L E T T E R T O T H E E D I T O R

Synovitis in Dogs with Stable Stifle Joints and IncipientCranial Cruciate Ligament Rupture

To the Editor: I thank Bleedorn et al (Vet Surg 2011; 40:531–543) for calling attention to cranial cruciate ligamentinjury in the contralateral stifle joint of dogs presented forcranial cruciate ligament injury in one of their stifles. I agreewith the statement in the conclusion that “Synovitis is anearly feature of the CrCLR arthropathy in dogs before de-velopment of joint instability clinically” because for years,I have been stating that joint instability is not a diagnosticcriteria for cruciate ligament injury.

I have been performing stifle arthroscopy in dogs for 30years and have learned some interesting things about cruci-ate ligament injuries. I disagree with some of the statementsin this article. I disagree with the term “Incipient” in thetitle because the contralateral stifles in the cases describedhave cranial cruciate ligament pathology. I disagree with thesecond sentence in the conclusion that states “Severity ofsynovitis is correlated with radiographic arthritis in jointswith minimal or no clinically detectable CrCL damage”because in the absence of other radiographically definablecauses, these cases are cranial cruciate ligament injuries.From my experience in performing arthroscopy on over 600stifle joints, increased fluid density/fat pad displacement ona lateral radiograph of the stifle has a 99% correlation withcranial cruciate ligament injury. In the first paragraph, thetext makes a referenced statement that “increasing to 60%rupture with early radiographic changes” this should be99% because dogs with early radiographic changes havecruciate ligament damage. If bilateral stifle radiographs aretaken of all dogs presented with a cranial cruciate ligamentinjury, those with bilateral disease at the time of originalpresentation is in the 40–60% range stated as developingcontralateral clinical disease within 12–17 months.

In the second paragraph, I agree that CrCLR is likelyunderestimated but the pathology is present, not incipi-ent. With arthroscopy as a study tool, the pathology ofstable stifle joints can be understood. I disagree with theproposal that stifle synovitis may be a key factor in devel-opment of progressive CrCLR overtime and feel stronglythat the synovitis is secondary to the damaged cruciate lig-ament. If we examine stifles with arthroscopy, we see thatthe synovitis is equally distributed throughout the joint withequal or greater involvement in the suprapatellar pouch asthere is in the intercondylar area. This is also true of thechondromalacia with equal or greater cartilage damage inthe trochlear groove as there is on the tibial plateau. This isa biochemical disease as much or more as it is a biomechan-ical disease. The hypothesis in this study is not relevant to

understanding the pathophysiology of this disease processbecause instability is not relevant to the pathophysiologyand the contralateral joints have the same disease processas the clinical joints. The important take-home messagefrom this article is that the majority of dogs presented withcruciate ligament disease have bilateral pathology at thetime of initial presentation.

Timothy C McCarthy DVM, PhD, Diplomate ACVSCascade Veterinary Referral Center and VeterinaryMinimally Invasive, Surgery Training(VetMIST), Tigard,OR

The author’s reply: We thank Dr. McCarthy for his in-terest in Synovitis in dogs with Stable Stifle Joints andIncipient Cranial Cruciate Ligament Rupture: a Cross-Sectional Study (Vet Surg 2011;40:531–543) and the ob-servations provided from his clinical work performing stiflearthroscopy for noncontact cruciate rupture in dogs. Weagree with the concept that most dogs affected by this con-dition have bilateral stifle joint pathology, as was confirmedin our study. However, the underlying etiopathogenesis,particularly for the incipient phase of the disease, remainsunclear.

We encourage readers to review a follow-up manuscripton this cohort of dogs that provides long-term follow-updata (Muir et al., Contralateral cruciate survival in dogswith unilateral noncontact cranial cruciate ligament rup-ture. PLoS One 2011;6:e25331). The 1-year contralateralcranial cruciate ligament rupture rate in these dogs was31%. This offers additional support to the concept that thestifle abnormalities reported in the contralateral stifles inour report Veterinary Surgery are a valid reflection of in-cipient disease. All dogs that had contralateral rupture oftheir previous stable stifle had variable amounts of cranialcruciate ligament fraying documented arthroscopically andhistologic synovitis at initial investigation. The immuno-logic mechanism and other relevant factors associated withinitial development of cruciate ligament damage and syn-ovitis should be the focus of future work.

Jason Bleedorn, DVM, Diplomate, ACVSPeter Muir, BVSc, PhD, Diplomate ACVS & ECVSComparative Orthopaedic Research, LaboratoryUniversity of Wisconsin-MadisonSchool of VeterinaryMedicine, Madison, WI

540 Veterinary Surgery 41 (2012) 540 C© Copyright 2012 by The American College of Veterinary Surgeons