graduated Magna Cum Laude from Seton Hall University and attended medical school at Rutgers-New Jersey Medical School where she was a member of ΑΩΑ. Dr. Hanna completed her transitional year of residency at St. Joseph’s Hospital Health Center in Syracuse, NY followed by her radiology residency at Yale-New Haven Hospital. She is now the the section chief of MSK imaging and Associate Chair of Radiology at Northwell/Staten Island University Hospital.

Marlena Jbara, MD

Attending, Division of Musculoskeletal Imaging - Northwell/Staten Island University Hospital

Certified by the American Board of Radiology in 2001, Dr. Marlena Jbara has served as a member of the Bone and Joint division of Radiology at Staten Island University Hospital - Northwell Health since joining the team in 2008. Dr. Jbara, a summa cum laude graduate of the BA-MD Program at the State University of New York, was actively recruited by Dr. Javier Beltran for his nationally recognized MRI musculoskeletal and body fellowship program. Dr. Jbara is a leader in Podiatric Radiology, and has published articles and book chapters on the shoulder, knee and ankle. Her current interests include MRI evaluation of the Diabetic Foot and MR assessment of altered biomechanics, with respect to the foot and ankle.

Cheryl Lin, MD

Attending, Division of Musculoskeletal Imaging - Northwell/Staten Island University Hospital

Certified by the American Board of Radiology in 2012, Dr. Cheryl Lin attended the 7-year BA-MD combined Sophie Davis School of Biomedical Education and graduated from SUNY Downstate College of Medicine, completed diagnostic radiology residency training in Staten Island University Hospital and musculoskeletal radiology fellowship in SUNY Stony Brook University Hospital. Dr. Lin specializes in sports injury imaging, orthopedic oncologic imaging and biopsy, podiatric medicine, musculoskeletal and general ultrasound, and cardiac coronary CTA imaging. She is also Section Chief in General Ultrasonography, and has a special interest in image-guided head/neck biopsies and musculoskeletal interventions such as therapeutic and diagnostic injections of joints and soft tissues.

Ratheesraj (Raf) Ratinam, MBBS

Monash University. Melbourne, Australia

Dr. Raf Ratinam worked for several years as a surgical registrar at Monash Health in Melbourne, Australia. He has taken time away from his clinical work to undertake a PhD in the Department of Anatomy and Developmental Biology at Monash University. The PhD looks at applications of 3-Dimensional printing in hand surgery. Raf has worked for ten years as a medical illustrator and before commencing graduate medicine at Melbourne University he was working full time as an animator. His interests include oil painting, sculpting, calligraphy and archery.

Follow Dr. Ratinam on Twitter @RafRatinam