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Metacarpal Fracture


Metacarpal Fracture

Article Author:
Ryan Werntz
Article Editor:
Matthew Varacallo
Updated:
7/10/2020 10:41:28 AM
For CME on this topic:
Metacarpal Fracture CME
PubMed Link:
Metacarpal Fracture

Introduction

The metacarpals form the osseous base of the complex lever system of flexor and extensor tendons of the hand.  Understandably, fractures of the metacarpals and disrupt this mechanism causing significant disability for the active or working patient and can come about from several different mechanisms.[1] Due to the complexity of its form and function, orthopedic surgeons and other clinical providers must be able to recognize metacarpal fractures readily and treat these injuries in a timely fashion to avoid complications.  

Etiology

Metacarpal fractures can occur in a variety of settings, but most commonly occur as a result of direct trauma.[2] For metacarpal shaft fractures, direct blows to the dorsum of the hand can result in transverse fractures with varying degrees of comminution depending on the velocity of the injury.[1][3][4] Oblique fractures can be seen after rotational and axial loads, while bending forces with axial loads produce a butterfly fragment with differing degrees of comminution again depending on the amount of force imparted by the injury.[4][3][5] Perhaps the most well-known fracture type is the so-called “boxer's fracture,” implying a fracture of the neck of the fifth metacarpal with a volar displacement that presents in 20% of all hand fractures.[6] These neck fractures often result from a combination of axial load with a slight flexion moment, which causes the neck to fracture and displace volarly. Similarly, intraarticular fractures of the metacarpal base also arise from axial loads and can lead to carpometacarpal joint arthritis. 

Epidemiology

While the most common fracture types are of the upper extremity are distal radius followed by phalangeal fractures, metacarpal fractures are the third most common fracture. Metacarpal fractures account for approximately 40% of all hand injuries.[7][5] Moreover, in patients in the 18 to 34-year-old age distribution, metacarpal fractures are the most common injury in the hand, with an incidence of 12.5 patients per 10000.[8] Gender does appear to have a factor in these injuries, as 76% of all metacarpal injuries occur in males.[2]

History and Physical

When evaluating a patient with a suspected metacarpal fracture, looking for the hallmark signs of swelling, ecchymosis, tenderness to palpation, and pain with range of motion are expected to be seen. However, more specific signs of metacarpal fractures include loss of knuckle height, digit malrotation, or digit crossing over ("scissoring") should clue the physician into evaluating for an injury to the metacarpals. All of these signs, combined with a thorough history, will aid the practitioner in deciding to further assess for fracture. 

Other clinical pearls include evaluating the integrity of the skin. The latter is extremely important to rule out "fight bite" injuries, and dorsal wounds over the MCP joint are traumatic arthrotomies and/or open fracture patterns until proven otherwise.[9][10] Also, dorsal injuries often correlate with extensor tendon lacerations, and this should also be ruled out during the evaluation.[11][12]

Evaluation

Imaging of metacarpal fractures should include standard PA and lateral as well as an oblique view to further exam the ulnar-most digits. An external rotation oblique film allows for visualization of the fourth and fifth MC fractures and CMC dislocations, while an internal rotation oblique film allows for visualization of the second and third MC and CMC fracture/dislocations.[7]

Classification of these injuries has its basis on basic fracture characteristics. Examples include transverse, oblique, spiral, displaced, or comminuted. Location is also important and is usually divided into the distal aspect being the neck or head, the shaft, and the base being the most proximal portion. It is also important to consider rotational and shortening deformities as well as multiple metacarpal fractures and the amount of initial displacement, as these can be indicators of unstable fractures that will necessitate operative fixation.[1][13]

As loss of metacarpal height becomes more severe, extension lag of the digit in question becomes more significant. Metacarpal-phalangeal (MCP) joints show an average of 20 degrees of hyperextension. Still, for every 2 mm of metacarpal height that is lost, there are a concomitant 7 degrees of extensor lag at the MCP joint.[9] Because of the natural hyperextension at the MCP, a total of 5 to 6 mm of metacarpal height (21 to 30 degrees of extensor lag) is tolerable before detrimental effects occur.[14] In addition to simple fracture characteristics, the anatomical cascade of the metacarpals should play into the physician’s diagnosis.  For instance, the index and long finger are limited in motion relative to the ulnar most digits due to their attachment to the trapezoid and capitate and can only tolerate 10 to 15 degrees of angulation. However, the ring and small fingers articulation at the hamate permit a greater range of motion and, therefore, may tolerate more angulation of 30 to 45 degrees in the ring and up to 50 in the small finger.[1][15]

Treatment / Management

When considering the treatment of these fractures, the clinician has a wide range of options. While non-operative treatment is certainly an option for those fractures in an acceptable pattern or alignment, fractures that require operative fixation have several options that are available to them. Most commonly seen are percutaneous wires, intramedullary fixation, and open reduction internal fixation (ORIF) with plate fixation or lag screws is a common approach. The goal of treatment should be to begin early range of motion exercises 2 to 4 weeks postoperatively to avoid hand stiffness and to return to normal activities as soon as possible.

