PROXIMAL FEMORAL FOCAL DEFICIENCY
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| RADIOGRAPHIC CLASSIFICATION OF PROXIMAL FEMORAL FOCAL DEFICIENCY |
Proximal femoral focal deficiency is a randomly occurring congenital abnormality of the proximal femur and hip joint. It is usually unilateral and in 68% of patients is accompanied by fibular hemimelia on the ipsilateral side. About 50% of the patients have skeletal abnormalities of other limbs as well. Based on results of a large radiographic survey, proximal femoral focal deficiency has been classified into four types, according to the type and severity of the femoral and acetabular defects (see Plate 2-22).
Clinical Manifestations. Regardless of the extent of the anatomic defect, the clinical manifestations of proximal femoral focal deficiency are quite consistent (see Plate 2-23). The affected limb is held in varying degrees of flexion, abduction, and external rotation at the hip. The femoral segment of the limb is much shorter than the normal femur. In the patient with concomitant fibular hemimelia, the sole of the foot on the affected side is usually level with the knee joint on the unaffected side. Soft tissue contracture about the hip and some flexion contracture in the knee are also evident. These deformities result in a number of biomechanical problems: (1) leg-length discrepancy, (2) malrotation, (3) inadequacy of the proximal musculature, and (4) instability of the hip joint.
In patients with unilateral involvement, the unequal leg lengths
obviously hinder bipedal ambulation. In patients with bilateral involvement,
symmetric leg- length discrepancy results in a striking disproportionate
dwarfism.
Radiographic Findings. The radiographic
appearance of proximal femoral focal deficiency varies considerably according
to the extent of the anatomic defects (see Plate 2-22). The major diagnostic
problem is differentiating proximal femoral focal deficiency types A and B from
congenital short femur associated with coxa vara (see Plate 2-24). For both
conditions, radiographs taken in infancy are difficult to interpret. If the
diagnosis is uncertain, treatment should be postponed until the specific
deformity is conclusively demonstrated on serial radiographs.
Treatment. In formulating a management plan for this
complex deformity, it is important to establish early realistic goals for
rehabilitation. The primary aim is to facilitate bipedal ambulation. Although
correction of the flexion, abduction, and external rotation of the hip is desirable,
it is not always possible. Both nonsurgical and surgical methods are used to
help compensate for instability of the hip joint and inadequacy of the hip
musculature.
In the past, crutches were the only aid for patients with unilateral
involvement, and persons with dis- proportionate dwarfism simply ambulated on
their own malformed lower limbs. Later, orthoses such as shoe lifts were
devised to compensate for leg-length discrepancy
and allow some degree of unassisted ambulation. More recently, nonstandard
prostheses have been designed that better equalize limb lengths and improve
gait. In some patients, amputation facilitates the application and improves the
comfort of these prostheses.
Three general treatment options are available for patients with
unilateral involvement. The first is to fabricate a prosthesis that fits around
the deformity. The design of the
device is limited only by the ingenuity of the prosthetist. The second option
is to consider the deformity as a homologue of an above-knee amputation and to
devise the equivalent of an above-knee prosthesis that accommodates the
deformity. The third option is to consider the deformity as the equivalent of a
below- knee amputation and to design a suitable prosthesis (see Plate 2-23).
Treatment of the deformity as an above-knee amputation is facilitated by
removing the foot. The surgical procedure, which consists of ankle
disarticulation and Syme-type closure with the heel flap, produces a suitable
end-bearing stump.
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| CLINICAL PRESENTATION OF PROXIMAL FEMORAL FOCAL DEFICIENCY |
If the deformity is treated as a below-knee amputation, surgical
conversion is necessary. A 180-degree Van Ness rotational osteotomy of the
tibia is performed so that the retained ankle joint functions as a knee joint
and the remaining foot becomes the below-knee residual limb.
The patient with a bilateral condition whose primary
problem is disproportionate dwarfism should be
treated with bilateral extension prostheses that fit around the deformities.
The prostheses, which are lengthened as needed to establish peer height, make
the patient a precarious “stilt walker.” Many patients learn to ambulate quite
competently on these stilts with the assistance of a cane or crutches.
