Recognize the unique characteristics of the patellofemoral compartment
Unfortunately, the general treatment options for cartilage restoration in the United States have remained somewhat stagnant for more than 15 years. Fortunately, within this static group of specific cartilage treatments, orthopedic surgeons have expanded treatment options in the knee and other joints.
Initially, the technique was primarily used for femoral lesions. With relative success in those areas, surgeons gradually expanded the techniques to the patellofemoral (PF) compartment. While the compartment obviously has the same type of articular cartilage as the tibiofemoral (TF) compartments, certain factors are essential to optimize outcomes.
First and foremost, cartilage is aneural. Therefore, it must be appreciated that the cartilage lesion is secondarily contributing to the patient’s pain. The source of the pain must be exhaustively investigated. Cartilage treatment only should be contemplated after failure of thorough physical therapy (with up-to-date patellofemoral specific techniques) and adherence to the “envelope of function” principles by Scott Dye, MD.
The early failures of autologous cultured chondrocyte implantation (ACI) in the PF compartment highlighted the necessity of optimizing the PF environment. Brittberg and Peterson reported their initial failures in the New England Journal of Medicine article in which five of six PF ACIs failed, noting these had uncorrected patellar subluxation. Subsequently, Peterson reported a success rate that mimicked tibiofemoral ACI when the PF compartment environment was improved – typically with anteromedialization of the tibial tuberosity (Fulkerson anteromedialization osteotomy). These finding were then corroborated by numerous other authors, including Minas, Henderson, Farr, Cole and multicenter study submitted for publication by Gomoll.
In reviewing these reports, there are three overlapping categories of PF patients undergoing consideration for ACI:
1. chondral or osteochondral injury from patellar instability;
2. direct impact macro-trauma or repetitive impact micro-trauma; and
3. idiopathic chondrosis, which may be the form fruste of osteoarthritis.
Each category requires an understanding of all the underlying pathologies and a plan of treatment. Most commonly these comorbidities include one or all of the following:
- excessive femoral anteversion/external tibial torsion;
- excessive lateral position of the tibial tuberosity;
- patellar alta;
- trochlear dysplasia; and
- patholaxity of the medical patellofemoral ligament (and iatrogenic problems, such as overzealous lateral release of over medialization of the tibial tuberosity.
Treatment of comorbidities
Once identified, each of these factors are addressed to optimize patellar stability, tracking and stress (force per unit area). While the importance of treating these comorbidities was initially pioneered by ACI treatments, it follows that all forms of cartilage restoration will benefit from stress/stability optimization.
Marrow stimulation (microfracture and drilling) are the most commonly performed cartilage treatment at the tibiofemoral articulation. Caution is advised when expanding the treatment to the PF compartment. While several authors have reported good outcomes with TF chondral lesions, marrow stimulation outcomes for patellar and bipolar (PF) have been less optimal. This has led to some authors recommending that these lesions are better treated with alternative methods.
Outcomes for tibiofemoral osteochondral autograft plugs have been reported by numerous authors while there a many fewer reports about the PF compartment. The two main camps (Morgan and Bobic; and Hangody) use slightly different plug sizes. The literature has reports of both types of transfers. Bentley in a small series reported poor outcomes while Hangody and others have reported good outcomes even for bipolar lesions. Concerns remain for the mismatch of the cartilage thickness from donor to recipient, harvesting plugs from the trochlear margins to treat PF lesions and the potential of shearing forces from articulating plugs.
Osteochondral allograft (OCA) remains limited for TF applications because of availability. This limited availability is amplified at the PF articulation not only for the lack of donors, but also by the limited number of pristine patellae, unique topology and competition within tissue banks that can use one patella for two or three patellar tendon bon-tendon-bone allografts.
While studies that used truly fresh grafts, Spok-Torga and Teitge reported excellent results past 10 years, these cannot be directly applied to the “fresh stored grafts” available today. Gross long ago abandoned bipolar OCA. Bugbee reported only 50% good/excellent results at 5 years. These limitations make it imperative to attempt to optimize all factors (graft age/morphology and external factors) when transplanting OCA at the PF articulation.
When applying standard cartilage restoration techniques developed for the TF articulation in the PF compartment, it is important to recognize the unique characteristics of the PF compartment and optimize them.
Brittberg M. Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. N Engl J Med. 1994;331(14):889-895.
Peterson L. Autologous chondrocyte transplantation. Biomechanics and long-term durability. Am J Sports Med; 2002;30:2-12.
Torga Spak R. Fresh osteochondral allografts for patellofemoral arthritis: Long-term follow up. Clin Orthop Relat Res; 2006;444:193-200.