2.1 Search strategy and information sources

This systematic review is exempt from Institutional Review Board evaluation due to exclusive utilization of publicly available data lacking personal health identifiers. We queried PubMed, Google Scholar, and EBSCOhost databases for studies that reported on preoperative sarcopenia or sarcopenic obesity on TJA outcomes published from January 3rd, 2000 to December 2023 (Table 1). The keywords and Medical Subject Headings (Mesh) terms used are listed in Table 1. This systematic review protocol was registered with PROSPERO on January 3rd, 2024 (CRD42024498987).

2.2 Eligibility criteria

Inclusion criteria required that each study measured outcomes after total hip or total knee arthroplasty for patients with existing sarcopenia or sarcopenic obesity, and that a full-text manuscript was available in English. Articles were included if the sarcopenia diagnosis was in accordance with the revised European Working Group on Sarcopenia in Older People definition, including both clinical analysis of low muscle strength and quantitative imaging indicating low skeletal muscle mass or quality.^2,12 Study exclusion criteria were as follows: 1) studies that defined sarcopenia based only on screening tests; 2) case reports; 3) editorials and commentaries; 4) systematic reviews; 5) posters and abstracts; 6) duplicate studies among databases; and 7) publications without English text available. Additionally, studies were excluded if they reported results on patients with presarcopenia or on patients who developed sarcopenia postoperatively.

2.3 Study selection

This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.¹³ Following the search query, two independent reviewers (KJZ, KEA) assessed 877 articles for eligibility (Fig. 1). Disagreements were resolved by a third independent researcher (CJH) to determine eligibility for further review. Following title and abstract screening, 82 studies were considered for full-text review. Screening of the full texts resulted in 14 eligible articles to be included in our final analysis. The majority of the full-text screened studies were excluded because they did not mention sarcopenia as a diagnosis, despite categorizing patients by sarcopenia-related measurements (Table 2).

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Fig. 1 PRISMA diagram depicting the study selection process.

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2.4 Study characteristics

This collection of 14 studies comprised of 3 prospective observational studies,^9,10,14 4 case-controlled retrospective cohort studies,^1,3,7,11 and 7 retrospective cohorts.^6,8,15–19 Of these studies, 11 reported on data from a single institution, 1 included data from multiple centers, and 2 pulled from databases. A total of 7 studies reported on postoperative complications for patients with and without sarcopenia.^{1,6–8,14–16} Furthermore, 5 studies reported on functional outcomes after TJA,^8,9,15,17,19 whereas 6 studies reported on postoperative PROMs for sarcopenic and non-sarcopenic patients after total hip or total knee arthroplasty.^3,7–11 All studies specified that patients underwent TJA for osteoarthritis. These studies included a combined total of 16,821 patients with sarcopenia (Table 2).

2.5 Risk of bias in individual studies

This systematic review assessed the risk of bias for each included article via the Methodological Index for Nonrandomized Studies (MINORS) tool.²⁰ Each article was graded by two independent researchers (KEA, KJZ) and any disagreements were resolved by a third independent reviewer (CJH). This validated tool scores noncomparative studies on a scale from 0 to 16 and comparative studies from 0 to 24. Scores are based on criteria, scored 0–2, such as rigor of study design, statistical analyses, minimal loss to follow-up, and unbiased endpoints. Higher scores indicate a higher rigor of research quality. The mean MINORS scores were 14 ± 1 of 16 maximum for non-comparative studies, and 21 ± 2 of 24 maximum for comparative studies.

2.6 Outcomes and analysis

The primary study objective was to determine if patients with preexisting sarcopenia experienced altered outcomes after total hip or total knee arthroplasty when compared to patients without sarcopenia. To assess these outcomes, we compared postoperative complications, PROMs, and functional metrics. The postoperative complications consisted of metrics including but not limited to dislocation, periprosthetic fracture, hematoma, pulmonary embolism, and requirement of transfusion. The PROMs and functional metrics were sourced from existing questionnaires and function tests used in prior orthopaedic publications. Heterogeneity among studies precluded meta-analysis, so a qualitative narrative was presented.

