You are in: eMedicine Specialties > Orthopedic Surgery > KNEE Patellofemoral ArthritisArticle Last Updated: Sep 12, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 13
  Author: Kathleen A Hogan, MD, Fellow in Arthroplasty, Department of Orthopedics, Brigham and Women's Hospital Kathleen A Hogan is a member of the following medical societies: Sigma Xi Coauthor(s): H Del Schutte, Jr, MD, Associate Professor of Orthopedic Surgery, Department of Orthopedic Surgery, Medical University of South Carolina Editors: Charles T Mehlman, DO, MPH, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, Cincinnati Children's Hospital Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Thomas M DeBerardino, MD, Director, John A Feagin, Jr, Sports Medicine Fellowship at West Point, Associate Professor of Orthopedic Surgery, Uniformed Services University of the Health Sciences and Keller Army Community Hospital; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Carlos J Lavernia, MD, FAAOS, Adjunct Clinical Professor, Department of Orthopedic Surgery, University of Miami School of Medicine; Medical Director, Orthopedic Institute at Mercy Hospital Author and Editor Disclosure Synonyms and related keywords: patellofemoral arthritis, anterior knee pain, chondromalacia patellae, osteoarthritis, arthritis of the patella, arthritis of the kneecap, patellofemoral pain syndrome, patellofemoral pain, kneecap, joint disease, chondromalacia, knee pain, patellofemoral syndrome, patellofemoral joint syndromes, total knee arthroplasty, TKA, total knee reconstruction, TKR INTRODUCTIONSection 2 of 13
  Patellofemoral arthritis usually affects the same patient population affected by arthritis of other joints. Increasing age, obesity, overuse, chronic joint instability, prior interarticular fractures, and systemic inflammatory conditions are risk factors for the development of arthritis in the hip, knee, patella, and other weight-bearing joints. Patellofemoral arthritis can also occur in younger patients as a result of malalignment or trauma. History of the ProcedureLudloff, Axhausen, and Budinger reported damage to the articular cartilage of the patella after trauma in the early 1900s. In 1924, Koening first used the term chondromalacia to describe this condition. In the 1960s, Outerbridge described damaged articular cartilage of the patella in young patients undergoing open meniscectomy.1, 2 Subsequent research has focused on anatomic and biomechanical causes of damage to the patellofemoral joint, such as sheer and compressive forces, abnormal patellar tracking, and patella subluxation and tilting. Patellectomy was one of the first surgical procedures performed for patellofemoral arthritis. However, realization of the importance of the biomechanical role of the patella has led to the development of alternative surgical procedures (see Surgical therapy). ProblemArthritis of the patella refers to the presence of degenerative changes underneath the kneecap (the patella). This form of arthritis can have no symptoms, it may cause only vague anterior knee pain, or it may result in severe difficulties with stair climbing and ambulation. The term chondromalacia is used to describe early alterations in the articular cartilage of the patella that may eventually lead to patellofemoral arthritis. This article focuses primarily on the problem of osteoarthritis of the patellofemoral joint. Frequency
EtiologyPatellofemoral arthritis can be a result of inflammatory conditions or mechanical abnormalities. Inflammatory conditions include rheumatoid arthritis; often, the entire knee joint is involved. Mechanical abnormalities can be a result of prior fractures, inherent malalignment, muscle imbalances, or chronic instability. Association with anterior cruciate ligament reconstruction Some orthopedists believe that reconstruction of the anterior cruciate ligament (ACL) with a patella tendon graft may lead to later problems of patellofemoral pain, loss of motion, and arthritis. However, whether these late complications are a result of the injury itself, the anatomic alignment that contributed to the injury, or a result of the surgical reconstruction is not clear. In an animal model, ACL transection caused significant changes in joint pressure and the articular cartilage after only 4 months.3 The thickness of the articular cartilage significantly increased in the patella, the medial and lateral femoral condyles, and in the patellar groove, with total increases in the range of 42-100%. Although the joint contact area was increased, overall peak contact pressures were reduced. The thickening of the cartilage may provide a protective modification of joint pressure, or it may represent early arthritic changes. In a retrospective clinical study, Jarvela et al of Finland found an association between prior ACL reconstructions with bone-patella-bone allografts and the subsequent development of patellofemoral arthritis.4 