+1 for B.
Searched in other forums. OA is indeed B. Brilliant explanation provided by Eli Meyer, Kaplan GMAT instructor.
A is incorrect. In English, clauses (subject-verb structures) must be linked to one another by exactly one connecting phrase. In A, there is no connector between the clause "X-rays aren't needed" and "the OT rules were developed." It needs a "because," "since," or "so," to be correct; as written, it's a run-on sentence.
D is incorrect because the initial descriptive phrase, "developed to...", describes the OT rules, but the phrase is adjacent to "5% of patients." This is a modification error, and is incorrect.
E looks good; replacing a comma with a semicolon is one way to correct a run-on. However, the very last bit is garbled. 'when tested' is a descriptive phrase the needs to be followed by a comma, and "before the rules development" at the end of this version is a dangling modifier.
B and C are almost identical. Literally the only difference between the two is the order of the clauses. However, B has the superior order. B introduces "patients with foot pain" and "the OT rules" in it's first clause, then clearly refers back to "patients" and "the rules" in the second clause. C, on the other hand, starts by talking about the ambiguous "patients" and "the rules," and not until the second clause does it actually clarify the specifics of its subjects.
B is correct.