MRI of lesser metatarsophalangeal joint plantar plate tears and associated adjacent interspace lesions

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.

Differential Diagnosis of Metatarsalgia

Lesser (or central) metatarsalgia is defined as pain in the forefoot under or around the lesser metatarsals and their respective metatarsophalangeal joints. Two common causes of central metatarsalgia are Morton's neuroma (MN) and plantar plate (PP) injury. Because both clinical and imaging features overlap, establishing the correct differential diagnosis may be challenging. Imaging has a pivotal role in the detection and characterization of metatarsalgia. Different radiologic modalities are available to assess the common causes of forefoot pain, so the strengths and weakness of these imaging tools should be kept in mind. It is crucial to be aware of the pitfalls that can be encountered in daily clinical practice when dealing with these disorders. This review describes two main causes of lesser metatarsalgia, MN and PP injury, and their differential diagnoses.

MR Imaging–Ultrasonography Correlation of Acute and Chronic Foot and Ankle Conditions

Foot and ankle injuries are common musculoskeletal disorders. In the acute setting, ligamentous injuries are most common, whereas fractures, osseous avulsion injuries, tendon and retinaculum tears, and osteochondral injuries are less common. The most common chronic and overuse injuries include osteochondral and articular cartilage defects, tendinopathies, stress fractures, impingement syndromes, and neuropathies. Common forefoot conditions include traumatic and stress fractures, metatarsophalangeal and plantar plate injuries and degenerations, intermittent bursitis, and perineural fibrosis. Ultrasonography is well-suited for evaluating superficial tendons, ligaments, and muscles. MR imaging is best for deeper-located soft tissue structures, articular cartilage, and cancellous bone.

Diagnostic Considerations of Intermetatarsal Bursitis: A Systematic Review

Intermetatarsal bursitis (IMB) is an inflammation of the intermetatarsal bursas. The condition causes forefoot pain with symptoms similar to those of Morton's neuroma (MN). Some studies suggest that IMB is a contributing factor to the development of MN, while others describe the condition as a differential diagnosis. Among patients with rheumatic diseases, IMB is frequent, but the scope is yet to be understood. The aim of this paper was to investigate the diagnostic considerations of IMB and its role in metatarsalgia by a systematic review approach. We identified studies about IMB by searching the electronic databases Pubmed, Embase, Cochrane Library, and Web of Science in September 2022. Of 1362 titles, 28 met the inclusion criteria. They were subdivided according to topic: anatomical studies (n = 3), studies of patients with metatarsalgia (n = 10), and studies of patients with rheumatic diseases (n = 15). We conclude that IMB should be considered a cause of pain in patients with metatarsalgia and patients with rheumatic diseases. For patients presenting with spreading toes/V-sign, IMB should be a diagnostic consideration. Future diagnostic studies about MN should take care to apply a protocol that is able to differ IMB from MN, to achieve a better understanding of their respective role in forefoot pain.

Presurgical Perspective and Postsurgical Evaluation of Plantar Plate and Turf Toe

Capsuloligamentous injury of the first metatarsophalangeal (MTP) joint (eponymously called "turf toe") mostly occurs in athletes and involves acute trauma, whereas tears of the lesser MTP joint plantar plate typically are an attritional-degenerative condition. This article reviews the anatomy, pathophysiology, mechanism and patterns of injury, grading and classification of injury, imaging appearances (pre- and postoperative), and management of first MTP joint capsuloligamentous injuries and lesser MTP joint plantar plate tears. These two distinct pathologies are discussed in separate sections.

Incidental Finding of Plantar Plate Pathology on Routine Magnetic Resonance Imaging of the Foot and Ankle

BACKGROUND

We hypothesized that there would be a comparable and high incidence of an incidental torn plantar plate on routine magnetic resonance imaging (MRI) in asymptomatic patients.

METHODS

We included adult patients undergoing a foot MRI from 2019 to 2020. Based on the documented reason for MRI, patients were divided into symptomatic and asymptomatic. A separate musculoskeletal radiologist re-evaluated MRI images. Findings were categorized as "torn vs intact." We also used the anatomical grading system (AGS).

