The Accessory Navicular Bone

What is an accessory Navicular Bone?

accessoryAn Accessory Navicular Bone is an extra bone that may be attached or detached from the navicular bone. It is considered a normal variant and is present in approximately 10% of people. This accessory bone is usually located under the plantar medial aspect of the navicular and is often associated with a pes planus (flatfoot) deformity. Ossification of the navicular bone occurs at three years of age in females and five years of age in males. However, the accessory navicular bone does not begin ossification before eight years of age.


The majority of patients are asymptomatic but, females tend to be more symptomatic. The patient may present with an activity related limp and pain in the arch area. The condition may also be bilateral. During examination, there may be swelling, tenderness, warmth, or redness in the plantar medial aspect of the arch. Relative to a normal foot, a plain x-ray AP view can detect the accessory navicular. An external oblique view is considered to be the best imaging position to detect an accessory navicular bone. An MRI may also be obtained in order to determine the size and type of the accessory navicular as well as assess the posterior tibial tendon.

radiologyThe accessory navicular is classified into three types. In Type I classifications, the accessory ossicle is mainly in the substance of the posterior tibial tendon and is not attached to the navicular. In Type II, the accessory bone resides very close to the navicular tubercle and is connected to the navicular by a thick layer of cartilage. In Type III classifications, the accessory bone is considered an enlarged navicular tubercle. Type IIIs are essentially a type II that is fused with the navicular by a bony bridge.

accessory typesIn regards to prognosis, when skeletal maturity has been reached, almost all patients become asymptomatic.


Nonoperative treatment usually consists of activity modification, orthotics, or a short leg walking cast. Surgical excision is indicated only after all conservative treatment options have failed.




Differential Diagnosis of SI Joint Pain

Sacroiliac Joint pain can often be inappropriately treated or mistaken as lower back pain. There are several conditions that simulate sacroiliac joint pain.

1. Myofascial Painmyofacial pain

This is a chronic pain caused by multiple trigger points and fascial constrictions. This particular condition involves the muscles and fascial areas of the back. The patient may feel knots or hardening of the muscle with weakness and tenderness. Myofascial pain syndrome and fibromyalgia may present the same clinical picture but, they are different problems. The site location is close to the SI joint and can be confused with SI joint pain.

2. Trochanteric Bursitis

Inflammation of the greater trochanter bursa. This condition causes tenderness and pain bursapiriin the hip. Trochanteric bursitis occurs in middle aged women. The area of pain may overlap with the SI joint area of pain and can radiate close to the sacroiliac joint. The pain from this condition is sometimes severe and associated with iliotibial band syndrome. Trochanteric Bursitis is occasionally overlooked. This condition may present with arthritis of the hip and low back pain and other conditions.


3. Piriformis Syndrome

This condition occurs when the sciatic nerve is compressed by the piriformis muscle in the buttocks. Piriformis Syndrome may be associated with lower lumbar radiculopathy similar to spine pathology. It occasionally develops due to blunt trauma to the buttocks. Localized buttocks pain will increase with sitting or driving. Tenderness is commonly found in the sciatic notch.


4. Cluneal Nerve Entrapment

cluneal nerve entrapThe superior cluneal nerve has three branches. The medial branch of this nerve is confined within a tunnel which may cause impingement of the nerve producing pain close to the SI joint.

5. Lumbosacral Disc Herniation or Bulge

The disc may move out of place (herniate) or break open (rupture) from injury or strain. Disc herniation of the lumbosacral region could involve the nerve roots, creating lower back pain. The pain is usually found in the midline and can go down the leg.


6. Lumbosacral Facet Syndrome

facetThe facet provides stability for the spine and contain a joint. This joint may be affected by inflammations or degeneration which causes pain that can be mistaken for SI joint pain.


7. Lumbar Radiculopathy

Lumbar Radiculopathy is a major source of back pain. This condition occurs from inflammation, irritation, or impingement of the nerve root. It is commonly confused for SI joint pain.lumbarradi




Common Foot Conditions and Injections


Conditions which cause pain and inflammation are treatable with the use of diagnostic and therapeutic injections. The purpose of this article is to shed some light on common ankle and foot conditions that may require injections and where the proper sites to perform these injections are located.


Ankle Joint

The ankle joint is formed by articulation of the tibia and talus. Injections are performed here to alleviate pain occurring from trauma, arthritis, gout, or other ankleeeeinflammatory conditions. Anterolateral Ankle Impingement can occur due to the build-up of scar tissue in the ankle joint or from the presence of bony spurs. When executing an injection here, the ankle will need to be in a neutral position. The physician will mark the injection site just above the talus and medial to the tibialis anterior tendon. The injection site should be disinfected with betadine. Then, the needle is inserted into the identified site and directed posterolaterally. The solution is injected into the joint space and should flow smoothly without resistance. It may be helpful to pull on the foot in order to distract the ankle joint.

First Metatarsophalangeal Joint

The MTP joint is a common injection site frequently affected by gout and firstmetaosteoarthritis. The injection site is first disinfected with betadine and then the needle is inserted on the dorsomedial or dorsolateral surface. The needle is angled at 60-70° of the plane to match the slope of the joint. The solution is injected into the joint space and should flow smoothly without resistance. Pulling on the big toe is sometimes helpful in distracting the joint.


