TKA Wound Complications

How often. Wound complications follow 1-4% of primary TKAs, and 0.5-2% need surgical intervention. After revision TKA the rate is 4-12%, and 2-6% need flap coverage.

Persistent drainage. Persistent wound drainage (PWD) is the most studied marker. Large arthroplasty cohorts report a prevalence of roughly 3-6%; in Shahi's cohort of 4873 total joint arthroplasties it was 6.2%, and PWD carried about 17-fold higher odds of periprosthetic joint infection (PJI). The risk is dose-dependent: each additional day of wound drainage increases the risk of TKA infection by about 29% (Patel, JBJS 2007).

When they appear. Each period after surgery has its typical problem.

A thin envelope. The anterior knee soft-tissue envelope is thin and mobile, and there is no muscle padding over the implant. Any full-thickness loss therefore exposes capsule, extensor mechanism or prosthesis directly, which is why apparently minor problems can progress rapidly to an exposed prosthesis.

A medial blood supply. The skin has a tenuous, predominantly medial blood supply from the descending genicular and the superior and inferior medial geniculate vessels. Most TKA incisions are midline, so the lateral skin flap is perfused by medial perforators across a watershed. That explains why marginal necrosis tends to occur at the lateral wound edge, and why prior lateral scars or wide undermining are dangerous.

The evidence. Using transcutaneous oxygen tension, Johnson showed that skin viability is significantly reduced after knee arthroplasty and that the lateral wound edge is measurably more hypoxic than the medial edge, exactly where wound-edge necrosis tends to begin. There was no significant difference in viability between a midline and the two parapatellar incisions. Which of the standard incisions is chosen matters far less than respecting the blood supply.

Flexion. Anterior knee skin is stretched over the flexing joint, so skin tension rises and perfusion at the incision falls as the knee bends. A compromised envelope therefore tolerates gentle, progressive range of motion far better than aggressive early flexion. In a wound that is already marginal, the sensible levers are leg elevation, a period of relative wound rest, and cautious escalation of flexion rather than forced early continuous passive motion.

None of this argues against mobilising a healthy wound. It is the rationale for setting the rehabilitation tempo by the state of the soft tissues.

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Wound failure is the interaction of impaired host biology with mechanical and vascular insults from surgical technique. The literature consistently identifies patient-related factors as the primary determinants of wound healing, so understanding the modifiable ones is essential for prevention. Surgical technique is covered under Prevention Strategies.

Host Factors

Risk Stratification

The stratum sets the preventive plan.

Evidence: Modifiable Risk Factors

Anatomical Classification

Superficial. Skin and subcutaneous tissue only, without extension to deep fascia or joint. The deep fascia is intact on probing and there is no communication with the joint space; cultures typically grow skin flora, and systemic symptoms are absent or mild.

• Prolonged drainage: serous or serosanguinous discharge beyond 5-7 days
• Superficial dehiscence: partial separation without fascial involvement
• Skin necrosis: full-thickness skin death, of variable extent
• Superficial infection: cellulitis, suture abscess, superficial SSI

Deep. Extension through deep fascia, with potential or actual communication with the prosthetic joint. Fascial disruption is present and joint involvement is confirmed or suspected; a systemic inflammatory response is common, and these wounds require surgical intervention.

• Deep dehiscence: fascial separation with exposed capsule
• Full-thickness necrosis: skin, subcutaneous and fascial involvement
• Deep infection: DAIR criteria met
• Exposed prosthesis: the implant directly visible

Temporal Classification

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Severity Grading

Four grades, from local care to flap coverage:

• Grade I, minor: prolonged drainage under 10 days that responds to local measures; no skin necrosis; normal inflammatory markers
• Grade II, moderate: drainage for 10-14 days or superficial dehiscence, needing theatre for washout or closure; limited skin necrosis, under 2 cm; inflammatory markers elevated but improving
• Grade III, major: drainage beyond 14 days or deep dehiscence; skin necrosis over 2 cm; exposed capsule or extensor mechanism; persistently elevated inflammatory markers
• Grade IV, severe: exposed prosthesis; full-thickness necrosis; failed previous intervention; confirmed deep infection

The grades describe severity. Drainage is graded here by its duration, but the decision to operate on a draining wound follows the 5-7 day and 48-72 hour triggers under Management.

