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© 2003 The Journal of Bone and Joint Surgery, Inc.
Unicompartmental Arthritis of the Knee
Investigation performed at the Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts, and Boston Medical Center, Boston, Massachusetts
• Unicompartmental arthritis of the knee is a degenerative condition characterized by abnormal articular cartilage in the medial or lateral part of the tibiofemoral joint, which may be associated with meniscal disruption, ligamentous instability, and limb malalignment. • Nonoperative treatments for unicompartmental degenerative arthritis of the knee include oral and injectable medications, weight loss, exercise, physical therapy, canes, crutches, braces, and orthoses. • Arthroscopy for unicompartmental arthritis of the knee can provide a clinical benefit in terms of reduced pain and improved function for patients with mechanical symptoms, mild degenerative disease, and minimal or no malalignment. Meniscal tears, loose bodies, osteophytic spurs, or chondral flaps can cause mechanical symptoms, which can be treated successfully with arthroscopy. • Proximal tibial valgus osteotomy and distal femoral varus osteotomy for treatment of unicompartmental arthritis of the knee can realign a deformed limb, reduce pain, and improve function for active, high-demand patients with a projected life expectancy of twenty years or more. • As a patient's life expectancy and expectations for activity decrease as a result of age and disease, unicompartmental and total knee arthroplasty provide predictably successful surgical options for the treatment of unicompartmental arthritis of the knee. Arthritis of the knee is a common clinical problem: 2% of the United States population older than seventeen years of age and 10% of Americans over sixty-five years of age have clinically relevant arthritis of the knee 1 . Arthritis of the knee causes pain and restricts activity, and patients with arthritis are twice as likely to seek medical care as are their peers without arthritis 2 . Unicompartmental arthritis of the knee is defined as a condition characterized by degenerative articular cartilage in the medial or lateral aspect of the tibiofemoral joint, which may be associated with meniscal disruption, ligamentous instability, and malalignment 1-3 . The most common symptom of unicompartmental arthritis of the knee is pain confined to the affected compartment, which may be associated with swelling, effusion, instability, impingement, crepitus, stiffness, and malalignment. Radiographic findings of unicompartmental arthritis of the knee may include joint space narrowing, squaring of the femoral condyle, subchondral sclerosis, intercondylar spurring, joint line osteophytes, and varus or valgus malalignment of the affected limb 3,4 . We will review the natural history of unicompartmental arthritis of the knee in adults and discuss nonoperative and operative treatments. Isolated patellofemoral osteoarthritis and inflammatory arthritides will not be discussed. We believe that early diagnosis and early treatment may improve the functional well-being and long-term outcome in patients with unicompartmental arthritis of the knee.
The specific cause of degenerative arthritis of the knee is not clear, but when it occurs in an active patient, it is generally progressive 5,6 . Trauma is frequently a cause of the degenerative process, which results in deterioration of articular cartilage and symptomatic degenerative arthritis 7-12 . The degenerative process may include articular cartilage damage (chondrocytes and matrix), meniscal damage, ligament damage, and joint incongruity. Angular malalignment may contribute to the development and progression of unicompartmental arthritis of the knee by overloading the medial or lateral aspect of a tibiofemoral joint with abnormal articular cartilage. The spectrum of articular cartilage damage can range from minimal to severe. Small, superficial, focal defects of articular cartilage that are not associated with symptoms should be distinguished from extensive, full-thickness cartilage defects associated with symptomatic degenerative arthritis 13-15 . The location and size of articular cartilage defects determine the severity of symptoms and the need for treatment 15 . When an articular cartilage lesion is less than 2 to 3 cm 2 in area, or a lesion has good peripheral cartilage support (shoulders), it may take several years before degenerative arthritis develops 13-15 ( Table I ). Minas and Nehrer 15 suggested that articular cartilage defects in which the exposed subchondral bone is not supported by a peripheral cartilage border are often symptomatic and deteriorate more quickly. Symptomatic lesions of articular cartilage often progress with age, and treatment of isolated chondral or osteochondral defects may decrease or minimize the development of degenerative arthritis 13,15-18 .
