Biomechanical Effects of Lunate Excision Alone and Proximal Row Carpectomy on Dart-Throwing Motion, Circumduction, and Carpal Stability: A Cadaveric Study

Purpose: Lunate excision is a treatment option for advanced-stage Kienböck disease; however, its effects on wrist mobility and stability remain insufficiently understood. This study aimed to biomechanically compare the wrist kinematic changes following lunate excision alone and proximal row carpectomy (PRC), focusing on dart-throwing motion (DTM), circumduction, and midcarpal stability. Methods: Ten freshly frozen cadaveric upper limbs were mounted on a custom apparatus after isolating and tensioning the flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis, and extensor carpi ulnaris tendons. The simulated active DTM was produced by sequentially loading the flexor carpi ulnaris and extensor carpi radialis tendons, whereas wrist circumduction motion was generated through passive multidirectional traction. The range of DTM and circumduction motions was recorded using an electromagnetic tracking system. Each specimen was tested under the following three conditions: intact wrist, lunate excision, and PRC. Carpal stability was evaluated by measuring passive translations of the distal carpal row in four directions. Results: Lunate excision alone and PRC significantly reduced the arc of the simulated DTM, averaging 83% and 40% of that in the intact condition, respectively. In contrast, the circumduction range was relatively preserved, with significant differences observed only in selected directions. Dorsal instability increased after lunate excision, whereas PRC was associated with increased volar instability. Conclusions: Lunate excision alone preserved DTM more effectively than PRC. Clinical relevance: Although lunate excision alone can maintain functional wrist motion, it may lead to carpal instability.