Imaging of foot and ankle nerve entrapment syndromes: from well-demonstrated to unfamiliar sites

Magnetic Resonance Neurography of the Foot and Ankle

Peripheral neuropathies of the foot and ankle can be challenging to diagnose clinically due to concomitant traumatic and nontraumatic or degenerative orthopedic conditions. Although clinical history, physical examination, and electrodiagnostic testing comprised of nerve conduction velocities and electromyography are used primarily for the identification and classification of peripheral nerve disorders, MR neurography (MRN) can be used to visualize the peripheral nerves as well as the skeletal muscles of the foot and ankle for primary neurogenic pathology and skeletal muscle denervation effect. Proper knowledge of the anatomy and pathophysiology of peripheral nerves is important for an MRN interpretation.

High-resolution Ultrasound of the Foot and Ankle

High-resolution ultrasound (US) can be used to assess soft tissue abnormalities in the foot and ankle. Compared to MRI, it has lower cost, is widely available, allows portability and dynamic assessment. US is an excellent method to evaluate foot and ankle tendon injuries, ligament tears, plantar fascia, peripheral nerves, and the different causes of metatarsalgia.

Long-Term Donor-Site Morbidity Following Entire Sural Nerve Harvest for Grafting

PURPOSE

The sural nerve is the autologous nerve used most commonly for grafting. However, recent studies indicate a high rate of complications and complaints after sural nerve removal. In this prospective study, we evaluated donor-site morbidity following full-length sural nerve harvesting on long-term follow-up.

METHODS

Fifty-one legs from 43 patients who underwent complete sural nerve harvesting for brachial plexus reconstruction were included in the study. After an average of 5 years, with a minimum postoperative follow-up of 12 months, sensory deficits in the leg and foot were analyzed using 2.0-g monofilaments. Regions of sensory deficit were marked with a skin marker and photographed. Over these regions of decreased sensation, we tested nociception using an eyebrow tweezer. Patients were also asked about pain, cold intolerance, pruritis, difficulties walking, and foot swelling.

RESULTS

Regions most affected (84% of patients) were over the calcaneus and cuboid. However, in these regions, nociception was preserved. Regions of decreased sensation extended to the calf region in 11 of 51 legs. In 13 patients, we also observed regions of decreased sensation on the proximal leg. In five feet, the sensation was entirely preserved. No patient had any complaints about pain, cold intolerance, itchiness, difficulties walking, or foot swelling.

CONCLUSION

Decreased sensation with nociception preserved was most common along the lateral side of the foot over the calcaneus and cuboid. Removing the entire sural nerve produced no long-term complaints of pain. Sural nerve use appears safe.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

Nerve entrapment syndromes of the lower limb: a pictorial review

Peripheral nerves of the lower limb may become entrapped at various points during their anatomical course. While clinical assessment and nerve conduction studies are the mainstay of diagnosis, there are multiple imaging options, specifically ultrasound and magnetic resonance imaging (MRI), which offer important information about the potential cause and location of nerve entrapment that can help guide management. This article overviews the anatomical course of various lower limb nerves, including the sciatic nerve, tibial nerve, medial plantar nerve, lateral plantar nerve, digital nerves, common peroneal nerve, deep peroneal nerve, superficial peroneal nerve, sural nerve, obturator nerve, lateral femoral cutaneous nerve and femoral nerve. The common locations and causes of entrapments for each of the nerves are explained. Common ultrasound and MRI findings of nerve entrapments, direct and indirect, are described, and various examples of the more commonly observed cases of lower limb nerve entrapments are provided.Critical relevance statement This article describes the common sites of lower limb nerve entrapments and their imaging features. It equips radiologists with the knowledge needed to approach the assessment of entrapment neuropathies, which are a critically important cause of pain and functional impairment.Key points• Ultrasound and MRI are commonly used to investigate nerve entrapment syndromes.• Ultrasound findings include nerve hypo-echogenicity, calibre changes and the sonographic Tinel's sign.• MRI findings include increased nerve T2 signal, muscle atrophy and denervation oedema.• Imaging can reveal causative lesions, including scarring, masses and anatomical variants.

Anatomical study of the medial calcaneal nerve using high-resolution ultrasound

OBJECTIVES

To determine whether high-resolution ultrasound (US) can identify the course and relations of the medial calcaneal nerve (MCN).

METHODS

This investigation was initially undertaken in eight cadaveric specimens and followed by a high-resolution US study in 20 healthy adult volunteers (40 nerves) by two musculoskeletal radiologists in consensus. The location and course of the MCN as well as its relationship to adjacent anatomical structures were evaluated.

RESULTS

The MCN was consistently identified by US along its entire course. The mean cross-sectional area of the nerve was 1 mm2 (range 0.5-2). The level at which the MCN branched from the tibial nerve was variable, located a mean of 7 mm (range - 7-60) proximal to the tip of the medial malleolus. At the level of the medial retromalleolar fossa, the MCN was located inside the proximal tarsal tunnel a mean of 8 mm (range 0-16) posterior to the medial malleolus. More distally, the nerve was depicted in the subcutaneous tissue at the surface of the abductor hallucis fascia with a mean direct distance to the fascia of 1.5 mm (range 0.4-2.8).

