Benedikt Friemert

The role and interaction of visual and auditory afferents in postural stability

BACKGROUND Maintaining balance requires the integration of vestibular, proprioceptive and visual information and the translation of this input into appropriate motor responses. Although the role of the visual system has been widely investigated, there are no studies addressing the influence of non-specific distracting auditory inputs on postural stability. OBJECTIVE To analyze the role of the visual and auditory systems in the maintenance of postural stability and to assess potential interaction between the two sensory systems. METHODS Twenty-three healthy subjects were examined by computerized dynamic posturography. Stability index scores were calculated under each of six conditions: three visual conditions (sway feedback, eyes open without feedback, eyes closed) were combined with two auditory conditions (exposure or no exposure to non-specific auditory input). Analysis of variance (ANOVA) was used to test for differences among groups in the six test conditions. RESULTS Postural stability was much poorer in the eyes-closed (overall stability index (OSI): 6.8+/-2.1 degrees) than in the eyes-open condition (OSI: 2.2+/-1.2 degrees). Balance control significantly improved with visual feedback (OSI: 1.2+/-0.5 degrees). Exposure to non-specific auditory input (music through headphones) did not have a significant influence (OSI: 6.4+/-2.3 degrees /2.0+/-0.9 degrees /1.1+/-0.5 degrees). CONCLUSIONS Postural stability depended not only on whether the subjects were tested with their eyes open or closed but also on the presence or absence of visual feedback. Non-specific auditory information did not influence postural control. Since postural stability is regulated by multiple senses such as the vestibular system and proprioception, auditory stimuli may play an increasing role if one of the systems involved is impaired.

Non-resorbing osteoclasts induce migration and osteogenic differentiation of mesenchymal stem cells†

Osteoclast activity has traditionally been regarded as restricted to bone resorption but there is some evidence that also non‐resorbing osteoclasts might influence osteoblast activity. The aim of the present study was to further investigate the hypothesis of an anabolic function of non‐resorbing osteoclasts by investigating their capability to recruit mesenchymal stem cells (MSC) and to provoke their differentiation toward the osteogenic lineage. Bone‐marrow‐derived human MSC were exposed to conditioned media (CM) derived from non‐resorbing osteoclast cultures, which were generated from human peripheral blood monocytes. Osteogenic marker genes (transcription factor Runx2, bone sialoprotein, alkaline phosphatase (AP), and osteopontin) were significantly increased. Osteogenic differentiation (OD) was also proved by von Kossa and AP staining occurred in the same range as in MSC cultures stimulated with osteogenic supplements. Chemotactic responses of MSC were measured with a modified Boyden chamber assay. CM from osteoclast cultures induced a strong migratory response in MSC, which was greatly reduced in the presence of an anti‐human platelet‐derived growth factor (PDGF) receptor β antibody. Correspondingly, significantly increased PDGF‐BB concentrations were measured in the CM using a PDGF‐BB immunoassay. CM derived from mononuclear cell cultures did not provoke MSC differentiation and had a significantly lower migratory effect on MSC suggesting that the effects were specifically mediated by osteoclasts. In conclusion, it can be suggested that human non‐resorbing osteoclasts induce migration and OD of MSC. While effects on MSC migration might be mainly due to PDGF‐BB, the factors inducing OD remain to be elucidated. J. Cell. Biochem. 109: 347–355, 2010.

Effect of partial meniscectomy at the medial posterior horn on tibiofemoral contact mechanics and meniscal hoop strains in human knees.

We examined the influence of partial meniscectomy of 10 mm width on 10 human cadaveric knee joints, as it is performed during the treatment of radial tears in the posterior horn of the medial meniscus, on maximum contact pressure, contact area (CA), and meniscal hoop strain in the lateral and medial knee compartments. In case of 0° and 30° flexion angle, 20% and 50% partial meniscectomy did not influence maximum contact pressure and area. Only in case of 60° knee flexion, 50% partial resection increased medial maximum contact pressure and decreased the medial CA statistically significant. However, 100% partial resection increased maximum contact pressure and decreased CA significantly in the meniscectomized medial knee compartment in all tested knee positions. No significant differences were noted for meniscal hoop strain. From a biomechanical point of view, our in vitro study suggests that the medial joint compartment is not in danger of accelerated cartilage degeneration up to a resection limit of 20% meniscal depth and 10 mm width. Contact mechanics are likely to be more sensitive to partial meniscectomy at higher flexion angles, which has to be further investigated.

