Polished Trays Reduce Backside Wear Independent of Post Location in Posterior-stabilized TKAs

Background

Backside damage of the polyethylene in TKA is a potential source of debris. The location of the tibial post in posterior-stabilized implants may influence micromotion, and thus affect backside damage, as may surface roughness.

Questions

We used implant retrieval analysis to (1) examine if there were differences in backside damage among three modern posterior-stabilized implants attributable to variable surface roughness; (2) determine if the location of damage on the tibial post affected the pattern of backside damage; and (3) determine if demographics influenced backside damage.

Methods

We identified 403 posterior-stabilized tibial retrieved inserts (147 NexGen^®, 152 Optetrak^®, 104 Genesis^® II). The damage on the surfaces of the tibial posts was previously graded. The backside of the inserts (divided into quadrants) were scored for evidence of damage. The total quadrant damage was compared for each implant group, the relationship between post face damage and location of damage on the backside was determined for each implant group, and total backside damage was compared among the three implant groups.

Results

No correlation was found between the location of damage on the post and location of damage on the backside of the implant for any of the three groups. The Genesis^® II polyethylene implants, which articulate with a highly polished tibial tray, showed a significantly lower total backside damage score (p < 0.01) when compared with the other two implant groups. The Genesis^® II and Optetrak^® showed significantly more damage in the posterior quadrants of the implants (p < 0.01) when compared with the anterior quadrants. A linear regression analysis revealed that lower tibial tray surface roughness was correlated with decreased damage.

Conclusions

An implant design with a highly polished tibial tray was associated with decreased backside damage. However, tibial post design and location did not influence the location of backside damage.

Clinical Relevance

Our study showed that a highly polished tibial tray was associated with decreased damage to the backside of polyethylene inserts independent of post design and location. These findings should be taken into consideration when new generations of implants are designed.     

The 2012 Mark Coventry Award: A Retrieval Analysis of High Flexion versus Posterior-stabilized Tibial Inserts

Background

High flexion (HF) implants were introduced to increase ROM and patient satisfaction, but design changes to the implant potentially have deleterious effects on polyethylene wear. It is unclear whether the HF implants affect wear.

Questions/purposes

We therefore examined whether the design changes between HF and posterior-stabilized (PS) tibial inserts would affect overall damage or damage on their articular surface, backside, and tibial post and whether flexion angle achieved related to damage.

Methods

We matched 20 retrieved HF inserts to 20 retrieved PS inserts from the same implant system on the basis of duration of implantation, body mass index, and age. Inserts were divided into 16 zones and a microscopic analysis of surface damage was carried out. Five inserts were scanned using micro-CT to further quantify instances of severe post notching. We determined overall damage with a scoring system.

Results

We found greater backside and post damage in the HF group but no difference in the articular surface or overall damage scores. Backside and post damage scores correlated to flexion angle in the HF group. There was no flexion/damage correlation in the PS group. Notch depths around the post in both groups ranged from 0.6 to 1.9 mm.

Conclusions

HF inserts are more susceptible to post damage, possibly as a result of higher contact stresses from greater flexion. The increased backside damage was unexpected because the two groups have the same tibial component, locking mechanism, and sterilization method.

Clinical Relevance

The introduction of a highly crosslinked HF insert will require close scrutiny as a result of the potential for post damage demonstrated in this series.     

Biomechanical comparison of different fixation techniques for reconstruction of tibial avulsion fractures of the anterior cruciate ligament

Purpose

The most common fixation techniques for tibial avulsion fractures of the anterior cruciate ligament (ACL) described in the literature are screw and suture fixation. The fixation of these fractures with the TightRope® device might be an alternative. Up to now it has been commonly used in other injuries, such as acromioclavicular joint or syndesmosis ruptures. The purpose of this study was to evaluate the biomechanical properties of different fixation techniques for the reconstruction of tibial avulsion fractures.

Methods

Type III tibial avulsion fractures were simulated in 40 porcine knees. Each specimen was randomly assigned to one of four groups: (1) anterograde screw fixation, (2) suture fixation, (3) TightRope® fixation or (4) control group. The initial displacement, strength to failure and the failure mode were documented.

