Introduction: The cement mantle is a critical factor in the longevity of cemented total hip arthroplasty (THA). Concern has been raised about the reliability of plain radiographs for its assessment. A new high-definition, three-dimensional (3-D), in vitro method of cement mantle evaluation has been developed.

Aim: To compare cement mantle quality in six contemporary stem designs.

Methods: Exact resin replicas of six contemporary stem designs were implanted into cadaver femora using third generation techniques. The specimens were imaged with a high-speed, helical, computerised, tomographic scanner. Computer-assisted, 3-D analysis of the cement mantle thickness was made. Comparisons were made between different stem designs and also with plain film assessments of the mantles.

Results: Standard radiographs overestimated mantle thickness (p< 0.05) and underestimated the deficiencies. The percentage area of cement mantle that was thinner than 2mm ranged from 9% to 28%. Slight malrotation or malalignment of the stem with respect to the broach envelope produced deficient mantles. Characteristic patterns of deficiencies were seen for different stem designs.

Conclusions: Plain x-rays overestimated the cement thickness, frequently missed areas of substandard cement, and should, therefore, be interpreted cautiously. The cement mantle varies widely depending on the stem design and surgical technique, and commonly used designs have significant deficiencies in their mantles by standard criteria despite proper surgical technique. Surgeons should be familiar with the stem that they use and its instrumentation to maximise outcomes. This is a valuable technique for the study of the cement mantle as it relates to implant design, surgical technique and patient anatomy.

Introduction: Range of motion is an invariable outcome -measure in studies on total knee arthroplasty (TKA) and other knee surgery. Concluding that a certain change in motion equals a corresponding change in outcome may be invalid if true accuracy of current measuring techniques is unknown. This is integral to many studies. Surprisingly little has been done to validate these techniques.

Methods: Maximum extension and flexion were measured in 32 TKAs by four independent observers using three common techniques: visual estimate (VE), pocket and universal goniometers (PG and UG). Lateral radiographs in reproducible positions were measured using computer analysis, providing a gold standard for comparison with clinical measurements. The correlation coefficients and coefficients of reliability were calculated.

Results: There were no significant differences between observers using any method. Significant differences were found between each technique and radiographic measure (paired t-test, p< 0.001). Correlation coefficients were lower for extension estimates (0.76–0.80) than flexion (0.91–0.96). Coefficients of repeatability varied from 11.6 degrees to 12.1 degrees for extension measurements and from 13.8 degrees to 19.2 degrees for flexion measurements, with UG being the most accurate. The VE accuracy approached that of UG only at easily visualised angles such as 90 degrees. The coefficient of repeatability for radiographic measure was significantly lower at 2.9 degrees.

Conclusions: Clinical measurements of range of motion vary significantly from radiographic measurement, with the computer assisted radiographic measurement providing high reliability as the gold standard. UG is most accurate, followed by PG and VE. However, coefficients of repeatability were surprisingly large, indicating the degree of accuracy of each measurement technique and the necessary magnitude of difference for this to be outside measurement error. This has relevance for all outcome studies and everyday clinical practice.