Fares Haddad and Sujith Konangamparambath explain this easily missed sports injury
One of the more unusual forms of knee instability in sports is an unstable proximal tibiofibular joint. This injury occurs in various sports such as football, rugby, wrestling, gymnastics, long jump, dancing, judo and skiing. The range of significant symptoms it can cause – including outer knee pain, especially on weight bearing, locking and ‘popping’ in the knee and transient nerve symptoms – make this injury an important one to recognise and address, especially in high demand athletes.
Anatomy of the tibiofibular joint
The two long bones of the lower leg, the tibia (shin bone) and the fibula (outer leg bone) are bridged together at three distinct regions:
* the tibiofibular articulation at the knee
* the tibiofibular syndesmosis at the ankle
* a thin fibrous tissue along the length of the two bones, known as the interosseous membrane (1).
These connections enable the two bones to work together to coordinate ankle and knee movements.
The tibiofibular articulation at the top of the bones (connecting the head of fibula and lateral condyle of tibia) is an ‘arthrodial’ or ‘plane-type’ joint which allows only slight gliding movement between the two surfaces. The contiguous surfaces of the bones are covered with cartilage and are connected with an articular capsule. This is reinforced by two or three broad, flat bands of ligament (anterior superior ligament) in front and a single thick band of ligament (posterior superior ligament) behind. Both ligaments pass obliquely upwards from the head of the fibula to the lateral condyle of the tibia. The tendon of the popliteus muscle, which plays a significant role in posterolateral knee stability, lies close to the posterior superior ligament. An injury to this region may therefore involve both these structures.
A synovial membrane, similar to that found inside the knee joint lines the inner surface of the capsule of the proximal tibiofibular joint. In 10% of the population, this synovial space is continuous with that of the knee joint. The common peroneal nerve winds about the neck of the fibula close to the lower edge of the joint, where it is vulnerable to injury. Such an injury may lead to foot drop and loss of sensation in parts of the leg and feet.
What the tibiofibular joint does
The proximal tibiofibular joint transmits load from the ankle to the joints above, so is crucial to all sports activities involving movements at the ankle and the knee. The primary functions(2)of the joint are:
* to dissipate torsional load applied at the ankle
* to dissipate movement that bends the tibia outwards
* to transmit axial load in weight bearing. (It is thought that the joint bears about one-sixth of the static load applied at the ankle(3).)
Among the population at large, the proximal tibiofibular joint is equally likely to come in either one of two different forms(4): horizontal or oblique. In the horizontal variety, the two articulating surfaces are circular and planar, and their location provides some stability against displacement.
In the oblique type of joint, the articulating surfaces are much more variable in area, configuration and inclination. The more oblique joints have the least area of contact between bones. Because this type of joint is less able to rotate and accommodate torsional stresses than a horizontal joint, it is thought to be more likely to dislocate.
What brings on a dislocation?
Although dislocation may arise because of pathology or even without apparent cause, the most likely sporting scenario will be traumatic incident, such as twisting injuries, parachute landings, or a slipping injury where the athlete lands with the knee bent under their body. Dislocation may occur in isolation or it may be seen alongside a fracture of fibula or the ankle, or with dislocation of the hip(4).
Sports physicians should also be alert to subluxation of the joint (excessive forward to backward movement of the tibial head, causing symptoms), which is often associated with ligamentous laxity.
A complex play of muscles and ligaments
The nature of the traumatic event dictates the way in which the proximal tibiofibular joint will dislocate. Although there are three main reported types of dislocation, the usual one in sporting contexts is anterolateral. It occurs as a result of a complex interplay of sudden abnormal movements in the muscles controlling the ankle and knee, typically following a sudden inversion and plantar flexion of the foot, together with simultaneous knee flexion and twisting ofthe body.
