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.

Quantitative assessment of neural elements in a rat model using nerve growth factor after remnant-preserving anterior cruciate ligament reconstruction: a histological and immunofluorescence pilot study.

BACKGROUND: Immunofluorescence analyses of anterior cruciate ligament (ACL) allografts following remnant-preserving ACL reconstruction using Achilles tendon allografts have provided evidence for the presence of neural elements. In this study, we aimed to examine the expression of neural elements and quantify the presence of neural cells in ACL remnants and Achilles allografts using nerve growth factor (NGF) therapy after remnant-preserving ACL reconstruction. METHODS: Experiments were conducted on 5 pairs of rats (approximately 8 weeks old and weighing 320 g at the time of surgery). Longitudinally, split Achilles tendons from the paired rats were freshly frozen and later defrosted with warm saline and allografted onto the right ACL of the other rat that was partially detached at the femoral attachment site. A sham operation was conducted on the left knee to be used as a control. NGF was injected into both knee joints every week for 6 weeks after surgery. The presence of neural cells in the ACL of the sham-operated knee, allografted Achilles tendon, and ACL remnant was examined 6 weeks post-surgery using H and E and immunofluorescent staining. RESULTS: H and E staining did not reveal neural cells in any of the three groups. However, immunofluorescence analysis showed the presence of nestin-positive neural elements in the normal ACL tissues as well as ACL remnants. Additionally, neural elements were examined in 7 of the 8 (87.5%) allograft tissues. Quantitative analysis showed no difference in the number or area of nuclei among the three groups. However, the number and area of neural cells in the Achilles allografts were significantly lower than those in the other two groups (p = 0.000 and p = 0.001, respectively). CONCLUSION: Our observations indicate that ACL remnants promote the new ingrowth and persistence of neural cells. We suggest that the ingrowth of neural elements can support the persistence and new ingrowth of mechanoreceptors, thereby enhancing the functional stability of knee joints. Moreover, the expression of neural cells in the Achilles allografts was lower than that in normal ACL tissues and ACL remnants in the quantitative evaluation, thereby confirming the essential role of ACL remnants in knee joint functionalization.

Immunohistochemical analysis of sensory corpuscles in human transplants of the anterior cruciate ligament.

BACKGROUND: Sensory nerve endings in ligaments play an important role for the proprioceptive function. Clinical trials show that the sense of body position does not fully recover in the knee joint after reconstructive surgery of the ruptured anterior cruciate ligament. The aim of this study is to identify sensory corpuscles in autogenous and allogenous transplants of the ligament and to compare their quantity between the used allografts and autografts. METHODS: Thirty-three patients were included in this study. Three patellar tendon allografts, 14 patellar tendon autografts and 12 semitendinosus autografts were harvested during revision surgery after traumatic rerupture of the graft. The control consisted of 4 healthy anterior cruciate ligaments after fresh rupture. After haematoxylin staining, immunohistochemical analysis was performed using antibodies against S100, p75 and PGP9.5. Microscopical examination was carried out, and the number of mechanoreceptors was counted. Statistical analysis was performed using the Mann-Whitney U test. RESULTS: Two types of mechanoreceptors were identified in each graft: Ruffini corpuscles and free nerve endings. The number of Ruffini corpuscles per square centimeter was the highest in the control. Comparing the grafts, the highest number of receptors could be detected in the semitendinosus autograft. The amount of free nerve endings was higher in the semitendinosus and patellar tendon autografts than in the control; the allografts showed the lowest number of receptors. With increasing time after reconstruction, the number of both types of receptors showed a decrease in the semitendinosus graft, whereas it increased in the patellar tendon graft and allograft. The number of mechanoreceptors in the semitendinosus and patellar tendon graft decreased over time after graft-failure, whereas it increased slightly in the allograft. CONCLUSION: This study was the first to identify mechanoreceptors in human transplants of the anterior cruciate ligament. The partial increase in the number of receptors over time after reconstruction could indicate a reinnervation of the grafts.

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.

Quantitative correlation of mechanoreceptors in tibial remnant of ruptured human anterior cruciate ligament with duration of injury and its significance: an immunohistochemistry-based observational study.

