Overview of Endoprosthetic Reconstruction



Overview of Endoprosthetic Reconstruction


Martin M. Malawer

Kristen Kellar-Graney



BACKGROUND



  • Limb salvage—reconstruction following resection of malignant tumors of the extremities—has seen dramatic advances in a relatively brief period of time. The traditional surgical approach to the treatment of sarcoma, namely immediate amputation of the extremity, was advocated in the early 1960s and 1970s to ensure local control of disease.


  • Early pioneers in orthopaedic oncology worked diligently to define the optimal level of amputation and developed techniques to manage wounds of the pelvis and shoulder girdle following hind- or forequarter amputation. However, such aggressive surgical management failed to impact overall patient survival, with most patients dying of metastatic disease.


  • Only after the introduction of effective doxorubicin- and methotrexate-based chemotherapy protocols in the early 1970s could alternatives to amputation be considered. A handful of surgeons began to challenge the orthodoxy of amputation in children and adults with bone sarcomas. Marcove, Francis, and Enneking were among the pioneers who developed the rationale and basic techniques used in limb-sparing surgery. The former two surgeons were the first in the United States to develop endoprosthetic replacements for tumor patients.


  • Starting with a very few highly selected patients with extremity osteosarcoma, limb-sparing surgery now is a treatment option for most bone and soft tissue sarcomas not only of the extremities but of the pelvis and shoulder girdles as well.


  • Today, over 90% to 95% of tumor patients may be expected to undergo successful limb-sparing procedures when treated at a major center specializing in musculoskeletal oncology. This dramatic alteration in patient care required significant advances along many fronts, including the following:



    • Better understanding of tumor growth and metastasis


    • Determination of appropriate surgical margins


    • Use of effective induction (neoadjuvant or preoperative) chemotherapy


    • Development of improved approaches, preserving soft tissue vascularity


    • Deeper understanding of skeletal biomechanics


    • Advanced material engineering and manufacturing techniques


  • Development of inherently stable modular prostheses


  • The chapters in this section outline in specific detail many of the surgical approaches and techniques of oncologic resection and reconstruction currently used by leaders in the field of orthopaedic oncology. The importance of meticulous surgical technique cannot be overstated because this is vital to ensure an optimal oncologic and functional outcome for the patient. A successful limb-sparing surgery consists of three interdependent stages performed in sequence:



    • Tumor resection with appropriate oncologic margins


    • Reconstruction and stabilization of the involved bone and joints


    • Restoration of the soft tissue envelope for prosthetic coverage and function.


History of Endoprosthetic Reconstruction



  • Austin Moore and Harold Bohlman,9 in 1943, were the first to publish an example of endoprosthetic reconstruction for a bone tumor, consisting of a custom-designed Vitallium proximal femur used for a patient with a giant cell tumor of bone.


  • In the early 1970s, Francis and Marcove ushered in the current age of endoprosthetic reconstruction by developing prostheses to replace the distal femur and the entire femur for reconstruction following radical resection of osteosarcomas8 (FIG 1).


  • A major drawback for these custom implants quickly became evident: Each implant would take 6 to 12 weeks to manufacture, during which time the patient’s tumor could progress significantly. This led to the development of the concept of induction (initially called preoperative or neoadjuvant) chemotherapy, in which the newly proven drugs doxorubicin and methotrexate were administered during the interval between diagnosis and delivery of the manufactured custom implant.10 Both of these drugs had just been shown to have activity against bone sarcomas. Induction chemotherapy has since been adopted in the management of an increasingly large variety of other cancers.


  • As the demand for endoprosthetic reconstruction grew, a wide variety of custom implants became available from a number of orthopaedic manufacturers. Many of these early implants, however, suffered from design flaws and errors in manufacturing, resulting in significant problems with implant failures (FIG 2A).


  • However, improved material and manufacturing techniques developed for the profitable and ever-expanding market for total joint replacements eventually were applied to these “mega” prostheses. The adoption of the rotating hinge for implants around the knee and bipolar heads for the hip followed successful use of these designs for total joint replacement. Although these advances significantly improved the performance of custom implants, problems with the time required for manufacturing and the lack of flexibility at the time of implantation hampered the widespread acceptance of custom endoprosthetic reconstruction.


  • Manufacturers responded to this problem by incorporating the concept of modularity, adapting concepts and designs from modular total hip and knee prostheses to develop
    interchangeable and easily assembled endoprosthetic systems (FIG 2B,C). Although modularity increased the complexity of the mechanical construct and carried a risk of failure associated with the sum of all of the components, these potential problems were easily outweighed by significant benefits.






    FIG 1 • The first known distal femoral replacement was performed in the United States, by Kenneth Francis, at New York University in 1973. A. Distal femoral osteosarcoma treated with doxorubicin prior to surgical resection. B. Cemented distal femoral replacement with long intramedullary stems. This prosthesis used a modified Walldius fixed knee hinge. C. Scan of the front page of a historic Journal of Bone and Joint Surgery article. Original publication of the first prosthesis performed in the United States. D. Original prosthesis implanted by Drs. Bohlman and Moore for fibrous dysplasia of the proximal femur. E. Custom segmental prosthesis used during 1980s prior to the development of the MRS by Howmedica, Inc. (Rutherford, NJ). (A,B: Courtesy of Martin M. Malawer; C: From Moore AT, Bohlman HR. Metal hip joint: a case report. J Bone Joint Surg Am 1943;25[3]:688-692.)



    • The primary advantage of a modular endoprosthesis is the system’s flexibility: The surgeon can concentrate on performing the best possible oncologic resection knowing that any changes in the preoperative plan can be accommodated by selecting those components that fit the patient’s anatomy and actual skeletal defect optimally.


