Hips,elbows and Stifles

Abstract

Practical relevance Cats commonly present with joint disease and trauma. A methodical approach to diagnostics and treatment can aid the clinician in the management of these cases.

Clinical challenges Cats with joint disease may present with a vague history owing to their independent nature, and gait assessment is often challenging when compared with the dog. Knowledge of feline-specific anatomy is important to avoid over- or misinterpretation of physical examination or imaging findings.

Audience This review of feline joint disease focuses on the more common, non-traumatic conditions of the hip, stifle and elbow. It aims to provide first opinion clinicians with a guide to decision making that will assist them in achieving a diagnosis and formulating a management strategy.

Evidence base There is an extensive body of original articles and textbooks in the published literature relating to aspects of feline joint disease. This article combines information from key companion animal and feline-specific references together with the author’s clinical experience to provide a practical overview of joint disease, and highlight important differences between cats and dogs in terms of presentation and treatment.

What is normal?

Historically, there has been a tendency among clinicians to diagnose, manage and treat joint disease in cats as if they were small dogs. While the species share much in common with regard to diseases, diagnostic tests and management strategies, important differences do exist. In terms of the range of motion of the major joints, for example, most clinicians are familiar with what is normal for the dog. As cats with orthopaedic disease tend to be seen less frequently, clinicians may be less familiar with what is considered to be normal. Table 1 provides a useful reference. Differences between the cat and the dog with respect to specific anatomy relating to the hip, elbow and stifle joint are highlighted in the relevant sections of the text below.

Table 1

Range of motion (± SD) of the joints of the cat ¹

Joint	Flexion	Extension
Hip	33 ± 2°	164 ± 3°
Elbow	22 ± 1°	162 ± 4°
Stifle	24 ± 2°	164 ± 4°

The hip

Traumatic injuries to the hip joint in the cat such as fractures were the subject of a recent review in this journal. ² Hip luxation, hip dysplasia and osteoarthritis are the most common diseases of the hip joint.

Hip luxation

In the cat, hip luxation is often seen secondarily to a road traffic accident (RTA),^3,4 and so it is important to assess for any potential concurrent injuries. In order for a hip luxation to have occurred, parts of the joint capsule and teres ligament will have ruptured; in more severe cases the gluteals can be torn as a result of the end of the femur being forced through them. Some cases will have concomitant fractures.

While hip luxation does not represent a life-threatening emergency, prompt management is important to restore normal joint congruency and cartilage nutrition.

The most common form is a craniodorsal luxation (72%) (Figure 1); ventral luxations are exceedingly rare. ³ While these injuries do not represent life-threatening emergencies, prompt management is important to restore normal congruency and thus cartilage nutrition.

Figure 1

Ventrodorsal (a) and lateral (b) radiographs of a cat with craniodorsal hip luxation. This cat was severely lame and had an externally rotated stifle

Manual manipulation can be used to replace the hip. It is important not to make multiple attempts or be too forceful with a hip that won’t reduce, as this can damage cartilage. The reluxation rate in cats following closed reduction is about 50%. ⁵ The application of an Ehmer sling does not influence the reluxation rate; ⁴ additionally, these have a tendency to slip and are not well tolerated by cats.

Cases that do not respond to closed reduction will require surgical management. There are many options available but no one ‘best’ method. Techniques include:

• Suturing of the joint capsule;

• Hip toggle;

• Iliofemoral suture;

• Transarticular pinning.

Currently, a hip toggle is the author’s preferred technique for management of all hip luxations, in combination with suturing of the joint capsule (Figure 2). The procedure is the same as in the dog but, technically, is easier in the cat as the hip is not as deep and is easier to externally rotate.

Figure 2

Lateral (a) and ventrodorsal (b) radiographs of a cat with craniodorsal hip luxation following reduction and stabilisation with a toggle

For a detailed description of the various techniques, the reader is referred to an appropriate orthopaedics text.

