Timothy J. Levison

Functional pelvic orientation measured from lateral standing and sitting radiographs.

We prospectively obtained preoperative and 3-month postoperative lateral pelvic radiographs in the standing and sitting positions from 84 patients who underwent total hip arthroplasty. We measured pelvic orientation (flexion extension) using the anterior pelvic plane as defined by the anterior superior iliac spines and pubic tubercles as references. There was a trend towards upright pelvic alignment when standing, with a mean anterior pelvic plane angle of 1.2° (range, −22°-+27°). In the sitting position the pelvis tended to extend posteriorly, with a mean anterior pelvic plane angle of −36.2° (range, −64°-+4°). There was a wide variation in the arc of pelvic flexion extension as patients moved from standing to sitting, with arc of pelvic motion in some patients as mobile as 70° and in others as stiff as 5°. There was no significant variation between males and females or between preoperative and postoperative pelvic flexion extension. There were substantial variations in pelvic orientation when comparing standing and sitting for an individual patient and between different patients. This variation can be unpredictable, and may influence implant alignment and stability after total hip arthroplasty.Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

A Balance Exercise Program Appears to Improve Function for Patients With Total Knee Arthroplasty: A Randomized Clinical Trial

Background Patients with total knee arthroplasty (TKA) have impaired balance and movement control. Exercise interventions have not targeted these impairments in this population. Objectives The purposes of this study were: (1) to determine the feasibility of applying a balance exercise program in patients with TKA, (2) to investigate whether a functional training (FT) program supplemented with a balance exercise program (FT+B program) could improve physical function compared with an FT program alone in a small group of individuals with TKA, and (3) to test the methods and calculate sample size for a future randomized trial with a larger study sample. Design This study was a double-blind, pilot randomized clinical trial. Setting The study was conducted in the clinical laboratory of an academic center. Participants The participants were 43 individuals (30 female, 13 male; mean age=68 years, SD=8) who underwent TKA 2 to 6 months prior to the study. Interventions The interventions were 6 weeks (12 sessions) of a supervised FT or FT+B program, followed by a 4-month home exercise program. Measurements Feasibility measures included pain, stiffness, adherence, and attrition. The primary outcome measure was a battery of physical performance tests: self-selected gait speed, chair rise test, and single-leg stance time. Secondary outcome measures were the Western Ontario and McMaster Universities Osteoarthritis Index and the Lower Extremity Functional Scale. Results Feasibility of the balance training in people with TKA was supported by high exercise adherence, a relatively low dropout rate, and no adverse events. Both groups demonstrated clinically important improvements in lower-extremity functional status. The degree of improvement seemed higher for gait speed, single-leg stance time, and stiffness in the FT+B group compared with the FT group. Limitations Due to the pilot nature of the study, differences between groups did not have adequate power to show statistical significance. Conclusions There is a need for conducting a larger randomized controlled trial to test the effectiveness of an FT+B program after TKA.

Contribution of Hip Abductor Strength to Physical Function in Patients With Total Knee Arthroplasty

Background Investigating modifiable factors that contribute to functional limitations in patients with total knee arthroplasty (TKA) may guide changes in rehabilitation protocols and improve functional outcomes. Whereas quadriceps muscle weakness has been demonstrated to contribute to functional limitations in TKA, the role of hip abductor weakness has not received attention. Objective The purpose of this study was to determine whether hip abductor strength (force-generating capacity) contributes to physical function beyond what can be explained by quadriceps muscle strength in patients after a TKA. Design A cross-sectional design was used in the study. Setting The study was conducted in a clinical laboratory at an academic center. Patients Thirty-one people with TKA (74% female; mean age=68 years, SD=8; mean body mass index=31 kg/m2, SD=5) participated in the study. Measurements Strength of quadriceps muscles and hip abductors was measured using an isokinetic dynamometer. Performance-based physical function was assessed with 4 measures: self-selected walking speed, the Figure-of-8 Walk Test, the Stair Ascend/Descend Test, and the 5-Chair Rise Test. Self-reported physical function was assessed with the Western Ontario and McMaster Universities Osteoarthritis Index Physical Function Subscale. Results In hierarchical regression models, after accounting for demographic and anthropometric factors, quadriceps muscle strength was associated with performance on the Stair Ascend/Descend Test. After accounting for demographic, anthropometric, and quadriceps strength, hip abductor strength was associated with performance on the Stair Ascend/Descend Test, the Figure-of-8 Walk Test, and the 5-Chair Rise Test. Limitations The study design precluded ascertainment of causal relationships. Conclusions After TKA, hip abductor strength influenced physical function in participants more than did demographic or anthropometric measures or quadriceps strength. Longitudinal studies with larger samples are warranted. If findings are replicated, they will justify targeting the hip abductors during rehabilitation after TKA.

