CLINICAL OUTCOMES AND STIFLE OSTEOARTHRITIS ASSESSMENT OF NINE CATS BEFORE AND AFTER TIBIAL PLATEAU LEVELLING OSTEOTOMY

This study aimed to evaluate the clinical and radio graphical outcome of cats following TPLO surgery for cranial cruciate ligament de ﬁ ciency. Each cat underwent orthopedic assessment, pre-operative radio graphical evaluation, surgical procedure, postoperative management and clinical re-examination 1, 2, and 12 months following surgery. Age, body weights, TPAs, meniscal tears, implants and osteoarthritis progression were recorded. Postoperative OA score was compared with that obtained 1 year after surgery using a paired t-test with commercially available software. Radio graphical evaluation performed 1 year after surgery showed no signi ﬁ cant OA progression ( P-value > 0.1). Minor complications occurred in one case (#7) in which a mild to moderate seroma was observed ten days after surgery. No major complications were recorded. Although TPLO surgery in cats remains controversial, this study suggests that it was a suitable option for surgical treatment of feline cranial cruciate ligament rupture, but considering the ex vivo outcomes recently published, further in vivo evaluation is strongly recommended.

Tibial plateau levelling osteotomy (TPLO) is one of the most common surgical techniques in use, which aims to neutralize the cranial tibial thrust, achieving a caudal displacement of the tibial plateau, levelling the slope up to get a perpendicular angle between the tibial plateau and the patellar tendon, without restoring the cranial cruciate ligament [1,3,4,[8][9][10][11].
Cranial cruciate ligament defi ciency in cats is usually treated by performing extracapsular procedures [12][13][14][15][16][17].A single case of TPLO associated with cranial closing wedge ostectomy was described with an excellent outcome in 2005 [18] whilst in 2016, Mindner et al (2016) published a primary paper regarding TPLO application in eleven cats with CCLd.TPLO outcomes were very positive and further evaluations including longer-term clinical re-examination were encouraged by the authors [19].
For these reasons, this study was aimed to evaluate the clinical outcomes and the radiographic osteoarthritic changes of nine cats following TPLO for cranial cruciate ligament defi ciency one year after surgery.

MATERIAL AND METHODS
Inclusion criteria were cats referred with a diagnosis of cranial cruciate ligament defi ciency between 2016/2018.
The study protocol was under institutional guidelines for research on animals; owners were fully informed of the procedures and written informed consent was obtained.
Each cat underwent the same protocol including orthopedic assessment, preoperative radiographical evaluation, surgical procedure, postoperative management and clinical re-examination 1 month, 2 months and 1 year after surgery.Age, body weights, TPAs, meniscal tears, implants and osteoarthritis progression were recorded.
Stifl e radiographical assessment was performed under general anesthesia during the preoperative evaluation.
Complications were classifi ed as major in cases of additional surgery, and minor in cases of conservative management.

Postoperative management
Each cat was hospitalized and discharged 24 hours after surgery.Postoperative mediolateral and caudocranial radiographic views were performed to inspect implant position and measure the tibial plateau.A soft bandage was applied for 48 hours.
Cage rest was requested for 4 weeks.
The clinical and radiographical re-examination was performed one month, two months and one-year post-surgery to check the weight-bearing and the bone healing of the operated stifl e joint.

Statistical analysis
All OA scores were tested with the Shapiro Wilk test to evaluate a normal distribution.Postoperative scores were compared with those obtained one year after surgery using a paired t-test design with commercially available software (Prism 7, © 2018 GraphPad Prism®, La Jolla, California, USA) Mean and standard deviations were calculated, and P<0.01 was considered signifi cant.

RESULTS
Nine cats matched the inclusion criteria.Individual information on body weight (in kg) at the date of presentation, sex, pre-operative TPA, pre-operative OA/1 year postoperative OA are provided in Table 1.Pre-operative OA score was 4.66 ± 1.41.Post-operative score was 5.5 ± 2.12.
Minor complications occurred in one case (#7) in which a mild to moderate seroma was observed ten days after surgery.
No major complications were recorded.
A comparison between the immediate postoperative radiographic OA scores with that obtained one year after surgery showed no statistical differences between the two groups (P-value>0.5).
Tibial plateau levelling osteotomy has become very popular for the surgical treatment of cranial cruciate ligament defi ciency in dogs [22].
The application of TPLO in cats is a controversial subject.In 2018 an ex vivo study was published whose outcomes failed to demonstrate the stabilizing effects of tibial plateau levelling osteotomy on cranial tibial subluxation and tibial rotation angle in a feline model [23].
The author concluded that according to the model they proposed, the standard tibial plateau levelling osteotomy technique applied to stabilize the canine stifl e may not be appropriate in cats [21].This is contradictory to the results obtained with a similar canine model [9].
It is also contradictory to the good clinical results reported in a recent study in 11 cats, although the stability of the stifl e joint obtained with this technique was not assessed [19].
Our clinical outcomes were coherent with those obtained with another clinical study published in 2016 in which eleven cats underwent TPLO for cranial cruciate defi ciency [19].
Contradictory results from cadaveric to in vivo studies suggest that the biomechanical stifl e evaluation of cats require more assessment.Osteoarthritis changes in feline stifl e commonly include osteophytes, joint-associated mineralization, and cartilage damage.
In particular, Voss reported that small mineralizations were usually confi ned to the medial meniscus while larger mineralizations tended to be located cranially to the menisci potentially associated with osteoarthritis and cranial cruciate ligament disease [30].In this study, even cats had no history of major trauma and fi ve of them had large mineralization located cranially to the meniscus.In particular, signifi cant OA progression was not observed one year after TPLO surgery.We then speculate joint stability was achieved following TPLO procedure [31][32][33][34].Further evaluations for better understanding of muscle activation are strongly recommended.Tibial plateau levelling osteotomy surgery was performed without major complications; mean body weight of 6.1 kg suggesting that overweight may be signifi cant in the development of the stifl e instability.
In 2011 Ruthrauff et al observed 67% (65/98) of medial meniscal injuries in a study population of 98 cats affected by CCLd while Mindner et al reported 18% of meniscal damages (2/11) [19,35].In this study, the medial meniscus incidence was 44% (4/9).The axial meniscal tears were always positioned in the caudal horn of the medial meniscus; a large arthrotomy was required for a proper meniscal assessment.
Within this study, only one minor postoperative complication was observed, but a larger study is encouraged to assess all possible complications.
In our experience, TPLO is a suitable option for surgical treatment of cranial cruciate ligament rupture in cats.However, considering the ex vivo outcomes recently published, further in vivo evaluation is strongly encouraged.

Figure
Figure 1A-B.2-year-old dsh (domestic shorthair) female cat.Medio-lateral and caudocranial radiographic views of the stifl e joint performed postoperatively (A) and compared with that obtained one year after TPLO surgery (B).In A a soft tissue/fl uid increasing intraarticular opacity is visible, with compression of the fat pad, compatible with joint effusion and/or synovial thickening in the mediolateral view.The caudocranial view shows minimal mineralization of the medial meniscus and in the area of the CCL.In B the mineralization of the medial meniscus and in the area of the CCL is more visible in the caudocranial view.In the mediolateral view, the joint opacity appears normal, and only a minimal osteophyte formation at the proximal border of the femoral trochlea is present, suggesting very minimal arthritic changes.

Table 1 .
Medical records include breed, sex, age, bodyweight, pre-operative TPA, postoperative TPA, preoperative OA score and one year follow up OA score Axial meniscal tears were observed and treated in four cases.Median postoperative TPA was 6° ± 1.42.