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

Abstract

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.

Lesser metatarsophalangeal (MTP) instability is a condition where the MTP joint capsule is damaged, which allows for progressive joint hypermobility and functional impairment.^{5,17,26,39,40} It is very common, accounting for approximately 40% of cases of metatarsalgia.³⁹ If not treated, toe deformity and dislocation of the proximal phalanx will likely ensue.^{5,21-23,32,38}

Lesser MTP instability affects the second, third, and fourth MTP joints and is often bilateral.^27,32 Of these joints, the second MTP is the most commonly affected.^30,38-40 Women and the elderly are the populations at highest risk.^{4,13,27,30,32} The age range is wide, with a mean age of 60 years in the general population and 50 years in the athletic population.^{2,4,5,13,22,32} Athletes and active patients comprise 26% to 79% of cases depending on the clinic.^2,27,32 Cases occur in both acute and chronic settings across many sports.^5,7,17,29,37 Unfortunately, diagnosis is frequently delayed or missed altogether, leading to progressive instability that may require surgery.^{5,17,22,37,40}

Etiology of Lesser MTP Instability

The MTP joint is primarily stabilized by the plantar plate,^12,21,40 and damage through repetitive stress ultimately leads to an unstable joint.^6,21,34 The plantar plate is a critical anatomic structure composed of fibrocartilage that lies on the inferior aspect of the MTP joint (Figure 1).^12,14 Without its support, the proximal phalanx will deviate dorsally.^12,34

Figure 1.

Anatomy of the metatarsophalangeal joint and plantar plate.

Chronic physical stressors associated with lesser MTP instability include high heels,^5,27,30,38 a relatively long second metatarsal known as Morton’s toe,^{9,13,29,31,37} and hallux valgus.^13,37 Additionally, in aged individuals, fat pad atrophy makes the joint more vulnerable.⁹ Oftentimes, however, the cause is unknown.^{10,18,22,37,38}

The etiology is thought to be due to chronic MTP joint connective tissue damage.^6,37 As the capsule deteriorates, there is a stepwise progression of injury with synovitis, capsulitis, subluxation, and ultimately dislocation.^3,9,23,37,40 After dislocation, further deformity can occur as a crossover toe, hammertoe, or clawtoe.^{2,3,6,18,22,32,37}

Most patients present with chronic symptoms.^{10,18,19,37,38} In rare cases, some experience acute, traumatic instability.^{1,7,17,34,37,38} However, its generally slow progression allows for time to identify the condition at its earliest stage and achieve the best outcome.

Diagnosis

The signs and symptoms of a plantar plate tear are diagnostically reliable.¹⁵ Patients typically present with a gradual increase in pain and swelling at the base of the MTP joint,^{10,11,17,18,29,34,40} sometimes after increased physical activity.^38,40 Many describe the pain as similar to stepping on a marble,^31,40 making barefoot walking challenging.^15,29,40 The presentation is often due to continued pain and functional disability.^1,3,5 However, some patients may not present until deformity.¹⁸

The patient should be standing for physical examination.¹¹ The most common initial sign is inflammation and focal tenderness on the plantar aspect of the MTP joint.^10,14,16,31 Another early sign is subtle elevation of the phalanx from the ground, known as “loss of toe purchase” (Figure 2a). In severe cases, the patient can have a “crossover toe” (Figure 2b).^6,19

Figure 2.

(a) Loss of toe purchase. (b) Crossover of the second toe.

Grading the instability helps to understand severity, decide on treatment, and follow improvement. The grading system developed by Coughlin is widely used (Table 1).^6,27,29

Table 1.

Clinical staging system for second metatarsophalangeal (MTP) joint instability^a

Grade	Alignment	Physical Examination
0	MTP joint alignment; prodromal phase with pain but no deformity	MTP joint pain, thickening or swelling of the MTP joint, reduced toe purchase, negative drawer
1	Mild malalignment at MTP joint; widening of web space, medial deviation	MTP joint pain, swelling of MTP joint, loss of toe purchase, mild positive drawer (<50% subluxable)
2	Moderate malalignment; medial, lateral, dorsal, or dorsomedial deformity, hyperextension of toe	MTP joint pain, reduced swelling, no toe purchase, moderate positive drawer (>50% subluxable)
3	Severe malalignment; dorsal or dorsomedial deformity; second toe can overlap the hallux; may have flexible hammertoe	Joint and toe pain, little swelling, no toe purchase, very positive drawer (dislocatable MTP joint), flexible hammertoe
4	Dorsomedial or dorsal dislocation; severe deformity with dislocation, fixed hammertoe	Joint and toe pain, little or no swelling, no toe purchase, dislocated MTP joint, fixed hammertoe

