A study of mechanoreceptors in fibrocartilage masses in the defect of pars interarticularis

We investigated the origin of low back pain associated with lumbar spondylolysis and spondylolytic spondylolisthesis by removing fibrocartilage masses from the lytic sites in symptomatic patients and staining the masses by the Gairns gold chloride method to examine mechanoreceptors. The fibrocartilage masses were found to contain four types of mechanoreceptors: Pacinian corpuscles, Ruffini receptors, Golgi tendon organ-like receptors, and free nerve endings. All of these mechanoreceptors were present at the periphery of the specimens, and Ruffini receptors and free nerve endings were abundant. Some mechanoreceptors had a slightly atypical structure, in addition to those with typical morphology. Comparison with mechanoreceptors in normal lumbar facet joint capsules showed that there were more mechanoreceptors in the fibrocartilage masses and a greater proportion of atypical structures at lytic sites. The presence of mechanoreceptors at lytic sites suggests that the fibrocartilage masses are not simply scar tissue filling the defect. Rather, these masses also appear to play a protective role by sensing instability via mechanoreceptors and transmitting this information as pain, while at the same time acting as ligament-like tissue that connects and stabilizes the separated vertebral arches. Received for publication on Dec. 2, 1998; accepted on May 12, 1999     

Ultrastructure of sensory nerve endings in monkey (Macaca fascicularis) knee joint capsule

Ultrastructural studies of sensory endings in monkey posterior medial knee joint capsule were undertaken. Three distinct sensory nerve endings have been identified: free nerve endings, Ruffini corpuscles, and Pacinian corpuscles. The free nerve endings are present in all layers of the joint capsule excluding the synovium. Two types of Ruffini corpuscles have been found in the fibrous layer. The first type is characterized by a thin perineurial capsule, the second type by a thicker perineurial capsule, and extensive intracapsular space. Both types of Ruffini corpuscles are innervated by approximately one to four myelinated axons which lose their sheaths as they course through the corpuscle. They terminate on collagen fiber bundles as distinct swellings with spiny membrane projections that are covered by a thin basal lamina. These terminals contain abundant mitochondria, agranular vesicles, and irregularly arranged neurofilaments and neurotubules. Two types of Pacinian corpuscles were occasionally observed. The first was a small, typically laminated structure with an inner core at the layer between the synovium and the fibrous layer and between the fibrous layer and muscle/ligament; larger Vater-Pacinian corpuscles were noted only at the boundary between the fibrous layer and the muscle/ligament layer.     

Proprioception of the cruciate ligaments: receptor mapping in an animal model

Ten anterior and posterior cruciate ligaments (ACL and PCL) harvested from adult sheep were investigated under light microscopy for data on the frequency and localisation of neural structures. Serial sections of 25 μm thickness were stained with a modified gold chloride technique. Receptors were classified according to their histological structure. Topographic distribution and frequency within the ligament texture were determined with the help of computerized image analysis. Three distinct neural structures could be identified: Ruffini endings, Ruffini corpuscles of the Golgi tendon organ-like type and Pacinian corpuscles. Golgi tendon organs were not found. In total, 274 and 238 neural structures were present in the 10 ACL and 10 PCL, respectively. Pacinian receptors were the most common structures, with a mean frequency of 13.6 ± 5.3 (ACL) and 12.4 ± 5.1 (PCL), followed by Ruffini endings with 8.9 ± 3.2 (ACL) and 7.8 ± 2.9 (PCL), whereas Ruffini corpuscles had the lowest frequency with a mean value of 4.9 ± 2.1 (ACL) and 3.4 ± 1.1 (PCL). The majority of the neural structures were located in the subsynovial sheath or closely associated with endotenon structures. The tibial and femoral insertion areas had a significantly increased receptor density compared with the midpart of the ACL and PCL (P < 0.001), where only 19.3% and 23.7% of the receptors were located. These results emphasise the complex sensory structure of the cruciate ligaments and provide a valid morphological basis for further neurophysiological investigations. Received: 3 June 1997     

Mechanoreceptors of patellar tendon used for ACL reconstruction: Rabbit experiments

In 17 Japanese white rabbits (weighing 2.6-3.7kg), the anterior cruciate ligament of the right knee was resected and then reconstructed, using the lateral half of the patellar tendon. The contralateral side served as control. Rabbits were killed 10, 20, or 30 weeks postoperatively. Then the reconstructed ligament was harvested and stained, using a modified gold chloride method. Under the light microscope, sensory nerve endings in serial sections were counted after being morphologically identified.

