Delayed Diagnosis of Low-symptomatic Ceramic Acetabular Liner Fracture in Ceramic-on-Ceramic Total Hip Arthroplasty

October 2008

Alumina ceramics in total hip arthroplasty (THA) have been used in Europe since 1970. Over the years, ceramic-on-ceramic coupling became a valid option in THA because of excellent biocompatibility and tribological properties.^1,2 The major disadvantages are possible squeaking and risk of breakage, usually disclosed by pain and functional impairment.

Squeaking is an audible noise arising from ceramic-on-ceramic bearings, the incidence of which is reported to range from 1% to 7% of THAs. Component positioning, stripe wear, and edge loading have all been implicated.^3-5 Clicking sounds and scratching have also been anecdotally described.⁶

Breakage of a ceramic component due to brittleness of the material is a rare complication.^7,8 Trauma, high activity level, and obesity may increase the risk of fracture.^9,10 Defective ceramic manufacture, inadequate implant design, and errors in surgical technique may contribute to breakage.^1,11,12 Asian population lifestyle, including squatting, kneeling, and sitting cross-legged, has been correlated to liner rim impingement and fracture.^13-15 Additional reports concerning failure of various ceramic liners have recently been described.^6,16-18

We describe a case of delayed diagnosis of a low-symptomatic fracture of an acetabular liner occurring 6 years after implantation of an uncemented ceramic-on-ceramic modular THA.

Case Report

In July 1999, a 51-year-old man with a height of 175 cm, weight of 95 kg, and body mass index of 31 underwent a cementless Anca-Fit (Wright Medical Technology, Inc, Arlington, Tennessee) THA for avascular necrosis of his right femoral head. The Anca-Fit modular prosthesis includes a titanium-made hemispheric cup coated with hydroxylapatite. The internal truncated tapered cone is fitted with a ceramic liner that is slightly prominent out of the shell (Biolox Forte; CeramTec AG, Plochingen, Germany). The anatomical stem is titanium-made and proximally coated with hydroxylapatite. A modular titanium neck, available in 2 different lengths and 5 different models, is inserted in the stem by a double-tapered coupling. The ceramic head (Biolox Forte) is fitted to the modular neck by a tapered coupling.

Total hip arthroplasty was performed on the patient via an anterolateral approach. The 60-mm outer diameter acetabular cup accepted a ceramic liner. The stem size was 16 with a short, straight neck and a 28-mm medium alumina head. Neck-stem angle was 138° with a final stem offset of 30.4 mm. The cup abduction angle was 33° and the anteversion angle was 9°. No prosthetic impingement or instability was seen intraoperatively (Figure 1).

At the time of operation, the patient had been employed as a train cleaner for approximately 33 years. Six months postoperatively the patient fully resumed work activities, and worked a further 3 years before retiring.

Annual clinical and radiological evaluation was normal except for the development of Brooker grade IV periprosthetic ossification that was not responsible for significant motion impairment.¹⁹

In April 2005, the patient heard a clicking sound in the hip when standing up from a squatting position, followed by acute pain. Immediate radiographs did not show substantial modification in the implant status; however, a second look revealed a smooth outline to the acetabular liner (Figure 2). The pain resolved spontaneously within 15 days, and 6 months later the hip was found to be well functioning, with no pain or noise.

Figure 1: Immediate postoperative radiographs showing an abduction angle of 33 (A) and an anteversion angle of 9 (B) of the acetabular component. Figure 2: Conventional radiographs performed immediately after the onset of pain (6 years postoperatively) showing a smooth outline of the ceramic liner (arrows) (A, B). Figure 3: Seven-year postoperative radiographs clearly demonstrating the breakage of the ceramic liner (arrows).

