Background:

Osteochondritis dissecans (OCD) of the capitellum is common in throwing athletes and is believed to result from repetitive overloading on the radiocapitellar (RC) joint, although the cause and mechanism remain unclear. The torsional forces (moments) generated by the triceps during elbow extension pull only on the ulna; therefore, the radial head moves passively across the capitellum and is effectively “dragged along” by the ulna. Any laxity in the proximal radioulnar joint could lead to asynchronous motion between the radius and ulna, resulting in the radial head lagging behind the coronoid and possibly malarticulating with the capitellum during such motion.

Hypothesis:

Radial head motion on the capitellum lags behind ulnohumeral joint motion during simulated throwing.

Study Design:

Controlled laboratory study.

Methods:

A total of 8 cadaveric elbows were tested under simulated throwing, including active extension of the elbow generated by pulling of the triceps under valgus stress, as well as during passive extension under valgus stress to serve as a reference. Ulnohumeral motion was tracked using a video camera. Radial head motion was tracked using an intra-articular, thin-film pressure sensor mounted on the capitellum, and the longitudinal movement of the center of force (COF) of the radial head was measured. Radial head motion was compared between passive and active motion for each 10° of elbow extension from 90° to 20°.

Results:

Elbow motion during simulated active extension reached an angular velocity of 366 deg/s. Radial head motion during simulated active extension significantly lagged compared with its motion during passive extension at every elbow extension angle examined between 70° and 20° (P < .001). The maximal lag reached a mean of 4 mm (range, 2-7 mm). In other words, RC and ulnohumeral motion were asynchronous during simulated throwing.

Conclusion:

This study describes a novel phenomenon: motion of the radial head across the capitellum during rapid extension, such as in baseball pitching, lags behind that seen during passive elbow motion. According to a new proposed theory of OCD lesion development, this lag should result in RC incongruency and elevated shear forces on the capitellum due to edge loading.

Clinical Relevance:

We propose a new biomechanical explanation for OCD of the capitellum in baseball pitchers: radial head lag. Understanding this process is the first step in efforts to prevent this common injury.

中文翻译：

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桡骨头滞后：棒球投手小头骨剥脱性骨软骨炎的可能生物力学机制

背景：

小头的剥脱性骨软骨炎 (OCD) 在投掷运动员中很常见，据信是由桡小头 (RC) 关节重复超负荷引起的，尽管原因和机制尚不清楚。肘部伸展时三头肌产生的扭转力（力矩）仅作用在尺骨上；因此，桡骨头被动地穿过小头并被尺骨有效地“拖曳”。桡尺近端关节的任何松弛都可能导致桡骨和尺骨之间的不同步运动，导致桡骨头落后于冠状突，并可能在这种运动过程中与小头关节错位。

假设：

在模拟投掷过程中，小头的径向头部运动滞后于肱骨尺关节运动。

学习规划：

受控实验室研究。

方法：

在模拟投掷下测试了总共8个尸体肘部，包括在外翻应力下拉动肱三头肌产生的肘部主动伸展，以及在外翻应力下被动伸展作为参考。使用摄像机跟踪尺骨运动。使用安装在小头上的关节内薄膜压力传感器跟踪桡骨头运动，并测量桡骨头的力中心 (COF) 的纵向运动。从 90° 到 20°，肘部每伸展 10°，被动运动和主动运动之间的径向头部运动比较。

结果：

模拟主动伸展期间的肘部运动达到 366 度/秒的角速度。在 70° 和 20° 之间检查的每个肘部伸展角度（P < .001），模拟主动伸展期间的径向头部运动与其被动伸展期间的运动相比显着滞后。最大滞后达到平均 4 毫米（范围，2-7 毫米）。换句话说，在模拟投掷过程中，RC 和尺骨运动是异步的。

结论：

这项研究描述了一个新现象：在快速伸展过程中，桡骨头穿过小头的运动，例如在棒球投球中，落后于被动肘部运动时看到的运动。根据新提出的 OCD 病变发展理论，这种滞后应该导致 RC 不一致和由于边缘载荷而导致小头上的剪切力升高。

临床相关性：

我们对棒球投手小头的强迫症提出了一种新的生物力学解释：桡骨头滞后。了解这一过程是努力防止这种常见伤害的第一步。