With respect to the number of Pacinian and Ruffini corpuscles, there were no significant differences between the reconstructed ligament and the control patellar tendon at any time after surgery.     

Neurohistology of lumbar spine ligaments

A study was conducted to identify neural elements in the posterior ligaments of the lumbar spine by using a modified gold-chloride method. Three morphologic types of mechanoreceptors were identified: Ruffini corpuscles, Ruffini end organs, and pacinian corpuscles. Free nerve endings, which are thought to be responsible for pain production, were also demonstrated within the ligaments.     

Mechano-receptors in the flexor tendons of the hand

Flexor tendons of the hand obtained fresh at autopsy were studied histologically for free nerves and mechano-receptors. In addition to free nerves, Ruffini endings, Pacinian corpuscles and Golgi tendon organs were found throughout the tendons. Golgi tendon organs and Pacinian corpuscles were subjectively in greater numbers than Ruffini endings. The predominance of these two mechano-receptors indicates that position sense and kinetic activities of the fingers are well-served, as evidenced in hand movements.     

Effects of anterior lumbar spinal fusion on the distribution of nerve endings and mechanoreceptors in the rabbit facet joint: quantitative histological analysis

The purpose of this study was to investigate the density and distribution of neural endings in rabbit lumbar facet joints after anterior spinal fusion and to evaluate the effects of intervertebral immobilization. An extraperitoneal approach was applied, and L5/6 was fixed with a plate and screws. Bilateral L4/5, L5/6, and L6/7 facet joint capsules were harvested from the rabbits 4, 8, and 16 weeks postoperatively. Capsular tissues were processed using a modified gold chloride staining method, and the specimens were sliced into 15-m sections. All sections were analyzed microscopically, and neural ending numbers per unit volume were calculated. Three types of neural ending were identified in each specimen: Pacinian corpuscles, Ruffini corpuscles, and free nerve endings. In the L5/6 fusion segment there was a significant decrease in the number of Pacinian corpuscles at 4 weeks and of Ruffini corpuscles at 4, 8, and 16 weeks after the fusion compared with the control; and in the L4/5 upper adjacent segment there was a significant increase in the number of free nerve endings. The number of Ruffini endings for the L6/7 lower adjacent segment was significantly lower more than 8 weeks after the fusion. These results suggest that immobilization of the intervertebral segment causes a reduction in the number of mechanoreceptors in the facet joint capsules because of the reduction in mechanical stimulation. Moreover, in the upper adjacent facet joint there may be neural sprouting caused by nociceptive stimulation.     

Neurohistology of the sinus tarsi and sinus tarsi syndrome

The purpose of this study was to clarify the neural anatomy of the sinus tarsi. The nerve endings of the synovium in the sinus tarsi were examined. The synovial membrane in the sinus tarsi was excised in 20 patients with sinus tarsi syndrome (20 feet) and in 2 feet from subjects without symptoms (controls). In 15 of the 20 patients and the two controls, the excised synovial membrane was studied histologically with staining by a modified Gairns gold chloride method. Numerous neural elements were observed in the sinus tarsi in all examined synovium. There were abundant free nerve endings and three types of mechanoreceptors: Pacinian corpuscles, Golgi corpuscles, and Ruffini corpuscles. Macroscopic observation and histological examination, using hematoxylin and eosin, in the other 5 patients revealed chronic synovitis in the sinus tarsi. Our findings suggest that the sinus tarsi is not only a talocalcaneal joint space but a source of nociceptive and proprioceptive information on the movement of the foot and ankle. Sinus tarsi syndrome may result from disorders of nociception and proprioception in the foot. Received for publication on Dec. 14, 1998; accepted on Feb. 23, 1999     