Although evidence of arthritis along the lateral and medial tibial femoral joints was found in 15% and 18% of these patients, respectively, 47% had radiographic evidence of patellofemoral arthritis. At follow-up at a mean of 7 years, patellofemoral arthritis was mild in 34%, moderate in 12%, and severe in 1%. Shortening of the patella tendon after the index procedure was significantly associated with the development of arthritis. However, the location of the bone tunnel was not correlated with the development of arthritis. Relationship of osteoarthritis of the patellofemoral joint to arthritis in other knee compartments Osteoarthritis of the patellofemoral joint should be considered as an entity separate from disease in the medial and lateral tibiofemoral compartments of the knee. Not all patients with patellofemoral arthritis have osteoarthritis in the other compartments; arthritis may develop at different times and with different etiologies in the different compartments of the knee. Some studies have indicated that risk factors for the development of patellofemoral arthritis include increasing body weight, high-intensity running or weight lifting, prior knee injury, and prior patellar dislocation or subluxation. In 1995, Kujula and colleagues conducted a longitudinal study to address the mechanical factors leading to arthritis of the patellofemoral joint.5 A total of 292 patients with osteoarthritic knees were evaluated radiographically. Of those with radiographic evidence of patellofemoral arthritis, 70% had changes to the lateral side of the patella. In this subset of patients, the likelihood of a varus knee alignment was significantly increased compared with those with medial patellofemoral arthritis, who were more likely to have a valgus knee. In one third of the patients with patellofemoral arthritis, no radiographic evidence of osteoarthritis was present in other compartments of the knee. This isolated patellofemoral arthritis was seen more often in a valgus alignment than was isolated tibiofemoral arthritis. In another study, CT of 40 knees in flexion revealed that, in patients with patellofemoral arthritis, the tibial tubercle had a significantly more lateral position than it does in normal knees.6 However, whether this finding represents a cause or a result of arthritic damage to the joint was not determined. PathophysiologyArticular cartilage in the patella differs from that of other joints in several ways. The cartilage is not necessarily congruent with the contours of the underlying subchondral bone. In 60% of patellae, the thickest area of articular cartilage is located lateral to the thickest area of underlying bone. Some biomechanical studies have also indicated that this cartilage is less stiff and, thus, more compressible than that of other joints. One cadaveric comparison of femoral and patellar articular cartilage showed that patellar cartilage had a 66% higher permeability, a 30% lower compressive aggregate modulus, and a 23% increase in thickness.7 The proteoglycan content was 19% higher in the femoral compared with that of the patellar cartilage. The significance of these differences to prevent or promote arthritic changes in the patellofemoral joint is not yet clear. Using MRI, Herberhold and colleagues studied the relationship of static loading to cartilage deformation in fresh frozen cadaveric knees.8, 9 After 214 minutes of static loading with 150% body weight, the thickness of the articular cartilage was reduced by 44% in the patella and 30% in the femur. The changes in the thickness of articular cartilage of the patella were greatest at the lateral facet, the area of thickest cartilage. Of note, 7% of the final deformation occurred during the first minute, and 25% occurred in the first 8 minutes. In the initial response to loading, the cartilage appeared to be stiffer than it was in response to prolonged loading. In normal loading, fluid in the cartilage is thought to support the applied load and to prevent cartilage deformation from occurring. The main function of the patella is thought to be improving the mechanical advantage of the quadriceps extensor mechanism by increasing the lever arm of the muscle. The patella also acts to dissipate the forces generated in the patella tendon during knee flexion and extension. The angle of force of the quadriceps muscle group (ie, the Q angle) is thought to be a factor in the development of knee injuries and arthritis. However, no findings conclusively support this assertion. The Q angle is measured as the angle between a line connecting the patella to the tibial tubercle and a second line between the anterior superior iliac spine and the center of the patella. A larger Q angle is thought to increase the lateral tracking of the patella mechanism.10 Huberti and colleagues concluded that, at normal Q angles, pressure is evenly distributed across the patella.11 Increases in this angle, however, result