The metal itself won't be making any difference, since it quickly heats up to core body temperature and will stay at that temperature unless exposed to the outside (hopefully this isn't likely!) However, pain itself can be stirred up by cold and especially damp weather for several reasons, and it's likely that you would have got pain like this even without the metal. If you've damaged your back severely enough to break it, you will have jarred all the joints in your back. Joints are susceptible to changes in barometric pressure, which is why some people can predict the weather by the feeling in their bones. Also, surgical procedures are quite traumatic, and although you're asleep and don't feel it, your nerves are awake and remember it. Pain triggers muscle spasm, which is in itself painful, and muscle spasm is made worse by cold. If it's cold, damp and miserable, we all tend to huddle up - your posture goes to pot and this also increases pain. Plus in warm weather, not only does everyone stand more upright but sunshine and warmth also increase your own natural pain killers (endorphins.)
The British climate is particularly awkward. I worked with a Norwegian student who complained bitterly about the cold. I pointed out to him that he came from a country where the temp was regularly minus 30 degrees etc. Ah, he explained, but in England it's the wrong sort of cold!