Function and strain of the anterolateral ligament part II: reconstruction.

PURPOSE: Anterolateral rotatory instability (ALRI) may result from isolated ruptures of the anterior cruciate ligament (ACL) or combined lesions with the anterolateral ligament (ALL). Biomechanical studies have demonstrated that the ALL contributes to the overall rotational stability of the knee. The purpose of this study was to investigate the biomechanical function of anatomic ALL reconstruction (ALLrec) in the setting of a combined ACL and ALL injury and reconstruction. The hypothesis was that combined ACL reconstruction (ACLrec) and ALLrec (ACL/ALLrec) significantly reduces internal rotation and shows load sharing between both reconstructions compared with isolated ACLrec. METHODS: Eight fresh-frozen cadaveric knees were evaluated using a six degrees of freedom knee simulator. Continuous passive motion and external loads were tested. Kinematic differences between ACLrec and combined ACL/ALLrec were compared. Additionally, ACL graft tension and ALL graft strain were measured continuously throughout the testing protocol. RESULTS: Combined anatomic ACL/ALLrec significantly improved the internal rotatory stability compared with isolated ACLrec at 30°-90° under an internal rotation moment. During a static pivot-shift test, additional ALLrec showed no significant reduction of ap-translation. ALLrec resulted in an increase in ACL graft tension during continuous passive motion and with additional internal rotation moment. CONCLUSION: In the case of a combined ACL and ALL deficiency, concurrent ACLrec and ALLrec significantly improved the rotatory stability of the knee compared with solely reconstructing the ACL at flexion angles ≥ 30°. Nevertheless, additional ALLrec with fixation at 60° and with low tension could not restore extension-near rotatory stability. For that reason, ALLrec with fixation at 60° flexion cannot be recommended in clinical application.

Are Knotted or Knotless Techniques Better for Reconstruction of Full-Thickness Tears of the Superior Portion of the Subscapularis Tendon? A Study in Cadavers.

BACKGROUND: Knotted and knotless single-anchor reconstruction techniques are frequently performed to reconstruct full-thickness tears of the upper portion of subscapularis tendon. However, it is unclear whether one technique is superior to the other. QUESTIONS/PURPOSES: (1) When comparing knotless and knotted single-anchor reconstruction techniques in full-thickness tears of the upper subscapularis tendon, is there a difference in stiffness under cyclic load? (2) Are there differences in cyclic gapping between knotless and knotted reconstructions? (3) Are there differences in the maximal stiffness, yield load, and ultimate load to failure? (4) What are the modes of failure of knotless and knotted reconstruction techniques? METHODS: Eight matched pairs of human cadaveric shoulders were dissected, and a full-thickness tear of the subscapularis tendon (Grade 3 according to the Fox and Romeo classification) was created. The cadavers all were male specimens, with a median (range) age of 69 years (61 to 75). Before biomechanical evaluation, the specimens were randomized into two equal reconstruction groups: knotless single anchor and knotted single anchor. All surgical procedures were performed by a single orthopaedic surgeon who subspecializes in sports orthopedics and shoulder surgery. With a customized set up that was integrated in a dynamic material testing machine, the humeri were consecutively loaded from 10 N to 60 N, from 10 N to 100 N, and from 10 N to 180 N for 50 cycles. Furthermore, the gapping behavior of the tear was analyzed using a video tracking system. Finally, the stiffness, gapping, maximal stiffness, yield loads, and maximum failure loads of both reconstruction groups were statistically analyzed. Failure was defined as retearing of the reconstructed gap threshold due to rupture of the tendon and/or failure of the knots or anchors. After biomechanical testing, bone quality was measured at the footprint of the subscapularis using microCT in all specimens. Bone quality was equal between both groups. To detect a minimum 0.15-mm difference in gap formation between the two repair techniques (with a 5% level of significance; α = 0.05), eight matched pairs (n = 16 in total) were calculated as necessary to achieve a power of at least 90%. RESULTS: The first study question can be answered as follows: for stiffness under cyclic load, there were no differences with the numbers available between the knotted and knotless groups at load stages of 10 N to 60 N (32.7 ± 3.5 N/mm versus 34.2 ± 5.6 N/mm, mean difference 1.5 N/mm [95% CI -6.43 to 3.33]; p = 0.55), 10 N to 100 N (45.0 ± 4.8 N/mm versus 45.2 ± 6.0 N/mm, mean difference 0.2 N/mm [95% CI -5.74 to 6.04]; p = 0.95), and 10 N to 180 N (58.2 ± 10.6 N/mm versus 55.2 ± 4.7 N/mm, mean difference 3 N/mm [95% CI -5.84 to 11.79]; p = 0.48). In relation to the second research question, the following results emerged: For cyclic gapping, there were no differences between the knotted and knotless groups at any load levels. The present study was able to show the following with regard to the third research question: Between knotted and knotless repairs, there were no differences in maximal load stiffness (45.3 ± 8.6 N/mm versus 43.5 ± 10.2 N/mm, mean difference 1.8 [95% CI -11.78 to 8.23]; p = 0.71), yield load (425.1 ± 251.4 N versus 379.0 ± 169.4 N, mean difference 46.1 [95% CI -276.02 to 183.72]; p = 0.67), and failure load (521.1 ± 266.2 N versus 475.8 ± 183.3 N, mean difference 45.3 [95% CI -290.42 to 199.79]; p = 0.69). Regarding the fourth question concerning the failure modes, in the knotted repairs, the anchor tore from the bone in 2 of 8, the suture tore from the tendon in 6 of 8, and no suture slipped from the eyelet; in the knotless repairs, the anchor tore from the bone in 2 of 8, the suture tore from the tendon in 3 of 8, and the threads slipped from the eyelet in 3 of 8. CONCLUSION: With the numbers available, we found no differences between single-anchor knotless and knotted reconstruction techniques used to repair full-thickness tears of the upper portion of subscapularis tendon. CLINICAL RELEVANCE: The reconstruction techniques we analyzed showed no differences in terms of their primary stability and biomechanical properties at the time of initial repair and with the numbers available. In view of these experimental results, it would be useful to conduct a clinical study in the future to verify the translationality of the experimental data of the present study.

