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Partial knee arthroplasty has enjoyed renewed interest during the past decade. It is helpful to be familiar with the classic and current indications, contraindications, and technical aspects of partial knee arthroplasty, including patellofemoral, medial unicompartmental, and lateral unicompartmental knee arthroplasty. Various implant choices for partial knee arthroplasty can be compared and evaluated based on patient characteristics, design qualities, and reported outcomes. It is also helpful to review the indications and techniques for performing medial or lateral unicompartmental knee arthroplasty in combination with arthroscopically assisted reconstruction of the anterior cruciate ligament.

Unicompartmental knee arthroplasty (UKA) is a popular treatment for unicompartmental knee arthritis. Indications for UKA include mechanical axis of less than 10 degrees varus and less than 5 degrees valgus, intact anterior cruciate ligament (ACL), and absence of femorotibial subluxation. Appropriately selected patients can expect UKA to last at least 10 years. UKA failures are not common and involve technical errors that are thought to be corrected with use of newly developed robotic technology. The surgeon using this technology may be able to arrive at a set target, enhance surgical precision, and avoid outliers. Whether improved precision will result in improved long-term clinical outcome remains a subject of research. In this article, we describe the perioperative management of patients who undergo UKA whether with conventional techniques or robotic arm assistance. We also describe the distinct aspects of preoperative, intraoperative, and postoperative pain management and of intraoperative anesthesia and blood management.

Arthritic knee disease is increasingly more common in the active aging population. The pathology seen in this patient group can run a spectrum of localized degenerative change through tricompartmental arthritis. Nonsurgical options to treat early symptoms are well known and often are effective. When nonsurgical management has failed, surgical intervention often is warranted. Arthroscopic debridement is considered in select patients with mechanical symptoms. Osteotomy continues to have a role in the treatment of young, active patients and may be particularly appropriate in combination with articular cartilage procedures. Unicompartmental and total knee arthroplasty are reliable treatments for patients with advanced stages of degenerative arthritis.

This review summarizes past studies examining the progression of osteoarthritis (OA) of the knee that have led to the conclusion that the disease is slow, progressive, and typically limited to one tibiofemoral compartment. Treatments such as unicondylar knee arthroplasty (UKA) that address the single diseased compartment, preserving bone and soft tissue, seem appropriate. The senior author's minimally invasive surgical technique for performing UKA also is described.

Total knee replacement (TKR) has been well accepted as the definitive knee- salvage procedure. Existence of a predictable, reproducible, salvage procedure has allowed for re-evaluation of other surgical techniques, such as unicompartmental arthroplasty, to prolong or preserve knee function. Knee osteoarthritis has been described as highly segmental, primarily medial, and slowly progressive. Loss of articular cartilage is compensated by development of sclerotic bone, which although it supports weight, it deforms with weight-bearing and produces pain. Ligament imbalance is not compensated. A mini-invasive knee arthroplasty has been developed that features the following three criteria: (1) minimizes physiologic damage, (2) minimizes interference in life style, and (3) avoids interference with future treatment options. Unicompartmental knee arthroplasty can, therefore, be performed as a low-morbidity outpatient procedure while preserving bone for future TKR--in essence, a pre-TKR procedure. Techniques include limited surgical exposure, internal landmarks for prosthetic insertion, and pain management to facilitate out-patient status.

This retrospective study reports the senior author's (J.A.R.) results with minimally invasive unicondylar knee arthroplasty (UKA). A total of 136 UKAs were performed in 1992 for the treatment of unicondylar osteoarthrosis. The surgical technique involves a limited medial parapatellar incision that reduces perioperative morbidity and bone preparation techniques that emphasize preservation of bone for future arthroplasty procedures. At 8 years, 4% of Ahlback stage 2 and 3 patients had undergone revision. Minimally invasive UKA provides a low morbidity alternative treatment for symptomatic medial compartment osteoarthritis.

Between August 1992 and December 1996, more than 700 unicondylar knee arthroplasty (UKA) procedures were done by the senior author (JA.R.), using well-defined patient selection criteria, which is paramount to the outcome of the procedure. The UKA procedure described is done through a smaller incision than that required for total knee arthroplasty (TKA) (3 inches versus 8 inches), thus minimizing blood loss (less than 200 mL), avoiding normal tissue sacrifice (opposite compartment, patellar bone, and cruciate ligaments), and decreasing morbidity (no patellofemoral disruption). The UKA costs less because it is done as an outpatient procedure in 80% of cases; since postoperative physical therapy is minimal or unnecessary, recovery time is shorter (90% independent function at 2 weeks after operation). Whereas TKA can have universal application, UKA is patient specific and cannot replace TKA in all circumstances. Likewise, the techniques for TKA and UKA are not interchangeable. However, with the use of well-defined patient populations and surgical techniques, the intermediate results of UKA have paralleled reported outcomes of TKA.