The history and physical examination can provide useful information concerning joint line tenderness, meniscal damage, ligamentous instability, and malalignment associated with unicompartmental arthritis of the knee. Dynamic gait analysis can provide additional information about ligamentous insufficiency and malalignment. Before a specific treatment is selected, inflammatory arthritides should be excluded as a cause of unicompartmental arthritis.
Radiographic evaluation is an essential component of the diagnosis of unicompartmental arthritis of the knee. Radiographs made in the anteroposterior plane with the patient bearing weight
19 as well as lateral, tangential patellofemoral, and tunnel views
20 allow objective evaluation of the three compartments of the knee (
Table II ). However, these radiographs may not accurately predict the status of the articular cartilage as seen at arthroscopy
21,22 . Radiographic sensitivity with regard to showing deterioration of the articular cartilage may be improved by making posteroanterior views with the patient bearing weight and with the knee flexed 40° to evaluate the posterior aspects of the femoral condyles and tibial plateau, especially in the lateral compartment
17,19 . Radiographs of the hip, knee, and ankle made on one long film with the patient standing allow calculation of the static mechanical axis and identification of any angular deformity of the involved limb. The patient must be able to place full weight on the affected limb for a true measurement of limb deformity to be obtained. The mechanical axis is determined by a line drawn from the center of the femoral head to the center of the knee joint and a line drawn from the center of the knee joint through the center of the ankle joint
19,23 . A mechanical axis of 0° to 3° of varus is considered to be within normal limits
19,23 . Generally, a varus or valgus deviation of
Oral Medications, Nutritional Supplements, and Topical Analgesics Analgesic medications without anti-inflammatory properties, such as acetaminophen, are the initial medications used to treat degenerative arthritis of the knee. These medications are effective in relieving pain, they are associated with a low incidence of side effects, and they are inexpensive 24-26 . Nonsteroidal anti-inflammatory medications are the most commonly used drugs for treatment of degenerative arthritis of the knee and other joints 25-28 . These drugs, which inhibit cyclooxygenase 1 and 2, have analgesic and anti-inflammatory properties, but they can be associated with gastrointestinal and other side effects. In a short-term clinical trial in which acetaminophen and ibuprofen, in analgesic and anti-inflammatory doses, were compared as treatments for symptomatic arthritis of the knee, the efficacy of the two drugs was equivalent 24 . When nonsteroidal anti-inflammatory drugs are used chronically, it is important for patients to have medical monitoring of hepatic, renal, and gastrointestinal systems 28 . Specific cyclooxygenase-2 inhibitors have demonstrated clinical efficacy in the treatment of symptomatic arthritis of the knee, with decreased gastrointestinal and renal side effects. However, specific cyclooxygenase-2 inhibitors are more expensive, and risk-benefit and cost-benefit analyses must be completed to better define the role of these agents 26,28 . Nutritional supplements (so-called nutriceuticals), such as glucosamine and chondroitin sulfate, have been touted as chondroprotective agents. Double-blind, placebo-controlled, randomized trials have shown that glucosamine is mildly effective for relieving pain associated with degenerative arthritis 26,29-32 . In a study by Reginster et al. 33 , 212 patients with osteoarthritis of the knee were randomized to a glucosamine or a placebo treatment group. After three years of treatment, the glucosamine group had less joint-space narrowing and improved WOMAC (Western Ontario and McMaster University Osteoarthritis Index) scores when compared with the placebo group. However, we are not aware of any long-term studies demonstrating beneficial effects of glucosamine on the articular cartilage of an arthritic joint 26,29 . Some patients with unicompartmental arthritis of the knee report improvement with use of topical analgesics (e.g., methyl salicylate, capsaicin, and nonsteroidal creams) as either adjunctive treatment or monotherapy 34 .
Injectable Intra-Articular Medications Intra-articular injection of hyaluronan is intended to provide so-called viscosupplementation or restoration of the rheological properties of synovial fluid in the arthritic knee. These high-molecular-weight solutions are expected to supplement the reduced concentration of hyaluronan in arthritic knees. It has also been suggested that hyaluronan therapy may alter the progression of arthritis of the knee and may decrease inflammation of the synovial membrane compared with that associated with corticosteroid injections 17,36 . Short-term studies 17,37,38 have suggested that there is no advantage of hyaluronic acid viscosupplementation over nonsteroidal anti-inflammatory drugs in the treatment of an arthritic knee. When hyaluronan injection was compared with corticosteroid injection for treatment of arthritis of the knee, the effects of hyaluronic acid viscosupplementation were found to be slower in onset, the treatment was more expensive, and it was associated with a higher risk of a local inflammatory response 39 . However, the use of hyaluronic acid viscosupplementation in patients who were older than the age of sixty years and had severe disease provided longer-lasting relief of symptoms than did intra-articular corticosteroid injections 34,39,40 . More information on the appropriate use of this treatment is expected from prospective, double-blind, placebo-controlled studies.
