• Ravi Singla, Daniel Niederer, Alexander Franz, Kevin Happ, Christoph Zilkens, Patrick Wahl, and Michael Behringer.
• Institute of Cardiology and Sports Medicine, German Sport University Cologne, Cologne, Germany. ravi.singla@gmx.de.
• Arch Orthop Trauma Surg. 2023 Aug 1; 143 (8): 530353225303-5322.

PurposeMuscular strength loss and atrophy are postoperative complications. This systematic review with meta-analysis investigated the course of on knee extensor mass and strength from pre-surgery over total knee arthroplasty to rehabilitation and recovery.MethodsA systematic literature search was conducted in PubMed (Medline), Cochrane Library (CINAHL, Embase) and Web of Science (until 29th of June 2022). Main inclusion criteria were  ≥ 1 preoperative and  ≥ 1 measurement  ≥ 3-months post-operation and ≥ 1 objective assessment of quadriceps strength, muscle mass or neuromuscular activity, measured at both legs. Studies were excluded if they met the following criteria: further impairment of treated extremity or of the contralateral extremity; further muscle affecting disease, or muscle- or rehabilitation-specific intervention. The Robins-I tool for non-randomized studies, and the Cochrane Rob 2 tool for randomized controlled studies were used for risk of bias rating. Pre-surgery, 3 months, 6 months and 1 year after surgery data were pooled using random effects meta-analyses (standardized mean differences, SMD, Hedge's g) in contrast to the pre-injury values.Results1417 studies were screened, 21 studies on 647 participants were included. Thereof, 13 were non-randomized controlled trails (moderate overall risk of bias in most studies) and 7 were randomized controlled trials (high risk of bias in at least one domain in most studies). Three (k = 12 studies; SMD = - 0.21 [95% confidence interval = - 0.36 to - 0.05], I2 = 4.75%) and six (k = 9; SMD = - 0.10 [- 0.28 to - 0.08]; I2 = 0%) months after total knee arthroplasty, a deterioration in the strength of the operated leg compared with the strength of the non-operated leg was observed. One year after surgery, the operated leg was stronger in all studies compared to the preoperative values. However, this increase in strength was not significant compared to the non-operated leg (k = 6, SMD = 0.18 [- 0.18 to 0.54], I2 = 77.56%).ConclusionWe found moderate certainty evidence that deficits in muscle strength of the knee extensors persist and progress until 3 months post-total knee arthroplasty in patients with end-stage knee osteoarthritis. Very low certainty evidence exists that preoperatively existing imbalance of muscle strength and mass in favor of the leg not undergoing surgery is not recovered within 1 year after surgery.© 2023. The Author(s).

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