[Analysis of migration of screwed acetabular components following revision arthroplasty of the hip joint. Results of single-image roentgen analysis]

"Koehlers teardrop is not a reliable landmark for assessing the centre of rotation after Total hip arthroplasty" - a retrospective radiological study

PURPOSE

Various anatomical landmarks have become established in radiography for the assessment of cup positioning after total hip arthroplasty (THA). The most important one is Koehler's teardrop figure (KTF). However, there is a lack of data on the validity of this landmark, which is widely used clinically for assessing the centre of rotation of the hip.

METHOD

A retrospective measurement of the lateral and cranial distance of the KTF to the centre of hip rotation was performed on the basis of 250 X-ray images of patients who had undergone THA. In addition, the dependence of these distances on pelvic tilt was determined in 16 patients by means of virtual X-ray projections based on pelvic CTs.

RESULTS

It was shown that the distance of the KTF from the centre of hip rotation in the horizontal plane is gender-dependent (men: 42.8 ± 6.0 mm vs. women: 37.4 ± 4.7 mm; p < 0.001) and age-dependent (Pearson correlation  - 0.114; p < 0.05). Furthermore, the vertical and horizontal distances are subject to variation depending on height (Pearson correlation 0.14; p < 0.05 and 0.40; p < 0.001, respectively) and weight (Pearson correlation 0.158; p < 0.05). The distance between the KTF and the centre of hip rotation varies slightly depending on pelvic tilt.

CONCLUSION

The KTF is not a sufficiently valid landmark for assessing the centre of rotation after THA. It is influenced by many different disturbance variables. However, it is largely robust against changes in pelvic tilt, so that it can be used as a reference point when comparing different intraindividual radiographs to assess the change in the centre of rotation due to implantation or to detect cup migration.

Loosening after acetabular revision: comparison of trabecular metal and reinforcement rings. A systematic review

The best method of revision acetabular arthroplasty remains unclear. Consequently, we reviewed the literature on the treatment of revision acetabular arthroplasty using revision rings (1541 cases; mean follow-up (FU) 5.7 years) and Trabecular Metal, or TM, implants (1959 cases; mean FU 3.7 years) to determine if a difference with regard to revision failure could be determined. Failure rates of the respective implants were compared statistically using a logistic regression model with adjustment for discrepancies in FU time. In our study, TM shows statistically significant decreased loosening rates relative to revision rings for all grades including severe acetabular defects and pelvic discontinuity. The severe defects appear to benefit the most from TM.

Determination of the rotational center of the hip

We introduce a new method to determine the anatomic rotation center of the hip. In total, 214 healthy hip joints were examined and statistically analyzed. As a reference point we used the intersection between Koehler's line and a line between the upper rims of the two foramina obturatoria. In relation to the reference point the anatomic hip center is localized 7.7% in vertical direction and 17.4% in horizontal direction for male individuals and 7.75 and 15.4% for female individuals, respectively. Those data were referred to the pelvic height. Our data can be used to determine the anatomic hip center in an easy and reliable way, not only for preoperative planning but also for retrospective investigations.

Reconstruction of severe acetabular bone-deficiency: the Burch-Schneider antiprotrusio cage in primary and revision total hip arthroplasty

Ninety Burch-Schneider antiprotrusio cages in 87 patients implanted in primary and revision total hip arthroplasty were analyzed. Sixty-seven hips (64 patients) could be examined clinically and radiologically after an average of 50.3 months (minimum 23.6, maximum 131.0 months). Twenty patients (20 hips) died in interim and 3 patients (3 hips) were not available for follow-up. Of the 90 Burch-Schneider antiprotrusio cages, 4 had to be removed and 8 further cages were considered definitely loose. The survival rate is 93.4% (95% confidence interval, 74.3%-96.7%) after 131 months if the endpoint "cage explantation" is used. The average Harris Hip Score was improved from 28.2 preoperatively to 73.5 points at the time of follow-up. Radiolucent lines were often found in the Charnley/DeLee's zones II and III. In contrast, osteolyses were seldom seen.

Mueller reinforcement rings in acetabular revision: outcome in 164 hips followed for 2-17 years

BACKGROUND

In revision hip arthroplasty, cages are commonly used for acetabular reconstruction in cases with loss of bone stock. It is important to follow this patient group closely, in order to better understand failure mechanisms and the chance of long-term success.

PATIENTS AND METHODS

We followed our first 164 acetabular revisions with the Mueller reinforcement ring (ARR) in 164 patients, with an average follow-up period of 6 (2-17) years. Mean age at surgery was 69 (29-92) years. 39 patients died (39 hips) during follow-up, but only 3 patients (3 hips) were lost to follow-up.

RESULTS

In the observation period, 13 of the hips had to undergo acetabular re-revision for aseptic and septic loosening. Overall survival at 5 years was 95% (CI: 89%-98%) and 90% (CI: 76%-95%) at 8 years using acetabular re-revision or implant removal for all reasons as endpoint. In addition, mechanical and clinical failure was seen in 2 cases. The mean Harris hip score was 70 points, whilst the Merle d'Aubigné score averaged 7 points. Radiolucent lines according to DeLee and Charnley were observed twice in zone I, 6 times in zone II and 14 times in zone III.

INTERPRETATION

We found that mid- to long-term survival of the ARR is acceptable. However, failure of the implant due to allograft collapse/resorption or deep infection, and also poor clinical outcome, remain major concerns in acetabular revision arthroplasty. This should be recognized when advising patients.

Acetabular revision with impacted grafting and a reinforcement ring: 42 patients followed for a mean of 10 years

We analyzed the outcome of 42 cemented cup revisions (40 patients) with morselized bone grafts and a reinforcement ring after median 10 (7-16) years. The acetabular component migrated a mean of 7 (5-8) mm in 5 hips. The migration stopped after 2 years except in 1 hip, the only one revised because of mechanical loosening. 3 other hips were revised because of infection. Among the other 38 hips (36 patients), the Merle d'Aubigné score increased from 9 to 15 points.