Clinical History
We present a 3-year-old female, which was followed at our institution because of limb length discrepancy, with a shortening of the right lower limb.
Imaging Findings
Radiography showed absence of the fibula in both frontal and lateral incidences. Marked limb length discrepancy was noted (limb length discrepancy of 6, 2 cm), with both tibial and femoral shortening. The distal ephiphysis of the right tibia was small and deformed (Fig. 1a). There was associated talipes equinovalgus malformation of the right foot, with a normal anatomy of the foot documented at antero-posterior radiography (Fig. 1b). Similar findings are seen on MRI, and moreover, it was possible to observe some associated findings including absence of both cruciate ligaments and an abnormally elongated conjoint tendon of LCL and biceps femoris (Fig. 2 – 3).
Discussion
Fibular hemimelia (FH) is a complex congenital disorder with a clinical spectrum ranging from mild hypoplasia to complete aplasia [1, 2]. Although rare, with an incidence of 7 to 20 cases/million births, FH is the most common congenital long bone absence [3, 4]. Unilateral involvement is more common, with a slight male predominance. Most cases represent an isolated and sporadic event [2]. The precise aetiology of FH is unclear.
FH can be asymptomatic, but is usually obvious at birth with limb shortening and limb length discrepancy [3]. It may be detected antenatally during obstetric ultrasound. In these cases, a CT or preferentially an MRI precisely documents fetal skeletal abnormalities, enabling the clinician to inform on the possible management modalities, so that the couple can decide in favour or against a medical interruption of pregnancy [5].
Imaging demonstrates an absent or hypoplasic fibula and occasional associated lower limb findings: short and bowed tibia, tarsal and metatarsal abnormalities, and femoral shortening or deficiency [6]. Other associations may include small, subluxed, or dislocated patellae, hypoplastic femoral condyles, and knee ligamentous deficiencies [6]. Radiography shows absence of the fibula in frontal and lateral incidences. CT shows absence of the fibula, and some bone associated anomalies. MR shows the same features, but it is better in statement of the associated abnormalities, particularly if surgery is contemplated. Particularly significant is the MR role in characterization of knee abnormalities. The meniscal and the collateral ligament (LCL) abnormalities are lateral in location. The posterolateral corner structures are abnormal given the absence or hypoplasia of the proximal fibula. This manifests as an abnormally elongated conjoint tendon of LCL and biceps femoris. This conjoint tendon is often joined by a thickened ligament arising from the posterior horn of the lateral meniscus. It is common to see a dysplastic trochlear groove, abnormal patellar tendon, hypoplasia of the lateral femoral condyle and a hypoplastic posterior horn of the lateral meniscus. The findings of intercondylar dysplasia, absent tibial spines and absent cruciate ligaments are characteristic, but not always present. The abnormal posterolateral structures, combined with cruciate ligament deficiency could be associated with joint subluxation, stress change and early degenerative findings [1].
The surgical therapies for FH should be individualized and include limb-lengthening procedures and amputation. If there is a nonfunctional foot or a limb length discrepancy >30%, surgical amputation is generally recommended [2]. Knee joint associated abnormalities may influence orthopaedic management [1].
Differential Diagnosis List
Fibular hemimelia
Surgical absence of the fibula
Fibular hemimelia