Weight Loss
Exercise and Physical Therapy
Ambulatory Support Devices
Braces
Footwear Modification and Orthotics Heel and sole wedges can realign the foot 5° to 10° in either the varus or the valgus plane. With a lateral wedge and insole, the shift in alignment reduces medial joint-space loading 52 . Keating et al. 53 evaluated 121 knees with medial unicompartmental arthritis in eighty-five patients who were treated with a lateral heel and sole wedge. Sixty-one of the 121 knees had a good or excellent result after four to twenty-four months of treatment. Knees with all grades of arthritic involvement showed improvement. Patients with stage-II disease according to the modified Outerbridge classification 54 had the most improvement. The use of heel and sole wedges for patients with arthritis of the lateral compartment of the knee has not been reported, to our knowledge.
Arthroscopy Arthroscopy of a painful arthritic knee permits a surgeon to define the extent of degenerative disease, formulate a treatment plan based on those findings, and correct mechanical problems that are amenable to arthroscopic treatment 55-57 . It has been difficult to correlate the definition of the size and character (shape, depth, and integrity of the border) of articular cartilage lesions with the extent and degree of success of arthroscopic intervention by comparing studies of arthroscopic treatment of knees with degenerative arthritis. However, suboptimal outcomes following arthroscopic surgery of the knee have been associated with greater arthritic deterioration on preoperative radiographs, limb malalignment, and calcium pyrophosphate deposition 58,59 . The use of arthroscopy of the knee to treat unicompartmental arthritis is controversial because the procedure cannot alter the natural history of the disease 60,61 . Arthroscopic lavage of the knee without débridement may mitigate symptoms in the short term by dilution of inflammatory cytokines 17,58,62 , and there have been several retrospective studies of arthroscopic treatment of degenerative arthritis of the knee, with both favorable 57,58,63-66 and unfavorable 60,67-69 results. Moseley et al. 70 questioned the benefit of arthroscopic surgery as a treatment for arthritis of the knee in a study in which they compared a placebo group with a group treated with arthroscopic joint lavage and another group treated with arthroscopic débridement. All three treatment groups had a decrease in symptoms up to two years after intervention. This study was confined to older men in a Veteran's Administration Hospital. The extent of the arthritic involvement of the knee (in one, two, or three compartments) was not documented. The patients were not stratified according to the degree of malalignment, body weight, or type of symptoms. The authors concluded that arthroscopy of a knee with degenerative arthritis may not be indicated when there is only pain in the absence of other symptoms (such as catching, clicking, locking, or giving-way). Furthermore, they suggested that a decrease in symptoms after arthroscopy may be associated with a placebo effect. Arthroscopic débridement for isolated unicompartmental arthritis of the knee has been reported to be beneficial for patients with mild degenerative disease, normal alignment, and an unstable meniscal tear 59,66,71-73 . Varus malalignment is a more negative prognostic factor than is valgus malalignment when predicting whether arthroscopic débridement will be successful for the treatment of unicompartmental arthritis of the knee 66 .