Results

The maximum load to failure was 1,345?±?155.5 N for the control group, 402.5?±?117.6 N for the TightRope® group, 367?±?115.8 N for the suture group and 311.7?±?120.3 N for the screw group. The maximum load to failure of the control group was significantly larger compared to all other groups. The initial dislocation was 0.28?±?0.09 mm for the control group, 0.55?±?0.26 mm for the TightRope® group, 0.84?±?0.15 mm for the screw group and 1.14?±?0.9 mm for the suture group. The initial dislocation was significantly larger for the suture group compared to the TightRope® and control groups.

Conclusions

The TightRope® fixation shows significantly lower initial displacement compared to the suture group. The TightRope® fixation might be an alternative for the repair of ACL tibial avulsion fractures that can be used arthroscopically.     

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

Background

Wear 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/Purposes

We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear.

Methods

We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52 months 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.

Results

The average total wear was 254 ± 248 mm³. The average wear rate was 58 ± 41 mm³/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm³/year and the fixed-bearing rate was 74 ± 49 mm³/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate.

Conclusions

Micro-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.     

Less Midterm Damage and Oxidation Are Seen in Retrieved Highly Crosslinked Ultrahigh-Molecular-Weight Polyethylene Tibial Inserts than in Direct Compression Molded Polyethylene Inserts

Background

Highly crosslinked ultrahigh-molecular-weight polyethylene (XLPE) shows reduced wear in total hip arthroplasty compared to direct compression-molded polyethylene (compPE); however, minimal research evaluating polyethylene damage in XLPE tibial inserts in total knee arthroplasty exists.

Questions/Purposes

We evaluated damage and material properties in retrieved XLPE components at midterm (≥?2.5 years) follow-up.

Methods

We identified 19 XLPE tibial inserts with ≥?30 months in vivo using our institutional review board–approved implant retrieval system; 19 compPE retrieved inserts were matched based on age at index surgery, body mass index, sex, and length of implantation. Articular surface damage was assessed using a subjective grading system. Swell ratio testing and Fourier-transform infrared spectroscopy were used to measure crosslink density (XLPE) and oxidation (XLPE, compPE), respectively, at loaded and unloaded surface and subsurface regions.

Results

CompPE inserts had higher overall damage than XLPE inserts, specifically at the post of posterior-stabilized inserts. The XLPE inserts had lower crosslink density at the loaded surface (0.159 mol/dm³) than either unloaded region (0.183 mol/dm³). CompPE peak oxidation index (OI) was greater than XLPE peak OI in the loaded and unloaded surface regions (1.67 vs. 0.61 and 1.38 vs. 0.46, respectively).

Conclusions

Surface damage and oxidation are reduced in XLPE inserts compared to compPE at midterm follow-up. Peak OI greater than 1.0 in the compPE group suggests that mechanical-property degradation had occurred, a likely cause for increased damage. Longer-term retrievals will determine whether these trends continue. Based on midterm results, XLPE shows an advantage over compression molded PE in total knee arthroplasty.

     

Health-related quality of life in patients with an anterior cruciate ligament injury

Introduction

We evaluated the quality of life (QOL) in patients with an anterior cruciate ligament injury through SF-36 survey, which was a global health-related QOL survey, and investigated the correlation of its results with other clinical parameters.

Patients and methods

Fifty-one patients (mean age 28.7 years) with an anterior cruciate ligament injury were studied. Clinical evaluations using SF-36 version 2 and Lysholm scoring system were conducted, and the ratio of anterior tibial translation in affected compared to unaffected knees was obtained.

Results

In SF-36 survey, scores of both physical and mental health summary measures in our subjects were lower than the national standard values. The mean ratio of anterior tibial translation was 7.8 ± 6.0, and no correlation with SF-36 scores was observed. The mean Lysholm score was 53.3 ± 17.1; which tended to be correlated with the mental health score of SF-36, but not with the physical health score.

Discussion

Our results clearly demonstrated that patients with an anterior cruciate ligament injury had a deterioration of mental health as well as physical health.     

The biomechanical characteristics of arthroscopic tibial inlay techniques for posterior cruciate ligament reconstruction: in vitro comparison of tibial graft tunnel placement

Purpose

The hypothesis of the present study was that the biomechanical properties of arthroscopic tibial inlay procedures depend on tibial graft bone block position.

Methods

Five paired fresh-frozen human cadaveric knee specimens were randomized to a reconstruction with quadriceps tendon placing the replicated footprint either to the more proximal margin of the remnants of the anatomical PCL fibrous attachments (group A) or to the distal margin of the anatomical PCL fibrous attachments at the edge of the posterior tibial facet to the posterior tibial cortex in level with the previous physis line (group B). The relative graft-tibia motions, post cycling pull-out failure load and failure properties of the tibia-graft fixation were measured. Cyclic displacement at 5, 500 and 1,000 cycles, stiffness and yield strength were calculated.