    • Modular trial components allow the surgeon to mix and match pieces and test the reconstruction prior to selection and assembly of the actual final prosthesis.


    • Standardization of components permits the implant manufacturer to increase the level of quality control greatly while reducing the overall cost of manufacturing through economies of scale.


    • Modular systems reduce overall inventory and time to delivery while providing a large choice of prosthetic shapes and sizes.


    • Modular systems permit hospitals to maintain an on-site inventory that has allowed these systems to be available immediately as a backup option for selected nononcologic patients, such as those undergoing difficult joint revision surgery or patients with significant periarticular fractures.


  • A first-generation modular endoprosthetic system was the Howmedica Modular Replacement System (HMRS; Howmedica International, Limerick, Ireland), designed and manufactured in Europe. This system featured intramedullary cementless press-fit stems supported by external flanges and cortical transfixation screws while the knee mechanism

    consisted of a simple hinge design. Although the system truly was modular, in clinical practice, the long-term outcomes were disappointing. Significant problems encountered with this device included aseptic stem loosening (osteolysis), substantial stress shielding with bone resorption, screw fracture and migration, and a polyethylene failure rate higher than 40% for the knee mechanism.4,6 Consequently, this system rarely was used in the United States.






    FIG 2 • A. Examples of failed, retrieved, custom endoprosthetic implants used during the 1980s. The most common mode of mechanical failure was stem breakage or bending, typically due to small stem diameter or from stress risers caused by the sharp transition from the prosthetic body to the stem. B. Modular implant design featuring a Kinematic rotating hinge knee. Interchangeable components permit easy offthe-shelf flexibility in the operating room, allowing the implant to match the patient’s anatomy. C. Intraoperative assembly of the prosthesis requires impaction of locking Morse tapers to connect the stem, body segments, and joint modules. (Courtesy of Martin M. Malawer.)






    FIG 3 • Modular saddle prosthesis (Waldemar-Link) for reconstruction of acetabular defects. A. Originally designed for revision total hip surgery, modular components of increasing size permit reconstruction of the pelvis after periacetabular resection. The prosthesis consists of the saddle portion, which articulates with the ilium (1); the base element, which provides lateral offset and allows for rotation (2,3); and the femoral stem (4). B. Postoperative radiograph 9 months after partial pelvic resection demonstrating preservation of leg length. C. Custom distal femoral replacement used in 1982. D. Custom prosthesis (1984 to 1988) now incorporating a porous collar to permit extracortical bone fixation. E. Modular distal femoral replacement introduced in 1988, featuring interchangeable off-the-shelf components. This system, with minor modifications, is still in use today. (A,B: Courtesy of Martin M. Malawer.)


  • An example of a second-generation modular system is the saddle endoprosthesis (Waldemar-Link Mark II Endo-Model Modular Saddle Prosthesis; Waldemar-Link, Hamburg, Germany; FIG 3A,B). This prosthesis, originally designed for the treatment of infected failed total hip replacements, was modified to allow for reconstruction of the hip following resection of the pelvis.


  • The unique feature of this system is the saddle itself, which is a U-shaped component that straddles the ilium, allowing motion in flexion-extension and abduction-adduction in the anteroposterior and lateral planes against the bone.


  • The saddle is attached with a rotating polyethylene-lined ring, increasing the degree of freedom and allowing for hip rotation. These are attached to a series of interchangeable modular bodies that, in turn, connect to a standard cemented femoral stem.


  • This device preserves limb length following resection of the periacetabulum (eg, type II pelvic resection, modified internal hemipelvectomy) while functioning like a total hip prosthesis. The clinical and functional results following saddle reconstruction of the pelvis with this system have been promising.1


  • The first successful universal modular system was introduced in 1988 as the Modular Segmental Replacement System (MSRS; Howmedica, Inc., Rutherford, NJ), renamed the Modular Replacement System (MRS) and now available as
    the updated Global Modular Replacement System (GMRS; Stryker/Howmedica, Inc., Mahwah, NJ; FIG 3C-E).



    • This system was designed to provide modular replacements for the proximal humerus, proximal femur, total femur, distal femur, and proximal tibia and has been instrumental in the widespread adoption of endoprosthetic reconstruction following segmental bone resection.


  • The growing popularity of endoprosthetic reconstruction has led to the introduction of similar modular systems from several orthopaedic manufacturers (eg, Orthopaedic Salvage System [Biomet, Warsaw, IN], Guardian Limb Salvage System [Wright Medical Technology, Arlington, TN]).


  • Current implant manufacturers still offer customized solutions for challenging anatomic issues. However, these custom implants often consist of a custom module mated to an existing modular system to ensure maximal flexibility.






FIG 4 • Proximal femoral replacement. A. MRS proximal femoral replacement featuring porous coating and a lateral loop to facilitate reconstruction of the hip abductors. B. Postoperative radiograph demonstrating proximal femoral replacement following tumor resection. Note that bipolar arthroplasty of the hip is performed routinely to improve hip stability, and trochanteric reconstruction using a claw with cables is used to restore hip abduction. C. Periacetabular and proximal femoral replacement using a Howmedica customized pelvic replacement for osteosarcoma of the femoral head involving the hip joint. D. Intraoperative view showing cemented fixation of pelvic implant to iliac wing. E. Postoperative radiograph demonstrating restoration of leg length and lateralization of hip. (A,B: Courtesy of Martin M. Malawer.)


TYPES OF ENDOPROSTHETIC RECONSTRUCTION



  • Specific anatomic examples of endoprosthetic reconstruction are discussed in the following paragraphs.


Hip

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Jul 22, 2016 | Posted by in ONCOLOGY | Comments Off on Overview of Endoprosthetic Reconstruction

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