## 2 Materials and Methods
### Testing Protocol  
We simulated finger contact with the contours of irregular objects by gradually rotating and holding the instrumented paddle at multiple orientations from \(\pm 3^{\circ}\) to \(\pm 30^{\circ}\) at \(3^{\circ}\) intervals. A baseline tendon tension of 1 newton (N) simulated muscle tone on the ECRL, EIP, and EDC tendons to prevent tendon slack. We then measured the force applied by each finger on its paddle force plate for different simulated FDP tendon tensions from 3 N to 30 N.  
Both cadavers underwent the first of three test scenarios: implant (either rod or U implant)--this evaluated the implants' and suture performances gliding freely (see Figure 4, panel B). Since the rod implant could be repositioned, it was tested using this scenario for two positions (15 mm, 30 mm distal) from the tendon bifurcation point. The next scenario simulated scarring-related tissue adhesion of the implants using 3M\({}^{\text{TM}}\) Vetwond\({}^{\text{TM}}\). Finally, we removed the implants to test the suture-based surgery (see Figure 4, panel A). We compared the efficacy of each implant-/suture-based surgery in maintaining equal index and middle fingertip forces as paddle orientation and input tendon tension changed. The _difference in fingertip forces_ quantifies the absolute deviation from the ideal _zero_ difference in forces (see Figure 5, panel D: green dashed line). Similarly, we also quantified the _variation in fingertip force difference due to input tendon tension_ at each paddle rotation angle as the absolute deviation of its fingertip force difference from the mean fingertip force difference (see Figure 5, panel D: ilac dashed line) averaged across all tendon tensions. Figure 3: Experimental Setup: The cadaver hand specimen is mounted to an Agee-WristJack® (**A**) using bone pins drilled into the radial and ulnar bones to stabilize the wrist joint. The specimen is also attached to the experiment platform using the WristJack. A robotic arm (**B**) positions a sensorized paddle (**C**) so each finger can individually push on a force plate. The robotic arm can also rotate the paddle to simulate the contours of irregular objects. The donor ECRL flexor tendon, and the extensor EIP and EDC tendons are actuated by force-controlling DC motors (**D**). Illustrated by [PERSON]. Figure 4: Testing protocol: It involves rotating a properly positioned instrumented paddle to simulate the index and middle fingers attempting to adapt to the contours of irregular objects. We test both the current state-of-the-art suture-based surgical technique (panel (**A**); as a baseline) and our proposed implant-based technique (panel (**B**); with two types of implants). Illustrated by [PERSON]. Mean Average Error (MAE) for each of these two quantities--computed as the average of all deviations across every paddle rotation angle for each input tendon tension--gives us two metrics (see Equations (1) and (2)) for each of the following test configurations:  
* Rod implant (short tendon triangle)--free moving. * Rod implant (tall tendon triangle)
* Free moving
* Glued to surrounding tissue to simulate postoperative scarring. Figure 5: _Difference between 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 gray background highlights paddle orientations for which fingertip force differences were significantly different compared to the baseline suture configuration. The green dashed line in panel (**D**) highlights the fingertip force difference of the suture case for 30 N tendon tension at \(-12^{\circ}\) paddle orientation. Similarly, the iliac dashed line highlights the force difference variation at \(-24^{\circ}\) paddle orientation. Equations (1) and (2) are computed using fingertip forces measured at every orientation and input tension.