Terminology explained

A

Acetabular cup: the part of the implant that is placed where the acetabulum was. The liner sits inside it, and the prosthetic head turns against that liner.

Acetabulum: the cup-shaped hollow in the pelvic bone that the head of the femur sits in. This is where the implant cup goes.

Avascular necrosis: a condition in which part of the femoral head stops receiving blood and the bone tissue dies. At a late stage the head collapses and loses its round shape. See avascular necrosis.

B

Bearing surface: the two surfaces of the implant that slide against each other, the head and the liner. The materials they are made of determine how fast they wear.

Bikini incision: the incision used in the anterior approach, following the natural crease of the groin. It is usually five to six centimetres long. See the bikini incision.

Body mass index: a figure that relates weight to height. Above 30 it is a factor to take into account when planning surgery. See excess weight and the joint.

Bursa: a small fluid-filled cushion between a tendon and a bone that reduces friction. Inflammation of a bursa is bursitis.

C

Calibration marker: a small ball or plate of known size that shows up on the X-ray and lets the scale of the image be worked out. See digital planning.

Cartilage: the smooth, elastic tissue covering the surfaces of a joint, which lets them move without friction. Cartilage that has been lost does not grow back on its own.

Cemented fixation: fixing the implant with a special bone cement, which holds firmly straight away.

Cementless fixation: fixing the implant so that the bone itself grows into its porous surface. See cemented and cementless fixation.

Ceramic: a very hard, very smooth material used for the prosthetic head and sometimes for the liner. See what an implant is made of.

Conservative treatment: treatment without surgery: exercise, weight control, medication, injections. The result is judged after about five months on average. See conservative treatment.

Core decompression: an operation used at an early stage of avascular necrosis that lowers the pressure inside the femoral head and aims to preserve the bone.

Corticosteroid injection: an anti-inflammatory medicine injected into the joint. At least three months must pass between such an injection and hip replacement.

D

Deep vein thrombosis: a blood clot forming in a deep vein of the leg. After surgery the risk is reduced by getting up early and by the prevention your doctor prescribes.

Digital planning (templating): choosing the size and position of the implant on the X-ray, on a computer, before the operation. See digital planning.

Direct anterior approach: the approach to hip replacement from the front of the thigh, in which muscles are not cut but moved aside. See the anterior approach.

Dislocation: a condition in which the prosthetic head comes out of the cup. It happens most often in the first weeks, before the tissue around the joint has healed.

Drain: a thin tube that carries blood and fluid out of the wound after surgery. See why I operate without a drain.

F

Femoral head: the upper, ball-shaped part of the thigh bone, which turns inside the acetabulum.

Femoral neck: the narrow part of the thigh bone that connects the head to the rest of the bone.

Femoral stem: the part of the implant that sits inside the thigh bone and anchors the construction.

Fixation: the way the implant is held to the bone: with cement, without cement, or a combination of the two.

G

Gait: the individual way a person walks. It changes with arthritis of the hip, and a limp appears.

Greater trochanter: the bony prominence on the outer side of the thigh bone that can be felt under the skin. It is not part of the joint: the tendons of the buttock muscles attach to it. See pain on the outer side of the thigh.

H

Hip dysplasia: a condition in which the acetabulum is too shallow and does not fully cover the femoral head. It is a common reason for arthritis developing early. See hip dysplasia.

Hip joint: the joint between the pelvis and the thigh bone, deep behind the groin. The femoral head turns inside the acetabulum. See groin pain.

Hip osteoarthritis (coxarthrosis): osteoarthritis of the hip joint. See the first signs of hip arthritis.

Hip prosthesis (implant): the artificial joint that replaces the damaged surfaces of the joint. It is made up of a cup, a liner, a head and a stem. See what a hip implant is.

Hyaluronic acid: a substance that occurs naturally in joint fluid and can be injected into the joint. The effect lasts seven to eight months on average, depending on the stage of the joint. See injection therapy.

