Locating the true flexion-extension axis of the knee can play an important role in component placement in a total knee arthroplasty, especially using contemporary computer-assisted surgical navigation. We determined if the commonly used transepicondylar axis is an accurate and reproducible substitute for the flexion-extension axis. Twenty-three fresh-frozen cadaveric distal femurs with intact soft tissue were imaged with computed tomography and reconstructed in three-dimensional virtual space. The transepicondylar axis was compared with a line equidistant from the articular surface of each femoral condyle. Measures were performed by three observers three times for each specimen. Interobserver and intraobserver variations were small, but the differences between axes were approximately 5 degrees. The difference between axes decreased when projected from three-dimensional space to traditional two-dimensional planes (coronal and transverse), explaining why this discrepancy has not been previously documented. The greater difference in three-dimensional space may account for midrange instability reported in total knee arthroplasty. The increased accuracy afforded by computer-assisted surgical navigation in total knee arthroplasty may be lost and increased malposition of components may occur if this discrepancy between reference axes is not appreciated and addressed.

Patients with lumbar fusion are at increased risk for post-operative dislocations requiring revision. Together, lower pelvic incidence and decreased sacral slope are associated with increased risk of dislocation in these patients.

Objective-The purpose of this study was to explore the relationship between patients' selfreported and performance-based function after total hip arthroplasty (THA).Design-Twenty-three patients (age 61.4 ± 8.3 years) undergoing primary THA for hip osteoarthritis participated. Self-reported function and recovery was measured using The Hip Dysfunction and Osteoarthritis Outcome Score (HOOS) ADL and Pain subscales. Performancebased functional measures included Timed Up and Go Test (TUG), Stair Climbing Test (SCT), and the 6 Minute Walk Test (6MW). Outcome measures were assessed pre-and post-operatively at one and six months.Results-One month after THA, performance-based function declined compared to baseline as follows: TUG: −22.1 ± 25.4%; SCT: −58.5 ± 63.6%; and 6MWT: −22.6 ± 31.7%. In contrast, self-reported function on the HOOS ADL significantly improved one month after THA compared to baseline: 40.8 ± 33.3%. One to six months after THA, there were significant improvements in TUG, SCT and 6MWT which paralleled improvements on the HOOS subscales, although changes were not significantly correlated. Conclusion-The disparity between changes in HOOS scores and functional performance postoperatively suggests that patients may overestimate their functional capacity early after THA, likely in response to pain improvements over the same time period. Therefore, outcomes assessment after THA should include both self-report and performance-based functional measures.