The following article deals with isolated patellofemoral osteoarthritis. It is assumed throughout the article that previous conservative treatment and/or joint preserving surgical procedures were tried before or are deemed no longer appropriate.
In isolated patellofemoral osteoarthritis (PFOA), patellofemoral arthroplasty (PFA) is said to have the following advantages compared with total knee arthroplasty (TKA): better kinematics, thanks to the preservation of both cruciate ligaments; preservation of bone-stock; and therefore, also advantages regarding possible future revisions. However, it is necessary to look at the literature to see whether these theoretical advantages are confirmed.
Michael C. Liebensteiner
Results of patellofemoral arthroplasty
Many authors reported their PFA results in terms of case series. Publications with the longest follow-up refer to the Richards PFA (Smith & Nephew). These three publications congruently reported good knee scores and 10-year survival ranging between 84% and 90%. The second-longest follow-up is available for the Avon PFA (Stryker) and the Journey PFA (Smith & Nephew). For the Avon PFA, the developer’s center reported a 5-year survival of 96% and good knee score outcome. Other groups could reproduce the good results of that PFA during follow-up periods of up to 7 years. The Journey PFA was also seen to have good functional outcome and a 7-year prosthesis survival of 88%. Also, the Hemicap-Wave PFA (Arthrosurface) is supported by good results in several publications. The authors reported good outcome in terms of knee scores and physical activity with a follow-up period of up to 2 years. With regard to other types of PFA, there exist either only single publications (Hermes, Ceraver) or the respective PFA type was found to lead to inferior results and might be regarded as obsolete (Femoro-Patella Vialla, Wright; Lubinus, Link; LCS patellofemoral; Depuy). Viewed in the context of the mentioned case series, it seems the success of PFA is closely related to the individual design features.
Similarly, also in arthroplasty registries, the outcome of PFA appears to differ. For example, the Australian arthroplasty registry reported 1,519 PFA cases with a 5-year survival of 85%. However, that relatively poor finding might also be explained by the fact that the Australian registry contains a high volume of the above-mentioned obsolete PFAs. The English registry reported a better PFA survival, namely approximately 90% after 5 years.
Several authors stated that patients with PFOA secondary to patellofemoral instability show extraordinary benefit from PFA. However, sometimes concomitant procedures are needed to stabilize the patella. Likewise, patients with PFOA secondary to patella fracture also reap above-average benefit from PFA.
Many case series have investigated the use of TKA in patients with isolated PFOA. Those studies reported good knee score outcomes and no revisions within 5 years. Therefore, TKA is a good option for patients with isolated PFOA and advanced age.
Patellofemoral arthroplasty and total knee arthroplasty in direct comparison
Direct comparison of PFA vs. TKA in isolated PFOA has been rarely performed to date. One retrospective comparative study undertook precisely this comparison. Based on comparable clinical outcomes within 2 subsequent years, the authors suggested PFA be performed for cases of PFOA as it is a less invasive procedure. On the same level of evidence, others performed a meta-analysis of PFA vs. TKA. The authors found the outcome in two groups to be equal regarding revision rates and pain when older, obsolete PFA types were excluded from the analysis. The only prospective comparative study of TKA vs. PFA is still in the phase of data collection.
Summarizing recommendations found in the literature and my own experiences, PFA might be performed in patients with the following conditions:
• chronic anterior knee pain (with/without patella instability); and
• advanced degenerative changes in the patellofemoral joint (eg, Iwano classification > Stage 2 in the radiographs); and
• no or mild degenerative changes in the tibiofemoral compartments (eg, < IKDC stage C in the Rosenberg view or chondral lesions grade 0 to grade 2 in the MRI); and
• non-successful conservative therapy spanning 3 months to 6 months.
Widely accepted contraindications are:
• chronic-inflammatory disease;
• extension deficit greater than 5° to 10 °; and
• maximum knee flexion greater than 90°.
In addition, with respect to potential concomitant procedures, the surgeon should also assess patella height, tibia tuberosity — trochlea groove distance, torsion of the femur and the lower leg — and the presence of a severe valgus or varus knee leg axis.
Figure 1. Partial lateral facetectomy is shown
The following principles apply for PFA and TKA likewise. Overstuffing should be strictly avoided. This means the thickness of the prosthetic trochlea should be equal to (or less than) the thickness of the anterior bony resection. The same principle should be followed for the patella. In the case of a lateralized patella, a medialized and slightly undersized patella implant (with partial lateral facetectomy) can help decrease tension. Both TKA and PFA can be performed with and without a patella implant. Factors like age, stability and conformity between the trochlea implant and the native patella should be considered. If a patella implant is not performed, a partial lateral facetectomy is useful in many cases (Figure 1). At the latest, at the trial run, it should become obvious whether an additional stabilizing procedure is needed (transfer the tibial tuberosity, medial patellofemoral ligament plasty, etc.) (Figure 2).
Figure 2. Sometimes, additional techniques are needed to stabilize the patella in PFA or TKA (eg, MPFL reconstruction).
In PFOA, when joint preserving procedures (tuberosity transfer, cartilage procedures, etc.) are no longer deemed appropriate, an established PFA is a good option for patients without tibiofemoral degeneration. In the case of tibiofemoral degeneration, TKA should be preferred. Otherwise, early revisions must be expected.
In the case of post-traumatic PFOA and PFOA, based on previous patella instability, the indication for PFA might be widened. Slight tibiofemoral degeneration, as well as older age, can be tolerated.
A comprehensive preoperative evaluation of factors that influence the patellofemoral joint (torsion, tibia tuberosity — trochlea groove distance, frontal plane leg axis, etc.) is recommended independently of whether TKA or PFA is planned. Particularly in cases of PFOA and previous patella instability, the surgeon must be prepared to perform additional patella stabilizing procedures.
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Michael C. Liebensteiner, MD, PhD, is from the Medical University Innsbruck in Innsbruck, Austria.
Disclosure: Liebensteiner reports no relevant financial disclosures.