The trabecular metal Monoblock TKR is comprised of a porous tantalum base plate with the polyethylene liner embedded directly in the porous metal. An alternative design, the trabecular metal Modular TKR, allows polyethylene liner insertion into the locking base plate after base plate implantation, but removes the low modulus of elasticity that was inherent in the Monoblock design. The purpose of this study was to compare the fixation of the Monoblock and Modular trabeucular metal base plates in a randomised controlled trial.

Fifty subjects (30 female) were randomly assigned to receive the uncemented trabecular metal Monoblock or uncemented trabecular metal Modular knee replacement. A standard procedure of tantalum marker insertion in the proximal tibial and polyethylene liner was followed with uniplanar radiostereometric analysis (RSA) examinations immediately post-operatively and at 6 week, 3 month, 6 month, and 12 month follow-ups. The study was approved by the Research Ethics Board and all subjects signed an Informed Consent Form.

Twenty-one subjects received Monoblock components and 20 received Modular components. An intra-operative decision to use cemented implants occurred in 5 cases and 4 subjects did not proceed to surgery after enrollment. The clinical precision of implant migration measured as maximum total point motion (MTPM) was 0.13 mm (upper limit of 95% confidence interval of double exams). Implant migration at 12 months was 0.88 ± 0.64 mm (mean and standard deviation; range 0.21 – 2.84 mm) for the Monoblock group and 1.60 ± 1.51 mm (mean and standard deviation; range 0.27 – 6.23 mm) for the Modular group. Group differences in 12 month migration approached clinical significance (p = 0.052, Mann Whitney U-test).

High early implant migration is associated with an increased risk for late aseptic loosening. Although not statistically significant, the mean migration for the Modular component group was nearly twice that of the Monoblock, which places it at the 1.6 mm threshold for “unacceptable” early migration (Pijls et al 2012). This finding is concerning in light of the recent recall of a similar trabecular metal modular knee replacement and adds validity to the use of RSA in the introduction of new or modified implant designs.

Reference: Pijls, B.G., et al., Early migration of tibial components is associated with late revision: a systematic review and meta-analysis of 21,000 knee arthroplasties. Acta Orthop, 2012. 83(6): p. 614–24.

Purpose

To determine if minimally invasive surgery (MIS) for primary hip replacement surgery increases the risk of long term aseptic loosening as predicted by implant micromotion measured with radiostereometric analysis (RSA).

Purpose: To determine if MIS for primary hip replacement surgery increases the risk of long term aseptic loosening as predicted by implant micromotion measured with radiostereometric analysis (RSA).

Method: Ninety patients undergoing primary THA for osteoarthritis (exclusion criteria: post-traumatic arthritis, rheumatoid arthritis, hip dysplasia, previous hip infection) were randomized to undergo THR surgery utilizing the standard direct lateral approach (n=45; 24 male; age=58 yrs; BMI=27) or MIS via a one-incision direct lateral approach using specific instrumentation (n=45; 23 male; age=55; BMI=29). Uncemented acetabular and femoral (ProfemurZ) components were used with ceramic on ceramic bearings. The femur was marked with 9 tantalum beads placed in the greater trochanter, lesser trochanter, and femoral shaft distal to the tip of the prosthesis. Post-operative care was be standardized according to the care maps at our institution. Primary outcome measure was femoral stem MTPM (maximum total point motion) measured using Model-based RSA. Stereo supine X-rays were taken before weight bearing and 3, 6, and 12 months postoperatively. At the same time intervals Harris Hip Score, Oxford-12, WOMAC, and SF36 questionnaires were administered. Rates of infection, dislocation and revision were recorded.

Results: Eleven patients were lost to follow-up (4 due to missing post-op exams; 5 did not have enough beads placed during surgery; 2 were revised due to failure of the ceramic femoral head). There were five long neck fractures at 17–30 months postop that are reported in detail in a related abstract. There were no differences between groups for all outcome measures. Mean MTPM at 12 months was 2.5mm (SD=1.8mm) for the MIS group and 2.6mm (SD=1.2mm) for the standard group.

Conclusion: No difference between groups at one year indicates MIS for uncemented primary THR through a direct lateral approach does not appear to negatively affect stability of the femoral stem. Although promising, these results require confirmation with 2-year RSA data.

Purpose: To report a series of unexpected femoral neck failures in a series total hip replacement surgeries using a modular femoral component.

Method: A series of 443 hip replacement patients received modular necks as part of a non cemented hip replacement with ceramic articulations at the acetabulum and femoral head interface. The first implant of the device was on June 8, 2004 and the last on June 12, 2009. Ninety-one of those patients were enrolled in a RSA study of component stability within the proximal femur.

