Background 

Studies have suggested that automated synovial cell counting may overestimate the white blood cell (WBC) count, resulting in false positive tests when evaluating patients for the possibility of periprosthetic joint infection (PJI) after THA. However, associations between WBC counts high enough to mimic PJI in patients whose arthroplasties are not infected but rather are experiencing a variety of aseptic problems—including but not limited to metallosis, polyethylene wear, and recurrent dislocation—have not, to our knowledge, been adequately addressed. In addition, there is a lack of analyses about the polymorphonuclear percentage (PMN%) when assessed by automated analyzers in this context.

Questions/purposes 

In the context of different indications for aseptic revision and different periprosthetic hip pathologic findings, we asked: (1) What were the synovial WBC count levels, and what proportion of values were above the 2018 International Consensus Meeting (ICM) cutoff (3000 cells/μL)? (2) What were the synovial PMN% levels, and what proportion of values were above the 2018 ICM (70%)?

Methods 

We retrospectively studied the preoperative cell count analyses of synovial fluid in patients who underwent revision THA for aseptic reasons at our tertiary referral arthroplasty center between January 2015 and December 2017. We considered all revisions performed on patients during that time potentially eligible, and after prespecified exclusions were applied (exclusions mainly included 15% [197 of 1306] sporadic missing data and 12% [155 of 1306] insufficient synovial fluid obtained in the aspirate), a total of 702 patients undergoing revision THA for aseptic reasons remained for the final analysis. As far as we know, no patients underwent re-revision for PJI at a mean follow-up of 46 ± 11 months, which tends to confirm our impression that indeed these hips did not have PJI. Cell count analyses were conducted using an automated analyzer. Clinical findings, preoperative radiographs, and surgical reports––confirmed by available histologic results––were used to establish diagnoses. We evaluated these hips considering the recommendations of the 2018 ICM (WBC count of 3000 cells/μL and PMN% of 70%) to see what proportion of them would have been characterized as likely having PJI on basis of those cutoff values. The mean WBC count for the entire cohort was 2120 ± 2395 cells/μL. The mean PMN% for the entire cohort was 36% ± 22%.

Results 

Compared with aseptic loosening and recurrent dislocation, polyethylene wear had the highest mean WBC count (3817 ± 3711 cells/μL; p < 0.001). Of the investigated periprosthetic conditions, wear-induced synovitis had the highest value (4464 ± 3620 cells/μL; p < 0.001). Considering the ICM threshold, polyethylene wear showed the highest proportion of WBC counts above 3000 cells/μL among the indications for aseptic revision (60% [25 of 42]; p < 0.001). Of the periprosthetic conditions, wear-induced synovitis showed the highest proportion beyond the ICM cutoff (60% [50 of 83]; p < 0.001). The mean PMN% for aseptic causes ranged between 28% and 44% without differences among them (p = 0.12). Patients with metallosis had the highest mean PMN% of the periprosthetic conditions investigated (45% ± 25%; p = 0.007). Regarding the ICM threshold, metallosis resulted in the largest proportion of patients with a PMN% above 70% (21% [10 of 47]; p = 0.003), and that for wear-induced synovitis was 6% (5 of 83; p = 0.42) and for osteolysis was 3% (1 of 33; p = 0.51). There were no differences among aseptic loosening, recurrent dislocation, and polyethylene wear in terms of the proportion above 70% among the aseptic revision causes.

Conclusion 

Using automated cell counting, we found that WBC counts differ widely across indications for aseptic revision THA, and a high proportion of patients who underwent revision THA for aseptic reasons had WBC counts above the commonly used threshold of 3000 cells/μL. However, the PMN% was much less affected in several common indications for aseptic revision THA, making this measure more reliable for interpreting aspiration results using an automated analyzer. Based on the data distributions we observed, manual counting techniques might be considered in particular among patients with polyethylene wear, metal-on-metal bearing surfaces, or suspected metallosis. However, an elevated WBC count alone, observed using an automated analyzer in the context of polyethylene wear, should not be considered to be strongly suggestive of PJI, since that finding occurred so commonly among patients without infection.

Level of Evidence 

Level III, diagnostic study.

