Scandinavian Journal of Surgery 0: 1 8, Department of Surgery, North Karelia Central Hospital, Joensuu, Finland 2

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1 577022SJS / UKA mid-term resultss. S. A. Miettinen et al. research-article2015 ORIGINAL ARTICLE Scandinavian Journal of Surgery 0: 1 8, 2015 Mid-Term Results Of Oxford Phase 3 Unicompartmental Knee Arthroplasties At A Small-Volume Center S. S. A. Miettinen 1,2, S. K. Torssonen 1, H. J. A. Miettinen 2, T. Soininvaara 1 1 Department of Surgery, North Karelia Central Hospital, Joensuu, Finland 2 Department of Orthopaedics, Traumatology and Hand Surgery, Kuopio University Hospital, Kuopio, Finland Abstract Background and Aims: Unicompartmental knee arthroplasty is considered as an alternative to total knee arthroplasty for patients who have osteoarthritis limited to the medial compartment of the knee. The aim of this retrospective study was to find out clinical and radiological outcomes and related complications using the Oxford phase 3 prosthesis at a small-volume center. Material and methods: In all, 95 Oxford unicompartmental knee arthroplasties (87 patients) were performed between 2000 and 2010 in North Karelia Central Hospital. Of these, five patients had undergone revision surgery. In all, 52 unicompartmental knee arthroplasties (46 patients) participated in this study. The mean age of patients was 61.4 years, and 78.2% of patients were females. Pain and function levels were evaluated by using the Knee Society score. Radiographic analyses were performed on preoperative and postoperative and follow-up radiographs. Results and Conclusions: The mean follow-up time was 6.5 years, and the Kaplan Meier estimated 9-year implant survival rate was 88.9% (95% confidence interval = 78.7% 99.1%). The median Knee Society score of 77 (range: 18 93) at follow-up was considered good (range: 70 79). In this study, we found out that medial knee pain remains in 10% of unicompartmental knee arthroplasties several years after surgery, although the reason for the pain remained unclear. These mid-term results are promising, and good results can be achieved also at a small-volume center when strict patient selection is followed. Key words: Knee; orthopedics; osteoarthritis; unicondylar knee arthroplasty; clinical follow-up study; radiography Correspondence: Simo S. A. Miettinen Department of Orthopaedics, Traumatology and Hand Surgery Kuopio University Hospital P.O. Box 1777 Puijonlaaksontie Kuopio Finland simo.miettinen@kuh.fi

2 2 S. S. A. Miettinen et al. Fig. 1. Patient flowchart. Introduction A typical symptom of knee osteoarthritis (OA) is medial knee pain. There are a number of surgical options for treating medial unicompartmental OA of the knee, including high tibial osteotomy (HTO), unicompartmental knee arthroplasty (UKA), and total knee arthroplasty (TKA) (1, 2). Early reports of UKA implant survival were not promising (3). However, recent studies with newer generation UKA implants have shown 10-year survival rates of >95% (4, 5). Indications for UKA are unicompartmental OA or femoral avascular necrosis with intact patellofemoral and lateral compartments (6). Other factors that favor the use of UKA are age over 60 years, low patientactivity demand, relatively low body mass index (BMI), and minimal pain at rest (6, 7). The range of motion (ROM) arc should be >90, with flexion contracture of <5, and <10 axial malalignment that can be passively corrected to almost neutral (6, 7). Contraindication for UKA has been pre-existing patellofemoral joint degeneration and anterior cruciate ligament (ACL) deficiency (8, 9). The advantages of UKA over TKA are conservation of normal structures, knee kinematics and proprioception, rapid recovery, and a wider ROM (10 13). Other advantages are lower blood loss and less postoperative pain and total hospital stay is shorter (14, 15). Disadvantages of UKA have been high rate of mechanical complications and UKA is likely to need revision sooner than TKA (16). The aim of this retrospective study was to evaluate clinical and radiological results of Oxford UKAs at a small-volume center (North Karelian Central Hospital) by inviting patients