Kinematic analysis of a four-corner fusion

BACKGROUND: A young motor cyclist with a history of several wrist surgeries: first, a left-sided scapholunate ligament repair, reoperated with a ligament reconstruction, and later with a four-corner fusion (4CF). One-year after the 4CF, the CT images showed a remaining scaphoid, misplaced screws in the lunotriquetral joint, screw fractures of the lunate, and pseudoarthrosis of the 4CF. In a fourth wrist surgery the scaphoid was removed, the pseudoarthrosis areas were treated with bone grafts, and a new implant was placed. However, two years after 4CF the patient suffered from diffuse radial wrist pain, mainly upon loading, and the CBCT images lead us to suspect partial non-union.

EXAMINATION: A CBCT kinematic study in flexion, extension, and neutral position was performed as well as an assessment of ossification to rule out non-union as a cause of wrist pain. The CBCT images were sent to Disior™ for further kinematics analysis. The results of the custom kinematic analysis of the 4CF are shown in Table 1.

When comparing the capitolunate angle in neutral position and in flexion, there was a 9-degree difference in motion. Similarly, the lunotriquetral angle in neutral and extended position showed a 12-degree difference. Moreover, a rotation and translation analysis was performed to investigate how the other carpal bones moved compared to the lunate during motion. This analysis showed rotation around the flexion-extension motion axis (sagittal), as well as translation towards volar direction for all other carpal bones.

A flexion-extension motion analysis of the lunate and the capitate revealed that motion occurred between these carpal bones. The custom ossification analysis confirmed the non-fusion of the previous 4CF as shown in Figure 1.

TREATMENT: Based on these findings, a new 4CF with complete debridement of the joint, bone grafting, and placement of more solid cannulated screws was performed.  

“The kinematic analysis, performed as an in-house service by Disior, enabled us to plan personalized surgical treatment in this complex case of a failed four corner fusion."

Table 1. Inter-axis angles during flexion-extension poses.

Figure 1. Level of ossification measured by assessment of radiodensity values (Hounsfield Units, HU), showed lower values across joint gaps.