My partner works for a local, Southampton based firm of solicitors in the clinical negligence department and she has said the following:
At the end of the day, if the hospital had x-rayed the knee on attendance at A&E, the problem would have been discovered at that point - which is likely to be called negligent. If the result is likely to have been the same, i.e. you would still have to have surgery to fix the problem then there is no real financial value to the claim. You have had pain and suffering for an additional 6 months but this wouldn't be worth a particularly large amount, probably only £1,000 or so.
If surgery wouldn't have been necessary if it had been diagnosed at the time of your attendance (i.e. it just put in a cast) then this is a claim worth something because you've had to have unnecessary surgery.
With regard to the lady with the broken neck - sue them!!