Unicompartmental Arthroplasty for Young and Active Patients
Dr. Michel Malo, from the University of Montreal, and Dr. Geoffrey Dervin, from the University of Ottawa, present opposing opinions on the use of unicompartmental arthroplasty for the young and active patient.
This debate illustrates the ongoing discussion on how to best meet the expectations of patients undergoing arthroplasty procedures in terms of return to full activities while minimizing the risk of early reoperation.It is becoming evident that implants such as unicompartmental knee replacements and hip resurfacing, which are less invasive, have a significantly smaller margin of error in terms of implantation technique as well as patient selection. Having said that, it is probably not fair to criticize an implant or a surgical technique simply because it is not applicable to all patients or of ease to all surgeons.
Hopefully with continued surgical tool development as well as implant materials, our capacity to provide patients with high-performing implants, without increasing the risk of early revision, will continue to evolve over the next decade.
Drs. Malo and Dervin make very good arguments that surgeons can contemplate when considering arthroplasty as a treatment for the active patient.
Reprinted with permission from the Spring 2010 issue of COA Bulletin
Viewpoint 1: Geoffrey Dervin, MD, MSc, FRCSC
Unicompartmental Knee Arthroplasty Is Superior to Total Knee Arthroplasty for Functional Outcome
Unicompartmental knee arthroplasty (UKA) is now being reconsidered by a new generation of orthopaedic surgeons for the treatment of unicompartmental osteoarthritis (OA). Minimally invasive surgery techniques and comparable survivorships with fixed1 and mobile-bearing designs2,3 have permitted decreased short-term morbidity and faster recuperation,4,5 allowing even outpatient procedures for healthy patients.
Patient expectations now extend beyond pain control, and are more rooted in functional preservation or restoration, not often realized with total knee arthroplasty (TKA). A survey with validated self-administered questionnaire confirmed increased limitation of functional activities involving the knee in 52% of patients who had TKA, compared with 22% of the age- and gender-matched patients with no previous knee disorders.6 Further, satisfaction with the outcome of TKA was highly variable: 14% were "dissatisfied" or "very dissatisfied."7 It was further asserted that satisfaction with TKA is primarily determined by meeting patient expectations, and not the absolute level of function. For younger patients, the treating surgeon has the double challenge of restoring the desired activity and performance while being mindful of the increased revision rate,8 so why chose UKA?
There is paucity of data for any direct prospective comparisons of UKA and TKA. Newman et al9 randomized 102 patients (mean age 69) suitable for either a UKA or TKA after arthrotomy. Patients in the UKA group showed less perioperative morbidity, regained knee movement more rapidly, and were discharged from the hospital sooner. At 5 years, two UKAs and one TKA had been revised; another TKA was radiologically loose. Pain relief was good in both groups, but the number of knees able to flex ? 120º was significantly higher in the UKA group (p < 0.001) and there were more excellent results in this group.
Ackroyd et al showed comparable survivorship in a non-randomized study between fixed-bearing UKA St Georg Sled and Kinemax knees at 10 years with better flexion in the UKA group.10 Amin at al11 also found higher postoperative range of motion in mobile-bearing UKA vs. matched cases of TKA. Walton et al12 also confirmed in a retrospective comparative study that patients with UKA had better activity and Oxford knee scores with increased return to sport than age, gender, and preop activity matched controls undergoing TKA. Willis-Owen et al13 have recently shown in a case control study that both medial and lateral UKA patients scores were indistinguishable from normal age- and gender-specific controls and clearly superior to TKA using the validated TKQ.14
Fixed vs. Mobile
A major consideration for the surgeon is whether to consider fixed- or mobile-bearing UKA.
In randomized studies of medial UKA, Li et al,15 Gleeson et al,16 and Confalonieri et al17 were unable to show any difference in functional outcomes of fixed-bearing vs. mobile-bearing UKA. Gleeson did find that the pain component of the Bristol Knee Score was significantly better for the fixed-bearing group (St Georg Sled) and that there was a higher early revision rate in the Oxford group. Conversely, the improved mobile-bearing kinematics may favour the latter in longer-term survivorship based on retrieval studies.18,19 Further, Li15 described improved kinematics of mobile-bearing (Oxford) UKA compared with patients treated with fixed-bearing (Miller-Galante) with a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05).
