Arthroplasty Knee Unicompartmental


Article Author:
T. David Luo


Article Editor:
John Hubbard


Editors In Chief:
Sisira Reddy
Joseph Nahas


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes


Updated:
4/2/2019 2:38:48 PM

Introduction

Unicompartmental knee arthroplasty (UKA) is a surgical technique used for the treatment of osteoarthritis in one compartment of the knee, most commonly in the medial compartment.[1][2] In contrast, a total knee arthroplasty (TKA) is used for the treatment of osteoarthritis in all three compartments of the knee. UKA was first introduced in the 1970s.[2] Proponents for UKA argued that the procedure more closely mimics normal knee kinematics, leads to lower perioperative morbidity and intraoperative blood loss, and allows for earlier mobilization and rehabilitation compared to conventional bicondylar knee arthroplasty.[3] Early results, however, demonstrated high rates of failures, with 28% rate of conversion to TKA at an average follow-up of six years.[4] Over time, modifications in the implant design, surgical technique and the expansion of surgical indications have led to renewed interest in UKA. Furthermore, the increased demand for minimally invasive approaches has also increased the popularity of UKA, which requires a smaller incision compared to traditional TKA. The development of robotic-assisted techniques have improved surgical precision and component alignment in an effort to increase survivorship.[5]

Anatomy

The knee has three compartments: medial, lateral, and patellofemoral. The medial compartment is the articulation between the medial condyle of the femur and the medial aspect of the tibial plateau. The lateral compartment is the articulation between the lateral femoral condyle and the lateral aspect of the tibial plateau. The patellofemoral compartment is the articulation between the patella and the trochlear groove of the femur. A patient can develop arthritis in one, two, or all three of these compartments. The alignment of the limb is one factor that can determine the location of osteoarthritis development. Patients with varus (or bow-legged) malalignment will have greater contact stresses in the medial compartment of the knee and be more likely to develop medial compartment arthritis. Patients with valgus (or knock-kneed) malalignment will be more likely to develop arthritis in the lateral compartment.

Indications

As with other elective procedures, prior to considering surgery, the patient should have attempted treatment with conservative measures, including activity modification, physical therapy, anti-inflammatory medications, bracing, and/or injections. Surgical intervention can be considered only if these conservative measures fail to provide relief. The indications for UKA are controversial and have evolved since its introduction. Kozinn and Scott established a set of indications in 1989.[6] They included: low-demand patients older than 60 years of age, weight less than 82 kg (181 lbs.), osteoarthritis or osteonecrosis confined to one compartment, low pain at rest, greater than 90 degrees of preoperative arc of motion, less than 5 degrees of flexion contracture, and less than 15 degrees of angular deformity that is passively correctable to neutral. Strict adherence to these criteria is difficult, with one analysis of over 4,000 TKAs demonstrating that only 6.1% of the cases met the anatomic indications and that only 4.3% met the clinical indications for UKA as outlined above.[7]

More recent evidence has shown improved outcomes and survivorship in younger (age less than 60 years) and obese patients.[8][9][10][11] The improvements in implant design have, in part, contributed to the expansion of traditional indications for UKA. Conventional teaching suggested that high BMI does lead to a risk of aseptic loosening from the excess load on the components. Similarly, younger patients typically have a more active lifestyle and higher functional expectations, which may also predispose to early loosening from excess wear. A meta-analysis that included six registry studies demonstrated no increased likelihood of revisions or poor outcomes in obese patients compared to control.[11] The same study found a higher risk of revisions in younger patients and females.[11]

Contraindications

The contraindications to UKA as initially described by Kozinn and Scott [6] continue to be challenged, as strict conformity to their selection criteria severely limits the number of eligible patients.[7] In addition to the patient demographics and anatomic factors listed above, contraindications also include arthritis of the patellofemoral joint (PFJ) and the opposite compartment, inflammatory arthritis, and insufficiency of the anterior cruciate ligament (ACL).

