Clinical signs and results of treatment in cats with patellar luxation: 42 cases (1992–2002)

Catherine A. Loughin Long Island Veterinary Specialists, 163 S Service Rd, Plainview, NY 11803.

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Sharon C. Kerwin Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Giselle Hosgood Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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P. Brendon Ringwood Long Island Veterinary Specialists, 163 S Service Rd, Plainview, NY 11803.

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Jamie Williams Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Joseph D. Stefanacci Long Island Veterinary Specialists, 163 S Service Rd, Plainview, NY 11803.

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Robert J. McCarthy Foster Hospital for Small Animals, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA 01536.

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Abstract

Objective—To describe clinical signs and results of treatment in cats with patellar luxation.

Design—Retrospective case series.

Animals—42 cats in which patellar luxation had been diagnosed on the basis of results of palpation of the stifle joints.

Procedures—Degree of luxation was graded on a scale from 1 to 4, and severity of lameness was graded on a scale from 0 to 5. Radiographs of stifle joints were evaluated for signs of osteoarthritis. Long-term function was classified as poor, fair, good, or excellent.

Results—34 cats had bilateral luxation and 8 had unilateral luxation. Only 7 (17%) cats had a history of trauma. Mean age of the cats was 3.3 years, and mean weight was 4.26 kg (9.4 lb); 26 (62%) were domestic shorthairs. Seventy-three of the 76 (95%) affected joints had medial patellar luxation. Luxation grades could be assigned to 65 joints, with grade 2 (30 joints) and 3 (22 joints) luxation being most common. Lameness grades could be assigned to 73 joints, with grade 1 lameness (27 joints) most common. Outcome was excellent for 8 of 17 joints treated without surgery and for 23 of 35 joints treated surgically. Complications attributable to surgery were reported in 8 cats.

Conclusions and Clinical Relevance—Patellar luxation should be considered as a cause of hind limb lameness in cats. Low-grade luxation can be associated with lameness of the same severity as high-grade luxation. Surgical correction of patellar luxation in cats with grade 2 or 3 lameness can result in a favorable outcome.

Abstract

Objective—To describe clinical signs and results of treatment in cats with patellar luxation.

Design—Retrospective case series.

Animals—42 cats in which patellar luxation had been diagnosed on the basis of results of palpation of the stifle joints.

Procedures—Degree of luxation was graded on a scale from 1 to 4, and severity of lameness was graded on a scale from 0 to 5. Radiographs of stifle joints were evaluated for signs of osteoarthritis. Long-term function was classified as poor, fair, good, or excellent.

Results—34 cats had bilateral luxation and 8 had unilateral luxation. Only 7 (17%) cats had a history of trauma. Mean age of the cats was 3.3 years, and mean weight was 4.26 kg (9.4 lb); 26 (62%) were domestic shorthairs. Seventy-three of the 76 (95%) affected joints had medial patellar luxation. Luxation grades could be assigned to 65 joints, with grade 2 (30 joints) and 3 (22 joints) luxation being most common. Lameness grades could be assigned to 73 joints, with grade 1 lameness (27 joints) most common. Outcome was excellent for 8 of 17 joints treated without surgery and for 23 of 35 joints treated surgically. Complications attributable to surgery were reported in 8 cats.

Conclusions and Clinical Relevance—Patellar luxation should be considered as a cause of hind limb lameness in cats. Low-grade luxation can be associated with lameness of the same severity as high-grade luxation. Surgical correction of patellar luxation in cats with grade 2 or 3 lameness can result in a favorable outcome.

Clinically normal cats have some degree of laxity in the stifle joint, with subluxation of the patella considered to be a common finding in healthy cats.1 In contrast, patellar luxation has been reported infrequently in cats.1–11 In cats with patellar luxation, the patella usually luxates medially, and the condition may be unilateral or bilateral.7 Patellar luxation can result from congenital malformations or trauma, and there are conflicting reports regarding the relative frequency of congenital versus traumatic patellar luxation in1–5,7,9,10 In general, however, congenital luxation is believed to be more common.1,7 It has also been suggested that there is a weak association between patellar luxation and hip dysplasia in cats.1

Clinical signs of patellar luxation may include intermittent locking of the stifle joint following extension7 or a shuffling or crouching gait.5 Although patellar luxation may result in lameness, affected cats are not always lame, and occult patellar luxation may be an incidental finding.3,5,7 Surgical repair has been reported to provide favorable results5,7; however, it has been stated that lame cats have a better clinical outcome following nonsurgical rather than surgical treat-ment.12 In contrast, others have reported that nonsurgical management is not associated with improvements in the severity of lameness.5

To our knowledge, information on the severity of lameness in cats with patellar luxation or grade of patellar luxation has not been published, nor have radiographic abnormalities in cats with patellar luxation been reported. The purposes of the study reported here, therefore, were to describe clinical signs, including severity of lameness, grade of patellar luxation, and radiographic abnormalities, in cats with patellar luxation and to report outcome following surgical and nonsurgical treatment.

