Otosclerotic obliteration of oval window niche: an analysis of the results of surgery.

1. The massive otosclerotic focus, obliterating the oval window niche, has a relatively high case incidence of 11-2 per cent in South Australia. The three classes of obliterated footplate are defined. 2. Basic data of 109 consecutive surgical cases of obliterative otosclerosis are given. A brief description of operative techniques--vein graft and polyethylene tube in nine, and piston technique in 100--is given and the difficulties and complications arising at or after surgery are discussed. 3. Post-operative follow-up of patients with yearly audiometric assessment has been achieved in 105/109 (= 96-33%) at four years, and in 94/109 (= 86-26%) at five years. 4. The results of surgery are presented by many and varied methods including bar diagrams, post-operative hearing gains, post-operative bone-air gaps, speech discrimination studies and standard statistical analysis techniques. 5. The vein graft technique (nine cases) is very much inferior to the piston technique. Vein graft cases had a 33% incidence of profound sensori-neural loss due to bony reclosure of the window. 6. The piston technique (100 cases) gave hearing gains of 20 decibels or more in 91%, 30 decibels or more in 71%, and 40 decibels or more in 41% of cases at five years post-operatively. The bone-air gap at five years post-operatively was diminished to 20 decibels or less in 88%, to 15 decibels or less in 85%, to 10 decibels or less in 77%, and complete closure or over-closure occurred in 52% of the patients. 7. Data analysis has established there is no change with time of the post-operative mean bone-air gap 500--2,000 Hz. over a period of at least five years, and thus that the piston operation gives a persisting and stable hearing result. 8. In predicting the effect of the piston operation only a rough guide can be obtained from other variables. In particular bone hardness, mucosal characteristics, sex and piston diameter appear to be irrelevant. Patients with a large bone conduction reading or a large air-bone gap appear to do slightly worse than patients with smaller values for these variables. There are no grounds for excluding a patient from operation on account of age, or the finding of active otosclerosis (soft bone and thickened vascular muco-periosteum). 9. From the data of piston operations, the estimated mean bone-air gap for the five-year examination period was 4-14 db. with a standard deviation of 12-5 db. 10. The piston operation is highly recommended as a safe and suitable method of alleviating, in the long-term, the conductive hearing loss of patients with obliterative otosclerosis of the oval window.