Surgical Anatomy. — The structure of the metacarpals resembles that of other long bones with the exception of the ossification. The ossification of the inner four bones is the same. One center for the shaft and base, and one for the distal end or head. The center for the single epiphysis is first seen about the third year and joins the shaft during the twentieth. The metacarpal of the thumb has its single epiphysis located at the base. It begins to ossify during the third year and joins the shaft in the twentieth. Occasionally this bone has an additional epiphysis for the head which is visible at the seventh or eighth year. The first metacarpal may thus resemble both phalanx and metacarpal in its process of ossification. The positions of the epiphyseal cartilages are of importance in interpreting Rontgenograms of this region. The shaft of a metacarpal is composed of a tube of compact tissue, while the extremities are cancellated and enclosed in a thin layer of compact bone. This change in structure between the shafts and extremities accounts for the not uncommon impaction of the shaft into the head following: a blow on the knuckle. Fracture of the metacarpal shaft usually results from direct violence, while fracture of the distal end is almost always caused by indirect violence. Fracture of the distal end is almost invariably produced in boxing or fighting. A 'punch' is 'landed' on some bony prominence such as the jaw, or skull, and the head of the most prominent metacarpal is driven upward onto the shaft of the bone and also displaced slightly into the palm of the hand. This forward displacement is due largely to the normal curvature of the shaft and to the fact that the palmar aspect of the head is not as well supported as the dorsal. When the hand is tightly closed in a fist the heads of the metacarpals form the prominence of the metacarpo-phalangeal knuckles and the impact of violence sustained on these knuckles is the most common cause of fracture. Fracture is not uncommon in any of the metacarpals but is most frequently seen in the third and fourth. The most usual site of fracture in the inner four bones is just above the head while the most common seat of the break in the metacarpal of the thumb is through the base and involving the articular surface. Fracture of the base of the first metacarpal is known as Bennett's fracture. The clinical appearance and X-ray findings in this lesion are well shown in Figs. 422 to 424. The first metacarpal is isolated and can be palpated without difficulty, while the posterior surfaces of the inner four bones are subcutaneous and can be palpated from end to end unless the hand is markedly swollen, A number of metacarpals may be fractured simultaneously but it is much more common to see an isolated fracture of one of them a short distance above the head. <Callout type="warning" title="Be cautious with X-rays">X-ray findings are crucial for diagnosis and treatment.</Callout> Symptoms. — Pain, swelling, tenderness and loss of function are constant. The disturbance in function accompanying fracture of one or more of the metacarpals usually consists in an inability to completely flex the fingers. This is due to pain, swelling and the fact that the head of the fractured metacarpal is displaced so that there is a mechanical interference with complete flexion of the first phalanx. The deformity is usually characteristic (see Figs. 428 to 433). The head of the injured bone is usually displaced into the palm and when the fingers are flexed the corresponding knuckle will be found at a lower level than normal. It will often be possible to palpate the head of the bone in the palm of the hand. When the fracture is at or near the middle of the shaft the 'dropping' of the knuckle will be less marked while the backward bowing of the shaft will be pronounced. Crepitus can, as a rule, be elicited unless the fracture is near the distal end and impacted. <Callout type="important" title="Always inspect for crepitus">The presence of crepitus indicates proper alignment.</Callout> Diagnosis. — There should be little difficulty in recognizing fracture of any of the metacarpals. It is, however, not uncommon to see these cases mistaken for and treated as a 'sprain.' There is no excuse for this mistake if the parts are carefully examined following the injury. The deformity is usually so characteristic and pronounced that the diagnosis can be made by inspection alone unless the swelling is exceptionally pronounced. Bennett's fracture is most frequently mistaken for a sprain or subluxation of the articulation between the first metacarpal and trapezium. Manupulation of the thumb will almost invariably elicit crepitus and disclose the nature of the injury without the aid of the X-ray. <Callout type="tip" title="Use manual manipulation for quick diagnosis">Quickly diagnose by manipulating the thumb.