Biomechanical Considerations In Treating Metatarsalgia

Metatarsalgia can have a multitude of causes, making it vital to identify the etiology and treat the specific causes of this complex condition. This author evaluates the research on conservative treatment of metatarsalgia, specifically the use of metatarsal pads, and offers pearls on effective custom orthosis prescriptions.

Metatarsalgia is a broad term we use to describe pain in the ball of the foot. Often considered a symptom, a diagnosis or both, the condition can be complex. The patient may have symptoms in or near the metatarsal heads, the metatarsophalangeal joints (MPJs) or soft tissue structures. There can be multiple causes of metatarsalgia, including biomechanical imbalance, systemic disease or localized pathology, which all require different approaches to treatment. A differential diagnosis should include neuroma, capsulitis, bursitis, plantar plate tear, stress fracture, fat pad atrophy, Freiberg’s infraction, rheumatoid arthritis, sesamoiditis and calluses.

Several authors have classified metatarsalgia. Scranton identified 23 different causes of metatarsalgia in 98 patients using force plate analysis and nerve blocks.¹ Forty-five patients had primary metatarsalgia, 12 of whom had static disorders and 12 of whom had iatrogenic etiologies. Thirty-three had secondary metatarsalgia, 11 of whom had rheumatoid arthritis and 10 of whom had sesamoiditis. Twenty patients had pain under the forefoot.

Helal also classified metatarsalgia as primary and secondary with primary metatarsalgia being an anatomic abnormality resulting in increased pressure under the metatarsal heads.² Examples of primary metatarsalgia include short/long first metatarsals, hallux valgus, hallux rigidus and first ray hypermobility. Secondary metatarsalgia is pain not originating in the metatarsal area. Secondary causes include Morton’s neuroma, rheumatoid arthritis, equinus deformities and Freiberg’s infraction. Regnauld classified metatarsalgia as diffuse, localized, subcutaneous soft tissue and cutaneous tissue.³

When it comes to metatarsalgia, it is often a process of elimination to identify a definitive diagnosis. The physician must identify the etiology and focus treatment on the specific cause. Besides taking the history and physical findings into consideration, other modalities like ultrasound or magnetic resonance imaging, with or without contrast, may be necessary to obtain a definitive diagnosis.
The foot functions to balance and support forward locomotion by acting as a mobile adaptor to the ground and as a rigid lever during propulsion at the early and late phases of stance. Forefoot pathomechanics result from an overload of the anterior support or an irregular distribution of the metatarsal weightbearing load.

Most studies evaluating gait and patients with biomechanical imbalances have focused on patients with rheumatoid arthritis. A gait specific study of 11 patients with rheumatoid arthritis versus five non-rheumatoid arthritis patients with metatarsalgia addressed joint motion.⁴ The authors found that all the patients with rheumatoid arthritis had a decreased range of motion in all planes of motion. During the gait cycle, there was more rearfoot eversion and reduced forefoot motion. The authors hypothesized that this led to shorter strides, slower walking and limited propulsion, leading to metatarsalgia.

How Effective Are Orthoses In Treating Metatarsalgia?
When considering treatment for metatarsalgia, one must weigh surgical versus non-surgical options. The one consistent approach for podiatrists in treating metatarsalgia is the use of orthotics. While very few studies support the use of orthotics, podiatrists and other medical professions have used them for years. The goals of orthotic therapy in treating metatarsalgia are rebalancing the metatarsal load and, when necessary, cushioning the affected metatarsal heads. Not much has changed in the last several years in treating metatarsalgia with orthotics and the same modifications apply today as they did decades ago. What has changed, though, is the use of plantar pressure analysis to monitor proper placement and evaluate the effectiveness of the orthotic and pads.

Over the course of time, there have been modifications to orthotics to assist in relief of metatarsalgia symptoms. Metatarsal pads, metatarsal bars and reverse Morton’s extensions are some of the more common additions to orthotics to help address metatarsalgia. The use of metatarsal pads is the most common accommodation for treating metatarsalgia with orthotics.

