Knee pain gets a lot of clinical attention, and the most common causes, such as patellofemoral pain syndrome, IT band syndrome, meniscal tears, and osteoarthritis are relatively well known. Most people who Google their knee symptoms will land on one of these within the first few results.
But there are several causes of knee pain that are considerably less well known, frequently misdiagnosed, and often left untreated for months or years because nobody thought to look for them. If your knee pain hasn’t responded to standard treatment or doesn’t fit the typical patterns, one of these may be worth considering.
Pes Anserine Bursitis
The pes anserine bursa is a small fluid-filled sac located on the inner side of the knee, just below the joint line, where three tendons - the sartorius, gracilis, and semitendinosus - attach to the tibia. Like all bursae, its job is to reduce friction between moving structures.
When this bursa becomes inflamed, the result is pain on the inner side of the knee that is often worse at night, frequently described as an aching or burning sensation, and characteristically located lower than the joint line - which helps distinguish it from medial meniscal pain.
Pes anserine bursitis is most common in middle-aged and older adults, in people with osteoarthritis of the knee, and in runners with tight hamstrings or poor hip mechanics. It’s often overlooked because medial knee pain is reflexively attributed to the meniscus, and imaging doesn’t always show bursitis clearly.
Treatment is typically conservative - load modification, addressing the contributing biomechanical factors, and targeted rehabilitation. It responds well to PT when correctly identified.
Plica Syndrome
A plica is a fold of synovial tissue, or the membrane lining the knee joint. Most people have plicae; they’re remnants of tissue partitions from fetal knee development that don’t fully resorb. In most people, they cause no problems at all.
In some people, particularly after trauma or with repetitive loading, a plica becomes thickened and inflamed. As it moves over the femoral condyle during knee flexion and extension, it can produce a snapping or catching sensation, as well as pain, typically on the inner or front of the knee.
Plica syndrome is commonly confused with patellofemoral pain or a meniscal problem. The snapping or catching with movement is a useful distinguishing feature. It tends to affect younger active adults and is frequently associated with an increase in training volume.
Conservative management, using activity modification and rehabilitation to reduce the inflammatory cycle, resolves most cases. Surgery to remove the plica is rarely necessary but occasionally required in persistent cases.
Hoffa’s Fat Pad Impingement
The infrapatellar fat pad, or Hoffa’s fat pad, sits just below the kneecap, between the patellar tendon and the knee joint. It’s one of the most densely innervated structures in the knee, which means when it’s irritated, it can be quite painful.
Fat pad impingement occurs when the fat pad is repeatedly pinched between the femur and tibia during knee extension, particularly at end-range extension. The pain is typically at the front of the knee, just below the kneecap, and is often worsened by activities that involve full knee extension: standing from a chair, going downstairs, or pressing the knee flat.
It’s frequently mistaken for patellar tendinopathy, which sits in a similar location. A key distinguishing feature is that fat pad impingement tends to be worse with full extension, while patellar tendinopathy tends to be worse with loading in flexion - jumping, squatting, stairs.
This matters because the treatment approaches differ. Aggressive quadriceps loading, which is appropriate for patellar tendinopathy, can worsen fat pad impingement. Getting the diagnosis right is essential before beginning a rehab program.
Proximal Tibiofibular Joint Dysfunction
The proximal tibiofibular joint, where the fibula articulates with the tibia just below and to the outside of the knee, is rarely discussed in the context of knee pain, which is part of why it’s frequently missed.
This small joint can become hypomobile, hypermobile, or irritated, producing pain on the outer side of the knee that is easily confused with IT band syndrome or lateral meniscal pathology. The pain is typically well-localized to the joint itself, and movement of the joint - which can be assessed manually - often reproduces the symptoms.
It’s particularly relevant in patients who have had ankle sprains, as the fibula is involved in ankle mechanics and dysfunction at the ankle can transmit stress to the proximal end of the bone. Manual therapy directed at the joint, combined with addressing contributing factors, typically resolves it efficiently.
The Common Thread
What these conditions share is that they require a clinician who is looking for them. A knee assessment that goes directly to the most common diagnoses - without systematically evaluating the less common ones - will miss them.
At Aureum Physio, a thorough knee assessment covers the full range of structures that can produce knee pain; not just the familiar ones. For patients who have been treated for one diagnosis without improvement, revisiting the assessment with fresh eyes is often how the real problem is finally identified.
If your knee pain hasn’t responded to what you’ve tried, or if it doesn’t quite fit the patterns you’ve read about, come in for a proper assessment. The answer is usually there; it just needs to be found.
