Washington University School of Medicine, St Louis, MO, USA.
Clin Orthop Relat Res. 2012 Jan;470(1):299-306. doi: 10.1007/s11999-011-2131-4. Epub 2011 Oct 18.
Surface replacement arthroplasties are commonly performed in young, active patients who desire return to high-impact activities including heavy manual labor and recreational sports. Femoral neck fracture is an arthroplasty-related complication unique to surface replacement arthroplasty. However, it is unclear regarding whether patients are at lower risk for fracture after a certain postoperative time.
QUESTIONS/PURPOSES: We therefore raised the following questions: (1) does stress shielding occur after surface replacement arthroplasty, and (2) when does bone mineral density return to normal so patients can return to high-impact activities without excessive risk of fracture?
We prospectively enrolled 90 patients (96 hips) with either surface replacement arthroplasty or THA, and performed dual energy x-ray absorptiometry scans at 6 weeks, 6 months, 1 year, and 2 years. We analyzed bone density by Gruen zone in both groups, and six femoral neck zones in the patients who had surface replacement arthroplasties. We calculated 6-month, 1-year, and 2-year ratios for the change in bone density compared with baseline.
Bone density was greater in patients who had surface replacement arthroplasties than for patients who had THAs at 6 months and 1 year in Gruen Zones 1, 2, 6, and 7, with the largest increase in femoral neck bone density on the tension side at 6 months in Zone L1. We saw no decrease in bone density in patients who had surface replacement arthroplasties in any Gruen zone at any time, and observed no decrease in bone density in female patients.
Increased bone density at 6 months postoperatively in patients who had surface replacement arthroplasties provides evidence that clinically relevant stress shielding does not occur after surface replacement arthroplasty. Owing to the increased bone mineral density at 6 months, we believe patients who underwent surface replacement arthroplasties may to return to high-impact activities at that time without increased risk of fracture.
表面置换关节成形术常用于年轻、活跃的患者，他们希望恢复高影响活动，包括重体力劳动和娱乐性运动。股骨颈骨折是表面置换关节成形术特有的关节置换相关并发症。然而，尚不清楚患者在术后特定时间后骨折风险是否较低。
问题/目的：因此，我们提出了以下问题：（1）表面置换关节成形术后是否会发生应力遮挡，（2）骨密度何时恢复正常，以便患者可以恢复高影响活动而不会增加骨折的风险？
我们前瞻性纳入了 90 例（96 髋）接受表面置换关节成形术或全髋关节置换术的患者，并在术后 6 周、6 个月、1 年和 2 年进行双能 X 线吸收法扫描。我们分析了两组的骨密度，包括Gruen 区和接受表面置换关节成形术的患者的六个股骨颈区。我们计算了与基线相比，6 个月、1 年和 2 年的骨密度变化比率。
在 Gruen 区 1、2、6 和 7 中，接受表面置换关节成形术的患者在术后 6 个月和 1 年时的骨密度均高于接受全髋关节置换术的患者，且在 6 个月时张力侧股骨颈骨密度增加最大。在任何 Gruen 区，我们都没有看到接受表面置换关节成形术的患者的骨密度降低，也没有看到女性患者的骨密度降低。
接受表面置换关节成形术的患者术后 6 个月时骨密度增加，这表明表面置换关节成形术后不会发生临床相关的应力遮挡。由于 6 个月时骨矿物质密度增加，我们认为接受表面置换关节成形术的患者可能在此时恢复高影响活动，而不会增加骨折的风险。
