Investigation of Muscle Activity Pattern of Gluteus Medius and Tensor Fascia Lata in Patients with PFPS

Background：Previous literature reported that patients with patellofemoral pain syndrome (PFPS) have impaired hip abductors. Gluteus medius(Gm) is the major component of hip abductors muscle group. Janda V. stated in 1983 that weakness in the Gm leads to early firing, overactivation, and tightness of the tensor fascia lata (TFL) and iliotibial band(ITB). There are no electromyography studies of Gm and TFL in patients with PFPS, and no studies about the relationship between strength of hip abductors, flexibility of ITB and muscle activity patterns of Gm and TFL in this population.
Purposes：To investigate the muscle activity patterns of Gm and TFL in a healthy control group and a group of patients with PFPS in submaximal isometric muscle contraction. If the results of the investigation show a difference, then a second phase of research will be conducted to identify the relationship between strength of hip abductors, flexibility of ITB and muscle activity patterns of Gm and TFL.
Methods and Measurements：The experimental group was comprised of thirty patients with PFPF, while the control group for this study was composed of thirty gender- and age- matched healthy subjects. The study examined electromyography（BIOPAC MP100WSW system）firing patterns, including pre-motor time and muscle firing amplitude in gluteus medius and tensor fascia lata during eight second submaximal isometric muscle contraction while patients lied on their sides. Isokinetic muscle strength of hip abductors was tested using Cybex 6000 with the speed set at 30 degrees per second. ITB flexibility was measured with the Ober test using electro-inclinometer and pelvic stabilizer. Independent tests were performed on all variables between the two groups. Pearson correlation coefficient was used to identify the relationship between strength of hip abductors, flexibility of ITB and muscle activity pattern of Gm and TFL.
Results：In the PFPS group, Gm demonstrated delayed onset (p=.035) and higher muscle firing amplitude（p=.004）; TFL demonstrated lower muscle firing amplitude（p=.027）than the control group . The PFPS group had weak hip abductors(p=.014) and tightness of ITB(p<.000) . Muscle activity pattern of Gm and TFL only correlated with flexibility of ITB, not with strength of hip abductors.
Conclusion：Patients with PFPS had significant neuromuscular dysfunction, including pre-motor time and muscle firing amplitude, in Gm and TFL compared with the healthy control group. But the hypothesis that weakness in the Gm leads to early firing, overactivation, and tightness of the tensor fascia lata (TFL) and iliotibial band(ITB) was not observed in this study.