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. 2026 Jul 11;12(4):e71085. doi: 10.1002/vms3.71085

Modified Tibial Plateau Levelling Osteotomy in a Cat With a Cranial Cruciate Ligament Rupture and a Concurrent Medial Patellar Luxation

Ji‐Hwan Pahk 1, Kyu‐Won Kang 1, Byung‐Jae Kang 1,2,✉
PMCID: PMC13354939  PMID: 42433122

ABSTRACT

Case Summary

A 12‐year‐old, castrated male Russian Blue cat presented with chronic right pelvic limb lameness that had markedly worsened over the previous week. Orthopaedic examination revealed cranial cruciate ligament rupture with concurrent Grade 3 medial patellar luxation (MPL) in the right stifle. Pain was elicited upon patellar reduction. Radiographs showed a tibial plateau angle (TPA) of 35° and medial deviation of the tibial tuberosity. A modified tibial plateau levelling osteotomy (mTPLO) was planned for the right pelvic limb to correct both cranial tibial thrust and MPL in a single procedure. The right stifle was explored by lateral arthrotomy, and adjunctive surgical techniques, including trochlear block recession, medial release and lateral imbrication, were performed to correct the MPL. The proximal tibial segment was rotated to achieve a post‐operative TPA of 5° and stabilized using an Arix‐vet 1.5/2.0 mTPLO plate with a 2‐mm offset. Post‐operative imaging confirmed correction of the TPA and lateral translation of the tibial tuberosity. The bone apposition ratio was 0.83. At 4 months post‐operatively, radiographic union was confirmed. Gait pattern and orthopaedic examination findings, including patellar stability and absence of cranial tibial thrust, were comparable to the pre‐deterioration clinical state.

Relevance and Novel Information

To our knowledge, this is the first report of mTPLO in a feline patient. Given the difficulty of post‐operative exercise restriction in cats, the single‐cut design and maintenance of bone apposition of the mTPLO may offer enhanced stability. No significant alteration in the mechanical medial proximal tibial angle was observed, supporting the safety of a 2‐mm offset in this case.

Keywords: cats, cranial cruciate ligament disease, patellar luxation, stifle, tibial plateau levelling osteotomy

A 12‐year‐old castrated male Russian Blue cat presented with cranial cruciate ligament rupture and concurrent grade 3 medial patellar luxation. A modified tibial plateau‐levelling osteotomy (mTPLO) using an Arix‐vet plate with a 2‐mm offset was performed, simultaneously correcting cranial tibial thrust and patellar luxation in a single procedure. At 4 months postoperatively, radiographic union was confirmed and limb function returned to its pre‐deterioration state, representing the first reported feline mTPLO case.

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1. Introduction

Cranial cruciate ligament rupture (CrCLR) and medial patellar luxation (MPL) are more uncommon in cats compared with in dogs (McLaughlin 2002; Grierson 2012), and their concomitance is even rarer (Ruthrauff et al. 2011; Loughin et al. 2006). In the limited feline literature available, surgical management has typically involved combining lateral extracapsular suture stabilization with traditional MPL repair techniques (Ruthrauff et al. 2011), though these approaches have notable limitations, including a relatively high complication rate and suboptimal long‐term outcomes (Boge et al. 2020; Bula and Perry 2021). In dogs, a modified tibial plateau levelling osteotomy (mTPLO) has recently been introduced to address CrCLR and MPL concurrently via a single osteotomy that simultaneously reduces tibial plateau angle (TPA) and corrects medialized tibial tuberosity alignment (Langenbach and Marcellin‐Little 2010). This technique has shown promising results in small‐breed dogs, minimizing implant conflict and maintaining bone alignment without significantly altering the mechanical medial proximal tibial angle (mMPTA) (Langenbach and Marcellin‐Little 2010; Flesher et al. 2019; Dallago et al. 2023; Jung and Kang 2025). We applied mTPLO in a cat presenting with concurrent CrCLR and Grade 3 MPL, and report the evaluation of its clinical feasibility and outcomes.

