Medial patellar luxation (MPL) and cranial cruciate ligament rupture (CCLR) are reported to be less common in cats than in dogs (3,17,23). The difficulty of finding lameness and spontaneous resolution without treatment in a proportion of cats may contribute to this relatively low prevalence (3,17). Traditionally, treatment methods for MPL in cats, such as trochleoplasty, soft tissue balancing, and tibial tuberosity transposition (TTT), are similar to those of dogs (12,16). Dynamic stabilization of CCLR disease using osteotomy procedures, such as cranial tibial wedge osteotomy (CTWO), tibial plateau leveling osteotomy (TPLO), tibial tuberosity advancement (TTA), or CORA based leveling osteotomy, are considered to be favorable surgical methods than extracapsular stabilization (ECS) in dogs, but ECS is the most routinely performed procedure in cats (2,12,13,17,20,23). When the dog is concomitantly affected by MPL and CCLR, a combination of both surgical techniques may be needed (8,14). Furthermore, this may be achieved by modification of traditional dynamic stabilization of CCLR, such as modified TPLO and tibial tuberosity transposition-advancement (TTTA) (7,8,14,24).

Although the incidence of cats with concomitant CCLR and MPL is increasing, there are only a few reports that describe surgical technique options and clinical outcomes for this condition (17,23). Recently, several reports described the surgical procedure, results, and postoperative complications of the osteotomy technique in cats with CCLR disease (9,17,20). Furthermore, a case report of three cats with concomitant CCLR and MPL described the treatment and clinical outcomes using a combination of TTTA and corrective surgery for MPL (3). However, there was no reports describing surgical methods and clinical outcomes in immature cats, and TPLO and TTA are not appropriated for immature patients (13). Because TPLO and TTA have a risk of impairing the growth plates in the proximal tibia, these techniques are difficult to apply to immature cats (13). Considering several limitations of TPLO and TTA, CTWO may be an optimal surgical option to treat concomitant CCLR and MPL in immature cats as in dogs.

The purpose of this report is to show successful case that CTWO assisted by patient-specific surgical guides can be the best surgical option for treatment of an immature cat with concomitant CCLR and MPL.

A 7-month-old, 5.2 kg, spayed female Norwegian Forest cat presented with chronic lameness of the left hind limb. The cat had no traumatic events and stayed indoors only. The patient had not responded to the administration of nonsteroidal anti-inflammatory drugs (NSAIDs) and conservative management for more than 3 months.

On gait examination, the patient was non-weight-bearing with grade 5 lameness in the left hind limb (6). Orthopedic examination revealed positive cranial drawer motion and tibial compression test in the left hind limb. The grade 3 MPL disease was confirmed in the left hind limb. Radiographic examination revealed infrapatellar fat pad signs, joint mice in the fat pad region, periarticular osteophytes, and proximal tibial physis (Fig. 1A). The MPL was also revealed and no significant bone deformity was identified (Fig. 1B). Based on the results of the examination, the patient was diagnosed with concurrent CCLR and MPL in the left hind limb there was no other diseases, such as collateral ligament injuries.

Figure 1. Preoperative radiograph and computed tomography (CT) images of the immature cat. (A) Mediolateral view of the left hind limb. Infrapatellar fat pad sign, joint mice in the fat pad region (yellow arrow), periarticular osteophytes, and growth plates in the proximal tibia (yellow arrow head) are observed. (B) Craniocaudal view of the left hind limb. The medial patellar luxation is revealed (yellow circle). (C) The 3D reconstruction image of the left hind limb shows medial patellar luxation, and there is no notable bone deformity.

Computed tomography (CT) scan (Revolution ACT; GE Medical Systems, New York, USA) of the patient’s left hind limb was performed to evaluate the bone deformity. CT data were reconstructed as 3D model images using the software Xelis 3D (Infinitt, Seoul, Korea), and there was no remarkable bone deformity (Fig. 1C). The patient’s preoperative TPA was 25.3°, and the postoperative target TPA was planned to be 5.8°. It was the most suitable angle to accommodate three screws in the proximal segment and we planed target TPA was 5.8 degrees. The osteotomy was designed as proximally as possible while conserving a large enough proximal bone segment to allow fixation with at least three screws in each segment and not damage of the tibial tubercle apophysis.