Criteria for Selection of Cases

Medical records of all cats examined at the Louisiana State University Veterinary Teaching Hospital between June 1992 and November 1999, the Foster Hospital for Small Animals at Tufts University between June 1979 and March 1999, and the Long Island Veterinary Specialists between October 1998 and October 2002 were searched. Cases were included in the study if a diagnosis of patellar luxation had been made on the basis of results of palpation of the stifle joints.

Procedures

For cases included in the study, information on history, age, sex, breed, body weight, clinical findings, radiographic abnormalities, treatment, complications, and outcome was obtained from medical records. In all cats, degree of patellar luxation had been graded on a scale from 1 to 4 on the basis of criteria developed for grading patellar luxation in dogs.a Grade 1 luxation was defined as luxation that occurred when manual pressure was applied to the patella with the limb in extension with spontaneous reduction when the patella was released. Grade 2 luxation was defined as luxation that occurred spontaneously with spontaneous reduction and with the patella in a normal position most of the time. Grade 3 luxation was defined as continuous luxation although the patella could be reduced to its normal position with manual pressure. Grade 4 luxation was defined as continuous luxation with an inability to reduce the patella to its normal position with manual pressure.

For cases included in the study, a lameness grade ranging from 0 to 5 was assigned if there was sufficient information in the medical record to accurately assess the severity of lameness. Criteria used to grade severity of lameness were based on criteria used to grade severity of lameness in dogs with patellar luxation.13 Grade 0 was defined as no clinical evidence of lameness. Grade 1 was defined as mild intermittent weight-bearing lameness. Grade 2 was defined as frequent, intermittent weight-bearing lameness. Grade 3 was defined as continuous weight-bearing lameness. Grade 4 was defined as weight-bearing lameness with occasional non–weight-bearing lameness. Grade 5 was defined as continuous non–weight-bearing lameness.

Available radiographs of the affected stifle joints were reviewed by a board-certified veterinary radiologist. Radiographs from Tufts University and Louisiana State University were scored by a single radiologist (JW), and radiographs from Long Island Veterinary Specialists were reviewed by a second radiologist (JS). Radiographs were only scored if 2 views (mediolateral and caudocranial or craniocaudal) were available. Severity of radiographically evident osteoarthritis of the stifle joint was scored, as described.13,14 In brief, 9 anatomic sites in each joint were examined, with each site given a score from 0 to 3. Scores for the 9 sites were then added to obtain the overall severity score; possible scores ranged from 0 to 27. Radiographs were also examined for evidence of soft tissue and joint capsule thickening, medial or lateral location of the patella, and tibial or femoral deformity. When radiographs of the hip joints were available, these radiographs were examined for signs of hip dysplasia.

Long-term function was evaluated on the basis of results of follow-up orthopedic examinations performed at the participating institutions or through telephone conversations with the referring veterinarians and owners. When possible, patellar position at the time of reevaluation was determined. Clinical outcome was classified as poor (non–weight-bearing or weight-bearing lameness with severe gait abnormality), fair (weight-bearing lameness with moderate gait abnormality), good (bears weight on the limb with minimal gait abnormality), or excellent (bears full weight on the limb with no gait abnormality).

Statistical analysis—Statistical analyses were performed to compare cats that underwent medical versus surgical treatment. The Fisher exact test was used to compare proportion of cats lost to follow-up after nonsurgical treatment with proportion lost to follow-up after surgical treatment. The Wilcoxon rank sum test was used to compare duration of clinical signs prior to examination between cats that received nonsurgical versus surgical treatment. The Cochran-Mantel-Haenszel test was used to compare distribution of lameness and patellar luxation grades between cats with unilateral luxation treated without surgery and cats with unilateral luxation treated surgically, between cats with bilateral luxation treated without surgery and cats with bilateral luxation in which both stifle joints were treated surgically, and between stifle joints for cats with bilateral luxation in which 1 joint was treated without surgery and the other was treated surgically. All analyses were performed with standard softwareb; values of P ≤ 0.05 were considered significant.