Description of Anatomic Coordinate Systems and Rationale for Use in an Image-Guided Total Hip Replacement System

Lowering the risks of a surgical procedure is extremely important, especially for high-volume procedures such as total hip replacement. Significant work has been done to study total hip replacement procedures and provide the surgeon with techniques and tools to achieve better patient outcomes. Computer-assisted intervention allows surgeons to “close the loop” in medical research, allowing the surgeon to preoperatively plan, interoperatively navigate, and postoperatively analyze medical procedures, then use the results to repeat or improve the quality of future procedures. In order to expedite the cycle of planning, execution, and analysis amoung multiple research groups, standards for description, measurement, and procedure are necessary. In this work, the authors preset the coordinate systems used in their suite of computer-based tools for planning, executing, and evaluating the total hip replacement procedure. Rationales for the choices of each system are given along with experimental data which support the definitions.

Surgical Navigation for THR: A Report on Clinical Trial Utilizing HipNav

Computer-assisted Total Hip Replacement (THR) surgery using the HipNav surgical navigational system was evaluated. This summary reports on the first 100 HipNav clinical trial patients and focuses on: 1) patient demographics, 2) post-operative clinical outcomes, 3) incision length measurements, 4) mechanical guide measures, and 5) functional pelvic tilt measurements. Results from this clinical trial have shown no system-related complications, an improvement in post-operative clinical outcomes, reductions in soft tissue dissection, an unreliability of traditional mechanical alignment guides, and a variability of pelvic orientation during functional activity.

CupAlign: Computer-Assisted Postoperative Radiographic Measurement of Acetabular Components Following Total Hip Arthroplasty

Clinical problems following total hip replacement surgery, such as dislocation and implant wear, remain as significant clinical problems with many contributing factors. Although it is intuitive to surgeons that acetabular component alignment is one important factor, large clinical series have produced conflicting results with respect to cup alignment as a risk factor in predisposing to dislocation. One reason is that postoperative measurements of alignment are limited to single or biplanar radiographic measurements. However, the radiographic measurements are limited only to radiographic alignment and may not accurately detail true anatomic orientation of the cup. In this paper, software designed to accurately measure radiographic alignment is described. Postoperative measurements using this system are compared to the actual intraoperative measurements of cup orientation determined by the HipNavTM image-guided surgical system to assess the accuracy of radiographic evaluation of cup orientation.

Dose-Associated Changes in Gait Parameters in Response to Exercise Programs after Total Knee Arthroplasty: Secondary Analysis of Two Randomized Studies

Background Rehabilitation plays an important role to improve the outcomes of total knee arthroplasty (TKA). Evidence about the appropriate dose of exercise to recover gait dysfunction after TKA is limited. We posed the research question: In patients during the post-acute stage after TKA, is increased dose of exercise associated with larger improvements in gait parameters such as step length and single support time? Methods This was a secondary analysis from two randomized studies on exercise after TKA to investigate dose-dependence of gait parameters in response to exercise. Participants were 50 years or older who underwent unilateral TKA at least two months prior. They participated in 2 months of supervised exercises followed by 4 months of a home exercise program. The primary outcome was change in gait parameters from baseline to 6 months. Participants were divided in three groups according to the dose of exercise: group 1 (light-to-moderate intensity exercise), group 2 (high intensity + functional exercise), and group 3 (high intensity + functional + balance exercise). Jonckheere-Terpstra test was used to test if the magnitude of changes in gait parameters increased from group 1 to group 3 in an ordered fashion. Results Increased dose of exercise was associated with progressive increases in step length in the operated-limb (p=0.008) and decreases in step length in the non-operated limb (p=0.011). Increased dose of exercise was associated with ordinal decreases in loading response time (p=0.049) and increases in single-leg support time (p=0.021) on the operated- limb, but not on the non-operated-limb. Increased dose of exercise was associated with decreases in unloading time on the non-operated-limb (p=0.011) but not on the operated-limb (p=0.400). Conclusions Significant dose-response of exercise on gait parameters support the promotion of more intensive exercise programs that combine functional and balance training programs after TKA.