Safety and outcome of simultaneous bilateral unicompartmental knee arthroplasty: A systematic review

Abstract

Purpose

Simultaneous bilateral unicompartmentsl knee arthroplasty (BUKA) is considered safe and effective. We performed a systematic review to assess the postoperative outcomes.

Methods

The US National Library of Medicine (PubMed/MEDLINE), Google Scholar, and the Cochrane Database of Systematic Reviews were queried for publications.

Results

Ten articles were included with 765 simultaneous BUKA. Overall complication rate was 7.0%, survivorship was 97.6% at mean 17 months follow-up. No differences were reported between simultaneous and staged BUKA.

Conclusion

Simultaneous BUKA is as safe as staged BUKA, it is associated with decreased length of stay and operative time, although it has an increased rate of blood transfusion.

1. Introduction

Unicompartmental knee arthroplasty (UKA) is a good surgical alternative to total knee arthroplasty (TKA) for patients suffering from single-compartment osteoarthritis (OA).1, 2, 3 In the proper setting, UKAs can potentially spare more bone, and are associated with less bleeding, shorter anesthetic time, and shorter length of stay compared to TKA.4, 5, 6 Furthermore, UKAs can result in improved knee kinematics and quicker postoperative recovery compared to TKAs in treating single-compartment OA.^7,8

In bilateral knee OA patients who are suffering from single-compartment disease, an alternative option to staged bilateral unicompartmental knee arthroplasty (BUKA), which requires multiple hospitalizations, is simultaneous BUKA. While a number of papers have been published reporting on the safety and efficacy of simultaneous BUKA, no systematic review of the literature has been published to date. We therefore performed a systematic review of the contemporary literature to assess the effect of simultaneous BUKA on postoperative outcomes. Specifically, we aimed to answer the following questions: 1) What are the complication and revision rates of simultaneous BUKA? 2) What is the mortality rate of simultaneous BUKA? 3) Is simultaneous BUKA a significant risk factor for postoperative complications? Secondarily, we aimed to examine if simultaneous BUKA is associated with increased blood transfusion rate compared to staged BUKA and if it results in decreased length of stay compared to the cumulative length of stay of the staged procedure.

2. Methods

2.1. Search criteria

The US National Library of Medicine (PubMed/MEDLINE), Google Scholar, and the Cochrane Database of Systematic Reviews were queried for publications utilizing the following keywords: “simultaneous” OR “one stage” OR “one-stage” AND “bilateral” AND “unicompartmental” AND “knee” AND “arthroplasty” OR “replacement”. Only abstracts that evaluated the outcome of simultaneous bilateral unicompartmental knee arthroplasty were included in this review.

2.2. Inclusion and exclusion criteria

The inclusion criteria were: 1) studies describing human subjects of any age and gender, 2) studies that include a population of at least ten patients who underwent simultaneous (both procedures performed under a single anesthesia) BUKA. The exclusion criteria were: 1) general reviews or systematic reviews, 2) case studies, 3) editorial comments, 4) studies stratifying patients based on perioperative management (anesthesia protocol, limitation of blood loss, surgical technique, prosthesis type, etc.), 5) non-english language publications, 6) studies that only observed perioperative and not postoperative outcomes (regardless of the follow-up) following BUKA, 7) studies without clinical, functional, or radiological outcomes, 8) studies with results including mixed types of operations without stratification for sub-cohorts receiving simultaneous BUKA, 9) non full text articles, 10) preclinical studies, 11) studies published after July 30th, 2019. For articles that met these criteria, the reference lists were reviewed for additional studies not captured using the initial search terms.

2.3. Data collection

Two authors (PM, MM) independently conducted the search. All authors compiled a list of articles after application of the inclusion and exclusion criteria. Discrepancies between the authors were discussed and resolved. In case of any disagreement amongst reviewers, the final decision was made by the senior author. During initial review of the data, the following information was collected for each study: title, author, study design, number of patients, number of knees, gender, American Society of Anesthesiologists (ASA) score, functional scores, length of stay (LOS), blood transfusion rate, mortality rate, revision rate, infection rate, rates of cardiac events, thromboembolic events and postoperative complications.

