Avoid taper contamination!
Contamination between stem taper and femoral head reduces the pull-off force for metal as well as ceramic femoral heads. Fatty contamination causes severe, saline only a small reduction, as Krull et al. found out. Cleaning and drying with gauze after contamination improved pull-off strength to values similar to the pristine condition. The authors concluded that drying after cleaning is beneficial for avoiding a large variation in taper fixation.
The study examined the effect of taper contamination and cleaning on head taper fixation. Cobalt-chromium (CoCr) and ceramic (Ce) femoral heads were impacted by a standardized method. Five conditions were investigated: pristine, contaminated with fat, cleaned after contamination with fat, contaminated with saline and cleaned after contamination with saline. Pull-off forces in pristine conditions were similar for both head materials (Ce: 2’272 ± 337 N, CoCr: 2’288 ± 248 N). Contamination with fat had a dramatic influence on the pull-off forces (Ce: 26 ± 16 N, CoCr: 28 ± 21 N). By contrast, saline caused only a small reduction in pull-off strength. Cleaning and drying with gauze after contamination with either fat or saline solution yielded pull-off forces close to those of pristine tapers. The authors concluded that intraoperative taper contamination with fat or saline solution has a major impact on the taper fixation strength.
The taper contamination affects the burst strenght
CoC shows excellent long-term results
Ceramic-on-ceramic (CoC) bearings made of third-generation ceramics (BIOLOX®forte) show excellent long-term results in a study from Italy. Overall survivorship after 15 years with revision as endpoint was 93.2%; considering implant failure as endpoint the figure was 97.2%. Toni et al. analyzed 248 cementless THA with 28mm CoC bearings in 235 patients with a mean age of 55.5 years at the time of surgery. All stems were made of titanium alloy, with a modular titanium alloy neck.
One acetabular component had to be revised because of instability. One stem initially rated fibrous stable was exchanged after loosening. There were 4 cases (1.6%) of squeaking (2 intermittent) and 3 cases of ceramic liner fracture after about 5 years. Two of the squeaking cases were linked to ceramic liner fracture. In the 3 patients with a fractured ceramic liner, posterior neck-to-cup impingement was identified as a reason during revision. The authors conclude that the use of third-generation CoC bearings in cementless THA provides excellent long-term results, similar to literature data on CoC bearings with correctly positioned and functionally stable components.
The primary diagnoses in the study were mostly primary osteoarthritis (57.3%) and osteoarthritis due to developmental dysplasia (23.8%). The mean follow-up was 16.5 years. The Merle-d’Aubigné and Postel hip score was used for clinical assessment. At final follow-up, it had improved significantly from 11.4 to 17.4. Early posterior dislocation occurred in three hips. These were treated by closed reduction without recurrence. Partial periprosthetic radiolucent lines were found in 17 cases but remained asymptomatic. Squeaking may be a sign for impending ceramic fracture if the position of the components leads to neck-liner impingement.
Significantly lower noise incidence with navigation
Computer navigation can help to position implants appropriately, leading to a significantly reduced incidence of noise for CoC bearings. Shah et al. came to this conclusion after analyzing 173 conventional and 202 computer-navigated THA. The risk of reported noise was lower by a factor of 2.7 in the navigated subgroup examined and lower by a factor of 5.8 for noises other than squeaking. Radiographic comparison showed that cup anteversion was significantly lower for squeaking than for silent hips.
The authors evaluated 375 ceramic-on-ceramic (CoC) total hip arthroplasties (THA) with a head size of mostly 32mm. No patient in either group required revision for noise. Noise was reported in 14.7% of the THA, of which 7% were non-squeaking noises such as clicking, grunting, grinding or crunching. In the navigated group, noise was not associated with pain. Only noises other than squeaking (5 patients) were associated with pain in the conventional THA group. Patients under 65 years had a significantly higher incidence of self-reported noise.
A subgroup was analyzed for further comparison between 118 conventional and 68 navigated THA. Subgroup analysis suggested that navigated CoC THA have a 2.7-fold lower risk of reported noise and a 5.8-fold lower risk of noise other than squeaking. Radiographic comparison showed that cup anteversion was significantly lower for squeaking than for silent hips.
XPE wear study wins award
This year’s Heinz Mittelmeier Research Award was granted to Dr. Constantin Mayer and colleagues from Düsseldorf/Essen (Germany) for a study on wear kinematics of conventional and crosslinked polyethylene. Analyzing X-rays, they found that wear patterns are similar for both materials. They recorded an alarming rise in the wear rate of the crosslinked PE after nine years post-op. The study also showed elevated wear rates in male patients and with large bearing diameters.
The study has been accepted by the Journal of Arthroplasty.