knee joint moments and patellofemoral pain syndrome in runners part i

KNEE JOINT MOMENTS AND PATELLOFEMORAL PAIN SYNDROME IN RUNNERS
PART I: A CASE CONTROL STUDY; PART II: A PROSPECTIVE COHORT STUDY
D.J. Stefanyshyn 1 , P. Stergiou 1 , V.M.Y. Lun 2 , W.H. Meeuwisse 2 , B.M. Nigg 1
1 Human Performance Laboratory, University of Calgary, Calgary, Alberta
2 Sport Medicine Centre, University of Calgary, Calgary, Alberta
INTRODUCTION
The knee has been shown to be the most common site of running injuries and
Patellofemoral Pain Syndrome (PFPS) has been shown to be the most common diagnosis
within the area of the knee 1 . There is a lack of understanding as to the factors responsible
for the onset of PFPS in runners. Some researchers have speculated that the mechanical
etiology of PFPS in runners may be an increased internal rotation of the tibia caused by an
increased pronation of the foot during the stance phase in running 2,3 . Others have shown
factors such as Q-angle to be strong discriminators between runners with and without
PFPS 4 . It may be speculated that knee joint loading (i.e., knee joint moments) may play a
functional role in the onset of PFPS in runners. Also, there exists a lack of prospective
studies which have identified risk factors related to running injuries 5 . Therefore, the
purposes of these studies were to 1) identify functional variables which may be related to
PFPS in runners through a Case Control study design and 2) to see if these factors are
related to the onset of PFPS in a group of runners with the use of a Prospective Cohort
Study.
METHODS
Case Control Study
Two groups of runners were used as subjects in this study. The first group (n=20) included
runners who had been positively diagnosed with PFPS. The second group (n=20) included
runners who had never been diagnosed with PFPS. Kinematic data were collected using a
4-camera high speed (200 Hz) 3-dimensional motion analysis system. Reflective markers
(3 per segment) were placed on the rearfoot, lower leg and upper leg. Kinetic data were
collected (1000 Hz) using a force platform. Three trials were collected per subject. The
running speed (4.0 +/- 0.2 m/s) was monitored using two photo cells at shoulder height.
All trials were collected with the subject running in the same shoe (Adidas Cushion). A
standard inverse dynamics approach was used to calculate the knee joint moments in 3-
dimensions and these were compared between the two groups using an ANOVA.
Prospective Cohort Study
Baseline biomechanical data were collected using a similar procedure as mentioned above
on 145 runners prior to the beginning of the summer running season. During a 6 month
period, a total of 6 runners were diagnosed with PFPS. These 6 injured subjects were
matched to 12 non-injured subjects (2 matched controls per injured subject). The criteria
for matching subjects included that the non-injured subjects had similar weekly training
distances, similar years of running experience, similar mass and same gender. A
comparison of knee joint moments in 3 dimensions was performed similar to the methods
used in Part I. Additionally, three barefoot running trials were collected for this part.
Results
Figures 1 and 2 present average curves of all of the subjects for the Case Control and the
Prospective studies, respectively. Table 1 summarizes all of the maximal values for both
studies. Table 2 summarizes the individual differences for each injured subject in the
Prospective Cohort Study.

Figure 1: Stance phase knee joint moments in the sagittal, frontal and transverse planes comparing asymptomatic
(n=20) to PFPS (n=20) runners, running heel-toe, with a shoe, at 4.0 m/s.(CASE CONTROL Study Design)
Figure 2: Stance phase knee joint moments in the sagittal, frontal and transverse planes comparing asymptomatic
(n=12) to PFPS (n=6) runners, running heel-toe, with a shoe, at 4.0 m/s.(PROSPECTIVE Study Design)
Knee Moment [Nm]
study condition group n
max extension (SD) p-value max abduction (SD) p-value max ext rotation (SD) p-value
asymp 20 124.1 (47.5) -103.1 (35.6) 27.9 (16.2)
case control shoe
0.69 0.16 0.14
pfps 20 129.1 (29.6) -127.3 (66.1) 35.8 (16.5)
asymp 12 132.1 (31.2) -49.9 (33.6) 12.9 (10.2)
shoe
0.05
0.16
0.12
pfps 6 101.7 (18.8) -74.7 (29.2) 21.5 (10.5)
prospective
asymp 12 128.9 (33.0) -45.5 (31.2) 11.8 (7.8)
barefoot
0.03 *
0.08
0.03 *
pfps 6 94.6 (16.1) -75.2 (27.0) 22.4 (10.2)
Table 1: Comparison of average maximal knee moments and standard deviations in the sagittal, frontal and transverse
planes for both study designs. Only shoe running was collected for the Case Control Study.
condition variable [unit] sub 1 sub 2 sub 3 sub 4 sub 5 sub 6
∆ (max extension moment) % -25.5 -23.8 -3.9 -18.5 -19.1 -47.5
shoe ∆ (max abduction moment) % 139.9 21.2 72.7 -48.1 73.8 38.6
∆ (max external rot moment) % 176.2 -14.0 96.9 -57.5 81.4 119.2
∆ (max extension moment) % -35.6 -27.5 -2.6 -32.0 -35.9 -25.8
barefoot ∆ (max abduction moment) % 165.1 81.5 89.4 -21.3 54.3 22.4
∆ (max external rot moment) % 239.7 74.5 129.2 -13.7 74.2 34.1
Table 2: Individual subject values for the Prospective Study. Values shown are differences in % from the average of the
asymptomatic group. A positive value indicates a higher moment compared to the asymptomatic average.
DISCUSSION
Increased knee joint loading in the frontal (ab-adduction moments) and transverse
(external-internal rotation moments) planes may lead to increased stresses within or around
the patellofemoral joint and thus leading to pain. Both maximal abduction and maximal
external rotation knee moments were approximately 20% higher for the injured runners in
the case control study. No statistical differences were seen. Results of the prospective
study showed a similar trend. These differences became statistically significant for the
external rotation moment when looking at barefoot running. More importantly, the PFPS
group had a 65% higher maximal knee abduction moment and a 90% higher maximal
external knee rotation moment. For the prospective study, individual differences revealed
that 5 of the 6 injured subjects had a 30% or greater value for the abduction and external
rotation moment for barefoot running. This pattern was also evident for 8 of the 20 injured
subjects in the Case Control study. There is a strong possibility that increased knee joint
moments are contributing factors leading to the onset of PFPS in runners.
REFERENCES
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2. James, S.L. et al. Amer J Spts Med 6(2): 40-49, 1978.
3. Nigg, B.M. et al. J Biomech 26(8): 909-916, 1993.
4. Messier, S.P. et al. Med Sci Spts Exec 23(9): 1008-1015, 1991.
5. Van Mechelen, W. Sports Med 19(3): 161-165, 1995.