My involvement in the DEFENSE side of MoM hip litigation has allowed me the luxury of reflection and continued study of the basic and clinical science and voluminous medical and scientific literature concerning this particular wear couple. Much of what I have learned is relevant to other articular couples, and might help you in your next THR. While useful, Although MoM implants underwent rigorous pre-market testing and evaluation by the industry and appropriate regulatory approval in both the US and EU, the process cannot assure the clinical safety or success of new designs and materials for all implant recipients. Two year results obtained in pre-market (IDE) studies are of insufficient follow-up for accurate evaluation of the short, and certainly medium, or long-term clinical performance of new materials or designs, as demonstrated by the two year data from the Australian Joint Registry. In certain populations, MoM bearings have performed satisfactorily (to date) in individuals for whom traditional bearings were a poor option. Be conservative. Use appropriate clinical judgment and careful informed consent if you recommend new designs or materials to your patient.Conclusions
No, not my mother, but metal-on-metal (MoM) hips! My involvement in the DEFENSE side of MoM hips has allowed me the luxury of reflection and continued study on the basic and clinical science of this particular wear couple. Much of what I have learned is relevant to other articular couples, and might help you in your next THR. No amount of in vitro laboratory testing can replicate or predict in vivo behavior of a particular wear couple. (Mother Nature always has something new to teach us!) Although MoM implants went through complete pre-market evaluation and approval in both the US and EU, the process is inadequate and does not assure safety or success of new designs and materials. Two year results obtained in pre-market (IDE) studies are of insufficient follow-up for accurate evaluation of new materials or designs. Be conservative! Be neither the first, nor the last, to embrace new technology! Clinical experience and retrieval analysis of MoM devices has revealed factors that are not as apparent for other wear couples such as metal-on-polyethylene (MoP), or ceramic-on-ceramic (CoC). For instance: All THR's are at risk of micro-lateralization, or displacement of the femoral head from the acetabular wear couple during swing phase, resulting in edge loading. In addition, impingement or displacement related to component malposition or failure to balance the soft tissues about the hip can produce subluxation, producing edge loading and accelerated wear. In the case of MoM implants, the tribology and wear properties of MoM produce identifiable wear scars; all MoM designs appear to be subject to these phenomena. However, evidence now exists that both MoP and CoC wear couples are at similar risk for accelerated wear, although at different rates than MoM. Hard-on-hard wear couples (ceramic, metal) are less tolerant of edge loading than hard-on-soft (e.g., MoP or CoP) wear couples, and therefore require a higher degree of surgical precision in implant placement and reconstruction of the soft tissue balance of the hip. One of the previously unrecognised factors that can change relative implant position (and therefore, the risk of subluxation or edge loading) is the effect of the lumbar spine on apparent acetabular component position (e.g., changes between sitting, standing, or lying prone). This is largely due to the effect of lumbar spine flexibility, as shown in both orthogonal x-ray (“EOSr”) studies, and dynamic CAT scan studies. There is currently no validated algorithm or technique to assess these factors; however, surgeon awareness and at least clinical assessment preoperatively may result in better positioning of implants. Femoral component position can also have a major effect of the risk of impingement or subluxation of the femoral head; the combined anteversion concept of Dorr et al. should be rigorously adhered during THR. Other issues such as fretting corrosion associated with large diameter femoral heads and tissue response to wear debris may not be anticipated until a very large cohort population is available for examination and analysis. No matter how extensive in vitro testing may be, only clinical experience and retrieval analysis can provide the ultimate reassurance as to the success of a new design or material.
The following checklist is derived from the “Proceedings of the International Consensus Meeting on Peri-prosthetic Joint Infection”, under the auspices of the Musculoskeletal Infection Society, August 1, 2013. It is available online at Pre-Operative: Patient Factors, AODM, Obesity, Smoking, Immunodeficiency, ASA score > 2, Prior open surgery?, MRSA history, EtOH abuse, Malnutrition, Anemia, Recurrent infections Peri-Operative: Avoid pre-op hospitalization, Chlorhexidine scrub < 6 h pre-op, Hair removal: depilatory or clipper, Appropriate Antibiotic Prophylaxis, Cephalosporin 30–60 min pre-incision, or Vancomycin 1 hour pre-incision, Alcohol based hand emollient after antiseptic soap hand scrub, Limit OR Traffic and Talking!, Double glove, change gloves q2h, ABC bone cement: revisions, high risk patients (immunocompromised), Dilute Betadiner lavage? Post-Operative: Careful wound closure (Sealed, dry), Sterile, impervious dressing x 24 h, Drain optional, < 48 h, Antibiotic prophylaxis x 24 h, Aggressive drainage hematomas
The following checklist is derived from the “Proceedings of the International Consensus Meeting on Periprosthetic Joint Infection”, under the auspices of the Musculoskeletal Infection Society, August 1, 2013. It is available online at Pre-Operative: Patient Factors, AODM, Obesity, Smoking, Immunodeficiency, ASA score > 2, Prior open surgery?, MRSA history, EtOH abuse, Malnutrition, Anemia, Recurrent infections Peri-Operative: Avoid pre-op hospitalisation, Chlorhexidine scrub < 6 h pre-op, Hair removal: depilatory or clipper, Appropriate Antibiotic Prophylaxis, Cephalosporin 30–60 min pre-incision, or Vancomycin 1 hour pre-incision, Alcohol based hand emollient after antiseptic soap hand scrub, Limit OR Traffic and Talking!, Double glove, change gloves q2h, ABC bone cement: revisions, high risk patients (immunocompromised), Dilute Betadine lavage? Post-Operative: Careful wound closure (Sealed, dry), Sterile, impervious dressing × 24 h, Drain optional, < 48 h, Antibiotic prophylaxis × 24 h, Aggressive drainage hematomas
Total knee arthroplasty is a reliable and durable solution to knee arthritis that fails conservative management. However, there are clinical pitfalls awaiting the surgeon, which can be avoided with forethought and analysis. The majority of early TKR failures are related to technical error on the part of the surgeon! The top 10 errors are:
The knee attached to secondary gain: worker's comp, depression, etc. will make a successful outcome less likely. Wound complications: raising large subcutaneous flaps, failure to respect pre-existing incisions about the knee, and delay in obtaining closure with flaps, etc. will almost guarantee infection! Prolonged observation of the draining wound: another invitation to infection! Internal rotation of the femoral component: patellar maltracking, and flexion instability await! Infection: discipline for the OR staff and surgeon alike are necessary to minimise this complication. Varus position of the tibial component: early loosening and accelerated polyethylene wear are assured. Failure to restore a neutral mechanical axis of the limb: early wear and loosening are the outcome of failure to pay attention to this very important basic principle of TKR. Patellar tilt or dislocation: lateral retinacular release is less common with current designs, but is still required for proper patellar tracking. Failure to balance soft tissue: collateral ligament, and the posterior cruciate ligament must be balanced throughout the range of motion for a successful result. And the #1 way to ruin a good result is… Operating too early! Don't operate on the x-ray, and exhaust all reasonable conservative therapy and non-arthroplasty alternatives before resorting to prosthetic arthroplasty. The patient needs to understand the limitations of technology, and have reasonable expectations. Make sure the pre-op symptoms justify the procedure!
This session will offer insight into what five leading surgeons have learned throughout their careers and lives. Their presentations should be invaluable, both for the challenges of the present, and planning for your future after orthopaedics!
