Clicking

There a number of possible causes for clicking and clunking after a total hip replacement. In the first few weeks most patients will experience some odd symptoms around the hip. Once the soft tissues have healed, say after 6-10 weeks, most of these symptoms should have settled.

Persisting clicking can be subdivided as extrinsic (arising from the surrounding tendons and muscles) and intrinsic (problems with the artificial articulating surfaces).

Extrinsic Clicking

The hip joint is a ball and socket joint and this allows a wide range of movements, both angulation and axial rotation. During these movements the muscles and tendons slide over the proximal femur. Problems with the smooth sliding of these muscle and tendons can cause pain or snapping in a normal hip (see Snapping Hip).

After a total hip replacement this type of problem is much more likely and this is the commonest cause of clicking in artificial joints. In these cases the click or clunk is usually reproducible under specific loads and with specific movements.

	Where the hip is most superficial tends to coincide with the scar tissue in the fascia, this is a common cause of clicking. The most likely way to reproduce this symptom is to rotate the leg in adduction - pressing the fascia onto the trochanter. This may occur when rising from a seated position, or getting in and out of a car.
Post operative trochanteric snapping
	When the clicking is felt with the leg in extension it is possible that the iliopsoas tendon is catching on the front of the total hip replacement. This may be on the head, the neck, the rim of the cup or on an exposed bone edge. In the normal hip this tendon uses the femoral neck as a pulley, after hip replacement pressure on this part of the total hip may cause symptoms. Once the tendon is inflamed it may cause pain when the muscle is contracted, such as when the hip is flexed.
Post operative iliopsoas snapping

Intrinsic Clicking

The articulating surfaces of a total hip replacement should move smoothly over each other, without noticeable noise. In the first few months after a total hip replacement the joint capsule, muscles and tendons may not control this movement and there are commonly some clicks and pops! There should not be significant pain associated with this cause of clicking. After full healing of the soft tissues the clicking should subside and there should not be any noise within a normal range of motion.

	At the extremes of the permissible range of motion there may be contact between the neck of the stem and the rim of the cup (impingement) - causing a click. This type of clicking is reproducible with the leg a a specific position. If this click is infrequent and painless it can be ignored.
Hip Impingement

Another cause of intermittent clicking is separation of the joint surfaces, and their subsequent reunion. Micro-separation is known to occur when the leg is dangling and swinging through during gait. As the joint surfaces re-engage there is often a vibration; a squeak or a click. This is much more prominent in hip replacements with hard bearing surfaces ("metal on metal", "ceramic on ceramic") and rarely noted in hips with polyethylene bearings.

	Macro-separation or "partial dislocation" (also called subluxation) it is difficult to diagnose. The hip may be very lax allowing the head to droop out of the cup, only to snap back on weight bearing. More commonly this type of click arises due to a combination of impingement and laxity. As the neck of the stem contacts the rim of the cup the head is lifted out of the cup and then snaps back.
Hip Subluxation

Separation and re-engagement of the joint surfaces may cause localised wear a total hip replacement. Depending upon the materials used for these surfaces this can go on to cause problems. Polyethylene debris is known to cause local inflammation, which may be painful. In the longer term these particles are implicated in the process of loosening of the implant fixation.

	Ceramic components are vulnerable to chipping after impingement and this may lead to the formation of loose flakes of ceramic in the joint. A few small fragments may cause intermittent problems, sand in the hip will cause constant grinding. A CT scan may be required to identify small marginal chips.
Ceramic liner chipping

Metal on metal hip replacements may also suffer from clicking and squeaking caused by any of the mechanisms noted above. The articulating metal surfaces do not shed visible fragments but instead microscopic particles. Dissolution of these particles may cause local tissue toxicity - see measuring metal ions. All patients with squeaking metal on metal joints should have regular blood tests for metal ions.

If there is a constant clicking or grinding arising from the hip joint this suggests a significant problem at the bearing surface. A referral for investigation is recommended.