大运动量跑步对大鼠膝关节软骨蛋白多糖的影响

目的 观察平板跑步运动对大鼠关节软骨蛋白多糖的影响.方法 将Wistar大鼠10只随机分为对照组和跑步组.对照组笼养,跑步组每天以20m/min速度,连续跑步1000m,每天1次.连续训练45d后,处死大鼠,切取双膝关节,固定,脱钙,包埋,沿矢状面整体切片,苏木素-伊红(HE)及番红O染色.观察股骨内侧髁负重区和胫骨内侧平台负重区软骨形态结构和基质染色差异,利用图像分析系统,测量胫骨平台软骨厚度,并对软骨各层染色深浅进行吸光度定量.结果 对照组软骨结构正常,跑步组软骨表面完整,胫骨内侧平台负重区非钙化层厚度较对照组显著下降(P<0.05);番红O染色,负重区软骨非钙化层平均吸光度较对照组明显下降(P<0.05),其中表层下降66%(P<0.01),中层下降56%(P<0.01),深层与对照组差异无统计学意义(P>0.05),而钙化层吸光度较对照组上升38%(P<0.05).结论 大鼠连续平板运动45d后,膝关节负重区软骨虽然结构完整,但已经出现退行性改变.

Abstract：

Objective To study the influences of the strenuous running training program on the knee joint articular cartilage. Methods At the age of 16 weeks, 5 male Wistar rats started running on a horizontal treadmill. Thereafter, the rats were trained for 45 days continuously. The rats ran 1 km/day at the speed of 20 m/min. Five matched male rats served as controls. Knees of the rats were studied by whole-mounted section, Hematoxylin and Eosin (HE) stain, safranin O stain. Results The cartilage surfaces were intact after the running exercise. The glycosaminoglycan concentration was decreased by an average of 66% in the superficial zone, 56% on the middle zone, but no difference was found in the deep zone. The glycosaminoglycan concentration was increased by 38% in the calcified cartilage. Conclusion Strenuous running induced marked decrease of proteoglycan in the uncalcified cartilage, but induced no osteoarthritis in this rat strenuous running model.     

Proteoglycan alterations following immobilization and remobilization in the articular cartilage of young canine knee (stifle) joint

The distribution of proteoglycans (PGs) at 11 sites on the knee (stifle joint) cartilage of young female beagle dogs was studied following cast immobilization for 11 weeks in 90° flexion and after a subsequent remobilization for 15 weeks. Immobilization induced a reduction in PG uronic acid at all sites (mean of ?38%), but the greatest depletion ( ?64%) occured at the anterior and posterior extremes of the femoral condyles, i.e., at locations where the immobilized cartilage lost contact to the opposing cartilage. Following remobilization, the content of uronic acid remained lower than in the agematched controls (?18% on average), particularly at the minimum contact sites most affected by immobilization (?33%). The chondroitin-6-sulfate to chondroitin-4-sulfate ratio was reduced by immobilization in most locations (average of ?14%) and returned to control values after remobilization. There was no consistent change in the percentage of aggregating PGs observed in Sephacryl S-100 gel filtration after immobilization or remobilization. However, following remobilization, the aggregating PGs showed an enhanced proportion of the slower mobility band in agarose gel electrophoresis, indicative of a larger monomer size. In the contralateral, load-bearing knee joint, both the uronic acid content and PG monomer type distribution were identical to those observed in the experimental joint, suggesting that the state reached after the remobilization period was due to factor(s) influencing both side. The results suggest that contact forces between articulating surfaces are required to maintain normal PG content and that the control mechanism works locally at each cartilage site. Restriction of joint mobility and loading in young animals is concluded to cause persistent changes in cartilage matrix. Furthermore, the use of the contralateral joint as the sole control in this kind of studies, although experimentally convenient, seems not to be appropriate.     

High susceptibility of human articular cartilage glycosaminoglycan synthesis to changes in inorganic sulfate availability

The effect of sulfate concentration in the medium on glycosaminoglycan synthesis in articular cartilage of five different species was examined in relation to the physiological serum sulfate concentration in these species. Only the rate of sulfated glycosaminoglycan synthesis in human articular cartilage was sensitive to small deviations from the physiological sulfate concentration. A reduction in the sulfate concentration from 0.3 mM (physiological) to 0.2 mM resulted in a 33% reduction in glycosaminoglycan synthesis. In addition, we studied the effect of arthritic and "osteoarthritic" alterations in murine cartilage on the dependence of glycosaminoglycan synthesis on low sulfate concentrations. Arthritic and "osteoarthritic" cartilage had a similar dependence on the sulfate concentration in the medium as normal cartilage. Glycosaminoglycan synthesis in human articular cartilage appears to be very sensitive to the potential sulfate-depleting effects of drugs used in the treatment of rheumatoid arthritis and osteoarthritis.     