The functional results and outcomes for younger patients with fixed and mobile-bearing UKA would appear to be acceptable. Pennington et al20 reported on 41 consecutive patients 60 years of age or younger with Miller-Galante fixed-bearing UKR. At mean follow-up of 11 years, the Hospital for Special Surgery (HSS) score was excellent in 93% of cases. Although nine knees had progression of arthritis in the unresurfaced compartment, none of these knees were revised, and none of the patients had deterioration in the HSS Score, yielding 11-year survivorship of 92%.
Price et al21 reported the experience for the Oxford knee related to patient’s age and showed the 10-year all-cause survival for patients in the under 60 years of age group was 91% (95% CI 12), with mean HSS score at 10-year follow-up of 94 out of 100. Indeed, it is this author’s observation that some of the greatest benefits lie with active patients in their 50s who can benefit from the permissive activities of a well functioning UKA without sacrificing future conversion to TKA (Figures 1a,b).
Figure 1a. Postoperative AP radiograph of a 57-year-old male 7 years after mobile-bearing UKA for medial osteoarthritis of the knee
Figure 1b. Postoperative lateral radiograph of the same patient
What about Revision?
Of particular interest for the young active patient is the potential need for future revision. Several authors have confirmed that the majority of revisions of well performed UKA can be to primary components22-24 with comparable results to primary TKA. The evidence would also suggest that contrary to proximal tibia osteotomy survivorship, UKA shows greater longevity in a relatively undercorrected coronal alignment so as to minimize contralateral compartment wear (Figure 2). The benefits of smaller surgical exposures with UKA seem to cause less scarring in the joint and pretibial region with significantly less postoperative patella baja,25 easing exposure for later revisions. Robertsson et al26 surveyed Swedish patients operated on between 1981 and 1995 and found no difference in proportions of satisfied patients whether they had primarily been operated on with a TKA or a medial UKA, although patients revised from medial UKA were more satisfied than patients revised from primary TKA.
Figure 2. Standing AP radiographs 2 years post left medial mobile-bearing UKA in a 53-year-old man, showing preservation of the patient’s natural coronal tibiofemoral alignment.
Registry data show the usage of UKA to be at 7-8 % of all knee arthroplasty - significantly less than the 25% suggested by high-volume and designing surgical centres. For the surgeon treating medial or, less commonly, lateral unicompartment OA, there is clearly wide variation in the adoption and utilization of this technique. Nonetheless, the reported experience supports Scott,27 who claimed “Unicompartmental knee arthroplasty is the right operation for the right patient when performed by the right surgeon using the right surgical technique.”
Reprinted with permission from the Spring 2010 issue of COA Bulletin
- Berger RA, Nedeff DD Barden RM, et al. Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year follow-up. Clin Orthop 1999 Oct;(367):50-60.
- Murray DW, Goodfellow JW, O'Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg Br 1998 Nov;80(6):983-9.
- Svard UC, Price AJ. Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series. J Bone Joint Surg Br 2001 Mar;83(2):191-4.
- Beard DJ, Murray DW, Rees JL, Price AJ, Dodd CA. Accelerated recovery for unicompartmental knee replacement-a feasibility study. Knee 2002 Sep;9(3):221-4.
- Reilly KA, Beard DJ, Barker KL, et al. Efficacy of an accelerated recovery protocol for Oxford unicompartmental knee arthroplasty--a randomised controlled trial. Knee 2005 Oct;12(5):351-7.
- Noble PC, Gordon MJ, Weiss JM, et al. Does total knee replacement restore normal knee function? Clin Orthop 2005 Feb;(431):157-65.
- Noble PC, Conditt MA, Cook KF, et al. The John Insall Award: Patient expectations affect satisfaction with total knee arthroplasty. Clin Orthop 2006 Nov;452:35-43.
- Harrysson OL, Robertsson O, Nayfeh JF. Higher cumulative revision rate of knee arthroplasties in younger patients with osteoarthritis. Clin Orthop 2004 Apr;(421):162-8.
