In Vitro Evaluation of Hemiarthroplasty Bearing Materials: A Scoping Review (Part I)

Hemiarthroplasty is used to treat joint damage confined to one side, aiming to preserve the remaining healthy cartilage and bone while addressing conditions like femur fractures and osteonecrosis; however, challenges persist due to cartilage wear and inconsistent clinical outcomes. This scoping review evaluates in vitro studies on hemiarthroplasty bearing materials (HBM), focusing on the HBM tested, cartilage specimens, experimental setups, outcome variables, and the comparability of results. Of 1798 identified studies, 72 met the inclusion criteria, with 48 classified as in vitro. HBMs tested included metals (42%) and soft polymers (30%) and 45% of studies utilized multiple distinct HBMs. Cartilage specimens were predominantly bovine (65%), mostly from the tibial-femoral joint (69%). The two most common experimental set ups were tribometers (75%) and simulators (25%) both using commercial and custom-built rigs. Tribometer configurations included pin-on-disc and pin-on-plate models and simulators highlighted ball-on-joint set ups. Tribometer motions included linear reciprocating (62%) or multidirectional reciprocating (24%). Input parameters included contact stress (8.8 kPa to 23.3 MPa, mean 2.1 MPa), velocity (0.5-100 mm/s, mean 16.46 mm/s), testing duration (0.03-33.8 h, mean 5.4 h), and distance (5.4 cm to 9000 m, mean 393 m). Simulators used inputs of loads ranging from 25 N to 1.5 kN, 500 to 500,000 cycles and a variety of flexion-extension profiles together with secondary motions. Lubricants were mostly bovine calf serum (38%) and saline-based solutions (21%). Outcome variables mainly included coefficient of friction and damage to cartilage and/or HBM, but the methods to assess these outputs varied. Methodological differences and inconsistent reporting of outcomes limited the ability to draw firm conclusions about the relative performance of HBMs.