VI./1.: Deformities of the hip joint – prearthroses

VI./1.: Deformities of the hip joint – prearthroses
In this chapter we describe the different anatomical variations and deformities of the
hip joint that lead to clinical signs and symptoms. After readers familiarize
themselves with this chapter they will be able to recognize these diseases and
evaluate them in a differential diagnostic scenario. We will also give a short
overview of surgical treatment options.
VI./1.1.: Definition
The most common disease of the hip joint in adults is degeneration of the cartilage surfaces,
in other words primary osteoarthritis of the hip. Certain anatomical variations or deformities
may also create biomechanical circumstances that lead to secondary degradation of the
cartilage, namely secondary osteoarthritis of the hip. These preceding pathologies are called
prearthroses. In these cases the hyaline cartilage surface of the femoral head is still intact
but more rapid degradation of the cartilage and the development of arthritis may be
foreseen.
Figure :1.: Radiograph showing primary osteoarthritis Figure 2.: Radiographs showing secondary osteoarthritis
of the hip
of the hip.
VI./1.2.: Etiological factors
Certain pediatric disorders of the hip joint (i.e. slipped capital epiphysis, Legg-CalvéPerthes-disease) or congenital impairments (i.e. dysplasia of the hip) may lead to
deformities that cause incongruence within the joint (see in the appropriate chapter).
Inflammatory diseases (i.e. purulent coxitis), tumors or injuries (so-called post-traumatic
conditions) may also cause an imbalance between the femoral head and the acetabulum.
Figure 3.: Radiograph of slipped capital epiphysis on
the left side.
Figure 4.: Radiograph of a hip after history of purulent
coxitis on the left side.
Figure 5.: Radiograph showing secondary arthritis following hip fracture on the left side.
The extent of cartilage degradation is a factor of the pressure on the hip joint (body weight),
friction and congruence (the size of the connecting surfaces). If a small region of the hyaline
cartilage comes to be under the great amount of pressure, and certain regions are no longer
connected to the opposing surfaces, cartilage degrades – arthritis begins.
VI./1.3.: Clinical presentation
Abnormal collodiaphyseal angles, incongruences in the joint surface and subluxation are
conditions that cause degeneration, and are therefore prearthroses. The angle between the
femur and the femoral neck (CCD or collodiaphyseal angle) is normally between 126 and
135° in adults.
VI./1.3.1.: Coxa valga
Coxa valga is a deformity where the femoral neck is steeper than usual, meaning that the
CCD angle is greater than 135°. This means that part of the femoral head (the craniolateral
part) may no longer be covered by the bony acetabulum, so the size of weight-bearing
surface decreases, leading to incongruence of the joint (coxa valga subluxans). This is often
associated with dysplasia of the acetabulum, meaning that the acetabulum is steeper,
shallower and flatter than normal. This makes the incongruence more severe.
We often see dysplasia and coxa valga together. Severity varies and the deformity may be
classified according to three categories (based on Hartofilakidis): dysplasia without
subluxation (A), mild subluxation, when femoral head is in line with the acetabulum (B)
and high subluxation, with a secondary joint socket is located cranial to the primary
acetabulum. If the deformity is unilateral patients may develop a significant difference in
the length of the lower extremities.
Patients with coxa valga develop symptoms in the 2nd-4th decade of life after a long
symptom free period, complaints include pain around the groin and the greater trochanter,
tiredness, limited range of motion and limping. We may expect that degeneration of the
cartilage will become more rapid after the appearance of symptoms.
Figure 6. : Radiograph showing coxa valga
subluxans.
Figure 7.: Radiograph showing high dislocation on the left
hip.
VI./1.3.2.: Coxa vara
This deformity is characterized by a more horizontal and usually short femoral neck and a
CCD below 120°. This deformity may be caused by a dislocated hip – that was not treated
appropriately (osteochondritis) or Legg-Calvé-Perthes-disease (see the appropriate chapter).
Slipped capital epiphysis may also result in the femoral neck becoming more horizontal
thereby causing incongruence in the hip joint.
Shortening of the extremity may be conspicuous in unilateral cases.
Figure 8.: Radiograph showing coxa vara infantum on the right side.
Coxa vara may also develop due to other underlying causes: hip fracture that healed in an
incorrect position, osteomalacia, rickets and fibrous dysplasia (see the appropriate chapters).
Similar to coxa valga, clinical symptoms vary widely. The limitation in a range of motion is
usually more severe in coxa vara, walking patterns are disharmonic.
