Sorrel J. Langley‐Hobbs and Eva Schnabl‐Feichter Cranial cruciate ligament (CCL) rupture in cats is much less common than it is in dogs. Both traumatic ruptures [1] and degenerative ruptures are suspected [2]. In the cat, most published reports describe or assume a traumatic etiology, but there is a subset of cats that parallels the older, overweight, canine patients in which degenerative rupture of the CCL is seen [3]. Bilateral degenerative rupture in the younger large‐breed cat has also been recognized. Conservative management and surgery, most commonly extracapsular repair or tibial osteotomies, have been used to address this condition, with osteotomies being used with increasing frequency more recently, paralleling the situation in the dog. The cruciate ligaments and the medial and lateral collateral ligament are the primary stabilizing structures of the feline stifle. Secondary stabilizers are the joint capsule, the menisci, and the muscles and tendons that span the joint [4]. The CCL prevents stifle hyperextension, excessive internal rotation, and cranial translation of the tibia. The caudal cruciate ligament prevents caudal translation of the tibia. The CCL is larger and stronger than the caudal cruciate ligament in cats which may preclude its rupture in the cat compared to the dog [4]. There are thought to be two main forms of cruciate ligament rupture in the cat: traumatic and degenerative. Seven of 50 cats developed bilateral rupture in an epidemiological study [2]. In another series of cases, the cats that had suffered cruciate ligament rupture were heavier than the general population of cats and it was purported that this injury parallels the degenerative CCL ruptures seen in overweight small‐breed dogs [3]. Periarticular osteophytosis (Figure 16.1) may be present when the cat presents with an apparent acute onset of lameness, similar to the situation in dogs. Osteoarthritis was graded as moderate to severe in 10 of 11 stifle joints in cats with CCL rupture, a finding that does not support the assumption of acute traumatic CCL rupture and making a degenerative etiology more likely [5]. Figure 16.1 Intraoperative view of the stifle of a cat with a cranial cruciate ligament rupture showing osteophytosis along the abaxial trochlear ridge (arrow). Source: © Sorrel J. Langley‐Hobbs. In the traumatic form, there may be an isolated CCL rupture but there can also be damage to other periarticular structures such as the collateral ligaments, menisci and caudal cruciate ligament, usually known as multiligamentous, disrupted or deranged injuries. In the most severely affected stifles, the femorotibial joint may be dislocated. It is very important to distinguish between an isolated CCL rupture and a deranged stifle with rupture of other ligaments as the treatment and prognosis are dramatically different between the two. Misdiagnosing a multiligamentous injured stifle as an isolated CCL rupture can have serious consequences for the outcome in the cat. Cats with complete CCL ruptures will have hindlimb lameness and stifle joint swelling, and the cranial drawer test and tibial thrust test will be positive. Partial cranial cruciate rupture has been seen in cats and in this situation the drawer test may be negative. A retrospective study evaluating 98 feline stifle joints with naturally occurring CCL disease identified 6% partial ruptures [6]. Only one partial CCL rupture was detected in another study [7] which might be due to a low incidence in cats, low case numbers, or the fact that the minimal clinical signs are not observed by owners. Traumatic ruptures may be more sudden in onset and other conditions may be present such as rupture of other ligaments (medial or lateral collaterals and caudal cruciate), patella luxation or fractures and concurrent injuries elsewhere in the body. In a cadaveric study utilizing normal cats, CCL sectioning resulted in a cranial tibial translation of nearly 9 mm [8]. Instability in cats with traumatic rupture can be pronounced and the cranial drawer can be dramatic. The diagnosis of CCL rupture is made by a combination of the history and physical examination and radiographic changes (Algorithm 16.1). Radiographs are taken to confirm the suspected diagnosis and rule out other potential causes or comorbidities (Table 16.1). Affected stifles will show compression of the infrapatellar fat pad associated with a joint effusion. It can be more difficult to detect stifle joint effusion on a radiograph in a cat compared to a dog; good‐quality radiographs and careful interpretation are required so compression of the intraarticular fat pad is not missed [9] (Figure 16.2). Intraarticular mineralization may be present and this has commonly been associated with medial compartment degenerative joint disease [10], particularly if lesions are large [11]. Small discrete lesions are common, and these may be normal or incidental findings [12]. The cat should be sedated or anesthetized prior to performing testing for