Partial restoration of immobilization-induced softening of canine articular cartilage after remobilization of the knee (stifle) joint

The restoration of the biomechanical properties of articular cartilage was studied after 15 weeks of remobilization of the knee joint in beagles previously immobilized with a cast for 11 weeks. The shear moduli were determined with an indentation creep test immediately after load application and at equilibrium at six predefined test points of femoral, tibial, and patellar cartilages. Permeability of the cartilage was estimated from the creep measurements. The values were compared with nontreated, age-matched (55 weeks) controls and with cartilage collected immediately after immobilization. Remobilization reduced the high creep rates created by immobilization and shifted the depressed equilibrium shear moduli towards those of the controls. However, in the femoral condylar cartilage, the equilibrium shear modulus remained at lower level (p < 0.05) and permeability at higher level (p < 0.05) as compared with the controls. We conclude that articular cartilage, showing signs of atrophy after long-term immobilization, was capable of restoring its biomechanical properties during remobilization. This repair was not, however, completed in all parts of the knee joint by the end of the observation period.     

MRI序列及三维重建在膝关节软骨损伤的诊断价值

目的观察脂肪抑制三维扰相梯度回波序列（FS-3D-SPGR）、FS-FSE-T2W序列及三维重建对软骨损伤的诊断价值。方法41个膝关节关节面共205个区域进入研究,MR检查至少包括FS-FSE-T2W、3D-FS-SPGR序列,对损伤进行分级。在工作站上采用HDMIP进行三维重建,其结果与关节镜对照。结果3D-FS-SPGR序列对软骨损伤显示的敏感度为89．47％,特异度为97．65％;FS-FSE-T2W序列的敏感度为78．57％,特异度为94．71％。结论3D-FS-SPGR能准确评价关节软骨的损伤程度,但对软骨下骨及骨髓损伤不敏感;FS-FSE-T2W能准确反应软骨下骨及骨髓损伤的程度及范围,二者结合是目前诊断软骨损伤的最佳扫描序列。关节软骨的三维重建图像能够较真实准确地显示软骨损伤的部位与范围。     

健康青年人的膝关节软骨厚度3.0T MRI的定量研究

目的:探讨3.0T MRI精确测量健康青年膝关节软骨厚度为骨关节炎的定量诊断和关节置换精准截骨提供可靠的解剖参数。方法:自2013年1月至2013年12月于吉林省长春地区招募30名健康青年志愿者,男14名,女16名,年龄22~33(25.8±2.4)岁。对每名志愿者的双膝关节进行3.0 T MRI扫描,对股骨外侧髁(lateralis femoris condylus,LFC)、股骨内侧髁(medialis femorisc ondylus,MFC)、胫骨外侧平台(lateral tibial plateau,LTP)、胫骨内侧平台(medial tibial plateau,MTP)进行软骨厚度测量。结果:在LFC、MFC、LTP、MTP 4个区域中,无论青年男性或女性,左、右侧膝关节软骨厚度比较,差异均无统计学意义(P>0.05);健康青年男性与女性之间膝关节软骨厚度比较,差异有统计学意义(P<0.05)。在同一性别组,LFC软骨厚度中间较薄,前、后方较厚;MFC软骨厚度前方最薄,从前方向后方逐渐增厚;LTP软骨厚度中间最厚,后方次之,前方最薄;MTP软骨厚度前方最薄,中间、后方相对均匀且均较前方厚。结论:在我国22~33岁正常健康青年人中,性别差异可能是膝关节各个区域软骨厚度差异的重要因素。无论男性或女性健康青年人,整个膝关节软骨厚度分布不均匀,但左、右侧膝关节相同区域软骨厚度无明显差异。     