Sensory innervation of temporomandibular joint disk

PURPOSE: To investigate the nerve endings of the adult temporomandibular joint disk, in particular the presence and configuration of the sensory nerve endings by silver staining and electron microscopy. METHODS: 20 cadaveric temporomandibular joints impregnated with silver stain were studied using an optical microscope; 2 other joints were studied using a transmission electron microscope. RESULTS: Free nerve endings were found in the disk parenchyma of all joints. Golgi-Mazzoni corpuscles, Ruffini corpuscles, and articular corpuscles were also observed as sensory nerve end organs. Myelinated and nonmyelinated nerve fibres were visualised in the disk parenchyma using the transmission electron microscope. CONCLUSION: Free nerve endings and sensory nerve end organs are present in the disk parenchyma of the human temporomandibular joint and are associated with sensation and proprioception, just as they are in the acetabular labrum, glenoid labrum, triangular fibrocartilage complex, and meniscus.     

Neural anatomy of the transverse carpal ligament

Carpal tunnel syndrome is one of the most commonly diagnosed disorders of the upper extremity. The etiology of the neuropathy is known to be associated with many disorders, with the etiology of carpal tunnel syndrome mainly attributable to ischemia of the median nerve. The purpose of this study was to determine the presence of neural elements within the transverse carpal ligament. Fourteen transverse carpal ligaments were harvested from seven male and seven female fresh frozen cadavers with an average age of 76 years. The tissues were stained with S-100 using a standard immunoperoxidase technique used to localize neural tissue. The transverse carpal ligament consisted of interwoven bundles of fibrous connective tissue. It was found to have an intraligamentous and extraligamentous neural network consisting mostly of free nerve endings and pacinian corpuscles. Ruffini's corpuscles were not identified. This study showed that there is neural innervation to the transverse carpal ligament. Pacinian corpuscles have been shown to be mechanoreceptors which respond to changes in joint position, whereas free nerve endings have been identified as nociceptors. Neural innervation were present in the transverse carpal ligament, and the nociceptive information relayed by these neural elements may contribute to the pain associated with carpal tunnel syndrome. In addition to being a mechanical wrist stabilizer, the transverse carpal ligament also may play a role in proprioception of the wrist.     

Differences in the presence of mechanoreceptors and nerve structures between wrist ligaments may imply differential roles in wrist stabilization.

The purpose of this study was to analyze human wrist ligaments with regard to presence of general innervation and mechanoreceptors. The ligaments studied were: dorsal radiocarpal (DRC), dorsal intercarpal (DIC), long radiolunate (LRL), radioscaphocapitate (RSC), ulnocarpal (UC), scapholunate interosseous (SLI) and lunotriquetral interosseous (LTI) ligaments. Specific immunohistochemical markers were used to target neural/perineurial structures. Both Ruffini and Pacini-like mechanoreceptors (sensory corpuscles) as well as nerve fascicles/free nerve fibers were identified. Ruffini corpuscles were primarily identified via their dendritic intracapsular nerve endings, whereas the Pacini-like corpuscles were identified through their thick perineurial capsules with marked p75 immunoreaction. The wrist ligaments were found to vary in innervation, the DIC, DRC and SLI being richly innervated, whereas the LRL being almost without innervation. The difference in innervation between the ligaments might reflect differential function. Ligaments without innervation might act as structures of passive restraint, whereas ligaments with rich innervation are proposed to also provide proprioceptive information. Wrist ligament injuries should, therefore, be regarded as a disturbance not only of the intrinsic carpal kinematics, but also of the coordination and proprioception of the entire wrist joint.     

A sensory role for the cruciate ligaments

Morphologic, physiologic, and clinical evidence for the sensory role of the cruciate ligaments is reviewed. The cruciate ligaments accommodate morphologically different sensory nerve endings (Ruffini endings, Pacinian corpuscles, Golgi tendon organlike endings, and free nerve endings) with different capabilities of providing the central nervous system with information not only about noxious and chemical events but also about characteristics of movements and position-related stretches of these ligaments. A survey of available data reveals that low threshold joint-ligament receptor (i.e., mechanoreceptor) afferents evoke only weak and rare effects in skeletomotor neurons (alpha-motor neurons), while they frequently and powerfully influence fusimotor neurons (gamma-motor neurons). The effects on the gamma-muscle-spindle system in the muscles around the knee are so potent that even stretches of the cruciate ligaments at relatively moderate loads (not noxious) may induce major changes in responses of the muscle spindle afferents. As the activity in the primary muscle spindle afferents modifies the stiffness in the muscles, the cruciate ligament receptors, via the gamma-muscle-spindle system, may participate in the regulation and preprogramming of the muscular stiffness around the knee joint and thereby of the knee joint stiffness. Thus, the sensory system of the cruciate ligaments is able to significantly contribute to the functional stability of the knee joint.     