In a flexed knee the biceps femoris tendon and lateral collateral ligaments are relaxed. This, along with the external rotational torque of the tibia on the foot during twisting of the body, springs the head of the fibula out laterally. At this point a violent contraction of the peroneal muscles, the extensor digitorum longus and the extensor hallucis longus (caused by sudden inversion and plantar flexion of the foot), pulls the fibula forward.
Signs and symptoms
It is easy to miss this injury, as the findings on examination may be subtle. Diagnosis is often based on history of presentation and a strong clinical suspicion. Clinical features may include:
* outer-knee pain which is aggravated by pressure over the fibular head
* limited knee extension
* crepitus (grinding) on knee movement
* pain on weight bearing
* visible deformity
* locking or popping.
Ankle movement may exacerbate the knee pain. There may be temporary peroneal nerve palsy, presenting as pins and needles or numbness on the outer side of the leg (although this symptom is less likely in the anterolateral form of dislocation associated with athletic trauma).
Plain x-ray may show the subtle signs of increased interosseous space and displacement of the fibula from its normal position but a CT scan may be needed to confirm the diagnosis(5,6). MRI scanning is an option, and has the advantage of revealing ligament injuries as well as the dislocation.
There is no single agreed best option for the surgical treatment of acute dislocations. Over the years, different surgeons have managed their patients in different ways, such as closed reduction and immobilisation in plaster cast, closed reduction without immobilising, temporary operative stabilisation of the joint and repair of the joint capsule, immediate joint fusion (arthrodesis) and resection of the fibular head.
The treatment options also vary with the pattern of dislocation. In acute anterior dislocation, the joint is treated with closed reduction and immobilisation of the knee in extension for two or three weeks.
In cases of chronic instability, a more complicated surgical process is advocated, involving resection of fibular head, reduction and temporary internal fixation, arthrodesis and tendon reconstruction(7-9).
Unrecognised dislocations often present with peroneal nerve symptoms such as pins and needles in the leg or feet, or weakness of foot movements. Failed conservative management may bring about chronic knee pain and ankle pain. This may also follow arthrodesis(10) of the joint. Resection of the fibular head is believed to affect knee stability and gait.
Dislocation of the proximal tibiofibular joint is a less well known sports-related knee injury. Early diagnosis and treatment are essential to enable prompt rehabilitation. Treatment options vary according to the time of presentation, nature of injury and associated morbidity. A return to sport is possible after successful treatment.
1. Gray, H, Anatomy of the Human Body, 20th edition.
2.Ogden, JA (1974) ‘The anatomy and function of the proximal tibiofibular joint’. Clin Orthop, 101:186-191.
3. Lambert, KL ( 1971) ‘The weight bearing function of the fibula’. JBone Joint Surg(Am), 53:507-513.
4. Ogden, JA (1974) ‘Subluxation and dislocation of the proximal tibiofibular joint’, J Bone Joint Surg(Am), 56-A:145-154.
5.Voglino J, Denton J(1999) ‘Acute traumatic proximal tibiofibular dislocation confirmed by computed tomography’. Orthopaedics; 22(2): 255-257.
6.Keogh, P, Masterson, E et al (1993) ‘The role of radiography and computed tomography in the diagnosis of acute dislocation of proximal tibiofibular joint’. Br J Radiol;66;108-11.
7. Mena, H, Brautigan, B and Johnson, DL (2001) ‘Split biceps tendon reconstruction for proximal tibiofibular joint instability’, Arthroscopy, 17(6), 668-671.
8. Tanner SM, Brinks KF (2007) ‘Reconstruction of the proximal tibiofibular joint’ Clin J Sport Med, 17(1), 75-77.
9. Miettinen H, Kettunen J, Vaatainen U (1999) ‘Dislocation of the proximal tibiofibular joint a new method of fixation’, Acta Orthp trauma Surg119:358-359.
10.Ogden, JA (1974) ‘Subluxation of the proximal tibiofibular joint’ Clin Orthop; 101:192-197.