Results

Forty-two cases met the criteria for inclusion in the study (16 examined at Louisiana State University, 16 examined at Long Island Veterinary Specialists, and 10 examined at Tufts University). Of these, 34 (81%) had bilateral luxation and 8 (19%) had unilateral luxation (5 with left patellar luxation and 3 with right patellar luxation). Thus, a total of 76 stifle joints were affected.

Of the 42 cats included in the study, 5 were sexually intact females, 16 were spayed females, 4 were sexually intact males, and 17 were neutered males. Information on body weight was recorded for 40 cats; for these cats, mean body weight was 4.26 kg (9.4 lb; median, 4.5 kg [9.9 lb]; range, 0.9 to 7 kg [1.98 to 15.4 lb]). Information on age was recorded for 41 cats; for these cats, mean age was 3.3 years (median, 2 years; range, 5 months to 15 years). There were 2 Abyssinians, 1 Birman, 1 Chartreaux, 1 Maine Coon, 1 Manx, 1 Occicat, 3 Persians, 2 Persian crossbreds, 1 Russian Blue, 1 Siamese crossbred, 2 domestic longhairs, and 26 domestic shorthairs. Duration of lameness at the time of initial examination ranged from 1 day to 9 years (median, 1 month).

Seven (17%) cats had a history of trauma (eg, falling off a table or previous femoral fracture with malunion), but no history of trauma was included in medical records for the remaining 35 (83%) cats. For 39 cats, sufficient information was included in the medical record to allow assignment of a lameness grade (lameness grades could not be assigned for 1 cat with unilateral luxation and 2 cats with bilateral luxation). Of the 7 cats with unilateral patellar luxation for which a lameness grade was assigned, 1 had grade 1 lameness, 1 had grade 2 lameness, 3 had grade 3 lameness, 1 had grade 4 lameness, and 1 had grade 5 lameness. One cat with a unilateral patellar luxation was also grade 1 lame on the opposite limb; however, a cause for the lameness was not reported and radiographs were not obtained. Of the cats with bilateral patellar luxation with lameness scores recorded, 6 were lame in only 1 hind limb, with the remainder lame bilaterally. For the 32 cats with bilateral patellar luxation for which lameness grades could be assigned, a separate grade was assigned for each limb; thus, 6 limbs were assigned a lameness grade of 0, 29 were assigned a lameness grade of 1, 13 were assigned a lameness grade of 2, 13 were assigned a lameness grade of 3, and 3 were assigned a lameness grade of 4.

A luxation grade was recorded at the time of initial examination in 36 cats, including 5 cats with unilateral luxation and 31 cats with bilateral luxation. For the 5 cats with unilateral luxation, 1 had grade 1 luxation, 3 had grade 2 luxation, and 1 had grade 3 luxation. In all cats, the luxation was medial. For the 31 cats with bilateral patellar luxation for which luxation grades were assigned, a separate grade was assigned for each limb. Thus, 9 limbs had grade 1 luxation, 26 had grade 2 luxation, 21 had grade 3 luxation, and 6 had grade 4 luxation. In 1 limb, the patella could be luxated both medially and laterally, and in 1 cat, both patellae luxated laterally. In the remaining limbs, luxations were medial. A ruptured cranial cruciate ligament was observed in 1 cat with bilateral grade 3 medial patellar luxations.

Radiographs of the stifle joints suitable for scoring were available for 27 cats (44 stifle joints). Radiographic scores for individual joints ranged from 0 to 27 (median, 2; mode, 0), with 14 joints assigned a score of 0, 24 joints assigned a score of 1 to 9 (mild osteoarthritis), 3 joints assigned a score of 10 to 18 (moderate osteoarthritis), and 3 joints assigned a score of 19 to 27 (severe osteoarthritis; Figure 1). Cats with moderate or severe osteoarthritis ranged from 3 to 15 years old. All 3 cats with severe osteoarthritis had grade 4 medial patellar luxation. None of the cats with moderate or severe osteoarthritis had concurrent cranial cruciate ligament rupture. Other radiographic abnormalities included malunion of a femoral fracture in 1 cat, apparently free floating osteochondral fragments in 5 stifle joints, and mineralization of the joint capsule in 1 stifle joint. Radiographic evidence of hip dysplasia was observed in 6 of 14 cats for which radiographs of the pelvis were available for review.

