Associations of blood pressure and arterial stiffness with knee cartilage volume in patients with knee osteoarthritis.

OBJECTIVE: To describe the associations of blood pressure and arterial stiffness with knee cartilage volume in patients with knee OA. METHODS: A secondary analysis was performed on the data from participants in a randomized controlled trial that identified the effects of vitamin D supplementation on knee structures and symptoms among patients with symptomatic knee OA. Brachial and central blood pressure, arterial stiffness indicators and knee cartilage volume were measured at baseline and the 2 year follow-up. Associations were assessed using generalized estimating equations. RESULTS: Among 231 participants (average age 63.2 years), 48.9% were females. Higher supine systolic and diastolic pressures were significantly associated with lower tibial cartilage volume (systolic: lateral ß -6.23, medial ß -5.14, total ß -11.35 mm3/mmHg; diastolic: lateral ß -10.25, medial ß -11.29, total ß -21.50 mm3/mmHg). Higher supine systolic pressure was associated with lower femoral cartilage volume (lateral ß -17.35, total ß -28.31 mm3/mmHg). Central systolic pressure and arterial stiffness indicators (including pulse wave velocity, central pulse pressure and peripheral pulse pressure) were largely not associated with knee cartilage volume; however, higher augmentation index was associated with lower tibial and femoral cartilage volume (tibial: medial ß -8.24, total ß -19.13 mm3/%; femoral: lateral ß -23.70, medial ß -26.42, total ß -50.12 mm3/%). CONCLUSIONS: Blood pressure and arterial stiffness are associated with knee cartilage volume at several sites in knee OA patients. This supports that blood pressure and arterial stiffness may involve in the progression of knee OA.

Exercise on a vibratory platform increases blood perfusion on the stifle joint and rectal temperature in healthy dogs / Exercício em plataforma vibratória aumenta a perfusão sanguínea da articulação do joelho e a temperatura retal de cães saudáveis

The effects of two vibration platform (VP) exercise protocols on stifle and rectal temperatures were evaluated. Eleven animals participated in two exercise protocols, different in duration in each exercise. Exercise protocol 1 (EP1) took 30 seconds and EP2, 60 seconds, with different vibratory levels in both cases (L1 = acceleration ≅ 1g, L4 = acceleration ≅ 2.5g, and L7 = acceleration ≅ 5g). The animals were evaluated before and 1 minute after the exercise, using infrared thermography to obtain stifle temperatures. The rectal temperature (RT) was also checked at each moment. The dogs had higher stifle temperatures in EP1 at all vibratory levels compared to the time before the exercise; EP2 resulted in higher temperature only at maximum vibration intensity (L7). Increase in TR was observed only in EP2. The results suggested that the short duration protocol (EP1) increased the muscular and peripheral vascular activities of the joint, regardless of the vibration intensity. The long duration protocol (EP2) with maximum vibration intensity increased the RT, demonstrating activity beyond the stifle muscle group. It is concluded that exercises on the VP can be used as complementary therapy for low-impact muscle activity in dogs and may be adequate for efficient energy consumption.(AU)

Foram avaliados os efeitos de dois protocolos de exercício em plataforma vibratória (PV) sobre as temperaturas dos joelhos e retais. Onze animais participaram de dois protocolos de exercício, diferentes na duração de cada exercício. O protocolo de exercício 1 (PE1) foi de 30 segundos e o PE2 foi de 60 segundos, com diferentes níveis vibratórios em ambos (L1 = aceleração ≅ 1g; L4 = aceleração ≅ 2,5g; e L7 = aceleração ≅ 5g). Os animais foram avaliados antes e um minuto após os exercícios, por meio de termografia infravermelha para a obtenção das temperaturas dos joelhos. A temperatura retal (TR) foi aferida em cada momento. Os cães apresentaram temperaturas dos joelhos mais elevadas em PE1, em todos os níveis vibratórios, em comparação a antes do exercício; o PE2 resultou em temperatura mais alta apenas na intensidade máxima de vibração (L7). Aumento na TR foi observado apenas no PE2. Os resultados sugerem que o protocolo de curta duração (PE1) aumentou as atividades muscular e vascular periférica da articulação, independentemente da intensidade da vibração; o protocolo de longa duração (PE2) com intensidade máxima de vibração aumentou a TR demonstrando atividade além do grupo muscular do joelho. Conclui-se que os exercícios na PV podem ser utilizados como terapia complementar para atividade muscular de baixo impacto em cães e pode ser adequada para o consumo eficiente de energia.(AU)

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

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

Effects of blood flow restriction exercise with very low load and low volume in patients with knee osteoarthritis: protocol for a randomized trial.