either in a shifting of pressure to the lateral facet or a change in the distribution of force. Cadaveric studies demonstrate that, with an increasing Q angle, the patella shifts more laterally and rotates medially as the knee is flexed. This change is thought to increase lateral contact at the patellofemoral joint and, possibly, to increase the incidence of patella subluxation and dislocation. In closed-chain exercises with the foot planted on the floor (eg, squatting), contact forces increase with progressive degrees of knee flexion. However, in open-chain exercise in which the foot is off the floor (eg, hamstring curls), no corresponding increase in patella contact force occurs as the knee progresses through a range of motion. The portion of the patella that is in contact with the trochlea also changes during range of motion.12 With the knee extended, only the distal aspect of the patella contacts the trochlear groove. With progressive flexion, the contact shifts to the proximal aspect of the patella. At greater than 90° of flexion, the contact area is predominately in the center of the patella, which corresponds to the thickest area of articular cartilage. The medial facet of the patella articulates with the trochlea only during positions of full flexion. The force on the patella increases with knee flexion from 0-60°. However, no consensus exists among researchers regarding the relative amount of force generated with progressive flexion. The contact forces likely are related to the amount of force being generated by the quadriceps muscles during deep flexion exercises. Gait lab analysis has shown that walking with the foot plantar flexed, as occurs when high-heeled shoes are worn, increases the forces in the patellofemoral joint and in the medial compartment of the knee. ClinicalHistory taking The patient should be asked the following questions regarding a history of trauma or instability:
Arthritis and conditions of malalignment typically result in pain that is worse with activity. Constant pain that does not vary with activity suggests a referred or nonmechanical origin. Isolated patellofemoral arthritis may cause anterior knee pain that worsens with stair climbing or when rising from a seated position and is not present with other activities, such as walking or running on level surfaces. Patella instability is associated with intermittent sharp pain at the kneecap. A feeling of "giving way" may be related to muscle weakness or to instability. Recurrent patellar subluxation or dislocation may cause an acute osteochondral fracture or chronic cartilage damage as a result of repeated microtrauma. Observation Astute observations of gait and of lower-extremity alignment are an essential component of the physical examination. Leg-length discrepancies, Q angle, and torsional deformities of the femur, tibia, and foot should be noted. Flexion contractures of the limb should be noted. Gait should be observed carefully, with the patient not wearing shoes. Excessive pronation of the feet, patella tracking, and rotation of the lower limb should be observed. Muscle tone and atrophy of the quadriceps and hamstrings should be assessed. Patella tracking with passive flexion and extension and with squatting should be determined. Physical findings must be evaluated in the context of patient complaints. A study of 210 adults with asymptomatic knees revealed abnormal radiographic or physical examination findings in 95% of women and 79% of men.13 Patellar crepitus, a hypermobile patella, and lateral position of the patella on the axial radiographs were common in this group of patients. Unfortunately, no long-term follow-up was performed to determine whether subjective complaints developed; however, these findings emphasize the point that a diagnosis cannot be based on physical findings alone. Physical examination The physician should determine the presence of ligamentous laxity, instability, and patella maltracking, and attempt to elucidate the source of pain. One should try to elicit whether the pain arises predominately from the soft tissues or from articular degeneration.
Differential diagnosis The differential diagnosis in patients presenting with anterior knee pain includes the following conditions:
Related eMedicine topics: INDICATIONSSection 3 of 13
Patients typically present with anterior knee pain. Indications for surgical management include pain, loss of functional ability, arthritis that is correlated with the symptoms, and symptoms that do not respond to physical therapy. Medical conditions such as hypertension, coronary artery disease, and diabetes should be medically managed and stabilized as much as possible prior to surgery. The patient must understand the procedure and be willing to participate in his or her postoperative rehabilitation. In patients with patellofemoral arthritis, the goal of surgical procedures should be to improve patellar biomechanics and to correct articular damage. RELEVANT ANATOMYSection 4 of 13
