Age / Sex : 49 / M

Chief complaint: Left ankle injury during badminton two weeks ago

What is your impression?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy of Sang Min Lee, CHA Bundang Medical Center, CHA University

Discussion

Answer: Dislocation of the peroneus longus tendon with Type I injury of the superior peroneal retinaculum

Findings:

<Ankle ultrasonography>

- On neutral position of the foot, normal echogenicity and continuity of the peroneus longus and brevis tendons

- Hypoechoic thickening of the fibular insertion of the superior peroneal retinaculum

- The superior peroneal retinaculum is not torn, but becomes detached from the lateral malleolus together with stripping and elevation of the periosteum to which it is attached, forming a false pouch.

- On dorsiflexion and eversion of the foot, dislocation of the peroneus longus tendon as it moves anteriorly over the lateral malleolus

- Ultrasonographic snapping of the peroneal tendons (real time US sign)

- Fluid accumulation (effusion) in the peroneal synovial sheath

- The peroneus brevis tendon is in retromalleolar area.

Differential Diagnosis:

Diagnosis: Dislocation of the peroneus longus tendon with Type I injury of the superior peroneal retinaculum

Discussion:

1. Introduction

< Mechanism of Injury >

- Injury of the superior peroneal retinaculum (SPR) occurs with peroneal dislocation through forceful ankle dorsiflexion and concomitant reflex peroneal muscle contraction.

e.g. numerous sports activities, particularly snow skiing

- Nontraumatic dislocations:

congenitally - e.g. calcaneovalgus feet

acquired - e.g neuromuscular disease.

< SPR injury, Oden classification >

Type 1 (most common) - the SPR is not torn, but becomes detached from the lateral malleolus together with stripping and elevation of the periosteum to which it is attached, forming a false pouch.

Type II - the SPR is torn near the lateral fibular margin.

Type III - associated avulsion fracture, which may be detected radiographically as a small fleck of bone detached from the lateral fibular margin.

Type IV - tear of the posterior portion of the SPR.

- With any of these types of injury, the incompetent retinaculum can no longer restrain the tendons and recurrent subluxations or dislocations may occur.

- Concomitant lateral ligamentous injuries are frequently seen and may cause ankle instability.

2. Imaging Finding

- US: effective in real-time demonstration of recurrent peroneal subluxation or dislocation.⁴

- MRI: complete assessment of the structures at risk, associated pathology, and diagnostic mimics.

- The diagnosis of dislocation of the peroneal tendons is made when either or both tendons are not identified in their normal anatomic positions posterior to the lateral malleolus and the diagnosis of complete tendon rupture and retraction is excluded.

- With peroneal tendon dislocation, the periosteum is stripped and elevated together with the attached superior peroneal retinaculum, forming a false pouch lateral to the fibular margin. The tendons may reduce, but the SPR remains incompetent, allowing recurrent subluxation and/or dislocation. The resultant abnormal stress leads to tendon degeneration and tearing.

- Identification of periosteal stripping and an abnormal pouch is particularly important in patients with recurrent episodes of tendon subluxation, who may have normally positioned tendons at the time of imaging.

References:

1. Mason RB, Henderson JP. Traumatic peroneal tendon instability. Am J Sports Med. 1996;24(5):652-8.


2. Oden RR. Tendon injuries about the ankle resulting from skiing. Clin Orthop Relat Res. 1987;(216):63-9.


3. Neustadter J, Raikin SM, Nazarian LN. Dynamic sonographic evaluation of peroneal tendon subluxation. AJR Am J Roentgenol. 2004;183(4):985-8.


4. Wang XT, Rosenberg ZS, Mechlin MB, Schweitzer ME. Normal variants and diseases of the peroneal tendons and superior peroneal retinaculum: MR imaging features. RadioGraphics. 2005;25(3):587-602.