Vascular structure and function in the medial collateral ligament of anterior cruciate ligament transected rabbit knees

To determine if decreased vascular responsiveness in the medial collateral ligament (MCL) of anterior cruciate ligament transected (ACL‐t) rabbit knees is due to pericyte deficiency associated with angiogenesis. Vascular responses to potassium chloride (KCl), phenylephrine, acetylcholine, and sodium nitroprusside (SNP) were evaluated in ACL‐t rabbit knees (n = 6) and control knees (n = 5) using laser speckle perfusion imaging. Ligament degeneration was determined by ultrasound imaging. Vascular and pericyte volume were measured using quantitative immunohistochemical volumetric analysis using CD31 and α‐smooth muscle actin antibodies with co‐localization analysis. Perfusion was increased in the ACL‐t rabbits 2.5‐fold. Responsiveness to phenylephrine, SNP, and acetylcholine was significantly decreased in the ACL knee while no change in KCl responses was seen. MCL ultrasound imaging revealed decreased collagen organization, increased ligament thickness, and increased water content in the ACL‐t MCL. Vascular Volume was increased fourfold in ACL deficient knees, while pericyte volume to endothelial volume was not changed. No difference in CD31 and α‐SMA co‐localization was found. Blood vessels in the MCL of ACL‐t knees do not lack smooth muscle. The MCL vasculature can undergo constrictive response to KCl, but have impaired receptor mediated responses and impaired nitric oxide signaling. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1104–1110, 2014.     

Immediate ACL reconstruction prevents microvascular pathophysiology in the Uninjured MCL that is not fully reversed by delayed ACL reconstruction

Anterior cruciate ligament (ACL) injury induces maladaptive vascular responses that degrade medial collateral ligament (MCL) function. The purpose of this study was to determine if early or delayed ACL reconstruction can prevent or reverse the abnormal changes in vascular function that occur in the uninjured MCL after ACL injury. Twenty‐four rabbits were divided into four groups (n = 6); control, ACL‐deficient (ACL‐X), immediate ACL reconstructed (ACL‐IR) and delayed ACL reconstructed (ACL‐DR). After 8 weeks, MCLs were assessed for blood flow, responses to acetylcholine (ACh) and phenylephrine (Phe) and autoregulatory responses, using laser speckle perfusion imaging. In ACL‐X knees, blood flow in the MCL increased by 2.5‐fold compared to control. MCL hyperemia was diminished in ACL‐DR knees and was unaltered in ACL‐IR knees. MCL vasculature was unresponsive to ACh and Phe in ACL‐X. These responses were partially restored by ACL reconstruction. Autoregulatory responses were not significantly different between groups. ACL‐DR decreased hyperemia in the MCL and partially attenuated abnormal MCL vascular responses. ACL‐IR was more effective at preventing MCL hyperemia and preserving vascular responsiveness to ACh and Phe. This suggests that the vascular alterations in the uninjured rabbit MCL are largely caused by abnormal mechanical loading resulting from ACL deficiency and can be prevented through early reconstruction. Early ACL reconstruction could limit the progression of microvascular dysfunction of the MCL, and preserve physiological joint homeostasis. This might prevent joint degeneration and delay the progression of osteoarthritis. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1390–1396, 2011     

Complete ACL/MCL deficiency induces variable degrees of instability in sheep with specific kinematic abnormalities correlating with degrees of early osteoarthritis