CONCLUSIONS

High-resolution US can identify the MCN at the level of the medial retromalleolar fossa, as well as more distally in the subcutaneous tissue at the surface of the abductor hallucis fascia. In the setting of heel pain, precise sonographic mapping of the MCN course may enable the radiologist to make diagnosis of nerve compression or neuroma, and perform selective US-guided treatments.

CLINICAL RELEVANCE STATEMENT

In the setting of heel pain, sonography is an attractive tool for diagnosing compression neuropathy or neuroma of the medial calcaneal nerve, and enables the radiologist to perform selective image-guided treatments such as diagnostic blocks and injections.

KEY POINTS

• The MCN is a small cutaneous nerve which rises from the tibial nerve in the medial retromalleolar fossa to the medial side of the heel. • The MCN can be depicted by high-resolution ultrasound along its entire course. • In the setting of heel pain, precise sonographic mapping of the MCN course may enable the radiologist to make diagnosis of neuroma or nerve entrapment, and perform selective ultrasound-guided treatments such as steroid injection or tarsal tunnel release.

Magnetic Resonance Neurography of the Foot and Ankle

Peripheral neuropathies of the foot and ankle can be challenging to diagnose clinically due to concomitant traumatic and nontraumatic or degenerative orthopedic conditions. Although clinical history, physical examination, and electrodiagnostic testing comprised of nerve conduction velocities and electromyography are used primarily for the identification and classification of peripheral nerve disorders, MR neurography (MRN) can be used to visualize the peripheral nerves as well as the skeletal muscles of the foot and ankle for primary neurogenic pathology and skeletal muscle denervation effect. Proper knowledge of the anatomy and pathophysiology of peripheral nerves is important for an MRN interpretation.

High-resolution Ultrasound of the Foot and Ankle

High-resolution ultrasound (US) can be used to assess soft tissue abnormalities in the foot and ankle. Compared to MRI, it has lower cost, is widely available, allows portability and dynamic assessment. US is an excellent method to evaluate foot and ankle tendon injuries, ligament tears, plantar fascia, peripheral nerves, and the different causes of metatarsalgia.

Imaging of Anatomical Variants of the Lower Limb Nerves: Clinical and Preoperative Relevance

Anatomical variants of peripheral nerves of the lower limb are relatively frequent and vulnerable to injury if not considered by the surgeon. Surgical procedures or percutaneous injections are often performed without knowing the anatomical situation. In a patient with normal anatomy, these procedures are mostly performed smoothly without major nerve complications. But in the case of anatomical variants, surgery may be challenging as "new" anatomical prerequisites complicate the procedure. In this context, high-resolution ultrasonography as the first-line imaging modality to depict peripheral nerves, has become a helpful adjunct in the preoperative setting. It is crucial, on the one hand, to gain knowledge of anatomical nerve variants and, on the other hand, to depict the anatomical situation preoperatively, to minimize the risk of surgical trauma to a nerve and make surgeries safer.

Sural nerve: imaging anatomy and pathology

High resolution ultrasound (US) and magnetic resonance (MR) neurography are both imaging modalities that are commonly used for assessing peripheral nerves including the sural nerve (SN). The SN is a cutaneous sensory nerve which innervates the lateral ankle and foot to the base of the fifth metatarsal. It is formed by contributing nerves from the tibial and common peroneal nerves with six patterns and multiple subtypes described in literature. In addition to the SN being a cutaneous sensory nerve, the superficial location enables the nerve to be easily biopsied and harvested for a nerve graft, as well as increasing the susceptibility to traumatic injury. As with any peripheral nerves, pathologies such as peripheral nerve sheath tumors and neuropathies can also affect the SN. By utilizing a high frequency probe in US and high-resolution MR neurography, the SN can be easily identified even with the multiple variations given the standard distal course. US and MRI are also useful in determining pathology of the SN given the specific image findings that are seen with peripheral nerves. In this review, we evaluate the normal imaging anatomy of the SN and discuss common pathologies identified on imaging.

Imaging of Entrapment Neuropathies in the Ankle

Entrapment neuropathies of the ankle and foot pose a major diagnostic challenge and thus remain underdiagnosed. Recent advancements in imaging modalities, including magnetic resonance neurography (MRN), have resulted in considerable improvement in the anatomical localization and identification of pathologies leading to nerve entrapment. MRN supplements clinical examination and electrophysiologic studies in the diagnosis of neuropathies, aids in assessing disease severity, and helps formulate management strategies. A comprehensive understanding of the anatomy and imaging features of the ankle is essential to diagnose and manage entrapment neuropathies accurately. Advancements in imaging and their appropriate utilization will ultimately lead to better diagnoses and improved patient outcomes.

