The Open Orthopaedics Journal




ISSN: 1874-3250 ― Volume 13, 2019
RESEARCH ARTICLE

Midterm Results of Cementless and Cemented Unicondylar Knee Arthroplasty with Mobile Meniscal Bearing: A Prospective Cohort Study



Radosław Stempin1, *, Wiesław Kaczmarek1, Kacper Stempin2, Julian Dutka3
1 Department of Orthopedic Surgery Promienista Clinic, Poznan, Poland
2 Department of Orthopedic & Trauma Surgery Westallgäu Clinic, Wangen, Germany
3 Department of Orthopedic& Trauma Surgery S. Zeromski Memorial Hospital Cracow, Poland

Abstract

Background:

Cemented unicompartmental knee arthroplasty (UKA) yields good clinical outcome but common revision reasons are loosening and pain. Cementless UKA may reduce the revision rate.

Objective:

The current study was designed to assess clinical and radiographic outcome of cemented and cementless UKA, using bone quality as determined by the Bone Hardness Test (BHT) as selection criterion for cementless implantation.

Methods:

In this prospective comparative cohort study we analyzed 50 cementless and 29 Oxford consecutive UKA cases. Patients with sufficient bone quality were eligible for cementless UKA. Bone quality was assessed with the BHT, which consisted of exercising pressure with the thumb on the bone surface created after resection of the tibia.

Results:

The average surgical times were 62.5 ± 12.6 and 78 ± 16 minutes in the cementless and the cemented group, respectively (p < 0.01). The average thickness of the polyethylene insert was 4.3 ± 1.2 (range, 3 – 9) and 3.7 ± 0.8 (range, 3 – 6) mm, respectively (p = 0.02). Both types of implants yielded excellent clinical and functional results. At an average follow-up time of seven years, we found non-significant differences between clinical results of cementless versus cemented implants.

Conclusion:

Shorter surgical time makes cementless implantation more attractive to surgeons when considering UKA options for their patients. The average thickness of the polyethylene insert in cementless group was 0.6 mm thinner than in the cemented group. The BHT is a simple and useful test to assess whether patients are eligible for cementless UKA.

Keywords: Osteoarthritis, knee, Unicompartmental knee arthroplasty, Mobile meniscal bearing, Cohort study, Implant fixation, Clinical outcome, Bone hardness test.


Article Information


Identifiers and Pagination:

Year: 2017
Volume: 11
First Page: 1173
Last Page: 1178
Publisher Id: TOORTHJ-11-1173
DOI: 10.2174/1874325001711011173

Article History:

Received Date: 07/07/2017
Revision Received Date: 20/8/2017
Acceptance Date: 12/09/2017
Electronic publication date: 31/10/2017
Collection year: 2017`

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© 2017 Stempin et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to this author at the Department of Orthopedic Surgery Promienista Clinic, Poznan, Poland, Tel: + 48 601 727 982; Email: rstempin365@gmail.com