The quality of the evidence was then classified using the US Preventive Services Task Force system for ranking level of evidence.⁹ The methodological quality of each study and the different types of detected bias were assessed independently by each reviewer with the use of modified Coleman methodology score.¹⁰

3. Results

3.1. Search results

The literature search identified 430 abstracts related to the use of simultaneous BUKA (Fig. 1). Among those, 29 duplicate articles were identified and removed from the search. Following the removal of duplicate articles, the 401 articles were subject to application of the predetermined inclusion and exclusion criteria. Following the application of these criteria, 15 articles were subject to a full text screening process. Ultimately, 10 articles met the inclusion criteria.11, 12, 13, 14, 15, 16, 17, 18, 19, 20 There were seven retrospectives,11, 12, 13, 14^,16, 17, 18 and three prospective case control study^15,19,20 included in this review. The total mean modified Coleman score was 60, ranging from 55¹⁹ to 76,¹⁵ indicating a moderate-to-good quality of evidence (Table 1).

Fig. 1.

Flow chart of study selection according to PRISMA guidelines for reporting systematic reviews and meta-analyses.

Table 1.

Authors, Type of study, Modified Coleman Methodology Score, Operation, Joint Compartment, and Type of Implant.

Authors (year)	Type of study (LoE)	MCMS	Operation	Joint Compartment	Type of Implant
Feng et al. (2019)	Retrospective Case Control (III)	58	Bilateral UKA versus Staged UKA	Medial	Mobile-bearing unicompartmental implants
Biazzo et al. (2018)	Retrospective Case Control (IV)	58	Bilateral UKA versus Staged UKA	Medial or Lateral	Fixed-bearing unicompartmental implants
Clavé et al. (2018)	Prospective Case Control (III)	61	Bilateral UKA versus Unilateral UKA	Medial	Mobile-bearing unicompartmental implants
Ahn et al. (2017)	Retrospective Case Control (III)	58	Bilateral UKA versus Unilateral TKA	Medial	Fixed-bearing unicompartmental implants
Ma et al. (2015)	Prospective Case Control (III)	55	Bilateral UKA versus Staged UKA	Medial	Mobile-bearing unicompartmental implants
Romagnoli et al. (2015)	Retrospective Case Control (III)	59	Bilateral UKA versus Unilateral UKA	Medial	NR
Winder et al. (2014)	Retrospective Case Control (III)	50	Bilateral UKA, Staged UKA 2nd surgery before 3 months, Staged UKA 2nd after 3 months, Bilateral TKA	NR	Mobile-bearing unicompartmental implants or Fixed-bearing unicompartmental implants
Chen et al. (2013)	Prospective Case Control (III)	76	Bilateral UKA versus Staged UKA	Medial	Fixed-bearing unicompartmental implants
Berend et al. (2011)	Retrospective Case Control (III)	66	Bilateral UKA versus Staged UKA	Medial	Mobile-bearing unicompartmental implants
Chan et al. (2009)	Retrospective Case Control (IV)	60	Bilateral UKA versus Staged UKA	NR	Mobile-bearing unicompartmental implants

LoE Level of Evidence, UKA Unicompartmental Knee Arthroplasty, TKA Total Knee Arthroplasty, NR Not Reported, MCMS Modified Coleman Methodology Score.

Patient cohorts undergoing simultaneous bilateral UKA (simBUKA) were included in all ten studies of the review.11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Seven studies utilized simBUKA only in the medial compartment,11, 12, 13^,15,17,19,20 one study reported simBUKA performed either in the medial or the lateral compartment,¹⁶ and two studies did not provide any information about side.¹⁴ (Table 1).

Seven studies included a second patient cohort treated with staged UKA (stagedBUKA).^12,14, 15, 16, 17, 18, 19 Two studies compared simBUKA and unilateral UKA,^11,20 one study compared simBUKA and unilateral TKA.¹³ In addition, one study compared simBUKA with staged BUKA and simultaneous bilateral TKA (BTKA).¹⁴ (Table 1).