VI./1.3.3: Torsion deformities of the femoral head
Torsion is the rotation of the proximal end of the femur around the longitudinal axis of the
femur. If ventral torsion is greater than the 12-15 degrees normally found in adults it is
called antetorsion. If ventral torsion if less than 12° it is considered retrotorsion.
Increased antetorsion is the most frequently associated with hip dysplasia with the proximal
femur twists forward making the diameter smaller (narrow intramedullary canal). We often
see increased antetorsion in patients suffering from infantile cerebral palsy.
Figure: 9.: Radiograph showing coxa valga and antetorsion deformities.
A pronounced antetorsion causes patients to walk with their lower extremity rotated inward,
making their walking pattern unique.
Figure 10.: Characteristic position of the lower extremity of patients suffering from infantile cerebral palsy.
Patients X-ray may be seen on figure 9.
VI./1.3.4.: Acetabular protrusion
The basis of this deformity is that the medial wall of the acetabulum thins out, which makes
the socket deeper, so the rotational point of the femoral head and the femur becomes more
medial. This leads to an unfavorable biomechanical conditions causing cartilage
degeneration of accelerated progression. Because most of the femoral neck is situated
within the socket, range of motion in the hip becomes limited very quickly, and motions
become uniaxial.
We differentiate between three forms: juvenile, protrusion seen in the elderly, and secondary
protrusion, caused by some underlying disease (osteoporosis, inflammation, trauma, etc.).
Figure 11.: Coxa vara deformity in a patient suffering from osteoporomalatia, which leads to secondary
acetabulum protrusion and consequential osteoarthritis.
VI./1.4.: Physical examination of hip deformities
VI./1.4.1.: Examination of walking pattern
Observation of patients walking pattern may reveal limping which is caused by the patient
wanting to stress the painful hip for a short period of time only. In these cases steps also
become shorter. Walking also becomes less dynamic if pain is severe, and the patient will
walk with slow steps. The difference in lower limb length causes the patient to try and
compensate with a special kind of limping, tilting the pelvis on the shorter side and bending
of the knee of the longer side (semiflection position). In case of coxa vara or a subluxated
hip joint insufficient function of the hip abductors (primarily the gluteus medius muscle)
leads to Trendelenburg’s gait. In these cases the insufficient abductor muscles are unable to
keep the pelvis in the horizontal position causing it tilt to the other side.
Video 1.: Physical examination of the hip joint
Figure 12.: Positive Trendelenburg’s sign
on the left side- the insufficiency of the
gluteus muscles cause the pelvis to tilt
lower than horizontal on the non weightbearing side. Patient tilts toward the
weight bearing side because this is the
only way they can retain balance.
VI./1.4.2.: Physical examination of the lower extremity
Range of motion and contractures in the hip joint are tested for primarily. Extension in the
hip decreases soon, which may be examined if the patient lies down or stands upright. A
decrease in abduction may also be an early symptom. If the cartilage is already affected
forced internal rotation may be painful if the hip is flexed. Flexion contracture of the hip
may be examined with the Thomas’ maneuver. Protrusion causes a concentric decrease in
range of motion in the hip and motions become uniaxial.
Video 2.: Thomas-maneuver
VI./1.4.3.: Evaluating limb length
We frequently see a difference in the length of the lower extremities if patient suffering
from prearthrosis. In case of unilateral impairments when the contra-lateral hip shows
normal anatomy, the difference is clear and conspicuous. If the impairment is bilateral a
difference in limb length may be difficult to diagnose.
When examining a patient who is lying down care should be taken that the lower
extremities are parallel and the pelvis is horizontal. Adduction and abduction positions may
cause virtual differences in length. In this case length of the extremity should be measured
according to fix anatomical positions (i.e. the distance between the anterior inferior iliac
spina and the medial malleolus, as we may see on the image showing examination of the
hip). When examining a patient who is standing upright care must be taken that the knees
are extended and we should try to place the pelvis in a horizontal position by putting
padding under the shorter extremity. The height of the padding will give us the difference in
length between the two extremities.
VI./1.5.: Radiological studies
An overview of the pelvis, meaning an A-P image provides much information on the
relationship of the femoral neck and the socket. The CCD angle is determined primarily
which helps evaluate whether patient has coxa valga or coxa vara. The rotational point of
the femoral head is also determined, and the position of the rotational point (the hip center)
compared to the primary acetabulum should also be assessed (subluxation/luxation). The
shape of the femoral head may also be revealing: it may draw attention to earlier
inflammations, trauma or other diseases.
