Innervation of the anterior cruciate ligament

Effects of Preserving Anatomically Positioned and Adequate Remnant ACL Tissue in Double-Bundle ACL Reconstruction

Background

The advantages of remnant tissue preservation in anterior cruciate ligament (ACL) reconstruction (ACLR) remain controversial.

Hypothesis

It was hypothesized that a large amount of remnant tissue, especially if anatomically positioned, would improve patient-reported outcomes and second-look graft appearance after preserved double-bundle ACLR (DB-ACLR).

Study Design

Cohort study; Level of evidence, 3.

Methods

This retrospective study included 89 consecutive patients who underwent unilateral remnant-preserving DB-ACLR using 2 hamstring tendon autografts. The authors categorized the arthroscopic findings into 3 groups according to the location and volume of the ACL remnant tissue in the femoral notch: (1) anatomical attachment (group AA; n = 34); (2) nonanatomical attachment (group NA; n = 33); and (3) no remnant (group NR; n = 22). Based on second-look arthroscopy, the reconstructed graft was graded as excellent, fair, or poor. Patient-reported outcomes were evaluated at 2 years after surgery using the Knee injury and Osteoarthritis Outcome Score (KOOS) and the Japanese Anterior Cruciate Ligament Questionnaire-25 (JACL-25).

Results

The AA and NA groups had a significantly shorter time from injury to surgery compared with the NR group (P = .0165). Considering the second-look arthroscopic findings, the authors found a significant difference in synovial coverage of the grafts between the 3 groups (P = .0018). There were no significant differences in the overall KOOS and JACL-25 score among the 3 groups; however, the KOOS-Sport and Recreation and KOOS-Quality of Life subscale scores were significantly higher in the AA group compared with the NA and NR groups (P = .0014 and .0039, respectively). The JACL-25 score for middle- to high-speed flexion and extension was significantly better in the AA group versus the NR group (P = .0261).

Conclusion

This study showed that preserving anatomically positioned and adequate remnant tissue during DB-ACLR improved second-look graft appearance and KOOS-Sport and Recreation and KOOS-Quality of Life scores.

Study of the nerve endings and mechanoreceptors of the medial meniscotibial ligament of the knee: A structural and distribution analysis

BACKGROUND

The aim of the present study is to describe the morphology and distribution of the nerve endings of the meniscotibial ligament (MTL) of the knee, in order to understand the interaction between the proprioceptive system and knee mechanics.

METHODS

Twenty medial MTLs were obtained from deceased organ donors. The ligaments were measured, weighed and cut. Sections (10 mm) were prepared on hematoxylin and eosin-stained slides for analysis of tissue integrity, and 50 mm sections were submitted to immunofluorescence with the protein gene product (PGP) 9.5 as primary antibody and Alexa Fluor 488 as secondary antibody, followed by microscopic analysis.

RESULTS

The medial MTL was identified in 100% of the dissections, with average length, width, thickness and weight of 7.07 ± 1.34 mm, 32.25 ± 3.09 mm, 3.53 ± 0.27 mm and 0.67 ± 0.13 g, respectively. The hematoxylin and eosin-stained histological sections exhibited typical ligament structure, with dense well-organized collagen fibers and vascular tissue. All the specimens analyzed contained type I (Ruffini) mechanoreceptors and free (type IV) nerve endings, varying from parallel to intertwined fibers. Nerve endings not classified with different irregular shapes were also found. Most type I mechanoreceptors were found close to the MTL insertions on the tibial plateau, while the free nerve endings were found adjacent to the capsule.

CONCLUSION

The medial MTL showed a peripheral nerve structure, primarily type I and IV mechanoreceptors. These findings suggest that the medial MTL is important for proprioception and medial knee stabilization.

Comparing Analgesic Efficacy of a Novel Dual Subsartorial Block Using Two Different Volumes in Patients Undergoing Total Knee Arthroplasty: A Prospective, Double-Blind, Monocentric, Randomised Trial

Introduction: Total knee arthroplasty (TKA) is a life-changing joint surgery that improves health-related quality of life and functional status. Patients in need of this surgery mostly belong to the geriatric age group with limited functional reserves and multiple co-morbidities requiring utmost perioperative care with the most suitable analgesic modalities. Regional analgesia (RA) should provide effective analgesia while allowing early mobility, reduced opioid consumption, and early discharge. Dual subsartorial block (DSB) is a novel procedure-specific, motor-sparing, and opioid-sparing RA technique for TKA surgeries. Our study compared the analgesic efficacy of the two different combinations of volumes used in DSB.

Methods: This prospective randomized comparative study included patients between 25-75 years of age of American Society of Anesthesiology (ASA) I-II grades who underwent an elective cemented unilateral total knee replacement performed via medial approaches under neuraxial anesthesia. A total of 104 patients were divided into two equal groups based on the local anesthetic (LA) volumes (Group A 10/20 ml and Group B 20/10 ml) used in the DSB. Postoperative pain scores (using a visual analog scale) and quadriceps strengths (using neurological exam), and opioid consumption were measured at regular intervals till discharge.

Results: Most patients (71.2%) remained pain-free and comfortable until discharge, while 28.8% complained of pain within 12 hours of DSB. Mean quadriceps strength remained almost normal (4-5/5) until the discharge with no incidences of buckling or fall in either group. Over time, the postoperative trend between the groups showed a significant difference for dynamic pain (p = 0.002) and quadriceps strength (p = <0.001). There was an insignificant difference (p = 0.161) between the groups regarding opioid consumption, with the median oral morphine equivalent of zero in both groups. 

Discussion: The effective analgesic coverage of DSB is based on the involvement of all innervations of the procedure-specific pain generators of TKR surgeries. The specific focus on selective sensory innervations and the type/volume of the LA used makes DSB a motor-sparing RA alternative that facilitates early mobility and discharge. It can provide effective postoperative analgesia without compromising the motor strength of the quadriceps muscle when administered in either 10/20 or 20/10 volumes.