Benefits of active motion for joint position sense

Anterior cruciate ligament (ACL) ruptures lead to a proprioceptive deficit and therefore joint position sense. This study examined whether active motion is better suited than passive motion to address this deficit. Sixty patients with ACL rupture were prospectively randomised into two groups [continuous active motion (CAM)/continuous passive motion (CPM)]. All patients had an ACL reconstruction. An angle reproduction test was used to assess the proprioceptive deficit. The relevant examinations were performed before surgery (pre-op evaluation) and after the seventh postoperative day. No preoperative difference was found between the two groups. After postoperative treatment, the deficit was reduced in both groups. Significantly better results were, however, obtained in the CAM group (CPM, 4.2±1.6°; CAM, 1.9±1.2°; P<0.001). During the first postoperative week, a CAM device produced a significantly greater reduction in the proprioceptive deficit and should be the first choice in immediately postoperative rehabilitation after ACL replacement.

Effects of mechanical strain on human mesenchymal stem cells and ligament fibroblasts in a textured poly( l- lactide) scaffold for ligament tissue engineering

The purpose of this study was to prove the effect of cyclic uniaxial intermittent strain on the mRNA expression of ligament-specific marker genes in human mesenchymal stem cells (MSC) and anterior cruciate ligament-derived fibroblasts (ACL-fibroblasts) seeded onto a novel textured poly(l-lactide) scaffold (PLA scaffold). Cell-seeded scaffolds were mechanically stimulated by cyclic uniaxial stretching. The expression of ligament matrix gene markers: collagen types I and III, fibronectin, tenascin C and decorin, as well as the proteolytic enzymes matrix metalloproteinase MMP-1 and MMP-2 and their tissue specific inhibitors TIMP-1 and TIMP-2 was investigated by analysing the mRNA expression using reverse transcriptase polymerase chain reaction and related to the static control. In ACL-fibroblasts seeded on PLA, mechanical load induced up-regulation of collagen types I and III, fibronectin and tenascin C. No effect of mechanical stimulation on the expression of ligament marker genes was found in undifferentiated MSC seeded on PLA. The results indicated that the new textured PLA scaffold could transfer the mechanical load to the ACL-fibroblasts and improved their ligament phenotype. This scaffold might be suitable as a cell-carrying component of ACL prostheses.

Effects of knee bracing on postural control after anterior cruciate ligament rupture

STUDY DESIGN Randomized clinical trial. OBJECTIVES To investigate the effects of functional knee braces on postural control in patients with anterior cruciate ligament (ACL) rupture. BACKGROUND ACL rupture leads to both mechanical knee instability and deficits in proprioception. Although elastic knee braces do not increase mechanical stability, patients report improved stability when wearing a brace. Elastic braces were found to reduce the loss of proprioception. It is, however, still unclear whether they also improve postural control, which involves the processing of proprioceptive input at a higher level. METHODS We studied 58 patients with isolated unilateral ACL rupture using computerized dynamic posturography and compared overall stability index (OSI) scores for injured and uninjured legs with and without a knee brace. In addition, patients were classified as copers and non-copers depending on knee function. RESULTS Within subjects, OSI scores were 3.0 ± 1.1° for uninjured legs when unbraced, 2.8±1.3° for uninjured legs when braced (p=0.17), 3.7 ± 1.5° for unbraced injured legs, and 2.9 ± 1.3° for braced injured legs (p<0.001). For the injured legs of copers and non-copers, OSI scores were 3.4° ± 1.2° for copers and 4.0° ± 1.6° for non-copers in the unbraced condition (p=0.11) and 2.7 ± 1.0° for copers and 3.1 ± 1.4° for non-copers in the braced condition (p=0.26). CONCLUSION Elastic knee braces increase postural stability by approximately 22% in patients with ACL rupture. There was no difference in postural stability between uninjured and injured legs in the braced condition. One possible explanation is that bracing improves both proprioception and postural control.

Evaluation of platelet-rich plasma and hydrostatic pressure regarding cell differentiation in nucleus pulposus tissue engineering

Generation of a biological nucleus pulposus (NP) replacement by tissue engineering appears to be a promising approach for the therapy of early stages of intervertebral disc degeneration. Thereby, autologous mesenchymal stem cells (MSCs) represent an attractive cell source compared to cells of the NP that are already altered in their phenotype due to degenerative processes. This study compares the influence of 3D pellet culture and alginate beads, as well as that of different media compositions, by the addition of human platelet‐rich plasma (PRP) or transforming growth factor (TGF‐β1) in interaction with hydrostatic pressure on chondrogenic differentiation of human MSCs compared to NP cells. We found that gene expression of the chondrogenic markers aggrecan, collagen type 2 and collagen type 1 and Sox9 was considerably lower in cells cultivated with PRP compared to TGF‐β1. Immunohistology confirmed this result at protein level in pellet culture. Additionally, the pellet culture system was found to be more suitable than alginate beads. A positive influence of hydrostatic pressure could only be shown for individual donors. In summary, in comparison to TGF‐β1, human PRP did not induce adequate chondrogenic differentiation for both culture systems and cell types used. The mixture of growth factors in PRP promoted proliferation rather than chondrogenic differentiation. Based on these results, an application of PRP in human NP tissue‐engineering approaches cannot be recommended. Copyright

Group I afferent pathway contributes to functional knee stability.