RESULTS

We reviewed 218 records, including 165 asymptomatic and 53 symptomatic patients. The chance of finding a plantar plate (PP) tear on MRI of symptomatic patients was 28% (21% in PP2, 5.7% in PP3, 5.7% in PP4, and 2% in PP5), while PP tear in asymptomatic patients was only apparent in 2% of MRIs (1.5% in PP2, 0 in PP3, 0 in PP4, and 0.6% in PP5). Cohen's kappa coefficient was 0.92, showing excellent agreement between the radiologists. Odds calculation revealed that the chance of finding a torn PP in an asymptomatic patient is 2.5%. In comparison, the chance of finding an intact PP in a symptomatic patient is 72%, showing 2.5 times more likely to find an intact PP than a torn PP in symptomatic individuals.

CONCLUSION

Interestingly, there was a low rate of abnormal PP appearance on MRI in both symptomatic and asymptomatic patients, which suggests that the chance of finding a false-positive PP tear in an asymptomatic patient is minimal and probably negligible.

LEVEL OF EVIDENCE

Level IV diagnostic.

Anatomy: Plantar Plate

The fibrocartilaginous component of the plantar plate offers stability at the metatarsophalangeal joint. In conjunction with the attachments of the deep transverse metatarsal ligaments and collateral ligaments, the plantar plate complex resists tensile forces anchored by the plantar fascia and compression forces under the metatarsal heads.

Degenerative injuries of the metatarsophalangeal plantar plate on magnetic resonance imaging: a new perspective

Objective

The magnetic resonance imaging diagnostic criteria for a complete tear of metatarsophalangeal plantar plate are well-established. However, more subtle abnormalities can also occur and be a source of pain. The objective of this study is to determine the prevalence of degenerative plantar plate injuries in patients with metatarsalgia who underwent forefoot magnetic resonance imaging and describe the main abnormalities found. The hypothesis is that mild capsular fibrosis will have high sensitivity but low specificity for plantar plate degenerative injuries.

Methods

A retrospective cross-sectional study was conducted with 85 patients (105 feet) with metatarsalgia who underwent forefoot magnetic resonance imaging using a specific protocol to study metatarsophalangeal plantar plate. The experiment observer classified second toe plantar plate as normal, complete rupture or degenerative lesion and described the main magnetic resonance imaging findings.

Results

A normal plantar plate was observed in 75 (71.4%) of the 105 feet assessed, in 25 (24%) feet there were degenerative plantar lesions, and in 5 (4.6%) feet there were complete ruptures. Degenerative injury of the plantar plate was best identified in coronal short axis intermediate-weighted images, with high sensitivity (92%). Pericapsular fibrosis below the intermetatarsal ligament was identified in 96% of cases, with high sensitivity (96%) for diagnosis of degenerative plantar plate injury.

Conclusion

Degenerative lesions of the metatarsophalangeal plantar plate were more prevalent than complete ruptures and were best viewed in coronal short axis intermediate-weighted sequences. Pericapsular fibrosis below the intermetatarsal ligament was the indirect finding most strongly associated with degenerative plantar plate injury.

A problem-based approach in musculoskeletal ultrasonography: central metatarsalgia

Ultrasonography (US) is a useful diagnostic method that can be easily applied to identify the cause of metatarsalgia. The superficial location of structures in the foot, dynamic capability of US, and the ability to perform direct real-time evaluations of the pain site are also strong advantages of US as a modality for examining the foot. Moreover, knowing the possible pain sources to investigate when a patient has a specific site of pain will enhance the diagnostic quality of US, and will help radiologists to perform US efficiently and effectively. The purpose of this article is to review the common etiologies of metatarsalgia including Morton’s neuroma, plantar plate injury, synovitis, tenosynovitis, bursitis, and metatarsal fractures, and to discuss their US features.

