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J Wrist Surg
DOI: 10.1055/a-2568-8592
Scientific Article

Excision of the Proximal Pole of the Scaphoid Affects the Midcarpal Joint

Nicholas Parody
1   Department of Orthopedic Surgery, New York University, School of Medicine, New York, New York
,
Paul Izard
1   Department of Orthopedic Surgery, New York University, School of Medicine, New York, New York
,
Steven Glickel
1   Department of Orthopedic Surgery, New York University, School of Medicine, New York, New York
,
Sallie Yassin
1   Department of Orthopedic Surgery, New York University, School of Medicine, New York, New York
,
Ronit Wollstein 
1   Department of Orthopedic Surgery, New York University, School of Medicine, New York, New York
2   Department of Orthopaedic Surgery, University of Alabama Heersink School of Medicine, Birmingham, Alabama
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Abstract

Background

Excision of the proximal pole of the scaphoid causes wrist instability. The often small proximal fragment can be challenging to retain, and multiple procedures are used to preserve the proximal pole. However, the mechanical implications of a proximal pole loss remain unclear. Possibly, under certain circumstances, the proximal pole can be excised without causing instability.

Purposes

This study aimed to use a validated finite element model (FEM) of normal Type 1 and Type 2 wrists to examine the effect of removal of the proximal scaphoid pole on forces moving through the midcarpal joint. We hypothesize that the amount of bone removed alters the transfer of forces through the midcarpal joint and that this effect will differ between Type 1 and Type 2 wrists.

Materials and Methods

Fourteen wrist computed tomography (CT) scans were converted to .stl files: five Type 1 and nine Type 2. Using an established wrist FEM model, the proximal scaphoid was sequentially excised up to 50%. A 100-N computer-generated load was applied to the dorsal crests of the trapezoid and capitate. Carpal bone displacement was recorded in the x, y, and z directions. The percentage change from intact was calculated for Type 1 and 2 wrists, the direction of bony translation was recorded, and an index quantifying instability based on translation upon loading was calculated.

Results

The excision of the proximal pole of the scaphoid caused significant translation of the carpal bones in both wrist types, p < 0.001. Type 2 wrists reached significant displacement after 15% excision, compared to 25% for Type 1 wrists.

The direction of translation differed between Type 1 and 2 wrists.

In general, Type 1 wrists seem to be less stable than Type 2 wrists.

Conclusion

This study supports the importance of scaphoid proximal pole for wrist stability and the difference in carpal–bone translation between midcarpal joint types.

This can be used in surgical planning when faced with fractures, nonunion, and complex fracture-dislocations.

Keywords

proximal pole of the scaphoid - lunate type - midcarpal - joint - scaphoid - wrist

Supplementary Material



Publikationsverlauf

Eingereicht: 04. November 2024

Angenommen: 28. März 2025

Artikel online veröffentlicht:
30. April 2025

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