Total knee arthroplasty in a case of diffuse idiopathic skeletal hyperostosis; challenges in ligament balancing and deformity correction.

Diffuse skeletal idiopathic hyperostosis is a non-inflammatory systemic skeletal condition in which there is ossification of ligaments, tendons, and joint capsule. Although the radiological changes and clinical manifestation of diffuse idiopathic skeletal hyperostosis (DISH) in the spine have been well defined in the literature, the changes in the knee and their implications on knee replacement are unclear.A 60 year -year-old patient presented with pain, stiffness, and decreased arc of movement at the right knee. The X-rays showed ossification of the joint capsule, ligaments, and quadriceps expansion. The spine had has calcification of the anterior longitudinal ligament and '"wax drop' drop" enthesophytes. Based on the complete skeletal survey, a diagnosis of DISH was made. During knee arthroplasty, it was difficult to correct the deformity with a measured resection technique. Additional resection of 4 mm was done both from the distal femur and proximal tibia to correct the deformity and achieve optimal kinematics. This unpliable nature of the soft tissues due to enthesitis ossification of periarticular tissues led to decrease flexion postoperatively.Surgeons should keep the diagnosis of DISH in mind when dealing with a stiff knee and be prepared for additional bone resection with extensive soft tissue release to balance the prosthetic knee joint.