BACKGROUND: Proprioception is a specialized sensory modality encompassing the movement of the joint and its position in space. Reconstruction of the anterior cruciate ligament (ACL) does not always yield expected outcome, suggesting that successful reconstruction depends on not only the ultimate strength of the graft but also recovery of proprioception. Treatment delay is a significant concern in developing countries, e.g., in Asia. Thus, presence of mechanoreceptors is one of the factors having paramount importance for successful outcome. We conducted this study to identify mechanoreceptors via immunohistochemical staining and correlate their presence with duration of injury. MATERIALS AND METHODS: A total of 38 injured native ACL stumps were harvested from patients undergoing ACL reconstruction and stained with neurofilament protein stain to detect functional mechanoreceptors. RESULTS: Of the specimens, 44.7% stained positive for monoclonal antibody. No association was found between duration of injury and presence of mechanoreceptors (p = 0.897). No correlation was seen between age and side. CONCLUSIONS: No correlation was found between duration of injury and presence of viable mechanoreceptors, hence it is beneficial to preserve the native ACL stump irrespective of the time interval between injury and surgery. LEVEL OF EVIDENCE: III.

Cross-education does not accelerate the rehabilitation of neuromuscular functions after ACL reconstruction: a randomized controlled clinical trial.

PURPOSE: Cross-education reduces quadriceps weakness 8 weeks after anterior cruciate ligament (ACL) surgery, but the long-term effects are unknown. We investigated whether cross-education, as an adjuvant to the standard rehabilitation, would accelerate recovery of quadriceps strength and neuromuscular function up to 26 weeks post-surgery. METHODS: Group allocation was randomized. The experimental (n = 22) and control (n = 21) group received standard rehabilitation. In addition, the experimental group strength trained the quadriceps of the non-injured leg in weeks 1-12 post-surgery (i.e., cross-education). Primary and secondary outcomes were measured in both legs 29 ± 23 days prior to surgery and at 5, 12, and 26 weeks post-surgery. RESULTS: The primary outcome showed time and cross-education effects. Maximal quadriceps strength in the reconstructed leg decreased 35% and 12% at, respectively, 5 and 12 weeks post-surgery and improved 11% at 26 weeks post-surgery, where strength of the non-injured leg showed a gradual increase post-surgery up to 14% (all p ≤ 0.015). Limb symmetry deteriorated 9-10% more for the experimental than control group at 5 and 12 weeks post-surgery (both p ≤ 0.030). One of 34 secondary outcomes revealed a cross-education effect: Voluntary quadriceps activation of the reconstructed leg was 6% reduced for the experimental vs. control group at 12 weeks post-surgery (p = 0.023). Both legs improved force control (22-34%) and dynamic balance (6-7%) at 26 weeks post-surgery (all p ≤ 0.043). Knee joint proprioception and static balance remained unchanged. CONCLUSION: Standard rehabilitation improved maximal quadriceps strength, force control, and dynamic balance in both legs relative to pre-surgery but adding cross-education did not accelerate recovery following ACL reconstruction.

The role of anterior cruciate ligament in the control of posture; possible neural contribution.

The anterior cruciate ligament (ACL) is not only a mechanical structure for knee joint stability but is also a source of sensory information which could be used in the control of standing posture. It has been shown that the center of pressure (COP) time series during normal standing may be decomposed into two components which are hypothetically governed by different neural mechanisms, namely rambling and trembling. The aim of the present study was to investigate to what extent an injury to the ACL structure would affect these two control mechanisms. In this study the balance of a group of ACL deficient (ACLD) patients during double and single leg standing was examined and compared with that of a group of healthy individuals. We not only calculated the traditional measures of COP, but also decomposed this complex signal to investigate if ACL deficiency would affect the rambling and trembling components differently. The results showed that rambling was not significantly different between the two groups; however the trembling component was significantly greater for the ACLD group in both the single leg and the double leg condition. Further, there was also a component (rambling/trembling) by direction (anterior-posterior/mediolateral) interaction for both groups, indicating that the rambling component exhibited differences between directions of sway whereas the trembling component did not. This study provided evidence that the two components of postural control are differently affected by ACL deficiency, and that the rambling component is influenced by direction of sway.