Micro-computed tomography with contrast enhancement: An excellent technique for soft tissue examination in humans

Manual dissection and histologic examination are commonly used to investigate human structures, but there are limitations in the damage caused to delicate structures or the provision of limited information. Micro-computed tomography (microCT) enables a three-dimensional volume-rendered observation of the sample without destruction and deformation, but it can only visualize hard tissues in general. Therefore, contrast-enhancing agents are needed to help in visualizing soft tissue. This study aimed to introduce microCT with phosphotungstic acid preparation (PTA-microCT) by applying the method to different types of human tissue. Specimens from human cadavers were used to examine the orbicularis retaining ligament (ORL), nasolabial fold (NLF), and the calcaneal tunnel of the sole. Using PTA-microCT, relevant information of human structures was identified. In the ORL study, tiny and delicate ligamentous fibers were visualized in detail with multidirectional continuity. In the NLF study, complex structural formation consisting of various types of soft tissue were investigated comprehensively. In the calcaneal tunnel study, the space surrounded by diverse features and its inner vulnerable structures were examined without damage. Consequently, we successfully applied the PTA-microCT technique to the analysis of specific human soft tissue structures that are challenging to analyze by conventional methods.

MRI appearance of jogger's foot

OBJECTIVE

To characterize the MRI findings present in patients with clinically proven or suspected jogger's foot.

MATERIALS AND METHODS

Ten years of medical charts in patients clinically suspected of having jogger's foot and who had MRI studies completed were identified utilizing a computer database search. Six study cases were identified. The MRI examinations of the study cases and an age- and gender-matched control group were reviewed in a blinded fashion by two musculoskeletal radiologists. Size and signal intensity of the medial plantar nerve were measured and characterized. The medial foot musculature was assessed for acute or chronic denervation changes.

RESULTS

The medial plantar nerve was found to have moderately increased T2 signal compared with normal skeletal muscle in 3/6 study group cases and markedly increased T2 signal in the remaining 3/6 cases. In all control cases, the nerve was reported to have T2 signal equal or minimally higher than normal skeletal muscle. The mean total size of the medial plantar nerve was significantly larger in the study group when compared with that in the control group at all measured locations (p < 0.04).

CONCLUSIONS

Abnormal thickness and T2 hyperintensity of the medial plantar nerve centered at the master knot of Henry are characteristic MRI findings in patients with jogger's foot when compared with control subjects. Muscular denervation changes may also be seen, most commonly in the flexor hallucis brevis muscle.

Changes of Peripheral Nerve Function and Vitamin B12 Level in People With Parkinson's Disease

Background and Purpose: Peripheral nerve function plays an important role in balance control. Impairment of peripheral sensory information appears in people with Parkinson's disease (PD). Furthermore, there is a link between peripheral nerve disorders and vitamin B₁₂ level. Here, we studied whether there were deficits of peripheral nerve function and vitamin B₁₂ level, which may lead to decreased postural stability in PD.

Methods: Fifty PD and 50 age-matched healthy subjects were enrolled in the study. This study evaluated folic acid and vitamin B₁₂ levels in serum. Postural balance was studied according to the clinical Tinetti scale. Some comprehensive physiological assessments of peripheral nerve functions, including peripheral sensation, the perception of temperature, pain, and touch sensations, were also undertaken in this study.

Results: Compared with the control group, vitamin B₁₂ and folic acid were decreased in PD (P < 0.05). Furthermore, the PD group exhibited declines in peripheral nerve functions, including touch, temperature, pain, and nerve conduction velocity (P < 0.05). Statistical tests identified a significant association between decreased peripheral nerve function and poor balance according to the Tinetti scale (P < 0.05). Low vitamin B₁₂ levels were also associated with deficits of peripheral nerve function, cumulative levodopa dose, and poor balance in PD (P < 0.05).

Conclusions: Data suggested that peripheral nerve function was impaired in people with PD. Deficits of sensory input and low vitamin B₁₂ level may contribute to balance deficits in PD.

Ultrasound Imaging of Cutaneous Innervations of the Lower Extremity

Ultrasound (US) is commonly used to evaluate the cutaneous innervation of the lower extremity, owing to the following advantages: (1) US is a high-resolution soft tissue imaging modality; (2) it is feasible in patients who are deemed unsuitable to undergo magnetic resonance imaging; and (3) it enables dynamic and real-time imaging. The evaluation of cutaneous nerves requires accurate knowledge of the anatomy as well as technical details. We present a review of the US anatomy of the cutaneous nerves in the lower extremity in addition to a description of a few pathologic conditions.

An Anatomical Basis for the Myofascial Trigger Points of the Abductor Hallucis Muscle

Myofascial pain syndrome is characterized by pain and a limited range of joint motion caused by muscle contracture related to motor-end-plate dysfunction and the presence of myofascial trigger points (MTrPs). It is the most frequent cause of musculoskeletal pain, with a worldwide prevalence varying between 13.7% and 47%. Of the patients with myofascial pain syndrome, approximately 17% have pain in the medial hindfoot area. The abductor hallucis muscle is located in the medial, posterior region of the foot and is related to painful plantar syndromes. The objective of this study was to describe the distribution of the medial plantar nerve and their anatomical relationship with MTrPs found in the literature. Thirty abductor hallucis muscles were dissected from 15 human cadavers (8 males and 7 females). The muscles were measured, and the distribution data of the medial plantar nerve branches in each quadrant were recorded. For statistical analysis, we used generalized estimation equations with a Poisson distribution and a log logarithm function followed by Bonferroni multiple comparisons of the means. The data are expressed as the mean ± standard deviation. The level of significance was adjusted to 5% (p < 0.05). A high concentration of nerve branches was observed in the first quadrant (Q1) of the abductor hallucis muscle, which is the same area in which the MTrPs are described. The topography of the entry points of the branches of the medial plantar nerve to the abductor hallucis muscle correlates with the topography of the muscular trigger points. The anatomical structure of the MTrPs may be useful for a better understanding of the pathophysiology of myofascial disorders and provide a basis for surgical and clinical treatments.