Neurological structures and mediators of pain sensation in anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) tears is a devastating injury and one of the most common knee injuries experienced by athletes in the United States. Although patients reach maximal subjective improvement by one-year following ACL reconstruction, many patients often experience moderate to severe post-operative pain. Opioids, intra-articular injections, and regional anesthesia have been previously implemented to mediate post-operative pain. However, chronic opioid usage has become an epidemic in the United States. Alternative analgesic modalities, such as nerve blocks, have been implemented in clinical practice to provide adequate pain relief and minimize opioid usage. Periarticular injections targeted towards local neurological structures performed concomitantly with nerve blocks provides superior pain relief and satisfaction than isolated nerve blocks. Therefore, it is imperative for physicians to understand local neurological anatomy around the knee joint in order to provide adequate analgesia while minimizing opioid consumption. This purpose of this investigation is to summarize (1) neurogenic origins of pain generators and mediators in sites affected by ACL reconstruction and autograft harvest sites and (2) analgesia utilized in ACL reconstruction.

A Morphologic and Quantitative Study of Mechanoreceptors in the Remnant Stump of the Human Anterior Cruciate Ligament

PURPOSE

To investigate the morphology and quantity of mechanoreceptors in the remnant stumps of injured anterior cruciate ligaments (ACLs) and the association of the number of mechanoreceptors with the time from injury to surgery.

METHODS

Complete ACL stump specimens were collected from 40 volunteer patients who underwent arthroscopic ACL reconstruction surgery. Serial sections, 20 μm in thickness, were prepared from each specimen. After H&E staining and immunohistochemical labeling, the morphology, type, size, and quantity of the mechanoreceptors were observed under an optical microscope.

RESULTS

A total of 176 Ruffini corpuscles, 61 pacinian corpuscles, 15 Golgi-like tendon organs, and 66 atypical mechanoreceptors were observed. Free nerve endings were commonly present in the specimens. The time from injury to surgery (log10 days) was negatively correlated with the number of total mechanoreceptors (r = -0.43, P < .006), Ruffini corpuscles (r = -0.45, P < .003), and the volume of the ACL stump (r = -0.52, P < .01), and these correlations were independent of age, gender, injury side, and career.

CONCLUSIONS

The number of mechanoreceptors in an ACL stump and the volume of the stump decreased with the time from injury to surgery.

CLINICAL RELEVANCE

This study provides a further theoretical basis for ACL reconstruction with remnant preservation.

Functional changes in muscle afferent neurones in an osteoarthritis model: implications for impaired proprioceptive performance

Background

Impaired proprioceptive performance is a significant clinical issue for many who suffer osteoarthritis (OA) and is a risk factor for falls and other liabilities. This study was designed to evaluate weight-bearing distribution in a rat model of OA and to determine whether changes also occur in muscle afferent neurones.

Methodology/Principal Findings

Intracellular recordings were made in functionally identified dorsal root ganglion neurones in acute electrophysiological experiments on the anaesthetized animal following measurements of hind limb weight bearing in the incapacitance test. OA rats but not naïve control rats stood with less weight on the ipsilateral hind leg (P = 0.02). In the acute electrophysiological experiments that followed weight bearing measurements, action potentials (AP) elicited by electrical stimulation of the dorsal roots differed in OA rats, including longer AP duration (P = 0.006), slower rise time (P = 0.001) and slower maximum rising rate (P = 0.03). Depolarizing intracellular current injection elicited more APs in models than in naïve muscle afferent neurones (P = 0.01) indicating greater excitability. Axonal conduction velocity in model animals was slower (P = 0.04).

Conclusions/Significance

The present study demonstrates changes in hind limb stance accompanied by changes in the functional properties of muscle afferent neurones in this derangement model of OA. This may provide a possible avenue to explore mechanisms underlying the impaired proprioceptive performance and perhaps other sensory disorders in people with OA.

Delayed onset of changes in soma action potential genesis in nociceptive A-beta DRG neurons in vivo in a rat model of osteoarthritis

BACKGROUND

Clinical data on osteoarthritis (OA) suggest widespread changes in sensory function that vary during the progression of OA. In previous studies on a surgically-induced animal model of OA we have observed that changes in structure and gene expression follow a variable trajectory over the initial days and weeks. To investigate mechanisms underlying changes in sensory function in this model, the present electrophysiological study compared properties of primary sensory nociceptive neurons at one and two months after model induction with properties in naïve control animals. Pilot data indicated no difference in C- or Adelta-fiber associated neurons and therefore the focus is on Abeta-fiber nociceptive neurons.

RESULTS

At one month after unilateral derangement of the knee by cutting the anterior cruciate ligament and removing the medial meniscus, the only changes observed in Abeta-fiber dorsal root ganglion (DRG) neurons were in nociceptor-like unresponsive neurons bearing a hump on the repolarization phase; these changes consisted of longer half width, reflecting slowed dynamics of AP genesis, a depolarized Vm and an increased AP amplitude. At two months, changes observed were in Abeta-fiber high threshold mechanoreceptors, which exhibited shorter AP duration at base and half width, shorter rise time and fall time, and faster maximum rising rate/maximum falling rate, reflecting accelerated dynamics of AP genesis.

CONCLUSION

These data indicate that Abeta nociceptive neurons undergo significant changes that vary in time and occur later than changes in structure and in nociceptive scores in this surgically induced OA model. Thus, if changes in Abeta-fiber nociceptive neurons in this model reflect a role in OA pain, they may relate to mechanisms underlying pain associated with advanced OA.

Arthroscopic treatment of mucoid hypertrophy of the anterior cruciate ligament

PURPOSE

The purpose of this study was to examine the clinical features and diagnosis of patients with mucoid hypertrophy of the anterior cruciate ligament (ACL) and to assess the results of arthroscopic treatment.

METHODS

Between May 1999 and August 2005, 156 knees in 132 patients were diagnosed with mucoid hypertrophy of the ACL and underwent arthroscopic treatment. Of these, 106 knees in 91 patients (86 women and 5 men), with a mean age of 61 years (range, 42 to 80 years), were followed up for at least 2 years. All 106 knees had central knee pain on terminal extension without preceding trauma, and 83 (78.3%) had extension deficit. Magnetic resonance imaging showed thickened, ill-defined ACLs with increased intraligamentous signals. Arthroscopy showed osteoarthritic changes of varying degrees in all, with 84 (79.2%) having intercondylar notch narrowing and 102 (96.2%) having additional degenerative pathologies. The posterolateral portion of the ACL appeared hypertrophied, which impinged on the lateral wall and roof of the notch. Arthroscopic debridement of hypertrophied ACLs was performed with or without notchplasty, according to the severity of impingement.