Permanent knee sensorimotor system changes following ACL injury and surgery.

The cruciate ligaments are components of the knee capsuloligamentous system providing vital neurosensory and biomechanical function. Since most historical primary ACL repair attempts were unsuccessful, reconstruction has become the preferred surgery. However, an increased understanding of the efficacy of lesion-site scaffolding, innovative suturing methods and materials, and evolving use of biological healing mediators such as platelet-rich plasma and stem cells has prompted reconsideration of what was once believed to be impossible. A growing number of in vivo animal studies and prospective clinical studies are providing increasing support for this intervention. The significance of ACL repair rather than reconstruction is that it more likely preserves the native neurosensory system, entheses, and ACL footprints. Tissue preservation combined with restored biomechanical function increases the likelihood for premorbid neuromuscular control system and dynamic knee stability recovery. This recovery should increase the potential for more patients to safely return to sports at their desired intensity and frequency. This current concepts paper revisits cruciate ligament neurosensory and neurovascular anatomy from the perspective of knee capsuloligamentous system function. Peripheral and central nerve pathways and central cortical representation mapping are also discussed. Surgical restoration of a more physiologically sound knee joint may be essential to solving the osteoarthritis dilemma. Innovative rehabilitative strategies and outcome measurement methodologies using more holistic and clinically relevant measurements that closely link biomechanical and neurosensory characteristics of physiological ACL function are discussed. Greater consideration of task-specific patient physical function and psychobehavioral links should better delineate the true efficacy of all ACL surgical and non-surgical interventions. Level of evidence IV.

Does Anterior Cruciate Ligament Innervation Matter for Joint Function and Development of Osteoarthritis?

Complications following anterior cruciate ligament (ACL) injury and reconstruction that include chronic dysfunction, second ACL injury, and posttraumatic osteoarthritis (OA) may be interrelated and stem from the inability to fully restore native ACL integrity and function. The loss of ACL sensory input following injury may significantly contribute to joint dysfunction. We developed a novel preclinical animal model to assess the contributions of ACL sensory afferents to knee joint function and health. We hypothesized that ACL sensory denervation would manifest in knee joint dysfunction and development of early OA. Purpose-bred, adult research dogs (n = 9 dogs, 18 knees) underwent arthroscopic surgery to create three treatment groups: (1) partial ACL tear, (2) ACL denervated, and (3) whole-joint denervated. A neurotoxin injected directly into the ACL or into the joint space was used to induce sensory denervation, and sham procedures were done on contralateral knees. After intervention, dogs participated in a regimented exercise program. Gait analysis and clinically relevant functional assessments were performed. At week 12, the animals were humanely euthanatized for arthroscopic, gross, and histologic assessments. ACL partial tear group demonstrated the greatest overall knee dysfunction. Clinical measures of function revealed a significant difference between the ACL partial tear and ACL denervated group (p < 0.05), but these differences were not observed between the ACL and whole-joint denervated groups (p > 0.05). A significant reduction in limb loading was experienced by the ACL partial tear group compared with controls (p < 0.05) but not between other groups. Arthroscopic evaluation found no evidence for overt articular cartilage damage, meniscal pathology, or osteophyte formation was noted in any group. No significant differences (p > 0.05) were observed in ACL pathology and OA severity scores between the ACL partial tear and the ACL denervated groups. The results of our study indicate that ACL sensory loss may contribute to joint dysfunction and subsequent OA changes. Further investigation and development of this model are important to improve clinical therapies and optimize patient outcomes following ACL injury.

Can Flexible Instruments Create Adequate Femoral Tunnel Lengths at 90° of Knee Flexion in Anterior Cruciate Ligament Reconstruction?

