The 5th metacarpal is the long bone that runs from the base of the little finger down to the wrist, forming the outer edge of the palm on the ulnar (pinky) side. It is one of five metacarpal bones in each hand, but it draws outsized clinical attention because it breaks more often than any of the others and plays a surprisingly important role in grip strength and hand function. Its unique anatomy, vulnerability to punch injuries, and the treatment debates surrounding its fractures make it one of the most discussed bones in hand surgery.
Where It Sits and How It Moves
The 5th metacarpal connects at its base to the hamate bone of the wrist, forming the 5th carpometacarpal (CMC) joint. At its head, it meets the proximal phalanx of the little finger at the metacarpophalangeal (MCP) joint, the knuckle you see when you make a fist. The joint at the base has characteristics of a saddle joint, meaning its articular surface curves in two directions. This shape allows the bone to flex roughly 10 to 15 degrees and then rotate in a twisting motion of another 10 to 15 degrees, a movement that helps cup the palm and bring the little finger toward the thumb in opposition.
1PubMed. Functional anatomy of the fifth carpometacarpal jointAmong the five metacarpals, the 5th has the greatest overall range of motion at the CMC joint. A three-dimensional analysis of the carpometacarpal joints found that the 5th CMC joint allows about 27 degrees of flexion-extension, 13 degrees of side-to-side deviation, and 22 degrees of rotation, far more than the rigid 2nd and 3rd metacarpals that anchor the center of the palm. The 4th metacarpal is a close partner in this mobility, and when it is immobilized, the 5th metacarpal’s flexion-extension drops by about 40%. The two bones work as a functional pair, allowing you to wrap your hand around objects of different shapes.
2PubMed. Three-dimensional kinematic analysis of the second through fifth carpometacarpal jointsThat cupping motion is what lets you grip a hammer handle, turn a doorknob, or catch a ball. The 2nd and 3rd metacarpals act as a relatively fixed central pillar, while the 4th and 5th flex and rotate to mold the palm around whatever you are holding. Comparative mobility studies rank the metacarpals in a specific order at the CMC joint, with the 1st (thumb) the most mobile, followed by the 5th, then the 4th, then the 2nd, and the 3rd as the most rigid.
3PubMed. Movements at the carpometacarpal and metacarpophalangeal joints of the hand and their effect on the dimensions of the articular ends of the metacarpal bonesWhy It Breaks So Often
The 5th metacarpal is the most commonly fractured metacarpal bone, and it is not close. In a study of over 400 patients who arrived at an emergency department after punching something, the 5th metacarpal was injured in about two-thirds of cases, with the 4th metacarpal a distant second at 10%. More than half of those patients reported punching a wall or another hard surface rather than a person. The classic “boxer’s fracture,” a break through the neck of the 5th metacarpal just below the knuckle, made up about a third of all 5th metacarpal fractures in that group.
4Journal of Trauma and Injury. Patients with intentional punch injuries in the emergency department: a retrospective cohort studyThe demographics are striking. Metacarpal fractures in general occur about five times more often in males, and the highest rates are in teenagers and young adults. The most common causes across the full population are punching a wall or door and falling onto an outstretched hand.
5PubMed Central. Incidence of metacarpal fractures in the US populationThe reason the 5th metacarpal takes the brunt is partly anatomical. It sits at the edge of the hand, where it absorbs impact that the more centrally placed metacarpals share between them. A closed fist concentrates force on the 4th and 5th knuckles, and the 5th metacarpal neck, where the bone narrows before flaring into the knuckle head, is structurally the weakest point. The bone also has thinner cortical walls than the 2nd and 3rd metacarpals, giving it less resistance to bending forces.
Diagnosing and Measuring the Break
When doctors suspect a 5th metacarpal fracture, they take X-rays of the hand from multiple angles. For neck fractures, the key measurement is “apex dorsal angulation,” the degree to which the knuckle head has tilted toward the back of the hand. That number drives treatment decisions: most guidelines allow up to about 30 to 40 degrees of angulation in the 5th metacarpal before recommending surgery, because the 5th CMC joint’s natural mobility can compensate for some malalignment. But there is a problem with relying on this number too heavily.