RESULTS

Good to excellent pain relief on terminal extension was obtained in 92 of 106 knees (86.8%), including complete pain relief in 57 (53.8%). The extension deficit was normalized in 68 of 83 affected knees (81.9%). Lachman and anterior drawer tests showed a firm endpoint in all, and 85.8% showed good to excellent subjective satisfaction.

CONCLUSIONS

Mucoid hypertrophy of the ACL should be suspected in elderly women presenting pain on terminal extension without preceding trauma, especially when associated with extension deficit. The magnetic resonance imaging findings are specific for preoperative diagnoses. Partial ACL debridement with notchplasty provides safe and effective symptom relief. Extension pain improved significantly in 92 of 106 knees (86.8%), and extension deficit was normalized in 68 of 83 knees (81.9%).

Histomorphometric evaluation of mechanoreceptors and free nerve endings in human lateral ankle ligaments

INTRODUCTION

Joint mechanoreceptors have been studied and most of investigators recognize the potential role of mechanoreceptors in the proprioceptive function of joint. The aim of this study was to analyze the general innervation and the possible existence of sensory receptors in the lateral ankle ligament.

METHODS

Lateral ankle ligaments including anterior talofibular, posterior talofibular and calcaneofibular were obtained from 24 ankles of 13 male cadavers with ages ranging from 18 to 65 (mean 41.6) years. Each ligament was divided into three parts according to the bony attachments (proximal, central, and distal segments). Histologically mechanoreceptors (Ruffini, Pacini and Golgi) and free nerve endings were identified, and classified. Histomorphometric determination and evaluation of the density of the area of the receptor was performed by the point-counting methods.

RESULTS

The anterior talofibular, posterior talofibular, and calcaneofibular ligaments were endowed with mechanoreceptor and free nerve endings. There was a significant prevalence of Pacini (p<0.001) compared with Ruffini and Golgi. However, there was no significant difference in the mechanoreceptors density in the different ligaments analyzed (p>0.05)

CONCLUSION

Innervation of the lateral ankle ligaments was confirmed in this study, suggesting that the presence of mechanoreceptors could have clinical implication as well as relevance in the proprioceptive function. Future electrophysiological studies will be required to define the role in the proprioceptive and nociceptive system of the ankle.

Proprioceptive comparison of allograft and autograft anterior cruciate ligament reconstructions

The aim of this study is to search if there is any proprioceptive difference between auto and allograft anterior cruciate ligament (ACL) reconstructions, and also to determine if there is any relationship between instrumented anterior knee laxity and proprioception after an ACL reconstruction. The following four groups were constituted for this purpose: group I, control group; group II, autograft reconstructions; group III, allograft reconstructions and group IV, people with injured ACLs. Each group consisted of 20 patients/volunteers. Two subgroups were constituted according to the findings of KT-1,000 laxity testing in group II and III; patients/volunteers found to have a laxity of 3 mm or less were enrolled in the normal subgroup and those with a laxity of more than 3 mm were enrolled in the lax subgroup. Two proprioceptive tests were used: threshold to detect passive motion (TDPM) and joint position sense (JPS) by using Cybex Norm dynamometer. Patients underwent ten tests and the discrepancy in degrees was averaged for ten trials. Comparisons were made to evaluate the proprioceptive differences between groups/subgroups; ANOVA and t test was used for comparisons where appropriate, and the significance was set at P < 0.05. There was a significant difference in degrees between patients with injured ACLs and the other three groups in TDPM evaluations (injured: 1.93 degrees vs. control: 1.03 degrees , autograft: 1.01 degrees , allograft: 0.96 degrees ; P < 0.001). Auto and allograft reconstructions were not different from each other and controls. Allo and autograft ACL reconstructions are not different from each other according to proprioceptive measurements. Also, proprioception is not correlated to postoperative anterior knee laxity; many variables involve joint proprioception and mostly the anterior knee laxity may not be the sole determining element, and a lax ACL still may fulfill some of its afferent arc functions as long as it bridges the femur and tibia.

Submaximal fatigue of the hamstrings impairs specific reflex components and knee stability

Rupture of the anterior cruciate ligament (ACL) is one of the most serious sports-related injuries and requires long recovery time. The quadriceps and hamstring muscles are functionally important to control stability of the knee joint complex. Fatigue, however, is an important factor that may influence stabilizing control and thus cause ACL injuries. The objective of this study was therefore to assess how submaximal fatigue exercises of the hamstring muscles affect anterior tibial translation as a direct measure of knee joint stability. While 15 test participants were standing upright with the knees in 30 degrees of flexion, anterior tibial translation was induced by a force of 315 N. Two linear potentiometers placed on the tibial tuberosity and the patella recorded tibial motion relative to the femur. Reflex latencies and neuromuscular hamstring activity were determined using surface electromyography (EMG). Muscle fatigue produced a significant longer latency for the monosynaptic reflex latencies, whereas no differences in the latencies of the medium latency component were found. Fatigue significantly reduced EMG amplitudes of the short and medium latency components. These alterations were in line with significantly increased anterior tibial translation. Our results suggest that hamstring fatigue is effectively associated with mechanical loss of knee stability. This decrease in joint stability may at least in part explain higher risk of ACL injury, especially in fatigued muscles. Furthermore, we discuss why the present findings indicate that reduced motor activity rather than the extended latency of the first hamstring response is the reason for possible failure.

