Thomas Turgeon

The Influence of Head Size on Corrosion and Fretting Behaviour at the Head-Neck Interface of Artificial Hip Joints

The primary goal of this study was to determine if head size affects corrosion and fretting behaviour at the head-neck taper interface of modular hip prostheses. Seventy-four implants were retrieved that featured either a 28 mm or a 36 mm head with a metal-on-polyethylene articulation. The bore of the heads and the neck of the stems were divided into eight regions each and graded by three observers for corrosion and fretting damage separately using modified criteria as reported in the literature. The 36 mm head size featured a significant difference in the corrosion head scores (p=0.022) in comparison to the 28 mm heads. This may be attributed to a greater torque acting along the taper interface due to activities of daily living.

Fatal cardiomyopathy after revision total hip replacement for fracture of a ceramic liner

Symptomatic cobalt toxicity from a failed total hip replacement is a rare but devastating complication. It has been reported following revision of fractured ceramic components, as well as in patients with failed metal-on-metal articulations. Potential clinical findings include fatigue, weakness, hypothyroidism, cardiomyopathy, polycythaemia, visual and hearing impairment, cognitive dysfunction, and neuropathy. We report a case of an otherwise healthy 46-year-old patient, who developed progressively worsening symptoms of cobalt toxicity beginning approximately six months following synovectomy and revision of a fractured ceramic-on-ceramic total hip replacement to a metal-on-polyethylene bearing. The whole blood cobalt levels peaked at 6521 µg/l. The patient died from cobalt-induced cardiomyopathy. Implant retrieval analysis confirmed a loss of 28.3 g mass of the cobalt-chromium femoral head as a result of severe abrasive wear by ceramic particles embedded in the revision polyethylene liner. Autopsy findings were consistent with heavy metal-induced cardiomyopathy.We recommend using new ceramics at revision to minimise the risk of wear-related cobalt toxicity following breakage of ceramic components.

Randomized Trial of Computer-Assisted Knee Arthroplasty: Impact on Clinical and Radiographic Outcomes

Computer-assisted surgery in knee arthroplasty is gaining popularity; however, the resulting outcome improvement is controversial. A double-blinded trial was performed with subjects randomized to undergo surgery with either computer-assisted or nonassisted instruments. Postoperatively, limb and implant alignment and rotation were assessed using both full-length radiographs and computed tomography in addition to clinical scores. One hundred twenty patients (141 knees) were randomized. No differences in Western Ontario MacMaster Osteoarthritis Score, Short Form-36, or flexion were seen. More varus limb alignment was seen in the computer-assisted group (1.9°) vs the nonassisted group (0.9°, P = .04) with no improvement in alignment precision. Rotational alignment of the components did not differ between groups. Computer-assisted surgery appeared to have minimal effect on knee implant arthroplasty with no improvement in limb alignment or early functional outcome.

Biochemical analyses of human osteoarthritic and periprosthetic synovial fluid

Biochemical analyses were performed on osteoarthritic and periprosthetic synovial fluid in order to propose changes to lubricant specifications currently outlined in orthopaedic wear testing standards. Osteoarthritic and periprosthetic synovial fluid samples were obtained from the hip and knee joints of 40 patients. The samples in each group were analysed and compared in order to identify differences between the protein concentration, constituent fractions, osmolality, thermal stability and the hyaluronic acid concentration and molecular weight distribution of osteoarthritic and periprosthetic synovial fluid. The average total protein concentration was approximately 30 g/L, which was much higher than the 20 g/L currently specified in the knee wear testing standard; however, the 30 g/L protein concentration matched the recently revised standard for hip simulator wear testing. No significant difference was found between the protein concentration, osmolality, thermal stability, and hyaluronic acid concentration of osteoarthritic and periprosthetic synovial fluid. The clinical data provided should be used to better define the composition of a more clinically relevant lubricant for orthopaedic wear testing.

Clinical failure analysis of contemporary ceramic-on-ceramic total hip replacements

The present study investigates the performance of ceramic-on-ceramic total hip replacements by combining a retrieval analysis with a survivorship analysis to elucidate mechanisms that led to clinical failure. Semiquantitative surface damage assessment, contact profilometry, contour measurements, and scanning electron microscopy were performed to characterize the types and quantify the extent of surface damage on the retrieved ceramic components. The implantation period was positively correlated with both damage scores of the femoral heads (R = 0.573, p < 0.001) and the acetabular cups (R = 0.592, p < 0.001). Increased maximal out-of-roundness values of the femoral heads correlated with both increased metal transfer damage score (R = 0.384, p = 0.023) and increased stripe damage score (R = 0.729, p ≤ 0.001) of the acetabular liners. The damage rate (damage score/year) for both the retrieved heads and acetabular liners was at least 2.2-fold greater at inclination angles of >45° than the damage rate at inclination angles of ≤45°. For the retrieved femoral heads only, the linear wear rate of 25.5 ± 21.3 µm/year at inclination angles of >45° was 6-fold greater than the linear wear rate of 4.2 ± 2.3 µm/year at inclination angles of ≤45°. Metal transfer on the ceramic bearing surface could possibly contribute to fluid-film starvation and, in combination with an increased inclination angle, may facilitate an adhesive wear mechanism associated with stripe surface damage. At our institution, the clinical survivorship of ceramic-on-ceramic total hip replacements was 98.9% (a total of 9 out of 815 patients were revised within 10 years after total hip arthroplasty) with revision as the end point, suggesting their safe use in younger patients.

