Chelsea N. Koch

Flexural Rigidity, Taper Angle, and Contact Length Affect Fretting of the Femoral Stem Trunnion in Total Hip Arthroplasty

BACKGROUND Modularity at the head-neck junction in total hip arthroplasty allows for intraoperative adjustments but may be a source of metallic debris. We determined how flexural rigidity, taper angle, contact length, and lever arm affect fretting and corrosion at this junction. METHODS A total of 77 metal-on-polyethylene total hip arthroplasties retrieved over a 10-year period at a single institution were obtained. Head tapers and stem trunnions were graded for fretting and corrosion. RESULTS Stem fretting was inversely related to rigidity and taper angle, while positively correlated to contact length. Head fretting and head and stem corrosion were not associated with any of these parameters. CONCLUSION Design and assembly factors at the modular head-neck connection affected stem fretting among the retrieved components, suggesting that these parameters are important to consider when choosing a modular system.

Posterior Stabilized Polyethylene Inserts in Total Knee Arthroplasty: A Retrieval Study Comparing Conventional to High-Flexion Designs

BACKGROUND High-flex (HF) total knee arthroplasties are modified posterior-stabilized (PS) implants designed to accommodate greater flexion. METHODS We examined differences between HF and PS retrieved tibial inserts with regard to polyethylene surface damage. Twenty HF inserts from each of 3 manufacturers were matched using patient demographics with 20 PS inserts from the same manufacturers. Ranges of motion between matched patients were not different. RESULTS Based on subjective damage scores, no differences were detected between HF and PS groups. Differences were found, however, among manufacturers, consistent with design approaches taken for PS and HF implants. CONCLUSION In our series, high flexion did not influence damage, although this was likely influenced by the fact that few HF patients in our study had larger range of motions than their PS counterparts.

Patellofemoral arthroplasty conversion to total knee arthroplasty: Retrieval analysis and clinical correlation

BACKGROUND Patellofemoral arthroplasty (PFA) can be a successful, bone-sparing treatment for isolated patellofemoral arthritis. However, progression of tibio-femoral arthritis or incorrect indications may predispose patients to early conversion to total knee arthroplasty (TKA). The purpose of this study was to review the clinical cases and perform retrieval analysis of PFA conversions to TKA at our institution. METHODS Twenty one patellofemoral arthroplasties in 18 patients that were converted to TKA were identified through our implant retrieval registry. Sixteen implants were available for review by biomechanical engineers, who recorded surface markings, wear patterns, and integrity of fixation. Patient charts were reviewed and time to conversion, tourniquet time, conversion implant, additional surgeries, infections, and Kellgren & Lawrence grade of the tibio-femoral joint on pre-operative radiographs were recorded. RESULTS PFAs converted to TKAs at our institution were implanted for an average of 2.7years. The most common reason for conversion was pain, but most patients had significant tibio-femoral arthritis, as indicated by an average Kellgren & Lawrence grade of 2.6. The average tourniquet time for these conversions was 67min. These patients underwent an average of one additional surgery per PFA converted, and the infection rate of these conversions was approximately 14%. CONCLUSION Success of PFA depends upon correct patient selection rather than implant failure or wear. Conversion of PFA to TKA is technically similar to primary TKA, with similar post-operative pain relief and range of motion. However, infection rates and complications requiring further surgery are more consistent with results seen in revision TKA. LEVEL OF EVIDENCE IV.

Does Achieving High Flexion Increase Polyethylene Damage in Posterior-Stabilized Knees? A Retrieval Study

BACKGROUND Increased range of motion to higher degrees of flexion following total knee arthroplasty has been postulated to increase implant damage and revision rates, even in designs modified to accommodate high flexion. METHODS We examined posterior-stabilized and high-flexion retrieved tibial inserts to look for differences in polyethylene surface damage with light microscopy and 3D deviation with laser scanning between inserts from patients who achieved a high degree of flexion (≥120° postoperatively) and inserts from patients who did not reach a high degree of flexion. RESULTS No differences were found in damage scores on the articular and backside surfaces, except for abrasion in the posterior articular regions, or in 3D deviations between patients who reached a high degree of flexion and patients who did not. These results were independent of the reason for revision. CONCLUSION In our series, reaching a high degree of flexion did not influence surface damage or 3D deviation of the polyethylene inserts.