Changes in Stretch Reflex Excitability Are Related to “Giving Way” Symptoms in Patients With Anterior Cruciate Ligament Rupture

A rupture of the anterior cruciate ligament (ACL) usually leads to an altered stretch reflex excitability of the thigh muscles that stabilize the knee. The purpose of this study was to quantitatively assess reflex activity in the m. semitendinosus/semimembranosus after anterior tibial translation in 21 patients with isolated ACL ruptures. The patients were divided into a group with “giving way” symptoms (noncopers, n = 12) and a group without “giving way” symptoms (copers, n = 9). While the patients were standing upright with 30° knee flexion, a force of 300 N was applied to the knee to induce posterior–anterior tibial translation. Activity of m. semitendinosus/semimembranosus was measured using surface electromyography (EMG). A linear potentiometer was placed on the tibial tuberosity and measured maximum tibial translation during standing (i.e., functional condition). In addition, knee laxity was assessed with a KT1000 arthrometer under passive conditions. After ACL rupture, the short-latency response (SLR) latency remained unchanged ( P = 0.21), whereas for the medium-latency response (MLR) it was significantly longer ( P < 0.001). Significantly longer MLR latencies were noted for noncopers compared with copers ( P < 0.01), whereas SLR latencies were similar. Significant differences between healthy and injured legs were noted after tibial translations using KT1000 ( P < 0.001) and during stance ( P < 0.001). Mechanical knee instability was found to be unchanged between copers and noncopers (KT1000: P = 0.97; tibial translation: P = 0.31). These results indicate that ACL rupture is associated with altered stretch reflex excitability, which may lead to “giving way” symptoms, and that altered stretch reflex excitability may be more important for the development of “giving way” than the mechanical instability of the knee.

Anatomy of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is a band of dense connective tissue which courses from the femur to the tibia. The ACL is a key structure in the knee joint, as it resists anterior tibial translation and rotational loads. When the knee is extended, the ACL has a mean length of 32 mm and a width of 7-12 mm. There are two components of the ACL, the anteromedial bundle (AMB) and the posterolateral bundle (PLB). They are not isometric with the main change being lengthening of the AMB and shortening of the PLB during flexion. The ACL has a microstructure of collagen bundles of multiple types (mostly type I) and a matrix made of a network of proteins, glycoproteins, elastic systems, and glycosaminoglycans with multiple functional interactions. The complex ultrastructural organization and abundant elastic system of the ACL allow it to withstand multiaxial stresses and varying tensile strains. The ACL is innervated by posterior articular branches of the tibial nerve and is vascularized by branches of the middle genicular artery.

Differentiation of hamstring short latency versus medium latency responses after tibia translation

After injuries to the anterior cruciate ligament (ACL) a functional instability is frequently observed which has been attributed to a disturbed sensorimotor function. In light of the clinical importance of ACL injuries and the resulting functional instability, it is of enormous clinical interest to elucidate the role of sensorimotor pathways that involve the ACL. In animals and humans a direct reflex pathway between the ACL and the hamstrings has been shown. The onset latencies of responses reported after ventral tibia translation were around 40-50 ms (range 17.9-65) and were regarded as medium latency responses (MLR). However, ventral tibia translation should also induce a stretch of the hamstring muscles and evoke a short latency response (SLR). Before any muscle response after ventral tibia translation can be ascribed to anatomical structures, it is crucial to analyze the obtained muscle responses carefully. The aim of the present study was the development of an algorithm to differentiate SLR and MLR responses after ventral tibia translation. In ten healthy subjects reflex responses of the hamstrings after anterior tibia translation and after tendon taps on the biceps femoris tendon were evaluated. To investigate the influence of skin afferents, control experiments were performed after lidocain injection of the dorsal calf. The mean onset latency of the tendon jerk reflex was 21.9 +/- 3.1 ms (range 17.3 - 28.7 ms). Both SLR responses (mean onset latency: 20.3 +/- 3.5 ms; range 15.4 - 25.8) and MLR responses (mean onset latency: 38.9 +/- 4.2 ms; range 32.9 - 46.7) were obtained in all subjects. Skin afferents from the calf do not play a major role. The development of an evaluation algorithm is presented that allows a safe differentiation between these partly superimposed SLR and MLR components. It is demonstrated that by measuring the first part of the SLR from the onset to the first peak the end of the SLR can be predicted and that the onset latency of the MLR component can be assessed reliably. Possible reasons are discussed why previous studies only reported responses at MLR latencies. The fact that both SLR and MLR components can be observed after anterior tibia translation underlines the necessity to differentiate the responses before they can be ascribed to any anatomical structures. As a basis for future work the algorithm presented may become a useful tool to differentiate which afferent pathways play a role in initiating hamstring activity.

Review of knee proprioception and the relation to extremity function after an anterior cruciate ligament rupture

Several tests of human conscious knee proprioception have been described, but there is no consensus or reference standard established. Difficulties remain in the separation of information originating from muscles, tendons, and joints, and the tests cannot discriminate between loss of afferent signals or altered activity in the remaining receptors. There is convincing evidence from several descriptive studies that the afferent information is altered after a knee ligament injury and severely disturbed in some patients with anterior cruciate ligament (ACL) injuries. However, an inherent inferior proprioceptive ability may also exist in some individuals, which makes them vulnerable to injuries. The deficits in proprioception have mostly been studied and related to the consciously registered sense, whereas the extent of possible disturbances of the unconscious or reflectory mechanisms is largely unknown. The latter may, at least from a theoretical point of view, be predominantly contributing to the overall afferent regulation, and a possibility for major defects thus exists, since there is no knowledge of the quantified relation between the conscious and unconscious part. The clinical importance of the altered afferent information has not been evaluated properly, and the role of proprioception that contributes to function has yet to be investigated. A higher physiological sensitivity to detecting a passive joint motion closer to full extension has been found both experimentally and clinically, which may protect the joint due to the close proximity to the limit of joint motion. Proprioception has been found to have a relation to subjective knee function, and patients with symptomatic ACL deficiency seem to have larger deficits than asymptomatic individuals. Little is known about whether training can restore defects in sensory information or by which mechanisms possible compensatory pathways are established. In rehabilitation, each patient must, however, create muscle strength, alertness, and stiffness in harmony with the disturbed mechanics of the knee, which are present both after nonoperative treatment of the ACL and after a reconstruction of the ACL.

Dynamic knee stability: current theory and implications for clinicians and scientists

We will discuss the mechanisms by which dynamic knee stability may be achieved and relate this to issues that interest clinicians and scientists concerned with dynamic knee stability. Emphasis is placed on the neurophysiologic evidence and theory related to neuromuscular control. Specific topics discussed include the ensemble firing of peripheral mechanoreceptors, the potential for muscle stiffness modulation via force and length feedback, postural control synergies, motor programs, and the neural control of gait. Factors related to answering the difficult question of whether or not knee ligament injuries can be prevented during athletic activities are discussed. Prevention programs that train athletes to perform their sport skills in a safe fashion are put forth as the most promising prospect for injury prevention. Methods of assessing neuromuscular function are reviewed critically and the need for future research in this area is emphasized. We conclude with a brief review of the literature regarding neuromuscular training programs.

