Surgical treatment of canine stifle disruption using a novel extracapsular articulated stifle stabilizing implant

Abstract

A 5-year-old Labrador retriever mixed breed dog was presented for an acute non-weight-bearing left hind limb lameness. A stifle disruption was diagnosed. The patient was treated using a novel extracapsular articulated stifle stabilizing implant (Simitri™). Twelve weeks after surgery the patient had full range of motion of the affected stifle and had begun to return to pre-injury activity. This is the first reported case of this condition being surgically managed successfully in this manner.

Canine stifle disruption, derangement, or luxation is a rare but potentially devastating orthopedic event (1,2) and is characterized by damage to more than one of the primary or secondary stifle stabilizing structures (1–3). The primary stabilizers of the canine stifle are the 4 main ligaments: the cranial cruciate, the caudal cruciate, the medial collateral, and the lateral collateral. The stifle is further stabilized by secondary structures: the menisci and the associated periarticular soft tissues (2,4,5). Stifle disruption injuries are generally considered a result of high energy trauma and most commonly involve the cranial cruciate ligament, the caudal cruciate ligament, and the medial collateral ligament (3,6,7).

The goal of treatment of stifle disruption should be to stabilize the joint in order to limit further articular surface damage, restore anatomical alignments, and maintain normal joint kinematics (8). There are 2 general categories of repair for these injuries; primary reconstruction of the damaged ligaments or use of internal or external supports to provide functional stability. Primary reconstruction is usually the recommended technique, provided adequate tissues are available, but may not be sufficient in cases with severe damage to secondary structures especially the caudal joint capsule and menisci (2). External or internal supports hold the joint in a functional position to allow the periarticular tissues to heal by fibroplasia (7,9,10). Transarticular pinning of the stifle joint (3,6,10) and the use of a hinged or rigid transarticular external fixator are examples of such supports (7–10). Transarticular pinning alone is only recommended in cats and small dogs (6,10). Studies of stifle disruption repair have demonstrated a reduction in range of motion of the stifle joint after surgery, with most of the limitation occurring in flexion (3,7,9,10). In cases with extreme damage, stifle arthrodesis or hind limb amputation may be recommended (9,10). It has been suggested that early return to mobility of the affected limb results in a better range of motion and therefore success of the repair (3).

The Simitri™ (patent pending, New Generation Devices, Glen Rock, New Jersey, USA) implant is an experimental device that has been in development since 2009 (Figure 1). The rationale behind its design was to provide a completely extracapsular means of immediate and continuous stifle stabilization regardless of the cause of the instability, the angle of the stifle, or the phase of the stride, to allow unimpeded normal stifle kinematics, and to help facilitate early mobilization of the affected limb.

Figure 1.

Computer generated image of Simitri implanted over the medial aspect of a stifle joint showing femoral component (A), tibial component (B), and sliding articulation engaged into position over femoral ball (C). Image courtesy of New Generation Devices.

Case description

A 5-year-old, spayed, female, Labrador retriever mixed breed dog, weighing 46.0 kg was presented to the referring veterinarian for sudden onset left hind limb lameness. The owner reported that the patient had been running at a high rate of speed and had slipped and fallen on ice. The owner indicated that the patient cried out and was immediately non-weight-bearing on the left hind limb. On examination by the referring veterinarian on the day of injury, the patient was found to have a non-weight-bearing left hind limb lameness. The physical abnormalities were limited to the left stifle, which was noted to be unstable in multiple directions. A lameness score of 5/5 was noted (11). A presumptive diagnosis of stifle disruption was made. Five days after injury the case was referred for surgical assessment and treatment. At a body weight of 46 kg, the only viable currently available surgical option for this patient was primary repair of the damaged structures with adjunctive external support for a minimum of 3 to 6 wk (8). A comprehensive discussion of all available procedures, including the possible use of a novel extracapsular, articulated stifle stabilizing implant (Simitri) was conducted with the referring veterinarian and the client. The referring veterinarian was familiar with the use of the Simitri implant as 2 of his clients’ dogs were already taking part in a clinical trial of the device. The client was fully aware of the experimental nature of the procedure. After full consideration of the medical and surgical options the owners gave their informed consent to allow us to proceed with a surgical repair using the Simitri implant in combination with primary repair of any collateral ligament damage found.

