AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Patellofemoral joint complaints are one of the most common musculoskeletal complaints in all age groups. Complaints vary from anterior knee pain to peripatellar knee pain to retropatellar knee pain.^{1, 2, 3, 4, 5, 6, 7} Nonspecific complaints may include global or generalized knee pain, joint line pain, or posterior knee pain. Often, there is a paucity of objective findings despite subjective complaints. The problem may vary from one of short duration to one of a recurrent or chronic nature.

The etiology of patellofemoral joint syndrome is multifactorial and results from a combination of intrinsic and extrinsic factors.^{1, 2, 3, 4, 5, 6, 7} Treatment is often conservative in nature. Because of the variable nature of the complaints and an often lack of objective identifiable pathologic cause of patellofemoral joint complaints, this condition can be difficult to evaluate, diagnose, and treat, which may cause great frustration for the physician and patient alike.⁵

For excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center; Breaks, Fractures, and Dislocations Center; Arthritis Center; and Osteoporosis and Bone Health Center. Also, see eMedicine's patient education articles Knee Pain Overview and Knee Injury.

Frequency

United States

Patellofemoral joint syndrome may affect as many as 25% of all athletes.

Functional Anatomy

The patellofemoral joint is composed of the articulation of the patella with the femoral condyles of the femur. The patella has a configuration of a triangle with its apex directed inferiorly. Superiorly, it articulates with the trochlea, the distal articulating surface of the femur.

The patella is the largest sesamoid bone in the body and protects the knee from direct trauma. Localized within the quadriceps tendon, the patella also acts as a fulcrum for extension of the quadriceps.

Medial movement of the patella is controlled by the vastus medialis oblique (VMO) muscle. Lateral tracking is guided by both the vastus lateralis and the iliotibial band. Patellar motion is further constrained by the patellofemoral ligament, the patellotibial ligament, and the retinaculum.

The patella is engaged with the trochlea at 20-30º of knee flexion. At 90º, the patella contacts the lateral and medial femoral facets within the condylar fossa. At 130-135º of knee flexion, the medial facets of the patella contact the articulating surface of the femoral condyles. In knee extension, the patella abuts the suprapatellar fat pad.

Sport-Specific Biomechanics

The patella lies within the quadriceps tendon and thereby increases the mechanical advantage of the quadriceps mechanism. Not only does the patella increase the force of knee extension by 50%, but it also provides stability to the patellar tendon and minimizes the forces placed on the femoral condyles.

Tracking of the patella begins with the lower patellar border lying in contact with the suprapatellar fat pad when the knee is fully extended. With knee flexion, the patella moves proximally with a lateral shift, which is limited in excursion by the lateral retinaculum. As the knee continues to flex, the tibia internally rotates and the patella moves upward. The amount of force placed on the patellofemoral joint increases with increasing knee flexion. On the other hand, knee hyperflexion increases patellofemoral stress, as does extreme extension.

The vector force placed on the patella may be affected by the Q-angle. The Q-angle is a line created from the anterior superior iliac spine (ASIS) to the mid patella, which intersects with a line from the mid patella to the tibial tubercle when the knee is in full extension. An average Q-angle for a male is 14º, whereas that for a female is 17º. Q-angles larger than average can indicate abnormal patellar tracking.

Other factors that may affect the vector force on the patella include the following:

• Femoral anteversion
• Tibial torsion
• Hyperpronation of the foot
• Atrophy of the VMO muscle
• A tight lateral retinaculum
• Patella position (patella alta/baja or subluxation)
• Inflexibility of the quadriceps, hamstring, iliotibial, and calf muscle-tendon units
• General ligamentous laxity

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

The presenting symptom in patients with patellofemoral joint syndrome is knee >pain.