Hip dysplasia and secondary osteoarthritis

Hip dysplasia is well recognised in the dog, as reflected by a plethora of evidence-based articles and well-defined treatment plans. ⁶ Feline hip dysplasia was first reported in the 1970s,^7,8 and more recently studies have shown a radiographic prevalence varying from 7–32%.^9,10 Purebred cats have a higher incidence of hip dysplasia (12%), compared with the typical domestic shorthair (6%).^9,10 The role of genetics in hip dysplasia in the cat is not well defined.

Breeds with a higher prevalence of hip dysplasia^9,10

• Maine Coon

• Himalayan

• Siamese

• Abyssinian

• Devon Rex

• Persian

As in dogs, hip osteoarthritis can develop secondarily to hip dysplasia, and also to joint trauma such as luxations and acetabular fractures, and inevitably leads to pain and loss of function.

Due to the fact that hip dysplasia in cats is not well recognised by owners, and given that the majority of cats will exercise out of sight of their owners, it can be difficult to pick up on the more subtle signs. Typically, clinical signs of hip dysplasia and hip osteoarthritis include behavioural changes such as inactivity, reluctance to jump or go up and down stairs, and lameness. Physical examination may reveal muscle atrophy, reduced range of movement in the hip joint, pain on manipulation and crepitus.

The radiographic features of hip dysplasia share some similarities with the dog, such as a shallow acetabulum and subluxation of the femoral head. The degenerative changes seem to develop later and are less marked than in the dog (Figure 3), with the changes being recognisable at the cranial border of the acetabula. It is important to remember that, as in the dog, there is a poor correlation between radiographic signs of joint disease and clinical signs of joint disease. It is, therefore, of the utmost importance that decision making is based on a good clinical history and a full physical examination to determine the source and severity of discomfort.

Figure 3

Ventrodorsal radiograph of a cat with osteoarthritis secondary to hip dysplasia. This cat exhibited quite subtle clinical signs, with reluctance to jump onto the kitchen worktop being the most noticeable to the owner

Conservative management plan for cats with hip dysplasia

• Administer NSAIDs and ensure strict rest for 2 weeks to reduce pain and inflammation. Confinement to a cage may be needed for some individuals.

• Commence physiotherapy after 2 weeks rest. Ideally, this should be under the supervision of a registered physiotherapist and may involve land- and/or water-based activities (Figure 4) to improve muscle mass, fitness and mobility.

  Figure 4

  Although not tolerated by all, some cats can respond well to water-based activities. Courtesy of Karl Jones

• During weeks 3–8 introduce regular, but controlled, exercise of gradually increasing intensity and duration.

• Avoid excessive playing, in particular unrestricted access to the house and garden, in the first 4 weeks following confinement.

• Weight loss (when needed) should involve a strict calorie-controlled diet; regular evaluation is important to ensure compliance and assess progress towards the target weight.

• Oral nutraceuticals such as chondroitin sulphate and glucosamine may benefit some individuals. However, their use is controversial and recent studies in man show that, compared with placebo, glucosamine, chondroitin, and their combination, do not reduce joint pain or have an impact on narrowing of joint space. ¹¹

Management strategies are similar to those employed in the dog, with conservative management consisting of rest, non-steroidal anti-inflammatory drugs (NSAIDs) and weight management. The plan outlined in the box above provides a good starting point and can obviously be adapted for each individual and their circumstances. More severely affected cats may require longer rest periods to allow inflammation and associated pain to reduce; mildly affected individuals may require only a few days of rest.

The majority of cats can be managed successfully in this way. For those cats that are refractory to conservative management surgical options are available. Femoral head and neck excision (FHNE) currently remains the most common procedure because it is simple to perform, has few complications and does not require expensive surgical equipment or specialist skills. This surgery is carried out via a craniolateral approach to the hip with partial tenotomy of the deep gluteal. An assistant then externally rotates the limb so that the stifle joint is perpendicular to the floor and the patella is pointing towards the ceiling, and an oscillating saw is used to make a vertical cut from just medial to the greater trochanter to just proximal to the lesser trochanter (Figure 5). Alternatively an osteotome, bone cutters or rongeurs can be used. In the author’s experience, the majority of cat owners report a good outcome following FHNE with high owner satisfaction.