Recent studies have demonstrated no difference in function and revision rates in patients with and without PFJ arthritis.[10][11] Traditionally, UKA in ACL-deficient knees were associated with high failure rates.[12] Cadaveric and in vivo studies have demonstrated biomechanical instability in ACL-deficient knees that may predispose to polyethylene wear and worsening degeneration in the lateral and patellofemoral compartments.[13][14] Recent studies have shown acceptable outcomes in patients with deficient ACL when UKA is compared to ACL-intact patients.[11][15] Simultaneous reconstruction of the ACL at time of UKA has also been described and has demonstrated greater implant survival rate compared to ACL-deficient knees without reconstruction.[16]

Preparation

Preoperative evaluation should include a detailed history and physical examination. Evaluation of the knee should encompass testing for ligamentous stability and range of motion limitations based on criteria established by Kozinn and Scott.[6] Weight-bearing radiographs should be scrutinized for varus or valgus deformity. A merchant view is helpful to evaluate the PFJ and lateral patella subluxation. Advanced imaging, such as CT, may be necessary for preoperative mapping for robotic-assisted UKA to guide positioning of the implants and soft-tissue balancing.[5] MRI is often unnecessary and may overestimate the severity of articular pathology.[17][18]

Technique

The surgical approach to UKA should allow adequate exposure of the medial compartment while minimizing the release of the soft tissues. The tibial resection should match the native tibial slope. The sagittal resection should be as close to the tibial spine as possible to maximize the area for positioning of the component without causing damage to the ACL. In the coronal plane, the part should be placed perpendicular to the long axis of the tibia.[19] Undersizing of the tibial component should be avoided to prevent implant subsidence. Over-correction of varus deformity may result in excess stress on the medial soft tissues and increased lateral compartment degeneration.[20] This may be prevented by not formally releasing the medial collateral ligament and sizing the polyethylene insert that allows for 2 mm of joint laxity in both full extension and flexion.

The ideal position of the femoral component is central or slightly lateral on the femoral condyle to optimize tracking with the tibial component.[1] For lateral UKA, femoral component impingement on the patella has been described.[21] These were noted to be associated with anterior placement and oversizing of the femoral component. The sulcus terminalis of the lateral femoral condyle has been described as a landmark beyond which the femoral component should not be sized or implanted.[19]

Other considerations in UKA include the use of mobile- (MB) versus fixed-bearing (FB) implants. MB implants were introduced in the 1980s and were designed to distribute loads over a large surface area to decrease polyethylene wear.[22] Modern FB implants are characterized by low conformity between the femoral and tibial components that permit greater ROM and decreased backside wear.[23] Long-term outcomes in the literature have failed to demonstrate the superiority of one type of bearing over the other concerning implant survival and patient outcomes.[22][24]

Another consideration is whether to use cement during component implantation. Cementing in UKA can prove challenging given the limited exposure and surface area. Furthermore, cementing prolongs the operative duration and may result in cementation errors.[25] Another disadvantage of cementing is the greater rate of radiographic subsidence; however, most of those cases do not correlate with aseptic loosening.[26] Short- and mid-term follow-up has shown similar survival rates between cemented and uncemented UKA.[27][28][29]

Complications

Since the introduction of UKA several decades ago, the primary mechanism of failure has remained consistent in the literature, most commonly stemming from aseptic loosening, followed by progressive osteoarthritis.[1] A systematic review of UKA demonstrated that aseptic loosening (25%) and osteoarthritis progression (20%) accounted for more than half of all revisions in the first five years, while infection (5%) and polyethylene wear (4%) were less frequent.[11] Approximately 40% of mid- and late-term revisions were attributed to osteoarthritis progression.[29] Despite technological advances in UKA implants, the revision-free survival rate has remained constant, unlike improvements seen in TKA survival rate trends.[30] Some authors attribute this to the lower threshold by the surgeon to convert a UKA to a TKA, whereas a TKA revision is viewed as more technically demanding, with higher morbidity. Recent literature has refuted these claims by demonstrating similar complication and revision rates after UKA conversion and after primary TKA.[31]

Clinical Significance

Since its initial introduction, indications for UKA has continued to expand. Data from large case series, registries, and meta-analyses have consistently demonstrated the long-term efficacy and survivorship of UKA in the appropriate patient populations. When performed for the correct indications and in the appropriate settings, UKA is a minimally invasive surgery that can return the patient to their previous level of recreational activity. Heightened patient expectations especially in younger and more active patients, however, can lead to early wear of the implant and need for revision. Nevertheless, conversion of a failed UKA to total knee arthroplasty is associated with lower morbidity compared to revision of a TKA.

