BROKEN THUMB

(FIRST METACARPAL FRACTURE)

our website is for educational purposes only.  the information provided is not a substitution for seeing a medical doctor.  for the treatment of a medical condition, see your doctor.  we update the site frequently but medicine also changes frequently.  

related topics: broken hand, thumb ligament injury; thumb arthritis, broken finger, broken wrist, nailbed injury

What is a Broken Thumb?

When a thumb is broken, it almost always occurs at the base of the thumb (over 80% of the time) .  

The thumb has three bones: one hand bone (the first metacarpal) and two finger bones (the proximal and distal phalanx).  The base of the metacarpal is the common site of injury.  Most occur when jamming your thumb (known as an axial force).

How is a Broken Thumb diagnosed?

The simple answer is to get an x-ray.  

However, doctors dont get x-rays of everyone that hurts a finger.  So which thumb injuries get x-rays?  A broken thumb is suspected if theres significant swelling at this region of the finger, and point tenderness (one specific area of the thumb is very painful).  Also if a person cannot move the thumb joint, this is a good indicator to get an x-ray.  Diagnosis is confirmed with x-rays looking at the finger in three views.  

How is a Broken Thumb treated?

The thumb is very mobile, it has great motion in every direction, and because of this, the thumb is very forgiving of any break that causes it to bend out of position.

As discussed in the broken finger section (see talk), your other fingers can only be bent by 10 degrees or less, anything more and the finger will not function normally.  In contrast, because your thumb is so mobile, it can compensate for an abnormal bend caused by the broken bone much better than your rigid index finger.  Generally speaking your thumb can be bent out of position up to 30 degrees before it really starts to affect position.   So a little bend is not that bad.   Most cracks can be pulled straight (or almost straight) and then casted for a few weeks.

However, because the thumb so mobile, the bone rare breaks in the middle.  Instead, the energy is transferred to the base of the thumb (at the joint) and this is where injury occurs.  

Doctors are therefore much much more worried about an injury to our thumb joint (meaning a break that enters into the joint, also known as an "intraarticular fracture"). 

Our thumbs are like a high performance car tires, they are in constant use for daily tasks, and therefore they will "wear out" (aka develop thumb arthritis, see talk) if the joint cannot glide smoothly.  Anything that increases friction within the joint, like an uneven surface caused by a crack in the bone, can cause long-term damage .  

Therefore, a crack that go into the joint needs to be treated aggressively, usually with surgery.

There are two types of thumb fractures that involve the joint (also know as the CMC joint).  

1) If there is a single fragment at base of the thumb. Its called a "Bennetts fracture".  The fracture pattern is usually very similar among people: there is a small fragment in the front  that remains in contact with the wrist bone, while the rest of the thumb bone gets pulled backward and out of position by your thumb muscles (the AbPL, EPL, AdPL).  A tiny ligament called the Anterior Oblique Ligament ("Beak Ligament") holds that small fragment in place.  If the thumb breaks but doesnt move out of position (<2 mm displacement), which is uncommon, then a cast alone can treat the injury.  However, more commonly two pins are needed to hold the thumb in position for about 6 weeks until the bone has healed, and then the pins are removed.  Sometimes a screw is used instead, which allows people to start moving their thumb after only about 1 week, but its a more challenging surgery.  

About 30 years ago this injury was treated with a cast, and doctors that followed patients 10 years after the injury showed that they did just fine.  However, the doctors continued to watch their patients more than 25 years after the injury, and they began to see that most suffered from decreased thumb mobility and strength, which are signs of arthritis.  That is why surgery is now used more commonly as a treatment.  

2) Multiple cracks of at the base of the thumb is called a "Rolando Fracture".  Oftentimes, the break looks like a "Y" (as in "Y did this happen to me?").  This is a more severe injury, and almost always requires surgery (unless the bone is so smashed that even surgery cant help).  Typically a small plate and screws will be used to realign the broken fragments, and give the bone stability while it heals.    

What is the long term outcome?  

Long term outcome really depends on how badly the thumb joint (called the 1st CMC joint) was injured, and how well it was repaired.  If the joint surface is smooth after recovery, there is theoretically less friction in the joint and the cartilage will last longer.  However, some cartilage is damaged during the injury itself, and this cannot be recovered (no matter how good your surgeon is).  If post-traumatic arthritis does occur, there are a lot of successful treatments for this condition, which is discussed separately (see talk).

Reference

1. Soyer AD. Fractures of the base of the first metacarpal: current treatment options. JAAOS 1999; 7: 403-412. see article. review.

2. Carlsen BT, Moran SL. Thumb trauma: Bennett fractures, Rolando fractures, and ulnar collateral ligament injuries. J Hand Surg 2009; 34(5); 945-52. see article. review.

3. Edmunds JO. Traumatic dislocations and instability of the trapeziometacarpal joint of the thumb. Hand Clin 2006; 22: 365-92. see article. eview.

4. Bettinger PC et al. An anatomic study of the stabilizing ligaments of the trapezium and trapeziometacarpal joint. J Hand Surg 1999; 24: 786-98. see article. anatomy of CMC joint. 

5. Timmenga EJ et al. Long-term evaluation of Bennett's fracture: a comparison between open and closed reduction. J Hand Surg 1994; 19: 373-77. see article. 11 pts. 10 yr follow-up, fxr reduction correlates with arthritis, almost all pt had some degree arthritis. 

6. Oosterbos CJ, de Boer HH. Nonoperative treatment of Bennett's fracture: a 13-year follow-up. JOT 1995; 9: 23-7. see article. 20 pts. 6/7 pts with arthritis had nonanatomic reduction.  

. Cullen JP et al. Simulated Bennett fracture treated with closed reduciton and percutaneous pinning: a biomechanical analysis of residual incongruity of the joint. JBJS 1997; 79: 413-20. see article. biomech study determined 2 mm step off threshold. 

8. Kjaer-Peterson et al. Bennett's fracture. J Hand Surg 1990; 15: 58-61. see article. 41 pts, <1 mm step off (anatomic reduction) showed 85% no residual sx, while >1 mm only 46% had no sx. 

9. Rolando S [trans Meals RA]. Fracture of the base of the first metacarpal and a variation that has not yet been described: 1910. CORR 2006; 445: 15-18. see article. original paper citing volar-ulnar frag (bennetts fragment) plus radial dorsal fragment. 

10. Langhoff O et al. Rolando's fracture. J Hand Surg 1991; 16: 454-59. see article. only 11 pts, 6/11 had sign of arthritis at 6 yrs, but quality of reduction doesnt correlate with sx.