People are not equally disabled by combined anterior cruciate ligament (ACL)/medial collateral ligament (MCL) injuries, nor do they all develop osteoarthritis (OA). Although biological/biomechanical causes are not clear, some association presumably exists between joint instability and OA development. We hypothesized that degree of OA development following standardized complete ACL/MCL injuries will vary directly with the degree of biomechanical abnormality between individuals. Three groups of sheep were used to test the hypothesis: 17 normal, 9 ACL/MCL transected, and 7 sham animals. Normal joints were assessed morphologically while sham and experimental animals had gait assessment pre‐ and at 4 and 20 weeks post‐surgery, with cartilage and bone changes being mapped and graded at sacrifice at 20 weeks. Sham joints were morphologically normal and had only one minor kinematic change at 20 weeks. Although variable, ACL/MCL deficient animals showed significant kinematic abnormalities in 4/6 degrees of freedom (DOFs), as well as cartilage/bone damage by 20 weeks (p < 0.05). Linear regression analysis revealed that changes in medial–lateral (ML) translation were related to the current level of joint degradation as represented by total gross OA score (p = 0.0044, R² = 0.71) in the ACL/MCL transected group. Even identical ACL/MCL injuries result in inter‐animal variations in instability and OA, however significant kinematic abnormalities in ML translation do relate to early OA in sheep. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:384–392, 2012     

A canine hybrid double‐bundle model for study of arthroscopic ACL reconstruction

Development and validation of a large animal model for pre‐clinical studies of intra‐articular anterior cruciate ligament (ACL) reconstruction that addresses current limitations is highly desirable. The objective of the present study was to investigate a translational canine model for ACL reconstruction. With institutional approval, adult research hounds underwent arthroscopic debridement of the anteromedial bundle (AMB) of the ACL, and then either received a tendon autograft for “hybrid double‐bundle” ACL reconstruction (n = 12) or no graft to remain ACL/AMB‐deficient (n = 6). Contralateral knees were used as non‐operated controls (n = 18) and matched canine cadaveric knees were used as biomechanical controls (n = 6). Dogs were assessed using functional, diagnostic imaging, gross, biomechanical, and histologic outcome measures required for pre‐clinical animal models. The data suggest that this canine model was able to overcome the major limitations of large animal models used for translational research in ACL reconstruction and closely follow clinical aspects of human ACL reconstruction. The “hybrid double‐bundle” ACL reconstruction allowed for sustained knee function without the development of osteoarthritis and for significantly improved functional, diagnostic imaging, gross, biomechanical, and histologic outcomes in grafted knees compared to ACL/AMB‐deficient knees. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1171–1179, 2015.     

Multiple injections of leukoreduced platelet rich plasma reduce pain and functional impairment in a canine model of ACL and meniscal deficiency

Platelet rich plasma (PRP) is used to treat many musculoskeletal disorders. We used a canine model to determine the effects of multiple intra‐articular injections of leukoreduced PRP (ACP) on anterior cruciate ligament healing, meniscal healing, and progression of osteoarthritis (OA). With Animal Care and Use Committee (ACUC) approval, 12 dogs underwent partial ACL transection and meniscal release in one knee. At weeks 1, 2, 3, 6, and 8 after insult, dogs were treated with intra‐articular injections (2 ml) of either ACP (n = 6) or saline (n = 6). Dogs were assessed over 6 months to determine comfortable range of motion (CROM), lameness, pain, effusion, kinetics, and radiographic and arthroscopic assessments. At 6‐month endpoint, dogs were assessed for ACL material properties and histopathology. Saline‐treated dogs had significantly (p < 0.04) more CROM loss, significantly (p < 0.01) more pain, significantly (p < 0.05) more severe lameness, significantly (p < 0.05) lower function, and significantly (p < 0.05) lower %Total Pressure Index in affected hindlimbs compared to ACP‐treated dogs. Radiographic OA increased significantly (p < 0.01) over time within each group. Arthroscopically, saline‐treated knees showed moderate to severe synovitis, further ACL disruption, and medial compartment cartilage loss, and ACP‐treated knees showed evidence of ACL repair and less severe synovitis. ACL material properties in ACP‐treated knees were closer to normal than in saline‐treated knees, however, the differences were not statistically significant. ACL histopathology was significantly (p< 0.05) less severe in ACP‐treated knees compared to saline‐treated knees. Five intra‐articular injections of leukoreduced PRP had beneficial effects for ACL healing, improved range of motion, decreased pain, and improved limb function for up to 6 months in this model. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:607–615, 2016.     