Nine of the studies included in this review mentioned the type of unicompartmental implants used.12, 13, 14, 15, 16, 17, 18, 19, 20 Three studies utilized fixed-bearing unicompartmental implants,^13,15,16 while five studies implemented mobile-bearing implants,^12,17, 18, 19, 20 and one study used both fixed- and mobile-bearing implants.¹⁴ (Table 1).

Six out of the ten studies reported that they used a tourniquet during surgery^13,15,17, 18, 19, 20 and two studies reported that they did not use any tourniquet.^11,16

3.2. Demographics

In total 1676 patients were included in this review. Amongst them, 765 patients underwent simBUKA, 462 patients underwent stagedBUKA, 399 patients underwent unilateral UKA, 52 patients underwent unilateral TKA and 56 patients underwent simultaneous BTKA.11, 12, 13, 14, 15, 16, 17, 18, 19, 20 There were 649 males and 806 females included in this review.^11,13, 14, 15, 16, 17, 18 The mean age ranged from 58 years¹² to 70 years¹⁶ in the simBUKA group. The mean follow-up for simBUKA patients was 17 months, ranging from 1^15,16,18 to 50 months,¹⁹ indicating a short-term follow-up (Table 2).

Table 2.

Demographics data of the studies.

Authors	No. of Patients	No. of patients Bilateral UKA	No. of patients Unilateral UKA	No. of Patients Staged UKA	Sex (M/F)	Mean age (range)	BMI (range)	Mean follow-up, months (range)
Feng et al. (2019)	93	39	–	54	Bilateral Male 3, Female 33 Staged Male 5, Female 49	Bilateral 65 ± 8 Staged 64 ± 6	Bilateral 24 ± 2.5 Staged 24 ± 2.5	42 (32–133)
Biazzo et al. (2018)	102	51	–	51	Bilateral Male 13, Female 38 Staged Male 19, Female 32	Bilateral 70 (68–73) Staged 69 (65–72)	Bilateral 29 (28–31) Staged 29 (27–30)	1
Clavé et al. (2018)	150	50	100	–	Bilateral Male 35, Female 15 Unilateral Male 66, Female 34	Bilateral 64.4 (50–86.7) Unilateral 68.1 (56–87)	Bilateral 28.8 (22.1–38.9) Unilateral 29.8 (21.9–47.6)	Bilateral 44 (24–84) Unilateral 61 (24–96)
Ahn et al. (2017)	104	52	52 unilateral (TKA)	–	Bilateral Male 48, Female 4 Unilateral (TKA) Male 48, Female 4	Bilateral 65.1 (49–87) Unilateral (TKA) 65.6 (51–83)	Bilateral 28.1 (22–35) Unilateral (TKA) 28.3 (21.8–37.9)	6
Ma et al. (2015)	81	36	–	45	Bilateral Male 15, Female 21 Staged Male 18, Female 27 (p = 0.88)	Bilateral 65.6 ± 6.1 Staged 65.3 ± 5.6 (p = 0.8)	Bilateral 25.0 ± 1.9 Staged 25.5 ± 2.0 (p = 0.25)	50 (12–84)
Romagnoli et al. (2015)	490	191	299	–	Bilateral Male 72, Female 119 Unilateral Male 120 Female 179	Bilateral 67.5 (66–69) Unilateral 68.2 (67–69)	Bilateral 30 (29–31) Unilateral 29 (28–29)	6
Winder et al. (2014)	72	28	–	44	Bilateral Males 16, Females 12	Bilateral 64 ± 10	NR	3
Chen et al. (2013)	171	124	–	47	Bilateral Male 33, Female 91 Staged Male 11, Female 36	Bilateral 62.9 (45–86.1) Staged 61.6 (51.0–82.3)	Bilateral 27.3 (19.1–42.3) Unilateral 26.8 (19.5–33.7)	1
Berend et al. (2011)	176	35	–	141	NR	Bilateral 58 (55–62) Staged 63 (61–64)	Bilateral 31 (29–32) Staged 33 (32–35)	Bilateral 19.4 Staged 13.9
Chan et al. (2009)	239	159	–	80	Bilateral Male 92, Female 67 Staged Male 35, Female 45	Bilateral 66 (42–85) Staged 66 (48–86)	NR	1

TKA Total Knee Arthroplasty, NR Not Reported, BMI Body Mass Index, BUKA Bilateral Unicompartmental Knee Arthroplasty, BTKA Bilateral Total Knee Arthroplasty.

