Why do toes turn purple in a cast while standing? (+1 facts)

In this article, we will discuss why your toos turn purple in the cast when standing. We will also discuss physiological and metabolic changes that may cause purple toes while wearing a cast.

Why do toes turn purple in a cast while standing?

The toes turn purple in a cast while standing mainly because of reduced blood supply and muscle tone in the lower limb. Experimental data suggests that extravascular fluid accumulates in the foot due to capillary fragility when wearing a leg cast (1).

This causes venous engorgement, swelling, and inflammation that alters the blood supply to the toes. Total blood volume may decline by 5.4% due to immobilization in a cast (1). Purple toe is an indication of tissue ischemia and cyanosis (reduced blood flow and oxygen).

Immediately consult your orthopaedic surgeon if you observe purple toes to prevent prolonged damage to the tissues. Most physiological functions are restored to normal after three to four weeks of applying a cast. Exercise tolerance and leg girth may take four to six weeks. 

What causes toes to turn purple while standing in a cast?

Tissue ischemia and purple toe may occur due to poorly fitted cast or improper cast application. However, if the cast has been applied correctly and still purple toe is seen while standing then this may indicate an underlying disease.

Cast issues

When the cast is too tight it may cause compression of the nerves and blood vessels. This is known as compartment syndrome and causes toes to turn purple while standing or lying down. It may also cause numbness, severe pain, and nerve damage.

A firmly wrapped cast acts as a stiff compression on the extremities, Increased pressure causes the area to be poorly perfused, resulting in pressure sores, decreased blood supply and cyanosis. Below-knee casts that stop at the fibula neck put undue pressure on the location and may cause peroneal nerve palsy. 

Prolonged immobilization may cause joint stiffness, muscular atrophy, and osteoporosis. It may also cause degeneration, ligament weakness, and tissue ischemia. Due to improper circulation of the blood, deoxygenated blood (blue/purple) becomes evident at the site of a cast.

Disease condition

Inflammation and swelling due to prolonged standing or sitting while keeping the leg lower may cause tightening and increase the pressure of the cast on the leg. This may hinder the blood supply, leading to purple toes. 

The purple toe may also be caused by a lack of blood circulation to the feet due to a plaque on the interior of the arteries. The plaque fragment or a blood clot may stop the blood supply in the foot.

Deep nerve thrombosis is a prominent concern in the adult population following lower limb immobilization due to cast. Two independent studies discovered that people with a lower limb cast (3 weeks or more) had a deep nerve thrombosis incidence of 15-36% (2, 3).

What physiological changes turn toes purple in a cast?

Various physiological and metabolic changes may turn the toes purple in the cast when standing. Prolonged immobilization alters the mechanism essential for blood circulation in the lower limb region, including a reduction in venous or muscle tone.

The blood capillaries become fragile, which allows the interstitial fluid to seep into the adjoining area. The total blood volume also decreases by 5.4% in the immobilized area. Purple toes may also occur due to increased blood urea nitrogen levels in the blood (1).

Studies have shown that nitrogen excretion increases on the fifth day of wearing a cast and peaks in the first half of the second week. Even though creatine and creatinine excretion remain constant, there is a significant decrease in creatine tolerance while wearing a cast.

This reduction in creatinine tolerance reduces the muscle mass and strength in the limb while standing up. If the patient has an increased level of creatinine then it may signify renal failure associated with blue toe syndrome (4).

How to prevent toes from turning purple in a cast?

Limb casting should be done by an experienced orthopaedic doctor or cast technician who is skilled with the application of padding over pressure points. He should also know the strategic placement of cast windows to prevent pressure sores.

While sitting, you should keep your cast raised (horizontally) to reduce the occurrence of swelling and interstitial fluid accumulation. To help increase circulation, exercise with the other leg or arms, knee, fingers and even toes.

Do not put unnecessary weight on the fractured leg or foot, use crutches as required. You may take pain killers like ibuprofen and paracetamol for mild pain. If you are allergic to ibuprofen, you may take naproxen. If the pain is excruciating, intravenous opioids may be given.

Wearing a cast for a prolonged time is a nuisance in itself as your movements become restricted. However, improper cast fitting may worsen the daily routines. You should consult your orthopaedic surgeon about the complications of wearing a cast. Purple toes may turn into ulcers if not corrected quickly.

Apart from purple toes, you should also monitor signs of pain, foul odour, numbness, tingling sensations, and drainage of fluid from beneath the cast. In addition, monitor your cast for loosening, splitting, or breakage of cast material.

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Deitrick JE, Whedon GD, Shorr E. Effects of immobilization upon various metabolic and physiologic functions of normal men. The American journal of medicine. 1948 Jan 1;4(1):3-6. https://www.sciencedirect.com/science/article/abs/pii/0002934348903702


Lapidus LJ, Rosfors S, Ponzer S, Levander C, Elvin A, Lärfars G, de Bri E. Prolonged thromboprophylaxis with dalteparin after surgical treatment of achilles tendon rupture: a randomized, placebo-controlled study. Journal of orthopaedic trauma. 2007 Jan 1;21(1):52-7. https://pubmed.ncbi.nlm.nih.gov/17211270/


Jørgensen PS, Warming T, Hansen K, Paltved C, Berg HV, Jensen R, Kirchhoff-Jensen R, Kjær L, Kerbouche N, Leth-Espensen P, Narvestad E. Low molecular weight heparin (Innohep) as thromboprophylaxis in outpatients with a plaster cast: a venografic controlled study. Thrombosis research. 2002 Mar 15;105(6):477-80. 


Minatohara K. Renal failure associated with blue toe syndrome: effective treatment with intravenous prostaglandin E-1. Acta dermato-venereologica. 2006 Jul 29;86(4):364-5. https://www.medicaljournals.se/acta/content/html/10.1080/00015555-0091