Patellofemoral pain syndrome (PFPS) is one of the most prevalent musculoskeletal injuries seen by physiotherapists and sport medicine practitioners (Clement et al., 1981; Taunton et al., 2002). The aetiology of PFPS is not fully understood and may consist of multiple factors including lower leg and foot malalignment (Austermuehle, 2001; Fredericson et al., 2002; Tiberio, 1987). Bony abnormalities of the foot may cause a compensatory motion at the subtalar joint in order to attain normal function of the lower leg and foot during the gait cycle (Root et al., 1977; Tiberio, 1987). Excessive pronation of the subtalar joint particularly is thought to lead to patellofemoral disorders (Buchbinder et al., 1979; Duffey et al., 2000; Tiberio, 1987). The excessive subtalar joint pronation may delay external rotation of the leg, and therefore will inhibit supination of the foot (Donatelli, 1987; Tiberio, 1987). Excessive rearfoot pronation therefore may lead to abnormal tibia internal rotation which could possibly translate to greater stress on the knee structure, altering patella tracking (Buchbinder et al., 1979; Donatelli, 1987; Kaufman et al. , 1999; McClay et al., 1998; Tiberio, 1987). The delay in the external rotation of the leg appears to be a compensatory reaction at the tibiofemoral joint, hence it may produce patellofemoral pain symptoms (Buchbinder et al., 1979; Jernick et al., 1979; Tiberio, 1987).

There is controversy in the literature regarding the rearfoot posture of PFPS patients and it’s contribution to PFPS (Messier et al., 1991; Powers et al., 1995; Sutlive et al., 2004; Thomee et al., 1995; Witvrouw et al., 2000). Messier et al. (1991) found normal arched feet for subjects with anterior knee pain while, Witvrouw et al. (2000) indicated no significant differences in foot types between normals and subjects with patellofemoral pain. Additionally Thomee et al. (1995) reported no differences in the Relaxed Calcaneus Standing (RCS) angle relative to the lower leg or to the horizontal between controls and subjects with PFPS. Power et al. (1995) and Sutlive et al. (2004) however reported a varus rearfoot posture of subjects with PFPS when measuring subtalar joint neutral. Therefore rearfoot varus was suggested to be a factor in contributing to PFPS (Powers et al., 1995). The rearfoot angle in RCS was also shown to be in a valgus position in PFPS individuals (Sutlive et al., 2004). Differences between these studies may be related to the use of diverse population samples, the differing measures focused on the varying protocols and also the absence of a control group in some studies.

A study which includes Subtalar Joint Neutral and RCS clinical measurements and a video based methodology may assist to more fully understand the contribution of the rearfoot posture to PFPS. Functionally, measuring the Subtalar Joint Neutral Position during non-weight bearing position may provide information about leg alignment and existence of deformities (Elveru et al., 1988b; Root et al., 1977) in the rearfoot in PFPS subjects. Deformities in the rearfoot however may lead to a compensatory mechanism during weight bearing (Donatelli, 1987; Donatelli et al., 1999; Root et al., 1977). Consequently, accurate biomechanical assessment of the subtalar joint should also be done in a weight bearing position which represents the human function during walking as well as in a non weight bearing position (Lattanza et al., 1988).

As the functional structure of the foot is inherently three-dimensional (3D) the use of 3D static measurement of the rearfoot may reflect more accurately the rearfoot frontal plane position (Dahlman et al., 2002). Additionally measuring the 3D rearfoot may eliminate the possibility of bias from the examiner during relaxed standing, and therefore may assist objectively in identifying the rearfoot posture of PFPS subjects. Since measuring the Subtalar Joint Neutral Position requires manipulation of the foot by the examiner it may be difficult to measure it three dimensionally. However measuring the RCS posture three dimensionally in addition to the clinical simple two dimensional (2D) RCS measurement may provide complete and objective information about the rearfoot posture in this population during weight bearing position. As the aetiology of PFPS is still not fully clear, this study addressed the importance of including static rearfoot measurements in a clinical practice. Evaluation of rearfoot posture may assist clinicians to better understand the effect of rearfoot posture on PFPS and may add to the limited base evidence of studies with PFPS population. Currently, rearfoot measurements are not necessary included in routine musculoskeletal assessment in PFPS. The purpose of this study was to examine the rearfoot posture of subjects with PFPS including Subtalar Joint Neutral and 2D and 3D RCS postures in comparison to healthy controls. It was hypothesised that subjects with PFPS may show altered rearfoot posture in the rearfoot clinical measurements.

