Epidemiology and imaging of the subchondral bone in articular cartilage repair

Articular cartilage and the subchondral bone act as a functional unit. Following trauma, osteochondritis dissecans, osteonecrosis or osteoarthritis, this intimate connection may become disrupted. Osteochondral defects—the type of defects that extend into the subchondral bone—account for about 5% of all articular cartilage lesions. They are very often caused by trauma, in about one-third of the cases by osteoarthritis and rarely by osteochondritis dissecans. Osteochondral defects are predominantly located on the medial femoral condyle and also on the patella. Frequently, they are associated with lesions of the menisci or the anterior cruciate ligament. Because of the close relationship between the articular cartilage and the subchondral bone, imaging of cartilage defects or cartilage repair should also focus on the subchondral bone. Magnetic resonance imaging is currently considered to be the key modality for the evaluation of cartilage and underlying subchondral bone. However, the choice of imaging technique also depends on the nature of the disease that caused the subchondral bone lesion. For example, radiography is still the golden standard for imaging features of osteoarthritis. Bone scintigraphy is one of the most valuable techniques for early diagnosis of spontaneous osteonecrosis about the knee. A CT scan is a useful technique to rule out a possible depression of the subchondral bone plate, whereas a CT arthrography is highly accurate to evaluate the stability of the osteochondral fragment in osteochondritis dissecans. Particularly for the problem of subchondral bone lesions, image evaluation methods need to be refined for adequate and reproducible analysis. This article highlights recent studies on the epidemiology and imaging of the subchondral bone, with an emphasis on magnetic resonance imaging.     

The basic science of the subchondral bone

In the past decades, considerable efforts have been made to propose experimental and clinical treatments for articular cartilage defects. Yet, the problem of cartilage defects extending deep in the underlying subchondral bone has not received adequate attention. A profound understanding of the basic anatomic aspects of this particular site, together with the pathophysiology of diseases affecting the subchondral bone is the key to develop targeted and effective therapeutic strategies to treat osteochondral defects. The subchondral bone consists of the subchondral bone plate and the subarticular spongiosa. It is separated by the cement line from the calcified zone of the articular cartilage. A variable anatomy is characteristic for the subchondral region, reflected in differences in thickness, density, and composition of the subchondral bone plate, contour of the tidemark and cement line, and the number and types of channels penetrating into the calcified cartilage. This review aims at providing insights into the anatomy, morphology, and pathology of the subchondral bone. Individual diseases affecting the subchondral bone, such as traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis are also discussed. A better knowledge of the basic science of the subchondral region, together with additional investigations in animal models and patients may translate into improved therapies for articular cartilage defects that arise from or extend into the subchondral bone.     

MR imaging of the knee. Part II. Chronic disorders

Sixty patients with symptoms of chronic disease of the knee joint were evaluated with high-resolution, thin-section magnetic resonance (MR) imaging. MR imaging depicted a wide variety of knee joint abnormalities including osteochondritis dissecans, medullary infarcts, epiphyseal osteonecrosis, intraarticular osteochondral fragments, synovial cysts, joint effusions, intraarticular soft-tissue tumors, synovial disease, leukemic infiltration of bone marrow, Osgood-Schlatter disease, and nonossifying fibroma. In two cases MR imaging depicted bone infarcts not seen on both radionuclide bone scans and standard radiographs. The highly detailed depiction of the articular cartilage was of particular importance in predicting arthroscopic findings in cases of osteochondritis dissecans. In two cases, a soft-tissue mass (pigmented villonodular synovitis) and a large osteochondral fragment undetected at arthroscopy were accurately localized with MR imaging. The results indicate that MR imaging is capable of providing information that might otherwise require multiple, sometimes invasive diagnostic procedures.     

