Why Doesn't the Body Fully Recover After Surgery on Its Own - and What Role Does Physiotherapy Play?

⚠ Clinical Note

This article is for educational purposes only. It is based on current clinical practice guidelines and peer-reviewed research and is not a substitute for personalised medical advice, diagnosis, or treatment. If you are experiencing severe, sudden, or rapidly worsening symptoms - or symptoms described in this article as urgent - seek immediate medical attention. For all other concerns, consult a qualified healthcare professional before starting any exercise or treatment program.

Key Facts

✔ Arthrogenic muscle inhibition (AMI) has been reported in up to 56% of people six weeks after ACL injury; it can also remain relevant during rehabilitation after reconstruction. [4]
✔ In an experimental model, injecting as little as 5 mL of fluid into a healthy knee reduced knee-extension strength, an indirect measure related to AMI. [3]
✔ In one trial after knee replacement, daily neuromuscular electrical stimulation (NMES) was associated with nearly 30% greater quadriceps strength at 3.5 weeks than standard rehabilitation alone. [3]
✔ A wound-healing review reports that normal skin scar tissue regains about 50–80% of the original tensile strength, but this figure should not be applied to every orthopaedic repair. [1]
✔ Continuous passive motion (CPM) has not shown meaningful added benefit over active rehabilitation after uncomplicated knee replacement and is not recommended routinely in the cited TKA and ACL guidance. [6,7,8]
✔ Early movement after rotator cuff repair is not one-size-fits-all: evidence differs for small or medium tears and larger tears, so the repair findings and surgeon’s instructions matter. [10]

30-Second Summary

Surgery starts biological healing, but full recovery also requires the return of muscle activation, movement, strength, and task-specific function. AMI, immobilisation, swelling, and procedure-specific tissue constraints can all affect that process. Physiotherapy may be one part of recovery, but its timing and content must match the operation and the treating team’s instructions. [3,6,7,10]

Introduction

When recovery feels slower or less complete than expected, it is natural to wonder whether the operation has healed properly. People may also hear “successful surgery” and “full recovery” used as though they mean the same thing. This article explains why those ideas can diverge.

It focuses on what adults recovering from orthopaedic or musculoskeletal surgery may want to understand before changing their activity. The discussion includes knee replacement, ACL reconstruction, rotator cuff repair, and lumbar spinal fusion. It also explains how physiotherapy fits into recovery without assuming that one programme suits every operation.

Main Explanation: Healing and recovery are different processes

Wound healing is described as a sequence of overlapping phases: haemostasis, inflammation, proliferation, and maturation or remodelling. The process lays down and reorganises collagen, but the resulting tissue is not automatically identical to the tissue that was injured. [1]

A wound-healing review reports that normal skin scar tissue regains about 50 to 80 percent of the original tensile strength of normal skin. It also describes differences in collagen density, fibre size, and orientation between scar and unwounded skin. [1] This is useful general wound biology, but the figure should not be treated as a tensile-strength estimate for every tendon, ligament, joint, or spinal repair.

The timing and amount of loading therefore need to match the tissue and the operation. The rotator-cuff review describes collagen remodelling in the direction of mechanical stress, while the immobilisation review describes tension and stretching effects mainly in experimental contracture models. [2,10]

Immobilisation can add another barrier. The contracture review describes fibrosis, collagen changes, and signalling involving TGF-β1 and HIF-1α in experimental immobilisation models; these mechanisms help explain why rehabilitation timing is procedure-specific rather than universally interchangeable. [2]

Arthrogenic muscle inhibition: a neural contributor to weakness

After knee injury or surgery, weakness may persist even when a repair is progressing. One important contributor is arthrogenic muscle inhibition (AMI), a reflex reduction in the ability to voluntarily activate muscles around an affected joint. [3,5]

AMI can involve altered sensory input from joint damage, inflammation, swelling, or surgery, with effects on spinal and supraspinal motor pathways. The result can be reduced quadriceps activation despite a person’s effort. [3,5]

The ACL systematic review reports AMI in up to 56% of people six weeks after ACL injury, while also discussing AMI during rehabilitation after reconstruction. [4] After total knee replacement, quadriceps strength deficits of approximately 20 to 40 percent have been observed months to years after surgery. [5] At one month after TKA, failure of voluntary activation contributed nearly twice as much to quadriceps strength loss as atrophy in the cited study. [3]

Joint fluid is one reason swelling is relevant to activation. In an experimental model, injecting as little as 5 mL of fluid into a healthy knee reduced knee-extension strength, an indirect measure related to AMI; the TKA review notes that the causal relationship between reducing clinical swelling and improving activation still needs more study. [3]

