Final Management Plan:

Medical management is generally best tolerated in patients weighing less than 10 kg.  In a conservative protocol, animals are restricted in their activity and prescribed a course of anti-inflammatory drugs.  A return to normal function is usually seen in approximately six weeks.  In general, though, surgical stabilization is recommended for animals of any size.  Without surgical management, instability of the joint persists and degenerative joint disease inevitably develops.  Subsequently, the patient will tend to shift weight to the uninvolved opposite limb.  This abnormal stress combined with normal degenerative aging processes certainly predisposes the opposite limb to cruciate rupture.  This may be of particular importance in Bonnie's case in that a cranial drawer of 2-3 mm can be elicited from the right stifle.  Considering that a normal drawer is less than or equal to 2mm, this finding can either be normal for Bonnie or indicative of an early weakening of the ligament. Excessive loading in addition to other complicating factors already mentioned, make her a likely candidate for bilateral rupture.  Bilateral rupture cases are definitely more difficult to treat than unilateral situations and have a poorer prognosis for return of function.  Furthermore, surgery allows for further examination and assessment of joint structures, particularly meniscus.  Damage to the medial meniscus is seen in about 50-75% of ruptured cranial cruciate ligament cases.  Considering that Bonnie is a 6 year old large breed dog and already overweight, medical management can not be considered a viable option for Bonnie although it may be more economically feasible for the client.
Based on Bonnie's signalment, body condition, and activity level, surgical management would be the optimal treatment option.  In general, this method is especially recommended for animals over 15 kg.  Furthermore, surgery speeds rate of recovery, helps to minimize subsequent degenerative changes, and enhances return to function.  Prior to surgery, placing Bonnie on a weight reducing diet, such as Hill's r/d, for approximately two weeks is recommended.  During this time, Bonnie's activity should also be restricted. This time frame will allow for Bonnie to lose a target amount of 2-4 pounds but is short enough to avoid further degeneration of the joint before surgery. Pre- and postoperative weight reduction is of primary concern with Bonnie since excess weight will place increased stress on her healing stifle. Since previous hematology and chemistry were performed on initial exam, preanesthetic bloodwork can be foregone.  Bonnie is an aging large breed dog that is overweight so intracapsular ligament reconstruction coupled with extracapsular joint stabilization should be performed.  
The primary goal of intra-articular surgery is to anatomically and functionally restore the cranial cruciate.  A medial parapatellar approach will be used to visualize the joint.  Prior to reconstruction, the remnants of the cranial cruciate should be removed from their attachments.  Even though no crepitus was noted on orthopedic exam, any meniscal damage should be assessed while the joint capsule is open.  If damage is present, depending on severity, partial or total menisectomy is indicated due t o poor blood supply and subsequent compromised healing.  Once debridement of the joint is complete, it should be lavaged to clean out any loose debris.  An autogenous tissue graft will be passed through the intercondylar notch to mimic the course of the cranial cruciate ligament.  The lateral one third of the patella tendon and the distal fascia lata are placed in a predrilled tibial tunnel, pulled through the fat pad, under the intermensical ligament, and into the joint.  An incision is made through the femoral fabellar ligament and forceps are used to pull the graft through the joint and over the top of the lateral condyle.  The tibial tunnel must enter the joint at a point that is caudal and inferior to the point where the normal cruciate ligament originated.  Widening of the intercondylar notch should be considered in order to allow adequate room for the tissue graft.  After the graft is passed over the top of the lateral condyle it is sutured in place to the femoral fabellar ligament, fibrous joint capsule, and the patella tendon.  The graft can also be attached to the femoral condyle with a spiked washer and bone screw.  However, these require additional surgery to remove them. Before closing the surgical site, be sure that a 2-3mm cranial drawer is present.  Completely eliminating the cranial drawer would place excessive tension within the graft, which is inherently weaker than the original ligament.  Also, make sure the graft does not impinge on any tissue lying between itself and the adjacent bone.  Impingement could potentially cause reduced tissue perfusion and subsequent necrosis. At this point, the joint capsule can be closed with absorbable sutures. 
In extracapsular reconstruction, a double strand of heavy nonabsorbable suture is passed between the lateral fabella and femur to provide increased stability to the stifle.  The suture passes through the deep fascia surrounding the fabella and travels cranially and distally to a predrilled hole in the tibial crest.  Tying the suture will eliminate excessive tibial displacement during weight bearing. A small percentage, approximately 10 %, of patients may have a reaction to this type of suture.  Metal wire can be used in place of suture material, but has been found to break over time.  This typically results in a transient lameness.     During this part of the procedure, special care should be taken to identify and avoid the peroneal nerve.  The soft tissue layers can be sequentially placed back in opposition with absorbable suture. The skin incision can then be closed with intradermal absorbable suture. 