Conversion of bilateral deformities to above-knee or below-knee
amputations is not recommended because patients with bilateral involvement can
ambulate without assistance. Bilateral Syme amputations and rotational
osteotomies may rob the patient of this ability. When the deformity is treated
as a below-knee or above-knee amputation, surgical stabilization of the hip
improves gait characteristics. However, establishing a stable valgus
relationship between the head of the femur and the diaphysis is possible only
in types A and B, which have a competent acetabulum, a femoral head that
eventually ossifies, and a congruent relationship between the femoral head and
the acetabulum. Thus, hip reconstruction is indicated in types A and B only.
Other surgical modalities to promote a more stable hip (e.g., fusing the femur
to the ilium and using the knee joint as a hip joint) have not improved patient rehabilitation.
Arthrodesis of the knee is useful in selected patients. If a unilateral
deformity is converted to an end-bearing, above-knee
stump, knee arthrodesis overcomes any residual knee flexion deformity. This
technique is also beneficial in a unilateral deformity considered as a
below-knee amputation. Thus, if the rotational osteotomy is successful, the
child may be fitted with a standard below-knee prosthesis that is secured with
a thigh corset (and knee joints), without the need to use other types of
auxiliary suspension such as a suction socket.
CONGENITAL SHORT FEMUR WITH COXA VARA
Congenital short femur is classified into three distinct types: (1)
miniaturization of the femur without other deformity, (2) miniaturization of
the femur with coxa vara, and (3) miniaturization with later l bowing or angulation of
the femur (see Plate 2-24).
Coxa vara is an abnormality of the proximal femur characterized
by a neck-diaphysis angle of less than 120 degrees. Causes are multiple.
Although it is often congenital, it may also result from a metabolic aberration
or trauma. Coxa vara is associated with several types of generalized skeletal
abnormalities and often accompanies congenital short femur.
Clinical Manifestations. Leg-length discrepancy
is the major deformity in short femur with coxa vara. Unlike proximal femoral
focal deficiency, there is no flexion, abduction, and external rotation
deformity of the hip. However, fibular hemimelia with a moderately severe
valgus deformity of the ankle may also be present on the affected side,
exacerbating the leg-length discrepancy.
Radiographic Findings. Radiographs of
congenital short femur with associated coxa vara usually show the proximal end
of the femoral diaphysis in bony continuity with the femoral head and neck, and
the proximal end of the femur does not ride above Hilgenreiner’s line. On the
other hand, in proximal femoral focal deficiency types A and B, the proximal
femur usually rides above the superior rim of the acetabulum; this finding is a
useful factor in the differential diagnosis (see Plate 2-22).
Treatment. Management of a deformity of this
magnitude requires a team of specialists, including a physician interested in
such problems, an experienced prosthetist, and a skilled physical therapist, to
collectively evaluate the problem and select the most appropriate treatment modalities.
It is most important to describe to the patient and the family the overall
management plan that will result in maximal function.
Coxa vara should be treated as soon as the diagnosis is certain. The
primary goal is to establish a stable valgus relationship between the diaphysis
and the head and neck of the femur. Subtrochanteric osteotomy is performed to
produce a position of maximum valgus, not simply to restore the neck-diaphysis
angle to greater than 120 degrees. (This procedure is not appropriate for
proximal femoral focal deficiency.) Any incompetence of the acetabulum on the
affected side should be treated with appropriate hip reconstruction techniques.
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| CONGENITAL SHORT FEMUR WITH COXA VARA |
Treatment of the combined deformities of short femur and coxa vara
varies. Because the major defect is leg-length discrepancy primarily owing to
the short femur and concomitant fibular hemimelia, it is usually
difficult to equalize the levels of the knees. Shoe lifts to accommodate for
the unequal limb lengths are successful in some patients. The Syme amputation,
which produces an end-bearing below-knee stump, permits the use of a below-knee
prosthesis; in many patients, this result is both more cosmetic and possibly
more functional than a simple shoe lift with or without an orthotic device.
Some children with stable hips and knees may be
candidates for leg-lengthening procedures.
The use of shoe lifts and conversion to a below-knee amputation does not
equalize the levels of the knees, however. This can be accomplished by an
end-bearing above-knee amputation. In this procedure, a portion of the tibia is
fused to the femur and the amputation is done at a level that matches the
contralateral normal knee joint.
