Tibial Post Wear in Posterior-stabilized Knee Replacements is Design-dependent

Polyethylene tibial post wear in posterior-stabilized knee designs is a major problem. The Insall-Burstein II (IB PS II) reportedly has severe anterior wear of the post in retrieved implants. We hypothesized the more anterior placement in the IB PS II would be reflected in greater wear at the anterior face than the IB PS I. We examined 234 retrieved inserts using subjective scales to grade post damage and wear. Of the IB PS II inserts, 38% demonstrated severe wear compared with only 25% of IB PS I inserts. The most prevalent damage location for the IB PS II was the anterior face, whereas the IB PS I sustained wear mainly on the medial face. While the IB PS post was not designed to constrain posterior femoral displacement, our observations confirm contact in hyperextension or other paradoxic anterior tibial translation is common and design-dependent. Minimizing wear and damage through proper post placement and changes in implant design to anticipate contact on the anterior post should be considered for future posterior stabilized knee replacements. These changes cannot occur in isolation, however, because changes in post placement and design also depend on their relation to the shape and location of the tibial bearing surfaces. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.     

Implant Design Influences Tibial Post Wear Damage in Posterior-stabilized Knees

Background

The tibial post in posterior-stabilized total knees is a potential source of polyethylene wear debris, but the relationship between the shape and location of the tibial post in relation to the tibiofemoral bearing surfaces and the subsequent wear damage patterns remains unknown.

Questions/purposes

We used observations made on retrieved implant components from three contemporary posterior-stabilized knee designs to examine how differences in tibial post design affected wear damage on the post.

Methods

We examined 113 retrieved Zimmer NexGen^®, 103 Exactech Optetrak^®, and 58 Smith and Nephew Genesis^® II posterior-stabilized inserts using a subjective scale to grade post damage.

Results

All 274 inserts demonstrated wear damage. Total wear scores and scores for wear damage on the anterior post differed among designs: Optetrak^® 20 ± 4 and 5 ± 1, NexGen^® 13 ± 4 and 3 ± 1, and Genesis^® II 8 ± 3 and 1 ± 1, respectively. The Optetrak^® had predominantly anterior wear damage, the NexGen^® had more global wear damage, and the Genesis^® II had predominantly posterior wear damage. Tibial post wear damage and anterior post wear damage were primarily determined by implant design and to a lesser extent by length of implantation and revision diagnosis.

Conclusions

Although tibial post wear damage is multifactorial, the primary determinant of wear damage, and specifically anterior wear damage, is implant design.

Clinical Relevance

The constraint provided by the posterior-stabilized post-cam contact in modern knee arthroplasties is reflected in the wear damage patterns that occur during in vivo use. Unintended constraint such as anterior impingement should be addressed through design modifications for future posterior-stabilized knee arthroplasties.     

Backside Wear in Modern Total Knee Designs

Although modularity affords various options to the orthopedic surgeon, these benefits come at a price. The unintended bearing surface between the back surface of the tibial insert and the metallic tray results in micromotion leading to polyethylene wear debris. The objective of this study was to examine the backside wear of tibial inserts from three modern total knee designs with very different locking mechanisms: Insall-Burstein II® (IB II®), Optetrak®, and Advance®. A random sample of 71 inserts were obtained from our institution’s retrieval collection and examined to assess the extent of wear, depth of wear, and wear damage modes. Patient records were also obtained to determine patient age, body mass index, length of implantation, and reason for revision. Modes of wear damage (abrasion, burnishing, scratching, delamination, third body debris, surface deformation, and pitting) were then scored in each zone from 0 to 3 (0 = 0%, 1 = 0–10%, 2 = 10–50%, and 3 = >50%). The depth of wear was subjectively identified as removal of manufacturing identification markings stamped onto the inferior surface of the polyethylene. Both Advance® and IB II® polyethylene inserts showed significantly higher scores for backside wear than the Optetrak® inserts. All IB II® and Advance® implants showed evidence of backside wear, whereas 17% (5 out of 30) of the retrieved Optetrak® implants had no observable wear. There were no significant differences when comparing the depth of wear score between designs. The locking mechanism greatly affects the propensity for wear and should be considered when choosing a knee implant system.Key words: polyethylene, wear, knee, backside, back surface, locking mechanism     

Knee Wear Measured in Retrievals: A Polished Tray Reduces Insert Wear

Background  

Polyethylene wear is often cited as the cause of failure of TKA. Rotating platform (RP) knees show notable surface damage on the rotating surface raising concerns about increased wear compared to fixed bearing inserts.     

Weight of Polyethylene Wear Particles is Similar in TKAs with Oxidized Zirconium and Cobalt-chrome Prostheses

Background  

The greater lubricity and resistance to scratching of oxidized zirconium femoral components are expected to result in less polyethylene wear than cobalt-chrome femoral components.     