Research has shown that measuring the angle on standard X-rays is surprisingly unreliable. When three fellowship-trained hand surgeons independently measured the same set of 5th metacarpal neck fractures, both the agreement between them and the consistency of each surgeon’s own repeat measurements were poor. Their treatment recommendations varied as a result.
6The Journal of Hand Surgery. Radiographic assessment of small finger metacarpal neck fracturesMore recent work has explored whether an oblique hand X-ray can do the job of a CT scan. Comparing the two, researchers found that angulation measurements taken from an oblique radiograph were statistically equivalent to those from a sagittal CT, with high agreement between observers and between the two imaging methods. The average difference between an oblique X-ray measurement and a CT measurement was only about 3 degrees.
7PubMed Central. Oblique Hand Radiograph as a Method to Measure Fifth Metacarpal Neck Fracture AngulationThe practical takeaway is that while the oblique X-ray view is a reasonable and accessible tool, the whole measurement system is less precise than it looks. A patient whose fracture measures 38 degrees on one reading could easily measure 30 or 46 degrees on the next, depending on the view and the reader. This is one reason many hand surgeons factor in the patient’s symptoms, activity level, and degree of rotation rather than relying on the angle alone.
Treating the Boxer’s Fracture
The good news for most people with a 5th metacarpal neck fracture is that surgery is usually unnecessary. Conservative management is preferred for closed fractures without significant rotation, as long as the fracture fragments are not displaced into the joint surface.
8PubMed Central. Management of Fifth Metacarpal Neck Fracture (Boxer’s Fracture): A Literature ReviewThe more interesting debate is about what “conservative management” should look like. The traditional approach involves reducing the fracture (pushing the knuckle back into alignment) and immobilizing the hand in a plaster cast or ulnar gutter splint for three to four weeks. But a growing body of evidence suggests that simply buddy-taping the little finger to the ring finger and allowing early movement produces equivalent or better results.
A randomized trial comparing buddy taping to plaster casting found identical functional scores at 12 weeks in both groups, with patients in the buddy-taping group missing a median of zero days of work compared to two days in the casting group.
9PubMed. Is Buddy Taping as Effective as Plaster Immobilization for Adults With an Uncomplicated Neck of Fifth Metacarpal Fracture? A Randomized Controlled Trial A separate multicenter trial confirmed no significant differences in pain, satisfaction, MCP joint mobility, or grip strength between the two approaches at four months.
10PubMed. Fifth metacarpal neck fractures treated with soft wrap/buddy taping compared to reduction and casting: results of a prospective, multicenter, randomized trialA meta-analysis pooling data from multiple trials found that patients treated with buddy taping and early mobilization had statistically better disability scores and pain scores than those immobilized in a splint.
11Acta Medica Philippina. Comparative functional and outcomes of protected early mobilization with buddy taping versus splint immobilization in fifth metacarpal neck fractures: A meta-analysisThis does not mean casts are useless. Some patients prefer the reassurance and pain relief that comes from rigid immobilization in the first week or two, especially if there is significant swelling. And rotational deformity, which causes the little finger to overlap the ring finger when you make a fist, typically does require more active treatment. But for the garden-variety boxer’s fracture with acceptable angulation and no rotation, buddy taping with early movement is becoming the standard of care in many centers.
When Surgery Is Needed
Surgery enters the picture for open fractures, fractures with significant rotational deformity, severe angulation that would compromise hand function, and intra-articular fractures where the break extends into the joint surface. The two most common surgical options are K-wire fixation, where thin metal wires are driven through the bone to hold it in place, and plate-and-screw fixation using a small locking plate.
A study comparing the two approaches for 5th metacarpal neck fractures found no significant differences in pain, disability scores, grip strength, or time off work. However, active finger mobility was substantially better in the K-wire group, with near-normal MCP flexion compared to only about 60% of normal in the plate group. Both techniques had roughly similar complication rates, though the types of complications differed: plates tended to cause stiffness, while K-wires were more likely to migrate or irritate nearby nerves.
