Case Reports

Dynamic Magnetic Resonance Imaging of Partial-Thickness Retearing of Distal Biceps Tendon After Endobutton Repair

Am J Orthop. 2014 November;43(11):517-520

References

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A much rarer complication of repair is rerupture, which can be asymptomatic or symptomatic.⁵ The most common failure site, discovered during surgery, is the fixation site.^2,13 The true incidence of rerupture is unknown, as MRI typically is not obtained for asymptomatic patients. However, Marnitz and colleagues⁵ recently found increased intratendinous signal and thickness of repaired tendons in the majority of intact postoperative cases and no significant correlation between any MRI features, including tendon rerupture, and clinical measures. This was confirmed in our patient’s case, in which the MRI-based diagnosis of partial retear was not correlated with adverse clinical outcome at 1-year follow-up. Marnitz and colleagues⁵ hypothesized that the increased thickness of the repaired tendon would predispose the patient to impingement.

Our patient had no demonstrable loss of motion during surgery. However, postoperative dynamic MRI clearly showed insufficient room in the pronated radioulnar space for both heterotopic bone and repaired biceps tendon. It is possible that a space-occupying peritendinous hematoma or HO soon after surgery caused early loss of pronation. In a study of 10 volunteers, mean radioulnar distance was 4.0 mm (range, 2.1-6.0 mm) at its minimum in pronation.¹⁴ We used the same technique to measure our patient’s radioulnar space in active semipronation: 7 mm. This diameter was the same as that of the distal biceps tendon during surgery (Figure 3D). Had our patient been in maximum pronation during imaging, we would have expected a further decrease in radioulnar distance. Given the insufficient room in this case, it is possible that, during the attempt to regain full pronation, attritional wear of the repaired biceps tendon occurred with a corresponding maturation of the focus of heterotopic bone. Supporting this theory is the patient’s lack of history of traumatic loading, which would have suggested tensile failure of the repair. By 1-year follow-up, scar-tissue maturation and remodeling had occurred, and there was sufficient overall biomechanical strength to withstand return to normal activity.

The literature includes multiple reports of in vitro biomechanical studies of various types of distal biceps tendon fixation,^15-17 and multiple authors have demonstrated the superior pullout strength of cortical fixation buttons,^18,19 such as the Endobutton. It is important to note that all biomechanical tests are performed in cadaveric specimens and are therefore likely applicable only at time zero, after in vivo repair. In part stemming from the results of these cadaveric biomechanical tests, earlier and more aggressive rehabilitation protocols have been developed with the assumption that time zero is the weakest point.²⁰ If in fact the native repaired biceps tendon is retorn and remodeled, there will exist a nadir in strength because of the high concentration of biomechanically inferior type III collagen in scar tissue (as opposed to the very strong type I collagen in native tendons).²¹ In the absence of complete rerupture, biomechanical strength would continue to improve during scar maturation and continued healing, leading to the typical excellent clinical result, as seen in our case.

This case report illustrates the dynamic MRI appearance of a small focus of HO after distal biceps tendon repair and adds to the time-zero cadaveric data of distal biceps tendon repair. The small focus of HO near the repaired distal tendon may have caused tendon impingement in pronation because of its space-occupying nature and possible attritional tendon wear. A gentler rehabilitation protocol for this pattern of HO, during a period in which biomechanically inferior scar tissue is maturing, may be warranted. Despite the high rates of clinical success with distal biceps tendon repair, there is lack of agreement between ex vivo cadaveric studies and the in vivo scenario. A prospective study involving a larger series of patients with postoperative dynamic MRI examinations would be useful to better understand the true in vivo course of distal biceps tendon repair.