Operative Treatment of Damaged Articular Cartilage With the arthroscopic microfracture technique, an awl is used to crack exposed or eburnated condylar bone, create subchondral bleeding, and stimulate development of fibrocartilage 76,77 . Arthroscopic abrasion arthroplasty 78 is an arthroscopic modification of open débridement 75,79-81 . With that procedure, arthroscopic tools are used to débride the joint and a rotatory instrument is employed to abrade sclerotic bone and stimulate fibrocartilage formation. Lesions >2 cm 2 are more likely to progress to arthritis because of the inability of fibrocartilage to effectively replace hyaline cartilage in these defects 13-15 . In patients with focal defects of articular cartilage in whom arthroscopic débridement is not successful and microfracture or abrasion arthroplasty is not likely to succeed, implantation or transplantation of articular cartilage may be a reasonable treatment option. Three methods of implantation of articular cartilage are available at this time: (1) autologous osteochondral plug transfer, (2) autologous chondrocyte implantation, and (3) osteochondral allograft transplantation 13,15,82-98 . To our knowledge, a comparison of the long-term results of these procedures has not been published. We are also not aware of any studies on the use of these techniques in the treatment of unicompartmental arthritis; their role remains to be defined. For cartilage implantation or transplantation to be successful, as defined by reduced pain, improved function, and a satisfied patient, the limb must be well aligned and the knee must be stable. If the mechanical axis of the limb passes through the compartment with the damaged articular cartilage, alignment must be shifted to relieve the stress on that compartment. Realignment can be achieved with osteotomy 99,100 . Instability secondary to ligamentous or meniscal pathology can be associated with progression of chondral damage, and instability must be corrected to minimize force transmission to the surgically altered articular cartilage 16,17,101 . Patients with low-grade unicompartmental arthritis of the knee (Outerbridge stage II or lower) and a previous meniscectomy have been reported to have had good results at a maximum of five years after meniscal transplantation 17,102-105 . Meniscal allografts may not be useful in patients with advanced osteoarthritis, instability, or deformity. Short-term follow-up of patients treated with meniscal allograft transplantation combined with osteotomy and/or anterior cruciate ligament reconstruction has shown promising results 106 .
Osteotomy Patient selection is critical to the success of knee osteotomy 100 , which may be considered for patients with a high-demand, active lifestyle whose life expectancy exceeds the expected survival of a knee prosthesis. Stability of the knee and a functional range of motion are generally required for a successful osteotomy, and inflammatory arthritis and knee stiffness are generally contraindications 17,19 . Instability due to anterior cruciate ligament insufficiency can be corrected with reconstruction of that ligament. The reconstruction can be combined with osteotomy, as staged or simultaneous procedures, in order to unload an arthritic compartment and restore stability of the knee 101 . Correction of deformity is critical to the success of a knee osteotomy. The normal mechanical axis of the limb, defined as a line from the center of the hip joint to the center of the ankle joint, should pass through or just medial to the center of the knee joint. Angular deformity of the limb can be measured as the angle subtended at the knee by a line through the center of the femoral head and the center of the knee, and extended to the floor, and a line from the center of the knee to the center of the ankle. An angle of 0° to 3° of varus is considered normal 19,23 . The angle of correction of an osteotomy is determined by adding to the deformity of the limb an overcorrection of 2° to 4° to ensure a shift of the weight-bearing force to the uninvolved compartment 110 .
Varus Unicompartmental Arthritis The most common technique for proximal tibial valgus osteotomy is creation of a lateral closing wedge, which can be stabilized with internal fixation (staples, plate, screws, or tension band), external fixation, or a cast. Billings et al. 113 described a technique involving plate-and-screw fixation that provided reproducible angular correction, created stability at the osteotomy site, allowed early motion of the knee, and provided predictably successful results. Other methods of performing proximal tibial valgus osteotomy include a dome cut (which permits greater angular correction without shortening the limb 114 ), an interlocking-wedge osteotomy (which can advance the tibial tubercle anteriorly 115 ), and proximal tibial valgus osteotomy combined with tibial tubercle elevation osteotomy (which permits a more distal wedge cut) 110 . Proximal tibial valgus osteotomy can also be performed with a medial opening-wedge osteotomy in the proximal part of the tibia. Methods of fixation for medial opening-wedge osteotomy include plate-and-screw fixation with or without autogenous or allogeneic bone graft 116 , a hemicallotasis technique with external fixation 117 , and small-wire external fixation. The potential advantages of medial opening-wedge osteotomies fixed with plates and screws include a simple reproducible bone cut, no disruption of the proximal tibiofibular joint, minimized risk of peroneal nerve injury, avoidance of patella infera, and prevention of contracture of the patellar tendon due to its resultant redundancy 116 . Medial opening-wedge osteotomy of the proximal part of the tibia with use of porous hydroxyapatite to treat osteoarthritis of the medial compartment of the knee was successful in a series of twenty-one knees in eighteen patients followed