- Newman JH, Ackroyd CE, Shah NA. Unicompartmental or total knee replacement? Five-year results of a prospective, randomised trial of 102 osteoarthritic knees with unicompartmental arthritis. J Bone & Joint Surg - Br 1998 Sep;80(5):862-5.
- Ackroyd CE, Whitehouse S., Newman JH, Joslin CC. A comparative study of the medial St Georg sled and kinematic total knee arthroplasties. Ten-year survivorship. J Bone & Joint Surg- Br 2002 Jul;84(5):667-72.
- Amin AK, Patton JT, Cook RE, Gaston M, Brenkel IJ. Unicompartmental or total knee arthroplasty?: Results from a matched study. Clin Orthop 2006 Oct;451:101-6.
- Walton NP, Jahromi I, Lewis PL, Dobson PJ, Angel KR, Campbell DG. Patient-perceived outcomes and return to sport and work: TKA versus mini-incision unicompartmental knee arthroplasty. J Knee Surg 2006 Apr;19(2):112-6.
- Willis-Owen CA, Brust K, Alsop H, Miraldo M, Cobb JP. Unicondylar knee arthroplasty in the UK National Health Service: an analysis of candidacy, outcome and cost efficacy. Knee 2009 Dec;16(6):473-8.
- Weiss JM, Noble PC, Conditt MA, et al. What functional activities are important to patients with knee replacements? Clin Orthop 2002 Nov;(404):172-88.
- Li MG, Yao F, Joss B, et al. Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics. Knee 2006 Oct;13(5):365-70.
- Gleeson RE, Evans R, Ackroyd CE, Webb J, Newman JH. Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study. Knee 2004 Oct;11(5):379-84.
- Confalonieri N, Manzotti A, Pullen C, Confalonieri N, Manzotti A, Pullen C. Comparison of a mobile with a fixed tibial bearing unicompartimental knee prosthesis: a prospective randomized trial using a dedicated outcome score. Knee 2004 Oct;11(5):357-62.
- Psychoyios V, Crawford RW, O'Connor JJ, Murray DW. Wear of congruent meniscal bearings in unicompartmental knee arthroplasty: a retrieval study of 16 specimens. J Bone Joint Surg Br 1998 Nov;80(6):976-82.
- Collier MB, Engh CA Jr, McAuley JP, et al. Factors associated with the loss of thickness of polyethylene tibial bearings after knee arthroplasty. J Bone Joint Surg Am 2007 Jun;89(6):1306-14.
- Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg Am 2003 Oct;85-A(10):1968-73.
- Price AJ, Dodd CA, Svard UG, et al. Oxford medial unicompartmental knee arthroplasty in patients younger and older than 60 years of age. J of Bone & Joint Surg - Br 2005 Nov;87(11):1488-92.
- McAuley JP, Engh GA, Ammeen DJ. Revision of failed unicompartmental knee arthroplasty. Clin Orthop 2001 Nov;(392):279-82.
- Levine WN, Ozuna RM, Scott RD, Thornhill TS. Conversion of failed modern unicompartmental arthroplasty to total knee arthroplasty. J Arthroplasty 1996 Oct;11(7):797-801.
- Saldanha KA, Keys GW, Svard UC, et al. Revision of Oxford medial unicompartmental knee arthroplasty to total knee arthroplasty - results of a multicentre study. Knee 2007 Aug;14(4):275-9.
- Weale AE, Murray DW, Newman JH, Ackroyd CE. The length of the patellar tendon after unicompartmental and total knee replacement. J Bone Joint Surg - Br 1999 Sep;81(5):790-5.
- Robertsson O, Dunbar M, Pehrsson T, Knutson K, Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand 2000 Jun;71(3):262-7.
- Scott RD. Unicondylar arthroplasty: redefining itself. Orthopedics 2003 Sep;26(9):951-2.
Viewpoint 2: Michel Malo, MD, FRCS
Unicondylar Knee Replacement Provides a Superior Functional Outcome to Total Knee Arthroplasty in the Young and Active Adult - In Opposition
Arthritic disease in people younger than age 55 years is increasingly common. Younger, active individuals often present to orthopaedic surgeons requiring treatment for knee osteoarthritis. Knee arthroplasty has been offered as a viable option to provide pain relief and improve function in the middle-aged patient.1 According to the Canadian Joint Replacement Registry,2 when age-gender-specific rates for joint replacements are examined, the most notable increases for knee replacement in the last decade occurred in the 45-to-54 age group (more than doubled for both males and females).