to clinical and radiological follow-up. Material And Methods A total of 95 UKA operations (87 patients) were performed between January 2000 and December 2010 in North Karelia Central Hospital. There were 10 UKAs whose follow-up time did not exceeded 2 years and they were excluded due to short follow-up time. Four UKAs had moved out of our local hospital area of responsibility and were excluded. We also excluded three UKAs suffering from severe dementia and were permanently hospitalized. A total of 78 UKAs (70 patients) were included to this study (Fig. 1). Seven of these UKA patients had died during follow-up time and five UKAs had had revision surgery to TKA. There were eight bilateral UKAs, and three of them were synchronous. All patient records and patients were examined in autumn Included patients were invited to clinical followup and 52 UKAs (46 patients) participated which turned out to be 66.7% of the included UKAs. Radiographic grading of the knee OA was done according to the Kellgren Lawrence (K-L) scale (17). In this study, criteria for UKA were no or K-L 1 OA for patellofemoral or lateral tibiofemoral joints in radiographs or previous arthroscopy. Patients with a medial OA of K-L 2 3 were operated (Table 1). Other inclusion criteria for UKA were no anterior cruciate ligament deficiency and varus knee with correctable varus alignment. Two senior orthopedic surgeons performed all UKAs: One did 81 (85.3%) operations and another did 14 (14.7%) operations. The patellofemoral and lateral tibiofemoral joints were monitored with arthroscopy or by using a medial parapatellar approach. UKA was not performed if there was significant arthrosis (K-L 2 4) in other compartments. At the time of surgery, the anterior cruciate ligament was intact in all knees. No technical

3 UKA mid-term results 3 Table 1 Baseline demographic data and operative information. n (%) Sex Male 11 (21.2) Female 41 (78.8) Operation indication Primary osteoarthritis 49 (94.2) Osteochondrosis 2 (3.8) Posttraumatic osteoarthrosis 1 (1.9) Operation side Right 25 (48.1) Left 27 (51.9) Kellgren Lawrence scale 1. Doubtful 0 (0) 2. Minimal 32 (61.5) 3. Moderate 20 (38.5) 4. Severe 0 (0) Previous knee operation None 28 (53.8) Meniscus resection or suture 6 (11.5) Arthroscopy 17 (32.7) Osteochondral Autograft Transfer System (OATS) 1 (1.9) Extension lag None 26 (50.0) <5 6 (11.5) (7.7) >10 0 (0) Unknown 16 (30.8) Flexion lag None 18 (34.6) <10 4 (7.7) (17.3) >20 5 (9.6) Unknown 16 (30.8) complications such as fractures or medial collateral ligament injuries occurred during the procedures. The Oxford phase 3 prosthesis (Biomet Orthopaedics Inc., Warsaw, Indiana, USA) was first introduced in The main difference between the Oxford phase 3 prosthesis and other UKAs is a congruent and mobile tibial bearing, which reduces polyethylene wear and allows a wide ROM. The Oxford knee system consists of femoral and tibial components in a cobalt chromium alloy and a compression-molded polyethylene tibia insert. Palacos cum gentamicin cement was used to attach components to the bone. All procedures were performed using a standard medial parapatellar opening and a tourniquet. Patients received antibiotic prophylaxis with 3 g cefuroxime; those patients allergic to cephalosporin were given 300 mg clindamycin. Low-molecular-weight heparin was generally given as a thrombosis prophylaxis; however, warfarin was given to patients who had used this drug prior to arthroplasty. All patients and knees were evaluated and examined by the first author (S.M.) at the final clinical follow-up. Postoperative knee function was evaluated using the Knee Society score (KSS) (18). Radiological assessments were done by the first author (S.M.) from anteroposterior and lateral full-weight-bearing radiographs (19). Mechanical axis radiographs were taken both preoperatively and at the final clinical follow-up. Radiolucencies and osteolysis and component migration were analyzed and radiolucencies more than 2 mm were considered significant (19). Statistics Statistical differences were analyzed with the nonparametric Pearson s chi-square test and p < 0.05 was considered to be statistical significant. A Kaplan