November 2014

The role of hip mobility in patellofemoral pain

11PFP-iStock11923686Findings of an association between hip mobility and patellofemoral pain suggest practitioners may be putting the cart before the horse by implementing strength programs in individuals with PFP without first measuring and addressing deficits in hip extension.

By Sean Roach, PhD, DPT, ATC

Patellofemoral pain (PFP) is a common condition seen in health provider practices.1 PFP is present in both men and women who are involved in running and running-related sports. The complaint can be described as general, spot-specific, or more often as anteromedial knee pain. It can also be referred to as anterior knee pain.2 Despite efforts aimed at the best management of PFP, its exact cause and ideal treatment remain somewhat elusive. Part of the problem may be the lack of an objective means of diagnosis. Although there is no general consensus as to the exact etiology of the condition, there are a number of proposed models.

One of the primary reasons for the lack of agreement on the mechanism of PFP may be due to the popularity of a symptom-based diagnostic model. In this common medical paradigm practitioners attempt to diagnose painful conditions by identifying the primary pain generators (eg, ligaments and muscles) associated with a condition as the primary causes of that condition.

LER-RG-Products-ad-patellofemoral

Historically, in the case of PFP, both investigators and practitioners appear to have decided that the patella and the trochlear groove—the painful regions—are involved in the primary mechanism underlying the condition. This is despite the fact that most sufferers of PFP cannot relate their pain to any specific mechanistic event, such as direct impact or other mechanical distortions of the knee region.

The symptom-based diagnostic model for PFP is in opposition to viewing the painful structures as the end result of abnormal loading from either distal or proximal segments.

Classical approach to PFP

In hopes of designing more effective prevention and treatment strategies, it is important to reflect on past historical perspectives of PFP management. Clinicians’ main focus in treating PFP traditionally has been on the patella and the soft tissue elements surrounding it. In particular, much work has been done evaluating the tracking and positioning of the patella within the femoral trochlea. The thought was (and remains among some adherents) that the patella is failing to move correctly within its intended path during flexion and extension of the knee in the performance of functional tasks.3

Although this maltracking, as it is referred to in the literature, does occur in some patients with PFP, imaging studies have been unable to differentiate between individuals with and without PFP on the basis of patellar tracking. In particular, axial radiographs of the knee joint demonstrate no significant differences between individuals who do and do not have PFP.4

Often, this maltracking is considered a result of the lateral knee components being overly tight and the medial structures being too weak. The implicated lateral structures are the iliotibial band (ITB) and its fascial components.5 The implicated medial structure is primarily the vastus medialis oblique (VMO) muscle, one of the muscles comprising the quadriceps group.6

The popularization of this paradigm, in which the etiology of PFP originates from the symptomatic region, resulted in a significant emphasis on anatomical correction of the knee structures through direct physical interventions. In the surgical world, this was manifested by releasing the “tightness” of the lateral knee soft tissue by incorporating procedures designed to correct patellar misalignment. The literature on the effectiveness of these procedures suggests the outcomes have been less than satisfactory.7

Other interventions focused on modalities to heat and stretch the ITB in hopes of achieving increased mobility and decreased lateral pulling. Although there is some evidence that “ITB stretching” can result in an increase in mobility of lateral trunk flexion, there is not strong evidence that the ITB itself is capable of being stretched.8 What many practitioners fail to recognize is that the ITB may not be amenable to isolated stretching.