PURPOSE: This study aims to study femoral tunnel lengths drilled with a flexible reamer and the distance to important lateral structures obtained by flexing the knee at various angles and by drilling the guide pins arthroscopically to resemble clinical practice. The purpose of this cadaveric study was twofold: 1. to determine whether femoral tunnel lengths of greater than 20 mm can be created with a flexible reamer system at 90 ° of knee flexion and 2. to determine whether the lateral structures of the knee are safe with this technique. METHODS: Ten fresh cadaveric knees were utilized. The intra-osseous length can be measured with a specially de - signed flexible guide pin. Flexible pins were inserted with the knee at 70°, 90°, and 120° of flexion. The intra-osseous length was measured with the measuring device. Each speci - men was dissected around the lateral aspect of the knee to identify the critical structures, the common peroneal nerve, and the LCL. The distance from the guide pins to the com - mon peroneal nerve and femoral attachment of the LCL were measured with a standard flexible paper ruler to the nearest millimeter. RESULTS: There is a trend for progressively increasing mean intra-osseous length associated with increased flexion of the knee. The mean intra-osseous length for 70° flexion was 25.2 mm (20 mm to 32 mm), which was statistically significant when compared to mean intra-osseous lengths of 32.1 mm (22 mm to 45 mm) and 38.0 mm (34 mm to 45 mm) in the 90° and 120° flexion groups, respectively (p < 0.05). There were no significant differences among the groups with respect to distance to the LCL. There is a trend toward longer distances to the common peroneal nerve with increased flexion. There was a statistically significant dif - ference when comparing 120° versus 70° (p < 0.05). CONCLUSIONS: This study that shows that adequate femoral tunnel lengths can be safely created without knee hyperflex - ion using flexible instruments via an anteromedial portal.

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.

Altered movement patterns and muscular activity during single and double leg squats in individuals with anterior cruciate ligament injury.

BACKGROUND: Individuals with Anterior Cruciate Ligament (ACL) injury often show altered movement patterns, suggested to be partly due to impaired sensorimotor control. Here, we therefore aimed to assess muscular activity during movements often used in ACL-rehabilitation and to characterize associations between deviations in muscular activity and specific altered movement patterns, using and further exploring the previously developed Test for substitution Patterns (TSP). METHODS: Sixteen participants (10 women) with unilateral ACL rupture performed Single and Double Leg Squats (SLS; DLS). Altered movement patterns were scored according to TSP, and Surface Electromyography (SEMG) was recorded bilaterally in six hip, thigh and shank muscles. To quantify deviations in muscular activity, SEMG ratios were calculated between homonymous muscles on injured and non-injured sides, and between antagonistic muscles on the same side. Correlations between deviations of injured/non-injured side SEMG ratios and specific altered movement patterns were calculated. RESULTS: Injured/non-injured ratios were low at transition from knee flexion to extension in quadriceps in SLS, and in quadriceps and hamstrings in DLS. On injured side, the quadriceps/hamstrings ratio prior to the beginning of DLS and end of DLS and SLS, and tibialis/gastrocnemius ratio at end of DLS were lower than on non-injured side. Correlations were found between specific altered movement patterns and deviating muscular activity at transition from knee flexion to extension in SLS, indicating that the more deviating the muscular activity on injured side, the more pronounced the altered movement pattern. "Knee medial to supporting foot" correlated to lower injured/non-injured ratios in gluteus medius (rs = -0.73, p = 0.001), "lateral displacement of hip-pelvis-region" to lower injured/non-injured ratios in quadriceps (rs = -0.54, p = 0.03) and "displacement of trunk" to higher injured/non-injured ratios in gluteus medius (rs = 0.62, p = 0.01). CONCLUSIONS: Deviations in muscular activity between injured and non-injured sides and between antagonistic muscular activity within injured as compared to non-injured sides indicated specific alterations in sensorimotor control of the lower limb in individuals with ACL rupture. Also, correlations between deviating muscular activity and specific altered movement patterns were suggested as indications of altered sensorimotor control. We therefore advocate that quantitative assessments of altered movement patterns should be considered in ACL-rehabilitation.

Neuroplasticity following anterior cruciate ligament injury: a framework for visual-motor training approaches in rehabilitation.