The patella is a sesamoid bone, the largest in the body, and embedded in the quadriceps and patella tendons. A subcutaneous bursa separates the patella from the overlying skin. The articular surface of the patella consists of 4 facets: inferior, middle, superior, and medial vertical. During flexion, the patella moves within a groove in the femur, the trochlea. The patella is thought to travel in a J-shaped pattern, moving laterally with knee extension.14 The lateral aspect of the trochlea, the vastus medialis, and the medial patella-femoral ligament prevent excessive lateral translation. The anatomy of the distal femur and the vastus lateralis and lateral patella-femoral ligaments provides restraints against medial subluxation. The patellar plexus, an anastomosis of the superior and inferior genicular arteries that are branches of the popliteal artery, provides the blood supply to the patella. CONTRAINDICATIONSSection 5 of 13
The procedures described for the surgical treatment of patellofemoral arthritis are elective; patients should be in relatively good health prior to the operation. Contraindications for surgery include hemodynamic instability, current respiratory infection, recent myocardial infarction, and compromised skin integrity in the surgical field. Medical issues, such as hypertension, pulmonary disease, coronary artery disease, and diabetes, should be well controlled prior to surgery. Medical clearance prior to surgery is recommended for patients with multiple medical issues. Additionally, patients should be able to comply with postoperative rehabilitation regimens. WORKUPSection 6 of 13
Lab Studies
Related eMedicine topics: Imaging Studies
Histologic FindingsNormal articular cartilage is smooth and glistening. Degenerative changes observed in the articular cartilage of the patella are similar to those observed in other joints. In one of the earliest descriptions of the pathology of the patellofemoral joint, Outerbridge described dulling of the color and softening of the cartilage as the earliest changes in chondromalacia patellae. With progressive degeneration, osteoarthritis develops, and fissures and erosion of the cartilage occur. These changes are typically more pronounced on the medial patellar facet than elsewhere, but eventually extend throughout the patella. TREATMENTSection 7 of 13
Medical therapyNonoperative treatment involves nonsteroidal anti-inflammatory drugs (NSAIDs), activity modification, and muscle-strengthening activities. Strengthening of the quadriceps muscle group can be beneficial, especially in patients with maltracking and weakness of these muscles. Activities should be modified so that prolonged flexion (as with squatting) and stair climbing are avoided. A knee sleeve may also relieve symptoms. Some have advocated taping of the patella to push it into a more medial position, especially in young patients undergoing rehabilitation for anterior knee pain. Interestingly, a recent group who used CT to evaluate patellar position found that taping had absolutely no effect on either patellar displacement or patellar tilt. A prospective, randomized, double-blind study of nonoperative treatment in younger patients (aged 20-55 y) with patellofemoral pain (not arthritis) revealed that symptoms resolved in 67% of patients within 6 months of initiating physical therapy, and 80% graded their knee as excellent after 7 years. However, clinical findings in these patients worsened with time. Significantly more patients had positive apprehension and compression test results and had crepitus at 7-year follow-up, and 5% of patients developed arthritis. Although conservative management may help in resolving symptoms, no evidence indicates that it prevents the progression of arthritic changes in the joint. Surgical therapyBefore proceeding with surgery, the surgeon and patient must be in agreement regarding the goal of the procedure. Malalignment can be corrected, soft tissues can be balanced, and articular damage can be assessed and treated. Arthroscopy can be used diagnostically to assess the size, severity, and location of articular degeneration and to determine whether subluxation of the patella is present. Arthroscopy Arthroscopy is an excellent tool for diagnosing patellofemoral arthritis. The surface of the patellofemoral and tibiofemoral joints can be evaluated under direct visualization, and the motion of the patella with flexion and extension can be observed. Arthroscopic debridement has been used to smooth and clean up fibrillated cartilage on the joint surface. No evidence indicates that this provides long-term relief of pain, however. Articular cartilage does not regenerate; instead, it is replaced by fibrocartilage. Although not as mechanically protective as articular cartilage, fibrocartilage may induce less of an inflammatory response than damaged articular cartilage.
