Dr. Trostle attended the 2012 AAEP Hind End Lameness Focus meeting in Oklahoma City. Here are some of his key points from the the meeting.
General Perineural anesthesia and intra-articular anesthesia are important to help determine the source of lameness. However, they are probably not as specific as we have originally been taught to believe. Local anesthetics can diffuse into surrounding tissues and be carried into adjacent tissue via lymphatics and potentially other sources. From Dr. Sue Dyson "It is crucial to be aware of the potential for perineural local analgesic techniques to reduce pain not only distal to the site of the blocks, but also at the level of, or proximal to, the sites of the blocks". As an example she talked about a close anatomical relationship between the plantar outpouchings of the tarsometatarsal (TMT) joint capsule and the suspensory ligament (SL). The volume of the TMT joint is small. Intra-articular (IA) pressure increases as local anesthetic solution is injected, and the horse may become uncomfortable, manifest as the horse flexing the limb and possibly kicking. If more than 3-4 ml of local anesthetic solution is injected there may be leakage through the injection site, thus 'bathing' the proximal aspect of the SL. Thus it is important to use a small volume of local anesthetic solution (3-4 ml). The difficulty in interpreting partial (50-70%) improvement in areas was also discussed and how to proceed from there (stop, continue blocking, wait give it more time, re-visit at another time with different blocking strategy).
Suspensory- Lots of discussion here about diagnosis and imaging especially of proximal suspensory desmitis ( PSD). Many people discussed the blocking of the deep branch of the lateral plantar nerve by a single injection.A Many questions were raised about how specific it was vs. the typical high 4-point and direct infiltration blocks. The difficulty in obtaining a good US image of the suspensory origin was discussed and many believe now that cross sectional area (CSA) is no more sensitive indicator of a problem the looking at fiber pattern and alignment. It is interesting to compare how US images look very different than MRI images of the same area. Some suggest that MRI is the only true method of evaluating the origin of the suspensory because of how it has both muscle and ligament in the area. From Dr. Rich Redding "A comparison of MRI (as the gold standard) and diagnostic ultrasound was performed to determine ultrasound's sensitivity and specificity for accurately localizing desmopathy lesions of the proximal suspensory. The sensitivity and specificity of a diagnostic ultrasound for detecting PSD were 0.84 and 0.37, respectively. For localizing lesions accurately the sensitivity of diagnostic ultrasonography was 0.76 and the specificity was 0.33 for detection of disease and 0.66 and 0.33 for accurately localizing disease". In general, most people thought there needs to be an aggressive approach to treating high limb PSD. Most favored the fasciotomy deep branch neurectomy surgery ± desmoplasty in sport horses. Although many race horse practitioners including Dr. Larry Bramlage have found it to NOT be helpful in race horses and arguably even problematic. Unfortunately, there was no consensus on the use of regenerative medicine in PSD. Many people using some form of regenerative medicine, but no evidence of that any one in particular was better.
Hock Discussion on the blocking of the lower hock joints (tarsometatarsal [TMT] and distal intertarsal [DIT]) and communication between and with the surrounding joints. There is recognition that the TMT and DIT do communicate in some horses. Most believe that the more disease or pathology in the lower joints decreases the chances of there being a functional communication. Most believe it is most complete to block and treat both TMT and DIT joints separately. Dr. Mike Ross talked about the alternative "dorsolateral approach to the injection of the DIT joint was described. The site is identified as a point 2-3 mm lateral to the long digital extensor tendon and 6-8 mm proximal to a line drawn perpendicular to the long axis of MTIII at the level of the proximal aspect of MTIV. The success rate for arthrocentesis at this site was equal to that for the traditional medial approach, with supported advantages being improved safety for the clinician and easily identified landmarks."B There was also a good discussion about ethyl alcohol (EO) in distal hock joints. Many believe it is a chemical synovectectomy /joint capsule neurectomy that gives the clinical response rather than fusion or anklyosis which is supported by some of the research work. None the less, it does appear to be helpful and is generally used in horses that are refractory to intra-articular steroids. Concern was also raised for communication into the PIT or TC joint. It is strongly recommended that a contrast study be performed to assess communication before injecting any EO. Some clinicians report even though there was no communication at the time of injection, they see some manifestation of bony changes in the PIT and TC joints. Some believe this is some form of EO getting into those joints by another means (diffusion?), while other postulated that when lower hock joint are fused the upper joints experience more loading and shearing forces and undergo a changes , because they are no longer distributed to all of the joints.
Dr. Marybeth Whitcomb gave an excellent talk about ultrasounding the stifle. She had a split screen setup with one half being an animated body part,and how the US probe was being held and moved and the other side she had real-time videos of the ultrasound images. She discussed the meniscus in great detail. She reported that the "vertical hypoechoic striations are commonly seen in normal menisci and should not be misinterpreted as injury". She and Dr. Chris Kawcak also emphasized that it is important to remember that ultrasonography and arthroscopy are complimentary imaging modalities for meniscial injury. The midbody region of the meniscus is not a visible arthroscopically, but is well visualized ultrasonographically. As such, negative findings on arthroscopy do not rule out meniscial injury. Arthroscopy is better suited to visualize small tears of the cranial and caudal horns of the menisci that may be challenging or impossible to visualize ultrasonographically. Dr. Kawcak also talked about how the CSU group felt that regenerative medicine therapies (IRAP and or stem cells were important in the treatment of soft t issue injuries of the stifle.
Consider attending the AAEP Focus meeting in the future. The smaller meeting format that concentrates on a singular topic has a lot to offer both professionally and personally.
A Hughes TK, Liashar E, Smith RK: In vitro evaluation of a single injection technique for diagnostic analgesia of the proximal suspensory ligament of the equine pelvic limb. Vet Surg
BJust EM, Patan B, Licka TF. Dorsolateral approach for arthrocentesis of the centrodistal joint in horses, Am J Vet Res, 2007;68:946.