Isolated patellofemoral arthritis and treatment options
Severe arthritis of the knee is a common and disabling condition. Over 50,000 patients require a knee arthroplasty each year in the UK at an estimated cost of 300 million pounds. Arthritis confined to the patellofemoral joint (the articulation between the patella and the trochlear groove of the femur) occurs in over 10% of these patients. The average age of those affected by isolated arthritis of the patellofemoral joint is significantly lower than those with severe generalised arthritis [
1]. Commonly, patients complain of anterior knee pain which limits their daily activities and in severe cases patients are unable to continue in employment. Initially, these symptoms can be successfully treated non-operatively. However, in severe debilitating cases the efficacy of these non-surgical modalities is minimal and the only alternative treatment is surgery. The operative treatment options for this disease include arthroscopic procedures, patellectomy (removal of the knee-cap), Total Knee Arthroplasty (TKA) and more recently, Patellofemoral Arthroplasty (PFA). Arthroscopic surgery is seldom beneficial in severe disease and patellectomy often leads to poor long-term function, therefore the choice for patients is usually between TKA and PFA.
Whilst many surgeons believe TKA is the 'gold standard' treatment for severe knee arthritis, PFA has certain potential advantages. Primarily, this operation allows the patient to keep the majority of their own knee joint; preserving bone-stock and the patients' own ligaments. PFA has also been recognised as a less 'invasive' operation than TKA, facilitating a more rapid recovery [
2]. Despite these perceived advantages, early PFA designs yielded less than satisfactory results due to residual patella mal-alignment, wear of polyethylene and failure secondary to disease progression in the other parts of the joint [
3]. More recent studies, however, have shown significantly better results with PFA. This is due to improved implants, an appreciation of the need to balance the soft tissues and more appropriate patient selection when considering PFA [
4].
In a retrospective case series study, Cartier et al. [
5] reported excellent functional outcome in 77% of patients at a mean of 10 years follow-up. These findings substantiate those of an earlier retrospective consecutive case study, where good or excellent functional results were reported, using the Knee Society Score (KSS), in 86% of 'residual' cases at 17 years [
6]. Most recently, Odumenya et al. [
7] and Stark et al [
8] have reported excellent functional outcomes with 100% survivorship at 5 and 2 years follow-up, respectively. Therefore, there is some evidence to suggest that PFA provides positive results for patients with isolated patellofemoral arthritis. It is however not clear how the latest generation of PFA compare with the excellent long-term results of Total Knee Arthroplasty [
9]. The majority of the remaining literature consists of case series with short-term results and includes only a small number of studies on the use of TKA for primarily severe patellofemoral arthritis. Mont et al. [
10] reported 97% good or excellent clinical results using the KSS at a mean follow-up of over 6 years. These results are in agreement with the findings of Laskin et al. [
11] who reported on forty-two patients managed with TKA for primary patellofemoral arthritis. This study compared the use of TKA in patients with patellofemoral arthritis and tricompartmental arthritis. They concluded that the results of TKA in the patellofemoral subgroup were superior to those patients with tricompartmental arthritis. However, these inferences are uninformative when deciding between TKA and PFA for the treatment of isolated patellofemoral arthritis.
There are currently no published results of randomised clinical trials comparing the two arthroplasty techniques. At present the only registered study (ISRCTN22478626) directly comparing TKA and PFA was not performed. We therefore propose the first trial comparing TKA with PFA to provide surgeons and patients with accurate information regarding knee function. The null hypothesis for this trial is that there is no difference in functional score (WOMAC - Western Ontario and McMaster Universities Osteoarthritis Index score) at one year post-operation between Total Knee Arthroplasty and Patellofemoral Arthroplasty.