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Anterior Knee Pain

Introduction

The differential diagnosis list is long when considering the etiology of anterior knee pain. Patellofemoral symptoms may be either of pain or instability (dislocation/subluxation).

Anatomy

  • The patella has the thickest articular cartilage in the body and may be up to 6.5mm thick.
  • The patella has a medial and lateral facet. Additionally, ~75% of people have an additional medial facet, "the odd facet", that articulates with the femur beyond 120 degrees of flexion .
  • The femoral articulation consists of the trochlea and the femoral condyles. The ridge of the lateral condyle is more prominent than the medial ridge on lateral radiographs of the knee. The "central sulcus" or "trochlear groove" is located between the condyles. 
  • Many ranges of normal Q angles have been reported and range from 10 -20 degrees in females and 8-14 degrees in males .
  • Static stabilizers: quadriceps and patellar tendons, congruence of articular surfaces, medal patellofemoral ligament (MPFL), patellomeniscal ligaments.
  • Dynamic stabilizers: quadricep muscles,
  • Patellar height: Insall-Salvati ratio 
    • Normal ratio = 0.8 - 1.2 
    • Patella Baja < 0.8 
    • Patella Alta > 1.2
  • Anatomy associated with abnormal patellar tracking:** hypoplastic trochlea** hypoplastic vastus medialis oblique** rotational malalignment of the proximal tibia
    • abnormal structure of patellar articular surface

Biomechanics

  • The forces acting on the patella include the pull of the quadriceps, tension from the patellar tendon, and the joint reaction force of the patellofemoral joint. As the knee flexes the point of articulation on the patella moves from distal to proximal. Forces through the patella range from approximately 1.5x body weight at 30 degrees of flexion to 6 times body weight at 90 degrees of flexion .
  • Patellofemoral joint reaction force for various activities:** Walking: ½ body weight** Descending and ascending stairs: 2-3x body weight** Squatting/running: 6.5x body weight

Pathogeneis

Describe the biologic basis of the disorder or the mechanism of injury

Natural History

Describe the natural history,epidemiology and prognosis

Patient History

Patellofemoral Arthritis: anterior knee pain that may radiate medially or posteriorly and is exacerbated with descending stairs or with prolonged knee flexion.

Physical Findings

The exam is performed in three parts: standing, sitting and supine

1. Standing

  • Axial alignment (Toes must be pointed straight forward)
    • Note orientation of patella
    • measurement of the Q angle
      • angle formed by lines drawn from the anterior superior iliac spine to the center of patella, and from the center of the patella to the tibial tubercle.
      • Many ranges of normal Q angles have been reported and range from 10 -20 degrees in females and 8-14 degrees in males .
      • Increased Q angles may result in increased valgus forces on the patella leading to lateral subluxation, lateral tilt, and increased joint reaction forces at the lateral facet.
      • A wide pelvis and increased femoral anteversion contribute to genu valgum and an increased Q angle
  • Gait assessment
    • antalgic? varus/valgus thrust? limb length discrepancy?
  • Half-squat test: patient is asked to hold a squat position. Pain is highly suggestive of patellofemoral symptoms.

2. Sitting

  • Thigh circumference/symmetry
  • Vastus medialis size
  • Position of patella
    • patella alta is common in patients with patellofemoral disorders
    • "grasshopper eyes" - patella alta with lateral tilt
    • patellar rotation (inferior pole is normally lateral to superior pole)
  • assessment of patellar tracking
    • J sign - lateral subluxation of patella in terminal extension (abnormal).