GDF‐5/7 and bFGF activate integrin α2‐mediated cellular migration in rabbit ligament fibroblasts

Cellular activities responding to growth factors are important in ligament healing. The anterior cruciate ligament (ACL) has poor healing potential compared to the medial collateral ligament (MCL). To assess the differences, we investigated the proliferation, migration, adhesion, and matrix synthesis responding to growth factors in rabbit ACL and MCL fibroblasts. ACL cell proliferation to basic fibroblast growth factor (bFGF), bone morphogenetic protein‐2, growth and differentiation factor (GDF)‐5, and GDF‐7 treatment was similar to that of MCL cells. GDF‐5 enhanced Col1a1 expression in ACL and MCL fibroblasts up to 4.7‐ and 17‐fold levels of control, respectively. MCL fibroblasts showed stronger migration activities in response to bFGF and GDF‐5 than ACL cells. GDF‐5/7 and bFGF also changed the stress fiber formation and cellular adhesion by modulating the distribution of integrin α2. Functional blocking analyses using anti‐integrin α2 antibodies revealed that cellular migration responding to growth factors depended on the integrin α2‐mediated adhesion on type I collagen. The expression of integrin α2 was also increased by growth factors in both cells. Our results demonstrate that GDF‐5/7 and bFGF stimulate cellular migration by modulating integrin α2 expression and integrin α2‐dependent adhesion, especially in MCL fibroblasts. These findings suggest that the different healing potential between ACL and MCL may be caused by different cellular behavior in the integrin α2‐mediated cellular migration in response to growth factors. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:225–231, 2010     

Valgus medial collateral ligament rupture causes concomitant loading and damage of the anterior cruciate ligament

This study tested the hypothesis that application of a valgus force necessary to create a complete medial collateral ligament (MCL) injury causes damage to the anterior cruciate ligament (ACL). Twelve cadaveric knees were used to measure concomitant loading and damage to the ACL in valgus knee loading sufficient to cause a grade III MCL injury. Displacement sensors were placed on the anteromedial bundle of the ACL and posterior oblique ligament to monitor tensile strain during creation of the MCL injury. A valgus moment was applied to knees flexed at 30 degrees, displacing the joint into valgus rotation beyond MCL rupture. Following valgus loading and MCL injury, femur-ACL-tibia specimens were tested to failure to compare ACL mechanical integrity to noninjured control specimens. Average ACL strength in MCL ruptured knees (1250 +/- 90 N) was statistically lower (P < or = .05) than that for control knees (2110 +/- 50 N). Strain measurements exhibited concomitant posterior oblique ligament strain during valgus loading, whereas ACL strain increased substantially only after MCL rupture. These data indicate that the ACL can be compromised in isolated grade III MCL injuries.     

ACL transection influences mRNA levels for collagen type I and TNF-alpha in MCL scar.

To assess the mRNA expression of extracellular matrix genes which might correlate with or contribute to mechanically weaker medial collateral ligament (MCL) scars in the ACL-deficient rabbit knee joint compared to those in anterior cruciate ligament (ACL) intact knee joints, a bilateral MCL injury was induced in 10 skeletally mature female NZW rabbits. As part of the same surgical procedure, the ACL was transected in one of the knees while the contralateral knee had a sham procedure. The side having the combined MCL and ACL injury was randomly assigned. After six weeks, the rabbits were euthanized. Histological assessments were performed on samples of the MCL scars from each operated knee (n = 3 animals) and mRNA levels for collagen type I, III, V, decorin, biglycan, lumican, fibromodulin, TGF-beta, IL-1, TNF-alpha, MMP-1, MMP-13, and a housekeeping gene (GAPDH) were assessed using semiquantitative RT-PCR on RNA isolated from the MCL scar tissue of the remaining animals (n = 7 animals). Levels of mRNA for each gene were normalized using the corresponding GAPDH value. Results showed that the total RNA yield (per mg wet weight) in the MCL scar of the ACL-deficient knee was significantly greater than that in the MCL scar from the ACL-intact knee. Collagen type I mRNA levels were significantly lower and mRNA levels for TNF-alpha were significantly greater in the scars of ACL-deficient knees compared to scars from ACL-intact joints. There were no significant differences between ACL-deficient and ACL-intact knees with respect to MCL scar mRNA levels for the remaining genes assessed. Histologically, the "flaw" area, which has been shown to correlate with mechanical properties in previous studies, was significantly greater in MCL scars from ACL-deficient knees than in the ACL-intact MCL scars. The mean number of cells/mm2 in MCL scars from ACL-deficient knees was significantly greater than in MCL scars from ACL-intact knees. The present study suggests that MCL scar cell metabolism is differentially influenced by the combined injury environment.     

