Manuel Llusa-Perez

Effects of forearm muscles on carpal stability

Thirty cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and to rotate around the pronosupination forearm axis. Five wrist motor tendons (FCR, FCU, ECU, ECRL and APL) were loaded with specific weights. Reactive rotations of the scaphoid, triquetrum and capitate were measured by an electromagnetic motion tracking device. When all five tendons were loaded simultaneously, the capitate supinated and the proximal row predominantly supinated and flexed. By contrast, when the ECU was loaded in isolation, it caused pronation to both proximal and distal rows. The FCR exhibited a mixed effect pronating the capitate and triquetrum, whilst supinating the scaphoid. Based on this, a hypothesis is proposed linking wrist stability to the balance of wrist pronators (ECU and FCR) and supinators (FCU, ECRL and APL).

Role of the extensor carpi ulnaris and its sheath on dynamic carpal stability

Ten cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and rotate around the axis of pronosupination. The extensor carpi ulnaris (ECU) was loaded with specific weights. Reactive rotations of the scaphoid, triquetrum, and capitate were measured by an electromagnetic motion tracking device. Loading the ECU caused pronation of both proximal and distal rows. After sectioning its sheath, the overall direction of the movement remained unchanged, but there was a 40% and 50% decrease of the pronation power over the distal and proximal carpal row, respectively. In addition to stabilizing the distal radiolunar joint, the ECU is an important structure that contributes to the dynamic stability of the wrist. Furthermore, its sheath plays a crucial role in maintaining the effect of the ECU muscle on the carpus.

Tendon Transfer Fixation in the Foot and Ankle: A Biomechanical Study

Background: Tendon transfers are often used in foot and ankle surgery. Different fixation devices and techniques have been described. The most recently developed ones are bone anchors and interference screws. Materials and Methods: A biomechanical study was designed to compare tendon transfer fixation, using Corkscrew bone anchors 5 × 15.5 mm and Biointerference screws (8 × 23 mm). Fifteen fresh cadaver specimens underwent both fixation techniques for split anterior tibial tendon transfer at the cuboid bone. All the specimens underwent standardized X-rays in order to evaluate mineral bone density using a standardized measurement system. All were tested until maximal load to failure. Results: The ultimate load to failure of the tendon secured to the cuboid using anchors was 103 N (SD, 52), compared with 150 N (SD, 68) for tendons secured to the bone with interference screws (p = 0.003). No difference was found between the techniques that could be related to bone density. Conclusion: Interference screws provided greater strength than bone anchors. Clinical Relevance: This study demonstrated increased strength in securing bone to tendon in vitro for SPLATT tendon transfer with interference screws as compared to suture anchors.

Role of the extensor carpi ulnaris in the stabilization of the lunotriquetral joint. An experimental study.

STUDY DESIGN Experimental laboratory-based research in biomechanics. INTRODUCTION The mechanisms by which some lunotriquetral (LTq) ligament disruptions remain stable are not known. PURPOSE OF THE STUDY To investigate the contribution of muscles in preventing carpal destabilization when the LTq ligaments are torn. METHODS Ten fresh cadaver wrists, set vertical in a jig, were isometrically loaded through five wrist motor tendons. Changes in carpal alignment secondary to the application of loads were monitored by a Fastrak™ electromagnetic motion tracking device, before and after sectioning the LTq ligaments. RESULTS After LTq ligaments sectioning, wrist loading forced the triquetrum into flexion (5.4° average) and supination (2.9 ). The only muscle capable of extending and pronating the collapsed triquetrum was the extensor carpi ulnaris (ECU). CONCLUSIONS Inadequate ECU muscle function is an important destabilizing factor in LTq deficient wrists. Dynamic LTq instabilities may benefit from proprioceptionally training the ECU muscle, while avoiding carpal supination torques.

How to Avoid Ulnar Nerve Injury When Setting the 6U Wrist Arthroscopy Portal.