3.1 Functional outcomes

Based on our review, preoperative sarcopenia is not a risk factor for inferior range of motion or independent walking ability after TKA, nor inferior gait speed or strength after THA, while sarcopenia is associated with a prolonged time to achieve independent walking after THA.^8,9,15,19 Of the three TKA studies, two found no difference for postoperative range of motion between sarcopenic and non-sarcopenic patients.^8,15 Additionally, a third study found that sarcopenia is not a risk factor for independent walking after TKA (HR = 0.55, p = 0.297).¹⁷ Notably, this study also investigated THA and found that sarcopenia is a risk factor for independent walking after THA (HR = 0.55, p < 0.001).¹⁷ The final two studies that investigated outcomes after THA found there is no difference in postoperative gait speed between sarcopenic and non-sarcopenic patients.^9,19 Furthermore, both studies assessed for differences in strength between groups and one study⁹ reported no difference between groups, while the other study¹⁹ lacked sufficient power to execute a robust statistical analysis (Table 3).

3.2 Patient reported outcome measures

After TKA or THA, sarcopenia patients have inferior PROMs regarding pain, function, and satisfaction when compared to non-sarcopenia patients. After TKA, Shon et al.⁸ reported that sarcopenic patients scored lower in all domains, except pain, for the Knee injury and Osteoarthritis Outcome Score (KOOS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at 3-months and 6-months post-TKA, but these differences were negligible at 12-months. In contrast, one study found no difference between groups in all KOOS categories at 3-months after TKA.¹⁰ Additionally, two studies found worse PROMs for sarcopenic patients after TKA at 12 months postoperatively, where sarcopenia is a predictor for worse PROMIS scores after TKA (OR = 0.26, p = 0.02).^3,7 Among the studies that investigated post-THA outcomes, one study found no difference in Japanese Orthopaedic Association (JOA) scores between groups 12 months postoperatively.⁹ Yet another study found that sarcopenic patients have inferior postoperative satisfaction, worse lower back pain, and inferior functional PROMs via EQ-5D after 3.6 years average postop, with a 95 % confidence interval of the odds ratio between 0.63 and 0.91 (p = 0.028) (Table 4).¹¹

3.3 Complications

While six studies reported on medical or orthopaedic complications following TKA, one study reported on complications following THA. Higher total 90-day medical complications (OR = 2.8, p < 0.01) were observed in sarcopenic patients post-TKA compared to non-sarcopenic patients.⁶ Two studies reported greater rates of post-TKA renal and respiratory complications in sarcopenic patients, including greater rates of acute kidney failure (OR = 2.33, p < 0.01), pneumonia (OR = 1.94, p = 0.01), and urinary retention (13.9 vs 0.6 %, p < 0.01).^6,7 A different study¹⁶ reported no difference in the incidence of acute kidney injury (AKI) in sarcopenic patients post-TKA but was limited by a smaller sample size (n = 35) than the aforementioned studies (n = 15,073 and n = 525).^6,7 A study investigating sarcopenic and non-sarcopenic patients following THA found no difference in the rates of pulmonary embolism, AKI, or pneumonia within 90 days postoperatively, but found that sarcopenic patients were 79 % more likely to experience a UTI and had significantly greater total 90-day medical than non-sarcopenic patients.¹ Among studies that investigated cardiovascular and hematological complications post-TKA, sarcopenic patients experienced greater rates of anemia (8.3 vs 1.4 %, p < 0.01; OR = 4.43, p < 0.01),^6,7 a minimum of double the rate of requirement for transfusions,^6,7,16 and a higher incidence of deep vein thrombosis (DVT; 3.3 vs 0 %, p < 0.01)⁷ than non-sarcopenic patients. A separate study reported that sarcopenic patients post-TKA had higher rates of postoperative blood transfusions (29 vs 5 %, p < 0.01) but no differences compared to non-sarcopenic patients in the rates of proximal DVT, distal DVT, infection, or systemic cardiovascular complications, yet this study was limited by short-term follow up and a demographically homogenous patient population.⁸ In the study on post-THA complications, there was no difference between sarcopenic and non-sarcopenic cohorts in incidence of hematoma, transfusion requirement, cardiac arrest, DVT, or wound disruption within 90 days postoperatively.¹ Furthermore, sarcopenic patients demonstrated greater incidence of orthopaedic-related complications following both TKA and THA, including implant instability (post-THA OR = 2.2, p < 0.01), prosthetic dislocation within 2 years (post-THA OR = 1.97, p = 0.02; post-TKA OR = 1.99, p < 0.01), fragility fractures within 2 years (post-THA OR = 1.58, p < 0.01; post-TKA OR = 2.12, p < 0.01), fall risk (2-year post-THA OR = 1.7, p < 0.01; 90-day post-TKA OR = 3.54, p < 0.01), hospital readmission (55 % greater risk 1 year post-THA), 2-year total mechanical complications (post-TKA OR = 2.51, p < 0.01), and 1-year total orthopaedic-related complications (post-THA OR = 1.7, p = 0.01).^1,6 Of studies on TKA patients, two studies^6,8 found higher rates of periprosthetic fracture (OR = 2.12, p < 0.01) and periprosthetic joint infection (OR = 1.51, p < 0.01) in patients with sarcopenia within 2 years post-TKA, while one study¹ limited by poor control of confounding factors found no difference in these rates in THA patients. Neither operative time¹¹ nor time to full weight bearing⁷ differed between sarcopenic and non-sarcopenic TKA patients. However, surgical costs were greater for sarcopenic patients. Compared to non-sarcopenic patients, sarcopenic patients undergoing TKA in one study⁶ had 9 % greater day of surgery costs and 17 % greater global 90-day cost of care, while sarcopenic patients undergoing THA in another study¹ had 29 % greater day of surgery costs and 28 % greater global 90-day cost of care. While two studies^7,14 reported no difference in hospital length of stay (LOS) for TKA patients, two other studies r^6,15 eported up to a 5 % greater in-hospital LOS for sarcopenic compared to non-sarcopenic TKA patients, which may account for greater costs (Table 5).