For patients with anterior knee pain directly associated with poor patellar positioning, surgical procedures that attempt to correct the malalignment may be beneficial. A lateral retinacular release is performed to change the tilt of the patella, decreasing pressure on the lateral patellar facet by releasing the lateral constraints of the patella. These constraints include the iliotibial band, vastus lateralis, and patellofemoral and patellotibial ligaments. This procedure is often performed with patellofemoral and total knee arthroscopy when lateral patellar malalignment is noted. Medialization of the tibial tuberosity has been advocated to improve patella tilt and subluxation by decreasing the valgus moment acting on the patella. Anteriorization of the tibial tubercle is used in more severe cases and increases the power of the quadriceps by increasing the length of the lever arm. Patellofemoral joint reactive forces are decreased with this procedure. The multiple procedures used to correct malalignment indicate that no single procedure consistently results in excellent outcomes. The goal of these procedures is to decrease pain by changing the distribution of force across the patella. They may be beneficial for young patients with intractable knee pain unresponsive to medical therapy or in some patients with early arthritic changes. For patients with severe patellofemoral arthritis, a more extensive surgical procedure is required to address the articular damage. Cartilage transplantation The ideal solution to articular cartilage damage is cartilage regeneration. Unlike bone, damaged articular cartilage lacks the ability to repair itself. Techniques such as subchondral drilling, microfracturing, and abrasion arthroplasty have been used to stimulate healing of the articular cartilage in the knee joint. Some have theorized that undifferentiated progenitor cells in the marrow are stimulated to form articular cartilage. Histologic studies, however, have demonstrated that healing of the defect occurs primarily with fibrocartilage, which has inferior mechanical properties compared with those of hyaline cartilage. Because of the limitations of these techniques, research is currently being undertaken to replace the defect with chondrocytes or osteochondral autografts or allografts to restore the hyaline cartilage of the articular surface.19 Autologous cartilage transplantation and osteochondral autografting Briefly, the procedure of autologous chondrocyte transplantation involves harvesting chondrocytes from a relatively non–weightbearing portion of the medial tibia condyle. The cells are cultured for 11-21 days, at which time they are implanted into the defect. The defect is covered with a periosteal patch from the proximal medial tibia to keep the cells in place. Patients must be non–weight bearing for approximately 8 weeks to avoid damaging the transplanted cells. Brittberg et al published their intermediate (39-mo) follow-up on 23 patients with full thickness cartilage defects in the knee that were treated with autologous cartilage transplantation.20 Of 16 patients with femoral condylar defects, 14 (87%) had good-to-excellent clinical results. Transplants to the patella region had less favorable results, with only 2 (29%) of 7 patients having good-to-excellent results. Hyaline cartilage was found on biopsy in 11 of 16 femoral transplants compared with 1 of 7 patellar transplants. Peterson et al reported that 91% of 58 patients had good-to-excellent results, based on clinical examination and results self-assessment questionnaires.21 In this series, however, all of the patients had femoral condylar defects and none were treated for osteochondral defects of the patella. The limitations of this type of autologous cartilage transfer include the requirement of 2 surgical procedures, the risk of infection being introduced when the cells are grown in vitro, and the facilities and expertise needed for the successful in vitro growth of chondrocytes. A similar method, autologous osteochondral mosaicplasty is performed to achieve the same results without these limitations. In this technique, multiple, small (2.7- to 8.5-mm-diameter) plugs of hyaline cartilage and underlying subchondral bone are taken from non–weightbearing surfaces. They are then implanted into the osteochondral defect. The donor site fills with fibrocartilage, but, theoretically, the hyaline cartilage of the transplant should be preserved. Patients are typically advised not to bear weight for 2 weeks following the procedure, and then partial weight bearing is allowed for 2 weeks. Hangody et al reported results in 831 consecutive patients who underwent this procedure during a 10-year study period. Complications included deep infection (n = 4) and painful hemarthroses (n = 36). Clinical evaluation with standard knee scores indicated good-to-excellent results following mosaicplasty in 92% of femoral (n = 597) procedures, 94% of talar procedures (n = 76), 87% of tibial procedures (n = 25), and 79% of patellar procedures (n = 118). Patients younger than 35 years had better results than those in older patients.22 Bentley et al published a prospective randomized comparison of autologous cartilage transplantation and mosaicplasty.23 At 19-month follow-up, functional assessment revealed that 88% of patients (n = 58) with cartilage transplants and 69% of patients (n = 42) had good-to-excellent outcomes at an average follow-up of 19 months. Both autologous cartilage transfer and mosaicplasty may hold promise for the treatment of patellofemoral osteochondral lesions. However, results for osteochondral lesions of the patellofemoral