Below is an article written for MikeReinold.com…
Anterior cruciate ligament (ACL) rupture1,2 and patellofemoral pain syndrome (PFPS)3,4,5 are two of the most common lower extremity complaints that physicians or physical therapists will encounter. In addition to the high incidence of these pathologies, with regards to ACL injury, very high ipsilateral re-injury and contralateral injury have also been reported6,7,8. With the importance of treating and/or preventing these injuries, several researchers have taken it upon themselves to determine what movement patterns predispose athletes to developing these injuries. This research indicates that greater knee abduction moments9,10, peak hip internal rotation11 and hip adduction motion12 are risk factors for PFPS development. Whereas, for ACL injury, Hewett and colleagues13 conducted a prospective cohort study identifying Knee abduction angle at landing as predictive of injury status with 73% specificity and 78% sensitivity. Furthermore, as the risk factors for developing both disorders are eerily similar, Myer et al performed a similar prospective cohort study finding that athletes demonstrating >25 Nm of knee abduction load during landing are at increased risk for both PFPS and ACL injury14. With a fairly robust amount of research supporting a hip etiology in the development of these injuries, it would make sense that weakness of the hip musculature would also be a risk factor, right?
A recent systematic review found very conflicting findings on the topic. With regards to cross-sectional research, the findings were very favorable with moderate level evidence indicating lower isometric hip abduction strength with a small effect size (ES) and lower hip extension strength with a small ES15. Additionally, there was a trend toward lower isometric hip external rotation and moderate evidence indicates lower eccentric hip external rotation strength with a medium ES in individuals with PFPS15. Unfortunately, the often more influential prospective evidence told a different story. Moderate-to-strong evidence from three high quality studies found no association between lower isometric strength in hip abduction, extension, external rotation or internal rotation and the risk of developing PFPS15. The findings of this systematic review indicated hip weakness may be a potential consequence of PFPS, rather than the cause. This may be due to disuse or fear avoidance behaviors secondary to the presence of anterior knee pain. Regardless of its place as a cause or consequence, hip strengthening has proved beneficial in patients with both PFPS16,17,18 and following ACL Reconstruction19, but does it actually help to change the faulty movement patterns?
Gluteal strengthening can cause several favorable outcomes, from improved quality of life to decreased pain, unfortunately however marked changes in biomechanics is not one of the benefits. Ferber and colleagues20 performed a cohort study analyzing the impact of proximal muscle strengthening on lower extremity biomechanics and found no significant effect on two dimensional peak knee abduction angle. In slight contrast however, Earl and Hoch21 found a reduction in peak internal knee abduction moment following a rehabilitation program including proximal strengthening, but no significant change in knee abduction range of motion was found. It should be noted that this study included strengthening of all proximal musculature and balance training, so its hard to conclude that the results were due to the strengthening program. Potentially, gluteal endurance may be more influential than strength itself, so it would make sense that following isolated fatigue of this musculature, lower extremity movement patterns would deteriorate.
Once again, this belief is in contrast to the available evidence. While fatigue itself most definitely has an impact on lower extremity quality of movement, isolated fatigue of the gluteal musculature tells a different story. Following a hip abductor fatigue protocol, patients only demonstrated less than a one degree increase in hip-abduction angle at initial contact and knee-abduction angle at 60 milliseconds after contact during single-leg landings22. In agreement with these findings, Geiser and colleagues performed a similar hip abductor fatigue protocol and found very small alterations in frontal plane knee mechanics, which would likely have very little impact on injury risk23. The biomechanical explanation for why weakness or motor control deficits in the gluteal musculature SHOULD cause diminished movement quality makes complete sense, but unfortunately, the evidence at this time does not agree.
While the evidence itself does not allow the gluteal musculature to shoulder all of the blame, this does not mean we should abandon addressing these deficits in our patients. As previously stated, posterolateral hip strengthening has multiple benefits, but it is not the end-all-be-all for rehabilitation or injury prevention of lower extremity conditions. Proximal strength deficits should be assessed through validated functional testing in order to see its actual impact on lower extremity biomechanics on a patient-by-patient basis. Following this assessment, interventions should be focused on improving proximal stability, movement re-education, proprioception, fear avoidance beliefs, graded exposure, and the patient’s own values, beliefs, and expectations.