	Pre-operative medications include acepromazine and oxymorphone given for sedation and analgesia respectively.  They are administered subcutaneously approximately 30 minutes prior to surgery.  A second dose of oxymorphone is given at extubation to sustain analgesia through recovery.  Also, oxymorphone is administered post-operatively every 6-8 hours as needed for the first 24 hours.  Five days worth Rimadyl or Tylenol with codeine, if the Bonnie is particularly painful, should be sent home with the owner for continued analgesia.  Single doses of Cefazolin are administered intravenously pre-operatively and post-operatively to help control potential contamination and subsequent infection of the surgical site.  Cephalexin should be given orally every 8 hours for 7 days after surgery.  Prophylactic use of antibiotics was chosen in this case based on length of surgery and the invasion of the joint capsule.  Bonnie will also be sent home with a chondroprotective agent, such as Glycoflex, that will promote long term joint health.
	Bonnie will remain in the hospital 24 hours after surgery for observation.  The leg will not be wrapped unless there is significant post-surgical swelling. In which case, a Robert-Jones bandage should be applied and maintained for approximately 2-3 days. Therapeutic flexion and extension of the stifle joint should begin two days after surgery and be performed daily to maintain range of motion. Until swelling subsides, the leg should be iced several times a day for 20 minute increments.  Following this period, heat and massage should be applied to increase circulation to the joint and promote healing.  Throughout the first two weeks, Bonnie should be kept in a crate and only taken out for bathroom breaks. Leash walking and swimming with a gradual increase in the time and distance can be instituted over the next 10 weeks. 					
There are many surgical techniques available for the repair of the cranial cruciate ligament.  At this time, no single technique has been proven more effective or economical.  These various procedures can either be classified as primary repair with augmentation or reconstruction techniques.  Primary repair of a midsubstance cranial cruciate ligament rupture is not feasible.  The ability of the ligament to heal directly with scar tissue is limited due to insufficient vasculature.  The ligament stumps will invariably atrophy.
Reconstructive techniques can be divided into intracapsular and extracapsular procedures.  Intracapsular reconstruction employs biological tissues, synthetic material, or a combination of both to replace the ruptured cranial cruciate ligament.  An autogenous tissue graft was chosen to reconstruct Bonnie's knee due to convenient harvesting and lack of potential immune response associated with synthetic implants.   There are numerous variations on which tissues to use for the graft.  The distal fascia lata and lateral third of the patella tendon were chosen in this case because these tissues are frequently used and have proven efficacy.  There are also many different methods used for placement of the graft.  The attachment sites on the tibia and femur are generally agreed upon, but there are several variations on how to place the graft through the joint.  The Under and Over technique was chosen in this case as it is one of the most commonly used procedures.    Extracapsular reconstruction involves placement of sutures outside the joint or redirection of the lateral collateral ligament by displacing the fibular head cranially and caudally.  Both procedures provide stability to the joint and the choice to use one instead of the other is typically surgeon preference.  
	Another technique that is gaining in popularity, is the Tibial Plateau Leveling Procedure.  The angle of the tibial plateau is changed, by doing an osteotomy of the proximal tibia.  This allows the femur to move cranially during weight bearing making the caudal cruciate ligament more involved with joint stability than the cranial cruciate.  This technique is usually only done by specialist surgeons in referral institutions.  
 Prognosis for long term function for patients that have undergone reconstructive surgery is good with or without menisectomy, regardless of the surgical technique chosen.  Overall success rate is approximately 85%.   Twenty percent of dogs over 15 kg markedly improve or are normal by six months post-operatively. Long term prognosis is mostly influenced by the dog's size, activity level, and intended use. In Bonnie's case, the occurrence of some degree of degenerative joint disease remains highly probable and she probably won't show a full return to prior activity level. Subsequent meniscal damage in the affected limb brings 10-15% of reconstruction patients back in for surgery.   Furthermore, 20-40% of dogs with a cranial cruciate ligament tear will rupture their contralateral ligament within 17 months. In order to help avoid these sequelae and improve her chance for long term function, Bonnie must remain on a strict weight management plan that includes her present weight, a calculated target weight, and her initial decrease in activity. The protocol will include biweekly weight rechecks to assess how Bonnie is progressing according to program goals. 

Based on our facilities and the limited small animal orthopedic experience of the veterinarians at our rural mixed animal practice, surgical referral is recommended for Bonnie.   Our practice could then take over her post-surgical management and care.  Even though the recommended management plan may be costly, it must be made clear to the owner that in order for Bonnie to return to normal function and have a good quality of life, it is the best option.