- Tibial hemimelia is a spectrum of deformity characterized by a shortened or absent tibia and relatively unaffected fibula; duplication of the great toe may be the only clinical finding in subtle deformity
- Tibial hemimelia is usually associated with lower extremity deformities and other organ system malformations, most commonly of the foot
- The Jones radiographic classification of tibial hemimelia is the most widely utilized system and assists in treatment planning
- Decision to amputate versus reconstruct depends on, amongst other things, the ability to completely extend the knee joint with active quadriceps function
- Most patients will require some form of amputation, almost all patients will require surgical intervention, and all patients will require orthotic treatment at some point in their lives
Tibial hemimelia has been referred to in the literature by many names, including paraxial tibial hemimelia, congenital deficiency or absence of the tibia, congenital longitudinal deficiency of the tibia, congenital dysplasia of the tibia and congenital tibial deficiency. These names are utilized to describe not a single disorder but a spectrum of deformity that affects the lower limb in general and the tibia in particular. This spectrum begins with the mildest form, where only mild hypoplasia or shortening of the tibia is observed, and ranges to the most severe, where the tibia is absent in its entirety. The term ‘tibial hemimelia’ is more widely accepted in the pediatric orthopaedic literature and is therefore preferred in this text.
The incidence of tibial hemimelia has been estimated to be 1 in 1 million live births (Brown, 1971), making it one of the rarest congenital lower-limb deformities seen. The condition may be bilateral in about 30% of patients and associated with other anomalies (Brown, 1971; Clinton, 2014), the most common of which is deformities of the foot, although deformities of the ipsilateral femur, hip dysplasia, upper extremity and spinal anomalies have also been reported. A definite genetic pattern of inheritance has not been identified; most cases occur spontaneously although autosomal dominant or recessive transmission patterns have been reported in the literature (Richieri-Costa, 1987). Four syndromes include tibial hemimelia as their component: Werner syndrome (polydactyly-triphalangeal thumb syndrome), tibial hemimelia diplopodia, tibial hemimelia-split hand/foot syndrome and tibial hemimelia-micromelia-trigonal brachycephaly syndrome (Morrissy, 2006).
The characteristic appearance of a child with isolated tibial hemimelia is of a shortened lower limb bowed to variable degree. There may be a skin dimple in the area of the proximal tibia. The tibia is absent or hypoplastic, but if present may be palpated below the femur. The fibula is intact and may be palpable as a distinct bony prominence near the knee. The foot is in stiff equinovarus[ZDO1] especially of the hindfoot, with the plantar surface pointing toward the perineum. Often, foot anomalies such as duplication of rays, shortening of the first metatarsal, and loss of medial rays with multiplication of lateral rays may be seen. In very mild deformities duplication of the great toe may be the only clinical sign of tibial hemimelia. Flexion contracture of the knee to a variable degree is almost always present. Quadriceps function will determine prognosis and choice of surgical procedures, and should be carefully assessed. If the tibia is completely absent, distal femoral hypoplasia may be noted on clinical examination (Clinton, 2014;Jones, 1978;Kalamchi, 1985;Morrissy, 2006;Weber, 2008).
Radiographically, there is tibial hypoplasia or absence with an intact fibula. In young children, the proximal tibial anlage may be cartilaginous in nature and therefore will not appear on x-ray. A good determinant for its presence is the appearance of the distal femoral epiphysis which, in the case of complete tibial absence, will be obviously hypoplastic in nature. MRI is very helpful for evaluation of a cartilaginous anlage in a younger patient, although its precise role is still unclear due to the rarity of the condition. The exact radiographic appearance of tibial hemimelia depends on its type and is summarized below.
Jones classified tibial hemimelia into four types based on radiographic appearance of 29 patients of variable age. It remains the most commonly utilized classification for tibial hemimelia at this time (Jones, 1978).
In type I tibial hemimelia the tibia is completely absent. Depending on the appearance of the distal femoral epiphysis, it is further subdivided into Type Ia, where the femur is hypoplastic, and Type Ib where the femoral epiphysis is normal. This latter situation is an indication of the presence of a cartilaginous tibial anlage and it should be expected to ossify as the child grows.
The proximal epiphysis is preserved with a short segment of tibia; the distal epiphysis is absent.
In this type, the distal epiphysis is present with a short segment of tibia; the proximal epiphysis is absent. This is the least common type of tibial hemimelia (Clinton, 2014; Jones, 1978; Schoenecker, 1989), and it has been postulated that a true Type III tibial hemimelia does not exist but will transform into Type 1B given time (Clinton, 2014).
The radiographic deformity noted in this patient population is diastasis of the ankle. The fibula is relatively longer and displaced proximally at the knee. This form demonstrates wide variability in severity and may be diagnosed later in life.
