August 2017
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Figure 1 Orthogonal radiographs of the left stifle joint 6 weeks after tibial tuberosity advancement


A 4-year-old neutered male Labrador retriever is presented for lameness in the left pelvic limb. Another veterinarian previously diagnosed cranial cruciate ligament (CrCL) rupture and performed a tibial tuberosity advancement (TTA) 6 weeks before presentation. The otherwise healthy patient did well for 4 weeks postoperatively, then became acutely more lame in the operated limb. 

The general physical examination is considered normal, aside from signs of the recent surgery (ie, shaved left pelvic limb, a healing surgical scar over the medial aspect of the proximal tibia). Orthopedic examination reveals a grade 4 of 5 (ie, toe-touching) left pelvic limb lameness at a walk and trot. The patient abducts and externally rotates the left stifle during gait and shifts weight off of this limb while standing. There is moderate muscle atrophy of the left pelvic limb and joint effusion of the left stifle. An implant is palpable along the proximal medial tibia with a prominent tibial tuberosity. 

Mild discomfort and crepitus can be noted on passive range of motion of the left stifle. There is positive cranial drawer but negative cranial tibial thrust of the left stifle. There is mild effusion of the right stifle joint; otherwise, no pain, instability, or limitations on passive range of motion are appreciated. The dog is sedated, and radiographs of the left stifle joint are obtained (Figure 1). 

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What are the next steps?

Choice 1

Suspicious of a meniscal tear, you recommend revision surgery to re-explore the left stifle joint.

Choose this Option

Choice 2

Suspicious of infection, you perform arthrocentesis of the left stifle joint.

Choose this Option

Case Progression

In a discussion with the patient’s previous clinician, you learn the operative findings from the initial TTA procedure: intact medial and lateral menisci, full rupture of the CrCL, and fraying of the caudal cruciate ligament. You make an arthroscopic portal to inspect the joint. There is moderate synovitis (Figure 2). You confirm a fully torn CrCL. 

Figure 2 Arthroscopic view of the caudal cruciate ligament with surrounding synovial membrane inflammation

The caudal cruciate ligament is intact, with mild frays and splits in the ligament and surrounding synovial inflammation. Both the medial and lateral menisci have mild superficial frays but are largely intact (Figure 3). You elect to perform a medial meniscal release.

Figure 3 Arthroscopic view of normal (A) medial and (B) lateral menisci

Clinical Considerations

In this clinical scenario, meniscal tear would be near the top of the differential diagnoses list. Other differential diagnoses include infection, implant failure, bone failure, and patellar luxation. 

The reported rate of medial meniscal tears associated with an unstable CrCL rupture is approximately 50%.1-3 The rate of meniscal tears in dogs with a stable partial CrCL tear is not well described but is likely less than unstable joints.1,4 Despite the meniscus appearing normal at the time of TTA, it is possible that the clinical signs relate to a meniscal tear. Presence of a palpable or audible click is reported to increase the likelihood that meniscal pathology is present by a factor of 11.3 and has a positive predictive value of 85%.5,6 

A meniscal tear noted on revision surgery may either be a subsequent meniscal tear that occurred sometime after TTA stabilization or was present during the original TTA procedure but missed during joint examination (ie, a latent tear). Regardless of the cause, the occurrence rate of meniscal tears is estimated to be 12% to 28% following TTA and 2% to 12% after tibial-plateau–leveling osteotomy (TPLO).1,2,7,8 

A key step in any cruciate surgery is to obtain adequate exposure for a thorough visual examination of the joint. Several instruments (eg, self-retaining Gelpi retractors, stifle distractors, small [1.5-mm] meniscal probes) can be useful in this approach. 

Stifle arthroscopy, although limited to select practices and associated with a steep learning curve, also provides magnification and illumination and is particularly useful in the stifle joint. Probing the menisci, in addition to using arthroscopy, increases the sensitivity of tear detection by 1.5 to 2 times as compared with arthrotomy alone.9 Tears are almost exclusively confined to the caudal horn of the medial meniscus because of its firm attachment on the tibial plateau. The most common tear pattern is a displaced vertical longitudinal or “bucket-handle” tear, which accounts for the palpable click as the torn meniscus flips caudal-to-cranial in the joint. 

