A metacarpal neck fracture of a ring and little finger commonly occurs as result of direct trauma12. If these fractures are stable, they can be treated nonsurgically and severe functional problems are rare3. Surgical treatment is justified for unstable, displaced fractures, open fractures, palmar dislocation over 30° and shortening over 5 mm, which affect extension and flexion of the hand4. These surgical techniques include percutaneous Kirschner wire (K-wire) fixation, external fixation, and plate and screw fixation567. K-wire is widely used for fixation in metacarpal bone fractures8. It is a simple and effective method with a low incidence of complications. But, in case of exposing outside the skin, it has some problems such as pin infection, damage to adjacent soft tissue, need for pin removal, and unattractive dorsal scarring. Moreover it is difficult to start early active motion exercise. To overcome these problems, we replaced the K-wire with a bioresorbable implant and evaluated the results.

This prospective study was conducted from March 2014 to May 2016 and involved 10 consecutive patients with 10 metacarpal neck fractures that were treated operatively. The operative indication and acceptable angulation are debatable, but a dorsal apex angulation of greater than 30° at the ring and little fingers and shortening of more than 5 mm were corrected by operation. All cases underwent surgery within 7 days after injury, and the average follow-up period was 13 months (range, 12–15 months). Comminuted fractures and irreducible metacarpal spiral shaft fractures by closed manipulation were excluded. At the final follow-up, all cases were assessed in terms of total active motion (TAM), bony union and angular deformity based on plain radiographs.

Seven cases were males and 3 were females. Their average age was 33.8 years (range, 18–45 years). Seven cases were fourth metacarpal neck fractures, and 3 were fifth metacarpal neck fractures. Regarding the causes of injury, 5 cases were direct blows, 3 cases were slip downs, and 2 cases were sports injuries (Table 1). Regarding radiographic findings, fractures united in all cases in about 6 weeks (range, 5–7 weeks) after the operation (Fig. 4). Angulation of less than 5° was observed in 1 case. No case showed rotational deformity and shortening. The patients started active motion exercise within 1 week, and the patient regained full range of motion after average 4 weeks. The TAM results were excellent at 250° to 270° in all cases. There were no postoperative complications.

Fifth metacarpal neck fracture, commonly referred to as boxer's fracture, is the most common injury, accounting for 20% of total hand fractures10. It is relatively easy due to the fifth metacarpal bone is thinner than others and the weak protection of surrounding tissues. The treatment of unstable metacarpal fractures is very diverse and is performed in a variety of ways depending on the location of the fracture, fracture type, presence of coexisting injuries, soft tissue condition, and experience or preference of the surgeon11.

Many articles have reported that conservative treatment alone has resulted in excellent results in the treatment of fifth metacarpal neck fractures. However, it can occur depressed knuckle on dorsum of hand due to residual angular deformity after conservative treatment. Then, conservative treatment alone is difficult to obtain satisfactory treatment12. Surgical treatment can effectively correct the angulation and maintain the fixation of the fracture. In addition, unlike conservative treatment, it has the advantage of minimizing the fixation period and enabling early joint motion.

Internal fixation using a metal plate has been widely used because it has the strongest fixation force and enables early exercise131415. However, there is an increased risk of soft tissue damage, resulting in extension problems, stiffness, tendon rupture due to metal plates and screws. And the removal of the metal plate is required. K-wire is widely used for fixation in metacarpal bone fractures8. Pin fixation was first described as a retrospective method for treatment of metacarpal fracture by Lord16 in 1957. Later various surgical techniques were devised, which transformed this method, and good clinical outcomes were reported5817. Choi and Chang18 reported good clinical outcomes without damage and adhesion of the proximal extensor tendon, no disturbance of metacarpophalangeal joint movement, using retrograde intramedullary pin fixation of the fourth and fifth metacarpals. However, accordingly skin irritation due to the pin and local infection can occur, and in particular, movement of the pin and perforation of the condyle are major complications8. In case of exposing outside the skin, it has some problems such as pin infection, damage to adjacent soft tissue, need for pin removal, and unattractive dorsal scarring. Moreover it is difficult to start early active motion exercise.

Therefore, we replaced the K-wire with ActivaPin, a bioresorbable implant constructed of bioresorbable PLGA, which is degraded in vivo by hydrolysis into alpha hydroxy acids and metabolized by the body. ActivaPin does not protrude from the skin, and so does make less the problems such as pin infection, damage to adjacent soft tissue, need for pin removal, and unattractive dorsal scarring. Its bioresorbability eliminates the risk of long-term complications and removal surgery. ActivaPin may be considered weak for the force of rotational deformity since only one was used. But, the locking of the pin occurred with adjacent the bone because of having been designed the grooved surface. It is of high strength and enables stable fixation, easy insertion and safe medical use.

The period of active motion after K-wire fixation in the medullary canal differs among studies. Various periods have been reported, including active motion immediately and 4 weeks after surgery56819. However, during early movement of the joint, K-wire fixation may cause irritation due to the pin, movement of the pin and reduction loss. If joint movement is delayed, contracture occurs in the joint region, and a normal range of motion is unlikely to be achieved. In contrast, ActivaPin does not protrude from the skin, early active motion was possible. Patient started gentle active motion exercise within 1 week, and splinting was completely removed after 3 weeks. They all regained full range of motion after postoperative 4–5 weeks.

It is difficult to use fixation with ActivaPin for shaft fractures for which closed reduction is impossible, comminuted fracture and condylar and base fractures, and in patients with an extremely narrow medullary canal of the metacarpal shaft. Because ActivaPin pass through the articular surface of the metacarpal head when it is inserted, they may also damage the metacarpal joint. Lastly, in our study, we applied this method only to the fourth and fifth metacarpal fracture because we had only a small case of other metacarpal fracture. And it has a limitation that the observation period is only 1 year. More studies will be needed in the future with more surgery and a longer follow-up period.

K-wire exposed to the outside of the skin has some problems such as pin infection, damage to adjacent soft tissue, and unattractive dorsal scarring. And it is difficult to start early active motion exercise. Moreover it needs to be removed. Replacement of a K-wire with a bioresorbable pin prevented soft tissue damage, dorsal scarring and no need to remove. It does not also protrude from the skin, early active motion was easily possible. And our percutaneous intramedullary bioresorbable pin fixation technique resulted in early recovery of range of motion and prevention of stiffness. It helps patients regain close to normal range of motion and returned to daily life early.