A Case of Bilateral Baxter's Neuropathy Secondary to Plantar Fasciitis

Heel pain is 1 of the most common presentations to the foot surgeon, and its causes are multifactorial. Baxter's neuropathy is caused by an impingement of the inferior calcaneal nerve and has been reported to be responsible for up to 20% of heel pain. The diagnostic imaging features are striking, with inflammation or atrophy of the abductor digiti minimi muscle. Multiple studies have found that the prevalence of this finding is much greater than initially thought. However, it is more unusual to find bilateral and symmetrical features. The possible causes of this condition lie along the course of the inferior calcaneal nerve. Management is focused on treating the underlying condition, with conservative therapy and steroid injection as the mainstay. Refractory cases may require surgical release. We present the case of a 56-year-old female presenting with bilateral foot pain. Imaging reveals symmetrical abductor digiti minimi atrophy associated with bilateral plantar fasciitis. These appearances are well demonstrated on both magnetic resonance imaging and ultrasound.

The Patient Acceptable Symptomatic State of the 12-Item International Hip Outcome Tool at 1-Year Follow-Up of Hip-Preservation Surgery

PURPOSE

To determine the patient acceptable symptomatic state (PASS) cutoff score for the 12-item International Hip Outcome Tool (iHOT-12) for patients after hip-preservation surgery.

METHODS

A multicenter hip arthroscopy registry containing deidentified patient data was analyzed to discriminate patients who achieved satisfactory results from patients who did not. Patients eligible for inclusion in the study were between 18 and 75 years of age, consented to undergo elective hip arthroscopy, and completed preoperative patient-reported outcome questionnaires. A receiver operating characteristic analysis was performed to determine the PASS cutoff score for the iHOT-12 at 1 year after surgery based on the sensitivity and specificity of achieving satisfaction with surgery. A visual analog scale rating patient satisfaction 1 year after surgery was documented and compared between subjects who achieved the PASS score for the iHOT-12 and those who did not achieve it through an independent t test with an a priori α set at .05.

RESULTS

A total of 647 subjects (66% women) aged between 18 and 73 years (mean, 36.5 years; standard deviation [SD], 12.0 years) were included in the study. A cutoff score of 75.2 for the iHOT-12 yielded a sensitivity of 0.91 and specificity of 0.81. Satisfaction averaged 89.5% (SD, 18.0%) for the patients with iHOT-12 scores greater than the PASS cutoff score versus 60.9% (SD, 30.61%) for those who did not achieve the PASS iHOT-12 score.

CONCLUSIONS

The PASS cutoff score of 75.2 for the iHOT-12 establishes a "minimal" target score at which the patient is highly likely to be satisfied with the physical state of his or her hip joint at 1 year after hip arthroscopy.

LEVEL OF EVIDENCE

Level III, case-control study.

Interfascicular septum of the calcaneal tunnel and its relationship with the plantar nerves: A cadaveric study

The relationship between the plantar nerves and internal fascial structure of the calcaneal tunnel is clinically important to alleviate pain of the sole. The study aimed to investigate the three-dimensional (3D) anatomy of the calcaneal tunnel and its internal fascial septal structure by using microcomputed tomography (mCT) with a phosphotungstic acid preparation, histologic examination, and ultrasound-guided simulation. Twenty-one fixed cadavers and three fresh-frozen cadavers (13 men and 11 women, mean age 82.1 years at death) were used in this study. The 3D images of the calcaneal tunnel harvested by mCT were analyzed in detail. Modified Masson trichrome staining and serial sectional dissection after ultrasound-guided injection were conducted to verify the 3D anatomy. Within the calcaneal tunnel, the interfascicular septum (IFS) commenced proximal to the malleolar-calcaneal line and distal to the bifurcation of the tibial nerve into the plantar nerves. The medial and lateral plantar nerves were separated by the IFS, which divided the calcaneal tunnel into two compartments. The plantar nerves were ramified into two or three branches within each compartment. The IFS terminated around the talocalcaneonavicular joint, and the plantar nerves traveled into the sole. Clinical manipulation of the plantar nerves should be performed in consideration of the fact that they are clearly separated by the IFS. Clin. Anat. 32:877-882, 2019. © 2019 Wiley Periodicals, Inc.

Ultrasound-guided decompression surgery of the tarsal tunnel: a novel technique for the proximal tarsal tunnel syndrome-Part II

Background

The aim of this study is to provide a safe ultrasound-guided minimally invasive surgical approach for a proximal tarsal tunnel release concerning nerve entrapments.

