Patellar luxation in cats: classification and treatment guidelines
Despite a wealth of information on patellar luxation in dogs, there are still very few publications on the topic in cats.1–3
Introduction
In contrast to dogs, patellar luxation in cats has traditionally been considered a rare condition.1–5 A recent publication, however, has described it as a common problem.6
In terms of its management, it is crucial to remember that cats are not small dogs and there are significant anatomical differences between the two species’ stifle joints.
Patellar luxation in cats: aetiopathogenesis
Compared to dogs, a cat’s patella is wider in the mediolateral axis relative to the trochlear groove, and flatter in the craniocaudal axis. This results in a degree of physiological laxity in the patellofemoral joint, which is why patellar subluxation is considered a normal finding in cats.1,3
Patellar luxation in cats can occur following trauma or due to a developmental disease; the latter now considered the more frequent cause.3,6 It has been reported that breeds such as Devon Rex and Abyssinian cats may be predisposed to patellar luxation. Although the pathogenesis is not well understood, it has been suggested that its development may relate to the existence of congenital hypoplasia of the medial femoral condyle, with a shallow trochlear groove or hip dysplasia.1,5,6
To learn more about this topic, check out the webinar “Ortopedia felina: ¿los gatos son perros pequeños? (Feline orthopaedics: are cats small dogs?)” by Nuria Vizcaíno.
Patellar luxation in cats: clinical presentation
The most common clinical presentation in cats is that of medial, bilateral luxations, although cases of unilateral, lateral luxations have also been observed.1,6
The clinical signs associated with patellar luxation in cats include:
- Intermittent locking of the stifle joint after being extended and changes in gait (dragging the affected limb or a crouched gait).
- Lameness is not an ever-present clinical sign and its severity does not correspond to the severity of the luxation.1
- Although osteoarthritis is not considered a very common finding, it can occur in animals with severe luxation.
- Unlike dogs, in cats there does not appear to be any association between patellar luxation and cranial cruciate ligament rupture.1,4
- In some cases, the luxation does not provoke any clinical signs and the diagnosis is down to an incidental finding during a routine visit.1,3
Classification of patellar luxation in cats
The severity of patellar luxation in cats is based on the same clinical criteria as for dogs.4
- Grade 1: the patella can be manually luxated but regains its original position when the pressure is released.
- Grade 2: the patella can be luxated manually or by flexing the stifle joint and remains luxated until the stifle is extended or it is manually repositioned.
- Grade 3: the patella is permanently luxated but can be repositioned manually. When the pressure is released, it luxates again.
- Grade 4: it is permanently luxated and cannot be repositioned manually.
Patellar luxation in cats: treatment
As with dogs, patellar luxation in cats can be treated medically (analgesics/anti-inflammatories and rest) or surgically.
It may seem logical that conservative treatment should be indicated in cats with low-grade luxations and a mild clinical picture, while surgical correction of luxation should be reserved for patients with more severe luxations and clinical pictures., but the matter is still a subject of debate.
In the past, some authors even advised against operating on patellar luxation in cats because of the risk of deformities in the proximal portion of the tibia, asserting that better results could be obtained with conservative management.7
More recently, another study recommended initiating all cases with conservative treatment before considering surgery (especially if the lameness has been present for less than 2 months). Nevertheless, the same authors concluded the prognosis is generally favourable in cats that require surgery, provided that the appropriate technique is used.1 Tibial deformity was radiologically verified in cats that underwent a tibial crest transposition, but it does not appear to be clinically relevant.1
Normally, the same techniques used in dogs are applied cats: trochlear sulcoplasty, tibial tuberosity transposition, imbrication and/or release of soft tissue in the area, and corrective femoral osteotomies. These procedures can be combined in the same stifle to achieve a stable joint.3 Excellent results have been reported in approximately 74% of patients using these techniques. The remaining 26% can expect complications; these are minor in 6% of cases, and moderate/major in 20% (5% of all patients suffer reluxation).1,3
The anatomical differences between the patellae of cats and dogs may play a role in the joint instability occasionally reported after a trochlear sulcoplasty. This has led to the development and application of other surgical techniques specifically for cats, such as partial parasagittal patellectomy and, more recently, the placement of polyethylene prostheses in the trochlear groove.2,6
Conclusions
Although patellar luxations are less prevalent in cats than dogs, the clinician should not ignore this possible diagnosis in patients with hindlimb lameness. Despite limited literature in this regard, initial conservative management is probably recommendable in most cases. In patients that require surgery, it is important to consider the anatomical differences between the stifle joint of cats and dogs.
References
1. Loughin CA, Kerwin SC, Hosgood G, et al. (2006). Clinical signs and results of treatment in cats with patellar luxation: 42 cases (1992–2002). J Am Vet Med Assoc; 228:1370–1375.
2. Rutherford L, Arthurs GI. (2014). Partial parasagittal patellectomy: a novel method for augmenting surgical correction of patellar luxation in four cats. J Feline Med Surg; 16: 689–694.
3. Rutherford L, Langley-Hobbs SJ, Whitelock RJ, et al. (2015). Complications associated with corrective surgery for patellar luxation in 85 feline surgical cases. J Feline Med Surg; 17: 312–317.
4. Perry KL, Déjardin LM. (2021). Canine medial patellar luxation. J Small Anim Pract. 2021 May; 62: 315–335.
5. Harasen G. (2006). Patellar luxation. Can Vet J; 47:817–818.
6. Mills J, Hargittai T. (2020). Treatment of feline patellar luxation with polyethylene sulcal ridge prostheses. J Small Anim Pract; 61: 704–709.
7. Nunamaker DM. (1985). Patellar luxation. In: New CD, Nunamaker DM, eds. Textbook of small animal orthopedics. Philadelphia: JB Lippincott.
