Elisabet Hagert

Various ankle ligaments have different structural composition. The aim of this study was to analyze the morphological structure of ankle ligaments to further understand their function in ankle stability. One hundred forty ligaments from 10 fresh-frozen cadaver ankle joints were dissected: the calcaneofibular, anterior, and posterior talofibular ligaments; the inferior extensor retinaculum, the talocalcaneal oblique ligament, the canalis tarsi ligament; the deltoid ligament; and the anterior tibiofibular ligament. Hematoxylin-eosin and Elastica van Gieson stains were used for determination of tissue morphology. Three different morphological compositions were identified: dense, mixed, and interlaced compositions. Densely packed ligaments, characterized by parallel bundles of collagen, were primarily seen in the lateral region, the canalis tarsi, and the anterior tibiofibular ligaments. Ligaments with mixed tight and loose parallel bundles of collagenous connective tissue were mainly found in the inferior extensor retinaculum and talocalcaneal oblique ligament. Densely packed and fiber-rich interlacing collagen was primarily seen in the areas of ligament insertion into bone of the deltoid ligament. Ligaments of the lateral region, the canalis tarsi, and the anterior tibiofibular ligaments have tightly packed, parallel collagen bundles and thus can resist high tensile forces. The mixed tight and loose, parallel oriented collagenous connective tissue of the inferior extensor retinaculum and the talocalcaneal oblique ligament support the dynamic positioning of the foot on the ground. The interlacing collagen bundles seen at the insertion of the deltoid ligament suggest that these insertion areas are susceptible to tension in a multitude of directions. The morphology and mechanical properties of ankle ligaments may provide an understanding of their response to the loads to which they are subjected.

To analyze ligament innervation and the structural composition of wrist ligaments to investigate the potential differences in sensory and biomechanical functions. The ligaments analyzed were the dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous, scaphotrapeziotrapezoid, radioscaphoid, scaphocapitate, radioscaphocapitate, long radiolunate, short radiolunate, ulnolunate, palmar lunotriquetral interosseous, triquetrocapitate, and triquetrohamate ligaments. The ligaments were harvested from 5 cadaveric, fresh-frozen specimens. By using the immunohistochemical markers p75, Protein Gene Product 9.5, and S-100 protein, the mechanoreceptors and nerve fibers could be identified. The innervation pattern in the ligaments was found to vary distinctly, with a pronounced innervation in the dorsal wrist ligaments (dorsal radiocarpal, dorsal intercarpal, scaphotriquetral, dorsal scapholunate interosseous), an intermediate innervation in the volar triquetral ligaments (palmar lunotriquetral interosseous, triquetrocapitate, triquetrohamate), and only limited/occasional innervation in the remaining volar wrist ligaments. The innervation pattern also was reflected in the structural differences between the ligaments. When present, mechanoreceptors and nerve fibers were consistently found in the loose connective tissue in the outer region (epifascicular region) of the ligament. Hence, ligaments with abundant innervation had a large epifascicular region, as compared with the ligaments with limited innervation, which consisted mostly of densely packed collagen fibers. The results of our study suggest that wrist ligaments vary with regard to sensory and biomechanical functions. Rather, based on the differences found in structural composition and innervation, wrist ligaments are regarded as either mechanically important ligaments or sensory important ligaments. The mechanically important ligaments are ligaments with densely packed collagen bundles and limited innervation. They are located primarily in the radial, force-bearing column of the wrist. The sensory important ligaments, by contrast, are richly innervated although less dense in connective tissue composition and are related to the triquetrum. The triquetrum and its ligamentous attachments are regarded as key elements in the generation of the proprioceptive information necessary for adequate neuromuscular wrist stabilization.

Surgical approaches to the wrist joint have traditionally been focused on providing wide exposure to allow adequate access to the carpus. In light of recent investigations on the innervation and proprioception of the wrist joint, one should also take into consideration not to denervate the wrist capsule and ligaments. In this manuscript, we propose 2 surgical approaches to the dorsal and volar radiocarpal joint, intended to minimize damage to the innervation of the capsule while providing ample access to the wrist.