Fretting and Corrosion at the Backside of Modular Cobalt Chromium Acetabular Inserts: A Retrieval Analysis

BACKGROUND Adverse local tissue reaction formation has been suggested to occur with the Modular Dual Mobility (MDM) acetabular design. Few reports in the literature have evaluated fretting and corrosion damage between the acetabular shell and modular metal inserts in this modular system. We evaluated a series of 18 retrieved cobalt chromium MDM inserts for evidence of fretting and corrosion. METHODS We assessed the backsides of 18 MDM components for evidence of fretting and corrosion in polar and taper regions based on previously established methods. We collected and assessed 30 similarly designed modular inserts retrieved from metal-on-metal (MoM) total hip arthroplasties as a control. RESULTS No specific pattern of fretting or corrosion was identified on the MDM inserts. Both fretting and corrosion were significantly greater in the MoM cohort than the MDM cohort, driven by higher fretting and corrosion scores in the engaged taper region of the MoM inserts. CONCLUSION MoM components demonstrated more fretting and corrosion than MDM designs, specifically at the taper region, likely driven by differences in the taper engagement mechanism and geometry among the insert designs. The lack of significant fretting and corrosion observed in the MDM inserts are inconsistent with recent claims that this interface may produce clinically significant metallosis and adverse local tissue reactions.

Polyethylene Damage Increases With Varus Implant Alignment in Posterior-stabilized and Constrained Condylar Knee Arthroplasty

BackgroundImplant malalignment in primary TKA has been reported to increase stresses placed on the bearing surfaces of implant components. We used a longitudinally maintained registry coupled with an implant retrieval program to consider whether preoperative, postoperative, or prerevision malalignment was associated with increased risk of revision surgery after TKA.Questions/purposes(1) What is the relative polyethylene damage on medial and lateral compartments of the tibial plateaus from revised TKAs? (2) Does coronal TKA alignment affect implant performance, such that TKAs aligned in varus are predisposed to experience increased polyethylene damage? (3) Does TKA alignment differ between postoperative and prerevision radiographs, and if so, what does this difference suggest about the mechanical contact load placed on a knee with a TKA?MethodsBetween 2007 and 2012, we performed 18,065 primary TKAs at our institution. By March 2016, 178 of those TKAs (1%) were revised at our center at least 2 years after primary surgery at our institution. Eighteen of those TKAs were excluded from this analysis because the tibial insert was not explanted during revision surgery, and four more were excluded because the inserts were lost or returned to the patient before the study was initiated, leaving 156 retrieved polyethylene tibial inserts (in 153 patients) revised at greater than 2 years after the primary TKA for this retrospective study. Patients who underwent revision surgery elsewhere were not considered here, since this study depended on having retrieved components. Polyethylene damage modes of burnishing, pitting, scratching, delamination, surface deformation, abrasion, and third-body debris were subjectively graded on a scale of 0 to 3 to reflect the extent and severity of each damage mode. On preoperative, postoperative, and prerevision radiographs, overall alignment, femoral alignment, and tibial alignment in the coronal plane were measured according to the protocol recommended by the Knee Society.ResultsKnees with more overall varus alignment after TKA had increased total damage on the retrieved tibial inserts (Spearman’s rank correlation coefficients of −0.3 [95% CI, −0.4 to −0.1; p = 0.001]). We also found revised TKAs tended to drift back into greater varus before revision surgery, with a mean (SD) of 3.6° ± 4.0° valgus for postoperative alignment compared with 1.7° ± 6.4° prerevision (p = 0.04).ConclusionsDespite surgical efforts to achieve neutral mechanical alignment, remaining varus alignment places an increased contact load on the polyethylene articular surfaces. The drift toward further varus alignment postoperatively is consistent with the knee adduction moment remaining high after surgery.Clinical RelevanceWhile we found a predisposition toward recurrence of the preoperative varus deformity, we did not find increased medial as opposed to lateral polyethylene damage, which may be explained by the curve-on-curve toroidal design of the articulating surfaces of the TKA implants in this study.

Have large femoral heads reduced prosthetic impingement in total hip arthroplasty

Background: Prosthetic impingement is implicated in dislocation after total hip arthroplasty (THA). While use of larger diameter femoral heads reduces the incidence of dislocation, the effect of larger heads upon impingement rate is unknown. We assessed retrieved THA components for evidence of impingement to determine if large femoral heads reduced the rate of impingement in primary THA and what factors might influence impingement. Methods: Liners from 97 primary THAs retrieved at revision arthroplasty were scored for evidence of impingement, defined as wear or deformation on the rim of the component. Component inclination and version were measured from anteroposterior and cross-table lateral radiographs. Results: Independent of revision diagnosis, 77% of liners demonstrated evidence of impingement. Impingement was less prevalent and less severe as head size increased. Severe impingement was observed in 50% of the liners with 28-mm heads, 15% of liners with 32-mm heads, and 21% of liners with 36-mm heads. Regardless of head size, 76% of liners revised for instability demonstrated impingement. Decreased head-neck ratio, use of an elevated liner, increased length of implantation, and increased version were associated with increased severity of impingement. Discussion: We showed that larger head sizes are associated with decreased incidence of impingement on retrieved acetabular liners when compared to smaller head sizes. Larger heads have reduced but not eliminated impingement, which remains a potential source of instability.