Immobilisation and passive motion can add barriers

Rest can be part of protecting a repair, but extended immobilisation is not interchangeable with active rehabilitation. In rats, knee contracture that developed after two weeks of immobilisation could be restored, while complete restoration became difficult after more than four weeks; these findings should not be treated as fixed human timelines. [2]

The same review describes progressive muscle fibrosis and collagen changes with longer immobilisation. It also reports that reduced tension weakens mechanical properties in experimental models, which supports careful movement and loading when they are permitted by the surgical plan. [2]

Continuous passive motion (CPM) moves a joint without requiring active muscle contraction. Three Level I studies in the TKA review found no additional benefit from CPM over active rehabilitation, and the 2026 TKA guideline and ACL guideline recommend against routine CPM use in their respective populations. [6,7,8]

CPM therefore should not be presented as a universal substitute for active rehabilitation. The evidence supports a more limited conclusion: passive movement alone has not shown the additional clinical benefit expected over active care in the cited TKA and ACL evidence. [6,7,8]

Causes: Why recovery can stall after surgery

Recovery can stall for more than one reason. The operation, the tissue repaired, swelling, muscle activation, immobilisation, and the timing or progression of rehabilitation can all matter; the evidence differs between TKA, ACL reconstruction, shoulder repair, and lumbar fusion. [2,3,6,7,10]

This is an illustrative case. Consider a person six months after total knee replacement who walks without pain but cannot climb stairs normally and whose quadriceps strength is about 60% of the other leg. Persistent activation failure, residual swelling, muscle loss, movement-control limitations, or another clinical issue could contribute; the pattern cannot establish AMI without assessment. [3,5]

Symptoms: What incomplete recovery may look like

People may notice weakness, difficulty climbing stairs or rising from a chair, limited range of motion, swelling, pain, reduced confidence, or difficulty returning to work, exercise, or sport. These signs are not a diagnosis: similar symptoms can reflect different tissue, joint, neurological, or rehabilitation factors. [3,5,6,7,10]

After TKA, quadriceps deficits can remain for months or years, and AMI-related weakness can affect gait and stair performance. After rotator cuff repair, the relevant concern may instead be protecting tendon integrity while restoring movement, with the timing of active motion depending on tear size and repair details. [3,5,10]

Treatment Options: What physiotherapy and other care may involve

Physiotherapy after surgery is not one standard package. It may include active exercise, movement retraining, progressive strengthening, monitoring of swelling and range of motion, and selected adjuncts such as NMES when the procedure and presentation make them appropriate. [6,7,10]

In one TKA trial, daily NMES started within one week and used frequently was associated with nearly 30% greater quadriceps strength at 3.5 weeks than standard rehabilitation alone. The 2026 TKA guideline recommends daily quadriceps NMES in the early postoperative period, while the ACL guideline recommends NMES in the very early phase with 93.4% expert-panel agreement. These findings support use in the cited knee populations; they do not establish one NMES protocol for every surgery. [3,6,7]

For TKA, the 2026 guideline recommends physical therapy, including early mobilisation, within 24 hours of surgery and supports progressive strengthening. For ACL reconstruction, the guideline recommends active knee motion and progressive weight-bearing while emphasising surgical instructions and objective progression criteria. It presents specific running and sport thresholds as proposed criteria and notes that they are not fully validated. [6,7]

How treatment differs by operation

RHECORE’s [Post-Surgical Recovery](https://rhecore.com.au/programs/post-surgical-recovery-program) programme is designed with reference to the general principles outlined in the guideline cited below and does not guarantee any specific clinical outcome.

For total knee replacement, the evidence supports early mobilisation, progressive strengthening, and selected adjuncts such as NMES. A systematic review found that CPM did not add benefit over active care, while the current guideline recommends progressive strength and exercise programmes beginning in the early post-acute period. [6,8]

For ACL reconstruction, exercise is described as the foundation of rehabilitation, with NMES as an adjunct in the early phase when appropriate. The guideline proposes strength, movement, swelling, and psychological criteria for progression and return to running or sport, but acknowledges low certainty and incomplete validation. [7]

For rotator cuff repair, early motion protocols do not appear to affect healing or retear rates for small and medium tears in the reviewed evidence. For larger tears above 3 cm, early active motion may be associated with impaired tendon integrity, and the review notes limited high-quality evidence for these tears. [10]

For lumbar spinal fusion, the Rushton review reports that 40% of patients experience significant back-related disability at 12 months and that 25% report static or worsening pain. Its pooled analysis found a short-term disability effect size of −0.85 favouring complex rehabilitation, although the review notes heterogeneity and uncertainty about which components drive the gains. [9]

