The diagnostic aspects of patellofemoral disorders are patellar dislocation or patellar instability, patellofemoral hypertension syndrome, and patellofemoral arthritis. These diagnoses make the correlation between pathophysiology and clinical symptoms and point the way to the appropriate treatment. Anterior knee pain is a common symptom in all of these disorders. However, when anterior knee pain was proposed as a disease diagnosis, it was suggested to be limited to anterior knee discomfort without a clear etiology. Therefore, some scholars have classified patellofemoral disorders into four categories: anterior knee pain without a definite etiology, patellar instability (patellar dislocation), patellofemoral hypertension, and patellofemoral arthritis. For the latter three types of patellofemoral disorders, there are appropriate and reliable treatments; however, the treatment of anterior knee pain without a clear etiology is quite challenging. When discussing anterior knee pain, we need to understand where the symptoms are being felt, the possible anatomical origin, the possible pathophysiological and pathological anatomical changes, and finally the association to the possible disease. This will allow for symptom relief in terms of treating the disease. However, the variability and complexity in each step of the correlation makes the diagnosis and treatment of anterior knee pain a “black hole” in orthopedic science, with great uncertainty in the outcome of treatment. Anterior knee pain is perceived at different sites and can be limited to the patellofemoral region, as well as to the superior, inferior, medial, and lateral aspects of the patella. Localized pain is easy to find an associated etiology. For example, anteromedial pain may be associated with medial synovial crease syndrome, and anterolateral pain may be associated with excessive tension in the lateral patellar support band (patellofemoral joint hypertension). However, in most cases, anterior knee pain is not confined or has no exact location, making the search for an etiology difficult. When exploring the anatomical origin of anterior knee pain, it is necessary to analyze it from the perspective of the patellofemoral joint in a broad sense. The patellofemoral joint in the narrow sense refers to the patella, femoral trochlea, and medial and lateral supporting bands. The broad patellofemoral joint refers to the anatomical or mechanical coupling of the entire knee extension apparatus to the femur. Anatomically and hierarchically, anterior knee pain may originate from the subchondral bone of the patella and femoral trochanter, synovium, joint capsule, medial and lateral support bands, quadriceps tendon and patellar tendon, or from outside the knee joint, such as the quadriceps, hip, etc. The ability to identify the anatomical source allows for a search for the etiology. The anatomic origin of the pain can be generally determined by determining the location of the perceived symptoms and by local physical examination, especially the examination of pressure points. If the anterolateral knee pain is combined with pressure pain in the lateral support band, the source of the pain can be presumed to be the lateral support band. Unfortunately, local anatomic localization of anterior knee pain is often not possible, making it difficult to identify the source. Patients with anterior knee pain often have a combination of anatomic, biomechanical, and kinematic abnormalities. Anatomic abnormalities include cartilage, bone, and soft tissue abnormalities such as degeneration of the cartilage, patellofemoral mismatch, and tears of the medial patellofemoral ligament; biomechanical abnormalities such as patellar instability; and kinematic abnormalities include abnormal gait throughout the lower extremity, abnormal knee motion and motion status, particularly with the knee extension device during lower extremity motion. Anatomic abnormalities need to be determined by imaging, biomechanical abnormalities need to be determined by clinical physical examination and special instrumentation, and the most reliable method of examining kinematic abnormalities is three-dimensional dynamic analysis of the knee joint. However, in clinical practice it is first difficult to define the boundary between abnormal and normal, for example, the tibial tuberosity-femoral glide spacing (TT-TG spacing) is different in different populations and ethnic groups. In addition, it is often difficult to correlate these abnormal changes with anterior knee pain. When faced with a patient with anterior knee pain, clinicians most routinely look for structural and functional abnormalities, speculate on their association with anterior knee pain, and expect to correct the abnormality to relieve the patient’s pain. This led to the emergence of hypotheses regarding anterior knee pain: the patellar chondromalacia theory, the abnormal patellofemoral force line theory, the disruption of the intra-tissue environment theory, the neurogenic hypothesis, and the neuropathic pain model. Until the 1960s, anterior knee pain was often attributed to chondromalacia of the patella. Some studies have shown that anterior knee pain is not clearly correlated with chondromalacia patellae, but may be related to the overload that causes chondromalacia patellae. Because chondromalacia patellae has no diagnostic, therapeutic, or prognostic significance, it is now advocated that the term chondromalacia patellae be abandoned. In the 1970s, anterior knee pain was often attributed to patellofemoral joint alignment abnormalities. Abnormal