Page 24 - ISAKOS 2018 Winter Newsletter

CURRENT CONCEPTS
Patellofemoral Replacement
Arthroplasty options include total knee replacement (TKR) and patellofemoral replacement (PFR). Several authors have reported excellent results following TKR for the treatment of isolated patellofemoral degeneration. However, TKR needlessly removes the normal tibiofemoral articulation, which may impair proprioception and functional activities. Additionally, the recovery period is longer and the morbidity rate is higher in association with TKR. Finally, if needed, revision TKR presents greater challenges, especially in terms of bone loss. Therefore, in our opinion, PFR is preferable to TKR for the treatment of a knee with advanced patellofemoral degeneration and a well-preserved tibiofemoral articulation when non-surgical treatment has failed.
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Implant Design
In a study of normal knees, we found wide variation in the position and orientation of the trochlear groove. In the coronal plane, the orientation of the groove, measured from the distal condylar line, varied from 12.5° of varus to 13.3° of valgus. Other investigators have noted similar findings. It is important to be aware of the design differences between commercially available PFR devices (Fig. 1). PFR implants can be classified as either an inlay or an onlay type. With first- generation designs, there was a clear distinction between the 2 types. With the inlay type, the damaged articular surface is replaced but the original trochlear shape is maintained. With the onlay type, the anterior part of the trochlea is removed and is replaced by with prosthetic trochlea. The advantage of the onlay type is that a dysplastic trochlea can be replaced with a normally shaped trochlea. With second-generation designs, the differences between the inlay and onlay types are less pronounced, with some of the newer inlay designs also reshaping the trochlea but to a lesser extent than is the case with the onlay type. There is a marked difference between prostheses in terms of trochlear design and groove orientation. With onlay designs, the trochlear groove angle has been found to vary from 0° to 13° of valgus.
Introduction
Spike Erasmus, MD Kneeclinic Stellenbosch SOUTH AFRICA
Daniel C. Wascher, MD Professor of Orthopedic Surgery University of New Mexico UNITED STATES
Isolated patellofemoral degeneration is a common problem in patients over 55 years of age and has been reported to affect 2% – 11% of males and 8% – 24% of females. The cause of isolated patellofemoral degeneration is multifactorial. The most common cause is degeneration secondary to abnormal patellofemoral biomechanics caused by factors such as trochlear dysplasia, patella alta, increased tibial tuberosity-trochlear groove (TT-TG) distance, and rotational abnormalities. This condition results in chronic overload of the articular cartilage and eventual degeneration. Other causes include post-traumatic arthritis (resulting from patellar fractures or articular cartilage injuries) or chronic repetitive overload (resulting from non-physiological exercises such as squats, box jumps, etc.). When treating this condition, it is important to identify the cause as this factor has an effect on the preferred treatment options.
Treatment
Treatment of patellofemoral degeneration can be divided into non-surgical and surgical treatments. Non-surgical treatment consists of quadriceps and gluteal muscle strengthening, activity modification (avoiding stairs, squats, etc.), and symptomatic treatment with non-steroidal anti-inflammatory medications. Surgical treatment involves either a joint- preserving procedure or an arthroplasty.
When joint preservation is an option, symptoms can be relieved by improving patellar tracking with use of procedures such as tibial tubercle transfer, medial patellofemoral ligament (MPFL) reconstruction, and lateral retinacular release. The tibial tubercle can be moved medially, distally, and anteriorly, depending on the area of degeneration in the patellofemoral joint. Anteriorization of the tibial tubercle can decrease joint- reaction forces on the patella. A lateral patellar facetectomy can remove the area of the patella that is frequently most affected.
22 ISAKOS NEWSLETTER 2018: VOLUME I