Patellofemoral Update

Patellofemoral chondrosis/arthrosis is extremely common. It is often an incidental finding and has been reported in almost 50% of MRIs in asymptomatic players of the National Basketball Association.

The articular cartilage is aneural and most pain originates in the soft tissues. The treating orthopedic surgeon must be careful in attributing a patient’s anterior knee pain to the presence of a patellofemoral articular cartilage lesion. Often times, they are incidental findings and it is imperative to search for other causes. Most patellofemoral pain will go away if treated conservatively despite the presence of a significant articular cartilage lesion. Always look at the soft tissues closely as a source of pain.

The etiology of articular cartilage lesions is often secondary to malalignment, instability or trauma. However in the United States, it is most commonly secondary to overload from exogenous obesity and an increased body mass index, which has been shown to increase the incidence of patellofemoral degenerative joint disease. Surgical intervention should be considered only when other causes have been carefully ruled out and all rehabilitation efforts have failed.

If the primary etiology is malalignment or instability, unless the lesion is a large traumatic full-thickness lesion or associated with bone loss, then it is generally best to just address the primary etiology and perform a simple debridement of the lesion. More than 90% of patients with a history of a traumatic patellar dislocation will have a significant chondral lesion on the medial facet of their patella.

Likewise, in patients with malalignment requiring a tibial tubercle osteotomy, a cartilage restoration procedure is generally not necessary as a primary procedure unless the lesion is large, full thickness, associated with bone loss or very symptomatic and in a geographical location not likely to be helped by a realignment/unloading procedure.

Some patients will require cartilage restoration – many cases in association with a realignment/unloading procedure – and most commonly anteromedialization of the tibial tubercle. It is generally accepted that chondroplasty as an isolated procedure is of limited benefit. I usually present it to the patient as a diagnostic or “staging” arthroscopy, which may have some therapeutic benefit. Because of the thickness of the articular cartilage, microfracture has a poor track history on the patella and works better on the trochlea. However, microfracture is sometimes a reasonable first-line procedure in association with a carefully constructed rehabilitation program.

Cartilage restoration procedures fall into two main categories: cell-based therapies and osteochondral transfer procedures (either autograft or fresh allograft). The most common and longest used cell-based therapy is autologous chondrocyte implantation. My experience has been better with its use on the trochlea, especially full-thickness lesions that cross the groove more than the patella because the articular cartilage thickness is difficult to reproduce. However, there are many orthopedic surgeons who have had good results with this procedure on the patella, usually in combination with a realignment/unloading osteotomy. A number of surgeons have had short-term success with the implantation of juvenile chondrocytes, however, long-term results and prospective comparative studies are lacking.

For full-thickness traumatic defects secondary to a prior osteochondral fracture or osteochondritis dissecans of the patella, my preference is press fit implantation of a fresh osteochondral plug from a donor patella – one of similar width, length and configuration (Wiberg type) of the recipient. This reproduces the articular cartilage thickness of the patella in my hands better than cell-based therapies. I also prefer this on the trochlear side for full-thickness lesions, unless the defect crosses the groove, in which case I will use a cell-based therapy.

Osteochondral autologous transfer system (OATS) has never made much sense to me. OATS transfers plugs from the relative non-weight-bearing surface of the trochlea to the patella, with a major mismatch of articular cartilage thickness, as well as transfer in the same symptomatic compartment.

Patellofemoral arthroplasty in the aging athlete for end-stage patellofemoral arthritis has made resurgence in recent years, probably with better overall results because of better technology and a better understanding of biomechanics. The same principles of proper realignment and stabilization should be followed for these procedures as well.

Significant articular cartilage lesions in the patellofemoral joint are common. If the lesions are a cause of symptoms, they often respond well to simple debridement in association with addressing the primary etiology when present. Do not rush into a major cartilage restoration procedure as a primary procedure unless it is deemed absolutely necessary or if the lesion is large, full thickness or associated with bone loss.