Studies demonstrate that the ITB is a lateral thickening of the deep fascia of the lower extremity and has a fewer numbers of elastic fibers than the upper limb.9 In the author’s opinion these differences may help explain why stretching of the upper extremity can be a successful intervention, but the benefits may not be transferable to all components of the lower limb. Further evidence has raised questions about the relationship between ITB length and lateral displacement of the patella.10

Research regarding contractile elements affecting alignment of the patella has focused principally on quadriceps muscle strengthening.11 In particular, the VMO has often been singled out as a primary target. Some researchers have implicated the VMO as a primary anatomical structure involved in opposing lateral displacement of the patella.12 This concept may have been derived from examination of the muscle and the orientation of its fibers that extend into the patella.13 The view that the VMO plays a role in patellar maltracking has led to considerable effort, in practice and in studies, to isolate the VMO; it was believed that preferential recruitment of the VMO relative to the vastus lateralis (VL) would result in more ideal tracking of the patella. However, evidence has raised questions about whether the VMO is capable of being preferentially recruited.14

A recent systematic review and meta-analysis (total of six studies) investigated whether individuals with PFP demonstrated atrophy of the quadriceps compared with the unaffected extremity of those with unilateral PFP and compared with individuals without PFP.15 Interestingly, the authors noted that, in individuals with PFP, atrophy of the quadriceps was evident on images but not in terms of girth measurements. There was no or only insufficient evidence to show greater atrophy of the VMO than the VL.

The hip and PFP

This background is useful to keep in mind when discussing the emerging consideration of the hip, rather than the knee, as a primary mechanical factor in the development of PFP. Several investigators in the late 1990s and early 2000s began to examine in more detail how motion at the hip affected the structures about the knee. One important study looked at a small group of female patients with PFP and lateral subluxation of the patella using kinematic magnetic resonance imaging (MRI).16 This study compared nonweight-bearing (NWB) knee extension and weight-bearing (WB) knee extension during a single-leg squat movement. The results demonstrated that, in NWB knee extension, the patella was rotating over the femur, while in WB extension it could be more accurately described as the femur rotating under the patella. This was one of the first studies to assess objectively dynamic weight bearing in patients with PFP and began a shift in focus from the knee itself to the possible involvement of the hip.

This new paradigm started to consider the femur as a movable track and the patella as the equivalent of a passenger vehicle traveling along the track. If the patella position relative to the femur was primarily dependent on the underlying track, the question became which planes of motion needed to be evaluated during examination to best identify any abnormalities. The answer appeared to be the frontal and transverse planes.

Greater than normal hip adduction in the frontal plane and internal rotation of the femur in the transverse plane have been associated with excessive loading of the undersurface of the patella.17 These motions are controlled eccentrically through the gluteus medius and minimus in the frontal plane and the gluteus maximus and the small muscles involved in hip rotation in the transverse plane. Growing evidence has demonstrated that excessive hip motion in either plane can occur in individuals with PFP.18,19 Further investigations have demonstrated clear deficits in hip muscle force production, in particular the eccentric component of force production, in those with PFP compared with control groups.20,21

In the last decade we have witnessed a significant emphasis in PFP management on hip and trunk strengthening and neuromuscular reeducation. The focus on proximal structures affecting the patellofemoral joint is aimed at controlling the eccentric and isometric mechanics of the lateral and posterior structures about the hip.17 This is an issue of particular interest with regard to female PFP patients, as the risk for proximal factors contributing to PFP is higher in female patients than in their male counterparts.22

The interventions designed to influence force production at the hip include both weight-bearing and nonweight-bearing exercises. The strategies include a broad range of differing contractions in
isometric and isokinetic modes. It is important to include different forms of contractions into the rehabilitation process as functional tasks can require muscles to work at various lengths and speeds.23

Hip mobility and PFP

With the change in direction from the knee itself to more proximal variables as a primary factor in PFP, it is somewhat surprising that a major component may have been overlooked. The preponderance of research has focused on training the motor control and contractile elements, almost to the full exclusion of hip mobility. Few studies have examined hip mobility and its role in subjects with PFP.

In a case study of a girl aged 15 years, Cibulka noted asymmetry in hip rotation that, when normalized with interventions, ameliorated the PFP.24 Additional studies examining hip mobility asymmetries in relationship to their potential role in influencing conditions other than the hip are scarce. Those that are available focused on nonspecific chronic low back pain and further demonstrated a need for additional investigation of this important variable.