Direct coronal computed tomography arthrography of osteochondritis dissecans of the talus

Although radiographs, arthrography, tomography, and computed tomography can all be used to diagnose osteochondritis dissecans of the talus, these imaging methods may not demonstrate whether an undisplaced osteochondral fragment has any attachment to the articular cartilage or bony bed of the talus. As lack of such attachment is a relative indication for surgery, we studied the feasibility of using coronal computed tomography (CT) after double contrast arthrography to demonstrate attachment in four patients with osteochondritis dissecans seen on radiographs. Direct coronal CT arthrographic images showed intact articular cartilage in three patients. In the fourth patient, overlying cartilage was virtually absent and contrast tracked beneath the fragment, an appearance that correlated with arthroscopic findings of partial articular cartilage attachment and no union at the osteochondral fracture line. Our initial experience suggests that direct coronal CT arthrography clearly shows the state of attachment of the osteochondritic fragment to the talus.     

Subchondral bone and cartilage disease: a rediscovered functional unit

The role of subchondral bone in the pathogenesis of cartilage damage has likely been underestimated. Subchondral bone is not only an important shock absorber, but it may also be important for cartilage metabolism. Contrary to many drawings and published reports, the subchondral region is highly vascularized and vulnerable. Its terminal vessels have, in part, direct contact with the deepest hyaline cartilage layer. The perfusion of these vessels accounts for more than 50% of the glucose, oxygen, and water requirements of cartilage. Bony structure, local metabolism, hemodynamics, and vascularization of the subchondral region differ within a single joint and from one joint to another. Owing to these differences, repetitive, chronic overloading or perfusion abnormalities may result in no pathological reaction at all in one joint, while in another joint, these same conditions may lead to osteonecrosis, osteochondritis dissecans, or degenerative changes. According to this common etiological root, similar pathological reactions beginning with marrow edema and necrosis and followed by bone and cartilage fractures, joint deformity, and insufficient healing processes are found in osteonecrosis, osteochondritis dissecans, and degenerative disease as well.     

Radiological and pathological manifestations of osteochondritis dissecans of the distal femur. A study of 50 cases

The specimens from 50 operated cases of osteochondritis dissecans of the distal femur were analyzed histopathologically. Radiodensity of the specimens of osteochondritis dissecans was due (a) attached subchondral bone, (b) degenerative secondary calcification of articular cartilage, (c) revascularization with new bone, and, in the free bodies, (d) calcification in new surface layers of cartilage and bone. The pathological findings in the specimens suggested an etiology from trauma rather than avascular necrosis. Half of the specimens of osteochondritis dissecans contained no subchondral bone but only articular cartilage. It was postulated that the relationship of the attached lesions to the intercondylar notch of the femur, which permitted a partially retained blood supply, created a spectrum of different histopathological changes in the subchondral bone of those specimens with attached bone.     

Radiographic evaluation of joints resurfaced with osteochondral shell allografts

The radiographic features of 41 cadaveric osteochondral shell (low ratio of subchondral bone to articular cartilage) allografts placed in 24 patients for articular resurfacing as an alternative to arthroplasty are presented. Underlying causes of joint disease included ischemic necrosis (20 grafts), osteochondritis dissecans (nine), chondromalacia patellae (10), and posttraumatic osteochondral fracture with degenerative disease (two). Congruity with the adjacent native articular surface and the opposite side of the joint was evident on immediate postoperative radiographs in all patients, and proved to be critical to the ultimate success of the procedure. On follow-up radiographs over a period of 2-28 months, successful incorporation of the allograft was characterized by progressive loss of the relative increased density of the graft, in association with diminished lucency related to new bone formation at the graft-native bone interface, as well as maintained alignment. Graft failure was associated with positional changes including collapse, persistent increased density, and poorly defined fragmentation that occasionally simulated infection radiographically and resulted in intraarticular bodies. Resurfacing of diseased articulations with osteochondral shell allografts constitutes a potentially desirable alternative to total joint arthroplasty, particularly among younger patients. Consequently, an awareness of the expected radiographic alterations associated with graft incorporation and failure is important.     

