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A Cadaveric Analysis of Mallet Finger Splinting and Associated Subluxation
Jacob Glueck, BA
1,2, Jacob Johnson, BS
3, Katherine M. Connors, MD
4, Nora Kinslow, OTR/L
2, Talia O'Kane, OTR/L
2, Julie Katarincic, MD
3; Joseph A Gil, MD
5(1)The Warren Alpert Medical School of Brown University, Providence, RI, (2)University Orthopedics, Providence, RI, (3)Brown University, Providence, RI, (4)SUNY Downstate Health Sciences University, Brooklyn, NY, (5)Orthopaedic Surgery, Warren Alpert School of Medicine, Brown University, Providence, RI
IntroductionBony mallet injuries occur when an overwhelming flexion force causes avulsion of the extensor tendon and a fragment of the distal phalanx. Conservative management with splinting is typically preferred, but residual volar subluxation has been reported. We hypothesized that splinting the distal interphalangeal (DIP) joint in hyperextension would result in more cases of volar subluxation. This cadaveric study aimed to compare rates of volar subluxation in bony mallet injuries splinted at 0° versus 15° of hyperextension.
Materials and MethodsNine cadaveric fingers were prepared with mallet finger-type avulsion fractures involving approximately 20% of the articular surface of the distal phalanx. DIP joint stability was assessed with fingers splinted either in full extension or in 15° of hyperextension to evaluate for volar subluxation of the distal phalanx. Following complete resection of the collateral ligaments, joint stability was re-evaluated using both splinting positions. Lateral fluoroscopic images of the splinted fingers were independently reviewed by three orthopedic hand surgeons to determine the presence of joint subluxation. Subluxation was defined as any breach of the articular surface of the middle phalanx head by a line drawn tangent to the dorsal cortex of the distal phalanx. The frequency of subluxation between the two splinting methods was compared using McNemar's test.
ResultsAll nine specimens remained stable in both splinting positions (full extension and 15° hyperextension) with and without intact collateral ligaments. There were no cases of subluxation under either condition, resulting in no discordant pairs. McNemar's test could not be performed due to an undefined test statistic.
ConclusionsDespite concerns that splinting a bony mallet injury in 15° of hyperextension could lead to volar subluxation of the distal phalanx, no subluxation was observed with either splinting position, regardless of whether the collateral ligaments were intact. This suggests that cases of volar subluxation following splinting may stem from improper splint application or, more commonly in pediatric patients, from increased joint laxity. Further research is warranted to better understand why certain populations are more susceptible to volar subluxation after splinting a bony mallet injury.
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