Unicompartmental knee arthroplasty: state of the art
2017; Elsevier BV; Volume: 2; Issue: 2 Linguagem: Inglês
10.1136/jisakos-2016-000102
ISSN2059-7762
AutoresLaura J. Kleeblad, Hendrik A. Zuiderbaan, Gary J. Hooper, Andrew D. Pearle,
Tópico(s)Orthopaedic implants and arthroplasty
ResumoThe popularity of unicompartmental knee arthroplasty (UKA) for the treatment of isolated compartment osteoarthritis of the knee has risen over the past 2 decades. Currently, UKA covers 10% of all knee arthroplasties worldwide. Although indications have been extended, results have proven that patient selection plays a critical role in the success of UKA. From the current perspective, age, body mass index, patellofemoral osteoarthritis, anterior cruciate ligament deficiency and chondrocalcinosis are no longer absolute contraindications for UKA. Motivated by the desire to improve survivorship rates, patient-reported outcomes and reduce complications, there have been many technological advances in the field of UKA over the recent years. The aim of this review was to evaluate the current indications, surgical techniques, modes of failure and survivorship results of UKA, by assessing a thorough review of modern literature. Several studies show that innovations in implant design, fixation methods and surgical techniques have led to good-to-excellent long-term survivorship, functional outcomes and less complications. Until now, resurgence of interest of cementless designs is noted according to large national registries to address problems associated with cementation. The future perspective on the usage of UKA, in particular the cementless design, looks promising. Furthermore, there is a growing interest in robotic-assisted techniques in order to optimise result by controlled soft-tissue balancing and reproduce alignment in UKA. Future advances in robotics, most likely in the field of planning and setup, will be valuable in optimising patient-specific UKA. The popularity of unicompartmental knee arthroplasty (UKA) for the treatment of isolated compartment osteoarthritis of the knee has risen over the past 2 decades. Currently, UKA covers 10% of all knee arthroplasties worldwide. Although indications have been extended, results have proven that patient selection plays a critical role in the success of UKA. From the current perspective, age, body mass index, patellofemoral osteoarthritis, anterior cruciate ligament deficiency and chondrocalcinosis are no longer absolute contraindications for UKA. Motivated by the desire to improve survivorship rates, patient-reported outcomes and reduce complications, there have been many technological advances in the field of UKA over the recent years. The aim of this review was to evaluate the current indications, surgical techniques, modes of failure and survivorship results of UKA, by assessing a thorough review of modern literature. Several studies show that innovations in implant design, fixation methods and surgical techniques have led to good-to-excellent long-term survivorship, functional outcomes and less complications. Until now, resurgence of interest of cementless designs is noted according to large national registries to address problems associated with cementation. The future perspective on the usage of UKA, in particular the cementless design, looks promising. Furthermore, there is a growing interest in robotic-assisted techniques in order to optimise result by controlled soft-tissue balancing and reproduce alignment in UKA. Future advances in robotics, most likely in the field of planning and setup, will be valuable in optimising patient-specific UKA. Knee osteoarthritis (OA) is highly prevalent worldwide. It is the leading cause of musculoskeletal disability and associated with activity limitation, working disability, reduced quality of life and increased healthcare costs.1Bindawas SM Vennu V Auais M Health-related quality of life in older adults with bilateral knee pain and back pain: data from the Osteoarthritis Initiative.Rheumatol Int. 2015; 35: 2095-210110.1007/s00296-015-3309-yCrossref PubMed Scopus (15) Google Scholar 2Hooper G Lee AJ Rothwell A et al.Current trends and projections in the utilisation rates of hip and knee replacement in New Zealand from 2001 to 2026.N Z Med J. 2014; 127: 82-93PubMed Google Scholar Partial or total joint replacement of the affected knee is a surgical intervention to treat the disease when conservative strategy fails. Both procedures are commonly performed in developed countries and the number is expected to increase dramatically in the upcoming decade.2Hooper G Lee AJ Rothwell A et al.Current trends and projections in the utilisation rates of hip and knee replacement in New Zealand from 2001 to 2026.N Z Med J. 2014; 127: 82-93PubMed Google Scholar 3Kurtz S Ong K Lau E et al.Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030.J Bone Jt Surg Am. 2007; 89: 780-785Crossref PubMed Scopus (5876) Google Scholar Unicompartmental knee arthroplasty (UKA) has gained popularity recently because several studies have shown that it is less invasive and has a reduced operative time, larger postoperative range of motion (ROM), improved pain relief, earlier return to daily activities and sports, and cost reduction in comparison to total knee arthroplasty (TKA).4Amin AK Patton JT Cook RE et al.Unicompartmental or total knee arthroplasty? Results from a matched study.Clin Orthop Relat Res. 2006; 451: 101-10610.1097/01.blo.0000224052.01873.20Crossref PubMed Scopus (112) Google Scholar, 5Lyons MC MacDonald SJ Somerville LE et al.Unicompartmental versus total knee arthroplasty database analysis: is there a winner?.Clin Orthop Relat Res. 2012; 470: 84-9010.1007/s11999-011-2144-zCrossref PubMed Scopus (179) Google Scholar, 6Noticewala MS Geller JA Lee JH et al.Unicompartmental knee arthroplasty relieves pain and improves function more than total knee arthroplasty.J Arthroplasty. 2012; 27: 99-10510.1016/j.arth.2012.03.044Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar, 7Witjes S Gouttebarge V Kuijer PPFM et al.Return to sports and physical activity after total and unicondylar knee arthroplasty: a systematic review and meta-analysis.Sports Med. 2016; 46: 269-29210.1007/s40279-015-0421-9Crossref PubMed Scopus (137) Google Scholar, 8Laurencin CT Zelicof SB Scott RD et al.Unicompartmental versus total knee arthroplasty in the same patient. A comparative study.Clin Orthop Relat Res. 1991; 273: 151-156Crossref PubMed Google Scholar National and annual registries show similar usage with an increasing incidence over the past 10 years, currently ranging from 5% to 11% globally in 2014.9American Joint Replacement RegistryAmerican Joint Replacement Registry—annual report 2014.http://www.ajrr.net/images/annual_reports/AJRR_2014_Annual_Report_final_11-11-15.pdfDate: 2014Google Scholar, 10Australian Orthopaedic Association National Joint RegistryHip and knee arthroplasty annual report 2015.https://aoanjrr.sahmri.com/documents/10180/217745/HipandKneeArthroplastyDate: 2015Google Scholar, 11National Joint Registry for England, Wales and Northern Ireland12th Annual report 2015.http://www.njrreports.org.uk/Portals/0/PDFdownloads/NJR_12th_Annual_Report_2015.pdfDate: 2015Google Scholar, 12New Zealand Joint RegistryThe New Zealand Registry annual report.http://nzoa.org.nz/system/files/Web_DH7657_NZJR2014Report_v4_12Nov15.pdfDate: 2014Google Scholar, 13Swedish Knee Arthroplasty Register Annual report 2015—Swedish Knee Arthroplasty Register.http://www.myknee.se/pdf/SVK_2015_Eng_1.0.pdfDate: 2015Google Scholar, 14Norwegian National Advisory Unit on Arthroplasty and Hip Fractures Norwegian Arthroplasty Register. Report 2015.http://nrlweb.ihelse.net/Rapporter/Report2015_english.pdfDate: 2015Google Scholar The aim of this review is to provide an overview of different aspects concerning UKA in terms of diagnostics, indications, patient selection, surgical techniques, clinical outcomes and geographical differences. The concept of replacement of a single compartment of the knee joint originated in the 1950s, when McKeever15McKeever DC The choice of prosthetic materials and evaluation of results.Clin Orthop. 