Conversion of Prior Surgery to Total Hip Arthroplasty

CASE STUDY

A 50-year-old male presented with severe right hip pain, Trendelenberg gait, and limb length discrepancy. He had an open reduction with internal fixation for a childhood hip fracture. Radiographic evaluation demonstrated severe arthritic changes with proximal femoral deformity, retained hardware, and a limb length discrepancy ( Fig. 67.1 ). The patient elected to undergo total hip replacement. A cementless socket was utilized; while in the femur, a modular, cementless implant was utilized with distal fixation. The screws were removed from the plate, while the proximal end of the plate was resected to minimize hardware irritation ( Fig. 67.2 ).

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Chapter Synopsis

This chapter addresses the major issues encountered during conversion to total hip arthroplasty (THA) after an earlier nonarthroplastic procedure.

Important Points

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Although each case requires individualized attention, a thorough physical examination should be standard.
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The most common reasons for conversion procedures are childhood osteotomies and failed repairs of hip fractures.
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Issues to consider include leg length discrepancies, functional status of the abductors, anatomic distortions and old hardware that may affect implant selection, and choice of implants to achieve stability and functional range of motion.

Clinical/Surgical Pearls

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Preoperative evaluation of periarticular infection should be considered.
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Patients should be educated about expectations regarding function, gait abnormalities, and leg length discrepancy.
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Standard extensile approaches should be considered in conversion procedures.
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A trochanteric slide or osteotomy may improve exposure and avoid traumatic abductor rupture.
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Hardware should be left in situ when possible before hip dislocation to prevent iatrogenic fracture.
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Knowledge about the retained hardware can aid in its efficient removal.

Clinical/Surgical Pitfalls

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Standard implants may not be appropriate, and specialty implants that provide stability without hardware removal may be a reasonable option.
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In the early postoperative period, weight bearing may be limited, and hip abduction braces may be required.

Introduction

Conversion of a prior nonarthroplasty procedure to a total hip arthroplasty (THA) can be difficult due to retained hardware, anatomic distortions, and contractures that have developed. Each case requires individualized treatment and surgical techniques. Standard revision or specialty implants may be needed to accomplish stability and a functional range of motion (ROM). Creative planning may be necessary to achieve the appropriate outcome while minimizing the risk of perioperative complications.

Indications and Contraindications

Indications for conversion to a THA include previous pelvic or femoral osteotomies for hip containment, failed hip fracture repairs, and takedown of hip fusions. The cause of failure, which typically is specific for each patient, may be degenerative changes in the childhood osteotomy patient, articular cartilage damage, articular penetration of hardware in failed hip fracture repair, and development of ipsilateral joint arthritis after hip arthrodesis. Most patients can tolerate leg length discrepancies, limited hip ROM, and a Trendelenburg gait pattern.

A detailed history and physical examination can determine the condition that necessitated the prior surgery, any complications that occurred, and the durability of the procedure. The physical examination should include the assessment of the prior skin incisions, limb length discrepancies, abductor function, gait pattern, and neurologic status.

Leg length discrepancies should be measured and assessed as true or apparent. True leg length discrepancies are measured from the anterior superior iliac spine (ASIS) to the medial malleolus. Anatomic landmarks may be difficult to palpate, making clinical measurements inaccurate. Long leg computed tomography (CT) scanograms may be necessary for a more accurate assessment. Apparent leg length discrepancies stem from conditions that give the appearance of a shorter limb, such as pelvic obliquity from a lumbar spine condition, hip or knee flexion contractures, and hip abduction contractures.

Patients should be instructed about the difference between true and apparent leg length discrepancies and the goals of surgical intervention. The limits of limb lengthening should be explained. Rarely, a limb may need to be shortened. If shortening by more than 2 cm is required, a trochanteric advancement is required to obtain adequate abductor tension and decrease the risk of dislocation.

Abductor function and gait patterns should be assessed, and patients should be counseled about the results expected after surgical intervention. A shortened limb or decreased offset may decrease the abductor moment arm, producing a Trendelenburg gait pattern. Childhood osteotomies or hip fusions may lead to abductor atrophy or complete dysfunction. Clinical examination may not predict the overall function of the abductors. Electromyography (EMG) may provide further evidence about abductor function.

Finally, there must be a low threshold to rule out sepsis as a cause of failure. Rapid failure after hip fracture repair or a history of postoperative infection should trigger an evaluation for sepsis. Routine studies may include determinations of the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and white blood cell (WBC) count. Further evaluation can be done with CT and magnetic resonance imaging (MRI) with contrast enhancement. In cases with retained hardware, nuclear medicine scans may demonstrate a reasonable level of specificity. Elevated blood test results or a high index of suspicion necessitates preoperative culture of a hip aspirate. Intraoperative cultures should also be performed on a routine basis.

