Medial Malleolus Osteotomy with OATS for Ankle Osteoarthritis
A medial malleolus osteotomy with OATS (Osteochondral Autograft Transfer System) is a joint-preserving surgical technique that involves cutting the medial malleolus to access deep osteochondral lesions of the talus, followed by transplanting autologous osteochondral plugs from non-weight-bearing areas to reconstruct the damaged cartilage and underlying bone.
Surgical Technique Overview
The procedure consists of two main components that work synergistically:
Medial Malleolar Osteotomy Component
The osteotomy creates surgical access to posterior and medial talar dome lesions that cannot be adequately visualized or treated through arthroscopy alone 1, 2.
A partial step-cut technique involving the anterior one-third to two-thirds of the medial malleolus provides adequate intra-articular exposure while avoiding injury to the posterior tibial tendon 2.
The triplane osteotomy approach offers superior stability and lower complication rates compared to traditional straight osteotomy techniques, with healing typically occurring within 7-8 weeks 1, 2.
OATS (Autologous Osteochondral Transplantation) Component
Osteochondral plugs are harvested from non-weight-bearing areas of the talus itself, rather than from the knee, which reduces donor site morbidity 1.
The grafts are press-fit into the prepared recipient site on the talar dome where the osteochondral lesion has been debrided 1.
This technique addresses both the cartilage surface defect and the underlying subchondral bone pathology simultaneously 1.
Clinical Indications
This combined procedure is specifically indicated for:
Symptomatic osteochondral lesions of the talus (OLTs) that are inaccessible through standard arthroscopic approaches, particularly posterior-medial lesions 1, 2.
Lesions with significant size (mean 141.5 mm² in published series) that require structural bone grafting in addition to cartilage restoration 1.
Patients with preserved ankle joint space and minimal to moderate osteoarthritis who are candidates for joint preservation rather than fusion or replacement 3, 4.
Expected Outcomes
Based on the available research evidence:
Pain scores improve dramatically, with VAS scores decreasing from approximately 5.6-6.4 preoperatively to 0.7-1.8 postoperatively 1, 2.
Functional outcomes show significant improvement, with AOFAS ankle-hindfoot scores increasing from 54-55 preoperatively to 84-85 postoperatively 1, 2.
Return to sport occurs at a mean of 7.4 months, with 91% of patients returning to their previous activity level 1.
Weight-bearing activity typically resumes at 8 weeks postoperatively, with osteotomy healing confirmed by CT imaging 1.
Critical Technical Considerations
The partial step-cut osteotomy technique is superior to traditional straight osteotomy because it provides adequate exposure while maintaining posterior cortical continuity, which prevents displacement and protects the posterior tibial tendon 2.
Harvesting grafts from the non-weight-bearing talus rather than the knee eliminates donor site complications at the knee and provides better size-matched osteochondral plugs 1.
Meticulous fixation of the osteotomy with screws is essential, though screw placement must avoid the posteromedial ankle to prevent flexor hallucis longus tendon irritation 1.
Complications and Pitfalls
Overall complication rates are low (4.3% in one series), significantly better than traditional osteotomy techniques 1.
Malunion risk is minimized with the step-cut technique, though slight incongruence (≤1mm displacement) may occur in approximately 21% of cases without clinical significance 2.
Hardware irritation can occur if screws are placed too posteriorly, potentially requiring removal 1.
Distinction from Supramalleolar Osteotomy
It is crucial to distinguish this procedure from supramalleolar osteotomy (SMOT), which is a different operation:
Supramalleolar osteotomy is performed proximal to the ankle joint in the distal tibia to realign the mechanical axis and redistribute load in asymmetric ankle osteoarthritis 3, 5, 4.
SMOT does not involve opening the joint or addressing focal cartilage lesions; instead, it corrects varus or valgus deformity to shift load away from the arthritic compartment 3, 4.
The medial malleolar osteotomy with OATS directly accesses and repairs the intra-articular pathology rather than correcting extra-articular alignment 1, 2.