Unicompartmental Knee Arthroplasty
N.P. Kort, MD, PhD
Kort ,Nanne P., MD, van Raay, Jos J.A.M., PhD, van Horn, Jim J.
Osteochondritis Dissecans of the knee can be treated operatively as well as non-operatively ; many treatment options are available. We describe the successful mid-term result of a unicompartmental knee arthroplasty as treatment of a large Osteochondritis Dissecans in the medial femoral condyle of a young man.
Initial results of unicompartmental knee arthroplasty were discouraging,11-13but advancing developments in patient selection, surgical techniques and implant design have improved clinical outcomes over the past thirty years.14-16The indications for the Oxford Phase III ® unicompartmental knee with a mobile bearing device (Biomet) are clearly formulated.17The primary indication is medial compartment osteoarthritis with the following conditions: the anterior cruciate ligament should be functionally intact; flexion limitation should be less than 15 degrees; varus deformity should be correctable; and the original cartilage in the lateral compartment should have full thickness. Observed cartilage damage in the patellofemoral joint, age, activity level, obesity and chondrocalcinosis are not considered to be contraindications for this specific prosthesis.
In October 2000, a 42 year-old adult came to our hospital for evaluation of a 28-year history of pain in his right knee. His pain had no obvious traumatic cause. His pain clearly has no traumatic cause. Between 1972 and 1994 his right knee was treated operatively three times because of Osteochondritis Dissecans of the medial femoral condyle: in 1972 he had an arthrotomy in which a loose bone fragment was removed, and in 1986 and 1994 an arthroscopic debridement that involved bone drilling in the OD crater. He is 196 cm tall and weighs 90 kg. The initial physical examination revealed no knee instability or meniscus pathology. the leg had a slight varus axis. The knee had a good range of motion of 145° flexion and 5° extension deficit. The patient indicated specifically that the pain was around the medial compartment.
X-rays revealed a small bone lesion without peripheral bone sclerosis in the right medial femoral condyle (Fig 1). The MRI showed a lesion in the right medial femoral condyle with a low intensity on the T1-weighted image and a high intensity on the T2-weighted image. Technetium scan revealed a high uptake in the medial femoral condyle.We advised the patient to discontinue his sporting activities and started conservative treatment. At four months after his first visit to our hospital, his right-knee pain continued.
In February 2001, arthroscopic surgery on the right knee joint was performed. During the arthroscopy a crater of 2.0 by 3.5 cm in the medial femoral condyle in the weight-bearing articulating area was found; the cartilage of the lateral femoral condyle was intact and the patellofemoral compartment appeared normal. The menisci were intact. Because earlier bone drilling failed and the OD lesion was too big for autologous osteochondral transplantation, we discussed the high tibial osteotomy option. Our patient definitely did not want a high tibial osteotomy and insisted on a unicompartmental knee arthroplasty. An Oxford mobile-bearing Phase III ® unicompartmental knee prosthesis was placed using a minimally invasive operative approach, without violating the suprapatellar pouch and the quadriceps mechanism and without everting the patella. The surgery was performed under tourniquet control and using an anteromedial approach. The incision was 8.5 cm long. Operating time was 65 minutes. The classic OD lesion in the medial femoral condyle did not influence appropriate positioning of the spigot, allowing adequate balancing of the knee through the milling of the femoral condyle for the flexion/extension gap. The defect did not require autologous bone grafting. Postoperative X-rays of the knee evidenced a 10° valgus angle of the femoral component, which is acceptable according to the operating instructions for this prosthesis. The patient had full range of flexion (flexion/extension of 140-5-0) after two weeks. There were no complications.
The 4-year postoperative follow-up standing anterior/posterior (Fig 2A) and lateral (Fig 2B) radiographs of the right knee show no radiolucent lines around the tibial and femoral components and no degenerative changes in the lateral compartment. There is a neutral alignment of the leg. There was no difference compared to the immediate postoperative radiographs.
At the 4-year follow-up, the Knee Society function score was 80 (preoperatively 70), the mean KSS is 87.5 (preoperatively 49). The WOMAC pain score is 85 (preoperatively 40). The WOMAC function score is 74 (preoperatively 44). With respect to the SF-36 questionnaire, physical functioning improved from 25 points preoperatively to 100 points and role-physical from 40 to 70 points after four years. Range of motion of the knee is 140° flexion and the 5° extension deficit remains unchanged.
Osteochondritis Dissecans (OD) lesions affecting children frequently heal on their own,7but adult forms of OD in the knee rarely heal spontaneously.21Those lesions that do not heal often lead to separation of the segment and a consequent increasing incongruity of the knee articular surface. Progression of this process can lead to degeneration of the entire joint. Optimal treatment for OD still remains controversial.5
Especially young patients with an incongruity of the knee articular surface due to an OD lesion and severe unicompartmental osteoarthritis tend to present a difficult and challenging therapeutic dilemma. High tibial osteotomy and minimally invasive unicompartmental knee arthroplasty are among the treatment options for medial compartment osteoarthritis. The high tibial osteotomy option is preferred for young active patients, but was firmly rejected by our young patient. The other cartilage-sparing procedures failed, therefore our patient insisted on a unicompartmental knee arthroplasty.
Placement of a unicompartmental knee arthroplasty relieves pain, restores limb alignment and improves function with minimal morbidity, without interfering with future total knee arthroplasty.18Using minimally invasive operative techniques, unicompartmental knee arthroplasty is being performed with increasing frequency on younger patients with medial osteoarthritis.22Unicompartmental knee replacement using minimally invasive techniques is a proven concept for the treatment of medial osteoarthritis of the knee as long as the described indications and surgical techniques are strictly followed.15, 17, 18
When nonoperative and operative (non-arthroplastic) treatments for OD lesions of the knee fail and progression to unicompartmental osteoarthritis can be expected, unicompartmental knee replacement can offer both patient and surgeon a successful short- to mid-term treatment option.23This case report describes the youngest patient (age 43) reported in the literature with Osteochondritis Dissecans of the knee treated with a mobile-bearing unicompartmental knee arthroplasty using a minimal invasive operative technique. Only time and careful follow-up will show the long-term outcome for this relatively young patient.
Standing anteroposterior radiograph of the right knee showing a typical image of OD of the medial femoral condyle.
4-year postoperative standing anteroposterior (A) and lateral (B) radiographs of the right knee showing an Oxford unicompartmental medial knee replacement.
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