Lateral meniscus tears are rare because robust caudal meniscofemoral attachments allow the meniscus to move with the femur during active range of motion. The original descriptions of both TPLO and TTA procedures advocated for a meniscal release at time of stabilization to prevent late tears. 

A meniscal release involves cutting through the meniscus. The meniscus drops to the back of the joint and reduces the potential for a subsequent tear after stabilization. This can be done at the meniscotibial ligament (via craniomedial approach) or midbody just caudal to the medial collateral ligament (more often via a blind caudomedial approach). In a cadaveric model, the efficacy of release was only 56% to 81%, depending on the approach used.10 Surgeon skill and experience likely impacted this result, so it is important to confirm by visual examination once complete. Meniscal release is effectively the same as meniscal excision; therefore, the decision should be based on individual case selection and scientific evidence.11


The patient is discharged the next day with instructions for activity restrictions and initiation of physical therapy. On recheck examination at 6 weeks, slow progressive increases in weight bearing and mobility are documented. 

Your Choice’s Implications

In this scenario, immediate surgical exploration was elected. Although the outcome was successful, revision surgery was costly, and release of the meniscus could lead to long-term medial compartment osteoarthritis and impaired mobility.12  

Show results from the other option.

Case Progression

Arthrocentesis of the left stifle yields a large volume (>6 mL) of straw-colored joint fluid with poor viscosity. Fluid and cytologic analysis is performed (Table). Aerobic and anaerobic culture of the synovial fluid reveals no growth. You prescribe a course of NSAIDs and antibiotics (ie, cephalexin [30 mg/kg PO q12h for 30 days]) for a presumptive surgical site infection. 

The dog initially does well and returns in 4 weeks for evaluation. The general physical and orthopedic examination are similar to previous examinations with grade 4 lameness and effusion. You perform repeat radiography and arthrocentesis of the left stifle (Table). Aerobic culture of synovial fluid reveals no growth. You elect to continue NSAIDs and antibiotics for an additional 4 weeks. 

Synovial fluid cytology
 Total Nucleated Cell Count
 Left StifleRight Stifle
Initial visit (post TTA)81.65 × 103/µL (109L); 91% neutrophilsN/A
Recheck #111.04 × 103/µL(109L); 63% neutrophilsN/A
Recheck #240 × 103/µL(109L); 79% neutrophils2.34 × 103/µL(109L); 98% mononuclear cells

Normal values: joint fluid <3000 cells; >90% mononuclear cells


The dog, now lame on both pelvic limbs, returns 8 weeks after the initial examination, and the owner is unhappy. All examination findings are similar, except you appreciate increased joint effusion in the right stifle joint and detect positive cranial drawer and tibial thrust. 

You elect to perform radiography and arthrocentesis of multiple joints. Synovial fluid cytology results of both carpi are normal; left and right stifle joints are detailed in Table. You elect to perform arthroscopy and TPLO on the right stifle and concurrent arthroscopy of the left stifle. Arthroscopic findings of the left stifle include full tear CrCL, intact (but with superficial frays) caudal cruciate ligament, and intact medial and lateral menisci. You perform a biopsy of the left stifle joint synovial membrane/capsule. Histologic evaluation demonstrates moderate lymphoplasmacytic synovitis. Aerobic culture of the synovial biopsy reveals no growth.

Clinical Considerations

In this scenario, the synovial fluid contained a high nucleated cell count of predominantly neutrophils. Septic arthritis would be the top differential diagnosis. If effusion were present in multiple joints, other immune-mediated or infectious arthropathies should be considered. Surgical site infection is an inherent risk of any procedure, particularly one that involves orthopedic implants. The reported surgical site infection rate in elective orthopedic procedures is 5%,13 although rates as high as 10% have been reported for certain procedures (eg, TPLO).14Staphylococcus spp and Streptococcus spp are the most common isolates to colonize the joint and/or implants.13 

Infections following TTA may present as septic arthritis or implant-associated deep tissue infections, which typically have disparate clinical signs. Septic arthritis rapidly destroys joint surfaces and can cause profound pain, inflammatory infiltrates, and—in severe cases—dependent limb swelling.15 High neutrophilic cell counts are observed in septic synovial fluid, but bacterial organisms are rarely seen.15 Microbial culture may also be falsely negative as bacteria trap in the synovial membrane. Use of blood culture flasks (rather than culture swabs) may improve culture efficacy.16,17 Implant-associated infections typically present as soft tissue draining tracts with local swelling and inflammation. Although plates and screws engage the bone, osteomyelitis is uncommon unless infections are neglected. Implant infections are problematic due to formation of biofilms—which are notorious in staphylococcal infections—and are unlikely to be completely eradicated without implant removal.18 Use of postoperative antibiotics has become common but remains a topic of debate, as efficacy data are conflicting.19 The increasing incidence of antibiotic-resistant bacterial infections suggests that alternative strategies are needed.14 