Coracoacromial ligament release for shoulder impingement syndrome using the Universal Subcutaneous Endoscope system.

We developed a new operative procedure of coracoacromial ligament release for shoulder impingement syndrome. The operative procedure was confirmed by cadaveric studies and applied to clinical cases in 40 shoulders of 37 patients who suffered from shoulder impingement without bony abnormalities. The subacromial space was observed under local anesthesia using the Universal Subcutaneous Endoscope (USE) system on an outpatient basis. A popping phenomenon was observed between the coracoacromial ligament and the greater tuberosity of the humerus, which was covered by the rotator cuff, and the coracoacromial ligament was resected with a rongeur under endoscopic visualization in all shoulders. Resection of the coracoacromial ligament relieved the impingement and clinical signs, as in open or arthroscopic resection of the coracoacromial ligament. Resection of the coracoacromial ligament using the USE system is a safe and less-stressful surgical invasion than open or standard arthroscopic resection of the coracoacromial ligament.     

Proprioception in the anterior cruciate ligament of the human knee joint--morphological bases. A light, scanning and transmission electron microscopy study]

In 21 human anterior cruciate ligaments removed with their synovial sheaths during autopsy and operation, nerves and nerve endings were demonstrated by light microscopy, scanning electron microscopy and transmission electron microscopy. Ultrastructural examination allowed a classification of nerve endings into three types: Ruffinian corpuscles, Pacinian corpuscles and free (afferent and efferent) nerve endings. The nerve endings corresponded to those characteristic of articular capsules. The anterior cruciate ligament shows evidence of a proprioceptive function besides its stabilizing function, which is based on its collagenous structure. Together, they probably represent the most important factor in the dynamic stabilization of the knee joint. At present it is only possible to speculate on the potential clinical significance of these findings, for example in development of rehabilitation programs and prevention strategies offering protection against anterior cruciate tears. This also applies to the question of whether to preserve the ligament during surgery for ruptures and knee-joint prostheses.     

兔踝关节外侧韧带Brostr(o)m重对韧带本体感觉的影响

目的探讨兔踝关节外侧韧带Brostr(o)m重建术对韧带本体感觉的影响。方法取63只成年新西兰大白兔,随机选取9只处死后切取踝关节外侧韧带(空白对照组);余54只全部切断踝关节外侧韧带,随机选取其中27只行Brostr(o)m重建术(实验组),27只旷置韧带(实验对照组)。术后第2、6和12周,两个实验组分别随机选取9只动物,处死后切取踝关节外侧韧带,行改良O'Connor and Gonzales氯化金染色后于光镜下观察、计数本体感受器小体。结果在踝关节外侧韧带内找到并识别了四种机械感受器：Ruffini小体、Pacini小体、Golgi腱器官及游离神经末梢。对前三种进行计数,空白对照组机械感受器小体总数为(21.0±3.5)个;实验组术后2、6、12周分别为(12.7±2.1)、(13.0±3.0)、(16.0±2.0)个;实验对照组术后2、6、12周分别为(7.7±1.5)、(4.7±1.5)、(6.3±0.6)个。实验组术后2,6,12周之间的差异有统计学意义(F=7.53,P=0.00),随时间推移小体数逐渐增多。实验对照组类似(F=16.27,P=0.00)。术后2、6、12周三组间的差异有统计学意义(F=88.75,102.91,122.53,P=0.00),实验组较实验对照组多,较空白对照组少。结论兔踝关节外侧韧带断裂后,不论手术与否,均会出现机械感受器小体数量下降;Brostr(o)m解剖重建术较韧带旷置能保留更多的机械感受器小体。     

Mechanical properties of regenerated coracoacromial ligament after subacromial decompression

Recent publications suggest that the coracoacromial ligament regenerates after it has been partially excised during subacromial decompression or acromioplasty. This observation may aid the understanding of the successes and failures of this very commonly performed surgical procedure. This study determines the mechanical properties of the apparently regenerated ligament. Eight regenerated coracoacromial ligaments were excised during revision surgery after subacromial decompression and were taken for mechanical testing. It appears that the ligament does have the ability to re-form relatively quickly after subacromial decompression or acromioplasty but takes time to regain strength. The results indicate that the ligament may possibly regain normal mechanical properties after regeneration times in excess of 3 years.     

