Nicola Pilati, Maria Chiara Pressanto, Angela Palumbo Piccionello, Francesco De Angelis Corvi, Francesca Beccati

Background

Overriding dorsal spinous processes (ORSPs), also known as “kissing spine syndrome,” describe a skeletal abnormality in horses where the interspinous space narrows (<4 mm) and adjacent spinous processes touch or overlap. The condition predominantly affects the mid- and caudal thoracic vertebrae (Th13–Th18), leading to chronic back pain and reduced performance, especially in sport horses. Despite its prevalence, the true relationship between ORSPs and clinical pain remains unclear, as radiographic abnormalities often occur in horses without symptoms. The review aims to synthesize current literature on anatomy, pathogenesis, diagnosis, and management of ORSPs to improve understanding and guide future research.

Methods

A narrative literature review was conducted using PubMed and Google Scholar for studies published between 2000 and May 2025. Search terms included combinations of “equine,” “horse,” “spinous process,” “kissing spine,” and “thoracolumbar spine.” Seventy-seven peer-reviewed studies met inclusion criteria after screening 175 articles. All data were qualitatively analyzed to assess current diagnostic and therapeutic approaches and identify research gaps.

Results

The review describes ORSPs as a multifactorial condition likely influenced by biomechanics, genetics, and conformation. While often considered acquired through repetitive mechanical stress and poor saddle fit, recent studies suggest a developmental or hereditary component. Clinical signs are typically vague—resistance to saddling, reluctance to bend, or performance decline. Diagnosis relies on a combination of clinical evaluation, radiography, ultrasonography, and scintigraphy, though imaging findings often do not correlate with pain. Treatment approaches include conservative management (rest, physiotherapy, local corticosteroids, or bisphosphonates), surgical interventions (partial ostectomy or interspinous ligament desmotomy), and adjunctive rehabilitation therapies such as shockwave therapy, acupuncture, and strengthening exercises targeting core musculature (e.g., multifidus). Long-term outcomes vary; surgical desmotomy appears most effective in selected cases. Emerging research emphasizes the importance of multimodal management and structured rehabilitation for sustained recovery.

Limitations

The available evidence is limited by heterogeneous study populations, lack of standardized diagnostic protocols, absence of randomized control groups, and variability in clinical assessment. Moreover, most studies focus on adult sport horses, limiting generalizability to other breeds and disciplines. The subjective nature of back pain evaluation further complicates the establishment of diagnostic benchmarks.

Conclusions

ORSPs are a prevalent yet complex cause of equine back pain. The review underscores the need for standardized diagnostic protocols, objective assessment methods, and long-term controlled studies to evaluate treatment efficacy. Integrating imaging, biomechanics, and rehabilitation science could refine diagnosis and management. Future research should also explore the developmental and genetic aspects of ORSPs, potentially redefining it as a developmental orthopedic disease.

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