Meier (K-M) survival analysis was done for all included 78 UKAs. A worst-case scenario survivorship analysis (K-M) was done due to large number of UKAs lost to follow-up. In the worst-case scenario analysis, 14 UKAs lost to follow-up were considered as revised UKA at the end day of the follow-up, so in this analysis there were a total of 19 revisions. A life table analysis was conducted to evaluate follow-up time point where at least 20 UKA patients are still in risk. All data were analyzed using SPSS version (IBM, Chicago, IL, USA). ETHICAL APPROVAL Approval (72/2011) was obtained from the Regional Ethics Committee of the University of Eastern Finland. Written informed consent for participation was obtained from every participant. Results The mean follow-up time for included 78 UKAs was 6.5 years (range, years; SD = 2.7). The mean age of the patients at the time of UKA operation was 61.4 years (range, years; SD = 9.2). There were 17/78 (21.8%) UKAs operated on male patients and 61/78 (78.2%) UKAs on female patients and 8 of these UKAs were bilateral (1 male and 7 females). Preoperative data of the participated 46 patients (52 UKAs; 6 bilateral UKAs) were analyzed (Table 1). The physical status of patients was assessed preoperatively using the American Society of Anesthesiologists (ASA) physical status classification system and median ASA was found to be 2 (range: 1 3). The mean surgery time was 77 min (range: min) and the mean 24-h postoperative bleed volume was 179 ml (range: ml). The median KSS at the follow-up was 77 (range: 18 93; Table 2). Of the patients, 15/52 (28.8%) had an excellent score (80 100), 23/52 (44.2%) had a good score (70 79), 11/52 (21.1%) had a fair score (60 69), and 3/52 (5.8%) had a poor score (<60). The median Knee Society function score was 90 (range, ; Table 2). At the follow-up, the median KSS of the patients aged <65 years (n = 37) was 77 and aged of patients 65 years (n = 15) was 78 (p = 0.441). The median Knee Society function score of the patients aged <65 years was 90 and aged 65 years was 70 (p = 0.398). Unfortunately pre- and postoperative KSS were poorly harvested by that time they were collected, so these data were not reliable to use for any analysis for this study. Patient satisfaction to UKA was assessed and 38/52 (73.1%) of patients considered their experience of UKA

4 4 S. S. A. Miettinen et al. Table 2 Knee Society Score statistics of 52 included UKAs at follow-up. Knee score Pain, n (%) None 29 (55.8) Mild/occasional 13 (25.0) Mild (stairs only) 1 (1.9) Mild (walking and stairs) 4 (7.7) Moderate occasional 3 (5.8) Moderate continual 2 (3.8) Severe 0 (0.0) Flexion contracture Mean, (range) (5 20 ) Extension lag Mean, (range) <10 (<10 20 ) Total range of flexion Mean, (range) 118 ( ) Alignment (varus) Mean, (range) 5 10 (0 14 ) Stability Mean, mm (range) <5 (<5 >10) Mediolateral Mean, mm (range) <5 (<5 >15) Knee Society score, median (SD, range) 77 (14.9, 18 93) Knee Society score: function Walking, n (%) Unlimited 26 (50.0) >10 blocks 12 (23.1) 5 10 blocks 10 (19.2) <5 blocks 4 (7.7) Housebound 0 (0.0) Unable 0 (0.0) Stairs, n (%) Normal up and down 19 (36.5) Normal up, down with rail 20 (38.5) Up and down with rail 12 (23.1) Up with rail, down unable 1 (1.9) Unable 0 (0.0) Walking aids used, n (%) None 45 (86.5) Single cane/walking stick 1 (1.9) Two canes/walking sticks 5 (9.6) Crutches or walking frame 1 (1.9) Function score, median (SD, range) 90 (19.8, ) to be good or excellent. Of patients, 46/52 (88.5%) would agree to undergo UKA again, even though 14/52 (26.9%) of UKAs only had a fair or poor KSS outcome. Five patients had TKA in one knee and UKA in the other: Of these, four found UKA to be better than TKA. The preoperative extension lag was <10 in 62.2% of knees. At the end of the follow-up time, an extension lag of <10 was measured in 93.4% of the knees. The preoperative flexion lag was <20 in 54.9%; at the end of follow-up, this value was reached in 98.3% of knees (Table 2). The cumulative Kaplan Meier survival rate at 9 years was 88.9% (95% CI = 78.7% 99.1%; Fig. 2). In the life table analysis, only 13.5 UKA patients were at risk between 9 and 10 years of follow-up