A 25 yo karate competitor presents with a right hand injury after punching wood panels at the end of training. Pain and tenderness was felt on the ulnar side of his right wrist at the hypothenar eminence. No parathesias, no swelling, pinch strength normal. Hook of hamate pull test negative.
Figure 1: Plain x-ray AP view of the right hand showing fragmentation of the hamate bone suggestive of avulsion fracture.
Figure 2: Plain x-ray oblique view of the right hand showing fragmentation of the hamate bone near the 4th and 5th metatarsal suggestive of avulsion fracture.
Figure 3: Plain x-ray lateral view of the right hand. Visualization of the hamate bone is difficult due to carpal bone overlap.
Carpel bone fractures are generally rare and account for 6% of all fractures. Hamate bone fractures are less common accounting for 2% of all carpel bone fractures, whereas scaphoid bone fractures account for about 70%. Hamate fractures can be broadly classified as hook or body fractures. Avulsion fractures of the hamate are not as well documented.
The hamate bone articulates with the 4th and 5th metacarpals distally and the triquetrum and lunate proximally (see figure 4). The hook of the hamate protrudes in a palmar direction and provides the ulnar attachment of the transverse carpal ligament, forming the roof of the carpel tunnel. Fractures involving the hook of the hamate may cause injury to the ulnar nerve and artery, thus it is important to ensure blood flow and sensation are intact in the 4th and 5th fingers.
Hook of hamate fractures are the most common type of fracture of the hamate and usually occur from falls of outstretched hand, or when the end of the golf club, racquet, or bat is forced into the palm. Fractures of the hamate body are less common and typically occur from direct blows to the ulnar aspect of the wrist or clenched fist striking a wall.
Diagnosis can prove challenging for the treating physician due to complex anatomy and rarity of condition. Patients will usually present with pain and tenderness over the hypothenar eminence aggravated by direct palpation or gripping. The hook of hamate pull test is useful to assess hook fractures. Flexion of the 4th and 5th finger is resisted by the examiner, which displaces the fracture and causes pain. Hamate fractures may also present with parathesias and weakness due to the hamate’s intimate proximity to the ulnar nerve.
Plain radiographs may make hook fracture diagnosis difficult due to the overlap of hamate hook and body. Therefore, CT scans with wrists in “praying position” using axial and sagittal planes is the imaging modality of choice. However, standard AP and oblique plain radiographs can reveal small avulsion (“flake”) fractures from distal articular surfaces (see figure 1+2). Carpel tunnel or oblique views are also useful for fracture identification.
Indications for surgical referral are: injuries associated with neurovascular deficits, dislocations, displaced body fractures, acute hook fractures requiring rapid return to sport or that fail to improve with several weeks of immobilization, delayed diagnosis (greater than 6 weeks), fractures associated with rupture of the flexor digit minimi tendon.
Diagnosis: Avulsion fracture of the right hamate.
Patient splinted for 6 weeks with wrist ROM exercises daily. Vitamin D 2000 units daily. Patient was pain free by 6 weeks and was allowed to return to contact with hand at 10 weeks.
Figure 4: An AP view of the carpel bones labelled on a plain film.
Author: Lucas Nguyen October 17, 2018 (PRND)