Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA
The key to successful management of patellar luxations is to identify and correct each of the factors contributing to mal-tracking of the patella in the specific patient being treated. No single treatment nor collection of treatments will be consistently effective in all patients. Bony contributions to patellar luxation may include a shallow and/or shortened trochlear sulcus, a displaced tibial tubercle or other skeletal malformations. Similarly, chronic and persistent patellar luxation (grade 3 and grade 4 luxation) tend to distort the proper balance of soft tissue tension surrounding the patella. Often, especially with grade 3 and grade 4 luxations, soft tissue reconstructions are required to balance the tension in the soft tissues that surround the patella.
Soft tissue reconstructions include capsular/retinacular/muscular release, imbrications, and anti-rotation sutures. Soft tissue reconstructions, by themselves, will not correct bony conformational abnormalities. Soft tissue reconstructions are most commonly performed in conjunction with skeletal reconstructions. Release of thickened and contracted medial joint capsule/retinaculum is achieved by their incision from the tibial plateau to the suprapatellar recess. In most grade 4 and some grade 3 MPL cases, the quadriceps muscle group is medially displaced (Figure 1) and must be elevated from the suprapatellar region to the proximal femur, being careful to protect the descending genicular vessels (this, alone, is a good reason to refer these cases to a trained orthopedic surgeon). The pes anserinus muscle group (sartorius, gracilis, and semitendinosus muscles) can be released by elevation of their insertions on the medial aspect of the proximal tibia if their tension is causing internal rotation of the stifle. Stretched lateral joint capsule/retinaculum often need to be tightened to achieve balanced soft tension upon the patella. In grade 4 MPL cases, redundant joint capsule lateral to the patella must usually be excised. Reconstruction of the lateral joint capsule helps to properly balance the tension in the peri-patellar tissues. Extracapsular lateral fabello-tibial anti-rotation sutures can be placed to limit excessive stifle rotation and are particularly beneficial in dogs with combined MPL and cranial cruciate ligament rupture. The tibial anchor point of the extracapsular suture can either be to paired bone tunnels at the level of the extensor sulcus of the tibia (adjacent to the long digital extensor) or to a pre-formed eyelet in a tibial tension band wire.
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