Extracellular matrix‐blood composite injection reduces post‐traumatic osteoarthritis after anterior cruciate ligament injury in the rat

The objective of this study was to determine if an injection of a novel extracellular matrix scaffold and blood composite (EMBC) after anterior cruciate ligament (ACL) injury would have a mitigating effect on post‐traumatic osteoarthritis (PTOA) development in rat knees. Lewis rats underwent unilateral ACL transection and were divided into three groups as follows: (1) no further treatment (ACLT; n = 10); (2) an intra‐articular injection of EMBC on day 0 (INJ0; n = 11); and (3) an intra‐articular injection of EMBC on day 14 (INJ14; n = 11). Ten additional animals received capsulotomy only (n = 10, SHAM group). The OARSI histology scoring of the tibial cartilage and micro‐CT of the tibial epiphysis were performed after 35 days. The ratio of intact/treated hind limb forces during gait was determined using a variable resistor walkway. The OARSI cartilage degradation sum score and total degeneration width were significantly greater in the ACLT group when compared to the INJ0 (p = 0.031, and p = 0.005) and INJ14 (p = 0.022 and p = 0.04) group. Weight bearing on the operated limb only decreased significantly in the ACLT group (p = 0.048). In the rat ACL transection model, early or delayed injection of EMBC ameliorated the significant decrease in weight bearing and cartilage degradation seen in knees subjected to ACL transection without injection. The results indicate that the injection of EMBC may slow the process of PTOA following ACL injury and may provide a promising treatment for PTOA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:995–1003, 2016.     

The patella ligament insertion angle influences quadriceps usage during walking of anterior cruciate ligament deficient patients

Following ACL injury a reduction in the peak knee flexion moment during walking (thought to be created by a decrease of quadriceps contraction) has been described as an adaptation to reduce anterior tibial translation (ATT) relative to the femur. However, the amount of ATT caused by quadriceps contraction is influenced by the patellar ligament insertion angle (PLIA). The purpose of this study was to test the hypothesis that quadriceps usage during walking correlates to individual anatomical variations in the extensor mechanism as defined by PLIA. PLIA and gait were measured for ACL‐deficient knees, using subjects' contralateral knees as controls. In ACL‐deficient knees, PLIA was negatively correlated (R² = 0.59) to peak knee flexion moment (balanced by net quadriceps moment), while no correlation was found in contralateral knees. Reduction in peak flexion moment in ACL‐deficient knees compared to their contralateral knees was distinctive in subjects with large PLIA, possibly to avoid excessive ATT. These results suggest that subject‐specific anatomic variability of knee extensor mechanism may account for the individual variability previously observed in adaptation to a quadriceps reduction strategy following ACL injury. The average (±1 SD) PLIA of ACL‐deficient knees (21.1 ± 3.4°) was less than the average PLIA of contralateral knees (23.9 ± 3.1°). This altered equilibrium position of the tibiofemoral joint associated with reduced PLIA and adaptations of gait patterns following ACL injury may be associated with degenerative changes in the articular cartilage. In the future, individually tailored treatment and rehabilitation considering individuals' specific extensor anatomy may improve clinical outcomes. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1643–1650, 2007     

In-situ force in the medial and lateral structures of intact and ACL-deficient knees