The dorsal sensory branch of the ulnar nerve (DSBUN) is at risk in setting the 6U wrist arthroscopy portal. Although surgeons know the risk and are careful when they set the 6U portal, DSBUN injuries still occur. The purpose of the present anatomical study was to evaluate the possibility that DSBUN undergoes dynamic anatomical variations in its location during wrist arthroscopy. The goal of the study was to clarify (1) whether the nerve-to-portal (NTP) distance changes with flexion/extension wrist and/or hand/forearm rotation, and (2) whether there is any particular combination of flexion-extension/hand-forearm rotation where the NTP distance is maximal. Six fresh cadaver arms were suspended in a traction tower with forearm rotation locked, the skin and subcutaneous tissue around the ulnar head was removed, and the NTP distance measured in three predetermined loading/positional conditions. Of all options, the one that consistently showed the longest and safest NTP distance involved wrist flexion and radiocarpal supination when forearm rotation is limited. In conclusion, when an arthroscopic traction device restricts the forearm rotation, the 6U portal should not be set under traction with the hand passively pronated. Failure to observe this precaution can result in serious neuropathic pain.

Kinetics of the Wrist in Scapholunate Advanced Collapse

Objective: Recent published experimental investigations have shown the relevance of the forearm muscles in providing dynamic stability to the scapholunate joint, in the wrists without osteoarthritis. Some chronic scapholunate advanced collapse (SLAC) wrists remain long time asymptomatic; the reason is unknown. How do forearm muscles influence on SLAC wrists? The kinetic behavior of an experimentally acute sectioned ligament compared with a SLAC wrist has not been determined. The hypothesis of this experimental biomechanical study was that there are no differences in SLAC and recent scapholunate instability wrists kinetics. Methods: The kinetic effects of isometric loading of 5 wrist motor tendons (abductor pollicis longus [APL], extensor carpi radialis longus [ECRL], extensor carpi ulnaris [ECU], flexor carpi ulnaris [FCU], and flexor carpi radialis [FCR]) on 12 fresh normal cadaver arms in which scapholunate ligament was sectioned and in 5 wrists with a SLAC pattern of carpal osteoarthritis were analyzed. A custom-designed testing apparatus was used to hold the forearm and wrist vertical in neutral position. A 6 degree-of-freedom electromagnetic motion tracking device with sensors attached to the scaphoid, triquetrum, capitate, and radius was used to monitor spatial changes in carpal bones alignment. The rotation sustained by the scaphoid in both experimentally acute sectioned scapholunate ligament and chronic SLAC groups were measured and statistically compared. Results: When all tendons were simultaneously loaded, no statistical differences were observed between the 2 groups: The proximal carpal row, as opposed to the normal wrist, tended to pronate in both situations. Under individual muscle loading, the kinetic carpal behavior of both groups was also the same, with no statistical differences between them: The ECU is the only muscle that provokes scaphoid pronation; all other muscles induce its supination. Isometric ECU contraction causes significant radioscaphoid subluxation, with the scaphoid rotating into substantial pronation (average 4.50°; confidence interval [CI], −1.33° to −1.67°) and extension (0.69°; CI, −0.72° to 2.69°). None of the other muscles exhibited such an obvious destabilizing effect. The experimental kinetic behavior of the chronic SLAC wrist is similar to the one with a recent scapholunate dissociation without carpal collapse associated. In both groups (1) the direction of the scaphoid displacement is the same (flexion, pronation and radial deviation), although the magnitude of the scaphoid displacement is greater in the SLAC wrists group, and (2) the ECU muscle load destabilizes the scapholunate joint, although SL joint destabilization is greater in the SLAC wrist group. Conclusions: These findings suggest that, in SLAC wrists, the capsular distension associated to a chronic malfunction of the carpus plays a significant role in the magnitude of the carpal bones displacement under load, and that in patients with scapholunate instability, both with and without carpal collapse associated, ECU muscle contraction should always be avoided.