• The quality of the knee pain varies from dull and achy to sharp and shooting; occasionally, there is a burning sensation.
• The location of the pain may also vary. The pain may be described as anterior knee pain, retropatellar knee pain, peripatellar knee pain, global knee pain, posterior knee pain, joint line pain, or a combination of these.
• Patients may complain of painful or painless retropatellar crepitation. Symptoms may also include a painful catching sensation and a painful giving way of the knee.
• The pain may have an obvious etiology. Pain is often related to overuse or a change in exercise intensity.
• • Some activities that frequently trigger symptomatology are stair climbing, uphill running, hiking, deep knee bends, and squatting. The pain is often not noted until completion of the activity. The patient may also complain of pain with prolonged sitting in which the knees are in flexion.
  • Pain may be related to trauma, most frequently from falls onto the anterior knee or from the impact of the knees on the dashboard in motor vehicle accidents. Most commonly though, an inciting event cannot be determined.
  • A family history of anterior knee pain may be positive.
  • Children going through growth spurts may experience painful knees, which occurs as the bone grows and stimulates musculotendinous growth through traction. This results in a relative period of inflexibility, which translates to abnormal vector forces placed at the patella and patellar maltracking.

Related eMedicine topics:
Knee Injury, Soft Tissue
Knee Osteochondritis Dissecans
Osgood-Schlatter Disease
Overuse Injury

Related Medscape topics:
Resource Center Adolescent Medicine
Resource Center Exercise and Sports Medicine
Resource Center Genomic Medicine

Physical

• The clinician should make a general observation for the presence of any predisposing factors, which may include the following:
• • Gait (walking and running) – Inversion/eversion of the hindfoot
  • Femoral anteversion or tibial torsion
  • Genu varus, genu valgus, or genu recurvatum
  • Foot with pes planus or pronation
• Examination of the tibiofemoral joint (the anterior knee, not the joint lines) should include the following:
• • Assess range of motion (ROM). Most often the ROM is within normal limits; genu recurvatum may be present.
  • Look for the presence of any effusion, which is often absent.
  • Assess for ligamentous laxity. No laxity should be noted.
  • Assess for joint line tenderness, which is more prone to be present anteriorly if it is elicited.
  • Perform the McMurray maneuver, in which the examiner concurrently extends and rotates the patient's affected lower limb. When the patient complains of pain with this maneuver, the pain is usually localized to the anterior knee.
• Examination of the patellofemoral joint
• • Observe the position of the patella with the knee in 90° of flexion. Patella alta, patella baja, or patellar lateralization may be present.
  • Observe patellar tracking in terminal extension (30-0°). A J-curve may be present.
  • Assess the patellar glide. A tight lateral retinaculum can decrease the medial glide. A medial glide of less than 5 mm (1 quadrant) can indicate a tight retinaculum. If a positive apprehension sign (fear of the patella popping out of position) is elicited with assessment of the patellar glide, suspect a patella subluxation or dislocation.
  • Palpate for pain. Tenderness is often found on the patellar facets, the trochlea, and the peripatellar soft tissue. Tenderness to palpation at the superior or inferior poles of the patella usually indicates another pathology.
  • Assess the patella compression test. Compress and push the affected patella distally. Pain is a positive test associated with anterior knee pain. An active test, in which the patient contracts the quadriceps tendon against a compressed patella, has a high false-positive rate.
  • Assess the Q-angle. The Q-angle is the angle formed by a line created from the ASIS to the mid patella intersecting with a line created from the mid patella to the tibial tubercle with the knee in full extension. The average Q-angle for males is 14°, and the average for females is 17°. An increase in this angle can indicate abnormal patellar tracking.
• Muscle force vectors may be unequal and cause patellar maltracking.
• • Assess hamstring flexibility. Tight hamstrings antagonize the quadriceps function and increase patellofemoral joint loading. Iliotibial band and rectus femoris flexibility should likewise be assessed.

    In a study of 12 patients with patellofemoral pain syndrome, Hudson and Darthuy noted that these patients had a tighter iliotibial band.⁸ However, it was unclear whether patellofemoral pain syndrome is caused by or results in a tighter iliotibial band.

  • Assess the muscle bulk of the VMO. The VMO controls medial movement of the patella.

