Ruling on not obeying parents with regard to medical treatment
Question

I am a young unmarried woman, 23 years old. I had an accident that affected my back muscles. The doctors say that it is essential to treat this problem before I get married, but my parents are refusing the treatment because of their lack of knowledge, and for fear of what people may say. I cannot bear the pain any longer, and obeying them is killing me, but I have no way of going out without their permission.
My question is: what should I do – obey them or go against their wishes?
Praise be to Allah.Firstly: 
Obedience to parents is not absolute, as is the case with obedience to Allah and His Messenger; rather there are some situations in which one is not obliged to obey one’s parents and in fact it is forbidden to do so, such as if they tell one to do something which involves disobedience to Allah. 
Ibn Daqeeq al-‘Eid (may Allah have mercy on him) said: The son is not obliged to obey them in everything they tell him to do or in everything they tell him not to do, according to scholarly consensus.
End quote from Ihkaam al-Ahkaam Sharh ‘Umdat al-Ahkaam, 2/296
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 
With regard to that which is beneficial to the individual and is not harmful to the parents, there is no obligation to obey the parents, whether they forbid it or allow it, because it does not cause any harm and it serves an interest (for the child). Any father who forbids his son to do something that is in his best interests and would not cause any harm to the father is mistaken and is severing the ties of kinship, because what the father should do is encourage his children, both sons and daughters, to do everything that is good. An example is when some women prevent their daughters from fasting during the ayaam al-beed (13th, 14th and 15th of the Hijri month), or fasting on Mondays and Thursdays, on the grounds that this is too hard for them, even though the one who is going through the difficulty and hardship is the daughter who is fasting. Therefore the parent has no right to prevent the child, male or female, from doing any act of worship, unless that will cause some harm to either of the parents, such as if the father of mother needs nursing in illness, for example, and if the son or daughter focuses on this act of worship it will cause harm to the father or mother. In that case they may tell him or her not to do it, and they are required to refrain, because honouring parents is obligatory whereas doing voluntary acts of worship is not obligatory.
End quote. Ash-Sharh al-Mumti‘, 8/13-14 
Secondly: 
To sum up the words of the scholars, there are conditions for obedience to parents: 
1.Obeying them should not involve disobedience to Allah, because there is no obedience to any created being if it involves disobedience to the Creator. See the answer to question no. 162423.
2. Obedience to them should be for the purpose of bringing some benefit to them or warding off some harm from them, without being unreasonable or causing too much trouble for the children. But if they are telling their child to do something because of a lack of reason or knowledge, or because of being unreasonable and stubborn, and obeying them will be detrimental to the interests of the child, then the scholars are of the view that it is not obligatory to obey them in this case.
Al-Haafiz Ibn Hajar (may Allah be pleased with him) said: What is meant by disobedience to parents that is haraam is doing or saying anything will hurt the parents, but there is no obedience if they call their child to shirk or sin, or if the parents are being unreasonable and stubborn.
End quote from Fath al-Baari, 10/406 
Ibn Hajar al-Haytami (may Allah have mercy on him) said: The guideline on that disobedience to parents which is haram and is a major sin, is that the son does or says something to both parents or one of them that is extremely hurtful according to custom. But if the father is extremely foolish or feebleminded, and he tells his son to do or not to do something that if he goes against them it would not customarily be regarded as disobedience, then his son is not committing an evil action by going against his wishes in that case.
End quote from az-Zawaajir ‘an ‘Iqtiraab al-Kabaa’ir, 2/76 
3.Obeying the parent should not cause harm to the child, because in cases where harm will result, obligations and duties are waived.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: The individual is obliged to obey his parents in that which does not involve sin, even if they are evildoers … This applies to that which is beneficial for them and will not harm him… Because obligations are waived if they will result in harm, and it is haraam to obey in that which involves sin, and there is no obedience to any created being if it involves disobedience to the Creator.
End quote from al-Akhbaar al-‘Ilmiyyah min al-Ikhtiyaaraat al-Fiqhiyyah by al-Ba‘li, p. 170 
It says in al-Furooq by al-Quraafi (1/267-268): Just as we say that it is not allowed for him to hurt them, we also say that it is not allowed for them to hurt him. End quote. 
Al-‘Adawi al-Maaliki (may Allah have mercy on him) said: Likewise there is no obligation to obey them in giving up something when that will result in harm to the child, such as if he tells him to give up his livelihood or craft.
End quote from Haashiyat al-‘Adawi, 4/289 
Thirdly: 
From the above it is clear that if not having medical treatment will be harmful to you or will cause increased pain, and your parents are not letting you get medical treatment or have surgery simply because of what people will say, or because of traditions and customs, or other invalid reasons, then you are not obliged to obey your parents in this case. Having surgery and going against their wishes is not regarded as disobedience and is not mistreating them. 
But it remains to be seen how this aim will be achieved, especially since you are not able to go out of the house without their permission, let alone have this surgery, and afford the necessary costs, consultations with doctors, and so on. 
In that case, we do not think that your problem can be solved except by communicating with your parents and trying to convince them; you could seek the help of rational and wise people among your family and relatives, who could convince your parents. 
You could also come to an agreement with them, with the help of advisors, to get a second medical opinion from a trustworthy doctor who is known for having the skills that you need. Perhaps his words will convince them and win their approval. 
If there is a way to get government-sponsored treatment in a safe and trustworthy manner, which does not need any money from you, there is nothing wrong with making use of it, even if your parents do not agree, but you should try hard to make sure that some trustworthy women among your relatives will accompany you. 
However, we do not think that you should escalate this matter to the level of a conflict with your parents that may sour your relationship with them in the future and make it worse than the pain of the sickness that you are suffering at present. 
We ask Allah to grant you complete healing and well-being, and to help your parents and guide them to that which is good and beneficial. 
And Allah knows best.