For 37 of the 76 stifle joints, treatment consisted of rest. This included 6 cats with bilateral patellar luxations in which both joints were treated without surgery (1 cat with bilateral patellar luxations was euthanized), 21 cats with bilateral luxations in which 1 joint was treated without surgery and the other was treated surgically, and 4 cats with unilateral luxation in which the joint was treated without surgery. Of these 37 joints treated without surgery, 8 were classified as grade 1 luxation, 20 were classified as grade 2 luxation, 4 were classified as grade 3 luxation, and 1 was classified as grade 4 luxation (luxation grade was not available for 2 stifle joints). Follow-up information was available for 17 of the 37 joints treated without surgery. Follow-up time ranged from 1 month to 7 years (median, 4.5 years). Outcome was excellent for 8 joints, good for 5, fair for 2, and poor for 2. The 2 joints with a fair outcome had grade 3 and grade 4 luxation. Poor outcomes were reported for both joints in a 15-year-old cat with bilateral grade 4 patellar luxations with bilateral severe (radiographic score, 27) osteoarthritis; this cat was euthanized because of difficulty ambulating. Duration of clinical signs prior to examination was recorded for 9 cats treated without surgery and ranged from 1 to 8 weeks (median, 4 weeks; mean, 3.8 weeks).

For 39 of the 76 stifle joints, treatment consisted of surgery. This included 7 cats with bilateral luxations in which both joints were treated surgically, 21 cats with bilateral luxations in which 1 joint was treated with surgery and the other was treated without, and 4 cats with unilateral luxation in which the affected joint was treated with surgery. Of these 39 joints, 2 were classified as grade 1 luxation, 9 were classified as grade 2 luxation, 17 were classified as grade 3 luxation, and 4 were classified as grade 4 luxation (luxation grade was not available for 7 joints).

Surgical techniques that were used included medial or lateral release (22 joints), lateral or medial imbrication (38 joints), wedge recession (13 joints), sulcoplasty (2 joints), placement of an antirotational suture (4 joints), and tibial crest transposition (26 joints). Techniques were generally used in combination, depending on surgeon preference and luxation grade. In 20 of the 21 cats with bilateral luxations in which only 1 joint was treated surgically, surgery was reportedly performed on the limb on which the cat was more severely lame. In 12 of these 20 cats, luxation grade was higher for the joint treated surgically than for the joint treated without surgery, and in 5, luxation grades for the 2 joints were the same. In 3 cats, luxation grade was lower for the joint treated surgically than for the joint treated without surgery. In 1 cat, surgery was performed on the limb on which the cat was less severely lame but luxation grade was higher for this joint than for the joint treated without surgery.

Figure 1
Figure 1

Lateral (A) and caudocranial (B) radiographic views of the left stifle joint of a 15-year-old cat with bilateral grade 4 medial patellar luxation. Radiographic osteoarthritis score was 27 on a scale from 0 to 27.

Citation: Journal of the American Veterinary Medical Association 228, 9; 10.2460/javma.228.9.1370

For cats with unilateral luxation, distribution of lameness grades for cats treated surgically was not significantly (P = 0.29) different from distribution for cats treated without surgery; however, luxation grades were significantly (P = 0.007) higher for cats treated surgically than for cats treated without surgery. Lameness grades for cats with bilateral luxation in which both joints were treated surgically were not significantly (P = 0.25) different from lameness grades for cats with bilateral luxation in which both joints were treated without surgery; however, luxation grades for cats with bilateral luxation in which both joints were treated surgically were significantly (P = 0.006) higher than grades for cats with bilateral luxation in which both joints were treated without surgery. For cats with bilateral luxation in which 1 joint was treated surgically and the other joint was treated without surgery, lameness (P = 0.007) and luxation (P = 0.006) grades were significantly higher for the joints treated surgically than for the joints treated without surgery.

Often it could not be determined from the medical records whether nonsurgical management had been attempted prior to surgical intervention. However, information on nonsurgical management consisting of rest combined, in some instances, with analgesics or other medications (ie, dexamethasone, prednisone, triamcinolone, aspirin, butorphanol, and chondroitin sulfate) was recorded in medical records for 8 cats that underwent surgery. Nine cats that underwent surgery had a history of a progressively worsening lameness, but no information on nonsurgical treatment was included in the record. Duration of clinical signs prior to examination was available for 25 cats that underwent surgery and ranged from 1 to 465 weeks (median, 4 weeks; mean, 48 weeks). Duration of clinical signs prior to examination was not significantly (P = 0.92) different between cats treated surgically and cats treated without surgery.