BACKGROUND: Knee osteoarthritis (OA) is characterized by chronic pain, physical dysfunction, and reduced quality of life. Low-load resistance exercises with blood flow restriction (BFR) have presented results similar to those of high-intensity resistance exercise (HIRE) without BFR provided that the exercise volume in both is paired. However, it is unclear whether BFR exercise with reduced load and volume generates clinical improvements similar to those of HIRE. The aim of the proposed study is to evaluate the effects of BFR resistance exercise with very low load and low volume against HIRE in patients with knee OA for the outcomes of knee pain, muscle performance, physical function, disease severity, quality of life, perceived exertion during the exercises, adherence, and patient satisfaction with treatment. METHODS: This two-arm, prospectively registered, randomized controlled trial with blinded assessors and volunteers will involve 40 patients with knee OA. Two weekly treatment sessions will be provided for 12 weeks. Patients will perform very low-load (10% of 1-RM) and low-volume BFR exercise or HIRE (60% of 1-RM) for strengthening thigh muscles. The primary outcome will be the knee pain measured after 12 weeks of treatment. The secondary outcomes include knee pain 6 months after randomization, physical function, disease severity, quality of life, muscle performance, knee pain and perceived exertion during exercise, adherence, and patient satisfaction with treatment. DISCUSSION: If the improvements in the outcomes are similar in the two groups, BFR exercise with reduced load and volume may be an interesting alternative in the treatment of knee OA, especially when exercises with high loads generate joint pain. TRIAL REGISTRATION: Registro Brasileiro de Ensaios Clínicos (REBEC), RBR-6pcrfm . Registered on July 10, 2018.

Technically Successful Geniculate Artery Embolization Does Not Equate Clinical Success for Treatment of Recurrent Knee Hemarthrosis after Knee Surgery.

PURPOSE: To evaluate technical details, clinical outcomes, and complications in patients undergoing geniculate artery embolization for treatment of spontaneous hemarthrosis after knee surgery. MATERIALS AND METHODS: During 2009-2014, 10 consecutive patients (seven women; mean age, 57.4 y) underwent geniculate artery embolization at a single tertiary care center. All patients except one had hemarthrosis after total knee replacement (TKR). One patient presented with hemarthrosis after cartilage surgery. Two patients in the TKR group had a history of TKR revisions before the embolization. Embolization was performed with polyvinyl alcohol particles (range, 300-700 µm). In one patient requiring repeat embolization, N-butyl cyanoacrylate/ethiodized oil was used. The endpoint for embolization was stasis in the target artery and elimination of the hyperemic blush. RESULTS: In 10 patients, 14 embolizations were performed with 100% technical success. Hemarthrosis resolved in six patients. Four patients required repeat embolization for recurrent hemarthrosis, which subsequently resolved in two of four patients. Three of the four patients who required repeat embolization had serious comorbidities, either blood dyscrasias or therapeutic anticoagulation. There were two minor skin complications that resolved with conservative management. The average length of follow-up after embolization was 545 days (range, 50-1,655 d). One patient was lost to follow-up. CONCLUSIONS: Geniculate artery embolization is a safe, minimally invasive treatment option for spontaneous and refractory knee hemarthrosis after knee surgery with 100% technical success. However, limited clinical success and higher repeat embolization rates were noted in patients with serious comorbidities.

[Needle-knife combined with pseudo-ginseng-cake moxibustion for primary knee osseous arthritis of blood stasis syndrome:a randomized controlled trial].

OBJECTIVE: To observe the clinical efficacy differences between needle-knife combined with pseudo-ginseng-cake moxibustion and oral administration of western medication for primary knee osseous arthritis (PKOA) of blood stasis syndrome. METHODS: Sixty cases of PKOA of blood stasis syndrome were randomly assigned to an observation group and a control group. Patients in the observation group (30 patients, 38 knees) were treated with needle-knife combined with pseudo-ginseng-cake moxibustion, while patients in the control group (30 patients, 36 knees) were oral administration of western medication. The treatment was given three weeks continuously. The knee osteoarthritis outcome score (KOOS) was adopted to observe the knee pain, symptoms and stiffness, daily life, sport and entertainment function, daily life quality score and total score in the two groups before and after treatment. The follow-up visit was performed two months after the treatment to evaluate the long-term efficacy. RESULTS: The total effective rate was 97.4% (37/38) in the observation group, which was significantly superior to 77.8% (28/36) in the control group (P<0.05). Each item of KOOS was increased in the observation group after treatment and follow-up visit (P<0.05, P<0.01); the KOSS in the control group was also increased (all P<0.01) after treatment, and daily life and daily life quality score of knee in the follow-up visit were significantly increased (both P<0.01). The scores other than sport and entertainment function score in the observation were significantly higher than those in the control group (all P<0.01). CONCLUSIONS: The needle-knife combined with pseudo-ginseng-cake moxibustion could significantly improve the symptoms of PKOA of blood stasis syndrome, which was superior to oral administration of western medication alone and had better long-term effects.