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History

The questions. Establish the story of the drainage and of the patient:

• Timing of symptom onset relative to surgery
• Character of drainage: serous, serosanguinous, purulent or haemoserous
• Volume of drainage: saturating dressings, frequency of changes
• Associated fever, increasing pain or swelling
• Comorbidities and anticoagulation
• Compliance with postoperative instructions
• Any trauma or falls

Red flags. Any of these changes the pace:

• Fever over 38.5°C
• Increasing pain after initial improvement
• Purulent drainage at any time
• Systemic symptoms: malaise, rigors
• Failure of the wound to progress after 5-7 days

Examination

Inspection. Mark and date the margins of erythema. Then look at the character of the drainage on the dressing, for necrosis (eschar, purple discolouration), at how well the wound edges are approximated and at the tension on the closure, and for evidence of haematoma. Around the wound, note tissue turgor and quality, previous scars, skin grafts or flaps, and evidence of venous insufficiency.

Palpation. Fluctuance suggests a collection, and crepitus raises concern for gas-forming organisms. Assess wound edge stability and the consistency of the underlying tissue. At the joint, a guarded range of motion suggests effusion or infection; feel for an effusion, compare warmth with the other knee, and check patellar mobility.

Probing and circulation. A sterile probe assesses depth and tracking along fascial planes; if communication with the joint is suspected, probe in theatre. Check capillary refill and peripheral pulses, with an ankle-brachial index if there is concern.

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The aim is to distinguish a settling superficial problem from established or impending deep infection. No single test is definitive.

Blood tests. FBC, CRP and ESR. CRP is the most sensitive, the white cell count may be normal, and the trend matters more than any absolute value.

Joint aspiration. Aspirate if deep infection is suspected. A cell count over 3000 with over 80% PMNs is diagnostic; culture sensitivity varies.

Swabs and tissue. Superficial swabs are often contaminated. Deep tissue samples are more reliable, and the request should specify prolonged culture.

Imaging. Plain radiographs give a baseline, CT is used if a collection is suspected, and MRI is limited by metal artefact.

Differential Diagnosis

Decision Framework

Treat the draining wound as deep infection. A draining wound over a prosthesis is treated as a deep infection until proven otherwise. The drainage is the visible end of a tract that may run to the implant. Every day of watchful waiting allows organisms to establish a biofilm on the components, and once that has happened the operation required escalates from debridement with liner exchange to a staged revision.

Waiting and operating. Three studies frame the decision. Most persistent drainage settles with local wound care, so a short trial is reasonable; delayed surgery and malnutrition predict failure of the first debridement; and over-anticoagulation is a modifiable contributor to wound-related infection.

ObservationTheatre InterventionFlap Coverage

Who can be watched. Drainage under 5 days with a decreasing trend, superficial erythema responding to elevation, normal or minimally elevated inflammatory markers, no systemic symptoms and a stable wound appearance.

What observation means. Active care, reviewed daily:

• Bed rest with the leg elevated
• Dressing changes as needed, with sterile technique
• Cease anticoagulation if safe
• Consider compression
• Daily wound review
• Oral antibiotics if there is superficial infection, bearing in mind that in a draining wound they risk masking early PJI (see Controversies)

When it has worked. The wound has been dry for 48 hours, the erythema has resolved, the inflammatory markers are normalising and the patient is afebrile.

When it has failed. Any of these means theatre:

• No improvement at 48-72 hours
• Progression of drainage or erythema
• Rising inflammatory markers
• New systemic symptoms

Indications. Take the patient to theatre for:

• Persistent drainage beyond 5-7 days
• Wound dehiscence, superficial or deep
• Skin necrosis over 2 cm
• Suspected haematoma requiring drainage
• Failed conservative management

Irrigation and debridement. A thorough washout with 6-9 L of saline and debridement of non-viable tissue, with deep tissue samples sent for culture. Close directly if possible, and consider NPWT if there is tension.

DAIR, if there is deep infection. Extended debridement with polyethylene exchange, and antibiotic treatment per protocol.

After theatre. Immobilise in an extension splint and continue extended antibiotics pending culture. Review the wound daily, with a low threshold for return to theatre.