SYNOPSIS: The neuroplastic effects of anterior cruciate ligament injury have recently become more evident, demonstrating underlying nervous system changes in addition to the expected mechanical alterations associated with injury. Interventions to mitigate these detrimental neuroplastic effects, along with the established biomechanical changes, need to be considered in the rehabilitation process and return-to-play progressions. This commentary establishes a link between dynamic movement mechanics, neurocognition, and visual processing regarding anterior cruciate ligament injury adaptations and injury risk. The proposed framework incorporates evidence from the disciplines of neuroscience, biomechanics, motor control, and psychology to support integrating neurocognitive and visual-motor approaches with traditional neuromuscular interventions during anterior cruciate ligament injury rehabilitation. Physical therapists, athletic trainers, strength coaches, and other health care and performance professionals can capitalize on this integration of sciences to utilize visual-training technologies and techniques to improve on already-established neuromuscular training methods. LEVEL OF EVIDENCE: Therapy, level 5.

Importance of anatomically locating the infrapatellar branch of the saphenous nerve in reconstructing the anterior cruciate ligament using flexor tendons / Importância da localização anatômica do ramo infrapatelar do nervo safeno na reconstrução do ligamento cruzado anterior com tendões flexores

Objective: To describe the path of the infrapatellar branch of the saphenous nerve (IBSN) using the medial joint line, anterior tibial tuberosity (ATT), tibial collateral ligament and a horizontal line parallel to the medial joint line that passes over the ATT, as reference points, in order to help surgeons to diminish the likelihood of injuring this nerve branch during reconstruction of the anterior cruciate ligament (ACL) using flexor tendons. Methods: Ten frozen knees that originated from amputations were examined. Through anatomical dissection performed with the specimens flexed, we sought to find the IBSN, from its most medial and proximal portion to its most lateral and distal portion. Following this, the anatomical specimens were photographed and, using the ImageJ software, we determined the distance from the IBSN to the medial joint line and to a lower horizontal line going through the ATT and parallel to the first line. We also measured the angle of the direction of the path of the nerve branch in relation to this lower line. Results: The mean angle of the path of the nerve branch in relation to the lower horizontal line was 17.50 ±6.17°. The mean distance from the IBSN to the medial joint line was 2.61 ± 0.59 cm and from the IBSN to the lower horizontal line, 1.44 ±0.51 cm. Conclusion: The IBSN was found in all the knees studied. In three knees, we found a second branch proximal to the first one. The direction of its path was always from proximal and medial to distal and lateral. The IBSN was always proximal and medial to the ATT and distal to the medial joint line. The medial angle between its direction and a horizontal line going through the ATT was 17.50 ± 6.17°...

Objetivo: Descrever o trajeto do ramo infrapatelar do nervo safeno (RIPNS) com o uso da linha articular medial, da tuberosidade anterior da tíbia (TAT), do ligamento colateral tibial e de uma linha horizontal, paralela à linha articular medial e que passa sobre a TAT, como pontos de referência, a fim de poder auxiliar os cirurgiões a diminuir a probabilidade de lesão desse ramo nervoso na reconstrução do ligamento cruzado anterior (LCA) com tendões flexores. Métodos: Foram examinados 10 joelhos congelados, originados de amputações. Na dissecação anatômica, feita com as peças flexionadas, procuramos encontrar o RIPNS, desde a sua porção mais medial e proximal até sua porção mais lateral e distal. Em seguida, as peças anatômicas foram fotografadas e, com o programa ImageJ, determinamos a distância do RIPNS até a linha articular medial e até uma linha horizontal inferior, que passa pela TAT e é paralela à primeira. Medimos, também, o ângulo da direção do trajeto do ramo nervoso em relação a essa linha horizontal inferior. Resultados: O ângulo médio do trajeto do ramo nervoso, em relação à linha horizontal inferior, foi de 17,50° ±6,17°. A distância média do RIPNS até a linha articular medial foi de 2,61 ± 0,59 cm e até a linha horizontal inferior, de 1,44 ± 0,51 cm. Conclusão: O RIPNS foi encontrado em todos os joelhos estudados; em três, encontramos um segundo ramo, proximal ao primeiro. A direção de seu trajeto foi sempre de proximal e medial para distal e lateral. O RIPNS esteve sempre proximal e medial à TAT e distal à linha articular medial. A angulação média de sua direção, em relação a uma linha horizontal que passa pela TAT, foi...

Histological assessment of mechanoreceptors in Achilles allografts after anterior cruciate ligament reconstruction.