The anterior cruciate ligament (ACL) is the major contributor to limit excessive anterior tibial translation (ATT) when the knee is subjected to an anterior tibial load. However, the importance of the medial and lateral structures of the knee can also play a significant role in resisting anterior tibial loads, especially in the event of an ACL injury. Therefore, the objective of this study was to determine quantitatively the increase in the in-situ forces in the medial collateral ligament (MCL) and posterolateral structures (PLS) of the knee associated with ACL deficiency. Eight fresh-frozen cadaveric human knees were subjected to a 134-N anterior tibial load at full extension and at 15°, 30°, 60°, and 90° of knee flexion. The resulting 5 degrees of freedom kinematics were measured for the intact and the ACL-deficient knees. A robotic/universal force-moment sensor testing system was used for this purpose, as well as to determine the in-situ force in the MCL and PLS in the intact and ACL-deficient knees. For the intact knee, the in-situ forces in both the MCL and PLS were less than 20 N for all five flexion angles tested. But in the ACL-deficient knee, the in-situ forces in the MCL and PLS, respectively, were approximately two and five times as large as those in the intact knee (P < 0.05). The results of this study demonstrate that, although both the MCL and PLS play only a minor role in resisting anterior tibial loads in the intact knee, they become significant after ACL injury. Received: December 3, 1999 / Accepted: July 19, 2000     

Randomised double‐blinded comparison of phenylephrine vs ephedrine for maintaining blood pressure during spinal anaesthesia for non‐elective Caesarean section*

In a randomised, double‐blinded study, we compared boluses of phenylephrine 100 μg with ephedrine 10 mg for treating hypotension (systolic blood pressure < 100 mmHg) in 204 patients having non‐elective Caesarean section under spinal anaesthesia. Umbilical arterial (UA) and venous (UV) pH and base excess were similar between groups. In the ephedrine group, UA lactate concentration was higher (median 2.6 [interquartile range 2.3–3.3] vs 2.4 [1.9–3.0] mmol.l^?1, p = 0.002) and UV lactate concentration was higher (2.5 [2.2–3.2] vs 2.3 [1.9–2.8] mmol.l^?1, p = 0.016) and more patients had nausea or vomiting (12.7% vs 3.9%, p = 0.02). Clinical neonatal outcome was similar. Of the protocol‐compliant patients (n = 148), UA Po ₂ and UV Po ₂ were lower in the phenylephrine group although oxygen content was similar. We conclude that phenylephrine and ephedrine are both suitable vasopressors for use in non‐elective Caesarean sections.     

Effects of epoxygenases on the nonadrenergic noncholinergic relaxant responses induced by electrical field stimulation in rabbit corpus cavernosum

We aimed to investigate the effects of epoxygenases on electrical field stimulation (EFS)‐mediated nitric oxide (NO)‐dependent and NO‐independent nonadrenergic noncholinergic (NANC) relaxations in isolated rabbit corpus cavernosum. The tissues of 20 male adult albino rabbits (2.5–3 kg) were suspended in organ baths containing aerated Krebs solution, and isometric contractions were recorded. EFS‐mediated NANC relaxations were obtained on phenylephrin (3 × 10^?5 M)‐contracted tissues in the presence of guanethidine (10^?6 M) and atropine (10^?6 M). Miconazole (10^?9–10^?4 M), 17‐octadecynoic acid (ODYA) (10^?10–10^?5 M), 14,15‐epoxyeicosatrienoic acid (EET) (10^?11–10^?8 M), 11,12‐EET (10^?12–3 × 10^?8 M) and 20‐hydroxyeicosatetraenoic acid (HETE) (10^?11–3 × 10^?8 M) were added cumulatively (n = 5–7 for each set of experiments). For NO‐independent relaxations, N^ω‐nitro‐l ‐arginine methyl ester (l ‐NAME) (10^?4 M) was added before a group of experiments. Depending on the concentration, miconazole, 17‐ODYA, 14,15‐EET, 11,12‐EET, and 20‐HETE significantly enhanced both NO‐dependent and NO‐independent EFS‐mediated relaxations (p < 0.05). Epoxygenases showed similar effect on NO‐dependent and NO‐independent relaxant responses except 20‐HETE which caused significantly more enhanced relaxation on NO‐dependent responses (p < 0.05). No drug caused a significant relaxation response on tissues contracted with phenylephrine. Epoxygenases contribute to EFS‐mediated NO‐dependent and NO‐independent NANC relaxations by presynaptic mechanisms, offering a new treatment alternative for erectile dysfunction which needs to be explored in further in vivo, molecular and clinical studies.     