For the decision to be made to pursue non-operative treatment, we must revisit the concept of metacarpal stability.  The stability of the metacarpal is determined by both physical and radiographic evaluation focusing on the loss of height, scissoring of the digit, normal digit cascade, multiple fractures, and angulation of the fracture specific to the digit. If the fracture falls within the acceptable ranges, the clinician should attempt non-operative treatment. However, if fractures are outside this range and non-operative treatment is preferred, a reduction is necessary.

In general, reductions of metacarpal fractures, regardless of their location, should begin an appropriate anesthetic application with axial traction to disimpact the fracture and dorsal pressure on the hand as the majority of fractures displace with dorsal angulation; this is especially true for fractures of the metacarpal shaft. For metacarpal neck fractures, flexion of MCP joints to 90 degrees allows for tightening of the MCP ligaments allowing greater control of the distal fragment. Particular attention should be made for neck fractures in the small finger as these injuries do tend to be more and may require fixation.[16]  For intraarticular injuries, axial traction and dorsal pressure are also used to both disimpact and stabilize comminuted articular fragments.  After reduction is completed and verified on imaging, the hand must be immobilized in the “intrinsic plus” position, such that there is flexion of the MCP joints to 90 degrees with full extension of interphalangeal joints; this is done to put the capsule and ligaments on a stretch to prevent any contractures while immobilized. This positioning is for 2 to 3 weeks with interval plain film evaluation to detect loss of reduction.

If the reduction is maintained, patients may be graduated to buddy tapping of the involved digit and begin range of motion exercises until obtaining clinical union.  However, even with a pristine reduction, these fractures may displace during treatment, and in doing so, will require fixation in most cases.

For fractures that have either failed non-operative treatment, are open, or are outside the accepted criteria previously mentioned, either closed or open reduction with internal fixation will be the treatment of choice.  Height, rotation, and proper angulation must be achieved to restore hand motion and grip strength. Management of open fractures should always begin with the rapid administration of IV antibiotics, tetanus prophylaxis, and early irrigation and debridement.

Metacarpal head fractures are uncommon injuries, but most arise due to direct trauma and require operative fixation when there is a significant defect in the articular surface or instability is detected on the exam.[17] Fractures with large articular pieces are readily fixed with small screws, while condylar plates are useful in injuries with metaphyseal extension.  For those fractures that are extensively comminuted, K-wire fixation is appropriate as small fragments do not provide adequate screw purchase.  However, for both of these options, the practitioner must be careful not to violate the joint and must be immobilized for two weeks.[19]

For metacarpal neck fractures, intramedullary or trans-metacarpal K-wires are the mainstay of treatment to help control angulation and restore height. These fixation options, however, don’t readily control rotation even with post-operative immobilization.  Careful examination of rotation can be aided by contralateral hand films to ensure proper alignment. A downside to intramedullary K-wire placement is the necessity for a secondary procedure for the removal of hardware. Other options include intramedullary headless screws, which still present the issue of rotational control postoperatively, but do not necessitate a second procedure for hardware removal.[18] With either option, brief post-operative immobilization is in order, followed by early ROM exercises. Recent studies have shown radiographic union on an average of 49 days with an average return to daily activities at 4 to 6 weeks.

The most common fracture site in the metacarpal is the shaft, and those with oblique and spiral fracture types have a higher likelihood of rotational deformity, therefore requiring operative fixation.  Primary options for fixation of these injuries include intramedullary K-wires, plate and screws, and, more recently, headless intramedullary compression screws.  Percutaneous K-wires provide a minimally invasive approach. Intramedullary K-wires allow for length stability and can be supplemented with trans-metacarpal K-wires to achieve rotational stability as well, but are inferior in stability to plate and screws.  For more rigid fixation, plates and screws can be viable in multiple modes for different fracture types.  For oblique and spiral, lag screws can be applied with neutralization plating, while transverse fractures should have plates used in compression mode. This approach allows for more inherent stability and provides the opportunity for earlier ROM exercises in the post-operative period with favorable outcomes in ROM and return to activity.[1] However, recent studies and literature reviews have shown that while complication rates in both methods are similar, functional impairment requiring reoperation is significantly higher in patients undergoing ORIF with plate fixation compared to percutaneous pinning.[13][19]

Metacarpal base fractures can present as both extra and intra-articular injuries.  While extra-articular fractures are mostly seen independent of other injuries, intra-articular fractures can present with concomitant carpometacarpal joint dislocation, especially in the ring and small fingers.[20] For extra-articular base fractures, many occur in the meta-diaphyseal junction and can be sufficiently fixated percutaneously with K-wires to avoid devascularizing fracture fragments, but sometimes require an open approach with plate and screw fixation for direct visualization in complex fracture types. For intra-articular fractures, percutaneous pinning is again the preferred method of treatment for the ring and small fingers.  However, for the index and long fingers, thought must be given to the deep palmar arterial arch and the motor branch of the ulnar nerve.  Because of these vital structures being close to the long finger metacarpal base, open reduction with plate and screw application should be undertaken to preserve them. Again, rigid fixation does provide the option for early range of motion, but risks anatomic structures and may damage fracture fragments. Several studies in the past have found near equivalent outcomes for non-operative management and surgical treatment. Nearly half of the patients treated with surgical means had residual pain after their procedure, which was comparable to those that were treated with reduction and splinting.[21][22] Because of these findings, care much be taken in selecting which patients will benefit from either surgical or non-operative management with intra-articular base fractures. 