BACKGROUND: There is a lack of histological studies investigating the presence of mechanoreceptors in anterior cruciate ligament (ACL) allografts. HYPOTHESIS: Mechanoreceptors would not grow in Achilles allografts after ACL reconstruction. STUDY DESIGN: Case series study; Level of evidence, 4. METHODS: Tissue samples were obtained from 11 patients who underwent ACL reconstruction using Achilles tendon allografts. They underwent biopsies during second-look arthroscopies. The mean period from ACL reconstruction to harvesting tissue was 26.63 months (range, 12-120 months). The control group consisted of 2 normal ACLs procured from 42- and 45-year-old men who underwent amputation above the knee due to trauma. RESULTS: Ruffini corpuscles and free nerve endings were shown to be present in the specimens of the control group by processing hematoxylin-eosin stains and immunohistochemical stains with monoclonal antibodies against S-100. In the Achilles allografts, mechanoreceptors were not observed. However, fibroblasts, collagen fibers, and vessels that were not present in fresh-frozen Achilles allografts before surgery were observed. CONCLUSION: The results demonstrate that Achilles tendon allografts appeared similar to normal ligaments except for the lack of histological evidence of mechanoreceptors. In other words, there are no newly ingrown mechanoreceptors in ACL allografts.

The effect of remnant preservation on patterns of gene expression in a rabbit model of anterior cruciate ligament reconstruction.

BACKGROUND: Anterior cruciate ligament (ACL) reconstruction with remnant preservation technique had been thought to be a more favorable milieu for graft reinnervation, revascularization, and ligamentization. However, the influence of preserving tibial residual fibers on mRNA expression during the graft remodeling process has never been investigated. MATERIALS AND METHODS: Healthy mature New Zealand white rabbits were randomly assigned to one of four groups: remnant dissected, remnant preserved, sham operated, and normal control. Ligament tissue was dissected at 2, 6, and 12 wk after surgery, and real-time PCR was performed using primers for VEGF, TGF-ß1, COLlAl, COL3A1, GAP-43, and NT-3. RESULTS: In the remnant preservation group, mRNA levels for matrix components COL l Al, COL3A1, growth factor TGF-ß1, and nerve-related genesGAP-43 all increased 6 wk after surgery, compared with the remnant dissection group (P < 0.05). An increased level of VEGF mRNA was also detected in the remnant preservation group 12 wk after operation (P < 0.05). An increased level of NT-3 mRNA was also observed in the remnant preservation group 2 and 12 wk after operation (P < 0.05). CONCLUSIONS: Our results suggest that there is a time dependent alteration of angiogenesis-promoting, repair-related, and nerve-related gene expression after ACL reconstruction during the process of graft remodeling. Furthermore, they demonstrate that remnant preservation in ACL reconstruction determines the different molecular profiles of these target genes, especially during the early stages of graft remodeling, which perhaps explains the potential role in promoting revascularization, reinnervation, and ligamentization.

Efficacy of immunohistological methods in detecting functionally viable mechanoreceptors in the remnant stumps of injured anterior cruciate ligaments and its clinical importance.

PURPOSE: Various histological and immunological methods have been used to detect the mechanoreceptors and nerve fibers on the intact ACLs as well as on the remnant stumps. However, some of these methods lack standardization, and the variable thickness of slices used often leads to misinterpretation. The study was based on the hypothesis that immunohistological methods are easier and more reliable means to demonstrate mechanoreceptors in the remnant ACL stumps as compared with the conventional methods. We also attempted to validate the methodology of immunohistology as a means of characterizing functional mechanoreceptors in the residual stump of an injured ACL. METHODS: The remnants of the ruptured ACL in 95 patients were harvested during arthroscopic ACL reconstruction and evaluated immunohistologically using hematoxylin and eosin (H&E), and monoclonal antibodies to S-100 and NFP. Multiple sections from each specimen were serially examined by two histologists. RESULTS: The positivity of monoclonal antibody against NFP showed a statistically significant relationship with the presence of morphologically normal mechanoreceptors, whereas the positivity of monoclonal antibody against S-100 showed a statistically significant relationship with the presence of free nerve ending in the residual stump of an injured ACL. CONCLUSIONS: Immunological methods are more reliable and easier to use as compared with the conventional methods of histological staining for identifying remnant stumps likely to be of some proprioceptive benefit after an ACL injury. Such an identification might help us preserve certain remnant stumps during ACL reconstruction which might in turn improve the postoperative functional outcomes.

