Longitudinal Split of the Peroneus Longus and Peroneus Brevis Tendons with Disruption of the Superior Peroneal Retinaculum

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1 Longitudinal Split of the Peroneus Longus and Peroneus Brevis Tendons with Disruption of the Superior Peroneal Retinaculum Gregory C. Diaz, MD, Marnix van Holsbeeck, MD, Jon A. Jacobson, MD Longitudinal split and subluxation of the peroneus brevis tendon have been reported in surgery literature, but few publications report on longitudinal tears of the peroneus longus tendon. The most likely proposed mechanism is a mechanical one. This report discusses the ultrasonographic appearance of peroneus longus and peroneus brevis tendon splits and the mechanism of injury. ABBREVIATIONS MR, Magnetic resonance; CT, Computed tomography Received August 8, 1997, from the Department of Radiology, Henry Ford Hospital, Detroit, Michigan (G.C.D., M.v.H); and the Department of Radiology, University of Michigan Medical Center, Ann Arbor, Michigan (J.A.J.). Revised manuscript accepted for publication May 16, Address correspondence and reprint requests to Marnix van Holsbeeck, MD, Department of Radiology, Henry Ford Hospital, 2700 West Grand Boulevard, Detroit, MI CASE REPORT A 56 year old man was referred with 2 weeks of progressive pain and swelling of his left ankle. He described the discomfort as a burning along the lateral aspect of his ankle, radiating up the back of his calf. He had no history of acute injury. By physical examination, he was obese and walked with a shuffling gait, leaning somewhat to the left. Observation of foot alignment showed eversion of the left foot and ankle. He had swelling of the soft tissues around his lateral malleolus. A radiograph of his left ankle showed a fragment of avulsed bone at the lateral aspect of the lateral malleolus (Fig. 1). The location of the fragment suggested avulsion of the superior peroneal retinaculum. Ultrasonography of the left ankle demonstrated significant swelling of the peroneus longus and peroneus brevis tendons (Fig. 2), which were three to four times normal size when compared to the asymptomatic side (Figs. 3, 4). All sonographic images were obtained with a 10 MHz compact linear probe. Within each peroneal tendon sonograms showed abnormal central hypoechogenity on transverse images (Fig. 5) and hypoechoic clefts within the tendon axis longitudinally (Fig. 6). The split peroneus longus tendon showed a characteristic C shape, which Deely and associates described as boomerang-shaped. 1 Beltran and coworkers described the tendon as partially wrapping around the peroneus longus tendon, which we were able to demonstrate. 2 Similar to the cases reported by Beltran and coworkers the tears were centered at the retromalleolar groove. 2 Abnormal lateral subluxation of the tendons rela by the American Institute of Ultrasound in Medicine J Ultrasound Med 17: , /98/$3.50

2 526 LONGITUDINAL SPLIT OF PERONEAL TENDONS J Ultrasound Med 17: , 1998 tive to the lateral malleolus was noted in ankle dorsiflexion and eversion (Fig. 2B).The avulsed fibular fragment was visualized by sonography in the expected location of the superior peroneal retinaculum (Fig. 6). The patient underwent elective debridement and repair of longitudinal splits of the peroneus longus and peroneus brevis tendons 4 1 / 2 months after his initial examination. His avulsed superior peroneal retinaculum was also reattached. He was placed in a non weight-bearing soft cast. The cast was removed 7 weeks later. No edema was present. The patient was very comfortable, walking with a mildly antalgic gait. He had fully recovered from his injury and surgery 1 1 / 2 years after the injury. DISCUSSION Ultrasonography allowed us to diagnose peroneal tendon instability and longitudinal splitting of the peroneus longus and peroneus brevis tendons. The finding of an avulsion fracture at the insertion of the superior peroneal retinaculum suggested the mechanism for the pathology. This information was found valuable for the surgical planning. 3 Disruption of the superior peroneal retinaculum is a predisposing factor for peroneal tendon subluxation. 4 This lateral displacement positions the tendons over the sharp posterior edge of the fibula, resulting in a longitudinal tendon tear or split. 5 Other proposed mechanisms for peroneal tendon subluxation predisposing to tear include anatomic factors, such as a shallow fibular groove, a prominent calcaneofibular ligament, and congenital absence of the superior peroneal retinaculum. Hyperelasticity or laxity of the superior peroneal retinaculum secondary to chronic pronation of a paralyzed extremity is another cause, as well as mechanical crowding in the fibular malleolar groove due to a low lying muscle belly of the peroneus brevis or the presence of a peroneus quartus muscle. 2 Similar to MR imaging, most of these features can be seen with ultrasonography. Ebraheim and colleagues state that an avulsion fracture of the posterior lateral portion of the fibula at the insertion of the superior peroneal retinaculum is pathognomonic for subluxation of the peroneal tendons. 6 The bone fragment is easiest to identify on the anterposterior or the internal oblique views on standard radiographs. 6 It is also diagnosed on CT. 5 However, this fracture is seen in only 15 to 50% of injuries to the superior peroneal retinaculum. 4 Without a fracture, ultrasonography can still demonstrate retinacular injury. The retinaculum can be torn, leaving an abnormal hypoechoic space anterior to the tendons on the transverse views. 7 Many mechanisms of injury of the superior peroneal retinaculum have been proposed, including eversion, 5,8 inversion, 9,10 dorsiflexion, plantar flexion, 9 or a combination of these. 4 Laxity of the superior peroneal retinaculum combined with forceful contraction of the peroneus longus tendon causes the peroneus brevis tendon to splay out and split from prolonged mechanical attrition. 5 In our case, as well as in other reports, eversion and dorsiflexion were able to reproduce the abnormal subluxation of the tendons. 5,11 Longitudinal tears of peroneus longus tendons are rare in comparison with longitudinal tears of the peroneus brevis tendons. 12 However, Sobel and associates reported a peroneus longus tendon to have a frayed surface of its inner aspect that corresponded to the portion of the tendon which was in contact with the fibula through a split in the adjacent peroneus brevis tendon tear. 12 Figure 1 Anteroposterior radiographic image showing fragment of avulsed bone (arrow) at the lateral aspect of lateral malleolus is pathognomonic of avulsion at the attachment site of the superior peroneal retinaculum.