Effect studies of Uyghur sand therapy on the hemodynamics of the knee-joint arteries.

This paper studies the effect of Uyghur sand therapy on dynamics of arterial flow of knee joints via experiments and numerical simulations. Experiments have been carried out on 30 volunteers, with their diameter and flow rate of arteries of knee joints measured before and after Uyghur sand therapy. It has been found that Uyghur sand therapy will increase the inner diameter of knee arteries and speed up the blood flow. Experimental results show that Uyghur sand therapy can help relieve obstacles in local blood flow. By choosing one volunteer for CT scanning, three-dimensional reconstruction of knee-joint arteries via MIMICS software is achieved. Calculation model is the established with numerical calculations performed by ANSYS software. According to the calculations, the blood flow of the knee arteries speeds up and the uniform distribution of velocity enlarges after Uyghur sand therapy, which further confirms the experimental results. Besides, the research also suggests that Uyghur sand therapy has stronger effect on blood flow of knee-joint arteries than the inner diameter.

Instrument-assisted cross fiber massage increases tissue perfusion and alters microvascular morphology in the vicinity of healing knee ligaments.

BACKGROUND: Ligament injuries are common clinical problems for which there are few established interventions. Instrument-assisted cross fiber massage (IACFM) was recently shown to accelerate the restoration of biomechanical properties in injured rodent knee medial collateral ligaments (MCL). The current study aimed to investigate the influence of IACFM on regional perfusion and vascularity in the vicinity of healing rodent knee MCL injuries. METHODS: Bilateral knee MCL injuries were induced in female Sprague-Dawley rats. Commencing 1 week post-injury, 1 minute of IACFM was introduced unilaterally 3 times/week for 3 weeks. The contralateral injured MCL served as an internal control. Regional tissue perfusion was assessed in vivo throughout healing using laser Doppler imaging, whereas regional microvascular morphology was assessed ex vivo via micro-computed tomography of vessels filled with contrast. RESULTS: IACFM had no effect on tissue perfusion when assessed immediately, or at 5, 10, 15 or 20 min following intervention (all p > 0.05). However, IACFM-treated hindlimbs had enhanced tissue perfusion when assessed 1 day following the 4th and 9th (last) treatment sessions (all p < 0.05). IACFM-treated hindlimbs also had greater perfusion when assessed 1 wk following the final treatment session (32 days post-injury) (p < 0.05). Subsequent investigation of microvascular morphology found IACFM to increase the proportion of arteriole-sized blood vessels (5.9 to <41.2 µm) in the tibial third of the ligament (p < 0.05). CONCLUSIONS: These findings suggest IACFM alters regional perfusion and vascularity in the vicinity of healing rodent knee MCL injuries. This effect may contribute to the beneficial effect of IACFM observed on the recovery of knee ligament biomechanical properties following injury.

The anti-arthritic effects of Aconitum vilmorinianum, a folk herbal medicine in Southwestern China.

ETHNOPHARMACOLOGICAL RELEVANCE: Aconiti Radix (AC) and Aconiti Kusnezoffii Radix (AK) are two traditional Chinese medicines commonly used to treat joint pain and arthritis. In Southwestern China, Huangcaowu (AV), the root of Aconitum vilmorinianum Kom., has long been used as a local substitute for these herbs for analgesia and anti-inflammation. However, its anti-arthritic effects have not been investigated. AIM OF STUDY: To investigate the anti-arthritic effects of Huangcaowu (AV). MATERIALS AND METHODS: Mono-arthritis in SD rats was induced by unilateral intra-articular injection of Freund's complete adjuvant. Physiological saline was injected in the contralateral knee. Seventy five percent ethanol extracts of AV (10 mg/kg/day and 100 mg/kg/day), AC (100 mg/kg/day) and AK (100 mg/kg/day) were administered to rats by oral gavage for 14 consecutive days (Day -6 to Day 7) while arthritis was induced at the seventh day (Day 0). The anti-arthritic effects of the herbs were assessed by measuring allodynia, swelling, hyperaemia and the vascular permeability of the knee joints. RESULTS: AV (10 mg/kg/day and 100 mg/kg/day), AC (100 mg/kg/day) and AK (100 mg/kg/day) suppressed joint allodynia. AV (10 mg/kg/day and 100 mg/kg/day) and AK (100 mg/kg/day) significantly reduced join swelling and hyperaemia while AC (100 mg/kg/day) did not. AV (100 mg/kg/day) attenuated vascular permeability while AC (100 mg/kg/day) and AK (100 mg/kg/day) showed no improvement. CONCLUSIONS: Huangcaowu (AV) significantly improved allodynia, swelling, hyperaemia and vascular permeability in arthritic knee joints. It showed the highest anti-arthritic effects among the three tested Aconitum herbs.