Equipment

Diligent preoperative planning is necessary for these procedures. Two major issues to consider are anatomic distortions and retained hardware. In the childhood osteotomy patient, underdevelopment of the hip joint leads to excessive acetabular anteversion and decreased lateral bony coverage of the hip. Because of poor bony coverage, use of porous-coated metal acetabular components may improve fixation. Autogenous bone graft from the removed femoral head or porous-coated metal augments may help to provide adjunctive coverage when necessary. Smaller sockets should be made available along with smaller femoral heads because the anteroposterior width of the acetabulum may be smaller than expected.

Standard proximal implants on the femoral side may not provide adequate fixation due to an incompetent proximal femur. Combined distal fixation with ingrowth or smooth, cylindrical, splined implants may be necessary for adjunctive fixation. Due to sclerotic bone and anatomic distortions that misdirect the location of the femoral canal, high-speed burs may be necessary for safe passage down the canal. Flexible reamers may be required for safer distal reaming.

Retained hardware produces a new set of challenges for removal and maintaining bone stock to obtain stable fixation. Instrumentation specific for hardware removal (e.g., intramedullary nails, blade plates, pins, screws) may aid the process. Special screwdrivers for older implants and trephines and metal-cutting instruments may be necessary to remove broken hardware. Old implants often have a layer of corticalized bone over plates and screws. Selective removal of canal hardware while retaining peripheral hardware may enable a successful reconstruction without increasing iatrogenic complications. If hardware removal is difficult or causes excessive bone loss, the procedure may be staged.

Excessive femoral anteversion and narrow diaphyseal canals may be encountered in the childhood osteotomy patient. Standard fit-and-fill implants may not properly match the situation. To obtain the appropriate anteversion, modular implants (S-ROM, DePuy, Warsaw, Ind.) or conical implants (Wagner stem, Zimmer, Warsaw, Ind.) that allow the anteversion to be adjusted should be considered. Another option is to cement an implant in a larger cement mantle at the intended anteversion. In cases of failed hip fracture repair, stabilization of the proximal femur separate from the distal fragment may be necessary. Longer revision implants may be necessary to obtain fixation in the diaphysis. Cables, wires, and plates may be necessary to stabilize the axial and rotational stability of the proximal femur.

Surgical Techniques

Preoperative Planning

Implant selection and the choice of surgical approach for revision THA depend on the physical examination results and a detailed history that considers the patient’s complaints and the timing, cause, and complications of failed prior procedures. A concise physical examination is necessary to dictate appropriate surgical approaches and implant selection. Evaluation includes documentation of apparent versus true leg length discrepancies, functional status of the abductors, preoperative hip ROM, neurologic status of the limb, and gait analysis. Femoral anteversion can be identified by an in-toeing gait, increased internal rotation, and limited external rotation. The physical examination should assess a Trendelenburg gait pattern caused by abductor dysfunction, functional hip ROM, and adjacent joint issues. A workup to rule out infection or sepsis may be necessary.

Standard anteroposterior radiographs of the pelvis and orthogonal views of the hip can identify anatomic distortions that may preclude standard implants from fitting appropriately. Oblique or Judet views of the pelvis can confirm the stability of the acetabular columns for stable socket placement. CT may provide more details about the bony anatomy, although it may be shrouded by retained hardware. Newer techniques allow improved osseous imaging with suppression of the metal hardware.

After joint reconstruction has been elected, precise preoperative planning is necessary to identify retained hardware and choose the best implant design to provide stable fixation in the specific patient. Prior operative reports can identify the retained hardware and the instrumentation needed to ease its removal. Standard screw-extraction sets and metal-cutting burs and wheels should be available. Bone-cutting bur tips are used to remove the layer of cortical bone that may have overgrown on top of a plate.

A preoperative plan includes the safe removal of retained hardware and conversion to a THA. Hardware may be retained with the placement of shorter implants that can skirt the original component. Surface replacement implants may also be considered for the correct indication. Other situations require complete hardware removal with placement of a longer femoral implant that bypasses the last screw hole by two cortical diameters to prevent a stress riser. A stress riser also may be fortified by a cortical graft strut or plate. Modular implants or conical implants can be used to adjust excessive femoral anteversion.

Approaches

Prior incisions should be used when possible with the option to extend them to longer approaches. The gluteus maximus tendon may require release to improve mobilization of the proximal femur and untethering of the sciatic nerve distally. Standard dislocation of the hip may be difficult due to anatomic distortion and adhesions. A Charnley trochanteric osteotomy or trochanteric slide may be necessary to improve hip joint visualization. When a trochanteric osteotomy is performed, a good bone bed must be available to allow fixation. A trochanteric slide is the preferred technique because the distal pull of the vastus lateralis prevents proximal migration of the fragment ( Fig. 67.3 ). A trochanteric osteotomy may be necessary for the patient with a hip fusion takedown. A basic tenet is to dislocate the hip before removal of the hardware. This prevents iatrogenic fracture of a compromised femur.