2. Case Description

A 12‐year‐old castrated male Russian Blue cat weighing 5.3 kg presented with chronic right pelvic limb lameness that had deteriorated over the past week. Pre‐operative lameness was scored as 4 on a 6‐point lameness scale (Torres 2020). Orthopaedic examination revealed palpable effusion of the right stifle, laxity in the cranial tibial thrust and cranial drawer of both stifle joints. Grade 3 MPL (Putnam grading scale) was identified in the right stifle (Putnam 1968), with a pain response elicited upon reduction of the displaced patella. Radiographic evaluation revealed effacement of the infrapatellar fat pad and mineralization in the cranial aspect of both stifle joints. Although bilateral stifle involvement was noted, the left stifle findings were considered chronic and relatively stable at initial presentation, whereas the recent clinical deterioration, more pronounced lameness and painful Grade 3 MPL were associated with the right pelvic limb, which was the primary concern reported by the owner. Based on these findings and the recent clinical worsening, surgical intervention with mTPLO was planned for the right stifle.

Pre‐operative planning comprised orthogonal radiographic evaluation of the skeletal alignment to determine the optimal osteotomy position, implant configuration and required tibial tuberosity translation. The procedure was simulated using digital templating software (vPOP Pro, VETSOS Education Ltd.). The medial deviation of the tibial tuberosity was evaluated on frontal radiographs, and the use of a 2‐mm pre‐contoured modified TPLO plate was deemed appropriate to correct the deviation (Figure 1). The osteotomy centre was aligned with the intercondylar tubercles or the level of the articular surface along the functional tibial axis (Krotscheck et al. 2012; Reif et al. 2004). Key reference distances (D1, D2, D3) were measured to confirm adequate bone stock for stabilization, with a planned D1 distance of 7.3 mm (Redolfi and Grand 2024). The pre‐operative TPA was 35° (Krotscheck et al. 2012; Reif et al. 2004), with a target post‐operative angle of 5° (Witte and Scott 2011; Jeong et al. 2024). The mMPTA measured 94.6°, within the reported range for normal feline tibia (Piccionello et al. 2020).

FIGURE 1.

FIGURE 1

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Frontal plane radiographs for the pre‐operative planning and post‐operative assessment. (a) Pre‐operative radiograph of the right stifle. (b) Digital surgical planning using templating software, illustrating the anticipated lateral translation of the tibial tuberosity and placement of a 2‐mm offset modified tibial plateau levelling osteotomy (TPLO) plate to correct the measured medial deviation. (c) Post‐operative radiograph confirming the lateral repositioning of the tibial tuberosity and implant alignment.

Under general anaesthesia, the right stifle was explored via arthrotomy. Multiple intra‐articular mineralized bodies ranging from 2–25 mm2, were identified and removed; these findings are often associated with degenerative joint disease or CrCLR in feline stifle joints (Voss et al. 2017). A complete rupture of the cranial cruciate ligament was confirmed without evidence of meniscal injury. The MPL was repaired using conventional techniques, including trochlear block recession, medial retinacular release and lateral capsular imbrication (Hayashi et al. 2018). Subsequently, a mTPLO was performed. The distal tibial segment was gently translated laterally by 2 mm while rotating the proximal segment to achieve the targeted reduction of the TPA. A 2‐mm offset pre‐contoured modified 1.5/2.0 mm locking TPLO plate (Jeil Medical Corp.) was used to maintain correction. Post‐fixation assessment confirmed lateralization of the tibial tuberosity and proper alignment of the patellar ligament axis (Figure 2).

FIGURE 2.

FIGURE 2

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Intraoperative photographs illustrating 2‐mm offset modified TPLO plate placement. (a) Medial view and (b) frontal view of the tibia. The yellow double‐headed arrow in (b) indicates the lateral translation at the level of the osteotomy achieved using the pre‐contoured plate.

Immediate post‐operative radiographs confirmed appropriate implant placement with the TPA reduced to 5°. Following a previously described method, the bone apposition ratio was calculated as 1 − MI, where MI = MED/WIDTH; MED represents the magnitude of proximal tibial segment medialization at the level of the osteotomy line, and WIDTH represents the tibial diaphyseal width at the same level (Dallago et al. 2023). In this case, with a MED of 2.0 mm and a WIDTH of 12.1 mm, the bone apposition ratio was calculated as 1 − (2.0/12.1) = 0.83. The mMPTA increased slightly from 94.4° pre‐operatively to 94.6° post‐operatively, which was clinically insignificant. No laxity was present on cranial tibial thrust testing, and the patella remained stable without reluxation. The cat was discharged 24 h post‐operatively. NSAIDs were not administered after an individual risk‐benefit assessment, considering the cat's advanced age and pre‐existing hypertrophic cardiomyopathy (Taylor et al. 2024). Analgesic management comprised gabapentin (10 mg/kg PO q12h [Donga ST]) and tramadol (2 mg/kg PO q12h [Tridol, Yuhan]) for 14 days. Cefovecin (8 mg/kg SC [Convenia, Zoetis]) was administered immediately pre‐operatively. Strict cage confinement was recommended for 8 weeks to ensure proper bone healing and limit post‐operative complications.

