The patellofemoral joint is in the center of multiple forces due to its function as the quadriceps hypomochlion and magnifier of the moment arm of the extensor mechanism. Stressors on the anterior knee joint are frequent and include altered biomechanics and structural pathologies leading to an increased anterior joint reaction force, decreased anterior joint contact area, and increased shear stress. Therefore, patellofemoral (PF) osteoarthritis (OA) is common, presenting with symptoms in about 25% of the population in studies investigating population-based cohorts (aged >20 years) and 39% in studies investigating symptom-based cohorts (aged >30 years), which consist of patients with either isolated PF OA or combined tibiofemoral OA [12]. The frequency of isolated patellofemoral OA and tricompartmental OA is similar, with 10% of patients demonstrating isolated PF OA as compared to 14% with combined OA [12]. When assessing a population >55 years, the number of isolated PF OA is reduced to only 5% [16]. Overuse and trauma are particularly important causes of PF OA among athletes, including a variety of sports disciplines such as volleyball [17], basketball [6], and running [24]. However, intrinsic risk factors for PF OA such as PF maltracking and instability may also be present. These intrinsic factors are commonly seen in runners and increase cartilage shear forces, thus increasing the risk for symptomatic PF OA [25].

Patellofemoral OA combined with tibiofemoral OA is typically seen in the older population, while patients with isolated PF arthritis are often young with active lifestyles. There are four radiographic types of PF OA [10], which differ in etiology. Global PF OA is associated with primary OA and is mostly seen in combination with tibiofemoral OA, as typically identified in the older population. Global PF OA additionally occurs due to post-traumatic causes or systemic inflammatory entities such as rheumatoid arthritis. Lateral based PF OA is associated with patellofemoral dysplasia and patellar maltracking, often with antecedent instability episodes documented earlier in life. Medial based PF OA is associated with a medialized pulling vector of the quadriceps as seen in genu varum or previous patellar stabilizing surgical procedures. Central trochlear groove OA is associated with high central compressive forces as seen when patients experience high anterior knee forces, in activities such as kneeling and jumping.

Management approaches encompass a spectrum of treatment regimens, including non-operative measures (e.g. physiotherapy, weight optimization, brace, injections, pain management), and surgical procedures. Conservative treatment is the first line of therapy in knee OA. Surgery is typically indicated in patients with persistent pain, swelling or functional limitation after a trial of conservative management. We will focus mainly on realignment osteotomy and PF arthroplasty for the purposes of this manuscript. However, it is important to note there are other surgical options that may have an adjunct role in treating PF OA including limited arthroscopic debridement/loose body removal, lateral facetectomy/lateral lengthening, amongst others.

Tibial tubercle osteotomy aims to realign the patellofemoral joint and to reduce patellofemoral contact stress [20]. This procedure allows for multiplanar corrections. Anteromedialization is most commonly performed for patellofemoral OA, primarily due to the reduction of compressive loads and realignment of the lateralized force vector of the extensor mechanism. Both patellar and trochlear cartilage lesions are, therefore, simultaneously addressed. In contrast, patellofemoral arthroplasty replaces the damaged cartilage with one of the various implant systems available (e.g. inlay or onlay design). These intend to restore the native shape of the patella and trochlea groove while preserving native tibiofemoral anatomy. Given the unique advantages and considerations associated with each procedure, patient selection necessitates a comprehensive understanding not only of the procedures but also of the patient's individual condition, lifestyle, and treatment objectives.

The goal of this review is to present the current literature essential for the decision-making process around patellofemoral arthroplasty versus osteotomy for the management of PF OA.

