The aim of this research was to determine biomechanical markers which differentiate medial knee osteoarthritis (OA) patients who do and do not show structural progression over a 2-year period.

A cohort of 36 subjects was selected from a longitudinal study (Meireles et al 2017) using Kellgren-Lawrence (KL) scores at baseline and 2-year follow-up. The cohort consisted of 10 healthy controls (HC) (KL=0 at both time points), 15 medial knee OA non-progressors (NPKOA) (KL≥1 at baseline and no change over 2 years), and 11 medial knee OA progressors (PKOA) (KL≥1 at baseline and increase of ≥1 over 2 years). 3D integrated motion capture data from three walking trials were processed through a musculoskeletal modelling framework (Smith et al 2016) to estimate knee joint loading parameters (i.e., magnitude of mean contact pressure, and centre of pressure (COP)). Parameters at first and second peak were extracted and compared between groups using Kruskal-Wallis and Mann-Whitney tests.

Higher magnitudes were observed in PKOA vs NPKOA, and PKOA vs HC groups at both time points. Additionally, a posterior (1st and 2nd peak), and lateral (2nd peak) shift in medial compartment COP was shown between PKOA and NPKOA, and PKOA and HC subjects. Interestingly, in the studied parameters, no differences were observed between NPKOA and HC groups.

Significantly higher magnitude, and a more posterior and lateral COP was observed between PKOA and NPKOA patients. These differences, combined with an absence of difference between NPKOA and HC suggest structural OA progression is driven by a combination of altered loading magnitude and location. These results may serve as guidelines for targeted gait retraining rehabilitation to slow or stop knee OA progression whereby shifting COP anterior and medial and reducing magnitude by ~22% may shift patients from a PKOA to a NPKOA trajectory.

The increasing success rates of total hip replacements (THR) have led to a younger patient population with an increased probability for revision. The survival of revised components is improved by a good bone quality. This has led to an increased interest in bone preserving THR designs. A novel type of THR was developed of which the femoral component is cemented in the neck. The load carrying area of this prosthesis is reduced in comparison with conventional cemented implants. Whether an adequate stability can be achieved was biomechanically evaluated during simulated normal walking and chair rising. In addition, the failure behaviour was investigated.

Bone mineral density (BMD) was measured in 5 fresh frozen proximal human cadaver femora. The femoral heads were resected and a 20 mm diameter canal was created in the femoral necks. Bone cement was pressurised in this canal and the polished, taper-shaped prosthesis was subsequently introduced centrally. A servohydraulic testing machine was used to apply dynamic loads up to 1.8 kN to the prosthetic head. Radiostereophotogrammetric analysis was used to measure rotations and translations between prosthesis and bone. In addition, the constructions were loaded until failure in a displacement-controlled test.

During the dynamic experiments, the femoral necks did not fail, and no macroscopical damage was detected. The initial stability of the implant did not seem to be sensitive to bone quality. Maximal values were found for normal walking with a mean rotation of about 0.2 degrees and a mean translation of about 120 microns. These motions stabilised during testing. The failure loads in this study varied between 4.1 and 5.5 kN, higher failure loads were associated with higher BMD values. Most specimens showed subtrochanteric spiral fractures.

In conclusion, the stability of the prosthetic device may be adequate under dynamic, physiological loading conditions. The static failure loads were relatively low and require further optimisation of the prosthetic implant.