Laboratory Studies
Laboratory studies are infrequently used in evaluating a patient for peroneal tendon pathology. If infection is a consideration, a complete blood count (CBC) with differential, an erythrocyte sedimentation rate (ESR), and a C-reactive protein (CRP) level may be obtained. Likewise, if undiagnosed rheumatologic disease is suspected, screening laboratory tests may be indicated.
Imaging Studies
Plain radiography
Standard radiographs [18] of the foot and ankle, including weightbearing anteroposterior (AP), lateral, and mortise views, are usually obtained first. These can reveal fractures, large osteochondral defects of the talus, spurring of the retrofibular groove, lateral ankle impingement, and hypertrophy of the peroneal tubercle. Acute injuries with avulsion of the superior peroneal retinaculum (SPR) insertion on the fibula may demonstrate a characteristic "fleck" sign. Dislocation of the peroneal tendons should be considered in talus and calcaneus fractures. [19, 20]
Plain radiographs are also used to assess the hindfoot for arthritis that may contribute to the pain. Stress radiographs can rule out the presence of ankle instability.
Although the tendons cannot be imaged directly by means of radiography, the presence of an os peroneum fracture or proximal migration of the os peroneum is suggestive of peroneus longus rupture.
The os peroneum is best visualized on the oblique radiograph of the foot; it is less well seen on the other standard foot films. The AP view of the foot can reveal a fracture of the base of the fifth metatarsal, suggesting avulsion of the peroneus brevis insertion. The Harris view may be useful for demonstrating an enlarged peroneal tubercle on the calcaneus. The Canale view is used for visualizing the talar neck.
Tenography
Tenography is infrequently used but may be of benefit if combined with anesthetic injection into the tendon sheath for diagnostic purposes. It has been shown to be useful for demonstrating peroneal tendon impingement in patients with lateral ankle pain after calcaneal fracture. [21]
Magnetic resonance imaging
Magnetic resonance imaging (MRI) has been the imaging modality of choice for the peroneal tendons. [22, 23, 24] MRI features of normal variants and diseases of the peroneal tendons, as well as the SPR, have been very elegantly demonstrated. [25] (See the images below.) Increased fluid within the tendon sheath, tenosynovitis, or the presence of scar tissue may be apparent on MRI. Dynamic MRI can detect dislocatable peroneal tendons.
Appearance of normal peroneal tendons on MRI. Axial turbo spin-echo (TSE) T1-weighted image (left) shows peroneus brevis (short arrow). TSE proton density (PD)-weighted fat-suppressed (FS) image (center) shows peroneus longus (arrowhead). Sagittal TSE T2-weighted FS image (right) shows peroneus longus (arrowhead).
Axial turbo spin echo (TSE) T1-weighted and TSE T2-weighted fat-suppressed (FS) MRI shows split of peroneus brevis tendon into two subtendons.
Longitudinal tears in the peroneus brevis have been readily identified on MRI. In addition, associated findings on MRI have been described for peroneus brevis tears. These include chevron-shaped tendon, high signal, flat peroneal groove, abnormal lateral ligaments, and fibular spurring.
The peroneus quartus muscle, which, when present, may contribute to attritional rupture of the peroneus brevis, can be noted on MRI as well. MRI also is excellent in imaging ruptures of the peroneus longus tendon. With peroneal tendon subluxation, MRI may allow identification of a small avulsion of the posterolateral fibula or redundancy of the SPR to aid in diagnosis. MRI is also invaluable in the diagnosis of ligament disorders, the grading of SPR injuries, the evaluation of the retrofibular groove, and the definition of tendon contours. (See the images below.)
Turbo spin-echo (TSE) T1-weighted MRI shows hypointense peroneus quartus tendon (arrow) with muscle belly seen posterior to peroneus longus and peroneus brevis tendon.
Coronal short TI inversion recovery (STIR)-sequence MRI shows hyperintense calcaneofibular ligament at fibular attachment (left) and calcaneal attachment (right).