Methods and results

The study was carried out on ten fresh-frozen feet. All of them were examined by high resolution ultrasound at the medial ankle region. The surgical approach was marked throughout the course of the flexor retinaculum (laciniate ligament). Once the previous steps were done, the flexor retinaculum release technique was carried out with a 2-mm entry only. As a result, an effective and safe release of the flexor retinaculum was obtained in all fresh-frozen feet.

Conclusion

The results of our anatomic study indicate that our novel ultrasound-guided minimally invasive surgical approach for the release of the flexor retinaculum might be an effective, safe and quick decompression technique treating selected patients with a proximal tarsal tunnel syndrome.

Ultrasonography of the Sural Nerve: Normal and Pathologic Appearances

Ultrasonography (US) of peripheral nerves has gained wide popularity because of the increased definition of modern high-frequency electronic transducers, as well as the well-known advantages of US, which include easy availability, low cost, and the possibility of realizing a dynamic examination. Traditionally, US has been deployed to assess the major nerves of the limbs. More recently, US has also been used to assess the normal appearance and pathologic changes of smaller subcutaneous nerves. The sural nerve is a small sensory nerve in the subcutaneous tissues of the calf that can be affected by a variety of disorders. This pictorial essay illustrates the normal anatomy of the sural nerve, the technique for its examination by US, as well as the US appearance of its main pathologic changes.

Isolated atrophy of the abductor digiti quinti in patients with rheumatoid arthritis

OBJECTIVE

We aim to discuss the association of isolated atrophy of the abductor digiti quinti muscle in patients with rheumatoid arthritis as well as review the anatomy and imaging findings of this condition on MRI.

MATERIALS AND METHODS

A consecutive series of 55 patients diagnosed with rheumatoid arthritis according to the 2010 ACR/EULAR classification criteria were recruited. MRI of the clinically dominant feet was performed using a 1.5-T scanner.

RESULTS

The study population was predominantly female (94.5%), and the age range was 31-79 years (mean 57.5 ± 11). A total of 55 ankles were examined by MRI, and 20 patients (36.3%), all females, showed abductor digiti quinti denervation signs. Seven patients demonstrated severe fatty atrophy of the abductor digiti quinti, corresponding to Goutallier grade 4, 2 patients showed moderate fatty atrophy (Goutallier grade 3), and the remaining 11 patients showed less than 50% fatty atrophy, corresponding to a Goutallier grade 2. Substantial agreement was found for both intra- and interobserver agreement regarding the Goutallier grading system.

CONCLUSION

Prevalence of signs of abductor digiti quinti denervation on MRI was high in the studied population, suggesting that rheumatoid arthritis may be associated with inferior calcaneal nerve compression.

CT and MR Imaging of the Postoperative Ankle and Foot

A variety of surgical procedures exist for repair of both traumatic and degenerative osseous and soft-tissue pathologic conditions involving the foot and ankle. It is necessary for the radiologist to be familiar with these surgical procedures, so as to assess structural integrity, evaluate for complicating features, and avoid diagnostic pitfalls. Adequate interpretation of postoperative changes often requires access to surgical documentation to evaluate not only the surgery itself but the expected timeline for resolution of normal postoperative changes versus progressive disease. Appropriate use of surgical language in radiology reports is another important skill set to hone and is instrumental in providing a high-quality report to the referring surgeons. The pathophysiology of a myriad of surgical complaints, beginning from the Achilles tendon and concluding at the plantar plate, are presented, as are their common appearances at computed tomography and magnetic resonance imaging. Commonly encountered entities include Achilles tendon tear, spastic equinus, nonspastic equinus, talar dome osteochondral defect, tarsal tunnel syndrome, plantar fasciitis, pes planovalgus, pes cavovarus, peroneal tendinosis, lateral ligament complex pathology, Morton neuroma, plantar plate tear, and metatarsophalangeal joint instability. Computer-generated three-dimensional models are included with many of the procedures to provide a more global view of the surgical anatomy. Correlation with intraoperative photographs is made when available. When appropriate, discussion of postoperative complications, including entities such as infection and failure of graft integration, is presented, although a comprehensive review of postoperative complications is beyond the scope of this article. Notably absent from the current review are some common foot and ankle procedures including hallux valgus and hammertoe corrections, as these are more often evaluated radiographically than with cross-sectional imaging. ^©RSNA, 2016.

The plantar calcaneal spur: a review of anatomy, histology, etiology and key associations

The plantar calcaneal spur (PCS) is a bony outgrowth from the calcaneal tuberosity and has been studied using various methods including cadavers, radiography, histology and surgery. However, there are currently a number of discrepancies in the literature regarding the anatomical relations, histological descriptions and clinical associations of PCS. Historically, authors have described the intrinsic muscles of the foot and/or the plantar fascia as attaching to the PCS. In this article we review the relationship between the PCS and surrounding soft tissues as well as examining the histology of the PCS. We identify a number of key associations with PCS, including age, weight, gender, arthritides, plantar fasciitis and foot position; these factors may function as risk factors in PCS formation. The etiology of these spurs is a contentious issue and it has been explained through a number of theories including the degenerative, inflammatory, traction, repetitive trauma, bone-formers and vertical compression theories. We review these and finish by looking clinically at the evidence that PCS causes heel pain.

