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History | Physical
Examination | Radiology Studies
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Discussion | Clinical
Course |Case
Discussion|References
Case
Report # 2: Severe Post-traumatic Protrusio Acetabuli
Scott
I. Berkenblit, M.D., Ph.D. and David S. Hungerford, M.D.
History
This
patient is a 52-year-old male with progressive left groin pain.
The patient sustained a central fracture-dislocation of his left
hip as well as a large degloving injury to his left lateral thigh
at age 15 in a motor vehicle collision. He was treated in traction.
In spite of this injury, he has sustained a high level of physical
activity including hiking, nontechnical mountain climbing, and
backpacking. However, over the past 3 years, he has developed
progressively worsening left groin pain, radiating to the thigh,
which now limits these activities. The pain is severe and continuous
with weightbearing, only slightly relieved with rest, and moderate
at night. He has been taking oxycodone and celecoxib with partial
relief and on several occasions has taken a Medrol Dosepak, usually
just prior to going on a longer hiking expedition, with good relief.
He previously had a complete left foot drop, but over the past
few years he has regained some dorsiflexion strength in his left
ankle. Two other orthopaedic surgeons have recommended a total
hip arthroplasty. Because of his severe residual hip deformity,
he was referred to the JHU Division of Arthritis Surgery.
Past medical
and surgical history are non-contributory.
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Physical
Examination
He is
in no acute distress. He ambulated with an antalgic gait. The
left thigh and calf were significantly atrophic as compared with
the right; however, overall he appeared quite physically fit.
A well-healed wound was noted over the proximal portion of the
left lateral thigh. The left lower extremity was approximately
15mm shorter than the right. Range of motion of the left hip was
as follows: flexion from a fixed contracture of 20°
to 90°, no internal rotation, only a few degrees of external
rotation, abduction to 30°, and adduction to 30°. With
flexion of the left hip, he had obligate abduction and external
rotation. He had 2+ posterior tibial and dorsalis pedis pulses
bilaterally and intact light touch sensation throughout both lower
extremities. Motor testing revealed 4/5 strength in the left EHL
and tibialis anterior, with 5/5 strength otherwise.
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Radiology
Studies
An AP pelvis
radiograph (Fig. 1) showed marked degenerative changes in the
left hip, with a severe protrusio deformity, the medial wall of
the acetabulum having been displaced nearly to the midline of
the pelvis. This was also seen on the pelvic inlet view (Fig.
2).
 Figure
1
Figure 2
On CT scanning,
coronal slices (Fig. 3) demonstrated that the medial wall was
intact, though deformed. Axial slices (Fig. 4) revealed no defects
in the anterior or posterior columns of the acetabulum. 3-dimensional
reconstructions were also obtained (Fig. 5) and confirmed these
findings.
 Figure
3
Figure 4
 Figure
5
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Diagnosis
Post-traumatic
osteoarthritis of the left hip with severe protrusio deformity.
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Clinical
Course
The
patient elected to undergo a left total hip replacement. The preoperative
plan was to use the modified Hardinge lateral approach to the
hip and to implant a proximally porous-coated femoral component
and, if possible, a press-fit acetabular component with morcellized
bone graft.
A lateral
skin incision was made which incorporated the previous incision
distally. The modified Hardinge lateral approach was performed.
Despite obtaining adequate exposure, the hip could not be dislocated
because of the severe protrusion; thus, the femoral neck cut was
made in situ. The femoral head was retrieved from the acetabulum
and morcellized using a bone mill for use in grafting the defect.
Examination of the acetabulum revealed no defects in the rim or
the medial wall, consistent with the preoperative CT scan. On
the femoral side, a proximally porous-coated stem was implanted
in the usual fashion. On the acetabular side, the medial wall
was gently decorticated using a small acetabular reamer. The acetabular
rim was then reamed, and solid fit was obtained with a trial component.
Supplemental screw fixation was thus felt to be unnecessary. An
intraoperative cross-table AP radiograph (Fig. 6) was then obtained
to confirm adequate lateralization of the acetabular component
prior to implanting the definitive component. The psoas tendon
was found to be very tight; thus, an intrapelvic psoas tenotomy
was performed. The gap between the cup and the medial wall was
packed with the morcellized femoral head autograft.
 Figure
6
At his 3-month
postoperative visit, the patient was pain-free, had excellent
range of motion of the hip, and was eager to return to physical
activity. Radiographs at that visit (Fig. 7) revealed incorporation
of the bone graft and good alignment of his prosthesis.
