The Patello-Femoral joint (PFJ) in your knee is considered one of the most complex in the body. It consists of several structures:
- The patella (kneecap)
- The patella ligament (the elastic tissue that contains the kneecap and inserts on your shin bone and your thigh bone)
- The trochlear groove (the V-shaped bone surface in the middle of the knee joint that the kneecap rides in)
- A complex assortment of ligaments, tendons and soft tissues that surround the knee
Normal movement of the patella femoral joint relies on an orchestration of soft tissues, bony architecture and the mechanical axis between your hip and ankle. All of these structures and forces work together to keep your kneecap in the groove as you flex and straighten your leg. Clearly, anything that disrupts this anatomical symphony not only risks compromising normal motion and if the balance is not maintained, increased loads can be translated to other parts of the knee causing additional problems.
Recently, a study compared two different types of implant commonly used in Patellofemoral surgery:
- Group I received an in-lay implant that is designed to sit “in” the surface and match the surrounding PFJ anatomy (HemiCAP Wave, Arthrosurface, Franklin, MA)
- Group II received an on-lay implant that essentially sits “on” top of the damaged surface so that it covers the bone and cartilage ( Journey™ PFJ, Smith & Nephew, Andover, MA)
No significant progression of osteoarthritis (OA) was observed in the rest of the knee joint for the inlay group, whereas, over half of the patients in the onlay group had developed knee Osteoarthritis (53%) in their other knee compartments. While the mechanism of the disease progression was unclear, the authors hypothesized that the “onlay” device overloaded the Knee joint leading to chronic inflammation (synovitis). Synovitis is a known risk factor for arthritis as it results in the secretion of inflammatory chemicals (cytokines) which can damage the tissues inside the knee. In addition, because the onlay implant raises the height of the trochlear groove, it may have abnormally stretched the patella ligament. When this “biological elastic” is overtightened it pulls the thigh and shin bones together as you move, which may put more pressure on the other parts of the joint. Based on this study, the PF HemiCAP® design may improve long-term results, reduce the risk of OA progression and provide patients with a more anatomical option.
Read the Study Abstract here: http://www.ncbi.nlm.nih.gov/pubmed/26231153