Patellofemoral Pain: An Enigma Explained by Homeostasis and Common Sense
We present a rational, scientific, low-risk approach to patellofemoral pain (anterior knee pain) based on an understanding of tissue homeostasis. Loss of tissue homeostasis from overload and/or injury produces pain. Bone overload and synovial inflammation are common sources of such pain. Chondromalacia and malalignment are findings that almost always do not need to be “corrected” to relieve pain. Patience and persistence in nonoperative care results in consistent success. Surgery should be rare and done only after extensive nonoperative management and in the setting of clearly defined pathology. Rational surgical treatment is explained in the context of restoring tissue homeostasis to relieve pain.
Patellar Bone Overload—Part of the Problem
Patellar bone has been long assumed to be a source of AKP. To understand this better, Dr. Dye had one of his residents push a 15-gauge needle into the medial facet of his asymptomatic right patella to obtain real-time intraosseous pressure measurements as a control. This was done under local anesthesia, so no pain was felt as the needle entered the patella. However, when an arterial line was connected and flushed prior to pressure measurements, Dr. Dye experienced sharp lancinating pain. Patellar bone is richly innervated, and even mildly increased intraosseous pressure can produce severe symptoms. Dr. Dye’s patella was sore for about 7 months afterward. 
Loss and restoration of osseous homeostasis occur often in AKP patients whose positive patellar bone scans (focal or diffuse) show resolution to normal (homeostasis) after symptom dissipation (Figures 9A, 9B). 
The Mosaic of Anterior Knee Pain
The densely innervated synovial, fat-pad, and patellar bone tissues are nociceptive sources of AKP in the absence of homeostasis. 
Clinical Applications of Homeostasis and Common Sense
Essential points to be covered in the history include overuse, injury, weight gain, systemic illness (which may produce weakness and deconditioning), prior treatment (especially physical therapy) and response to medications or injections. In the case of prior surgery, preoperative and postoperative identification of the patient’s exact symptoms can shed light on the underlying diagnosis and on any symptom changes resulting from treatment.
Sudden pain in the anterior knee can result in pain-mediated reflex quadriceps inhibition and the sensation that the knee is “giving way.” Typically, patients describe the knee collapsing into flexion and when asked if their knee is “unstable” after experiencing such episodes they will readily say yes. However, such a knee is not “unstable” in the sense that there is patholaxity that might require surgery. This is a critical distinction to avoid tragic-ally unnecessary surgery.
Careful evaluation for areas of tenderness may direct treatment to focal pathology, such as patellar or quadriceps tendinitis or tendinosis, pathologic medial parapatellar plica, or postoperative neuroma. Palpation and Tinel testing can uncover a neuroma or neuropathy of the infrapatellar branch of the saphenous nerve (Figure 11) that no other diagnostic tools can. 
Poor flexibility, which increases tension and load in peripatellar soft tissues, is very common. In many cases, evaluation of hamstring, prone quadriceps, hip, and gastrocsoleus flexibility with contralateral comparison reveals a need to include stretching in a homeostasis-restoring program.
Insufficient muscular strength and endurance can also result in overload of patellofemoral bony and soft tissues. As all ground reaction force must be absorbed somewhere in the body, and since eccentric muscle contraction absorbs load, other tissues become overloaded if muscle function is insufficient to absorb enough force. Weakness of the hip and core have shown to respond to rehabilitation with resolution to AKP. Proximal weakness screening with step-down or single-leg squat is important.
Joint effusion is an important finding indicative of objective intra-articular pathology and inflammation. Such inflammation may be from overuse resulting in loss of homeostasis (synovitis, cartilage breakdown, symptomatic arthrosis).
Screening examinations for hip and lumbar pathology are mandatory and take only a few minutes.
Treatment Options
Activity Modification
Avoid aggravating the problem. Consider this like a fire. If you are trying to put out a fire (AKP), would you throw sticks (increased activity/aggressive exercise) on it? Of course not. You would turn a hose on it (nonsteroidal anti-inflammatory drug [NSAID] regularly) or perhaps throw a bucket of water (steroid injection) on it. You would not throw gasoline (excessive exercise or activity) on it. Explaining to patients how to remain within their envelope by avoiding any activity that increases symptoms is crucial. No pain no gain is a lie from hell for patients with AKP. Don’t throw sticks on the fire.