and this was not considered enough to calculate survival rate. Therefore, survivorship values beyond 9 years are not reported. Because the proportion of patients who were lost to follow-up was as high as 18% (14/78 included UKAs), we conducted a worst-case scenario survivorship analysis. In this worst-case scenario, revised UKAs were considered revised and also all UKAs who were lost to follow-up were categorized as being revised at the end of the follow-up. The cumulative Kaplan Meier survival rate in worst-case scenario at 9 years was 48.6% (95% CI = 30.8% 66.4%). All UKA revision surgeries were made to patients aged <65 years, but there was no statistically significant difference between the UKA patients aged under 65 years (n = 56) and over 65 years (n = 26; p = 0.138). Radiological Analysis Of The Knees Preoperative and postoperative and follow-up radiological data are given in Table 3. Median preoperative K-L grade OA of the medial tibiofemoral joint was 2 (SD = 1.0, range: 1 3). The median K-L grade OA of the patellofemoral joint was 1 (SD = 0.4, range: 1 2) preoperatively and 2 (SD = 0.5, range: 1 3) at follow-up (p = 0.001). Patellofemoral OA progressed in 15/52 (28.8%) of UKA patients during follow-up. The distance between tip of the patella and the tibial joint line from radiographs taken both before and after the operation to determine whether the joint line had changed (Fig. 3): This distance changed by >2 mm in 18/52 (34.6%) of cases (Table 3). The average correction of the mechanical axis was 0.9 at follow-up (Table 3). Varus did not change to valgus in any of the UKAs. The average change of the Harris angle and change in the mechanical axis line (Mikulicz line) were analyzed (Table 3, Fig. 4). Radiolucent lines were seen in three of the X-rays at the follow-up. One UKA had showed progressive radiolucencies during follow-up and led to revision. The positions (flexion and extension/varus and valgus) of the femur and tibia components were examined from the preoperative and postoperative radiographs (Fig. 3). There were only minor changes in component positions, and they were not clinically significant. Revision Surgery And Other Related Problems The surgical revision rate for included 78 UKAs was 6.4%: Five patients underwent revision surgery and conversion to TKA. The mean time to revision surgery was 4.4 years (SD = 3.3, range: years). Three UKA revisions were done to males and two to females. The revision rate for males was as high as 3/17 (17.6%, SD = 0.82, 95% CI = 7.96% 11.18%), and for females, it was 2/61 (3.4%, SD = 0.21, 95% CI = 10.68% 11.51%) (p = 0.025). Two knees underwent conversion to TKA because of OA progression in the patellofemoral joint and/or the lateral femorotibial compartment. One knee underwent revision surgery because of tibia component malalignment, which caused pain and reduced ROM. Polyethylene insert dislocation occurred in one patient. Formation of radiolucent lines was related to implant loosening in only one patient. There were also two other UKAs with radiolucent

5 UKA mid-term results 5 Fig. 2. The cumulative Kaplan Meier survival rate at 9 years was 88.9% (95% CI = 78.7% 99.1%). Table 3 Radiological measurements of 52 included UKAs. Preoperative Follow-up p-value Mean (SD, range) Mean (SD, range) Anatomical axis varus, 0.6 (1.5, 0 7) 1.2 (2.5, ) Anatomical axis valgus, 2.8 (2.3, 0 9) 2.4 (2.9, ) Mechanical axis varus, 7.1 (3.0, ) 6.2 (3.5, ) Harris angle, 4.7 (2.4, ) 3.5 (1.9, ) Movement of Mikulicz line (mechanical axis), mm 21.4 (10.0, ) 21.0 (12.0, ) Distance from the tip of the patella to the tibial joint line, mm 30.1 (4.9, 20 45) 33.1 (4.4, ) lines but they were asymptomatic and remain under surveillance. All three complete and partial radiolucent lines were <2 mm thick. There were 12 UKAs with minor problems related to surgery (Table 4). Discussion Medial unicompartmental knee OA can be treated surgically by UKA, HTO, or TKA. UKA is a treatment option for carefully selected patients. Good results at UKA are achieved using strict inclusion criteria, for example, patients aged >65 who are only moderately active, are nonobese, have a good preoperative ROM, and have mild