磁共振技术评估膝关节软骨退变研究进展

磁共振成像(magnetic resonance imaging,MRI)扫描序列及参数的合理选择对清晰成像及临床研究结果的客观评价至关重要。全膝关节磁共振成像积分,波士顿利兹骨关节炎评分系统,MRI膝骨关节炎评分系统,膝骨关节炎软骨修复评分系统等全膝关节的半定量评分系统都能够全面评价膝骨关节炎进展时各组织的影像学改变。随着MRI技术的不断发展,关节软骨的形态学及生理成分的改变可以被定量评估。T2图、弥散加权成像、延迟动态增强成像等软骨成分的定量评估技术能定量监测软骨基质成分的变化,可以在关节软骨形态学破坏之前更早地发现软骨病变。这些定量、半定量评价技术有助于膝骨关节炎的早期诊断和早期预防,同时也为精确评价干预措施的疗效提供了可能。     

Microinjury to the synovial membrane may cause disaggregation of proteoglycans in rabbit knee joint articular cartilage

Proteoglycans (PGs) isolated from articular cartilage (AC) of mature rabbits subjected to two or more consecutive intraarticular (IA) injections of sterile saline 24 h apart showed an aggregation defect in the presence of excess hyaluronic acid (HA). Although the PG contents of experimental and control cartilages were indistinguishable, a higher proportion of PGs were extractable from the 3 X IA tissues, as assessed by uronic acid analysis. Proteoglycans from experimental and control cartilages when examined by Sepharose CL-2B chromatography showed two subunit populations, the smaller (KAV = 0.70) containing more ketatan sulphate than the larger (KAV = 0.31). Cultures of AC from IA joints released more 35SO4-labelled PGs into the media over 72 h than control tissues and consisted mainly of PG degradation products although 20% could aggregate in the presence of HA. Examination of PG aggregation 2 weeks after 2 X IA or 3 X IA injections showed that the defect initiated was still present; however, cartilage of immature rabbits was not affected by the 2 X IA procedure.     

Site-specific immunostaining for type X collagen in noncalcified articular cartilage of canine stifle knee joint

Type X collagen is a short-chain collagen that is strongly expressed in hypertrophic chondrocytes. In this study, we used an immunohistochemical technique exploiting a prolonged hyaluronidase unmasking of type X collagen epitopes to show that type X collagen is not restricted to calcified cartilage, but is also present in normal canine noncalcified articular cartilage. A 30° valgus angulation procedure of the right tibia was performed in 15 dogs at the age of 3 months, whereas their nonoperated sister dogs served as controls. Samples were collected 7 and 18 months after the surgery and immunostained for type X collagen. The deposition of type X collagen increased during maturation from age 43 weeks to 91 weeks. In the patella, most of the noncalcified cartilage stained for type X collagen, whereas, in the patellar surface of the femur, it was present mainly in the femoral groove close to cartilage surface. In femoral condyles, the staining localized mostly in the superficial cartilage on the lateral and medial sides, but not in the central weight-bearing area. In tibial condyles, type X collagen was often observed close to the cartilage surface in medial parts of the condyles, although staining could also be seen in the deep zone of the cartilage. Staining for type X collagen appeared strongest at sites where the birefringence of polarized light was lowest, suggesting a colocalization of type X collagen with the collagen fibril arcades in the intermediate zone. No significant difference in type X collagen immunostaining was observed in lesion-free articular cartilage between controls and dogs that underwent a 30° valgus osteotomy. In osteoarthritic lesions, however, there was strong immunostaining for both type X collagen and collagenase-induced collagen cleavage products. The presence of type X collagen in the transitional zone of cartilage in the patella, femoropatellar groove, and in tibial cartilage uncovered by menisci suggests that it may involve a modification of collagen fibril arrangement at the site of collagen fibril arcades, perhaps providing additional support to the collagen network.     

Surgical technique for articular cartilage transplantation to full-thickness cartilage defects in the knee joint

Focal arthritic defects in the knee lead to pain, swelling, and dysfunction. Treatment of the defects has includeddrilling, abrasion, and grafting. This report describes our surgical technique of autogenous articular cartilage grafting of arthritic and traumatic articular cartilage lesions. Articular cartilage grafting can be performed as a single arthroscopic outpatient procedure. The mixture of articular cartilage and cancellous bone appears to provide a supportive matrix for cartilage formation. Pain relief is excellent if careful surgical technique and a defined rehabilitation program is followed. Further collagen typing data and additional biopsies will reveal more about the durability of the newly formed cartilage.     