for an average of 78.6 months (range, thirty-eight to 114 months) 118 . All patients had pain relief and improvement in walking ability. No patient required conversion to total knee arthroplasty or had graft collapse. External fixation methods can be associated with pin track infection, nonunion, and deep venous thrombosis. In addition, an external frame is required for an average of seven weeks. A nine-year survivorship analysis of 113 knees treated with proximal tibial valgus osteotomy demonstrated a tendency for recurrence of varus alignment of >5° (in 18% of the knees), progression of lateral compartment arthritis (in 60%), and progression of medial compartment arthritis (in 93%) 119 . The probability of progression of the arthritis was much higher than was the probability of recurrence of varus malalignment. The Mayo Clinic has a forty-year experience with proximal tibial osteotomy for treatment of medial tibiofemoral arthritis and varus deformity of the knee. Prior to the popularization of total and unicompartmental knee arthroplasty, Coventry et al. 120 reported the results of eighty-seven osteotomies in seventy-three patients followed for a median of ten years. With failure defined as the performance of a total knee arthroplasty after the osteotomy, the survivorship was 89% at five years and 75% at ten years. If, at one year after the operation, the valgus angulation of the anatomic axis (femorotibial angle) was <8° or if the patient's weight was more than 1.32 times the ideal body weight, the survivorship decreased to 38% at five years and to 19% at ten years. Insall et al. 112 reported on ninety-five knees followed for an average of 8.9 years (range, five to fifteen years) after a proximal tibial valgus osteotomy. Eighty-one knees had a good or excellent result at five years, and sixty had a good or excellent result at nine years. Twenty-two knees underwent conversion to a total knee arthroplasty. Although varus deformity recurred after the osteotomy in twenty-nine knees, the lack of "ideal" alignment (10° of femorotibial valgus) was not necessarily associated with an unsatisfactory result. The authors concluded that total knee arthroplasty is a more suitable operation for patients who are more than sixty years old and that high tibial osteotomy should be reserved for more active patients. In a subsequent outcome study by the same group, proximal tibial valgus osteotomy met the expectations of twenty-eight of thirty-four men with high demands (average age, forty-nine years) 121 . Noyes et al. 101 evaluated the results of proximal tibial valgus osteotomy and anterior cruciate ligament reconstruction in forty-one patients (mean age, thirty-two years; range, sixteen to forty-seven years) with symptomatic varus malalignment and chronic anterior cruciate ligament insufficiency. At a mean of fifty-eight months (range, twenty-three to eighty-six months), ten of fifteen patients with severe arthritis of the medial compartment had a significant decrease in symptoms (p < 0.05). The authors recommended anterior cruciate ligament reconstruction and proximal tibial osteotomy for patients with medial unicompartmental arthritis and functional instability who plan to return to high-demand athletic activities.
Holden et al.
122 studied fifty-one knees in forty-five patients who had undergone proximal tibial valgus osteotomy before the age of fifty (average age, forty-one years; range, twenty-three to fifty years). At an average of ten years, 70% of the knees were rated good or excellent. Deficiency of the anterior cruciate ligament at the time of the osteotomy did not prevent a good result. In a study of 106 high tibial valgus osteotomies in eighty-five patients followed for a minimum of ten years, Naudie et al.
123 reported a survivorship of 73% at five years, 51% at ten years, 39% at fifteen years, and 30% at twenty years. An age of more than fifty years, previous arthroscopic débridement, a lateral thrust, preoperative knee flexion of <120°, insufficient valgus correction, and delayed union or nonunion were significantly associated with early failure (p Total knee arthroplasty after a failed proximal tibial closing-wedge osteotomy can be more difficult to perform than a primary knee replacement because of a shift of the proximal tibial articular surface in relation to the medullary canal, osseous insufficiency of the lateral aspect of the proximal part of the tibia, and altered patellofemoral mechanics caused by patella infera and contraction of the patellar tendon. The clinical results of total knee arthroplasty after high tibial osteotomy vary. Windsor et al. 126 reported that they were not as satisfactory as those after primary total knee arthroplasty, with thirty-two of forty-five knees having a good or excellent result at a minimum of two years. Katz et al. 127 compared the results of twenty-one total knee arthroplasties after high tibial osteotomy with those of twenty-one primary total knee arthroplasties. Seventeen of the arthroplasties done after an osteotomy had a good or excellent result, whereas all twenty-one of the primary total knee arthroplasties had a good or excellent result. In contrast, Staheli et al. 128 reported that thirty-one of thirty-five patients treated with total knee arthroplasty after an osteotomy of the proximal part of the tibia had a good or excellent result. Meding et al. 129 evaluated the results of ninety-five consecutive total knee replacements performed in eighty-two patients at an average of ten years and four months after high tibial osteotomy. While the number of previous operative procedures and the severity of preoperative flexion contracture were related to diminished postoperative motion, the previous high tibial osteotomy had no adverse effect on the eventual results of the posterior cruciate ligament-retaining total knee arthroplasty performed with cement fixation.
