Comparison of hip and knee strength in males with and without patellofemoral pain

Highlights

• Unlike females, males with patellofemoral pain (PFP) did not exhibit hip weakness.

• Males with PFP demonstrated less knee extensor strength than controls.

• Males with PFP may benefit more from a knee-based strengthening protocol.

• Clinicians should consider implementing sex-specific interventions for managing PFP.

Abstract

Objectives

The primary purpose of this study was to compare hip strength in males with and without patellofemoral pain (PFP). The secondary purpose was to compare knee strength in males with and without PFP.

Design

Secondary analysis of cross-sectional data for males with and without PFP from a larger randomized controlled trial examining hip and core versus knee-muscle strengthening for the treatment of PFP.

Setting

Laboratory setting.

Participants

Sixty-six males with PFP and 36 controls.

Main outcome measures

Peak isometric force for the hip abductors, external rotators, internal rotators, extensors, and knee extensors expressed as a percentage of body mass (%BM).

Results

No differences existed with respect to any of the hip strength measures (P > .05). Males with PFP demonstrated almost 17% less knee extensor strength than controls (mean difference = 7.3 %BM; 95% confidence interval, 1.3–13.4 %BM; t = 2.41; P = .02).

Conclusions

Unlike females, males with PFP did not demonstrate hip muscle weakness. However, differences did exist with knee extensor strength. These data provide preliminary evidence for the potential need for sex-specific interventions for individuals with PFP.

Introduction

Patellofemoral pain (PFP) is one of the most common knee pathologies experienced by active adults (Kannus et al., 1987, Taunton et al., 2002). PFP is thought to result from abnormal patella tracking that can lead to excessive lateral patellofemoral joint stress (Fulkerson, 2002). Factors like quadriceps weakness (Lankhorst et al., 2012, Pappas and Wong-Tom, 2012), delayed and/or reduced vastus medialis activation (Boling et al., 2006, Van Tiggelen et al., 2009), and reduced knee flexibility (Piva et al., 2005, Witvrouw et al., 2000a) have been identified in individuals with PFP. These factors have been examined based on the assumption that the patella moves laterally relative to a “fixed” femur during activities of daily living. Under this theory, clinicians typically have prescribed quadriceps strengthening exercises. Although quadriceps exercise has been considered the “gold standard” approach (Bolgla and Malone, 2005, Natri et al., 1998), many individuals continue to experience residual symptoms following this treatment approach (Nimon, Murray, Sandow, & Goodfellow, 1998).

Suboptimal outcomes have led researchers to investigate factors other than the patellofemoral joint. Powers (2003) has theorized that altered hip movement can increase the quadriceps angle (Q-angle) and lead to abnormal lateral patella tracking. Both excessive hip adduction and hip internal rotation increase the Q-angle by positioning the patella more medial relative to the fixed tibial tuberosity. Results from cadaveric studies have shown that these femoral movements cause increased lateral patella stress (Lee, Morris, & Csintalan, 2003).

Powers, Ward, Fredericson, Guillet, and Shellock (2003) and Souza, Draper, Fredericson, and Powers (2010) investigated this theory using kinematic magnetic resonance imaging in subjects with patella instability and PFP, respectively. For individuals with patella instability, Powers et al. (2003) assessed patella movement during non-weight bearing and weight bearing knee extension. These individuals demonstrated greater movement of the patella on the femur during non-weight bearing knee extension. The opposite movement occurred during weight bearing knee extension. Images during this maneuver showed movement of the femur under a relatively fixed patella.

Souza et al. (2010) compared patella movement in females with and without PFP during weight bearing knee extension. Like Powers et al. (2003), those with PFP demonstrated greater femoral internal rotation under a relatively stable patella than controls. Together, these data from both investigations were clinically important as individuals with PFP typically complain of pain during weight bearing activities (e.g., stair ambulation, running and jumping). They further highlighted the need to better understand the interrelationship between hip external rotator and abductor muscle function and lower extremity kinematics (Powers, 2010).

Souza and Powers (2009b) assessed the gluteus maximus, the strongest hip external rotator, in female runners with PFP. They identified gluteus maximus weakness as the only predictor variable for increased hip internal rotation. Dierks, Manal, Hamill, and Davis (2008) also reported increased hip adduction and hip abductor weakness following prolonged running in individuals with PFP. Moreover, Ferber, Kendall, and Farr (2011) reported increased hip abductor strength and reduced pain in runners with PFP following a 3-week hip abductor strengthening program.

Based on a systematic review, results from several studies support the presence of hip abductor and external rotator muscle weakness in females with PFP (Prins & van der Wurff, 2009). There also is emerging evidence regarding the benefits of hip abductor and external rotator strengthening exercises for females with PFP (Fukuda et al., 2012, Fukuda et al., 2010, Khayambashi et al., 2012, Mascal et al., 2003).

Only one investigation has compared the effects of hip strengthening to knee strengthening in males and females with PFP (Khayambashi, Fallah, Movahedi, Bagwell, & Powers, 2014). Eighteen males and 18 females with PFP participated in either a strengthening program targeting the posterolateral hip or quadriceps muscles. All subjects, regardless of group assignment, demonstrated improvements in pain and function. However, subjects in the hip strengthening group exhibited superior outcomes compared to those in the quadriceps group. These findings suggested that males with PFP also may benefit from a hip strengthening program. A limitation of this study was the exclusion of controls to determine if males with PFP exhibited hip weakness.

Although females are 2.2 times more likely to develop PFP than males (Boling, Padua, Marshall, Guskiewicz, Pyne, & Beutler, 2009), PFP remains a common overuse injury in active adults (Kannus et al., 1987, Taunton et al., 2002). Despite substantial evidence of hip and knee strength deficits in females with PFP, very little is known if similar impairments exist in males. Identification of these differences will help determine the need for sex-specific interventions for PFP.

The primary purpose of this study was to compare hip strength in males with and without PFP. The secondary purpose was to determine if males with PFP exhibited knee weakness compared to controls. We hypothesized that males with PFP would demonstrate less hip and knee strength than controls.