Tibial tubercle osteotomy (TTO) addresses the altered biomechanical environment and malalignment of the patellofemoral joint, which may contribute to the pain generation and pathogenesis of patellofemoral osteoarthritis. It aims to decrease and redistribute PF contact forces by altering the alignment of the extensor mechanism. In the context of PF OA, an isolated anteriorization or combined anteromedialization of the tibial tubercle is commonly performed. Anteriorization is used to reduce compressive patellofemoral loads [21], while medialization addresses the increased shear forces seen in patellar maltracking and decreases the load on the lateral patellar facet [8]. [Figure 1, 2]

Given its mechanism of action in rebalancing forces on the patellofemoral joint, tibial tubercle osteotomy can be advantageous in cases where biomechanical anomalies are present. This is highlighted in situations characterized by more pronounced biomechanical abnormalities. Therefore, tibial tubercle osteotomy can be beneficial for individuals patellofemoral maltracking and malalignment. Specifically, when evaluating the radiographic presentation of isolated lateral patellofemoral arthritis, the clinical examination should emphasize diagnostic assessments associated with patellofemoral instability or maltracking. This approach then aids in selecting a treatment option that mitigates shear forces exerted across the patellofemoral joint. TTO can alter biomechanics while preserving the native joint, and is indicated for early-stage osteoarthritis, isolated patellofemoral arthritis without tibiofemoral involvement, and patients with chondromalacia as a result of malalignment with the desire to maintain an active lifestyle and continue participation in physical activities that place stress on the PF joint. In particular, isolated TTO can be a viable option for patients with patellar instability. Those with a lateralized force vector (TT-TG distance greater than 20 mm) would require a medialization TTO, and patients with patellar alta (Caton Deschamps ratio >1.4) would be indicated for a distalization-type TTO. Additionally, it can be used in patients with patellar focal cartilage defects or chondromalacia. Isolated anteromedialization is recommended to unload focal, distal lateral patella lesions, whereas combined anteromedialization and cartilage restoration should be considered for medial, central, or panpatellar cartilage pathology. All of these are more common in the younger, athletic population, although athletes who are deemed physiologically young at advanced ages may be candidates for this procedure as well. However, isolated TTO should generally be avoid in those with central, medial or diffuse PF chondral defects or arthrosis.

Tibial tubercle osteotomy is a reliable procedure to lower the contact forces on the PF joint and to reduce pain. Prior clinical outcome study have demonstrated clinically meaningful improvement in patient reported outcomes of Lysholm, Kujala, International Knee Documentation Committee Subjective Knee Form (IKDC), and Visual Analogue Scale (VAS) pain scores following TTO in patients with patellar maltracking across varying degrees of degenerative changes. Return to work rates following TTO anteromedialization due to isolated patellofemoral osteoarthritis are greater than 90% at an average of 2.8 months [2]. Even in high-activity occupations, a short-term follow-up showed a 63% return to military function [9]. Liu et al. investigated the return to sports rate and found that 83% resumed sports activities at an average 8 months post-operatively, with 78% returning to their previous performance level [15]. In patients over 50 years with isolated PF OA, average post-operative Lysholm score was 83, with 63% good to excellent outcomes. The overall complication rate has been reported to be 4.6% with a major complication rate of 3%. Hardware was removed in of 37% of the cases [19]. Thus, the possibility of re-operation including hardware removal should be discussed with the patient pre-operatively. While tibial tubercle osteotomy with anteriorization and anteromedialization shows encouraging results for the treatment of patellofemoral osteoarthritis, comprehensive pre-operative evaluation, proper patient selection, and meticulous surgical technique is crucial for successful outcomes. Additionally, global assessment of the extensor mechanism and the knee joint must take placement pre-operatively to appropriately plan for concomitant soft tissue and cartilage procedures at the time of the TTO or in a staged manner. (Table 1).

