Patellofemoral Arthroplasty

Introduction

Isolated patellofemoral joint (PFJ) arthritis affects ∼10% of the population over the age of 40, with a mean age of onset reported between 40 and 55 years old. There is a relative preponderance in women compared with men, which may be a result of the increased frequency of subtle PF dysplasia and malalignment commonly observed in women. Despite its incidence, PFJ arthritis is rarely debilitating or severely limiting, and isolated patellofemoral arthroplasty (PFA) represents only 1% of primary knee arthroplasty procedures. Additionally, this lower rate of PFA procedures, compared with what would be predicted based on disease prevalence, could be partially attributable to the mixed results observed with early-generation implants. Instead, many surgeons have likely utilized other surgical options, including arthroscopic debridement, patellar unloading procedures (e.g., tibial tubercle osteotomy), cartilage grafting and restoration techniques, and even patellectomy. However, these have had satisfactory results on the order of 60% to 70%. Total knee arthroplasty (TKA) has also been successfully used for the treatment of isolated PFJ arthritis. However, it represents a more extensive treatment option that may not be ideal or necessary for the young, active patient typically seeking treatment of PFJ arthritis.

Patellofemoral arthroplasty, when performed well, positioned well, and in the appropriately selected patient, ameliorates the symptoms of arthritis while retaining bone stock and the cruciate ligaments, thereby maintaining normal knee kinematics. In successful PFAs, functional outcomes have been remarkable, particularly compared with TKA. ^, Unfortunately, registry data have historically shown relatively high failure rates, with a cumulative percent revision over 5 years for any reason ranging from 8% to 18%, the majority (42%) related to progressive arthritis, suggesting poor patient selection. A study conducted by van der List et al. evaluating over 9000 PFAs yielded 5-, 10-, 15-, and 20-year PFA survivorship rates of 91.7%, 83.3%, 74.9%, and 66.6%, respectively, with an annual revision rate of 2.18%. Earlier studies and even contemporary analyses have found high rates of early failures related to patellar maltracking, often secondary to trochlear component malposition. While these problems have been mostly eliminated with onlay designs, which can be predictably positioned perpendicular to the femoral AP axis, many surgeons have shied away from PFA in favor of ongoing, often ineffective, nonoperative treatments or TKA. This chapter will discuss the common complications and pitfalls in PFA, and review strategies to minimize the risk of failures and their treatment options when they occur.

Patient Selection

Appropriate patient selection is paramount to success in PFA. Failure to do so increases the risk of persistent pain, patient dissatisfaction, or an early “failure” requiring reoperation. There are several crucial aspects of a patient’s history that the surgeon should elicit when considering PFA. First, the patient’s pain should be triggered and exacerbated by activities that increase pressure and strain in the PFJ, including hyperflexion, kneeling, squatting, lunging, ambulating on stairs or hills, prolonged sitting with knee flexed and standing from a seated position. In contrast, patients should experience little if any pain when walking on level ground. If a patient has as much pain while walking on level ground as when climbing stairs, this should alert the surgeon that the individual would not benefit from PFA and may have more extensive intraarticular disease or pain originating from outside of the knee. Second, patients should describe their pain as predominantly anterior or anterolateral. Patients with isolated PFJ arthritis typically note retropatellar and/or peripatellar pain; a more diffuse pain pattern is not consistent with isolated PFJ arthritis. There are several risk factors for PFJ arthritis that should also be considered, such as a history of patellar dislocation/subluxation and direct anterior trauma to the knee. Physical examination should corroborate these historical elements, with reproducible pain with patellar compression and inhibition, anterior crepitus with moving between flexion and extension, and the absence of medial or lateral tibiofemoral joint line tenderness. Patellar tracking (or maltracking) should be assessed as well as the Q angle, as both may predispose the patient to PFJ arthritis and will need to be considered and addressed at the time of eventual PFA.

Careful analysis of imaging studies is also imperative, as the pattern of patellofemoral disease and absence of substantial tibiofemoral cartilage wear are critical determinants of success in PFA. Radiographs include weight-bearing anteroposterior (AP), weight-bearing mid-flexion posteroanterior (PA), lateral, and 30-degree patella skyline views to evaluate the extent of osteoarthritis (OA) in each compartment. ^, Radiographs should also be scrutinized for the presence of patella alta or baja and the presence of tilt or subluxation. Routine preoperative MRI is also recommended to ensure appropriate patient selection. The critical findings should include advanced patellofemoral chondromalacia involving the lateral patellar facet and/or lateral trochlea or diffuse patellofemoral arthritis. Isolated medial patellar facet and/or medial trochlear degeneration, or no more than Grade II to III patellofemoral chondromalacia, should be considered contraindications to PFA given subpar outcomes in those cohorts. Equally important, MRI should also confirm a lack of Grade III or IV chondral thinning in the tibiofemoral compartments or subchondral tibiofemoral condylar edema. However, focal, full-thickness femoral condylar defects can be treated with chondral grafting techniques and do not necessarily preclude PFA.

Patients must also be screened for conditions that predispose to failure. A history including inflammatory arthritis, chondrocalcinosis, neuropathic joint, joint instability, and/or morbid obesity makes rapid progression to tricompartmental disease likely; thus, these factors should be considered contraindications to PFA. Though not an absolute contraindication, the presence of depression should give the surgeon pause, as coexisting mental health issues can diminish patient satisfaction despite a technically successful surgery. Kazarian et al. found that patients with lower preoperative SF 36 mental health section scores were less satisfied and less likely to have their expectations met after PFA. Efforts should be made in these patients to address preexisting mental health comorbidities before surgery or to make sure that the patients understand the impact of preexisting characteristics on their perception of outcomes after PFA. Additionally, patients who require narcotic medications for PF pain or who display apparent symptom magnification should not be considered candidates for PFA unless these risk factors are modifiable.