3. Supine

  • Palpation
    • Effusion?
    • Patellar pole, patellar facets, femoral epicondyles, joint lines, gerdy's tubercle, fibular head, pes anserinus
  • Active Quadriceps pull test - with knee in full extension ask patient to flex quadriceps. Lateral deviation of patella is abnormal.
  • Patellar grind test - Push patella into the femoral sulcus and ask patient to flex quadriceps
  • Patellar apprehension sign of Fairbank - A test for patellofemoral instability. With knee flexed 20 degrees, a laterally directed force is applied to the patella. A positive test occurs when the patient fears patellar dislocation and guards by contracting their quadriceps muscle.
  • Passive patellar glide test - Knee is flexed to 20-30 degrees. Medial or laterally directed force is applied to the patella. if There is >100% displacement laterally, the medial retinaculum is likely incompetent. If the patella subluxes less than 33% medially, the lateral retinaculum is likely tight.
  • Passive patellar tilt test - With knee in full extension the examiner attempts to tilt the lateral edge of the patella away from the femur. Normally it is possible to elevate the lateral patella. If one is unable to tilt the patella, a neutral or negative patellar tilt angle is present and indicative of a tight lateral retinaculum.

Imaging and Diagnostic Studies

Plain X-ray
  • malalignment, abnormal patellar height, patellar tilt, hypoplastic trochlea, patella alta/baja
CT
  • tibial tuberosity - trochlear grove (TT-TG) distance
MRI
Arthroscopy

Outerbridge Classification of chondral lesions:

  • Grade 0 - normal
  • Grade I - cartilage with softening and swelling
  • Grade II - partial thickness defect with fissures  that do not reach the depth of subchondral bone nor exceeds 1.5 cm in diameter
  • Grade III - fisures to the level of subchondral bone with diameter greater than 1.5 cm
  • Grade IV - exposed subchondral bone

International Cartilage Repair Society (ICRS) Hyaline Cartilage Classification System

  • ICRS 0 - normal
  • ICRS 1a - intact surface but fibrillation and/or slight softening
  • ICRS 1b - Includes ICRS 1a lesions and additional superficial lacerations and fissures (nearly normal)
  • ICRS 2 - lesions that involve <50% of cartilage thickness (abnormal)
  • ICRS 3 - lesions that extend through >50% of the cartilage thickness but not through subchondral bone plate (severely abnormal)
    • 3a - lesions > 50% of cartilage depth but do not extend to the calcified layer
    • 3b - lesions that extend to the calcified layer
    • 3c - lesions that extend down to, but not through, the subchondral bone
    • 3d - blisters
  • ICRS 4 - lesions that extend into subchondral bone (severely abnormal) (excluding osteochondritis dissicans lesions, which have their own classification system)

Differential Diagnosis

Differential diagnosis by symptoms:

Constant pain, not activity related:

  • Sympathetic-mediated
  • Postoperative neuroma
  • Referred radicular pain

Sharp, intermittent pain

  • Loose bodies
  • Unstable chondral pathology

Activity-related pain

  • Patellofemoral Pain Syndrome
  • Soft tissue overload without patellar malalignment
    • patellar tendonitis
    • quadriceps tendonitis
    • pathologic plica syndrome
    • fat pad syndrome
    • ITB syndrome
    • early lateral patellar compression syndrome
  • Articular tissue overload
    • posttraumatic chondromalacia or arthrosis
    • degenerative arthrosis from chronic malalignment
  • Inflammatory arthritides, myalgias
  • Systemic disease or illnesss producing weakness and general deconditioning

Instability

Treatment - Patellofemoral Pain Syndrome

Nonoperative treatment

  • Medical therapy
  • Physical therapy: Typically involves three months of therapy. Therapy should focus on quadriceps strengthening, as well as strengthening of muscles crossing the hip joint. Increasing flexibility, particularly stretching the quadriceps, is an important component as well. One prospective randomized trial has reported no difference in subjective or functional outcomes at 5 years follow up when comparing closed to open kinetic chain exercises . A Cohrane Database systematic review has come to similar conclusion regarding open vs. closed kinetic chain exercises for the treatment of patellofemoral pain syndrome . Rehabilitation programs should consider keeping the knee within the 0-45 degree flexion arc, where the patellofemoral joint reaction force is smallest (50-90% the force of the quadriceps).

Operative treatment

  • Lateral retinacular release: Consider for patients with patellar tilt and/or increased lateral facet pressure (patellar tilting on CT scan, Sage sign). A lateral release that includes the deep transverse component of the tendon of the vastus lateralis may be effective in correcting the patellar tilt. Results are not as good in patients with grade III/IV chondromalacia affecting the patellofemoral articulation and patients in whom the predominant pathology is patellar instability rather than lateral tightness .
  • Chondroplasty: Consider for patients with grade II/III chondral lesions.