US of the Peripheral Nerves of the Lower Extremity: A Landmark Approach

Ultrasonography (US) is commonly used to assess the peripheral nerves of the lower extremity because of its many advantages over magnetic resonance (MR) imaging. The most obvious advantages over MR imaging are superior soft-tissue resolution, low cost, portability, lack of magnetic susceptibility artifact, and the ability to image patients who cannot undergo MR imaging. US has been shown to have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves. Additional benefits are the capability of real-time and dynamic imaging, and the ability to scan an entire extremity quickly without the need for a patient to lie motionless for long periods of time, as with MR imaging. Any abnormal findings can be easily compared against the contralateral side. Published literature has shown that US has clinical utility in patients suspected of having peripheral nerve disease: US can be used to guide diagnostic and therapeutic decisions, as well as help confirm electrodiagnostic findings. Common indications for lower extremity peripheral nerve US are the evaluation for injury due to penetrating trauma, entrapment by scar tissue, or tumor. To confidently perform US of the peripheral nerves of the lower extremity, it is important to gain a thorough knowledge of anatomic landmarks and the course of each nerve. Readers who may not be familiar with US will be introduced to the basics of scanning the peripheral nerves of the lower extremity. Important anatomic landmarks and common sites of injury and entrapment will be reviewed.

Compressive neuropathy of the first branch of the lateral plantar nerve: a study by magnetic resonance imaging

OBJECTIVE

To assess the prevalence of isolated findings of abnormalities leading to entrapment of the lateral plantar nerve and respective branches in patients complaining of chronic heel pain, whose magnetic resonance imaging exams have showed complete selective fatty atrophy of the abductor digiti quinti muscle.

MATERIALS AND METHODS

Retrospective, analytical, and cross-sectional study. The authors selected magnetic resonance imaging of hindfoot of 90 patients with grade IV abductor digiti quinti muscle atrophy according to Goutallier and Bernageau classification. Patients presenting with minor degrees of fatty muscle degeneration (below grade IV) and those who had been operated on for nerve decompression were excluded.

RESULTS

A female prevalence (78.8%) was observed, and a strong correlation was found between fatty muscle atrophy and plantar fasciitis in 21.2%, and ankle varices, in 16.8% of the patients.

CONCLUSION

Fatty atrophy of the abductor digiti quinti muscle is strongly associated with neuropathic alterations of the first branch of the lateral plantar nerve. The present study showed a significant association between plantar fasciitis and ankle varices with grade IV atrophy of the abductor digiti quinti muscle.

Percutaneous Ultrasound-Guided Hydrodissection of a Symptomatic Sural Neuroma

Symptomatic neuromas of the sural nerve are a rare but significant cause of pain and debilitation in athletes. Presentation is usually in the form of chronic pain and dysesthesias or paresthesias of the lateral foot and ankle. Treatment traditionally ranges from conservative measures, such as removing all external compressive forces, to administration of nonsteroidal anti-inflammatory drugs, vitamin B6, tricyclic antidepressants, antiepileptics, or topical anesthetics. This article reports a case of sural nerve entrapment in a 34-year-old male triathlete with a history of recurrent training-induced right-sided gastrocnemius strains. The patient presented with numbness in the right lateral foot and ankle that had persisted for 3 months, after he was treated unsuccessfully with extensive nonoperative measures, including anti-inflammatory drugs, activity modification, and a dedicated physical therapy program of stretching and strengthening. Orthopedic assessment showed worsening pain with forced passive dorsiflexion and manual pressure applied over the distal aspect of the gastrocnemius. Plain radiographs showed normal findings, but in-office ultrasound imaging showed evidence of sural nerve entrapment with edema and neuromatous scar formation in the absence of gastrocnemius or soleus pathology. Percutaneous ultrasound-guided hydrodissection of the sural nerve at the area of symptomatic neuroma and neural edema was performed the same day. The patient had complete relief of symptoms and full return to the preinjury level of participation in competitive sports. This case report shows that hydrodissection, when performed by an experienced physician, can be an effective, minimally invasive technique for neurolysis in the setting of sural nerve entrapment, resulting in improvement in clinical symptoms.

Tarsal tunnel syndrome masked by painful diabetic polyneuropathy

•

The real cause of symptoms in patients with neuropathy may not be related with diabetes.

•

It is essential to investigate the etiology of the disease with more localized pathologies in such complicated cases.

•

Tarsal tunnel syndrome gives a more segmental clinical profile with nerve entrapment.

Introduction

Various causes influence the etiology of tarsal tunnel syndrome including systemic diseases with progressive neuropathy, such as diabetes.

Presentation of case

We describe a 52-year-old male patient with complaints of numbness, burning sensation and pain in both feet. The laboratory results showed that the patient had uncontrolled diabetes, and the EMG showed distal symmetrical sensory-motor neuropathy and nerve entrapment at the right. Ultrasonography and MRI showed the cyst in relation to medial plantar nerve, and edema- moderate atrophy were observed at the distal muscles of the foot.