Related eMedicine topics:
Osgood-Schlatter Disease
Osteochondritis Dissecans
Patellar Injury and Dislocation
Pes Planus

Related Medscape topics:
Resource Center Adolescent Medicine
Resource Center Exercise and Sports Medicine

Causes

• Genetics may predispose a person to develop patellofemoral joint syndrome. Genetic factors that are commonly associated with this condition include the following:
• • Hyperlaxity of the knee (genu recurvatum) or patellofemoral joint
  • Genu varus or genu valgus
  • Femoral anteversion or tibial torsion
  • Wide pelvic girdle
  • Pes planus or pronation of the foot
  • Muscle tightness, which itself may have a genetic component
  • Abnormal concentration of forces over a smaller articular surface of the patellofemoral joint.
• This condition may either be caused or aggravated by overuse or a change in activity level. Repetitive knee flexion, especially on a weighted joint (eg, stair climbing, hiking, uphill running, kneeling, squatting, prolonged sitting with knee flexion) can cause symptomatology.
• Trauma can be the underlying cause.
• A forceful compression of the patellofemoral joint (eg, a fall onto the anterior knees, impact of the knees on a dashboard during a motor vehicle accident) may precipitate this condition.
• • Patellofemoral syndrome may occur after a patella subluxation or dislocation.
  • Patients may develop this condition after having ACL reconstruction with a bone-patellar tendon-bone technique. One year postoperatively, one third of these patients may have patellofemoral symptoms secondary to a weak quadriceps from patellar irritability or flexion contracture.
• Osgood-Schlatter disease may be a predisposing factor to the development of patellofemoral pain later in life.
• • These patients continue to have the predisposing factors, such as muscle imbalance, that caused the Osgood-Schlatter disease.
  • Assess muscle strength, particularly VMO strength. Weakness is often associated with a decrease in muscle bulk. VMO weakness causes poor patellar tracking. The VMO displaces the patella medially during knee extension, thus guiding it through the trochlear groove during quadriceps contraction.

Related eMedicine topics:
Knee Injury, Soft Tissue
Osgood-Schlatter Disease
Overuse Injury
Patellar Injury and Dislocation
Pes Planus

Related Medscape topics:
Resource Center Adolescent Medicine
Resource Center Exercise and Sports Medicine

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to Be Considered

Chondromalacia patella
Complex regional pain syndrome type I (Reflex sympathetic dystrophy)
Crystal arthropathy
Excessive lateral pressure syndrome
Infection
Legg-Calve-Perthes Disease
Loose body
Meniscal tear
Neoplasm
Osteochondritis dissecans
Rheumatoid arthritis / Psoriatic arthritis
Patellar/quadriceps tendinitis
Patellar subluxation
Plica
Postoperative considerations (after ACL reconstruction)
Sinding-Larsen-Johansson disease
Stress fracture of the hip or femur
Suprapatellar/prepatellar/infrapatellar tendinitis
Trauma from a direct blow to the knee

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Laboratory studies are not indicated for patellofemoral joint syndromes, unless there is a need to rule out other potential causes, such as systemic, inflammatory, or metabolic disease.
• • Erythrocyte sedimentation rate (ESR) is elevated in an inflammatory process.
  • Liver and renal function may be abnormal in metabolic disease.
  • Antibody tests are elevated for rheumatoid arthritis or ankylosing spondylitis.
  • Knee aspirates show an elevated white blood cell (WBC) count in an inflammatory process, an abnormal Gram stain and culture in infection, and crystals when crystal arthropathy is present.

Imaging Studies

• Radiographic imaging is not necessary to make the diagnosis of patellofemoral joint syndrome, but these studies can be helpful to the physician when excluding other potential causes (see Differentials and Other Problems to Be Considered). Particular findings can support the diagnosis, including the following:
• • Lateral plain films show the presence of patella alta or patella baja.
  • A sunrise or Merchant's view reveals lateral tilt and the relative height of the femoral condyles.
  • Magnetic resonance imaging (MRI), computed tomography (CT) scanning, and bone scanning are not needed in the evaluation of patellofemoral joint syndromes, but these imaging modalities may be used to evaluate other pathologic conditions of the knee if the diagnosis is in doubt. Dynamic CT scanning, 0-120º, is useful in assessing patellar tracking in recalcitrant cases in which surgery is being considered. This study can be used in the rare patient who is suspected of having a patellar tilt or subluxation but whose radiographs are normal.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Acute Phase

Rehabilitation Program

Physical Therapy

Conservative treatment is successful in 80% of cases of patellofemoral joint syndromes. The goal of treatment is to control the symptoms. Underlying strength and flexibility deficits need to be addressed. 

