Purpose: Pinch strength has been shown to be a predictor of the ability to grip objects and perform functional hand-related tasks. As the sole flexor of the thumb IP joint, the flexor pollicus longus (FPL) muscle has previously been shown to play an essential role in directing thumb tip force as well as contribute to overall pinch strength. The relative contribution of FPL to pinch strength is unknown however. As the FPL may be affected in several acute and chronic conditions, determining the contribution of FPL to pinch strength may be useful in planning as well as evaluating treatment options. The purpose of this study was to estimate the contribution of FPL to pinch strength in-vivo using an EMG-guided, selective motor blockade, test-retest protocol.

Method: 11 healthy volunteers were recruited to participate in the study. All participants completed a brief questionnaire regarding prior hand injuries and subsequently underwent a physical examination to assess baseline hand function. Baseline pinch strength was recorded using three different pinch techniques: key pinch, 3-point chuck grasp, and tip pinch. Participants then underwent EMG-guided lidocaine blockade of the FPL muscle. Motor evoked potentials as well as skin potentials were used to confirm adequate FPL blockade. The physical exam was repeated as were pinch strength measurements. Post block splinting was necessary to stabilize the thumb IP joint. Grip strength, in addition to clinical examination, was utilized pre and post block to assess for inadvertent blockade of other muscle groups or nerves. A final clinical evaluation was conducted at study completion to note any complications or adverse effects.

Results: All three types of pinch strength showed a significant difference between pre and post measurements (p< 0.01). The mean differences pre and post were 9.7N,6.4N, and 5.2N in key, 3-point chuck, and tip pinch respectively (p< 0.01). The relative contribution of FPL for each pinch type was 53.2%,39.5%, and 44.3%. EMG, motor evoked potentials, and skin potentials confirmed adequate paralysis of the FPL. Physical examination did reveal decreased sensation in median and radial nerve distributions in some individuals, however the effect on observed motor function was negligible. Grip strength decreased by only 4N post blockade confirming no clinically significant median nerve motor blockade. The protocol was well tolerated and no serious complications were noted.

Conclusion: Using an in-vivo model we were able to estimate the contribution of FPL to overall pinch strength. In our study, FPL’s contribution to pinch strength was estimated to be 9.7N,6.4N, and 5.2N in key, 3-point chuck, and tip pinch respectively (p< 0.01). The relative contribution of FPL for each pinch type was 53.2%, 39.5%, and 44.3%. Inherent limitations in study design may have tended to overestimate the contribution of FPL to pinch. This information may be useful in planning and evaluating treatments for acute and chronic conditions affecting FPL function.

Purpose: Open reduction internal fixation with a volar plate is a popular surgical option for distal radius fractures. The pronator quadratus (PQ) must be stripped from the distal radius in this procedure. PQ is an important pronator of the forearm and stabilizer of the distal radioulnar joint. The purpose of this study was to investigate pronation torque in healthy volunteers before and after temporary paralysis of the PQ with lidocaine under EMG guidance.

Method: A custom-made apparatus was built to allow isometric testing of pronation torque at 5 positions of rotation: 90° of supination, 45° of supination, neutral, 45° of pronation and 80° of pronation. It was validated using a test-retest design with 10 subjects. For the study, 17 (9 male, 8 female) right hand dominant volunteers were recruited. They were tested at all 5 positions in random order and then had their PQs paralyzed with lidocaine. Repeat testing was performed in the same random order 30 minutes after injection. Three subjects underwent unblinded testing with saline injected instead of lidocaine.

Results: After paralysis of PQ with lidocaine, pronation torque decreased by 23.2% (p=0.0010) at 90° of supination, 16.7% (p=0.0001) at 45° of supination, 22.9% (p=0.0002) in the neutral position, 20.4% (p=0.0066) at 45° of pronation and 22.2% (p=0.0754) at 80° of pronation. All were statistically significant except 80° of pronation. Peak torque values before and after injection were highest in the supinated positions (8.2 Nm at 45° supination) and decreased gradually as the subjects were in more pronated positions (1.8 Nm at 80° pronation). The test-retest trial demonstrated no evidence of fatigue with repeated testing. The subjects who underwent injection of saline demonstrated no evidence of pronation torque loss secondary to pain or a pressure effect of the injectate.

Conclusion: This study demonstrated a significant decrease in pronation torque with controlled elimination of PQ function. Open reduction internal fixation of distal radius fractures damages the PQ. This may result in a pronation torque deficit. Functional significance of this loss should be shown. Pronation torque measurement may add to postoperative outcome analysis of surgical procedures about the wrist.