Chanlalit Cholawish, Shukla Dave R, Fitzsimmons James S, An Kai-Nan, O'Driscoll Shawn W
Biomechanics Laboratory, Department of Orthopedic Surgery, Mayo Clinic, Rochester MN, USA.
J Hand Surg Am. 2012 Oct;37(10):2118-25. doi: 10.1016/j.jhsa.2012.06.020.
Stress shielding is known to occur around rigidly fixed implants. We hypothesized that stress shielding around radial head prostheses is common but nonprogressive. In this study, we present a classification scheme to support our radiographic observations.
We reviewed charts and radiographs of 86 cases from 79 patients with radial head implants from both primary and revision surgeries between 1999 and 2009. Exclusion criteria included infection, loosening, or follow-up of less than 12 months. We classified stress shielding as: I, cortical thinning; II, partially (IIa) or circumferentially (IIb) exposed stem; and III, impending mechanical failure.
Of 26 well-fixed stems, 17 (63%) demonstrated stress shielding: I = 2, II = 15 (IIa = 12, IIb = 3), and III = 0. We saw stress shielding with all stem types: cemented or noncemented; long or short; and straight, curved, or tapered. The only significant difference was that stems implanted into the radial shaft had less stress shielding than stems implanted into the neck or tuberosity (P = .03). The average follow-up was 33 months (range, 13-70 mo). Stress shielding was detectable by an average of 11 months (range, 1-15 mo). The pattern of bone loss was similar in 16 of 17 cases (94%), starting on the outer periosteal cortex. The 3 cases with circumferential exposure of the stem (stage IIb) averaged 2.6 mm (range, 1-4 mm) of exposed stem. Stress shielding never extended to the bicipital tuberosity, and there were no cases of impending mechanical failure.
Stress shielding around radial head prostheses is common, regardless of stem design. However, it is typically minor, nonprogressive, and of questionable clinical consequence.
TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.
已知在刚性固定的植入物周围会发生应力遮挡。我们推测桡骨头假体周围的应力遮挡很常见，但不会进展。在本研究中，我们提出一种分类方案以支持我们的影像学观察结果。
我们回顾了1999年至2009年间79例患者86例初次和翻修手术中桡骨头植入物的病历和X线片。排除标准包括感染、松动或随访时间少于12个月。我们将应力遮挡分为：I级，皮质变薄；II级，部分（IIa级）或周向（IIb级）暴露的柄部；III级，即将发生机械故障。
在26个固定良好的柄部中，17个（63%）出现应力遮挡：I级 = 2个，II级 = 15个（IIa级 = 12个，IIb级 = 3个），III级 = 0个。我们在所有柄部类型中均观察到应力遮挡：骨水泥型或非骨水泥型；长柄或短柄；直柄、弯柄或锥形柄。唯一显著的差异是，植入桡骨干的柄部比植入颈部或结节的柄部应力遮挡更少（P = 0.03）。平均随访时间为33个月（范围13 - 70个月）。平均11个月（范围1 - 15个月）可检测到应力遮挡。17例中的16例（94%）骨质流失模式相似，始于外侧骨膜皮质。3例柄部周向暴露（IIb期）的患者柄部暴露平均为2.6毫米（范围1 - 4毫米）。应力遮挡从未扩展至肱二头肌结节，且无即将发生机械故障的病例。
无论柄部设计如何，桡骨头假体周围的应力遮挡都很常见。然而，它通常较轻，不会进展，且临床后果存疑。
研究类型/证据水平：治疗性IV级。