A growing number of studies have looked at the relationship between hip kinematics and PFP.17,25 These studies have noted a significant difference in kinematics between those with PFP and controls. The differences include increased knee valgus, hip internal rotation, and hip adduction in persons with PFP compared with controls.26 It may be that the altered kinematics are the result of, or have some correlation with, changes in hip mobility.

Our research

Given the lack of literature on hip mobility and PFP, a recent study on the topic was undertaken by this author and colleagues to determine if differences existed in passive hip mobility between individuals with PFP and controls.27

In this study we compared passive hip mobility in 30 healthy individuals and 30 patients with PFP. Specifically, we measured hip extension, hip internal (IR), and hip external rotation (ER). We used a digital inclinometer for all measurements, a device that has been found to have good reliability and concurrent validity for measurements of the hip.28,29

We measured hip extension using the modified Thomas test, and measured hip IR and ER with participants prone, as described in previous studies using these positions.30,31 We found that the patients with PFP had, on average, 11° less hip extension than individuals without PFP. No statistically significant differences between groups were noted for hip IR or ER.

The results of this study are a valuable contribution to the literature. To our knowledge, it is the first study to demonstrate a significant difference in hip extension within this population. A common model used in clinical practice and sports and performance training is “mobility before stability,” based on the need to have sufficient joint mobility before strength training is initiated.

After examining the PFP literature, it appears that practitioners may be putting the cart before the horse by implementing strength programs in individuals with PFP without first measuring and addressing deficits in hip extension. This may change in the near future, however, in light of new findings on hip flexor tightness effects on gluteus maximus (GM) muscle activation.

Mills et al have demonstrated that hip flexor tightness, as measured with the modified Thomas test and a digital inclinometer, results in decreased GM activation in female soccer players during squatting tasks compared with players without hip flexor tightness.32 This is an exciting observation that needs to be further explored in additional groups, including those with PFP.

The next concern should be whether the lack of hip mobility can be improved with selective interventions. Recently Moreside and McGill have conducted two important studies related to this topic.33,34

First, they examined 24 asymptomatic young men with limited hip mobility and randomly assigned them to one of three different intervention groups or to a control group.33 The interventions included stretching, stretching with motor control exercises for hip and trunk, and core endurance and motor control exercises. The two stretching groups demonstrated statistically significant improvements, with rotation improving as much as 56%. Interestingly, the nonstretching group also made moderate improvement for all assessed hip motions, but the improvement was statistically significant only for rotation. This study suggests hip mobility can be improved not just with stretching, but with motor control and core endurance exercises.

The second study by Moreside and McGill attempted to determine if improvements in passive hip mobility carried over to functional movement patterns.34 The researchers used a motion capture system to assess the kinematics of body segments, in particular the hip and lumbar regions. The authors found that, despite the significant improvements in passive hip range of motion, there was no evidence that the increased motion carried over into the observed functional tasks. They suggested that, in addition to increasing passive mobility, the addition of motor reeducation training might be necessary to incorporate a functional carryover.

These two studies have particular relevance on two fronts to patients with PFP. First, they demonstrate that, at least in a normal healthy male population, it is possible to increase hip mobility. This finding needs to be demonstrated in patients with PFP, however, to determine if the same outcomes can be achieved or if alternative interventions are needed. Secondly, it would appear that neuromuscular retraining is going to be especially important in patients compromised with PFP, given that healthy controls lacked functional carryover of improved passive mobility. In particular, given the prevalence of PFP in this group, it will be necessary to include female study participants.

Current position on PFP

There remains much work to be done in examining the potential importance of hip mobility in managing patients with PFP. In particular, it still needs to be determined if a successful intervention strategy can be devised that demonstrates a carryover of increased mobility to the activities in which the patient with PFP participates. Even more important, studies need to examine if a return of functional passive mobility results in improved pain levels and performance. Future studies are currently planned to answer these and other questions.

Sean Roach, PhD, DPT, ATC, is the owner of Tensegrity Physical Therapy in Eugene, OR, and is a full-time clinician actively involved in clinical research.

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