Sonographic Evaluation and Sonographic-Guided Therapeutic Options of Lateral Ankle Pain: Peroneal Tendon Pathology Associated with the Presence of an Os Peroneum
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- Sofka, C.M., Adler, R.S., Saboeiro, G.R. et al. HSS Jrnl (2010) 6: 177. doi:10.1007/s11420-010-9154-3
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Clinical implications of acute injuries of the os peroneum have been described, with the recommendation in some cases being the excision of the bone fragments. We describe the spectrum of sonographic appearances associated with pain in the region of the os peroneum, document associated peroneal tendon pathology, and describe the use of sonography to direct and guide therapeutic and/or diagnostic injections. All sonographic examinations in our ultrasound database from Jan 1, 2001–Jan 30, 2007 with the words “os peroneum” were reviewed. Patients were cross-referenced in our radiology database to find relevant foot or ankle radiographs for correlation. There were 47 patients (18 men and 29 women, age range 16 to 83) referred for sonographic evaluation of lateral foot and/or ankle pain who had an os peroneum identified during the sonographic evaluation. Eighteen patients were referred specifically for targeted injection of the lateral ankle, including peroneal tendon sheath injections (N = 10), calcaneocuboid joint injections (N = 1), and injections around symptomatic os peroneum (N = 7). All 47 patients had tendinosis of the peroneus longus, in varying degrees of severity. Radiographs were available for correlation in 28 patients. The causes of lateral ankle pain with a co-existent os peroneum are multifactorial and may not directly relate to the presence of an os peroneum. Ultrasound can be of value in separating out the specific etiology for pain, as well as provide a method for problem solving by the performance of targeted diagnostic or therapeutic injections in the lateral ankle.
Keywordsultrasoundos peroneumperoneal tendons
Plantar, lateral foot pain is a common presenting symptom to foot and ankle clinics, and while there are many causes of lateral foot pain, including peroneal tendinopathy, arthritis, and anterolateral ankle impingement, pathology related to the os peroneum is an often overlooked cause of plantar lateral foot pain.
Ultrasound has been shown to be highly efficacious in evaluating foot and ankle pain, especially tendinopathy and tendon tears . High-resolution ultrasound can also be used to evaluate the presence of mineralization, such as calcification or, in the setting of accessory ossicles, cortical bone.
We describe the sonographic appearance of pain in the region of the os peroneum and associated peroneal tendon pathology as well as define the role of sonography in directing treatment options for patients with what may present as a painful “os peroneum syndrome” . The aims of our review were (1) to characterize the types of tendon pathology associated with the presence of an os peroneum and (2) to assess the use of ultrasound in performing therapeutic injections about the os peroneum.
Materials and methods
The study received the Institutional Review Board approval, and waiver of informed consent was obtained. From our ultrasound database, we retrospectively reviewed all foot and ankle ultrasounds performed between January 1, 2001, and January 30, 2007, for the key phrase “os peroneum.” All cases were cross-referenced in our imaging database for foot and ankle radiographs performed within 6 months of the ultrasound exams, if available, for correlation.
Ultrasound examinations (N = 50) were performed by a fellowship trained musculoskeletal radiologist with special expertise in musculoskeletal imaging using either a Siemens Elegra (Siemens Medical Solutions, Mountainview, CA, USA) or a Philips iU22 (Philips Medical Systems N.A. Bothell, WA, USA) in patients with a history of plantar, lateral foot pain. Exams were performed using a high frequency (12–17 MHz) linear transducer.
The peroneal tendons were identified and were analyzed using previously published criteria for tendon morphology . A tendon was considered normal if it had the usual appearance of a compact linear band of echogenic (“bright”) tissue containing a fine internal mixed hypo-/hyperechoic fibrillar pattern and as abnormal when thickened and of decreased echogenicity; tears were identified when discrete defects or gaps in the tendon were observed . The degree of tendon degeneration was not standardized between observers; however, all of the sonologists were trained similarly and, anecdotally, have a reasonably high interobserver reliability.
A subset of patients (N = 18) were specifically referred for either peroneal tendon sheath injection or os peroneum injection. For the injections, a short 25-gauge needle was used via a short-axis (transverse) approach. A 2-cm3 mixture of 0.5 cm3 1% lidocaine (Abbot Laboratories, North Chicago, IL, USA), 0.5 cm3 0.5% bupivacaine (Sensorcaine, Astra Pharmaceuticals, Westborough, MA, USA), and 1 cm3 triamcinolone (Kenalog, 40 mg/1 mL) (Apothecon, a Bristol-Myers Squibb Company, Princeton, NJ, USA) was injected into the peroneal tendon sheath, with slightly less total volume injected around the os peroneum. Ten patients had the peroneal tendon sheath injected (three men and seven women, age range 27–83 years), and seven had injections around the os (two men and five women, age range 16–57 years.) One patient was referred for injection specifically of the calcaneocuboid joint.