3.3. Comparison of the baseline demographic and clinical characteristics between simBUKA and stagedBUKA

Nine studies that compared the outcomes of simBUKA with either staged BUKA, UKA or TKA, reported comparable baseline demographic characteristics as stated by the authors in the methods of the studies.^11,13, 14, 15, 16, 17, 18, 19, 20 One study reported a statistical difference among the two cohorts with patients who underwent simBUKA that were younger and had lower BMI compared to those who underwent stagedBUKA.¹²

Furthermore, six studies included the American Society of Anesthesiologists score (ASA score) for their preoperative evaluation.15, 16, 17, 18, 19, 20 The majority of the patients were ASA I and II in both the simBUKA and stagedBUKA groups. When comparing simBUKA to stagedBUKA, five studies showed comparable ASA scores.^15,17, 18, 19, 20 One study reported a significantly higher ASA score in the simBUKA group compared to the stagedBUKA group (p = 0.023).¹⁶

3.4. Complications and mortality

The overall complication rate for patients treated with simBUKA was 7.0% (54 out of 765 patients. The overall complication rate for patients treated with stagedBUKA was 11.5% (53 out of 462 patients). The three most common complications encountered in either group were cardiopulmonary events, wound drainage and DVT (Table 3). The overall mortality rate for the simBUKA was 0.1% (n = 1) at short-term follow-up. One study reported a death in the simBUKA group, which was attributed to pulmonary embolism.¹⁸ Remaining studies reported no deaths.^12,15, 16, 17

Table 3.

Complications reported per study.

Authors	Complications	Cardiopulmonary Complications	Wound drainage	DVT	PE
Feng et al. (2019)	Bilateral 4 Staged 5 (n.s.)	Bilateral 1 Staged 2	Bilateral 3 Staged 2	Bilateral 0 Staged 0	Bilateral 0 Staged 0
Biazzo et al. (2018)	Bilateral 4 Staged 2	Bilateral 1 Staged 0	Bilateral 0 Staged 0	Bilateral 0 Staged 0	Bilateral 0 Staged 0
Clavé et al. (2018)	Bilateral 5	Bilateral 0	Bilateral 0	Bilateral 2	Bilateral 1
Ahn et al. (2017)	Bilateral 1 Unilateral (TKA) 7 (p = 0.028)	Bilateral 0 Unilateral (TKA) 0	Bilateral 1 Unilateral (TKA) 3	Bilateral 0 Unilateral (TKA) 2	Bilateral 0 Unilateral (TKA) 3
Ma et al. (2015)	Bilateral 3 Staged 5	Bilateral 0 Staged 0	Bilateral 1 Staged 1	Bilateral 1 Staged 2	Bilateral 0 Staged 0
Romagnoli et al. (2015)	Bilateral 9 Unilateral 19 (n.s.)	NR	NR	NR	NR
Winder et al. (2014)	Bilateral 2	Bilateral 0	Bilateral 1	Bilateral 1	0
Chen et al. (2013)	Bilateral 5 Staged 5 (n.s)	Bilateral 2 Staged 0 (n.s.)	Bilateral 0 Staged 3 (p = 0.02)	Bilateral 1 Staged 2 (n.s.)	Bilateral 2 Staged 0 (n.s.)
Berend et al. (2011)	Bilateral 4 Staged 31	Bilateral 2 Staged 10	Bilateral 2 Staged 7	Bilateral 0 Staged 0	Bilateral 0 Staged 0
Chan et al. (2009)	Bilateral 17 Staged 5	Bilateral 3 Staged 0 (p < 0.005)	Bilateral 4 Staged 2	Bilateral 10 Staged 3	Bilateral 6 Staged 0

DVT Deep Venous thrombosis, PE Pulmonary Embolism, NR Not Reported, TKA Total Knee Arthroplasty, n.s. Not Significant.

