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Presentation highlights why preventing TKA bone loss is critical
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WAILEA, Hawaii, USA — The treatment of bone loss in revision total knee arthroplasty often requires a careful team approach. The use of bone defect classifications and an awareness of all the options available to the surgeon are important when planning these often challenging cases, according to a presenter at Orthopedics Today Hawaii 2014.
At the meeting, Andrew S. Shimmin, MD, MBBS, FRACS, of Melbourne Orthopedic Group, in Windsor, Victoria, Australia, discussed preoperative planning strategies for managing bone loss during revision total knee arthroplasty (TKA) and noted that those surgeons who are unfamiliar with these procedures should work with a team.
The surgeon should assess the patient’s skin, extensor mechanism, the type and fixation of the implant to be removed, the ligament integrity and instability patterns, according to Shimmin.
Furthermore, he said the orthopaedic surgeon needs to know about the available options for constraint, bone grafts, and metal stems and augments. The surgeon should anticipate the possible requirements for morselized or structural allograft or the use of trabecular metal augments or cones. In severe cases of bone loss, hinged implants or megaprostheses may be required.
Measure and classify
Shimmin said the goal of reconstruction is to restore structural support for the revision implant and joint line. He explained the distal and posterior aspect of the femoral component should be 25 mm from the lateral epicondyle and 30 mm from the medial epicondyle,. The reconstructed proximal tibia should be 10 mm above the fibular head.
The options the surgeon uses for reconstruction depend on the bone defect classification and the patient’s general health, according to Shimmin, who reviewed the differences between Anderson Orthopedic Research Institute (AORI) class I, II and III defects.
Class I bone defects are minor defects in the femur or tibia that do not affect the joint line. “Anderson Orthopedic Institute class I is the most common and easiest to deal with,” he said. “The stability of the implant and implant fixation is not going to be compromised and bone loss can often be managed with morselized allograft or cement.”
Class II defects
According to Shimmin, AORI class II(A) defects are associated with damage and loss of metaphyseal bone on only one side of the condyle of the involved femur or tibia, whereas in class II(B) defects there is damage and loss of metaphyseal bone on both condyles of the involved tibia or femur.
“The collateral ligaments are usually still intact, but these defects require reconstruction to allow for stable implant fixation,” he said.
The reconstruction options the surgeon should consider for these defects are metal augments, bone grafts and trabecular metal cones. Stem augments on the implants will usually be required.
AORI class III patients present with significantly deficient metaphyseal segments in the femur or tibia and significant cortical bone loss and compromised ligaments. “This requires the big guns,” Shimmin said. “[Options] include structural allografts, trabecular metal sleeves or cones and always stems. Hinged implants find their place with these defects.” – by Renee Blisard Buddle
- Reference:
- Shimmin AS. Preoperative planning and management of bone loss in revision knee replacement. Presented at: Orthopedics Today Hawaii 2014; Jan. 19-23, 2014; Wailea, Hawaii, USA.
- For more information:
- Andrew S. Shimmin, MD, MBBS, FRACS, can be reached at Melbourne Orthopedic Group, 33 The Avenue, Windsor 3181 Victoria, Australia; email: ashimmin@optusnet.com.au.
Disclosure: Shimmin is a consultant to and receives royalties from Corin Group and MatOrtho.