Valgus Unicompartmental Arthritis
Proximal tibial varus osteotomy can be used to treat lateral unicompartmental arthritis in patients with a tibiofemoral angular deformity of Distal femoral varus osteotomy can be used to treat lateral tibiofemoral arthritis in patients with a preoperative tibiofemoral angle of >12° or a predicted joint-line obliquity of >10° after osteotomy 72,99,135-137 ( Figs. 1-A , 1-B , and 1-C ). Healy et al. 99 reported the results of twenty-three distal femoral varus osteotomies in twenty-one patients followed for an average of four years (range, two to nine years). Nineteen of the twenty-three knees had a good or excellent result as rated with The Hospital for Special Surgery knee score. Fifteen of sixteen knees with lateral tibiofemoral arthritis and valgus deformity had a good or excellent result. Rheumatoid arthritis and inadequate preoperative motion were associated with poor results. Intermediate-term results reported by other authors 135-137 confirmed these findings. In a long-term evaluation of twenty-one patients treated with distal femoral varus osteotomy for lateral unicompartmental arthritis, Finkelstein et al. 138 found a ten-year survivorship of 64%, with conversion to total knee arthroplasty as the end point. In patients with severe valgus deformity in whom a single osteotomy will result in excessive bone loss or joint line obliquity, a distal femoral varus osteotomy can be combined with a proximal tibial medial osteotomy to obtain correction 72 .
Unicompartmental Knee Arthroplasty Arthroplasty is considered for treatment of painful unicompartmental arthritis when restoration of the articular cartilage and osteotomy are not indicated. The choice of unicompartmental or total knee arthroplasty depends on the patient, the knee, and the surgeon. The ideal candidate for unicompartmental knee arthroplasty has low activity demands, a stable knee with <15° of flexion contracture, no varus or valgus malalignment or minimal malalignment that can be passively corrected on examination, and unicompartmental osteoarthritis with no or minimal degeneration of the articular cartilage of the contralateral compartment or patellofemoral joint 139,140 ( Figs. 2-A , 2-B , 2-C , and 2-D ). In general, patients with unicompartmental osteoarthritis and osteonecrosis are suitable candidates for unicompartmental knee arthroplasty 19,141 , while patients with inflammatory arthritis are not 140 .
The early results of unicompartmental knee arthroplasty were discouraging 142-144 , but evolution of patient selection, surgical technique, and implant design over the past thirty years has refined the indications and improved the clinical outcome. The optimal age for unicompartmental knee arthroplasty is not clear, and there is controversy about its use in active younger patients (less than sixty years old). Youth and high activity demand have been associated with poorer results 141,145 . In patients with medial unicompartmental arthritis, the best results are obtained when the postoperative mechanical axis is in the center or slightly medial to the center of the knee. Overcorrection and severe undercorrection have been associated with early failure 146 . In patients with lateral unicompartmental arthritis, the corrected mechanical axis should be in the lateral compartment, medial to the preoperative mechanical axis 143,147,148 . Poor results have been reported as a result of technical problems such as inadequate implant fixation, poorly designed articulating surfaces (nonconforming articulations), and insufficient polyethylene thickness 143,145,148-154 . Unicompartmental knee arthroplasty has several potential advantages over total knee arthroplasty. The surgical approach and surgical dissection can be considerably less extensive for unicompartmental knee arthroplasty 155 . Patellar resurfacing is avoided. Requirements for perioperative blood transfusion are diminished 156 . The range of motion following unicompartmental knee arthroplasty is generally greater 156-158 . Properly selected patients have a shorter postoperative recovery time, and they return to work or to preoperative activities faster. Furthermore, revision of a unicompartmental arthroplasty is less difficult than is revision of a total knee arthroplasty 156 . More recent intermediate and long-term follow-up studies of unicompartmental knee arthroplasty performed with a well-designed implant in properly selected patients have demonstrated predictably good results comparable with those of total knee arthroplasty during the first postoperative decade 145,147 . In a study of 100 unicompartmental arthroplasties followed for eight to twelve years, in patients with a mean age of seventy-one years at the time of the operation, Scott et al. 147 reported an 85% survivorship at ten years, with the end point defined as revision arthroplasty. Thirteen patients underwent revision. Stockelman and Pohl 159 reported forty-three satisfactory results and four revision operations at an average of 7.4 years (range, five to twelve years) after forty-seven unicompartmental knee arthroplasties. In a study of sixty-two unicompartmental knee arthroplasties in patients with an average age of sixty-eight years (range, fifty-one to eighty-four