Study selection

A total of 4868 articles were identified from literature databases and through reference and citation searches. After exclusion of duplicates, there were 2062 remaining, which were assessed for relevance by reviewing the title and abstract. One hundred eighty-eight articles were found relevant and the full text was available for 107 articles which were all in English despite absence of language restriction in the search and selection strategy. After the exclusion criteria were applied, a total of 20 articles were included in the final systematic review [4, 6, 7, 9,10,11,12, 15, 17, 19, 20, 28, 32, 35, 38, 40, 48, 51, 54, 55] (Fig. 1).

Fig. 1
figure 1

Flow chart for selection of studies for systematic review on long-term effects of tourniquet use in TKA

Study characteristics

A total of 1884 subjects were undergoing total knee arthroplasty in the 20 included studies. The patients had a primary diagnosis of osteoarthritis and rheumatoid arthritis [4, 6, 7, 9,10,11,12, 15, 17, 19, 20, 28, 32, 35, 38, 40, 48, 51, 54, 55]. Tourniquet pressure was reported in all but one study and ranged between approximately 200–300 mmHg. The mean follow-up time was 12.2 months (Table 1) [4, 6, 7, 9,10,11,12, 15, 17, 19, 20, 28, 32, 35, 38, 40, 48, 51, 54, 55]. BMI, age and male:female ratio was reported by all studies. BMI ranged from 24.8–33 kg/m2 and mean age ranged from 62 to 73 years and male:female ratio ranged from 0.22 (13/59) to 9 (09/01) (Additional file 1: Appendix 2). There was no significant difference reported in baseline demographics between treatment groups.

Table 1 Characteristics of studies included in systematic review on mid-term and long-term effects of tourniquet use. (See additional characteristics in Additional file 1: Appendix 2)

Risk of bias within studies

Eleven RCTs were determined as low overall risk of bias [6, 7, 9, 10, 19, 28, 32, 38, 51, 54, 55] and five RCTs were determined to have some overall concerns [11, 12, 15, 20, 33] according to the Revised Cochrane Risk Assessment Scale (Additional file 1: Appendix 3). There were some concerns present in mainly two domains: deviation from intended intervention and bias in measurement of the outcome in the RCTs with respectively, 11% and 19% of the values under these domains for all studies combined, belonging to “some concern” (Fig. 2A). All prospective cohort studies were reported as good quality according to the Newcastle Ottawa Scale Criteria [4, 17, 40, 48] (Fig. 2B). All studies received the maximum in the ‘selection’ criteria i.e., four stars. Three studies [4, 17, 40] were unable to control for, or adjust for disease severity of the participants and hence, only scored one star in ‘comparability’ and one study did not provide information regarding blinding of assessors and hence, only scored two stars in outcome assessment [4] (Additional file 1: Appendix 4).

Fig. 2
figure 2

A Methodological quality assessed using Risk of Bias Assessment tool of RCTs included in review of long-term effects of tourniquet use in total knee arthroplasty (see additional details in Additional file 1: Appendix 3). B Methodological quality assessed using Newcastle Ottawa scale of prospective cohort studies included in review of long-term effects of tourniquet use in total knee arthroplasty (see additional details in Additional file 1: Appendix 4)

Seven studies reported that no funding had not been received and declared no conflict of interest [6, 9, 16, 35, 38, 39, 54]. Seven studies did not mention whether funding had been received but, confirmed that no conflict of interest was present [4, 7, 11, 12, 20, 28, 48]. Three studies reported that funding had been received and reported conflict of interest [10, 17, 19] while, two studies reported that funding had been received and reported no conflict of interest [51, 56]. Finally, one study failed to report receiving funding or lack of conflict of interest [32].

