Knee pain - Patellofemoral

Summary

Dx and Mx a challenge. Overuse and muscular dysfunction common contributors. Initial management includes quads strengthening. Check footwear and add arch supports if necessary.

Background

Retropatellar / peripatellar pain from changes in patellofemoral joint.

Also referred to as anterior knee pain, runner’s knee, and chondromalacia patellae.

All ages but max younger adults and teenagers (growth spurt).

Causes

Overuse/overload, biomechanical and muscular dysfunction. Theories in bold below

Pes Planus (Pronation) - "Flat feet"

Combination of eversion, dorsiflexion and abduction of foot leads to compensatory internal rotation of tibia and femur, stressing patellofemoral fxn
Treat with medial foot arch support and footwear advice

Pes Cavus (High arched foot, supination)

Less cushioning for leg when foot strikes ground causes more stress on patellofemoral mechanism especially when running
Advise proper (cushioned) footwear with arch support

Muscular causes

Quads weakness causes instability. Treat with MVO exercises

Key Clinical Features

Gradual onset anterior knee pain (±bilateral) with exercise - particiularly squatting, hiking, running. Often worse going down hill
Rarely after patellar dislocation or direct trauma
±patellar crepitus
Pain free at rest but can also occur with prolonged sitting (movie-goer's sign)
Clinical Dx with Hx and patellar pain on squatting (80%) and patellar margin tenderness (70%)

Red Flags

Consitiutional symptoms
Effusion
Focal warmth/tenderness of infection/osteomyelitis?
Limp or limited hip ROM - perthes / SUFE
Effusion with locking - osteochondritis dessicans?

Investigations

Consider plain x-rays only if concern about Osteochondritis dessicans or rare neoplasm (red flags or lock / letting down)

Differential diagnoses

Hip pathology in children / adolescents
Lower patellar tender - Sinding Larson or Osgood Schlatter?
Effusion = another (cartilage/meniescal/ligamentous) pathology
Popping patellar subluxation?
Check for other joint symptoms (arthropathy)

Management

Quadriceps (especially VMO) exercises.
- Physiotherapy supervised hip, hamstring and calf iliotibial band stretching exercises (NNT 3.6)
Relative rest - initially, e.g. change to swimming in runners
Patient education (NNT 5 at 24 months)
Movie-goers should start walking regularly
Ice - particularly immediately after running (for 10 - 20 minutes)
No strong evidence for (or against) NSAIDs
Do not use knee splint / braces (unless physiotherapist requests)
Taping the knee - no strong evidence either way - physiotherapist can educate patient how to tape their knee for trial
Quality footwear - Arch support usually helps (NNT 4)
Surgery only for true chondromalacia (fraying retropatellar cartilage)
Spontaneous resolution. Masterful inactivity (by physician) may be best option in growing adolescents

Prognosis

Most patients do well with conservative management.