Unicompartmental knee arthroplasty (UKA) has been performed for more than 30 years with variable results. Over the last decade, there has been a renewed and increased interest in UKA generated by reports of improved results. Although UKA was originally reserved for more older and sedentary patients, the inclusion criteria for UKA have progressively broadened to include younger and more active individuals due to the evolution of the technique and implant design and the growing confidence of better results. This has been a source of debate in recent years,3,4 and there are many reasons to be concerned.
First of all, it is very important to note that better results of UKA have been obtained using strict patient selection criteria. The classic criteria for UKA have been defined by Kozinn and Scott,5 including specifically elderly and sedentary patients with isolated tibiofemoral unicompartmental osteoarthritis, correctible deformity, stable joint, and no eburnated bone in the patello-femoral articulation. Essentially all of the available survivorship studies for UKA showing long-term results comparable to total knee arthroplasty (TKA) adhered to a conventional group of aged patients.6-10
There are only a limited number of studies reporting results of UKA in younger patients. The first reports emerged in the late 1990s. Engh and McAuley11 suggested UKA as an acceptable alternative for the young and high-demand patient. However, at that time, almost no substantial clinical results specifically addressed this issue. Their analysis was primarily an estimation based on information extracted from long-term outcome studies of UKA in a general patient population. They estimated the success rate of UKA in younger, active patients to be about 80% at 10 years.
Schai et al12 reported the early results at the Brigham Hospital with the PFC system (Johnson & Johnson) in a small cohort of 28 patients with a mean age of 52 years (range, 37-60 years). Activity level analysis using the Tegner scale revealed only a slight increase from a preoperative mean of 2.3 to 2.7 points. Two (7%) femoral components were revised for loosening. Schai et al concluded that “UKA in middle-aged patients yields 2- to 6-year results competitive with osteotomy but inferior to TKA in terms of early reoperation rate.”12
Tabor and Tabor13 reported data of 67 knees (58 patients) with minimum 5-year follow-up (mean, 9.7 years; range, 5-20 years) using a Marmor-style non-metal-backed cemented tibial component. The average age was 61 years (range, 41--80), and 31 knees were in patients younger than 60 years old at surgery. Overall survivorship was 91% at 5 years, 84% at 10 years, and 79% at 15 years. Pennington et al14 reviewed retrospectively 46 Miller-Galante (Zimmer) UKA in 41 patients of 60 years of age or younger and physically active. Survivorship was 92% at 11 years. The University of California (UCLA) activity-level average score was 6.6 ± 1.4 for the knees in which the original prosthesis had been retained and 7.3 ± 1.5 for those revised.3
More recently, a few other reports15,16 have shown favourable results of another system (Oxford phase III-Biomet) at short-term follow-up. One of these studies15 assessed, specifically, the sporting and physical activity level of patients following a UKA with a mean age of 66 years at review and at a mean follow-up time of 18 months (range, 4-46). They recorded a significant improvement in UCLA activity-level scores from 4.2 to 6.5, with 93% of patients successfully returning to their regular sporting and physical activities following surgery. Nevertheless the authors acknowledged the relatively short-term follow-up of their review and the necessity for “a more detailed study to evaluate the long-term effects of sporting activity on the Oxford UKA.”
Therefore, UKA might offer good, early performance benefits with near normal kinematics, quicker recovery and regained mobility, and accelerated return to physical activity. All of these make UKA an attractive treatment option. However, although the short-term results look promising in a younger group of patients, consistent long-term data are lacking. It is very questionable whether the long-term encouraging results of UKA in the conventionally selected patients could be reproduced in the younger, active patients. This has not yet been proven. As new indications are introduced, it is imperative to compare the outcomes with established standards. As indications for UKA expand to include younger and more active patients, there is reasonable concern that this could lead to more complications and failures, and poorer survival outcomes (Figure 1).17
Figures 1a-c. A 51-year-old active female with a 5-year postop painful cemented UKA. Anteroposterior (a), lateral (b), and merchant (c) views showing loosening of the tibial component and appearance of osteoarthritis in the patellofemoral and lateral compartment.