Imaging in metatarsalgia

Metatarsalgia is a common clinical conundrum that requires careful assessment. There are a variety of causes and understanding these can help manage the pain. These causes have different imaging characteristics and require specific imaging. By understanding core imaging principles and how they apply to causes of metatarsalgia, pathology can be more efficiently investigated. This article covers primary, secondary and iatrogenic causes of metatarsalgia with the most appropriate imaging modalities for each and the salient imaging findings. This article reviews the common forefoot pathologies and how they may be optimally radiologically investigated, with an emphasis on the key imaging findings.

Ultrasound findings of plantar plate tears of the lesser metatarsophalangeal joints

Lesser metatarsophalangeal (MTP) joint plantar plate tears are a common and increasingly recognised cause of metatarsalgia, MTP joint instability and forefoot deformity. Increased interest in early accurate diagnosis of plantar plate tears follows recent surgical innovations allowing direct plantar plate repair. The purpose of this review is to describe the ultrasound features of normal lesser MTP joint plantar plates and to characterise and illustrate the direct and indirect ultrasound findings of plantar plate tears. Lesser MTP joint plantar plate tears are most commonly located at the 2nd MTP joint, involving the lateral distal plantar plate insertion with variable propagation medially and proximally. The most common ultrasound appearance of a plantar plate tear is a discrete partial or full thickness hypoechoic defect in the plate substance. Flattening and attenuation or non-visualisation of the plantar plate represent more extensive tears. Dynamic imaging with toe dorsiflexion improves visualisation of tears and augments MTP joint subluxation. A common indirect finding is pericapsular fibrosis along the MTP joint capsule adjacent to a plantar plate tear, which requires differentiation from Morton's neuroma, and key distinguishing features at ultrasound are described. Other indirect findings include the cartilage interface sign, flexor tendon subluxation onto the metatarsal head or medial to the midline, flexor tenosynovitis, proximal phalangeal enthesophytes or avulsion and MTP joint synovitis. Ultrasound offers several advantages over MR imaging but requires a meticulous ultrasound examination, and optimisation of scanning technique is described.

Presence of Neovascularization in Torn Plantar Plates of the Lesser Metatarsophalangeal Joints

BACKGROUND

Recent surgical techniques have focused on anatomic repair of lesser toe metatarsophalangeal (MTP) plantar plate tears, yet it remains unknown whether the plantar plate has the biological capacity to heal these repairs. Therefore, a better understanding of the plantar plate vasculature in response to injury may provide further insight into the potential for healing after anatomic plantar plate repair. Recently, a study demonstrated that the microvasculature of the normal plantar plate is densest at the proximal and distal attachments. The purpose of this study was to compare the intact plantar plate microvasculature network to the microvasculature network of plantar plates in the presence of toe deformity using similar perfusion and nano-computed tomographic (CT) imaging methods.

METHODS

Seven fresh-frozen human cadaveric lower extremities with lesser toe deformities including hammertoe or crossover toe were perfused using a barium solution. The soft tissues of each foot were counterstained with phosphomolybdic acid (PMA). Then using nano-CT imaging, the second through fourth toe metatarsophalangeal joints of 7 feet were imaged. These images were then reconstructed, plantar plate tears were identified, and 11 toes remained. The plantar plate microvasculature for these 11 toes was analyzed, and calculation of vascular density along the plantar plate was performed. Using analysis of variance (ANOVA), this experimental group was compared to a control group of 35 toes from cadaveric feet without deformity and the vascular density compared between quartiles of plantar plate length proximal to distal. A power analysis was performed, determining that 11 experimental toes and 35 control toes would be adequate to provide 80% power with an alpha of 0.05.

RESULTS

Significantly greater vascular density (vascular volume/tissue volume) was found along the entire length of the plantar plate for the torn plantar plates compared to intact plantar plates (ANOVA, P < .001). For the first quartile of length (proximal to distal), the vascular density for the torn plantar plates was 0.365 (SD 0.058) compared to 0.281 (SD 0.036) for intact plantar plates; in the second quartile it was 0.300 (SD 0.044) vs 0.175 (SD 0.025); third quartile it was 0.326 (SD 0.051) vs 0.117 (SD 0.015); and fourth (most distal) quartile was 0.600 (SD 0.183) vs 0.319 (SD 0.082).