^aFrom Coughlin et al.⁶

The best first test is the drawer test (Figure 3),^5,6,18,34 which has an 80.6% sensitivity and 99.8% specificity.¹⁹ This maneuver involves applying vertical pressure to move the phalanx dorsally relative to the MTP joint. If subluxation or dislocation is felt, the test is positive.¹⁰ A positive result is reliable and pathognomonic for lesser MTP instability.^5,18

Figure 3.

(a) Demonstration of the drawer test on a skeleton model to show dorsal movement of the proximal phalanx upon the metatarsal head. (b) Demonstration of the drawer test on a patient.

Another helpful test is the plantar grip test. The clinician places a strip of paper under the pulp of the toe. The patient grips onto the paper to prevent the clinician from pulling it out. If the paper is pulled out without tearing, the test is positive.^2,6

When diagnosing metatarsalgia, it is important to consider other possible diagnoses such as Morton’s neuroma, gout, degenerative joint disease, stress fractures, intractable plantar keratosis, and Freiberg disease.^11,14-16,32 Weightbearing anteroposterior, lateral, and oblique radiographs will narrow the diagnosis.^14,15 If the phalanx is dorsally elevated on radiograph, it is indicative of instability.^9,40 Additionally, radiographs also are helpful to demonstrate possible risk factors for MTP instability such as Morton’s toe or hallux valgus.

Symptoms of lesser MTP instability may be indistinguishable from those of neuroma, and it is not uncommon for the 2 conditions to coexist in the same foot.^24,40 Patients with lesser MTP instability have often been misdiagnosed with a neuroma, and 3% to 14% have undergone unsuccessful neuroma resection.^4,5,18 Numbness, shooting pains, and pain between the metatarsal heads are all indicators of neuroma.^3,9,14,32 In cases of high-grade instability, the drawer test will easily differentiate the 2 conditions.

Magnetic resonance imaging (MRI) is very helpful when the diagnosis is still in doubt, and it can even define the characteristics of grade 0 instability.^15,25 MRI gives excellent visualization of the plantar plate and is preferred to joint arthrography or ultrasound.^{10,14,16,19,20,35} In a diagnostic study, 0.31-T MRI without contrast with 3.5-mm slice thickness had 95% sensitivity, 100% specificity, 100% positive predictive value, and 67% negative predictive value in diagnosing a plantar plate tear.³⁵

Conservative Options

Patient education is a key aspect of treatment. Conservative treatment relies on adherence to a cumbersome treatment plan. Better adherence rates are shown to occur when providing more information, being friendly and responsive, justifying the treatment (and acknowledging inconveniences), emphasizing the importance of adherence, and monitoring for lapses.^8,36

Conservative treatment modalities are best suited for patients in the early stages (grades 0-2 on the Coughlin grading system).^34,40 Offloading and immobilizing the joint is first-line treatment for acute inflammation.^17,29 A postoperative shoe serves this purpose^1,17,29 and should be worn full-time while the acute inflammation subsides (1 week to 6 months).^1,17,29 Weightbearing athletic activities should be suspended until the pain and swelling have greatly decreased.^1,17,29 For those who cannot tolerate a postoperative shoe, rocker bottom or stiff-soled shoes can be used instead.^6,37,40

While wearing the postoperative shoe, the toe should be sling-taped in a 10° plantarflexed position to allow for fibrosis and joint stabilization (Figure 4).^1,6,17,31,40 To accommodate for a toe that is taped in plantarflexion, a customizable insole such as the Darco Peg-Assist provides a recess for the phalanx.¹⁷ Some feel that taping is not helpful if complete dislocation has occurred and also warn that chronic taping can lead to ulceration.³ In cases where taping is problematic, the joint can be stabilized with a Budin splint, which is a flat sole pad with an elastic band that wraps around the toe.^1,29,33

Figure 4.

Sling-taping technique for metatarsophalangeal stabilization. (a) Dorsal view. (b) Plantar view.