Effects of immobilization on thickness of superficial zone of articular cartilage of patella in rats

Background:

Articular cartilage normally functions as a load-bearing resistant material in joints. Patella is composed of hyaline cartilage and spongy bone. Chondrocytes form only 1–5% volume of the articular cartilage. They receive their nutrition by diffusion through the matrix. The alteration in articular cartilage become apparent following immobilization, from 4 to 6 weeks. Until now, focus of research has been the whole cartilage. Zonal changes have not been studied in detail. Since superficial zone bears maximum load and is the first zone to come in contact, the present study was designed to determine changes in thickness on immobilization and remobilization in superficial zone after dividing it into proximal, central, and distal segments.

Materials and Methods:

Forty male rats belonging to Sprague Dawley strain were divided into two groups. Group 1 (n=20) subdivided into an experimental subgroup of 10 rats that were immobilized in plaster of Paris (POP) for 4 weeks and a control subgroup of 10 that were not immobilized. Group 2 (n=20) subdivided into an experimental subgroup of 10 rats that were immobilized for 4 weeks and remobilized for next 4 weeks and a control subgroup of 10 animals that were not immobilized. At the end of the experimental period, the knee joint was dissected and was cut in sagittal plane. The section was fixed in 10% formalin for 48 hours. Specimen was decalcified using ethylenediaminetetraacetic acid (EDTA). The paraffin blocks of 7 μm sections were cut and stained by H and E stain for routine histology and Alcian blue stain and Mallory Trichrome for fine structural microscopy. The zones were named as superficial transitional, radial, and hypertrophic according to the shape of cells present in each zone. The superficial zone was divided into superior part, central, and inferior parts. These parts were labeled as central, proximal, and distal segments. The calibrated stage micrometer was used to calibrate the ocular micrometer under objectives of different power. The ocular micrometer was placed inside the ocular lens. It was calibrated with the stage micrometer under objective lenses of different power. The number of divisions of ocular covering each zone was calculated. These divisions were converted into micrometer and the actual thickness was calculated.

Results:

The significant decrease in thickness of superficial zone in proximal, central and distal segment was observed in experimental group in comparison to control group. When the experimental subgroup of group 2 was compared with experimental subgroup of group 1 (group immobilized for 4 weeks), no significant reversal was seen in superficial zone and instead significant decrease was observed in distal segment. Fibrous connective tissue was increased adjacent to superficial zone.

Conclusion:

Each segment of superficial zone behaves differentially on immobilization and remobilization. Perhaps a much longer duration of remobilization is required to reverse changes of immobilization in articular cartilage and plays a significant role in knee joint movements.     

Material properties and biosynthetic activity of articular cartilage from the bovine carpo-metacarpal joint

OBJECTIVE: To determine the site variation of material properties and cellular biosynthetic activity, and to compare these at each site, of articular cartilage from the bovine carpo-metacarpal joint in order to test its usefulness as a model system for investigating the metabolic effects of mechanical stimuli. DESIGN: The mechanical properties and composition of full-depth biopsies of articular cartilage were measured at defined sites in bovine carpometacarpal joints. Metabolic activity at the same sites was assessed by incubating further biopsies in medium containing 35S-sulfate and 3H-leucine then measuring the incorporated radioisotope and cell density. These results were compared with an estimate of the distribution of forces across the joint. RESULTS: Topographical variation of water content, stiffness, cell count or incorporated radioisotope was not significant whereas collagen and glycosaminoglycan varied in different ways. A moderate correlation was found between water and collagen contents, but the correlation between water and glycosaminoglycan contents was poor. Neither compressive stiffness nor creep compliance was predicted strongly by any of the composition measurements. A negative correlation was found between metabolic activity and cell density. CONCLUSIONS: Defining the variation of tissue properties across the bovine carpometacarpal joint and the lack of variation in biosynthetic activity will enable proper matching of experimental and control groups of biopsies in studies of the effects of mechanical stimuli on the composition and mechanical properties of articular cartilage. In addition, the lack of correlation between stiffness, water and glycosaminoglycan contents is further evidence that the mechanical properties of the tissue depend significantly on factors other than these broad measures of composition.     

