Highly cross-linked polyethylene is a durable medical plastic used in joint replacement implants. It is most commonly used as the “liner” or bearing surface in total hip replacement. It is designed to reduce wear compared with earlier forms of polyethylene. It is also used in other joints, such as the knee and shoulder, depending on implant design.

A High offset stem is a femoral implant option used in total hip arthroplasty (hip replacement). “Offset” describes how far the hip’s center of rotation sits from the femur’s shaft. A High offset stem is designed to increase that distance compared with a standard-offset stem. It is commonly selected to help restore hip biomechanics, stability, and muscle tension.

Heterotopic ossification is the formation of bone in soft tissues where bone does not normally belong. It most often develops near large joints such as the hip, after injury, surgery, or neurologic illness. It can limit motion and cause stiffness or pain by “bridging” tissues that should stay flexible. The term is commonly used in orthopedics, sports medicine, trauma care, and rehabilitation medicine.

Herring classification is a radiographic grading system used in pediatric hip care. It describes how much of the outer (lateral) part of the femoral head has lost height during Legg–Calvé–Perthes disease. Clinicians use it to estimate prognosis and to support treatment planning. It is most commonly applied when reviewing plain X-rays of a child’s hip.

Hemarthrosis hip means bleeding into the hip joint space. It is a type of joint effusion, which is extra fluid inside a joint. Clinicians use this term when hip pain and swelling are linked to blood in the joint. It most often comes up in trauma care, postoperative care, and bleeding disorders.

Hemiarthroplasty is a joint replacement surgery where only one side of a joint is replaced. In the hip, it typically replaces the femoral head (the “ball”) while leaving the natural socket in place. It is commonly used after certain hip fractures, especially in older adults. It can also be performed in other joints, but the hip is the most well-known example.

Head-neck offset measurement describes how much the femoral head “steps out” from the femoral neck. It is a way to quantify hip shape that can influence how smoothly the ball-and-socket joint moves. Clinicians most often use it when evaluating femoroacetabular impingement (FAI) and related hip pain. It is commonly performed on hip X-rays and may also be assessed on MRI or CT images.

Head size is the diameter of the “ball” portion of the hip joint, called the femoral head. It can describe a person’s natural anatomy or the size of a prosthetic femoral head used in hip replacement. In orthopedics, Head size is most commonly discussed during total hip arthroplasty (THA) planning and implant selection. It is measured as a simple dimension (usually in millimeters) and used to help match anatomy and joint mechanics.

Hardinge approach is a surgical pathway to reach the hip joint through the side of the hip. It is also called a direct lateral approach or transgluteal approach in many clinical settings. Surgeons use it to perform hip operations such as hip replacement and fracture-related procedures. The approach is defined by how the tissues over the hip are opened and protected to access the joint.

Hamstring stretching refers to techniques used to lengthen the hamstring muscle–tendon unit at the back of the thigh. It is commonly used in sports medicine, physical therapy, and orthopedic rehabilitation. People often associate it with flexibility, comfort during activity, and movement quality. Clinicians may also use it as part of an exam to understand pain patterns and motion limits.