• Start by having the patient modify his/her activity level. Decrease activities that increase patellofemoral pressure (eg, jumping, squatting, kneeling). Gentle eccentric loading activities may be initiated.
• Apply ice for 10-15 minutes, 4-6 times per day, especially after activity.
• Increase muscle strength, especially of the VMO, with short-arc quadriceps sets, knee presses, isometric quadriceps sets, and straight-leg raises with the leg externally rotated. Biofeedback may aid in teaching recruitment of the VMO.
• Improve flexibility of the hamstrings, vastus lateralis, and iliotibial band. Stretch tight retinacular structures.
• Initiate proprioceptive exercises.
• Ultrasound or phonophoresis may decrease pain symptoms.
• A patellofemoral brace with a patella cutout and lateral stabilizer or McConnell taping/Kinesio Taping may improve neuromotor control of the patellofemoral joint by affecting the osseoligamentous structures through alteration of patellar tracking, improving proprioception, or a combination of these factors.^{9, 10}
• Provide arch supports or orthotics to correct foot malalignments.

Related eMedicine topics:
Lower Limb Orthotics
Virtual Reality Biofeedback in Chronic Pain and Psychiatry

Related Medscape topic:
Resource Center Exercise and Sports Medicine

Recreational Therapy

The patient should avoid any exacerbating activity (eg, deep knee bends, stair climbing, running, hiking). Initiate a home therapy program of flexibility, strengthening, and proprioceptive exercises. In addition, eccentric loading activities may be initiated.

Related Medscape topic:
Resource Center Exercise and Sports Medicine

Medical Issues/Complications

Give special consideration to young patients in whom conservative therapy fails. In such cases, entertain the possibility of referred pain from the hip (eg, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis).

Related eMedicine topics:
Legg-Calve-Perthes Disease
Slipped Capital Femoral Epiphysis

Related Medscape topic:
Resource Center Adolescent Medicine

Surgical Intervention

Surgical intervention is not appropriate in the acute phase. Surgery should be reserved for those in whom a conservative course of treatment of 6 months' duration was unsuccessful.^{9, 11, 12} Other more specific causes of anterior knee pain should be excluded first. Lateral retinacular release with or without medial capsular reefing may benefit active young adult patients who have not been helped by 12 months of nonoperative treatment and who have patellar tilt and/or subluxation.

Other Treatment

Analgesics, which may reduce pain, do not possess anti-inflammatory properties. Acetaminophen may be helpful for moderate pain; tramadol hydrochloride (HCl) may abort severe pain.¹³

Nonsteroidal anti-inflammatory drugs (NSAIDs) can aid in pain reduction and reduce the inflammatory component, which can be associated with this condition. In the acute phase, administer NSAIDs on a scheduled basis at sufficient doses to confer the anti-inflammatory benefits. Narcotics are not appropriate for this condition. For severe pain, corticosteroid injections may be beneficial.

Dietary food supplements may prove beneficial in a select group of patients. Glucosamine/chondroitin sulfate and hyaluronic acid may have the potential to provide the substrates used in regenerating the articular cartilaginous surfaces.¹⁴ To date, however, no scientific proof has been presented that this occurs, despite anecdotal reports that some people who take these supplements have reported decreased pain, decreased swelling, and improved joint mobility.

Potential future treatment may include viscosupplementation with an intra-articular injection. However, this is not a US Federal Drug Administration (FDA)–indicated treatment thus far, and future research needs to be undertaken. Hyaluronic acid may provide a scaffolding for rebuilding worn articular cartilage surfaces. 

Related Medscape topics:
Resource Center Pain Management: Advanced Approaches to Chronic Pain Management
Resource Center Pain Management: Pharmacologic Approaches

Recovery Phase

Rehabilitation Program

Physical Therapy

If formal physical therapy was utilized in the acute phase, the patient should start to be weaned to a home therapy program. Activity may be advanced as tolerated in a slow, progressive manner. The patient should be sure to continue the following:

• Emphasize flexibility, strengthening, and proprioception exercises. Maintain eccentric loading activities.
• Use ice as needed for pain or inflammatory relief, especially following activity.
• Use a patellofemoral brace or McConnell taping as needed for activity.
• Use arch supports or orthotics, as needed.

Recreational Therapy

Advance activity as tolerated in a slow, progressive manner. One suggested approach may be to decrease the previous volume and intensity training by 50%, and then if symptoms do not return, to increase activity by 10% each week.