CONCLUSION

Torn plantar plates showed increased vascular density throughout the length of the plantar plate with an increase in density most notable in the region at or just proximal to the attachment to the proximal phalanx. Our analysis revealed that torn plantar plates exhibit neovascularization around the site of a plantar plate tear that does not exist in normal plantar plates.

CLINICAL RELEVANCE

The clinical significance of the increased vascularity of torn plantar plates is unknown at this time. However, the increase in vasculature may suggest that the plantar plate is a structure that is attempting to heal.

Is Second Metatarsal Protrusion Related to Metatarsophalangeal Plantar Plate Rupture?

OBJECTIVE. The purpose of this study was to determine whether the relative length of protrusion of the second metatarsal, measured on MRI and weight-bearing foot radiography, predicts the diagnosis of second metatarsophalangeal (MTP) joint plantar plate (PP) tear on MRI. MATERIALS AND METHODS. We retrospectively evaluated 166 consecutive patients (211 feet). Patients had undergone weight-bearing foot radiography and forefoot MRI. Using the Coughlin method, two independent observers measured second meta-tarsal protrusion length on radiography and MRI. MRI findings were classified as normal PP, complete PP tear, or degenerative or partial PP tear. RESULTS. Patients had a mean age of 47 ± 14.6 (SD) years, and 131 (78.9%) were women. MRI measurements were highly correlated with radiographic measurements (r = 0.882; 95% CI, 0.866-0.898; p < 0.001). A significant correlation was found between length of protrusion and cases classified as either normal PP or PP tear. Patients with a normal PP had a mean protrusion length of 4.11 ± 1.35 mm on radiographs and 2.61 ± 1.31 mm on MR images, whereas those with a PP tear had a mean protrusion length of 4.75 ± 1.53 and 3.05 ± 1.34 mm, respectively. ROC curve analysis showed that protrusion length cutoff values of 5.47 mm measured on radiographs and 3.17 mm on MR images were correlated with MTP PP tear. CONCLUSION. We identified a linear correlation between second metatarsal protrusion measured on MRI and that measured on radiography, with values about 35% higher for the latter. Our study showed an association between length of protrusion of the second metatarsal and PP rupture and identified a cutoff value for the second meta-tarsal overlength that is associated with these tears.

Magnetic resonance imaging of the ankle and foot

This article reviews the magnetic resonance imaging (MRI) findings of the normal anatomy and various pathologic conditions of the ankle and foot commonly encountered in clinical practice. The spectrum of entities discussed includes osseous and osteochondral injuries, ligamentous injuries, common traumatic and degenerative tendon pathology, abnormalities of transverse tarsal joint (Chopart) and tarsometatarsal joint (Lisfranc) complexes, pathological conditions affecting capsuloligamentous structures of the great toe and lesser toes, as well as pedal infection, with a focus on diabetic osteomyelitis and neuropathic osteoarthropathy.

Lesser Metatarsophalangeal Instability: Diagnosis and Conservative Management of a Common Cause of Metatarsalgia

CONTEXT

Lesser metatarsophalangeal (MTP) instability is a common condition that can become debilitating and require surgery.

EVIDENCE ACQUISITION

An extensive literature review was performed through MEDLINE and Google Scholar for publications relating to the etiology, diagnosis, and treatment of lesser MTP instability using the keywords metatarsophalangeal instability, athlete, forefoot pain, and metatarsalgia from database inception to 2019.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 4.

RESULTS

Lesser MTP instability is a common condition, especially in the active and aging populations. It is frequently misdiagnosed, causing delays in treatment that allow for progressive pain and deformity, which prevents an active lifestyle. Fortunately, MTP instability can be diagnosed easily with the drawer test. Magnetic resonance imaging is helpful when still in doubt. Conservative treatment entails joint immobilization and gradual return to play with taping and offloading metatarsal pads.