3.4.1. Simultaneous vs. staged BUKA

Six studies compared mean complication rates of simBUKA-treated patients and stagedBUKA-treated patients.^12,15, 16, 17, 18, 19 Five out of these six studies reported no significant differences amongst groups on complication rates.^12,15, 16, 17^,19,20 One study reported significantly increased complication rate (p = 0.005) in the simBUKA group compared to the stagedBUKA group.¹⁸

3.5. Cardiopulmonary complications and thromboembolic events (DVT)

Nine studies reported on cardiopulmonary complications and DVT events.12, 13, 14, 15, 16, 17, 18, 19, 20 The overall rate of DVT events for simBUKA patients was 2% (15 out of 574 patients). When considering patients treated with stagedBUKA it was 1.4% (7 out of 467 patients). The overall rate of PE events for simBUKA patients was 1.6% (9 out of 574 patients) and for patients treated with stagedBUKA it was 0% (Table 3).

3.5.1. Simultaneous vs. staged BUKA

Six studies compared DVT rates and PE events between simBUKA and the stagedBUKA-treated patients.^12,15, 16, 17, 18, 19 Five studies did not report any significant differences amongst groups,^12,15, 16, 17^,19 whereas one study reported a significantly higher DVT rate (p = 0.036) in the stagedBUKA group compared to the simBUKA group.¹⁸

3.6. Surgical site infections

Nine studies included in this review reported on superficial wound infection rate as well as periprosthetic joint infection (PJI) rate.12, 13, 14, 15, 16, 17, 18, 19, 20 The overall rate of superficial wound infections for simBUKA patients was 2.1% (12 out of 574 patients). When considering the patients treated with staged BUKA the overall rate of superficial wound infections was 3.2% (15 out 467 patients). One study reported significant difference between simultaneous BUKA (0 cases out of 124) and staged BUKA (3 cases out of 47) at 30-days follow-up (p = 0.02)¹⁵ The PJI rate for simBUKA patients was 0.2%, while for the stagedBUKA patients it was 0% (Table 3).

3.7. Revision rate

Nine studies included in this analysis reported on revision rates.11, 12, 13, 14, 15, 16, 17^,19,20 The overall revision rate for the simBUKA group was 2.4% (16 out of 679). The overall revision rate for the stagedBUKA group was 2.9% (11 out of 382). (Table 4).

Table 4.

Revision rates, Length of Stay, Operation Time, and Blood Transfusion per Study.

Authors	Revision	Length of Hospital Stay (days)	Total Operation Time (min)	Blood Transfusion (rate)
Feng et al. (2019)	0	Bilateral 4.2 ± 0.7 Staged 7.5 ± 1.5 (p < 0.01)	Bilateral 120.2 ± 9.7 Staged 141.6 ± 8.7 (p < 0.01)	Bilateral 1 (2.6%) Staged 0 (n.s.)
Biazzo et al. (2018)	0	NR	Bilateral 93 (88–98) Staged 102 (p = 0.023)	Bilateral 4 (8%) Staged 0 (p = 0.041)
Clavé et al. (2018)	2	–	–	Bilateral 3 (6%) Unilateral 5 (5%) (p = 0.6)
Ahn et al. (2017)	0	Bilateral 8.4 (4–21) Unilateral-TKA 12.7 (9–44) [p < 0.001]	NR	Bilateral 9 (17.3%) Unilateral-TKA 44 (84.6%) [p < 0.001]
Ma et al. (2015)	Bilateral 1 Staged 2	–	Bilateral 113 ± 8.7 Staged 133 ± 9.9 (p < 0.005)	–
Romagnoli et al. (2015)	Bilateral 13 Unilateral 9 (n.s.)	Bilateral 4 (3.8–4.2) Unilateral 4.2 (4.0–4.3)	Bilateral 61.3 Unilateral 29.7	Bilateral 24 (10.9%) Unilateral 13 (3.8%) [p < 0.001]
Winder et al. (2014)	0	Bilateral 3.9 ± 1.2	Bilateral 150 (114–206)	NR
Chen et al. (2013)	0	Bilateral 5 (3–20) Staged 8 (4–23) [p < 0.001]	Bilateral 130 Staged 153 [p < 0.001]	Bilateral 1 (0.8%) Staged 0 (n.s)
Berend et al. (2011)	Bilateral 0 Staged 0	Bilateral 1.7 Staged 1.3 (p < 0.001)	Bilateral 109 Staged 6 [p < 0.001]	NR
Chan et al. (2009)	NR	Bilateral 5 (2–19) Staged 6 (2–15)	Bilateral 113’ (45–180) Staged 129’ (80–190) [p < 0.001]	–

NR Not Reported, TKA Total Knee Arthroplasty.

