Temperature effect on the shear-induced cell damage in biofabrication.

Biofabrication that incorporates living cells to manufacture various bioproducts is often carried out at different temperatures as the process demands. In the process, cells are subjected to mechanical forces, which may damage cells if the forces reach a certain level. Previous studies have shown that the cell damage is mainly caused by shear stress; however, none of them looked at the temperature effect on cell damage. In the present work, the influence of temperature on shear-induced cell damage was investigated experimentally by using a cone-and-plate rheometer, and based on the experimental results, a cell damage law was established to quantitatively describe the relationship between the cell damage percent and temperature. The so-established cell damage law was then applied to the modeling of the cell damage percent that occurs in the biofabrication process in which pressurized air was applied to dispense Schwann cells suspended in the alginate solution at different temperatures. The agreement between the model predictions and the experimental results suggests that the method presented in this article is effective for use in the investigation of the temperature effect, thereby providing a cue to preserve cell viability in the biofabrication processes.

Periprosthetic changes in bone mineral density in 5 stem designs 5 years after cemented total hip arthroplasty. No relation to stem migration.

Changes in bone mineral density (BMD) at the proximal femur were evaluated in 83 cemented total hip arthroplasties (THAs) 5 years after surgery. The BMD changes were compared among 5 stem designs and were related to the stem migration. A greater BMD decrease was found in Scientific Hip Prosthesis (Biomet, Bridgend, UK) and SPII CoCr stems (Link, Hamburg, Germany) than in Exeter (Howmedica, London, UK), Spectron (Smith & Nephew, Memphis, Tenn), and SPII Titanium stems (P < .05), and the stiffer SPII CoCr stems (Link) had a larger bone loss than the SPII Titanium stems (Link). However, no overall relationship was found between the BMD changes and stem migration or stem stiffness.

The constrained acetabular component for hip instability.

One hundred four hips in 107 patients undergoing revision arthroplasty of the hip were identified at risk of dislocation and treated with the constrained cup. Radiostereometric analysis was performed to assess prosthesis migration. Mean follow-up was 3.0 years (range, 2.0-4.8). At last review, 19 patients had died and 6 were lost to follow-up. There were 5 revisions for cup loosening and a further 4 with radiographic evidence of loosening. There were 3 dislocations and 3 dissociations in 5 patients. Radiostereometric analysis demonstrated that cup migration at 24 months was up to 0.82 mm of translation and 1.58 degrees of rotation. Our results confirm that the constrained acetabular component is a highly effective option for the treatment for patients with instability of the hip. The aseptic loosening rate was higher than previously reported.

No increased migration in cups with ceramic-on-ceramic bearing: an RSA study.

UNLABELLED: Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migration was followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07-0.40 mm vs. 0.05-0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31-0.92 degrees vs. 0.57-1.40 degrees). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender. LEVELS OF EVIDENCE: Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics.

The literature contains limited yet controversial information regarding whether a fixed or a mobile bearing implant should be used in unicompartmental knee arthroplasty (UKA). This randomized study was to further document the performance and comparison of the two designs. Fifty-six knees in 48 patients (mean age of 72 years) undergoing medial UKA were randomized into a fixed bearing (Miller/Galante) or a mobile bearing (Oxford) UKA. The 2 year clinical outcomes (clinical scores), radiographic findings, and weight bearing knee kinematics (assessed using RSA) were compared between the two groups. The mobile bearing knees displayed a larger and an incrementally increased tibial internal rotation (4.3 degrees, 7.6 degrees, 9.5 degrees vs. 3.0 degrees, 3.0 degrees, 4.2 degrees respectively at 30 degrees, 60 degrees, 90 degrees of knee flexion) compared to the fixed ones. The medial femoral condyle in the mobile bearing knees remained 2 mm from the initial position vs. a 4.2 mm anterior translation in the fixed bearing knees during knee flexion. The contact point in the mobile bearing implant moved 2 mm posteriorly vs. a 6 mm anterior movement in the other group. The mobile bearing knees had a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05). The incidence of lateral compartment OA and progression of OA at patello-femoral joint were equal. No differences were found regarding Knee Society Scores, WOMAC, and SF-36 scores (p > 0.05). This study indicates that mobile bearing knees had a better kinematics, a lower incidence of radiolucency but not yet a better knee function at 2 years.

Decreased precision for BMD measurements in the prosthetic knee using a non-knee-specific software.

Non-knee-specific software has been widely used for bone mineral density (BMD) measurement at the knee, which coincide with a higher measurement error. This study was conducted to test whether software developed for BMD measurement at the hip could be used in the knee by using dual-energy X-ray absorptiometry (DXA) and whether knee rotational alignment or differences in soft tissue substitutes would influence the precision of the BMD measurement. Twelve knees operated with total knee arthroplasty were included. The knees were scanned four to six times each in four rotational positions using DXA with either a Plexiglas rod or rice bags as a soft tissue substitute. The BMD was measured in one manually defined region at the proximal tibia by using the software of Orthopedic. The precision (coefficient of variation) at the knee was 5.1-9.0% when using the Plexiglas rod and 7.3% when using rice bags. The poor precision was mainly explained by inconsistency in tissue baseline establishment and/or by low baseline bone density (Adj R2 = 0.78-0.90, p < 0.000). Neither intentional rotation of the knee nor using different soft tissue substitutes significantly altered the precision. The results suggest that the use of a non-knee-specific software in the prosthetic knee is not appropriate.

Increased bone turnover as reflected by biochemical markers in patients with potentially unstable fixation of the tibial component.

INTRODUCTION: Whether biochemical markers of bone metabolism can be used in assessing the conditions of implant fixation is unknown. In this study, the serum levels of three bone markers were measured prospectively in patients undergoing total knee arthroplasty (TKA) to determine if patients with different fixation conditions of the tibial component showed any differences in the levels of the markers. MATERIALS AND METHODS: The fixation of the tibial component in 40 knees (40 patients, 14 male and 26 female, average age 71 years) was assessed by radiostereometric analysis (RSA), and based upon the pattern of migration, implants with stable fixation ( n=25) and potentially unstable fixation ( n=15) were identified. Serum levels of carboxyterminal propeptide of type I procollagen (PICP), osteocalcin (OC) and cross-linked carboxyterminal telopeptide of type I collagen (ICTP) were assessed and compared between the two fixation groups. Blood samples were obtained preoperatively (baseline) and repeated postoperatively at 1 week, 3, 6, 12, and 24 months. RESULTS: The baseline levels of the markers were statistically the same ( p>0.05) between the two fixation groups. Postoperatively, ICTP levels in the unstable group were significantly higher than in the stable group from 6 to 24 months ( p=0.02). Levels of OC in the unstable group were higher at 12 and 24 months compared with the stable group, reaching statistical significance only at 12 months ( p=0.03). No difference in the levels of PICP was found between the two groups. CONCLUSION: The findings indicate a more active bone turnover probably at the bone-cement/implant interface in knees with potentially unstable fixation. It reveals the potential value for biochemical markers in monitoring implant fixation and aseptic loosening and suggests a possibility for improving implant fixation by drugs which inhibit osteolysis.