Effect of fatigue on knee proprioception: implications for dynamic stabilization

The high incidence of injuries that occur later during a session of sports or recreational activities suggests that fatigue may contribute to altered neuromuscular control of the lower limb and an individual's subsequent altered ability to dynamically stabilize the knee joint. One possible mechanism is a fatigue-mediated alteration in proprioception. This paper reviews experimental evidence of fatigue-induced changes in knee joint position sense and movement sense, or kinesthesia. We will discuss the possible physiological mechanisms behind these changes, including the role of joint and muscle receptors in proprioception and neuromuscular control of the knee, and the role of fatigue in changes in afferent output from muscle and joint receptors. We will then explore the implications that alteration in proprioception may have for dynamic stabilization of the knee joint.

Anterior cruciate ligament reconstruction affects proprioception in the cat's knee

To study the cat's knee after anterior cruciate ligament reconstruction, we compared its neural and muscular activity with that in the normal and the unstable knee. We recorded the electric activity in the articular nerves (posterior -PAN and medial -MAN) and periarticular muscles (quadriceps and hamstring) while performing passive flexion, extension, external and internal rotation, and also anterior translation of the tibia at 30 degrees and 90 degrees of flexion. The same series of maneuvers was performed in the same knees after surgical section of the anterior cruciate ligament and then after anterior cruciate reconstruction. The electric activity recorded in the reconstructed knee was compared to that in the same knee before surgery and in the same unstable knee after anterior cruciate section. We observed that the reconstructed knee, compared to the injured knee, showed a decrease in articular nerves and quadriceps activity while it regained stability. This decrease converged to the recordings in the normal knee. However, differences in MAN, PAN and hamstring activity were still present in the reconstructed knee. This suggests that, although anterior cruciate reconstruction seems beneficial for restoring articular nerve and periarticular muscle activities to a certain degree, proprioception in the reconstructed knee does not match that in the normal knee.

Refixation of femoral anterior cruciate ligament tears combined with a semitendinosus tendon augmentation. Technique and results

As part of a retrospective study, 76 patients with acute tears of the anterior cruciate ligament who underwent reinsertion and augmentation with the semitendinosus tendon were examined. The follow-up took place on average 4.5 years (range 3-7 years) after surgery. A decreased range of motion upon comparison with the uninjured opposite side was seen in 43 patients. The Lachman test revealed a grade 1 instability in 42 patients, grade 2 in 17 and grade 3 in 2, while 15 patients had a negative test result. The average Lysholm score was 92 points and the Tegner activity score had an average of 7.1 points. KT-1000 measurements showed an identical degree of anterior translation for both knees at 89 N in 25 individuals. The analysis revealed a difference of 2 mm in 15 patients, 4 mm in 19,6 mm in 15 and greater than 6 mm in 2. The radiographic follow-up examination revealed a deterioration of the degenerative change of 1 deg in 17 patients and 2 deg in 4 patients. Isometric testing showed no loss in flexion strength of the operated knee joints compared to the healthy opposite side. The ratio between flexion and extension strength was also identical for both knees. The reinsertion and augmentation with a single strand of semi-tendinosus tendon is not, as this study demonstrates, the appropriate reconstructive technique for the majority of ACL tears.

Encapsulated Ruffini-like endings in human lumbar facet joints

The innervation of the human lumbar facet joint capsule was studied by light and electron microscopy. Small numbers of encapsulated corpuscular endings were identified in the dense fibrous layer. Clusters of 2 types of endings were found: small cylindrical corpuscles (type 1) and large fusiform corpuscles (type 2). The corpuscles were classified structurally as Ruffini-type endings. The 1st type was predominant and characterised by a compartmentalised receptor complex, a thin perineurial capsule and a narrow subcapsular space. The 2nd type was characterised by a thicker perineurial capsule, a 'spindle-like' receptive complex, and an extensive subcapsular space with capillaries and concentrically oriented fibroblast-like cells. Both types of endings were innervated mainly by thinly myelinated group III (A delta) and unmyelinated group IV (C) nerve fibres that branched and terminated in the receptor complex. Their sensory endings were intimately related to the collagen fibre bundles as multiple enlarged axonal segments ('beads') with ultrastructural features which were characteristic of receptive sites: an accumulation of mitochondria and vesicles, and 'bare' areas of axolemma lacking a Schwann cell investment but covered by a thin basal lamina. Some beads in the 2nd type of ending contained granular vesicles, 30-60 mm in diameter, resembling sympathetic nerve endings. Small diameter collagen fibrils situated within multilayered basal laminae were found among the multiple receptive sites in the receptive complex in both types of ending. Their possible functional significance in mechanoreception is discussed. Particular attention has been given to their apparent variable orientation to the mechanoreceptive site.

Neural and muscular electric activity in the cat's knee. Changes when the anterior cruciate ligament is transected

We studied the response of the normal and unstable knee to passive motion and anterior tibial displacement in the cat. 6 cats were anesthetized and the deep level of anesthesia was controlled by electroencephalograms. We recorded electric activity in the articular nerves (posterior PAN and medial MAN) and periarticular muscles (quadriceps and hamstring), while performing passive flexion, extension, internal and external rotation. We then produced anterior displacement of the tibia at 30 degrees and 90 degrees of flexion, as in the Lachman and the anterior drawer maneuvers. The anterior cruciate ligament was surgically sectioned and the same series of passive displacements was performed. We observed statistically significant increased activity in the MAN, the PAN and the quadriceps muscle during knee flexion, in the MAN during extension, and in the PAN and hamstring during external rotation with the knee 90 degrees flexed. Anterior cruciate transection caused anterior displacement of the tibia during stress. This produced a significant increase in the MAN activity and a significant decrease in the hamstring electric activity at 30 degrees and 90 degrees of flexion, as in Lachman and anterior drawer maneuvers. We conclude that electric activity in the articular nerves and periarticular muscles, in response to passive motion and anterior tibial displacement, is altered in the cat's knee after anterior cruciate transection. This suggests that various patterns of periarticular muscle reaction in the anterior cruciate-deficient knee may be related to the unconscious perception of abnormal motion.

