The contraindications for both techniques are by and large the same.
However, it is important to distinguish between absolute and relative contraindications. There are very few 'nevers' in medicine and this is no exception. Most of the contraindications can be broken where the risks of the alternative are greater.
Click here for an example.
Example: Coagulation disorder
A patient requires fixation of a badly soiled open ankle fracture. The surgeons are keen to operate within the hour but the patient had a large three course dinner two hours ago. The patient has a potentially difficult airway (Mallampati 3) and, both you and the patient, are keen to use spinal anaesthesia. However, the patient also has a history of chronic idiopathic thrombocytopenia.
Performing a spinal carries a finite risk of causing a spinal canal haematoma. However, it brings the benefit of reducing the risk of airway difficulties in a patient who has a very full stomach and a predicted difficult intubation.
The risk-benefit ratio will vary according to the platelet count. Faced with a count of 70 x 10^9 you may decide spinal is the better option. Faced with 10 x 10^9, you hopefully would not.