Patellofemoral Arthritis

Introduction

Patellofemoral arthritis is a condition that occurs due to loss of cartilage from the articulating surfaces of the patella and/or the femoral trochlear groove. Davies and colleagues1 found isolated patellofemoral arthritis in 9.2% of patients over age 40, and patellofemoral arthritis occurs in 11% of men and 24% of women over the age of 55, who have symptomatic osteoarthritis of the knee.2 Non-surgical and surgical management options exist for managing anterior knee pain and patellofemoral arthritis, which may be refractory to treatment modalities.3

Pathoanatomy and Biomechanics

Several factors contribute to pain and degeneration in the patellofemoral joint. These include patellofemoral instability, malalignment, and abnormal biomechanics. The stability of the patella within the trochlear groove depends on limb alignment, including varus or valgus lower extremity alignment. The primary static stabilizers are bony articulations and the medial and lateral soft tissue ligamentous attachments about the knee. The biomechanics of the pelvis, lower limb strength, and any foot and ankle pathology may also play into patellar stability.

Malalignment is a common underlying etiology, because chondral wear occurs with greatest prevalence on the lateral patellar facet,4 which may become overloaded with abnormally directed lateral forces across the patella.3 Other factors associated with patellofemoral pathology include patella alta, trochlear dysplasia, an increased quadriceps or Q angle, weak vastus medialis oblique muscle, tight lateral retinaculum, or a compromised medial patellofemoral ligament.2 Other factors may include acute or chronic trauma, genetic predisposition to arthritis, and activities that frequently load the patella in deep knee flexion. Rising rates of obesity have contributed to formation of arthritis.5

History and Physical

Patellofemoral arthritis pain is located anteriorly or in the retropatellar or immediately peripatellar region. Pain may be referred or radiate to the medial and lateral aspects of the knee or the posterior capsule. Pain occurs during activities that load the patellofemoral articulation, such as climbing up and down stairs, squatting, and kneeling. Pain is less severe when walking on level ground. When sitting, patients are more comfortable with the knee held straight, rather than in a flexed position (theater sign).

A careful history should include chronicity, quality, and nature of the pain, trauma, nonsurgical therapies tried, and history of patella dislocations, both acute and chronic. Physical examination should begin with assessing patella tracking and Q angle. Subtle abnormalities of patellar tracking can be observed when the patient moves from flexion to extension or with active quadriceps contraction. The J sign indicates patellar malalignment or muscular imbalance. A Q angle of greater than 15º in males and greater than 20º in females may point to a bony alignment issue potentially correctable with tibial tubercle transfer (versus primary soft tissue etiology).6 Examiners also should look at the quadriceps active sign, patellar subluxation upon palpation (consider patella quadrants for grading subluxation), and patellar apprehension signs. Systemic signs of hyperlaxity, measurement of leg lengths, and assessment of quadriceps/hamstring tightness may also be helpful.

Physicians should note patellofemoral crepitus and pain. Tenderness on palpation of the medial and lateral joint may suggest a more diffuse arthritic process. Physicians should ensure pain is not emanating from the quadriceps or patellar tendon mechanism, bursae, or the lumbar spine or hip. Quadriceps atrophy or weak vastus medialis oblique muscle may also be appreciated on examination.

Ancillary Studies

An imaging work-up for patients includes a series of radiographs (Slide 1) with standing anteroposterior, 45º posteroanterior flexion weightbearing,7 lateral, and dedicated patellar/trochlear views (e.g. skyline/ Merchant/ Lauren views.8 Full-length alignment radiographs may also be used. Computed tomography scanning may be useful when maltracking is suspected, and the scan can be obtained at differing degrees of flexion to assess patellar subluxation and bony dysplasia. Measured angles, including the patellar congruence angle, sulcus angle, patellar height, or patellar tilt may quantitatively describe patellofemoral pathology.

Slide 1

Magnetic resonance imaging (MRI) will provide information on soft tissues about the knee, including ligamentous and retinacular structures, such as the medial patellofemoral ligament, and the extensor mechanism. MRI will also aid in diagnosing other concomitant internal knee derangements, subtle chondral pathology, or bone bruising associated with trauma (Slide 2).