Liner Exchange and Bone Grafting: Rare Option to Treat Wear & Lysis of Stable TKAs

Background  

Liner exchange and bone grafting are commonly performed for wear and osteolysis around well-fixed modular acetabular components that otherwise would require structural allografting and revision THA. However, liner exchange in the face of substantial lysis around TKA has been performed rarely with reports of failure rates of up to 25% at 3 year followup.     

Second-Generation Locking Mechanisms and Ethylene Oxide Sterilization Reduce Tibial Insert Backside Damage in Total Knee Arthroplasty

This study evaluated the effects of polyethylene quality and locking mechanism on damage to the nonarticulating (backside) surface of retrieved tibial inserts in total knee arthroplasty. Inserts with peripheral capture (PC) locking mechanisms and ethylene oxide (EtO)-sterilized polyethylene were hypothesized to prevent major backside damage. A total of 156 inserts were sorted by locking mechanism and sterilization method and analyzed by damage scoring methods. Ninety-seven specimens exhibited burnishing. Significant positive linear correlations were observed between damage score and age in vivo for all combinations, but damage occurred at a significantly lower rate for second-generation PC implants with EtO sterilization. Most specimens in this group were undamaged (46/72), with others exhibiting only burnishing. Sex, body mass index, and weight did not influence backside damage.     

Optimization of Orthopedic Surgical Instrument Trays: Lean Principles to Reduce Fixed Operating Room Expenses

BackgroundOptimization of surgical instrument trays improves efficiency and reduces cost. The purpose of this study is to assess the economic impact of optimizing orthopedic instrument trays at a tertiary medical center.MethodsTwenty-three independent orthopedic surgical instrument trays at a single academic hospital were reviewed from 2017 to 2018. Using Lean methodology, surgeons agreed upon the fewest number of instruments needed for each of the procedure trays. Instrument usage counts, cleaning times, room turnover times, tray weight, holes in tray wrapping, wet trays, and time invested to optimize each tray were tracked. Cost savings were calculated. Student’s t-test was used to determine statistical significance, with P < .05 considered significant.ResultsThe mean instrument usage before and after Lean optimization was 23.4% and 54.2% (P < .0001). By Lean methods, 433 of 792 instruments (55%) were removed from 11 unique instrument trays (102 total trays), resulting in a reduction of 3520 instruments. Total weight reduction was 574.3 pounds (22%), ranging from 2.1-16.2 pounds per tray. The number of trays with wrapping holes decreased from 13 to 1 (P < .0001). The process of examining and removing instruments took an average of 7 minutes 35 seconds per tray. The calculated total annual savings was $270,976 (20% overall cost reduction).ConclusionIn addition to substantial cost savings, tray optimization decreases tray weights and cleaning times without negatively impacting turnover times. Lean methodology improves efficiency in instrument tray usage, and reduces hospital cost while encouraging surgeon and staff participation through continuous process improvement.Level of EvidenceEconomic Quality Improvement, Level III.     

旋转铰链型膝关节假体临床应用30例随访观察

[目的]探讨采用旋转铰链式人工膝关节假体进行全膝关节置换术的早期及中期临床疗效、并发症、假体选择的适应证.[方法]回顾性分析1998年7月～2008年7月10年间使用旋转铰链式膝关节假体行人工全膝关节置换的28例患者(30例膝) 临床效果.其中男7例,女21例;平均年龄62岁(42～75岁);左膝10例,右膝20例.病因: 膝内翻合并重度骨关节炎8膝, 类风湿关节炎2膝,创伤性关节炎3膝,畸形性骨炎1膝,严重膝外翻畸形6膝,全膝关节置换术后假体松动翻修10膝(6例感染后松动,4例无菌性松动).术前术后使用KSS评分进行评价.[结果]本组病例平均手术时间为3 h10 min(1 h 30 min～6 h30 min),术中平均失血量为990 ml(150～3 000 ml),术中及术后平均输异体血1 300 ml.28例病例平均随访51个月(12～120个月).膝关节评分从术前的19.5分增加到术后的平均77.9分(28～93 分),功能评分从术前的22.5(0～50分)增加到术后的50.5分(0～90分).膝关节平均活动范围从术前58.4°( 0°～90°)提高到术后的72.8°(10°～100°).1例发生髌腱断裂,1例发生假体断裂,5例发生>10°的伸膝迟滞,8例出现明显的膝前痛.[结论]旋转铰链式膝关节假体作为治疗严重膝关节疾病的方法,可以一定程度恢复膝关节功能,中期随访结果满意,但因其手术损伤大,要严格把握手术适应证,预防并发症的发生.     