The study design was a cross sectional comparative investigation of the rearfoot measurements in a clinical group (patellofemoral pain syndrome) and a control group (asymptomatic). Prior to participation, all subjects were informed about the nature of the study and signed an informed consent, which was approved by the Human Ethics Committee of Southern Cross University (ECN-02-101).

The clinical group consisted of 13 females with unilateral PFPS diagnosed by a physiotherapist. Subjects mean age, body mass and height are presented in Table 1. PFPS subjects had symptoms on their right knee for mean of 11 years (range 1.5-30 years) and complained of pain during either ascending stairs, descending stairs, squatting or after prolonged sitting. Subjects with traumatic injury in the patellofemoral joint, patellar tendonitis (jumper’s knee), previous surgery, patella plica, ligament and meniscal disorders were excluded from the study. The control group consisted of 14 asymptomatic females with no history of congenital or traumatic deformity to their lower extremity (knee or foot). Subjects’ age, body mass and height are presented in Table 1. Asymptomatic subjects with severe foot deformities such as pes cavus and pes planus were excluded from the study.

The subject lay prone with the foot and ankle (to be measured) hanging 15-20 cm over the end of the table. The opposite limb was positioned in hip flexion, abduction and external rotation with the knee flexed and resting on the supporting surface (Elveru et al., 1988a; Wooden, 1990). With the foot perpendicular to the floor the examiner bisected the posterior lower leg and the posterior calcaneus using Sliding Calipers. The palpation method of measuring the Subtalar Joint Neutral position was based on Wooden (1990) and Elveru et al. (1988b). The foot to be measured was in dorsiflexion and the rearfoot passively pronated and supinated. When the head of the talus was felt equally between the lateral and medial sides, the subtalar joint was in neutral position (Elveru et al., 1988b; Wooden, 1990). The position of the subtalar in the neutral position was maintained and the angle formed by the longitudinal midline of the posterior calcaneus and the line drawn on the posterior lower leg was measured (Elveru et al., 1988b). One arm of the goniometer was placed on the lower leg bisection line while the other arm was placed on the calcaneal bisection line (Figure 1). The axis of the goniometer was placed between the malleoli in the frontal plane (McPoil et al., 1985).

The 2D Relaxed Standing position of the calcaneus was measured using a small international standard SFTR pocket joint goniometer (Baseline, overall length 15cm) while subjects were standing in full extension of the knee and relaxed on a raised platform (20 cm) with both heels on the edge of the platform (Lattanza et al., 1988; McPoil et al., 1996). The calcaneal bisection line was measured relative to the horizontal surface (Wooden, 1990). One arm of the goniometer was placed on the horizontal surface while the other arm was placed on the calcaneal bisection line (Figure 2). Subtalar Joint Neutral position and the 2D RCS were measured by the same examiner and reported for three trials. The static measurements were recorded as a deviation in degrees into inversion (negative values) or eversion (positive values) from the vertical.

The 3D RCS measurement of the rearfoot relative to the tibia was measured by attaching external retro-reflective markers to a tibia shell and the calcaneus. Four Panasonic WV-CL830/G colour CCTV cameras were used to record the external markers during the relaxed standing posture for a single trial. Peak Motus (version 7) software was used to capture and optimally filter the 3D trajectories of each marker. Filter level for smoothing was chosen for each axis using Jackson knee method and a Quintic Spline processor (Peak Performance Technologies, Peak Motus, version 7, user manual).