Acute fatigue impairs neuromuscular activity of anterior cruciate ligament-agonist muscles in female team handball players.

In sports, like team handball, fatigue has been associated with an increased risk of anterior cruciate ligament (ACL) injury. While effects of fatigue on muscle function are commonly assessed during maximal isometric voluntary contraction (MVC), such measurements may not relate to the muscle function during match play. The purpose of this study was to investigate the effect of muscle fatigue induced by a simulated handball match on neuromuscular strategy during a functional sidecutting movement, associated with the incidence of ACL injury. Fourteen female team handball players were tested for neuromuscular activity [electromyography (EMG)] during a sidecutting maneuver on a force plate, pre and post a simulated handball match. MVC was obtained during maximal isometric quadriceps and hamstring contraction. The simulated handball match consisted of exercises mimicking handball match activity. Whereas the simulated handball match induced a decrease in MVC strength for both the quadriceps and hamstring muscles (P<0.05), a selective decrease in hamstring neuromuscular activity was seen during sidecutting (P<0.05). This study shows impaired ACL-agonist muscle (i.e. hamstring) activity during sidecutting in response to acute fatigue induced by handball match play. Thus, screening procedures should involve functional movements to reveal specific fatigue-induced deficits in ACL-agonist muscle activation during high-risk phases of match play.

Absence of sensory function in the reconstructed anterior cruciate ligament.

Cruciate ligaments provide sensory information that cause excitatory as well as inhibitory effects to the activity of the muscles around the knee. The aim of the study was to determine whether these muscular reflexes are reestablished after anterior cruciate ligament (ACL) re-construction. Wire electrodes were inserted during arthroscopy into the normal posterior cruciate ligament (PCL) and the reconstructed ACL in 11 patients who had a successful ACL re-construction 8 months to 12 years earlier. After the anesthesia had subsided, the PCL was stimulated electrically through the electrodes and the sensory threshold was determined. Stimulus amplitudes were increased to 1.5-2.0 times the sensory threshold, and inhibitory reflexes could be elicited from PCL in the quadriceps during active extension and in the hamstrings muscles during active flexion in all patients. Subsequently the ACL re-constructions were stimulated. The sensory threshold was 3.4 times higher in the ACL than in the PCL. Stimulus amplitudes were increased to 1.5-2.0 times the sensory threshold, and a typical inhibitory reflex could be elicited in 9 patients. The latency was the same as for the reflex from the PCL. The stimulus amplitudes necessary to elicit reflexes from the ACL re-constructions were 2, 9 times higher than amplitudes that elicited reflexes from the PCL. Sensation and afferent reflex activity required a much stronger stimulus in the ACL graft compared to normal PCL. We suggest that the reason for this is that the ACL grafts were not reinnervated, and that the reflexes were elicited by spread of stimulus current to the PCL.

Immunohistological evaluation of proprioceptive potential of the residual stump of injured anterior cruciate ligaments (ACL).

To evaluate proprioceptive potential in residual remnants, tissue harvested from ruptured ACLs in 63 consecutive patients was examined for evidence of residual proprioceptive fibres using H&E, and monoclonal antibodies to S-100 and NFP (neurofilament protein). Histological examination showed good subsynovial and intra-fascicular vascularity with free nerve endings in the majority. Morphologically normal mechanoreceptors (H&E) and proprioceptive fibres (positivity with monoclonal antibody for NFP) were found in 46% and 52.4% of stumps, respectively. A statistically significant correlation between injury duration and persistence of mechanoreceptors and proprioceptive fibres was noted. More fibres were seen where ACL remnant was adherent to PCL. Our study has shown that persistent residual proprioceptive fibres in injured ACLs (especially early cases with PCL adherence) are significant; not shaving ACL remnants may be of potential benefit during ACL reconstruction, as some re-innervation and recovery of proprioceptive potential may be possible, thus improving clinical outcomes.