patellofemoral alignment refers to the outward deviation and tilting of the patella in the more extended knee position and the less flexed knee position, and may be more accurately referred to as trajectory and position abnormalities. Abnormal patellofemoral alignment causes lateral patellofemoral hypertension syndrome. Because the patellofemoral alignment anomaly theory is biomechanically sound, it has led to an overheating of orthopaedic surgery, but the overall results have been unsatisfactory and unpredictable. This hypothesis fails to explain why some people have patellofemoral alignment abnormalities without anterior knee pain and why anterior knee pain occurs at rest. Studies have shown that the degree of alignment abnormality does not correlate with the degree and location of cartilage degeneration. Because of the unpredictable outcome of orthopedic surgery, which may even result in medically induced patellofemoral alignment abnormalities, this hypothesis is currently being questioned and has affected clinical practice accordingly. In the 1990s, Scott F. Dye proposed the theory of a stable environment within normal tissues. Normal tissues can withstand a certain frequency and degree of load and maintain the stability of the internal environment. Each individual has a different load tolerance level. Based on this, the doctrine of imbalance in the internal environment of anterior knee pain was proposed, suggesting that overuse or overload causes disturbance in the internal environment, which results in pain. This theory is actually the overload theory, which can be combined with the abnormal patellofemoral alignment theory. Abnormal patellofemoral alignment reduces the overall load capacity. Individuals with patellofemoral alignment abnormalities may be more likely to have symptoms, but if they are carried within limits, they can be asymptomatic. The main conclusion of the intra-tissue environmental imbalance theory is that there is no need to correct patellofemoral alignment abnormalities without symptoms. The flaw of the intra-tissue environmental imbalance theory is that it fails to address the prevention of anterior knee pain in the first place: Why does each individual have a different loading capacity? How is the loading potential of each individual known? What is the best way to avoid abnormal patellofemoral alignment leading to an imbalance in the tissue environment? Secondly, the doctrine fails to explain why once an imbalance in the tissue environment has occurred, even if the load is reduced, the stability of the internal environment cannot be restored. Critically, it fails to provide a deeper explanation of why pain arises and fails to provide guidance for the treatment of tissue environmental imbalances. Clinically, imbalances in the tissue environment of bone tissues can be detected by PET CT or MRI, but there is a lack of reliable methods to detect imbalances in the tissue environment of soft tissues. Sanchis-Alfonso proposed a neurogenic theory of anterior knee pain by histopathological examination. It was found that patients with anterior knee pain had increased expression of VEGF (vascular endothelial growth factor) in the lateral patellar support band, increased innervation of the extravascular membrane, increased expression of NGF (nerve growth factor), and had demyelinating changes of the nerve, neuroma formation, and increased content of substance P. Therefore, it is presumed that local tissue pressure increases when patellofemoral joint alignment abnormalities occur. Local ischemia occurs because of vascular distortion, which induces the release of NGF and VEGF, resulting in excessive innervation and hypervascularization. Free nerve endings release substance P, which attracts mast cells. substance P induces the release of prostaglandin E2 and mast cells release histamine. Prostaglandin E2 stimulates nociceptive receptors to produce pain, and histamine induces pain. the Sanchis-Alfonso neurogenic doctrine provides some guidance for clinical management, such as relieving support band tension through lateral support band release, alleviating serial nerve responses through patellofemoral denervation, and relieving substance P release through pharmacotherapy, thereby relieving pain. However, Sanchis-Alfonso has only studied the lateral patellar support band and not the medial support band, nor the bone tissue, which can be considered as an explanation for the soft tissue changes in the doctrine of tissue internal environmental imbalance. Woolf has performed a clinical analysis of anterior knee pain. Anterior knee pain has been classified in terms of etiology, pathology and possible mechanisms as follows: injury-receptive pain, which refers to a transient response to a noxious stimulus; endoenvironmental restorative stability pain, which refers to pain that restores stability to the endoenvironment during tissue healing; neuropathic pain, which refers to spontaneous or allergic pain; and functional pain, which refers to an abnormal central response to normal nerve conduction. Some patients with minor knee trauma followed by prolonged severe pain are generally associated with neuropathic pain and functional pain. This analysis contributes to a comprehensive understanding of anterior knee pain, but does not indicate methods for identifying specific mechanisms and countermeasures for various mechanisms. In conclusion, anterior knee pain is not clearly associated with patellar tenderness, and its etiology remains a great challenge for orthopedic and sports medicine surgeons to identify.