The presence of wrist proprioceptive reflexes after stimulation of the dorsal scapholunate interosseous ligament has previously been described. Because this ligament is primarily innervated by the posterior interosseous nerve (PIN) we hypothesized altered ligamento-muscular reflex patterns following desensitization of the PIN. Eight volunteers (3 women, 5 men; mean age, 26 y; range 21-28 y) participated in the study. In the first study on wrist proprioceptive reflexes (study 1), the scapholunate interosseous ligament was stimulated through a fine-wire electrode with 4 1-ms bipolar pulses at 200 Hz, 30 times consecutively, while EMG activity was recorded from the extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris, with the wrist in extension, flexion, radial deviation, and ulnar deviation. After completion of study 1, the PIN was anesthetized in the radial aspect of the fourth extensor compartment using 2-mL lidocaine (10 mg/mL) infiltration anesthesia. Ten minutes after desensitization, the experiment was repeated as in study 1. The average EMG results from the 30 consecutive stimulations were rectified and analyzed using Student's t-test. Statistically significant changes in EMG amplitude were plotted along time lines so that the results of study 1 and 2 could be compared. Dramatic alterations in reflex patterns were observed in wrist flexion, radial deviation, and ulnar deviation following desensitization of the PIN, with an average of 72% reduction in excitatory reactions. In ulnar deviation, the inhibitory reactions of the extensor carpi ulnaris were entirely eliminated. In wrist extension, no differences in the reflex patterns were observed. Wrist proprioception through the scapholunate ligament in flexion, radial deviation, and ulnar deviation depends on an intact PIN function. The unchanged reflex patterns in wrist extension suggest an alternate proprioceptive pathway for this position. Routine excision of the PIN during wrist surgical procedures should be avoided, as it alters the proprioceptive function of the wrist. Therapeutic IV.

For the distal radioulnar joint (DRUJ) to be stable, not only do the articulating surfaces need to be congruent and well aligned but also the capsule and ligaments need to be mechanically and sensorially competent. According to recent investigations, ligaments should not be regarded as simple static structures maintaining articular alignment but as complex arrangements of collagen fibers containing mechanoreceptors, which are able to generate neural reflexes aiming at a more efficient and a more definitive muscular stabilization. By careful planning and meticulous execution of surgical incisions to approach the DRUJ, the nerve endings innervating the capsule and DRUJ ligaments may be safeguarded, thus preserving the proprioceptive function of the joint.

The scapholunate interosseous ligament (SLIL) is biomechanically important in maintaining wrist motion and grip strength in the hand, but its possible sensory role in the dynamic muscular stability of the wrist joint has not been examined. The aim of this study was to use immunohistochemical methods to analyze the general innervation and the possible existence of sensory corpuscles in the SLIL. The ligament was excised in its entirety from 9 patients. Antibodies against the low-affinity p75 neurotrophic receptor (p75) were used to reveal sensory corpuscles as well as general innervation. Furthermore, antibodies against the general nerve marker protein gene product 9.5 (PGP 9.5) and the glial marker S-100 were used to additionally depict innervation and corpuscular structures. Blood vessels occurred in areas interspersed throughout the homogeneous collagenous structure. In these vascularized areas, the SLIL was found to be supplied with nerve fascicles and sensory corpuscles of both the Ruffini and lamellated type. p75 immunoreactivity (IR) was detected in association with the nerve fascicles and the corpuscles, particularly in their capsule. S-100 IR was found in the Schwann cells in the central regions of the corpuscle, and PGP 9.5 IR marked the axonal structures in the corpuscles. New information on neurotrophin receptor distribution in ligaments has been obtained here. The presence of nerve fascicles and particularly sensory corpuscles in the SLIL suggests that the ligament has a proprioceptive role in the stability of the wrist. The marked p75 IR further indicates that neurotrophins play a part in a proprioceptive system in the ligament, given the importance of neurotrophins in maintaining sensory function.