Comparison of caudal wedge ostectomy with cranial wedge ostectomy for treatment of overriding/impinging spinous processes in horses

Background:
Caudal wedge ostectomy has not been investigated for treatment of overriding/impinging spinous processes (SPs) in horses.
Objectives:
Establish the feasibility of caudal wedge ostectomy using thoracolumbar cadavers. Compare measures of surgical trauma (volume of bone removed and length of ostectomy cut) and error (angle the ostectomy exits the SP and risk of creating a never ending cut) between hypothetical caudal and cranial wedge ostectomies on SPs of different inclinations.
Study Design:
Experimental, method comparison study
Methods:
Computed tomography and caudal wedge ostectomy surgery were performed on four cadavers. Observations, technical difficulties and surgical errors were recorded.
Radiographs from 67 horses with overriding/impinging SPs were reviewed. Hypothetical ‘ideal’ caudal and cranial wedge ostectomies, and ‘error’ ostectomies diverging 12˚ from ideal, were drawn at sites of impingement. Ostectomy area/SP width, ostectomy length/SP width, absolute difference of exit angles (angle the ostectomy exits the SP) from 90˚, and number of error ostectomies failing to exit the SP (never-ending-cuts [NEC]) were calculated. Continuous variables were compared between techniques in caudally and cranially inclined SP groups using Wilcoxon signed-rank tests. Proportions of error ostectomies resulting in NEC were compared using McNemar’s tests.
Results:
No surgical errors were recorded with caudal wedge ostectomy. Median ostectomy area/SP width (measure of ostectomy volume) was lower for caudal compared to cranial wedge ostectomy in caudally and cranially inclined SP groups. Median exit angles were closer to 90˚for caudal compared to cranial wedge ostectomies in caudally and cranially inclined SP group. The proportion of NEC was lower for caudal compared to cranial wedge ostectomy in caudally but not cranially inclined SP groups

Conclusions:
Experimentally, caudal wedge ostectomy was a feasible technique to perform, removed less bone and resulted in reduced frequency of NEC in caudally inclined SPs. Further investigation of the technique is warranted in vivo.