3.7.1. Simultaneous vs. staged BUKA

Six studies compared the revision rates between simBUKA and the stagedBUKA.^12,14, 15, 16, 17^,19 However, none of the studies reported statistically different results among the two groups.

3.8. Clinical and functional outcome variables

Six studies included postoperative functional outcome variables.^{12,13,15,17,19,20} Four studies used the Knee Society Score (KSS),^12,13,15,17 and all of them reported a significant improvement compared to preoperative values. When comparing the KSS score in patients who underwent simBUKA with patients who underwent staged BUKA, none of the studies reported a significant difference among the two protocols. One study¹² reported significant difference at mean follow-up of 19 months regarding the “functional” section of the KSS with a score of 87.9 in the simBUKA group and 72.9 in the staged BUKA group (p < 0.001). When the KSS was compared between simBUKA and UKA it was noticed a significant difference at final follow-up (89.2 vs 83.4; p < 0.001).¹³ The Oxford Knee Score (OKS) was used in three studies^15,19,20 and all of them compared simBUKA with staged BUKA. Improved OKS score was reported at final follow-up compared to the preoperative value, however, none of the studies achieved statistically significance when comparing the two surgical protocols. The Range of Motion (ROM) was used in two studies.^13,15 One study [13] compared the outcomes of simBUKA with UKA and reported significant improvement of 136.9° and 121.3°, respectively (p < 0.001). One study¹⁵ compared the ROM after simBUKA and staged BUKA reporting improvement respect to the preoperative values, but no significant difference was noticed between the two surgical protocols. Finally, one study used the Lower Extremity Score (LEAS) and reported a significantly higher postoperative value in the simBUKA group compared to the stagedBUKA group (11.3 vs 10.2; p < 0.001).¹² (Table 5).

Table 5.

Clinical reported outcomes.

Authors	Bilateral	Staged	Unilateral
Feng et al. (2019)	KSS 88 KSSf 82	KSS87 (n.s.) KSSf 80 (n.s.)	–
Biazzo et al. (2018)	NR	NR	–
Clavé et al. (2018)	OKS 44.5	OKS 42.2 (p = 0.61)	–
Ahn et al. (2017)	KSS 89.2 KSSf 84.2 ROM 136.9	–	KSS 83.4 (p < 0.001) KSSf 76.0 (p < 0.001) ROM 121.3 (p < 0.001)
Ma et al. (2015)	OKS 18.3	OKS 18.0 (p = 0.52)	–
Romagnoli et al. (2015)	NR	–	NR
Winder et al. (2014)	NR	NR	NR
Chen et al. (2013)	KSS 89 KSSf 80 ROM 0–128° OKS 18	KSS 88 KSSf 80 (n.s.) ROM 0–126° (n.s.) OKS 18 (n.s.)	–
Berend et al. (2011)	KSSc 91.4 KSSp 44.6 KSSf 87.9 LEAS 11.3	KSSc 90.1 (n.s) KSSp 46.8 (n.s) KSSf 72.9 (p < 0.001) LEAS 10.2 (p < 0.001)	–
Chan et al. (2009)	NR	NR	NR

KSS Knee Society Score, KSSf Knee Society Function Score, KSSc Knee Society Clinical Score, KSSp Knee Society Pain Score, LEAS Lower Extremity Activity Score, OKS Oxford Knee Score, ROM Range of Motion, NR Not Reported.

3.9. Perioperative blood transfusion

Six studies of this analysis reported on perioperative blood transfusion rates in patients treated with simBUKA.^11,13,15, 16, 17^,20 The overall transfusion rate (number of patients transfused) in the simBUKA was 8.1% (41 out of 507). (Table 4).

