BATTLE OF THE WEBSPACES

MORTON’S NEUROMA VS. INTERMETATARSAL

BURSITISCaitlin gardiner

BEFORE THE BATTLE BEGINS…A healthy web space will be composed of fat and connective tissue. Two commonly encountered pathologies of the webspaces include Morton’s Neuromas and Intermetatarsal Bursitis. Such pathologies are often

difficult to distinguish on ultrasound.

BEFORE THE BATTLE BEGINS…A healthy web space will be composed of fat and connective tissue. Two commonly encountered pathologies of the webspaces include Morton’s Neuromas and Intermetatarsal Bursitis. Such pathologies are often

difficult to distinguish on ultrasound.

MORTON’S NEUROMA Morton’s Neuroma is a lesion caused by fibrous degeneration of the plantar digital nerve characteristic to the forefoot (McNally, 2005). The condition, however, is not necessarily an abnormal growth of the nerve and may be attributed to fibrous and vascular anomalies (Hauser et al, 2012). Chronic irritation, trauma or excessive motion between metatarsal heads gives rise to the condition (Hauser et al, 2012). Morton’s neuromas are frequently encountered in the third/fourth and second/third web spaces and are rare in the first/second and fourth/fifth. It is rare for multiple neuromas to occur in both or one foot (Hauser et al, 2012). Typically occurring in middle-aged women, presentation is often a complaint of pain and paraesthesia in the web space particularly in weight-bearing exercise (Hauser et al, 2012). Tight footwear has been attributed to the disease aetiology (McNally, 2005). Ultrasound technique has greatest sensitivity when assessed from the plantar aspect of the foot. A Morton’s neuroma is characterised by a hypoechoic, poorly defined mass within the metatarsal heads. Limitations include narrow metatarsal head spaces. Both a transverse and longitudinal assessment should be undertaken from both the dorsal and plantar aspect of the foot. Dorsal approach is best employed with the knee flexed and the patient’s foot flat on the bed with a relaxed ankle. Extend the leg with the ankle gently flexed to assess from a plantar approach. Improved sonographic technique includes the ability to palpate the foot from a dorsal approach, or gently squeezing the metatarsal heads. Upon doing so, the neuroma should displace surrounding tissues, but not itself be compressible (Lee, 2009) Often a clicking noise, a Moulder’s Click, will be audible (McNally, 2005). CASE STUDYPresentation: A 52 year old male presents with long-standing foot pain in the 2/3 webspace. Over the past 2 years he has been managing the pain with over-the-counter medications and trying various footwear with little success. The patient describes the sensation of a palpable mass in his shoe. Findings:Routine assessment of the flexor and extensor tendons, MTPJ joints and plantar plates is undertaken. Synovitis and mild bony degeneration is noted of the 1st MTPJ as seen in the following image. No other joint anomaly is noted.

All webspaces of no clinical significance show no pathological features. Dorsal assessment of the clinical region, the right 2/3 webspace, shows a poorly-definable, heterogeneous, hypoechoic ovoid lesion measuring 26*16*15mm (see image below).

When the same webspace is assessed from a plantar aspect, it allows for better manipulation to assess the solidity of the lesion. By applying significant probe pressure from a plantar approach against the sonographer’s fingers on the dorsal side, the lesion appears non-compressible and causes a slight displacement of the surrounding connective tissues (see following image). The same effect is noted when the metatarsal heads are compressed, known as the Moulder’s Test (Bianchi and Martinoli, 2007).

The lesion is, therefore, described as a likely Morton’s neuroma.

INTERMETATARSAL BURSITIS The intermetatarsal bursa facilitate movement of the metatarsal heads and surrounding structures. In asymptomatic patients it contains only a small amount of fluid but is considered inflamed when the transverse diameter exceeds 3mm (Bianchi). Inferiorly, the bursa are in close proximity to the neurovascular bundles, attributing to the pain felt by sufferers (Hauser)Similarly to assessment for a Morton’s Neuroma, both a transverse and longitudinal assessment should be undertaken from both the dorsal and plantar aspect of the foot. On ultrasound evaluation, intermetatarsal bursitis appears as an echo-free structure with posterior enhancement that displaces with compression (Bianchi and Martinoli, 2007).CASE STUDYPresentation: A 54 year old women presents with pain in her right 2/3 webspace. She describes the pain as longstanding, with fluctuations in severity. Findings: Routine assessment of the flexor and extensor tendons, MTPJ joints and plantar plates is undertaken to reveal no anomaly. All webspaces of no clinical significance also show no pathological features.When assessed from a dorsal approach, the clinical region, the right 2/3 webspace, shows little difference on comparison to the other joint spaces. Plantar assessment, however, shows an irregular, hypoechoic region. When compression is applied to the lesion, it displaces significantly as seen below. The lesion, is assumed to be fluid and therefore suggestive of intermetatarsal bursitis.

ALTERNATIVE DIAGNOSISStress and fatigue injuries of the foot may be visualised during US assessment commonly involving the second and third metatarsals (Bianchi and Martinoli, 2007). Freiberg infraction is a disorder of both trauma and vascular predisposition involving the second or third metatarsal head. Freiberg infarction presents with pain and limited motion and is seen as degenerative arthrosis (McNally). Turf toe is caused by hyper extension injury at the first metatarsophalangeal which has resulted in disruption of the volar fibrocartilaginous plantar plate (Bianchi and Martinoli, 2007). Increased distance between the sesamoid and the base of the 1st ray can indicate complete rupture (McNally)

References:Bianchi S and Martinoli C, 2007. Ultrasound of the Musculoskeletal System. Springer, New York. Hauser RA, Feister WA, Brinker DK, 2012. Dextrose Prolotherapy Treatment for Unresolved ‘Morton’s Neuroma’ Pain. The Foot and Ankle Online Journal; 5(6):1Lee KS, 2009. Musculoskeletal Ultrasound: How to Evaluate for Morton’s Neuroma. AJR; 193(3): McNally EG, 2005. Practical Musculoskeletal Ultrasound. Elsevier, Philadelphia.