Results

The cyclic displacement at 5, 500 and 1,000 cycles measured consistently more in group A without statistically significant difference (4.11?±?1.37, 7.73?±?2.73 and 8.18?±?2.75 mm versus 2.81?±?1.33, 6.01?±?2.37 and 6.46?±?2.37 mm). Mean ultimate load to failure (564.6?±?212.3) and yield strength (500.2?±?185.9 N) were significantly higher in group B (p?Conclusion Replicating the anatomical PCL footprint at the posterior edge of the posterior tibial facet yields higher pull-out strength and less cycling loading displacement compared to a tunnel position at the centre of the posterior tibial facet.     

Can Joint Contact Dynamics Be Restored by Anterior Cruciate Ligament Reconstruction?

Background

Rotational kinematics has become an important consideration after ACL reconstruction because of its possible influence on knee degeneration. However, it remains unknown whether ACL reconstruction can restore both rotational kinematics and normal joint contact patterns, especially during functional activities.

Questions/purposes

We asked whether knee kinematics (tibial anterior translation and axial rotation) and joint contact mechanics (tibiofemoral sliding distance) would be restored by double-bundle (DB) or single-bundle (SB) reconstruction.

Methods

We retrospectively studied 17 patients who underwent ACL reconstruction by the SB (n = 7) or DB (n = 10) procedure. We used dynamic stereo x-ray to capture biplane radiographic images of the knee during downhill treadmill running. Tibial anterior translation, axial rotation, and joint sliding distance in the medial and lateral compartments were compared between reconstructed and contralateral knees in both SB and DB groups.

Results

We observed reduced anterior tibial translation and increased knee rotation in the reconstructed knees compared to the contralateral knees in both SB and DB groups. The mean joint sliding distance on the medial compartment was larger in the reconstructed knees than in the contralateral knees for both the SB group (9.5 ± 3.9 mm versus 7.5 ± 4.3 mm) and the DB group (11.1 ± 1.3 mm versus 7.9 ± 3.8 mm).

Conclusions

Neither ACL reconstruction procedure restored normal knee kinematics or medial joint sliding.

Clinical Relevance

Further study is necessary to understand the clinical significance of abnormal joint contact, identify the responsible mechanisms, and optimize reconstruction procedures for restoring normal joint mechanics after ACL injury.     

Void filling of tibia compression fracture zones using a novel resorbable nanocrystalline hydroxyapatite paste in combination with a hydroxyapatite ceramic core: first clinical results

Introduction

It is a generally accepted standard surgical practice to fill-in the metaphyseal defect zones resulting from the reduction of tibia compression fractures. The development of various innovative bone substitutes is also currently on the increase.

Materials and methods

In our prospective study, we used Ostim^®, a novel resorbable nanocrystalline hydroxyapatite paste, together with Cerabone^®, a solid hydroxyapatite ceramic, in combination with angularly stable osteosynthesis to treat 24 tibia compression fractures. Types B2 and B3, as well as types C2 and C3 fractures, according to the AO classification, were included in the study.

Results

The mean total range of joint motion in terms of flexion and extension was improved from the immediate postoperative value of 79 ± 14° to 97 ± 13° at 6 weeks after surgery, to 109 ± 16° at 3 months, and finally to 118 ± 17° at 1 year. In three patients, a delayed wound healing was observed as a local complication.

Conclusion

The use of the Ostim^® and Cerabone^® combination is an effective method in treating tibia compression fractures with large defect zones left after reduction.     

Mid-term results of a new cementless hydroxyapatite coated anatomic unicompartmental knee arthroplasty

Introduction

We report the mid term results of a cement less HA coated unicompartmental knee prosthesis.

Material and methods

One hundred and fifty-nine Unicompartmental knee arthroplasties were done between 1995 and 2000 with ALPINA^® UNI, a cementless HA coated anatomic prosthesis. One hundred and twenty knees were available for the mid-term follow-up at a mean of 6.5 years.

