Late Dislocations After Total Hip Arthroplasty: Is the Bearing a Factor?

BACKGROUND: Dislocation is a leading cause of revision after primary total hip arthroplasty (THA). Although more common in the first few years after the procedure, dislocation can occur at any time. This study investigated the difference in late dislocation in ceramic-on-ceramic (CoC) bearings compared with metal-on-polyethylene and ceramic-on-polyethylene bearings in THA. METHODS: Data were used from the Australian Orthopaedic Association National Joint Replacement Registry, and the cumulative percent revision for dislocation was estimated using the Kaplan-Meier method for the different bearing surfaces. There were 192,275 THAs included in the study with 101,915 metal-on-cross-linked polyethylene (MoXLPE), 30,256 ceramic-on-cross-linked polyethylene (CoXLPE), and 60,104 CoC. RESULTS: The cumulative percent revision for dislocation at 13 years for MoXLPE, CoXLPE, and CoC groups was 1.2 (95% confidence interval [CI], 1.1-1.3), 1.0 (95% CI, 0.7-1.4), and 0.9 (95% CI, 0.8-1.1), respectively. There was an increased risk of revision for dislocation for MoXLPE compared with CoXLPE and CoC. When stratified for head size, there was no difference in the risk of revision for dislocation between MoXLPE, CoXLPE, and CoC in the 28- and 32-mm head sizes. With a head size of 36 mm, MoXLPE had a higher rate of dislocation compared with other materials. CONCLUSION: Bearing surface has little impact on revision for dislocation.

Two-year serum metal ion levels in minimally invasive total conservative hip resurfacing: preliminary results of a prospective study.

BACKGROUND: Metal-on-metal (MoM) hip resurfacings have been associated with the potential development of metallic debris and its associated pathology. Serum cobalt and chromium levels are a reliable surrogate marker of wear rates in MoM bearings. The aim of the study was to examine the trend in serum metal ion levels in the initial 2-year post-operative period following implantation of the minimally invasive total conservative hip MoM hip resurfacing and to determine whether head size, acetabular component orientation, clinical outcome scores or post-operative range of movement would affect these levels. METHODS: In this prospective cohort study, serum cobalt and chromium ion levels were measured pre- and post-operatively in 25 patients who underwent minimally invasive total conservative hip MoM hip resurfacing. The results were correlated with acetabular component orientation, head size, outcome scores and post-operative range of movement. RESULTS: The mean serum cobalt and chromium levels at 2 years were 1.2 ppb (0.4-4.4 ppb) and 2.1 ppb (0.7-5.7 ppb). The mean cup inclination was 43° (30°-60°) and anteversion was 18° (1°-47°). There was no clear relationship between serum ions and acetabular component orientation, outcome scores or range of movement. Patients with a head size ≤52 mm had significantly higher metal ion levels (cobalt P = 0.02, chromium P = 0.045). CONCLUSION: Our preliminary results show all patients had cobalt and chromium levels below those indicating a high-risk implant, suggesting successful early outcome from minimally invasive total conservative hip resurfacing surgery.

Squeaking in large diameter ceramic-on-ceramic bearings in total hip arthroplasty.

We analyzed the results of 206 consecutive total hip arthroplasties performed using large diameter ceramic-on-ceramic bearings. At an average follow-up of 28months, the mean Harris Hip Score improved from 54 to 92. Fifteen (7.3%) hips were noted to squeak. There was no significant difference between silent and squeaking hips with regards to age, weight, height, BMI, range of movement, femoral head diameter, leg length, and offset or center of rotation. No correlation was present between incidence of squeaking and increasing cup inclination and anteversion. 5.2% of cups orientated within Lewinnek's safe zone squeaked. No hips required revision for squeaking. While large diameter ceramic bearings may produce squeaking, our early results of surgery using large head ceramic bearings are encouraging. However, long-term follow-up is required.

The effect of obesity on the clinical, functional and radiological outcome of cementless total hip replacement: a case-matched study with a minimum 10-year follow-up.

1420 primary cementless THRs with a minimum follow-up of 10-years were stratified according to BMI: non-obese (BMI<30kg/m(2)) and obese (BMI≥30kg/m(2)). Median age at surgery was younger in obese patients (P<0.001). We case-matched 82 THRs in obese patients with 162 THRs in non-obese patients. No difference between groups was found in improvement in HHS (P=0.668), satisfaction with surgery (P=0.644), range of movement, prosthesis orientation, or radiological loosening. The obese cohort was further separated into those with a BMI below and above 35. No difference was found between groups in improvement in HHS, satisfaction with surgery, component orientation, or radiological loosening. There was no difference in the incidence of post-operative complications between obese and non-obese patients. After 10-years, the results of THR are not compromised by obesity.

Cementless hip arthroplasty in Paget's disease at long-term follow-up (average of 12.3 years).

We present a long-term follow-up report of 33 cementless total hip arthroplasties in 27 patients who have an established diagnosis of Paget's disease. The medium term results of this series were reported in 2007 (Lusty et al. Journal of Arthroplasty. 2007;22:692). Fourteen cases were available for follow-up at an average of 12.3 years (range 10-17). Harris Hip scores improved from 56/100 preoperatively (16-98/100) to 83/100 post operatively (72-90/100). All surviving components were radiographically ingrown. Based on these findings, cementless total hip arthroplasty has a good long-term outcome in Paget's disease.