One must be familiar with the “magic-angle phenomenon,” in which fibers of the tendon, when oriented 55º to the magnetic field axis, show an artifact appearing as an intratendinous signal that can be mistaken for tenosynovitis, degeneration, or tearing of the tendon.
However, a study comparing preoperative MRI findings with intraoperative findings for peroneal tendon pathologies found significant discordance between the former and the latter. [26] The authors accordingly suggested caution in relying on MRI in the evaluation of these pathologies.
Computed tomography
Computed tomography (CT) may show retrofibular groove anatomy, small avulsion fractures (fleck sign), and os peroneum pathology. (See the image below.) Axial CT images can reveal peroneal tendon dislocation. Three-dimensional (3D) color volume-rendered CT imaging of the ankle was studied by Ohashi et al in cases of peroneal tendon dislocation associated with acute calcaneal fractures but was found to be not as good as multiplanar imaging for the diagnosis of peroneal tendon dislocation in these patients. [27]
Plain lateral radiograph (left) shows os peroneum. Axial CT (right) shows os peroneum adjacent to cuboid bone .
Ultrasonography
Ultrasonography (US) is rapidly gaining popularity for the evaluation of peroneal tendon disorders. It is easily available, inexpensive, noninvasive, and free of ionizing radiation, though it is operator-dependent and has a substantial learning curve.
US can reveal tendon thickening, partial or complete ruptures, and fluid around tendons. Moreover, it allows dynamic real-time evaluation of peroneal subluxation on provocative maneuvers and tendon splits that may be missed on MRI. US has been reported to be more sensitive and accurate than MRI for the diagnosis of tendon lesions around the ankle. [28]
Procedures
If peroneal tendon pathology is suspected, local anesthetic may be injected into the tendon sheath to aid in the diagnosis. Mizel et al injected bupivacaine mixed with contrast material into the peroneal tendon sheath to ensure accurate placement. [29] Frequently, injections communicated with the ankle or subtalar joints, raising questions about the purity of the results.
Peroneal tendoscopy has been employed to diagnose the peroneal tendon pathologies. Tendoscopy allows exploration of the whole tendon surface from the myotendinous junction to the peroneal tubercle, using a minimally invasive approach that reduces the likelihood of postoperative scarring and nerve entrapment. Moreover, it allows dynamic evaluation of peroneal tendons under direct visualization by passive movements at the ankle. [30]
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Lateral view of ankle, with marking of distal fibula, base of fifth metatarsal, and intended incision.
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Peroneus brevis degeneration forming ganglion-type mass.
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Peroneus longus tendon next to peroneus brevis tendon.
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Peroneus brevis above after resection of degenerative mass and peroneus longus below.
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Partial repair of peroneal tendon sheath.
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Repaired peroneal tendon sheath.
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Skin closed over peroneal tendon repair.
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Cystic mass (ganglion) on right arising from peroneal tendon (×40).
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Ganglion with myxoid degeneration and connective tissue with myxoid material pools with cystic change (×400).
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Appearance of normal peroneal tendons on MRI. Axial turbo spin-echo (TSE) T1-weighted image (left) shows peroneus brevis (short arrow). TSE proton density (PD)-weighted fat-suppressed (FS) image (center) shows peroneus longus (arrowhead). Sagittal TSE T2-weighted FS image (right) shows peroneus longus (arrowhead).
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Turbo spin-echo (TSE) T1-weighted MRI shows hypointense peroneus quartus tendon (arrow) with muscle belly seen posterior to peroneus longus and peroneus brevis tendon.
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Plain lateral radiograph (left) shows os peroneum. Axial CT (right) shows os peroneum adjacent to cuboid bone .
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Axial turbo spin echo (TSE) T1-weighted and TSE T2-weighted fat-suppressed (FS) MRI shows split of peroneus brevis tendon into two subtendons.
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Coronal short TI inversion recovery (STIR)-sequence MRI shows hyperintense calcaneofibular ligament at fibular attachment (left) and calcaneal attachment (right).
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Ganglion arising from peroneal tendon sheath as cause of painful swelling. Left image shows palpable tender swelling behind lateral malleolus; center image shows ganglion as seen intraoperatively; right image is view after excision.
