Perthes lateral pillar classification is a way clinicians describe how much of the femoral head is affected in Legg–Calvé–Perthes disease. It is based on what the hip looks like on an X-ray at a specific stage of the condition. The system groups hips into categories that broadly reflect severity and expected shape during healing. It is commonly used in pediatric orthopedics and in research to communicate prognosis in a standardized way.

Perthes disease is a childhood hip condition where the ball of the hip joint temporarily loses part of its blood supply. This can weaken the top of the thighbone (the femoral head) and change its shape over time. It is most commonly discussed in pediatric orthopedics, sports medicine, radiology, and physical therapy. People often encounter the term when a child develops a limp, hip or groin pain, or reduced hip motion.

Periprosthetic joint pain is pain felt in or around a joint that has an artificial implant. It most often refers to symptoms after hip or knee replacement surgery. Clinicians use the term to describe a problem area, not a single diagnosis. It signals the need to consider implant-related and non-implant-related causes.

Periprosthetic joint infection is an infection involving the tissues around an artificial joint implant. It can occur after joint replacement surgery or later if bacteria reach the implant through the bloodstream. It is most commonly discussed in hip and knee arthroplasty (joint replacement) care. Clinicians use this diagnosis to guide testing, treatment planning, and follow-up.

Periprosthetic fracture Vancouver A is a classification label for a specific kind of fracture near a hip replacement. It refers to fractures around the *trochanteric region* of the femur (the bony prominences near the top of the thigh bone). It is most commonly used after total hip arthroplasty (hip replacement) to describe where the break is and what structures may be involved. Clinicians use it as part of the Vancouver classification system to help communicate findings and plan care.

Periprosthetic fracture means a bone fracture that happens around an orthopedic implant. It is most commonly discussed after joint replacement surgery, such as a hip or knee replacement. It can occur during surgery or at any time afterward. Clinicians use the term to guide evaluation and treatment planning.

Periprosthetic acetabular fracture means a break in the hip socket bone around a hip replacement cup. It can happen during hip replacement surgery or after surgery, sometimes after a fall or with weaker bone. Clinicians use this term when evaluating hip pain, loss of function, or implant instability in a replaced hip. It is commonly discussed in total hip arthroplasty (THA) follow-up and revision planning.

Periacetabular osteotomy is a hip-preserving surgical procedure that reshapes how the hip socket covers the femoral head. It is most commonly used for symptomatic hip dysplasia, where the socket is too shallow or misoriented. The goal is to improve joint mechanics and reduce abnormal load on cartilage and the labrum. It is typically performed by orthopedic surgeons with specialized training in young adult hip conditions.

Pelvic tilt abnormality describes a pelvis position that is tilted more than expected for a person’s posture and movement. It is most often discussed as an *anterior* (forward) or *posterior* (backward) tilt, but side-to-side tilt and rotation also matter. Clinicians use the term when evaluating hip pain, low back pain, posture, gait, and “hip–spine” mechanics. It is a descriptive finding, not a diagnosis by itself.

Pelvic tilt describes how the pelvis is angled in space. It is commonly discussed in posture, gait, low back pain, and hip conditions. Clinicians use it to describe alignment between the pelvis, spine, and legs. It is also used in imaging and surgical planning to interpret pelvic orientation.