Currently, simple lateral closing wedge osteotomy, step-cut osteotomy, and dome rotational osteotomy are commonly performed for cubitus varus deformity. They can provide satisfactory results in children due to their remodeling capacity and rapid healing ability [5, 6, 11]. However, the distal humerus in adults has large and protrusional condyles. In addition, surgical correction associated with sufficient medial shift of the distal fragment is necessary to achieve satisfactory correction and prevent S-shaped deformity because adults have less healing ability and remodeling capacity than those who are younger [9, 10]. So far, only a few studies have dealt with correction of cubitus varus deformity in adult patients. Labelle et al.  have reported that lateral closing wedge osteotomy is difficult to achieve strong internal fixation. In addition, protrusion of the lateral condyle or S-shaped deformity of the elbow may develop postoperatively [20, 21]. Buß et al.  have recommended supracondylar humerus closed wedge osteotomy with a locking plate fixation in adults. Moon et al.  have suggested medialization of the distal fragment for an effective treatment of cubitus varus deformity with minimized risk of ‘lazy S’ deformity. Oblique closing wedge osteotomy with lateral plating can also be used as a modified procedure to resolve these issues. However, Gong et al.  have reported that this technique could result in shortening of the humerus due to larger bone resection than other osteotomies. The simple step-cut osteotomy does not allow translation of the distal fragment after osteotomy. In addition, it induces lateral condylar prominence after correction. This requires a long-term cast immobilization which is not desirable in adults . Dome osteotomy can correct the deformity in coronal and horizontal planes simultaneously with just one bone cut . However, the contracture of the soft tissue around the deformed elbow in adults can often make it difficult to correct the deformity .
On the other hand, translation step-cut osteotomy is a simple osteotomy that enables three-dimensional correction of coronal, sagittal, and rotational deformities. The planned osteotomy can be easily performed with the triangular template created before surgery. A triangular wedge-shaped surface created by osteotomy provides firm stability . Y plate provides a sufficiently rigid fixation that permits early active motion and prevents possible complications related to implant failure in cubitus varus deformity of adults [13, 26, 27]. Supplementary bone grafts of excised triangular fragments can also be used to improve bone union. A posterior approach is familiar to elbow surgeons. It has a better surgical field. Supine position is also easy to check whether correction angle achieved by the osteotomy is sufficient or not using an image intensifier with a gross examination.
In the present study, we could correct a mean of 26° of cubitus varus deformity with this osteotomy in adults. The lateral prominence index (LPI) also improved by 9.6% from its preoperative value, showing no significant difference compared to LPI of a normal elbow. None of our patients had lateral prominence after deformity correction. Their post-correction radiological indicators were maintained without significant differences until the final follow-up (Table 3).
Meanwhile, O’Driscoll et al.  have suggested that for a tardy posterolateral rotatory instability caused by cubitus varus, osteotomy alone may be adequate if there is only subtle instability or if the patient places only limited demands on the elbow. Carlo et al.  have suggested that even high function demand patients (for whom ligament reconstruction is indicated) should be initially treated with a brief period of rehabilitation for at least 3 months. In the present study, although the cubitus varus deformity before surgery had a mean value of 26°, only corrective osteotomy was performed since there was no posterolateral instability.
If a flexion contracture or hyperextension elbow is present, it can be corrected by excising the bone fragment in the posterior part of the V-shaped proximal part during the initial osteotomy. Subsequently, we could correct additional flexion contracture or hyperextension elbow. This study showed good clinical results. All patients had good or excellent results based on DASH and MEPS during the final follow up.
Meanwhile, two cases with poor clinical results were noted based on the Oppenheim criteria. One had a high radial nerve palsy after the primary surgery. Chung et al.  have reported a high risk of radial nerve injury with the standard posterior approach during a three-dimensional osteotomy. The radial nerve gives muscular branches to long, medial, and lateral heads of the triceps before lying in a spiral groove on the posterior aspect of the humerus. It then pierces the lateral intermuscular septum to enter the anterior compartment [29, 30]. Uhl et al.  have reported that the distance from the articular surface (at the mid-portion or dip of the trochlea) to the radial nerve as it crosses the middle of humerus is 15.8 cm in men and 15.2 cm in women. The mean distance to the point where the radial nerve pierces the septum is 10.0 cm in men and 9.4 cm in women . Carlan et al.  have found that the radial nerve is immobilized by obliquely oriented lateral intermuscular septum well distal to its entrance into the anterior compartment. It is known that the radial nerve has very little mobility in this area. Thus, we performed careful dissection to avoid the risk of radial nerve injury during the operation. Nevertheless, radial nerve palsy occurred in one case. Exploration finding showed that the radial nerve was compressed at the anterolateral aspect of the osteotomy site. This might have occurred while medially translating the lateral cortex of the distal fragment after osteotomy. Although iatrogenic injury to peripheral nerves and brachial artery is usually preventable with a posterior approach, careful osteotomy or translation of the distal fragment would be needed due to the possibility of a radial nerve injury.
Another case showed delayed union with screw loosening during the postoperative period. In a previous study of Chung et al. , callus was detected at a mean of 4.4 weeks after a three-dimensional corrective osteotomy. Xiao et al.  have reported that bone union is achieved for all cases at a mean of 10 weeks after supracondylar closing wedge osteotomy. Lim et al.  have reported that osseous union of the closing wedge osteotomy site is obtained for all patients at an average of 17.5 weeks after the operation.
In the present study, all patients except one achieved osseous union of the osteotomy site at a mean of 12.7 weeks. The recovery time to the final range of elbow motion was a mean of 14.3 weeks postoperatively. These clinical results demonstrate that translation step-cut osteotomy using Y plate provides a sufficiently rigid fixation that permits early active motion for adults. Nevertheless, patient 9 had delayed union with screw loosening. Since he had severe deformity compared to a normal elbow, primary surgery was performed with the goal of correction 30° of HEW and internal rotation. The large correction angle inevitably caused a lack of bone contact area during correction. It was also technically demanding to apply a well-contoured plate on the distal humerus. Re-fixation was undertaken using dual plates and concurrent autogenous bone grafting at 6 months after the initial surgery. Other previous reports have shown that osteotomy has similar difficulties due to the lack of bone contact area for severe rotational deformity correction. Complete derotation is difficult to maintain stable fixation stable. It may cause loss of correction . Meanwhile, residual rotation deformity is well tolerated because it is easily compensated by rotation of the shoulder joint. We also agree that complete correction of rotation deformity is not always required. Dual plating can be an alternative choice for osteotomy stabilization in adults requiring large correction angles.
Limitations of this study included its retrospective design, small sample size, short-term follow-up, and the lack of comparative osteotomy groups. The lack of preoperative functional assessment was another limitation of this study. However, the management of distal humeral fracture in children has improved. Cubitus varus deformities are now uncommon in adults. We believe that our study for this deformity in adults will help other surgeons because of its clinical applicability. In future studies, more cases should be assessed and objectivity should be improved by monitoring changes in functional outcomes over time instead of performing one-time assessments.