Self-Management

Follow the operating team’s restrictions and the progression set by the treating clinician. The ACL guideline specifically advises adapting early rehabilitation to surgical instructions when additional injuries are present, and the shoulder review describes different protection and movement requirements according to the repair. [7,10]

Use time as context, not as the only reason to advance an activity. For ACL reconstruction, objective physical and psychological criteria are intended to complement time since surgery, while TKA guidance supports monitoring pain, range of motion, swelling, and function when progressing exercise. [6,7]

If exercises or activity consistently increase symptoms, or progress has stopped, ask the treating team to review the plan rather than adding intensity independently. Remote or home-based rehabilitation can be comparable to in-person care in some TKA studies, but the interventions remain procedure-specific and monitored care may still be appropriate. [6,8]

When to See a Physiotherapist

Arrange a clinical review if weakness, stiffness, swelling, pain, or loss of function is not progressing as expected, or if you are unsure which movements are safe after the operation. A physiotherapist can assess movement, strength, range of motion, swelling, and functional tasks, then coordinate advice with the surgical team where needed. [6,7,10]

Seek urgent medical attention for severe, sudden, or rapidly worsening symptoms. Do not use this article to decide whether a wound, implant, graft, or repair is safe to load.

⚠ Signs of Infection - Contact Your Surgical Team Without Delay
If any of the following occur, do not wait for your next scheduled appointment - contact your surgical team or emergency medical services right away:

• Fever, redness, or warmth at the surgical site that is increasing or worsening over time
• Discharge from the wound that is purulent (pus-like) or foul-smelling
• A fever of 38°C (100.4°F) or above, or chills
• Surgical site pain that suddenly worsens or becomes worse than it was initially

Key Takeaways

• The body heals after surgery but cannot independently restore the strength, neural control, and tissue quality needed for full functional recovery.
• AMI is one important contributor to weakness after knee injury or surgery, and voluntary activation failure contributed substantially to early quadriceps strength loss after TKA. [3,5]
• Rehabilitation must be matched to the operation: NMES has guidance-level support in the cited TKA and ACL populations, while rotator-cuff loading depends on tear size and repair details. [6,7,10]
• Passive motion has not shown meaningful added benefit over active rehabilitation in the cited TKA and ACL evidence. [6,7,8]
• Readiness to return to activity should consider objective function, symptoms, tissue protection, and the treating team’s instructions - not calendar time alone. [6,7,10]

References

1. Mathew-Steiner SS, Roy S, Sen CK. Collagen in wound healing. *Bioengineering (Basel).* 2021;8(5):63.
2. Wang F, Zhang QB, Zhou Y, et al. The mechanisms and treatments of muscular pathological changes in immobilization-induced joint contracture: a literature review. *Chin J Traumatol.* 2019;22(2):93-98.
3. Churchill L, Bade MJ, Koonce R, Stevens-Lapsley JE, Bandholm T. The past and future of peri-operative interventions to mitigate arthrogenic muscle inhibition after total knee arthroplasty. *Osteoarthritis Cartilage Open.* 2024;6:100429.
4. Paço M, Peysson M, Dumont E, et al. The effect of physiotherapy on arthrogenic muscle inhibition after ACL injury or reconstruction: a systematic review. *Life.* 2024;14:1586.
5. Kakavas G, Sasse C, Królikowska A, Wong S, Becker R, Prill R. Rehabilitation of arthrogenic muscle inhibition in patients with knee osteoarthritis and after knee arthroplasty. *Curr Rev Musculoskelet Med.* 2026;19:44.
6. Bove AM et al. Clinical practice guideline for physical therapist management of total knee arthroplasty: revision 2026. *Phys Ther.* 2026;106(7):pzag058.
7. Kotsifaki R et al. Aspetar clinical practice guideline on rehabilitation after ACL reconstruction. *Br J Sports Med.* 2023;57(9):500-514.
8. Dávila Castrodad IM et al. Rehabilitation protocols following total knee arthroplasty: a review of study designs and outcome measures. *Ann Transl Med.* 2019;7(Suppl 7):S255.
9. Greenwood J, Dunn KM, Rushton A. An investigation of the impact of rehabilitation on outcomes after lumbar spinal fusion surgery. *Spine J.* 2016;16(1):31-43.
10. Corban J, Shah S, Ramappa AJ. Current evidence-based recommendations on rehabilitation following arthroscopic shoulder surgery. *Curr Rev Musculoskelet Med.* 2024;17:247-257.