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The information - metatarsalgia

Musculoskeletal GPSI Dr Louise Warburton continues our series on common presentations based on PUNs and DENs

 

The patient's unmet needs (PUNs)

A 38-year-old woman attends with a painful left forefoot. She's a keep-fit enthusiast and is finding that the pain is interfering with her activities. There is no history of trauma. Six weeks ago she consulted and was given some simple advice about rest, padding and analgesia. She's tried taking a break from exercise and has taken some anti-inflammatories – to no avail. Now she wants a specific diagnosis and definitive treatment. Examination reveals tenderness and slight swelling on the dorsum of the foot over the middle metatarsals, and tenderness on the sole in the same area.

The doctor's educational needs (DENs)

What are the likely differential diagnoses? What clues are present in the history or examination?

The likely differential diagnoses in a keep-fit enthusiast must always include trauma, even if it is not reported. Stress fractures can occur after minimal trauma, which is often not recalled by the patient. As this patient has had problems for over six weeks, the swelling may be bony callus formation. The callus is easily felt and will be tender – careful palpation will reveal this.

Inflammatory arthritis is another differential diagnosis – the area will be tender and there will be a positive metatarsal squeeze test. Movement of one metatarsal head against another may produce an audible click, called a Mulder's click, and a feeling of a sudden release between the bones. In rheumatoid arthritis, you would expect hand symptoms as well.

Morton's neuroma is a swelling on an inter-digital nerve in the foot due to poorly fitting shoes or foot deformities. The pain tends to come in sharp flashes, similar to trigeminal neuralgia, and there may be numbness in the associated toes. The patient describes feeling like they are walking on a pebble. Again, a metatarsal squeeze test will be positive.

Osteoarthritis can also present with a painful swelling in the foot, so look for further signs such as Heberden's nodes and hammer toes. This is more common in the over-50s, but can occur in younger patients.

Plantar fasciitis typically causes pain in the heel due to tendonopathy within the attachment of the plantar fascia to the calcaneum. But occasionally it causes pain in the forefoot at the other end of the plantar fascia where it attaches to the metatarsal heads – causing metatarsalgia.1

Gout can present in the feet, though it is more common in the first metatarsal and is not common in athletes. Finally, don't forget to consider peripheral neuropathy, due to diabetes or other causes.

Cases like this are common in general practice and may present relatively early – is it possible to make a confident diagnosis at this stage, and is it likely to alter the initial management?

Many of the causes of metatarsalgia are initially difficult to diagnose, since most causes present with the same ill-defined pain in the sole of the foot, made worse by standing and exercise. Initial conservative measures will often relieve the symptoms, regardless of the underlying cause. If these measures are successful then it is not necessary to pursue a definite cause.

In a mild case without a clear diagnosis, what measures should be suggested?

Conservative measures include advising well-padded footwear and shoes that have plenty of room in the toe area. You can also advise on weight loss if appropriate. If the patient has only recently started exercising, a gradual increase in duration and intensity is recommended – generally not more than 10% per week.

The patient could also try using metatarsal pads, which are available over the counter. The pad should be placed just proximal to the area of tenderness to reduce pressure.

At what point should X-rays or bone scans be considered? What other investigations are likely to be useful?

Initially, formal investigations should not be necessary – though an assessment of BMI and of gait may be useful.

If the condition does not respond to conservative measures within a couple of months, then an X-ray of the foot would be indicated to look for evidence of osteoarthritis, subluxed metatarsal heads and hammer toes.

Stress fractures do not always show up on X-rays taken immediately after presentation, so repeat the X-ray after four to six weeks if the condition is not settling.

If an X-ray is unhelpful, then a referral may be indicated. Ultrasound scanning can identify plantar fasciitis and Morton's neuroma very well, and an MRI will demonstrate synovitis, neuromas, and any bone or soft tissue abnormality. Isotope bone scans are useful to identify infection or acute inflammatory arthritis.

Further investigations include:

  • ESR and C-reactive protein – these will be raised in inflammation and infection 
  • rheumatoid factor and anti-nuclear factor immune markers – if there is any suspicion of inflammatory arthritis
  • FBC – can show the anaemia of chronic disease, in the case of inflammatory arthritis
  • serum urate level – to screen for gout, but this may be normal in an acute attack, so is best done two to three weeks afterwards
  • U&E – to screen for renal impairment, which may cause gout or osteomalacia
  • LFTs – raised alkaline phosphatise may point to a fracture or bony destruction
  • fasting glucose levels – to exclude diabetes.

At what point is referral appropriate? Are patients best directed to a physiotherapist, a podiatrist or an orthopaedic surgeon?

Mild cases can be managed entirely within primary care and consist of basic lifestyle modifications as discussed above. Remember that advice for this condition will tick many of the QOF indicators around obesity, and it is a good opportunity to screen for other comorbidities such as hypertension and diabetes.

If the pain is preventing the patient from walking or taking exercise and has not responded to conservative measures over a couple of months, then referral is indicated.

If the cause is unclear, a podiatrist would be an excellent person to take over the assessment and management. They will be able to fashion insoles to take the load off the problem parts of the foot and may have access to some investigations such as ultrasound. They can also help with conservative measures.

Physiotherapists have a complementary role to podiatrists and often step in in areas where podiatry services are over-stretched or nonexistent.

If there is a red-flag diagnosis or suspicion of fracture or inflammatory arthritis – even if blood tests are normal – then referral to orthopaedics or rheumatology is indicated.

Key points

Common contributing factors

  • Obesity.
  • Change in exercise habit – the patient may have started exercising having been sedentary for years.
  • Poorly fitting footwear – it can be useful to get the patient to draw around their foot on a piece of paper and then place their shoe on top. It is often clear that the foot is being compressed.
  • Footwear with a thin sole does not offer any shock absorbing capacity and can cause metatarsalgia. Training shoes lose their shock-absorbing capacity after a few months, so advise patients to buy new trainers regularly.

Red flags

  • Is the swelling bony? Could it represent a sarcoma?
  • Septic arthritis could present as a swollen area within the foot. This is more common in patients with diabetes and those with multiple other pathologies.

Treatment

  • In osteoarthritis, X-ray guided injection of steroid and local anaesthetic into the affected joints is often successful.
  • Steroid injection is also useful in Morton's neuroma  for reducing pain in the short term. But it does not reduce the need for surgical intervention.
  • Steroid injection with a local anaesthetic may be effective in Plantar fasciitis.
  • Management of hammer toes includes padding within footwear, metatarsal bars in the shoes which take the weight off the metatarsal area and ultimately surgery to correct the deformities.

 

Dr Louise Warburton is a GPSI in rheumatology and musculoskeletal medicine for NHS Telford and Wrekin, and president of the Primary Care Rheumatology Society

The Primary Care Rheumatology Society (PCRS) is a group of GPs and allied health professionals who promote best practice in musculoskeletal disorders. Annual membership is £75 and free for GP registrars and medical students. Membership gives you access to the PCRS's guidelines and best practice guides. The PCRS has an annual conference in York in autumn each year. Go to pcrsociety.org for more information.

 

References

1 The Arthritis Research Campaign. Hands on: information and exercise sheet (HO2) – plantar fasciitis, inflammation of the instep tendons. February 2004

Further reading

  • The Arthritis Research Campaign. Reports on the rheumatic diseases, series 5. Hands on: common foot disorders. October 2006
  • Clinical Knowledge Summaries. Musculoskeletal. 2011.cks.nhs.uk

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