Over 50 million adults in the United States report doctor-diagnosed osteoarthritis (OA), which includes almost 50% of all people over the age of 65. There are no current treatments to stop the progression of OA; therefore, joint replacement is generally considered the final step to improve function and reduce pain in weight bearing joints. Increased varus-valgus laxity has been reported in participants with knee OA compared to controls, while passive stability is a major concern for orthopaedic surgeons during total knee arthroplasty (TKA). The purpose of this dissertation is to better understand the role of passive varus-valgus laxity on biomechanical, clinical and self-reported function in individuals with severe OA and following TKA.
Chapter 1 provides background information on tibiofemoral OA and TKA, while outlining the impact of knee stability on disease progression and outcomes. Chapter 2 is a systematic review of the literature containing varus-valgus laxity measurements in patients with OA. This research unearthed consistent findings indicating increased varusvalgus laxity is a characteristic of knee joints with OA. Large variances exist in reported varus-valgus laxity and may be due to differences in measurement devices. The remaining chapters include experimental data collected before, during, and after TKA from study volunteers. Chapter 3 assessed passive varus-valgus laxity in 30 osteoarthritic knees and found greater laxity was significantly associated with more varus-valgus excursion during gait (R²=0.34, p=0.002). However, no relationship was observed between passive varus-valgus laxity and knee flexion strength, perceived instability, or any Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales. Chapter 4 investigated the relationship between passive varus-valgus laxity and active stability of the knee joint provided by muscle activation and co-contraction. This analysis utilized data from 22 knees and found no relationship between active stability measures and passive laxity. There was also no association between active stability measures and varus-valgus excursion during gait, knee strength, and perceived instability. Chapter 5 quantified varus-valgus laxity intra-operatively and identified relationships to biomechanical and surgical outcomes. Thirty three knees were included in this analysis and laxity of the replaced joint was significantly associated with knee strength (extension p=0.027; flexion p=0.024) and KOOS quality of life (p=0.046). However, knee laxity was unrelated to a majority of the biomechanical, clinical performance and self-reported outcome measures. Relationships were also found between the change in varus-valgus laxity and the overall varus-valgus laxity in the osteoarthritic and replaced knee joint.
The main purpose of this research was to identify the contribution of soft-tissue knee stabilizers to biomechanical, clinical, and self-reported function in participants with severe OA and after TKA. Identifying the impact of passive and active knee stability on function may allow for improved surgical techniques and altered treatment and rehabilitation strategies for patients. The information presented in this dissertation improves the basic understanding regarding the influence of passive varus-valgus laxity on function. This work will help in achieving the long-term goal of improving patient function and reducing the costs and disability associated with knee OA and TKA.