Ultrasonography of osteochondritis dissecans of the knee. A preliminary report

Twenty-five radiographically proven cases of osteochondritis dissecans of the femoral condyles were examined by real-time sonography using a 5 MHz linear transducer. The medial condyle was involved in 19 cases and the lateral in 6. The size of the lesions varied from a few mm to more than 30 mm in diameter. The fragmentation of the subchondral bone was demonstrated in all cases, and furthermore the osteochondral fragment and the condition of the overlying articular cartilage could be assessed. The exact indications for the technique have not yet been defined, but awaits further clinical studies.     

MR imaging of the shoulder: correlation with plain radiography

Osteochondritis dissecans is a lesion of articular surfaces that is of uncertain etiology. These lesions are seen on radiographs as a bony defect or fragmentation of the subchondral bone. A bony defect may be an actual surface hole or the defect may be filled with fibrous tissue or fibrocartilage. Similarly, the apparent bone fragments may be only partially attached so they are unstable and prone to displacement or they may be firmly attached with fibrous tissue. Knowledge of fragment stability and the presence of an articular cartilage defect is useful in deciding on treatment. This information cannot be determined on plain films or clinical examination. We correlated MR examinations with arthroscopic findings in 21 patients with osteochondritis dissecans of the knee to see if MR imaging could be used to predict lesion stability and articular cartilage defects. A high-signal interface between the lesion and the femur was used as evidence of lesion instability and was found in 15 lesions. One of these lesions was questionably stable at surgery; the remainder were unstable and partially attached. The other six patients had displaced fragments with large articular defects that were clearly visualized on the MR examinations. We conclude that MR imaging is useful in evaluating articular surface defects and lesion stability in patients with osteochondritis dissecans.     

Magnetic resonance imaging ofarticular cartilage injuries of the knee

Magnetic resonance imaging (MRI) is a widely available, powerful imaging modality in the United States that has rapidly become a mainstay for evaluation of the musculoskeletal system, largely because of its unparalleled depiction of most osseous and soft-tissue pathology. The application of MRI to detect cartilage injuries has evolved to the point where it is possible to noninvasively diagnose cartilage lesions that previously required an invasive examination, eg, arthrography or arthroscopy. However, successful cartilage imaging requires knowledge of the unique technical considerations and limitations of MRI. In this chapter we review current state-of-the-art knee MRI for three groups of chondral disorders: acute osteochondral fractures, osteochondritis dissecans, and degenerative lesions. The role of MRI in osteochondral fractures includes the demonstration of purely chondral intra-articular fragments and the identification of associated injuries, especially previously unrecognized subchondral bruises. MRI may also play a role in surveillance for osteochondral sequelae after injury. For osteochondritis dissecans, MRI can provide evidence supporting the diagnosis of a loose fragment and may aid in the evaluation of cartilage overlying osteochondral defects. Current MRI techniques can show moderate and severe lesions of chondromalacia and chondrosis. Newer techniques show potential for diagnosing these degenerative conditions at earlier stages when the changes are mild. We review these issues and provide examples showing the MRI appearance of common articular injuries.     

Osteochondral autograft transplantation for osteochondritis dissecans of the elbow in juvenile baseball players: minimum 2-year follow-up

BACKGROUND: Osteochondral autografts have recently become popular to treat articular cartilage defects, and they are used for unstable osteochondritis dissecans lesions as a means of biological fixation. PURPOSE: To evaluate the clinical results of osteochondral autograft transfer for osteochondritis dissecans of the elbow. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Osteochondral autograft transfer was performed on 18 baseball players (mean age, 13.6 years) with osteochondritis dissecans of the elbow. These included 9 lesions that were grade 3 (separated but in situ) and 9 lesions that were grade 4 (displaced fragment with osteochondral defect) based on magnetic resonance imaging. All patients were evaluated with a scoring system, radiographs, and magnetic resonance imaging, with the mean follow-up at 3.5 years. RESULTS: In patients with grade 3 lesions, the subjective score was increased, but the objective score did not change. Six of 9 patients returned to their previous sports performance levels. One quit baseball because of academic reasons, 1 changed his position, and 1 changed to softball. In patients with grade 4 lesions, both subjective and objective scores were increased significantly. All but 1 patient returned to their previous sports performance levels. In the 3 grade 4 lesions with a wide osteochondral defect, the irregularity of the articular surface remained on magnetic resonance imaging. CONCLUSION: Osteochondral autograft transplantation is a useful treatment for reattachment of the lesion as well as osteochondral resurfacing of elbow osteochondritis dissecans.     