The primary purpose of metatarsal pads is to transfer the weight proximally to the metatarsal shafts. Authors believe that theoretically, such reductions occur by redistributing plantar forces across a larger area of the foot.⁵ The addition of metatarsal pads is a mainstay in treating neuromas with orthotics with the purpose of separating the metatarsal heads. Studying a total of 28 patients, Koenraadt and colleagues found the use of metatarsal pads increased the width of the forefoot, which they say supports the use of metatarsal pads in the treatment of neuromas.⁶

Metatarsal pads come in different shapes, sizes and thicknesses, thus making it difficult to know what works best. Podiatrists often use metatarsal pads, not only for metatarsalgia but for diabetic ulcers, rheumatoid arthritis and pes planus deformities as well.

A Closer Look At The Research On Metatarsal Pad Placement
While a variety of forefoot pads exist, the effectiveness of these different pads in reducing forefoot pressures is inconsistent.⁷ Hayda and colleagues found inconclusive results with proper placement of metatarsal pads, and noted that improper placement of the pads may in fact increase plantar pressures.⁸ Evaluating 10 volunteers with normal, asymptomatic feet, the authors found that the small felt pad caused the greatest and most consistent decrease in pressure at the metatarsal heads while distal positioning tended to cause the greatest decreases in pressure for all pad types.

Landorf and colleagues found that positioning a PPT metatarsal pad (Langer) 5 mm distal to the metatarsal head was more effective in relieving pressure than a metatarsal bar or positioning a metatarsal pad 10 mm distal to the metatarsal head.6 In a study of 20 patients with diabetic neuropathy and a history of forefoot plantar ulcers, Hastings and coworkers identified proper placement for the best pressure reductions to be 6.1 to 10.6 mm proximal to the metatarsal head.⁹ Hsi and coworkers, in a study of 10 patients with metatarsalgia, concluded that optimum pressure reduction occurs by placing the metatarsal pad just proximal to the metatarsal head.¹⁰

In a study of 35 patients, Deshaies and colleagues found that metatarsal bars were better than metatarsal pads at reducing the impulse at the second metatarsal head when physicians placed them obliquely as opposed to perpendicular.¹⁰ This can be somewhat misleading because most metatarsal bars referenced in the literature are bars attached to the outsole of a shoe and not ones placed on a custom foot orthotic.

Nordsiden and colleagues studied the effect of three different metatarsal pads on peak pressure: a metatarsal dome, a U-shaped pad and a donut-shaped pad in 20 patients.¹² They found the metatarsal dome pads to be most effective at reducing both peak pressures and mean plantar pressures, and that the metatarsal dome pads were slightly better than the U-shaped pads. Comfort was another factor and participants found the metatarsal dome pad to be the most comfortable.  

In-shoe pressure measurements are one exceptional way of evaluating the effectiveness and placement of metatarsal pads but this is limited in a clinical setting by cost. While adding metatarsal pads to orthotics occurs widely in the podiatric community, the results of some studies have uncovered mixed results.

Only a small sample size of peak pressure studies have used some form of an orthotic in patients with metatarsalgia. Postema and co-workers looked at peak pressure changes and pain score changes using custom orthotics and prefabricated orthotics with and without the use of a rocker bar in 42 patients with a history of primary metatarsalgia.¹³ The study authors noted that at the central distal forefoot, a rocker bar caused a decrease in force impulse of 15.1 percent and a decrease in peak pressure of 15.7 percent while the custom-molded insole produced decreases of 10.1 percent in force impulse and 18.2 percent in peak pressure. Postema and colleagues also found that pain scores were significantly lower for interventions with a custom-molded insole while the rocker bar showed no influence on pain scores.

