although mallet fracture is a common sports or work - related injury , its treatment remains controversial . wehbe and schneider concluded that splinting is a safe and reliable treatment for most mallet injuries and that reduction is not crucial because of bone remodeling . however , surgical treatment has been suggested for fractures involving > 30  % of the articular surface or for fractures with volar subluxation [ 2 , 3 ] . patients with such fractures are at an increased risk for secondary osteoarthritis and esthetically unacceptable outcomes . various surgical techniques such as kirschner wire ( k - wire ) pinning [ 46 ] , pull - out wiring , compression pin fixation , hook plate fixation , and microscrew fixation   have been described . although open reduction has been proposed , soft tissue damage may occur with this approach ; furthermore , complications such as infection , skin necrosis , nail deformities , and joint stiffness are a possibility . therefore , closed reduction with extension block was described in 1988 by ishiguro et al .   to avoid the disadvantages of open reduction . as per previous studies , however , many patients complain about exposed wires , which delay their return to sports and causes inconvenience while performing tasks requiring the hands during the early postoperative period . therefore , we introduced a novel microscrew fixation technique that leaves no exposed wire on the skin . this report presents our novel closed reduction technique with extension block and flexion block using k - wires followed by microscrew fixation for mallet fractures and retrospectively evaluates the clinical results of this procedure . we treated 20 displaced mallet fractures ( 14 males and six females ; mean age 38.4  years ; range 1768  years ) using our novel technique between january 2009 and january 2012 . the institutional review board approved this study , and informed consent was obtained from each patient . the fingers affected included seven middle fingers , five ring fingers , five little fingers , and three index fingers . no patient had any medical history of bone diseases that could have influenced surgical outcomes . the indication for surgery was the presence of a displaced fracture involving > 30  % of the articular surface . according to wehbe and schneider s classification   ( table  1 ) , there were 12 type ib , six type iib , and two type ia fractures . the mean duration from injury to surgery was 9.2  days ( range 116  days ) . functional outcomes were determined using crawford s evaluation criteria   ( table  2 ) . full flexion of the distal interphalangeal ( dip ) joint was considered for the angle of the uninjured joint on the opposite hand . radiographs were obtained at 2 , 4 , 6 , 8 , and 10  weeks , followed by every 6  months after bone union was complete . the mean follow - up duration was 12.6  months ( range 631  months).table  1wehbe and schneider s classification classificationnumbertype i ( no joint subluxation )  subtype a2  subtype b12  subtype c0type ii ( subluxation of dip joint )  subtype a0  subtype b6  subtype c0type iii ( physis of the distal phalanx involved )  subtype a0  subtype b0  subtype c0subtype a : < 1/3rd of the articular surfacesubtype b : 1/32/3rd of the articular surfacesubtype c : > 2/3rd of the articular surfacetable  2crawford s evaluation criteria excellentfull distal joint extension , full flexion , no paingood010 of extension deficit with full flexion , no painfair1025 of extension deficit , any flexion loss , no painpoor>25 of extension deficit , persistent pain wehbe and schneider s classification   subtype a : < 1/3rd of the articular surface subtype b : 1/32/3rd of the articular surface subtype c : > 2/3rd of the articular surface crawford s evaluation criteria   this novel procedure , combining extension block and flexion block using k - wires with closed reduction followed by microscrew fixation , is a less invasive procedure and leaves no exposed wires on the skin . all procedures were performed under digital block anesthesia with an image intensifier . with the dip joint passively maintained in maximum flexion , the first 1.0-mm k - wire was placed into the head of the middle phalanx from the dorsal side of the bone fragment for extension block ( fig . , we have been performing a two extension block technique to stabilize the bone fragment ( fig . 