Isolated patellofemoral arthritis can occur in as many as 9% of patients older than 40 years and is particularly common in women, who often have subtle patellofemoral maltracking or malalignment. In fact, 24% of women with symptomatic knee arthritis have localized patellofemoral arthritis. Arthroplasty options can provide predictable pain relief, whereas other surgical measures for refractory patellofemoral arthritis—arthroscopic debridement, cartilage grafting, patellectomy, tibial tubercle unloading procedures—often have unsatisfactory results. While total knee arthroplasty (TKA) yields excellent results in >90% of patients with isolated patellofemoral arthritis, it is not desirable in patients who are young and active. Therefore, patellofemoral arthroplasty has a legitimate role in the treatment of isolated anterior compartment arthritis. Early patellofemoral implants were plagued by a high incidence of patellar maltracking, catching and subluxation, due to design features of the trochlear components, inadequate soft tissue balancing, and component malposition. Most importantly, contemporary onlay style trochlear components, implanted perpendicular to the anteroposterior axis of the femur, have substantially reduced the patellar maltracking that was so prevalent with inlay style prostheses for 3 decades. With onlay trochlear designs, early patella instability problems have been reduced, leaving late tibiofemoral degeneration as the primary cause of failure of patellofemoral arthroplasties. Several long-term studies have shown a rate of tibiofemoral degeneration of approximately 20% at 15 years. Finally, the results of TKA do not seem to be compromised by the presence of a prior patellofemoral arthroplasty.
Patellofemoral arthroplasty is an effective treatment for isolated patellofemoral arthritis. Outcomes, however, are impacted by trochlear component design, patient selection, and meticulous surgical technique. Onlay style designs have substantially reduced the tendency for patellar instability seen with inlay components.
Patellofemoral arthroplasty is indicated for peri- or retro-patellar pain from isolated patellofemoral arthritis or Grade IV chondromalacia. Although it can be most effective in the presence of patellofemoral dysplasia, patellofemoral arthroplasty should be avoided in patients with severe patellar maltracking or malalignment, unless they are correctable. Moderate patellar tilt or subluxation can easily be corrected with a lateral retinacular recession or release and appropriate implant positioning. Patients with excessive Q angles should undergo tibial tubercle realignment before or during patellofemoral arthroplasty (although some trochlear prosthesis shapes may accommodate a slightly increased Q angle). Proximal realignment may be necessary in some cases. There are no age criteria for patellofemoral arthroplasty provided the other criteria are met.1,2
Contraindications to patellofemoral arthroplasty include inflammatory arthritis, Grade III or IV chondromalacia of the tibiofemoral chondral surfaces, or the presence of medial or lateral joint line pain. Combining patellofemoral arthroplasty with medial or lateral unicompartmental knee arthroplasty (as a modular or monolithic construct) or autologous osteochondral grafting may expand the application of patellofemoral arthroplasty.3,4 Patients with inappropriate expectations and those with unusually excessive pain requiring narcotics may not be suitable candidates. Flexion contractures and limited range of motion (ROM) are contraindications because they subject the patellofemoral articulation to excessive loads and are indicative of knee pathology that extends beyond the patellofemoral compartment. While there are intuitive concerns, there is no data available on whether obesity or cruciate ligament insufficiency put the patellofemoral arthroplasty at risk for failure.1.2
Radiographic evaluation with weight bearing anteroposterior (AP) and midflexion posteroanterior (PA) views are important to rule out tibiofemoral arthritis (Figure 1A). Mild squaring of the femoral condyles and small marginal osteophytes are acceptable provided there is no pain or significant chondromalacia. Lateral radiographs may show patellofemoral osteophytes, joint space narrowing, and the presence of patella alta or baja (Figure 1B). Axial radiographs can demonstrate the position of the patella in the trochlear groove and a rough assessment of trochlear dysplasia or patellar tilt or subluxation (Figure 1C). High resolution magnetic resonance imaging scans can help determine whether there is cartilage loss in the tibiofemoral compartments. If applicable, previous arthroscopy photos should be reviewed to confirm isolated patellofemoral arthritis and rule out associated tibiofemoral pathology.