3.10. Simultaneous vs. staged BUKA

Three studies compared the transfusion rates of the simBUKA group and the stagedBUKA group.15, 16, 17 One study reported significant increased transfusion rate in the simBUKA group (8%) compared to the stagedBUKA group (0%) (p = 0.041),¹⁶ while the remaining two studies did not report any significant difference amongst groups.^15,17

3.11. Length of stay

3.11.1. Simultaneous vs. staged BUKA

Seven studies reported on inpatient length of stay (LOS).11, 12, 13, 14, 15^,17,18 Four studies compared the LOS of the simBUKA group and the stagedBUKA group, and all them reported a significant difference among the groups.^12,15,17,18 When comparing the cumulative LOS of the patients in the simBUKA group and the stagedBUKA group, three studies found that mean LOS was significantly longer in the stagedBUKA group (simBUKA:1.7 days vs. stagedBUKA:2.5 days; p < 0.001,¹² simBUKA:5 days vs. stagedBUKA:8 days; p < 0.001,¹⁵ and simBUKA:4.2 days vs. stagedBUKA:7.5 days; p < 0.01).¹⁷ (Table 4).

3.12. Operative time

Eight studies reported on mean operative (OR) time of simBUKA and compared them to either stagedBUKA,^12,14, 15, 16, 17, 18, 19 UKA,¹¹ and simultaneous BTKA.¹⁴ Cumulatively, the mean OR time of the simBUKA patient cohort varied per study between 93 and 150 min, while the mean OR time of the stagedBUKA cohort ranged per study from 101.6 min to 152.5 min. Six studies reported that the cumulative mean OR time of stagedBUKA was significantly higher^12,15, 16, 17, 18, 19 than that of simBUKA (Table 4).

4. Discussion

The key finding of our analysis was that simultaneous BUKA resulted in satisfactory clinical outcomes, with minimal postoperative mortality (0.1%), acceptable medical complication rates (7.0%) and good early to short-term implant survivorship (97.6%). Moreover, all clinical/functional subjective scores which were reported in the studies included in this review were significantly improved compared to the preoperative values and compared to unilateral UKA. However, no significant difference was reported among the studies included when compared to staged BUKA. In addition, simBUKA was significantly associated with reduced LOS and mean OR time, potentially affecting the postoperative complication rate and the hospital costs. Despite that, further high-quality studies with longer follow-up comparing the mid-to-longterm outcomes of simBUKA and stagedBUKA are necessary to confirm these preliminary outcomes. However, based on these findings, it seems that simBUKA can be considered a safe and effective option in selected patients with bilateral single-compartment OA.

It has been routinely recommended by physicians that patients with serious comorbidities should be advised against a simultaneous bilateral knee arthroplasty procedure. Surprisingly, in most studies comparing simBUKA with stagedBUKA patients with statistically comparable baseline clinical and demographic characteristics, it was demonstrated that there were no differences amongst groups in the overall complication rates as well as mortality rate, cardiopulmonary complication rates, and rate of thromboembolic events.^12,15, 16, 17, 18, 19, 20 A recent systematic analysis comparing simultaneous bilateral TKA and staged bilateral TKA reported also comparable overall complication, DVT, cardiac complication, and mortality rates amongst groups.21, 22, 23, 24 Recent advances in all aspects of perioperative care and patient optimization might explain these comparable peri- and post-operative morbidity rates between simultaneous and staged knee arthroplasty procedures.

This does not mean that all patients are ideal candidates for simultaneous BUKA. In our analysis, the simBUKA-treated cohort mainly comprised of patients suffering from mild (ASA grade 2) diseases. We still feel that patients who are at increased risk for cardiac events or they are suffering from a severe systemic disease should be recommended to have a staged BUKA.

Interestingly, while there was no statistical difference reported in the individual studies comparing PE rates between simultaneous and staged BUKA cohorts, there was a trend towards higher risk for PE in the simultaneous BUKA cohort (1.6% versus 0% in the staged group) when comparing overall PE rates. Taking into consideration the increased invasiveness of simultaneous BUKA compared to unilateral BUKA, we feel that patients undergoing simultaneous BUKA should be postoperatively protected with stronger anticoagulation than those treated with a unilateral BUKA.