The patient was premedicated with acepromazine (Atravet; Boehringer Ingelheim, Burlington, Ontario), 0.025 mg/kg body weight (BW), IM and hydromorphone (Sandoz, Boucherville, Quebec), 0.1 mg/kg BW, IM. Anesthesia was induced using propofol (Diprivan; AstraZeneca Canada, Mississauga, Ontario), 4.0 mg/kg BW, IV. Anesthesia was maintained on isoflurane (IsoFlo; Abbott, Chicago, Illinois, USA), inhalant anesthetic at 1.5% in 2 L of oxygen/min. An epidural of hydromorphone (Sandoz), 0.1 mg/kg BW, qs to 4 mL with sterile saline was administered after induction. A prophylactic antibiotic, cefazolin sodium (Cefazolin sodium inj; Novopharm, Toronto, Ontario), 22 mg/kg BW, IV was administered preoperatively and 90 min after the first dose. After induction, extended lateral and cranial-caudal stifle radiographs were taken and the affected stifle was examined. Radiographs of the affected limb showed marked stifle effusion and no evidence of fractures. On examination, the affected stifle was found to be markedly distended when compared to the contralateral stifle. The affected stifle was unstable in both craniocaudal and varus valgus directions. Internal and external rotation of the tibia exceeded normal limits. Based on these findings the presumptive diagnosis of stifle disruption was confirmed. A goniometer was used to measure range of motion of the stifle of both hind limbs. The range of motion was found to be from 40° flexion to 150° extension on the affected limb as compared to 35° and 155°, respectively on the contralateral limb.

The left hind leg was clipped from the greater trochanter to the distal tibia and aseptically prepared for surgery. A medial approach was made to the distal femur and proximal tibia. A 15-cm curvilinear skin incision was centered over the medial stifle. A 15-mm medial parapatellar arthrotomy was performed. The joint capsule was hemorrhagic and swollen. An estimated 20 mL of a blood tinged synovial fluid drained from the arthrotomy site. The cranial cruciate ligament was completely torn. The caudal cruciate ligament had a 45% tear. The remaining caudal cruciate ligament was markedly stretched and unable to resist caudal tibial translation. The menisci were intact. The torn portions of the cranial and caudal cruciate ligaments were debrided and removed. The arthrotomy was closed using a simple continuous pattern of 0 poliglecaprone 25 suture material (Monocryl; Ethicon, Guaynabo, Puerto Rico). After closure of the arthrotomy, a 6-cm incision was made into the insertion of the conjoined tendons of the sartorius, gracilis, and semitendinosus muscles (pes anserinus), exposing the proximal tibia and medial collateral ligament. The medial collateral ligament had a tear estimated to be 50% of its total width. A 2-cm incision in the lateral retinaculum was made, exposing the torn section of the lateral collateral ligament. The torn section was approximately 25% of its total width. The torn edges of each collateral ligament were apposed with 2-0 polydioxanone suture material (PDS*II; Ethicon) in a far near, near far pattern. The lateral retinaculum was closed using 0 Monocryl in a simple interrupted pattern. The fascial incision of the pes anserinus was extended 6 cm proximally between the cranial and caudal bellies of the sartorious musculature to expose the vastus medialis. The vastus musculature was bluntly dissected and reflected cranially, exposing the distal aspect of the medial femoral diaphysis. The descending genicular artery and medial articular nerve were spared during the dissection.

Based on positioning measurements obtained from the pre-operative radiographs, the pre-contoured femoral component of the Simitri implant was then positioned over the distal femur and temporarily held in position with two 5/64 inch 316L stainless steel holding pins (Jorgensen Labs, Loveland, Colorado, USA). The sliding articulation of the tibial component was positioned to engage the ball of the femoral component. Prior to implantation of the tibial component, the stifle joint was aligned in the coronal, transverse, and sagittal planes. This was achieved by placing the limb in full extension and direct visualization and palpation of the joint during surgery. The caudal edge of the tibia was aligned with the caudal edge of the femur based on palpation to ensure craniocaudal alignment. The limb was also visualized from the cranial aspect to ensure there was no valgus, varus, medial, or lateral translation. The primary repair of the collateral ligaments also aided in the alignment. The tibial component was then positioned over the proximal tibia and temporarily held in place with one 5/64 inch 316L stainless steel holding pin (Figure 2). Correct positioning of the implant was confirmed by lack of binding and confirming that the travel of the femoral ball was within the limits of the travel channel of the sliding articulation while placing the limb through a full range of motion (2). The femoral and tibial components were permanently attached using three 3.5-mm bicortical stainless steel locking screws (New Generation Devices). The limb was again placed through a full range of motion. Abnormal cranial-caudal tibial translation could not be elicited and internal and external tibial rotation was visualized to be within normal limits. Excessive varus and valgus instability was also eliminated. The fascial layer between the bellies of the sartorious muscle and the insertional fascia of the pes anserinus were closed over the implant using a simple continuous pattern with 0 Monocryl. The subcutaneous fascia was closed with a simple continuous layer of 2-0 Monocryl. The skin was closed using stainless steel skin staples (Appose; Covidien, Mansfield, Massachusetts, USA). Postoperative radiographs were taken to assess the location of the implant relative to pre-operative implant location planning and to assess adequate alignment of the tibia in relation to the femur (Figure 3). Both the implant location and alignment were satisfactory based on the criteria discussed.