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Indications. Soft-tissue coverage is needed for:

• Exposed prosthesis
• Failed previous closure
• Extensive skin necrosis, over 5 cm
• Inadequate local tissue for closure
• A prior radiation field

Principles. Involve plastic surgery early. Debride adequately before coverage so that the flap goes onto a healthy recipient bed, and consider a staged approach. The gastrocnemius flap is the workhorse; the options are set out under Soft Tissue Coverage Options.

Specific Scenarios

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Algorithm

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NPWT (Negative Pressure Wound Therapy)

Its role. NPWT is a bridge to definitive closure. It promotes granulation tissue, reduces oedema and drainage, and allows serial debridement. It is not a definitive treatment for an exposed prosthesis.

Technique. The settings to know:

• White foam over exposed tissue (less adherent)
• Black foam for granulation (more aggressive)
• Continuous pressure of 75-125 mmHg
• Changes every 48-72 hours
• Not through the joint capsule if it is exposed

Contraindications. Active bleeding, malignancy in the wound, untreated osteomyelitis, and exposed vessels without coverage.

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Closed-incision NPWT. On an intact incision the evidence divides by operation: it reduces SSI in revision arthroplasty, but in primary TKA it increases non-infectious wound complications, blistering in particular.

Local Flaps

Gastrocnemius FlapOther Local FlapsFree Flaps

Anatomy. The gastrocnemius has two heads, medial and lateral; the medial head is larger and more commonly used. Its vascular pedicle is the sural arteries, branches of the popliteal, and it pivots at the musculotendinous junction.

Reach. The flap covers the proximal two-thirds of a TKA wound: proximal and middle-third wounds, exposed proximal prosthesis, and soft-tissue defects up to 10x15 cm. It cannot reach the distal third.

Technique. For the medial head:

1. Medial approach
2. Identify and protect the saphenous nerve
3. Divide the tendon at the musculotendinous junction
4. Rotate into the defect
5. Split-thickness skin graft over the muscle

Trade-offs. The blood supply is reliable, the bulk good, the technique well established, and it can be performed under tourniquet. The costs are a cosmetic deficit of the calf and a minor functional impact, with minimal weakness.

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Soleus. For middle to distal third defects. A hemisoleus, medial or lateral, preserves function; the arc of rotation is smaller than the gastrocnemius, and the two can be combined.

Sartorius. A small muscle with limited coverage and limited use around the knee. It is useful for medial defects but rarely used for TKA wounds.

Propeller and perforator flaps. Propeller flaps are perforator-based rotations, useful for smaller defects; they require preoperative perforator mapping and are less robust than muscle flaps. Perforator flaps (ALT, SCIP) are other local options.

Fasciocutaneous flaps. Local advancement or rotation, useful for superficial defects. They are limited by prior incisions and less reliable in irradiated tissue.

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Indications. Free tissue transfer is reserved for:

• Failed local flap options
• Very large defects
• Prior radiation
• Multiple previous surgeries

Latissimus dorsi. A large muscle with a reliable pedicle that can cover extensive defects. The donor site is well tolerated, and the long pedicle allows flexibility in positioning.

Anterolateral thigh (ALT). Fasciocutaneous or myocutaneous, thinner than latissimus, with less donor morbidity. It suits moderate-sized defects.

What it costs. Microsurgical expertise, a longer operation and recipient vessel selection (popliteal, genicular). The complexity is higher, but it is an excellent salvage option; manage expectations.

Coverage Algorithm by Location

Weight, steroids and immunosuppression, uncontrolled diabetes and poor nutrition are the highest-yield modifiable targets to optimise before elective TKA.

Preoperative Optimisation

Diabetes. Target an HbA1c under 8%, ideally under 7%, with endocrinology referral for poor control; 3-6 months is the ideal optimisation period. Perioperative glucose control is critical, with a target under 10 mmol/L:

• A perioperative glucose monitoring protocol, with continuous glucose monitoring recommended
• An insulin sliding scale in hospital

Nutrition. Target an albumin over 3.5 g/dL, with dietitian referral. Measures include preoperative oral supplements (e.g. Ensure, Resource) and vitamin C and zinc supplementation; consider parenteral nutrition if the patient is severely malnourished.

Smoking. Cessation for a minimum of 4 weeks preoperatively is recommended, and 8 weeks is optimal for microvascular recovery. Referral to a structured smoking-cessation service is standard practice. Nicotine replacement therapy is acceptable; consider varenicline or bupropion.

