1
Background
Instability of the proximal tibiofibular joint (IPTFJ) is a relatively rare cause of knee pain. Patients with this condition typically have no history of trauma or injury. This instability may also be seen in patients with generalized ligamentous laxity. In a few cases, this instability occurs following a recent high energy trauma.
IPTFJ is most commonly seen in patients who practice sports that require violent twisting motions of the flexed knee. It has been reported most frequently in wrestling, parachute jumping, martial arts, gymnastics, skiing, collective ball games, tennis, and skateboarding [ ].
Recently, it has been reported that IPTFJ may be more common than previously thought and many cases are being misdiagnosed [ ].
Instability of this joint may be anterolateral, posteromedial, or inferosuperior.
Mechanisms of the condition include posterior traction on the proximal fibula during knee extension. This traction generates an anterior-posterior motion that is more evident in young children than in adults. A laxity in the joint capsule appears in knee flexion and as a result injuries to this joint generally occur with the knee in a flexed position [ ].
Some studies have demonstrated an association between particular anatomic variations of the proximal tibiofibular joint and the potential for developing instability [ , , ].
Anterolateral dislocation is the most common dislocation of the proximal tibiofibular joint and involves injury to the anterior and posterior capsular ligaments. The dislocation is frequently associated with injury to the lateral collateral ligament [ ].
While patients with acute injury usually complain of pain and a prominence in the lateral aspect of the knee, others with microtraumatic dislocation or subluxation report lateral knee pain and instability with popping and blocking which may be confused with lateral meniscal injury.
Symptoms of subluxation are usually treated nonsurgically, but for patients with chronic pain or instability, surgical options are considered.
2
Clinical Study
2.1
Symptoms
It is very important to evaluate the patient’s history since this condition may be associated with generalized ligamentous laxity, muscular dystrophy, or Ehlers–Danlos syndrome [ , , ]. In the latter, most patients are typically preadolescent females and symptoms decrease with skeletal maturity [ ].
Subluxation of the proximal tibiofibular joint has also been described in runners who have recently increased their mileage, in patients with history of osteomyelitis, rheumatoid arthritis, and septic arthritis [ ].
Typically patients complain of pain and swelling in the lateral aspect of the knee, which is exacerbated by direct pressure over the fibular head [ ] ( Fig. 14.1 ).
Some patients may complain of difficulty when climbing stairs [ ] and weight-bearing activities may become impossible in many cases because of the pain [ ]. Dorsiflexion of the ankle aggravates the lateral knee pain [ ]. Knee motion is also very painful and patients may be unable to fully extend the knee [ ].
In most cases, no history of trauma is found and the condition is frequently bilateral [ ]. Peroneal nerve compression or irritation symptoms may be present especially with posteromedial dislocation [ ].
Recurrent or chronic dislocation of the proximal tibiofibular joint can be associated with a wide range of symptoms. Most commonly, knee instability and clicking or popping can be often mistaken for lateral injury of the meniscus [ ]. Patients in the chronic stage usually have no difficulty with daily activities, but symptoms may reappear during sports movements that require sudden changes in direction. These movements may produce symptoms of feeling of laxity and the sensation of a prominent dislocation [ ].
2.2
Physical Examination
Typically a prominent lateral mass is identified in the lateral aspect of the knee, without associated knee effusion [ ]. With anterolateral dislocation, there is usually severe pain near the fibular head and along the course of the BF tendon [ ].
Tightness of the BF muscle may be present [ ].
Pain at the lateral knee aspect is exacerbated by dorsiflexing and everting the foot and with knee extension.
The optimal method for examining the joint requires flexing the knee to 90 degrees, which relaxes the lateral collateral ligament and BF tendon. The knee is palpated for tenderness at this position. Laxity is assessed by translating the fibular head anteriorly and posteriorly while grasping it between the thumb and index finger [ ]. This test is positive if the translation reproduces the patient’s symptoms ( Fig. 14.2 ).
The Radulescu sign [ ] requires the patient to lie prone, with one hand of the examiner stabilizing the thigh and the knee flexed to 90 degrees, the leg is rotated internally with the other hand in an attempt to subluxate the fibula anteriorly.
IPTFJ present in the full extension position of the knee suggests an associated injury to the lateral collateral ligament and posterolateral structures [ ].
Examination in all patients with suspected proximal tibiofibular injuries should include an assessment of the integrity of the lateral collateral ligament and posterolateral structures of the knee. These structures are frequently injured during a proximal tibiofibular dislocation and may cause a problem in the differential diagnosis. In addition, tenderness at the popliteus tendon or BF tendon should be investigated.
3
Differential Diagnosis
The differential diagnosis for IPFTJ requires excluding a variety of pathologic conditions related to the lateral side of the knee.
3.1
Meniscal Tears or a Discoid Lateral Meniscus
These diagnoses should be suspected in patients presenting with a locking or catching sensation with positive meniscal tests.
3.2
Lateral Knee Osteophytes
Osteophytes are frequently present in case of knee osteoarthritis.
3.3
Intraarticular Loose Bodies
A history of knee trauma is suggestive of the condition, and OCD is also a possible cause of these loose bodies.
3.4
Lateral Collateral Ligament Injury
A history of knee trauma can be found and a feeling of instability can be reported by the patient.
3.5
Biceps Femoris (BF) Tendinopathy
Posterolateral signs are suggestive of this condition and positive tendinous tests help establish the diagnosis.
3.6
Iliotibial Band Syndrome (ITBS)
Lateral knee pain and a snapping a sensation of the knee in runners and cyclists is suggestive of this syndrome. Specific clinical tests confirm the diagnosis when they are present.
4
Imaging
4.1
Standard X-rays
Bilateral knee X-rays allow a comparison between the two sides and enhance diagnostic sensitivity [ ].
The accuracy of diagnosis with the anteroposterior and lateral radiographs alone is reported to be of 72.5% and up to 81.3% when the comparison views are included [ ].
Resnick et al. [ ] described a line on lateral radiographs that follows the lateral tibial spine distally along the posterior aspect of the tibia and defines the most posteromedial portion of the lateral tibial condyle. In a normal knee, this line is found over the midpoint of the fibular head. In anterolateral dislocations, the fibular head will be anterior to this line on the lateral view. In posteromedial dislocations, the whole or most of the fibular head is posterior to this line on the lateral view ( Fig. 14.3 ).