2a , b ) , and this technique was used in six patients in this study . the k - wire on the ulnar side was inserted 3  mm apart from and parallel to the radial side k - wire . the second 1.0-mm k - wire was inserted into the head of the middle phalanx from the center of the volar side for flexion block following closed reduction by extending the dip joint ( fig . we used the third 0.7-mm k - wire as a substitute for a 0.7-mm drill bit . this wire , which is perpendicular to the fracture line , was inserted through the center of the bone fragment from the dorsal to the volar side ( fig . the length of the screw can be determined using another k - wire of the same length and an image intensifier . a digital tourniquet with a nelaton s catheter tube was placed . a 1.0-mm microscrew ( nippon martin k.k . , osaka , japan ) was inserted following placement of a transverse minimum incision ( approximately 3  mm ) along the skin crease ( fig . the first and second blocking k - wires were removed once the screw was fixed ( fig . suturing of the wound was not considered necessary ; this was confirmed by an image obtained 3  days after surgery , which showed that the wound had already healed ( fig . the dip joint was immobilized with a splint for 13  weeks on an individual case basis . passive and active dip joint exercises were encouraged after splint removal.fig .  1 
 a the kirschner wire for extension block is inserted . f an image of the wound 3  days after surgeryfig .  2 
 a two extension blocks are performed since january 2011 . b a 1.0-mm microscrew is inserted between the two extension blocks 
 a the kirschner wire for extension block is inserted . f an image of the wound 3  days after surgery 
 a two extension blocks are performed since january 2011 . b a 1.0-mm microscrew is inserted between the two extension blocks this novel procedure , combining extension block and flexion block using k - wires with closed reduction followed by microscrew fixation , is a less invasive procedure and leaves no exposed wires on the skin . all procedures were performed under digital block anesthesia with an image intensifier . with the dip joint passively maintained in maximum flexion , the first 1.0-mm k - wire was placed into the head of the middle phalanx from the dorsal side of the bone fragment for extension block ( fig . , we have been performing a two extension block technique to stabilize the bone fragment ( fig . 2a , b ) , and this technique was used in six patients in this study . the k - wire on the ulnar side was inserted 3  mm apart from and parallel to the radial side k - wire . the second 1.0-mm k - wire was inserted into the head of the middle phalanx from the center of the volar side for flexion block following closed reduction by extending the dip joint ( fig . we used the third 0.7-mm k - wire as a substitute for a 0.7-mm drill bit . this wire , which is perpendicular to the fracture line , was inserted through the center of the bone fragment from the dorsal to the volar side ( fig . the length of the screw can be determined using another k - wire of the same length and an image intensifier . a digital tourniquet with a nelaton s catheter tube was placed . a 1.0-mm microscrew ( nippon martin k.k . , osaka , japan ) was inserted following placement of a transverse minimum incision ( approximately 3  mm ) along the skin crease ( fig . the first and second blocking k - wires were removed once the screw was fixed ( fig . suturing of the wound was not considered necessary ; this was confirmed by an image obtained 3  days after surgery , which showed that the wound had already healed ( fig . the dip joint was immobilized with a splint for 13  weeks on an individual case basis . passive and active dip joint exercises were encouraged after splint removal.fig .  1 
 a the kirschner wire for extension block is inserted . b a 1.0-mm microscrew is inserted between the two extension blocks 
 a the kirschner wire for extension block is inserted . f an image of the wound 3  days after surgery 
 a two extension blocks are performed since january 2011 . b a 1.0-mm microscrew is inserted between the two extension blocks bone union was achieved in all 20 fractures within a mean period of 6.8  weeks ( range 410  weeks ) . minimum displacement was observed in one patient and immobilization with a splint was continued for 4  weeks . at the final follow - up , anatomical reduction was observed in 14 patients and articular incongruity was < 1.0  mm in four patients and 1.02.0  mm in two . mean dip extension loss was 6.5 ( range 020 ) and mean dip flexion was 67.8 ( range 4580 ) . no infection , skin necrosis , permanent nail deformity , or secondary osteoarthritis was observed . only two complications were observed ; nail ridging in one patient , which disappeared after 5  months , and a dorsal bump caused by the screw in one patient , which was removed . according to crawford 's evaluation criteria , the surgical outcomes were excellent in seven patients , good in nine , and fair in four . a 38-year - old male industry worker injured his left middle finger while he was on duty . radiographs showed a displaced mallet fracture involving > 50  % of the articular surface , without volar subluxation of the distal phalanx ( fig . he wished to resume work as early as possible ; therefore , we treated the fracture using the procedure described above . we used a 0.7-mm k - wire as a substitute for a 0.7-mm drill bit and inserted a 1.0-mm microscrew with closed reduction ( fig . this patient exhibited active dip motion from 0 to 75 without pain 12  months after surgery , and his surgical outcome was excellent as per crawford s evaluation criteria.fig . 3 