Influence of Menisci on Tibiofemoral Contact Mechanics in Human Knees: A Systematic Review.

Purpose: Menisci transfer axial loads, while increasing the load-bearing tibiofemoral contact area and decreasing tibiofemoral contact pressure (CP). Numerous clinical and experimental studies agree that an increased CP is one predominant indicator for post-traumatic osteoarthritis (PTOA) of the knee joint. However, due to the immense variability in experimental test setups and wide range of treatment possibilities in meniscus surgery, it is difficult to objectively assess their impact on the CP determination, which is clearly crucial for knee joint health. Therefore, the aim of this systematic review is to investigate the influence of different meniscal injuries and their associated surgical treatments on the CP. Secondly, the influence of different test setups on CP measurements is assessed. On the basis of these results, we established the basis for recommendations for future investigations with the aim to determine CPs under different meniscal states. Methods: This review was conducted in accordance with the PRISMA guidelines. Studies were identified through a systematic literature search in Cochrane, PubMed and Web of Science databases. Literature was searched through pre-defined keywords and medical subject headings. Results: This review indicates a significant increase of up to 235% in peak CP when comparing healthy joints and intact menisci with impaired knee joints, injured or resected menisci. In addition, different test setups were indicated to have major influences on CP: The variety of test setups ranged from standard material testing machines, including customized setups via horizontal and vertical knee joint simulators, through to robotic systems. Differences in applied axial knee joint loads ranged from 0 N up to 2,700 N and resulted unsurprisingly in significantly different peak CPs of between 0.1 and 12.06 MPa. Conclusion: It was shown that untreated traumatic meniscal tears result in an increased CP. Surgical repair intervention were able to restore the CP comparable to the healthy, native condition. Test setup differences and particularly axial joint loading variability also led to major CP differences. In conclusion, when focusing on CP measurements in the knee joint, transparent and traceable in vitro testing conditions are essential to allow researchers to make a direct comparison between future biomechanical investigations.

Neuromapping of the Capsuloligamentous Knee Joint Structures.