Sensory innervation of the cat knee articular capsule and cruciate ligament visualised using anterogradely transported wheat germ agglutinin-horseradish peroxidase

Wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was injected into the dorsal root ganglia (L5-S1) of the cat and used as an anterograde tracer substance for intra-axonal labelling of peripheral nerve endings in joint capsule and cranial (anterior) cruciate ligament (CCL). We believed that the high specificity of WGA-HRP for neural tissue along with the high visibility of its reaction product could help resolve controversies concerning the sensory innervation of the cruciate ligaments. Substantial amounts of WGA-HRP were transported in tibial nerve axons to the level of the knee. However, using standard HRP histochemistry we found that the capsular tissue and ligament synovia disintegrated during the incubation reaction. This problem was avoided by air drying the tissue slices on glass slides prior to reaction. Abundant labelling occurred in the posterior capsule with dense filling of axons and terminal endings. Sensory endings displayed features consistent with Ruffini endings and pacinian corpuscles. Sensory endings were located throughout the CCL in its sagittal plane, in the subsynovial layers and between collagen fascicles. In each CCL we observed 5-17 ovoid and elongated endings with dense terminal arborisations. These endings were between 100 and 150 microns long, were encapsulated, and gave rise to 1 or 2 axons. Large (up to 1.5 mm in maximum extent) elongated regions of dense, inhomogeneous labelling were found in the body of several CCLs. These resembled Golgi tendon-like endings, with the exception of their large size. We conclude that anterograde transport of HRP to the knee is a useful technique for labelling mechanoreceptors and axons in knee tissue. However, recently developed immunohistochemical analysis of peripheral tissue using protein gene product 9.5 appears to be the method of choice and should be employed for further study of human and animal cruciate ligament innervation.

Segmental sensory innervation of the anterior cruciate ligament and the patellar tendon of the cat's knee

We performed a study in cats to describe and quantify the segmental sensory innervation of the anterior cruciate ligament of the knee. We also studied the patellar tendon to show that transport occurs from an extraarticular, dense connective tissue structure and to obtain comparable quantitative information. We injected a tracer (horseradish peroxidase HRP, coupled to wheat germ agglutinin WGA) in the anterior cruciate ligament and observed the reaction product in the articular nerves of the injected knee and in the cell bodies of ipsilateral dorsal root ganglia. In these experiments, we found an average of 26 (13-52) labeled neurons, mostly large, after injecting the anterior cruciate. More than half of the labeled neurons were found in the dorsal root ganglion of L7 (last lumbar segment in the cat). We counted an average of 204 (17-426) labeled neurons, mostly small, after injecting the patellar tendon. More than half of these labeled neurons were found in the L5 spinal ganglion. No product was observed in contralateral spinal ganglia. Surgical ablation of the medial and lateral articular nerves (MAN and LAN) before injecting HRP-WGA in the anterior cruciate ligament, showed that the remaining afferents in the posterior articular nerve (PAN) projected mainly to L7. After excision of PAN, the projection was maintained through MAN and LAN, mostly to L5. Our quantitative data show that the anterior cruciate ligament is poorly innervated, if compared to the patellar tendon. The anterior cruciate segmental sensory innervation is directed to L7 (corresponding to the main ventral root forming the sciatic nerve in the cat), but also to L5 and L6 (main femoral nerve ventral roots). These segmental data indicate that anterior cruciate innervation influences muscle tone regulation, not only of the hamstrings (neuromuscular system of the sciatic nerve), but also of the quadriceps muscle (neuromuscular system of the femoral nerve).

Proprioceptive mechanisms in the cruciate ligaments: an electromyographic study on reflex activity in the thigh muscles

The hypothesis of a proprioceptive mechanism arising from mechanoreceptors in the cruciate ligaments and with efferences to the thigh muscles is investigated in an animal model. Electromyographic (EMG) studies of the quadriceps and hamstrings muscles were performed in six sheep anesthetized by intravenous injection of chloralose on applying static and dynamic shear forces to isolated fascicle bundles in the anterior (ACL) and posterior (PCL) cruciate ligaments at 200 to 500 N and 50 to 200 N/sec, respectively. With the help of an external fixator, the knee joint position was varied at 25 to 150 degrees. The relative preload of the anteromedial and posterolateral fascicles in the ACL and the anterior and posterior fascicles in the PCL induced by variation of the joint angle was measured with the help of strain gages. By static and dynamic loading of the anteromedial group of the ACL, EMG activity in the hamstrings increases significantly to 159 +/- 22 and 257 +/- 46 microV seconds, respectively (p < 0.001), with a simultaneous suppression of the quadriceps activity. Static and dynamic loading of the posterolateral ACL group results in a significant excitation of the quadriceps with mean potentials of 142 +/- 29 and 173 +/- 23 microV seconds, respectively (p < 0.001). Mechanical shear applied both to the anterior and posterior fascicles of the PCL induces a significant activation of the ipsilateral quadriceps muscles with a simultaneous inhibition of the hamstrings (p < 0.001). The quality of mechanical loading, i.e., static or dynamic shear, determines the degree of muscular recruitment significantly (p < 0.01). The joint angle contributes to a modulation in the quantitative EMG excitation. Linear regression analysis of the integrated EMG potential values and the amount of passive preload induced by the respective joint position results in a close correlation (r = + 0.78 to + 0.86). The results lead to the conclusion that a proprioceptive mechanism exists that arises from the cruciate ligaments and influences the tone in the thigh muscles. The degree of muscle excitation on mechanical ligament loading is modulated by the amount of preload in the ACL and PCL and the quality of load applied.