Rehabilitation of an osteochondral fracture using blood flow restricted exercise: a case review.

OBJECTIVES: In this case review we report on a bodybuilder who used a practical model of blood flow restriction (BFR) training to successfully rehabilitate himself following an injury to his right knee. RESULTS: The patient originally thought he had torn his meniscus however repeat radiographs and magnetic resonance imaging (MRI) confirmed an osteochondral fracture. The patient initially sought out a low load alternative to help with the maintenance of skeletal muscle mass. However, following rehabilitation with low load BFR resistance training, radiographs indicated that the bone had begun to heal suggesting that this type of training may also benefit bone. CONCLUSIONS: In conclusion, this case review provides evidence that practical BFR using knee wraps can serve as an effective stimulus during rehabilitation from a knee injury.

[Effects of therapeutic complexes including balneoradonokinesitherapy, electromyostimulation and low-frequency magnetotherapy on regional blood flow in patients with postrraumatic gonarthritis].

Balneoradonokinesitherapy alone and its combination with electrostimulation and low-frequency magnetotherapy were used for the treatment of regional blood flow disorders in 76 patients with posttraumatic gonarthritis. Balneoradonokinesitherapy in combination with electromyostimulation improved blood circulation. When low-frequency magnetotherapy was added to the latter complex, the regress of regional blood flow disorders of a damaged extremity was most significant.

Capsaicin-induced vasoconstriction in the mouse knee joint: a study using TRPV1 knockout mice.

Capsaicin is the pungent component of chilli peppers that concomitantly activates and desensitizes C-fibre and Adelta sensory nerve fibres. Stimulation causes an acute neurogenic response including vasodilation, plasma extravasation and hypersensitivity. However, in the present study we have shown that capsaicin produces a dose-dependent vasoconstrictor effect in the mouse knee joint via Transient Receptor Potential Vanilloid 1 (TRPV1) receptor activation. A (125)I-albumin accumulation technique showed that the intravascular volume of capsaicin-treated joints in wild type (WT) mice was significantly reduced compared to TRPV1 knockout mice (p<0.01). Similarly, a laser Doppler technique showed significantly reduced blood flow in the capsaicin-treated joints of WT compared to TRPV1 knockout mice (p<0.001). Pretreatment with guanethinidine (50 mg kg(-1), i.p.) had no effect on the vasoconstriction. These data are important considering the involvement of TRPV1 receptors in joint disease. The mechanisms underlying the vasoconstriction therefore require further investigation.

Pathophysiology of vascular dysfunction in a rat model of chronic joint inflammation.

