A semi-colon indicates two independent clauses, so options A,B and C doesn't make sense and are fragment in nature. Whereas in option E use of superlative form-most is incorrect as there is comparison between two ligament injuries .
the correct option is D which uses the correct form -much more and correct in structure.

IMO D

A. is rare; rather ligament injuries are much more common--wrong, SV are correct, but use of rather after is not correct, because ; is used to seperate 2 IC where adverb can be used at start
B. is rare, but rather it is ligament injuries that are much more common----wrong, SV are correct, Usage of BUT rather is wrong leads to redundancy
C. is rare; rather it is ligament injuries that are much more common----wrong, SV are correct, usage of rather after semi colon is wrong
D. is rare; however, ligament injuries are much more common---correct
E. is rare; however, ligament injuries are most common---wrong, usage of MOST is superlative and changes the meaning

IMO B

A. is rare; rather ligament injuries are much more common --> wrong, needs IC due to semi colon
B. is rare, but rather it is ligament injuries that are much more common --> correct
C. is rare; rather it is ligament injuries that are much more common --> needs IC
D. is rare; however, ligament injuries are much more common --> needs IC
E. is rare; however, ligament injuries are most common --> 'the' is required before most. needs IC

i have doubt on the usage of ' but rather '.

however, ligament injuries are much more common --> is not it a dependent clause due to ' however '.

Official Explanation:

Since the underlined portion of the sentence has a semicolon connecting two clauses, check whether the clauses are connected correctly. In the sentence as written, rather, which implies one thing instead of another, does not correctly connect the two clauses in the sentence or establish the contrast between a rare injury and a much more common type. This is a clauses and connectors error, so eliminate choice A and look for any obvious repeaters. There are no obvious repeaters, so evaluate the remaining answer choices individually, looking for reasons to eliminate each.

Choice B correctly uses the coordinating conjunction but to join the two clauses. However, the word rather does not establish the contrast between a rare injury and a much more common type. This is a clauses and connectors error, so eliminate choice B. Choice C uses the word rather, which does not establish the contrast between a rare injury and a much more common type, so eliminate choice C. Choice D uses however, which correctly connects the two clauses and establishes the contrast between a rare injury and a much more common type, and introduces no new errors, so eliminate choice D. Choice E uses however to correctly connect the clauses and establish the contrasting relationship, but incorrectly uses the comparison word most to compare two items, so eliminate choice E.

Choice A: No. The word rather does not correctly connect the two clauses in the sentence. Clauses & Connectors.

Choice B: No. The word rather does not correctly connect the two clauses in the sentence. Clauses & Connectors.

Choice C: No. The word rather does not correctly connect the two clauses in the sentence. Clauses & Connectors.

Choice D: Correct

Choice E: No. The word most does not correctly compare two items. Quantity words.

The correct answer is choice D.
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I understand why D is correct when comparing two items. But why is it assumed that ligament injuries is being compared to only traumatic dislocation rather than the "many types of injuries"?

thoughtiana

In this sentence, different types of injuries are being compared. We cannot compare "many types of injuries" with Ligament injuries, because Ligament injuries are one of many types of injuries.

For example, we cannot say "Red cars are better than Cars", we can say "Red cars are better than blue cars" or "Red cars are better than all other Cars".

I hope this helps.

It may be easier for you to see the difference in a different sentence:

Although many types of balls exist, shiny balls are rare; however, black balls are (more / most) common.

It is much more natural to compare (shiny balls vs black balls) in this construction.

If you wanted to compare (rare vs common) in the universe of (many types of balls), then the second independent clause should be: black balls are the most common.

Posted from my mobile device

Although the knee joint is susceptible to many types of injuries, traumatic dislocation is rare; rather ligament injuries are much more common.

A. is rare; rather ligament injuries are much more common - "Rather" is a contrast word (such as 'however'). Contrast words are usually separated from the rest of the sentence by a comma. Here, 'rather' is not separated from the rest of the second independent clause by a comma. Hence, eliminate (A).

B. is rare, but rather it is ligament injuries that are much more common - the sentence would have had much better clarity if 'rather' was absent. But here, rather kind of makes the usage of 'but' redundant. Hence, eliminate (B).

C. is rare; rather it is ligament injuries that are much more common - same error as in (A). Hence, eliminate (C).

D. is rare; however, ligament injuries are much more common - (D) has no errors. Hence, (D) is the right answer.

E. is rare; however, ligament injuries are most common - you cannot use the superlative form ('most') to compare two items. Hence, (E) is incorrect.

aragonn sudarshan22 generis

Isn't it true that "MORE" , without "THAN" is incorrect ?? But the correct answer seems to contradict it ?