Selective muscle activation following rapid varus/valgus perturbations at the knee

Knee muscles are generally divided into groups based on their function as flexors or extensors. In this study we sought to determine if muscles were selectively activated according to their potential roles as varus or valgus stabilizers following rapid loads to the knee. While subjects were supine, varus or valgus moments were applied to the knees of 10 human subjects using a servomotor-driven perturbation device. During the experiments, electromyograms (EMG) were recorded from seven muscles, four of which had medial moment arms relative to the knee center, and three of which had lateral moment arms. It was observed that, for all medial muscles, a statistically significant increase in muscle activation followed valgus loads as compared with varus loads. All lateral muscles except the vastus lateralis showed the opposite response (as expected). These results suggest that muscles can be reflexively activated independent of their roles as flexors or extensors to provide stability to the human knee during varus or valgus loads. The timing of the reflex is consistent with that arising from joint mechanoreceptors, although polysynaptic stretch reflex may also be involved.

Knee joint proprioception: a comparison between female intercollegiate gymnasts and controls

The role of proprioception as a protective mechanism has gained interest in recent years. From the clinical standpoint, several studies have dealt with ways to enhance proprioception following surgery and during rehabilitation. If kinesthesia (ability to detect passive motion) can be enhanced as a consequence of long-term athletic training, such training must be included as a part of the rehabilitation process to protect the patient from reinjury. Consequently, the purpose of this study was to compare the kinesthetic knee pattern between trained gymnasts and healthy nongymnasts. The proprioception testing device (PTD) was used to evaluate knee kinesthesia. From 45 degrees of flexion, the knee was passively extended with the PTD. The device was stopped by the subject when this passive motion was detected. Fifteen healthy college-age female gymnasts (mean age 19.3 years) and 30 normal volunteers (mean age 20.7 years) comprised our study sample. A one-way analysis of variance (ANOVA) was used to compare the mean values of the dominant gymnastic knee to the dominant knee in the control group. Results revealed statistically significant mean differences between the trained gymnastic group and the untrained control group (F1.34(.95) = 7.17, P = 0.011). The results of this study suggest that extensive training has a positive influence on knee kinesthesia in addition to increasing muscle tone. According to the findings of this and other studies, highly trained athletes possess enhanced neurosensory pathways which are speculated to develop as a result of long-term athletic training. Although definite conclusions cannot be made from our investigation, prospective studies can determine the true role of athletic training in proprioceptive patterns.

Selective muscle activation following electrical stimulation of the collateral ligaments of the human knee joint

The objective of this study was to establish the presence of a local neurosensory reflex are from mechanoreceptors in human collateral ligaments and joint capsule to knee muscles and to determine if these muscles could be selectively activated as varus or valgus stabilizers using randomized trials. All studies were performed in the research department laboratories. Eleven subjects were recruited from the university staff and students based on no prior history of knee ailments. Subjects laid supine on an experimentation table as a current-modulated electrical stimulation was provided through the medial (MCL) or lateral collateral (LCL) knee ligaments. Latency of activation was measured for seven muscles, four by surface electrodes (semitendinosus, biceps femoris long head, vastus medialis, and lateralis), and three by intramuscular electrodes (sartorius, gracilis, tensor fascia lata). In the protocol, selective activation was defined as the relative increase in the activity of four muscles with medial moment arms following MCL stimulation compared with corresponding activity following LCL stimulation. For lateral muscles, the opposite was assumed (ie, that more activity would follow LCL than MCL stimulation). Monte Carlo simulations were performed on the data to determine significant selective muscle activation (p < .05). Statistically significant increases in activation were observed, most consistently, in the vastus medialis following MCL stimulation and in the vastus lateralis following LCL stimulation. These results suggest that a neurosensory reflex are from ligament mechanoreceptors may provide varus and valgus stabilization and knee muscles may be selectively activated to counter varus or valgus loads.

Histomorphometric analysis of innervation of the anterior cruciate ligament in osteoarthritis

The aim of this study was to determine whether there are quantitative changes in the innervation of the anterior cruciate ligament in osteoarthritis. Eleven whole anterior cruciate ligaments were obtained at autopsy from cadavera of individuals with advanced osteoarthritis: five healthy ligaments were used as controls. The ligaments were transected and stained with hematoxylin and eosin, oil red O for fat, and a modification of Gairn's gold chloride method. The latter stain permits visualization of axons, mechanoreceptors, and free nerve endings that are not apparent on routine stains. The ratio of nerve tissue to periligamentous synovial tissue was determined histomorphometrically by the point-counting method. The nerve tissue was located almost exclusively in the periligamentous synovial tissue. There was a statistically significantly greater area of nerve tissue (as a percentage of the total area) around the anterior cruciate ligaments in the osteoarthritic group than around the ligaments in the control group (p < 0.02). The nerve tissue was distributed evenly throughout the periligamentous synovial tissue in the specimens in both groups. A neurological role has been proposed for the anterior cruciate ligament in osteoarthritis. This study provides morphological evidence for neural pathology of the anterior cruciate ligament in subjects with osteoarthritis.

Reflex hamstring contraction latency in anterior cruciate ligament deficiency

Decreased dynamic stability of the knee joint associated with functional disability is a feature of anterior cruciate ligament deficiency (ACLD). The purposes of this study were to examine the between-limbs difference in reflex contraction latency of the hamstring muscles in patients with unilateral ACLD and to investigate its relationship with instability and function. Fifty patients with arthroscopically diagnosed unilateral ACLD were measured bilaterally for reflex hamstring contraction latency (RHCL), and 20 normal volunteers were similarly tested. The subjects were measured in a position of single-limb full weight-bearing with the knee flexed 30 degrees. An anteriorly directed shear force was applied to the tibia, and surface electromyographs (EMGs) recorded the activity of the hamstrings in response to the applied force. The latency of contraction was defined as the time from initial tibial movement, identified by accelerometry, to the onset of increased hamstring EMG activity. Both legs were tested and a between-limbs difference was computed. A significant difference in RHCL was found between the limb with ACLD and the control limb. The mean RHCL of the limb with ACLD was nearly double that of the unaffected limb, for a significant mean between-limbs difference (p < 0.05). The mean between-limbs difference for the control subjects was not statistically significant. The conclusion is that patients with ACLD have an increased RHCL of the injured leg. As the RHCL is dependent on proprioceptive activity around the joint, it can be used as a measure of proprioceptive ability. The loss of the neurophysiological protective reflex involving the anterior cruciate ligament and hamstrings in patients with ACLD is likely to be a contributory factor in the decreased joint stability experienced by these patients.