A new supraglottic airway device: LMA-Supreme™, comparison with LMA-Proseal™

Background and objective: The LMA‐Supreme^? (S‐LMA^?) is a new supraglottic airway device that presents combined features of flexibility, curved structure and single use and a different cuff structure. The purpose of this study was to compare the oropharyngeal leak pressures (OLP) of LMA‐Proseal^? (P‐LMA^?) and S‐LMA^?. Methods: Sixty adult patients were prospectively and randomly allocated to undergo insertion of P‐LMA^? (n=30) or S‐LMA^? (n=30). The cuffs were inflated until the intracuff pressure (ICP) reached 60 cm H₂O. Orogastric leak pressures, insertion times, first attempt success rates, fiberoptical assessment of position, cuff pressures, orogastric tube (OGT) placement and OGT insertion times were compared. Unblinded observers collected intraoperative data and blinded observers collected post‐operative data. Results: The first insertion attempts and time taken to provide an effective airway were similar between the groups. Two patients (P‐LMA^?, n=1; S‐LMA^?, n=1) were intubated due to excessive oropharyngeal leak and in one patient (P‐LMA^?, n=1) due to failed OGT placement. OLPs were similar (P‐LMA^?; 26.9±6.6 S‐LMA^?; 26.1±5.2). ICP increased significantly in the P‐LMA^? at the 30 and 60 min during anesthesia (P‐LMA^?; 80.1±12.8, 92.9±14.4, S‐LMA^?; 68.3±10.9, 73.7±15.6). OGT placement was successful in all patients in the S‐LMA^?, but failed in five patients in the P‐LMA^? (P=0.02). Fiberoptically determined anatomic position was better with the P‐LMA^? (P=0.03). Conclusion: Our findings suggest that S‐LMA^? had leak pressures similar to the P‐LMA^?, and this new airway device proved to be successful during both spontaneous and positive pressure ventilation.     

Antiresorptive therapy conserves some periarticular bone and ligament mechanical properties after anterior cruciate ligament disruption in the rabbit knee

The purpose of this study was to assess, in an osteoarthritic (OA) model, whether bisphosphonate (BP) antiresorptive therapy altered periarticular bone and bone–ligament biomechanics and OA progression. We surgically transected the anterior cruciate ligament (ACLX) in two groups of rabbits; the first group was dosed with BP (risedronate, 0.01 mg/kg s.c. daily for 6 wk), the second group remained untreated, and a third group of normal (unoperated) control rabbits was also evaluated. We measured distal femoral bone mineral density (BMD, Dual Energy X‐ray Absorptiometry [DEXA]), medial collateral ligament (MCL) laxity, and bone mechanical function (bone cores mechanically tested in compression). These measures were related to cartilage/joint gross morphology, histology, and measures of vascular volume (gelatin–dye perfusion) for evidence of inflammatory angiogenesis and early OA. BMD by DEXA in 6 wk ACLX animals was 18% less than normal controls (p < 0.05). In contrast, BP dosing conserved periarticular BMD; risedronate‐treated rabbits had distal femoral BMD only 5% less and not significantly different than normal controls. When the same bone cores were compressed to failure, both ACLX and BP‐dosed animals were significantly weaker than normal controls (p < 0.05). However, the bone energy to failure and elastic modulus of BP‐dosed animals was conserved and not significantly different from normal controls 6 wk after ACLX. Blocking bone resorption with BP also resulted in a significantly improved bone–ligament structural complex. MCL‐complex laxity was significantly less in BP‐dosed animals (1.2 times that of normal controls) compared to untreated ACLX animals (1.7 times that of normal controls; p < 0.05). Blocking bone resorption with risedronate did not suppress osteophytosis and inflammatory angiogenesis, which were significantly increased in the periarticular bone of both untreated and BP treated ACLX animals. Thus, administering BP immediately after ACL loss conserved some periarticular bone and MCL‐complex properties in an early OA model. © 2004 Published by Elsevier Ltd. on behalf of Orthopaedic Research Society.     