1955; 6: 17-21PubMed Google Scholar and MacIntosh introduced the metallic tibial plateau. In 1972, the first contemporary UKA, resurfacing both the femur and tibia of a single knee compartment, was performed by Marmor.16Marmor L The modular knee.Clin Orthop Relat Res. 1973; 94: 242-24810.1097/00003086-197307000-00029Crossref PubMed Scopus (91) Google Scholar Despite the theoretical advantages of this design, the survivorship rates were disappointing with more than 30% of patients undergoing revision surgery within 10 years.17Marmor L Unicompartmental knee arthroplasty. Ten- to 13-year follow-up study.Clin Orthop Relat Res. 1988; 226: 14-20PubMed Google Scholar Tibial loosening, subsidence and accelerated polyethylene wear were the dominant reasons for implant failure.18Lindstrand A Stenstrom A Lewold S Multicenter study of unicompartmental knee revision. PCA, Marmor, and St Georg compared in 3,777 cases of arthrosis.Acta Orthop Scand. 1992; 63: 256-259Crossref PubMed Scopus (61) Google Scholar In 1976, Insall and Walker19Insall J Walker P Unicondylar knee replacement.Clin Orthop Relat Res. 1976; : 83-85PubMed Google Scholar reported similar disappointing results at 2–4-year follow-up, finding good-to-excellent results in only 11 out of 24 UKAs and a 28% conversion rate to TKA. The reasons for these dissatisfying results were malposition of the implant, insufficient correction of the leg alignment and removal of the patella due to patellofemoral osteoarthritis (PFOA).20Insall J Aglietti P A five to seven-year follow-up of unicondylar arthroplasty.J Bone Joint Surg Am. 1980; 62: 1329-133710.2106/00004623-198062080-00013Crossref PubMed Scopus (248) Google Scholar Subsequently, Laskin21Laskin RS Unicompartmental tibiofemoral resurfacing arthroplasty.J Bone Joint Surg Am. 1978; 60: 182-18510.2106/00004623-197860020-00007Crossref PubMed Scopus (232) Google Scholar reported outcomes using the Marmor knee (Richards Manufacturing Company) with pain relief in only 65% of the patients and a 26% failure rate at a 2-year follow-up.21Laskin RS Unicompartmental tibiofemoral resurfacing arthroplasty.J Bone Joint Surg Am. 1978; 60: 182-18510.2106/00004623-197860020-00007Crossref PubMed Scopus (232) Google Scholar Following these disappointing results, interest for UKA further decreased and UKA was discouraged.20Insall J Aglietti P A five to seven-year follow-up of unicondylar arthroplasty.J Bone Joint Surg Am. 1980; 62: 1329-133710.2106/00004623-198062080-00013Crossref PubMed Scopus (248) Google Scholar 21Laskin RS Unicompartmental tibiofemoral resurfacing arthroplasty.J Bone Joint Surg Am. 1978; 60: 182-18510.2106/00004623-197860020-00007Crossref PubMed Scopus (232) Google Scholar In 1989, Kozinn and Scott22Kozinn SC Scott R Unicondylar knee arthroplasty.J Bone Joint Surg Am. 1989; 71: 145-15010.2106/00004623-198971010-00023Crossref PubMed Scopus (533) Google Scholar sought to improve these outcomes by proposing the use of strict inclusion criteria. As a result, better results were reported in the literature. Berger et al 23Berger RA Nedeff DD Barden RM et al.Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year followup.Clin Orthop Relat Res. 1999; 87-A: 50-60Google Scholar applied these criteria and showed a survival rate of 98% at 10-year follow-up, using the Miller-Galante prosthesis (Zimmer, Warsaw, Indiana, USA). Clinically, outcomes were graded excellent in 78% of patients and good in 20% of patients.23Berger RA Nedeff DD Barden RM et al.Unicompartmental knee arthroplasty. Clinical experience at 6- to 10-year followup.Clin Orthop Relat Res. 1999; 87-A: 50-60Google Scholar Simultaneously, Murray et al 24Murray DW Goodfellow JW O'Connor JJ The Oxford medial unicompartmental arthroplasty: a ten-year survival study.J Bone Joint Surg Br. 1998; 80: 983-98910.1302/0301-620X.80B6.8177Crossref PubMed Scopus (616) Google Scholar reported on 143 knees treated with a medial Oxford mobile-bearing UKA, revealing a survivorship of 97% with a mean follow-up of 10 years. The use of mini-invasive techniques was advocated to reduce tissue damage and improve the ease of revision surgery.25Repicci JA Total knee or uni? Benefits and limitations of the unicondylar knee prosthesis.Orthopedics. 2003; 26 (277): 274Crossref PubMed Google Scholar However, the results have been variable regarding the accuracy and reproducibility of this approach compared with standard techniques.25Repicci JA Total knee or uni? Benefits and limitations of the unicondylar knee prosthesis.Orthopedics. 