The rearfoot segment was defined by three 6-mm diameter external markers on the calcaneus: two markers on a line on the posterior aspect of the calcaneus, which bisected the heel in the frontal plane, one on the upper ridge and second on the lower ridge. A third marker was positioned on the lateral aspect of the calcaneus, approximately mid point in the vertical direction between markers one and two (McClay and Manal, 1998; Rattanaprasert et al., 1999). All the foot markers were attached to the calcaneus during weight bearing (resting standing) to decrease the error between skin marker and skeletal location (Maslen et al., 1994). Four 1.2-cm diameter reflective markers were attached to a tibia shell similar in position to Manal and McClay (2000). An individual tibia shell (20.5cm x 9 cm, 0.08kg), made of heated polyform material, (Rolyan), similar to Manal et al. (2000), was located at the lateral distal one third of the shank length while the subject was sitting with the tibia perpendicular to the floor. Sports tape was placed around the shank over the shell in order to maintain the position of the tibia shell. The first marker was located 30% of the shank length proximal to the lateral malleolus (Figure 3). Then the three markers remaining were positioned with a 20% of the shank length being the vertical and horizontal spacing between the four markers in lateral and anterior positions (Figure 3) (Manal et al., 2000). The angle of the rearfoot relative to the tibia was calculated according to Grood and Suntay (1983).

A one way ANOVA was used to investigate the differences between the groups in the rearfoot clinical measurements including Subtalar Joint Neutral and 2D and 3D RCS measurements. All variables were assessed for normal distribution (Shapiro- Wilk) prior to the statistical analyses and were conducted at the 95% level of significance. Intraclass Correlation Coefficient (ICC (3, 1)) and Percent Close Agreement (PCA) were used to assess reliability between trials for the Subtalar Joint Neutral and 2D RCS measurements for both groups.

The reliability trial to trial of the Subtalar Joint Neutral and 2D RCS for the control group was ICC (3, 1) = 0.76 and 0.82 respectively. For the clinical group the trial to trial showed ICC (3, 1) = 0.91 for subtalar joint neutral and ICC (3, 1) = 0.86 for RCS. The PCA between trial reliability showed 85% - 95% values were within one degree of agreement for the control group and 94% - 98% for the clinical group.

Significant (p < 0.001) difference was found for the mean age between the groups with no significant differences for body weight or height (Table 1). The 2D RCS was significantly different between the groups (p < 0.001, Table 1).

The 3D RCS showed significant differences between the groups (p = 0.001, Table 1). Also, Subtalar Joint Neutral position during non-weight bearing position showed a significant different between the groups (p = 0.04, Table 1).

The trial to trial reliability of the 2D RCS and Subtalar Joint Neutral position was good to excellent similar to previous reports (Diamond et al., 1989; Elveru et al., 1988a; Ogilvie et al., 1997; Sobel et al., 1999). Root et al. (1977) suggested that the “ideal foot ”should be when the Subtalar Joint Neutral position is aligned or parallel with the bisection line of the distal lower leg. However some investigators reported varus position of the calcaneus with values of 2°-8° to be normal, and therefore do not conform to the theoretical concept of the “ideal foot ”(Astrom et al., 1995; McPoil et al., 1988). For both the control and the clinical groups the mean of the Subtalar Joint Neutral was within the reported normal range (Astrom and Arvidson, 1995; McPoil et al., 1988). However, the clinical group demonstrated significantly more inverted position in Subtalar Joint Neutral measurement similar to Powers et al. (1995) and Sutlive et al. (2004). Rearfoot varus was found to be one of the most common bony deformities of the foot (Tiberio, 1988) which is present in 83% of a normal population (McPoil et al., 1988). It was suggested however that subjects with PFPS had higher incidence of rearfoot varus deformity (Powers et al., 1995). Although PFPS subjects were found to have some degree of rearfoot varus in the present study, the approximate 1 difference between the group means can be debated despite the statistical significance. Thus, rearfoot varus may be a factor in contributing to PFPS, however caution must be taken when generalising this finding to the entire PFPS population as only a small difference existed between the groups. Subtalar Joint Neutral position measurement provides information about the leg and foot alignment (Elveru et al., 1988b; Root et al., 1977) as well as adequate assessment of bony deformities (Powers et al., 1995). Therefore this measurement may be important to include in the evaluation process of PFPS individuals.