Surgical Intervention

Surgical intervention is usually not appropriate in the recovery phase. Surgery should be reserved for those in whom a 12-month trial of conservative therapy was unsuccessful.

Other Treatment (Injection, manipulation, etc.)

Analgesics (acetaminophen and tramadol HCl), as well as NSAIDs, should be continued for those with persistent pain; for those whose pain resolves, wean off these drugs. These medications may be continued on an as-needed basis for individuals with activity-related pain.

Intra-articular corticosteroid injections may be useful in recalcitrant cases. Corticosteroid injections should never be injected into the patellar tendon because of the predisposition for tendon rupture that is associated with this procedure.

Maintenance Phase

Rehabilitation Program

Physical Therapy

Flexibility, strengthening, and proprioception programs should be continued indefinitely. Arch supports and orthotics should also be continued indefinitely. Braces and taping, as well as ice, may be weaned as progress permits.

Recreational Therapy

Activity may be progressed as tolerated.

Surgical Intervention

Surgery may be useful for patients who have been compliant and in whom a 12-month trial of conservative therapy was unsuccessful. Surgery may completely resolve the patient's symptomatology, partially resolve the symptomatology, or may not change the symptomatology; rarely is the symptomatology exacerbated iatrogenically. Surgery is more successful when a specific diagnosis has been established and when clear surgical goals can be defined.

Surgical intervention includes arthroscopy for articular cartilage shaving, with or without lateral release of the retinaculum. Surgery may also include proximal or distal realignment. Open surgical procedures include patellar tendon transfer, or rarely, patellectomy.

Other Treatment

Analgesics (acetaminophen and tramadol HCl) and NSAIDs may be beneficial on an as-needed basis. Dietary supplements may be helpful on an individual basis. Corticosteroid injections may be beneficial for recalcitrant cases.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Analgesics may provide pain relief (acetaminophen for moderate pain, tramadol HCl for severe pain). NSAIDs may alleviate the pain, as well as reduce the inflammatory component. Narcotic medication is not indicated for this condition.

Related Medscape topics:
Resource Center Pain Management: Advanced Approaches to Chronic Pain Management
Resource Center Pain Management: Pharmacologic Approaches

Drug Category: Analgesics

Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial for patients who have sustained trauma or who have sustained injuries.

Drug Category: Nonsteroidal Anti-inflammatory Drug (nsaid), Cox-2 Selective

COX-2 selective drugs are:

• Indicated for the relief of the signs and symptoms of osteoarthritis, rheumatoid arthritis in adults, and ankylosing spondylitis
• Indicated for the management of acute pain in adults
• Indicated for the treatment of primary dysmenorrhea
• Indicated to reduce the number of adenomatous colorectal polyps in familial adenomatous polyposis

Drug Category: Nonsteroidal Anti-inflammatory Drug (NSAID), Oral

NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. The mechanism of action of these agents is not known, but they may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation and various cell membrane functions. Many NSAIDs are currently on the market. In general, the mechanism of action of these agents is the same. No evidence exists that one NSAID is more efficacious than another; however, individual response may differ.

Related eMedicine topic:
Toxicity, Nonsteroidal Anti-inflammatory Agents

Drug Category: Dietary Supplements

Dietary supplements may provide nutrients that may play a role in the formation of cartilage.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Return to Play

Return to play or previous activity may be resumed when 80% of the strength of the uninjured knee (as measured by isokinetic testing) has been reached in the affected knee. If there has not been a significant loss of strength, the athlete may continue to play as symptoms allow. For those with loss of strength, continued play predisposes to injury secondary to guarding by the athlete.

Related Medscape topic:
Resource Center Exercise and Sports Medicine

Prevention

Prevention consists of correcting biomechanical imbalances. The patient should wear arch supports or orthotics for pes cavus or pronation of the foot. Promote flexibility, strengthening, and proprioceptive programs (particularly for the VMO).

Other preventative measures may be sport specific, depending upon the equipment being utilized. For example, with cycling, the seat height should be properly adjusted. For cyclists with femoral anteversion or tibial torsion, floating clips or shims on the pedals may prevent patellofemoral syndromes. For runners, proper shoe maintenance can prevent problems.