Results: The index fracture of a femoral neck occurred on March 8, 2009 when the patient (28 months post hip replacement) reported a fall. Subsequently five patients have had a fracture of the modular neck. There were five fractures within the RSA study group and one within the non study group (all occurred 17 months to 30 months post op). All fractures were long necks (10.5 mm). There was no difference in femoral component micromotion as measured with RSA between the fractured group and the unrevised group.

Conclusion: Initial non-destructive testing of one retrieval revealed fatigue failure of the femoral neck. An independent study of all relevant data was implemented which included destructive testing of the implants and clinical data with respect to patient activity. We report the outcome of all those investigations.

A retrospective chart review of three hundred and eighty-seven PFC© and PFC Sigma© total knee replacements performed by a single surgeon over a seven-year period was completed. During that time, there were fourteen revisions for polyethylene failure. Survival analysis indicates a failure rate of 8%. Previous reports in the literature of the survivorship of the original PFC design demonstrated a five percent failure rate over a ten-year period. Gamma sterilization in air of the PFC polyethylene and the locking mechanism of the articular surface have been implicated in premature wear and failure of this prosthesis.

The purpose of this study was to determine the revision rate due to polyethylene failure for a cohort of PFC© and PFC Sigma© total knee prostheses implanted by a single surgeon.

The early to mid-term revision rate (8%) of the PFC© and PFC Sigma© polyethylene component appears to be abnormally high. The early failure of this tibial articulating component may be related to faulty polyethylene inserts and/or failure of the locking mechanism. Attention to preparation of the polyethylene and locking mechanism of the tibial insert may need to be addressed.

Three hundred and eighty-seven total knees were performed in a cohort of three hundred and twenty-two patients (64% female; mean age = 70 ± 9 years; mean BMI = 31 ± 6). Mean follow-up was forty-one months (± 23). The revision rate at seven years was 8%. At time of revision most prostheses were solidly fixed with no overt signs of loosening of the tibial component. However, there was movement of the polyethylene in the tibial tray in both the mediolateral and AP direction with obvious surface and backside wear. Marked synovitis with evidence of osteolysis, particularly on the femoral side, was also noted. Bone graft was required in almost all cases.

A retrospective chart review was conducted for PFC© and PFC Sigma© total knee systems implanted by a single surgeon between 1995 and 2002. Collected data included patient demographics, age, gender, body mass index, and reason for surgery. The amount of synovitis and osteolysis was documented during revision surgery.

During the routine follow-up of this cohort, patients were identified with marked synovitis and increasing pain in the knee even though there was no gross mal-alignment of the tibial or femoral component.

The demand for knee arthroplasty (TKR) is increasing yet there are no established criteria for prioritizing patients. We investigated surgeon inter-observer reliability and factors that influenced their prioritization of patients by having three surgeons each independently consult on twelve randomly selected patients waiting for TKR. Surgeons had high reliability and were most influence by the patient’s pain and gait pattern when assigning priority. Surgeon assigned priority also correlated with common subjective outcome metrics. Formalized gait assessment may allow for more objective prioritization of patients waiting for TKR.

The purpose of this study was to investigate the inter-observer reliability of surgeons assessing the priority of patients waiting for elective total knee arthroplasty (TKR) surgery, and to assess the discriminative methodology surgeons employ when assessing patients.

Surgeon’s can reliably assign a priority to their patients waiting for TKR. Surgeons generally consider the patients pain and gait pattern when assigning priority.

Wait lists for elective TKR are increasing and the demand will continue to grow. Objective criteria for prioritizing patients would allow for rational delivery of limited surgical resources.

Surgeons have high inter-observer reliability when assigning patient priority (ICC = 0.86). Pain and gait pattern have a significant impact on the surgeon’s assessment of priority (p=0.25 and p< 0.001, respectively). The oxford twelve most closely correlated to the surgeon’s prioritization (r=0.80).

Twelve patients waiting for TKR were randomly selected from three surgeons wait lists. Each surgeon independently examined all twelve patients and recorded their assessment of the patient’s acuity (priority) on a visual analogue scale. The impact of various aspects of the patient’s presentation on the surgeon’s assessment, such as pain control, function, gait, joint contracture and radiographic appearance, were recorded. All patients completed the SF-36, Oxford twelve and WOMAC questionnaires. Linear regression and Intra-Class Correlation Coefficients were used to assess the data.

Through the complex patient-surgeon interaction during a standard consultation, surgeons are able to prioritize their patient’s with high reliability. Improved objective metrics for prioritizing patient’s may be possible by more formalized methods of gait assessment.

Purpose: The Advance Medial Pivot (MP) knee has higher congruency and postulated different kinematics than traditional posterior stabilized knee implants. This could lead to increased micromotion at the tibial component/bone interface potentially resulting in premature loosening. To investigate the stability of the MP knee we used maximum total point motion (MTPM) as determined with RSA to compare micromotion at the tibial component/bone interface between the Advance MP and PS knees.