Figure 13.: Radiograph showing necrosis of the femoral
head on the left side.
Figure 14.: MRI image of the femoral head necrosis
feed(?) on figure 13.
Radiological imaging of the acetabulum deserves special attention. The angle of the
acetabular roof contains significant information on the depth of the socket. A value of
around 60° means that the socket is shallow. If the Wiberg-angle (CE-angle) is below 20°
that means that the acetabulum is dysplastic, and if it is above 40° that means that there is
protrusion in the joint (see the appropriate chapter).
The joint gap is intact in prearthrosis, and other radiological signs of arthrosis are also
absent in these cases.
CT imaging may reveal an increased antetorsion of the femoral neck, and will show the
position of the femoral head in comparison to the acetabulum, and possible incongruences
as well. 3D reconstruction may help better visualize the hip joint, for example in case of
surgical planning.
VI./1.6.: Surgical treatment options
Correctional operations, osteotomies performed around the hip have become less frequent
surgical procedures nowadays. One of the reasons is infants undergo screening and
congenital hip deformities are treated early-on. If surgical treatment is necessary it is
performed in childhood. The other reason is the development of joint endoprostheses and
minimally invasive techniques. Because of these it is possible to provide younger patients
with more difficult anatomical variations with joint endoprostheses. It may still be necessary
to perform corrective surgery on young patients suffering from prearthrosis, which may be
considered a preventive surgery as the aim is to prevent or delay the development of severe
arthrosis.
Video 3.: Post surgical X-ray of cemented total hip arthroplasty (THA)
VI./1.6.1.: Intertrochanteric femur osteotomy
The biomechanical conditions of the proximal femur may be corrected with osteotomies.
The goal of this surgical technique is to change the position of the femoral neck in
comparison to the acetabulum, thereby improving congruence. Bony coverage of the
femoral head must be ensured.
The effects of intertrochanteric osteotomies are complex: centralizing the femoral head
improves congruence of the joint and muscle strength improves as the distance between
origin and insertion is altered, and changing the CCD angle decreases the pressure on the
joint. Effects of surgery also include a so-called biological effect which is caused by
improved circulation of the bone following osteotomy.
VI./1.6.1.1.: Coxa valga
In case of coxa valga we may rotate the part of the femoral head that did not have bony
coverage before in under the acetabulum be performing a varus osteotomy. To do this we
have to cut a wedge with a medial base from the intertrochanteric region. We stabilize the
bone surfaces created with the oscillating saw in a corrected position with special plates
(stable ostesynthesis). This surgical procedure requires preoperative planning and
investigations. Having abduction reserves is a prerequisite for surgery.
Figure 15.ábra: Radiograph showing coxa valga. Surgical
solution is shown on figure 16.
Figure 16.: Varus, derotational femur osteotomy in
coxa valga. Preoperative X-ray is shown on figure
15.
VI./1.6.1.2.: Coxa vara
Correction of coxa vara may be done by performing a valgus intertrochanteric osteotomy,
where opposed to the previous the base of the wedge taken from the femur faces laterally.
This will increase the CCD angle and the tension of hip abductors will improve.
VI./1.6.2.: Pelvic osteotomy
If complete bony coverage of the femoral head cannot be achieved by intertrochanteric
osteotomy, we may perform a pelvic osteotomy as well. This procedure is seldom
performed on adults. The Chiari-osteotomy, which was often performed earlier was a
horizontal osteotomy where the cranial part of the pelvis was moved laterally to increase
bony coverage of the femoral head. One of its disadvantages is that the weight bearing zone
of the femoral head does not face the surface covered by hyaline cartilage. If the socket is
cranially augmented with a bone graft it increases the weight-bearing surface
extraarticularily, thereby improving joint congruence.
Both biomechanically and in terms of hyaline cartilage best results are achieved when the
entire acetabulum if mobilized and shifted into a favorable position. This complex surgery
is the Tönnis triple osteotomy. During this procedure all three bones of the pelvis are sawed
through (see the appropriate chapter).
Literature
Obligatory literature:
Miklós Szendrői: Orthopedics chapter 28.2
Recommended literature:
http://emedicine.medscape.com
http://www.wheelessonline.com/ortho/pelvic_osteotomy_for_ddh
R.Schneider: Die intertrochantere Osteotomie bei Coxarthrose (1998 Springer)