Residual Varus Alignment does not Compromise Results of TKAs in Patients with Preoperative Varus

Background   

Postoperative varus alignment has been associated with lower IKS scores and increased failure rates. Appropriate positioning of TKA components therefore is a key concern of surgeons. However, obtaining neutral alignment can be challenging in patients with substantial preoperative varus deformity and it is unclear whether residual deformity influences revision rates.     

规律轮换注射部位减轻低分子肝素注射致皮下出血的研究

目的探讨低分子肝素皮下注射时轮换注射部位与皮下出血发生率及出血面积的关系。找出有效的轮换注射部位的方法 ,以减少皮下出血的发生率及面积。方法选择急性心肌梗死和不稳定心绞痛病人 4 0例 ,将其分为实验组和对照组各 2 0例。实验组皮下注射低分子肝素时有规律地轮换注射部位 ,对照组随机轮换注射部位 ,两组各注射 2 4 0例次 ,观察两组皮下出血发生率及出血面积。结果实验组皮下出血发生率显著低于对照组 (P <0 .0 1) ,出血面积显著小于对照组 (P <0 .0 5 )。结论有规律地轮换注射部位可以减少皮下出血发生率及出血面积。     

Highly Crosslinked Polyethylene Can Reduce Wear Rate in THA for High-Demand Patients: A Matched-Paired Controlled Study

BackgroundThe average age of patients benefiting from total hip arthroplasty (THA) has been declining. In addition to pain relief, patients seek to return to physical activity. However, the latter may increase polyethylene wear and therefore the potential risk of early aseptic loosening. The introduction of highly crosslinked polyethylene (HXLPE) has reduced wear rates in the general patient population. The objective of this study was to evaluate the influence of impact sports in patients operated with THA using ceramic-on-conventional polyethylene (cPE) versus ceramic-on-HXLPE, in terms of wear and function, with a minimum of five year follow-up.MethodsSixty-eight patients practicing an impact sport (University of California Los Angeles score ≥8) who underwent a primary THA were included: 34 with a ceramic-on-cPE versus 34 with a ceramic-on-HXLPE using the same cementless acetabular and femoral component. Patients were matched-paired by age, sex, BMI, and University of California Los Angeles score. The wear analysis was performed using the IMAGIKA software. The Harris hip score and hip and osteoarthritis outcome score were collected.ResultsThe linear wear rate was statistically higher (P < .0001) in the cPE group (0.13503 ± 0.0630 mm/year) than in the HXLPE group (0.03059 ± 0.0084 mm/year). Postoperatively, the increase in Harris hip score was calculated at 37.64 for the entire cohort and was comparable in both groups (P = .3674). The hip and osteoarthritis outcome score for pain (P = .0009), daily life activities (P = .0016), and quality of life (P = .0179) were significantly higher in the HXLPE group, with, between groups, a difference inferior to the reported minimal clinical important difference. Three patients exhibited signs of periprosthetic osteolysis in the cPE group, one on the femoral side and two on the acetabular side. None were observed in the HXLPE group. No revision for aseptic loosening was reported in both cohorts.ConclusionPatients partaking in impact sports and receiving a ceramic-on-HXLPE THA demonstrated lower wear and osteolysis rates than those having a ceramic-on-cPE THA, with similar functional results.     

The Effect of Geometric Variations in Posterior-stabilized Knee Designs on Motion Characteristics Measured in a Knee Loading Machine

Background

In different posterior-stabilized (PS) total knees, there are considerable variations in condylar surface radii and cam-post geometry. To what extent these variations affect kinematics is not known. Furthermore, there are no clearly defined ideal kinematics for a total knee.

Questions/purposes

The purposes of this study were to determine (1) what the kinematic differences are caused by geometrical variations between PS total knee designs in use today; and (2) what design characteristics will produce kinematics that closely resemble that of the normal anatomic knee.

Methods

Four current PS designs with different geometries and one experimental asymmetric PS design, with a relatively conforming medial side, were tested in a purpose-built machine. The machine applied combinations of compressive, shear, and torque forces at a sequence of flexion angles to represent a range of everyday activities, consistent with the ASTM standard test for measuring constraint. The femorotibial contact points, the neutral path of motion, and the AP and internal-external laxities were used as the kinematic indicators.

Results

The PS designs showed major differences in motion characteristics among themselves and with motion data from anatomic knees determined in a previous study. Abnormalities in the current designs included symmetric mediolateral motion, susceptibility to excessive AP medial laxity, and reduced laxity in high flexion. The asymmetric-guided motion design alleviated some but not all of the abnormalities.

Conclusions

Current PS designs showed kinematic abnormalities to a greater or lesser extent. An asymmetric design may provide a path to achieving a closer match to anatomic kinematics.

Clinical Relevance

One criterion for the evaluation of PS total knees is how closely the kinematics of the prosthesis resemble that of the anatomic knee, because this is likely to affect the quality of function.