Of the 32 cats that underwent surgery, 1 died immediately after surgery and 3 were lost to follow-up. Median follow-up time for the remaining 28 cats (35 stifle joints) was 1.5 years (range, 2 weeks to 10 years). Outcome was excellent for 23 joints, good for 10, fair for 1, and poor for 1. The proportion of cats lost to follow-up following nonsurgical treatment was significantly (P = 0.01) higher than the proportion lost to follow-up after surgical treatment.

Complications directly attributable to surgery were reported in 8 cats. Three cats that underwent surgery because of medial patellar luxation had iatrogenic lateral patellar luxation at the time of the first follow-up examination. In 2 of these cats, the iatrogenic lateral patellar luxation was not treated surgically; outcome was poor 3 years after surgery in 1 cat and excellent 5 months after surgery in the other. In the third cat, additional surgery was performed to correct the iatrogenic lateral patellar luxation, and outcome was excellent 1 year after surgery.

Pin migration occurred in 3 cats, all of which had had unilateral surgery (Figure 2). All pins were removed from these 3 cats. Outcome was excellent in 2 of these cats (follow-up times were 5 months and 2 years) and good in 1 (follow-up time was 2 years). One cat with hip dysplasia in which ipsilateral femoral head and neck ostectomy was performed at the time of patellar luxation still had patellar luxation 2 months after surgery (this cat was 1 of the 3 cats with pin migration). Additional surgery was performed 4 months after the initial surgery, at which time pins associated with tibial crest transposition were removed and an antirotational suture was placed. Outcome was good 4 years after surgery. One cat had effusion of the stifle region when examined 3 weeks after surgery. The effusion resolved with warm compresses, and outcome was excellent 5 years after surgery. One cat would not bear weight on the limb until 6 weeks after surgery; outcome was excellent 5.5 years after surgery.

Figure 2
Figure 2

Lateral radiographic views of the stifle joint of a 5-month-old cat with grade 3 patellar luxation; radiographic views were obtained before (A), immediately after (B), and 10 months after surgical correction. Notice the separation of the pins resulting from partial closure of the growth plate 10 months after surgery. This cat had an excellent outcome after pin removal.

Citation: Journal of the American Veterinary Medical Association 228, 9; 10.2460/javma.228.9.1370

Discussion

Results of the present study suggest that in cats with patellar luxation, surgical correction is typically associated with a favorable outcome and minimal complications. Surgery was performed on cats with higher grades of luxation than those medically managed. Interestingly, cats treated medically, although having lesser grades of patellar luxation, displayed similar duration and severity of lameness. Thus, lameness may not be a good indicator of the need for surgical correction and it seems prudent to recommend a period of nonsurgical management (rest and analgesics) prior to surgical intervention, particularly in cats in which signs of lameness have been present for < 2 months. Surgery may be indicated for cats with higher grades of luxation that continue to be clinically affected despite nonsurgical management. Findings of the present study also suggest that grading systems for degree of luxation and severity of lameness developed for use in dogs with patellar luxation are applicable to cats.

Bilateral luxation was more common (81%) than unilateral luxation in the present study. There did not appear to be any sex or breed predisposition, although the study population was not statistically compared with a control population of cats. Finally, only 7 (17%) cats had a history of trauma, suggesting that congenital patellar luxation is more common than acquired luxation. Our findings that bilateral was more common than unilateral patellar luxation and that congenital was more common than acquired luxation agree with results reported previously for cats7 and dogs.15

All cats in the study were brought to one of the participating institutions because of lameness of 1 or both hind limbs. The severity of lameness varied widely, although most cats would bear weight on the affected limb. In addition, 6 of 31 (19%) cats with bilateral luxation had only unilateral hind limb lameness.

In the present study, we chose to use a grading system developed for use in dogsa to classify degree of patellar luxation. Because grades are easy to assign clinically, most veterinarians would be familiar with this grading system, and grades assigned by use of this grading system in dogs are thought to be useful in treatment decision-making.