In May 2006, further clinical and radiological assessment demonstrated a fracture of the acetabular liner, though the patient was still pain free (Figure 3). In August 2006, revision surgery was performed using the same anterolateral approach. A wide periprosthetic ossification was exposed immediately and removed. On arthrotomy, a fragmentation of the medial aspect of the liner and multiple small fragments were found. A thorough synovectomy was performed to optimize debris removal. After the stability of both prosthetic components was validated, acetabular revision consisted of the removal of the ceramic liner followed by the implantation of a polyethylene unit that firmly locked the cone of the metal shell. On the femoral side, a brand new short straight neck and 32-mm long head (Biolox Forte) were positioned. Intraoperatively only 2 predeposited autologous blood units were transfused.

Postoperatively, indomethacin as a prophylaxis for heterotopic bone formation was administered at 150mg/day for 10 days. Immediate full weight bearing was allowed, and the patient was discharged 5 days postoperatively. At 18 months the patient had resumed all activities of daily living with no hip pain and a successful radiological outcome.

Discussion

Over the years, ceramic-on-ceramic bearings in THA became a successful answer to periprosthetic osteolysis because of excellent tribological properties and improved resistance to wear.^1,2 However, the most serious complication related to THA with ceramic-ceramic couplings is the breakage of components, head and insert, alone or associated.^7,8 The risk of ceramic liner fracture can be correlated with a high level of activity, history of trauma, and obesity.^6,9,10,17 Other causes of breakage are related to ceramic manufacturing, implant design, surgical technique—such as cup and stem positioning—and hip instability.^1,11,12,16 Another possible mechanism is edge loading when the hip is flexed, as when rising from a chair or climbing a high step. The increased range of motion required to support squatting, kneeling, and sitting cross-legged can result in impingement and liner fracture.^13,14

In our case the patient was young but he had a low activity level at the time of ceramic failure. Moreover, the complication occurred later—6 years postoperatively—suggesting the absence of recurrent contact between the stem and the ceramic liner. Furthermore, the breakage of the liner occurred without significant trauma or persistent hip pain or noise. We concluded that the possible cause of impingement in this case was an acute conflict between the metal neck and the alumina liner induced by an unexpected movement of the hip over the usual range of motion. The fracture apparently occurred during squatting resulting in hyperflexion and wide hip abduction.

Acetabular cup inclination is an important factor affecting the risk of dislocation and impingement. Barrack et al¹² stated that in a ceramic-on-ceramic THA, the acetabular component should be placed at <45° abduction to minimize wear rate and surface damage. Conversely, adduction placement of the cup (33° in the reported case) could result in impingement between the acetabular liner and the neck of the stem.^{6,10,13,14,18}

We concluded that horizontal positioning of the shell was not a contributing factor for breakage: the patient did not experience any previous subluxation and relocation motion during working and daily living activities. Furthermore, the ceramic liner rim had no evidence of impingement damage at revision surgery.

At the time of revision, a new ceramic-on-ceramic articulation was considered in order to avoid third-body wear from residual ceramic debris, but the availability of ceramic liners sitting unprotected in the metallic shell should have been responsible for further neck liner conflicts. Consequently, meticulous debridement of the prosthetic joint was followed by implantation of a polyethylene unit.^14-16

Conclusion

Breakage of ceramic components results in mechanical problems and biological consequences if mismatched. This case confirms the need to carefully evaluate the status of ceramic-on-ceramic implants in symptomatic patients.

In the reported case, the patient should have been followed carefully for signs of failure of a ceramic component at the onset of pain. Immediate radiographic findings were misjudged, and early and persistent regression of pain and lack of clicking sounds led us to forgo further investigation.

Recently, computed tomography scanning and needle aspiration of the joint have been recommended in assessing painful and noisy ceramic-on-ceramic THA.^18,20

References

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Authors

Drs Regis, Sandri, and Bartolozzi are from the Department of Orthopedic Surgery, Verona University School of Medicine, Verona, Italy.

Drs Regis, Sandri, and Bartolozzi have no relevant financial relationships to disclose.

Correspondence should be addressed to: Dario Regis, MD, Clinica Ortopedica e Traumatologica, Policlinico GB Rossi, Piazzale LA Scuro 10, 37134 Verona, Italy.