12PubMed. Fifth metacarpal neck fracture fixation: Locking plate versus K-wire?K-wires are generally removed in the office after three to four weeks, once early healing has occurred. Plates typically stay in permanently unless they cause symptoms. The trend in hand surgery has been toward minimally invasive pin fixation when surgery is needed, reserving plates for comminuted fractures where the bone has shattered into multiple pieces and needs a scaffold to hold it all together.
Fractures at the Base
Not all 5th metacarpal fractures are boxer’s fractures. Breaks at the base of the bone, near the wrist, are less common but more consequential. An intra-articular fracture at the base of the 5th metacarpal is sometimes called a “reverse Bennett” or “baby Bennett” fracture, named by analogy to the well-known Bennett fracture at the base of the thumb metacarpal. These fractures are considered unstable because the pull of the extensor carpi ulnaris tendon, which inserts at the base, tends to displace the bone and prevent it from staying reduced in a cast.
13Research Square. Postoperative Rehabilitation and Functional Outcomes in Reverse Bennett Fracture: A Case ReportInadequate treatment of these base fractures can lead to chronic pain, weakness, and early arthritis at the CMC joint.
14PubMed. The ‘mirrored’ Bennett fracture of the base of the fifth metacarpal Because the evidence base is small and there is no consensus on the best approach, most hand surgeons lean toward surgical fixation for displaced intra-articular fractures at this location to ensure the joint surface is restored as precisely as possible.
15PubMed. Management of intra-articular metacarpal base fractures of the second through fifth metacarpalsWhat Shortening Does to Grip Strength
When a 5th metacarpal fracture heals with some shortening, which is common in neck fractures that are treated without surgery, the knuckle drops and the metacarpal effectively becomes shorter. This is not just a cosmetic issue. A cadaver study found that for every millimeter of metacarpal shortening, fingertip force drops by roughly 6.5%. A fracture that heals with 4 or 5 millimeters of shortening could therefore reduce little-finger strength by a quarter or more.
16PubMed Central. The Effect of Metacarpal Shortening on Finger Strength and Joint Motion: A Cadaveric Biomechanical StudyFor most people, this degree of weakness in the little finger is tolerable. The 5th finger contributes to grip power, but it is not the primary source. Where it becomes more of a problem is in people who depend on grip strength for their work or sport, such as rock climbers, martial artists, or manual laborers. Surgeons sometimes factor in occupation and hand dominance when deciding whether a fracture that might otherwise be treated conservatively warrants pinning to prevent shortening.
For patients who already have a malunited fracture with a dropped knuckle, surgical correction is possible. A palmar opening wedge osteotomy, where the surgeon cuts the bone and wedges it open on the palm side to restore the angle, has been shown to lengthen the metacarpal and improve the cosmetic contour of the knuckle line.
17PubMed. Palmar opening wedge osteotomy for malunion of fifth metacarpal neck fracturesAdolescents and the Growth Plate
Teenagers punch things too, and boxer’s fractures are common in the 10-to-19 age group. The concern in younger patients is the growth plate at the base of the 5th metacarpal, which is still open and responsible for longitudinal bone growth. If a K-wire passes through or near the growth plate during surgical fixation, there is a theoretical risk of growth arrest or angular deformity.
A study evaluating antegrade (base-to-head) K-wire fixation in adolescents with 5th metacarpal neck fractures found that the technique produced good functional and cosmetic outcomes with low impact on the growth plate, largely because most of the patients treated were at or near skeletal maturity when the growth plate is about to close on its own.
18PubMed Central. Antegrade intramedullary fixation for adolescent fifth metacarpal neck fracture and its impact on epiphyseal growthFor younger adolescents whose growth plates have significant remaining growth potential, the decision is more nuanced. Surgeons may opt for retrograde pinning that avoids the growth plate entirely, or favor conservative treatment with close follow-up. The metacarpal growth plate contributes relatively little to overall finger length compared to the phalangeal growth plates, so even minor growth disturbances at this site rarely cause clinically meaningful length discrepancy.
