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Persistent lateral foot pain.

Radiology Case of the Month

Presentation on page 182

DIAGNOSIS: Os Peroneum Syndrome

INTERPRETATION OF IMAGES

MR (Figure 1A) axial T1 weighted image demonstrates abnormal marrow signal within the os peroneum consistent with edema. MR (Figure 1B) axial proton density with fat saturation demonstrates edema of the os peroneum as the sesamoid courses within the peroneus longus tendon. (Figure 2) Coronal proton density with fat saturation further demonstrates edema of the soft tissues surrounding the tendon sheath. Correlating oblique radiograph (Figure 3) of the right foot demonstrates long curvilinear os peroneum along the anterolateral margin of the cuboid.

DISCUSSION

The os peroneum is a round or oval-shaped juxta-articular sesamoid bone that lies within the confines of the peroneus longus tendon. The sesamoid bone forms as the result of ossification of a fibrocartilaginous thickening within the peroneus longus tendon as it courses through the cuboid notch, which serves to protect the tendon from shear forces. (1,2) The cuboid notch is the location where the peroneus longus tendon is at greatest risk for injury due to the rapid change in its direction as it travels towards insertion on the the first ray. (2) Although the os peroneum is protective against shear forces and is thus physiologic in most individuals, its inherent rigidity may occasionally increase risk of peroneus longus tendon pathology. Whereas a fibrocartilaginous thickening of the peroneus longus tendon is universally present, ossification and formation of an os peroneum is seen within 5%-26% of individuals with a slight male predominance. (1) Ossification of this sesamoid bone occurs bilaterally within 60% of the affected patients and is bipartite within approximately 30%. (3)

Patients with painful os peroneum syndrome present with lateral foot pain that is attributed to a variety of derangements of the os peroneum and/or the peroneus longus tendon. Sobel et al described the etiology of the pain syndrome consisting of one or more of the following: creation of a discontinuity of the peroneus longus tendon either by acute fracture of the os peroneum or a diastasis through a multipartite os peroneum, chronic diastasis and/or a healing fracture of the os peroneum eventually leading to callus formation and peroneus longus tenosynovitis, attrition of the peroneus longus tendon, rupture of the peroneus longus tendon, or an associated enlarged peroneal tubercle on the lateral aspect of the calcaneus that entraps the peroneus longus tendon and the os peroneum during excursion of the peroneus longus tendon. (1)

Acute presentation is most often due to the sudden rupture of the peroneus longus tendon or diastasis of multipartite fragments. The pain of chronic os peroneal syndrome is similar to that of a sprained ankle and may persist for many years before diagnosis. This chronic presentation is generally due to erosion of the peroneus longus tendon or prolonged healing of an os peroneum fracture. Pain is typically localized to the distal peroneus longus tendon as it travels along the posterolateral aspect of the cuboid. (4) Symptoms include tenderness and soft-tissue swelling along the distal peroneus longus tendon. Localization of tenderness is aided by resisted plantar flexion of the first ray. (5) Numbness and paresthesias may develop secondary to sural nerve entrapment. (6)

Misdiagnosis of os peroneum pain syndrome may have significant consequences, including ankle instability and peroneal compartment syndrome. (3) This syndrome should be included in the differential diagnosis for all patients presenting with lateral ankle pain and instability, especially in the context of recent trauma. (7) On plain radiograph, the os peroneum may have a sclerotic appearance. Axial computed tomography, magnetic resonance imaging, and radionucleotide scans are commonly used diagnostic modalities. Bone scan may be helpful in diagnosis, demonstrating increased radiotracer uptake within the region of the os peroneum. (6) With image interpretation one must be aware that the os peroneum may be present as bipartite or multipartite, both of which may be confused with fractures on radiographs. (7)

Consensus guidelines for treatment do not currently exist. Acute management includes immobilization, non-steroidal anti-inflammatory medications, and steroid injections. In patients with persistent pain surgical intervention may be indicated. (4)

REFERENCES

(1.) Sobel, M, et al. "Painful Os Peroneum Syndrome: A Spectrum of Conditions Responsible for Plantar Lateral Foot Pain." Foot & Ankle 15.3 (1994): 112-24.

(2.) Marx, JA., Hockberger, RS, Walls, RM, Adams, J, and Rosen, P. Rosen's Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia: Mosby/Elsevier, 2010.

(3.) Fujioka, H, et al. "Subcutaneous Peroneus Longus Tendon Rupture Associated with Os Peroneum Fracture." Journal of Sports Science and Medicine 8 (2009): 705-08.

(4.) Blitz, NM, and Nemes, KK. "Bilateral Peroneus Longus Tendon Rupture Through a Bipartite Os Peroneum." Journal of Foot and Ankle Surgery 46.4 (2007): 270-77.

(5.) Canale, ST., and Campbell WC. Campbell's Operative Orthopaedics. 11th ed. St. Louis: Mosby, 2007.

(6.) Requejo, SM, Kulig, K, and Thordarson, DB. "Management of Foot Pain Associated With Accessory Bones of the Foot: Two Clinical Case Reports." Journal of Orthopaedic & Sports Physical Therapy 30.10 (2000): 580-94.

(7.) DeLee, J, Drez, D and Miller, MD. DeLee & Drez's Orthopaedic Sports Medicine: Principles and Practice. 3rd ed. Philadelphia: Saunders/Elsevier, 2009.

Chris Stark, BS; Neel D. Gupta, MD; Michael Serou, MD; Harold Neitzschman, MD ([dagger])

([dagger]) Deceased

Stark is a fourth year medical student at Tulane University School of Medicine in New Orleans, Louisiana; Dr. Gupta is a third year Radiology resident at Tulane University Health Sciences Center in New Orleans, Louisiana; Dr. Serou is musculoskeletal radiologist at Tulane University Health Sciences Center in New Orleans, Louisiana; Dr. Neitzschman was a professor of Radiology and the Chairman of the Department of Radiology at Tulane University Health Sciences Center in New Orleans, Louisiana; Olivares is the Digital Imaging Specialist and Graphic Designer for the Department of Radiology at Tulane University Health Sciences Center in New Orleans, Louisiana.
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Title Annotation:RADIOLOGY CASE OF THE MONTH
Author:Stark, Chris; Gupta, Neel D.; Serou, Michael; Neitzschman, Harold
Publication:The Journal of the Louisiana State Medical Society
Article Type:Clinical report
Date:Sep 1, 2016
Words:962
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