Distribution, quantity and gene expression of mechanoreceptors in ligaments and tendons of knee joint in rabbits

Periarticular Proprioception: Analyzing the Three-Dimensional Structure of Corpuscular Mechanosensors in the Dorsal Part of the Scapholunate Ligament

INTRODUCTION

Sensory nerve endings transmit mechanical stimuli into afferent neural signals and form the basis of proprioception, giving rise to the self-perception of dynamic stability of joints. We aimed to analyze the three-dimensional structure of periarticular corpuscular sensory nerve endings in a carpal ligament to enhance our understanding of their microstructure.

METHODS

Two dorsal parts of the scapholunate ligament were excised from two human cadaveric wrist specimens. Consecutive cryosections were stained with immunofluorescence markers protein S100B, neurotrophin receptor p75, protein gene product 9.5 (PGP 9.5), and 4',6-diamidino-2-phenylindole. Three-dimensional images of sensory nerve endings were obtained using confocal laser scanning microscopy, and subsequent analysis was performed using Imaris software.

RESULTS

Ruffini endings were characterized by a PGP 9.5-positive central axon, with a median diameter of 4.63 μm and a median of 25 cells. The p75-positive capsule had a range in thickness of 0.94 μm and 15.5 μm, consisting of single to three layers of lamellar cells. Ruffini endings were significantly smaller in volume than Pacini corpuscles or Golgi-like endings. The latter contained a median of three intracorpuscular structures. Ruffini endings and Golgi-like endings presented a similar structural composition of their capsule and subscapular space. The central axon of Pacini corpuscles was surrounded by S100-positive cells forming the inner core which was significantly smaller than the outer core, which was immunoreactive for p75 and PGP 9.5.

CONCLUSION

This study reports new data regarding the intricate outer and intracorpuscular three-dimensional morphology of periarticular sensory nerve endings, including the volume, number of cells, and structural composition. These results may form a basis to differ between normal and pathological morphological changes in periarticular sensory nerve endings in future studies.

Chronic Ankle Joint Instability Induces Ankle Sensorimotor Dysfunction: A Controlled Laboratory Study

BACKGROUND

Chronic ankle instability (CAI) is a clinical sequela that causes the recurrence of ankle sprain by inducing ankle sensorimotor dysfunction. Animal models of CAI have recently shown that ankle ligament injuries mimicking an ankle sprain result in chronic loss of ankle sensorimotor function. However, the underlying mechanisms determining the pathogenesis of CAI remain unclear.

HYPOTHESIS

Ankle instability after an ankle sprain leads to the degeneration of the mechanoreceptors, resulting in ankle sensorimotor dysfunction and the development of CAI.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four-week-old male Wistar rats (N = 30) were divided into 2 groups: (1) the ankle joint instability (AJI) group with ankle instability induced by transecting the calcaneofibular ligament (n = 15) and (2) the sham group (n = 15). Ankle instability was assessed using the anterior drawer test and the talar tilt test at 4, 6, and 8 weeks after the operation (n = 5, for each group at each time point), and ankle sensorimotor function was assessed using behavioral tests, including ladder walking and balance beam tests, every 2 weeks during the postoperative period. Morphology and number of mechanoreceptors in the intact anterior talofibular ligament (ATFL) were histologically analyzed by immunofluorescence staining targeting the neurofilament medium chain and S100 proteins at 4, 6, and 8 weeks postoperatively (n = 5 per group). Sensory neurons that form mechanoreceptors were histologically analyzed using immunofluorescence staining targeting the mechanosensitive ion channel PIEZO2 at 8 weeks postoperatively (n = 5).

RESULTS

Ankle sensorimotor function decreased over time in the AJI group, exhibiting decreased ankle instability compared with the sham group (P = .045). The number of mechanoreceptors in the ATFL was reduced (P < .001) and PIEZO2 expression in the sensory neurons decreased (P = .008) at 8 weeks postoperatively. The number of mechanoreceptors was negatively correlated with ankle sensorimotor dysfunction (P < .001).

CONCLUSION

The AJI model demonstrated degeneration of the mechanoreceptors in the ATFL and decreased mechanosensitivity of the sensory neurons, which may contribute to CAI.

CLINICAL RELEVANCE

Ankle instability causes degeneration of mechanoreceptors and decreases the mechanosensitivity of sensory neurons involved in the development of CAI. This finding emphasizes the importance of controlling ankle instability after ankle sprains to prevent recurrence and the onset of CAI.

Proprioception: A New Era Set in Motion by Emerging Genetic and Bionic Strategies?