The hamstring reflex response has been suggested to play a substantial role in knee joint stabilization during anterior tibial translation. The present study was performed to determine which afferent pathways contribute to the hamstring reflex as well as the potential effects of specific afferent pathways on functional knee stability. Short- and medium-latency hamstring reflexes (SLR and MLR) were evoked by anterior tibial translation in 35 healthy subjects during standing with 30 degrees knee flexion. Nerve cooling, tizanidine, and ischemia were employed to differentiate afferent pathways. Two hours of thigh cooling (n = 10) resulted in a significant increase in MLR latency and, to a lesser extent, SLR latency. No significant changes were recorded in reflex sizes or maximum tibial translation. The ingestion of tizanidine (n = 10), a suppressor of group II afferents, strongly reduced the MLR size while SLR size or latency of both reflex responses was not significantly affected. Maximum tibial translation was unchanged [5.3 +/- 1.9 to 4.8 +/- 2 (SD) mm; P = 0.410]. Ischemia in the thigh (n = 15) led to a highly significant depression in SLR size (89 +/- 4%; P < 0.001) but only a slight and not significant decline of MLR size. In these subjects maximum tibial translation increased significantly (6.9 +/- 1.6 to 9.4 +/- 3.2 mm; P = 0.028). It is concluded that the hamstring SLR is mediated by Ia afferents, while group II afferents mainly contribute to the MLR. Suppression of SLR may increase maximum anterior tibial translation, thus indicating a possible functional role of Ia afferents in knee joint stabilization.

Functional ultrasonography in the diagnosis of acute anterior cruciate ligament injuries: A field study

Functional ultrasonography is a rapid and inexpensive method of diagnosing anterior cruciate ligament (ACL) injuries. In previous studies, we assessed the diagnostic accuracy of this innovative method by experienced sonographers. The objective of the present study was to investigate whether an examiner without specialist expertise in arthrosonography can achieve similar positive results and whether this technique is effective as a screening tool that can help reduce the number of undetected ACL injuries. After a short period of training, a single examiner prospectively measured anterior tibial translation by ultrasonography in the injured and healthy knees of 41 patients with acute knee trauma. An ACL rupture was presumed to be present if the side-to-side difference in tibial translation exceeded 1 mm (Delta D>1 mm). All patients who were enrolled in the study underwent arthroscopy or at least magnetic resonance imaging (MRI). Ultrasonography revealed the presence of an ACL lesion in 32 of 33 patients with arthroscopically confirmed ACL rupture (sensitivity: 97%, specificity: 87.5%). The mean side-to-side differences (Delta D) between injured (3.8 mm+/-1.5 mm) and uninjured ACLs (0.1 mm+/-0.7 mm) were statistically significant (p<0.05). Our study shows that an examiner without specialist knowledge in ultrasonography can accurately diagnose acute ACL injuries using functional ultrasonography. No additional mechanical tests (KT-1000/KT-2000) or MRI examinations are required. Functional ultrasonography is easy to learn and ensures a high level of diagnostic accuracy. It is well suited for applications in private practices and smaller hospitals with basic medical/surgical care.

The reliability of a method for measuring the anterior cruciate ligament-hamstring reflex: an objective assessment of functional knee instability

Anterior cruciate ligament (ACL) rupture leads to mechanical and functional knee instability. Functional instability is likely attributable to a sensorimotor deficit. In previous studies, a method has been introduced which allows this deficit to be objectively assessed using ACL-hamstring reflex measurements. There is evidence that subjectively stable and unstable patients with ACL rupture can be objectively distinguished by this method. This study on 34 men was conducted to investigate the reliability of this method on the basis of several factors (intra-individual reproducibility, side-to-side differences, inter-examiner reliability, audiovisual stimuli, fatigue, height, weight, physical fitness, and level of activity at work). The role of gender was assessed in 20 men and 20 women. None of the factors had a relevant influence on reflex responses. The tests were reproducible and reliable. The method described here can thus be used for further research and the clinical diagnosis of functional instability following ACL rupture.