 Figure
7
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Discussion
Protrusio
acetabuli is a hip deformity characterized by bulging of the
femoral head and medial acetabular wall into the pelvis. It has
been classified by Golding[3] and Overgaard[6]
into a primary or idiopathic type (also known as Otto
pelvis or arthrokatadysis) and a much more common secondary
type. There are numerous causes of secondary protrusio, including
arthritis (particularly inflammatory arthritides such as rheumatoid
arthritis and ankylosing spondylitis), infection, metabolic bone
disease, connective tissue disorders (such as Marfan’s syndrome
and osteogenesis imperfecta), Paget’s disease, bone tumors of
the acetabulum, and trauma (acetabular fracture).[4,5]
Following prosthetic hip replacement, protrusio may result from
erosion of the medial wall by an endoprosthesis or excessive reaming
of the acetabulum during total hip arthroplasty.
The severity
of a protrusio deformity may be quantified by measuring the distance
by which the acetabular outline extends medial to the ilioischial
line (Kohler’s line) or by the center-edge angle of Wiberg, which
is normally less than 40°. [5] In the
present case, the protrusion extended 4cm medial to Kohler’s line,
while the center-edge angle was approximately 75°.
Patients
with protrusio typically have decreased active and passive range
of motion of the hip and may develop a fixed flexion contracture.
A Trendelenburg limp may be present due to functional shortening
of the hip abductors. Secondary protrusio deformity usually does
not cause significant pain until degenerative changes have occcurred.[4]
For this reason, arthroplasty is usually the surgical procedure
of choice for the symptomatic adult hip with medial protrusion.
The presence
of a protrusio deformity presents several technical challenges
to performing a total hip replacement. First, the exposure is
made more difficult by the excessively medial position of the
femoral head; in some cases, the femoral neck cut must be made
in situ before the hip can be dislocated. Second, care
must be taken to adequately lateralize the acetabular component
to restore the anatomic hip center so that the upward force of
the femoral head is directed toward the ilium and the hip abductors
will have an optimal mechanical advantage.[1,2] Achieving
this position may require significant inferomedial soft tissue
releases (such as a psoas tenotomy).
Finally, stable
fixation of the component must be achieved. For mild protrusion
(<5mm), Ranawat and Zahn[7] have recommended using
a standard cup with no bone grafting. With a greater degree of
protrusio but an intact medial wall, a press-fit cup can be used
(supplemented with screws if necessary) provided that solid "rim
fit" can be achieved. The defect between the cup and the
medial wall is typically filled with morcellized bone graft, althought
a technique of bulk femoral head grafting has also been described.
With gross deficiency of the medial wall (or an associated column
defect), a more extensive option, such as an anti-protrusio ring
or cage, may be needed. The cage should be solidly fixed to the
ilium and ischium using multiple screws. Morcellized bone graft
is then packed between the cage and the medial wall, and a polyethylene
liner is cemented into the cage. Weightbearing is generally limited
in the postoperative period in order to protect the graft.
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Case
Discussion
This
patient presented with left hip osteoarthritis in the setting
of a longstanding protrusio deformity secondary to old acetabular
trauma. As his acetabular defect was purely medial, solid fixation
was achieved with a porous-coated cup placed in a more lateral
(and therefore anatomic) position against the intact acetabular
rim. The patient’s own femoral head provided sufficient bone graft
to fill the defect.
To date,
the patient has achieved a significant reduction in pain and improvement
in hip function as a result of the surgery. It is hoped that he
will be able to return to his previous level of activity. However,
he was specifically counseled about the risk of sustaining a dislocation
while hiking in the backcountry.
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References
- Bayley
JC, Christie MJ, Ewald FC, Kelley K. Long-term results of total
hip arthroplasty in protrusio acetabuli. J Arthroplasty 2:275-9
(1987).
- Crowninshield
RD, Brand RA, Pedersen DR. A stress analysis of acetabular reconstruction
in protrusio acetabuli. J Bone Joint Surg [Am] 65-A:495-9
(1983).
- Golding
GC. Protorsio acetabuli (central luxation). Br J Surg
22:56-62 (1934).
- Goodman
SB, Schurman DG. Miscellaneous Disorders. In: The Hip and its
Disorders. Steinberg ME, ed. WB Saunders Co. Philadelphia, 1991,
pp. 683-6.
- McBride
MT, et al. Protrusio acetabuli: diagnosis and treatment.
J Am Acad Orthop Surg 9:79-88 (2001).
- Overgaard
K. Otto's disease and other forms of protorsio acetabuli. Acta
Radial 16:390-410 (1935).
- Ranawat
CS, Zahn MG. Role of bone grafting in correction of protrusio
acetabuli by total hip arthroplasty. J Arthroplasty 1:131-7
(1986).
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