Cartilage and bone morphology in osteochondritis dissecans

Osteochondritis dissecans (OD) is a syndrome that can be characterized as a non-infectious disturbance of enchondral ossification or as a post-traumatic event. OD occurs in the joint cartilage and physis of long bones, as well as in the talus or metacarpal head especially of young athletes. The medial femoral condyle is the most commonly affected site. The causes of osteochondritis dissecans are poorly understood. Thirty human osteochondral cylinders from patients (aged 16–44 years) with osteochondritis dissecans of the medial femoral condyle (grades IV and V according to Rodegerdts and Gleissner) were harvested intraoperatively from osteochondritic areas as part of a cartilage-bone transplantation. Light microscopy, electron microscopy, and immunohistochemistry using poly- and monoclonal antibodies against collagens and glycosaminoglycans revealed differences between osteochondrotic and normal cartilage. Staining with toluidine blue at pH 1 shows a decrease in acidic glycosaminoglycans in OD. Modified pentachrome staining showed a thinned subchondral growth plate compared to normal osteochondral samples. Borders to the healthy tissue are clearly visible micro- and macroscopically. Scanning electron microscopy revealed structural differences in the subchondral area. Immunohistochemistry found a general decrease in glycosaminoglycan content and a change in composition. Only faint staining for chondroitin and keratan sulfates was observed in osteochondritic cartilage, whereas increased staining was shown for keratan sulfate in bone. Received: 25 August 1996 Accepted: 31 October 1996     

Autologous osteochondral mosaicplasty for capitellar osteochondritis dissecans in teenaged patients

BACKGROUND: Autologous osteochondral mosaicplasty is a new technique to provide hyaline repair for articular defects. Although recent studies have reported the successful treatment of articular defects in the knee and ankle joints with this surgical procedure, little attention has been given to the surgical efficacy of mosaicplasty in the treatment of osteochondritis dissecans of the humeral capitellum. PURPOSE: To clarify the clinical outcomes of mosaicplasty for teenaged patients with advanced lesions of capitellar osteochondritis dissecans. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Eight teenaged patients with advanced lesions of capitellar osteochondritis dissecans underwent mosaicplasties. All patients were baseball players who were affected on the right side, which was also their throwing side. The surgical technique involves obtaining small-sized cylindrical osteochondral grafts from the lateral periphery of the femoral condyles and transplanting them to prepared osteochondral defects. At a mean follow-up of 24 months, all patients were evaluated clinically and radiographically. RESULTS: Seven of the 8 patients were free from elbow pain, and the remaining patient had mild pain occasionally. The mean clinical score described by Timmerman and Andrews (a maximum of 200 points) significantly improved from 140 points to 183 points postoperatively. All patients except one had excellent or good clinical results. Radiographically, the graft incorporation and a normal contour of the subchondral cortex were found in all patients. Magnetic resonance imaging showed that the preoperative heterogeneity of the lesion had disappeared and the signal intensity returned to normal. Six of the 8 patients, including all 3 pitchers, returned to competitive-level baseball. CONCLUSION: Mosaicplasty for advanced lesions of capitellar osteochondritis dissecans in teenaged baseball players can provide satisfactory clinical and radiographic results.     