Results

The mean IKS improved from 87.1 ± 22.1 points preoperatively to 168.2 ± 26.1 at the latest follow-up (P < 0.001). Ninety-four percent of the knees were rated good and excellent. The mean knee flexion has significantly improved from 120° preoperatively to 126° at the latest follow-up (P < 0.001). Ten knees were revised: three for degeneration of osteoarthritis in the opposite compartment of the knee, four for polyethylene insert fracture, one for severe polyethylene wear and two for tibial component loosening. When revision for any reason was defined as the end point, the 5-year Kaplan–Meier survival rate was 95.7% (95% confidence interval, 90.1–98.2%) and when revision due to implant mechanical failure (excluding degeneration of osteoarthritis in the opposite compartment of the knee) was defined as the end point, the 5-year survival rate was 96.6% (95% confidence interval, 91.2–98.7%).

Conclusion

This study confirms the reliability of HA coated unicompartimental knee replacement. With careful indications it seems to be a good alternative to osteotomy of total arthroplasty.     

Exakte Messung des Volumeneffektes von 6%iger Hydroxyethylstärke 130/0,4 (Voluven®) während präoperativer akuter normovolämer Hämodilution

Background

What is the effect of preoperative acute normovolemic hemodilution (ANH) with 6% hydroxyethyl starch (HES) 130/0.4 (Voluven^®) on blood volume?

Methods

In 10 patients undergoing radical hysterectomy, ANH was performed to a hematocrit of 21% using 6% HES 130/0.4 (Voluven^®) whereby a replacement of blood with 115% of colloid was planned. Plasma volume (indocyanine green dilution technique) and hematocrit were determined before, 30 and 60 min after ANH. Red cell volume (labelling erythrocytes with fluorescein) was determined before and 30 min after ANH.

Results

After removal of 1,431±388 ml of blood and simultaneous replacement with 1,686±437 ml of colloid, blood volumes were 218±174 ml higher than before (at 105±4%). The volume effect was 98±12%, 30 min after ANH. Even 60 min after ANH, mean blood volumes were with 4,228±986 ml slightly higher than before ANH (102±5%). The hematocrit decreased disproportionally in relation to the residual intravascular volume. Consequently, estimating the volume effect from the changes in hematocrit led to an overestimation (about +30%).

Conclusion

Double label measurements of blood volume demonstrated that the volume effect of 6% HES 130/0.4 (Voluven^®) is about 100% in the course of ANH. The reason for the disproportionally large decrease in hematocrits could be the mobilization of a fraction of the plasma volume which was retained within the endothelial glycocalyx.     

Reduziert ein erh?hter tibialer Slope den Abrieb bei unikondyl?ren Schlittenprothesen?

Introduction

Unicompartmental knee arthroplasty (UKA) has become a standard procedure with good clinical outcome in patients with isolated medial osteoarthritis of the knee. However, the survival rates of UKA are still inferior compared to that of total knee arthroplasty. Aseptic loosening and wear are responsible for more than 50% of revisions. Therefore, this study evaluated the influence of the tibial slope on the wear rate in a medial UKA.

Materials and methods

The wear rate of a medial mobile-bearing UKA (Univation? Aesculap, Tuttlingen, Deutschland) was evaluated according to the ISO 14243-1:2002(E) norm with a customized four-station servo-hydraulic knee wear simulator (EndoLab, Thansau, Germany). In the first group, the prostheses was medially implanted with 0° slope (n?=?3) and in the second group the prostheses was medially implanted with 8° slope (n?=?3). The lateral side was kept constant with 0° in both groups. For each implant, a total of 5.0 million cycles was performed and after every 0.5 million cycles the gravimetric wear rate was determined.

Results

The wear rate in the 0° slope group was 3.46?±?0.59?mg/million cycles and therefore significantly higher than in the 8° slope group with 0.99?±?0.42?mg/million cycles (p?Discussion An increase in the tibial slope leads to a reduced wear rate in a mobile-bearing UKA. Therefore, at least for this mobile-bearing UKA a higher tibial slope seems favorable to reduce the wear. However, before an optimal position of the tibial slope can be recommended, further investigations are required to evaluate the influence of the tibial slope on other factors, such as the ligament tension or the strain on the lateral compartment.     

Fibula head is a useful landmark to predict the location of posterior cruciate ligament footprint prior to total knee arthroplasty

Purpose

The hypothesis of our study is that a routine tibial cut during cruciate retaining TKA may result in a partial or a total removal of the PCL footprint. Therefore providing a reliable landmark is essential to estimate the probability of PCL damage with a tibial cut and to enable the surgeon to decide pre-operatively whether a cruciate retaining implant design is suitable.