PURPOSE: To investigate neuromuscular electromyographic response of the of the upper and lower leg muscles after the application of an intraoperative, isolated mechanical stimulus of the capsuloligamentous structures, including the anterior (ACL) and posterior cruciate ligaments (PCL), lateral (LM) and medial menisci (MM), plica mediopatellaris (PM), and Hoffa's fat pat (HFP). METHODS: The electromyographic response of the upper and lower leg muscles (M. rectus femoris; M. vastus medialis; M. semitendinosus; M. biceps femoris; M. gastrocnemius lateralis) of 15 male patients were measured after an isolated mechanical stimulus of the capsuloligamentous structures during an arthroscopic intervention using a customized intraoperative setup. Target parameters were the short (SLR; <30 milliseconds) and medium latency responses (MLR; >30 milliseconds) after the mechanically-induced trigger. RESULTS: The ACL, PCL, LM, and MM displayed high interindividual reproducibility of >76%. The MM was the only structure indicating both an SLR and MLR for all muscles. Although signals could be detected, there was no reproducibility in electromyographic signal activation for the HFP. The most rapid MLR was observed for the PM (quadriceps: 37 milliseconds). CONCLUSIONS: Each stimulated structure displayed an individual MLR response, which allowed us to create neuromapping combining the anatomical and quantitative representations of the individual muscular activation patterns after isolated mechanical stimulation of the capsuloligamentous knee joint structures, corroborating our hypothesis. LEVEL OF EVIDENCE: Diagnostic - Level II.

Biomechanics of a cemented short stem: a comparative in vitro study regarding primary stability and maximum fracture load.

PURPOSE: In total hip arthroplasty, uncemented short stems have been used more and more frequently in recent years. Especially for short and curved femoral implants, bone-preserving and soft tissue-sparing properties are postulated. However, indication is limited to sufficient bone quality. At present, there are no curved short stems available which are based on cemented fixation. METHODS: In this in vitro study, primary stability and maximum fracture load of a newly developed cemented short-stem implant was evaluated in comparison to an already well-established cemented conventional straight stem using six pairs of human cadaver femurs with minor bone quality. Primary stability, including reversible micromotion and irreversible migration, was assessed in a dynamic material-testing machine. Furthermore, a subsequent load-to-failure test revealed the periprosthetic fracture characteristics. RESULTS: Reversible and irreversible micromotions showed no statistical difference between the two investigated stems. All short stems fractured under maximum load according to Vancouver type B3, whereas 4 out of 6 conventional stems suffered a periprosthetic fracture according to Vancouver type C. Mean fracture load of the short stems was 3062 N versus 3160 N for the conventional stems (p = 0.84). CONCLUSION: Primary stability of the cemented short stem was not negatively influenced compared to the cemented conventional stem and no significant difference in fracture load was observed. However, a clear difference in the fracture pattern has been identified.

Adding Flexible Instrumentation to a Curved Videolaryngoscope: A Novel Tool for Laryngeal Surgery.

OBJECTIVES: Transoral surgery of the larynx with rigid instruments is not always possible. This may result in insufficient therapy or in an increased need for open surgery. For these patients, alternative surgical systems are needed. Here, we demonstrate a curved prototype for laryngeal surgery equipped with flexible instruments. STUDY DESIGN: Pre-clinical user study in an ex vivo porcine laryngeal model. METHODS: The prototype was built from established medical devices, namely a hyperangulated videolaryngoscope and modified flexible instruments as well as three-dimensional printed parts. Feasibility of laryngeal manipulation was evaluated in a user study (n = 19) with a porcine ex vivo laryngeal model. Using three different visualization technologies, the participants performed various fine motor skills tasks and rated the usability of the system on a 5-point Likert scale. RESULTS: Exposure, accessibility, and manipulation of important laryngeal structures were always possible using the new prototype. The participants needed considerably less time (mean, 96.4 seconds ± 6.4 seconds vs. 111.5 seconds ± 4.5 seconds, P = .18), reported significantly better general impression (mean score 3.0 vs. 3.8, P = .041) and significantly lower user head and neck strain (2.6 vs. 1.7, P = .022) using a 40-inch television screen as compared to a standard videolaryngoscope monitor. CONCLUSION: The results indicate that our curved prototype and large monitor visualization may provide a cost-effective minimally invasive alternative for difficult laryngeal exposure. Its special advantages include avoiding the need for a straight line of sight and a simple and cost-effective construction. The system could be further improved through advances in camera chip technology and smaller instruments. Laryngoscope, 131:E561-E568, 2021.

Differences between human septal and alar cartilage with respect to biomechanical features and biochemical composition.

