Dr Smallman discusses his surgical technique in some cases of anterior knee pain, and highlights the work still needed to fully understand this problem.
First published 2018, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)
Anterior Knee Pain (AKP) can be considered according to how it presents.
Caveat
Because AKP may occur in patients without an IPP substantial questions remain. To seek answers, it is clear that prospective studies need to be performed.
We have evaluated such patients on rare occasions. These patients had no IPP but had all the “classical” features of AKP. We have very limited experience with such patients. Two memorable cases had anomalies (congenital malformations) of the synovial layer, one a medial shelf, a broad band of dense connective tissue which spanned the inner wall of the synovial layer from above (superomedial) to the central body below, which appeared as a nodular structure in the midline of the fat pad. In the other case the anomaly was another thick band of dense connective tissue in the superolateral recess spanning from anterior to posterior. In both instances the patients were adolescent athletes. In each, the lesion was judiciously resected, and the AKP resolved. Our conjecture is that the innervated synovial layer was the source of the pain.
Scott Dye (ref. 1) had demonstrated that this synovial layer throughout the knee was moderately sensitive to mechanical pressure, and severely sensitive in the fat pad and surrounding structures. Our model for AKP that arises de novo, in the absence of previous surgery, is that the pain arises from perturbed noxious nerves contained within the fat pad and immediately adjacent structures. Most of the time the perturbations arise from the common factor that is the physiology of the IPP-fat pad complex. In situations where there is no IPP, our conjecture is that any dense connective tissue structure that substantially spans the synovial space and perturbing the fat pad can mimic the AKP associated with the IPP-fat pad complex.
After our paper was published, orthopaedic surgeons, who specialize in the management of limb alignment, and patellar instability, indicated to me that they often see AKP in multiple-operated knees in which the IPP has been resected. In such patients the physiology that is normally associated with the AKP is gone. Given the clear association between the release of the IPP-fat pad complex and relief of AKP, one could ask: Do such patients manifest all of the elements of the symptom complex of AKP or is their knee pain different in some way? Our experience is limited in the multiple-operated knee. We look forward, over time, to have an increased opportunity to evaluate such patients.
One of the paradoxes of AKP is the fact that patients who have malalignment will often have AKP in just one knee. Clearly, the mechanical factors of limb alignment (axial, rotational, patellar tilt) and patellar instability play an important role in the generation of osteoarthritis and in the generation of knee pain. The pain of osteoarthritis, however, lacks the features of AKP (see the discussion on pain above). The relationship between AKP, malalignment and osteoarthritis is a field of active research study at this time.
Our data was not collected prospectively, but when we looked at our experience over 18 years in adolescent AKP every patient had the IPP-fat pad complex, and 84% were cured, with an average follow-up of 64 months. We have performed this surgery throughout a career spanning 28 years on hundreds of adults as well as children and submitted our technique to the journal Arthroscopy Techniques. We see no down-side for a patient who is suffering from this profoundly disabling condition and offer the operation after 3 to 6 months. In children and adolescents, given the devastating cases that we have seen, we recommend the surgery after 3 months.
References
1. Dye SF, Vaupel GL, Dye CC. Conscious neurosensory mapping of the internal structures of the human knee without intraarticular anesthesia. Am J Sports Med. 1998;26(6):773-777.
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