I

Ilium: the upper, wing-shaped bone of the pelvis. What people usually point at as the “hip bone” on the outer side is in fact the greater trochanter, which belongs to the thigh bone.

Implant: an artificial part placed inside the body. In the case of the hip, the hip prosthesis.

Inflammatory arthritis: inflammation of a joint driven by the immune system, rheumatoid arthritis for example. Morning stiffness usually lasts longer than thirty minutes. See arthritis or osteoarthritis.

J

Joint capsule: the dense envelope that surrounds the joint and gives it stability.

Joint registry: a database in which every hip replacement and every revision in a country is recorded. It is the most reliable source on how long implants last. See how long a hip implant lasts.

Joint space: the gap left between two bones on an X-ray, which corresponds to the thickness of the cartilage. In a healthy hip it is three to five millimetres. See the stages of arthritis on an X-ray.

L

Labrum: the ring of cartilage on the rim of the acetabulum that deepens the socket and adds stability.

Lateral approach: the approach to hip replacement from the side of the thigh. It is the most widely used approach in Georgia. The incision is usually nine to ten centimetres. See anterior, posterior and lateral approach.

Learning curve: the number of operations after which a surgeon’s results with a new method become stable. For the anterior approach it is roughly one hundred cases.

Liner: the part of the implant inside the cup that forms the sliding surface the head turns against.

O

Offset: the distance between the midline of the pelvis and the thigh bone. It governs the tension of the muscles on the outer side and the way a person walks.

Osteophyte: a bony outgrowth at the edge of the joint, one of the signs of arthritis on an X-ray.

Osteoporosis: a loss of bone density that makes bone more fragile. It affects the choice of fixation.

P

Placebo: a dummy treatment with no active substance, used for comparison in research.

Polyethylene: a specially processed, high-density material from which the liner of the implant is most often made.

Posterior approach: the approach to hip replacement from the back of the thigh. It is widely used around the world.

PRP (platelet-rich plasma): plasma rich in platelets, prepared from the patient’s own blood and injected into the joint. Over the short term its results are roughly equal to those of hyaluronic acid. See injection therapy.

Pulmonary embolism: a condition in which a clot formed in a vein of the leg breaks loose and travels to the lung. It is rare but dangerous.

R

Referred pain: pain felt away from where it comes from. Pain from the hip joint is often felt in the knee. See knee pain coming from the hip.

Revision surgery: a repeat operation in which part of the implant, or the whole implant, is replaced.

S

Sacroiliac joint: the joint between the sacrum and the ilium, in the lower back. Pain from it is sometimes mistaken for hip pain.

Spinal anaesthesia: anaesthesia in which a medicine given in the lower back numbs the lower half of the body while you stay awake. It lasts two and a half to four hours. See anaesthesia for hip replacement.

Stiffness: difficulty moving the joint, especially in the morning or after sitting for a long time. With osteoarthritis it usually eases within thirty minutes.

Surgical approach: the route by which the surgeon reaches the joint: anterior, posterior or lateral. See the anterior approach.

Surgical helmet system: a ventilated helmet with a sterile hood that adds a barrier between the surgical team and the open wound. See the surgical helmet.

T

Tendon: the dense tissue that attaches a muscle to a bone.

Total hip replacement: the operation in which the damaged joint is replaced with a hip prosthesis.

Examinations

X-ray: the examination that shows bone and the joint space. It is the first examination in diagnosing arthritis of the hip.

MRI (magnetic resonance imaging): an examination using a magnetic field, which shows soft tissue and bone marrow. The early stage of avascular necrosis shows up on it.

CT (computed tomography): an examination that shows the three-dimensional shape of the bone. It is used when the anatomy is complex.

Ultrasound: an examination using sound waves. For the hip it is a supporting method: it shows fluid, the bursa and tendons close to the surface, but not bone or cartilage. It is also often used to guide an injection, because the joint lies deep and cannot be felt by hand.

See X-ray or MRI.