Oxidised zirconium versus cobalt alloy bearing surfaces in total knee arthroplasty : 3D laser scanning of retrieved polyethylene inserts

Aims We sought to establish whether an oxidised zirconium (OxZr) femoral component causes less loss of polyethylene volume than a cobalt alloy (CoCr) femoral component in total knee arthroplasty. Materials and Methods A total of 20 retrieved tibial inserts that had articulated with OxZr components were matched with 20 inserts from CoCr articulations for patient age, body mass index, length of implantation, and revision diagnosis. Changes in dimensions of the articular surfaces were compared with those of pristine inserts using laser scanning. The differences in volume between the retrieved and pristine surfaces of the two groups were calculated and compared. Results The loss of polyethylene volume was 122 mm3 (standard deviation (sd) 87) in the OxZr group and 170 mm3 (SD 96) in the CoCr group (p = 0.033). The volume loss in the OxZr group was also lower in the medial (72 mm3 (SD 67) versus 92 mm3 (SD 60); p = 0.096) and lateral (49 mm3 (SD 36) versus 79 mm3 (SD 61); p = 0.096) compartments separately, but these differences were not significant. Conclusion Our results corroborate earlier findings from in vitro testing and visual retrieval analysis which suggest that polyethylene volume loss is lower with OxZr femoral components. Since both OxZr and CoCr are hard surfaces that would be expected to create comparable amounts of polyethylene creep, the differences in volume loss may reflect differences in the in vivo wear of these inserts.

Ceramic Bearings with Titanium Adapter Sleeves Implanted During Revision Hip Arthroplasty Show Minimal Fretting or Corrosion: a Retrieval Analysis

BackgroundThe BIOLOX® option system, consisting of a BIOLOX® delta ceramic femoral head with a titanium alloy adapter sleeve, is being increasingly utilized in revision hip arthroplasty. The sleeve protects the ceramic head from fracture and improper motion about the stem trunnion when a damaged trunnion is encountered at revision surgery. Corrosion and fretting due to metal-metal contact at the taper region of hip prosthesis create the potential of causing periprosthetic osteolysis and adverse local tissue reactions.Questions/PurposesThe objective of this study was to identify the type and extent of damage to retrieved sleeves and ceramic heads to determine their in vivo performance.MethodsTwenty-four ceramic heads with titanium alloy sleeves were examined. The articular and taper surfaces for each ceramic head were assessed for metal transfer using a subjective grading system. All surfaces of the 24 titanium sleeves and stem trunnions (only available for 7 of 24 cases) were assessed for corrosion and fretting using an established grading system. Scanning electron microscopy and energy dispersive X-ray analysis were conducted on representative sample of sleeves.ResultsFretting and corrosion were higher at the inner surface of the taper sleeve than the outer sleeve. Mean fretting scores at the inner taper and outer taper sleeve surfaces were 1.8 and 1.2, respectively. The mean corrosion score at the inner taper surface was 1.8; no corrosion was observed on the outer surface of any taper sleeve. SEM and EDS analyses provided further indications of low levels of damage.ConclusionFretting and corrosion were less severe than previously reported for conventional THA metal-metal taper connections, indicating that a ceramic head and titanium sleeve is a safe alternative in revision THA.

Spontaneous Fractures of a Modern Modular Uncemented Femoral Stem

BackgroundFemoral stem fracture following total hip arthroplasty is an uncommon event that requires immediate revision surgery.Questions/PurposesWe report on four patients who experienced stem fractures of one design and a review of the US Food and Drug Administration adverse event reports on this design.MethodsFracture surfaces of four EMPERION™ (Smith & Nephew, Memphis, TN) femoral stems were analyzed under optical and scanning electron microscopy. A search of the FDA’s Manufacturer and User Facility Device Experience (MAUDE) that reports on all EMPERION™ adverse events was completed.ResultsFracture surfaces exhibited characteristics consistent with a fatigue fracture mechanism. Sixteen MAUDE reports claimed stem fracture or breakage of EMPERION™ stems.ConclusionThe four cases of EMPERION™ stem fractures were likely driven by small stem diameter, high offset, and high patient weight. Modular stem-sleeve femoral systems are susceptible to fatigue failure under high stress and should only be used in appropriate patients, whom are not considered obese.