Methods

In a case series of 175 cruciate retaining TKA, the routinely made standing postoperative AP-view radiographs were evaluated to determine the distance between fibula head and tibial cutting plane. In a second case series knee MRI of 223 subjects were consecutively used to measure the vertical distance between tibial attachment of PCL and fibula head. The probability of partial or total PCL damage was calculated for different vertical distances between tibial cut and fibula head.

Results

The vertical distance between the tibial cut and the most proximal point of the fibula head averaged 6.1 mm ±4.8 mm. The mean vertical distance from fibula head to proximal and to distal PCL footprint revealed to be 11.4 mm ±3.7 mm and 5.4 mm ±2.9 mm, respectively. The location of the insertion was not significantly different between subgroups such as age (<50 or >50 years), gender and side. Based on our results 11 (7 %) knees were considered at high risk of an entire PCL removal after implantation of a cruciate retaining TKA design.

Conclusions

Currently available routine tibial preparation techniques result in partial or total posterior cruciate ligament detachment. Fibula head as a landmark aids to predict the PCL location and to estimate its disruption pre- and postoperatively on AP-view radiographs.     

Short-term Wear Evaluation of Thin Acetabular Liners on 36-mm Femoral Heads

Background

Dislocation remains the leading cause of revision THA. One approach to decreasing prosthetic dislocation risk has been the use of larger femoral head component sizes. The upper limit of head size in metal-on-polyethylene hip arthroplasty has historically been limited because of concerns about increased wear on thin polyethylene components. It is not known to what degree this concern should apply to more wear-resistant polyethylene components.

Questions/purposes

We therefore determined (1) in vitro wear rates of polyethylene liners of varying thicknesses, (2) whether there were differences in the microscopic wear characteristics as a function of polyethylene thickness, and (3) whether thin polyethylene components resulted in early catastrophic failures.

Methods

We used a hip wear simulator to compare the wear performance of 12 highly crosslinked polyethylene acetabular inserts. The internal diameter of all components was 36 mm, and there were three samples tested of each thickness (1.9, 3.9, 5.9, or 7.9 mm). Testing was conducted for 2.4 million cycles. Gravimetric mass loss was converted to volumetric loss, which was subsequently converted to theoretical linear penetration rates.

Results

Wear rates decreased with increasing polyethylene thickness. Mean ± SD wear rates for the 1.9-, 3.9-, 5.9-, and 7.9-mm groups were 5.0 ± 0.5, 3.2 ± 0.3, 2.5 ± 1.1, and 2.2 ± 1.3 mm³/million cycles, respectively (p < 0.016). Calculated penetration rates were 0.015, 0.012, 0.011, and 0.010 mm/million cycles, respectively (p < 0.016). There were no catastrophic failures in any group.

Conclusions

Thinner polyethylene components demonstrated higher wear rates, although even the highest wear rate observed in the thinnest polyethylene specimen was lower than that commonly reported for noncrosslinked polyethylene components. While encouraging, these findings should be validated in vivo before clinical recommendations can be made.     

Treatment outcomes and resource use of patients with neurogenic detrusor overactivity receiving botulinum toxin A (BOTOX®) therapy in Germany

Purpose

To evaluate treatment outcomes and resource consumption of patients with neurogenic detrusor overactivity (NDO) before and after botulinum toxin A (Botox ^® ) therapy in Germany.

Methods

In a multi-center, cross-sectional, retrospective cohort study, data of patients with NDO 12 months before and after the first Botox ^® therapy were analyzed.

Results

214 patients (mean age 38 ± 14.8 years, 145 male, 69 female) with NDO due to spinal cord injury (81%); myelomeningocele (14%), or Multiple Sclerosis (5%) from seven hospitals were included. Mean interval between treatments was 8 months. Following treatment, mean maximum detrusor pressure, maximum cystometric capacity and detrusor compliance improved significantly. Prior to Botox ^® therapy, 68% reported urinary tract infections (UTI), 63% had incontinence episodes, and 58% used incontinence aids. These numbers decreased significantly (p < 0.05) after treatment to 28, 33, and 28%, respectively. In patients using incontinence aids, mean costs per patient decreased from €2 to €1 per day, whereas the mean cost of drugs to treat UTIs per patient decreased from €163 to €80 per year, respectively.

Conclusion

This is the first study demonstrating the clinical usefulness of Botox ^® therapy in clinical practice. Successful treatment resulted in lower costs for NDO associated morbidity due to less need for incontinence aids and UTI medication.