Zbýň Štefan, Brix Martin O, Juras Vladimir, Domayer Stephan E, Walzer Sonja M, Mlynarik Vladimir, Apprich Sebastian, Buckenmaier Kai, Windhager Reinhard, Trattnig Siegfried
From the *High-Field MR Center of Excellence, Department of Biomedical Imaging and Image-guided Therapy, and †Department of Orthopaedic Surgery, Medical University of Vienna, Vienna, Austria; ‡Department of Imaging Methods, Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia; and §High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
Invest Radiol. 2015 Apr;50(4):246-54. doi: 10.1097/RLI.0000000000000117.
The goal of cartilage repair techniques such as microfracture (MFX) or matrix-associated autologous chondrocyte transplantation (MACT) is to produce repair tissue (RT) with sufficient glycosaminoglycan (GAG) content. Sodium magnetic resonance imaging (MRI) offers a direct and noninvasive evaluation of the GAG content in native cartilage and RT. In the femoral cartilage, this method was able to distinguish between RTs produced by MFX and MACT having different GAG contents. However, it needs to be clarified whether sodium MRI can be useful for evaluating RT in thin ankle cartilage. Thus, the aims of this 7-T study were (1) to validate our sodium MRI protocol in cadaver ankle samples, (2) to evaluate the sodium corrected signal intensities (cSI) in cartilage of volunteers, (3) and to compare sodium values in RT between patients after MFX and MACT treatment.
Five human cadaver ankle samples as well as ankles of 9 asymptomatic volunteers, 6 MFX patients and 6 MACT patients were measured in this 7-T study. Sodium values from the ankle samples were compared with histochemically evaluated GAG content. In the volunteers, sodium cSI values were calculated in the cartilages of ankle and subtalar joint. In the patients, sodium cSI in RT and reference cartilage were measured, morphological appearance of RT was evaluated using the magnetic resonance observation of cartilage repair tissue (MOCART) scoring system, and clinical outcome before and after surgery was assessed using the American Orthopaedic Foot and Ankle Society score and Modified Cincinnati Knee Scale. All regions of interest were defined on morphological images and subsequently transferred to the corresponding sodium images. Analysis of variance, t tests, and Pearson correlation coefficients were evaluated.
In the patients, significantly lower sodium cSI values were found in RT than in reference cartilage for the MFX (P = 0.007) and MACT patients (P = 0.008). Sodium cSI and MOCART scores in RT did not differ between the MFX and MACT patients (P = 0.185). No significant difference in sodium cSI was found between reference cartilage of the volunteers and the patients (P = 0.355). The patients showed significantly higher American Orthopaedic Foot and Ankle Society and Modified Cincinnati scores after treatment than they did before treatment. In the volunteers, sodium cSI was significantly higher in the tibial cartilage than in the talar cartilage of ankle joint (P = 0.002) and in the talar cartilage than in the calcaneal cartilage of subtalar joint (P < 0.001). Data from the cadaver ankle samples showed a strong linear relationship between the sodium values and the histochemically determined GAG content (r = 0.800; P < 0.001; R = 0.639).
This study demonstrates the feasibility of in vivo quantification of sodium cSI, which can be used for GAG content evaluation in thin cartilages of ankle and subtalar joints at 7 T. A strong correlation observed between the histochemically evaluated GAG content and the sodium values proved the sufficient sensitivity of sodium MRI to changes in the GAG content of cartilages in the ankle. Both MFX and MACT produced RT with lower sodium cSI and, thus, of lower quality compared with reference cartilage in the patients or in the volunteers. Our results suggest that MFX and MACT produce RT with similar GAG content and similar morphological appearance in patients with similar surgery outcome. Sodium MRI at 7 T allows a quantitative evaluation of RT quality in the ankle and may thus be useful in the noninvasive assessment of new cartilage repair procedures.
微骨折术（MFX）或基质相关自体软骨细胞移植术（MACT）等软骨修复技术的目标是生成具有足够糖胺聚糖（GAG）含量的修复组织（RT）。钠磁共振成像（MRI）可对天然软骨和修复组织中的GAG含量进行直接无创评估。在股骨软骨中，该方法能够区分MFX和MACT产生的具有不同GAG含量的修复组织。然而，钠MRI是否可用于评估薄的踝关节软骨中的修复组织尚需阐明。因此，这项7-T研究的目的是：（1）在尸体踝关节样本中验证我们的钠MRI方案；（2）评估志愿者软骨中的钠校正信号强度（cSI）；（3）比较MFX和MACT治疗后患者修复组织中的钠值。
在这项7-T研究中，对5个人类尸体踝关节样本以及9名无症状志愿者、6名MFX患者和6名MACT患者的踝关节进行了测量。将踝关节样本的钠值与组织化学评估的GAG含量进行比较。在志愿者中，计算踝关节和距下关节软骨中的钠cSI值。在患者中，测量修复组织和对照软骨中的钠cSI，使用软骨修复组织磁共振观察（MOCART）评分系统评估修复组织的形态外观，并使用美国矫形足踝协会评分和改良辛辛那提膝关节量表评估手术前后的临床结果。所有感兴趣区域均在形态学图像上定义，随后转移到相应的钠图像上。进行方差分析、t检验和Pearson相关系数评估。
在患者中，MFX患者（P = 0.007）和MACT患者（P = 0.008）的修复组织中钠cSI值显著低于对照软骨。MFX和MACT患者修复组织中的钠cSI和MOCART评分无差异（P = 0.185）。志愿者的对照软骨和患者的对照软骨之间钠cSI无显著差异（P = 0.355）。患者治疗后的美国矫形足踝协会评分和改良辛辛那提评分显著高于治疗前。在志愿者中，踝关节胫骨软骨中的钠cSI显著高于距骨软骨（P = 0.002），距下关节距骨软骨中的钠cSI显著高于跟骨软骨（P < 0.001）。尸体踝关节样本的数据显示钠值与组织化学测定的GAG含量之间存在强线性关系（r = 0.800；P < 0.001；R = 0.639）。
本研究证明了体内定量钠cSI的可行性，其可用于在7 T下评估踝关节和距下关节薄软骨中的GAG含量。组织化学评估的GAG含量与钠值之间观察到的强相关性证明了钠MRI对踝关节软骨中GAG含量变化具有足够的敏感性。与患者或志愿者的对照软骨相比，MFX和MACT产生的修复组织钠cSI较低，因此质量较低。我们的结果表明，在手术结果相似的患者中，MFX和MACT产生的修复组织GAG含量相似，形态外观相似。7 T下的钠MRI可对踝关节修复组织质量进行定量评估，因此可能有助于对新的软骨修复程序进行无创评估。
