Importance of the posterior bundle of the medial ulnar collateral ligament.
BACKGROUND
There has been a renewed interest in the pathomechanics of elbow dislocation, with recent literature having suggested that the medial ulnar collateral ligament is more often disrupted in dislocations than the lateral ligamentous complex. The purpose of this serial sectioning study was to determine the influence of the posterior bundle of the medial ulnar collateral ligament (pMUCL) as a stabilizer against elbow dislocation.


METHODS
An elbow dislocation was simulated in 5 cadaveric elbows by mechanically applying an external rotation moment and valgus force. Medial ulnohumeral joint gapping was measured at 30°, 60°, and 90° of flexion in an intact elbow after sectioning of the medial collateral ligament's anterior bundle (aMUCL) and then after sectioning of the pMUCL as well.


RESULTS
After sectioning of the aMUCL, the pMUCL was able to stabilize the joint against dislocation. After aMUCL sectioning, the proximal joint space significantly increased by 4.2 ± 0.6 mm at 30° of flexion and 2.6 ± 0.3 mm at 60° of flexion, although it did not dislocate. The gapping increase of 0.9 ± 0.6 at 90° of flexion did not reach significance. After sectioning of the pMUCL (after having already sectioned the aMUCL), all of the specimens frankly dislocated at all flexion angles.


CONCLUSIONS
An intact pMUCL can prevent elbow dislocation and limited joint subluxation to within 6.6 mm. Our findings indicate that repair or reconstruction may be warranted in certain circumstances (ie, residual instability after operative management of a terrible triad injury or after aMUCL reconstruction).
Leni & Peter May Department of Orthopaedic Surgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA. Electronic address: dshukla@gmail.com.
Dave R
DR
Shukla
Maimonides Department of Orthopaedic Surgery, Maimonides Medical Center, Brooklyn, NY, USA.
Elan
E
Golan
Leni & Peter May Department of Orthopaedic Surgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
Philip
P
Nasser
Maimonides Department of Orthopaedic Surgery, Maimonides Medical Center, Brooklyn, NY, USA.
Maya
M
Culbertson
Leni & Peter May Department of Orthopaedic Surgery, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
Michael
M
Hausman
D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D000070637:Collateral Ligament, Ulnar / Q000502:physiology*; D004551:Elbow Joint / Q000502:physiology; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000517:prevention & control; D000092464:Elbow Injuries
Elbow instability; elbow dislocation; elbow trauma; medial collateral ligament posterior bundle; posterolateral rotatory instability; recurrent elbow instability