Unicompartmental Knee Arthroplasty
N.P. Kort, MD, PhD
This thesis concerns technical aspects of unicompartmental knee arthroplasty. Recent years have witnessed a resurgence of interest in unicompartmental arthroplasty, particularly with the introduction of the minimally invasive technique. In the light of the excellent long-term results of the total knee prosthesis, critical evaluation of the procedure is essential.
The three aims of this thesis are to provide an overview of the literature on unicompartmental knee arthroplasty in order to justify the introduction of this device, to evaluate the clinical results, and to focus on the potential pitfalls of the Oxford phase-3 mobile-bearing unicompartmental knee arthroplasty.
Chapters 2,3 and 4discuss the role of unicompartmental knee arthroplasty in the treatment of unicompartmental arthritis. The history of unicompartmental knee arthroplasty is highlighted. Indications and contraindications for the procedure, relevant anatomy, workup, operative technique, complications, outcome and prognosis are subsequently presented. The future of unicompartmental knee arthroplasty and controversies are emphasised.
Chapter 5presents the results of a study of the first 65 patients with unicompartmental knee arthroplasty operated in a community hospital. The follow-up period was 6 to 36 months. In 4 cases a revision was performed, and one patient died 14 months postoperatively due to cardiac arrest unrelated to the operation. All 4 revisions were due to indication or technical failure, suggesting a considerable learning curve for this prosthesis. The results of the remaining 60 patients after a mean follow-up of 12 months (12-36 months) were good to excellent. This led to the conclusion that the use of this device was rectified. Further follow-up is needed, and a total of 200 patients are included in a prospective study at the same hospital to acquire data to evaluate the long-term follow-up results in the future.
Chapter 6 presents the mid-term results of 46 unicompartmental knee arthroplasties in younger patients. Treatment of younger patients with isolated medial compartmental disease of the knee joint remains a challenging therapeutic dilemma. With the refinement of implant design, fixation and the minimally invasive techniques employed with unicompartmental knee replacement, indications have expanded to include its use in young patients. This study shows clinical results comparable to those of the older group. However, in our series more complications than in the designer’s series of younger patients were found. Obesity can cause technical difficulties with increased risks of complications and early failure of this prosthesis; a BMI of 33 or more is seen as a contraindication for the mobile-bearing unicompartmental knee arthroplasty. We conclude that unicompartmental knee arthroplasty is an important option for the treatment of medial compartment disease for patients aged 60 or younger.
In Chapter 7 we present the outcome of an independent prospective series of phase-3 Oxford medial mobile-bearing unicompartmental knee replacements using a minimally invasive surgical technique. Eight surgeons performed 154 procedures in a community-based hospital between 1998 and 2003 for patients aged 60 or older. Seventeen knees were revised, 14 leading to a total knee replacement; in three cases a component of the unicompartmental knee prosthesis was revised, resulting in a survival rate of 89%. This study shows that mobile-bearing unicompartmental knee replacement using a minimally invasive technique is a demanding procedure. The study emphasises the importance of routine in surgical management and strict adherence to indications and operative technique to reduce outcome failure.
Chapter 8 presents the analysis of a potentialerror in using femoral intramedullary rods of different lengths in unicompartmental knee arthroplasty for positioning the femoral component. The results of our study demonstrate that the short and long intramedullary femoral rods used for the Oxford phase-III unicompartmental knee arthroplasty may result in an excessive flexion alignment error of the femoral component. Extramedullary alignment for the Oxford phase-3 unicompartmental knee arthroplasty is not mentioned in the current literature, but a small yet informed opinion group is now moving towards extramedullary alignment. Understanding of both alignment possibilities and experience with the visual alignment of the femoral drill guide is crucial toward minimising potential errors in alignment of the femoral component.
Chapter 9presents the pitfalls, tips and tricks of the Oxford phase-III unicompartmental knee prosthesis. The introduction of minimally invasive techniques emphasises smaller skin and capsular incisions, limited violation of the extensor mechanism or suprapatellar pouch, better functional results and reduced morbidity, and decreased rehabilitation time. Nevertheless, with this minimally invasive technique the visual field is restricted, making the mobile-bearing unicompartmental knee arthroplasty a demanding procedure.
In Chapter 10 a case-report opens with a short description ofpopliteal vascular injury and compartment syndrome of the lower leg. These are rare but disastrous complications of knee arthroplasties. Early diagnosis and treatment are of paramount importance in preventing the devastating consequences of these conditions. To our knowledge, these complications have not been reported previously in the literature after unicompartmental knee arthroplasty. Low index of suspicion may delay the diagnosis, as popliteal vascular injury and compartment syndrome are not well recognised as possible complications of unicompartmental knee arthroplasty. We believe that orthopaedic surgeons should be aware of the possibility of popliteal vascular injury and compartment syndrome after unicompartmental knee replacement, so they can take preventive measures or enhance rapid recognition.
In a second case-reportin Chapter 10 new light is shed on the challenging therapeutic dilemma of a young patient with incongruity of the articular surface due to an OD lesion and advanced unicompartmental degenerative knee joint disease. Following unicompartmental knee replacement an excellent 2-year follow-up was noted. Unicompartmental knee replacement can offer patients a successful short-term treatment option.
When non-operative and arthroscopic procedures fail, the surgeon may consider high tibial osteotomy, unicompartmental arthroplasty or total knee arthroplasty. Unicompartmental knee arthroplasty appears to result in better function and pain relief, less morbidity and higher patient satisfaction compared to high tibial osteotomy and total knee arthroplasty. The long-term survival rate for unicompartmental knee arthroplasty is better than that for HTO, and might be as good as the long-term survival rate of a total knee arthroplasty.
With strict indications and attention to surgical technique, unicompartmental knee arthroplasty has become a valuable treatment for unicompartmental knee arthritis. Initial experiences with the Oxford unicompartmental knee prosthesis using a minimally invasive approach have been good. The complications described can be explained by experience related to the operative technique and patient selection. The current results of the Oxford unicompartmental knee prosthesis through a minimally invasive approach justifyfurther use of this treatment method.Being 60 years of age or younger does not seem to be a contraindication for this procedure. Obesity is a relative contraindication with an increased risk of complications and early failure of this prosthesis.For patients aged 60 and older, a survival rate of 89% was noted. This study shows that mobile-bearing unicompartmental knee replacement using a minimally invasive technique is a demanding procedure. The study emphasises the importance of routine in surgical management and strict adherence to indications and operative technique used to reduce outcome failure.
As the population ages and grows, the number of people with symptoms attributable to unicompartmental knee osteoarthritis will increase. Unicompartmental knee arthroplasty offers a more physiological alternative to HTO and total knee arthroplasty. Progress has been made in the design and implantation of unicompartmental knee arthroplasty, in particular for the medial compartment. However, complications do occur, and surgical expertise and knowledge of the presented pitfalls, tips and tricks are still important factors in determining a successful outcome.