A review of the differences between normal and osteoarthritis articular cartilage in human knee and ankle joints

BackgroundOsteoarthritis (OA) is the most common joint disease yet its pathophysiology is still poorly understood. It is more prevalent in some lower limb joints than others; in particular the knee is more commonly affected than the ankle. Research into articular cartilage and OA has primarily focussed on using animal models. However, it is apparent that articular cartilage differs between species, so more research is concentrating on human cartilage.ObjectiveThis paper reviews recent studies that have been undertaken to elucidate the reasons for this, and to discover if the findings would alter the conception that articular cartilage is not capable of repair.MethodPrimary research papers into human knee and ankle cartilage published since 1997 have been reviewed.ResultsDifferences in the structure, metabolism, physical properties and response to trauma have been found, implying that ankle cartilage may be more resistant to damage.ConclusionsMore research is needed before definitive conclusions can be reached, but the findings so far suggest that OA should not be accepted as the inevitable outcome of joint injury and individuals and practitioners, such as podiatrists, may be able to use simple measures to prevent or delay its onset.     

关节内注射富血小板血浆对膝关节软骨退行性变的治疗作用

目的富血小板血浆(platelet-rich plasma,PRP)能促进软骨细胞增殖和修复软骨缺损,通过比较膝关节退行性变患者关节内注射PRP及透明质酸钠的疗效,分析PRP治疗关节软骨退行性变的安全性和可行性。方法于2010年1月-6月收治的膝关节软骨退行性变患者中,选择符合标准的30例30膝患者纳入研究。根据注射药物不同,将患者随机分为PRP组(试验组)和透明质酸钠组(对照组),每组各15例。两组患者性别、年龄、体重指数、Kellgren-Lawrence分级等一般资料比较,差异均无统计学意义(P>0.05),具有可比性。试验组患者抽取自体静脉血制备PRP后,于关节腔内均匀注射3.5 mL PRP;对照组注射2 mL透明质酸钠。每3周注射1次,3次为一疗程。记录两组患者注射后不良反应发生情况,并采用国际膝关节文献委员会(IKDC)评分、美国西部Ontario与McMaster大学骨关节炎指数(WOMAC)评分及Lequesne指数评定关节功能。结果两组患者均获随访6个月。两组治疗后IKDC评分、WOMAC评分及Lequesne指数与治疗前比较,差异均有统计学意义(P<0.05);试验组治疗后3、4、6个月间比较,差异均无统计学意义(P>0.05);对照组治疗后6个月各评价指标较3、4个月差,但差异有统计学意义(P<0.05)。治疗后3个月及4个月,两组IKDC评分、WOMAC评分及Lequesne指数比较,差异无统计学意义(P>0.05);6个月时,试验组各指标均优于对照组(P<0.05)。试验组患者12例31次出现不良反应,对照组12例30次;两组不良反应起始时间、终止时间及持续时间比较,差异均无统计学意义(P>0.05)。结论关节内注射PRP治疗关节软骨退行性变安全,可缓解疼痛、肿胀等症状,提高患者生活质量,但需要大样本长期随访观察进一步验证其安全性和远期疗效。     

How to diagnose isolated articular cartilage lesions of the knee in a consulting room

Abstract In order to clinically diagnose articular cartilage lesions of the knee in a medical examination, 121 knees (117 cases) with isolated lesions were investigated. Lesions of the patella (PAT), facies patellaris (F-PAT), lateral femoral condyle (LFC), lateral tibial plateau (LTP), medial femoral condyle (MFC), and medial tibial plateau (MTP) were found in 15, 10, 9, 57, 24, and 6 knees, respectively. The lesions often occurred in athletes, but many cases with lesions did not have a history of trauma. Giving way, pain in maximal flexion, pain after exercise, and pseudolocking were relatively common symptoms. Atrophy of the thigh on the involved side was not severe. Mild limitations in both extension and flexion were often found. Hydrarthrosis was frequent in cases with F-PAT, LFC, and MFC lesions. Valgus alignment was found in LTP lesions, while varus alignment was found in MFC and MTP lesions. Findings of fibrillation in PAT, flaps, deep defects, and softening in F-PAT and MFC, deep defects in LFC, and softening and fissuring in LTP were often seen during arthroscopy. Cartilage lesions such as softening were also thought to be related to the symptoms. Increases in joint fluid may suggest lesions in F-PAT, LFC or MFC where deep and wide lesions often occur. Cases with valgus alignment may have LTP lesions and those with varus alignment may have MFC or MTP lesions.     

Biological reconstruction of the joint: Concepts of articular cartilage regeneration and their scientific basis

Articular cartilage injuries are common. The diagnosis of these injuries is often delayed and may lead to early osteoarthritis. Treatment depends on many factors but mainly on the stage and size of the lesion. The anatomy of articular cartilage is complex, and it is an avascular, aneural, and alymphatic structure. Recently, more emphasis is laid on its anatomy and biomechanics to understand the regeneration process of articular cartilage.     