Cartilage grafts have become popular in facial plastic surgery to reconstruct defects or to improve aesthetic outcomes in various applications. But there is a considerable rate of graft failure like resorption or deformation. To improve graft survival and function, accurate understanding of the properties of the recipient site is indispensable. Therefore 10 noses of human cadavers were meticulously dissected and specimens of alar and septal cartilage subjected to confined compression and tensile tests. Furthermore, cell number, glycosaminoglycan and hydroxyproline content were measured. RESULTS: showed a significant difference (p < 0.05) of alar and septal cartilage regarding Equilibrium Modulus, cell number and glycosaminoglycan but not hydroxyproline content. Tensile tests showed a significant difference (p < 0.001) between alar and septal cartilage (vertical vector of force) for E-modulus, maximal force and maximal strain but not for horizontal vector of force. There was a significant difference (p < 0.05) within septal cartilage samples depending on vector of force (vertical vs. horizontal). Finally multifactorial linear regression allowed an estimation of Equilibrium Modulus depending on compression, glycosaminoglycan content and cell number with statistical significance (p < 0.05). In conclusion, nasal cartilage differs in function and composition depending on anatomical location and the prevalent forces. Therefore further research will be necessary to evaluate if graft failure depends on a mismatch of functional properties and if grafts can be adapted to the recipient site.

Newly Defined ATP-Binding Cassette Subfamily B Member 5 Positive Dermal Mesenchymal Stem Cells Promote Healing of Chronic Iron-Overload Wounds via Secretion of Interleukin-1 Receptor Antagonist.

In this study, we report the beneficial effects of a newly identified dermal cell subpopulation expressing the ATP-binding cassette subfamily B member 5 (ABCB5) for the therapy of nonhealing wounds. Local administration of dermal ABCB5+ -derived mesenchymal stem cells (MSCs) attenuated macrophage-dominated inflammation and thereby accelerated healing of full-thickness excisional wounds in the iron-overload mouse model mimicking the nonhealing state of human venous leg ulcers. The observed beneficial effects were due to interleukin-1 receptor antagonist (IL-1RA) secreted by ABCB5+ -derived MSCs, which dampened inflammation and shifted the prevalence of unrestrained proinflammatory M1 macrophages toward repair promoting anti-inflammatory M2 macrophages at the wound site. The beneficial anti-inflammatory effect of IL-1RA released from ABCB5+ -derived MSCs on human wound macrophages was conserved in humanized NOD-scid IL2rγ null mice. In conclusion, human dermal ABCB5+ cells represent a novel, easily accessible, and marker-enriched source of MSCs, which holds substantial promise to successfully treat chronic nonhealing wounds in humans. Stem Cells 2019;37:1057-1074.

Surface analysis of sheep menisci after meniscectomy via infrared attenuated total reflection spectroscopy.

Menisci are very important fibrocartilaginous tissue, which maintain biomechanical functions and physiological stabilization of knee joint. Meniscectomy is known as a surgery to recover partial functions from acute meniscus tears. However, the late consequences of total or partial meniscectomy include signs of osteoarthritis and even ligament instability. Infrared attenuated total reflection (IR-ATR) spectroscopy is a very useful technique, which can reveal molecular characteristics via the analysis of vibrational bands. The present study has employed IR-ATR spectroscopy to investigate sheep menisci samples after meniscectomy in a label-free fashion. Several differences of peak absorbance change and peak shift were observed between the native healthy samples and the meniscectomy samples in distinct IR wavenumber regions, such as amide I band, amide II band, C-H bending band as well as the sugar band region. Combining the results from the collagen protein IR spectra, it can be speculated that six months after meniscectomy collagen fibrils on the incision lose its ordered arrangement and a decrease in the triple helical structure of collagen fibril is observed. In addition, the collagen fibrils and proteoglycan content might also be slight varied after meniscectomy.

Release of the medial collateral ligament is mandatory in medial open-wedge high tibial osteotomy.

PURPOSE: The purpose of this study was to quantify the effect of clinically relevant open-wedge high tibial osteotomies on medial collateral ligament (MCL) strain and the resultant tibiofemoral contact mechanics during knee extension and 30° knee flexion. METHODS: Six human cadaveric knee joints were axially loaded (1 kN) in knee extension and 30° knee flexion. Strains at the anterior and posterior regions of the MCL were determined using strain gauges. Tibiofemoral contact mechanics (contact area, mean and maximum contact pressure) were investigated using pressure-sensitive sensors. Open-wedge osteotomy was performed using biplanar cuts and osteotomy angles of 5° and 10° were maintained using an external fixator. Tests were performed first with intact and then with dissected MCL. RESULTS: Nonparametric statistical analyses indicated a significant strain increase (p < 0.01) in the anterior and posterior fibres of the MCL with increasing osteotomy angle of up to 8.3% and 6.0%, respectively. Only after releasing the MCL the desired lateralisation of the mechanical axis was achieved, indicating a significant decrease in the maximum contact pressure in knee extension of - 25% (p = 0.028) and 30° knee flexion of - 21% (p = 0.027). CONCLUSIONS: The results of the present biomechanical study suggest, that an open-wedge high tibial osteotomy is most effective in reducing the medial contact pressure when spreading the osteotomy to 10° and concomitantly releasing the MCL. To transfer the results of this biomechanical study to the clinical day-to-day practice, it is necessary to factor in the individual ligamentous laxity of each patient into the treatment options e.g. particularly for patients with distinct knee ligament laxity or medial ligamentary instability, the release of the MCL should be performed with care. LEVEL OF EVIDENCE: Controlled laboratory study.

