Objectives

The purpose of this study was to clarify the appearance of the reparative tissue on the articular surface and to analyse the properties of the reparative tissue after hemicallotasis osteotomy (HCO) using MRI T1ρ and T2 mapping.

This study presents the use of precision surface machining on artificial joint bearing surfaces in order to inhibit macrophage activation. Ultra-high molecular weight polyethylene (UHMWPE) is widely used as a bearing material in polymer-on-hard joint prostheses. However, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and implant loosening. Several studies report that wear particle size is a critical factor in macrophage activation, with particles in the size range of 0.1 – 1.0 μm being the most biological active. The surface for a conventional Co-Cr-Mo alloy joint implant generally has a 10.0 – 20.0 nm roughness. After precision machining, the Co-Cr-Mo alloy surface had a 1.0 – 2.0 nm roughness with scattered concave shapes up to 50 nm in depth. This precision surface machining method used a typical lapping method, but the relationship between the slurry and the machining surface was strictly controlled in order to emphasize the micro-erosion mechanism. A pin-on-disc wear tester capable of multidirectional motion was used to verify that the new surface was the most appropriate for joints. Tests were carried out in 25% (v/v) fetal calf serum with sodium azide to retard bacterial growth. UHMWPE pins, 12.0 mm in diameter with a mean molecular weight of 6.0 million, were placed on the Co-Cr-Mo alloy disc at a contact pressure of 6.0 MPa. A sliding speed of 12.1 mm/s, and a total sliding distance of 15.0 km were applied. The new surface reduced the amount of UHMWPE wear, which would ensure the long-term durability of joints. The new surface also enlarged the size of UHMWPE particles, but did not change their morphological aspect. Primary human peripheral blood mononuclear phagocytes were cultured with the particles. The wear particles generated on the new surface inhibited the production of IL-6, which indicates a reduction of induced tissue reaction and joint loosening.

We report the long-term outcome of 33 patients (37 knees) who underwent proximal tibial open-wedge osteotomy with hemicallotasis (HCO) for medial osteoarthritis of the knee between 1995 and 2000. Among these, 29 patients with unilateral HCO were enrolled and 19 were available for review at a mean of 14.2 years (10 to 15.7) post-operatively. For these 19 patients, the mean Hospital for Special Surgery knee score was 60 (57 to 62) pre-operatively and 85 (82 to 87) at final follow-up (p < 0.001; paired t-test). The femorotibial angle and tibial inclination angle (IA) were measured at short-term follow-up, one to four years post-operatively, and showed no significant subsequent changes. The clinical scores and radiological measurements showed little change over time. One patient required conversion to total knee replacement during this time. These results suggest that the coronal angle achieved at operation is maintained at long-term follow up after HCO without alteration of the IA, providing a good long-term clinical outcome.

Cite this article: Bone Joint J 2014;96-B:467–72.

An ultra-high molecular weight polyethylene (UHMWPE) is widely used as bearing material in artificial joints, however, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and loosening of implants. The wear particles activate macrophages, which release cytokines, stimulating osteoclasts, which results in bone resorption. The biological activity of the wear debris is dependent on the volume and size of the particles produced. Many researchers reported that the volume and size of particles were critical factors in macrophage activation, which particles in the size range of 0.1–1 mm being the most biological active.

To minimize the amount of wear of UHMWPE and to enlarge the size of UHMWPE wear particle, a nano-level surface textured on Co-Cr-Mo alloy as a counterface material was invented (Figure 1). Although the generally-used surface for a conventional artificial joint has 10 nm roughness (G-1), the nano-level surface has a superfine surface of 1 nm with groove and dimples against the bearing area. The existence probability of groove or dimples, and their surface waviness were adjusted (P-1, 2, 3, 4 and W-1, 2).

Pin-on-disc wear tester capable of multidirectional motions was used to verify that the nano-textured surface is the most appropriate for artificial joint. UHMWPE pin with an average molecular weight of 6.0 million was placed in contact with the disc and the contact pressure was 6.0 MPa. The disc and pin were lubricated by a water-based liquid containing the principal constituents of natural synovial fluid. Sliding speed of 12.12 mm/s had been applied for total sliding distance of 15 km.

The nano-textured surfaces reduced the amount of UHMWPE wear, this would ensure the long-term durability of artificial joint (Figure 2). The wear particles isolated from lubricating liquid were divided broadly into two categories; one is “simple type” and the other is “complicated type”. The lengths in a longitudinal direction (L_l) and its orthogonal direction (L_s) for each particles (>150) were measured, and the each aspect ratio (= L_l/L_s) was calculated. No significant difference was found in the ratio between simple type and complicated type, and in the distributions of aspect ratios. However, the distributions of L_l, which means the size of UHMWPE wear particle, were dramatically changed by using the nano-textured surface (Figure 3). These results suggest that the nano-textured surface does not change the morphological aspect of UHMWPE particle but enlarges the size of UHMWPE particle.

Cells (RAW264.7, blood, Mouse) were cultured with the particles in supplemented Dulbecco's modified Eagle's medium for 24 h in an atmosphere of 5% CO₂ in air at 37 degrees C, and the quantitative PCR was performed for genetic expression of IL-6. The wear debris generated on the nano-textured surface inhibited the genetic expression of IL-6, which does not induce the tissue reaction and joint loosening.