When the joint is no longer acutely inflamed, the patient can transition to sneakers with a metatarsal pad placed 3 to 4 cm posterior to the MTP joint (Figure 5).^{3,6,9,31,33,40} These offloading pads should be worn along with sling-taping while the joint fully stabilizes. During this time, the patient is allowed to be ambulate freely.⁴⁰ Athletic activities may be resumed when the drawer is stable on examination.¹⁷

Figure 5.

(a) Offloading metatarsal pad. (b) Proper placement proximal to the metatarsophalangeal joint.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are helpful for symptomatic relief.^6,31,40 Intra-articular steroid injections are also used, but repeated injection may increase the risk of dislocation by attenuating an already damaged plantar plate.^6,31,40 Therefore, they should be used judiciously. If an injection is performed, the joint should be stabilized by buddy-taping or splinting along with weightbearing restriction for 6 weeks.^31,40

The treatment approach should be individualized, with those involved in higher impact sports requiring more time.³³ Although recovery is lengthy, patients have even been able to resume their prior level of athletic ability.^17,29 A study using the strategy of offloading and immobilization in a postoperative shoe, followed by taping and offloading pads, allowed for resumption of prior athletic ability at 1 year.¹⁷ Further, there was MRI proof that the plantar plate incrementally healed over the year.

Another study followed the treatment of a ballerina with grade 2 instability. She was initially prescribed a postoperative shoe and Budin splint during an activity restriction period. She was transitioned to sneakers with an offloading metatarsal pad and sling-taping during a tapered reintroduction to dancing over 14 weeks. At 1 year, she was back to pain-free dancing.²⁹

Similar treatment strategies to the two aforementioned studies have been proposed¹; however, most studies neither immobilize the joint nor use offloading metatarsal pads. In the largest study of conservative care for lesser MTP instability, 99 patients were treated conservatively versus 55 treated operatively. The conservative group had 52% satisfaction with a treatment plan that included NSAIDs, footwear advice, steroid injections, functional taping, or a combination of the above.³⁰

Three early studies using intra-articular steroids with footwear modification claim 47% to 70% became asymptomatic.^23,32,38 Unfortunately, progressive deformities consistently developed in these studies, possibly due to steroid injections and lack of taping to stabilize the joint. Another study found NSAIDs, broad-soled shoes, and metatarsal padding were insufficient to prevent surgery.²² Finally, in a study of active individuals, simply taping the joint allowed some to maintain their activities with success. It is notable that 1 patient in this study who discontinued taping had progression of deformity that required amputation.⁵

Surgical Options

When conservative options are exhausted, surgical fixation can be considered.^{9,10,14,16,30,31} Referrals can be made to either foot and ankle surgeons or podiatrists experienced in surgical correction of MTP instability.

Surgery is not the panacea, with satisfaction ratings from 67% to 75%.^2,13,24 In a study comparing conservative treatment with surgery, there were no statistical differences in satisfaction, pain, or functionality.³⁰ In other studies, 31% had difficulty with weightbearing exercise at follow-up,² and 25% were unable to regain their previous level of function.²⁶ Common adverse outcomes are painful hardware, continued pain, recurrence of deformity, loss of toe purchase, neuritis, residual swelling, infection, and stiffness.^2,3,13,24

After surgery, patients should wear a postoperative shoe for 4 to 6 weeks.^2,26,28,33 During this time, the phalanx should be taped in a plantarflexed position, just as is recommended for conservative management.^2,26,28,33 Complete healing takes 3 to 6 months, during which time the patient should wear stiff-soled or rocker-bottom shoes to offload the joint.^2,28,33 High-impact sports should be avoided for 1 year, and return should be gradual.²⁸

Conclusion

Lesser MTP instability is a commonly encountered condition that is frequently misdiagnosed. When patients present with metatarsalgia, the clinician should note specific symptoms such as a gradual increase in pain and swelling of the MTP joint. During an examination, the physician should check for location of pain, phalanx position, and loss of toe purchase. Most importantly, a drawer test should be performed.

Lesser MTP instability is progressive, and, therefore, it is important to make the diagnosis in its earliest stages when conservative therapy is most effective. The optimal treatment plan is to initially immobilize the joint with a postoperative shoe and utilize taping for the acute phase of inflammation and swelling. This is followed by continued taping and an offloading metatarsal pad in sneakers. Return to activity should be gradual, and a stable drawer test can determine when it is advisable. Successful diagnosis and management can spare the patient the pain, expenses, and risks of an operation.