2003; 26 (277): 274Crossref PubMed Google Scholar 26Pandit H Jenkins C Gill HS et al.Minimally invasive Oxford phase 3 unicompartmental knee replacement: results of 1000 cases.J Bone Joint Surg Br. 2011; 93: 198-20410.1302/0301-620X.93B2.25767Crossref PubMed Scopus (256) Google Scholar Throughout the 1980s and 1990s, UKA usage continued, however, in varying degrees with corresponding results. Over the course of the years, surgeons sought to better understand the biomechanics and modes of failure of these devices to improve on the original UKA designs. In addition, special instrumentation was designed and better patient selection criteria were developed, all of which laid the groundwork for the eventual revival of UKA. Over the past decades, several reviews have been published about UKA. As time has progressed, reviews moved from patient selection criteria to surgical techniques and modes of failure. Recently, many authors emphasise different fixation methods, prostheses designs and new technologies (eg, robot-assisted surgery) as is shown in box 1. Box 1Key articles on unicompartmental knee arthroplasty (UKA)▸Insall and Walker19Insall J Walker P Unicondylar knee replacement.Clin Orthop Relat Res. 1976; : 83-85PubMed Google Scholar introduced the first unicompartmental knee arthroplasty in the 1970s.▸In 1989, Kozinn and Scott22Kozinn SC Scott R Unicondylar knee arthroplasty.J Bone Joint Surg Am. 1989; 71: 145-15010.2106/00004623-198971010-00023Crossref PubMed Scopus (533) Google Scholar described the strict patient selection criteria for UKA after disappointing results from the past.▸Murray et al 24Murray DW Goodfellow JW O'Connor JJ The Oxford medial unicompartmental arthroplasty: a ten-year survival study.J Bone Joint Surg Br. 1998; 80: 983-98910.1302/0301-620X.80B6.8177Crossref PubMed Scopus (616) Google Scholar reported 10-year survivorship of 98%, showing that long-term outcomes of UKA can be achieved in strictly selected patients.▸Pandit et al 27Pandit H Jenkins C Gill HS et al.Unnecessary contraindications for mobile-bearing unicompartmental knee replacement.J Bone Joint Surg Br. 2011; 93: 622-62810.1302/0301-620X.93B5.26214Crossref PubMed Scopus (140) Google Scholar demonstrated the unnecessary contraindications for mobile-bearing UKA, and thereby proposed to expand the indications for UKA.▸Liddle et al 28Liddle AD Pandit H O'Brien S et al.Cementless fixation in Oxford unicompartmental knee replacement: a multicentre study of 1000 knees.Bone Joint J. 2013; 95-B: 181-18710.1302/0301-620X.95B2.30411Crossref PubMed Scopus (71) Google Scholar showed good-to-excellent results at 10-year follow-up of 1000 cementless UKAs after resurgence of interest in the late 1990s.▸Chatellard et al 29Chatellard R Sauleau V Colmar M et al.Medial unicompartmental knee arthroplasty: does tibial component position influence clinical outcomes and arthroplasty survival?.Orthop Traumatol Surg Res. 2013; 99: S219-S22510.1016/j.otsr.2013.03.004Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar emphasised the high level of accuracy required for optimal position of the tibial component, to restore knee kinematics and prevent implant wear.▸Pearle et al 30Pearle AD O'Loughlin PF Kendoff DO Robot-assisted unicompartmental knee arthroplasty.J Arthroplasty. 2010; 25: 230-23710.1016/j.arth.2008.09.024Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar were the first to demonstrate successful robot-assisted UKA placement in a series of 10 patients, showing improvement of the accuracy in regard to component positioning and leg alignment.▸van der List et al 31van der List JP McDonald LS Pearle AD Systematic review of medial versus lateral survivorship in unicompartmental knee arthroplasty.Knee. 2015; 22: 454-46010.1016/j.knee.2015.09.011Abstract Full Text Full Text PDF PubMed Scopus (64) Google Scholar performed a systematic review demonstrating high survivorship rates of medial and lateral UKA, combined with high functional outcomes scores.▸Epinette et al 32Epinette JA Brunschweiler B Mertl P French Society for Hip and Knee 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: S124-S13010.1016/j.otsr.2012.07.002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar identified modes of failure of UKA in a large French multicentre study. They assessed the differences between early, mid-term and late stages of the arthroplasty.▸Jacofsky and Allen33Jacofsky DJ Allen M Robotics in arthroplasty: a comprehensive review.J Arthroplasty. 2016; 31: 2353-236310.1016/j.arth.2016.05.026Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar reviewed the current robotic systems for UKA and comment on future innovations in robotics. ▸Insall and Walker19Insall J Walker P Unicondylar knee replacement.Clin Orthop Relat Res. 1976; : 83-85PubMed Google Scholar introduced the first unicompartmental knee arthroplasty in the 1970s.▸In 1989, Kozinn and Scott22Kozinn SC Scott R Unicondylar knee arthroplasty.J Bone Joint Surg Am. 1989; 71: 145-15010.2106/00004623-198971010-00023Crossref PubMed Scopus (533) Google Scholar described the strict patient selection criteria for UKA after disappointing results from the past.▸Murray et al 24Murray DW Goodfellow JW O'Connor JJ The Oxford medial unicompartmental arthroplasty: a ten-year survival study.J Bone Joint Surg Br. 1998; 80: 983-98910.1302/0301-620X.80B6.8177Crossref PubMed Scopus (616) Google Scholar reported 10-year survivorship of 98%, showing that long-term outcomes of UKA can be achieved in strictly selected patients.▸Pandit et al 27Pandit H Jenkins C Gill HS et al.Unnecessary contraindications for mobile-bearing unicompartmental knee replacement.J Bone Joint Surg Br. 2011; 93: 622-62810.1302/0301-620X.93B5.26214Crossref PubMed Scopus (140) Google Scholar demonstrated the unnecessary contraindications for mobile-bearing UKA, and thereby proposed to expand the indications for UKA.▸Liddle et al 28Liddle AD Pandit H O'Brien S et al.Cementless fixation in Oxford unicompartmental knee replacement: a multicentre study of 1000 knees.Bone Joint J. 2013; 95-B: 181-18710.1302/0301-620X.95B2.30411Crossref PubMed Scopus (71) Google Scholar showed good-to-excellent results at 10-year follow-up of 1000 cementless UKAs after resurgence of interest in the late 1990s.▸Chatellard et al 29Chatellard R Sauleau V Colmar M et al.Medial unicompartmental knee arthroplasty: does tibial component position influence clinical outcomes and arthroplasty survival?.Orthop Traumatol Surg Res. 2013; 99: S219-S22510.1016/j.otsr.2013.03.004Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar emphasised the high level of accuracy required for optimal position of the tibial component, to restore knee kinematics and prevent implant wear.▸Pearle et al 30Pearle AD O'Loughlin PF Kendoff DO Robot-assisted unicompartmental knee arthroplasty.J Arthroplasty. 2010; 25: 230-23710.1016/j.arth.2008.09.024Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar were the first to demonstrate successful robot-assisted UKA placement in a series of 10 patients, showing improvement of the accuracy in regard to component positioning and leg alignment.▸van der List et al 31van der List JP McDonald LS Pearle AD Systematic review of medial versus lateral survivorship in unicompartmental knee arthroplasty.Knee. 2015; 22: 454-46010.1016/j.knee.2015.09.011Abstract Full Text Full Text PDF PubMed Scopus (64) Google Scholar performed a systematic review demonstrating high survivorship rates of medial and lateral UKA, combined with high functional outcomes scores.▸Epinette et al 32Epinette JA Brunschweiler B Mertl P French Society for Hip and Knee 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: S124-S13010.1016/j.otsr.2012.07.002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar identified modes of failure of UKA in a large French multicentre study. They assessed the differences between early, mid-term and late stages of the arthroplasty.▸Jacofsky and Allen33Jacofsky DJ Allen M Robotics in arthroplasty: a comprehensive review.J Arthroplasty. 