American Association for Hand Surgery
Theme: Beyond Innovation

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The Lasso Procedures For Intrinsic Minus Fingertip: A Three-Dimensional Biomechanical Study
Toshiyasu Nakamura, MD, PhD1; Yusaku Kamata, MD2; Mitsunori Tada, MD, PhD3; Takeo Nagura, MD, PhD2
1International University of Health and Welfare, Tokyo, Japan, 2Keio University, Tokyo, Japan, 3National Institute of Advanced Industrial Science and Technology, Digital Human Research Center, Tokyo, Japan

Zancolli?fs lasso procedure is one of the most popular operations for intrinsic muscle deficiency. Omer modified this procedure to loop the FDS tendon around the A2 pulley. The differences between the fingertip trajectory in these procedures had not been clarified yet.
Six fresh-frozen cadaver hands were used. We exposed four tendons (FDP, FDS, EDC, EIP) that contribute to the index finger motion, and tied a string into each tendon so that we can pull each tendon independently by our computer-controlled apparatus (Fig. 1). We cut the FDS tendon just distal the A2 pulley and sutured itself around the A2 or A1 pulley. FDP tendon was pulled by 2mm per second separately; two seconds after the other tendons were made slack. The FDP was pulled from full extended position until the index finger becomes fully flexed. Threaded stainless steel wires with diameter of 1.6mm were drilled into each bone in order to support a triangular platform where three optical markers with diameter of 4mm were glued. The optical markers were also attached to the base of the apparatus. The motions of these markers were recorded by a motion capture system. The 3D-CT was obtained to calculate the positional relationship between the markers and bones. Surface geometries of the markers and bones created from the CT images were fit into the marker trajectories from the motion capture data to reconstruct the bone motion. We measured the finger motion under nine different FDS activation levels, 0.00N, 0.10N, 0.20N, 39N, 0.48N, 0.96N, 1.47N and 1.96N achieved by a static weight. First we performed this experiment around the A2 pulley, and then performed around the A1 pulley.

Figure 2 show the fingertip trajectory in the A1 and the A2 group in one specimen. Figure 3 show the joint angles of each joint. These figures demonstrate that the fingertip trajectory forms larger arc in the A2 group than in the A1 group with the lower activation levels. In the A1 group, the PIP and DIP joint start flexing faster than in the A2 group with lower activation levels.

The arc of fingertip trajectory is larger in the A2 group the in the A1 group especially with lower activation levels. Omer modification is superior for finger trajectory than original Zancolli?fs procedure in weaker muscle power.

Fig. 1

Fig. 2

Fig. 3

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