closed mallet thumb injury without phalangeal fractures is extremely rare . according to doyles classification of mallet finger injuries , the closed terminal epl tendon rupture afterwards , several authors described successful conservative treatments using splinting of the interphalangeal joint of the thumb in extension in 1986 [ 36 ] . in the current literature only 36 reported cases exist , which leads to a present lack of information for a standardised treatment . published the first systematic literature review in this field and compared their case series of 10 patients with 26 comparable previously reported cases . they found no significant difference between conservative and surgical treatment on the final result , but surgery may lead to a more rapid recovery based on earlier mobilisation . a 28-year - old caucasian female applied to our emergency department immediately after sustaining a hyperflexion trauma of her right dominant thumb . she reported that a horse - rein wrapped her thumb while the animal severely pulled the interphalangeal ( ip ) joint multiple times in various directions . apart from that , the patient was healthy , a non - smoker and had no history of previous hand injuries . physical examination revealed an intact integument of the injured right thumb , the ip - joint in approximately 30 flexion and strong local pain . closer functional testing showed a distinctive inability of active extension and maintenance of full extension of the ip - joint when achieved passively . the metacarpophalangeal ( mcp ) joint of the affected thumb was compromised in its physiological range of motion ( rom ) due to the pain but unharmed . therefore , clinical diagnosis of closed rupture of the extensor pollicis longus ( epl ) tendon was set . plain x - rays confirmed our findings in the physical examination showing no osseous defects ( figure 1 ) . ultrasound examination was performed immediately at the emergency department to confirm the clinical diagnosis of closed mallet thumb injury and to assess if a surgical procedure is indicated . it showed a considerable gap of 17  mm between the torn ends of the epl tendon according to an avulsion of the proximal stump ( figure 2 ) . in wide awake anaesthesia a dorsal incision centred on the ip joint ( h - shaped ) was performed . surgical site presented a complete avulsion of the epl tendon with a remarkable gap ( figure 3(a ) ) . surgical reconstruction by anatomical reinsertion of the tendon was required . as the rupture was at the outermost distal end of the tendon the torn structure was reinserted anatomically using a mini quickanchor suture anchor ( usp 2/0 ; mitek - depuy synthes , raynham , ma ) . additionally , the ip - joint was transfixed with a kirschner wire ( 1.25  mm ) in full extension to ensure immobilisation during the initial healing process . preoperative sonography of the injured right thumb revealing an avulsion of the epl tendon with a gap of 17  mm in full extension . ( a ) total rupture of the epl close to the distal insertion ; ( b ) fixation of the epl tendon with the mini quickanchor suture anchor and transfixation of the ip - joint with kirschner - wire ( 1.25  mm ) . hand - physiotherapy was started immediately with initially forceless mobilisation until the percutaneous pin was removed three weeks after surgery . under the guidance of experienced hand therapists , active mobilisation and increased weight bearing followed . early mobilisation after trauma is necessary to maintain and restore the function of the joint and avoid adherences . one year after surgery the patient obtained a rom of 0/0/65 of the right ip - joint compared to 5/0/70 of the contralateral thumb ( figure 4(a , b ) ) . the right thumb presented a normal kapandji - score of 9 and the key pinch strength of 7  kg compared to 11  kg of the contralateral side . clinical outcome 1 year after surgery . ( a ) in full active extension ; ( b ) in maximal active flection . this resulted in a shortage of evidence and still little guidance for the diagnosis and treatment of closed mallet thumb injuries . patients , like the one described in our case report , are unlikely to regain adequate function with conservative treatment alone . surgical intervention is further beneficial for preserving the function of the hand due to early mobilisation . it is important to recognise indications for surgery such as the avulsion of the epl tendon presented in our case , when x - rays reveal no osseous defects . probably , such misguided treatment is supported by the successfully conservative treated cases of mallet thumb injury described in the literature . this case report proofs that decision for a surgical or conservative treatment of a closed mallet thumb injury has to be taken more differentiated . in our opinion sonography should be mandatory in the diagnosis of all closed tendon ruptures without bony lesions , especially of the thumb . this cost - effective tool is easy and quick to perform and provides reliable information to identify those cases that will fail healing without surgical intervention . magnet resonance imaging would be an alternative as suggested by tabbal et  al . as well as , we propose that ultrasound examination should become mandatory to identify all cases of closed mallet thumb injuries that require surgical treatment , especially in an emergency setting and acute injuries . a standardised treatment protocol for diagnostic methods and treatment regimen is needed for closed mallet thumb injuries , taking the tendon gap into account . this research received no specific grant from any funding agency in the public , commercial , or not - for - profit sectors .
abstractin this report a case of closed mallet thumb injury is described , which was diagnosed clinically and indication for surgical treatment was confirmed with ultrasound examination . 
 the epl - tendon was successfully reconstructed with an excellent result . 
 we propose a mandatory ultrasound examination of all closed mallet thumb injuries .