The impact of chronic joint inflammation on articular vascular function in rats was investigated to address whether joint swelling and the associated vascular dysfunction are dependent upon a common prostanoid mechanism. Urinary nitrate/nitrite (NO(x)) and PGE(2) excretion, knee joint diameter and body weight were measured following induction of adjuvant-induced arthritis (AIA). Ten days postinduction of AIA, joint vascular reactivity was assessed by measuring the perfusion response using a laser Doppler imager (LDI) to topical application of acetylcholine (ACh) and sodium nitroprusside (SNP). Four groups were compared: a non-inflamed control group and three AIA groups treated i.p. with vehicle, indomethacin or SC-236 (at equimolar doses). The selective cyclooxygenase-2 (COX-2) inhibitor (SC-236) was used to differentiate between COX-1 and -2-derived prostaglandins. Urinary NO(x) and PGE(2) levels increased substantially during the early phase of AIA but decreased thereafter. Toxicity to indomethacin but not SC-236 was observed, as indicated by a marked decrease in body weight. Joint swelling was similarly attenuated by indomethacin and SC-236 (P= 0.0001 cf. vehicle-treated AIA; n= 5-6 per group), indicating that this is due to COX-2 and not COX-1 inhibition. The AIA-induced changes in urinary NO(x) and PGE(2) were corrected by both COX inhibitors. While vascular reactivity to ACh and SNP was significantly attenuated by AIA (P < 0.002; n= 5-10 per group), the perfusion responses to these vasodilating agents were similar in all three AIA groups, demonstrating that the vascular dysfunction was not corrected by inhibition of either COX-1 or COX-2 enzymes. Furthermore, the attenuation of both ACh and SNP-induced responses in AIA suggest that vascular dysfunction was not exclusively endothelial in nature. In conclusion, the joint swelling and vascular dysfunction associated with AIA appear to be mediated, at least in part, by independent mechanisms. While COX-1/COX-2 inhibition reduced joint swelling, vascular dysfunction in AIA is independent of constitutive or inducible prostanoid mechanisms, and appears not to be solely endothelial-derived, but to involve other components such as the vascular smooth muscle.

Attenuation of knee joint inflammation by peripherally administered endomorphin-1.

Endomorphin-1 is a selective endogenous ligand for the micro-opioid receptor, and this study investigated the effect of endomorphin-1 on rat knee joint inflammation by examining the ability of the neuropeptide to modulate synovial protein extravasation. Acute joint inflammation was induced by intraarticular injection of 2% kaolin followed by 2% carrageenan and the animals allowed to recover for 3 h. Immunohistochemical examination of these inflamed joints revealed endomorphin-1-like immunoreactive nerves in deep synovium with a proportion of the nerve fibers occurring in close proximity to synovial blood vessels. Perfusion of inflamed knees with exogenous endomorphin-1 across the dose range 10-9-10-6 M produced a significant reduction in synovial vascular permeability with the 10-7M dose producing the greatest fall in protein exudation (approx 55%). These effects were blocked by the specific micro-opioid receptor antagonist CTOP. Destruction of knee joint unmyelinated afferent nerve fibers by capsaicin treatment significantly attenuated the anti-inflammatory effects of endomorphin-1, suggesting that the peptide is acting via a neurogenic mechanism. The findings of this study indicate that endomorphin-1 acts peripherally in knee joints to reduce synovial protein extravasation. These anti-inflammatory effects are mediated by micro-opioid receptors located on capsaicin-sensitive afferent nerves.

Electro-acupuncture stimulation to muscle afferents in anesthetized rats modulates the blood flow to the knee joint through autonomic reflexes and nitric oxide.

Recent reports have focused on the mechanisms of the action of electro-acupuncture stimulation (EAS) in the regulation of blood flow to different tissues. In the knee joint, blood flow is known to be modulated mainly by sympathetic postganglionic fibers, but recently the release or induction of nitric oxide (NO) synthesis in response to electrical stimulation has also been suggested. Therefore, a direct observation of the microcirculation is needed to further understand the mechanism by which blood flow is regulated by somatic afferent stimulation. In the present study, the effects of EAS to the vastus medialis muscle on systemic hemodynamics and the knee joint microcirculation were observed in vivo using a real-time confocal laser-scanning microscope system (CLMS). Electrical stimulation (5 mA, 0.5 ms, 5 Hz) was applied for 30 min using a pair of acupuncture needles introduced into the vastus medialis muscle. To clarify a plausible involvement of NO in the responses to EAS, the stimulus was applied either in the presence or absence of N(omega)-nitro-L-arginine methyl ester (L-NAME). Stimulation to either the muscle or the skin of the thigh after blockade of neuromuscular transmission was performed to determine the involvement of muscle contraction during EAS treatment. The changes in mean arterial pressure (MAP) and diameter of the arterioles supplying the knee joint were monitored continuously until 60 min poststimulus. Significant and persistent increases in arteriolar diameter by 26 +/- 6% and MAP by 17 +/- 2%, respectively, were observed after EAS to the muscle. Electro-acupuncture to the vastus medialis in the presence of L-NAME produced a strong decrease in diameter of the knee joint arterioles by -38 +/- 14% under the baseline with a simultaneous increase of 35 +/- 5% in MAP. EAS to the skin did not produce changes in arteriolar diameter while a slight increase in MAP by 12 +/- 6% over the baseline occurred after the stimulus. EAS to the muscle after neuromuscular blockade did not produce significant changes in diameter, while an increase in MAP by 24 +/- 8% was still observed, which facts suggest that the muscle contraction is required to produce vasodilatation. These responses suggest that a dynamic balance between the autonomic nervous system and the release of NO is the primary mechanism mediating the EAS effects on knee joint microcirculation.