varus malalignment without joint instability (20). In this study, the cumulative Kaplan Meier UKA survival rate at 9 years was 88.9% (95% CI = 78.7% 99.1%). There were five UKA revisions to TKA and other minor problems occurred in 12 knees. These UKA mid-term results are comparable to those of recent studies, which report survival rates varying from 89.9% to 94.4% (16, 21, 22). Over a decade ago, 10-year follow-up studies showed survival rates to vary from 93% to 98% (5, 23). In a recent 16-year survival study, Oxford UKAs were shown to be more durable, with a survival rate of 91.0% (24). In the Finnish Arthroplasty Register study, a total 10-year survival rate for all UKA models was 73% (25). Reasons for the high surgical revision rates are assumed to be the technically demanding surgery and inappropriate patient selection (22, 25). In our series, revisions cumulated to male patients and patients under 65 years of age. It remains open whether it applies to the patient selection, patient compliance with postoperative schemes, patient activity level, implant size, or other reasons. A common postoperative complaint in this study was persistent medial knee pain (in 10% of patients), even years after the surgery. However, reason(s) for this medial knee pain remain unclear. We originally

6 6 S. S. A. Miettinen et al. Table 4 UKA revisions. n Fig. 3. Lateral radiography of UKA. A) Measurements of the distance from the tip of the patella to the tibia plate are shown. B) Measurements of flexion of the femoral component and the posterior slope of the tibial component are shown. Fig. 4. Anteroposterior radiography showing measurements of A) the mechanical axis, B) the anatomical axis, and C) the Harris angle. hypothesized that a change in the joint line level (distance between the patella and tibial joint line) would change knee articulation and thus cause knee pain; however, we did not obtain clear evidence for this (Fig. 3; Table 3; p=0.096). In this study, radiological changes in component positions were so minimal that we think they do not explain medial knee pain. Medial Gender Male 2 Female 3 Reason for revision Progression of knee osteoarthritis 2 Component malalignment 1 Implant loosening 1 Dislocation of the polyethylene insert 1 Other minor problems (no revision done) Superficial infection 1 Pain 9 Pulmonary embolism 1 Loose bony bodies removed by arthroscopy 1 pain has been studied previously and shown not to correlate with radiographic findings, preoperative OA, or component positioning (22). The second most common reason for surgical revision was loosening of the tibial component, which occurs most often during the early postoperative period, that is, within 2 years (26). In this study, there was only one incidence of tibial component loosening. The stability of this implant component is encouraging and may be due to recent improvements in UKA prosthesis model designs. Other contributory factors may include (1) proper selection of patients with medially limited OA combined with preoperatively minor, easily correctable varus deformity and (2) precise surgical techniques, resulting in minimal tibial bone resection, which allows implant positioning without overcorrecting lower limb alignment. In this study, alignment corrections were minor and did not change much during follow-up (Table 3). Previous reports indicate that OA progression in other joint compartments is a common problem (16, 27). In this study, radiological findings showed slow progression of OA in other compartments; two surgical revisions were necessary for this reason. OA of the patellofemoral joint, in particular, was observed to progress. It is therefore necessary to rule out significant OA in other compartments before carrying out UKA. Postoperative and follow-up radiographs showed statistically significant differences in component positions but we think that these changes were not clinically significant because none of these implant positions changes led to revision or explained medial knee pain. The KSS for 52 UKAs was 77 and it was classified as good. An excellent result is defined as a score >80 (18). Our scores are comparable with other recently published mid-term results (21, 22). Overall, our patients were satisfied to UKA and would agree to undergo UKA surgery again even though 25.4% of UKAs only had a fair or poor KSS outcome (Table 2). This study was a retrospective cohort study and unfortunately some of the preoperative and postoperative data were missing and were poor in quality. Preoperative and postoperative KSSs were collected