Standing anteroposterior and lateral radiographs of the foot or ankle were available for review in 28 patients. Lateral ankle radiographs included the base of the fifth metatarsal and calcaneocuboid joint in all cases. The radiographs were evaluated independently by two fellowship-trained musculoskeletal radiologists, blinded to the ultrasound findings. Os peroneum morphology was evaluated using the method of Sobel et al. . Os peroneii were categorized as singular, bipartite, or multipartite, with the morphology of each fragment described as round or elongated, smooth, or fragmented. The relationship of the os to the calcaneocuboid joint and cuboid tunnel was also noted.
Os peroneum size and morphology (number of cases)
Os peroneum size and peroneal tendon pathology
Size of os (on X-ray)
Peroneal tendinosis only
Tendinosis ± tears
A painful os peroneum syndrome is a common cause of plantar, lateral foot pain, which can be caused by a spectrum of conditions such as os peroneum fracture, diastasis of a multipartite os peroneum, leading to stenosing tenosynovitis of the peroneus longus or attrition or tear of the peroneus longus  (Fig. 3). The prevalence of os peroneii is debated, with variable numbers reported in the literature. One cadaver study demonstrated a 90% prevalence with 96% being bilateral . The aim of this study was to evaluate our experience using ultrasound to characterize plantar lateral foot pain and peroneal tendon pathology as well as to assess the usefulness of this technique in performing specific site therapeutic injections for this condition.
Limitations of our study include the absence of long-term standardized outcome follow-up for the injections. We have no surgical correlation. Power Doppler was not routinely employed, which might have prospectively identified areas of potential inflammation in these potentially directing alternative sites of injection. As this was a retrospective study, we had no controls.
In our series, there was a higher detection rate of os peroneii with ultrasound, with 10% of os peroneii not seen on radiographs. The higher incidence in this series may be that it is a direct anatomic study with direct inspection as opposed to an X-ray study .
Os peroneii have been shown anatomically to have variable histologic structure with different degrees of ossification, composed of differing degrees of fibrous tissue, cartilage, and bone . Sesamoid bones form from cartilaginous rests leading to enchondral ossification . This may explain higher detection rates with ultrasound, as ultrasound is going to be exquisitely sensitive to detecting structures with differing acoustic impedence properties. Ultrasound also is a cross-sectional imaging modality, and it is possible to follow the course of the tendon in real time.
Our findings are similar to that reported by Peacock et al., noting that proximal migration of the os peroneum is not a consistent finding with fractures of the os peroneum . In our series, we found no relationship between the location or morphology of the os peroneum and the degree of peroneus longus abnormalities. These are differing observations from those reported from Brigido et al., although theirs was a specific subset of patients with documented os peroneum fractures .
There are variable genetic and mechanical factors leading to the development of an os peroneum. Age, sex, and race have not been shown to correlate with the presence of an os peroneum . Interestingly, the presence of an os peroneum has been shown to be genetically linked to the presence of a fabella. It has been suggested that since the peroneus longus is an adductor of the hallux, the lack of hallux opposability in homo sapiens may result in a lack of mechanical stimulus for formation and maintenance of an os peroneum, with changes in degree of plantar flexion in contrast to lower primates leading to lack of stimulus for formation of an os peroneum [5, 8].
There are multiple soft tissue tethers that anchor the os peroneum to the plantar fascia, fifth metatarsal base, cuboid, and peroneus brevis tendon . Mechanical factors, soft tissue abnormalities, and biomechanics of the foot affect peroneal tendons more than just the os peroneum. With regards to the injections, there is a bare synovial sheath about the os at the cuboid tunnel, which may explain the communication of fluid injected around the os with the peroneal tendon sheath.
In conclusion, peroneal tendon and os peroneum abnormalities are a cause of plantar, lateral foot pain. The complementary use of imaging, both X-rays and ultrasound, can help define both osseous and soft tissue abnormalities. Ultrasound can be utilized both as the primary diagnostic modality for diagnosis as well as a method to guide for therapeutic injections in this cohort of patients.