Equis ISSN 2398-2977

Spine: spinous processes - overriding

Synonym(s): Kissing spines, Impinging spinous processes

Contributor(s): Graham Munroe, Vetstream Ltd


  • Cause: periosteal irritation of thoracic dorsal spinous processes from impingement during exercise, especially jumping or disciplines requiring lateral movements such as dressage.
  • Signs: range of possible signs from none to severe signs of back pain Musculoskeletal: back pain. None of the clinical signs are pathognomonic for overriding spinous processes. 
  • Diagnosis: condition may be suggested by clinical signs, or various imaging modalities but definitive diagnosis is made from the response to local anesthetic infiltration Anesthesia: local - overview.
  • Treatment: rest, physiotherapy Musculoskeletal: physiotherapy, corticosteroid injections Dexamethasone, analgesic injections, extracorporeal shockwave therapy Extracorporeal shockwave therapy, surgical removal of impinging processes.
  • Prognosis: good - guarded.
Print off the Owner factsheet on Kissing spines to give to your clients. Clinical tip
Question: What is the prognosis for overriding spinal processes?
Answer: Fair for return to full work with conservative treatment; good following spinous process resection.



  • Short backed horses may have crowding of the normal number of spinous processes.
  • Overriding spinous processes can also arise when the back undergoes excessive dorsi-flexion, eg as potentially occurs in jumping horses, or spinal maneuvres, eg as occurs in high quality dressage horses. However, biomechanical studies have shown no evidence for increased movement in the T13-T18 region compared to other parts of the thoracolumbar spine and so this explanation may not be correct.
  • Another hypothesis is that the weight of a saddle and rider causes a downward force on the T13-T18 area, consequently forcing the spinous processes in this region to become close together. However, overriding spinous processes have been described in unbroken/unridden horses and horses that compete in athletic but non-ridden disciplines (driving, trotting races).
  • Most commonly seen between T13-T18.
  • Often painless false joints (pseudoarthrosis formation) form between impinging spinous processes in those animals showing no clinical signs.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Jacklin B D, Minshall G J & Wright I M (2014) A new technique for subtotal (cranial wedge) ostectomy in the treatment of impinging/overriding spinous processes: Description of technique and outcome of 25 cases. Equine Vet J 46 (3), 339-344 PubMed.
  • Perkins J D et al (2005) Subtotal ostectomy of dorsal spinous processes performed in nine standing horses. Vet Surg 34 (6), 625-629 PubMed.
  • Walmsley J P et al (2002) Impingement of the dorsal spinous processes in two hundred and fifteen horses: case selection, surgical technique and results. Equine Vet J 34 (1), 23-28 PubMed.

Other sources of information

  • Henson F M D & Kidd J A (2010) Overriding Dorsal Spinous Processes. In: Equine Back Pathology: Diagnosis and Treatment. Ed: Henson F M D. Blackwell Wiley, UK.