Autologous Osteochondral Transplantation (OATS): Large SONK lesion in a 60-Year-Old Female

Key message 

Autologous osteochondral transplantation (OATS) is a viable option among cartilage repair procedures, offering better long-term outcomes compared to microfracture.

This case presentation is intended for both patients and surgeons, providing valuable insights to aid in decision-making.

(Note: Although SONK [Spontaneous Osteonecrosis of the Knee] is a commonly used term, it is a misnomer. SIFK more accurately reflects the underlying pathophysiology.)

1st visit 

A 60-year-old female presented with an antalgic gait (severe pain that limits normal gait), to the extent that she could barely walk without a crutch. 

The lower extremity alignment was neutral. 

The physical examination revealed a significant knee effusion and pain on range of motion. 

As shown above, preoperative magnetic resonance imaging (MRI) demonstrated a large, collapsed osteonecrotic lesion of the medial femoral condyle with bone marrow edema.

This findings were consistent with an untreated SIFK (Subchondral Insufficiency Fracture of the Knee) lesion. 

Lateral compartment structures and ligaments were relatively intact and functional.

Treatment decision-making

Given the symptomatic nature of the lesion and the severe structural defect, surgical treatment was indicated.

For these types of unicompartmental lesions confined to the medial femoral condyle, the following treatment options can be considered:

1. Total Knee Arthroplasty (TKA)

  - Replaces the entire articular surface with a prosthesis.

  - Proven long-term longevity.

  - Technically easy procedure

2. Unicompartmental Knee Arthroplasty (UKA)

  - Replaces only the defective portion of the knee.

  - Shorter longevity compared to TKA, but involves a lower surgical burden.

  - Preserves the functional lateral compartment.

3. High Tibial Osteotomy (HTO)

  - Unloading the defective medial knee by realigning the lower limb toward the lateral compartment (valgization).

  - Reduces pain, although some discomfort may persist due to the large defect.

4. Variable Cartilage Repair Procedures

• Includes several different repair options. 

 

Given the large osteochondral defect, arthroplasty was initially considered. However, the patient was reluctant to undergo arthroplasty due to her relatively young age. 

Moreover, because the alignment was neutral, HTO was not necessary. 

For this patient, autologous osteochondral transplantation (OATS) emerged as the treatment of choice, as it simultaneously replaces both bone and cartilage.

  

Surgical procedures 

Intraoperatively, a very large osteochondral defect was observed, corresponding to the preoperative CT scan findings.

Not only was the overlying cartilage damaged, but the underlying bone marrow also appeared necrotic, exhibiting a dark yellow coloration, necessitating replacement.

 

Multiple autologous osteochondral grafts were harvested from the non-weightbearing portion of the femoral trochlea. Extreme caution was taken to ensure a flush articular surface.

The gaps between the osteochondral plugs were filled with high-concentration atelocollagen.

Rehabilitation

For patients who undergo multiple osteochondral plug transplantations, cautious rehabilitation is essential.

Immediate full range of motion exercises and quadriceps strengthening were encouraged. However, strict non-weightbearing for 3 months was emphasized in this patient, allowing only crutch-assisted ambulation.

Postoperative outcome 

The patient was allowed to walk without a crutch at 3 months postoperatively and became completely symptom-free by 6 months. 

As shown in the 6-month postoperative MRI above, the autologous osteochondral plugs had successfully achieved complete union at the recipient site with no evidence of bone marrow edema.

 

 

Compared to the preoperative images below, the large osteochondral defect was fully restored and successfully healed. 

The patient has now been followed up for 1.5 years postoperatively and remains satisfied with the clinical outcomes.

Conclusion 

Autologous osteochondral transplantation (OATS) is an efficient procedure that enables the simultaneous replacement of both bone and cartilage in a single stage.

Unlike other cartilage repair procedures, OATS does not require time for cartilage regeneration—only time for healing (bone union of the transplanted plugs). 

Hyo Yeol Lee, MD., PhD.

Department of Orthopaedic Surgery (Knee Surgery and Sports Medicine)

Chungbuk National University Hospital