Kang and coworkers investigated the effectiveness of accommodative insoles and plantar pressure distribution in patients with metatarsalgia.¹⁴ The authors examined the use of an ethylene vinyl acetate (EVA) control, 9 mm flat Plastazote and accommodative insoles with and without metatarsal and arch support in 18 feet. Using in-shoe pressure measurements to obtain peak pressures and the Visual Analogue Scale (VAS) to assess pain scores, they found that metatarsal pads improved maximum peak pressure and pressure-time intervals under the second metatarsal heads, and improved VAS scores in symptomatic patients.

In a study of patients with central metatarsalgia, Schuh and colleagues evaluated plantar pressures and pain levels in 42 feet using a normal walking shoe, a standard sandal, and a custom-made sandal with a metatarsal pad.¹⁵ They found that the average walking distance until symptoms started was 1,894 meters for the walking shoe, 1,812 meters for the standard sandal and 3,407 meters for the custom sandal with a metatarsal pad. Other studies involving patients with rheumatoid arthritis have concluded the use of orthotics with metatarsal pads reduced peak pressures and pressure-time intervals, and provided pain relief.^16,17

Current Insights On Writing Orthotic Prescriptions For Metatarsalgia
After determining the etiology, the physician can then write an orthotic prescription. One should be familiar with the primary and secondary cause of metatarsalgia when developing a custom orthotic prescription.

Based on the literature, a semi-rigid device is superior to a softer device. One can use a minimum arch fill to increase the contact of the orthotic with the plantar foot.¹⁸ Ki and colleagues found that orthoses with minimum arch fill were superior to flat insoles in redistributing peak pressures.¹⁹

Excessive rearfoot eversion can increase the ground reaction forces under the first metatarsal head, leading to first ray dorsiflexion, decreased first metatarsal weightbearing and increased lesser metatarsal weightbearing, especially the second metatarsal. When casting, fully load and pronate the midtarsal joint, and plantarflex the first metatarsal. This enhances the weightbearing under the first metatarsal and prescribing a wide plate increases contact with the medial foot. Most studies have identified unloading the metatarsals as a necessity in the treatment of metatarsalgia and adding a metatarsal pad will accomplish this goal. The consensus of the literature is that placement should be proximal to the metatarsal heads.^9-11

If fat pad atrophy is present and shock absorption is required, then a full-length, softer topcover using Poron, Plastazote or closed-cell neoprene would be the best choice. Rearfoot posting and a standard heel cup depth should be sufficient. If there is early heel off leading to overload of the metatarsal heads, add a heel lift to the rearfoot post.

In Summary
An orthotic prescription for metatarsalgia should involve a semi-rigid device, minimum arch fill, a wide plate, a metatarsal pad or bar, a rearfoot post with standard heel cup depth, and a full-length cushioned topcover using Poron, Plastazote or closed-cell Neoprene. One option is to leave the distal half of the topcover unglued so one can alter the metatarsal pad placement.   

Metatarsalgia can be a complex and frustrating condition to treat, but one must correctly identify the etiology and then focus on a treatment plan. Custom foot orthotics can be an important option in the treatment of metatarsalgia and understanding the literature and prescription options is imperative in order to achieve the desired result we all want.

Dr. Yakel is in private practice in Boulder, Colo. He is the Immediate Past President of the American Academy of Podiatric Sports Medicine and the team podiatrist for the Colorado Rapids of Major League Soccer.

