Department of Orthopaedic Surgery and Traumatology, Hospital Center, 177, rue de Versailles, 78150 Le Chesnay, France.
Orthop Traumatol Surg Res. 2010 May;96(3):249-55. doi: 10.1016/j.otsr.2009.12.005. Epub 2010 Apr 8.
Navigation tracker pins rigidly fixed to bone is a prerequisite for computer-assisted total knee arthroplasty. The first cases of fracture on navigation tracker pin sites have recently been reported.
The risk of fracture depends first on diaphyseal placement of the tracker pins, and second on "transcortical" tangential route of the tracker pin as well as failure to obtain rigid fixation.
In a continuous series of 385 total knee arthroplasties, five patients (four women, one man) on average 73.2 years old (range: 65-79 years old) have sustained femoral fractures at the tracker pin site (incidence 1.3%). We investigated the demographic and radiological factors contributing to this complication.
The patients with fractures were obese or overweight with an average body mass index of 32.56 (range: 25.14-39.45) but this was not statistically different from the BMI of the population of patients without fractures. The average delay from arthroplasty to fracture was 12.6 weeks (range 7-21). The fracture was always preceded by several days of thigh pain and occurred after a minor trauma. The fractures were always simple originating from the tracker pin site. In four out of five cases, the tracker pins were placed in the diaphyseal femur, and in all cases at least one pin was transcortical. Closed endomedullary nailing or ORIF were performed in five cases, with no bone graft. Union was obtained with functional results that were equivalent to those before the fracture.
Fractures at the navigation tracker pin site are a complication which must be understood and explained to patients undergoing computer-assisted TKA because of the 1.3% incidence described in our series. The circumstances systematically associated with this type of fracture were: occurrence a certain amount of time after arthroplasty in obese patients who had pain before the fracture occurred. These fractures are favored by suboptimal placement of the tracker pins, especially in the lower diaphysis of the femur and transcortical fixation of at least one of the pins. Treatment included stable osteosynthesis and did not affect the results of total knee arthroplasty. The development of thigh pain some time after surgery in high risk patients (obesity, tracker pin site in the lower diaphysis, transcortical fixation) should suggest this diagnosis and weight-bearing should be avoided because these fractures are assimilated with stress fractures. Bicortical metaphyseal fixation should be the preferred tracker pin positioning for navigated total knee arthroplasty.
Level IV retrospective study.
导航跟踪器钉刚性固定在骨头上是计算机辅助全膝关节置换术的前提。最近报道了首例导航跟踪器钉部位骨折病例。
骨折的风险首先取决于跟踪器钉的骨干放置，其次取决于跟踪器钉的“皮质下”切线路径以及未能获得刚性固定。
在连续 385 例全膝关节置换术中，5 名患者（4 名女性，1 名男性）平均年龄 73.2 岁（范围：65-79 岁），跟踪器钉部位发生股骨骨折（发生率 1.3%）。我们研究了导致这种并发症的人口统计学和影像学因素。
骨折患者肥胖或超重，平均体重指数为 32.56（范围：25.14-39.45），但与无骨折患者的体重指数无统计学差异。从关节置换到骨折的平均延迟时间为 12.6 周（范围 7-21 周）。骨折前总是有几天大腿疼痛，并且发生在轻微创伤后。骨折总是从跟踪器钉部位开始的简单骨折。在 5 例中，跟踪器钉放置在骨干股骨中，并且在所有情况下，至少有一个钉是皮质下的。在 5 例中进行了闭合髓内钉或切开复位内固定，没有植骨。在骨折发生之前，功能结果与骨折前相同。
在接受计算机辅助 TKA 的患者中，导航跟踪器钉部位骨折是一种必须理解和解释的并发症，因为我们的系列研究中描述的发生率为 1.3%。与这种类型的骨折系统相关的情况是：在肥胖患者中，在骨折发生之前，在关节置换后一段时间发生疼痛。这些骨折有利于跟踪器钉的位置不当，特别是在股骨的下部骨干和至少一个钉的皮质下固定。治疗包括稳定的骨合成，并且不会影响全膝关节置换术的结果。在高危患者（肥胖、跟踪器钉部位在骨干下部、皮质下固定）手术后一段时间出现大腿疼痛应提示这种诊断，应避免负重，因为这些骨折与应力性骨折相似。双皮质骺部固定应是导航全膝关节置换术首选的跟踪器钉定位。
IV 级回顾性研究。
