Structural and Sensorimotor Deficits Associated with Abnormal Frontal Plane Motion of the Knee during Gait: The Multicenter Osteoarthritis Study

Abstract

Varus knee thrust is a visible manifestation of excessive frontal plane knee motion (i.e., an abrupt change to varus knee alignment) during the mid‐stance phase of gait. Thrust is a potent mechanical risk factor for knee osteoarthritis (OA) progression and knee pain during weight bearing. Given the association of thrust with knee disease, determining the underlying causes of thrust could facilitate the development of strategies for early detection and prevention. These causes may be related to sensorimotor deterioration and may include impairments in afferent sensory input or efferent muscular strength. Alternatively, knee thrust could result from structural anomalies, such as static knee malalignment or instability (passive laxity) of the knee joint. Our objective was to determine associations between these sensorimotor and structural deficits and the presence of varus knee thrust in older adults that are at risk for knee OA. The Multicenter Osteoarthritis Study (MOST) is a longitudinal prospective cohort study of older Americans that have or are at risk for knee OA. Participants’ gait was recorded (via 60 Hz video) during two self‐paced walking trials on a 4.9 meter walkway. A trained video reader blinded to knee disease status assessed the presence of varus thrust on a majority of steps (κ = 0.73). Static knee alignment measures were obtained using full‐limb radiographs; passive varus knee joint laxity was measured as varus excursion following the application of a fixed load; isokinetic quadriceps strength was measured as the maximal torque produced over four trials; lower extremity vibration perception threshold was measured using a biothesiometer and defined as the voltage at which a subject first sensed vibration; and knee joint position sense was measured as the average error between ten preset and participant‐reproduced knee flexion angles. Using separate logistic regression models, we assessed the cross‐sectional relationship between varus thrust and increasing levels of each structural and sensorimotor exposure, accounting for non‐independence between two knees from the same subject and adjusting for age, sex, body mass index (BMI), and walking velocity. Our sample consisted of 1877 persons (age 66.69 ± 7.51, BMI 29.47 ± 4.75, 62.5% female) contributing 3730 knees. Varus thrust was observed in 31.3% of knees. Static varus alignment (< 179º) was most strongly associated with varus thrust (OR 2.39, 95% CI 1.96, 2.92), while increasing varus knee joint laxity had a surprising protective effect (p for trend = 0.0006). After adjusting for confounders, none of the sensorimotor deficits examined were significantly associated with thrust. These results suggest that varus thrust during walking occurs within the context of static varus knee malalignment and that knee laxity may be correlated with a decreased risk of thrust in at‐risk older adults.Support or Funding InformationThe current study was funded in part by a Rheumatology Research Foundation Health Professional Research Preceptorship Award. MOST is funded by the National Institutes of Health National Institute on Aging (Felson ‐ U01 AG18820, Lewis ‐ U01 AG18947, Torner ‐ U01 AG18832, Nevitt ‐ U01 AG19069). Relative Odds of Varus Knee Thrust with Increasing Exposure to Structural or Sensorimotor Impairments Structural Impairments Static Knee Alignment Mechanical Angle (Degrees) n/N† Adjusted OR‡ (95%CI) 160.0 – 178.9# (Varus) 747/1839 2.39 (1.96, 2.92)# 179.0 – 181.0# (Neutral) 162/768 1.00 (ref) 181.1 – 195.4# 131/720 0.90 (0.70, 1.16) Varus Knee Laxity Varus Excursion (Degrees) n/N† Adjusted OR‡ (95%CI) 0.00 – 1.00# (Least Lax) 432/1168 1.00 (ref) 1.25 – 2.00# 265/905 0.74 (0.61, 0.89)# 2.25 – 3.00# 247/837 0.73 (0.60, 0.90)# 3.25 – 11.00# (Most Lax) 215/781 0.69 (0.56, 0.85)# p for Trend ‐‐‐ 0.0006# Sensorimotor Impairments Isokinetic Quadriceps Strength (Sex‐Specific Quartiles) Maximum Torque (Nm) n/N† Adjusted OR‡ (95%CI) F:84 – 149/M: 145 – 253 (Strongest) 142/474 1.00 (ref) F: 68 – 83/M: 117 – 144 142/477 0.74 (0.52, 1.05) F: 51 – 67/M 91 – 115 197/616 0.78 (0.58, 1.05) F: 7 – 50/M: 9 – 90 86/360 0.87 (0.65, 1.16) p for Trend ‐‐‐ 0.07 Knee Joint Position Sense Average Error (Degrees) n/N† Adjusted OR‡ (95%CI) 0.6 – 2.9# (Least Deficit) 238/817 1.00 (ref) 3.0 – 3.9# 242/780 1.14 (0.87, 1.50) 4.0 – 5.2# 245/749 1.17 (0.89, 1.54) 5.3 – 13.8# (Greatest Deficit) 252/774 1.18 (0.90, 1.52) p for Trend ‐‐‐ 0.25 Vibration Perception Perception Threshold (Volts) n/N† Adjusted OR‡ (95%CI) 2.50 – 13.50 (Least Deficit) 207/805 1.00 (ref) 13.75 – 19.25 244/811 1.12 (0.91, 1.37) 19.50 – 28.75 270/826 1.08 (0.88, 1.33) 29.00 – 51.00 (Greatest Deficit) 330/818 1.17 (0.94, 1.46) p for Trend ‐‐‐ 0.24 number of knees with thrust/Number of knees analyzed Adjusted for age, sex, BMI, and walking velocity Results are Significant at the 0.05 level