Enhancing Healthcare Team Outcomes

Despite the excellent long-term survival rates after UKA in recent literature, there are substantial differences in outcomes demonstrated by cohort and registry data.[11] At 15 years, the average survival rate was 87% in cohort studies, as opposed to 67% in registry studies.[11] This discrepancy may be explained by variability in outcomes reporting and the inclusion of multiple surgeons with varying degrees of clinical volume. Registry studies offer the benefits of demonstrating trends in UKA over time and capturing a higher number of cases compared to cohort studies. For example, online data provided by the National Joint Registry for England, Wales, and Northern Ireland demonstrated better outcomes in UKA performed by surgeons who perform them 40-60% of the time compared to surgeons who perform them less than 5% of their total practice.[1] This data highlights that in addition to careful patient selection, surgeon experience plays a substantial role in optimizing outcomes after UKA. High-volume centers that employ dedicated orthopedic operating room staff, as well as nursing and therapy staff familiar with the procedure, will ensure both operational efficiency and postoperative care to optimize the patients’ outcomes. Preoperatively, a thorough assessment of the patient’s co-morbid medical conditions helps minimize postoperative complications and length of stay. [Level V]


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Arthroplasty Knee Unicompartmental - Questions

Take a quiz of the questions on this article.

Take Quiz
Which of the following is NOT attributable to the minimally invasive approach for medial unicompartmental arthroplasty?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is a contraindication to unicompartmental knee arthroplasty?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is the key landmark for femoral component placement in a lateral unicompartmental knee arthroplasty?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is true of unicompartmental knee arthroplasty (UKA) compared to total knee arthroplasty (TKA)?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 59-year-old active male undergoes right unicompartmental knee arthroplasty after several years of medial-sided knee pain. The patient should be warned that early complications requiring revision within the first five years after surgery is most commonly due to which of the following?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Arthroplasty Knee Unicompartmental - References