3 J Ultrasound Med 17: , 1998 DIAZ ET AL 527 A Figure 2 Transverse sonograms, and corresponding linear diagrams, demonstrate swelling of the peroneus longus tendon (white arrowhead; thick arrow in diagram) and peroneal brevis tendon (white arrowhead; thin arrow in diagram). Note the hypoechoic boomerang shape of the peroneus brevis tendon. F, Fibula; T, talus. The tendons are displayed subluxed laterally during dorsiflexion and eversion in (B), as evidenced by the difference in contour of the fibular cortex when compared to the ankle as shown in a neutral position in (A). B In summary, we propose ultrasonography as an effective means to affirm a suggestion or solidify the diagnosis of longitudinal tears of the peroneus longus and peroneus brevis tendons. Tendon size, shape, location, and integrity, as well as associated anatomic abnormality and variants, can be assessed with ultrasonography. Additionally, provocative maneuvers such as ankle dorsiflexion and eversion may demonstrate transient tendon subluxation only diagnosed with dynamic ultrasonography. Identification of the avulsed fibular fragment at the insertion of the superior peroneal retinaculum also aids in this diagnosis. These parameters allowed us to make a correct preoperative diagnosis of longitudinally split and unstable peroneus longus and peroneus brevis tendons.

4 528 LONGITUDINAL SPLIT OF PERONEAL TENDONS J Ultrasound Med 17: , 1998 Figure 3 Transverse sonogram and corresponding linear diagram of normal peroneus longus tendon (thick arrow) and peroneus brevis tendon (thin arrow). F, Fibula. Figure 4 Longitudinal sonogram and corresponding linear diagram of normal peroneus longus tendon (thick arrow) and peroneus brevis tendon (thin arrow). F, Fibula. Figure 5 Transverse sonogram shows thickened tendon sheath (curved open arrow); peroneus brevis tendon (long thin arrow), with hyperechoic region being a normal part of the tendon; avulsed bone (closed arrow); and hypoechoic peroneus longus tendon (short open arrow), consistent with a surgically proven tear. Figure 6 Longitudinal sonogram of peroneus longus tendon (curved arrow) shows enlargement (three to four times normal size), with multiple hypoechoic clefts. The avulsed fibular fragment (solid arrow) is seen at the site of attachment of the superior peroneal retinaculum.

5 J Ultrasound Med 17: , 1998 DIAZ ET AL 529 REFERENCES 1. Deely D, Ed M, Hecht P, et al: Using MR imaging to differentiate peroneal splits from other peroneal disorders. AJR 168:129, Beltran J, Cheung Y, Colon E, et al: MR features of longitudinal tears of the peroneus brevis tendon. AJR 168:141, van Holsbeeck M, Introcaso J, Kolowich P: Sonography of tendons: Patterns of disease. Instructional Course Lect 43:475, Butler B, Lanthier J, Wertheimer S: Subluxing peroneals: A review of the literature and case report. J Foot Ankle Surg 32:134, Sobel M, Geppert M, Olsen E, et al: The dynamics of peroneus brevis tendon splits: A proposed mechanism, technique of diagnosis, classification of injury. Foot Ankle 13:7, Ebraheim N, Zeiss J, Skie M, et al: Marginal fractures of the lateral malleolus in association with other fractures in the ankle region. Foot Ankle 13:4, van Holsbeeck, Introcaso JH: Musculoskeletal Ultrasound. 2nd Ed. St. Louis, Mosby Year Book (in press) 8. Davis W, Sobel M, Deland J, et al: The superior peroneal retinaculum: An anatomic study. Foot Ankle Int 15:5, Bassett F III, Speer K: Longitudinal rupture of the peroneal tendons. Am J Sports Med 23:3, Geppert M, Sobel M, Bohne W: Lateral ankle instability as a cause of superior peroneal retinacular laxity: An anatomic and biomechanical study of cadaveric feet. Foot Ankle 14:6, Sobel M, Geppert M, Warren R: Chronic ankle instability as a cause of peroneal tendon injury. Clin Orthop 296:187, Sobel M, DiCarlo E, Bohne E, et al: Longitudinal splitting of the peroneus brevis tendon: An anatomic and histologic study of cadaveric material. Foot Ankle 12:3, 1991 ERRATUM In the letter to the editor that appeared in the May 1998 issue of the Journal of Ultrasound in Medicine (J Ultrasound Med 17:340), a line of text was inadvertently omitted from the reply by Yang and Yuen. The first three sentences of paragraph 2 should have read as follows: We agree that malignancy and technical difficulty are indications for oophorectomy in premenopausal women. However, they are not the only indications. Clinical diagnosis or suspicion of malignancy is based on a combination of clinical history, menopausal state, tumor markers and sonographic appearance. 2 5