Geometric profile of the tibial plateau cartilage surface is associated with the risk of non‐contact anterior cruciate ligament injury

The purpose of this study was to determine if geometry of the articular surfaces of the tibial plateau is associated with non‐contact anterior cruciate ligament (ACL) injury. This was a longitudinal cohort study with a nested case–control analysis. Seventy‐eight subjects who suffered a non‐contact ACL tear and a corresponding number of controls matched by age, sex, and sport underwent 3 T MRI of both knees. Surface geometry of the tibial articular cartilage was characterized with polynomial equations and comparisons were made between knees on the same person and between ACL‐injured and control subjects. There was no difference in surface geometry between the knees of the control subjects. In contrast, there were significant differences in the surface geometry between the injured and normal knees of the ACL‐injured subjects, suggesting that the ACL injury changed the cartilage surface profile. Therefore, comparisons were made between the uninjured knees of the ACL‐injured subjects and the corresponding knees of their matched controls and this revealed significant differences in the surface geometry for the medial (p < 0.006) and lateral (p < 0.001) compartments. ACL‐injured subjects tended to demonstrate a posterior–inferior directed orientation of the articular surface relative to the long axis of the tibia, while the control subjects were more likely to show a posterior–superior directed orientation. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:61–68, 2014.     

α1 adrenergic receptor agonist,phenylephrine, actively contracts early rat rib fracture callus ex vivo

Early, soft fracture callus that links fracture ends together is smooth muscle‐like in nature. We aimed to determine if early fracture callus could be induced to contract and relax ex vivo by similar pathways to smooth muscle, that is, contraction via α₁ adrenergic receptor (α₁AR) activation with phenylephrine (PE) and relaxation via β₂ adrenergic receptor (β₂AR) stimulation with terbutaline. A sensitive force transducer quantified 7 day rat rib fracture callus responses in modified Krebs–Henseliet (KH) solutions. Unfractured ribs along with 7, 14, and 21 day fracture calluses were analyzed for both α₁AR and β₂AR gene expression using qPCR, whilst 7 day fracture callus was examined via immunohistochemistry for both α₁AR and β₂AR‐ immunoreactivity. In 7 day callus, PE (10^?6 M) significantly induced an increase in force that was greater than passive force generated in calcium‐free KH (n = 8, mean 51% increase, 95% CI: 26–76%). PE‐induced contractions in calluses were attenuated by the α₁AR antagonist, prazosin (10^?6 M; n = 7, mean 5% increase, 95% CI: 2–11%). Terbutaline did not relax callus. Gene expression of α₁ARs was constant throughout fracture healing; however, β₂AR expression was down‐regulated at 7 days compared to unfractured rib (p < 0.01). Furthermore, osteoprogenitor cells of early fibrous callus displayed considerable α₁AR‐like immunoreactivity but not β₂AR‐like immunoreactivity. Here, we demonstrate for the first time that early fracture callus can be pharmacologically induced to contract. We propose that increased concentrations of α₁AR agonists such as noradrenaline may tonically contract callus in vivo to promote osteogenesis. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:740–745, 2011     

Enhancement of pressor response to intravenous phenylephrine following oral clonidine medication in awake and anaesthetized patients

