Greater Q angle may not be a risk factor of Patellofemoral Pain Syndrome

Abstract

Background

A greater Q-angle has been suggested as a risk factor for Patellofemoral Pain Syndrome. Greater frontal plane knee moment and impulse have been found to play a functional role in the onset of Patellofemoral Pain Syndrome in a running population. Therefore, the purpose of this investigation was to determine the relationship between Q-angle and the magnitude of knee abduction moment and impulse during running.

Methods

Q-angle was statically measured, using a goniometer from three markers on the anterior superior iliac spine, the midpoint of the patella and the tibial tuberosity. Thirty-one recreational runners (21 males and 10 females) performed 8–10 trials running at 4 m/s (SD 0.2) on a 30 m-runway. Absolute and normalized knee moment and impulse were calculated and correlated with Q-angle.

Findings

Negative correlations between Q-angle and the magnitude of peak knee abduction moment (R² = 0.2444, R = − 0.4944, P = 0.005) and impulse (R² = 0.2563, R = − 0.5063, P = 0.004) were found. Additionally, negative correlations between Q-angle and the magnitude of weight normalized knee abduction moment (R² = 0.1842, R = − 0.4292, P = 0.016) and impulse (R² = 0.2304, R = − 0.4801, P = 0.006) were found.

Interpretation

The findings indicate that greater Q-angle, which is actually associated with decreased frontal plane knee abduction moment and impulse during running, may not be a risk factor of Patellofemoral Pain Syndrome.

Introduction

Q-angle is defined as the angle between the line connecting the anterior superior iliac spine (ASIS) to the center of the patella, and the extension of a line from the tibial tubercle to the same reference point on the patella (Brattstroem, 1964). An angle greater than 15° for men and 20° for women is considered clinically abnormal (Horton and Hall, 1989). Q-angle has been suggested as a risk factor that could account for the development of lower extremity overuse injuries such as stress fractures (Cowan et al., 1996) or Patellofemoral Pain Syndrome (PFPS) (Messier et al., 1991, Powers, 2003).

PFPS is known as the most common lower extremity injury encountered during running (Fagan and Delahunt, 2008). In their extensive review, Taunton et al. (2002) reported that the knee joint was the most commonly injured joint with almost half of these injuries being due to PFPS. Knee anatomy and various potential risk factors associated with PFPS have been studied in order to understand a possible injury mechanism and develop more effective treatments for injury. Several studies have suggested that a large Q-angle is a significant contributor to differences found between PFPS groups and non-injured groups (Messier et al., 1991, Moss et al., 1992). It has been speculated that enlarged Q-angles increase the lateral pull of the quadriceps muscles on the patella and place medial tensile stress on the surrounding soft tissues at the knee (Neely, 1998). Such increase of the lateral pull of the patella may lead to increased pressure on the lateral facet of the patella causing pain at the anterior knee (Tumia and Maffulli, 2002). However, other case studies (Caylor et al., 1993, Duffey et al., 2000) as well as a prospective study (Witvrouw et al., 2000) have suggested that Q-angle is not related to PFPS. Therefore, whether or not Q-angle is associated with the onset of PFPS in active runners is still under discussion.

The effect of Q-angle on the incidence of PFPS in an active population has been examined in prospective studies (Lun et al., 2004, Witvrouw et al., 2000). Witvrouw et al. (2000) monitored 282 male and female students in physical education classes over a two year period. They found 24 students who developed PFPS. The findings indicated that lower leg alignment, including Q-angle, is not associated with the development of PFPS. They suggested that muscle flexibility, general joint laxity and reflex response time of vastus medialis obligus and vastus lateralis muscles had a significant correlation with the incidence of PFPS. Lun et al. (2004) measured static lower limb alignment in 87 recreational runners before their training period and observed their injury history over six months of their usual training program. They found no strong evidence that lower extremity alignment is associated with running injuries, including PFPS. On the other hand, a retrospective analysis observed a total of 2002 patients with running related injuries (Taunton et al., 2002). The data showed that the most dominant overuse injury was PFPS, seen in 331 cases, followed by iliotibial band friction syndrome (168) and plantar fasciitis (158). Varus knee alignment was seen in 32% of PFPS patients while a high Q-angle was seen in only 6% of PFPS patients in their database. A prospective study by Cowan et al. (1996) monitored incidences of overuse injury in 294 male infantry trainees over twelve weeks' training and correlated these with the trainees' anatomic characteristics. They suggested that high Q-angles, more than 15°, increase the risk of overuse injury; however, they did not specify the types of overuse injuries in their study. Therefore, there is no strong support that greater Q-angle is associated with high increases of PFPS in recent prospective and retrospective studies.

Knee abduction impulse is quantified by integrating the resultant moment–time curve and represents the cumulative twisting load during the entire stance phase of running. Previous studies have suggested that joint moment, as measured by an inverse dynamics approach, is an indirect measure of joint loading (Andriacchi, 1994, Hurwitz et al., 1998, Schipplein and Andriacchi, 1991, Stefanyshyn et al., 2006). It has been suggested that knee abduction impulse is a good indicator of cumulative torque or twisting loads on the knee in the frontal plane (Stefanyshyn et al., 2006). Frontal plane knee abduction moment and impulse may be related to the development of PFPS since the disorder occurs on the lateral aspect of the patella (Cutbill et al., 1997). Stefanyshyn et al. (2006) have shown in both retrospective and prospective studies that PFPS patients exhibit greater knee abduction impulses than comparable healthy runners. Since Q-angle affects knee alignment in the frontal plane, the moment arm distance between knee joint center and the external ground reaction force during the stance phase may change, and the frontal plane knee abduction moment or impulse could also change. However, it is questionable whether Q-angle affects frontal plane knee moment and impulse in a manner that may be related to the onset of PFPS in an active sports population. Furthermore, whether Q-angle is associated with the dynamic internal loading of the knee is unknown since lower limb alignment is measured in a static situation (Harrington, 1983). We hypothesized that Q-angle would not be correlated with frontal plane knee moment or impulse during the stance phase of running. The purpose of this investigation was to determine the relationship between Q-angle and the magnitude of knee abduction moment and impulse in healthy subjects.