Post‐operative gait status was assessed using owner reports and owner‐provided home videos and categorized using the same 6‐point lameness scale (Torres 2020). Due to marked stress during handling, brief orthopaedic examinations were made, including assessment of patellar stability, pain response, cranial tibial thrust, gross range of motion and gross muscle mass. At 2 weeks post‐operatively, the skin sutures were removed and owner‐reported and video‐based assessment indicated noticeable improvement in right pelvic limb use, with the lameness score decreasing to 3. The patella remained seated within the trochlear groove without evidence of luxation, and cranial tibial thrust was absent. At 4 weeks post‐operatively, mild further within‐grade improvement in gait was reported. The patella remained within the groove but exhibited slight laxity, and cranial tibial thrust remained negative. Radiographs confirmed implant stability. At 16 weeks post‐operatively, the lameness score improved to 2, and the gait pattern was comparable to that observed before the episode of acute clinical deterioration. Orthopaedic examination findings remained unchanged, and radiographs showed progressive bone healing and remodelling. At 6 months post‐operatively, right pelvic limb use had improved beyond the pre‐deterioration status, although lameness score remained 2. Cranial tibial thrust remained negative. The patella remained seated within the trochlear groove, although subtle residual laxity was detected during manipulation; no clinically appreciable patellar displacement, reluxation, pain response or apparent discomfort was elicited. Gross muscle mass was comparable with previous examinations, and no obvious muscle atrophy was detected. Radiographs confirmed complete osseous union and maintained implant position, with no evidence of implant‐associated complications; however, progressive osteoarthritic changes, including increased periarticular osteophyte formation and mineralization around the stifle joint, were observed. The apparent mild medial position of the patella on the 6‐month radiograph was considered likely attributable to radiographic positioning/projection rather than clinically evident patellar displacement (Figure 3). Considering the cat's advanced age and relatively stable gait status, the owner elected continued conservative monitoring of the left stifle rather than additional surgical intervention. At 21‐month post‐operatively, the owner telephonically reported that the cat had remained clinically stable, with gait and activity levels comparable to those observed at the 6‐month follow‐up. Owner‐reported musculoskeletal pain was evaluated using the Feline Musculoskeletal Pain Index (FMPI) (Benito et al. 2013), with scores improving from 40 pre‐operatively to 24 at the 6‐month post‐operative follow‐up, indicating favourable outcomes. The presence of moderate residual pain, as reflected by the FMPI score, may be attributable to chronic bilateral hind limb lameness and suspected long‐standing osteoarthritic changes.

FIGURE 3.

FIGURE 3

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Serial radiographs of the right tibia before and after modified tibial plateau levelling osteotomy. (a) Pre‐operative lateral and anteroposterior radiographs, including the entire tibia, demonstrating cranial tibial translation, intra‐articular mineralized bodies and pre‐operative limb alignment. (b) Immediate post‐operative lateral and anteroposterior radiographs showing appropriate implant positioning, correction of the tibial plateau angle and lateral translation of the tibial tuberosity. (c) Radiographs obtained 16 weeks post‐operatively demonstrating progressive bone healing and cortical remodelling at the osteotomy site. (d) Six‐month post‐operative lateral and craniocaudal radiographs revealing complete osseous union and remodelling with maintained implant position and progressive osteoarthritic changes around the stifle joint. Apparent mild medial positioning of the patella on the craniocaudal view was considered likely related to radiographic projection rather than clinically evident patellar displacement.