joint with these procedures appears to be less favorable than for lesions in the femoral condyles, and the procedures require careful patient selection. These procedures are best suited for young, active patients who have focal degenerative lesions and in whom moderate-to-severe osteoarthritis has not yet developed. Additional surgical procedures to correct misalignment may also be necessary. Patients must be highly motivated and willing to cooperate with prolonged non–weightbearing periods. Osteochondral allografting Osteochondral plugs or wafers can also be obtained from allografts, which limit damage to the articular surface and increase the size of defect that can be repaired. Fresh allografts of articular cartilage and subchondral bone are implanted into the defect. The allograft bone is reabsorbed and remodeled, but the transplanted chondrocytes survive.24, 25 Chu et al reported their results in 55 consecutive patients.26 About 84% of patients with unipolar transplants, but only 50% with bipolar transplants, had good-to-excellent results. They also reported that 11 (73%) of 15 patients had good-to-excellent clinical results at 10-year follow-up. Shasha et al reported long-term follow-up results of osteochondral grafting for isolated posttraumatic tibial plateau defects.27 Kaplan-Meier analysis revealed a survival of 95% at 5 years, 80% at 10 years, and 65% at 15 years, with an endpoint of knee arthroplasty, revision of graft, or a Hospital for Special Surgery knee score of <70. Although this technique does not violate the native hyaline cartilage of the knee, fresh allografts must be used, as freezing or other processing destroys the viability of the chondrocytes. This limitation has limited enthusiasm for this procedure because, despite precautions, the risk of bacterial, viral, or fungal disease transmission remained increased with this type of transplant. Patellectomy Patellectomy is a surgical option after severe patella fractures. Surgeons have also used this procedure as a treatment for arthritis of the patella. Problems associated with patellectomy include loss of normal knee power and function, quadriceps weakness, and failure to resolve anterior knee pain. Cybex measurements after patellectomy demonstrate significant decreases in the peak torque of the quadriceps muscles, with preservation of normal hamstring function.28 Patellectomy in a rabbit model has been shown to result in arthritis of the tibiofemoral joint.29 Clinically, a retrospective review of 81 patients who underwent patellectomy for osteoarthritis during a 20-year period found that only 53% achieved a good result.30 With time, there was a statistically significant increase in radiologic changes at the tibiofemoral joint consistent with the development of arthritis. A case report of arthroscopic findings in 16 knees with a prior patellectomy showed severe medial compartment and trochlear articular damage in patients aged 22-64 years with a mean follow-up of 15.4 years.31 With progressive degeneration, these patients may later require a total knee arthroplasty (TKA) for arthritis of the knee. To the authors' knowledge, no large studies reveal whether patellectomy restricts future options for TKA. Joshi et al reported a complication rate of 36% in 19 patients with prior patellectomy compared with 0% in a matched cohort.32 A retrospective matched control study at the Hospital for Special Surgery examined the results of TKA in patients who either did or did not undergo previous patellectomy.33 Only 6 (30%) of 22 patients underwent patellectomy because of osteoarthritis. At 5-year follow-up, standardized knee scores did not differ between the 2 groups of patients. However, patellectomy results did differ depending on the prosthesis used. Patients with a posterior cruciate ligament (PCL)–sacrificing prosthesis had statistically higher postoperative knee scores than those with a PCL-retaining prosthesis. The subgroup of patients with PCL conservation had more pain, decreased range of motion, and more difficulty ascending stairs. The authors believe that the posterior stabilized implant increases the quadriceps lever arm. Considerable debate exists, however, regarding which implant provides better results after patellectomy, as other earlier groups have reported contradictory findings. Patellofemoral arthroplasty In 1955, McKeever performed the first replacement of the patella as an alternative to patellectomy for isolated patellofemoral arthritis. Since that time, the patellar prosthesis has been reengineered multiple times. The most commonly used implants are cemented polyethylene implants. The procedure can consist of a patella resurfacing procedure alone or may include femoral resurfacing and the replacement of the femoral groove with a metal implant. Isolated patellar resurfacing, however, has not been shown to be more effective than total knee replacement (TKR) in the older patient population.34 One significant advantage of arthroplasty over patellectomy is the preservation of the quadriceps function. Disadvantages of this procedure are that it is a technically demanding procedure that is not commonly performed and that second surgery may be needed for TKR if the patient also has tibiofemoral osteoarthritis. Some concern also exists about the effect of particulate metal debris developing in the joint from the metal-backed component, which may be associated with an increased risk of infection.35 Krajca-Radcliffe and Coker reported a retrospective study of 16 total patellofemoral arthroplasties in 13 patients conducted between 1975 and 1992 with a minimum 2-year follow-up and average