Figure 5

Radiograph of the femur of a cat showing the approximate position and angle for performing a femoral head and neck excision

With the advent of new technology total hip replacement (THR) has become an option in the cat. According to one study, hip flexion, hip extension and thigh girth after THR compared favourably with similar measurements made after FHNE. ¹² Functional outcomes after THR were reported as excellent, whereas functional outcomes after FHNE ranged from poor to excellent, suggesting that, in some cats, THR may offer the best choice for improved function. ¹²

For those vets involved with cat breeders on a regular basis it is worth noting that some studies have described a more objective method of assessment of hip dysplasia in cats, ¹⁰ based on radiographic measurements that are commonly used in dogs (eg, Norberg angle and distraction index [measure of joint laxity]). These require specific radiographic positioning. The results of one study showed that the distraction index of normal cats is higher than that of dogs and that the Norberg angle of normal cats is 95° (ie, lower than in dogs). Unless routine screening of young at-risk cats is performed to assess the likelihood of hip dysplasia progressing to osteoarthritis these measurements are of limited use to most vets on a day-to-day basis. This study concluded that cats with a Norberg angle of less than 84° and a distraction index of greater than 0.6 were likely to develop hip osteoarthritis. ¹⁰

Readers are referred to an accompanying article in this special issue by Bennett et al for further discussion on the management of feline osteoarthritis. ¹³

The elbow

Osteoarthritis

There are relatively few publications describing non-traumatic joint disease affecting the elbow of the cat. Review articles on feline degenerative joint disease have reported that the elbow shows a relatively high incidence of osteoarthritis, ¹⁵ begging the question as to why this might be the case. The possibility of elbow dysplasia in the cat has been raised following arthroscopic examination of the elbow joint, ¹⁶ resulting in the removal of fragmented medial coronoid process. There are, however, no other reports in the literature to support this and so no specific advice on the best management of elbow dysplasia can be given. Currently, there is no joint replacement available for the feline elbow; if conservative management were unsuccessful, then arthrodesis or amputation would become options for managing intractable joint pain.

Another cause of osteoarthritis of the elbow joint might be congenital elbow luxation.^17,18 Management of this condition would depend on the severity of the clinical signs, with the majority of cats undergoing conservative management, and elbow arthrodesis being reserved only for those cases that respond poorly to this. Elbow arthrodesis is not commonly performed in the cat. In the literature there is one report of surgery on three cats, which documented a good to moderate outcome in only two of the cases. ¹⁹

Epicondylitis

An unusual condition of the feline elbow is epicondylitis. This shows similarities to a condition described in the dog where there is partial or complete avulsion of the flexor muscles from the medial epicondyle. ²⁰ There is only one description of this condition available in the current literature, ²¹ which states that affected individuals can be asymptomatic or mildly affected, with pain elicited on palpation of the medial epicondyle of the humerus. Radiographic findings include mineralisation in the area of origin of the flexor tendons caudal and distal to the medial epicondyle. Treatment of affected individuals involves removal of the mineralised fragments and suturing of the debrided tendons to the surrounding fascia, followed by immobilisation in a Robert-Jones bandage for 10 days and restricted activity for a further 4 weeks. ²¹ No outcome was reported in the published case.

The stifle

Patellar luxation

Patellar luxation is well recognised and well defined in the dog, and there is good evidence underpinning the various therapeutic techniques performed. ²³ In cats the condition is less common, although its management is based on many of the same principles that apply in dogs. Breeds such as the Abyssinian and Devon Rex are reported to have a higher incidence of patellar luxation, although other breeds and non-pedigree cats can also be affected.^24–28 It is likely that there is a hereditary component but the exact details of this are unclear. An association with hip dysplasia has also been reported.^8,25,28,29

Medial luxation of the patella is the most common presentation and it is not unusual for both stifle joints to be affected. As in dogs, most cats presenting with patellar luxation are relatively young. One study found an average age of presentation of 3.3 years, ³⁰ but the wide range in age of cats involved in the study (5 months to 15 years) may have skewed the average. Compared with dogs there is more laxity of the patella in cats and care must be taken to avoid overinterpreting the physical examination findings. Some authors suggest that the grading scheme for dogs (I–IV) is used with caution because of this increased laxity and have devised an alternative A–D grading scheme (see box on page 27). ³¹ However, the grading scheme that applies to dogs can also be used and, in the author’s experience, works well in cats.

