Patellar Groove Replacement (PGR)
Patello-femoral degenerative joint disease is a frequent, often ignored consequence of some of the most common conditions of the canine stifle such as patellar luxation, or cruciate ligament degeneration and rupture. Surgical treatments of patellar luxation, whether by tibial tuberosity transposition or by corrective osteotomies of the femur and/or tibia, combined with patellar groove deepening by one of several methods, seek restoration of joint stability.
Progression of arthrosis to a chronically painful joint must be expected, but that seems to be an accepted, generally ignored consequence of these surgical interventions. Replacement of the severely effected and/or worn-out patellar groove by a prosthesis presents an option worthy of serious consideration. In an effort to address this need, Slobodan Tepic, Dr. Sci., CTO, KYON AG, and Dr. Jacek J. de Haan, DVM, DACVS have proposed a novel prosthesis, the KYON Patellar Groove Replacement (PGR)*.
The PGR should provide a low friction, scratch resistant surface that could indefinitely tolerate the contact pressures and gliding friction generated by the bare bone of the patella. The KYON Patellar Groove Replacement (PGR)* is thus comprised of two components:
an upper anatomically shaped groove component produced from Titanium alloy (TiAl6V4), highly polished and treated with Amorphous Diamond-Like Coating (ADLC) (Medthin™ 43 ADLC, Ionbond, Olten, Switzerland). ADLC shows exceptionally low friction against many solid surfaces, offering the possibility of maintaining heat generation below the threshold of thermal necrosis. ADLC is also very hard and scratch resistant when applied to a suitable substrate. It is chemically inert and thus biocompatible.
a perforated base plate produced from c.p. titanium, coated by glow discharge anodisation with addition of calcium phosphate to promote bony integration (Biocer®, a proprietary process of Steiger Galvanotechnique SA, Châtel-St-Denis, Switzerland).
Ostectomy of the patellar groove just cranially to the insertion of the tendon of the long digital extensor creates a broad, well perfused cancellous bone bed onto which the base plate is secured by titanium bone screws. The groove component is then attached to the base plate by means of 3 conical pegs fitted into receiving conical holes. The broad area of the ostectomy of the patellar groove allows for considerable freedom in medial-lateral positioning of the base plate that can be used to improve quadriceps-to-patellar tendon alignment, thus avoiding conventional tibial tuberosity transposition. Use of trial implants during surgery aids the search for an optimal position of the final implant.
Functional loading of the implant leads to compression of its interface to the bone, which is mechanically favourable to the ill-conditioned load transfer called for by conventional tuberosity transposition, where the full force of the patellar tendon is transferred to the tibia by pins and a figure eight wire.
Significant angular deformities can be treated by concurrent corrective osteotomies in addition to patellar groove replacement, should the condition of the patello-femoral joint call for it. The same is true for cruciate ligament ruptures that can be concurrently treated by, for example, Tibial Tuberosity Advancement (TTA).
Clinical application of the Kyon PGR was initiated in 2009 through a controlled clinical release with 15 surgeons (from USA, Europe and Japan) participating in this phase. By mid 2012, 35 surgeons had performed ~100 procedures. Surgical planning with templates and execution of the procedure are deemed simple and the risks as acceptable. Post-surgical recovery is rapid and, at this time, no signs of implant loosening have been observed. The procedure presents relatively low morbidity and is meeting the expectations of the early adopters in terms of clinical improvement.