4.1 Functional outcomes

Patients with sarcopenia undergoing THA or TKA have similar postoperative functional outcomes including strength, range of motion, gait speed, and mobility when compared to patients without sarcopenia, indicating that sarcopenia is not a risk factor for adverse postoperative functional outcomes.^8,9,15,17,19 Additional literature shows no association between sarcopenia and adverse postoperative functional outcomes after TJA,²² while research on functional outcomes after orthopaedic surgery in general is heterogeneous and insufficient to draw conclusions.²³ Notably, while low muscle strength is a diagnostic criteria for sarcopenia,¹² postoperative hip strength was not found to be inferior for sarcopenic patients.¹⁹ The primary postoperative functional difference found for sarcopenic patients was a prolonged time to achieve independent walking following THA only, with no difference after TKA.¹⁷ A separate study alternatively found no difference in post-THA independent walking ability between sarcopenic and non-sarcopenic patients, which may be explained by a significantly longer recovery time after THA, indicating that sarcopenic patients may take longer to recover following THA.¹⁷

4.2 Patient reported outcome measures

PROMs following THA or TKA are moderately inferior in sarcopenic patients compared to non-sarcopenic patients. These PROMs reported on various aspects of pain, mobility, and quality of life. The large variability in outcome measures required a general comparison of PROMs rather than analysis for each subcategory. While there were conflicting post-TKA PROMs reported by four studies,^3,7,8,10 two of the studies^8,10 reported no difference between groups at any point for postoperative pain. The heterogeneity in the remaining findings limits the certainty of the data but trends towards worse PROMs for sarcopenic patients after TKA, corroborating existing research.^12,22,25 At 12-months post-TKA, the conflicting findings between three studies^3,7,8 may be explained by the use of different surveys measuring slightly different outcomes. The inconsistent results between Tzartza et al.¹⁰ and Shon et al.⁸ at 3-months post-TKA may be due to a large difference in sample size, totaling 5 and 42 sarcopenic patients, respectively. For THA PROMs, Uoeka et al.⁹ found no difference between sarcopenic and non-sarcopenic patients measured at 12 months, while Okamoto et al.¹¹ found worse outcomes for sarcopenic patients after 3.6 years on average. Additional research also shows varied data between sarcopenic and non-sarcopenic groups with a general trend showing impaired PROMs for sarcopenic patients after TJA.²² The effect of sarcopenia on postoperative PROMs in TJA has been insufficiently studied to make substantial comparisons, warranting future research to clarify these inconsistencies.