References

Jennings JM,Kleeman-Forsthuber LT,Bolognesi MP, Medial Unicompartmental Arthroplasty of the Knee. The Journal of the American Academy of Orthopaedic Surgeons. 2018 Nov 7;     [PubMed]
Insall J,Walker P, Unicondylar knee replacement. Clinical orthopaedics and related research. 1976 Oct;     [PubMed]
Laurencin CT,Zelicof SB,Scott RD,Ewald FC, Unicompartmental versus total knee arthroplasty in the same patient. A comparative study. Clinical orthopaedics and related research. 1991 Dec;     [PubMed]
Insall J,Aglietti P, A five to seven-year follow-up of unicondylar arthroplasty. The Journal of bone and joint surgery. American volume. 1980 Dec;     [PubMed]
Lonner JH,Klement MR, Robotic-assisted Medial Unicompartmental Knee Arthroplasty: Options and Outcomes. The Journal of the American Academy of Orthopaedic Surgeons. 2018 Oct 4;     [PubMed]
Kozinn SC,Scott R, Unicondylar knee arthroplasty. The Journal of bone and joint surgery. American volume. 1989 Jan;     [PubMed]
Ritter MA,Faris PM,Thong AE,Davis KE,Meding JB,Berend ME, Intra-operative findings in varus osteoarthritis of the knee. An analysis of pre-operative alignment in potential candidates for unicompartmental arthroplasty. The Journal of bone and joint surgery. British volume. 2004 Jan;     [PubMed]
Pennington DW,Swienckowski JJ,Lutes WB,Drake GN, Unicompartmental knee arthroplasty in patients sixty years of age or younger. The Journal of bone and joint surgery. American volume. 2003 Oct;     [PubMed]
Tabor OB Jr,Tabor OB,Bernard M,Wan JY, Unicompartmental knee arthroplasty: long-term success in middle-age and obese patients. Journal of surgical orthopaedic advances. 2005 Summer;     [PubMed]
Hamilton TW,Pandit HG,Jenkins C,Mellon SJ,Dodd CAF,Murray DW, Evidence-Based Indications for Mobile-Bearing Unicompartmental Knee Arthroplasty in a Consecutive Cohort of Thousand Knees. The Journal of arthroplasty. 2017 Jun;     [PubMed]
van der List JP,Chawla H,Zuiderbaan HA,Pearle AD, The Role of Preoperative Patient Characteristics on Outcomes of Unicompartmental Knee Arthroplasty: A Meta-Analysis Critique. The Journal of arthroplasty. 2016 Nov;     [PubMed]
Goodfellow JW,Kershaw CJ,Benson MK,O'Connor JJ, The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases. The Journal of bone and joint surgery. British volume. 1988 Nov;     [PubMed]
Suggs JF,Li G,Park SE,Steffensmeier S,Rubash HE,Freiberg AA, Function of the anterior cruciate ligament after unicompartmental knee arthroplasty: an in vitro robotic study. The Journal of arthroplasty. 2004 Feb;     [PubMed]
Argenson JN,Komistek RD,Aubaniac JM,Dennis DA,Northcut EJ,Anderson DT,Agostini S, In vivo determination of knee kinematics for subjects implanted with a unicompartmental arthroplasty. The Journal of arthroplasty. 2002 Dec;     [PubMed]
Boissonneault A,Pandit H,Pegg E,Jenkins C,Gill HS,Dodd CA,Gibbons CL,Murray DW, No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2013 Nov;     [PubMed]
Mancuso F,Dodd CA,Murray DW,Pandit H, Medial unicompartmental knee arthroplasty in the ACL-deficient knee. Journal of orthopaedics and traumatology : official journal of the Italian Society of Orthopaedics and Traumatology. 2016 Sep;     [PubMed]
Sharpe I,Tyrrell PN,White SH, Magnetic resonance imaging assessment for unicompartmental knee replacement: a limited role. The Knee. 2001 Oct;     [PubMed]
Hurst JM,Berend KR,Morris MJ,Lombardi AV Jr, Abnormal preoperative MRI does not correlate with failure of UKA. The Journal of arthroplasty. 2013 Oct;     [PubMed]
Borus T,Thornhill T, Unicompartmental knee arthroplasty. The Journal of the American Academy of Orthopaedic Surgeons. 2008 Jan;     [PubMed]
Berger RA,Meneghini RM,Jacobs JJ,Sheinkop MB,Della Valle CJ,Rosenberg AG,Galante JO, Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. The Journal of bone and joint surgery. American volume. 2005 May;     [PubMed]
Hernigou P,Deschamps G, Patellar impingement following unicompartmental arthroplasty. The Journal of bone and joint surgery. American volume. 2002 Jul;     [PubMed]
Parratte S,Pauly V,Aubaniac JM,Argenson JN, No long-term difference between fixed and mobile medial unicompartmental arthroplasty. Clinical orthopaedics and related research. 2012 Jan;     [PubMed]
Netter J,Hermida JC,D'Alessio J,Kester M,D'Lima DD, Effect of Polyethylene Crosslinking and Bearing Design on Wear of Unicompartmental Arthroplasty. The Journal of arthroplasty. 2015 Aug;     [PubMed]
van der Voort P,Pijls BG,Nouta KA,Valstar ER,Jacobs WC,Nelissen RG, A systematic review and meta-regression of mobile-bearing versus fixed-bearing total knee replacement in 41 studies. The bone     [PubMed]
Pandit H,Liddle AD,Kendrick BJ,Jenkins C,Price AJ,Gill HS,Dodd CA,Murray DW, Improved fixation in cementless unicompartmental knee replacement: five-year results of a randomized controlled trial. The Journal of bone and joint surgery. American volume. 2013 Aug 7;     [PubMed]
Kendrick BJ,Kaptein BL,Valstar ER,Gill HS,Jackson WF,Dodd CA,Price AJ,Murray DW, Cemented versus cementless Oxford unicompartmental knee arthroplasty using radiostereometric analysis: a randomised controlled trial. The bone     [PubMed]
Schlueter-Brust K,Kugland K,Stein G,Henckel J,Christ H,Eysel P,Bontemps G, Ten year survivorship after cemented and uncemented medial Uniglide® unicompartmental knee arthroplasties. The Knee. 2014 Oct;     [PubMed]
Akan B,Karaguven D,Guclu B,Yildirim T,Kaya A,Armangil M,Cetin I, Cemented versus Uncemented Oxford Unicompartmental Knee Arthroplasty: Is There a Difference? Advances in orthopedics. 2013;     [PubMed]
Campi S,Pandit HG,Dodd CAF,Murray DW, Cementless fixation in medial unicompartmental knee arthroplasty: a systematic review. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2017 Mar;     [PubMed]
Dyrhovden GS,Lygre SHL,Badawy M,Gøthesen Ø,Furnes O, Have the Causes of Revision for Total and Unicompartmental Knee Arthroplasties Changed During the Past Two Decades? Clinical orthopaedics and related research. 2017 Jul;     [PubMed]
Sierra RJ,Kassel CA,Wetters NG,Berend KR,Della Valle CJ,Lombardi AV, Revision of unicompartmental arthroplasty to total knee arthroplasty: not always a slam dunk! The Journal of arthroplasty. 2013 Sep;     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Rheumatology. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Rheumatology, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Rheumatology, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Rheumatology. When it is time for the Rheumatology board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Rheumatology.