Methods: A power calculation determined that a minimum sample size of 40 (20/group) was required. Sixty-six patients (48 females) with primary osteoarthritis of the knee were randomized to receive the Advance MP (n=36) or PS (n=30) knee. Three experienced knee surgeons followed a standardized surgical technique (PCL resection, patella resurfacing, RSA bead placement in polyethylene and tibia) and post-operative protocol (CPM as tolerated, no drains, WBAT). SF-36, WOMAC, PCS, KSCRS were administered to all patients pre-operatively and at 6, 12 and 24 months post-operatively and BMI was recorded. Within 4 days of surgery and at 6, 12 and 24 months post-operatively patients underwent bi-planar x-rays.

Results: Fifteen patients were lost to follow-up (2 infections, 1 death, 2 dropped out, 10 lost due to technical issues). There was no difference in MTPM between groups at 2 years. Physical function was better (p< 0.03) for the PS group at 6 months but there was no difference at 1 year.

Conclusions: There was no difference in MTPM between groups at 2 years post-op. The Advance PS knee appears to result in earlier post-operative improvements in physical function. The altered kinematics and increased congruency of the Advance MP knee does not seem to alter the forces at the tibial component/bone interface and therefore does not appear to be more prone to migration and premature aseptic loosening.

Funding : Other Education Grant

Funding Parties : Unrestricted grant from Wright Medical Inc.

Purpose: To investigate the stability of an uncemented Trabecular Metal (TM) tibial component we used maximum total point motion (MTPM) as determined with RSA to compare micromotion at the tibial component/bone interface between the uncemented Nexgen TM monoblock and cemented Nexgen cobalt chrome modular knee prostheses.

Methods: A power calculation determined that a minimum sample size of 40 (20/group) was required. Sixty-seven patients with primary osteoarthritis of the knee were randomized to receive the Nexgen TM monoblock (n=34; 20 female; mean age=66 years; mean BMI=32) or cobalt chrome modular (n=33; 19 female; mean age=65 years; mean BMI=33) posterior stabilized knees. Four experienced knee surgeons followed a standardized surgical technique (PCL resection, patella resurfacing, RSA bead placement in polyethylene and tibia) and post-operative protocol (CPM as tolerated, no drains, WBAT). SF-36, WOMAC, PCS, KSCRS were administered to all patients pre-operatively and at 6, 12 and 24 months post-operatively and BMI was recorded. Within 4 days of surgery and at 6, 12 and 24 months post-operatively patients underwent bi-planar x-rays.

Results: The TM group had greater initial migration but appeared stabilized at 1 year. There were 2 significant subgroups in the TM group based on migration at 6 months: one group had mean values of 2.1 mm while the other had mean values of 0.4 mm which was comparable to the modular group (0.6 mm). There was no significant migration between 6 and 12 months for both implants indicating good fixation to the proximal tibia. There were no differences between groups in the outcome measures, age and BMI.

Conclusions: There was no difference in MTPM between groups at 1 year post-op and all knees appeared well fixed to the proximal tibia by 6 months postop. The Nexgen TM monoblock tibial component seemed to be prone to greater initial migration but it does not appear to compromise long-term bony in-growth and fixation. Long-term survivorship of the TM tibial component should be the same or better than a cemented cobalt chrome tray.

Funding : Other Education Grant

Funding Parties : Unrestricted grant from Zimmer Inc.

This is a retrospective assessment of the performance of the titanium cemented Gemini femoral component. The Gemini stem (DePuy) is a modular titanium femoral stem with a cobalt chrome femoral head. It has a roughened proximal surface finish to enhance cement bonding and a fixed distal centraliser.

205 total hip replacements were performed using a titanium cemented Gemini stem and an uncemented cup. All the operations were performed by a lateral approach using modern cementing technique. Patients were assessed clinically (Harris hip score) and radiologically. Kaplan Meier Survivorship analysis was used to assess survival.

8 patients were lost and 36 patients died with their total hip prosthesis in situ. The average follow-up in the remaining 161 hips was 70 months (range 37–124 months). The average age was 70 years (range 35–91). Osteoarthritis was the commonest diagnosis and majority of the patients was female. Using the Barrack’s criteria for cementing quality, more than 85% of the hips belonged either to grade A or B with an adequate proximal cement mantle. 28 hips have been revised (26 of which for aseptic loosening) and a further ten have been recognized as radiological failures. A small sized stem was used in over 85% of the failures. Mean time to revision was 3.1 years. Survival according to Kaplan-Meier Survivor curves at 6 years was 72%.

There is a high incidence of early failure associated with these cemented titanium stems (28%). The possible mechanism of failure is as follows. The rough surface finish and the flexible titanium alloy are likely to produce large amounts of wear debris and the centraliser which is fixed to the stem probably acts as an area of stress concentration causing accelerated destruction of the distal cement mantle. Based on our experience, the continued use of this cemented stem is no longer justified.