4.3 Complications

Compared to non-sarcopenic patients, sarcopenic patients undergoing TJA had comparable or greater rates of medical complications, orthopaedic complications, and greater costs, although the literature is widely varied. Of the six studies^{6–8,14–16} that reported complications in TKA patients and one study¹ investigating THA patients, there was a wide range of time scales used to investigate complications following TJA, ranging from just days to 2 years postoperatively. While the synthesis of evidence was unclear regarding the relationship between sarcopenia in TJA patients and pneumonia,^1,6 sarcopenia has been demonstrated as a predictor of community-acquired pneumonia risk in older adults in a Peruvian hospital.²⁶ The higher rates of UTI observed in sarcopenic THA patients and other renal complications seen in sarcopenic TKA patients may be explained by the impaired kidney function that has been previously associated with sarcopenia.^1,6,7,27,28 Renal complications in sarcopenic patients may be attributed to an imbalance between skeletal muscle breakdown and growth in a uremic environment.^27,28 A concern to consider is that following THA, sarcopenic patients given an indwelling catheter to prevent postoperative urinary retention can be particularly predisposed to UTI, give that they may require longer postoperative immobilization and consequent increased rates of catheter use.^29,30 The higher rate of postoperative blood transfusion observed in sarcopenic TKA patients is supported by previous literature, which indicates that sarcopenic patients are more likely to require transfusion.^{6–8,16,31,32} This may be attributed to the role of skeletal muscle as a vascular reservoir and lower skeletal muscle mass with resultant reduced blood volume that may make sarcopenic patients more susceptible to blood loss.^31,32 Greater rates of complications, reinjury, and readmission have also been associated with the increased surgical costs for sarcopenic patients, given that complications such as postoperative pneumonia and blood transfusion incur markedly greater medical costs.^1,6,33–35

Regarding the greater rates of orthopaedic complications demonstrated in sarcopenic patients, sarcopenia-related soft tissue weakness is thought to contribute to risk of falls and fragility fractures following THA as a consequence of displacement of the femoral head and impingement during motion, as well as decreased integrity of supporting hip musculature.^1,36–38 Additional literature has also suggested associations between sarcopenia and periprosthetic infection in TKA patients, which may be attributed to reduced physiologic protein reserves important for wound healing from reduced muscle volume in sarcopenia.^7,39 Non-orthopaedic procedures on sarcopenic patients have demonstrated similarly increased risk for postoperative infection as a result of skeletal muscle depletion.^40,41 Considering adverse complication rates and higher medical costs observed in sarcopenic TJA patients, preoperative assessment of sarcopenia can help to identify patients at risk for sarcopenia-related complications and to balance perioperative management.⁴² A systematic review of interventions for reducing sarcopenia in patients undergoing surgery indicated that sarcopenic status, and ultimately surgical outcomes, can be improved by nutritional, physical, and pharmacological interventions, with preoperative exercise therapy significantly improving muscle strength, muscle mass, and motor performance.²¹

4.4 Limitations

This study has several potential limitations. Postoperative outcomes for sarcopenic patients after TJA are an understudied topic, limiting the number of studies available for analysis. Across these few studies, there was variability in methods, including the type of postoperative outcomes and means of measurement. This limited the comparability between studies to more general findings within each category. The studies included in this review had considerable variability in cohort size and study design, potentially overinflating the significance of findings in studies with smaller cohorts of sarcopenic patients. However, cohort size and study design were considered in this review's analysis in an attempt to curb small study bias. These studies also varied their definition of sarcopenia, where most explicitly followed AWGS guidelines, others used aspects of the AWGS criteria methods, where database studies used International Classification of Diseases codes. While this may lead to variability in patient populations across studies, these alternative methods are similar to the AWGS guidelines, justifying the comparisons made between these cohorts.