1305 - Botulinum toxin injections improved dystonic knee flexion range of motion limitations following total knee arthroplasty

Case Diagnosis: Hamstring spastic dystonia following total knee arthroplasty

Case Description: A 69-year-old male with post-operative range of motion (ROM) limitations presented to clinic three months after a left total knee arthroplasty (TKA). Preoperative maximum knee extension ROM (15-95°; normal full extension 0°, full flexion 135°) was limited by remote femur fracture and advanced left knee osteoarthritis. He ambulated with a cane. Initial post-operative ROM marginally worsened (20-90°). On evaluation, he demonstrated asymmetric gait with slow cadence and a persistently flexed knee during stance phase. His ROM had further worsened (40-83⁰) with a Modified Ashworth Score (MAS) of 3 in his knee flexors and palpably taut medial hamstring tendons. The semitendinosus and semimembranosus were each injected with 150 units onabotulinum toxin A. He continued physical therapy weekly and wore an extension brace nightly. Within one month, ROM improved to 7-115° with a MAS of 1. Gait cadence was normal, and he ambulated without an assistive device.

Discussions: Post-operative ROM limitations commonly arise from arthrofibrosis or stiffness of the knee after TKA, manifesting as knee flexion contracture, or the inability to fully extend the knee, leading to poor functional and pain-related outcomes. Alternatively, some cases of ROM limitations can arise from increased muscle tone. Our patient’s ROM decreased despite conventional physical therapy and bracing, prompting consideration of muscle tonic imbalance.

Conclusions: Botulinum toxin use in post-operative knee flexor spastic dystonia after TKA improved mobility, range of motion, and gait. There is little but growing evidence that botulinum toxin effectively treats knee flexion spastic dystonia after TKA and has positive outcomes that last up to one year. Larger studies are warranted to demonstrate its clinical significance and cost-effectiveness in patients who remain functionally impaired despite physical therapy and bracing.