Early failure of the porous coated anatomic cemented unicompartmental knee arthroplasty. Aids to diagnosis and revision.
Unicompartmental knee arthroplasty (UKA) is performed less frequently than total (tricompartmental) knee arthroplasty (TKA). This study examined the range of presenting symptoms and usefulness of diagnostic tests to determine the failure mode; the outcome of surgical revision of failed UKA is also reported. From a consecutive prospective series of 43 Porous Coated Anatomic (Howmedica, Rutherford, NJ) UKAs performed between 1985 and 1992 and followed for an average of 64 months, 12 cases have come to revision surgery (28%). The average time to failure was 37 months. Symptoms preceded revision surgery by an average of 10 months. The most common presenting symptom was pain (100%), followed by swelling (92%), reduced range of motion (42%), instability (42%), and clicking (17%). Failure was caused by polyethylene wear in 50%, loosening of the femoral component in 42%, and progression of patellofemoral arthritis in one patient. The combination of single leg standing anteroposterior radiographs and supine lateral radiographs detected most causes of UKA failure. A bone scan was confirmatory in every case of suspected loosening of the femoral component. Arthroscopy diagnosed polyethylene wear in two cases and progression of joint arthritis in one case and was not helpful in one case. Revision surgery was done with primary TKA components, and follow-up periods averaged 27 months. Bone stock deficiency was found in 58%, but required bone-grafting in only one case. Revision surgery successfully restored pain-free function and range of motion in all cases. Two-year postrevision Hospital for Special Surgery scores are equal to those for primary TKA. Survivorship analysis showed a 33% failure rate at 57 months after Porous Coated Anatomic UKA when revision was the endpoint and a 41% failure rate when unsatisfactory clinical status was the endpoint. Regular follow-up evaluation is suggested for the Porous Coated Anatomic UKA.