Table 1

Inclusion and exclusion criteria among patients with PFPS
The first stage (evaluation in the ORTON Orthopaedic Hospital or in the outpatient clinics of the public hospitals in the Helsinki area)
Inclusion criteria	Exclusion criteria

Age 18 – 40 years	Disabling general illness
Female or male	Reported knee ligamentous or meniscal injuries
Characteristic history of PFPS and symptoms lasting at least 6 months	Previous knee surgery
Patellofemoral pain during knee loading physical activity, such as jumping, running, squatting, or going up or down stairs	Physician diagnosed knee osteoarthritis
Patellofemoral pain when the knee was kept in flexion for a prolonged period, with relief on extension	A history of patellar dislocation; however, subjects with patellar subluxation are included in the study
	Other knee problems than PFPS diagnosed clinically (such as jumper's knee)
	Other knee problems than PFPS diagnosed radiographically (such as osteochondritis dissecans)
	Physical therapy for PFPS within the previous 4 weeks
	Pregnancy
	Competitive athlete

The second stage (orthopedic surgeon's clinical and radiological evaluation in ORTON)
Inclusion criteria	Exclusion criteria

As in stage one	Clear medio-lateral instability in manual instability measurement
	Knee problems other than PFPS
	Knee osteoarthritis
	Osteochondritis dissecans, loose bodies in the patellofemoral and tibiofemoral joints

Kettunen et al. BMC Medicine 2007 5:38 doi:10.1186/1741-7015-5-38