</Callout> Treatment. — Reduction of the usual deformity is accomplished by traction on the finger corresponding to the injured metacarpal. The ligaments connecting the base of the first phalanx with the head of the metacarpal are thus employed in pulling the distal fragment back into position. During this manipulation the upper fragment is to be steadied by the thumb and fingers of the opposite hand. Seduction is, as a rule, easily accomplished but the deformity recurs as soon as the parts are released. The dressings, therefore, must be depended upon to retain the fragments in position during the process of repair. It will usually be possible to prevent overriding displacement by an engagement of the serrated fractured surfaces, but angular deformity can only be avoided by proper dressings. The method of fixation which will meet the requirements in the greatest number of cases is shown in Figs. 434 to 437. Following reduction a roller bandage is placed in the palm, the fingers flexed over it and secured in position by two strips of adhesive plaster. A machine rolled bandage such as put out by the supply houses should be used to secure the proper firmness. A roller four inches wide by ten yards in length is most appropriate. The diameter of this roll, however, is a little too great for the average size hand and should be reduced by removing the outer layers of the bandage until it is small enough to allow the first row of phalanges to be flexed to a right angle with the metacarpals as shown in Fig. 434. This position allows the head of the broken bone to be 'raised' into line with the other knuckles without making upward pressure on the lower fragment. After the roller has been placed in position diagonal strips of adhesive are used as shown in Fig. 436 to raise the injured knuckle. The entire hand is then covered with a bandage and carried in a sling. <Callout type="gear" title="Use appropriate bandages">Ensure you have suitable materials for dressing.</Callout> In some instances the fracture is situated in the shaft and oblique enough to prevent a firm engagement of the broken surfaces. Under such circumstances the roller bandage will not correct the tendency to overriding deformity and continuous traction will be necessary to keep the fragments in proper relation. A narrow splint is properly padded and secured to the palm of the hand by means of strips of adhesive plaster. This splint should extend about three inches beyond the end of the corresponding finger. Extension is then secured by means of light rubber tubing; one end of the tubing is attached to the end of the splint while the other is attached to the finger by means of strips of adhesive plaster. Fractures of any of the four inner metacarpals may be treated by means of two splints (dorsal and palmar) properly padded, though they are not as reliable and secure as the roller bandage, unless made of plaster of Paris. If plaster splints are used they should be applied with due regard for the nature and tendency of the deformity. Eight or ten thicknesses of gauze should be used and the material cut so that one splint will cover the dorsal aspect of the hand and wrist while the other covers the palm and ventral surface of the wrist. These two splints are then soaked in plaster cream, wrung out and rapidly secured in position by a roller bandage. While the plaster is setting the surgeon should grasp the hand in such a manner that pressure will be made in the palm opposite the displaced head, while counter pressure is exerted over the uninjured metacarpals on the dorsum of the hand. This raises the injured knuckle and the pressure exerted by the surgeon's fingers is continued by the splints after the plaster has set. The splints should be removed as soon as the plaster has hardened sufficiently to maintain its proper form, and reapplied only after the plaster has thoroughly set and dried out. Placing the splints on a radiator or in the sun will hasten the process. <Callout type="important" title="Secure splints properly">Ensure splints are correctly applied for effective treatment.</Callout> Fracture of the shaft of the first metacarpal is most satisfactorily treated by means of the splint shown in Fig. 440. The curves of the thumb and thenar eminence are such that an accurately fitting splint can be had only by using a material such as plaster which can be moulded. Bennett's fracture often requires no splint whatever. It is frequently possible to correct the lateral and backward displacement of the base of the bone by means of strips of adhesive plaster exerting pressure in the direction shown in Fig. 427. With the deformity thus corrected the thumb is immobilized with adhesive strapping similar to that employed in the treatment of a sprain. <Callout type="tip" title="Correct Bennett's fracture manually">Manual correction can be effective for Bennett’s fractures.