Extension gap is the space and soft-tissue “tension window” in the knee when the knee is fully straight (in extension). It is most commonly discussed during total knee replacement (total knee arthroplasty, TKA) and complex knee reconstruction. Clinicians use it to describe how the femur and tibia relate after bone preparation and soft-tissue balancing. In plain terms, it helps the surgical team judge whether the straightened knee will feel stable, smooth, and appropriately tight.

Flexion gap is the space between the thigh bone (femur) and shin bone (tibia) when the knee is bent. It is most commonly discussed during total knee replacement and other knee reconstructive procedures. Clinicians use it to describe how “open” or “tight” the knee feels in bending and how stable it is. In simple terms, it helps surgeons match knee motion with knee stability.

Gap symmetry is a way of describing how evenly the knee “opens” on the inside and outside when it is straight and when it is bent. It is most commonly discussed during knee replacement surgery planning and technique. Clinicians use it to describe balance between the ligaments and the joint surfaces. In simple terms, it aims for a stable knee that does not feel too tight on one side or too loose on the other.

Soft tissue balancing is the process of adjusting the tension of ligaments and other soft tissues around a joint so the joint moves smoothly and remains stable. In the knee, it commonly refers to balancing the tissues during knee surgery, especially total knee replacement. It can also describe non-surgical efforts to reduce uneven forces around the knee through rehabilitation strategies. The overall goal is a knee that tracks, bends, and straightens in a controlled and comfortable way.

Ligament balancing is the process of adjusting soft-tissue tension around a joint so the joint moves smoothly and feels stable. In the knee, it usually refers to balancing the collateral ligaments and surrounding capsule so the femur and tibia track correctly. It is most commonly discussed during knee replacement surgery, but the concept also applies to other knee procedures and rehabilitation planning. The goal is not “tight” or “loose,” but an appropriate, even tension that matches the person’s anatomy and the procedure being done.

Joint line restoration means re-establishing the knee’s normal “joint line” height and position. The joint line is the level where the femur (thigh bone) and tibia (shin bone) meet and move against each other. Joint line restoration is most commonly discussed in complex knee surgery, especially revision total knee replacement. It is used to improve knee mechanics when the original joint line has shifted due to arthritis, injury, or prior surgery.

Component malrotation is an unintended rotational misalignment of an implanted knee replacement part. It most commonly refers to femoral or tibial component rotation after total knee arthroplasty (knee replacement). It can affect how the kneecap tracks and how the knee feels during walking, stairs, or bending. Clinicians use the term when evaluating pain, stiffness, instability, or patellar symptoms after surgery.

Tibial rotation is the turning of the shin bone (tibia) relative to the thigh bone (femur) at the knee. It includes internal rotation (turning inward) and external rotation (turning outward). It is a normal part of walking, squatting, and changing direction. Clinicians use the term to describe knee motion, knee stability, and alignment in injuries and arthritis.

Femoral rotation describes how the thigh bone (femur) turns inward or outward around its long axis. It can refer to a normal movement during walking, squatting, or pivoting, or to a measurable alignment pattern. Clinicians use it to discuss hip-to-knee mechanics, patellar (kneecap) tracking, and overall lower-limb alignment. It is commonly referenced in orthopedics, sports medicine, and physical therapy when evaluating knee and hip symptoms.

Posterior tibial slope is the backward tilt of the top surface of the tibia (shinbone) where it meets the femur (thighbone). It is a measurable alignment feature of the knee, not a diagnosis by itself. Clinicians most often discuss it when reading knee imaging or planning ligament and knee replacement surgeries. In plain terms, it describes how “angled” the upper tibia is from front to back.