Discussion

Foot neuropathy in diabetic patients is a complex process. So, in planning the initial treatment, medical or surgical therapy is selected based on the location and type of the pathology. Foot deformities can be corrected with resting, anti-inflammatory treatment, appropriate shoes, orthesis and socks, and if required, ankle stabilization can be attempted. If the patient is still unresponsive, surgical treatment may be applied.

Conclusion

It is essential to investigate more localized reasons like tarsal tunnel syndrome that may mimic diabetic neuropathy, should be treated primarily.

Normal Anatomy and Compression Areas of Nerves of the Foot and Ankle: US and MR Imaging with Anatomic Correlation

The anatomy of the nerves of the foot and ankle is complex, and familiarity with the normal anatomy and course of these nerves as well as common anatomic variants is essential for correct identification at imaging. Ultrasonography (US) and magnetic resonance (MR) imaging allow visualization of these nerves and may facilitate diagnosis of various compression syndromes, such as "jogger's heel," Baxter neuropathy, and Morton neuroma. It may be difficult to distinguish the nerves from adjacent vasculature at MR imaging, and US can help in differentiation. The authors review the normal anatomy and common variants of the nerves of the foot and ankle, with use of dissected specimens and correlative US and MR imaging findings. In addition, the authors illustrate proper probe positioning, which is essential for visualizing the nerves at US. The authors' discussion focuses on the superficial and deep peroneal, sural, saphenous, tibial, medial and lateral plantar, medial and inferior calcaneal, common digital, and medial proper plantar digital nerves.

Entrapment of the superficial peroneal nerve: an anatomical insight

Entrapment of the superficial peroneal nerve is an uncommon neuropathy that may occur because of mechanical compression of the nerve, usually at its exit from the crural fascia. The symptoms include sensory alterations over the distribution area of the superficial peroneal nerve. Clinical examination, electrophysiologic findings, and imaging techniques can establish the diagnosis. Variations in the superficial peroneal sensory innervation over the dorsum of the foot may lead to variable results during neurologic examination and variable symptomatology in patients with nerve entrapment or lesions. Knowledge of the nerve's anatomy at the lower leg, foot, and ankle is of essential significance for the neurologist and surgeon intervening in the area.

The foot and ankle examination

Most foot and ankle disorders can be diagnosed after a proper history and clinical examination and can be effectively managed in a primary care setting. It is important to assess the entirety of patient disorders that present as they can be multifactorial in cause. A broad differential should include disorders of bones, joints, muscles, neurovasculature, and surrounding soft tissue structures. Physical examination should be thorough and focused on inspection, palpation, range of motion, and appropriate special tests when applicable. This article highlights some of the salient features of the foot and ankle examination and diagnostic considerations.

Ultrasound assessment of selected peripheral nerves pathologies. Part II: Entrapment neuropathies of the lower limb

Similarly to entrapment neuropathies of upper extremities, the ultrasound constitutes a valuable supplementation of diagnostic examinations performed in patients with suspicions of nerve entrapment syndromes of the lower limb. For many years, it was claimed that such pathologies were rare. This probably resulted from the lack of proper diagnostic tools (including high frequency ultrasound transducers) as well as the lack of sufficient knowledge in this area. In relation to the above, the symptoms of compression neuropathies were frequently interpreted as a manifestation of pathologies of the lumbar part of the spine or a other orthopedic disease (degenerative or overuse one). Consequently, many patients were treated ineffectively for many months and even, years which led to irreparable neurological changes and changes in the motor organ. Apart from a clinical examination, the diagnostics of entrapment neuropathies of lower limb is currently based on imaging tests (ultrasound, magnetic resonance) as well as functional assessments (electromyography). Magnetic resonance imaging is characterized by a relatively low resolution (as compared to ultrasound) which results in limited possibilities of morphological evaluation of the visualized pathology. Electromyography allows for the assessment of nerve function, but does not precisely determine the type and degree of change. This article presents examples of the most common entrapment neuropathies of the lower limb concerning the following nerves: sciatic, femoral, lateral femoral cutaneous, obturator, fibular and its branches, tibial and its branches as well as sural. The pathomorphological basis of the neuropathies as well as corresponding ultrasound images are presented in this paper. Attention has been drawn to echogenicity, degree of vascularization and bundle presentation of the trunk of a pathological peripheral nerve.

High resolution imaging of tunnels by magnetic resonance neurography

Peripheral nerves often traverse confined fibro-osseous and fibro-muscular tunnels in the extremities, where they are particularly vulnerable to entrapment and compressive neuropathy. This gives rise to various tunnel syndromes, characterized by distinct patterns of muscular weakness and sensory deficits. This article focuses on several upper and lower extremity tunnels, in which direct visualization of the normal and abnormal nerve in question is possible with high resolution 3T MR neurography (MRN). MRN can also serve as a useful adjunct to clinical and electrophysiologic exams by discriminating adhesive lesions (perineural scar) from compressive lesions (such as tumor, ganglion, hypertrophic callous, or anomalous muscles) responsible for symptoms, thereby guiding appropriate treatment.

Review of common and unusual causes of lateral ankle pain

Lateral ankle pain is a common clinical presentation having several important causes, including lateral ligament injury, peroneal tendon injury, sinus tarsi syndrome, and nerve entrapments. However, other causes should be kept in mind in patients with unusual patterns of pain or intractable symptoms. We present a review of common and some unusual causes of lateral ankle pain including a review of post-operative imaging findings following surgery for lateral ankle ligament and peroneal tendon injuries.

