The proximal tibiofibular joint (PTFJ) is just below the knee on the outside of the leg. It is a simple joint that does not move much, just a bit of sliding. It connects the top end of the large shin bone (tibia) to the top end of the much smaller leg bone (fibula) beside it. The tiba and fibula are the two main long bones of the lower leg. (The distal tibiofibular joint is part of the ankle.)
The PTFJ is obscure and unstudied, overshadowed by the exciting knee joint, and rarely considered in diagnosis — but it can be an important driver of lateral knee pain, or occasionally mistaken for a shin injury.
“The human proximal tibiofibular joint mechanics has been largely unknown due to lack of attention by both the clinicians and the anatomists alike.”
Sarma et al, “Proximal tibiofibular joint: Rendezvous with a forgotten articulation”1
A neglected cause of lateral knee pain
Injury to the PTFJ is “an often-forgotten cause of lateral knee pain,”2 and yet the PTFJ is not really a knee joint — it’s just nearby. If the knee was New York, the PTFJ would be Queens. Trauma to the knee can leave the PTFJ untouched, and vice versa. However, dislocation of the PTFJ can sometimes compromise knee joint stability, due to some (variable) shared ligamentous support.
Sometimes patients suffering mainly from PTFJ pain are repeatedly evaluated for knee trouble, even get knee surgery, all without even looking at the PTFJ. It’s surprising how diagnostically neglected this joint is, considering that it is close enough to the knee that it is usually imaged along with the knee.
The PTFJ is not a knee joint … except when it is
The knee and the PTFJ are not always entirely separate joints. In quite a few people — estimates vary from 10 to 60% — they are connected by a tunnel of joint cavity,3 sharing joint fluid. In this case, the PTFJ is a “fourth compartment” of the knee joint.
The main clinical implication is that swelling may be shared. If the knee swells, the PTFJ swells! Injury to either joint could potential change the mechanics of the other — although the knee affecting the PTFJ is probably more likely than the other way around.4
Symptoms of proximal tibiofibular joint disorders
Symptoms arising from PTFJ mainly are mostly low lateral knee pain, almost low enough to be mistaken for shin pain (but probably not often). Pain in this location is routinely mistaken for common knee injuries, chiefly runners’ knee, and strains of the lateral collateral ligament of the knee.
Injury to the common peroneal nerve around the head of the fibula can also result in tingling or numbness on the top of the foot and/or the side of the leg, and foot drop (the foot slapping down a bit with each step).
Tibiofibular pain versus IT band pain
ITB syndrome is one of the two major kinds of “runner’s knee” (along with patellofemoral pain). It’s a common and notorious injury, a tendinitis or bursitis-like injury on the side of the knee (and not the thigh or hip), and it is the most obvious diagnostic suspect for any lateral knee pain. It’s true that both IT band pain and tibiofibular pain cause “lateral knee pain,” and cause pain in very similar locations, the location of each kind of pain is specific and clear:
- Tibiofibular pain is definitely below the knee joint line.
- ITBS pain occurs on or just above the joint line, on the big bump of bone on the side of the femur at the knee (lateral epicondyle of the femur).
Also, ITBS always develops insidiuously, while tibiofibular injury is probably mostly traumatic.
Common PTFJ injuries and conditions
The most common issues with the PTFJ are:
- Sprains and partial dislocations.
- Injury to the common peroneal nerve. The common peroneal nerve (arrow) is quite exposed as it passed the fibular head and divides into superficial and deep components. This nerve is to the knee what the “funny bone” nerve (median nerve) is to the elbow: it is relatively exposed, easy to bang and traumatize.
- Tumours, cysts, and ganglions.
- Pigmented Villonodular Synovitis (PVNS) is a mysterious disease of the lining of the joint capsule, mostly affecting the knee, and it can include the PTFJ. The synovium produces too much joint fluid and some irritating compounds, causes swelling and pain.
The PTFJ may also get “stuck” (hypomobile). This is a plausible pathology, but it has never been formally described. There is just a single published case report of putative hypomobility.5
About Paul Ingraham
I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of ScienceBasedMedicine.org for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:
- Sarma A, Borgohain B, Saikia B. Proximal tibiofibular joint: Rendezvous with a forgotten articulation. Indian J Orthop. 2015;49(5):489–95. PubMed #26538753 ❐ PainSci #52026 ❐
- Forster BB, Lee JS, Kelly S, et al. Proximal Tibiofibular Joint: An Often-Forgotten Cause of Lateral Knee Pain. American Journal of Roentgenology. 2007;188(4):W359–W366. PainSci #52025 ❐
- Bozkurt M, Yilmaz E, Atlihan D, et al. The proximal tibiofibular joint: an anatomic study. Clin Orthop Relat Res. 2003 Jan;(406):136–40. PubMed #12579012 ❐
- The knee is a much more spacious joint — the largest joint capsule in the body. Plenty of “overflow” room. The PTFJ probably cannot produce enough synovial fluid to significantly affect it.
- Beazell JR, Grindstaff TL, Magrum EM, Wilder R. Treatment of lateral knee pain by addressing tibiofibular hypomobility in a recreational runner. N Am J Sports Phys Ther. 2009 Feb;4(1):21–8. PubMed #21509117 ❐ PainSci #52021 ❐ This paper describes a diagnosis of hypomobility made based mainly on palpation: the joint just felt stiff, basically. It’s a data point, but we really have no idea if PTFJ hypomobility is a real phenomenon.