34th Annual Scientific Meeting proceedings

The definition of a geriatric horse seems to vary between studies, probably depending on the design and the opinion of the researchers. Some early studies concentrating on the geriatric horse used ≥15 years of age (Ireland et al. 2011); however, different sources designate an older age of ≥20 years of age (Long et al. 2022).  Aging is a continuum and occurs at different ages and rates for different horses (and people) and likely is related to levels of physical activity.  For the definition of “geriatric” as regards a horse with osteoarthritis, one might be better to ask “what is the definition of a geriatric joint?”.  There is clear evidence from numerous sources that the ability to repair articular cartilage and other joint tissues, and to maintain the joint homeostasis, decreases with age.

 Osteoarthritis (OA) is a progressive deterioration of articular cartilage with accompanying alterations to the entire joint organ.  Progression of OA severity depends on the physiology (joint’s ability to maintain homeostasis, and the biomechanical loading of the joint.  A joint might be considered young in an older horse with minimal abnormalities associated with OA. A young horse might have a “geriatric” joint, if the disease progression has reached an end-stage; therefore, the joint may have very different chronological, physiological and functional ages

When discussing OA, each element of the joint organ – joint capsule, synovial membrane, synovial fluid, articular cartilage, subchondral bone, stabilising ligaments and tendons – must be considered since each is essential for efficient joint function. Particularly when considering the aging of a joint which is comprised primarily of connective tissues with few cells and a preponderance of matrix, repair of damaged tissue presents significant challenges.    The chondrogenic and osteogenic capabilities of bone marrow derived stem cells decline after just one year (Bagge et al).  In addition, as the joint ages, the processes of senescence and apoptosis must be considered.  Despite the fact that apoptosis and senescence are two distinct cellular states, each is a response to stress and results in decreased cell division.   Apoptosis is the process of programmed cell death. Removing the ability of a chondrocyte or osteocyte to secrete matrix, preventing the replenishment of articular cartilage or subchondral bone matrix. Senescence is a state in which the cells cease replicating but remain metabolically active.  In this state, a senescence associated secretory phenotype (SASP) develops, with continued production and release of inflammatory mediators that are detrimental to joint health.  The senescent cells contribute to the process of “inflammaging” within the joint by secreting pro-inflammatory proteins (cytokines, interleukins, ADAMTS, etc.) that promote catabolic rather than anabolic processes. In an effort to counter the effects of the SASP, some compounds labelled senolytics (block proteins associated with SASP) and senomorphs (potentiate the positive molecules associates with improved cartilage health) are being developed (Diekman and Loeser 2024; Liu et al. 2022).

The diagnosis of OA is similar in any age of horse, since reaching a specific diagnosis remains the gold standard to determine treatment options and prognosis for the horse.  First principles of a lameness evaluation should be followed with a clinical examination at rest and in motion, identify any relevant abnormalities and to identify the lame limb or limbs. If there is no obvious joint effusion or specific site of pain, then once a foot abscess is ruled out, nerve blocks would be undertaken to localise the lameness to a specific joint.  Once a particular joint or joints is/are identified, then diagnostic imaging would be utilised to detect evidence of osteoarthritis or other damage to the joint.  Once a diagnosis is reached then treatment options and prognosis can be discussed with the client. 

As equine surgeons, we have no shortage of options for treatment of osteoarthritis, regardless of the horse’s age; however, the owner of a geriatric horse may have different goals for that animal compared to a younger one.   The options for treatment include: rest from athletic activity, systemic medication, intra-articular medications (anti-inflammatory medication, corticosteroids, joint lubricants and a plethora of biologics and regenerative products), ancillary treatments (physiotherapy, chiropractic, acupuncture, etc.) and surgical therapy (arthroscopy, articular cartilage resurfacing, joint arthrodesis, neurectomy).  Reviewing the number of treatments available with the lack of a clear evidence-base for many, it becomes clear that treatment of OA is challenging, regardless of the age of the horse.

In addition to the general challenge of treating OA, selecting an appropriate treatment(s) for the geriatric horse could be either more or less difficult than for a younger animal.  The goals of the owner/trainer/responsible person may change over time, as the horse ages, particularly if the horse has had an athletic career which is of greater value to the owner compared to the quality of life.  Some owners might remain primarily concerned with the quality of life while others consider financial implications.  Depending on the severity of the OA, treatment decisions may involve some ethical or moral dilemmas related to quality of life.  Clear veterinary guidance becomes particularly important since veterinary opinion can influence the client’s decisions.   

As the horse ages, the discussion about treatment decisions may come to revolve around prognosis for a good quality of life more than a prognosis about athletic function.  There are three main participants in the decision-making process: the horse, the owner and the veterinary surgeon.  Unfortunately, the horse cannot speak which means that the other two parties need to be honest and objective about the quality of life of the horse.  The horse may express certain behaviours that provide clues to their pain score.  The veterinary surgeon should present the treatment options and likely prognosis to the client clearly and honestly, without bias in relation to the veterinary surgeon’s own ethical opinions or their own potential for financial remuneration.  The owner has the final say and needs to consider their own situation from a practical, financial, emotional and ethical position. 

 In this situation, it might be useful to have “the Conversation” as discussed by Atul Gawande (2014) in his book Being Mortal.  Perhaps it is too anthropomorphic to consider discussing the “wishes of the horse” but we certainly benefit from understanding the wishes of the owner as regards the horse.   “The conversation” as applied to the horse with OA might include: ensuring the client understands the severity, timeline and prognosis; the veterinary surgeon understanding the clients concerns for the horses’ future; the owner’s goals for the horse; what outcomes would be unacceptable; and what would a good quality of life be for their horse. 

References

1. Ireland et al. (2011) Equine Vet J. Jan;43(1):30-6. doi: 10.1111/j.2042-3306.2010.00145.x.
2. Long et al.  (2022) Animals (Basel) Jul 17;12(14):1822. doi: 10.3390/ani12141822.
3. Bagge et al. (2022) BMC Vet Res. Nov 3;18(1):388. doi: 10.1186/s12917-022-03475-2.
4. Diekman and Loeser (2024) OA and Cart 32(365-371) doi/10/1016/j.joca.2023.11.018
5. Liu et al. (2022) Arth Res Therapy 24:174 doi/10.1186/s13075-022-02859-x
6. Guwande, A (2014)   Being Mortal, Metropolitan Books, USA