patient age of 64 years.36 About 88% had good or excellent results, 7 of 13 were pain-free with all activities, and no patients had pain with routine activity. Quadriceps strength was 75% and 100% of the contralateral side. One patient required a revision procedure. In a larger series of 72 patellofemoral arthroplasties in 65 patients with an average 4-year follow-up, an 85% had good-to-excellent results. However, more than one half of the patients in this series had concurrent unicompartmental knee replacements. Furthermore, the authors reported complications in 14 patients (18%), 5 of whom required a repeat operation.37 Another review of 66 isolated patellofemoral arthroplasty procedures performed over a 10-year period with a 5.5-year average follow-up demonstrated that 16% required revision to a TKA.38 Total knee arthroplasty TKA is used to treat patients with severe osteoarthritis of the knee that has not improved with medical management and that has become detrimental to a patient's quality of life. It is usually performed in patients older than 60 years, but occasionally younger patients with significant arthritic changes are considered candidates for the procedure. At the Hospital for Special Surgery in New York, Laskin and van Steijn compared the results of TKA in 53 patients with severe patellofemoral but minimal tibiofemoral arthritis to sex- and age-matched patients undergoing the procedure for tricompartmental knee arthritis.39 All patients had a cemented tricompartmental PCL-sparing prosthesis. Preoperatively, the group with isolated patellofemoral arthritis had statistically significant increases in pain score, and fewer were able to rise from a chair or climb stairs without assistance. In this study, lateral release was required in 30% patients with patellofemoral arthritis versus 8% in the other group. Postoperatively, 82% of the patients were able to climb stairs, and only 3 complained of anterior knee pain. Average range of motion was 120°. These results were comparable to those in the other group. This study indicates that TKA may be the procedure of choice in older patients with severe patellofemoral arthritis. Patellar resurfacing versus nonresurfacing in TKA The need to perform a patella resurfacing procedure at the time of TKA is still being debated. Some surgeons advocate resurfacing in all patients, while others restrict resurfacing to patients with known patellofemoral arthritis. Patellofemoral complications after TKA with patella resurfacing are associated with obesity, metal-backed patellar implants, and noncemented patellar components.40 These complications can include pain, mechanical fracture, loosening, fracture, and maltracking. Retaining the native patella, however, can result in persistent symptoms of anterior knee pain that can compromise the functional ability of the patient. Furthermore, patients with known osteoarthritis in the tibiofemoral knee compartment are at increased risk for arthritis of the patellofemoral joint. Some surgeons have suggested that patella resurfacing does not have to be performed if the patellar articular cartilage is normal and if no malalignment is present. The results of several small retrospective studies support the practice of selective resurfacing. In a retrospective study of 185 patients with TKR, pain, functional outcome scores, range of motion, or complications did not differ between those undergoing resurfacing and those not (n = 140).41 In a 10-year retrospective follow-up study in 32 knees with a posterior cruciate-retaining Press-Fit condylar TKA and no resurfacing, only 1 patient required later revision for patella resurfacing.42 Several investigators have asserted that no difference exists between resurfacing and retaining the patella in terms of stair-climbing ability or functional outcome.43, 44 Furthermore, if the patella is resurfaced and if a complication requiring revision is present, the patella often cannot be resurfaced again because of bone loss. For this reason, some surgeons do not recommend resurfacing in young patients, even when some patellar chondromalacia is present. If the patella is left unresurfaced, the knee system should have an anatomic rather than dome-shaped trochlear groove in the femoral component. Other orthopedic surgeons believe that a resurfacing procedure should be performed in all patients at the time of a knee arthroplasty. Biomechanically, most prosthetic knees are designed for use with a resurfaced patella. A study examining the relationship of the patella to different femoral components revealed that retaining the patella results in changes in contact pressures and in the tracking motion in the patellofemoral joint.45 With flexion of 60° or more, the contact areas shifted from a transverse band across the patella to isolated areas of high pressure on both the medial and lateral sides of the patella. The percentage of patellar contact area subjected to contact pressures greater than 5 MPa was significantly greater with all of the tested prostheses compared with the normal knee with flexion >60°. The patella tracked 3-5 mm more laterally once a prosthesis was in place. This finding may help to explain why some patients without patellofemoral arthritis who have a retained patella may have more difficulty climbing stairs postoperatively than those who undergo a resurfacing procedure. In a prospective series of 40 patients, patients undergoing patellar resurfacing had clinically improved function at a 2-year follow-up in terms of stair climbing and higher functional k scores than those of patients not receiving this procedure.46 One group in Japan, which