It has been suggested that there may be an association between medial patellar luxation and hip dysplasia in cats; in 1 study,1 cats were 3 times as likely to have both conditions than to have either one alone. In that study, 19 of 78 cats (24%) had both medial patellar luxation and hip dysplasia, whereas in the present study, 6 of 14 cats for which pelvic radiographs were available had both conditions. Cats with signs of pain involving the hip joints may have been more likely to undergo pelvic radiography in the present study, artificially inflating the percentage of cats found to have both conditions. However, one of the participating institutions (Tufts University) routinely performed pelvic radiography in cats with patellar luxation. Additional studies are needed to assess the possible association between patellar luxation and hip dysplasia in cats.

Thirty-eight of the 44 (86%) stifle joints in the present study for which radiographs were available had no radiographic signs of osteoarthritis or had signs of only mild osteoarthritis. However, we were able to document severe osteoarthritis associated with grade 4 patellar luxation, which had not previously been reported in cats. Because follow-up radiography was rarely performed, we could not determine in the present study whether surgery delayed or decreased the development of osteoarthritis; however, surgical correction of grade 3 and 4 patellar luxations improves outcome in dogs,13 and the same may be true in cats.

Treatment of patellar luxation in cats has been controversial. Nunamaker12 has stated that surgical correction is not recommended because of development of deformities of the proximal portion of the tibia after osseous reconstruction. Although we have observed this radiographically in young cats undergoing tibial crest transposition, we have not identified any adverse clinical effects. In contrast, in a study7 of 21 cats with patellar luxation, outcome was excellent for 7 of 13 cats that underwent surgery. Additionally, in a study5 of 8 cats, outcome was good in 6 cats that underwent surgery but poor in the 2 cats treated without surgery; surgery was eventually performed in these 2 cats. In the present study, outcome was excellent for 8 of the 17 joints treated without surgery and for 23 of the 35 joints treated surgically. Importantly, we were able to obtain follow-up information for more of the joints treated surgically than without surgery; thus, care must be taken when interpreting the results of this study. In particular, our results do not allow us to conclude whether surgery resulted in a better outcome than nonsurgical management, as we could not directly compare these 2 groups.

Not surprisingly, for cats with bilateral luxation in the present study in which 1 joint was treated surgically and the other joint was treated without surgery, lameness and luxation grades were significantly higher for the joint treated surgically than for the joint treated without surgery (ie, surgery was performed on the more severely affected joint). Similarly, luxation grades for cats with bilateral luxation in which both joints were treated surgically were significantly higher than grades for cats with bilateral luxation in which both joints were treated without surgery, even though lameness grades for cats with bilateral luxation in which both joints were treated surgically were not significantly different from lameness grades for cats with bilateral luxation in which both joints were treated without surgery.

Additional study is needed to determine whether lameness grade, luxation grade, or radiographic osteoarthritis score is associated with outcome in cats with patellar luxation.

Major complications that necessitated additional surgery occurred in 2 cats in the present study (1 with iatrogenic lateral luxation and pin migration and 1 with persistent luxation), and a third cat with iatrogenic lateral luxation whose owner did not allow surgery presumably would have benefited from a second surgical procedure. One cat died immediately after surgery, but death was presumed to be a result of anesthetic, rather than surgical, complications. Minor complications that were encountered included pin migration that required sedation for pin removal, iatrogenic lateral patellar luxation that resolved without additional surgery, effusion of the stifle region, and delayed weight bearing. Previously reported complications in cats undergoing surgical treatment of patellar luxation include tibial crest avulsion,10 patellar tendon rupture,10 reluxation,5,7 iatrogenic luxation in the opposite direction,7 and patellar fracture.5

Surprisingly, only 1 cat in the present study had concurrent cranial cruciate ligament rupture. In dogs, it has been suggested that patellar luxation may lead to cranial cruciate ligament rupture as a result of loss of the stabilizing forces of the quadriceps muscles, which act to prevent cranial drawer motion. However, in a previous study,15 cranial cruciate ligament rupture was no more common in dogs examined because of patellar luxation than in a group of control dogs. In a study16 of cats with cranial cruciate ligament rupture, concurrent patellar luxation was not observed.

The present study describes clinical findings for a series of cats with patellar luxation. Interestingly, the severity of lameness appeared similar across luxation grades. Although medical management was applied to cats with lesser grades of luxation and surgical management was applied to cats with higher grades of luxation, both management strategies resulted in resolution of lameness in some cats. Patellar luxation should be considered as a possible cause of hind limb lameness in cats and may warrant treatment. The guidelines for surgical intervention are undetermined.

a.

Putnam RW. Patellar luxation in the dog. MS thesis, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada, 1968.

b.

SAS, version 9.0, SAS Institute Inc, Cary, NC.

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