Poly (vinyl alcohol) (PVA) hydrogel with high water content is one of the potential materials for artificial cartilage. In the previous study, the wear behavior of PVA hydrogel prepared by freeze-thawing (FT) method (PVA-FT gel) showed the excellent friction and wear property in simulated biological environment. However, the improvement of mechanical strength and wear resistance would be also needed for clinical application of PVA hydrogel as artificial cartilage. The different kind of physically-crosslinked PVA hydrogels prepared by cast-drying (CD) method (PVA-CD gel) and hybrid method of FT and CD (PVA-CD on FT hybrid gel) were also developed, and these two hydrogels have different mechanical properties and showed low friction compared with PVA-FT gel in saline. In this study, PVA hydrogel prepared by CD and hybrid methods were newly developed and friction and wear behavior of PVA-CD gel and PVA-CD on FT hybrid gel were evaluated in simulated biological environment.

A sliding pair of an ellipsoidal reciprocating upper specimen of hydrogel and a flat stationary lower specimen of hydrogel was tested in reciprocating friction test. The thicknesses of PVA-CD gel and PVA-CD on FT hybrid gel were 2.0mm and 1.7mm, respectively. The applied load was 2.94 N. The sliding velocity was 20 mm/s and the total sliding distance was 1.5 km. In this study, solutions that contain hyaluronic acid, phospholipid and proteins were prepared as simulated synovial fluid and used as a lubricant for friction test. Molecular weight of sodium hyaluronate was 9.2×10⁵. L-alpha dipalmitoylphosphatidylcholine (DPPC) was selected as phospholipid constituent and was dispersed in saline as liposome. This liposomal solution was used as a base lubricant. Albumin and gamma-globulin, which are main protein constituents in natural synovial fluid, were used as additives as protein constituents.

As shown in Fig.1, PVA-CD gel showed low friction such as below 0.02 at initial state of friction test. However, friction coefficient of PVA-CD gel rapidly increased and reached to about 0.5. In contrast, PVA-CD on FT hybrid gel kept low friction within the friction test. After friction test, many deep scratches were observed on the worn surface of PVA-CD gel (Figs. 2(a)-(c)). In contrast, the original surface structure of PVA-CD on FT hybrid gel almost remained while some scratches were observed (Figs. 2(d)-(f)).

These results indicated that PVA-CD gel could show low friction but low wear resistance. The hybridization of FT and CD improved the wear resistance of PVA-CD gel. Therefore, the hybridization of FT and CD method is one of the prospective preparation methods of artificial cartilage with low friction and low wear. It is important to elucidate the mechanism of excellent lubricating property of PVA-CD on FT hybrid gel and develop the highly-functioned artificial hydrogel cartilage with low friction and high wear resistance.

The purpose of the study was to compare prospectively and randomly two ACL reconstruction single bundle techniques, one referred to as traditional and the other referred to as anatomical, where the coronal angulation of the femoral tunnel aimed a more horizontal position at 2 and 10 o'clock. Orthopilot® System (Aesculap, Tuttlingen, Germany) was used to assist tunnel positioning in order to obtain and register translational and rotational stability.

Eighteen patients (14 men and 4 women), average age 33.8 years (range 18 to 49), with isolated ACL lesion were randomized in two groups, A (Conventional) and B (Anatomical). All patients were submitted to ACL navigated arthroscopic reconstruction with quadruple hamstrings grafts. Anteromedial portal access for femoral tunnel drilling was used in all patients. The tibial and femoral tunnels drillings were monitored by the Aesculap® Orthopilot Navigation System. In Group A, the femoral tunnel positioning aimed isometricity. In Group B, femoral tunnel was drilled at 25% of Blumensaat's line length from the posterior cortex, and 30° orientation in coronal plane. Initial and final Maximum Anterior tibial Displacement (MATD), Internal Tibial Rotation (ITR) and External Tibial Rotation (ETR) at 30° knee flexion data were recorded intra operatively by the navigation system.

No horizontal or rotational stability differences were found for MATD (p = 0.68), ITR (p = 014) and ETR (0.13). This study did not support the hypothesis that a more anatomical positioning leads to better rotational or anterior stability.