Arthroscopic fixation of osteochondritis dissecans of the knee: clinical, magnetic resonance imaging, and arthroscopic follow-up

BACKGROUND: Optimal treatment of osteochondritis dissecans of the knee is still controversial. PURPOSE: To review a group of patients with osteochondritis dissecans of the knee who were treated with arthroscopic compressive screw fixation and who were evaluated with magnetic resonance imaging studies and a second-look arthroscopic procedure at follow-up. STUDY DESIGN: Case series; level of evidence, 4. METHODS: A total of 14 patients (15 knees) with osteochondritis dissecans of the knee were treated with arthroscopic titanium Herbert screw fixation of the osteochondral fragment. A second-look arthroscopic procedure was performed to remove hardware and to evaluate fragment stability. At final follow-up, magnetic resonance imaging studies were used to evaluate potential healing of the subchondral bone. Outcomes were clinically evaluated at a mean follow-up of 50 months (range, 25-104 months) by the Lysholm score and by the International Knee Documentation Committee score. RESULTS: At second-look arthroscopy, 14 of 15 knees showed evidence of a stable fragment with an intact smooth surface. According to magnetic resonance imaging parameters, 14 knees showed evidence of a healing process of the osteochondral fragment. The average Lysholm score improved 18 points from a mean of 79 preoperatively to 97 postoperatively, and according to the International Knee Documentation Committee score, 13 of 15 knees showed a normal result. CONCLUSION: This study suggests that magnetic resonance imaging parameters of a healed osteochondral fragment and patients with satisfactory functional results correspond with arthroscopic evidence of fragment stability. According to this study, arthroscopic fixation with compressive screws is an effective method of repair for osteochondritis dissecans of the knee.     

The subchondral bone in articular cartilage repair: current problems in the surgical management

As the understanding of interactions between articular cartilage and subchondral bone continues to evolve, increased attention is being directed at treatment options for the entire osteochondral unit, rather than focusing on the articular surface only. It is becoming apparent that without support from an intact subchondral bed, any treatment of the surface chondral lesion is likely to fail. This article reviews issues affecting the entire osteochondral unit, such as subchondral changes after marrow-stimulation techniques and meniscectomy or large osteochondral defects created by prosthetic resurfacing techniques. Also discussed are surgical techniques designed to address these issues, including the use of osteochondral allografts, autologous bone grafting, next generation cell-based implants, as well as strategies after failed subchondral repair and problems specific to the ankle joint. Lastly, since this area remains in constant evolution, the requirements for prospective studies needed to evaluate these emerging technologies will be reviewed.     

兔运动对骨软骨骨折转归的影响:MRI表现与MMP-13表达

目的：观察实验兔运动对骨软骨骨折转归影响及骨片覆盖软骨MMP-13表达,探讨骨软骨骨折与剥脱性骨软骨炎的关系。方法：随机选用30只月龄及体重相近的健康新西兰大白兔,雌雄不限;试验组20只建立兔膝股骨髁骨软骨骨折模型,假手术对照组10只,所有模型均不进行内固定及外固定。术后即进行术侧膝关节间歇主动活动（IAM）与间歇被动活动（IPM）;术后1、2周分别从试验组中随机抽取10只实验兔行MRI检查、大体观察、组织学检查,假手术对照组10只于术后2周行上述检查。MRI扫描序列包括TSE-T1WI、TSE-T2WI、T2WI/SPAIR、3D/WATSc/FFE/T1WI。结果：术后1、2周,骨折线均清晰,骨软骨骨折片移位14（14/20）;骨片覆盖软骨术后2周较术后1周损伤重（P〈0.05）;骨折区成纤维细胞数术后2周较术后1周多（P〈0.05）。术后第2周,股骨髁骨折处骨质增生,MRI示薄层低信号,骨片内部分骨小梁坏死;骨片覆盖软骨MMP-13表达,术后2周较术后1周表达程度明显增高（P〈0.05）,对照组仅2（2/10）只轻度表达。结论：运动可使兔股骨髁骨软骨骨折愈合不佳,术后2周变化类似剥脱性骨软骨炎的特点;骨软骨骨折后骨片覆盖软骨MMP-13表达升高,对临床治疗骨软骨骨折及评价预后具有重要意义。     