1. INTRODUCTION

The Oxford unicompartmental knee arthroplasty (UKA; Zimmer-Biomet, Bridgend, UK) is a frequently used treatment of medial compartment knee osteoarthritis, and is used less commonly in lateral compartment affection. UKA is a unique implant containing a mobile meniscal bearing fully adapted to both spherical femoral and flat tibial components. John Goodfellow first used UKA in 1976 (Phase 1) [1Goodfellow JW, Kershaw CJ, Benson MK, O’Connor JJ. The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases. J Bone Joint Surg Br 1988; 70(5): 692-701.
[PMID: 3192563]
]. The insert reduces polyethylene wear and eliminates tangential forces acting on the tibial surface, thus improving implant survival [2Goodfellow JW, Tibrewal SB, Sherman KP, O’Connor JJ. Unicompartmental Oxford Meniscal knee arthroplasty. J Arthroplasty 1987; 2(1): 1-9.
[http://dx.doi.org/10.1016/S0883-5403(87)80025-6] [PMID: 3572406]
-6O’Connor JJ, Goodfellow JW. Theory and practice of meniscal knee replacement: designing against wear. Proc Inst Mech Eng H 1996; 210(3): 217-22.
[http://dx.doi.org/10.1243/PIME_PROC_1996_210_415_02] [PMID: 8885659]
]. The first clinical use of the Oxford UKA occurred in 1982 [1Goodfellow JW, Kershaw CJ, Benson MK, O’Connor JJ. The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases. J Bone Joint Surg Br 1988; 70(5): 692-701.
[PMID: 3192563]
]. Surgeons first used a spherical reamer in 1987 (Phase 2) [7O’Connor J, Goodfellow J, Murray DW. Principles of meniscal bearing arthroplasty for unicompartmental replacement. In: Cartier P, Epinette JA, Descamps G, Hernigou P, Eds. Unicompartmental knee arthroplasty 1st ed. 1997.], and since 1998, five sizes of femoral components and left and right sided tibial components have been available for clinical application (Phase 3). Cementless implants (with femoral compartments using a twin peg design) arrived in 2003. UKA in properly selected patients is a less invasive procedure than total knee arthroplasty (TKA) and closer to natural knee kinematics because the cruciate ligaments are retained, thus improving the functional results of surgery [5Murray DW. Mobile bearing unicompartmental knee replacement. Orthopedics 2005; 28(9): 985-7.
[PMID: 16190079]
, 6O’Connor JJ, Goodfellow JW. Theory and practice of meniscal knee replacement: designing against wear. Proc Inst Mech Eng H 1996; 210(3): 217-22.
[http://dx.doi.org/10.1243/PIME_PROC_1996_210_415_02] [PMID: 8885659]
, 8Goodfellow J, O'Connor J. The mechanics of the knee and prosthesis design. J Bone Joint Surg Br 1978; 60(3): 358-69., 9O’Connor JJ, Shercliff TL, Biden E, Goodfellow JW. The geometry of the knee in the sagittal plane. Proc Inst Mech Eng H 1989; 203(4): 223-33.
[http://dx.doi.org/10.1243/PIME_PROC_1989_203_043_01] [PMID: 2701960]
]. The advantages of UKA include less blood loss during surgery, a lower complication rate, and a lower cost of the implant [10Rougraff BT, Heck DA, Gibson AE. A comparison of tricompartmental and unicompartmental arthroplasty for the treatment of gonarthrosis. Clin Orthop Relat Res 1991; (273): 157-64.
[PMID: 1959265]
]. Also, revision procedures are easier in UKA cases than in TKA cases. Designers of the Oxford UKA phase 3 reported excellent survival rates of the prosthesis, reaching 98% at the ten-years follow-up and 96% when considering all related revision cases in the same follow-up period [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
]. Independent third-party studies reported slightly inferior results, with ten-year follow-up survival reaching only 83% to 90%. These differences may have resulted from a learning curve problem debated in the literature. Centers with higher caseloads and experience with UKA have better results than centers using UKA less frequently [12Hamilton TW, Rizkalla JM, Kontochristos L, et al. The interaction of caseload and usage in determining outcomes of unicompartmental knee arthroplasty: A meta-analysis. J Arthroplasty 2017; 32(10): 3228-3237.e2.
[http://dx.doi.org/10.1016/j.arth.2017.04.063] [PMID: 28641970]
]. In 2005, the Swedish Knee Arthroplasty Register reported a longer survival for third generation implants compared with second generation implants [13Robertsson O. New technologies and the Swedish Knee Arthroplasty Register. Bone Joint Res 2014; 3(7): 217-2.]. In February 2013, a published study analyzed the results of six years’ follow-up of 1000 cementless Oxford UKA phase 3 implants and reported a 97.2% survival rate [14Liddle 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(2): 181-7.
[http://dx.doi.org/10.1302/0301-620X.95B2.30411] [PMID: 23365026]
]. Porous coated titanium surface covered with hydroxyapatite provided excellent osseointegration. A prospective randomized comparative study reported a markedly reduced rate of radiolucent lines (RLLs) below the tibial component in cementless implants [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
, 15Pandit H, Jenkins C, Beard DJ, et al. Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year. J Bone Joint Surg Br 2009; 91(2): 185-9.
[http://dx.doi.org/10.1302/0301-620X.91B2.21413] [PMID: 19190051]
].

The current study presents clinical and radiographic outcome of cemented and cementless UKA, using bone quality as determined by the Bone Hardness Test as selection criterion for cementless implantation.

