Если бы это был вывих, хирург запретил бы мне наступать на ногу.

Because this is a counterfactual / unreal conditional: if it had been ..., he would have forbidden ...

In Russian, that idea is usually shown like this:

• если бы
  • past-tense form in the if clause
• past-tense form + бы in the main clause

So:

• Если бы это был вывих = If it had been a dislocation
• хирург запретил бы мне... = the surgeon would have forbidden me...

This is the normal way to express would in Russian.

In standard Russian, after если бы, you normally do not add another бы to the same clause.

So standard Russian is:

• Если бы это был вывих...

not:

• Если бы это был бы вывих...

You may occasionally hear double бы in colloquial speech, but it is generally treated as nonstandard or awkward. For learners, the safe rule is:

• если бы already covers the conditional meaning in that clause.

Because был agrees with вывих, which is a masculine noun.

• вывих = masculine
• therefore был

Compare:

• Это был вывих = It was a dislocation
• Это была травма = It was an injury
• Это было растяжение = It was a sprain/strain

In this kind of sentence, это is invariable and does not determine the gender. The gender is usually felt through the noun that identifies what it was.

That is a very common point of confusion.

In Russian:

• in the present tense, the verb to be is usually omitted:
  • Это вывих = It is a dislocation
• in the past tense, you must use the past form:
  • Это был вывих = It was a dislocation

So был is necessary here because the sentence refers to a hypothetical past/present situation from a past viewpoint: If it had been a dislocation...

Because запретить takes the dative for the person who is forbidden to do something.

Pattern:

• запретить кому? что делать?
• forbid someone to do something

So:

• хирург запретил бы мне наступать...
• literally: the surgeon would forbid to me to step / put weight...

More examples:

• Мне запретили бегать. = They forbade me to run.
• Ей запретили курить. = She was forbidden to smoke.

Because наступать is imperfective, and after запретить it usually expresses a general action or ongoing activity: to step on / to put weight on as an action in general.

Here the meaning is not one single completed step, but rather:

• not to put weight on the leg
• not to step on it

So наступать is the natural choice.

Compare:

• запретили наступать на ногу = forbade putting weight on the leg / stepping on it
• запретили наступить would sound much more like forbade one single act of stepping

Literally, yes, наступать на ногу can mean to step on someone’s foot/leg in other contexts.

But in a medical context like this, it usually means:

• to put weight on the leg
• to bear weight on it
• to step on it

So here it means the surgeon would not allow the speaker to use that injured leg for support.

This is a very natural Russian way to say it.

Because наступать на normally takes the accusative:

• наступать на что?
• на ногу

With this verb, Russian treats the action as movement/contact directed onto something.

Compare:

• наступать на пол = step on the floor
• наступать на ступеньку = step on a stair
• наступать на ногу = step on the foot / put weight on the leg

So the accusative here is required by the verb-preposition combination.

This is an important difference.

• Если бы это был вывих... = If it had been a dislocation...
  • unreal, hypothetical, contrary to fact or presented as not true
• Если это был вывих... = If it was a dislocation...
  • a real possibility, uncertainty, or neutral condition

So бы is what turns it into an unreal/hypothetical condition.

Yes. Russian word order is flexible, although each version may sound slightly different in emphasis.

The original:

• Если бы это был вывих, хирург запретил бы мне наступать на ногу.

Possible variations:

• Хирург запретил бы мне наступать на ногу, если бы это был вывих.
• Если бы это был вывих, мне хирург запретил бы наступать на ногу.

The original is the most neutral and natural way to present the condition first and then the result.

Because in standard Russian, бы usually attaches to the verb or to a nearby word in the clause, and with past-tense conditionals the most common pattern is:

• past-tense verb + бы

So:

• запретил бы
• сказал бы
• помог бы

You may sometimes see other placements, but запретил бы мне is the normal, straightforward version.

Yes, хирург literally means surgeon.

In English, with an injury like a dislocation, you might expect doctor more generally. In Russian, though, хирург is perfectly natural in a medical/injury context, especially when talking about bones, joints, dislocations, fractures, and whether a patient may put weight on a limb.

So it does mean surgeon, but it can sound broader in practical medical use than some learners expect.

Sometimes yes, depending on context.

Russian past-tense forms with бы can cover both:

• If it were ...
• If it had been ...

English chooses between those based on context more strictly than Russian does.

Here, because the second part is about what the surgeon would have forbidden, English often prefers:

• If it had been a dislocation, the surgeon would have forbidden me to put weight on my leg.

But in some contexts If it were a dislocation... might also be understandable. Russian itself is not making that distinction as sharply as English does.

Because Russian expresses that meaning differently.

English uses:

• would forbid
• would go
• would help

Russian usually uses:

• a past-tense verb
• plus бы

So:

• запретил бы = would forbid
• пошёл бы = would go
• помог бы = would help

That is one of the most basic patterns of the Russian conditional mood.