cruciate ligament integrity. Both the cranial drawer and tibial compression test should be conducted. Instability will be palpable with complete ruptures; this may be pronounced if the cat has a traumatic CCL rupture. The results of the tests may be inconclusive in the presence of partial ruptures. Table 16.1 Clinical and radiographic changes in cats with cranial cruciate ligament rupture. It is important to diagnose the cat with a deranged, disrupted or multiligamentous rupture where in addition to a CCL rupture, there will be other ligamentous structures injured, most commonly the medial or lateral collateral ligament, caudal cruciate ligament, and medial meniscus. In multiligamentous injuries, there is usually significant displacement of the tibiofemoral joint or complete luxation. With the cat sedated or anesthetized, in addition to the cranial drawer and tibial compression tests, varus and valgus maneuvers should be performed to detect concurrent collateral ligament injury. However, it is worth noting that some cats with traumatic rupture of the CCL can have marked subluxation of the stifle without disruption of other ligaments (Figure 16.3). The incidence of meniscal injuries in feline CCL‐deficient stifles has been reported to be between 18% and 67% [2, 6, 7]. In the largest retrospective study, meniscal tears were found in 67 of 100 cats [6]. Isolated medial meniscal injuries were found in most cases. There was no correlation between the presence of a meniscal injury and age, breed, sex, weight, duration of lameness, presence of concurrent medial patellar luxation, degree of degenerative joint disease, or presenting side of lameness. Figure 16.2(a) A radiograph of a normal feline stifle; arrows indicate the normal relationship of the femoral condyle adjacent to the tibial eminences. (b) The contralateral stifle with cranial cruciate ligament rupture has a joint effusion (white arrows) and subluxation of the stifle (indicated by black arrows at the center of the femoral condyle and at the center of the weight‐bearing axis at the level of the tibial eminences). Source: © Sorrel J. Langley‐Hobbs. Figure 16.3 Lateral stifle radiograph from a MN 7 kg Bengal. The cat had an acute onset of lameness after a fall. There is an isolated rupture of the cranial cruciate ligament with no other ligamentous injuries although the degree of subluxation on the radiograph is marked. There is a small ossification in the stifle (black arrow), which is an incidental finding in many cats, although a likely differential diagnosis in this cat would be an avulsion fracture. The cat has displacement of the popliteal sesamoid (white arrow) which is common in cats with CCL rupture; additionally it only has one fabella, also a common finding in cats with the medial fabella often absent (unossified). Source: © Sorrel J. Langley‐Hobbs. Intraarticular or meniscal mineralization is a common finding in domestic cats [10–12]. The prevalence was reported as 46% in a population of 100 cats with the cats being significantly older and having a lower body condition score than those without stifle pathology [10]. Smaller meniscal ossifications in cats are suspected to represent a normal anatomical finding, a meniscal sesamoid bone also referred as lunula [12, 13] (Figure 16.4a). Meniscal ossicles have also been found frequently in large cats like lions, tigers and leopards older than 1 year. Those ossicles were found in the cranial horn of the medial menisci [10–12, 14]. Larger mineralizations in cats were found to be ossifications, commonly located in the joint capsule and fat pad [11], so not isolated to the meniscus (Figure 16.4b). In cats, it has been shown that larger mineralizations cause significantly more cartilage damage on the femur and tibia and therefore lead to the development of medial compartment disease [10, 11]. Interestingly, pain scores in cats with meniscal mineralization were not different to others [10, 15]. Larger meniscal calcifications have also been found in cats with cruciate disease [11] and might be connected to a traumatic event [13, 16]. Figure 16.4 Intraarticular mineralization. (a) A small lesion is often a normal finding and incidental (arrow). (b) Larger lesions most likely affecting the fat pad and joint capsule. These large lesions (arrow) are often associated with degenerative joint disease and cranial cruciate ligament rupture and their careful dissection and removal should be considered. Source: © Sorrel J. Langley‐Hobbs. Histologically, the meniscus seems to undergo a process of ossification. It starts with a chondral to osseous transformation of the cartilage with ultimate mineral deposition. Finally, this organizes into cancellous bone and bone marrow structures [10]. Measuring the tibial plateau angle (TPA) in cats is done in a similar way as described in dogs (Figure 16.5) [17]. Overall, the medial tibial articular surface is less definable in cats compared to that in dogs [7, 18]. One study compared the TPA in cats with