Figure 2.

Simitri implant shown in situ, temporarily fixed in place with 3 holding pins. A threaded locking screw drill guide is shown in position in the distal screw hole of the femoral component.

Figure 3.

Post-operative extended lateral radiograph of left stifle.

After surgery the patient was treated with meloxicam (Metacam; Boehringer Ingelheim) 0.2 mg/kg BW, SQ, and buprenorphine (Vetergesic; Champion Alstoe, Hull, UK) 0.02 mg/kg BW, IV. Oral meloxicam (Boehringer Ingelheim) 0.1 mg/kg BW, q24h was prescribed starting 24 h after the postoperative loading dose injection of meloxicam and was to be continued for at least 8 wk after surgery. Cephalexin (Apo Cephalex; Apotex, Toronto, Ontario), 22 mg/kg BW, q12h was given beginning the morning after surgery and continued for 5 d. Tramadol (Ultram; Janssen-Ortho, Toronto, Ontario), 1 mg/kg BW, PO, q12h was given for 5 d after surgery. A light bandage was applied from the toes to the upper thigh and multiple ice packs were immediately applied to the surgical limb for 20 min. The icing process was repeated 3 times daily while in clinic. The bandage was removed the following morning and the patient was assessed to have a lameness score of 4/5 while weight-bearing.

The patient was discharged to the care of its owners in the afternoon the day following surgery. A written comprehensive rehabilitation program was provided to the owner which explained icing of the stifle, muscle massage, passive range of motion, and controlled leash walking activity. Seventeen days after surgery, the referring veterinarian reported that the patient was noticeably lame but continuously weight-bearing (lameness score of 2/5). At the 6-week postoperative examination by the surgeons, the patient had no abnormal tibial translation and a lameness score that had improved to 1.5/5. The patient was able to sit with the injured stifle fully flexed. Stifle flexion and extension as measured with a goniometer were 30° and 141°, respectively, compared to 40° and 150° before surgery in the affected limb. Internal and external tibial rotations were within normal limits (12). The owner reported that the patient was continuously weight-bearing and was comfortably walking 30 min twice daily. The owner was instructed to continue rehabilitation of the surgical limb by following the postoperative instructions provided. At 10 wk after surgery the owner reported that the patient was working off leash and had begun to return to pre-injury activity level. Based on evaluation of video provided by the owner of the dog walking off leash on a rocky river bed, the patient had very mild lameness (lameness score of 1/5) and was able to negotiate uneven terrain with ease. At the 12-week postoperative examination by the surgeons, the patient was able to fully flex and extend the surgical stifle and showed no resistance or resentment to this motion. The range of motion of the surgical stifle was 30° in full flexion to 150° in full extension. The lameness score was determined to be 0.5/5.

Discussion

Canine stifle disruption, derangement, or luxation is a rare but potentially devastating orthopedic event (1,2). Early stabilization and realignment of the stifle joint is necessary to prevent further trauma to the joint, minimize reduction in function of the joint, and minimize the degree of subsequent osteoarthritis (1,3,8). It has been postulated that the sooner the patient is able to use the limb the better the long-term outcome will be (3). Therefore treatments involving prolonged immobilization of the joint may have poorer outcomes than procedures that allow earlier return to function (1).