Synovial inflammation is an early feature associated with degenerative CrCL rupture. This is typically a lymphoplasmacytic response, although other inflammatory cell types may play a role in the pathophysiology of cruciate disease.20 The improvement and then recrudescent cellular infiltrate in this case may have been related to a profound inflammatory response associated with cruciate fiber rupture.20 Synovitis can cause further degradation of the CrCL21 such that stable partial tears typically progress to full tears over time.22 Radiographic joint effusion and osteophytosis are risk factors for subsequent CrCL rupture.23 

Many options, including immunomodulatory treatment (eg, doxycycline, leflunomide) and regenerative approaches (eg, platelet-rich plasma, stem cells), have been explored, but none have been effective in reducing stifle inflammation and subsequent CrCL rupture.20,24 Ultimately, the risk for contralateral rupture is between 40% and 60% within 12 to 17 months of CrCL diagnosis, and 10% to 15% of dogs present with bilateral CrCL rupture.22 


The dog recovers well. Recheck 8 weeks after surgery confirms radiographic healing of the right TPLO. Clinical function of both stifles continues to slowly improve.

Your Choice’s Implications

In this scenario, pursuing the more conservative approach initially is important to rule out a potentially treatable problem. If the synovial fluid from the initial culture had been positive, a more aggressive surgical route would have been avoided. The dog responded positively to empiric antibiotic therapy, suggesting the possibility this was a false-negative culture result. The initial cost of diagnostic evaluation and treatment was less than the cost in Case Route 1; however, owners should be prepared for repeat visits, sedation, and imaging.

Show results from the other option.

CrCL = cranial cruciate ligament, TPLO = tibial-plateau–leveling osteotomy, TTA = tibial tuberosity advancement