Biomechanical considerations are crucial for the success of tendon and meniscus allograft integration-a systematic review.

PURPOSE: This systematic review intends to give an overview of the current knowledge on how allografts used for the reconstruction of cruciate ligaments and menisci are integrated and specifically perform regarding their biomechanical function. METHODS: Two reviewers reviewed the PubMed and Central Cochrane library with focus on the biomechanical integration of tendon ligament and meniscus allografts. The literature search was conducted in accordance with the PRISMA statement for reporting systematic reviews and meta-analyses. RESULTS: The analysed literature on tendon allografts shows that they are more vulnerable to overstretching in the phase of degradation compared to autografts as the revascularization process starts later and takes longer. Therefore, to avoid excessive graft loads, allografts for cruciate ligament replacement should be selected that exhibit much higher failure loads than the native ligaments to counteract the detrimental effect of degradation. Further, placement techniques should be considered that result in a minimum of strain differences during knee joint motion, which is best achieved by near-isometric placement. The most important biomechanical parameters for meniscus allograft transplantation are secure fixation and proper graft sizing. Allograft attachment by bone plugs or by a bone block is superior to circumferential suturing and enables the allograft to restore the chondroprotective biomechanical function. Graft sizing is also of major relevance, because too small grafts are not able to compensate the knee joint incongruity and too large grafts may fail due to extrusion. Only adequate sizing and fixation together can lead to a biomechanically functioning allograft. The objective assessment of the biomechanical quality of allografts in a clinical setting is challenging, but would be highly desirable for monitoring the remodelling and incorporation process. CONCLUSIONS: Currently, indicators like ap-stability after ACL reconstruction or meniscal extrusion represent only indirect measures for biomechanical graft integration. These parameters are at best clinical indicators of allograft function, but the overall integration properties comprising e.g. fixation and graft stiffness remain unknown. Therefore, future research should e.g. focus on advanced imaging techniques or other non-invasive methods allowing for in vivo assessment of biomechanical allograft properties.

Do Prophylactic Knee Braces Protect the Knee Against Impacts or Tibial Moments? An In Vitro Multisensory Study.

BACKGROUND: Knee braces are prescribed by physicians to protect the knee from various loading conditions during sports or after surgery, even though the effect of bracing for various loading scenarios remains unclear. PURPOSE: To extensively investigate whether bracing protects the knee against impacts from the lateral, medial, anterior, or posterior directions at different heights as well as against tibial moments. STUDY DESIGN: Controlled laboratory study. METHODS: Eight limb specimens were exposed to (1) subcritical impacts from the medial, lateral, anterior, and posterior directions at 3 heights (center of the joint line and 100 mm inferior and superior) and (2) internal/external torques. Using a prophylactic brace, both scenarios were conducted under braced and unbraced conditions with moderate muscle loads and intact soft tissue. The change in anterior cruciate ligament (ACL) strain, joint acceleration in the tibial and femoral bones (for impacts only), and joint kinematics were recorded and analyzed. RESULTS: Bracing reduced joint acceleration for medial and lateral center impacts. The ACL strain change was decreased for medial superior impacts and increased for anterior inferior impacts. Impacts from the posterior direction had substantially less effect on the ACL strain change and joint acceleration than anterior impacts. Bracing had no effect on the ACL strain change or kinematics under internal or external moments. CONCLUSION: Our results indicate that the effect of bracing during impacts depends on the direction and height of the impact and is partly positive, negative, or neutral and that soft tissue absorbs impact energy. An effect during internal or external torque was not detected. CLINICAL RELEVANCE: Bracing in contact sports with many lateral or medial impacts might be beneficial, whereas athletes who play sports with rotational moments on the knee or anterior impacts may be safer without a brace.