The generation of an internal body model and its continuous update is essential in sensorimotor control. Although known to rely on proprioceptive sensory feedback, the underlying mechanism that transforms this sensory feedback into a dynamic body percept remains poorly understood. However, advances in the development of genetic tools for proprioceptive circuit elements, including the sensory receptors, are beginning to offer new and unprecedented leverage to dissect the central pathways responsible for proprioceptive encoding. Simultaneously, new data derived through emerging bionic neural machine-interface technologies reveal clues regarding the relative importance of kinesthetic sensory feedback and insights into the functional proprioceptive substrates that underlie natural motor behaviors.

Anterior and Posterior Cruciate Ligaments Mechanoreceptors: A Review of Basic Science

Proprioception is a specialized sensory modality encompassing the movement of the joint and its position in space, and it involves the conversion of mechanical deformation of tissues into neural signals. Mechanoreceptors are specialized nerve structures able to transmit mechanical deformation through electrical signals to dorsal root ganglion sensory neurons and are abundant in the muscles, tendons and ligaments of the knee joint. They are believed to play an important role in knee proprioception and dynamic knee stability. Proprioception should always be taken into consideration for successful reconstruction of the cruciate-deficient knee and for pain and function management in the arthritic knee. Advances in histological methods of detection are numerous and continue to highlight the presence and role of mechanoreceptors after ligament reconstruction, depending on choice of graft. In this review, we present the current knowledge of anterior and posterior cruciate ligaments and grafts mechanoreceptors, and their role in proprioception of knee joint, focusing on each type of mechanoreceptors.

Proprioceptive and Clinical Outcomes after Remnant Preserved Anterior Cruciate Ligament Reconstruction: Assessment with Minimal Confounding Factors

Objective

To evaluate the proprioceptive and clinical function of the knee joint after anterior cruciate ligament reconstruction (ACLR) with various amounts of remnant preserved with as few confounding factors as possible.

Methods

This retrospective study included 46 patients who underwent ACLR with remnant preservation between March 2013 and February 2019. These patients had less than 6 months injury‐to‐surgery interval and no concomitant injuries. The researchers divided these subjects into two groups based on the length of the remnant preserved after ACLR, with group A defined as having more than 1/3 of the original length preserved and group B defined as less than 1/3 of the original length preserved. Clinical scores were obtained using the Lysholm knee scoring scale and the Tegner activity scale. The Lysholm score was calculated preoperatively, at 3, 6, and 12 months postoperatively, and at the last follow up. The Tegner score was calculated preoperatively, at 12 months postoperatively and at the last follow up. Anterior laxity was measured using the KT2000 arthrometer preoperatively and at 12 months postoperatively. Proprioceptive function was evaluated through reproduction of passive positioning (RPP) and threshold to detection of passive motion (TDPM). Both RPP and TDPM were measured at the angle of 15° at 3, 6, and 12 months postoperatively. Unpaired t‐tests were performed to investigate the difference in each parameters between the two groups.

Results

In the present study, 20 patients were classified into group A and 26 into group B. All patients were followed up for an average of 34.70 ± 12.79 months. All 46 patients were satisfied with the outcome of the surgery and no complications were reported at the end of the study. No significant differences were found between the two groups in terms of the Lysholm score and anterior laxity by KT2000 at all time points. The Tegner score was significantly higher in group A at 12 months postoperatively and at the final follow‐up. In addition, group A's RPP was significantly better than that of group B's when tested at the angles of 15° and 30° at 3 months postoperatively, and at the angle of 15° at 6 months postoperatively. Group A's TDPM was also significantly better than that of group B's at all three tested angles at 3 months postoperatively, and at the angle of 15° at 6 months postoperatively.

Conclusion

Patients with ACLR with more than 1/3 of the original length preserved demonstrated a higher activity level 12 months postoperatively and better proprioceptive function at 15° of extension at 3 and 6 months postoperatively.

Mechanoreceptors observed in a ligamentous structure between the posterior horn of the lateral meniscus and the anterior cruciate ligament

PURPOSE

A histological study of a structure between the posterior horn of the lateral meniscus and the anterior cruciate ligament.

METHODS

Bilateral fresh-frozen cadaveric knees of two male donors (age 71 and 76 years) with no history of prior knee injury were examined. All dissections were performed by one experienced orthopaedic surgeon. Haematoxylin and Eosin staining was used to reveal tissue morphology. Goldner trichrome staining was used to evaluate the connective tissue. S100 and PGP 9.5 labelling were used for immunohistochemical analysis.

RESULTS

In all cadaveric knees, a structure between the posterior horn of the lateral meniscus and the anterior cruciate ligament was identified. Histological analysis confirmed the ligamentous nature of this structure. Furthermore, Golgi tendon organs were observed within the ligamentous structure.

CONCLUSION

This is the first study showing the presence of mechanoreceptors within the ligamentous structure between the posterior horn of the lateral meniscus and the anterior cruciate ligament. The ligamentous structure could contribute to stability of the knee by providing proprioceptive input, while preservation of the ligamentous structure might ensure a better functional outcome after surgery.