Moderation of frequency or intensity of activity can also prevent problems. When a new activity is initiated, it should be done in a slow, progressive manner. Intensity levels should not change drastically over relatively short time periods. Runners, in particular, often follow a 10% rule, in which distance or time is increased by 10% on weekly intervals.

Related Medscape topic:
Resource Center Exercise and Sports Medicine

Prognosis

Empiric treatment is successful in 80% of cases of patellofemoral joint syndrome. The treatment goal is to control the symptoms (ie, decrease the pain).

Education

Education consists of the clinician being able to describe the condition anatomically and biomechanically to the patient. Because the problem is primarily one of pain, educate athletes about flexibility, strengthening, and proprioceptive programs, as well as the importance of using the proper equipment.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• The only medicolegal pitfall is misdiagnosis of the condition.

Related Medscape topic:
Resource Center Medical Malpractice and Legal Issues

Special Concerns

• A special consideration in young patients is that knee pain can be referred from the hip. Those patients who fail to respond to treatment warrant radiography of the hip to rule out Legg-Calvé-Perthes disease or slipped capital femoral epiphysis.
• Additionally, pain and tenderness to palpation at the inferior pole of the patella may indicate apophysitis (Sinding-Larsen-Johansson disease).

Related eMedicine topics:
Legg-Calve-Perthes Disease
Slipped Capital Femoral Epiphysis

Related Medscape topics:
Resource Center Adolescent Medicine
Resource Center Pain Management: Advanced Approaches to Chronic Pain Management
Resource Center Pain Management: Pharmacologic Approaches

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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2. Scuderi GR, ed. The Patella. New York, NY: Springer-Verlag; 1995:xii-351.
3. Wertheimer C. Patellofemoral mechanics as a cause of anterior knee pain. Your Patient and Fitness. 1995;9:19-23.
4. Eilert RE. Adolescent anterior knee pain. Pediatric Orthopedics. Philadelphia, Pa: Lippincott-Raven; 1991:499-515.
5. Ruffin MT 5th, Kiningham RB. Anterior knee pain: the challenge of patellofemoral syndrome. Am Fam Physician. Jan 1993;47(1):185-94. [Medline].
6. Pizzutillo PD. Osteochondroses. In: Sullivan JA, Grana WA, eds. The Pediatric Athlete. Park Ridge, Ill: American Academy of Orthopaedic Surgeons; 1990:224.
7. Walsh WM. Knee injuries. In: Mellion MB, Walsh WM, Shelton GL, eds. The Team Physician's Handbook. Philadelphia, Pa: Hanley & Belfus; 1990:414-39.
8. Hudson Z, Darthuy E. Iliotibial band tightness and patellofemoral pain syndrome: a case-control study. Man Ther. Feb 28 2008;epub ahead of print. [Medline].
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10. Cowan SM, Bennell KL, Hodges PW. Therapeutic patellar taping changes the timing of vasti muscle activation in people with patellofemoral pain syndrome. Clin J Sport Med. Nov 2002;12(6):339-47. [Medline].
11. Earl JE, Vetter CS. Patellofemoral pain. Phys Med Rehabil Clin N Am. Aug 2007;18(3):439-58, viii. [Medline].
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13. Weil EK. Pain and pyrexia. Residents' Edition Prescribing Reference. 5^th ed. New York, NY: Prescribing Reference, Inc; 1996:164-8.
14. Kelly GS. The role of glucosamine sulfate and chondroitin sulfates in the treatment of degenerative joint disease. Altern Med Rev. Feb 1998;3(1):27-39. [Medline]. [Full Text].
15. Freeman AJ, Jacobson NA, Fogg QA. Anatomical variations of the plantaris muscle and a potential role in patellofemoral pain syndrome. Clin Anat. Mar 2008;21(2):178-81. [Medline].
16. Liebensteiner MC, Szubski C, Raschner C, et al. Frontal plane leg alignment and muscular activity during maximum eccentric contractions in individuals with and without patellofemoral pain syndrome. Knee. Feb 21 2008;epub ahead of print. [Medline].
17. Vicenzino B, Collins N, Crossley K, et al. Foot orthoses and physiotherapy in the treatment of patellofemoral pain syndrome: a randomised clinical trial. BMC Musculoskelet Disord. Feb 27 2008;9(1):27. [Medline]. [Full Text].

Article Last Updated: Mar 22, 2008