 a radiograph of a 38-year - old man with a type iib mallet fracture . b radiograph showing achievement of anatomical reduction 
 a radiograph of a 38-year - old man with a type iib mallet fracture . a 38-year - old male industry worker injured his left middle finger while he was on duty . radiographs showed a displaced mallet fracture involving > 50  % of the articular surface , without volar subluxation of the distal phalanx ( fig . he wished to resume work as early as possible ; therefore , we treated the fracture using the procedure described above . we used a 0.7-mm k - wire as a substitute for a 0.7-mm drill bit and inserted a 1.0-mm microscrew with closed reduction ( fig . this patient exhibited active dip motion from 0 to 75 without pain 12  months after surgery , and his surgical outcome was excellent as per crawford s evaluation criteria.fig . 3 
 a radiograph of a 38-year - old man with a type iib mallet fracture . b radiograph showing achievement of anatomical reduction 
 a radiograph of a 38-year - old man with a type iib mallet fracture . various surgical techniques for displaced mallet fractures , such as k - wire pinning , pull - out wiring , compression pin fixation , hook plate fixation , and microscrew fixation have been described . however , the ideal treatment for fractures involving > 30  % of the articular surface remains controversial . ishiguro s method   is easier and less invasive than most currently available methods ; moreover , it facilitates closed reduction and is a reliable method that permits indirect anatomical reduction of the fracture . we routinely performed ishiguro s method at our hospital for cases of mallet fracture with involvement of > 30  % of the articular surface . however , some patients complained of exposed wires that delayed their return to physical activity and affected their work during the early postoperative period . therefore , we developed a novel microscrew fixation procedure that leaves no exposed wire , allows rapid healing with good mobility , and does not delay the patient s return to physical activity and work . the microscrew fixation procedure for mallet fractures was described in 2004 by kronlage et al . . in their surgical technique , the fracture site is opened and cleared of hematoma and callus , the fragment is repositioned and held in a reduced position with forceps or a towel clip , and two or more 0.8-mm microscrews are inserted . hiwatari et al .   reported the chased method for mini - screw fixation in cases of mallet fractures in 2012 . the chased method is a percutaneous procedure in which the fixation screw chases the k - wire as a substitute for a drill bit . first , there is a possibility of inducing cracks in the bone fragment , and second , there can be a reduction loss during drilling and screw insertion . we consider that less invasive reduction is achieved using extension and flexion block without forceps . to decrease the possibility of cracking a bone fragment , we use a third 0.7-mm k - wire as a substitute for the 0.7-mm drill bit and insert a 1.0-mm microscrew into the bone fragment using blocked k - wires . reported a comparison among three different techniques ( extension block pinning , k - wires used as joysticks and miniscrew fixation with open reduction and internal fixation ) for unstable mallet fractures , and no statistically significant difference was observed in the functional results . open reduction and screw fixation allows for earlier mobilization and faster return to work . if the treatment results of these methods are not much different , then an early return to sports or work and a low rate of complications are important . most surgical techniques have the disadvantages of an open incision , difficulty in achieving earlier mobilization , and the incidence of nail deformity , skin necrosis , and pin tract infection . kang et al .   reported that 41  % of surgically treated mallet fractures developed postoperative complications . therefore , we consider that the complication rate in our study ( 2/20 patients ) was acceptable . our novel surgical procedure combining closed reduction with extension block and flexion block using k - wires followed by microscrew fixation for mallet fractures produces good clinical results with relatively few complications .