组织工程化软骨修复兔膝关节软骨缺损的实验研究

目的 评估同种异体组织工程软骨修复兔膝关节全层软骨缺损的有效性。方法分离收集成年新西兰大白兔软骨细胞进行体外培养。建立双侧兔膝关节软骨缺损模型，用去端肽胶原（atelocollagen）凝胶与所培养的异体兔关节软骨细胞共同植入兔膝关节软骨缺损处，并设对照组。分别于手术后4周、8周观察大体标本以及组织学修复结果，并进行Wakitan的评分，评估此方法的有效性。结果大体观察结果表明，与对照组相比，实验组缺损处由软骨组织修复而对照组缺损处由纤维样组织填充。组织学观察可以见到实验组关节软骨缺损处有密集的软骨细胞而对照组关节缺损处只有纤维细胞无软骨细胞。结论通过短期观察表明以同种异体软骨细胞-去端肽胶原复合物修复全层软骨缺损的方法是有效可行的，为其进一步临床应用提供了参考。     

Fine structural changes in the articular cartilage of the rat's knee following short-term immobilisation in various positions:

Summary The knee joints of 36 rats were immobilised in a padded plaster cast (18 in the flexed and 18 in the extended position) for 1, 2 and 3 weeks. The femoral articular cartilage was then examined under the scanning electron microscope.After 1 week's immobilisation in the flexed position, the surface layer of the cartilage showed disruption and the superficial chondrocytes were necrotic. The sites of the necrotic chondrocytes were seen as pits on the cartilage surface. In the animals whose knees were immobilised in the extended position, the changes were not so great in severity or extent. After 2 weeks, more advanced changes could be detected in both groups, but they were more severe in the flexed group.After 3 weeks the changes in articular cartilage were diffuse in the flexed, but focal in the extended group. Diffuse necrosis of chondrocytes, with pit formation on the surface and disruption and disintegration of the collagen fibres, was seen to some extent in all the animals. In the flexed group the changes extended to the whole weightbearing surface of the articular cartilage of the femur, except the intercondylar sulcus. In the extended group, a superficial fibre network was found without the formation of closely packed collagen fibre bundles, and the changes in the chondrocytes were seen only in localised zones.The authors suggest that during immobilisation, especially in the flexed position, articular hypoxia occurs due to a decreased amount of synovial fluid, the increased compression of the cartilage surfaces and the increased intra-articular pressure. This causes degeneration and necrosis of the superficial chondrocytes and the superficial cartilage layer.

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Résumé Les articulations du genou de 36 rats ont été immobilisées dans des plâtres matelassés (18 en flexion et 18 en extension) pendant 1,2 et 3 semaines. Le cartilage fémoral a été ensuite examiné au microscope à balayage électronique.Après une semaine d'immobilisation en flexion, la couche superficielle du cartilage présente des fissurations et les chondrocytes à ce niveau sont nécrosés. Ces zones de nécrose forment des trous sur la surface articulaire. Chez les animaux dont les genoux ont été immobilisés en extension, les altérations sont moins importantes et moins étendues. Après 2 semaines on peut observer des modifications plus marquées, mais elles le sont davantage dans le groupe immobilisé en flexion.Après 3 semaines les lésions cartilagineuses sont diffuses en cas de flexion, localisées en cas d'extension. Il existe chez tous les animaux, sur une certaine étendue, une nécrose diffuse des chondrocytes, avec des trous dans la surface articulaire ainsi que des ruptures et des dislocations des fibres collagènes. Dans le groupe en flexion les altérations atteignent la totalité de la zone portante de la surface articulaire du fémur, à l'exception de l'échancrure intercondylienne. Dans le groupe en extension on trouve un réseau de fibres superficielles sans formation de faisceaux de fibres collagènes étroitement serrées, et les modifications portant sur les chondrocytes ne sont trouvées qu'en des zones localisées. Les auteurs pensent que durant l'immobilisation, notamment en flexion, il se produit une hypoxie articulaire due à la diminution de volume du liquide synovial, à l'augmentation de compression des surfaces cartilagineuses et de la pression intra-articulaire. Ceci entraîne la dégénescence et la nécrose des chondrocytes et des couches superficielles du cartilage.