Nerve supply of anterior cruciate ligaments and of cryopreserved anterior cruciate ligament allografts: a new method for the differentiation of the nervous tissues

We investigated the nerve supply of anterior cruciate ligaments ((ACLs) and of cryopreserved bone-ACL-bone allografts in a rabbit model with immunohistochemical methods to establish the distribution pattern of the nervous tissues and to determine the reinnervation rate of ACL allografts. The ACL is innervated by three different classes of nerve fibre: (1) fibres of large diameter, characterized by neurofilament immunoreactivity, which are fast-conducting mechanoreceptive sensory afferents; (2) fibres of small diameter, characterized by substance P-immunoreactivity, which are slow-conducting nociceptive sensory afferents; and (3) sympathetic efferent vasomotor fibres, characterized by their immunoreactivity to the rate-limiting enzyme of noradrenaline synthesis, tyrosine hydroxylase. The ACLs showed numerous fibres of all three nerve classes; as specialised sensory nerve endings only Ruffini corpuscles were observed. All nerve fibres were located subsynovially, none within the collagen core of the ligament itself. No nerve fibres were detected in the ACL allografts at 3 and 6 weeks. Sparse fibres were detected at 12 weeks, while the 24-, 36- and 52-week specimens showed plenty of all three fibre types. No mechanoreceptors were found in the ACL allografts. To our knowledge, this method for the first time allows a differentiation of the nerve fibres of ACLs and ACL allografts into three different nerve fibre classes with known neurophysiological functions.

Mechanoreceptors in human myotendinous junction

The sensory-nerve-ending system of 40 myotendinous junctions of human palmaris longus and plantaris muscles was studied histologically. All the known four types of nerve endings were identified. The Ruffini corpuscles could be found in equally small numbers (one to five) in both the muscular and tendineal sites of the junction. Also the free nerve endings were distributed equally on both sites. The Pacini corpuscles were frequent in the tendineal site (six to 14), but rare in the muscular site (one to three). The Golgi tendon organs were, in turn, frequent in the muscular site (nine to 12) but rare in the tendineal site (one to four), respectively. Within the muscle and tendon parts of the junction, the distance between two mechanoreceptors was always more than 250 microns and the receptor distribution was homogeneous. Further studies are needed to give functional explanation for these anatomic findings.

Calcitonin gene-related peptide, substance P and GAP-43/B-50 immunoreactivity in the normal and arthrotic knee joint of the mouse

The aim of this study was to describe the normal distribution of calcitonin gene-related peptide (CGRP) and substance P (SP) containing fibres in the knee joint of the mouse and to obtain insight into the changes in innervation associated with degenerative processes in the joint. Arthrosis was induced by a single subpatellar intra-articular injection of bacterial collagenase. After decalcification in EDTA solutions, the CGRP and SP fibres were visualized by peroxidase-antiperoxidase pre-embedding immunocytochemistry for light microscopy. Control experiments on the mouse brain as a reference for the effect of EDTA on the immunostaining showed that the decalcification procedure with EDTA had not impaired the immunostaining. A rich innervation of thin varicose CGRP and SP immunoreactive fibres was found in most peri- and intra-articular tissue components. The periosteum, synovial tissues, the joint capsule and the intra-articular fat tissues were richly innervated. Less intense innervations were also found in the subchondral bone plates of the tibio-femoral joint and of the patella. Fibres were also found in the soft tissues between the patellar tendon and the femoral groove. No differences could be found between the location of CGRP and SP fibres with respect to the localization in the joint, but generally more CGRP fibres were found. The collagenase-induced osteoarthrosis was characterized by sclerosis of the subchondral bone, patellar dislocation, osteophyte formation, synovial proliferation and by severe cartilage abrasion, particularly on the medial side of the femoro-tibial joint. The overall distribution of CGRP and SP fibres was the same as in the control joints. However, major differences were found in all studied joints at specific locations around the cruciate ligaments, in the synovium around the patella, in the soft tissues lateral of the patella and in plica tissue between the patella and femoral groove. The CGRP and SP innervation was no longer detectable by immunolabelling with the antibodies. With a polyclonal antibody to the growth associated protein GAP-43/B-50, signs of degenerated axonal profiles were observed in these locations. At other peripheral locations, such as the muscles, the GAP-43/B-50 distribution was normal. In conclusion, the present study provides detailed information on the localization of CGRP and SP fibres, which may be involved in pain perception. Knowledge of the changes that occur during arthrosis may give more insight into the clinical symptoms.

[Combined injury of the anterior cruciate ligament and the medial collateral ligament of the knee joint--results of two to six years follow-up of surgical treatment]

A retrospective study of 148 combined acute knee injuries with anterior cruciate and medial collateral ligament injuries was performed. Follow-up included 115 patients, 95 of whom were personally examined two to six years postoperatively. Proximal anterior cruciate ligament ruptures were treated with reinsertion in 96 patients, in case of intraligamentous lesions (44 times), augmentation with the semitendinosus tendon was performed. Medial collateral ligament lesions were explored during the operation. Reconstruction of intraligamentous ruptures was performed with sutures (120 times). Distal lesions were refixed with Burri plate or staple. A modified Ellison procedure was routinely performed. Postoperative treatment was cast-free and included immediate physiotherapy using a functional brace. Between the two groups with anterior cruciate ligament reinsertion and augmentation, no significant differences were observed in subjective evaluation (Lysholm score 85 vs. 88), activity level (Tegner score 5.5 vs. 5.4) or anterior stability (KT 1000 at 89 N 6.6 vs. 6.1 mm displacement). A clear pivot shift sign was noted in two knees with reinsertion and in none of the augmented group. Medial stability was reestablished almost completely, independent of the site of lesion or the reconstruction technique (average valgus movement at 30 degrees flexion 0.7+ vs. 0.5+ on injured/contralateral side). We conclude that reinsertion of femoral anterior cruciate ligament ruptures will reestablish anterior stability in most cases, although semitendinosus augmentation appears to give slightly more reliable results. Medial stability is gained by the site-depending reconstruction techniques. Whether intraligamentous medial collateral ligament lesions can be left alone with only the anterior cruciate ligament being reconstructed, cannot be answered by this study.