中文翻译：

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自动滑膜细胞计数对不同无菌原因和与 THA 翻修相关的假体周围状况有何影响？

背景 

研究表明，自动滑膜细胞计数可能会高估白细胞 (WBC) 计数，从而在评估患者全髋关节置换术后假体周围感染 (PJI) 的可能性时导致检测结果出现假阳性。然而，据我们所知，在关节置换术未感染但正在经历各种无菌问题（包括但不限于金属沉积、聚乙烯磨损和复发性脱位）的患者中，WBC 计数之间的关联足够高，足以模拟 PJI。得到充分解决。此外，在这种情况下，通过自动分析仪评估时，缺乏对多形核百分比 (PMN%) 的分析。

问题/目的 

在无菌翻修的不同适应症和不同的假体周围髋关节病理结果的背景下，我们询问：（1）滑膜白细胞计数水平是多少，以及高于2018年国际共识会议（ICM）截止值（3000个细胞/微升）？(2) 滑膜 PMN% 水平是多少？高于 2018 年 ICM（70%）的值比例是多少？

方法 

我们回顾性研究了 2015 年 1 月至 2017 年 12 月期间在我们的三级转诊关节置换中心因无菌原因接受翻修 THA 的患者的术前滑液细胞计数分析。我们认为在此期间对患者进行的所有翻修都可能符合资格，并且在预先指定的排除后应用（排除主要包括15%[1306中的197]零星缺失数据和12%[1306中的155]抽吸中获得的滑液不足），总共702例因无菌原因接受翻修THA的患者仍待最终分析。据我们所知，平均随访 46 ± 11 个月后，没有患者接受 PJI 重新修复，这证实了我们的印象，即这些髋关节确实没有 PJI。使用自动分析仪进行细胞计数分析。临床发现、术前X光片和手术报告——经现有的组织学结果证实——被用来建立诊断。我们根据 2018 年 ICM 的建议（WBC 计数为 3000 个细胞/μL，PMN% 为 70%）对这些髋关节进行了评估，以了解根据这些截止值，其中有多少比例可能被描述为可能患有 PJI。整个队列的平均白细胞计数为 2120 ± 2395 个细胞/μL。整个队列的平均 PMN% 为 36% ± 22%。

结果 

与无菌性松动和反复脱位相比，聚乙烯磨损的平均 WBC 计数最高（3817 ± 3711 个细胞/μL；p < 0.001）。在所研究的假体周围状况中，磨损引起的滑膜炎具有最高值（4464 ± 3620 个细胞/μL；p < 0.001）。考虑到 ICM 阈值，在无菌翻修适应症中，聚乙烯磨损显示 WBC 计数超过 3000 个细胞/μL 的比例最高（60% [42 中的 25]；p < 0.001）。在假体周围状况中，磨损引起的滑膜炎所占比例最高，超出 ICM 截止值（60% [83 中的 50]；p < 0.001）。无菌原因的平均 PMN% 范围在 28% 到 44% 之间，之间没有差异 (p = 0.12)。在所调查的假体周围状况中，金属沉积患者的平均 PMN% 最高（45% ± 25%；p = 0.007）。关于 ICM 阈值，金属沉积导致 PMN% 超过 70% 的患者比例最大（21% [47 人中的 10 人]；p = 0.003），磨损引起的滑膜炎的比例为 6%（83 人中的 5 人；p = 0.003）。 = 0.42），骨质溶解为 3%（33 人中的 1 人；p = 0.51）。无菌性翻修原因中无菌性松动、反复脱位、聚乙烯磨损所占比例均在70%以上，无差异。

结论 

使用自动细胞计数，我们发现 WBC 计数在无菌翻修 THA 的适应症中差异很大，并且因无菌原因接受翻修 THA 的患者中，很大一部分 WBC 计数高于常用阈值 3000 个细胞/μL。然而，PMN% 在无菌翻修 THA 的几种常见适应症中受到的影响要小得多，使得该测量对于使用自动分析仪解释抽吸结果更加可靠。根据我们观察到的数据分布，特别是在聚乙烯磨损、金属对金属轴承表面或疑似金属沉积的患者中，可以考虑使用手动计数技术。然而，在聚乙烯磨损情况下使用自动分析仪观察到的白细胞计数升高，不应被视为强烈提示 PJI，因为这一发现在未感染的患者中非常常见。

证据水平 

III级，诊断研究。