Aims

To verify whether secretory leucocyte protease inhibitor (SLPI) can promote early tendon-to-bone healing after anterior cruciate ligament (ACL) reconstruction.

Acetabular tissue damage is implicated in osteoarthritis (OA) and investigation of in situ acetabular soft tissues behaviour will improve understanding of tissue properties and interconnections. The study aim was to visualise acetabular soft tissues under load and to quantify displacements using computed tomography (CT) scans (XtremeCT, Scano Medical).

A CT scan (resolution 82 μm) was performed on the disarticulated, unloaded porcine acetabulum. The femoral head was soaked in Sodium Iodide (NaI) solution and cling film wrapped to prevent transfer to the acetabular side. The joint was realigned, compressed using cable ties and re-scanned. The two images were down-sampled to 0.3 mm. Acetabular bone and soft tissues were segmented. Bony features were used to register the two background images, using Simpleware ScanIP 7.0 (Synopsys), to the same position and orientation (volume difference < 5%). Acetabular soft tissues displacements were measured by tracking the same points at the tissue edges on the two acetabular masks, along with difference in bone position as an additional error assessment.

The use of radiopaque solution provided a clear contrast allowing separation of the femoral and acetabular soft tissues in the loaded image. The image registration process resulted in a difference in bone position in the areas of interest equivalent to image resolution (0.3 mm, a mean of 3 repeats by same user). A labral tip displacement of 1.7 mm and a cartilage thickness change from 1.5 mm unloaded to 0.9 mm loaded, were recorded.

The combination of contrast enhancement, registration and focused local measurement was precise enough to reduce bone alignment error to that of image resolution and reveal local soft tissue displacements. These measurement methods can be used to develop models of soft tissues properties and behaviour, and therapy for hip tissue damage at early stage may be reviewed and optimised.

INTRODUCTION:

Successful tibial component placement during total knee arthroplasty (TKA) entails accurate rotational alignment, minimal overhang, and good bone coverage, each of which can be facilitated with a tibial component that matches the resected tibial surface. Previous studies investigated bony coverage of multiple tibial component families on digitized resections. However, these studies were based on manual placement of the component that may lead to variability in overhang and rotational alignment. An automated simulation that follows a consistent algorithm for tibial component placement is desirable in order to facilitate direct comparison between tibia component designs. A simulation has been developed and applied to quantify tibial coverage in multiple ethnicities, including Japanese, Indian, and Caucasian. Here, this approach is taken to evaluate tibial coverage of five contemporary tibial designs in Chinese subjects.

Introduction and Aims: Due to relative motion that can occur between the polyethylene articular surface and tibial tray, backside wear of modular tibial components can be a significant contributor to wear in TKR. This study examines the backside wear performance of a tibial component system from both a laboratory and clinical perspective.

Method: Polyethylene components, CR and PS, from the NexGen knee system (Zimmer Inc.) were evaluated for backside wear. These components were identified on the back surface by the manufacturer with engraved lettering of a depth ranging from 20 to 30 micrometers. Twenty-seven components retrieved after 24 to 80 months in-situ were evaluated along with six components having undergone three million cycles of laboratory knee function simulation. Backside wear was quantified by engraving mark depth and screw hole recess penetration measurements utilising a New View 5000 scanning white light interferometer (Zygo). The severity of third-body abrasion was also recorded.

Results: This particular knee system utilised a peripheral rail and dovetail polyethylene locking mechanism which demonstrated little relative polyethylene to tibial tray motion during joint function simulation. Simulator testing produced backside wear of 6.4 micrometers/million cycles or 4.5 mm3/million cycles. This backside wear represented 30% of total component wear as measured gravimetrically. Backside wear in the clinically retrieved components was sufficient to completely remove the manufacturer’s engraving marks on only three of 27 components. The remaining 24 components all experienced backside wear insufficient to remove all engraving. The severity of third-body abrasion (typically bone cement) was generally associated with greater backside wear. Two of the three clinically retrieved components with worn-through lettering had evidence of significant third-body wear. In 11 clinically retrieved components (utilised on tibial trays with screw holes), backside wear was measured by comparing engraving mark depth in unworn polyethylene areas over screw recesses with engraving mark depth in areas of polyethylene contact with the tibial tray. These components demonstrated 14 micrometers of wear at an average of 37 months in-situ or 4.4 micrometers per year. None of the retrieved components were clinically associated with osteolysis.

Conclusion: In this particular tibial component system, backside wear was moderate for both the joint simulator and clinically retrieved specimens. Backside wear does not appear to be the major contributor of total polyethylene wear in this implant system. The presence of third-body particles contributed to greater wear.

A method to extensively cross-link polyethylene for total hip application has been developed and tested in hip wear simulation. Extensively cross-linked polyethylene was prepared by exposing GUR 1050 polyethylene resin to 90 kg to 110 kg of e-beam radiation. For total hip application, the material was evaluated in an AMTI joint simulator in normal debris-free conditions and in a Shorewestern simulator for the adverse condition of added bone cement and aluminum oxide debris. The normal condition testing was conducted to 30 million cycles, while the adverse condition tests were conducted to 5 million cycles. Femoral head sizes from 22 mm to 46 mm were evaluated. The wear performance of extensively cross-linked material was compared to control material (GUR 1050 gamma sterilized in nitrogen). The results demonstrate a significant improvement in wear (greater than 80 percent reduction) of extensively cross-linked GUR 1050 acetabular components compared to the control acetabular components. The adverse condition wear of both materials was greater than the normal wear; however, when compared to the controls, the extensively cross-linked material had improved wear performance in both normal and adverse conditions. The wear of femoral heads larger than normal 32 mm sizes showed accelerated wear in the control material and desirable low wear in the extensively cross-linked condition. The polyethylene particles generated in the wear simulation were of similar size and shape between the extensively cross-linked and controlled polyethylene. As demonstrated in the laboratory simulation, this extensively cross-linked polyethylene has the potential to substantially reduce particular debris generation in total hip applications. A multicenter randomized controlled clinical study of extensively cross-linked and control acetabular components is ongoing.