Post-operative patients require immobilization in the intrinsic plus position as described previously to reduce joint capsule contraction.  Education to elevate their affected extremity as often as possible is also important, as dependent edema can significantly increase pain and limit range of motion, thus creating a stiff hand. For patients with plate and screw fixation, immobilization should cease at the first post-op visit, and gentle range of motion exercises should commence. For those patients who undergo percutaneous fixation, early ROM can be difficult due to soft tissue adhesions to the K-wire but should require implementation once a clinical union is obtained, commonly at 3 to 6 weeks.

Differential Diagnosis

Differential diagnosis includes the setting of trauma or general soft tissue injuries, including muscular, tendonous, and ligamentous. Identifying fractures is possible by obvious deformity to the hand, but are most readily identified with imaging.  

Complications

Complications of metacarpal fractures are similar to those of most fractures, including nonunion, malunion, hand stiffness, and infection. For post-surgical patients, infections require treatment with antibiotics, removal of hardware, and debridement of infected tissue. Depending on the timing of the infection, skeletal fixation or reconstruction may require postponement until the resolution of infection.[1]

Stiffness can be detrimental in patients with hand fractures, especially when they occur in the dominant hand.  For patients undergoing splinting or percutaneous pinning, exercises should begin at four weeks or as soon as achieving clinical union.  However, those with plate fixation can be exercises immediately upon the removal of the sutures, which commonly occurs at the first post-op visit.[1]

Metacarpal nonunions are rare and occur in as few as 0.2 to 0.7% of patients.[23] A clinical union is normally seen in 3 to 6 weeks from injury if treated non-operatively or from the time of surgery in operatively treated patients.[1] Delayed union is the progressive absence of bridging bone across the fracture site with persistent pain and can be due to loss of bone stock, poor immobilization, or infection.  Nonunion is diagnosed with similar findings but at nine months. For non or delayed union after surgery, the most common occurrence is in patients treated with K-wire fixation.[24][23][24] Treatment should include bone grafting with rigid fixation with plates and screws to disallow motion at the fracture site.[24]

Malunion can be best observed by physical examination and plain films looking at knuckle height or abnormal digit rotation and scissoring and can lead to post-traumatic arthritis in articular fractures. For rotational or length deformities, corrective osteotomies can help to restore proper digit cascade, and for articular malunions, arthroplasty and fusion are two salvage options to attain acceptable outcomes.[1]

As with any surgical procedure, damage to soft tissues, nerves, or arteries is a possibility. Care must be taken to preserve these structures, especially each neurovascular bundle and the dorsal sensory nerves in the hand when performing dorsal approaches to the metacarpals for ORIF.[1]

Postoperative and Rehabilitation Care

While there are many different options for fixation of metacarpal fractures depending on their location, operative treatment lends to good outcomes.  For those treated by closed means with K-wire, fixation outcomes do tend to show more mobility than with plate fixation, but other than mobility, DASH scores, grip strength, and pain are similar.[25] Even though these outcome measures were for fifth metacarpal necks due to their overabundance, it is reasonable to assume the results would be interchangeable with metacarpals 1 through 4. As with all intramedullary fixation, however, the surgeon must be cognizant of potential malrotation at the fracture site to avoid malunion.  

Deterrence and Patient Education

As the most common cause of these injuries relates to sporting and work injuries, athletes should receive education in safety for their given sport as well as proper safety protocols for the working patient.[1] 

Enhancing Healthcare Team Outcomes

Metacarpal fractures have several different presentations and can have detrimental effects on the hand if not treated correctly; thus, they require the efforts of an interprofessional team. Classifying these injuries appropriately will give the clinician the tools he or she needs to choose the correct treatment plan, and if necessary, engage in operative fixation. If there is any ambiguity, an orthopedic specialist should consult on the case. Orthopedic specialty nurses can also provide a significant contribution to these cases by assisting with both operative and non-operative reduction. The nurse can also answer patient questions, and perform appropriate followup, and inform the treating clinician of any concerns. Being vigilant throughout the treatment process will also help to identify complications to these injuries as to provide the best possible outcome for the patient for every level of health care provider on the interprofessional team. [Level 5]



(Click Image to Enlarge)
Fractured 5th metacarpal
Fractured 5th metacarpal
James Heilman, MD, from Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Fractured5thMetacarpalHead2018.jpg

(Click Image to Enlarge)
Metacarpal joint
Metacarpal joint
Image courtesy S Bhimji MD

References

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