CONCLUSION

Lesser MTP instability is a common diagnosis. Its early detection and conservative treatment can help the patient regain their previous level of activity and avoid surgery.

Forefoot Pain in the Lesser Toes: Anatomical Considerations and Magnetic Resonance Imaging Findings

Various conditions may result in forefoot pain. Magnetic resonance (MR) imaging allows accurate assessment of many of these conditions. We provide an overview of forefoot disorders divided into bones, capsule and plantar plate, musculotendinous structures, neurovascular structures, and subcutaneous tissue. We review normal anatomical features as well as MR imaging findings of common disorders.

Microvasculature of the Plantar Plate Using Nano-Computed Tomography

BACKGROUND:

Lesser toe plantar plate attenuation or disruption is being increasingly implicated in a variety of common clinical conditions. A multitude of surgical techniques and devices have been recently developed to facilitate surgical repair of the plantar plate. However, the microvascular anatomy, and therefore the healing potential in large part, has not been defined. We investigated the microvasculature of the plantar plate by employing a novel technique involving microvascular perfusion and nano-computed tomography (nano-CT) imaging.

METHODS:

Twelve human adult cadaveric lower extremities were amputated distal to the knee. The anterior and posterior tibial arteries were perfused with a barium solution. The soft tissues of each foot were then counterstained with phosphomolybdic acid (PMA). The second through fourth toe metatarsophalangeal (MTP) joints of 12 feet were imaged with nano-CT at 14-micron resolution. Images were then reconstructed for analysis of the plantar plate microvasculature and calculation of the vascular density along the length of the plantar plate.

RESULTS:

A microvascular network extends from the surrounding soft tissues at the attachments of the plantar plate on both the metatarsal and proximal phalanx. The midsubstance of the plantar plate appears to be relatively hypovascular. Analysis of the vascular density along the length of the plantar plate demonstrated a consistent trend with increased vascular density at approximately the proximal 29% and distal 22% of the plantar plate.

CONCLUSION:

There is a vascular network extending from the surrounding soft tissues into the proximal and distal attachments of the plantar plate.

CLINICAL RELEVANCE:

The hypovascular midportion of the plantar plate may play an important role in the underlying pathoanatomy and pathophysiology of this area. These findings may have significant clinical implications for the reparative potential of this region and the surgical procedures currently described to accomplish anatomic plantar plate repair.

Biomechanical Evaluation of Suture Configurations in Lesser Toe Plantar Plate Repairs

BACKGROUND

Lesser toe metatarsal-phalangeal (MTP) joint instability can be a major source of pain and dysfunction. Instability occurs when there is incompetence of the plantar plate and/or collateral ligaments. Newer operative treatments focus on performing anatomic repairs of the plantar plate. The goal of this study was to compare the biomechanical properties of 3 suture configurations that may be used for plantar plate repairs.

METHODS

Biomechanical analysis of 27 lesser toe plantar plates from fresh frozen human cadavers was completed. The plantar plate was detached from the proximal phalanx, and suture was placed in the distal plantar plate in a horizontal mattress, luggage-tag, or Mason-Allen suture configuration. Cyclic loading followed by load-to-failure testing was performed.

RESULTS

There was a significant difference in peak load-to-failure force between constructs (mattress: 115.53 ± 15.95 N; luggage-tag 102.42 ± 19.33 N; Mason-Allen: 89.96 ± 15.78 N; P = .015). Post hoc analysis demonstrated that the mattress configuration had significantly higher load-to-failure force compared with the Mason-Allen configuration ( P = .004). There were no significant differences between the mattress and the luggage-tag configurations or the luggage-tag and the Mason-Allen configurations. There were no differences in construct stiffness, axial displacement at the time of failure, or number of cycles required to produce 2 mm of displacement.

