What does overhang mean after a total knee replacement surgery?

After a total knee replacement (arthroplasty) surgery, overhang refers to the situation where one of the components (typically the bone or the prosthetic implant) extends further than the other, resulting in a misalignment or unequal distribution of weight-bearing forces.

There are two types of overhang: anterior overhang and posterior overhang.

- Anterior overhang: This occurs when the front part of the tibial component (the part of the prosthesis that replaces the shinbone) extends further than the front part of the femoral component (the part that replaces the thighbone). This can lead to increased pressure on the patellofemoral joint (between the kneecap and the thighbone) and pain.

- Posterior overhang: This occurs when the back part of the tibial component extends further than the back part of the femoral component. This can lead to instability of the knee and increased risk of dislocation.

Overhang can be caused by several factors, including:

- Incorrect sizing or positioning of the implants: If the implants are too large or too small, or if they are not properly positioned, it can lead to overhang.

- Bone loss or damage: If there is bone loss or damage around the knee joint, it can make it difficult to properly position the implants and prevent overhang.

- Soft tissue contractures: If the soft tissues around the knee joint are tight or contracted, it can pull the implants out of position and cause overhang.

- Ligamentous laxity: If the ligaments around the knee joint are loose or damaged, it can allow the implants to shift and cause overhang.

Overhang can be a problem because it can lead to pain, instability, and early wear and tear of the knee joint. If you are experiencing symptoms of overhang after knee replacement surgery, it is important to see your doctor for an evaluation. Treatment may involve surgical revision to correct the problem.