2. MATERIAL AND METHODS

In this prospective cohort study, we compared the clinical results of 79 consecutive minimally invasive operations using unicondylar cemented and cementless Oxford phase 3 implants from 2009 to 2010 for patients with knee osteoarthritis. To be included in the study, patients had to have primary medial compartment osteoarthritis with a well-preserved lateral compartment with competent cruciate ligaments and correctible intraarticular varus deformity (i.e., the same criteria for Oxford UKA implant use [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
]). Additional criteria were fixed flexion deformity of < 15°, flexion up to 110° under anesthesia and pain on the medial joint line. The degree of degenerative changes anteriorly, body mass index, age, sex, and bone mineral density did not affect the surgical decision. Patients with fixed varus deformity > 15°, inflammatory arthritis, previous high tibial osteotomy or ACL reconstruction were excluded [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
]. In addition, patients with severe arthritis of the lateral facet of the patella were not eligible for the procedure [16Beard DJ, Pandit H, Ostlere S, Jenkins C, Dodd CA, Murray DW. Pre-operative clinical and radiological assessment of the patellofemoral joint in unicompartmental knee replacement and its influence on outcome. J Bone Joint Surg Br 2007; 89(12): 1602-7.
[http://dx.doi.org/10.1302/0301-620X.89B12.19260] [PMID: 18057360]
]. The baseline characteristics of the study cohorts are presented in (Table 1).

Table 1
Baseline characteristics of the study cohorts.


Two patients with cemented implants and one patient with a cementless implant died due to unrelated causes during the course of the study; these patients were not included in the study.

Good stability and good bone quality were the essential criteria for implantation of the cementless UKA. Ligament stability was evaluated by verifying the tension in the ACL after it had been visualized intraoperatively. The decision whether to cement the implant was based on the results of an intraoperative visual inspection of bone quality, and on a Bone Hardness Test (BHT). Exercising pressure with the thumb (or the index finger in case of a small knee) on the surface created after resection of the tibia allowed the surgeon to assess the hardness of bone tissue. If the pressure exerted on the bone caused the deflection of resected surface (i.e., if the thumb delved into the bone tissue), the hardness of bone was not deemed to be sufficient to provide primary stability of the implant, and a cementless implant was not used. Based on the outcome of this test, 29 cases received the cemented version of the Oxford phase 3 implant, and 50 cases were deemed eligible for the cementless version. We based clinical results on initial preoperative clinical assessments and final postoperative results. The average follow-up period for the cemented implant group was 7.3 ± 0.4 (range, 6.8 to 7.5) years, and the average follow-up period for the cementless implant group was 6.5 ± 0.2 (range, 6.2 to 7.2) years.

The two senior authors (R.S., W.K.) performed all procedures. A clinical assessment and standing radiography provided the basis for the primary preoperative decision for surgery using an Oxford UKA implant. The final decision depended on an intraoperative assessment of ligamentous stability and tactile probing of bone quality. Most surgeries used epidural anesthesia and a few used general anesthesia. All surgeries used a minimally invasive anteromedial approach, minimized bone resection, and a tourniquet [17Price AJ, Webb J, Topf H, et al. Rapid recovery after oxford unicompartmental arthroplasty through a short incision. J Arthroplasty 2001; 16(8): 970-6.
[http://dx.doi.org/10.1054/arth.2001.25552] [PMID: 11740750]
, 18Tria AJ, Scuderi GR. Minimally invasive knee arthroplasty: An overview. World J Orthop 2015; 6(10): 804-11.
[http://dx.doi.org/10.5312/wjo.v6.i10.804] [PMID: 26601062]
]. Patients used routine anti-deep venous thrombosis prophylaxis for 14 days starting from the operation day, except for patients with an increased risk of thromboembolic complications (such as those with varicose veins of the lower limbs, or a history of deep-vein thrombosis or pulmonary embolism). In these cases, we extended anti-deep vein thrombosis prophylaxis for 30 days after surgery. Patients used prophylactic perioperative antibiotic therapy for three days. Early rehabilitation including knee exercises and protected weight bearing started within the first 24 hours after surgery.

