Total hip arthroplasty (THA) has enjoyed a long history of excellent implant performance, pain relief, restores mobility and improves quality of life for individuals with degenerative joint disease of the hip [1-3]. Boutin introduced ceramic-on-ceramic bearings as an alternative to the metal-on-polyethylene bearings most commonly used in 1971 [4]. The success of ceramic implants is attributed to the excellent properties of this material [5] associated with superior wear rates and a chemically inert nature which grants it biocompatibility and greater longevity compared with the traditional metal-on-polyethylene bearing surface [6-8]. However, there have been an increasing number of reports on audible noises that seemed linked to these hard bearing surfaces [9-13], leading some to believe the implant material or design was still to blame [5].

In this paper is presented the case of a “click” sound, which occurred in a 73 year old woman 6 years after THA implant.

A 67 year-old woman with a previous history of multiple sclerosis and advanced right hip osteoarthritis was operated in 2006 using a ABG II (Striker), uncemented total hip arthroplasty. The THA consisted in a 48-mm diameter cup and a size 4 stem with a 28-mm diameter femoral head (standard, +0 mm), with a ceramic-on-ceramic counterface. At the age of 73, 6 years after surgery, the patient referred to our Clinic complaining about total hip arthroplasty noise. She described a sort of click, which occurred in her right hip during walking and staring from a chair. This noise was daily and loud enough to create a social problem for the patient. Also, she referred that this sound started few months after the THA implant, but in the last year was worsening.

The clinical evaluation revealed: 110° of flexion, 15° of hyperextension, 10° of internal and 25° external rotation, 20° of adduction, and 45° of abduction. A click sound could be produced with the movement of hyperextension of the right hip. The radiographs showed no signs of loosening, mobilisation, wear or damages of the components. A CT scan and a bone scintygraphy were taken: no sign of bone loss and prosthesis loosening was found. The cup appeared anteverted (Figure 1 and 2).

Figure 1: A CT scan of ABG II ceramic-on-ceramic hip replacements shows that the cup is anteverted.

Figure 2: Pre-op x-rays exam.

The patients were scheduled for hip revision in order to evaluate eventual damages of the implant (such as fractures not detected by the imaging) or impingement of the soft tissues. Intraoperatively, after exposure of the THA, signs of impingement clearly appeared on the posterior part of the neck of the stem (Figure 3) against the posterior edge of the cup. A wide metallosis was also present (Figure 4). The stem and the acetabular component were well fixed and there was no sign of osteolysis. The click sound that was detected preoperatively with hyperextension and internal rotation, was caused by subluxation and relocation of the implant. This pattern with the correlated noise were reproducible intraoperatively. Then, the femoral head and the acetabular component were removed, and a 52 mm cup with a 32 mm head +4 mm were implanted with a spike and a 25 mm screw. The stem wasn’t revised. During the operation a particular attention was given to the orientation of the cup and to the tension of the soft tissues. The aim was to prevent any further joint laxity that might allow separation of the bearing surfaces during normal walking.

Figure 3: Intraoperative photograph shows an indentation in the trunion as a result of impingement.

Figure 4: Intraoperative photograph shows metallosis.

The patient followed a standard clinical protocol and rehabilitation and could walk with crutches after a few days. The click sound disappeared. A clinical and X-rays exam (Figure 5) after 6 months from the implant revision was conducted: no sign of osteolysis was observed. The patient was happy and revealed good range of movement (100° of flexion, no hyperextension, 15° of internal and 30° external rotation, 20° of adduction, and 40° of abduction).

Figure 5: Post-op x-rays exam.

Since the beginning of its use, ceramic materials for THA saw many changes to improve the results: aseptic loosenings decreased and moreover risks of fracture have been dramatically reduced with the use of the third-generation of alumina [14].

However, there have been an increasing number of reports on audible noises that seemed linked to these hard bearing surfaces: those sounds are described such as “grinding”, “crunching” and, above all, “squeaking”. Occurrence of squeaking has been reported as ranging from 0.7% to as high as 20.9% [13,15]. From a patient point of view, squeaking is usually not painful [16]. The intensity of the squeaking however can vary from isolated episodes to a continuous loud noise which follows every movement of the hip and that that becomes intolerable by the patient [16]. It is this last group of patients that usually seeks revision THA.

There have been several theories about the origin of the squeaking that include mismatched bearing surfaces, microseparation and/or subluxation of the femoral head [10], disruption of fluid film lubrication by “stripe wear” [10], wear debris from metal-on-metal impingement [17], edge loading due to acetabular component malpositioning [13], problem of lubrication with the role of a third body [17], impingement between the stem and the cup related to poor design [12,15,18], poor offset [19], vibration of the stem [20], microfractures [14], head size [11] and short neck lengths [15].

It has been hypothesized also that excessive range of motion may increase the probability of squeaking [21] theoretically, improved range of motion due to smaller neck geometry may lead to bony impingement at the extreme range of motion whereby the femur is levering against the pelvis, causing subluxation of the femoral head and edge loading, striping wear and squeaking [19]. A short neck may lead to earlier neck impingement and increased contact area between the neck itself and the acetabular ceramic [22]. Short necks may also lead to soft tissue laxity that can theoretically lead to microseparation and stripe wear [23].

The most commonly discussed surgical factor related to squeaking is cup positioning. A cup with an excessive anteversion angle may cause impingement, while a steep cup angle may increase edge loading and consequent squeaking [13]. However, other studies could not identify a correlation between cup position and squeaking [11,15].

Concerning this case, we faced with an unusual noise similar to a click. We hypothesized that the possible cause of “noising” was the impingement of the neck of the stem against the acetabulum ream or as another possibility some sort of movement between the metal back and the acetabular ceramic liner. According to the literature, a computed tomography scan should was organized to exclude ceramic fractures that may not be evident on plain radiographs. During the revision surgery the first hypothesis have been confirmed. Thus, we believed that correcting the position of the cup could reduce the possibility of the clicking caused from the impingement. Must be remembered that too much anteversion and a steep cup may cause anterior ceramic edge loading, while insufficient anteversion will cause posterior edge loading leading to squeaking with hip extension and flexion [13].

In addition, in this particular case the patient’s neurological diseases may have contributed by altering the muscular control of several movements during the walking.

We believe that a painless, infrequent sound of any kind is likely of little significance, but that if it becomes persistent, frequent, intense, or painful, it may be the harbinger of more serious problems. Whether earlier surgical intervention in patients with audible but otherwise asymptomatic noise is indicated has yet to be determined: the possible future damage and failure of the implant must be considered and may play a fundamental role in the decision making.

Clicking in ceramic-on-ceramic THRs is not a single factor related event but rather it is a multifactorial phenomenon. Although several theories have been suggested, the mechanisms responsible for noise generation in ceramic on ceramic bearing THA has not yet clearly identified.

When a patient presents a strange mysterious noise, major mechanical problems must be excluded. Then the patient should be informed and revision surgery should only be contemplated either if the patient is particularly troubled with the noise and/or if dangers for the survival of the implants are evident.