Slide 2

Arthroscopy may be both diagnostic and therapeutic for patellar problems, and tracking may be studied dynamically intraoperatively.

Non-operative Treatment

Most patients show improvement in their symptoms with nonsurgical management. Physical therapy should emphasize vastus medialis oblique/quadriceps strengthening, isometrics, stretching the lateral retinacular structures, stretching the quadriceps/hamstring muscles, and maintenance of range of motion.3 Weight reduction may improve patellofemoral pain, as the anterior compartment of the knee is exposed to excessive loads during knee flexion.

Patients can minimize patellofemoral joint pressures by avoiding provocative activities, such as climbing stairs, squatting, and jumping. Patellar unloading sleeves, braces, or McConnell-type taping may help manage the condition, although conclusive data is lacking.9,10

Anti-inflammatory medications, analgesics, and intra-articular corticosteroid or viscosupplementation injections may reduce arthritis pain. Surgical interventions may be considered if patients fail to respond to nonsurgical management after a minimum of 3 to 6 months, and if there is specific pathology that may be addressed with surgery.

Operative Treatment

Surgical interventions range from soft tissue procedures to arthroplasty, depending on the severity, chronicity, and character of disease. Soft tissue procedures include lateral retinacular release, proximal soft tissue realignment, or limited facetectomy/ synovectomy. Lateral retinacular release is a soft tissue procedure used for patellar facet arthrosis with radiographic evidence of patellar tilt without subluxation and no clinical instability. The procedure reduces the restraining forces across the patella, to relieve pressure on the diseased facet. Over or undercorrection of restraining forces and patellar subluxation are potential complications of the procedure.

Biologic resurfacing, including autologous chondrocyte implantation (ACI), osteochondral autografts, osteoarticular transfer system, or mosaicplasty may be used for discrete chondral defects. ACI is an alternative option for young patients who have symptomatic chondral lesions not alleviated by unloading of the compartment (e.g. via bracing, osteotomy). Attempts at biologic resurfacing are designed to stave off the need for arthroplasty.11 Concomitant bony/ soft tissue realignment procedures may be performed at the same time. Concern with any biologic resurfacing procedure is longevity of the implanted/ transferred tissue in the face of progressive arthrosis.

Bony realignment is achieved through osteotomy of the tibial tubercle in a number of forms (e.g. Fulkerson, Maquet, Trillat). Anterior transfer of the tibial tuberosity takes pressure off the patella while balancing the extensor mechanism. Overcorrection (eg, excessive anteriorization of the tibial tubercle) is a potential complication, along with nonunion, fracture, infection, and acute postoperative compartment syndrome.

Arthroplasty, including patellofemoral or total knee, may be a definitive solution for end-stage patellofemoral arthritis refractory to other treatment modalities. Total knee arthroplasty is the most reliable procedure to address patellofemoral arthritis in the older patient. Patellofemoral replacement is more conservative in terms of sparing bone, cruciate ligaments, and menisci in the other compartments of the knee, but its survivorship when compared to total knee arthroplasty must be weighed, especially in the younger patient. Patellofemoral replacement can be performed after prior bony realignment procedures. Inflammatory arthritis is a contraindication to unicompartmental replacement.

Patellectomy, or resection of the patella, should be considered a salvage procedure. This option is used in the situation where severe patellar bony loss exists or for symptoms refractory to other treatment methods. While pain may be relieved by this procedure, downsides include extensor mechanism lag and weakness.

Conclusion

Challenges remain in the treatment of patellofemoral arthritis. Pain in the anterior aspect of the knee can result from many factors, such as tendinitis, synovitis, abnormal patellar tracking, and arthritis. Surgeons must appropriately coordinate history and physical examination findings with imaging studies in the management algorithm of patellofemoral arthritis. Differing treatment modalities, both nonsurgical and surgical, may be employed to manage patellofemoral arthritis. The best treatment course for patellofemoral arthritis has not yet been determined, and options must be matched to patient age, symptoms, any instability, and specific anatomic/biomechanical pathology. Soft-tissue, biologic resurfacing procedures, and osteotomies are aimed towards younger patients with less severe degree of arthritis, while joint replacement surgery continues to be the most reliable option for older patients who have end-stage arthritis involving the patella.

References

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