3. Discussion

CrCLR and MPL are both recognized causes of hindlimb lameness in cats, albeit substantially less common than in dogs. (McLaughlin 2002; Grierson 2012) CrCLR in felines may result from a combination of traumatic and degenerative mechanisms, (Tacke and Schimke 1995) with recent studies highlighting associations with patient age, body weight and bilateral joint involvement (Harasen 2005). Similarly, MPL is considered a rare condition in cats, with a reported prevalence of approximately 0.15% among all feline orthopaedic disorders (Düzgün 2005), often underdiagnosed due to subtle clinical presentation (Flecknell 1977) and a wide spectrum of stifle laxity tolerated in the species (Smith et al. 1999). Concomitance of CrCLR and MPL is well documented in dogs, with a reported prevalence ranging from 13% to 25% among dogs presenting with MPL (Gibbons et al. 2006; Campbell et al. 2010). The proposed aetiologies include extensor mechanism malalignment and osteoarthritis‐related enzymatic degradation of the CrCL (Gibbons et al. 2006; Harasen 2002; Roy et al. 1992). While similar biomechanical interactions may be expected in cats, reports remain scarce: One study identified concurrent CrCLR in 13% of affected cats (Ruthrauff et al. 2011), whereas another study found only one such case among 42 cats with MPL (Loughin et al. 2006).

Most surgical techniques used to correct CrCLR and MPL in cats are adaptations of canine procedures, and reports on the surgical correction of concomitant diseases in cats are rare. The primary method for CrCLR stabilization in cats is the lateral extracapsular suture technique using either bone anchors or tunnels (Boge et al. 2020; Harasen 2005; R. J. De Sousa et al. 2014; R. De Sousa et al. 2015), which is also frequently combined with traditional patellar luxation procedures when both conditions coexist (Ruthrauff et al. 2011). However, a recent study reported a 27.3% complication rate following lateral suture stabilization, with non‐surgically managed cats showing lower FMPI scores, indicating less chronic pain (Boge et al. 2020). In dogs with concurrent CrCLR and MPL, TPLO is commonly performed for CrCLR repair and can be combined with tibial tuberosity transposition (TTT) to address MPL (Redolfi and Grand 2024; Leonard et al. 2016). However, this approach poses significant anatomical and mechanical challenges in small‐breed dogs, where limited proximal tibial space increases the risk of implant interference and tibial tuberosity fracture or avulsion (Langenbach and Marcellin‐Little 2010; Leonard et al. 2016; Birks and Kowaleski 2018; Priddy et al. 2003; Kergosien et al. 2004). Given that cats have similar bone size and cortical thickness as small‐breed dogs, these risks are likely considerations when applying the technique in cats.

mTPLO was introduced to address the challenges of simultaneously correcting CrCLR and MPL in small‐breed dogs (Langenbach and Marcellin‐Little 2010). Unlike the conventional TPLO, which focuses solely on reducing the TPA, the modified technique involves intentional lateral translation of the distal tibial segment, allowing concurrent correction of both excessive TPA and medialized tibial tuberosity through a single osteotomy (Langenbach and Marcellin‐Little 2010; Flesher et al. 2019). This dual‐purpose approach reduces surgical time, minimizes anaesthesia risks from multiple procedures and eliminates the need for more invasive techniques such as TTT (Dallago et al. 2023). Pre‐contoured TPLO plates with an integrated 2‐mm lateral offset were developed for small breeds to streamline the procedure, enabling accurate post‐osteotomy positioning of the tibial tuberosity and enhancing surgical consistency while potentially minimizing complications (Dallago et al. 2023; Jung and Kang 2025). Reportedly, mTPLO combined with MPL correction produces clinical outcomes comparable to or better than those of conventional TPLO (Langenbach and Marcellin‐Little 2010; Flesher et al. 2019; Dallago et al. 2023; Jung and Kang 2025).

To date, published feline literature addressing mTPLO is lacking. However, many theoretical and practical advantages of mTPLO, such as simultaneous deformity correction and the feasibility of a single osteotomy, are highly appealing in feline orthopaedic surgery, particularly considering the unique post‐operative management challenges in cats. In this study, the mTPLO technique was applied in a cat presenting with concomitant CrCLR and Grade 3 MPL, providing novel insights into its viability and clinical impact in cats.

