The effects of quadriceps contraction on different patellofemoral alignment subtypes: an axial computed tomography study.
METHODS
Controlled laboratory study.


BACKGROUND
The effect of quadriceps contraction on patellar alignment in patients with patellofemoral pain syndrome (PFPS) is debated and may vary based on patellar alignment subtypes measured with the quadriceps relaxed.


OBJECTIVE
To determine if the effects of quadriceps contraction on patellar alignment differs (1) with respect to patellar alignment subtype in individuals with PFPS and (2) between symptomatic and asymptomatic knees in individuals with unilateral PFPS.


METHODS
Seventy-eight individuals, 47 with bilateral and 31 with unilateral PFPS, participated in the study. On axial computed tomography images with the knee in extension with quadriceps relaxed as well as contracted, patellar lateral condyle index (PLCI) and patellar tilt angle (PTA) were measured and analyzed. Based on the median PLCI and PTA alignment values measured with quadriceps relaxed for the 78 subjects, 4 subgroups of subjects were created: type 1, laterally displaced; type 2, laterally displaced and tilted; type 3, laterally tilted; and type 4, neither.


RESULTS
Quadriceps contraction caused an increase in PLCI in all patellar alignment types (P<.01), with no difference in the magnitude of the increase between types (P>.05). PTA decreased with quadriceps contraction in the subjects with the type 3 initial patellar alignment (P<.01), with a significant difference in the change in patellar alignment between the subjects with type 3 and type 1 initial patellar alignment (P=.004). For the 31 subjects with unilateral PFPS, quadriceps contraction caused a similar change in PLCI and PTA in both the symptomatic and asymptomatic knees.


CONCLUSIONS
The initial position of the patella with the quadriceps relaxed did not influence the change in PLCI with quadriceps contraction. For the 31 subjects with PFPS, there was no difference in initial alignment as well as in change of alignment with quadriceps contraction between symptomatic and asymptomatic knees.
School of Physical Therapy, College of Medicine, National Taiwan University, and Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan.
Mei-Hwa
MH
Jan
Da-Hon
DH
Lin
Chien-Ho Janice
CH
Lin
Yeong-Fwu
YF
Lin
Cheng-Kung
CK
Cheng
D000293:Adolescent; D000328:Adult; D046789:Chondromalacia Patellae / Q000000981:diagnostic imaging* / Q000503:physiopathology; D003937:Diagnosis, Differential; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D046788:Patellofemoral Pain Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult