The Knee 22 (2015) 338–340
Contents lists available at ScienceDirect
The Knee
Modes of failure and revision of failed lateral unicompartmental knee arthroplasties Mustafa Citak a,⁎, Michael B. Cross b, Thorsten Gehrke a, Kathrin Dersch a, Daniel Kendoff a a b
Department of Orthopaedic Surgery, Helios ENDO-Klinik Hamburg, Hamburg, Germany Department of Orthopaedic Surgery, Hospital for Special Surgery, NY, USA
a r t i c l e
i n f o
Article history: Received 23 June 2014 Received in revised form 10 March 2015 Accepted 16 March 2015 Keywords: Lateral UKA Failure Aseptic loosening Lateral compartment osteoarthritis
a b s t r a c t Background: Even with the resurgence of interest in unicompartmental knee arthroplasty (UKA) in recent years, lateral UKA is still performed 10 times less frequently than medial UKA. Hence, because of the infrequency of this procedure, a paucity of outcome studies exist on lateral unicompartmental knee arthroplasty. This retrospective study was performed to analyze the main causes of failure, as well as the time to failure following lateral UKA. Methods: A total of 16 consecutive failed lateral UKAs were revised at our institution and were retrospectively reviewed. Causes of failure and time to failure were analyzed based on the medical records and radiographs at the time of revision. Results: The mean time from index arthroplasty to revision surgery was 9.4 years. In three cases, lateral UKA was converted to primary TKA and in the remaining thirteen cases, revision knee joint systems were used. Seven out of the 16 patients (43.8%) were revised within five years after the index surgery. Overall, the most common reason for failure was progression of arthritis of the medial and/or patellofemoral compartments (56.3%) followed by aseptic loosening (18.8%). Conclusions: In conclusion, similar to published reports on medial UKA, the main reason for early and late failure after lateral UKA was progression of arthritis in other compartments. Level of evidence: IV © 2015 Elsevier B.V. All rights reserved.
1. Introduction Isolated lateral compartment knee osteoarthritis (OA) is a relatively uncommon clinical problem, with a lower incidence than isolated medial compartment knee OA [1,2]. Even with the resurgence of interest in unicompartmental knee arthroplasty (UKA) in recent years, lateral UKA is still performed 10 times less than medial UKA and represents less than one percent (b1%) of all knee arthroplasty procedures performed [2]. Hence, because of the infrequency of this procedure, a paucity of outcome studies exist on lateral unicompartmental knee arthroplasty [1–12]. Nevertheless, the available data shows that lateral UKA is an acceptable treatment for isolated lateral compartmental knee OA. However, concerns remain regarding the long term survivorship and main causes for early and late failures of lateral UKA. Therefore, we performed a retrospective case series to analyze the modes of failure and to understand the complexity of revising a failed lateral UKA. We
⁎ Corresponding author at: Department of Orthopaedic Surgery, Helios ENDO-Klinik Hamburg, Holstenstrasse 2, 22767 Hamburg, Germany. Tel.: +49 176 61987317; fax: + 49 31970. E-mail address: [email protected] (M. Citak).
http://dx.doi.org/10.1016/j.knee.2015.03.008 0968-0160/© 2015 Elsevier B.V. All rights reserved.
hypothesized that failure mechanisms would be similar to those published for medial compartment knee arthroplasty. 2. Materials and methods An ethics board at our institution approved the study. All patients surgically revised for failed lateral unicompartmental knee arthroplasty at our institution between January 2000 and December 2012 were retrospectively reviewed in the cohort of failure study. A total of 16 consecutive failed lateral UKAs were included in this retrospective case series. Demographic information including age, gender, body mass index (BMI) and surgical side at the time of revision was obtained from the patients' medical records (Tables 1, 2). Twelve patients were females and four were males with an average age of 68.8 years (range, 44 to 85 years; SD = 12.9) at time of revision surgery (Tables 1, 2). The mean age at time of index surgery was 58.8 years (range, 31 to 81 years; SD = 14.1). In 13 cases, lateral UKA was performed due to primary osteoarthritis and in three cases due to secondary osteoarthritis (post-traumatic). In all patients, the index surgery was performed at another institution, which means that the indications for the initial lateral UKA were not standardized. The dates of index and revision surgery were also obtained in all patients. Reasons for failure were recorded based on patient symptoms,
M. Citak et al. / The Knee 22 (2015) 338–340
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Table 1 The table reveals detailed information of all failed lateral UKA's. Progression of osteoarthritis was with nine cases the most common reason for failure. Combined progression of OA in the medial and patellofemoral compartment was found in six cases.*OA = osteoarthritis; MCA = Medial compartment arthritis; PFA = patellofemoral compartment arthritis. N
Gender
Age at revision surgery (in years)
Time from index arthroplasty to revision surgery for (in years)
Reason failure
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Female Female Female Female Female Male Female Female Male Female Female Male Male Female Female Female
47 78 80 61 83 44 85 70 59 81 82 71 64 60 60 76
3.1 1.1 8.0 11.1 21.1 12.1 4.0 3.0 1.1 12.1 19.1 18.1 18.1 3.0 16.1 0.1
Arthrofibrosis Progression of OA (MCA) Progression of OA (MCA & PFA) Progression of OA (MCA & PFA) Polyethylene wear Progression of OA (MCA & PFA) Aseptic loosening Progression of OA (MCA) Progression of OA (MCA) Aseptic loosening Progression of OA (MCA & PFA) Progression of OA (MCA & PFA) Polyethylene wear Aseptic loosening Progression of OA (MCA & PFA) Instability
documented history, diagnostic imaging, and intra-operative findings. Failure was defined as requiring revision surgery following lateral UKA. In our cohort, late failure was defined as failure occurring greater than 10 years after the index procedure. Preoperatively, aspiration of synovial fluid was performed to rule out a periprosthetic joint infection (PJI) in all patients. No cases of periprosthetic joint infection were included in our cohort. All revision surgeries were performed by well-experienced arthroplasty surgeons. All failed lateral UKAs were converted after the removal of the lateral UKA implant and subsequent preparing of the femur and tibia in either conventional TKA or revision knee joint systems. Two revision knee joint systems were implanted, the Rotational Knee Prosthesis (Roknep); Endo-Model® (LINK, Germany, Hamburg) and the Hinge Knee System (Toknep); Endo-Model® (LINK, Germany, Hamburg). The used conventional TKA was Zimmer NexGen® LPS-Flex Mobile (Zimmer, Warsaw, USA). 3. Statistical analysis All data were processed using GraphPad Prism (Version 5.0d, La Jolla, CA, USA). Descriptive statistics are presented in the form of number of occurrences, percentage, mean, standard deviation (SD) and/or range.
15 years. Overall, the most common reason for failure was progression of OA in nine cases. Progression of OA in the patellofemoral compartment and medial compartment was found in six patients (Fig. 2). Medial compartment OA was noted in three patients (Table 1). The most common reason for early (b10 years) failure was the development of arthritis in the medial and/or patellofemoral compartment (56.3%), followed by aseptic loosening (18.75%) (Fig. 1). The progression of arthritis in adjacent compartments was also the main reason for late (N10 years) failure; however, polyethylene wear was the second most common reason for failure in patients with implant survival more than 10 years (Fig. 1). Instability and arthrofibrosis as a cause for revision surgery were only found in one patient respectively, each of whom failed within five years of the index arthroplasty. (Fig. 1).
5. Discussion Only a few clinical studies on a variety of lateral unicondylar prostheses have been reported in the current literature, with medium to long term survival rates ranging from 72 to 100% [1–12] (Table 2); however, few studies have had large enough failure cohorts to define the most common failure modes of lateral UKAs. Similar to published failure mechanisms of medial UKA, we discovered the most common reason for early and late failure after lateral UKA is progression of arthritis in adjacent compartments. An important finding of our study is that the mean time to failure was 9.4 years after index surgery. However, over 40% failed within five years, while 30% survived greater than 15 years. The wide range
4. Results In three cases, lateral UKA were converted to a conventional TKA. In the remaining thirteen cases, revision knee joint systems were used, while the Rotational Knee Prosthesis (Roknep) was used in 10 cases and the Hinge Knee System (Toknep) was implanted in three cases. Patellar replacement was not performed in all cases. Overall, in six cases bone graft were required, while in four cases femoral and tibial bone graft and in two cases only tibial bone graft was performed. The mean time from index arthroplasty to revision surgery was 9.4 years (range, 0.1 to 21.1 years; standard deviation, SD = 7.4). Seven out of 16 patients (43.8%) were revised within five years after index surgery (Table 1). Interestingly, more than 30% of failed cases had a survivorship of more than
Table 2 Demographics of patients at time of revision. Variable
Mean
Age (years) Gender Male Female BMI (kg/m2) Preoperative HSS knee score Surgical side Left Right Time to failure (years)
68.8 (44–85) 4 12 27.5 (24–34) 50.3 (17–69) 10 6 9.4 (0.1–21.1)
Fig. 1. The figure reveals the causes for failure following lateral UKA. The most common cause was the development of other compartment arthritis. Poylethylene wear was the second common reason in patients with survival more than 10 years. Instability and arthrofibrosis were only noted in patients with a survival less than five years.
340
M. Citak et al. / The Knee 22 (2015) 338–340
Fig. 2. Anteroposterior and tangential patella radiographs showing the progression of OA.
of time to failure in our cohort highlights that lateral UKA is a challenging operation, and thus, surgical technique and patient selection is crucial to achieving long-term survival. However, if performed correctly, lateral compartment UKA can be a long term solution for isolated lateral UKA. The prior published survivorship of lateral UKA has been similarly variable. Pennington and colleagues found a 100% survival rate after a mean follow-up of 12.4 years following lateral UKA in 29 patients [11]. However, other studies have been less impressive. Argenson et al. published a survivorship of 92% at ten years and 84% at 16 years after index surgery [4]. Similarly, in a study by Ashraf et al., the cumulative survival rate was 83% at ten years and 74% at 15-years [5]. Finally, the longest follow-up following lateral UKA was reported in a study by O'Rourke and colleagues, who found a survival rate of 72% at mean follow-up of 24 years in 14 lateral UKAs. Similar to our study, prior work on a small numbers of patients has published the main reason for failure was the development of osteoarthritis in the medial and/or patellofemoral compartment, followed by aseptic loosening [5]. Interestingly, in our study, 30% of failed lateral UKAs were revised 15 years or greater after index surgery. While the mean reason for failure after 15 years in vivo was the development of OA in other compartments, 40% of failures after 15 years were due to polyethylene wear. The main limitation of the study is that primary lateral UKA was performed at outside institutions and therefore primary lateral UKA indications were not standardized. Since the denominator of index surgery is unknown, we cannot report on the failure rate following primary lateral UKA. Furthermore, it must be noted that the implant type/brand was not analyzed in our study, since the information about the implant type did not exist in every case. Because all index arthroplasty procedures
were performed at outside institutions, we did not have standardized radiographic parameters for assessing the preoperative position of the implants; thus, we cannot determine with certainty whether early failures were due to poor surgical technique. Another limitation of our study is the inherent bias of our retrospective study design. However, to our knowledge, our cohort is the largest published cohort of failures after lateral UKA. In summary, the mean time of failure after lateral UKA was 9.4 years; however, lateral UKA can be a long lasting solution to isolated lateral compartment knee OA, as approximately one third of failed cases were revised 15 years or greater after index surgery. The main reason for early and late failure after lateral UKA was advancing arthritis in other compartments; however, polyethylene wear was the second main reason for late failure. It must be also noted, that the majority of failed lateral UKAs were converted in constrained implant type. This can be answered basically by the general philosophy (in previous times) of the authors' institution. Although this has much improved/ changed over the last years, the mentioned time period did often include an implant exchange to a constrained implant type. More or less also based on surgeons preference at our hospital.
References [1] Sah AP, Scott RD. Lateral unicompartmental knee arthroplasty through a medial approach. Study with an average five-year follow-up. J Bone Joint Surg Am 2007; 89:1948–54. [2] Scott RD. Lateral unicompartmental replacement: a road less traveled. Orthopedics 2005;28:983–4. [3] Argenson JN, Chevrol-Benkeddache Y, Aubaniac JM. Modern unicompartmental knee arthroplasty with cement: a three to ten-year follow-up study. J Bone Joint Surg Am 2002;84-A:2235–9. [4] Argenson JN, Parratte S, Bertani A, Flecher X, Aubaniac JM. Long-term results with a lateral unicondylar replacement. Clin Orthop Relat Res 2008;466:2686–93. [5] Ashraf T, Newman JH, Evans RL, Ackroyd CE. Lateral unicompartmental knee replacement survivorship and clinical experience over 21 years. J Bone Joint Surg Br 2002;84:1126–30. [6] Carr A, Keyes G, Miller R, O'Connor J, Goodfellow J. Medial unicompartmental arthroplasty. A survival study of the Oxford meniscal knee. Clin Orthop Relat Res 1993;295:205–13. [7] Cartier P, Sanouiller JL, Grelsamer RP. Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty 1996;11:782–8. [8] Marmor L. Lateral compartment arthroplasty of the knee. Clin Orthop Relat Res 1984;186:115–21. [9] O'Rourke MR, Gardner JJ, Callaghan JJ, Liu SS, Goetz DD, Vittetoe DA, et al. The John Insall Award: unicompartmental knee replacement: a minimum twenty-one-year followup, end-result study. Clin Orthop Relat Res 2005;440:27–37. [10] Ohdera T, Tokunaga J, Kobayashi A. Unicompartmental knee arthroplasty for lateral gonarthrosis: midterm results. J Arthroplasty 2001;16:196–200. [11] Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Lateral unicompartmental knee arthroplasty: survivorship and technical considerations at an average followup of 12.4 years. J Arthroplasty 2006;21:13–7. [12] Sah AP, Scott RD. Lateral unicompartmental knee arthroplasty through a medial approach. Surgical technique. J Bone Joint Surg Am 2008;90(Suppl. 2 Pt 2):195–205.
Contents lists available at ScienceDirect
The Knee
Modes of failure and revision of failed lateral unicompartmental knee arthroplasties Mustafa Citak a,⁎, Michael B. Cross b, Thorsten Gehrke a, Kathrin Dersch a, Daniel Kendoff a a b
Department of Orthopaedic Surgery, Helios ENDO-Klinik Hamburg, Hamburg, Germany Department of Orthopaedic Surgery, Hospital for Special Surgery, NY, USA
a r t i c l e
i n f o
Article history: Received 23 June 2014 Received in revised form 10 March 2015 Accepted 16 March 2015 Keywords: Lateral UKA Failure Aseptic loosening Lateral compartment osteoarthritis
a b s t r a c t Background: Even with the resurgence of interest in unicompartmental knee arthroplasty (UKA) in recent years, lateral UKA is still performed 10 times less frequently than medial UKA. Hence, because of the infrequency of this procedure, a paucity of outcome studies exist on lateral unicompartmental knee arthroplasty. This retrospective study was performed to analyze the main causes of failure, as well as the time to failure following lateral UKA. Methods: A total of 16 consecutive failed lateral UKAs were revised at our institution and were retrospectively reviewed. Causes of failure and time to failure were analyzed based on the medical records and radiographs at the time of revision. Results: The mean time from index arthroplasty to revision surgery was 9.4 years. In three cases, lateral UKA was converted to primary TKA and in the remaining thirteen cases, revision knee joint systems were used. Seven out of the 16 patients (43.8%) were revised within five years after the index surgery. Overall, the most common reason for failure was progression of arthritis of the medial and/or patellofemoral compartments (56.3%) followed by aseptic loosening (18.8%). Conclusions: In conclusion, similar to published reports on medial UKA, the main reason for early and late failure after lateral UKA was progression of arthritis in other compartments. Level of evidence: IV © 2015 Elsevier B.V. All rights reserved.
1. Introduction Isolated lateral compartment knee osteoarthritis (OA) is a relatively uncommon clinical problem, with a lower incidence than isolated medial compartment knee OA [1,2]. Even with the resurgence of interest in unicompartmental knee arthroplasty (UKA) in recent years, lateral UKA is still performed 10 times less than medial UKA and represents less than one percent (b1%) of all knee arthroplasty procedures performed [2]. Hence, because of the infrequency of this procedure, a paucity of outcome studies exist on lateral unicompartmental knee arthroplasty [1–12]. Nevertheless, the available data shows that lateral UKA is an acceptable treatment for isolated lateral compartmental knee OA. However, concerns remain regarding the long term survivorship and main causes for early and late failures of lateral UKA. Therefore, we performed a retrospective case series to analyze the modes of failure and to understand the complexity of revising a failed lateral UKA. We
⁎ Corresponding author at: Department of Orthopaedic Surgery, Helios ENDO-Klinik Hamburg, Holstenstrasse 2, 22767 Hamburg, Germany. Tel.: +49 176 61987317; fax: + 49 31970. E-mail address: [email protected] (M. Citak).
http://dx.doi.org/10.1016/j.knee.2015.03.008 0968-0160/© 2015 Elsevier B.V. All rights reserved.
hypothesized that failure mechanisms would be similar to those published for medial compartment knee arthroplasty. 2. Materials and methods An ethics board at our institution approved the study. All patients surgically revised for failed lateral unicompartmental knee arthroplasty at our institution between January 2000 and December 2012 were retrospectively reviewed in the cohort of failure study. A total of 16 consecutive failed lateral UKAs were included in this retrospective case series. Demographic information including age, gender, body mass index (BMI) and surgical side at the time of revision was obtained from the patients' medical records (Tables 1, 2). Twelve patients were females and four were males with an average age of 68.8 years (range, 44 to 85 years; SD = 12.9) at time of revision surgery (Tables 1, 2). The mean age at time of index surgery was 58.8 years (range, 31 to 81 years; SD = 14.1). In 13 cases, lateral UKA was performed due to primary osteoarthritis and in three cases due to secondary osteoarthritis (post-traumatic). In all patients, the index surgery was performed at another institution, which means that the indications for the initial lateral UKA were not standardized. The dates of index and revision surgery were also obtained in all patients. Reasons for failure were recorded based on patient symptoms,
M. Citak et al. / The Knee 22 (2015) 338–340
339
Table 1 The table reveals detailed information of all failed lateral UKA's. Progression of osteoarthritis was with nine cases the most common reason for failure. Combined progression of OA in the medial and patellofemoral compartment was found in six cases.*OA = osteoarthritis; MCA = Medial compartment arthritis; PFA = patellofemoral compartment arthritis. N
Gender
Age at revision surgery (in years)
Time from index arthroplasty to revision surgery for (in years)
Reason failure
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Female Female Female Female Female Male Female Female Male Female Female Male Male Female Female Female
47 78 80 61 83 44 85 70 59 81 82 71 64 60 60 76
3.1 1.1 8.0 11.1 21.1 12.1 4.0 3.0 1.1 12.1 19.1 18.1 18.1 3.0 16.1 0.1
Arthrofibrosis Progression of OA (MCA) Progression of OA (MCA & PFA) Progression of OA (MCA & PFA) Polyethylene wear Progression of OA (MCA & PFA) Aseptic loosening Progression of OA (MCA) Progression of OA (MCA) Aseptic loosening Progression of OA (MCA & PFA) Progression of OA (MCA & PFA) Polyethylene wear Aseptic loosening Progression of OA (MCA & PFA) Instability
documented history, diagnostic imaging, and intra-operative findings. Failure was defined as requiring revision surgery following lateral UKA. In our cohort, late failure was defined as failure occurring greater than 10 years after the index procedure. Preoperatively, aspiration of synovial fluid was performed to rule out a periprosthetic joint infection (PJI) in all patients. No cases of periprosthetic joint infection were included in our cohort. All revision surgeries were performed by well-experienced arthroplasty surgeons. All failed lateral UKAs were converted after the removal of the lateral UKA implant and subsequent preparing of the femur and tibia in either conventional TKA or revision knee joint systems. Two revision knee joint systems were implanted, the Rotational Knee Prosthesis (Roknep); Endo-Model® (LINK, Germany, Hamburg) and the Hinge Knee System (Toknep); Endo-Model® (LINK, Germany, Hamburg). The used conventional TKA was Zimmer NexGen® LPS-Flex Mobile (Zimmer, Warsaw, USA). 3. Statistical analysis All data were processed using GraphPad Prism (Version 5.0d, La Jolla, CA, USA). Descriptive statistics are presented in the form of number of occurrences, percentage, mean, standard deviation (SD) and/or range.
15 years. Overall, the most common reason for failure was progression of OA in nine cases. Progression of OA in the patellofemoral compartment and medial compartment was found in six patients (Fig. 2). Medial compartment OA was noted in three patients (Table 1). The most common reason for early (b10 years) failure was the development of arthritis in the medial and/or patellofemoral compartment (56.3%), followed by aseptic loosening (18.75%) (Fig. 1). The progression of arthritis in adjacent compartments was also the main reason for late (N10 years) failure; however, polyethylene wear was the second most common reason for failure in patients with implant survival more than 10 years (Fig. 1). Instability and arthrofibrosis as a cause for revision surgery were only found in one patient respectively, each of whom failed within five years of the index arthroplasty. (Fig. 1).
5. Discussion Only a few clinical studies on a variety of lateral unicondylar prostheses have been reported in the current literature, with medium to long term survival rates ranging from 72 to 100% [1–12] (Table 2); however, few studies have had large enough failure cohorts to define the most common failure modes of lateral UKAs. Similar to published failure mechanisms of medial UKA, we discovered the most common reason for early and late failure after lateral UKA is progression of arthritis in adjacent compartments. An important finding of our study is that the mean time to failure was 9.4 years after index surgery. However, over 40% failed within five years, while 30% survived greater than 15 years. The wide range
4. Results In three cases, lateral UKA were converted to a conventional TKA. In the remaining thirteen cases, revision knee joint systems were used, while the Rotational Knee Prosthesis (Roknep) was used in 10 cases and the Hinge Knee System (Toknep) was implanted in three cases. Patellar replacement was not performed in all cases. Overall, in six cases bone graft were required, while in four cases femoral and tibial bone graft and in two cases only tibial bone graft was performed. The mean time from index arthroplasty to revision surgery was 9.4 years (range, 0.1 to 21.1 years; standard deviation, SD = 7.4). Seven out of 16 patients (43.8%) were revised within five years after index surgery (Table 1). Interestingly, more than 30% of failed cases had a survivorship of more than
Table 2 Demographics of patients at time of revision. Variable
Mean
Age (years) Gender Male Female BMI (kg/m2) Preoperative HSS knee score Surgical side Left Right Time to failure (years)
68.8 (44–85) 4 12 27.5 (24–34) 50.3 (17–69) 10 6 9.4 (0.1–21.1)
Fig. 1. The figure reveals the causes for failure following lateral UKA. The most common cause was the development of other compartment arthritis. Poylethylene wear was the second common reason in patients with survival more than 10 years. Instability and arthrofibrosis were only noted in patients with a survival less than five years.
340
M. Citak et al. / The Knee 22 (2015) 338–340
Fig. 2. Anteroposterior and tangential patella radiographs showing the progression of OA.
of time to failure in our cohort highlights that lateral UKA is a challenging operation, and thus, surgical technique and patient selection is crucial to achieving long-term survival. However, if performed correctly, lateral compartment UKA can be a long term solution for isolated lateral UKA. The prior published survivorship of lateral UKA has been similarly variable. Pennington and colleagues found a 100% survival rate after a mean follow-up of 12.4 years following lateral UKA in 29 patients [11]. However, other studies have been less impressive. Argenson et al. published a survivorship of 92% at ten years and 84% at 16 years after index surgery [4]. Similarly, in a study by Ashraf et al., the cumulative survival rate was 83% at ten years and 74% at 15-years [5]. Finally, the longest follow-up following lateral UKA was reported in a study by O'Rourke and colleagues, who found a survival rate of 72% at mean follow-up of 24 years in 14 lateral UKAs. Similar to our study, prior work on a small numbers of patients has published the main reason for failure was the development of osteoarthritis in the medial and/or patellofemoral compartment, followed by aseptic loosening [5]. Interestingly, in our study, 30% of failed lateral UKAs were revised 15 years or greater after index surgery. While the mean reason for failure after 15 years in vivo was the development of OA in other compartments, 40% of failures after 15 years were due to polyethylene wear. The main limitation of the study is that primary lateral UKA was performed at outside institutions and therefore primary lateral UKA indications were not standardized. Since the denominator of index surgery is unknown, we cannot report on the failure rate following primary lateral UKA. Furthermore, it must be noted that the implant type/brand was not analyzed in our study, since the information about the implant type did not exist in every case. Because all index arthroplasty procedures
were performed at outside institutions, we did not have standardized radiographic parameters for assessing the preoperative position of the implants; thus, we cannot determine with certainty whether early failures were due to poor surgical technique. Another limitation of our study is the inherent bias of our retrospective study design. However, to our knowledge, our cohort is the largest published cohort of failures after lateral UKA. In summary, the mean time of failure after lateral UKA was 9.4 years; however, lateral UKA can be a long lasting solution to isolated lateral compartment knee OA, as approximately one third of failed cases were revised 15 years or greater after index surgery. The main reason for early and late failure after lateral UKA was advancing arthritis in other compartments; however, polyethylene wear was the second main reason for late failure. It must be also noted, that the majority of failed lateral UKAs were converted in constrained implant type. This can be answered basically by the general philosophy (in previous times) of the authors' institution. Although this has much improved/ changed over the last years, the mentioned time period did often include an implant exchange to a constrained implant type. More or less also based on surgeons preference at our hospital.
References [1] Sah AP, Scott RD. Lateral unicompartmental knee arthroplasty through a medial approach. Study with an average five-year follow-up. J Bone Joint Surg Am 2007; 89:1948–54. [2] Scott RD. Lateral unicompartmental replacement: a road less traveled. Orthopedics 2005;28:983–4. [3] Argenson JN, Chevrol-Benkeddache Y, Aubaniac JM. Modern unicompartmental knee arthroplasty with cement: a three to ten-year follow-up study. J Bone Joint Surg Am 2002;84-A:2235–9. [4] Argenson JN, Parratte S, Bertani A, Flecher X, Aubaniac JM. Long-term results with a lateral unicondylar replacement. Clin Orthop Relat Res 2008;466:2686–93. [5] Ashraf T, Newman JH, Evans RL, Ackroyd CE. Lateral unicompartmental knee replacement survivorship and clinical experience over 21 years. J Bone Joint Surg Br 2002;84:1126–30. [6] Carr A, Keyes G, Miller R, O'Connor J, Goodfellow J. Medial unicompartmental arthroplasty. A survival study of the Oxford meniscal knee. Clin Orthop Relat Res 1993;295:205–13. [7] Cartier P, Sanouiller JL, Grelsamer RP. Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period. J Arthroplasty 1996;11:782–8. [8] Marmor L. Lateral compartment arthroplasty of the knee. Clin Orthop Relat Res 1984;186:115–21. [9] O'Rourke MR, Gardner JJ, Callaghan JJ, Liu SS, Goetz DD, Vittetoe DA, et al. The John Insall Award: unicompartmental knee replacement: a minimum twenty-one-year followup, end-result study. Clin Orthop Relat Res 2005;440:27–37. [10] Ohdera T, Tokunaga J, Kobayashi A. Unicompartmental knee arthroplasty for lateral gonarthrosis: midterm results. J Arthroplasty 2001;16:196–200. [11] Pennington DW, Swienckowski JJ, Lutes WB, Drake GN. Lateral unicompartmental knee arthroplasty: survivorship and technical considerations at an average followup of 12.4 years. J Arthroplasty 2006;21:13–7. [12] Sah AP, Scott RD. Lateral unicompartmental knee arthroplasty through a medial approach. Surgical technique. J Bone Joint Surg Am 2008;90(Suppl. 2 Pt 2):195–205.
