## 3 Results  
### Rod Implant  
Our comparisons are enabled by evaluating the difference in fingertip forces between the index and middle fingers for each of the three test configurations of the rod implant (Figure 5, panels A-C) as well as the suture-based procedure (panel D), across every paddle orientation and donor tendon tension. We then computed the MAEs as comparison metrics for each configuration using Equations (1) and (2). The short-triangle rod implant (panel A) was the best performer with an average fingertip force difference of 1.35 N--a 22.57% reduction in fingertip force differences relative to the suture-based baseline configuration (seen in panel D) across all paddle orientations and tendon tensions. This configuration also had the lowest variation in these fingertip force differences due to tendon tension at 1.75 N--a 24.66% reduction compared to the suture-based procedure. This reduction could mean the difference in the ability of the hand to acquire an irregularly-shaped object without twisting it as it is grasped. With a \(p\)-value \(<\) 0.05%, this configuration also showcased significantly different fingertip force differences for paddle orientations in the range \([-30^{\circ},\ -9^{\circ}]\) and \([9^{\circ},\ 30^{\circ}]\) compared to the baseline. These results show promise for clinical impact [19,20].  
While the tall triangle configurations--both free-moving (panel B) and glued (panel C)--do not perform as well, they did outperform the baseline with average reductions in fingertip force differences of over 18% (compared to the baseline). These cases also displayed similar reductions in the variation of fingertip force differences due to tendon tension of about 20%. This suggests that a larger triangle formed by the rod implant with the bifurcating tendons has lower force redistribution capabilities. Additionally, the tissue adhesion simulated by gluing the implant did not significantly alter performance. The exact values are listed in Table 1.  
These differences in fingertip forces were computed from the fingertip forces of the index and middle fingers for each test configuration of the rod implant-based and suture-based procedures (see Figure 6, panels A-D). The negative orientations pushed against and caused extension of the index finger. Positive orientations did the same for the middle finger. The figure clearly shows that these extensions caused the fingertip force to increase. This is because neither the implant nor the suture can perfectly redistribute forces. Unsurprisingly, increasing tendon tension proportionately increased fingertip forces.  
Here too, we see that the free-moving short triangle configuration had the best performance, showcasing the lowest variations/spread of absolute fingertip forces relative to tendon tension. Both the free-moving and glued tall triangle configurations performed about the same as each other and not, as well as the first case but also outperformed the suture configuration. However, for a given tendon tension, maximum fingertip forces were lower with the implant since it redistributed forces between the two fingers.  
Figure 6: _Index and middle fingertip forces_ measured at various paddle orientations and tendon tensions with and without the _rod implant_: (**A**) short triangle configuration; (**B**) tall triangle configuration; (**C**) glued tall triangle configuration; and (**D**) baseline suture configuration. The negative paddle orientations force the index finger to extend and increase its fingertip force. Positive orientations do the same for the middle finger.