Fabulous Feline Orthopedic Oddities #1 – Spontaneous Slipped Capital Femoral Epiphysis

Who knows why these topics pop in to my head, but today I am excited to celebrate all of those little eccentricities that make cats … cats. These little creatures can stir the affections of some – converting an otherwise normally functioning individual into a borderline (or worse?), self-admitted “crazy cat lady” … but also ignite fears in the eyes of the toughest of cowboys. Yet this mysterious and all-powerful little creature known simply as “the domestic housecat” has often been relegated to almost an afterthought in the world of veterinary orthopedics.  One can almost imagine the late, great comedian Rodney Dangerfield as a cat, uttering his famous catchphrase “I don’t get no respect” as he ruffles his shirt collar. So, I think I’ll celebrate some of the many fabulous feline orthopedic oddities in a series beginning today with oddity #1 – Spontaneous Slipped Capital Femoral Epiphysis (SSCFE).

One of the themes that I will explore from time to time in this series is the instinctive need for cats to use vertical space. What other creature will sit on the kitchen floor, themselves standing only a few inches high at the shoulder, and think to themselves “I really need to get on top of that refrigerator”?   That classic “cat need” for verticality is instinct that is deeply rooted, in part, to their need for rest, safe from their predators. It is the cat’s instinctive need to use vertical space that is critical to understanding the impact of orthopedic disease and injury upon them … and can even be a clue to help the otherwise unsuspecting cat owner to identify a problem in their furry friend.  One may even question does this feline “attitude for altitude” have anything to do with why we commonly see this unusual condition of SSCFE in cats, but less so in other species?

What is SSCFE?   Slipped Capital Femoral Epiphysis is exactly what it sounds like … the epiphysis of the femoral head simply slips out of its normal place atop the femoral neck. It is a unique atraumatic, apparently spontaneous Salter I fracture of the proximal femur. Wait a minute … why would that happen?  Read on … it only gets crazier!   As we’d expect for many a feline malady, there’s been relatively little research on the matter.  The research that has been done is primarily retrospective, but reveals unique clues into this crazy condition. SSCFE is reported as more common in overweight, neutered, male cats …. And when the timing of neuter was known, was almost exclusively performed at less than 6 months of age.  Wait … it gets wackier still!  The mean age of cats was 22.5 + 6.5 months … seems pretty old for a physeal fracture doesn’t it?  Let’s see if we can tie this all together.

Physeal Injury in a 2-year old cat?  It is well-recognized in several species that early, prepubertal gonadectomy contributes to prolonged physeal function. The physes don’t grow any faster, they simply remain open and functioning for a longer duration. In the case of our feline friends, this means that their proximal femoral physis (amongst others) is going to be subjected to more cycles of loading. In the case of this particular physis, many of those forces are shear loads looking to shift the femoral head off of its metaphyseal neck. Considering some of those amazing feline vertical jumps (the equivalent of me jumping up 6 stories … which I almost never do), it comes as no surprise that we see a few femoral heads slip off of their necks.  We should also not be surprised to hear that the condition can occur bilaterally; either simultaneously or as sequential events.

Clinical Presentation of Feline SSCFE:  The owner typically notices their cat’s lameness or inability to jump, but they may even perceive it as a neurologic disorder. You, the veterinarian, are presented with the ever-present challenge of conducting a meaningful feline orthopedic exam … more on that art form in a future blog … that’s where it gets fun!  Pain and crepitus may be localized to the hip and regional muscle atrophy may be noted.

Diagnostic Imaging:  Sedated pelvic radiographs are recommended and your findings may vary widely depending upon the condition’s duration. In early cases, there is only evidence of fracture and even that may not be obvious. Standard VD radiographs may show no displacement, so at least 2 views, including a lateral view, are advised.  I often also include a “frog leg” view in hopes of detecting displacement that eludes me on other views. Even if there is obvious fracture, be sure to closely scrutinize the contralateral hip; I like to do this with the pet owner (“I don’t see the same problem on the other hip … do you?”).  This leads me to discuss with them that the condition can develop in other hip in the near future even if I don’t see any evidence of it today. In more chronic states of this condition, there is progressive osteolysis of the femoral neck such that you may even imagine that you’ve just diagnosed Legg-Calve-Perthes disease in a cat!  In all likelihood you have not … you’re merely capturing a later progression of a pseudoarthrosis attempting to form at the SSCFE site. Additionally, the pathology of Legg-Calve-Perthes disease is primarily in the femoral head, not the neck, but let’s not get crazy … this is just a blog right?

What ya’ going to do?   Fracture repair, hip replacement or hip salvage?  Successful fracture repair using k-wires or screws in lag fashion can be achieved in early cases of fracture prior to neck resorption developing. Concerned about the possibility of need for a revision procedure, some cat owners may opt to consider either hip joint replacement or salvage with femoral head and neck excision (FHNE) and these should be more strongly considered once osteolytic changes of the femoral neck are noted.  “Wait … did you just say hip replacement and cat in the same sentence?”  I certainly did.  MicroTHR is a thing and while it may not be for every cat owner, for others, you’d probably better at least be aware of the possibility.  In a recent report on long-term follow-up of 44 cats undergoing total hip replacement, SSCFE was the most common surgical indication and there was very good owner satisfaction and acceptable complication rates with these microTHR’s.  To date, FHNE appears to be the most commonly performed treatment for SSCFE with acceptable subjective outcomes in most instances.  Some have suggested faster and better recoveries following ventral FHNE (in contrast to traditional craniolateral FHNE) and this may of particular benefit when the bilateral FHNE is required.

I know that ventral FHNE may be unfamiliar to some, but it is a technique worthy of your awareness.  You can learn to perform ventral FHNE and other practical hip procedures in our Practical Surgical Techniques of the Canine Hip: JPS, FHNE, Hip Lux, Epidurals & More Course, September 24-25, 2023.  The poor feline, once again, relegated to extrapolation from the canine!

Please tune in for future blogs on Fabulous Feline Oddities. There’s no shortage of these non-canine conundrums … which of them befuddles you most?   Is there one you’d really like to hear about?

Reference Reading & Resources:

1. McNicholas WT, et al. Spontaneous femoral capital physeal fracture in adult cats: 26 cases (1996-2001). JAVMA 2002;221:1731-1736.

2. Borak D, et al. Slipped capital femoral epiphysis in 17 Maine Coon cats. J Fel Med Surg 2017;19:13-20.

3. Rodiño-Tilve V, et al. Long-term follow up of 44 cats undergoing total hip replacement: cases from a feline hip registry (2010-2020). Vet Surg 2022;51:763-771

Ross’ career has spanned both private practice and academia. Along the way, he has assessed and treated his share of feline friends for all sorts of maladies. Ross is a professor Orthopedics at Colorado State University, Associate Director of Education at the Translational Medicine Institute and a frequent educator at orthopedic courses held around the world. You can catch up with him or other like-minded, experienced educators in our small animal orthopedic courses held here the CSU Translational Medicine Institute (www.CSUVetCE.com).