2016; 31: 2353-236310.1016/j.arth.2016.05.026Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar reviewed the current robotic systems for UKA and comment on future innovations in robotics. Physical and radiographic evaluation remains the cornerstone in the diagnostic process of knee OA and is particularly important to assess whether a knee with unicompartmental OA (medial or lateral) would be indicated for UKA. Evaluation of the presence of unicompartmental knee OA through medical history, physical examination and imaging is essential and all contribute to precise patient selection. Furthermore, it provides valuable information in surgical decision-making after diagnostic criteria are met. To assess whether or not a patient is indicated for UKA depends on many factors. On physical examination, it is important to evaluate the location of the pain over the joint line (medial or lateral), ROM, leg deformity, state of the anterior cruciate ligament (ACL) and patellofemoral (PF) discomfort. Pain should be isolated to one compartment, either medial or lateral, to be indicated for UKA. Assessing knee stability, the Lachman or anterior drawer test can be used to evaluate the integrity of the ACL clinically. Furthermore, varus and valgus stress tests assess the collateral ligaments and amount of correctability of a leg deformity if present. Box 2Validated outcome measures and classifications▸Hospital for Special Surgery (HSS) score;▸Knee Society Score (KSS);▸Oxford Knee Score (OKS);▸Tegner Activity Score;▸Western Ontario and McMaster Universities Arthritis Index (WOMAC). ▸Hospital for Special Surgery (HSS) score;▸Knee Society Score (KSS);▸Oxford Knee Score (OKS);▸Tegner Activity Score;▸Western Ontario and McMaster Universities Arthritis Index (WOMAC). Box 3Tips and tricks for successful unicompartmental knee arthroplasty (UKA)▸Patient selection is essential in UKA surgery, in which single knee compartment osteoarthritis and correctable leg deformity are the most important factors.▸Surgical goal is slight undercorrection of the deformity of the long leg axis.▸(medial UKA: 1–4° varus, lateral UKA: 3–7° valgus).▸In UKA, correct ligament balance is restored by positioning the components accurately and inserting an appropriate thickness of bearing.▸In high functional demand patients, it is recommended to reconstruct the anterior cruciate ligament simultaneously or staged in addition to UKA. ▸Patient selection is essential in UKA surgery, in which single knee compartment osteoarthritis and correctable leg deformity are the most important factors.▸Surgical goal is slight undercorrection of the deformity of the long leg axis.▸(medial UKA: 1–4° varus, lateral UKA: 3–7° valgus).▸In UKA, correct ligament balance is restored by positioning the components accurately and inserting an appropriate thickness of bearing.▸In high functional demand patients, it is recommended to reconstruct the anterior cruciate ligament simultaneously or staged in addition to UKA. Box 4Major pitfalls of unicompartmental knee arthroplasty (UKA)▸Osteoarthritis in the contralateral compartment is contraindicated for UKA; therefore, MRI could be useful to assess the chondral surface in case of doubt.▸Overcorrection during medial UKA (MUKA) or lateral UKA is associated with progression of osteoarthritis in the contralateral compartment and therefore should be avoided.▸Residual postoperative axis >8° to 10° varus following MUKA increases the rate of failure from polyethylene wear and loosening. ▸Osteoarthritis in the contralateral compartment is contraindicated for UKA; therefore, MRI could be useful to assess the chondral surface in case of doubt.▸Overcorrection during medial UKA (MUKA) or lateral UKA is associated with progression of osteoarthritis in the contralateral compartment and therefore should be avoided.▸Residual postoperative axis >8° to 10° varus following MUKA increases the rate of failure from polyethylene wear and loosening. Traditionally, knee OA is diagnosed on anteroposterior (AP) and lateral weight-bearing radiographs of the knee. Rosenberg et al's34Rosenberg TD Paulos LE Parker RD et al.The forty-five-degree posteroanterior flexion weight-bearing radiograph of the knee.J Bone Jt Surg Am. 1988; 70: 1479-148310.2106/00004623-198870100-00006Crossref PubMed Scopus (510) Google Scholar views and additional lower leg alignment radiographs are performed as part of the standard radiological work-up of patients with unicompartmental knee OA. This additional 45° posteroanterior flexion