Evaluating A Bunion For Surgery

We've already discussed some of the basic information about bunions on another web page, and we discuss some of the various surgical procedures available to the podiatric surgeon on another.  

Here we'll review some of the radiological (x-ray) and clinical factors a podiatric surgeon will consider in contemplating the type of bunion surgery a patient may require.  

Intermetatarsal Angle (Or IM Angle)

Abnormal 1st Intermetatarsal Angle

The Intermetatarsal Angle is the angle between the first and second metatarsals (the bones behind the toes that make up the ball of the foot).  On the left you can see a good example of a deviated first metatarsal angle, as the larger first metatarsal has drifted away from the second. 

Most bunion deformities have abnormal intermetatarsal angles, and most surgical procedures attempt to realign this angle in some way. 

A great number of procedures can be used by the podiatric surgeon to correct this abnormality--the advantages and disadvantages of the various procedures depends on other factors that need to be considered.  

Hallux Abductus Angle (or HA Angle)

The Hallux Abductus Angle refers to a deviated angle between the first metatarsal and the big toe.  A good example of an abnormal HA angle  can be seen to the right.  The big toe is clearly crooked relative to the metatarsal. 

There are several procedures that may be employed to correct an abnormal hallux abductus angle. 

Severe Hallux Valgus

PASA and DASA (Joint Cartilage Alignment)

Closely associate with the Hallux Abductus Angle (discussed above) is the alignment of the opposing joint surfaces (made of cartilage) found on the big toe and first metatarsal.  The orientation of the cartilage on the first metatarsal is known as PASA (Proximal Articular Set Angle) and the orientation of the cartilage on the base of the big toe is known as  DASA (Distal Articular Set Angle).

Congruous 1st Metatarsophalangeal Joint


A good example of proper alignment of the joint surfaces can be seen on the left.  PASA and DASA are in good alignment.  

Most cases involving a deviated Hallux Abductus Angle (as in the X-ray to the right) involve a concurrent deviation of the joint surfaces (PASA and DASA).  But this is not always the case when the bunion is progressing rapidly.  In these cases, the hallux abductus angle may be deviated, but the orientation of the cartilage (PASA and DASA) may not have had time to adapt to its misaligned position.  

Subluxed 1st Metatarsophalangeal Joint

How the alignment of PASA and DASA relate to each other will dictate whether the bunion is a structural deformity (where adaption of the joint structures has occurred), a positional deformity (where the joint structures have not yet adapted) or a combined deformity.  

Deviated Sesamoids

As the first metatarsal drifts away from the second metatarsal (as shown above with the abnormal intermetatarsal angle), the small bones beneath the first metatarsal (called 'sesamoids') may become misaligned. 

This deviation is usually graded on a 7 point scale, (illustrated on the X-ray to the right), with 7 being the most misaligned.  

But the sesamoid bones don't simply drift across on a flat plane of movement.  As they drift, they also tend to rotate around the first metatarsal bone.  This rotation is not appreciated on the view to the right; it is best visualized on the X-ray views below. 

Normal Sesamoid(7454 bytes)

To the left is an example of sesamoids in normal alignment.   Also visible on this view is the normal ridge of bone (called a 'crista') lying above and between the sesamoids.   


To the right, on the other hand, is an example of sesamoids that have become deviated.  The sesamoid deviation would be graded a 4 if judged on the 7-point scale, but on the view to the right you can see that the sesamoids have also rotated around the metatarsal.  

Note that in this example the crista has been worn away and is absent in this example, not surprising when the sesamoids are this deviated.   


Erosion of the crista (8452 bytes)

How much the sesamoids are deviated is quite variable, and how much this is corrected during the bunion surgery (if it needs to be at all) varies on a case-by-case basis.  

For additional information on this topic, please visit our web page on sesamoid problems

The Hallux Interphalangeus Angle (HI Angle)

Abnormal Hallux  Interphalangeus Angle

Sometimes the big toe itself is crooked.  Usually this occurs in the joint between the two toe bones found in the big toe (as seen in the example to the left).  Sometimes one of the big toe bones will be bowed within the shaft of the bone.

Several procedures have been designed to correct this abnormality.    