References and author information Show
  1. Fitzpatrick N, Solano MA. Predictive variables for complications after TPLO with stifle inspection by arthrotomy in 1000 consecutive dogs. Vet Surg. 2010;39(4):460-474. 
  2. Gatineau M, Dupuis J, Planté J, Moreau M. Retrospective study of 476 tibial plateau levelling osteotomy procedures. Vet Comp Orthop Traumatol. 2011;24(5):333-341. 
  3. Ralphs SC, Whitney WO. Arthroscopic evaluation of menisci in dogs with cranial cruciate ligament injuries: 100 cases (1999-2000). J Am Vet Med Assoc. 2002;221(11):1601-1604. 
  4. Ritzo ME, Ritzo BA, Siddens AD, Summerlott S, Cook JL. Incidence and type of meniscal injury and associated long-term clinical outcomes in dogs treated surgically for cranial cruciate ligament disease. Vet Surg. 2014;43(8):952-958. 
  5. Neal BA, Ting D, Bonczynski JJ, Yasuda K. Evaluation of meniscal click for detecting meniscal tears in stifles with cranial cruciate ligament disease. Vet Surg. 2014;44(2):191-194. 
  6. Dillon DE, Gordon-Evans WJ, Griffon DJ, Knap KM, Bubb CL, Evans RB. Risk factors and diagnostic accuracy of clinical findings for meniscal disease in dogs with cranial cruciate ligament disease. Vet Surg. 2014;43(4):446-450. 
  7. Thieman KM, Tomlinson JL, Fox DB, et al. Effect of meniscal release on rate of subsequent meniscal tears and owner-assessed outcome in dogs with cruciate disease treated with tibial plateau leveling osteotomy. Vet Surg. 2006;35(8):705-710. 
  8. Wolf RE, Scavelli TD, Hoelzer MG, Fulcher RP, Bastian RP. Surgical and postoperative complications associated with tibial tuberosity advancement for cranial cruciate ligament rupture in dogs: 458 cases (2007-2009). J Am Vet Med Assoc. 2012;240(12):1481-1487. 
  9. Pozzi A, Hildreth BE, Rajala-Schultz PJ. Comparison of arthroscopy and arthrotomy for diagnosis of medial meniscal pathology: an ex vivo study. Vet Surg. 2008;37(8):749-755. 
  10. Austin B, Montgomery RD, Wright J, Bellah JR, Tonks C. Evaluation of three approaches to meniscal release. Vet Comp Orthop Traumatol. 2007;20(2):1-6. 
  11. Pozzi A, Kowaleski MP, Apelt D, Meadows C, Andrews CM, Johnson KA. Effect of medial meniscal release on tibial translation after tibial plateau leveling osteotomy. Vet Surg. 2006;35(5):486-494.
  12. Luther JK, Cook CR, Cook JL. Meniscal release in cruciate ligament intact stifles causes lameness and medial compartment cartilage pathology in dogs 12 weeks postoperatively. Vet Surg. 2009;38(4):520-529.
  13. Turk R, Singh A, Weese JS. Prospective surgical site infection surveillance in dogs. Vet Surg. 2015;44(1):2-8. 
  14. Nazarali A, Singh A, Moens NMM, et al. Association between methicillin-resistant Staphylococcus pseudointermedius carriage and the development of surgical site infections following tibial plateau leveling osteotomy in dogs. J Am Vet Med Assoc. 2015;247(8):909-916. 
  15. Scharf VF, Lewis ST, Wellehan JF, et al. Retrospective evaluation of the efficacy of isolating bacteria from synovial fluid in dogs with suspected septic arthritis. Aust Vet J. 2015;93(6):200-203. 
  16. Montgomery RD, Long IR, Milton JL, DiPinto MN, Hunt J. Comparison of aerobic culturette, synovial membrane biopsy, and blood culture medium in detection of canine bacterial arthritis. Vet Surg. 1989;18(4):300-303.
  17. Font-Vizcarra LS, García SN, Martínez-Pastor JC, Sierra JM, Soriano A. Blood culture flasks for culturing synovial fluid in prosthetic joint infections. Clin Orthop Relat Res. 2010;468(8):2238-2243.
  18. Savicky R, Beale B, Murtaugh R, Swiderski-Hazlett J, Unis M. Outcome following removal of TPLO implants with surgical site infection. Vet Comp Orthop Traumatol. 2013;26(4):260-265.  
  19. Nazarali A, Singh A, Weese JS. Perioperative administration of antimicrobials during tibial plateau leveling osteotomy. Vet Surg. 2014;43(8):966-971. 
  20. Bleedorn JA, Greuel EN, Manley PA, et al. Synovitis in dogs with stable stifle joints and incipient cranial cruciate ligament rupture: a cross-sectional study. Vet Surg. 2011;40(5):531-543. 
  21. Bozynski C, Kuroki K, Stannard J, et al. Evaluation of partial transection versus synovial debridement of the ACL as novel canine models for management of ACL injuries. J Knee Surg. 2015;28(5):404-410. 
  22. Muir P, Schwartz Z, Malek S, et al. Contralateral cruciate survival in dogs with unilateral non-contact cranial cruciate ligament rupture. PLoS ONE. 2011;6(10):e25331. 
  23. Chuang C, Ramaker MA, Kaur S, et al. Radiographic risk factors for contralateral rupture in dogs with unilateral cranial cruciate ligament rupture. PLoS ONE. 2014;9(9):e106389. 
  24. Muir P, Hans EC, Racette M, et al. Autologous bone marrow-derived mesenchymal stem cells modulate molecular markers of inflammation in dogs with cruciate ligament rupture. PLoS ONE. 2016;11:e30159095. 

Jason Bleedorn

DVM, DACVS University of Wisconsin–Madison

JASON BLEEDORN, DVM, MS, DACVS (Small Animal), is a clinical assistant professor in small animal orthopedics at University of Wisconsin–Madison, where he instructs residents, interns, and veterinary students and conducts clinical research. He earned his DVM from University of Illinois and his MS in biomedical sciences from University of Wisconsin–Madison. He completed a rotating internship at Purdue University, a surgery internship at Dallas Veterinary Surgical Center, and a small animal surgery residency at University of Wisconsin–Madison. His research interests include biomechanics and augmentation of fracture healing, imaging assessment and treatment of bone deformities, 3-dimensional printing for surgical planning, limb salvage of bone tumors, and mechanisms of cruciate ligament disease in dogs.

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