The Simitri implant is comprised of 3 interlocking components (Figure 1): the tibial, femoral, and the sliding articulation. The femoral and tibial components are composed of surgical grade stainless steel. Each component has 3 screw holes and 2 temporary holding pin holes. The sliding articulation component is made from ultrahigh molecular weight polyethylene (UHMWPE) (GUR 1020; Ticona, Germany) and is pressure fitted into the proximal end of the tibial component. The distal end of the femoral component has a ball and stem attachment which locks into the travel channel of the sliding articulation of the tibial component. The femoral and tibial components are permanently fixed to the medial side of the distal femur and proximal tibia, respectively, using three 3.5 mm stainless steel bicortical locking screws (New Generation Devices) in each component. The distal end of the femoral component is designed to follow the curvature of the femoral condyle without impinging on the movement of the soft tissues of the stifle joint. The femoral ball is able to freely rotate and slide within the travel channel allowing unimpeded joint flexion and extension while preventing abnormal tibial translation in a cranial and caudal direction. Tolerances built into the sliding articulation allow for 10° of unimpeded internal and external rotation of the tibial component relative to the femoral component. The same degree of relative tibial valgus and varus movement is also permitted. Vertical travel of the ball within the travel channel allows for unimpeded normal compression and expansion of the joint, which is limited by the secondary supporting structures of the joint. The femoral component is positioned so that the femoral ball will be located in as isometric a position as possible (2,13). This location is predetermined on the preoperative lateral radiograph. The ball is positioned so that it is approximately equidistant from the caudal and distal aspects of the medial femoral condyle (Figure 4). With the implant temporarily fixed in place using one or two 5/64 inch 316L stainless steel holding pins (Jorgensen Labs) in each component, confirmation of a close to isometric positioning of the implant was made during surgery by observation of lack of binding while fully flexing and extending the limb. It is not critical to find the perfect isometric spot during surgery as the 6-mm travel allowance in the channel of the sliding articulation allows the ball to move distally or proximally during flexion and extension as needed. The direction of travel of the ball depends on whether the ball is caudal, or distal to the isometric point. Minimal ball travel indicates an isometric implantation. If travel of the ball exceeds the maximum limits of the travel channel or if there is binding during flexion and extension, the femoral component can be repositioned to find a more suitable position.

Figure 4.

Preoperative lateral radiograph showing ideal position of the femoral ball. Note X and Y are equidistant from the center of the ball.

An in silico study utilizing a 3-D computer model of the canine stifle developed at the University of Louisville, Kentucky for the purpose of evaluating stifle kinematics of the intact and cruciate ligament deficient stifle is currently being used to evaluate the Simitri implant during passive range of motion (12,14–16). The investigation is ongoing and the data have not yet been submitted for publication.

In vitro mechanical testing of the implant by the New Jersey Institute of Technology has been done using an Instron 3343 instrument (Instron Worlwide Testing, Norwood, Massachusetts, USA) to evaluate functional range of motion, strength of implant and resistance to wear. Results of this testing have demonstrated that the implant “allows for functional range of motion while providing the strength to prevent tibial thrust.” The implant was also shown to be durable over 1 000 000 cycles under forces greater than would be likely to occur in vivo (16–18).

Multicenter clinical trials of the implant on client-owned patients with stifle instability secondary to naturally occurring cranial cruciate ligament deficiency are currently being performed. To date there have been 66 implantations by the authors and an additional 10 implantations by 3 surgeons in the United States with up to 14 mo of postoperative follow-up. Data being collected include lameness score, stifle range of motion, and thigh muscle mass circumference. A radiographic investigation, evaluating progression of osteoarthritis of the affected stifle will also be performed beginning 1 y after implantation. Preliminary evaluation of the implant was presented at the 4th World Veterinary Orthopaedic Congress in Breckenridge, Colorado, USA in March 2014 (16). Results of the preliminary evaluation indicated that there was significant improvement in lameness scores of patients at 2 mo after surgery (16).

The Simitri implant was developed and primarily intended for use in patients with naturally occurring cranial or caudal cruciate ligament disruption and subsequent stifle instability. However it has been designed to provide rotational, cranial caudal, and valgus varus stability during all phases of the stride. It was hypothesized that the implant would also be an effective adjunctive treatment for multiple stifle ligament disruptions and could be successfully combined with primary repair of damaged collateral ligaments.

This patient was weight-bearing, able to ambulate and begin meaningful stifle rehabilitation exercises 24 h after surgery. Lameness scores decreased very rapidly, range of motion values returned to preoperative values, and the implant was well-tolerated by the patient. Twelve weeks after surgery, the patient was able to begin to return to pre-injury activities. Further long-term follow-up is necessary to fully assess the outcome in this patient. However, early results of this case suggest that this novel extracapsular articulated stifle stabilizing implant may be a viable alternative for the surgical management of this potentially devastating injury.

Update as of December 2014

At the 7 1/2 month postoperative examination of this case the injured limb had regained full range of motion (32 degrees flexion, 165 degrees extension), had an increased thigh muscle circumference to 44 cm, had a lameness score of 0/5, and the owner reported that the patient had returned to pre-injury activity levels. At 9 months after surgery, the owner reports that the patient continues to do well and accompanies them on daily outings. The Simitri implant has now been successfully used in 3 cases of stifle disruption and the authors have now performed over 100 implantations in total.