Despite the potential benefits of the mTPLO, concerns remain regarding its biomechanical implications. Lateral translation of the distal tibial segment may alter axial alignment, raising the possibility of iatrogenic tibial varus or valgus deformities (Fox and Tomlinson 2012). Furthermore, reduced cortical contact between tibial segments than that achieved by conventional TPLO may theoretically impair stability or delay bone healing. In our case, these concerns were mitigated by selecting a modest 2‐mm offset, which was considered sufficient to address the measured medial deviation while minimizing the alteration in the tibial alignment. Supporting this approach, an in vitro study in small‐breed dogs reported that when the offset is modest, the mMPTA remains largely unaffected, with no delay in bone healing (Flesher et al. 2019). Post‐operative radiographs revealed only a negligible change in mMPTA (from 94.4° to 94.6°), and adequate bone apposition (0.83) was maintained (Flesher et al. 2019; Fox and Tomlinson 2012). Radiographic union was confirmed by 16 weeks, and the patient demonstrated progressive clinical improvement throughout follow‐up, suggesting that the chosen offset provided sufficient correction without compromising stability or healing.

Radiographic progression of osteoarthritis was observed at the 6‐month follow‐up despite clinical improvement in right pelvic limb use. Although feline‐specific evidence regarding post‐operative osteoarthritis progression after TPLO or mTPLO is limited, this finding was not considered necessarily inconsistent with the clinical outcome. In dogs treated with TPLO for CrCLR, Shimada et al. (2020) reported that weight‐bearing function improved within 6 months and was maintained for up to 36 months, whereas radiographic osteoarthritis scores progressed over time, particularly in stifles with complete CrCLR. The authors suggested that post‐operative osteoarthritis progression may be multifactorial and related to factors such as the degree of pre‐operative joint pathology, surgical treatment of intra‐articular structures, post‐operative exercise frequency and weight change. Similarly, in dogs undergoing surgical correction of MPL using trochlear recession and TTT, mean osteoarthritis scores increased during long‐term follow‐up despite favourable owner‐reported outcomes (Vodnarek et al. 2024). In the present cat, the progression of osteoarthritis was therefore considered most likely to reflect the progression of established degenerative stifle disease associated with chronic complete CrCLR and concurrent MPL, rather than an implant‐associated complication.

Although the use of a 2‐mm offset appeared clinically acceptable in this patient, it should not be interpreted as universally sufficient for feline mTPLO. In the present case, pre‐operative planning and intraoperative assessment indicated that the 2‐mm offset plate provided adequate lateral translation of the tibial tuberosity and restoration of the patellar ligament axis; therefore, additional TTT was not considered necessary. Nevertheless, subtle residual patellar laxity was detected during manipulation, indicating that complete normalization of patellofemoral stability cannot be assumed. Larger offset plates, if available, may therefore be considered in selected feline cases with greater tibial tuberosity medialization or residual patellar laxity, while accounting for their potential effects on tibial alignment, bone apposition and healing. The applicability of mTPLO in cats with more pronounced medial deviation remains uncertain, and a larger offset may be required in selected cases. However, larger offsets could also lead to clinically relevant changes in mMPTA or reduced bone apposition. Additional studies are warranted to evaluate the appropriate offset distance across a wider range of feline tibial deformities and to assess its effects on patellar tracking, limb alignment, bone healing and long‐term clinical outcome.

4. Conclusions

This case demonstrates the feasibility of mTPLO to simultaneously address CrCLR and MPL in a feline patient. The use of a pre‐contoured 2‐mm offset modified TPLO plate enabled effective correction of both TPA and medialized tibial tuberosity through a single osteotomy while maintaining acceptable limb alignment and bone apposition. Radiographic and clinical outcomes over 6‐month follow‐up were favourable, with no evidence of reluxation or implant‐associated complications. Although further studies are required to evaluate the broader applicability and long‐term effects of mTPLO in cats, this report provides preliminary evidence supporting its potential as a surgical option for selected cases of concurrent stifle deformities.

Author Contributions

Ji‐Hwan Pahk: writing – original draft, writing – review and editing, investigation. Kyu‐Won Kang: writing – review and editing. Byung‐Jae Kang: writing – review and editing, conceptualization, methodology, supervision.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT) (No. 2023R1A2C1003001).

Ethics Statement

The authors confirm that the ethical policies of the journal, as noted on the journal's author guidelines page, have been adhered to. No ethical approval was required as this is an article with no original research data.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgements

The authors thank the cat owners for completing the questionnaires and providing updates.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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