In my previous post regarding Patellofemoral Pain Syndrome (PFPS), I delved into its etiological understanding. Now that we are beginning to learn more about this syndrome and its subsequent biomechanical considerations, we can begin to develop a more effective and targeted strength training program.
Posterolateral Hip Musculature
Last year, two systematic reviews were published that showed continued evidence for an association between weak hip abductors and PFPS. Lankhorst et al found significantly less hip abductor strength and less hip external rotator strength when adjusted to patient’s body weight in PFPS patients compared to the control subjects. Also, Barton et al investigated gluteal muscle activity and its association with those patients suffering from PFPS. They found that evidence indicates Gluteus Medius muscle activity is delayed and of shorter duration during stair ascent/descent and running. In contrast, Gluteus Maximus muscle activity is increased during stair descent in individuals with PFPS.
With these findings, logically, it makes sense to target both the hip abductors and external rotators, but is there evidence to support this?
In 2010, Fukuda et al conducted a randomized controlled trial (RCT) comparing the short-term effects of a combined hip abductor, lateral rotator, and quadriceps strengthening program (HKE) to that of a traditional quadriceps strengthening program alone (KE). After 4 weeks, those in the HKE group showed significantly superior improvements in function and reduced pain during stair negotiation. A previous study by Nakagowa et al found very similar results where one group focused on stretching the quadriceps, gastrocnemius, iliotibial band, and strengthening the quadriceps, whereas the experimental group program consisted of strengthening exercises for the transverse abdominal muscles, and the hip abductors/rotators. In this study, only the intervention group improved perceived pain symptoms during functional activities.
These studies show targeted hip strengthening as a viable option, but unfortunately, these early studies only provided outcomes between 4 and 6 weeks post-intervention. Khayambashi et al conducted a RCT looking at isolated hip abductor and external rotator strengthening 3 times per week for 8 weeks with a 6 month follow-up. At the conclusion of the study, the exercise group’s VAS Pain Scale decreased from 7.9 to 1.4 and maintained at 1.7 at the 6 month follow-up. This group’s WOMAC score showed similar improvements with a baseline rating of 54 and post intervention scores of 10.7 (8 week) and 10.8 (6 month). Both of these outcomes showed significantly superior results in comparison to both baseline and the control group. This study showed the utility of hip posterolateral musculature training in isolation from any other intervention. To build upon this study, Fukuda et al attempted to determine if adding hip strengthening exercises to a conventional knee exercise program produces better long-term outcomes than conventional knee exercises alone. Once again, the experimental group showed superior results in comparison to the traditional quadriceps strengthening program. The combined hip/knee strengthening program produced significant improvements in all outcome measures (LEPS, AKPS, Single-hop test, and NPRS ascending/descending stairs) at 3, 6, and 12 months post-treatment. In comparison, the traditional quadriceps program only showed decreases in pain at 3 and 6 months. The body of evidence supporting the targeted strengthening of the hip abductors and external rotators continues to grow with documented short and long-term functional and pain specific outcomes.
For further information regarding hip abductor (specifically gluteus medius) strength training, please read “Evidence-Based Strength Training: Gluteus Medius“.
As common sense would dictate, Lankhorst et al found quadriceps weakness to be a risk factor for developing PFPS. That being said, quadriceps strengthening with this patient population is an especially difficult task. As was discussed during my post on etiology, patellofemoral joint stress is of utmost importance during rehabilitation.
According to the research done by Steinkamp et al, patellofemoral joint stress increases with decreasing angles of knee flexion in the open kinetic chain (OKC). Whereas, stress increases with increasing levels of knee flexion in the closed kinetic chain (CKC). Based on this research, the most appropriate ranges for those with PFPS to exercise in are 0-45° in the CKC and 90-45° in the OKC. As chondral lesions and/or osteoarthritic changes are common within this population, you must be pay close attention where the joint contact area migrates during exercise. As knee flexion increases, the patella glides inferiorly on the femur, while contact on the patella gradually shifts from inferior to superior. This information aides us in exercise prescription, but it should not eliminate other ranges of motion during rehab. Pain is patient specific and can vary based on underlying pathology, experiences, and other biomechanical/neurophysiological factors. All exercises should be conducted within your individual patient’s tolerance and these ‘appropriate ranges’ should be used to help guide your prescription.
Upon implementing a more functional approach to your rehabilitation program (which should be started as soon as possible), patellofemoral joint stress should continue to guide your program. Chinkulprasert et al conducted a controlled laboratory study trying to determine what exercises elicit the greatest patellofemoral joint stresses amongst the lateral step-up (LSU), forward step-up (FSU), and forward step-down (FSD). The FSD, FSU, and LSU were performed by 20 healthy subjects at the same step-height across exercises. Upon completion of the study, it was determined that during the FSD, significantly greater patellofemoral stresses and reaction forces were recorded than during either of the other two exercises. Early in rehabilitation, the FSD should be withheld in favor of the other less intense exercises. As patient tolerance increases, the FSD can be a viable option to improve eccentric quadriceps control during stair ascension. Additionally, Dolak et al determined that prior to progressing to a functional strength program, those who completed a hip-specific strength program demonstrated increased pain reduction compared to those who completed a quadriceps-specific strength program. The hip-specific group’s VAS Pain Score decreased from 4.6 to 2.4, while the quadriceps-specific group only decreased from 4.2 to 4.1. In my opinion, this study shows the importance of controlling frontal and transverse plane movements prior to beginning an intensive functional strength program.
Notice how I left out the mystical VMO? Yep, me too.
It should be understood that PFPS is a multi-factorial condition and therefore warrants a multi-modal treatment strategy (NOT JUST STRENGTH TRAINING). I will continue to delve further into this topic as the year goes on, but in the meantime, I believe these two case reports will add some insight:
Mascal CL, et al. Management of patellofemoral pain targeting hip, pelvis, and trunk muscle function: 2 case reports. J Orthop Sports Phys Ther. 2003 Nov;33(11):647-60.