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, in vitro laboratory testing cannot wholly replicate or predict in vivo behavior of a particular wear couple. (Mother Nature always has something new to teach us!)

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.

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 http://www.msis-na.org/wp-content/themes/msis-temp/pdf/ism-peri-prosthetic-joint-information.pdf.

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 http://www.msis-na.org/wp-content/themes/msis-temp/pdf/ism-periprosthetic-joint-information.pdf.

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: 10.

The knee attached to secondary gain: worker's comp, depression, etc. will make a successful outcome less likely.

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!

Acetabular osteolysis not infrequently presents the hip surgeon with the daunting and conflicting challenges of bone stock restoration and implant stability. Recognition of the size, position, and extent of the defect preoperatively is necessary for safe navigation of these difficult seas!

Routine radiographic examination is the single most useful preoperative test, as techniques such as CAT scans or MRI examination will be frustrated in the presence of metal-backed devices because of metal artefact. A careful review of the preoperative x-rays will allow the surgeon to properly and accurately anticipate the type of bone defect.

Revision of the failed acetabulum when the peripheral rim is intact, with small (< 2 cm) medial defects, and in the absence of large cavitary defects may be reliably managed with simple hemispheric porous ingrowth prostheses, with adjunctive cancellous allograft. However, at least 50% of the prosthesis should be in contact with viable and stable host bone for reliable outcomes. In the absence of this, a revision ring is indicated.

The presence of medial wall defects, as indicated by the protrusion of the implant beyond the iliopectineal line on the AP radiograph, indicates the probability of an uncontained central defect. Consideration should be given to the use of a protrusio ring with allograft in these cases, particularly when the defect is larger than 2 cm in diameter. If significant rim defects also exist, the use of a revision cage with allograft in indicated.

Rim defects should be suspected in cases of implant “breakout”, or in the presence of implants significantly larger than the apparent diameter of the contralateral acetabulum. Rim defects may contraindicate the use of an oversized porous socket, particularly when more than 2 cm of implant is exposed posterosuperiorly, because of the difficulty in establishing a stable implant-bone interface. In these situations, use of a revision ring is advised.

The presence of large “blowout” lesions in the ileum or ischium will indicate the need for substantial quantities of cancellous allograft, which may make the use of a simple porous acetabular shell questionable. Frequently, these lesions will lead to severe peripheral rim defects, requiring the use of a reconstruction ring.

Acetabular defects can be recognised reliably with routine radiographs. However, the revision surgeon is advised to be prepared for unanticipated defects by having available reconstruction rings, allograft, and a variety of revision acetabular implants.

Total hip arthroplasty following pelvic or femoral trauma presents the joint surgeon with challenges not dissimilar to that of revision surgery. Careful preoperative evaluation and planning, and realistic assessment of risks and expectations is necessary.

Complex acetabular fractures present the surgeon with a variety of challenges in conversion to total hip replacement (THR). Bone stock is the critical factor in achieving a stable acetabular reconstruction, particularly with regard to the posterior column. In patients who have undergone prior open reduction and internal fixation, routine radiographic examination will often be inconclusive as to the status of healing of fractures due to the presence of metal, and CAT scans will be similarly obfuscated by metal artefact. Therefore, the surgeon must be prepared for the possibility of bone stock deficiency at the time of reconstruction.

Subclinical infection following ORIF is possible; all patients should be screened for this possibility with preoperative determination of the ESR and C-reactive protein. If these studies are elevated, aspiration of the hip under x-ray or ultrasound guidance should be considered. At the time of surgery, it is suggested that cultures be obtained prior to the administration of systemic antibiotics, and consideration given to intraoperative frozen section examination of tissue if infection is suspected. Removal of internal fixation devices, debridement, and second stage reconstruction after appropriate antibiotic therapy will be necessary in these cases.

Exposure of the hip will be complicated by scar tissue. Particular care is required to avoid sciatic nerve injury during the exposure and hardware removal. Extension of the hip and knee during posterior exposure of the acetabulum and internal fixation devices will aid in retraction and avoidance of neuropraxic sciatic injury.

Stainless steel screws and plates should not contact titanium alloy implants in order to avoid the possibility of fretting wear and corrosion of dissimilar metals. Intraarticular exposure of screws or plates mandates removal of the device. In the absence of such exposure, hardware may be left in place.

Post-traumatic hip arthritis is frequently associated with avascular necrosis of the femoral head. It is not unusual to see advanced bone loss and collapse of the femoral head, with associated limb shortening. If internal fixation has been performed in the proximal femur, consideration of the appropriate femoral component length is necessary to bypass any stress risers. Calcar replacement implants will be necessary in the face of proximal femoral deficiency.

The risk of dislocation following THR in the setting of post-traumatic arthrosis is increased in the presence of soft tissue defects, abductor dysfunction, or neuromuscular deficit. Postoperative bracing may be necessary to assure stability of the reconstruction. The use of a THR orthosis set at 10–15° abduction, 30–60° flexion for 12 weeks following surgery has been successful in preventing dislocation in the setting of abnormal soft tissues.