References

1.     Scranton PE. Metatarsalgia: diagnosis and treatment. J Bone Joint Surg Am. 1980; 62(5):723-732.  
2.     Helal B, Thomas N, Nissen KI. Disorders of the lesser ray. In: Helal B, Wilson D (eds.): The Foot. Churchill Livingstone, New York, 1988, p. 486.    
3.     Regnauld B. Selective overloading of metatarsal heads. In The Foot. Springer-Verlag, Berlin, 1986, pp. 75-97.
4.     Woodburn J, Nelson K, Siegel K. Multisegment foot motion during gait: proof of concept in rheumatoid arthritis. J Rheumatol. 2004; 31(1):1918-1927.
5.     Landorf KB, Lee PY, Bonanno DR, Menz HB. Comparison of the pressure-relieving properties of various types of forefoot pads in older people with forefoot pain. Foot Ankle Res. 2014; 7(1):18.
6.     Koenraadt, KL, Stolwijk NM, van den Wildenberg D, Duysens J, Keijsers NL. Effect of a metatarsal pad on the forefoot during gait. J Am Podiatr Med Assoc. 2012; 102(1):18-24.  
7.     Curran M. Mechanical therapeutics in the clinic. In: Turner WA, Merriman LM (eds): Clinical Skills in Treating the Foot, Second Edition. Elsevier Churchill Livingstone, Edinburgh, 2005, pp. 231-264.
8.     Hayda R, Tremaine MD, Tremaine K, Banco S, Teed K. Effect of metatarsal pads and their positioning: a quantitative assessment. Foot Ankle Int. 1994; 15(10):561-6.
9.     Hastings MK, Mueller MJ, Pilgram TK, Lott DJ, Commean PK, Johnson JE. Effect of metatarsal pad placement on plantar pressure in people with diabetes mellitus and peripheral neuropathy. Foot Ankle Int. 2007; 28(1):84-88.  
10.     Hsi WL, Kang JH, Lee XX. Optimum position of metatarsal pad in metatarsalgia for pressure relief. Am J Phys Med Rehabil. 2005;84(7):514-20.
11.     Deshaies A, Roy P, Symeonidis PD, LaRue B, Murphy N, Anctil E. Metatarsal bars more effective than metatarsal pads in reducing impulse on the second metatarsal head. Foot (Edinb). 2011;21(4):172-5.
12.     Nordsiden L, Van Lunen BL, Walker ML, Cortes N, Pasquale M, Onate JA. The effect of 3 foot pads on plantar pressure of pes planus foot type. J Sport Rehabil. 2010;19(1):71-85.
13.     Postema K, Burm P, Zande M, Limbeek J. Primary metatarsalgia: the influence of a custom molded insole and a rockerbar on plantar pressure. Prosthet Orthot Int. 1998; 22(1):35-44.
14.     Kang JH, Chen MD, Chen SC, Hsi WL. Correlations between subjective treatment responses and plantar pressure parameters of metatarsal pad treatment in metatarsalgia patients: a prospective study. BMC Musculoskelet Disord. 2006;7:95.
15.     Schuh R, Seeqmueller J, Wanivenhaus AH, Windhager R, Sabeti-Aschaf M. Comparison of plantar-pressure distribution and clinical impact of anatomically shaped sandals, off-the-shelf sandals, and normal walking shoes in patients with central metatarsalgia. Int Orthop. 2014; 38(11):2281-2288.  
16.     Hodge MC, Bach TM, Carter GM. Orthotic management of plantar pressure and pain in rheumatoid arthritis. Clinical Biomech. 1999;14(8):567-575.
17.     De Magalhaes E, Davitt M, Filho DJ. The effect of foot orthoses in rheumatoid arthritis. Rheumatology. 2006; 45(4):449-453.
18.     Chalmers AC, Busby C, Goyert J, et al. Metatarsalgia and rheumatoid arthritis—a randomized, single blind, sequential trial comparing two types of foot orthoses and supportive shoes. J Rheumatol. 2000; 27(7):1643-1647.
19.     Ki SW, Leung AK, Li AN. Comparison of plantar pressure distribution patterns between foot orthoses provided by the CAD-CAM and foam impression methods. Prosthet Orthot Int. 2008; 32(3):356-362.

Editor’s note: For related articles, see “A Guide To Orthotic Treatment For Metatarsalgia” in the April 2012 issue of Podiatry Today or “Lesser Metatarsalgia: Are Lesser Metatarsal Osteotomies Necessary?” in the February 2013 issue.