Charles A. Engh

A Prospective, Randomized Study of Cross-Linked and Non–Cross-Linked Polyethylene for Total Hip Arthroplasty at 10-Year Follow-Up

In 1999, our institution initiated a prospective study to compare the outcome of total hip arthroplasty patients randomized to either non-cross-linked liners or polyethylene liners that were cross-linked with 5.0 Mrad of gamma-irradiation and heat treated to eliminate free radicals. Among 230 randomized THAs, 13 have had reoperations, and 31 patients with 32 THAs died with less than 9-year follow-up. Follow-up for the remaining 185 THAs averaged 10.0 ± 1.8 years. There have been 9 wear-related liner exchanges among the non-cross-linked group and none among the cross-linked group. Using revision for wear-related complications as an endpoint, survivorship at 10-years was 94.7 ± 4.6% for non-cross-linked and 100% for cross-linked (P = .003). Among unrevised hips, the mean linear wear rate was 0.22 mm/yr for non-cross-linked and 0.04 mm/yr for cross-linked (P < .001). The incidence of clinically important osteolysis with an area of at least 1.5 square centimeters among unrevised hips was 22% for non-cross-linked and 0% for cross-linked (P < .001).

Metal-on-metal local tissue reaction is associated with corrosion of the head taper junction.

We evaluated taper corrosion in 36-mm diameter metal-on-metal (MOM) and metal-on-polyethylene (MOP) femoral heads from a single manufacturer retrieved for various reasons. Three reviewers visually graded taper corrosion with a 5-point scale on 19 MOM heads and 14 MOP heads. The MOM group had a higher corrosion score than the MOP group (mean, 3.5 vs 1.9; P < .001). There were 8 MOM heads (42%) and only 1 MOP head (7%) that demonstrated corrosion outside of the taper zone. Metal-on-metal patients revised secondary to adverse local tissue reactions (ALTRs) had greater scores than patients without ALTRs (mean, 4.36 vs 2.38; P < .01). Adverse local tissue reactions MOM patients were also likely to have corrosion outside of the taper junction. The corrosion score increased with implantation time, and at all time intervals, the corrosion score for the MOM group was greater. Because corrosion worsens with time, we are concerned that MOM ALTR failures will increase with longer follow-up.

Do you have to remove a corroded femoral stem

Corrosion at the head-neck taper has been recently identified as a cause of adverse local tissue reaction. There are no guidelines concerning removal of fixed femoral components when corrosion is present. The objective of this study is to report the survivorship when a new metal ball is placed on a corroded stem. We examined 86 retrieved femoral heads from metal-on-polyethylene THAs that underwent head and liner exchanges after a minimum 10 years in-vivo and evaluated the subsequent survivorship. There were 7 re-revisions (8.1%) but none were for corrosion-related diagnoses and there was no difference in the survivorship between the 32 THAs with high-grade head taper corrosion and the 54 THAs with low-grade corrosion. We do not currently recommend removing well-fixed femoral stems with corrosion.

The quality of osteolysis grafting with cementless acetabular component retention.

Periprosthetic osteolysis is a common cause for revision of total hip arthroplasty. When modular cementless acetabular components are stable, curettage and grafting of the osteo-lytic lesion while retaining the component are a good surgical option. Although the midterm outcome of this procedure is known, the quality of the surgical technique is not. We used preoperative and postoperative computed tomography to determine the percentage of periacetabular lesions that was grafted and the percentage of the lesion volume filled with an injectable bone graft substitute. We discovered, even with preoperative computed tomography reconstructions and surgical planning, four of 22 lesions were neglected at the time of surgery. In the 18 lesions that were treated, we were able to fill an average of 49% (range, 0-83%) of the lesion volume. These inconsistent results illustrate a need to further refine surgical techniques and instrumentation to treat one of the most common complications in total hip arthroplasty. Longer followup with repeat computed tomography scans or other imaging techniques would determine if the percentage of lesion fill has an effect on clinical outcome.

Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees

BackgroundWear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear.Questions/PurposesWe used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear.MethodsWe retrieved 12 fixed and 12 rotating-platform bearings after a mean 52xa0months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear.ResultsThe average total wear was 254xa0±xa0248xa0mm3. The average wear rate was 58xa0±xa041xa0mm3/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43xa0±xa025xa0mm3/year and the fixed-bearing rate was 74xa0±xa049xa0mm3/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate.ConclusionsMicro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.