</Callout> Operative Treatment. — Operation is almost never indicated in recent fractures of the metacarpals unless the condition is compound. When the fracture is open it should be treated according to the principles laid down under 'The Treatment of Compound Fractures and Luxations' on page 789. In old cases with deformity the patient may suffer considerable loss of function with persistent pain or tenderness in the palm opposite the displaced head. If these symptoms are pronounced and interfere with work operation is indicated. The incision is best made on the dorsal aspect of the hand and should avoid the extensor tendon of the corresponding finger. With the metacarpal exposed the bone is divided at the original site of fracture and the knuckle raised. The wound is then closed and the condition treated as a recent fracture with the deformity fully corrected. <Callout type="important" title="Correct deformities surgically if necessary">Surgery may be needed for severe deformities.</Callout> After-Treatment. — The after-care of these cases calls for frequent inspection of the dressings which are sure to become lax or slip no matter how well applied. As soon as the dressing becomes loose the deformity recurs and thus a deformed hand may follow even though the original reduction was perfect. Pressure points may show erosion during the after-treatment and call for treatment. If the roller bandage dressing is used the knuckles under the adhesive straps may become irritated and require relief from pressure. With the slightest signs of irritation the dressing should be reapplied and bits of cotton placed between the adhesive plaster and skin. The dorsum of the hand should be carefully watched for backward bowing of the shaft of the fractured metacarpal which may develop at any time. Direct pressure on the shaft may be necessary and is had by means of pads and adhesive straps. Backward bowing is not likely to occur if the first phalanges are fixed at a right angle with the metacarpals, as previously mentioned under 'Treatment.' Immobilization may be discontinued at the end of three weeks but the hand should not be subjected to strain for another two weeks as deformity may recur. Heavy work should be avoided for two months or more. <Callout type="risk" title="Avoid heavy work early">Early return to heavy work can cause recurrence.</Callout> Prognosis. — In an uncomplicated fracture of one of the metacarpals with correction of the deformity there should be complete restoration of function. If the deformity is not corrected there will be incomplete flexion of the corresponding finger, a weakened grip and more or less pain and tenderness in the palm of the hand opposite the displaced head. These symptoms will be present according to the degree of deformity.
Key Takeaways
- Metacarpal fractures are common in boxing and fighting, often involving the third and fourth metacarpals.
- X-ray findings are crucial for diagnosis and treatment of Bennett's fracture.
- Proper reduction and immobilization with bandages or splints is essential to avoid deformities.
Practical Tips
- Always inspect for crepitus during manual manipulation to ensure proper alignment.
- Use a roller bandage or properly padded splint for effective fixation, ensuring the first phalanges are at a right angle with the metacarpals.
- Avoid heavy work early on to prevent recurrence of deformities.
Warnings & Risks
- Be cautious when treating Bennett's fracture as it can be mistaken for a sprain or subluxation.
- Ensure proper alignment and immobilization to avoid angular deformity.
- X-ray findings are essential for accurate diagnosis, especially in complex cases.
Modern Application
While the techniques described here may seem archaic, understanding metacarpal fractures is crucial for any survival situation where medical resources might be limited. The principles of proper reduction and immobilization remain valid, though modern materials like advanced bandages and splints can improve outcomes.
Frequently Asked Questions
Q: How do you diagnose a Bennett's fracture?
Bennett’s fractures are often mistaken for sprains or subluxations. The diagnosis can be made by careful inspection of the hand, noting characteristic deformities such as an abnormal prominence at the base of the first metacarpal. Crepitus during manual manipulation is also a key indicator.
Q: What is the most common site for fractures in the inner four metacarpals?
Fractures in the inner four metacarpals are most commonly seen just above the head of the bone, while the thumb's fracture typically involves its base and articular surface.
Q: How long should immobilization continue after treating a metacarpal fracture?
Immobilization can be discontinued at the end of three weeks, but the hand should not be subjected to strain for another two weeks. Heavy work should be avoided for two months or more to prevent recurrence of deformities.