weight-bearing radiograph has a high sensitivity and specificity of detecting isolated lateral OA.34Rosenberg TD Paulos LE Parker RD et al.The forty-five-degree posteroanterior flexion weight-bearing radiograph of the knee.J Bone Jt Surg Am. 1988; 70: 1479-148310.2106/00004623-198870100-00006Crossref PubMed Scopus (510) Google Scholar For evaluation of the patella and trochlear surfaces of the femur, an adequate Merchant view may be helpful in determining gross malalignment and presence of PFOA. The severity of knee OA is classified according to the Kellgren-Lawrence (KL) Grading System35Kellgren JH Lawrence JS Radiological assessment of osteo-arthrosis.Ann Rheum Dis. 1957; 16: 494-50210.1136/ard.16.4.494Crossref PubMed Scopus (8403) Google Scholar or Ahlbäck classification36Ahlbäck S Osteoarthrosis of the knee. A radiographic investigation.Acta Radiol Diagn (Stockh). 1968; 277: 7-72Google Scholar (table 1). The most limiting aspect of classification based on radiographic imaging is that it detects joint degeneration only in a more advanced stage.37El-Tawil S Arendt E Parker D Position statement: the epidemiology, pathogenesis and risk factors of osteoarthritis of the knee.J ISAKOS. 2016; 1: 219-22810.1136/jisakos-2015-000002Abstract Full Text Full Text PDF Google ScholarTable 1Radiographical grading scalesGradeKellgren-LawrenceAhlbäck1Doubtful joint space narrowing and osteophyte formationJoint space narrowing ( 10 mm) Open table in a new tab To overcome this limitation, the clinical utility of MRI becomes more important to assess the early detection of OA in the contralateral compartment. Subtle degenerative changes in the subchondral bone, cartilage, abnormalities in the bone marrow, ligaments, menisci, synovium and joint fluid are all well detected with MRI technology.37El-Tawil S Arendt E Parker D Position statement: the epidemiology, pathogenesis and risk factors of osteoarthritis of the knee.J ISAKOS. 2016; 1: 219-22810.1136/jisakos-2015-000002Abstract Full Text Full Text PDF Google Scholar 38Roemer FW Guermazi A Osteoarthritis year in review 2014: imaging.Osteoarthritis Cartilage. 2014; 22: 2003-201210.1016/j.joca.2014.07.012Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar The radiographic indications for UKA is unicompartmental knee OA (figure 1), with preservation of the contralateral compartment as shown on weight-bearing and valgus/varus stress radiographs.39Gibson PH Goodfellow JW Stress radiography in degenerative arthritis of the knee.J Bone Jt Surg Br Vol. 1986; 68: 608-609Crossref PubMed Google Scholar Preoperatively, stress view radiographs could provide information by means of determining correctability of the deformity, ensuring maintenance of the contralateral joint space, and indirectly assessing the integrity of the ACL and medial collateral ligaments.39Gibson PH Goodfellow JW Stress radiography in degenerative arthritis of the knee.J Bone Jt Surg Br Vol. 1986; 68: 608-609Crossref PubMed Google Scholar, 40Argenson J-NA Parratte S The unicompartmental knee: design and technical considerations in minimizing wear.Clin Orthop Relat Res. 2006; 452: 137-14210.1097/01.blo.0000229358.19867.60Crossref PubMed Scopus (64) Google Scholar, 41Kreitz TM Maltenfort MG Lonner JH The valgus stress radiograph does not determine the full extent of correction of deformity prior to medial unicompartmental knee arthroplasty.J Arthroplasty. 2015; 30: 1233-123610.1016/j.arth.2015.02.008Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar Advocates of stress radiographs require the deformity to be correctable to neutral, with preservation of the contralateral joint space.22Kozinn SC Scott R Unicondylar knee arthroplasty.J Bone Joint Surg Am. 1989; 71: 145-15010.2106/00004623-198971010-00023Crossref PubMed Scopus (533) Google Scholar However, a preoperative MRI is used more often to document the absence of significant degenerative changes in the contralateral or PF compartment.37El-Tawil S Arendt E Parker D Position statement: the epidemiology, pathogenesis and risk factors of osteoarthritis of the knee.J ISAKOS. 2016; 1: 219-22810.1136/jisakos-2015-000002Abstract Full Text Full Text PDF
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