Insurance — Uninsured motorist — Causation — Damages — In action by insured against UM insurer, trial court erred in granting partial summary judgment for insured on issues of causation and damages where there was evidence of preexisting conditions which directly related to the issue of causation — By granting summary judgment, court improperly removed issue of whether accident caused insured’s claimed injuries from jury’s consideration — Evidence — Although insured had withdrawn his claim for damages for lower back injuries, trial court abused discretion in preventing introduction of evidence of insured’s prior lower back injuries, as lower back injuries were interconnected with neck and mid-back injuries for which insured did claim damages