Anterior knee pain: Remember to look up and be aware of structural anomalies
Unfortunately, when an orthopedic surgeon sees a patient with anterior knee pain in the office, he or she normally only focuses on the knee. If we do this we are making a big mistake.
We must remember to “look up” and evaluate the pelvis and proximal femur as well as psychological factors that modulate the pain to fully understand what is happening and to be able to solve this challenging problem. Moreover, we must be aware of structural anomalies (i.e., chondropathy and patellofemoral (PF) malalignment – patellar tilt and lateral patellar subluxation) given the correlation between structural anomalies and anterior knee pain is low.
Be aware of structural anomalies
Structural anomalies should not give us a “green light” to correct them surgically. In fact, in my experience, the worst cases of patients with anterior knee pain are secondary to a surgical procedure that aimed to correct structural anomalies that were possibly not the cause of the pain and disability.
However, we must not be dogmatic and remember that in selected cases, structural anomalies could be the cause of anterior knee pain. We have observed, as other authors have, that a softening of the cartilage of the distal pole of the patella can be a source of disabling pain completely recalcitrant to conservative treatment. In these cases, a focal bone overload can occur because the cartilage’s lack of absorption places excessive stress on the underlying innervated bone, causing pain.
John P. Fulkerson, MD, has observed that when he does a short steep anteromedial tibial tubercle transfer, pain goes away in the vast majority of patients. In my experience, similar results are obtained after a deepening trochleoplasty. With both surgical techniques, we decrease the PF joint reaction force and this could explain the resolution of pain. I believe this overload of the distal pole of the patella could be related among other causes to trochlear dysplasia. In fact, in all of my cases of severe chondropathy of the distal pole of the patella there was a trochlear dysplasia grade D.
In many patients the primary cause of anterior knee pain is not in the PF joint. There is a growing body of literature linking abnormal femur rotation with anterior knee pain. The rotation of the femur underneath the patella in the transverse plane leads to abnormal patellar tracking, PF imbalance and finally anterior knee pain. This means the primary problem is not in the patella but in the femur. In this sense, there is a growing body of literature supporting the link between anterior knee pain in young females and lack of dynamic control in lower limbs that may have an influence on the PF joint and may also be the main cause of pain. This link is supported by the fact that an isolated hip abductor and external rotator muscle strengthening is effective in improving pain in this subgroup of females with anterior knee pain. Finally, in a small number of patients this malrotation can be structural because of a femoral anteversion or any other torsional anomaly of the femur.
Interestingly, we have found a novel link between femoroacetabular impingement (FAI) and anterior knee pain. Once again, in some patients the underlying cause of anterior knee pain is not in the PF joint. In my experience, all of these patients went to the orthopedic surgeon for the first time due to anterior knee pain that was recalcitrant to conservative treatment. The patient gets tired of doing physical therapy because he or she does not get the expected results and stops going to the physician. After some time, the patient comes back to the office with hip pain that could be disabling. We hypothesize that in these patients there is a functional external femoral rotation to avoid the FAI, hence the hip pain. This femoral rotation could provoke a PF imbalance that could be responsible, in theory, for anterior knee pain. Our kinetic and kinematic findings are in agreement with our hypothesis. Moreover, FAI resolution is related to the resolution of pain and normalization of biomechanical parameters.
Patients with anterior knee pain often have severe pain with insignificant clinical and radiological findings. Moreover, many patients have allodynia or hyperalgesia. In addition, they have a high incidence of anxiety, depression, kinesophobia and catastrophizing. All this makes the orthopedic surgeon think that the main problem is in the psyche. It is incorrect. Psychological factors are the result of the severity of the patient’s pain, not the cause of pain.
Psychological factors only play a role as modulators. It has been demonstrated that clinical improvement in pain is associated with a reduction in catastrophizing and kinesophobia. This finding is clinically relevant because it contradicts the belief that patients with anterior knee pain are patients with pre-existing psychological problems frequently responsible for pain. We believe nothing is farther from the truth. Furthermore, we must not forget that in patients with anterior knee pain there is a biomechanical and neuroanatomical objective base for their pain.
Both the pelvifemoral dysfunction and the psychological factors must be included in our therapeutic targets for the multidisciplinary treatment of anterior knee pain patients. Moreover, in selected cases we must consider surgical techniques to unload areas that could be the source of pain, such as the softening of the distal pole of the patella.
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Vicente Sanchis-Alfonso, MD, PhD, is consultant orthopaedic surgeon, Hospital Nisa 9 de Octubre, Valencia, Spain. He is also member of the International Patellofemoral Study Group (IPSG). He can be reached at Valle de la Ballestera # 59, 46015 - Valencia, Spain; e-mail: email@example.com
Disclosure: Sanchis-Alfonso has no relevant financial disclosures.