The patient was positioned in dorsal recumbency, and the left hind limb was clipped and prepared for aseptic surgery. A standard lateral parapatellar arthrotomy was performed for lateral imbrication and allowed for exposure of the stifle joint. Stifle exploration revealed a shallow trochlear groove and complete rupture of the cranial cruciate ligament (Fig. 2A). The meniscal injury was not observed and patellar groove cartilage appeared normal. The surgical debridement of the cranial cruciate ligament remnants was performed to decrease inflammatory responses during the postoperative period. Then block recession trochleoplasty was performed to correct the shallow trochlear groove. Soft tissue balancing was adjusted through lateral imbrication and medial releasing.

Figure 2. Surgical procedure. (A) Stifle exploration revealed a shallow trochlear groove. (B) The osteotomy procedure guides the sagittal saw blade along with the osteotomy guide. (C) Bone reduction is performed using a reduction and compression guide, showing parapatellar arthrotomy skin incision (white dot line) for MPL. (D) The 2.0 mm plate is applied to fixation of two bone segments.

After corrective surgery for MPL, the second medial incision was made to the distal tibia to perform CTWO. Patient-specific surgical guide (Customedi; Daejeon, Korea) was used for the precise osteotomy. The material of the patient bone model is Harpiks resin (Zerone3D, Korea), the material of the patient specific surgical guide is SG-clear 1000 (Dentis, Korea), and these are made using 3D printing technique. The osteotomy guide was placed in the craniomedial of the proximal tibia and moved up and down to find the point where movement was minimized and the best contact with bone. Once the guide was fixed to the bone using K-wires, the osteotomy was performed by guiding the sagittal saw blade along with the osteotomy guide (Fig. 2B). A reduction guide was then used for bone reduction and a 2.0 mm locking plate (Jeil Medical; Seoul, Korea) to fix the osteotomized tibial segments (Fig. 2C, D). After fixation, the surgical guide was removed and a 24 gauge cerclage wire was placed on the cranial border of the tibia to further stabilize the tibial segments. The muscle, subcutaneous tissue, and skin were closed routinely (1,20).

After recovery from anesthesia, a transdermal fentanyl (25 μg/h; Fentanyl patch, Myungmoon, Seoul, Korea) and meloxicam (0.1 mg/kg PO q24h; Metacam, Boehringer Ingelheim, Ingelheim, Germany) were applied for 5 days, amoxicillin hydrate/potassium clavulanate (12 mg/kg; Lactamox tablet, amoxicillin 50 mg/tab; clavulanate 125 mg/tab; Aprogen Pharma, Sungnam, Korea) were administered orally twice per day for 14 days were used for postoperative management. The patient remained in the hospital for 1 day and was discharged with instructions for strict cage rest.

In the postoperative radiographic evaluation, the implants were properly positioned, and the osteotomy line did not impair both proximal tibial physis and tibial tubercle apophysis (Fig. 3A). The patella was also well located in the trochlear groove (Fig. 3B). Postoperative TPA was measured at 6°, and the result was similar to the preoperative planning target TPA. During the follow-up period, grade 5 non-weight-bearing lameness was shown for 14 days, and grade 4 toe touching lameness was observed from two to eight weeks. For eight weeks observation grade 2 intermittent lameness was showned. For twelve weeks observation there was no more lameness. The weight-bearing and range of motion of the affected hind limb had improved without complications. The patient showed a good clinical outcome without lameness, and the implants were removed 1 year postoperatively (Fig. 3C, D).

Figure 3. (A) Postoperative mediolateral radiograph of the left hind limb. The osteotomy line (yellow arrow) do not impair both proximal tibial physis and tibial tubercle apophysis (yellow arrow head). (B) Craniocaudal view of the left hind limb. The patella is well located in the trochlear groove (yellow circle). Mediolateral (C) and craniocaudal (D) radiographs of the left hind limb at 1 year postoperatively. The surgical plate and cerclage wire are removed. Osteotomy line are not observed and callus formation observed around the plate removal site. The patella is also located in the trochlear groove (yellow circle).