and without CCL rupture and found a significant difference in TPA measurements between inexperienced and experienced observers [18]. Possible causes were poor definition of the cranial and caudal bone landmarks; the amount of osteoarthritis present at the caudal point of the TPA can impede making correct measurements. Figure 16.5 Preoperative measurement of tibial plateau angle (TPA) before performing a tibial plateau leveling osteotomy (TPLO) in a cat. Red line: tibial functional axis. Yellow line: tibial plateau slope. Black line: perpendicular line to the tibial functional axis. α = tibial plateau angle (TPA). Source: © Eva Schnabl‐Feichter. According to Schnabl et al. [18], cats with CCL rupture had a significantly greater mean TPA (24.7°) compared to those without any evidence of CCL injury (21.6°). The conclusion was that cats with CCL rupture have a greater TPA, and this at least lends some credence to the possibility of higher TPA being a predisposing factor for cruciate injury in this species [18]. However, another study found no difference in the TPA when comparing 50 normal cats to 25 cats with CCL rupture [1]. The mean TPA in both normal cats and cats with CCL rupture in these two studies was between 23° and 24° [1, 18] (Table 16.2). Table 16.2 Tibial plateau angle (TPA) measurements in the cat. Surgical management of CCL rupture in cats will give a quicker return to function and is the preferred choice in most circumstances. Conservative management is an alternative if surgical stabilization is not a viable option for an individual cat. There is limited published evidence about the effectiveness and outcome of conservative management of CCL rupture in cats. In one study from the 1980s where 18 cats were treated conservatively, they took an average of 5 weeks to regain gait that was considered normal by veterinarian observation [19]. The conservative management consisted of keeping the cats indoors in a room or cage for 4 weeks and then restricting activity indoors for a further 4–6 weeks, together with instigating weight loss when appropriate. A satisfactory outcome was defined as a clinically normal gait with little or no apparent muscle atrophy at the time of follow‐up; this was considered to have been achieved in all cats in a mean duration of 4.8 weeks, with a range of 1–16 weeks. Experimental transection of the CCL in cats [5] caused a distinct unloading of the deficient hindlimb when compared with the nonoperated hindlimb, which persisted for about 16–18 weeks. A decrease in muscle mass was found from muscles of the experimental hindlimb compared to the mass of muscles from the contralateral hindlimb, which was largest at 4 weeks and smallest at 35 weeks post CCL transection [5]. There was a delayed appearance of osteophytes in this model compared with the dog, suggesting that cats may be better able to compensate for CCL deficiency. This may be associated with factors of loading, the smaller size of cats compared with dogs, or a better developed neuromuscular control system in the cat [5]. Complications with conservative management include persistent lameness [9]. Eighty percent of the cats in one study showed persistent cranial drawer motion and evidence of degenerative joint disease upon physical examination and radiography despite apparent resolution of the lameness [19]. In a study of 50 cats with CCL rupture, 28 were treated conservatively and they were found to experience less chronic pain at long‐term follow‐up, and better quality of life (QoL) on the feline musculoskeletal pain index (FMPI). However, one of the limitations of this study was a possible selection bias due to a clinical decision to treat less lame cats with less severe joint disease conservatively [2]. If lameness persists following conservative management then there are various options, including continuing conservative management for a longer period of time or opting for surgical management (Algorithm 16.2). The cat should be reassessed in case a multiligamentous injury has been missed or there is another cause for the lameness such as a meniscal tear which may require treatment. Surgery is purported to give a quicker return to function and given the high rate of meniscal pathology in cats with CCL ruptures, exploratory surgery for meniscal assessment and concurrent stifle stabilization should be considered in feline patients [6]. In an experimental model of CCL transection, the medial meniscus was often reported as ragged at 12 weeks and in one cat it was visibly torn [5]. Treatment of meniscal injury (Figure 16.6) is by partial meniscectomy and careful removal of the damaged portion, preserving the intact remainder of the meniscus. Treatment or removal of the small meniscal mineralizations is generally not recommended as they may be incidental findings and not pathological. Attempts at removal will cause damage to the meniscus. Nevertheless, due to the possibility of cartilage lesions secondary to or concurrent with the large