Isolated patellofemoral arthroplasty (PFA) is a viable option for severe, symptomatic patellofemoral osteoarthritis. There are two main implant designs based on the trochlear preparation technique. The trochlear component is implanted using an inlay or onlay technique. In the modern onlay designs, the morphology of the arthroplasty addresses native anatomical pathologies, such as trochlea dysplasia. By replacing the native anatomy, one can address the malalignment caused by trochlea dysplasia. Selecting an onlay design with the trochlea groove located more central to the pathologic state can alter the tibial tuberosity-trochlear groove (TT-TG) distance, avoiding the necessity for additional osteotomies to correct a lateralized force vector in most cases [23]. [Figure 3, 4]

Patellofemoral arthroplasty is a valuable salvage procedure for diffuse and severe patellofemoral osteoarthritis as it also involves removal of the pain generators. Often times, prospective PF arthroplasty patients have remote history of PF instability followed by quiescent period, only to reappear later in life exhibiting signs and symptoms of advanced patellofemoral arthrosis. Thus, this procedure may be considered for patients with extensive cartilage damage and older individuals seeking lasting pain relief. Indications include isolated degenerative PF OA [7; 13; 22] without underlying biomechanical issues, extensive grade III chondrosis (particularly pantrochlear), failed unloading procedures, and dysplasia-related degeneration without instability.

The most frequent contraindication for isolated PF arthroplasty is tricompartmental arthritis, and notably, the predominant cause for revision procedures was the progression of arthritic disease [14]. As a result, an extensive review of medial and lateral compartments of the knee should be completed pre-operatively to determine the degree of arthritis in all three compartments (Table 2). Radiographs, MRI, and bone scans have all been used for this evaluation [14]. Arthroscopic confirmation of relatively intact medial and lateral compartments is also reasonable to consider prior to proceeding with arthroplasty. Relative contraindications for an isolated patellofemoral arthroplasty include comorbid risk factors for arthritic progression including uncorrected coronal plane malalignment, post-meniscectomy syndrome, uncorrected ligamentous instability, inflammatory arthritis, untreated arthrofibrosis, chondrocalcinosis, and uncorrected patella baja or alta [14]. Obesity (BMI >30), age younger than 40 years, and excessive physical activity/unrealistic activity level expectations are also important to consider [14]. Obesity is a well-known risk factor for knee arthritic progression [4; 11] and patella alta poses the risk of impingement of the patella component on the upper flange of the femoral prosthesis in early flexion. Prosthetic-related failures in the cohort of Leadbetter et al. frequently had recurrent patellofemoral instability [14].

Ahearn and colleagues report a good medium-term outcome with 88% survivorship at an average of seven years [3]. Bohu and colleagues report on their cohort of 74 PFAs and found that the conversion rate to total knee arthroplasty was 14.3% after an average of 5.4 ± 3.4 years with an annual revision rate of 3.1% for all types of revision (partial/total PFA replacement or TKA) [5]. Dejour et al. highlighted the importance of proper patient selection, as a spread of arthritis in his patient cohort of 28 patients aged 63.3 ± 14.7 years lead to a high incidence of early revisions and concluded that isolated PF arthroplasty should not be performed in degenerative or age-related diseases, but only in patients with trochlear dysplasia and in patients with arthritis triggered by patellar instability and maltracking. PFA failure secondary to progression of multicompartmental osteoarthritis has been documented by several studies [1]. While the risk for conversion total knee arthroplasty should be communicated with the patients, an isolated PF arthroplasty may be preferred over a total knee arthroplasty in cases of isolated patellofemoral arthritis. Odgaard and colleagues have reported overall improved knee-specific quality of life in patients with PFA compared to TKA throughout the first 2 years postoperatively [18].

The decision between osteotomy and arthroplasty for patellofemoral osteoarthritis requires a thoughtful analysis of the patient's unique circumstances and treatment goals. The factors (1) disease severity (2) biological age (3) patellofemoral alignment (4) activity level and (5) patient preference (including willingness to undergo subsequent surgeries and a standard rehabilitation regime) should be considered (Table 3). Both procedures have their advantages and drawbacks, and both are not suited for all patients. Osteotomy offers the potential for preserving the natural joint and delaying as the need for arthroplasty, making it an attractive option for younger active patients with malalignment; Arthroplasty provides a reliable solution for painful bipolar patellofemoral chondrosis; however, concomitant tibiofemoral arthritis should be ruled out (Figure 5). Ultimately, the decision should be based on the patient's unique clinical presentation, expectations, and shared decision-making with the surgeon to achieve the best possible outcome and improved quality of life.