Background: 

Periprosthetic fracture is a leading reason for readmission following total hip arthroplasty. Most of these fractures occur during the early postoperative period before bone ingrowth. Before ingrowth occurs, the femoral component can rotate relative to the femoral canal, causing a spiral fracture pattern. We sought to evaluate, in a paired cadaver model, whether the torsional load to fracture was higher in collared stems. The hypothesis was that collared stems have greater load to fracture under axial and torsional loads compared with collarless stems.

Methods: 

Twenty-two cadaveric femora (11 matched pairs) with a mean age of 77 ± 10.2 years (range, 54 to 90 years) were harvested. Following dissection, the femora were evaluated with use of a dual x-ray absorptiometry scanner and T scores were recorded. We utilized a common stem that is available with the same intraosseous geometry with and without a collar. For each pair, 1 femur was implanted with a collared stem and the contralateral femur was implanted with a collarless stem with use of a standard broaching technique. A compressive 68-kg load was applied to simulate body weight during ambulation. A rotational displacement was then applied until fracture occurred. Peak torque prior to fracture was measured with use of a torque meter load cell and data acquisition software.

Results: 

The median torque to fracture was 65.4 Nm for collared stems and 43.1 Nm for uncollared stems (p = 0.0014, Wilcoxon signed-rank test). The median T score was –1.95 (range, –4.1 to –0.15). The median difference in torque to fracture was 29.18 Nm. As expected in each case, the mode of failure was a spiral fracture around the implant.

Conclusions: 

Collared stems seemed to offer a protective effect in torsional loading in this biomechanical model comparing matched femora.

Clinical Relevance: 

These results may translate into a protective effect against early periprosthetic Vancouver B2 femoral fractures that occur before osseous integration has occurred.

中文翻译：

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car骨衣领对早期扭转/螺旋骨膜周围股骨骨折具有保护作用：一对尸体生物力学分析。

背景： 

假体周围骨折是全髋关节置换术后再次入院的主要原因。这些骨折大多数发生在骨向内生长的术后早期。在向内生长之前，股骨组件可以相对于股管旋转，从而导致螺旋形骨折。我们试图在成对的尸体模型中评估颈状茎的骨折扭转载荷是否较高。假设是，与无领茎相比，有领茎在轴向和扭转载荷下具有更大的断裂载荷。

方法： 

收集平均年龄为77±10.2年（范围54至90岁）的22具尸体股骨（11对配对）。解剖后，使用双X线骨密度仪对股骨进行评估，并记录T评分。我们利用了一个普通的茎，该茎具有相同的骨内几何形状（带和不带项圈）。对于每对，使用标准的拉削技术将1个股骨植入颈状茎，将对侧股骨植入无颈状茎。施加68公斤的压缩负荷以模拟步行过程中的体重。然后施加旋转位移直到发生断裂。使用扭矩计称重传感器和数据采集软件测量断裂前的峰值扭矩。

结果： 

颈状茎的平均断裂扭矩为65.4 Nm，非颈状茎的平均断裂扭矩为43.1 Nm（p = 0.0014，Wilcoxon符号秩检验）。中位T评分为–1.95（范围从–4.1到–0.15）。断裂扭矩的中值差异为29.18 Nm。如每种情况所预期的，失败的方式是植入物周围的螺旋形断裂。

结论： 

与匹配的股骨相比，在该生物力学模型中，领状茎似乎在扭转负荷中提供了保护作用。

临床相关性： 

这些结果可能转化为对骨整合之前发生的早期假体温哥华B2股骨骨折的保护作用。