intraarticular mineralizations in the joint capsule or fat pad, excision can be performed if needed but taking care not to damage the meniscus or intermeniscal ligaments [10, 11]. Figure 16.6 A medial meniscal bucket handle tear in a cat with the torn portion folded forward (arrowed). Source: © Sorrel J. Langley‐Hobbs. Following arthrotomy or arthroscopy, the different categories of surgical options in use in the cat are extracapsular stabilization and osteotomies including tibial plateau leveling osteotomy (TPLO), tibial tuberosity advancement (TTA) and cranial closing wedge ostectomy (CCWO). Intraarticular stabilization is another option that could be considered but there is very limited evidence to support the use of this technique. Decision making in surgery can be aided by working through Algorithm 16.3. Surgical management with extracapsular suture stabilization gives an apparent quicker return to function compared to conservative management [3]. Extracapsular stabilization techniques are commonly used in the cat. The results of studies [20] showed that placing a suture between the fabella or through a suture screw close to the fabella to a hole through the tibia at the level of the insertion of the patellar ligament produced a suture that had minimal change in length during normal range of motion of the stifle and restored good function to a cadaveric stifle by elimination of cranial drawer [21]. Placement of the suture hole too far distal in the tibia is a common mistake that can result in failure of stabilization [9]. The femorofabellar ligament in the cat is fairly lax and clinically anchoring the suture around this ligament can produce a loose lateral suture. Placement of a suture through the eyelet of a suture anchor or suture screw in the femur adjacent to the lateral fabella may give better stability than placing the suture around the lateral fabella [21] and the use of suture anchors should be considered in clinical cases (Table 16.3). Table 16.3 Tips for extracapsular stabilization surgery for CCL rupture in the cat. In a retrospective study of 50 cats with CCL rupture, 22 had surgical stabilization with extracapsular sutures – the lateral fabellotibial suture (LFS) technique was used in all cats [2]. Arthrotomy was performed in 19/22 surgeries and a complete CCL rupture was noted in all 19 cats. Postoperative surgical complications were recorded in 6/22 cats (27%). Twelve surgeons with different levels of experience performed the procedures so it is possible that the low number of LFS surgeries per surgeon contributed to the complication risk. Notably multiligament stifle injuries were diagnosed in five surgically treated cats; four had collateral ligament damage and two of these had an additional complete rupture of the caudal cruciate ligament. The fifth cat had caudal cruciate ligament rupture but intact collateral ligaments. Two cats had one postoperative complication, while four cats had two. Three of the six cats with complications underwent a second surgery. Complications following extracapsular stabilization and their possible solutions are listed in Table 16.4. They include neurological deficits, seroma, persistent instability, infection, persistent lameness, stiffness on rising, osteoarthritis (Figure 16.7) and late meniscal tear [2, 3]. Reduced range in motion of the stifle following CCL surgery can be seen and may be associated with the presence of osteoarthritis. Recurrence of instability may occur due to breakage or loosening of the suture or suture anchor pullout. An algorithm is provided to aid in decision making about how to proceed with the different complications seen following surgery (Algorithm 16.4). One of the main reasons for complications in cats is when the cat is misdiagnosed as having an isolated CCL rupture when in fact it has a multiligamentous injury (e.g., collateral ligament ruptures, caudal cruciate ligament and meniscal tears). These injuries are associated with a high complication rate, and treatment options and postoperative stabilization are very different (Algorithm 16.5). Table 16.4 Complications following extracapsular stabilization in the cat, with initial, subsequent or other options for management. NSAID, nonsteroidal antiinflammatory drug; TPLO, tibial plateau leveling osteotomy; TTA, tibial tuberosity advancement. Figure 16.7(a,b) A 6‐year‐old British Blue cat presented with left cranial cruciate ligament rupture which was treated with extracapsular stabilization. A suture was threaded through a suture anchor in the femur and then through two bone tunnels in the proximal tibia. (c,d) The cat was represented 18 months later with right cranial cruciate ligament rupture and radiographs of the left stifle at this time show progression of the osteoarthritis with more pronounced periarticular osteophytosis and intraarticular mineralization. The suture anchor is unchanged in position. Source: Images (a‐c) © Sorrel J. Langley‐Hobbs. Image (d) Institution Langford Vet Services.