[Ultrasound of the tarsal tunnel: Normal and pathological imaging features]

Tarsal tunnel syndrome is a condition that is caused by compression of the tibial nerve or its associated branches. Diagnosis is based on clinical findings but imaging is performed to exclude a cause of compression, identified in 60 to 80% of cases. Ultrasound is a useful examination because of its high spatial resolution and ability to rapidly perform an axial survey of the nerves. The ultrasound imaging features of the tarsal tunnel are described. The etiologies and different types are illustrated through a review of clinical cases.

Imaging of nerve entrapment in the foot and ankle

Neuropathies can be a cause of chronic foot and ankle pain. The diagnosis can be elusive given the sometimes nonspecific clinical presentation. Although electrodiagnostic studies are primarily relied on for the diagnosis of nerve impairment, imaging is sometimes helpful in helping define the exact site of the entrapment and whether any masses are present. It is critical for the imager to understand the complex anatomy of these nerves and their adjacent structures, to know the most common locations for their entrapments or injury, and to select the proper imaging modality to improve detection of these difficult-to-diagnose clinical conditions.

Peripheral nerve entrapments of the lower leg, ankle, and foot

Peripheral nerve entrapments are a relatively rare and heterogeneous group of nerve disorders encompassing a wide variety of etiologies and clinical presentations. These conditions can present significant diagnostic challenges, owing to both the variety of symptoms these patients display, along with the anatomic variation that exists between individuals. Precise knowledge of the anatomic course, the common motor and sensory distributions of each of the peripheral nerves, and judicious use of imaging or electrodiagnostic testing can greatly assist in arriving at a correct diagnosis. In this article, we discuss in detail the anatomy, clinical presentation, diagnosis, and treatment options for peripheral nerve entrapments of the lower extremity involving the sural, saphenous and common, superficial, and deep peroneal nerves.

What's new in the diagnosis and treatment of peripheral nerve entrapment neuropathies

Entrapment neuropathies can be common conditions with the potential to cause significant disability. Correct diagnosis is essential for proper management. This article is a review of recent developments related to diagnosis and treatment of various common and uncommon nerve entrapment disorders. When combined with classical peripheral nerve examination techniques, innovations in imaging modalities have led to more reliable diagnoses. Moreover, innovations in conservative and surgical techniques have been controversial as to their effects on patient outcome, but randomized controlled trials have provided important information regarding common operative techniques. Treatment strategies for painful peripheral neuropathies are also reviewed.

Plantar fasciitis and calcaneal spur formation are associated with abductor digiti minimi atrophy on MRI of the foot

OBJECTIVE

To determine the association of atrophy of the abductor digiti minimi muscle (ADMA), an MRI manifestation of chronic compression of the inferior calcaneal nerve suggesting the clinical diagnosis of Baxter's neuropathy, with MRI markers of potential etiologies, including calcaneal spur formation, plantar fasciitis, calcaneal edema, Achilles tendinosis and posterior tibial tendon dysfunction (PTTD).

MATERIALS AND METHODS

Prevalence of calcaneal spur formation, plantar fasciitis, calcaneal edema, Achilles tendinosis and PTTD was assessed retrospectively on 100 MRI studies with ADMA and 100 MRI studies without ADMA. Patients ranged in age from 10-92 years. Pearson chi-square analyses and Fisher's exact test were used to compare prevalence of the above findings in patients with and without ADMA. Logistic regression was used to determine which variables were significantly associated with ADMA.

RESULTS

Among patients with ADMA, there was significantly greater age (57.2 years vs 40.8 years, p<0.001), presence of Achilles tendinosis (22.0% vs 3.0%, P<0.001), calcaneal edema (15.0% vs 3.0%, P=0.005), calcaneal spur (48.0% vs 7.0%, P<0.001), plantar fasciitis (52.5% vs 11.0%, P<0.001), and PTTD (32.0% vs 11.0%, P<0.001). After multivariate logistic regression analysis, only age [odds ratio (OR) 1.06, 95% confidence interval (CI) 1.03, 1.09], calcaneal spur (OR 3.60, 95% CI 1.28, 10.17), and plantar fasciitis (OR 3.35, 95% CI 1.31, 8.56) remained significant.

CONCLUSION

Advancing age, calcaneal spur, and plantar fasciitis are significantly associated with ADMA. Their high odds ratios support the notion of a possible etiologic role for calcaneal spur and plantar fasciitis in the progression to Baxter's neuropathy.

[Soft tissue tumors and pseudotumors of the foot and ankle]

Soft tissue masses around the foot and ankle are frequent. While benign lesions are two times more frequent than malignant lesions, the latter still represent one third of all lesions. The main purpose of this article is to propose a systematic approach to the differential diagnosis of soft tissue tumors of the foot and ankle based on a combination of 5 elements: clinical history and physical examination, top 10 most frequent diagnoses, patient age, lesion location, and MRI features of the mass. Selected soft tissue tumors will be described and illustrated with emphasis on these 5 elements.