Concurrent caudal cruciate and medial collateral ligament repair using a single Mini TightRope (Arthrex) fixation in a cat

Abstract

Case summary

A 2-year-old female spayed domestic shorthair cat presented with acute left pelvic limb lameness after suspected trauma. Orthopaedic and radiographic findings were consistent with rupture of the medial collateral and caudal cruciate ligaments. Surgical exploration identified complete rupture of the caudal cruciate and medial collateral ligaments, as well as a crushed medial meniscus, necessitating partial medial meniscectomy. Primary repair of the medial collateral ligament was performed and a Mini TightRope (Arthrex) prosthesis was positioned to concurrently aid stifle stability following the rupture of the two ligaments. At 8 weeks postoperatively, the cat demonstrated normal gait and pain-free stifle manipulation, with radiographs confirming implant stability and no complications. No lameness was reported by the owner 2 years postoperatively.

Relevance and novel information

This is the first case report of the use of bone tunnels and a Mini TightRope implant to address complete medial collateral and caudal cruciate ligament rupture and stabilise the stifle in a cat. This novel technique allowed for stabilisation without the need for external coaptation, enabling an early return to function.

Plain language summary

Repairing two torn knee ligaments in a cat with a single implant

A 2-year-old cat suddenly became lame on one back leg after an injury. Examination and radiographs showed that two important knee (stifle) ligaments – the medial collateral ligament and the caudal cruciate ligament – were torn. During surgery, both ligaments were confirmed to be completely ruptured, and part of the medial meniscus (a cushioning cartilage) was also found to be damaged and was removed. The torn medial collateral ligament was repaired, and the knee was stabilised using a Mini TightRope (Arthrex) implant placed through small bone tunnels. This single implant provided support for both injured ligaments. The cat walked normally and was pain free 8 weeks after surgery. Radiographs showed the implant was stable and there were no complications. Two years later, the cat remained sound with no lameness. This is the first reported case of using a Mini TightRope in a cat to stabilise both of these ligaments at once. The technique provided strong internal stabilisation, avoided the need for an external brace or cast and allowed the cat to regain normal function quickly.

Introduction

Isolated injury of the caudal cruciate ligament or a collateral ligament in cats is rare. ¹ More commonly, cats present with stifle luxation from high-energy trauma, such as motor vehicle accidents or falls. ¹ Multiligament injury is invariably present, involving various combinations of cranial cruciate, caudal cruciate, medial collateral and lateral collateral ligaments.^1,2 Meniscal injuries are frequently concurrent. ¹

Conservative management may be considered in the absence of stifle luxation for isolated caudal cruciate or medial collateral ligament injury. ³ However, surgery is indicated when both ligaments are ruptured, resulting in gross instability. Treatment of stifle luxation may be categorised into reparative or salvage procedures, such as total knee replacement, arthrodesis and amputation.^4,5 In cats, published reparative procedures involve extracapsular reconstruction. Cranial cruciate ligament rupture is typically treated with a lateral fabellotibial suture, while caudal cruciate ligament rupture is treated with a fibulopatellar suture.^1,4,6 Reparative procedures addressing collateral ligament rupture include a prosthetic transarticular suture and primary repair using a locking loop suture pattern where feasible.^1,4

Postoperative protection may involve transarticular stabilisation, such as a transarticular pin or static/hinged external skeletal fixation.^2,7,8 However, a multicentre retrospective study challenged this practice, reporting poorer outcomes and significantly higher complication rates. ¹

The TightRope (Arthrex) system achieves bone-to-bone fixation using long-chain ultra-high molecular weight polyethylene threaded through bone tunnels and secured with suture buttons. Its use in isolated cranial cruciate ligament rupture in dogs is well established.^9,10 The manufacturer has not described its use for caudal cruciate ligament-deficient stifles. However, based on its design and success for cranial cruciate ligament rupture, as highlighted in prior studies,^9,10 TightRope may be suitable for stabilising caudal cruciate ligament ruptures.

The authors describe an extracapsular technique involving primary repair of the medial collateral ligament and the use of bone tunnels and Mini TightRope as synthetic augmentation in a cat with complete rupture of the caudal cruciate and medial collateral ligaments. This is the first report of TightRope being used similarly to the fibulopatellar suture technique for caudal cruciate ligament rupture.

Case description

A 2-year-old female spayed domestic shorthair cat weighing 3 kg was presented with acute left pelvic limb lameness after suspected trauma, potentially from a fox altercation (caught on CCTV). The owner reported no previous clinical concerns. On examination, the cat was bright, alert and systemically well. Gait assessment revealed severe weightbearing lameness on the left pelvic limb. Small superficial wounds were present on both tarsi. Sedated examination demonstrated caudal cruciate ligament instability (caudal drawer motion) and medial (valgus) stifle instability.