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|Figure 1: Standing AP (A), lateral (B), and sunrise (C) radiographs showing isolated patellofemoral arthritis and slight patellar tilt. |
Several key steps in the procedure will enhance surgical outcomes by optimizing patellar tracking. The first is assuring the trochlear component is externally rotated parallel to the epicondylar axis (or perpendicular to the AP axis of the femur). This prerequisite may not be achievable with inlay trochlear designs, which explains why there is a higher incidence of patellar catching and subluxation with inlay styles5-7 than onlay-type trochlear prostheses.5-7 The trochlear component should not overhang beyond the medial or lateral femoral margins or the intercondylar notch. Preparation of the trochlear bed should be flush with or recessed approximately 1 mm from the adjacent articular condylar cartilage. Resurfacing the patella should follow the same principles as total knee arthroplasty (TKA), with restoration of proper patellar thickness and medialization of the component. The lateral patellar facet should be removed or beveled to avoid lateral impingement and enhance patellar tracking.
With the trial components in place, patellar tracking is assessed. If patellar tilt, subluxation, or catching of components is present, confirm proper component position and correct any deficiencies. A lateral retinacular recession or release can be performed. In severe cases of subluxation, a proximal realignment may be necessary. If the Q angle is high, a tibial tubercle realignment should be considered.
Clinical results of patellofemoral arthroplasty are most affected by trochlear component shape, as well as patient selection and surgical technique.2,5,7 Outcomes have improved after patellofemoral arthroplasty, and the need for secondary soft tissue surgery or revision to correct patellar maltracking have decreased, as a result of trochlear design improvements. Perhaps most importantly, contemporary onlay style designs, which are implanted perpendicular to the AP femoral axis, have substantially reduced the incidence of patellofemoral complications; however, patella catching and instability remain common with inlay style implants, which tend to be internally rotated (except in cases of severe lateral trochlear dysplasia) (Figures 2, 3). Early failures occur due to patellar instability that are often related to poor patient selection, technical errors, or most likely implant design. Late failures typically occur as a result of progressive tibiofemoral arthritis. Loosening and wear are uncommon.1,2,5,7-13
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| ||Figure 2: Standing AP (A), lateral (B), and sunrise (C) radiographs and axial CT scan (D) after patellofemoral arthroplasty using a contemporary inlay style trochlear prosthesis demonstrating internal rotation of the trochlear component and patellar subluxation due to rotational malalignment. |
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|Figure 3: Standing AP (A), lateral (B), and sunrise (C) radiographs after revision to an onlay trochlear prosthesis with improved trochlear component external rotation. The metal-backed patellar prosthesis was also revised to an all-polyethylene patellar prosthesis applied in a more medialized position. |
In a consecutive series of 30 first-generation implants and 25 second-generation implants, results varied depending on whether an inlay or onlay trochlear design was used.5 The incidence of patellofemoral dysfunction, subluxation, catching, and substantial pain was reduced from 17% with the inlay design to <4% with a more contemporary onlay prosthesis. In another series, 14 inlay-design trochlear implants were revised to an onlay implant that had a more favorable topography for patellar tracking. After revision, there was statistically significant improvement in knee scores and patellar tracking at a mean 5-year follow-up. Mild femorotibial arthritis (Ahlbach stage I) was predictive of a poorer clinical outcome. At most recent follow-up, there was no evidence of wear, loosening, or subluxation.10 This data was corroborated by the Australian Orthopaedic Association National Joint Replacement Registry, which found that the cumulative 5-year revision rate was 21.8% with an inlay-style trochlear prosthesis and 9.9% with an onlay-style implant. Data on newer systems is not yet available in that registry.6
Hendrix et al10 reported on 306 second generation onlay design patellofemoral arthroplasties and found that patellar tracking was substantially improved compared to a first generation implant. In that series, patellar subluxation occurred in 3% and residual anterior knee pain was noted in 4%. Four percent required revision to TKA, mostly for tibiofemoral arthritis and none for mechanical loosening or wear.11
Progression of tibiofemoral compartment arthrosis is the most common indication for late revision to TKA.8-13 Lonner et al13 reported on revision outcomes to TKA after patellofemoral arthroplasty in 12 patients after an average of 3.1 years. In their study, none of the patellar components were revised and standard implants were used without the need for stems, augments, or structural grafts. At latest follow-up, there was statistically significant sustained improvement in Knee Society Clinical and Functional Scores and no failures, leading the authors to conclude that TKA is not compromised when revised from patellofemoral arthroplasty.