Analysis of human menisci degeneration via infrared attenuated total reflection spectroscopy.

Degeneration of human meniscal tissue induces impairment of normal knee functions, and is a highly relevant etiology of knee joint tears and osteoarthritis. Currently, the grading scale of meniscus degeneration is conventionally derived from evaluating meniscal morphology and histological staining. However, mid-infrared attenuated total reflectance (IR-ATR) spectroscopy is a particularly useful technique that may analyze the biomolecular composition at a sample surface, and provide information on the intra- and/or inter-molecular chemical bonds. In the present study, 61 lyophilized human menisci samples at different grades of degeneration were analyzed via IR-ATR spectroscopy in a label-free fashion, and the data were evaluated via Gaussian peak fitting and 2D correlation analysis. During increasing meniscal degeneration (i.e., grade 1 to 4) along with calcification at grade 4, an evident blue shift of the amide I band (1700-1600 cm-1) was observed in the associated IR spectra. In addition, Gaussian peak fitting revealed significant area variance of the fitted sub-peaks. 2D correlation spectra provided further access to detailed changes of the amide I band during the degeneration process. Derived from this multi-tiered data analysis taking into account the protein secondary structure information within the amide I band, and the triple helical structure of meniscal collagen, the blue shift and peak area changes during meniscus degeneration are indicative of collagen fibril formation during evolving degeneration. Furthermore, a degradation of the water-binding proteoglycan and collagen network especially for degenerated menisci with calcification was observed. Results were compared with a collagen-chondroitin sulphate mixture model, confirming the observed changes in collagen fibrils and proteoglycans. In summary, this study confirms the utility of IR-ATR spectroscopy as a versatile tool providing access to meniscal tissue degeneration processes at molecular level detail, and may in future evolve into a useful diagnostic instrument for analyzing cartilage degeneration.

Diet-Induced Obesity Affects Muscle Regeneration After Murine Blunt Muscle Trauma-A Broad Spectrum Analysis.

Injury to skeletal muscle affects millions of people worldwide. The underlying regenerative process however, is a very complex mechanism, time-wise highly coordinated, and subdivided in an initial inflammatory, a regenerative and a remodeling phase. Muscle regeneration can be impaired by several factors, among them diet-induced obesity (DIO). In order to evaluate if obesity negatively affects healing processes after trauma, we utilized a blunt injury approach to damage the extensor iliotibialis anticus muscle on the left hind limb of obese and normal weight C57BL/6J without showing any significant differences in force input between normal weight and obese mice. Magnetic resonance imaging (MRI) of the injury and regeneration process revealed edema formation and hemorrhage exudate in muscle tissue of normal weight and obese mice. In addition, morphological analysis of physiological changes revealed tissue necrosis, immune cell infiltration, extracellular matrix (ECM) remodeling, and fibrosis formation in the damaged muscle tissue. Regeneration was delayed in muscles of obese mice, with a higher incidence of fibrosis formation due to hampered expression levels of genes involved in ECM organization. Furthermore, a detailed molecular fingerprint in different stages of muscle regeneration underlined a delay or even lack of a regenerative response to injury in obese mice. A time-lapse heatmap determined 81 differentially expressed genes (DEG) with at least three hits in our model at all-time points, suggesting key candidates with a high impact on muscle regeneration. Pathway analysis of the DEG revealed five pathways with a high confidence level: myeloid leukocyte migration, regulation of tumor necrosis factor production, CD4-positive, alpha-beta T cell differentiation, ECM organization, and toll-like receptor (TLR) signaling. Moreover, changes in complement-, Wnt-, and satellite cell-related genes were found to be impaired in obese animals after trauma. Furthermore, histological satellite cell evaluation showed lower satellite cell numbers in the obese model upon injury. Ankrd1, C3ar1, Ccl8, Mpeg1, and Myog expression levels were also verified by qPCR. In summary, increased fibrosis formation, the reduction of Pax7+ satellite cells as well as specific changes in gene expression and signaling pathways could explain the delay of tissue regeneration in obese mice post trauma.

Correction to: In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model.

The author would like to correct the errors in the publication of the original article. The corrected details are given below for your reading.

Function and strain of the anterolateral ligament part I: biomechanical analysis.