As in the dog, a shallow trochlear groove (Figure 6) and medial displacement of the tibial tuberosity are the most common changes seen with patellar luxation. However, the limb deformity reported in dogs ³² is not a recognised feature of patellar luxation in cats. Secondary changes such as cartilage erosions on the trochlear ridges and the caudal aspect of the patella, as well as osteoarthritis, can be seen in more severe or more chronically affected cases.

There is more laxity of the feline patella compared with the canine patella and care must be taken not to overinterpret physical examination findings.

Figure 6

Intraoperative photograph showing a shallow trochlear groove in a cat with grade B/C medial patellar luxation

Clinical signs in the cat are variable and can include reluctance to jump, a crouched and awkward gait with the stifles externally rotated, and lameness. Alternatively, signs may be acute in onset with a traumatic aetiology or concurrent cranial cruciate ligament rupture.

Decision making in the management of patellar luxation must always take account of the clinical signs, as a grade A luxation in an older cat with no clinical signs may not require intervention. The author’s preference in younger cats is to consider surgery in all clinically affected individuals, and those cats with grade B and above patellar luxation, as persistent/recurrent luxation will inevitably lead to cartilage erosions and secondary osteoarthritis, and early surgery in these cases can help to minimise the effects of this.

As in dogs, the main aim of surgery in cases of patellar luxation is to deepen the trochlear groove and restore normal alignment between the quadriceps muscle mass, patella and tibial crest. A number of well-described techniques are available to achieve this. These include soft tissue procedures such as fascial release and imbrications, and bone-altering procedures to deepen the groove such as wedge recession and block recession sulcoplasties, along with tibial crest transposition to improve alignment. The block recession sulcoplasty offers increased trochlear width and depth compared with a wedge recession, ³³ and is the author’s preference in cats as it is simple to perform (Figure 7). The key with patellar luxation is to capture the patella and maintain its position in the trochlear groove. With a block recession, the groove is wider and maintains depth more proximally than with a wedge recession. When performing a block recession care must be taken not to damage the thin trochlear ridges with the chisel.

Figure 7

Intraoperative photograph showing a trochlear groove following a block recession sulcoplasty (compare with Figure 6)

Grading system for patellar luxation in cats ³¹

As in the dog it is only on very rare occasions that soft tissue procedures alone would be used as the main treatment. Such occasions would include traumatic patellar luxation, when conformation is normal and luxation is secondary only to torn supporting structures. When performing tibial crest transposition in cats the author has found that the strength of the distal fascial attachment is often less than in the dog; therefore, a pin alone is not enough to maintain position of the crest and avulsion could potentially occur. For this reason, the author routinely places a tension band wire in cats unless a significant amount of bone stock and attachment can be preserved distally (Figure 8).

Figure 8

Lateral (a) and caudocranial (b) radiographs showing a tibial crest transposition in a young cat; note the preservation of distal bone on the lateral view to avoid avulsion on the tibial crest. The cuts from the trochlear block recession can also be seen

Cranial cruciate ligament rupture

Cranial cruciate ligament rupture is the most common orthopaedic condition in dogs; it has well recognised risk factors,^34,35 and usually occurs secondarily to a disease process, rather than as an acute traumatic injury. Some clinicians might automatically assume that a rupture of the cranial cruciate ligament in cats must have a traumatic aetiology. However, due to the fact that cats are not normally seen exercising, any trauma is rarely observed, which makes this assumption hard to prove. Some studies in cats have shown that the aetiology and presentation may actually be similar to that seen in some dogs. ³⁶

Clinical signs of cruciate rupture in cats are very similar to those of dogs, with marked lameness often being present. Physical examination findings include stifle effusion and pain on manipulation. Some authors report a click on manipulation of the stifle joint as being indicative of a meniscal tear. ³⁷ In the author’s hands this is not a consistent finding and the absence of a click should not deter the surgeon from performing a full and thorough exploration of the joint if surgery is being performed. As in dogs a positive cranial drawer test provides the definitive diagnosis. This is often easier to elicit in the cat than in a well muscled dog. Radiographs typically show joint effusion; sometimes cranial displacement of the tibia may be apparent and osteoarthritis may be present in some cases.