years), Berger et al. 160 reported a 98% survivorship at ten years, with revision to total knee arthroplasty as the end point. One patient required revision to a total knee arthroplasty at eighty-seven months. Christensen 161 reported that seven of 575 unicompartmental prostheses required revision to a total knee arthroplasty at two to eleven years. Squire et al. 162 reported that fourteen of 140 cemented unicompartmental knee prostheses in patients with an average age of seventy years required revision to a total knee arthroplasty after fifteen to twenty-two years of follow-up. In a study of 143 medial Oxford unicompartmental knee arthroplasties followed for a mean of 7.6 years, the survivorship was 98% at ten years 163 . Five knees required revision to a total knee arthroplasty. Revision of a failed unicompartmental knee arthroplasty to a total knee arthroplasty can be accomplished successfully but may be associated with technical difficulties. Barrett and Scott 164 reported a good or excellent result in thirteen of twenty-nine patients at an average of 4.6 years after they had undergone a revision to a total knee arthroplasty. Treatment of osseous insufficiency requiring augmentation with bone graft or bone cement and use of long-stem implants was necessary in 50% of these revision operations. The authors suggested that the technique of the original operation determines the technical difficulty of the revision surgery. When minimal bone was resected during the unicompartmental knee arthroplasty, and primary total knee arthroplasty implants can be used during the revision surgery without bone augmentation, stems, or constrained implants, revision to a total knee arthroplasty following unicompartmental knee arthroplasty can be as successful as primary total knee arthroplasty 164 . Unicompartmental knee arthroplasty and high tibial osteotomy have been used to treat unicompartmental arthritis in similar patients. Broughton et al. 165 compared the results of forty-two unicompartmental knee arthroplasties with those of forty-nine high tibial osteotomies after an intermediate five to ten-year follow-up. A good result was reported after thirty-two of the forty-two unicompartmental knee arthroplasties at an average of 5.8 years and after twenty-one of the forty-nine high tibial osteotomies at an average of 7.8 years. The authors concluded that the results of unicompartmental knee arthroplasty were better than those of osteotomy, and the knees had less late deterioration. Ivarsson and Gillquist 166 reported that patients who had had unicompartmental knee arthroplasty demonstrated better gait velocity and superior muscle strength compared with those who had had an osteotomy. Schai et al. 154 evaluated the results two to six years after twenty-eight unicompartmental knee arthroplasties performed in patients with an average age of fifty-two years. Twenty-five patients had satisfactory pain relief, and two patients required revision to a total knee arthroplasty. The conclusion of the study was that, at two to six years, unicompartmental knee arthroplasty in middle-aged patients yields results (with revision considered the end point) that are competitive with those of osteotomy but inferior to those of total knee arthroplasty. Long-term survivorship analysis comparing the results of unicompartmental knee arthroplasty in well-selected patients with those of total knee arthroplasty are not available, to our knowledge. In a short-term (six-month to four-year) study comparing the results of thirty-one unicompartmental knee arthroplasties with those of 133 total knee arthroplasties, Weale et al. 167 reported that the patient-perceived outcomes, pain scores, and functional results were equivalent in the two groups. Laurencin et al. 168 compared the results in twenty-three patients who had had a unicompartmental knee arthroplasty on one side and a total knee arthroplasty on the other; ten patients preferred the side with the unicompartmental procedure, three preferred the side with the total knee arthroplasty, and ten found no difference. Comparison studies 157,158 have shown that patients with unicompartmental knee arthroplasty have a better range of motion (flexion of >120°) and walk faster than do those treated with total knee arthroplasty. Recently developed minimally invasive techniques for unicompartmental knee arthroplasty have emphasized smaller skin and capsular incisions, limited quadriceps disruption, and decreased rehabilitation time. Long-term follow-up studies on these techniques are not available, to our knowledge. Peer-reviewed results have been reported for only 136 elderly patients (average age, sixty-six years) followed for an average of eight years; eleven patients required revision to a total knee arthroplasty 155 . Minimally invasive unicompartmental knee arthroplasty is an attractive surgical treatment option for elderly patients with unicompartmental arthritis, and it may be preferred over osteotomy or total knee arthroplasty in these patients. Minimally invasive unicompartmental knee arthroplasty has been described as a so-called pre-total knee arthroplasty operation for patients of all ages 155 ; however, this recommendation requires further investigation and scientific support.
