This study attempts to identify a relationship between cubitus varus and tardy posterolateral rotatory instability. It is a multi-center study including 11 surgeons from 9 institutions. 25 elbows in 24 patients with cubitus varus were studied following a pediatric distal humeral fracture (22 limbs) or from a congenital anomaly (3 limbs). The average varus deformity was 15 degrees (range 0-35 degrees). Treatment consisted of reconstruction of the LCL and osteotomy in 7 limbs, ligament reconstruction alone in 10 limbs, osteotomy alone in 4 limbs, and total elbow arthroplasty in 1. All patients had an improvement in their pre-operative Mayo Elbow Performance Score from 59 points (range, 30 – 85 points) to a post-operative score of 87 points (range, 50 – 100 points). 19 of 22 limbs had good or excellent results at a mean follow-up of 3 years. Two poor results were in patients receiving workman’s compensation and one fair result in a patient with a 7 degree residual varus deformity. There was 1 non-union which healed following revision ORIF and bone grafting.
This article adds further understanding to previous reports of posterolateral rotatory instability associated with cubitus varus. The authors present a hypothesis for the development of this instability due to the medial displacement of the mechanical axis which results in increased tensile strength in the lateral collateral ligament. It also displaces the triceps force vector medially to effectively put external rotatory torque on the ulna and increases stress on the lateral collateral ligament. Essentially all treatments in the non-workman’s compensation patients resulted in good to excellent results whether an osteotomy and/or ligament reconstruction were performed. The authors, however, report that in their experience, they found that either osteotomy alone, or ligament reconstruction alone, has a high likelihood of failure in the presence of a large (greater than 15 degree) osseous deformity. This data, however, is not presented, or substantiated, by the information provided in the article. Intuitively, however, one would expect that with long-term follow-up that recurrence of posterolateral rotatory instability would occur if the varus alignment is not corrected. At an average of only 3-year follow-up, recurrence was not yet observed in the ligament reconstruction alone patients.