Can the Volume of Pelvic Osteolysis be Calculated without Using Computed Tomography

AbstractThe most common method to diagnose and monitor osteolysis is the standard anteroposterior radiograph. Unfortunately, plain radiographs underestimate the incidence and extent of osteolysis. CT scans are more sensitive and accurate but also more expensive and subject patients to more radiation. To determine whether the volume of pelvic osteolysis could be accurately estimated without a CT scan, we evaluated the relationships between CT volume measurements and other variables that may be related to the size of pelvic osteolytic lesions in 78 THAs. Only the area of pelvic osteolysis measured on radiographs, heavy patient activity level, and total volume of wear were associated with the pelvic osteolysis volume measured on CT in the context of the multivariate regression analysis. Despite a strong correlation (rxa0=xa00.93, r2xa0=xa00.87) between these three variables and the volume of pelvic osteolysis measured on CT, estimates of pelvic osteolysis volume deviated from the actual volume measured on CT by more than 10xa0cm3 among eight of the 78 THAs in this study. CT images remain our preferred modality when accurate assessments of pelvic osteolysis volume are required.n Level of Evidence: Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

A Comparison of a Second- and a Third-Generation Modular Cup Design Is New Improved?

The highly cross-linked polyethylene liners currently used with modular uncemented cups have substantially decreased wear and osteolysis at early follow-up. However, retroacetabular osteolysis has still been reported in some cases with DePuy Orthopaedics (Warsaw, IN) second-generation Duraloc acetabular shell. DePuys third-generation Pinnacle cup incorporates a different shell-liner locking mechanism. We compared the clinical outcome among a matched series of 42 Duraloc and 42 Pinnacle cups at a mean follow-up of 5.9 years. Although the Harris Hip Scores and wear rates were not statistically different between the 2 cup designs, retroacetabular osteolysis behind the central hole was absent among the Pinnacle cups but noted among 19% of the Duraloc cups.

Radiographically measured total knee wear is constant and predicts failure.

Knee wear is commonly measured with the most recent radiograph based on the assumption that wear progresses at a constant rate. Changing patient activity or in vivo polyethylene deterioration are examples of factors that could cause wear rates to change over time. Using six or more radiographs on each of 251 knees over a mean 10-year follow-up, we determined the pattern of polyethylene wear. 92% of knees had linear wear with a mean wear rate of 0.09 ± 0.12 mm/yr. Ten knees (4%) had late accelerated wear. Knees with accelerated wear and those with a wear rate of 0.15 mm/yr or greater had lower survivorship rates. We conclude that wear is linear with rare exceptions and that higher wear is correlated with failure.

The effect of poly sterilization on wear, osteolysis and survivorship of a press-fit cup at 10-year followup.

BackgroundDuring the mid-1990s when our institution was using a press-fit porous-coated cup without supplemental initial fixation for primary THA, the manufacturer transitioned from gamma irradiation to gas plasma for the terminal sterilization of their polyethylene liners.Questions/purposesAt minimum 10-year followup, we asked whether the fixation achieved by solely relying on a press-fit would be durable and how different liner sterilization methods affected radiographic wear, osteolysis, and survivorship.Patients and MethodsWe retrospectively reviewed 373 patients who underwent 398 primary THAs with a press-fit porous-coated cup between March 1995 and December 1996. Mean age at time of surgery was 61.5xa0±xa013.3xa0years and mean followup was 10.4xa0±xa03.7xa0years. We determined reasons for revision, survivorship, femoral head penetration, osteolysis, and wear-related complications.ResultsAmong 20 revisions involving any component, seven were associated with wear and osteolysis. Kaplan-Meier survivorship, using component revision for any reason as an end point, was 95.7% (95% confidence interval, 93.6%–97.9%) at 10xa0years. Noncrosslinked liners sterilized with gas plasma demonstrated a mean head penetration rate of 0.20xa0±xa00.09xa0mm/year compared with 0.13xa0±xa00.07xa0mm/year for liners sterilized with gamma irradiation in air and 0.09xa0±xa00.04xa0mm/year for liners sterilized with gamma-irradiation with barrier packaging without oxygen. THAs with increased volumetric wear tended to demonstrate larger osteolytic lesions (rxa0=xa00.40) and there tended to be less osteolysis among the liners sterilized with gamma-irradiation with barrier packaging without oxygen. However, there was no difference in survivorship among the sterilization groups and there has been no cup or stem loosening associated with osteolysis.ConclusionsDurable biologic fixation through 10-year followup can be achieved by solely relying on an initial press-fit. Noncrosslinking gas plasma for terminal sterilization of the polyethylene liners was associated with greater head penetration rate than gamma irradiation.Level of EvidenceLevel IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Survivorship of polyethylene liner exchanges performed for the treatment of wear and osteolysis among porous-coated cups.

For the past 17 years, we have favored treating patients with polyethylene wear and osteolysis by performing a liner exchange with retention of the old shell when possible. Using our institutional database, we identified 187 acetabular revisions in which we had retained the old shell. Among this group, we found 25 rerevisions. These included 10 for hip instability, 9 for cup loosening, 3 for recurrence of excessive wear or osteolysis, 2 for infection, and 1 for dissociation of the replaced liner. The need for rerevision varied with the different retained shell designs. We rerevised 17% of the total hip arthroplasties with old spiked shells, 21% with Arthropor shells, 13% with Triloc shells and 5% with Duraloc shells. Before making a decision to retain or remove a well-fixed old acetabular shell, we recommend consideration of the designs past track record and careful inspection of the condition of the existing shell.