Post-Traumatic Arthritis at the Base
When a fracture or dislocation at the base of the 5th metacarpal is missed or inadequately treated, the CMC joint surface can degenerate over time. Post-traumatic arthritis at this joint is uncommon in the general population, but it causes a disproportionate amount of trouble: pain with gripping, weakness, and limited ability to cup the palm. Most cases trace back to a prior fracture-dislocation, often one that was initially treated as a simple sprain.
A systematic review of surgical outcomes for this condition found that all reported techniques, including arthrodesis (fusion), tendon-based arthroplasty, and implant arthroplasty, produced substantial pain relief. Post-operative pain scores were very low, and grip strength recovered to an average of about 83% of the opposite hand. The complication rate across all approaches was about 18%, with 8% requiring a second surgery.
19Journal of Wrist Surgery. Surgical Outcomes in Fifth Carpometacarpal Joint Post-Traumatic Arthritis: A Systematic ReviewOne specific technique involves fusing the bases of the 4th and 5th metacarpals together while removing the damaged joint surface. Long-term follow-up of this approach has shown reliable pain relief with maintained grip strength and MCP joint motion.
20PubMed. Intermetacarpal M4-M5 arthrodesis (Dubert procedure) for fifth carpometacarpal joint osteoarthritis: long-term functional outcomes The tradeoff is that fusion eliminates the 5th CMC joint’s independent motion, reducing the hand’s ability to cup deeply. In practice, most patients find this acceptable because the arthritic joint was already too painful to use through its full range.
Enchondromas and Other Non-Traumatic Problems
The 5th metacarpal is not only vulnerable to fractures. Enchondromas, benign tumors made of cartilage that grow inside bone, have a preference for the ulnar side of the hand. In a 20-year review of hand enchondromas, tumors appeared in the 5th ray (the little finger and its metacarpal) more than 40% of the time, and about a third of all tumors were located in the metacarpal bone itself rather than the phalanges. Most enchondromas are discovered incidentally on an X-ray taken for another reason, though some cause dull pain or weaken the bone enough to cause a fracture with minimal trauma.
21Revista Brasileira de Ortopedia. Enchondromas of the Hand: A 20-year ExperienceA separate case series confirmed that enchondromas in the 5th ray are the most common location in the hand and also noted that diagnosis tends to be delayed for tumors at this site compared to other parts of the hand. Most patients are treated with curettage (scraping out the tumor) and bone grafting, and over 90% regain full range of motion afterward.
22Lo Scalpello – Journal. Hand enchondromas: surgical treatment and function outcomes in a case seriesAn Evolutionary Perspective on Why the 5th Metacarpal Is Built the Way It Is
The human hand is often discussed in terms of the thumb’s unique opposition, but the ulnar border of the hand has its own evolutionary story. When early humans used clubs or thrown rocks, the impact at the point of contact would drive force back through the handle and into the base of the grip. The ulnar side of the hand, anchored by the 5th metacarpal, absorbed much of that shock. Over evolutionary time, the 5th metacarpal thickened and its base enlarged compared to the equivalent bone in other primates, an adaptation interpreted as a response to the mechanical demands of clubbing and striking.
23PubMed Central. Evolution of the human hand: the role of throwing and clubbingThis is an ironic detail when you consider that the most common modern injury to the 5th metacarpal is punching a wall. The bone evolved to absorb impact forces from tool use, but the closed-fist punch concentrates that force on the narrow neck of the bone rather than the reinforced base. In other words, the hand was adapted for gripping a handle that distributes force across the palm, not for bare-knuckle striking where all the energy funnels through two small knuckle heads. The next time someone describes a boxer’s fracture as a sign that humans are not built for fighting, the evolutionary anatomy at least partially supports that reading: we are built for gripping and swinging, not for punching bare-fisted.