In part one of this series, Chris Mallac explained the anatomy and complex biomechanics of the VMO and its role in relation to the patellofemoral joint. In part 2, he argues that regardless of cause and effect of the VMO on patellofemoral pain, VMO dysfunction in the presence of pain is very real, and thus exercises to rehabilitate the function of this muscle are necessary... MORE
The majority of clients that present to the clinic with anterior knee pain over the coming year will more often than not have a patellofemoral (PF) problem.
It may be a slight bit of biomechanical mal-alignment that has stirred up the knee cap – this is the good, or they may have started to wear the cartilage behind the knee cap and as a result it has softened – chondromalacia – this is the bad. They may even have worn a hole into the knee cap cartilage and they now have a chondral defect, or worse still an osteochondral defect – the downright ugly.
These problems affect runners, cross fitters, group exercise enthusiasts (PUMP classes) and simple recreational walkers who spend a lot of time on hills and stairs.
How these extremes are managed will differ.
The biomechanical irritations and the chondromalacia versions can be managed conservatively with a combination of local treatment modalities and correcting the biomechanical faults. The more serious chondral/osteochondral defects often need some surgical intervention as often the pathology is too advanced to respond to conservative treatment alone.
Understanding the exact mechanical contributions of the knee cap in relation to the femur is critical for the therapist to effectively manage these problems.
At the local PF level, the fault is usually a malposition of the patella in the femoral trochlear groove. Often the knee cap is being pulled too far laterally and superiorly in the groove, creating an uneven contact situation between the knee cap and the femur. The PF compression force during loaded knee flexion (squats, lunges etc.) is no longer optimal and usually a smaller portion of the patella cartilage is taking all the load. This wears the cartilage down and creates pain and pathology. This is most noticeable as the knee flexes to 30 degrees and onwards as it is this knee flexion angle where the knee cap enters the femoral trochlear groove.
The more distant (but often dominant) faults lie at the hip/pelvis and at the feet. Below is a breakdown of common biomechanical faults that may contribute to PF pain syndromes.
If the foot pronates (rolls in) for too long or too much, the pronated midfoot forces the tibia to remain internally rotated. The femur follows the tibia and also internally rotates. This creates a mal-alignment at the knee whereby the PF arrangement is altered and the knee cap shifts laterally. We are all familiar with the Q angle of the knee and how this affects the PF alignment.
Common causes of overpronation may be structural flatfoot problems that can be corrected with orthotics and shoe selection. However, tight soleus (that limits dorsiflexion) or a tight and overactive peroneal system that everts the foot and flattens the foot can also be a cause.
Stretching and loosening the soleus and peroneals along with strengthening the anti-pronation muscles such as tibialis posterior, flexor hallucis longus and flexor digitorum longus may help fix this problem.
2. Hip joint FADDIR
FADDIR represents a flexed, adducted and internally rotated hip joint at foot strike. This is often caused by tight and overactive hip flexors such as TFL and the adductors and weakness in the abductors (gluteus medius) and external hip rotators (gemellus, obturator muscles). This hip posture forces the femur to roll inwards and as a result the knee is deviated medially and away from the vertical line drawn up from the foot. This also increases the Q angle and PF misalignment results and perpetuates the local knee imbalance of tight and overactive lateral quadriceps and lateral hamstrings along with ITB tightness. As a result the VMO weakens.
Loosening the overactive TFL, adductors, lateral quad, ITB and lateral hamstring whilst strengthening the gluteus medius, hip external rotators and VMO may help this biomechanical mal-alignment.
3. Pelvic Trendelenburg
Defined as lateral pelvic shift whereby at stance phase the opposite side of the pelvis drops down below the height of the pelvis on the stance side. This is usually caused by a weak gluteus medius complex that is unable to hold the pelvis stable during stance phase. The implications again are that this causes the knee to roll in and increase the Q angle. The solution is to muscle up the gluteus medius.
4. Hip flexor to extensor imbalance
This often forgotten about imbalance creates a situation whereby the individual finds it difficult to attain hip extension at the end of stance phase. The hip remains locked in a degree of flexion.
The knock on effect is that the knee also stays locked in some flexion. With the knee in flexion, the knee cap is now compressed against the femur, compression on the underside of the kneecap may result. To fix this the therapist needs to stretch/loosen the hip flexors and strengthen the gluteus maximus to promote more hip extension.