Clonidine, an α₂-adrenergic agonist, augments the pressor response to intravenous ephedrine. If this effect is partly due to clondine-induced potentiation of α₁-adrenoceptor-mediated vasoconstriction, it is also assumed that clonidine would enhance the pressor effect of phenylephrine as an α₁-adrenergic agonist. The authors studied haemodynamic responses to intravenous phenylephrine in 80 patients who received either preanaesthetic medication with clonidine approximately 5 μg · kg^?1 po (clonidine group, n = 40), or no medication (control group, n =40). Each group was further divided into either awake subjects (n = 20) or subjects anaesthetized with enflurane and nitrous oxide in oxygen (n = 20). Haemodynamic measurements were made at one-minute intervals for ten minutes after phenylephrine 2 μg · kg^?1 iv was injected as a bolus. The magnitudes of maximal mean blood pressure increases in the clonidine group (26 ± 7% (mean ± SD) for awake and 32 ± 15% for anaesthetized subjects) were greater (P < 0.05) than in the control group (13 ± 7% for awake and 18 ± 7% for anaesthetized subjects). However, there was no difference in the pressor effect of phenylephrine between awake and anaesthetized patients in both groups. Oral clonidine preanaesthetic medication, 5 μg · kg^?1, augments the pressor responses to phenylephrine 2 μg · kg^?1 iv in awake and anaesthetized patients. These results suggest that the enhancement of the pressor responses to phenylephrine following oral clonidine may be due to clonidine-induced potentiation of α₁-adrenoceptor-mediated vasoconstriction. This implies that restoration of blood pressure can be achieved effectively by phenylephrine in hypotensive patients with clonidine premedication.     

Decreased posterior cruciate and altered collateral ligament loading following ACL transection: A longitudinal study in the ovine model

Although ACL deficiency is shown to lead to joint degeneration, few quantitative data are reported on its effect on soft tissue structures surrounding the knee joint, specifically, the posterior cruciate and collateral ligaments. The kinematics of the stifle joint of sheep (N = 5) were measured during “normal” gait, as well as 4 and 20 weeks after ACL transection. These motions were reproduced using a unique robotic manipulator and the loads borne by PCL, MCL, and LCL during gait were determined. Our results demonstrated a significant decrease in mean PCL loads 20 weeks post‐ACL injury, at hoof‐strike (0% of gait, p = 0.034), hoof‐off (66% of gait, p = 0.006), peak‐swing (85% of gait, p = 0.026), and extension‐before‐hoof‐strike (95% of gait, p = 0.028). Mean MCL loads did not significantly increase following ACL transection, maybe due to large between‐animal variation. Finally, mean LCL loads indicated a significant decrease (p < 0.047) at 20 weeks across the entire gait cycle. From a clinical perspective, the load redistributions observed in cruciate and collateral ligaments following ACL injury indicate that these tissues can carry/adapt to the altered mechanical environment of the joint. The considerable variability in the magnitudes of change following ACL injury among animals also simulates clinical variability in humans after trauma. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:431–438, 2014.     

Vascular physiology and long-term healing of partial ligament tears.

Functional outcomes of anterior cruciate ligament (ACL) injury are generally poorer than those of medial collateral ligament (MCL) tears. Following ligament damage, all phases of ligament healing require an adequate blood supply. We hypothesized that the differences in healing properties of the ACL and MCL would reflect their vascular responses to joint injury. This paper examines the long-term changes in blood flow and vascular volume of rabbit knee ligaments after direct injury, and under conditions of chronic joint instability induced by section of the posterior cruciate ligament (PCL). Standardized injuries were surgically induced in adult rabbit knee ligaments: partial MCL transection, partial ACL transection, or complete PCL transection (joint instability). Sixteen weeks later the blood flow and vascular volume of the ACL and MCL were measured and compared to control and sham-operated animals. Direct ligament injury induced significant increases in standardized blood flow and vascular volume of both ACL and MCL after 16 weeks; however, the vascular volume of the ACL was not higher than the control levels in the MCL. We conclude that direct injury to both the anterior cruciate and MCLs induces long-term physiological responses. Joint laxity is a common sequel to PCL injury. Chronic joint laxity failed to induce adaptive vascular responses in the ACL, while the MCL shows significant amplification of blood supply. Although both MCL and ACL showed increased weight after PCL transection, the lack of a long-term vascular response in the ACL may be a major factor in its the diminished healing potential.