As with dogs there are numerous techniques described for the management of cranial cruciate ligament rupture in the cat. Due to the paucity of case numbers reported in the literature it is hard to recommend any one management strategy over another. The author’s approach to this condition in the cat is summarised in the algorithm above right. Surgical management consists of exploration of the joint to further confirm the diagnosis and also to inspect both menisci thoroughly. Any damaged portions of meniscus are sharply excised with a blade. The author’s preferred technique for management in cats is extracapsular stabilisation, which involves passing a nylon suture (40 lb) around the lateral fabella and through a hole in the tibial crest before securing with a metal crimp. This surgical approach has proved very successful, with cats returning to normal use of the leg at just over 2 weeks postoperatively. ³⁶

Both tibial tuberosity advancement (TTA) and tibial plateau levelling osteotomy (TPLO) are now commonly performed in the dog, with many surgeons believing that they produce better mobility and function than conventional techniques. ³⁸ TTA and TPLO have been performed successfully in the cat,^39,40 but there is no research or biomechanical evidence to suggest that the forces involved in the stifle joint of cats mirror those in the dog and so it is hard currently to recommend these techniques over the simpler surgical solutions.

The author’s preferred technique for management of cranial cruciate ligament rupture in cats is extracapsular stabilisation.

Stifle disruption

Stifle disruption is a severe traumatic injury that results in complete dislocation of the tibiofemoral joint and severe instability. It involves damage to the collateral ligaments, cranial and caudal cruciate ligaments and joint capsule. The most common combination of injuries is rupture of the cranial and caudal cruciate ligaments and medial collateral ligament. ⁴¹ Meniscal injury is present in most cases. ⁴¹

Management of stifle disruption in cats

• Surgically explore the joint, resecting any damaged meniscus

• Place a temporary small diameter (1.0–1.2 mm) transarticular pin. ⁴³ Leave the pin long for easy removal. This pin helps to maintain reduction of the joint, making it easier to handle as well as preventing implant over-tightening

• Repair or replace ligaments – typically using screws and washers with nylon in a figure-of-eight pattern

• Flush and close the joint capsule

• Place a transarticular external skeletal fixator

• Remove the temporary pin

• Maintain the external skeletal fixator for 2–4 weeks

• Ensure strict cage rest initially. This restriction of activity is maintained following removal of support (such as an external skeletal fixator) for a further 2–4 weeks

Orthogonal radiographs taken under general anaesthesia help the clinician assess for any concurrent bony injuries (Figure 9), while careful palpation and surgical exploration is required to identify the degree of ligamentous injury present.

Figure 9

Lateral (a) and caudocranial (b) radiographs of a cat with a disrupted stifle joint showing the abnormal relationship between the femur and tibia

In all cases of stifle disruption surgical management is essential to restore function and mobility to the injured limb. The main aims of surgery are to repair or replace all ruptured structures and obtain joint reduction with adequate stability. This can be achieved in a number of ways:

• Ligamentous reconstruction using screws/washers/suture anchors and nylon;

• Temporary transarticular external skeletal fixation, ⁴¹ with or without ligamentous reconstruction;

• Transarticular pinning, ⁴² with or without ligamentous reconstruction

While a detailed description of the techniques for dealing with stifle disruption in the cat is beyond the scope of this article, a brief outline of the author’s preferred approach is presented in the box above.

The main aims of surgical management of stifle disruption are to repair or replace all ruptured structures and obtain joint reduction with adequate stability.

The anticipated outcome in most cats is a reasonable return of function. In the long term, restricted motion and joint thickening should be expected, and, as with all joint injuries, osteoarthritis is inevitable.

Key points

• Spend time taking a full history from the client and performing a thorough physical examination.

• Be aware of the common diseases affecting the joints of cats.

• Appreciate the radiographic differences that exist between cats and dogs.

• Understand the management strategies for joint diseases in cats.