routinely did not perform resurfacing, assessed results in 60 patients and found that two thirds had rheumatoid arthritis and one third had osteoarthritis. The percentage of patients complaining of postoperative peripatellar pain was higher than that of patients with rheumatoid arthritis (27% vs 12%).47 Boyd and colleagues from Brigham and Women's Hospital in Boston reported the largest retrospective series to date.48 This group examined the results of using an unconstrained, condylar, PCL-preserving prosthesis with and without resurfacing in 891 knees. Patella resurfacing was performed only for specific conditions: loss of cartilage, surface irregularities, and tracking abnormalities. The rate of complications was higher in those without resurfacing than in those with resurfacing (4% vs 12%). Ten percent of patients without resurfacing required revision for patella resurfacing because of chronic pain. Those with inflammatory arthritis were significantly more likely to require revision for patellar pain than those with osteoarthritis (13% vs 6%). To the authors' knowledge, no large prospective studies currently provide clarity in this debate. Patients with rheumatoid arthritis seem to do better with a resurfacing procedure. To decrease the incidence of a subsequent revision surgery, most patients would most likely benefit from patella resurfacing at the time of TKA. Functional outcomes, however, seem to be similar when selective nonresurfacing is performed. Follow-upThe type of follow-up care required depends on the type of surgical procedure performed. Postoperative physical therapy focused on quadriceps strengthening is often helpful to many patients. Those undergoing total knee arthroplasty (TKA) or patellofemoral arthroplasty have started range-of-motion exercises immediately after surgery, and, depending on their preoperative ambulatory status, patients may require a short stay in a rehabilitation hospital while they receive physical therapy. Procedures involving anteriorization of the tibial tubercle require a period of relative immobilization after surgery and before physical therapy. Cartilage transplantation and osteochondral grafts require a period of strict non–weigh bearing for several weeks to allow for the incorporation of the graft. Patient's understanding of and compliance with postoperative treatment protocols are an important factor in the success or failure of all of these surgical treatments. For excellent patient education resources, visit eMedicine's Arthritis Center. Also, see eMedicine's patient education articles Knee Pain, Osteoarthritis, and Knee Joint Replacement. COMPLICATIONSSection 8 of 13
Complications of patellectomy include quadriceps weakness, loss of normal knee function, and failure of the procedure to resolve the patient's pain. Some studies indicate that patellectomy may result in an increased incidence of knee arthritis. If osteoarthritis develops later, the patient may require a second surgery for total knee arthroplasty (TKA), and they may have a greater-than-expected complication rate after this procedure. Complications of patellofemoral arthroplasty include patellar fracture, infection, and adverse reactions to metal debris in the joint. Revision to a total knee occurs in an average of 16% of patients. Complications of TKA include the infection, loosening, patella fracture, and periprosthetic fracture. All surgical procedures have risks associated with anesthesia. The extent of the risk is related to the general medical condition of the patient. Knee surgeries are associated with a risk of deep venous thrombosis, which is reduced with the use of appropriate prophylaxis. Pulmonary embolism from propagation of thrombus after total knee reconstruction (TKR) occurs in less than 1% of patients. OUTCOME AND PROGNOSISSection 9 of 13
Medical therapy can improve the symptoms of patellofemoral osteoarthritis, but it has not been shown to halt the progression of disease. Weight loss, avoidance of aggravating activities, prevention of traumatic injury to the patella, and careful reduction of interarticular fractures of the patella by the surgeon may help to prevent the development of arthritis. Surgical therapy is beneficial for patients with intractable pain and radiographic evidence of arthritis. Patellectomy, patellofemoral arthroplasty, and total knee arthroplasty (TKA) reduce pain and increase function. Patellectomy, however, is associated with significant changes in joint biomechanics, and one study demonstrated that only 53% achieved a good result at long-term follow-up. FUTURE AND CONTROVERSIESSection 10 of 13
For patients with osteoarthritis affecting the patellofemoral and tibiofemoral joints, a total knee arthroplasty (TKA) with patella resurfacing is clearly the procedure of choice. For patients with isolated patellofemoral arthritis, however, there is no consensus regarding the best treatment. Some patients benefit from NSAIDs and physical therapy, others undergo patellofemoral arthroplasty, and still others may benefit from TKA. Future surgical directions include the redesign of the prosthesis used in isolated patellofemoral arthroplasty.49 Well-designed prospective studies should be performed to determine the best treatment for the young patient with isolated patellofemoral arthritis. Cartilage transplantation, cartilage allografts, and the stimulation of articular cartilage repair are areas of active research today. FURTHER READINGSection 11 of 13
AAOS clinical guideline on osteoarthritis of the knee (phase II). MULTIMEDIASection 12 of 13
REFERENCESSection 13 of 13
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