Other Factors To Be Considered

Other factors that are considered when a bunion surgery is contemplated are:

  • The relative length of the first metatarsal.  A long first metatarsal tends to speed up the arthritic process, and the first metatarsal may need to be shortened at the time of the bunion surgery.  A short first metatarsal may tend to cause pain beneath the second metatarsal, and the metatarsal may need to be lengthened.  There are different surgical procedures that have been designed to address long, short and normal metatarsal bones.  

  • The relative elevation of the first metatarsal.  An elevated first metatarsal tends to speed up the arthritic process in the great toe joint, and the first metatarsal may need to be dropped at the time of the bunion surgery.  (See our web page on Hallux Limitus and Hallux Rigidis.)  A dropped first metatarsal may cause the foot to twist in compensation, which may cause pain elsewhere.  In each case, the metatarsal relative degree of metatarsal elevation needs to be addressed at the time of surgery.  

  • The shape of the metatarsal head.  Some metatarsal are relatively round; some are square.  Others may have irregular joint surfaces.  Each may require a different type of procedure to keep the joint functioning as well as possible. 

  • The flexibility of the patient.  Patients with a great deal of soft-tissue flexibility in their feet (and in their bodies in general) may need to have a more aggressive procedure performed to prevent the return of the bunion.

  • The amount of arthritis in the big toe joint.  Because the joint no longer functions well when arthritis is present, a patient with severe arthritis may require a very different procedure than a patient with little arthritic change.  (See our web page on Arthritis.)

  • The age of the patient.  A 28 year-old female patient, for example, will generally have a more aggressive procedure performed because she will need to have more long-term correction than someone who is 78.  

  • The health of the patient.  Patients who are healthier can usually heal from larger procedures better than patients who are in relatively poorer health. 

  • The lifestyle of the patient.  Patients who are very active need to have a highly-functional foot, and may need a different sort of procedure than a patient who may be very sedentary and may simply need a procedure that provides comfort.

  • The type and degree of biomechanical abnormality that may be causing or exacerbating the bunion problem.  For a common example, see our web page on pronated feet.  

  • The degree of pain the patient experiences.  (Pain unresponsive to conservative treatment requires more urgent surgical intervention.)

  • Where the pain is felt.  (Is it pain with motion about the joint?  Pain from pressure to the enlarged bone?  Other types of pain?)  These factors may 

  • The degree of osteoporosis present.  (If you wish more information about this subject, we have a web page of information about osteoporosis.)  

  • The types of shoes the patient wears.  

  • Any associated calluses, which indicates abnormal pressure forces that must be considered. (If you wish more information about this subject, we have a web page of information about calluses.)

  • Any other associated deformities or pathologies.  For example, bunions are associated with Hammertoes, Tailor's bunions, Morton's Neuromas, Arch and Heel Pain, Excessive Pronation, and so forth, all of which need to be addressed in order to properly correct the foot.  

For more information on the general topic of bunions, please visit our web page on bunions.   

Putting It All Together

Only after reviewing the patient's complaints and medical history--and after performing a physical examination and assessing all appropriate studies (X-rays, blood work, for examples)--and after considering all the factors mentioned above (and others), the podiatric physician may begin to decide which of over 150 different surgical procedures that have been designed is most appropriate to address the various considerations associated with this deformity.  Please visit our web page on some of the more common surgical bunion procedures .    

Perhaps you can see why it's difficult to compare your surgery to the type your friend or neighbour may have had.  You may need a very different sort of procedure than your friend had.   Your right foot may even need a very different procedure than your left foot.  

It's important for the patient to fully understand the procedure being attempted, because the post-operative course is very different from procedure to procedure.  For example, in many procedures, you may be able to walk immediately.  In others you may be in a non-weight-bearing cast.  Some cases require the use of screws.  Others require pins.  Some require nothing.  So before you have any bunion surgery, sit down with your surgeon and discuss the procedure being considered and the post-operative course in detail. 



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This website is operated by 
The Achilles Foot Health Centre
S. A. Schumacher, D.P.M., F.A.C.F.A.S., F.A.C.F.A.O.M.  
Dr. S. A. Schumacher, Podiatric Corporation  

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