Mechanoreceptors and length of the patellar ligament after Ho-YAG laser treatment: A long-term follow-up in rabbits

We studied the shortening and the number of mechanoreceptors in the patellar ligament up to 18 months after Ho-YAG irradiation of the ligament's surface in 35 rabbits. The ligaments shortened an average 13% immediately after irradiation. After treatment, we divided the rabbits into a mobilized or immobilized group. At 2 weeks and 12 months after treatment both groups showed no shortening of the ligament, as compared to the intact ligament while that in the mobilized group had elongated at 12 months.

Fewer Pacinian and Ruffini corpuscles were found in the irradiated ligaments than in the intact ones at 2 weeks after treatment, but we found no difference between irradiated and intact ligaments at 18 months after treatment.     

Neurohistology of lumbar spine ligaments

A study was conducted to identify neural elements in the posterior ligaments of the lumbar spine by using a modified gold-chloride method. Three morphologic types of mechanoreceptors were identified: Ruffini corpuscles, Ruffini end organs, and pacinian corpuscles. Free nerve endings, which are thought to be responsible for pain production, were also demonstrated within the ligaments.     

Contact pressure and glenohumeral translation following subacromial decompression: how much is enough?

Subacromial decompression is a common surgical procedure that has historically included coracoacromial ligament resection. However, recent reports have advocated preserving the coracoacromial ligament to avoid the potential complication of anterosuperior escape. The optimal subacromial decompression would achieve a smooth coracoacromial arch and decreased rotator cuff contact pressures while preserving the function of the arch in glenohumeral stability. We hypothesized that a subacromial decompression with a limited acromioplasty with preservation of the coracoacromial ligament can decrease extrinsic pressure on the rotator cuff similar to a coracoacromial ligament resection, without altering glenohumeral translation. Three different subacromial decompressions, including a "smooth and move," a limited acromioplasty with coracoacromial ligament preservation, and a coracoacromial ligament resection, were performed on 6 cadaveric specimens with intact rotator cuffs. Glenohumeral translation and peak rotator cuff pressure during abduction were recorded. No change in translation was observed after a smooth and move or a limited acromioplasty. Compared to baseline specimens, anterosuperior translation was increased at 30° of abduction following coracoacromial ligament resection (P<.05). Baseline rotator cuff pressure was greatest during abduction with the arm in 30° of internal rotation. Peak rotator cuff pressure decreased up to 32% following a smooth and move, up to 64% following a limited acromioplasty, and up to 72% following a coracoacromial ligament resection. Based on the present study, a limited acromioplasty with coracoacromial ligament preservation may best provide decompression of the rotator cuff while avoiding potential anterosuperior glenohumeral translation.     

Effect of immobilization of the knee joint on mechanoreceptors in anterior cruciate ligament of the rabbit

We investigated the morphologic distribution of mechanoreceptors in the anterior cruciate ligament of the knee in rabbits and the effects of immobilization of the knee joint, and evaluated the qualitative and quantitative morphologic changes of the mechanoreceptors after resumption of movement of the knee joint. There was no significant difference in the total number of mechanoreceptors present after 4-week immobilization compared with the number of mechanoreceptors on the unfixed control side. However, there was a significant increase in Pacinian corpuscles and Ruffini receptors with an atypical morphology. When immobilization was performed for 6 weeks, the total number of mechanoreceptors, including typical and atypical ones, showed a significant decrease compared to the control. After 12 and 24 weeks of remobilization, the total number of mechanoreceptors had returned to a level not significantly different from that on the control side, but typical mechanoreceptors were still significantly decreased and the atypical mechanoreceptors had increased. These results suggest that immobilization brings about morphologic changes and a reduction in the number of mechanoreceptors. The total number of mechanoreceptors recovers after re-mobilization, but the typical mechanoreceptors do not return, and the number of atypical mechanoreceptors increas. These changes are thought to be irreversible.