TKA Has Proved Its Durability in the Young Population
On the other hand, TKA has an excellent history of long-term successful functional outcome and survival in the young population. Gill et al18 published results on 68 knees performed by a single surgeon in 50 patients younger than 55 years old with osteoarthritis and rheumatoid arthritis at an average of 9.92 years follow-up. The function score in both subgroups improved significantly at the latest follow-up. Two knees were revised for aseptic loosening. Based on the cumulative survivorship rate of 96.5% at 10 years, the authors concluded that cemented TKA in younger and more active patients can achieve outcomes comparable to those in the older population.
Insall et al19 reported the long-term results of 108 TKA using one implant in 84 patients younger than 55 years old (average, 51 years) who had either osteoarthritis or post-traumatic arthritis. The anticipated overall rate of survival was 94% at 18 years, with revision of the femoral or tibial component as the end point, and 87% when patella revision or spacer exchange were included in the failures. The Tegner activity average score improved from 1.3 to 3.5 points. Duffy et al20 from the Mayo Clinic reviewed 74 consecutive TKA in 54 patients who were 55 years of age or younger (average age, 43 years) at a minimum follow-up of 10 years (range, 10-17 years). The majority of patients had rheumatoid arthritis (64% of the total knee arthroplasties). Implant survivorship was estimated to be 99% at 10 years and 95% at 15 years.
Evidence for UKA or TKA in treating the middle-aged patient is based on individual, non-comparative survivorship series for both types of prostheses. There are very few direct comparative studies between UKA and TKA in comparable patients.21-23 The existing reports provide only short-term clinical results, and none are specific to a group of patients younger than 55 years. Some investigation has been done on the activity level following knee arthroplasty.24 Similarly, the current literature on this issue is limited, and there is no good-quality, objective, evidence-based information available.
National Joint Registries Are Valuable Sources of Data
The continuing contribution of data to national joint registries is a valuable aid in validating the current trends, particularly in knee survival after UKA or TKA. Register-based studies, despite some inherent limitations, provide valuable insights into the use and performance of a surgical procedure in a certain patient group.
Furnes et al25 reported the rates of failures of cemented UKA and TKA based on the Norwegian Arthroplasty Register. The 10-year survival probability of UKA (80.1%) was inferior to that of TKA (92%), with a rate of revision following UKA twice as high as that following TKA. The increased risk of revision following UKA was seen in all age categories. UKA was associated with more revisions because of pain, aseptic loosening of the tibial and of the femoral component, and periprosthetic fracture.
In a recently published study,26 relevant information is available specifically on patients younger than 55 years of age from the Swedish Knee Arthroplasty Register for the period 1998-2007. During the 10 years, the use of TKA in these patients increased fivefold and UKA increased threefold, but the use of UKA decreased in the last 2 years. The risk of revision increased in these patients and it was lower for TKA (9%) than for UKA (24%). The authors conclude that today, TKA is the preferred method for young osteoarthritic patients in Sweden.
Similar powerful conclusions are observed in the Australian Registry27 concerning the outcome of UKA. There is a significant difference in the risk of revision depending on age: the risk of revision decreases with increasing age. The highest revision rate occurs in the under-55 age group, with an 8-year cumulative revision rate of 18%.
Another study28 reported data also of patients younger than age 55 years, but from a community joint registry over a 14-year period. Cemented TKA performed best, with a cumulative revision rate of 15.5%, compared to 32.3% in UKA patients.
UKA Is a Technically More Demanding Procedure
The current enthusiasm for minimally invasive surgery has been a contributing factor in the recent explosion of interest for UKA. Undoubtedly, UKA is a technically more demanding procedure than TKA, particularly when done with a minimally invasive approach, even though the evolution of instrument systems has allowed more precision in performing UKA. In fact, there are reports of higher rates of early complications and failures after a minimally invasive technique.29,30 The learning curve is steep. Many pitfalls may occur, which could compromise the outcome, and attention to details is essential. Accurate component placement and limb alignment are critical to the long-term success of the prosthesis (Figure 2).
