Working Diagnosis:
Fracture of the left hook of hamate with neuropraxia of the deep branch of the ulnar nerve.

Treatment:
Surgical excision of the hook of hamate in its entirety Case Photo #7 . During surgery, care was taken to smooth the cortical surface of the hamate and suture-close the periosteum to prevent future attrition of the flexor tendons abutting the surface of the hamate. The patient was placed in a surgical cast for two weeks then transitioned to a custom volar resting splint from weeks 2-4. At week three he began physical therapy where he was able to gradually increase pain-free activity and begin baseball specific motions. He was provided a gel insert to wear under his catcher's mitt for comfort.

Outcome:
Seven weeks after surgery he returned to play during a playoff game. At week 10 he returned to daily practice. At week 16 he reported overuse soreness at the surgical site but otherwise felt 100%.

Author's Comments:
Hook of hamate fractures represent 2-4% of all carpal fractures and are most common at the base (76%) compared to mid (13%) and distal (11%) portions of the hamate. (1) The average time to diagnosis is 23 weeks (2), in large part due to the varying sensitivities and specificities of the available diagnostic techniques, as highlighted by this case. Radiographs have a sensitivity of 77-91% and specificity of 86-96% (3), whereas computed tomography has a sensitivity of 100% and specificity of 94% (4). Although there is a paucity of literature describing the use of ultrasound, this case demonstrates how ultrasound can help identify hook of hamate fractures at the point of care and evaluate for other soft tissue injuries in the differential diagnosis of ulnar-sided hand pain. In deciding on treatment, a non-surgical approach with immobilization for 6-weeks may be considered if the fracture is non-displaced and recognized within the first week of injury, though return to play averages 12 weeks and non-union rates range from 50-90% (5). Surgical excision of the fractured bone fragment is the preferred treatment given the high return to play rates at the same or higher level (91%) and faster return to play at 6-8 weeks (6), but patients should be counseled on the potential loss of a small amount (11%) of ulnar grip strength (7).

Editor comments:
Within Guyon's Canal the ulnar nerve bifurcates into the deep motor branch and the superficial sensory branch. The superficial sensory branch, located close to the tip of the hook of hamate, supplies sensation to the surface of the fifth digit and medial region of the fourth digit. The deep motor branch travels along the base of the hamate where it will innervate the hypothenar muscles. Injury to the ulnar nerve at Guyon's Canal can be separated into three zones. Zone 1 injuries occur proximal to the ulnar nerve bifurcation resulting in mixed motor and sensory symptoms. Common etiologies include hook of hamate fractures, hook of hamate malunions or nonunions, as well as ganglion cysts. Zone 2 injuries are distal to the bifurcation affecting the deep motor branch of the ulnar nerve causing only motor symptoms/weakness. Zone 3 injuries also occur distal to the bifurcation though ulnar to zone 2 injuries affecting the superficial sensory branch of the ulnar nerve creating primarily paresthesias (8,9).

Editor's Comments:
Within Guyon’s Canal the ulnar nerve bifurcates into the deep motor branch and the superficial sensory branch. The superficial sensory branch, located close to the tip of the hook of hamate, supplies sensation to the surface of the fifth digit and medial region of the fourth digit. The deep motor branch travels along the base of the hamate where it will innervate the hypothenar muscles. Injury to the ulnar nerve at Guyon’s Canal can be separated into three zones. Zone 1 injuries occur proximal to the ulnar nerve bifurcation resulting in mixed motor and sensory symptoms. Common etiologies include hook of hamate fractures, hook of hamate malunions or nonunions, as well as ganglion cysts. Zone 2 injuries are distal to the bifurcation affecting the deep motor branch of the ulnar nerve causing only motor symptoms/weakness. Zone 3 injuries also occur distal to the bifurcation though ulnar to zone 2 injuries affecting the superficial sensory branch of the ulnar nerve creating primarily paresthesias8,9.

References:
Mouzopoulos G, Vlachos C, Karantzalis L, Vlachos K. Fractures of hamate: a clinical overview. Musculoskelet Surg. 2019;103(1):15-21. doi:10.1007/s12306-018-0543-y
Stark, H H; Chao, E K; Zemel, N P; Rickard, T A; Ashworth, C R. Fracture of the hook of the hamate.. The Journal of Bone & Joint Surgery 71(8):p 1202-1207, September 1989.
Spencer J, Hunt SL, Zhang C, Walter C, Everist B. Radiographic signs of hook of hamate fracture: evaluation of diagnostic utility. Skeletal Radiol. 2019;48(12):1891-1898. doi:10.1007/s00256-019-03221-0
Andresen R, Radmer S, Sparmann M, Bogusch G, Banzer D. Imaging of hamate bone fractures in conventional X-rays and high-resolution computed tomography. An in vitro study. Invest Radiol. 1999;34(1):46-50. doi:10.1097/00004424-199901000-00007
David TS, Zemel NP, Mathews PV. Symptomatic, partial union of the hook of the hamate fracture in athletes. Am J Sports Med. 2003;31(1):106-111. doi:10.1177/03635465030310010201
Luxenburg D, Patel N, Narasimman M, et al. Return to Play After Hook of Hamate Fracture: A Systematic Review and Meta-Analysis. HAND. 2024;0(0). doi:10.1177/15589447241231303
Kuptniratsaikul V, Luangjarmekorn P, Kerr S, Vinitpairot C, Kitidumrongsook P. Grip strength after hamate hook excision and reconstruction surgery: A biomechanical cadaveric study. J Biomech. 2022;141:111221. doi:10.1016/j.jbiomech.2022.111221
Shea JD, McClain EJ. Ulnar-nerve compression syndromes at and below the wrist. J Bone Joint Surg Am. 1969 Sep;51(6):1095–1103.
Gross MS, Gelberman RH. The anatomy of the distal ulnar tunnel. Clin Orthop Relat Res. 1985 Jun;(196):238–247

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