We assessed clinical outcomes using the Knee Society Score (KSS) [19Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989; 248(248): 13-4.
[PMID: 2805470]
], the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [20Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988; 15(12): 1833-40.
[PMID: 3068365]
], and the Oxford Knee Score (OKS) [21Dawson J. Oxford Knee Score. In: Michalos AC, Ed. Encyclopedia of quality of life and well-being research 2014; 4554-5.
[http://dx.doi.org/10.1007/978-94-007-0753-5_2046]
]. Due to the observational nature of the study, patients were not examined radiographically at final follow-up. However, a substantial number of patients (cemented, n = 23 knees; cementless, n = 38 knees) brought their own radiographs at final follow-up, which were taken by their general practitioner. All available radiographs were examined for the presence of RLLs, implant loosening, and migration.

Continuous data are presented as the mean ± standard deviation (SD) and range. Categorical variables are presented as frequencies and percentages. To test for between-group differences, the Fisher exact test was used for categorical variables and the Student’s t-test for continuous variables. MedCalc 17.6 (MedCalc, Ostend, Belgium) was used for statistical analysis.

3. RESULTS

We found a significantly shorter average surgical time in the cementless group (62.5 ± 12.6 (range, 35 - 95) minutes) compared with the cemented group (78 ± 16 (range, 50 - 115) minutes) (p < 0.01). The average thickness of the polyethylene insert was 3.7 ± 0.8 (range, 3 – 6) cm in the cementless group and 4.3 ± 1.2 (range, 3 – 9) cm in the cemented group (p = 0.02). In the follow-up observation, mean score values in the cemented and cementless groups did not differ significantly (Table 2).

Table 2
Clinical and functional scores at latest follow-up.


Radiographic assessment yielded favorable findings in all of the cases. No implant displacement or implant loosening was found. In 3 out of 38 knees in the cementless group and 12 out of 23 knees in the cemented group, RLLs were observed (p < 0.01). RLLs were partial and small (< 1 mm) in all cases and not associated with clinical failure.

One patient in the cemented implant group (3.7%) had revision surgery to replace the patellofemoral joint due to painful arthrosis of this joint six years after the implant surgery. However, this did not affect the original implant. One patient with cementless UKA (2.0%) received revision surgery nearly five months after the initial implant to repair a dislocated meniscal bearing. Similarly, this case did not involve the medial compartment implant. The incidence of complications did not differ significantly between the two groups (p = 1.0).

4. DISCUSSION

The most important finding of this study was that both the cemented and cementless Oxford phase 3 implants yielded excellent midterm clinical and functional results. The outcome of the BHT was used to decide whether patients are eligible for cementless UKA. We found that cementless UKA offers shorter operation times and may lead to a lower incidence of postoperative RLLs. The average thickness of the polyethylene insert in cementless group was 0.6 mm thinner than in the cemented group.