CONCLUSION

The mattress configuration demonstrated better peak load-to-failure force compared with the Mason-Allen configuration but was not statistically different from the luggage-tag configuration. Although not significant, the mattress configuration trended toward higher load-to-failure force compared with the luggage-tag.

CLINICAL RELEVANCE

The horizontal mattress stitch may be the biomechanically superior configuration in plantar plate repairs.

Predictive MRI correlates of lesser metatarsophalangeal joint plantar plate tear

PURPOSE

To identify correlated signs on non-enhanced MRI that might improve diagnostic detection of plantar plate (PP) tear.

MATERIALS AND METHODS

We performed an IRB-approved, HIPAA-compliant retrospective analysis of 100 non-contrast MRI (50 PP tear, 50 controls). All were anonymized, randomized, and reviewed; 20 were duplicated to assess consistency. One musculoskeletal radiologist evaluated qualitative variables. A trained non-physician performed measurements. Consistency and concordance were assessed. Pearson's Chi-square test was used to test the correlation between qualitative findings and PP tear status. Correlation between measurements and PP status was assessed using t tests and Wilcoxon's rank-sum test (p values < 0.05 considered significant). Classification and regression trees were utilized to identify attributes that, taken together, would consistently distinguish PP tear from controls.

RESULTS

Quantitative measurements were highly reproducible (concordance 0.88-0.99). Elevated 2nd MT protrusion, lesser MT supination and rotational divergence of >45° between the 1st-2nd MT axis correlated with PP tear. Pericapsular soft tissue thickening correlated most strongly with PP tear, correctly classifying 95 % of cases and controls. Excluding pericapsular soft tissue thickening, sequential assessment of 2nd toe enthesitis, 2nd flexor tendon subluxation, and splaying of the second and third toes accurately classified PP status in 92 %.

CONCLUSIONS

Pericapsular soft tissue thickening most strongly correlated with PP tear. For cases in which it might be difficult to distinguish pericapsular fibrosis from neuroma, sequential assessment of 2nd toe enthesitis, flexor tendon subluxation and splaying of the 2nd and 3rd toe is most helpful for optimizing accurate diagnosis of PP tear.

Evaluation of lesser metatarsophalangeal joint plantar plate tears with contrast-enhanced and fat-suppressed MRI

OBJECTIVE

To present findings of plantar plate (PP) lesions from MRI with administration of gadolinium and to differentiate PP lesions from others causes of metatarsalgia.

MATERIALS AND METHODS

Two musculoskeletal radiologists reviewed 249 contrast-enhanced forefoot MRI scans from patients with metatarsalgia between June 2012 and June 2013. Evaluations focused on hyper-vascularized/fibrous tissue and other findings associated with PP tears.

RESULTS

Fifty-nine patients had PP tears, 59 % were female. Most of these patients, 48/59 (81.4 %), had a single metatarsophalangeal (MTP) PP lesion in one foot, although 7/59 patients had one lesion in each foot, 3/59 (5.1 %) had two in one foot, and 1/59 (1.7 %) had three lesions in one foot. The second MTP joint was the most common location for PP tears (n = 56), followed by the third (n = 12) and fourth (n = 3) MTP joints. Lateral (n = 33) and full thickness (n = 28) PP lesions were the most frequent, and central (n = 3) and lateral/central (n = 7) tears were less prevalent. Fifty (70.5 %) PP lesions showed pericapsular fibrosis in pre-contrast sequences, and 21 (29.5 %) were visible only after administration of gadolinium. All PP lesions had collateral ligament involvement. Others findings included interosseous tendon lesions (n = 29), interosseous tendon rupture (n = 29), synovitis (n = 49), flexor tenosynovitis (n = 28), crossover toe (n = 2), hammertoe (n = 1), intermetatarsal space (IS) neuromas (n = 11), and third IS neuromas (n = 12).

CONCLUSION

PP tears are a common cause of metatarsalgia, accounting for more than 20 % of cases in our sample. A substantial portion of the lesions (29.5 %) became visible only after the administration of gadolinium.