Figure 2. Malalignment of UKA femoral and tibial components.
A major issue with UKA is the limited experience most surgeons have with this procedure compared with TKA. The ideal criteria for UKA are encountered in only a small number of patients. The usual percent of suitable candidates for UKA among all knee arthroplasties is 6-10%.4,31 Infrequent performance of an arthroplasty may lead to poorer results, especially since UKA requires increased technical experience. It has been showed by Robertsson et al,32 based on the Swedish Arthroplasty Register, that the revision rate of UKA is affected by operating volume. Also, the long-term success and reliability of the procedure has been mainly reported by high-volume and experienced surgeons at specialized total joint centers. Thus, the widespread use of UKA is definitely an area of concern, especially in the general orthopaedic community where only a minimum number of cases are performed per year.
UKA procedure has been suggested by Scott and others as a time-buying operation before TKA. Ease of conversion of UKA to TKA has been debated, and controversy still exists. Advances in implant design and emphasis on preservation of bone stock during UKA may make revision to TKA less complicated, although this may be offset by potential severe UKA failures with greater damage in the younger, more active patient.
The painful osteoarthritic knee in the middle-aged population presents a therapeutic challenge. The younger and more active patient, often referred to as the "new" patient, is difficult to treat. Needs are somewhat different and expectations are high: not only are these patients looking for an end to pain, but they also want a return to normal function. The care of this group age of patients should be individualized.
Undoubtedly, UKA offers early potential benefits, but concern exists regarding the durability and survival of unicompartmental knee replacement in the younger and more active adult. Patient selection and surgical technique issues play a major role in the long-term functional outcome and longevity of UKA. The indications for UKA are specific, and strict adherence to them is predictive of successful results. UKA is a technically more challenging procedure, and expertise and surgical experience are required. Until further well-designed research provides more information, caution is advised.
To date, TKA has shown to be an effective, more reliable and established option with consistent long-term results in the active, younger patients. Despite long-term survival of TKA in the middle-aged population, wear, aseptic loosening, and osteolysis remain potential concerns, the same as those after UKA. The emergence of so-called modern high-performance implants and the recent development of improved biomaterials, notably, highly crossed-linked polyethylene and highly porous metals (trabecular metal),33 provide hope for even better results in treating this specific group of patients.
Reprinted with permission from the Spring 2010 issue of COA Bulletin
- Hanssen AD, Stuart MJ, Scott RD, Scuderi GR. Surgical options for the middle-aged patient with osteoarthritis of the knee joint. Instr Course Lect 2001 50:499--511
- Canadian Joint Replacement Registry. 2008-2009 Annual Report.
- Engh GA. Can we justify unicondylar arthroplasty as a temporizing procedure? In the affirmative. J Arthroplasty 2002;17(4) suppl 1:54-55
- Sculco TP. Can we justify unicondylar arthroplasty as a temporizing procedure? In Opposition. J Arthroplasty 2002;17(4) suppl 1:56-57
- Kozinn SC, Scott R. Unicondylar knee arthroplasty. J Bone Joint Surg (Am) 1989;71:145-150
- Murray DW, Goodfellow JW, O’Connor JJ. The Oxford medial unicompartmental arthroplasty: a ten-year survival study. J Bone Joint Surg (Br) 1998;80:983-989
- Squire MW, Callaghan JJ, Goetz DD, et al. Unicompartmental knee replacement. A minimum 15 year followup study. Clin Orthop 1999;367:61-72
- Naudie D, Guerin J, Parker DA, et al. Medial unicompartmental knee arthroplasty with the Miller-Galante prosthesis. J Bone Joint Surg (Am) 2004;86:1931-1935