The 2D calcaneus angle values were lower compared to the 3D RCS angle. We measured the 2D calcaneus angle in standing relative to the laboratory axis and the 3D calcaneus angle in standing relative to the tibia. By reporting the calcaneal angle relative to the vertical laboratory axis, the tibia deviation was not included, hence smaller values of the RCS angle were observed as also reported by Astrom and Arvidson (1995).

The control group exhibited a relaxed standing posture angle similar to the normal range reported for healthy subjects with no foot or leg injuries (Astrom and Arvidson, 1995; McPoil and Cornwall, 1996). The literature however is equivocal in reported normal range. Sobel et al. (1999) reported higher values. Foot types however were not stated and the inclusion of subjects with severe foot valgus or varus although asymptomatic may have influenced the results of Sobel et al. (1999).

According to McPoil and Brocato, (1985) one of the criteria for classification as excessively pronated was 3 eversion relative to the vertical. Furthermore a value of more than 6 in relaxed calcaneal posture relative to the lower leg was suggested to represent a moderately pronated foot (Subotnick, 1975). Therefore, the results of the current study for 2D and 3D RCS angle indicated a slight to moderately pronated foot for PFPS similar to Sutlive et al. (2004).

The 2D and 3D RCS angle were significantly different between the current groups indicating a slight valgus position of the calcaneus relative to the vertical and relative to the lower leg for subjects with PFPS. Previous studies however reported no differences in RCS angle between controls and PFPS subjects using a goniometer measurement (Thomee et al., 1995; Witvrouw et al., 2000). However, similar values of the rearfoot 3D RCS angle were reported in Sutlive et al., (2004) although there was no comparison to a control group. The conflicting results between studies may be due to differing sample population and also protocol. The use of a three dimensional video method has eliminated examiner bias which maybe possibly inherent in the use of a goniometer. Different sample population may occur as the aetiology of PFPS may consist of multiple factors, and hence sampling populations as occurs for research purposes, does not necessarily result in similar samples. Differences in samples may affect the research outcomes, and therefore may explain the conflicting results between these studies. RCS measurement therefore may be an important addition to other clinical measurements taken to explore the underlying aetiology of subjects with PFPS, as this population may demonstrate an increased pronation of the rearfoot during weight bearing position.

Although differences in the mean age were found between the groups, it is unlikely that the changes found would be a result of age difference or degenerative process in the knee joint related to aging in the PFPS group. Changes due to age are suggested to occur above 55 years (Yanagida et al., 1997). Age-related diseases process, such as osteoarthritis, affect females mainly over 50 years of age (Hart et al., 1999; Hudelmaier et al., 2001; Kee, 2000; Lanyon et al., 2003; Lethbridge-Cejku et al., 1994; Oliveria et al., 1995), thereby it is unlikely that the differences found between the groups in the rearfoot posture would be related to the age difference.

The relaxed standing posture in the present study in combination with the subtalar joint neutral may indicate a subtalar joint eversion excursion of more than 4° during standing for the clinical group. According to Wooden (1990), in order to evaluate the total amount of eversion, Subtalar Joint Neutral (if inversion) should be added to the calculation of eversion. The mean STJN of the clinical group was 2.20 ± 1.51° inversion while the mean relaxed standing was 2.35 ± 1.41° eversion; therefore the subtalar joint was in 4.55° eversion. In contrast, the control group demonstrated inversion position in both measurements, suggesting less than 1° of subtalar joint eversion excursion. The larger excursion for the clinical group may indicate an increased subtalar joint eversion during weight bearing position. As subtalar joint varus has been suggested to be compensated by excessive subtalar joint eversion during motion (McPoil and Brocato, 1985; Root et al., 1977; Subotnick, 1981; Tiberio, 1988; Vogelbach et al., 1987), this compensation may partly explain the increased eversion during relaxed standing in the clinical group.

The rearfoot posture of PFPS subjects in the current study showed a small varus position of Subtalar Joint Neutral and a rearfoot valgus in relaxed standing posture when measured relative to the vertical and relative to the tibia. Subtalar joint varus may contribute to the increased eversion during relaxed standing in the PFPS group. As such, RCS and Subtalar Joint Neutral Position measurements may be an important addition to other clinical measurements taken to explore the underlying aetiology of subjects with PFPS.