Peroneal Tendonitis

Peroneal Tendonitis is an irritation to the tendons that run on the outside area of the ankle, the peroneus longus and peroneus brevis. First, the injection site is disinfected with betadine. Then, the needle should be carefully inserted in a proximal direction when injecting the peroneus brevis and longus tendon sheath. The needle will need to advance distally to inject the peroneus brevis alone at its bony insertion.


Achilles Tendonitis

Achilles Tendonitis is an irritation and inflammation of the large tendon in the back of the ankle. Achilles tendonitis is a common overuse injury that occurs in athletes. needlingInjections of steroids should be given around the tendon, not through the tendon. The injections inserted directly into the tendon is not recommended due to the increased risk of tendon rupture. A platelet injection can be done through the tendon with needling and fenestration.


Tarsal Tunnel Syndrome

Tarsal Tunnel Syndrome is a condition of pain and paresthesia caused by irritation to the posterior tibial nerve. When performing an injection for this condition, the tarsal tunnelphysician will want to feel the pulse of the posterior tibial artery. The nerve is posterior and the physician will want to find the area of maximum tenderness. The injection site should be 1-2cm above the tender area, which is marked on the medial side of the foot and disinfected with betadine. The solution is injected at a 30° angle and directed distally. It is important to inform the patient that the foot may become numb and that care should be taken when walking and driving. Injections for Tarsal Tunnel Syndrome are usually performed after a treatment program which can include rest stretching and the use of shoe inserts.


Plantar Fasciitis

The plantar fascia is a band of connective tissue deep to the fat pad on the plantar aspect of the foot. Patients with plantar fasciitis complain of chronic pain symptoms that are often worse in the morning with walking. The injection site is identified and marked on the medial side of the foot and betadine is used as a disinfectant. The physician will need to avoid injecting through the fat pad at the bottom of the foot to avoid fat atrophy. The needle is inserted in a medial to lateral direction one finger breath above the sole of the foot, in a line that corresponds to the posterior aspect of the tibia. The solution is injected past the midline of the width of the foot.plantar


AVN Causes and Risk Factors

AVN femoralAvascular Necrosis or osteonecrosis is death of a segment of bone due to disruption of the blood supply. The causes of avascular necrosis are numerous as there are several different ways that could interrupt the blood supply.

AVN may occur due to trauma, such as with a dislocation or fracture of the femoral neck. These injuries may interrupt the blood supply to the hip. Avascular necrosis may occur due to an occlusion of the arterial blood supply by a fat embolism; nitrogen bubbles in the blood stream (Caisson disease) or with Sickle Cell disease. fat embolism

Due to the low oxygen levels of the cells in patients with Sickle Cell Anemia, the cells become sickle shaped and are unable to pass through the vessels. This results in a diminished blood flow, which could lead to AVN. A patient with sickle cell disease and asymptomatic AVN diagnosed by an MRI will have a higher incidence of progression to collapse the AVN and pain (75%). Deterioration of the AVN will be rapid and can be bilateral, so it is important for the physician to screen the other hip at the same time and periodically. The physician will also want to watch the humeral head for AVN.

sickle obstructionAn obstruction of the venous outflow is another cause of avascular necrosis. With an increase in interosseous pressure, an obstruction can limit the blood flow. Injury or pressure on the blood vessel wall can also cause AVN. An excellent example of this would be Gaucher’s Disease, an increase in fat cell size may prevent the arterial inflow and lead to ischemia. Fatty substances can accumulate in the cells and certain organs. Marrow gauchersdiseases such as lymphoma and leukemia may also cause AVN. Radiation, vasculitis, and cytotoxins are also risk factors for AVN. Avascular necrosis may be associated with hypercoagulable states such as decreased anticoagulants, protein S and protein C.

Other common causes of AVN:

  • Steroid use
  • Alcohol
  • Idiopathic (no cause)
  • Metabolic and genetic factors
  • Systemic lupus erythematosus (SLE)
  • Rental failure
  • Organ transplant
  • Hemophilia

All of these conditions may cause loss of the vascular supply, marrow necrosis, and osteocyte death. An important condition related to AVN is steroid use. High doses for 2-3 weeks or low doses for long durations may cause AVN. There is a direct connection between the dose and duration of steroid use in the development of AVN. Joint injections are not proven to cause AVN. Additionally, avascular necrosis of the femoral head is a complication in HIV infected patients. The increased incidence of AVN may be caused by an increased prevalence of predisposing factors for osteonecrosis, including protease inhibitors, hyperlipidemia, corticosteroid use, alcohol, and intravenous drug use. Protease inhibitors play a role in the development of osteonecrosis through a tendency to cause hyperlipidemia. An easy mnemonic tool to remember the causes of AVN is “ASEPTIC”: Alcoholism/AIDS, Sickle Cell Disease/SLE, Erlenmyer Flask (Gaucher’s), Pancreatitis/Pregnancy, Trauma, Idiopathic/Infection, Caisson’s (the bends).

resorpThe anterosuperior segment of the femoral head is the area usually affected by AVN. Resorption of some of the dead bone is done by the osteoclasts, while osteoblasts lay down new woven bone. Dead trabecular bone is resorbed, ready to be remodeled. This process is repeated and the bone becomes weak. At the weakest stage, the AVN will result in collapse. Remodeling is not enough to support the bone. Progressive collapse due to bone death, resorption, remodeling and microfracture will occur. Avascular necrosis ends by final collapse, joint changes, and arthritis.