Isolated patellofemoral arthritis is a significant problem, particularly in women, who often begin suffering at a young age. The inconsistent clinical results and unpredictability of earlier designs stifled enthusiasm for patellofemoral arthroplasty. However, improved designs, refined selection criteria, and meticulous surgical technique have enhanced the outcomes after contemporary patellofemoral arthroplasty and are now being considered with greater enthusiasm.
- Leadbetter WB, Seyler TM, Ragland PS, Mont MA. Indications, contraindications, and pitfalls of patellofemoral arthroplasty. J Bone Joint Surg Am. 2006; 88(Suppl 4):122-137.
- Lonner JH. Patellofemoral Arthroplasty. J Am Acad Orthop Surg. 2007; 15(8): 495-506.
- Lonner JH, Mehta S, Booth RE Jr. Ipsilateral patellofemoral arthroplasty and autogenous osteochondral femoral condylar transplantation. J Arthroplasty. 2007; 22(8):1130-1136.
- Argenson JN, Parratte S, Bertani A, et al. The new arthritic patient and arthroplasty treatment options. J Bone Joint Surg Am. 2009; 91(Suppl 5):43-48.
- Lonner JH. Patellofemoral arthroplasty: pros, cons, and design considerations. Clin Orthop Relat Res. 2004; (428):158-165.
- Australian Orthopaedic Association National Joint Replacement Registry. http://dmac.adelaide.edu.au/aoanjrr/publications.jsp. Accessed June 15, 2010.
- Lonner JH. Patellofemoral arthroplasty: the impact of design on outcomes. Orthop Clin North Am. 2008; 39(3):347-354.
- Cartier P, Sanouiller JL, Khefacha A. Long-term results with the first patellofemoral prosthesis. Clin Orthop Relat Res. 2005; (436):47-54.
- Kooijman HJ, Driessen AP, Van Horn JR. Long-term results of patellofemoral arthroplasty. A report of 56 arthroplasties with 17 years of follow-up. J Bone Joint Surg Br. 2003; 85(6):836-840.
- Hendrix MRG, Ackroyd CE, Lonner JH. Revision patellofemoral arthroplasty: 3-7 year follow-up [published online ahead of print March 14, 2008]. J Arthroplasty. 2008; (23):977-983.
- Ackroyd CE, Newman JH, Evans R, Eldridge JDJ, Joslin CC. The Avon patellofemoral arthroplasty: five-year survivorship and functional results. J Bone Joint Surg Br. 2007; 89(3):310-315.
- Argenson JNA, Fletcher X, Parratte S, Aubaniac JM. Patellofemoral arthroplasty: an update. Clin Orthop Relat Res. 2005; (440):50-53.
- Lonner JH, Jasko JG, Booth RE Jr. Revision of a failed patellofemoral arthroplasty to a total knee arthroplasty. J Bone Joint Surg Am. 2006; 88(11):2337-2342.
Dr Lonner is from the Department of Orthopedic Surgery, Pennyslvania Hospital, Philadelphia, Pennsylvania.
Dr Lonner is a consultant for Zimmer and Mako Surgical.
Presented at Current Concepts in Joint Replacement 2009 Winter Meeting; December 9-12, 2009; Orlando, Florida.
Correspondence should be addressed to: Jess H. Lonner, MD, Pennsylvania Hospital, 800 Spruce St, Philadelphia, PA 19107 (email@example.com).