[An experimental study on treatment of osteoarthritis with herbal compound capsule].

OBJECTIVE: To observe the effect of herbal compound capsule on knee arthritis. METHOD: Right knee arthritis model was established by knotting right femoral vein, so as to observe drug action. RESULTS: Compared with model group, herbal compound capsule could reduce intraosseous pressure, cardiac whole blood viscosity, plasma viscosity and concentration of nitric oxide, and inhibit degenerative changes of arthral cartilage. CONCLUSION: The herbal compound capsule can inhibit experimental osteoarthritis.

Tissue and intracellular pH in normal periarticular soft tissue and during different phases of antigen induced arthritis in the rat.

OBJECTIVE: To measure intracellular and tissue pH in periarticular soft tissue during different phases of antigen induced arthritis in the rat. METHODS: pH was calculated using the following values: (1) the distribution of [14C]-dimethyl-oxazolidinedione; (2) the total tissue water and the extracellular space water volume, which was measured as [14C]-sucrose distribution in nephrectomized rats. Experiments were performed during both maximal inflammation (Day 3) and the restorative phase (Day 14). RESULTS: In all animals both tissue (pHt) and intracellular (pHi) pH were lower in arthritic joints than in the contralateral control. Mean pHt in control joints was 7.37+/-0.03. In arthritic rats it was 7.30+/-0.05 on Day 3 after challenge and 7.27+/-0.03 on Day 14. The pHi ranges were 6.86-7.81 for controls, 6.65-7.28 for arthritis Day 3, and 5.66-6.91 for arthritis Day 14. CONCLUSION: In this model there is a reduction in pH in the periarticular tissue of arthritic joints. The magnitude is, however, relatively small and the pannus tissue is not uniquely acidic in comparison with other compartments. There does not seem to be a correlation between pH and changes in metabolic balance, pannus formation, or healing.

Microvascular architecture and exchange in synovial joints.

The microcirculation of the synovial lining of joints displays many fascinating adaptations to function. One primary function is to supply nutrients to the avascular cartilage, whose chondrocytes are metabolically active but are relatively vast distances from the nearest capillary (> 1 cm in the center of a human knee). Exchange is facilitated by a high density of fenestrated capillaries situated very close to the synovial surface (an arrangement disrupted in rheumatoid synovium) with fenestrations preferentially oriented toward the joint cavity. Even so, diffusion alone is too slow to supply central chondrocytes with glucose. The problem is solved by the synovial microcirculation generating intra-articular fluid (synovial fluid) that transports glucose by convection during joint movement. Synovial fluid is a plasma ultrafiltrate into which hyaluronan has been secreted, and it also serves to lubricate the joint. The joint cavity offers unusually easy access to the interstitial side of the microcirculation because the synovial cell layer is discontinuous, with an interstitial matrix between capillary and joint cavity. This allows the experimental study of the effect of the extravascular Starling "forces" (hydraulic and colloid osmotic pressure) on fluid exchange. One unexpected outcome has been the finding that a substantial part of the hydraulic resistance to fluid transport between blood and joint cavity resides in the series interstitial layer rather than in the capillary wall. Another is that, under appropriate boundary conditions (joint angle, etc.) fluid can simultaneously filter into the cavity in some regions (synovium directly overlying capillaries) and out of the cavity into subsynovium in other regions (synovium in the mesh space between capillaries) to produce a turnover of synovial fluid.

Effect of exercise on 99mTc-DTPA clearance from knees with effusions.

OBJECTIVE: To devise and use a method for assessing the effect of dynamic exercise on synovial blood flow in knees with effusions. METHODS: The clearance rate of intraarticular 99mTc-DTPA (diethylene triamine pentaacetic acid) was continuously monitored by a gamma camera during periods of rest or flexion. The rate of 99mTc-DTPA disappearance during a fixed period of exercise which was interposed between 2 rest periods was estimated by extrapolation between the clearance curves for the 2 rest periods. RESULTS: Cycling and walking increased the clearance rate, straight leg raising had no effect, and flexion decreased the clearance rate. CONCLUSION: Our results suggest that some dynamic exercises can increase the rate of synovial blood flow in joints with effusions. This outcome may be beneficial in inflamed joints which are chronically hypoxic due to elevated intraarticular pressure and consequent chronic synovial ischemia.