Paraneoplastic Clostridium septicum Infection of a Total Knee Arthroplasty

We describe a case of a well-functioning total knee arthroplasty acutely infected with Clostridium septicum. This is the first reported infection of a prosthetic joint with this organism. A search for the source of this infection uncovered a colonic malignancy. This organism is highly associated with gastrointestinal malignancy, and appropriate investigation should be carried out when it is discovered. The importance of full anaerobic bacterial identification by the microbiology laboratory is underscored by this case.

Corrosion on the Acetabular Liner Taper from Retrieved Modular Metal-on-Metal Total Hip Replacements

Eight retrieved metal-on-metal total hip replacements displayed corrosion damage along the cobalt-chromium alloy liner taper junction with the Ti alloy acetabular shell. Scanning electron microscopy indicated the primary mechanism of corrosion to be grain boundary and associated crevice corrosion, which was likely accelerated through mechanical micromotion and galvanic corrosion resulting from dissimilar alloys. Coordinate measurements revealed up to 4.3mm(3) of the cobalt-chromium alloy taper surface was removed due to corrosion, which is comparable to previous reports of corrosion damage on head-neck tapers. The acetabular liner-shell taper appears to be an additional source of metal corrosion products in modular total hip replacements. Patients with these prostheses should be closely monitored for signs of adverse reaction towards corrosion by-products.

The effect of adding tobramycin to Simplex P cement on femoral stem micromotion as measured by radiostereometric analysis: a 2-year randomized controlled trial.

Background Previous in vitro research on addition of antibiotics to bone cement has found no statistically significant deterioration in mechanical properties. However, no clinical studies have compared the performance of tobramycin-laden bone cement with that of standard bone cement (Simplex P). Patients and Methods 23 patients (25 hips) were randomized to receive an Exeter (Stryker Orthopaedics) femoral stem cemented with either Simplex P (standard) or Simplex T (tobramycin-laden) cement. There were 2 years of follow-up, with scheduled radiostereometric (RSA) examinations. Results All stems migrated distally and showed some degree of retroversion. No clinically significant differences in stem subsidence or retroversion were found between the Simplex T and Simplex P cement groups after 2 years. Overall subsidence was less than in previous studies, probably due to a postponed initial post-surgical examination. Rates of subsidence in both cement groups were consistent with those from previous studies of Exeter stems. Interpretation Subsidence of the femoral stem after 2 years was similar in the Simplex T (tobramycin-laden) and Simplex P (standard) groups.

Wear of a sequentially annealed polyethylene acetabular liner

Background and purpose — We previously reported on a randomized controlled trial (RCT) that examined the effect of adding tobramycin to bone cement after femoral stem migration. The present study examined femoral head penetration into both conventional and highly crosslinked polyethylene acetabular liners in the same group of RCT patients, with a minimum of 5 years of postoperative follow-up. Patients and methods — Linear penetration of the femoral head into an X3 (Stryker) crosslinked polyethylene (XLPE) liner was measured in 18 patients (19 hips) using radiostereometric analysis (RSA). Femoral head penetration was also measured in 6 patients (6 hips) with a conventional polyethylene liner (CPE), which served as a control group. Results — The median proximal femoral head penetration in the XLPE group after 5.5 years was 0.025 mm with a steady-state penetration rate of 0.001 mm/year between year 1 and year 5. The CPE liner showed a median proximal head penetration of 0.274 mm after 7.2 years, at a rate of 0.037 mm/year. Interpretation — The Trident X3 sequentially annealed XLPE liner shows excellent in vivo wear resistance compared to non-crosslinked CPE liners at medium-term implantation. The rate of linear head penetration in the XLPE liners after > 5 years of follow-up was 0.001 mm/year, which is in close agreement with the results of previous studies.

The biochemical characteristics of wear testing lubricants affect polyethylene wear in orthopaedic pin-on-disc testing.

Lubricant protein concentration is known to affect crosslinked polyethylene wear in in vitro testing; however, the biochemical nature of these lubricants may also have a significant effect on wear and dictate its clinical relevance. A modified approach to pin-on-disc testing was implemented to explore the effect of four biochemically different lubricants on the wear of two types of crosslinked polyethylene materials (XLK™ and Marathon™; DePuy Synthes, Warsaw, IN, USA). XLK was associated with higher wear rates than Marathon. In comparison to lubricants containing deionized water, lubricants containing phosphate buffered saline solution and hyaluronic acid increased osmolality by up to 1.2 times and thermal stability by up to 1.4 times. This biochemical change reduced wear by up to 12.5 times. Wear rates for XLK and Marathon differed by a factor of 3.2 using lubricants with phosphate buffered saline solution as the dilutive media, but only 2.0 for lubricants with deionized water. Interestingly, varying the concentration of hyaluronic acid did not have a significant effect on wear, and differences between XLK and Marathon wear rates were not found to be statistically significant when hyaluronic acid was added to the lubricant. The findings of this study showed that increasing the osmolality and thermal stability of lubricants to more clinical levels decreased wear; however, the effect of hyaluronic acid on wear may not be apparent in simplistic pin-on-disc testing. It was suggested that phosphate buffered saline solution be used as the dilutive media of choice in order to better differentiate the ranking of materials while maintaining some clinical relevance.