A modified titanium porous-coated and hydroxyapatite-coated implant enabled the excellent results of cementless Oxford UKA [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
, 14Liddle 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(2): 181-7.
[http://dx.doi.org/10.1302/0301-620X.95B2.30411] [PMID: 23365026]
, 15Pandit H, Jenkins C, Beard DJ, et al. Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year. J Bone Joint Surg Br 2009; 91(2): 185-9.
[http://dx.doi.org/10.1302/0301-620X.91B2.21413] [PMID: 19190051]
, 22Akan B, Karaguven D, Guclu B, et al. Cemented versus Uncemented Oxford unicompartmental knee arthroplasty: Is there a difference? Advances in Orthopedics 2013. 2013: 6, 23van Dorp KB, Breugem SJ, Bruijn DJ, Driessen MJ. Promising short-term clinical results of the cementless Oxford phase III medial unicondylar knee prosthesis. World J Orthop 2016; 7(4): 251-7.
[http://dx.doi.org/10.5312/wjo.v7.i4.251] [PMID: 27114932]
]. Several published papers reflect the increased interest in these implants [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
, 15Pandit H, Jenkins C, Beard DJ, et al. Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year. J Bone Joint Surg Br 2009; 91(2): 185-9.
[http://dx.doi.org/10.1302/0301-620X.91B2.21413] [PMID: 19190051]
, 24Kerens B, Schotanus MG, Boonen B, et al. Cementless versus cemented Oxford unicompartmental knee arthroplasty: Early results of a non-designer user group. Knee Surg Sports Traumatol Arthrosc 2017; 25(3): 703-9.
[http://dx.doi.org/10.1007/s00167-016-4149-3] [PMID: 27161197]
, 25Kendrick BJ, Kaptein BL, Valstar ER, et al. Cemented versus cementless Oxford unicompartmental knee arthroplasty using radiostereometric analysis: a randomised controlled trial. Bone Joint J 2015; 97-B(2): 185-91.
[http://dx.doi.org/10.1302/0301-620X.97B2.34331] [PMID: 25628280]
]. We compared the results of cemented and cementless Oxford UKA knee replacement after an approximate seven-year follow-up. Mean scores in the cemented and cementless groups did not differ significantly. Our findings of slightly better follow-up evaluations for the objective KSS, OKS, and WOMAC scores aligned with similar results reported by others [11Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
, 15Pandit H, Jenkins C, Beard DJ, et al. Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year. J Bone Joint Surg Br 2009; 91(2): 185-9.
[http://dx.doi.org/10.1302/0301-620X.91B2.21413] [PMID: 19190051]
, 24Kerens B, Schotanus MG, Boonen B, et al. Cementless versus cemented Oxford unicompartmental knee arthroplasty: Early results of a non-designer user group. Knee Surg Sports Traumatol Arthrosc 2017; 25(3): 703-9.
[http://dx.doi.org/10.1007/s00167-016-4149-3] [PMID: 27161197]
, 25Kendrick BJ, Kaptein BL, Valstar ER, et al. Cemented versus cementless Oxford unicompartmental knee arthroplasty using radiostereometric analysis: a randomised controlled trial. Bone Joint J 2015; 97-B(2): 185-91.
[http://dx.doi.org/10.1302/0301-620X.97B2.34331] [PMID: 25628280]
]. The cementless implant group had an average operating time of 15.5 minutes shorter than the cemented implant group. During the average seven-year follow-up period, we found no loosening of any component of either the cemented or cementless implants. Therefore, taking implant loosening as endpoint of interest, we noted 100% implant survival. One case in the cementless group required patellofemoral replacement, and one case in the cemented implant group required a meniscal insert exchange, but the femoral and tibial components were well fixed. The survival of the implants in both groups seems slightly better than previously published results. However, our small population size (79 cases) may account for this difference. Kerens et al. achieved 90% survival after a 34-month follow-up in patients with cementless implants, and 84% survival after a 54-month follow-up in patients with cemented implants [24Kerens B, Schotanus MG, Boonen B, et al. Cementless versus cemented Oxford unicompartmental knee arthroplasty: Early results of a non-designer user group. Knee Surg Sports Traumatol Arthrosc 2017; 25(3): 703-9.
[http://dx.doi.org/10.1007/s00167-016-4149-3] [PMID: 27161197]
]. Liddle et al. reported a 97.2% survival of cementless Oxford implants at a six-year follow-up [14Liddle 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(2): 181-7.
[http://dx.doi.org/10.1302/0301-620X.95B2.30411] [PMID: 23365026]
]. We believe the success of cementless Oxford UKA implants may rely on the intraoperative bone quality assessment and a more sparing tibial plateau resection. The more bone preserving resection of the tibia plateau should create a better condition for cementless UKA.

The major study limitation was that group allocation was based on patient characteristics; hence the outcomes are susceptible to confounding by indication. Another limitation was the relatively small number of cases and shorter follow-up time of the cementless group compared with the cemented group. Also, the number of patients without postoperative radiography was high. Finally, two experienced surgeons in a single institution performed all surgical procedures, so our findings are not readily generalizable.

CONCLUSION

Both cemented and cementless Oxford phase 3 implants yielded excellent midterm clinical and functional results. The present study was unable to confer significant differences between them. However, cementless UKA offers shorter operation times, and the average thickness of the polyethylene insert in cementless group was 0.6 mm thinner than in the cemented group. In our series of patients, the Bone Hardness Test has been shown to be a simple and useful way of assessing eligibility for cementless UKA. We found that the longevity of both the cementless and the cemented device was similar, and any revisions of the patellofemoral joint or exchange of inserts were not dependent on the type of fixation. As sample size and follow-up time in the current study were limited, further larger studies are required to assess whether cementless UKA reduces the need for revision compared to cemented fixation.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

In accordance with Polish law, ethics committee approval was not obtained, as the study was purely observation, with no changees to standard clinical practics.