Osteochondral tissue engineering approaches for articular cartilage and subchondral bone regeneration

Purpose

Osteochondral defects (i.e., defects which affect both the articular cartilage and underlying subchondral bone) are often associated with mechanical instability of the joint and therefore with the risk of inducing osteoarthritic degenerative changes. This review addresses the current surgical treatments and most promising tissue engineering approaches for articular cartilage and subchondral bone regeneration.

Methods

The capability to repair osteochondral or bone defects remains a challenging goal for surgeons and researchers. So far, most clinical approaches have been shown to have limited capacity to treat severe lesions. Current surgical repair strategies vary according to the nature and size of the lesion and the preference of the operating surgeon. Tissue engineering has emerged as a promising alternative strategy that essentially develops viable substitutes capable of repairing or regenerating the functions of damaged tissue.

Results

An overview of novel and most promising osteochondroconductive scaffolds, osteochondroinductive signals, osteochondrogenic precursor cells, and scaffold fixation approaches are presented addressing advantages, drawbacks, and future prospectives for osteochondral regenerative medicine.

Conclusion

Tissue engineering has emerged as an excellent approach for the repair and regeneration of damaged tissue, with the potential to circumvent all the limitations of autologous and allogeneic tissue repair.

Level of evidence

Systematic review, Level III.     

创伤性骨软骨损伤治疗的研究进展

创伤性骨软骨损伤(OL)在临床中常见,骨软骨在解剖上涉及软骨表面和软骨下骨,其解剖和生理功能存在特殊性,临床上处理OL时必须同时兼顾软骨及软骨下骨.目前对创伤性OL的手术及非手术治疗仍存在较多争议.而骨软骨组织工程多层支架设计更接近关节软骨到软骨下骨不同层次的解剖特性,目前已作为一个理想的选择应用于临床,以期达到更好地...     

Articular cartilage: injury pathways and treatment options

Articular cartilage injury and degeneration is a frequent occurrence in synovial joints. Treatment of these articular cartilage lesions are a challenge because this tissue is incapable of quality repair and/or regeneration to its native state. Nonoperative treatments endeavor to control symptoms, and include anti-inflammatory medication, viscosupplementation, bracing, orthotics, and activity modification. Techniques to stimulate the intrinsic repair (fibrocartilage) process include drilling, abrasion, and microfracture of the subchondral bone. Currently, the clinical biologic approaches to treat cartilage defects include autologous chondrocyte implantation, periosteal transfer, and osteochondral autograft or allograft transplantation. Newer strategies employing tissue engineering being studied involve the use of combinations of progenitor cells, bioactive factors, and matrices, and the use of focal synthetic devices. Many new and innovative treatments are being explored in this exciting field. However, there is a paucity of prospective, randomized controlled clinical trials that have compared the various techniques, treatment options, indications and efficacy.     

Fresh osteochondral allografting

The treatment of articular cartilage defects in the knee is a difficult challenge. Fresh, small-fragment osteochondralallografting is a technique involving the transplantation of articular (hyaline) cartilage into the defective joint surface. The graft, a composite of living cartilage and a thin layer of underlying subchondral bone, provides a mature matrix with viable chondrocytes along with an osseous component that provides a surface for fixation and integration with the host. Fresh allografting is particularly useful in larger lesions (greater than 2 cms) or when associated osseous defects are present. Clinical experience with fresh osteochondral allografts now extends over 2 decades. Up to 90% of individuals treated for femoral condyle lesions are improved. The allograft tissue appears well tolerated by the host, with documented long-termsurvival of chondrocytes and intact matrix. Successful clinical outcomes have established fresh osteochondrall allografting as an appropriate alternative in the treatment of chondral and osteochondral lesions of the knee.