Radiographs revealed increased soft tissue/fluid opacity of the left stifle (consistent with joint effusion) and caudal displacement of the tibial plateau relative to the femoral condyles (Figure 1). The contralateral stifle appeared normal. Complete rupture of the caudal cruciate and medial collateral ligaments was suspected, and surgery was recommended because of instability.

Figure 1

Mediolateral and caudocranial radiographic projections of the left stifle demonstrating increased stifle soft tissue/fluid opacity and caudal displacement of the tibial plateau relative to the femoral condyles. In contrast, the mediolateral and caudocranial radiographic projections of the unaffected right stifle demonstrate correct positioning of the tibia relative to the femur

The cat was positioned in dorsal recumbency, and the affected limb aseptically prepared. Arthroscopic stifle inspection using a 1.9 mm diameter 30° arthroscope (Arthrex) revealed a complete tear of the caudal cruciate ligament and an intact cranial cruciate ligament (Figure 2). The medial meniscus was crushed and partially detached. A mini craniomedial arthrotomy facilitated partial medial meniscectomy. A routine craniomedial approach to the left stifle was performed with the pes muscle elevated off the proximal tibia. A complete mid-substance (proximal end) tear of the medial collateral ligament and joint capsule were identified (Figure 3). The medial collateral ligament was repaired with 3.5 metric polydioxanone (PDS; Ethicon) with a locking-loop suture (Figure 3). A 1.1 mm Kirschner wire was driven through the proximal tibia from caudal to the medial collateral ligament in a distocranial direction exiting on the lateral side of the proximal tibia, and over-drilled with a 2.0 mm cannulated drill (the entry location was as proximal and as caudal as safely possible). A similar tunnel was created in the distal femur, commencing at the distocranial aspect of the medial condyle (immediately proximal to the cranial end of the Blumensaat line) and directed caudoproximally to exit on the lateral side of the femoral metaphysis (Figure 3). Using a nitinol suture passer (Arthrex), a Mini TightRope (Arthrex) was tunnelled backwards through the tibial and femoral tunnels, so that the toggle was on the lateral tibia and the round button on the lateral femur (Figure 4). With the stifle in a standing angle (120° extension), a suture tensioner (Arthrex) secured the Mini TightRope. Caudal drawer motion and valgus instability were negative before closure. The medial joint capsule was closed with 3 metric polydioxanone (PDS; Ethicon) in a cruciate pattern, and the subcutaneous tissue and skin were routinely closed.

Figure 2

Intraoperative arthroscopic images of the left stifle demonstrating a complete tear of the caudal cruciate ligament (black arrows) and an intact cranial cruciate ligament (red arrows)

Figure 3

Intraoperative photographs demonstrating the surgical steps, including (a) identification of the ruptured medial collateral ligament (MCL); (b) primary repair of the MCL using a single locking-loop suture; (c) Kirschner wires demonstrating the location and direction of the femoral and tibial bone tunnels; and (d) the Mini TightRope secured in situ

Figure 4

Schematic drawing of the medial stifle showing the position of the Mini TightRope

Postoperative radiographs confirmed good bone tunnels/anchor placement and correction of caudal tibial translation (Figure 5).

Figure 5

Mediolateral and caudocranial radiographic projections of the left stifle immediately postoperatively demonstrating the femur and tibial bone tunnels with the Mini TightRope in situ. There is no radiographic evidence of caudal tibial translation relative to the femur

Pre- and intraoperative analgesia included methadone (0.2 mg/kg IV q4h, Comfortan; Dechra) and ketamine constant rate infusion (5 µg/kg/min, Anesketin; Dechra). Postoperatively, methadone (0.2 mg/kg IV q4h, Comfortan; Dechra) was continued for 12 h, followed by buprenorphine (0.02 mg/kg IV q6h, Buprevet; Virbac) until discharge. The cat was weightbearing on the operated limb immediately after recovery from anaesthesia. The cat was discharged 48 h postoperatively on gabapentin (10 mg/kg PO q8h, Gabapentin; BOVA) for 6 weeks and meloxicam (0.05 mg/kg PO q24h, Metacam; Boehringer Ingelheim) for 2 weeks. The cat was confined to a cage for 4 weeks, followed by 4 weeks in a small room without furniture.

At the 8-week recheck, the owner reported no concerns. Gait assessment revealed no overt lameness. Stifle manipulation was well tolerated, with no discomfort and a full range of motion. Sedated radiographs confirmed unchanged anchor positions, suggesting no implant-related complications (Figure 6). Sedated stifle assessment revealed good joint stability. Further confinement for 3 weeks was advised, followed by 3 weeks of house rest before resuming outdoor activity.

Figure 6

Mediolateral and caudocranial radiographic projections of the left stifle 8 weeks postoperatively demonstrating static Mini TightRope positioning

The owner was contacted 2 years after surgical repair and reported no concerns with the operated limb.