HUMAN AND ANIMAL RIGHTS

No Animals/Humans were used for studies that are base of this research.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

Dr. Günter Sinz, Krankenhaus der Barmherzigen Brüder Eisenstadt, Austria, for sharing his experience with the Bone Hardness Test as selection criterion for cementless TKA.

REFERENCES

[1] Goodfellow JW, Kershaw CJ, Benson MK, O’Connor JJ. The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases. J Bone Joint Surg Br 1988; 70(5): 692-701.
[PMID: 3192563]
[2] Goodfellow JW, Tibrewal SB, Sherman KP, O’Connor JJ. Unicompartmental Oxford Meniscal knee arthroplasty. J Arthroplasty 1987; 2(1): 1-9.
[http://dx.doi.org/10.1016/S0883-5403(87)80025-6] [PMID: 3572406]
[3] Argenson JN, O’Connor JJ. Polyethylene wear in meniscal knee replacement. A one to nine-year retrieval analysis of the Oxford knee. J Bone Joint Surg Br 1992; 74(2): 228-32.
[PMID: 1544958]
[4] Psychoyios V, Crawford RW, O’Connor JJ, Murray DW. Wear of congruent meniscal bearings in unicompartmental knee arthroplasty: a retrieval study of 16 specimens. J Bone Joint Surg Br 1998; 80(6): 976-82.
[http://dx.doi.org/10.1302/0301-620X.80B6.8176] [PMID: 9853488]
[5] Murray DW. Mobile bearing unicompartmental knee replacement. Orthopedics 2005; 28(9): 985-7.
[PMID: 16190079]
[6] O’Connor JJ, Goodfellow JW. Theory and practice of meniscal knee replacement: designing against wear. Proc Inst Mech Eng H 1996; 210(3): 217-22.
[http://dx.doi.org/10.1243/PIME_PROC_1996_210_415_02] [PMID: 8885659]
[7] O’Connor J, Goodfellow J, Murray DW. Principles of meniscal bearing arthroplasty for unicompartmental replacement. In: Cartier P, Epinette JA, Descamps G, Hernigou P, Eds. Unicompartmental knee arthroplasty 1st ed. 1997.
[8] Goodfellow J, O'Connor J. The mechanics of the knee and prosthesis design. J Bone Joint Surg Br 1978; 60(3): 358-69.
[9] O’Connor JJ, Shercliff TL, Biden E, Goodfellow JW. The geometry of the knee in the sagittal plane. Proc Inst Mech Eng H 1989; 203(4): 223-33.
[http://dx.doi.org/10.1243/PIME_PROC_1989_203_043_01] [PMID: 2701960]
[10] Rougraff BT, Heck DA, Gibson AE. A comparison of tricompartmental and unicompartmental arthroplasty for the treatment of gonarthrosis. Clin Orthop Relat Res 1991; (273): 157-64.
[PMID: 1959265]
[11] Pandit H, Liddle AD, Kendrick BJ, et al. Improved fixation in cementless unicompartmental knee replacement: Five-year results of a randomized controlled trial. J Bone Joint Surg Am 2013; 95(15): 1365-72.
[http://dx.doi.org/10.2106/JBJS.L.01005] [PMID: 23925740]
[12] Hamilton TW, Rizkalla JM, Kontochristos L, et al. The interaction of caseload and usage in determining outcomes of unicompartmental knee arthroplasty: A meta-analysis. J Arthroplasty 2017; 32(10): 3228-3237.e2.
[http://dx.doi.org/10.1016/j.arth.2017.04.063] [PMID: 28641970]
[13] Robertsson O. New technologies and the Swedish Knee Arthroplasty Register. Bone Joint Res 2014; 3(7): 217-2.
[14] Liddle 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(2): 181-7.
[http://dx.doi.org/10.1302/0301-620X.95B2.30411] [PMID: 23365026]
[15] Pandit H, Jenkins C, Beard DJ, et al. Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year. J Bone Joint Surg Br 2009; 91(2): 185-9.
[http://dx.doi.org/10.1302/0301-620X.91B2.21413] [PMID: 19190051]
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