PURPOSE: Because reconstruction of the anterior cruciate ligament (ACL) in a double-bundle technique did not solve the problem of persistent rotatory laxity after surgery, new potential answers to this issue are of great interest. One of these is an extraarticular stabilization based on the rediscovery of the anterolateral ligament (ALL). Knowledge about its biomechanical function and benchmark data for an optimal reconstruction remain lacking. Therefore, the purpose of this study was to assess the function of the ALL under passive motion, anterior tibial translation and tibial rotational moments. METHODS: Continuous passive motion (0°-120° flexion), ap-translation and static pivot shift tests were performed on eight cadaveric knees. The knees were measured in intact, ACL-resected (ACLres) and ACL + ALL-resected (ALLres) conditions. Ap-translation and static pivot shift under 134 N anterior shear load were determined at 0°, 30°, 60° and 90° flexion. Strain of the ALL was recorded in intact and ACLres conditions. RESULTS: During continuous passive motion under unloaded conditions, no significant difference in internal rotation between ACLres and ALLres was observed. With an additional internal tibial torque of 1-4 Nm, internal rotation increased significantly between 60° and 120° after resection of the ALL (p ≤ 0.05). Anterior tibial translation was significantly higher at 30° in ALLres (p = 0.01) and for a simulated pivot shift at 60° and 90° in ACLres (p ≤ 0.01). The ALL was not strained under unloaded passive motion. Adding different internal tibial torques led to strain starting at 60° flexion (1 N m internal torque) and 15° flexion (4 N m internal torque) in intact ligaments. In ACLres, significantly greater ALL strains under lower flexion angles were seen for each condition (p ≤ 0.05). CONCLUSIONS: This study demonstrated the ALL to be without function under passive motion and with no influence on tibial rotation. On application of extrinsic loads, the ALL had a low but significant stabilizing effect against anterior tibial shear load at low flexion angles. For this reason, it can be concluded that the ALL is supporting the ACL against internal tibial loads to a minor degree. A relationship between the ALL and the pivot shift cannot be concluded. With these results ALL-reconstruction cannot be recommended at the moment without further biomechanical investigations.

The role of lesser trochanter fragment in unstable pertrochanteric A2 proximal femur fractures - is refixation of the lesser trochanter worth the effort?

BACKGROUND: Instability of osteoporotic pertrochanteric fractures is defined by loss of medial/lateral cortical integrity with the posteromedial fragment including the lesser trochanter being pivotal for load distribution. Literature addressing the importance of lesser trochanter refixation is scarce. To clarify the effect of lesser trochanter refixation on primary stability in these fractures, following study was performed. METHODS: 21 femora were match-paired in 3 groups and osteotomized, creating pertrochanteric fractures (AO-31A2). Group 1 was stabilized with a proximal femoral nail, group 2 with a dynamic hip screw and group 3 with an augmented proximal femoral nail. Each femur was tested non-destructively at 200 and 400N with and without refixation of the lesser trochanter (configuration A/B). The overall stiffness and movement of the femoral neck was recorded. FINDINGS: At 200N, refixation reduced movement of the femoral neck and increased overall stiffness significantly in group 1 and 3. At 400N, refixation decreased movement of the femoral neck not significantly in all groups (1=38%, 2=36%, 3=43%). The augmented proximal femoral nail after refixation showed the highest stability of all constructs. INTERPRETATION: Refixation of the lesser trochanter may increase the primary stability of pertrochanteric fracture osteosynthesis as all groups showed a higher primary stability. Therefore, refixation should be considered in unstable, osteoporotic fractures. If additional trauma through refixation appears inappropriate, cement augmentation should be performed as it showed only 9% less stability than a non-augmented proximal femoral nail with refixation of the lesser trochanter.

ACL double-bundle reconstruction with one tibial tunnel provides equal stability compared to two tibial tunnels.