Treatment - Patellofemoral Arthritis

Nonoperative treatment

Physical therapy - Quadricpes and hamstring stretching. VMO strengthening. Isometric and short-arc closed-chain concentric and eccentric strengthening . Core strengthening. Soft tissue stretching directed at the lateral retinacular structures . Patellar McConnell tape technique may be useful in cases where significant patellar subluxation and/or tilt are present. Aquatic therapy may be useful when standard therapy exacerbates symptoms, particularly for the obese patient.

Bracing - Variable results and limited data, however their use is reasonable.

Oral antiinflamatories -

Activity Modification -

Operative treatment

Proximal realignment procedures

If one is to consider realignment of a patella that has radiographic evidence of subluxation, at a minimum one must address the medial soft tissue restraints.

  • Lateral retinacular release - Consider an isolated lateral retinacular release when there is lateral patellofemoral arthritis, radiographic evidence of lateral patellar tilt without subluxation, and no history of patellar instability .
Distal Realignment Procedures

Tibial Tubercle Transfer Osteotomies -The four principles of successful tibial tubercle transfer are: 1)restore or maintain proper balance of the extensor mechanism; 2) Transfer load from degenerative area of patellofemoral joint onto healthier cartilage; 3) Treat retinacular sources of pain; 4) perform the osteotomy in a way that allows early motion and rapid healing . Relative contraindications to osteotomies include tobacco use, morbid obesity, and diabetes. In general, anteromedial transfer is the best option in a young patient with distal and/or lateral patellar articular lesions, even when there is bone on bone arthritis laterally . Diffuse degenerative changes may require patellofemoral replacement.

  • Medial tibial tubercle transfer - Consider if there is a lateral articular lesion and the patella is tracking laterally
    • Elmslie-Trillat Osteotomy:
    • Hauser Osteotomy: Has had poor results and is no longer indicated
  • Anterior tibial tubercle transfer - Consider is there is an isolated distal articular lesion and normal patellofemoral alignment. This technique brings the superior portion of the patella into contact with the femur earlier during flexion.
    • Maquet Osteotomy: Has had poor results and is no longer indicated
  • Anterolateral tibial tubercle transfer - Consider in patients status post prior realignment procedures who now have overload of the medial articulation and subsequent chondral pathology.
  • Anteromedial tibial tubercle transfer "The Fulkerson Procedure" - allows unloading of the distal and lateral aspects of the patella. -Distal and lateral patellar cartilage degeneration is the most common pattern seen .
Autologous Chondrocyte Implantation

Treatment of choice for patients with disabling anterior knee pain due to large (4-6 sq. cm), contained chondral defects, in which the patellofemoral joint space remains intact radiographically . Correcting the cause of the chondral injury is essential. Postop rehab is significant as patients are nonweightbearing and must use a CPM 6-8 hours per day for approximately 6 weeks. Full weight bearing begins by four months, inline running at 12-18 months, and cutting activities no earlier than 18 months.

Patellectomy

Associated with poor results, including variable pain relief, substantial loss of power, instability, and extensor lag . Results have been best in patients with severe patellofemoral arthrosis, however, it should be viewed as a salvage procedure .

Patellofemoral Replacement

Indicated in younger patients with isolated, end-stage patellofemoral arthritis in which the patellofemoral degeneration is diffuse, and there is minimal or no malalignment. Improved results have been seen with patellofemoral replacement .

Total Knee Arthroplasty

Age younger than 55 is considered a relative contraindication . Special attention must be given to proper alignment of the extensor mechanism. Complications involving the extensor mechanism and patellofemoral joint remain the most common noninfectious reason for performing a revision total knee arthroplasty .

Pearls and Pitfalls

Tips and problems to avoid

Postoperative Care

Include immediate postoperative care and rehabilitation

Outcome

Include functional and prosthetic survivorship data as applicable

Complications

Include overview of complications

Selected References

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