Implant stability

Implant stability was reported by seven studies [11, 12, 17, 20, 28, 35, 48] which included 529 knees and one study [17] reported long-term stability (Table 2). Implant stability was evaluated by measuring tibial cement penetration, progressive radiolucent lines (RLL) measured according to the Knee Society Roentgenographic Evaluation System (KSRES), percentage of radiolucency at the tibial bone–cement interface, translation and rotation of the tibia and recurrence rate. Notably, the studies did not include revision rate due to implant instability as a primary outcome or conduct statistical analysis of the outcome. Two studies found a significant increase in RLLs in the non-tourniquet groups. Touzopoulos, et.al found a significant decrease in percentage of radiolucency in anteroposterior (AP) view in the tourniquet group: (zone 1: 1.36 vs. 2.72 and zone 4: 1.14 vs. 2.67) and cumulative AP view (3.48 vs. 7.74) at 3 years [48]. Hedge, et al found a significant decrease in RLLs in the tourniquet group: AP view (zone 1: 0.33 vs. 1.53) and cumulative lateral view (0.79 vs. 5.58) at 5 years [17]. The remaining studies did not find a significant difference in outcomes in the treatment groups [11, 28, 35].

Table 2 Mid-term and late implant loosening in studies included in review on mid-term and long-term effects of tourniquet use

Functional outcomes

Functional outcomes appeared in 17 of the 20 included studies [4, 6, 7, 9, 10, 12, 15, 19, 20, 28, 32, 38, 40, 48, 51, 54, 55] including 1850 knees with no studies recording long-term outcomes (Table 3). Only two studies [10, 48] reported a statistically significant difference in functional outcomes. A study found a significant decrease in extension contracture in the tourniquet group at 36 months (1.51° vs. 5.61°) [48] while, another study found a significant decrease in quad strength in the tourniquet group at 3 months (127.6 Nm vs. 136.7 Nm) [10]. Functional outcomes were assessed by measuring range of motion, knee flexion, EMG activation signal, Quadriceps lag, stair ascent/descent time, straight leg raise, unilateral balance test, timed up and go test, muscle strength and force. A variety of tools including WOMAC, KOOS, NKSS, HSS and KSS were also used. Eleven studies used multiple tools to assess function [6, 7, 9, 10, 12, 20, 28, 32, 40, 48, 54, 55].

Table 3 Mid-term functional outcomes in studies included in review on mid-term and long-term effects of tourniquet use

Pain

Pain was reported in 11 studies [6, 7, 9, 10, 12, 15, 19, 20, 40, 48, 55] with 1227 knees (Table 4). Of the studies reporting pain, only one study reported a statistically significant increase in pain in the non-tourniquet group at 3 months, measured using the visual analogue scale (2.9 vs. 4.7) [6]. A variety of tools were used for the assessment of pain including the Western Ontario and McMaster Universities Osteoarthritis Index Pain score, Knee Injury and Osteoarthritis Outcome Score, Visual Analog Scale (VAS), Oxford Knee Score, Numeric Analog Scale, New Knee Society Score (NKSS), Hospital for Special Surgery knee score; Numeric Pain Rating Scale, Knee Society Score, Clinical, Short Form 36 and Physical Component Score with the most common being the VAS [6, 10, 12, 15, 19, 20, 40, 48, 55]. The VAS was used by four studies [15, 19, 40, 55] and scores ranged from to 0.14–4.7. Three studies used multiple tools to assess pain [20, 40, 55].

Table 4 Mid-term pain outcomes in studies included in review on mid-term and long-term effects of tourniquet use

Other outcomes

Other outcomes were reported by 10 studies including 973 knees [6, 9, 10, 12, 19, 20, 28, 35, 40, 48] (Table 5). The outcomes and outcome measurement tools included limb inflammation (limb circumference), limb alignment (Hip-knee-ankle index), patient satisfaction (patient satisfaction scale, Knee Injury and Osteoarthritis Outcome Score (KOOS), EuroQol, Manusco, Knee Society Score), patient anxiety (Hospital Anxiety and Depression Score, quality of life (KOOS and 12-Item Short Form Health Survey), and general health (Physical Component Score, Mental Component Score) with limb inflammation [6, 10, 28, 40] and patient satisfaction [19, 20, 48] being the most frequently reported outcomes. A study reported a significant increase in knee circumference in the non-tourniquet group at 12 months (41.27 vs. 42.62) [28]. There were no other reported significant differences in other outcomes.

Table 5 Mid-term other outcomes in studies included in review on mid-term and long-term effects of tourniquet use

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