Clinton et al. reported on their experience with 125 limbs in 90 children with tibial hemimelia. In this series, the authors report that 11-15% of their patients were not classifiable per the Jones classification, and proposed a 5th group for these patients, all having a similar appearance with global tibial deficiency of variable severity with relative proximal and distal fibular overgrowth. (Clinton, 2014) This group had a stable or resolving anterolateral bow and multiplication of the great toe. Other classification systems such as the Kalamchi classification and the Weber scoring system exist, but have not gained widespread acceptance. (Kalamchi, 1985; Weber, 2008)
The treatment of tibial hemimelia aims to achieve a functional limb equal in length to the normal limb at maturity, with a plantigrade, stable and flexible foot. Treatment of tibial hemimelia should be highly individualized to the patient and undertaken in experienced centers with access to multidisciplinary teams. Patients should be screened for associated anomalies before surgical treatment is initiated.
A great majority of patients with tibial hemimelia will require surgical treatment of some form for their deformity. Most, if not all, will benefit from orthotic treatment, with many requiring specialized and custom-made orthoses.
The decision to amputate or salvage a limb with tibial hemimelia depends on the presence of a competent quadriceps mechanism. Reconstructive treatment in the absence of this criterion has uniformly resulted in suboptimal results. While projected limb-length discrepancy may play a role in the presence of a reconstructable knee, with today’s modern limb lengthening methods where lengthening in excess of 25 cm have been reported with acceptable complications, this is a secondary concern.
Surgical Treatment According to Jones Type
In the complete absence of the proximal tibial anlage, there will be no attachment of the quadriceps mechanism to the lower leg. Knee disarticulation and prosthetic treatment is preferred over above-knee amputation as in the latter case stump overgrowth may become problematic later. As femoral growth is also stunted in this subtype, at maturity a knee disarticulation will essentially function as an above-knee amputation. The hypoplasia of femoral condyles may interfere with prosthetic fitting and require specially designed orthoses.
Brown described a reconstruction for this subtype where the fibula is centralized under the intercondylar notch of the femur, with modest success. Modern series have failed to replicate his results. Loder et al. reported on nine limbs in six patients who underwent fibular centralization for tibial hemimelia. Although initially the reconstructed knees appeared satisfactory, all nine knees eventually developed knee flexion contractures, with only one knee preserving quadriceps function (Loder, 1987). In their series of 57 patients, Schoenecker et al. had good results with knee disarticulation for type 1A limbs, and recommended tibiofibular synostosis in type 1B limbs. Of note, 61 of their 71 limbs with tibial hemimelia required an ablative procedure such as Syme’s or Chopart’s amputation (Schoenecker, 1989).
More recently, the indications for the Brown procedure were redefined to include children younger than 1 year, preferably 6 months, with the physical potential to walk, a functioning quadriceps and full passive extension of the knee. However, even with these indications, 45% patients in one series required at least one reoperation (Jayakumar, 1979). In order to fulfill these new surgical criteria, a proximal tibial anlage generally is required, in which case a tibiofibular synostosis may become indicated, which is discussed further below. At present, the most common treatment for unilateral type 1A tibial hemimelia is knee disarticulation and prosthetic fitting.
Type 1B and 2
In these patients, a proximal tibial anlage exists, and with it, an attachment site for the quadriceps. Generally, the knee is functional and therefore reconstruction is a viable option.
For proximal reconstruction, a tibiofibular synostosis is generally preferred. The fibula is cut at the level of the distal tibial stump and transferred underneath the tibia to create a synostosis. This may be done side-to-side or, more commonly, end-to-end. After this transfer, the fibula can be observed in time to increase in size and become tibia-like in shape. Without reconstruction, the fibula generally exhibits variable degrees of bowing and worsening of the deformity.
If a functional ankle cannot be obtained, a Syme or similar partial amputation can be employed.
Type 2 and 4
In these types where the proximal tibia is present in its entirety, leg-length equalization and the establishment of a stable ankle gains priority. The knee in these patients is functional. Amputation may be required distally, depending on the extent of foot and ankle deformities. A procedure has been defined where the foot is fused to the tibia in maximum equinus to utilize its length. Especially in type 4, although the clinical appearance may appear more benign, there is a great deal of variability requiring individualized treatment, including but not limited to distal tibiofibular synostosis, epiphysiodesis and lengthening procedures (Clinton, 2014; Schoenecker, 1989). The family should be counseled that although the tibia is present, the deformity is profound and may require amputation of the foot due to an unreconstructable ankle joint and/or severe limb-length deficiency.
Seen 1 in 1 million live births, tibial hemimelia is a spectrum of deformity that can range from mild hypoplasia and shortening of the tibia to its complete absence, and accompanied by a variety of abnormalities affecting the foot. The most significant determinant for treatment selection is the presence of a functional knee joint including active quadriceps extension. Reconstruction in the absence of a functional, fully-extendable knee joint has met with poor results in the past. For patients with functional knee joints, the severity of foot deformity and expected limb-length discrepancy at maturity becomes the determinant of prognosis. Treatment should be highly individualized and undertaken in centers experienced in congenital lower extremity anomalies, with access to sufficient equipment and multidisciplinary staff.
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Z. Deniz Olgun, M.D.
Raymond W. Liu, M.D.