- Berger RA, Meneghini RM, Jacobs JJ, et al. Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg (Am) 2005;87:999-1006
- Price AJ, Waite JC, Svard U. Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty. Clin Orthop 2005;435:171-180
- Engh GA, McAuley JP. Unicondylar arthroplasty: an option for high-demand patients with gonarthrosis. Instr Course Lect 1999;48:143-148
- Schai PA, Suh JT, Thornhill TS, Scott RD. Unicompartmental knee arthroplasty in middle-aged patients: a 2- to 6-year follow-up evaluation. J Arthroplasty 1998;13:365-372
- Tabor OB Jr, Tabor OB. Unicompartmental arthroplasty: a long-term follow-up study. J Arthroplasty 1998;13:373-379
- Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Unicompartmental knee arthroplasty in patients sixty years of age or younger. J Bone Joint Surg (Am) 2003;85:1968-1973
- Fisher N, Agarwal M, Reuben SF, Johnson DS, Turner PG. Sporting and physical activity following Oxford medial unicompartmental knee arthroplasty. Knee 2006;13:296-300
- Kort NP, van Raay JJAM, van Horn JJ_._ The Oxford phase III unicompartmental knee replacement in patients less than 60 years of age. Knee Surg Sports Traumatol Arthrosc 2007;15:356--360
- Vince KG, Cyran LT. Unicompartmental knee arthroplasty: new indications, more complications? J Arthroplasty 2004;19(4) Suppl 1:9-16
- Gill SG, Chan KC, Mills DM. 5- to 18-year follow-up study of cemented total knee arthroplasty for patients 55 years old or younger. J Arthroplasty 1997;12:49--54
- Diduch DR, Insall JN, Scott WN, Scuderi GR, Font-Rodriquez D. Total knee replacement in young, active patients: long-term followup and functional outcome. J Bone J Surg (Am) 1997;79:575--582
- Duffy GP, Trousdale RT, Stuart MJ. Total knee arthroplasty in patients 55 years old or younger 10- to 17-year results. Clin Orthop 1998;356:22--27
- Newman JH, Ackroyd CE, Shah N. Unicompartmental or total knee replacement? Five-year results of a prospective randomized trial of 102 osteoarthritic knees with unicompartmental arthritis. J Bone Joint Surg (Br) 1998;80:862--865
- Yang KY, Wang MC, Yeo SJ, Lo NN_. Minimally invasive unicondylar versus total condylar knee arthroplasty-early results of a matched-pair comparison._ Singapore Med J 2003;44:559--562
- Amin AK, Patton JT, Cook RE, Gaston M, Brenkel IJ. Unicompartmental or total knee arthroplasty? Results of a matched study. Clin Orthop 2006;451:101--106
- Healy WL, Sharma S, Schwartz B, Iorio R. Athletic activity after total joint arthroplasty. J Bone Joint Surg (Am) 2008;90:2245-2252
- Furnes O, Espehaug B, Lie SA, Vollset E, Engesaeter L, Havelin L. Failure mechanisms after unicompartmental and tricompartmental knee replacement with cement-a comparison of failure mechanisms. J Bone Joint Surg (Am) 2007;89:519--525
- W-Dahl A, Robertsson O, Lidgren L. Surgery for knee osteoarthritis in younger patients. Acta Orthopaedica 2010;81(2):161-4.
- Australian Orthopaedic Association National Joint Replacement Registry. 2009 Annual Report.
- Gioe TJ, Novak C, Sinner P, Ma W, Mehle S. Knee arthroplasty in the young patient: survival in a community registry. Clin Orthop 2007;464:83-87
- Hamilton WG, Collier MB, Tarabee E, McAuley JP, Engh CA, Engh GA. Incidence and reasons for reoperation after minimally invasive unicompartmental knee arthroplasty. J Arthroplasty 2006;21(6) Suppl 2:98-106
- Song M-H, Kim B-H, Ahn S-J, Yoo S-H, Lee M-S. Early complications after minimally invasive mobile-bearing medial unicompartmental knee arthroplasty. J Arthroplasty 2009;24(8):1281-1284
- Stern SH, Becker MW, Insall JN. Unicondylar knee arthroplasty. An evaluation of selection criteria. Clin Orthop 1993;286:143-148
- Robertsson O, Knutson K, Lewold S, Lidgren L. _The routine of surgical management reduces failure after unicompartmental knee arthroplasty_. J Bone Joint Surg (Br) 2001;83(1):45-9
- Meneghini RM, Hanssen AD. Cementless fixation in total knee arthroplasty: past, present and future. J Knee Surg 2008; 21(4):307-313