An ultra-high molecular weight polyethylene (UHMWPE) is widely used as bearing material in artificial joints, however, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and loosening of implants. The wear particles activate macrophages, which release cytokines, stimulating osteoclasts, which results in bone resorption. The biological activity of the wear debris is dependent on the volume and size of the particles produced. Many researchers reported that the volume and size of particles were critical factors in macrophage activation, which particles in the size range of 0.1–1 mm being the most biological active.

To minimize the amount of wear of UHMWPE and to enlarge the size of UHMWPE wear particle, a nano-level surface texturing on Co-Cr-Mo alloy as a counterface material was invented. Although the generally-used surface for a conventional artificial joint has 10 nm roughness (Surface A), the nano-level textured surface invented has a superfine surface of 1 nm with 3% of groove and dimples against the bearing area. The depths of groove and dimples are less than 50 nm (Surface F).

Pin-on-disc wear tester capable of multidirectional motions was used to verify that the nano-textured surface is the most appropriate for artificial joint. UHMWPE pin with an average molecular weight of 6.0 million was placed in contact with the disc and the contact pressure was 6.0 MPa. The disc and pin were lubricated by a water-based liquid containing the principal constituents of natural synovial fluid. Sliding speed of 12.12 mm/s had been applied for total sliding distance of 15 km.

The superfine surface with nano-level grooves and dimples (Surface F) reduced the amount of UHMWPE wear, this would ensure the long-term durability of artificial joint. The wear particles isolated from lubricating liquid were divided broadly into two categories; one is “simple type” and the other is “complicated type”. The lengths in a longitudinal direction (L_l) and its orthogonal direction (L_s) for each particles (>150) were measured, and the each aspect ratio (= L_l/L_s) was calculated. No significant difference was found in the ratio between simple type and complicated type, and in the distributions of aspect ratios. However, the distributions of L_l, which means the size of UHMWPE wear particle, were dramatically changed by using the nano-textured surface (Figure 2). These results suggest that the nano-textured surface does not change the morphological aspect of UHMWPE particle but enlarges the size of UHMWPE particle.

Cells (RAW264.7, blood, Mouse) were cultured with the particles in supplemented Dulbecco's modified Eagle's medium for 24 h in an atmosphere of 5% CO₂ in air at 37 degrees C, and the quantitative PCR was performed for genetic expression of IL-6 (Figure 3). The wear debris generated on the nano-textured surface inhibited the genetic expression of IL-6, which does not induce the tissue reaction and joint loosening.

We have investigated in vitro the release kinetics and bioactivity of fibroblast growth factor-2 (FGF-2) released from a carrier of fibrin sealant. In order to evaluate the effects of the FGF-2 delivery mechanism on the repair of articular cartilage, full-thickness cylindrical defects, 5 mm in diameter and 4 mm in depth, which were too large to undergo spontaneous repair, were created in the femoral trochlea of rabbit knees. These defects were then filled with the sealant.

Approximately 50% of the FGF-2 was released from the sealant within 24 hours while its original bioactivity was maintained. The implantation of the fibrin sealant incorporating FGF-2 successfully induced healing of the surface with hyaline cartilage and concomitant repair of the subchondral bone at eight weeks after the creation of the defect.

Our findings suggest that this delivery method for FGF-2 may be useful for promoting regenerative repair of full-thickness defects of articular cartilage in humans.

Conventional high tibial osteotomy for osteoarthritis of the medial compartment of the knee with closed-wedge or dome osteotomy (DMO) may produce shortening of the patellar tendon and loss of inclination of the proximal tibial plateau or of the offset of the tibial condyle relative to its bony axis. This can make subsequent total knee arthroplasty technically demanding.

We undertook a prospective study comparing these changes after DMO with those after using open-wedge osteotomy hemicallotasis (HCO). A total of 50 knees with arthritis of the medial compartment in 46 consecutive patients was randomly allocated to either DMO or HCO. There were no significant differences between the groups with regard to age, gender, femorotibial angle before operation or the angle of correction.

Radiological studies showed that HCO caused little change in the length of the patellar tendon or the inclination angle of the tibial plateau, while after DMO both gradually decreased. The degree of tibial condylar offset increased in both groups, but less so in the HCO group.

We describe the results of conservative treatment for complete midsubstance tears of the anterior cruciate ligament (ACL) in 18 skeletally immature patients, followed for a minimum of 36 months. Six patients had an ACL reconstruction during the follow-up period and were assessed immediately before their operation. The average time from initial injury to evaluation was 51 months. All patients had symptoms when reviewed. The modified Lysholm knee score showed one excellent result, one good, eight fair, and eight poor with a mean score of 64.3. Only one patient had returned to her preinjury level of athletics. Secondary meniscal tears were confirmed in six patients, and three more had the clinical signs of a tear at follow-up. Radiological evidence of degenerative changes was found in 11 of the 18 patients. We conclude that the results of non-operative treatment for ACL injuries in this age group are poor and not acceptable.