Discussion

This case report describes the successful use of a Mini TightRope system to manage a complex traumatic stifle injury in a cat, involving complete rupture of both the medial collateral and caudal cruciate ligaments, along with medial meniscal damage. Although this injury pattern has been documented, it accounts for only 7% of feline traumatic stifle injuries. ¹

The caudal cruciate ligament prevents caudal tibial translation, and with the cranial cruciate ligament, limits internal stifle rotation.^11,12 Experimental evidence suggests that dogs with isolated caudal cruciate ligament transection may recover good limb function without surgical intervention, with minimal radiographic evidence of osteoarthritis and lameness at 6 months after transection despite persistent caudal drawer motion. ¹³ However, similar studies have not been conducted in cats; therefore, these findings cannot be directly extrapolated. Coppola et al ¹ highlighted that 66.6% of traumatic stifle luxations with caudal cruciate ligament pathology treated surgically had persistent caudal drawer motion on follow-up examination; however, the study did not specifically address how this finding impacted clinical outcomes in these cases. ¹

An experimental study in dogs with surgically transected medial collateral ligaments showed non-repaired ligaments managed with early cage-restricted activity achieved better stifle joint stability and structural properties by 12 weeks than surgically repaired ligaments with immobilisation. ¹⁴ No studies have specifically evaluated isolated stifle collateral ligament rupture in cats.

When gross instability arises from combined ligamentous rupture, as in this case, surgical intervention is advised. Multiple surgical stabilisation techniques exist for traumatic multiligament stifle injuries, with extracapsular repair and immobilisation by far the most commonly cited.^{1,2,4,6,11,15} In cases of caudal cruciate ligament rupture, the fibulopatellar suture technique has been employed to prevent caudal tibial translation.^1,4

A recent case report demonstrated successful restoration of limb function after cranial cruciate, caudal cruciate, medial and lateral collateral ligament rupture with medial meniscus pathology using a combination of tibial plateau levelling osteotomy and extracapsular repair techniques in a cat. ¹⁶ In that case report, caudal tibial translation was addressed using a three-point suture anchored on the distal medial femur and the caudal medial tibia (an additional anchor was placed to the cranial medial tibia to help resist persistent rotational instability). ¹⁶ Follow-up examination and radiographs revealed that caudal tibial displacement persisted. It is not known if that was due to implant failure but we recommend that the femoral bone tunnel/anchor point is placed more cranially on the medial side of the femur to create a more oblique angle for the extracapsular suture, better mimicking the native caudal cruciate ligament. This may better counteract caudal tibial translation. In addition, routing the Mini TightRope along the medial aspect of the stifle was implemented to augment the primary repair of the medial collateral ligament. In this case, the Mini TightRope was positioned in such a trajectory that the single device could resist both caudal drawer motion and genu valgum to provide stifle stability.

TightRope stabilisation for cranial cruciate ligament rupture in dogs has yielded promising results. One study successfully demonstrated that the TightRope system was more resistant to cyclic loading failure than a nylon lateral fabellotibial suture. ⁹ Similarly, a feline cadaveric study showed fixation of transected cranial cruciate ligaments using a Mini TightRope provided good biomechanical stability and neutralised cranial tibial thrust. ¹⁷

Medial meniscal injury in cats with stifle luxation has been associated with poorer outcomes. ¹ This case presented with significant crushing damage and partial detachment of the medial meniscus, necessitating partial meniscectomy. Follow-up phone consultation 2 years postoperatively revealed no concerns, but the absence of an orthopaedic examination and radiographs limits assessment of long-term limb function and progression of osteoarthritis.

Postoperative immobilisation techniques after multi-ligament stifle damage in cats involve external skeletal fixators or transarticular pinning. ¹ These aim to protect the primary repair through maintaining joint reduction and promoting fibrous tissue formation.^4,18 Routine use of ancillary immobilisation is not without debate, with concerns raised as to the deleterious effects of immobilisation on synovial fluid production, articular cartilage, range of motion, muscle mass and bone density.^2,10 Transarticular pinning has demonstrated higher complication rates, with pin loosening, pin migration and pin failure being previously reported.^1,19 Furthermore, the largest retrospective feline stifle luxation study found no benefit from postoperative coaptation. ¹ In this case, postoperative immobilisation was omitted. The owner reported good early limb use with progressive weightbearing in the immediate postoperative period. This was supported with no lameness appreciable at the 8-week reassessment.

Conclusions

The favourable outcome in this case suggests that the Mini TightRope system is a viable option for complex stifle injuries in cats, offering effective stabilisation and the potential for early and functional recovery without the need for supplementary immobilisation. Despite an excellent outcome with no reported complications, further studies with larger case numbers are needed to fully assess the long-term efficacy and complication rates associated with this surgical technique.