In regard to surgical site infection rate and all cause revision rate, neither were increased in the simBUKA group.^12,15, 16, 17, 18 Similarly, a recent analysis^21,25 showed that almost all studies comparing simultaneous bilateral TKA and staged bilateral TKA reported no significant differences in infection rates amongst groups. Overall, we suggest that simultaneous BUKA does not appear to increase the rate of revision or devastating complications such as surgical site infections.

For postoperative functional scores, no study showed inferior outcomes with simBUKA compared to stagedBUKA.11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Therefore, it might be supported that simultaneous BUKA is correlated with at least equivalent functional outcomes compared to staged BUKA, but further studies are required to clarify whether the former leads to better functional outcomes compared to the latter procedure.

As expected, the rate of postoperative blood transfusion was increased in the simultaneous group (8.1%) compared to the staged group (0%) throughout the studies of this review. Similarly, a recent systematic analysis comparing simultaneous bilateral TKA and staged bilateral TKA reported increased blood transfusion rates in the simultaneous cohort.²¹ As such, we suggest that candidates for BUKA who have been diagnosed with preoperative anemia either avoid simBUKA or are counseled that they are at increased risk of perioperative blood transfusion if they choose to undergo the simultaneous BUKA procedure.

Finally, it was shown that patients treated with simultaneous BUKA had significantly decreased cumulative LOS compared to the cumulative LOS of stagedBUKA-treated patients^12,15,17 which might correlate with decreased costs. In addition, all studies reporting cumulative OR time found it significantly decreased in the simBUKA group compared to the stagedBUKA group.^12,15, 16, 17, 18 Likewise, a systematic review comparing simultaneous bilateral TKA and staged bilateral TKA reported significantly decreased cumulative LOS in the simultaneous cohort.²¹

The overall quality of the studies included in this review was not high; however, most studies were rated as either moderate or good according to the mean modified Coleman methodology score. The vast majority of the studies were retrospective, and there was no randomized controlled trial level I studies amongst them. Therefore, all studies were susceptible for various types of potential biases. Further studies of higher quality are required to lead to more definitive conclusions in relation to the safety of simultaneous BUKA in comparison with staged BUKA.

The studies included in this analysis were not without limitations. The number of BUKA-treated patients was rather low, while time interval between the first and the second surgery in patients treated with staged BUKA varied widely amongst studies. Follow-up was another variable that varied amongst studies, and no studies reported mid-to long-term follow-up. Nonetheless, the rationale for these studies was to compare simultaneous and staged BUKA, and simultaneous and UKA as for the early postoperative morbidity and mortality rates.

5. Conclusion

There was moderate-to-good quality evidence to show that simultaneous BUKA might be as safe as the staged procedure in selected patients who are not suffering from severe comorbidities. Furthermore, simultaneous BUKA is associated with decreased cumulative LOS and OR time compared to staged BUKA. In contrast, simultaneous BUKA correlates with increased perioperative blood transfusion rate when compared to staged BUKA and to UKA. Since perioperative tranexamic acid has been proven effective in decreasing perioperative blood loss, we feel that it should be routinely used in simultaneous BUKA-treated patients. Furthermore, simultaneous BUKA trends towards increased PE rates compared to staged BUKA and to UKA. Taking this finding into consideration, we suggest that stronger anticoagulation might be needed in simultaneous BUKA-treated patients. Finally, while simultaneous BUKA is associated with satisfactory short-term clinical outcomes, further research of higher quality is required to generate more evidence-based conclusions regarding the mid- and long-term outcome of simultaneous BUKA compared to the standard staged procedure.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Availability of data and material

Not applicable.

Code availability

Not applicable.

Contributions

MAM, PPM, FM, MD, PKS: designing the work. MAM, PPM, FM, SJJ, AG: acquisition and analysis of the data and drafting the work. DG, MD, VSN, PKS: revised it critically for important intellectual content. PKS: final approval of the version to be published.

Declaration of competing interest

All authors declare that they have no conflict of interest. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Dr. Sculco reports grants from Intellijoint, personal fees from Lima Corporate, grants from DePuy, personal fees from EOS Imaging, outside the submitted work.