PURPOSE: The purpose of this study was to investigate whether an anterior cruciate ligament (ACL) double-bundle reconstruction with one tibial tunnel displays the same in vitro stability as a conventional double-bundle reconstruction with two tibial tunnels when using the same tensioning protocol. METHODS: In 11 fresh-frozen cadaveric knees, ACL double-bundle reconstruction with one and two tibial tunnels was performed. The two grafts were tightened using 80 N in different flexion angles (anteromedial-bundle at 60° and posterolateral-bundle at 15°). Anterior tibial translation (134 N) and translation with combined rotatory and valgus loads (10 Nm valgus stress and 4 Nm internal tibial torque) were determined at 0°, 30°, 60° and 90° flexion. Measurements were taken in intact ACL, resected ACL, three-tunnel reconstruction and four-tunnel reconstruction. Additionally, the tension on the grafts was determined. Student's t test was performed for statistical analysis of the related samples. Significance was set at p < 0.017 according to Bonferroni correction. RESULTS: The two reconstructive techniques displayed no significant differences in comparison with the intact ACL in anterior tibial translation at 0°, 60° and 90° of flexion. The same results were obtained for the anterior tibial translation with a combined rotatory load at 60° and 90°. When directly comparing both reconstructive techniques, there were no significant differences for the anterior tibial translation and combined rotatory load at all flexion angles. The measured tension on grafts displayed similar load sharing between both bundles. Except at full extension, both grafts displayed a significantly different tension increase under anterior tibial translation for both techniques (p = 0.0086). CONCLUSIONS: Tightening both bundles in ACL double-bundle reconstruction with one or two tibial tunnels in different flexion angles achieved comparable restoration of stability, although there was different load sharing on the bundles. With regard to individualized ACL reconstruction, the double-bundle technique with one tibial tunnel offers a possibility to address small tibial insertion sites without compromising the advantages of a double-bundle procedure.

Primary stability of a shoulderless Zweymüller hip stem: a comparative in vitro micromotion study.

BACKGROUND: The Zweymüller stem design has proven long-term stability with a 20-year survival rate of over 90 %. Primary stability necessitates implant-bone micromotions below 150 µm, otherwise bony ingrowth is negatively influenced. METHODS: Using fresh paired human femurs, we investigated a modification of the Zweymüller-type stem design with reduced proximal lateral shoulder in reference to primary stability. Relative motion between the implant and the cortical bone as well as the irreversible implant migration was investigated under dynamic loading (100-1600 N) over 100,000 cycles using miniature displacement transducers. RESULTS: Micromotions were below the critical threshold for both implants at all measurement points. Axial reversible and irreversible micromotions were not influenced by reducing the shoulder of the prosthesis. Resistance against rotational moments was less pronounced after reduction of the shoulder without statistical significant results. CONCLUSIONS: Reducing the proximal shoulder of the Zweymüller-type stem design does not negatively influence axial stability but might negatively influence rotational stability. Even though, comparable results still suggest a reasonable resistance against rotational forces.

Effect of a Simple Collagen Type I Sponge for Achilles Tendon Repair in a Rat Model.

BACKGROUND: Several sophisticated approaches to tendon engineering have been investigated as ways to improve tendon healing with the early formation of repair tissue with possibly a high amount of type I collagen. Besides the new formation of collagen type I, there is evidence for the natural integration of surrounding collagen type I from healthy tendon parts into the healing defect. However, the simple application of a type I collagen sponge to the healing site to increase the amount of local collagen type I has not been investigated. HYPOTHESIS: Healing of the rat Achilles tendon can be accelerated by an additional supply of collagen type I, resulting in increased tear resistance. STUDY DESIGN: Controlled laboratory study. METHODS: The right Achilles tendons of 42 rats were transected. In half of the animals, a type I collagen sponge was placed into the gap. Animals were allowed to move freely in their cages to simulate early functional therapy. After 1, 2, and 4 weeks, tendon length, width, maximal load to failure, and stiffness were measured and the healing site studied histologically according to the Bonar score. Inflammation was evaluated by the appearance of macrophages and neutrophilic and eosinophilic granulocytes. RESULTS: Defects receiving collagen sponges showed improved healing, with significantly stronger (29.5 vs 5.0 N, respectively, at 1 week; P = .00003), shorter (11.6 vs 14.5 mm, respectively, at 4 weeks; P = .005), thicker (10.0 vs 1.8 mm(2), respectively, at 1 week; P = .00002), and less stiff (19.5 vs 30.5 N/mm, respectively, at 4 weeks; P = .02) tendons than control tendons. Overall, the biomechanical properties of the collagen-treated tendons appeared to be significantly closer to those of native, uninjured tendons compared with tendons in the control group. Histologically, no inflammatory reaction due to the collagen sponge was found. CONCLUSION: Tendon healing was accelerated by the type I collagen sponge. Moreover, the mechanical properties of collagen-treated tendons appeared to be significantly closer to those of normal, uninjured tendons compared with control tendons without collagen treatment. CLINICAL RELEVANCE: As a simple type I collagen sponge seems to increase the amount of local collagen type I, the careful use of such sponges might be an option for tendon augmentation during Achilles tendon surgery.