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How Do Elbows Dislocate?

Commentary on an article by Marc Schnetzke, MD, et al.: “Determination of Elbow Laxity in a Sequential Soft-Tissue Injury Model. A Cadaveric Study”

O’Driscoll, Shawn W., PhD, MDa

doi: 10.2106/JBJS.17.01448
Commentary and Perspective
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Mayo Clinic College of Medicine, Rochester, Minnesota

aE-mail address: odriscoll.shawn@mayo.edu

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Commentary

The report by Schnetzke et al. documents fluoroscopic measurements of varus-valgus joint angulation with sequential ligament and anterior capsular release. Two messages come from this paper. The first, which is supported by the data, is that fluoroscopic assessment is accurate for determining varus-valgus laxity in the coronal plane in proportion to the degree of soft-tissue release. A strength of this study is its carefully controlled methodology in which humeral rotation and forearm rotation were controlled with transfixing pins and valgus and varus torques were applied using reproducible techniques. Schnetzke et al. correlate these findings with their clinical experience using stress fluoroscopy, which I also routinely use in assessing grossly unstable elbows and fracture-dislocations. I have not used it routinely for simple elbow dislocations that remain reduced following closed reduction.

The second message presented in this paper represents its main weakness. The authors claim that their observations support an idea proposed by Schreiber et al.1 that elbow dislocations occur by a valgus mechanism commencing with medial soft-tissue disruption and then progressing around laterally. The present study involved transfixing the humerus and forearm with pins to prevent rotation, making it impossible to relate this model to elbow dislocations. In a kinematic study of elbow subluxation and dislocation, my colleagues and I established that injuries occur by a coupled 3-dimensional posterolateral rotatory motion pattern involving angulation around all 3 axes and displacement along ≥1 axes2 (Fig. 1). Unfortunately, Schnetzke et al. fail to reference or discuss that work when presenting their argument. In that same investigation, we documented what has come to be known as the “Horii circle” of soft-tissue disruption beginning laterally and progressing around anteriorly and posteriorly to the medial side with increasing degrees of subluxation2 (Fig. 2).

Fig. 1

Fig. 1

Fig. 2

Fig. 2

Schreiber et al. studied public-domain YouTube videos of accidental elbow dislocations1. Their methodology was flawed in that rotational motion of the humerus and forearm while the elbow is in any degree of angulation (whether from reflection or varus/valgus) cannot be determined from 2-dimensional analyses. We proposed the posterolateral rotatory mechanism long before YouTube videos existed and before there was any documented video of an elbow dislocation. Subsequently, we have received videos of elbow dislocations showing a mechanism very similar to that proposed in our original study2.

Careful use of the literature is important when presenting evidence for one’s arguments. The authors incorrectly quote my clinical report of posterolateral rotatory instability as a cadaveric experiment3. They also cite a second paper by Schreiber et al., on magnetic resonance imaging (MRI) analysis of elbow ligaments4. In that paper, Schreiber et al. included elbow dislocations that had occurred up to 8 weeks before the MRI as acute injuries, but soft-tissue changes in a 4 to 6-week-old dislocation are substantial and can hardly be considered acute.

The study by Schnetzke et al. lacks some details, such as where the ligaments were cut. This is important because the ligaments are bonded to the adjacent tendon structures to which loads can be transferred. Schnetzke et al. released the anterior aspect of the capsule but do not mention the posterior aspect of the capsule, which must be released to dislocate the elbow. They did not define dislocation, and in fact the elbows did not dislocate 24% to 50% of the time after completion of all of the releases. This highlights the limitations of their method in studying dislocation.

In conclusion, this paper demonstrates a common phenomenon in which the question that was answered differs from the question that was asked. The authors used a setting “intended to resemble clinical conditions,” but the model did not manage to do so with respect to how an elbow dislocates. The goal of any research study should be to advance our understanding and/or to generate insight. Understanding shapes our beliefs, and our beliefs determine our actions. Ultimately our actions determine patient outcomes, for better or for worse. The one message that we can take from this study is that fluoroscopic assessment is reliable for assessing varus-valgus laxity. I recommend that it also be performed in the sagittal plane to assess posterolateral and posteromedial rotatory instabilities.

Disclosure: The author indicated that no external funding was received for any aspect of this work. On the Disclosure of Potential Conflicts of Interest form, which is provided with the online version of the article, the author checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work (http://links.lww.com/JBJS/E624).

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References

1. Schreiber JJ, Warren RF, Hotchkiss RN, Daluiski A. An online video investigation into the mechanism of elbow dislocation. J Hand Surg Am. 2013 Mar;38(3):488-94. Epub 2013 Feb 5.
2. O’Driscoll SW, Morrey BF, Korinek S, An KN. Elbow subluxation and dislocation. A spectrum of instability. Clin Orthop Relat Res. 1992 Jul;280:186-97.
3. O’Driscoll SW, Bell DF, Morrey BF. Posterolateral rotatory instability of the elbow. J Bone Joint Surg Am. 1991 Mar;73(3):440-6.
4. Schreiber JJ, Potter HG, Warren RF, Hotchkiss RN, Daluiski A. Magnetic resonance imaging findings in acute elbow dislocation: insight into mechanism. J Hand Surg Am. 2014 Feb;39(2):199-205.

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