Total Knee Arthroplasty
At the beginning of the twenty-first century, unicompartmental arthritis of the knee is a common clinical problem in the United States, and many diverse nonoperative and operative treatments are available. Oral and injectable medications, weight loss, exercise, physical therapy, canes, crutches, braces, orthotics, arthroscopy, cartilage resurfacing, osteotomy, and arthroplasty offer patients and surgeons a wide spectrum of successful treatment options. Arthroscopic surgery for unicompartmental arthritis of the knee should be reserved for patients with mechanical symptoms (catching, clicking, locking, instability, or giving-way) that are consistent with loose meniscal fragments, chondral articular flaps, loose bodies, and/or impinging intercondylar spurs. When arthroscopy of the knee is performed for mechanical symptoms, the outcome is predictably successful. However, in sharp contrast, arthroscopic surgery performed merely for a painful arthritic knee without mechanical symptoms may not have a lasting benefit 63 . Future studies are warranted to determine whether arthroscopic surgery can benefit patients who have primary mechanical symptoms with concomitant arthritic symptoms 179 . When unicompartmental arthritis has developed in a knee, consideration should be given to an attempt to delay or ameliorate the degenerative process with biological treatments. Historically, this advice was proposed for younger, high-demand patients. However, as patients with arthritic knees now live longer and desire active lifestyles, treatment options for unicompartmental osteoarthritis should be considered in light of life expectancy and a patient's desire for activity. Osteotomy is an attractive surgical option for active patients with unicompartmental arthritis and limb deformity who are expected to live twenty years or more. As a patient's life expectancy and expectations for activity decrease as a result of age or disease, unicompartmental knee arthroplasty and total knee arthroplasty become more attractive options for the surgical treatment of unicompartmental arthritis of the knee. Unicompartmental knee arthroplasty can be a successful option, with enduring results, for unicompartmental, noninflammatory arthritis. When patient selection, surgical technique, and implant utilization are optimized, unicompartmental knee arthroplasty can offer patients a knee that is functionally superior to a total knee prosthesis, and conversion to total knee arthroplasty can be performed without substantial surgical difficulty. Minimally invasive unicompartmental knee arthroplasty may offer advantages with regard to short-term rehabilitation over traditional arthroplasty approaches. Total knee arthroplasty is a predictably successful treatment for unicompartmental arthritis in the older population. The surgical technique of total knee arthroplasty is more commonly mastered by general orthopaedic surgeons than are alternative operations such as osteotomy and unicompartmental knee arthroplasty. Wear of bearing surfaces and implant loosening are concerns in young active patients treated with total knee arthroplasty; however, a well-performed total knee arthroplasty in this population will provide an excellent functional outcome for many years. Surgeons must consider surgical skill and patient demands when choosing a surgical treatment for unicompartmental arthritis of the knee.
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Introduction
Natural History of Degenerative...
10° is associated with symptoms of unicompartmental arthritis
0.05). A subset of patients who were younger than fifty years of age and who had had preoperative knee flexion of >120° had a probability of survival (no need for conversion of the high tibial osteotomy to a total knee arthroplasty) approaching 95% at five years, 80% at ten years, and 60% at fifteen years
