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History | Physical Examination | Radiology Studies | Diagnosis| 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 Marfanís syndrome and osteogenesis imperfecta), Pagetís 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 (Kohlerís 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 Kohlerís 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 patientís 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

  1. Bayley JC, Christie MJ, Ewald FC, Kelley K. Long-term results of total hip arthroplasty in protrusio acetabuli. J Arthroplasty 2:275-9 (1987).

  2. 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).

  3. Golding GC. Protorsio acetabuli (central luxation). Br J Surg 22:56-62 (1934).

  4. Goodman SB, Schurman DG. Miscellaneous Disorders. In: The Hip and its Disorders. Steinberg ME, ed. WB Saunders Co. Philadelphia, 1991, pp. 683-6.

  5. McBride MT, et al. Protrusio acetabuli: diagnosis and treatment. J Am Acad Orthop Surg 9:79-88 (2001).

  6. Overgaard K. Otto's disease and other forms of protorsio acetabuli. Acta Radial 16:390-410 (1935).

  7. 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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