MPL is considered a predisposing factor for CCLR in dogs (14). It is theorized that malalignment of the quadriceps mechanism with MPL increases tension on the cranial cruciate ligament or osteoarthritis associated with MPL may facilitate degeneration of the cranial cruciate ligament (3,8). The concomitance of CCLR and MPL is well recognized, with concurrent CCLR identified in 13-25% of dogs with MPL (7,13). In theory, the risk of developing concurrent CCLR and MPL is similar for cats, and one study reported that approximately 13% of cats had CCLR and MPL concurrently (3,18). Reports described detailed information on the surgical method and the outcome of concomitant CCLR and MPL in cats that are very rare. Traditionally, the management of feline patients has been conservative management or extracapsular stabilization (2,15,23). However, the 80% of the patients showed continuous clinical signs, such as instability of the stifle joint, reduced ROM, and radiographic signs of osteoarthritis as a result of conservative therapy (21,22). Moreover, other studies have presented that early surgery may provide better clinical outcomes and reduce the incidence of meniscal tears (17,23).

ECS is the most routinely performed surgical stabilization of CCLR in cats and may be combined with surgical procedures to treat MPL in cats with CCLR and MPL concurrently (24). However, compared to osteotomy techniques, using ECS alone or ECS combined with MPL surgery, such as TTT, can be associated with higher postoperative complications and poorer clinical outcomes in dogs (7,10). ECS combined with the TTT method increases the risk that the suture would be anchored at non-isometric sites due to the osteotomy site of the tibial tuberosity, which may lead to suture failure (10). Furthermore, compared to dynamic stabilization using TTTA, the postoperative complication rate is 2.7 times higher than in the ECS combined with the TTT group (7). Although many of these studies in dogs may not be directly translatable to feline patients, a recently published report that described the successful use of TTTA surgery for concomitant CCLR and MPL in three cats indicates that osteotomy techniques in cats can be suitable surgical options as in dogs (3). However, in our case, the patient was an immature cat with open growth plates. According to published reports, TPLO and TTA can be good surgical options for cats, but these methods are not suitable for immature animals (13). To eliminate a force within the stifle joint that thrusts the tibia cranially, both techniques are needed in the osteotomy position, including the proximal tibial physis (12). Additionally, these methods create instability of the tibial tubercle apophysis and may increase the incidence of tibial tuberosity avulsion fracture (3,5). Because of these problems, CTWO was usually performed to treat CCLR in immature dogs. CTWO accompanies the leveling of the TPA by resecting a cranially based wedge of the proximal tibia, apposing the margins of the ostectomy site, and then stabilizing the two segments with a medially applied bone plate (11). In this procedure, CTWO could be performed for an osteotomy distal to the proximal tibial physis and tibial tubercle apophysis in immature animals so that this technique can be applied to immature cats (13). Furthermore, comparing the outcomes following TPLO and CTWO for the treatment of CCLR in dogs, the complication rates did not differ between the surgical techniques (5). To achieve the postoperative target TPA, CTWO may be demanded more accuracy than other osteotomy techniques (11). When performing the CTWO procedure, preoperative planning is commonly aimed at achieving a target postoperative TPA of 5° (11). However, the difficulty in achieving the target TPA may be attributed to the variability in the site and size of the ostectomy and tibial long axis shift (12). Another study revealed that dogs with a more proximal osteotomy and aligned cranial cortices were more likely to achieve a target TPA near 6° (1). Therefore, to achieve the target TPA, the surgeon must prepare the proper preoperative planning and perform precise surgery as planned. In both human and veterinary surgery, the use of a 3D patient-specific surgical guide in osteotomy procedures reduces surgeon’s error, decreases surgical time, and simplifies the osteotomy process (4,19). In our case, we were able to achieve surgery close to the exact target using a 3D-printed patient-specific surgical guide, demonstrating that such guides are feasible in immature cats and can enhance surgical precision. As a result, postoperative TPA was nearly the same as preoperative target TPA. The patient showed good clinical outcomes without complications, such as patellar reluxation, impaired growth plates, fracture of the tibia, and failure of the plate.

This case study is the first report performing that CTWO assisted by patient-specific surgical guides for treatment of an immature cat with concomitant CCLR and MPL. CTWO combined with surgical procedures to correct MPL can be successfully used to treat concomitant CCLR and MPL in an immature cat. The patient showed improvement in lameness scores and gait conditions during 1 years follow-up periods without complications but long term follow-up was not performed as the limitations of the case. Regardless of the growth plates in the proximal tibia, the use of the CTWO can safely reduce TPA. Furthermore, using a patient-specific surgical guide facilitates surgical procedures, minimizes surgical errors, and increases the precision of surgery.

The authors have no conflicting interests.