16
Complications Associated with Feline Cranial Cruciate Ligament Techniques
16.1 Introduction
16.2 Anatomy
16.3 Cranial Cruciate Ligament Rupture
16.3.1 Etiopathogenesis
16.3.2 Clinical Signs
16.3.3 Diagnosis
Stifle pain on manipulation, particularly on extension
Periarticular thickening especially medially
Hindlimb muscle atrophy, particularly thigh muscles
Positive cranial drawer (partial rupture may be minimal or negative)
Positive tibial thrust or compression test (partial rupture may be minimal or negative)
Joint effusion
Periarticular osteophytosis
Enthesophytes
Distal displacement of the popliteal sesamoid bone on lateral radiographs
Intraarticular radiodense bodies and mineralization
16.4 Meniscal Injury
16.4.1 Intraarticular and Meniscal Mineralization
16.5 Tibial Plateau Angle Measurement
Number of cats/stifles
Tibial plateau angle
Reference
Healthy/normal cats with no stifle disease
(50 cats, 100 stifles)
24.84 ± 4.05 (16–33)
[1]
(34 cats, 68 stifles)
21.6 ± 3.7 (12–27)
[18]
Mean angles
23.52 (12–33)
Cats with CCLR
(25 cats, 25 stifles)
22.72 ± 4.51 (13–30)
[1]
(21 cats, 21 stifles)
24.7 ± 4.5 (17–37)
[18]
Mean angles
23.62 (13–37)
16.6 Management Considerations
16.6.1 Conservative Management
16.6.2 Surgical Stabilization
16.7 Extracapsular Stabilization
Arthrotomy or arthroscopy to inspect meniscus and perform partial meniscectomy if torn
Suture placement – placing a suture between the femorofabellar ligament or through a suture anchor close to the fabella to a hole in the tibia at the level of the insertion of the patella ligament [20]
Material – large gauge [3] or 40 lb monofilament nylon, tightened at 20 N, produced favorable biomechanical stabilization of cruciate‐related stifle instability directly after surgery in an ex vivo model [22]
16.7.1 Complications with Extracapsular Stabilization
Complication
Initial management
Subsequent or other options
Persistent lameness
Pain medication (NSAIDs), rest, possibly physical rehabilitation
Investigate for other causes of lameness such as multiligamentous injury, neoplasia or patella luxation; consider an alternative surgical strategy
Meniscal tear
Arthrotomy or arthroscopy and partial meniscectomy
Pain medication (NSAIDs), rest
Infection
Culture and sensitivity and antibiotics.
Revision surgery or an alternative surgical strategy may be required later on (e.g., different suture material, TPLO, TTA)
Osteoarthritis
Pain medication (NSAIDs), rest, nutraceuticals, weight loss, environmental adaption, possibly physical rehabilitation
Salvage surgery – amputation, arthrodesis, joint replacement
Reduction in range of motion
Pain medication, physical rehabilitation
Reevaluation of the stifle stability, extracapsular suture removal?
Neurological deficits
Gabapentin or amantadine
Removal of the extracapsular suture if concerned about the suture being around popliteal nerve
Seroma
Aspiration, bandage, heat
Explore and drain or resect seroma, culture and sensitivity, extracapsular suture removal
Instability persistent
Rest; if in pain – NSAID
Revision surgery or an alternative surgical strategy may be required (i.e., TPLO + extracapsular ligament repair)
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