Biomechanical Comparison of Two Surgical Methods in Treating Stage IIIb Lunate Necrosis

This study aims to determine the biomechanical changes and basis for treatment using two surgical methods (scaphotrapeziotrapezoid [STT] fusion and capitoscaphoid [CS] fusion) for stage IIIb lunate necrosis. Eighteen fresh frozen upper extremities of adult cadavers were randomly divided into three groups. In group A, only the radioscaphoid and radiolunate spaces were exposed to place pressure sensors. Groups B and C underwent STT and CS fusion, respectively. The advanced I-scan pressure measurement system was used. Piezoelectric films were placed at the radioscaphoid and radiolunate spaces of wrist joints, and connected to the computerized I-scan system, which was then connected to a biaxial hydraulic material testing system (MTS). Pressure (up to 100 N) was applied to the wrist in inferior neutral position at a 10 N/s compression rate. The pressure distribution, pressure loading, and other data on the radioscaphoid and radiolunate articular surfaces for each sample were dynamically recorded and analyzed. After application of pressure with the wrist in neutral position, the radioscaphoid and radiolunate pressure values of the normal wrist group A were 41.39 +/- 6.93 N/cm(2) and 39.22 +/- 6.61 N/cm(2), respectively; those of the STT arthrodesis group B were 83.89 +/- 11.27 N/cm(2) and 22.55 +/- 11.27 N/cm(2); and those of the SC arthrodesis group C were 86.45 +/- 8.10 N/cm(2) and 34.11 +/- 8.10 N/cm(2). Compared with CS fusion, STT fusion surgery has much greater value in preventing rotatory semidislocation of the scaphoid bone, as well as in maintaining the stability of the wrist. It is the preferred surgical treatment for stage IIIb lunate necrosis.