7 UKA mid-term results 7 inadequately by that time so we were not able to compare preoperative KSS to the follow-up KSS. Therefore, the data can give appropriate results at the final follow-up. Small cohort size and long follow-up time set limitations to this study. There were only few UKA surgeries per year in our hospital and therefore number of UKAs per orthopedic surgeon was also small. When UKA is done seldomly, it may affect the results of the operation. The number of patients excluded or lost during follow-up was also quite high in our study and that is why the worst-case scenario survivorship analysis was conducted. In the worst-case scenario, the hypothetical number of revisions was high and therefore the survival was poor. The use of UKA for the treatment of medial knee OA remains controversial. The UKA procedure was previously shown to have a poorer long-term survival than TKA; moreover, UKA is less cost effective than TKA (28). If surgical revision is needed, the outcomes of UKA revisions are poorer than those of TKA (16, 29). Further research is needed to find out the reason for persistent and unexplained medial knee pain. In summary, UKA surgeries should be focused to well-trained orthopedic surgeons to achieve better results. In this study, we find out that good results of this seldomly made operation can also be achieved at small number of hospitals. Based on our results, we prefer to limit the use of UKA only to a small group of aged (over 65 years) female patients with medial knee OA (K-L 2-3) and who have good preoperative range of motion. Acknowledgements We thank PhD Tapio Hakala for his assist and help of organizing Finnish Government EVO-funding for this study. We also like to thank MSc Tuomas Selander for helping us with statistical analysis. Contribution Of Authors All authors participated in the planning and design of the study and in interpretation of the results. S.T. and another orthopedic surgeon performed the UKAs. S.M. examined patients and radiographs. Approval (72/2011) was obtained from the Regional Ethics Committee of the University of Eastern Finland. Declaration Of Conflicting Interests The authors declare that they have no competing interests. Funding There was no external financial support for investigators. This study was made possible by Finnish Government EVOfund. References 1. Rönn K, Reischl N, Gautier E, et al: Current surgical treatment of knee osteoarthritis. Arthritis 2011; Epub ID report=reader (accessed 10 September 2014). 2. Takeuchi R, Umemoto Y, Aratake M, et al: A mid term comparison of open wedge high tibial osteotomy vs unicompartmental knee arthroplasty for medial compartment osteoarthritis of the knee. J Orthop Surg Res 2010;5: Laskin R: Unicompartmental tibiofemoral resurfacing arthroplasty. 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8 8 S. S. A. Miettinen et al. 26. Epinette JA, Brunschweiler B, Mertl P, et al: Unicompartmental knee arthroplasty modes of failure: Wear is not the main reason for failure: A multicentre study of 418 failed knees. Orthop Traumatol Surg Res 2012;98: Berger RA, Meneghini RM, Sheinkop MB, et al: The progression of patellofemoral arthrosis after medial unicompartmental replacement: Results at 11 to 15 years. Clin Orthop Relat Res 2004;428: Koskinen E, Eskelinen A, Paavolainen P, et al: Comparison of survival and cost-effectiveness between unicondylar arthroplasty and total knee arthroplasty in patients with primary osteoarthritis. Acta Orthop 2008;79: Järvenpää J, Kettunen J, Miettinen H, et al: The clinical outcome of revision knee replacement after unicompartmental knee arthroplasty versus primary total knee arthroplasty: 8 17 years follow-up study of 49 patients. Int Orthop 2010;34: Received: June 3, 2014 Accepted: February 11, 2015