Weight. Target a BMI under 40 for elective surgery. Weight loss of 5-10% significantly reduces risk, with dietitian and exercise physiologist referral; consider bariatric referral at a BMI over 45-50.

Skin conditions. Treat the skin before operating on it:

• Psoriasis: dermatology review and disease control
• Eczema: optimise before surgery
• Chronic wounds: heal before elective surgery
• Venous ulcers: compression, consider vascular input

Hair removal. Use clippers only, not a razor; this reduces SSI. Clip on the day of surgery rather than the night before, and not at all if hair does not obscure the field.

Chlorhexidine. Washes with 2% chlorhexidine for 5 days preoperatively give a documented reduction in skin colonisation. Avoid mucosal contact; povidone-iodine is the alternative for allergy.

Staphylococcus decolonisation. Nasal mupirocin for 5 days preoperatively if the MRSA screen is positive reduces SSI by 50% in carriers. Consider a chlorhexidine bath in addition.

Surgical Technique

Technique is the only wholly intraoperative lever, and a tension-free, well-perfused, layered closure is the single best preventive measure.

Incision planning. Use the previous incision if adequate. Where there are several, the most lateral usable one is preferred, leaving a skin bridge of at least 7 cm between incisions; avoid crossing previous scars if possible, and avoid multiple parallel scars. For revision, the prior medial parapatellar approach is preferred. Place incisions parallel to Langer lines.

Flaps and handling. Raise full-thickness skin flaps, medially based, and avoid undermining, particularly on the lateral side. Handle the skin edges with a no-touch technique:

• Avoid sharp retractors, and Army-Navy retractors on the skin edges
• Use self-retaining retractors with care
• Keep cautery to the dermis minimal
• Preserve the subcutaneous fat layer

Haemostasis. Meticulous point haemostasis before closure avoids haematoma, and tranexamic acid, topical or IV, reduces it. Tourniquet use is controversial; if one is used, release it before closure. Consider a drain in high-risk patients, though this is also controversial.

Closure. Layered closure, under minimal tension on the skin edges, is essential:

• Capsule: absorbable braided suture; consider barbed suture
• Deep dermal: absorbable monofilament, closed meticulously, the critical layer
• Skin: staples or running subcuticular

Postoperative Care

Dressing. Occlusive dressings are preferred. Leave the dressing undisturbed for 48-72 hours unless soaked, and change it with sterile technique.

Drain. If used, remove it when output falls below 30 mL in 24 hours, typically on day 1-2; extended drainage is concerning.

Mobilisation. Balance mobilisation against wound rest, with physiotherapy guidance, and avoid excessive flexion, over 90°, initially.

VTE prophylaxis. Balance the risk of clot against the risk of bleeding and haematoma. Over-anticoagulation feeds the haematoma-drainage-infection pathway (Parvizi, under Management).

The risk-stratification table includes extended antibiotics in the high-risk pathway. In selected high-risk primary arthroplasty patients, a short course of oral antibiotics continued after discharge has been proposed to interrupt the wound-complication-to-infection pathway before it starts.

Where it fits. Inabathula's 7-day postdischarge oral course was associated with a roughly 4-to-5-fold lower 90-day PJI rate in high-risk primary TKA and THA. Frame it as a selective, not routine adjunct: one lever within the high-risk bundle, alongside Staphylococcus decolonisation, glycaemic and nutritional optimisation, chlorhexidine skin preparation, and closed-incision NPWT for revision wounds. It presupposes that the modifiable host factors have already been addressed, and it is no substitute for a clean tension-free closure.

The caveats. The evidence is retrospective (Level III), the definition of "high risk" varies between units, and widespread use raises legitimate stewardship concerns: resistance and C. difficile. It is therefore best reserved for patients whose comorbidity burden genuinely places them in the highest-risk group, and delivered under a defined protocol rather than ad hoc.

Global Epidemiology

Knee arthroplasty volume is rising worldwide, so the absolute burden of wound complications is growing even as rates stay broadly stable (1-4% primary, higher in revision). Registries consistently identify infection — for which a wound complication is often the gateway — as a leading cause of early revision within the first 1-2 years. Persistent wound drainage prevalence clusters around 3-6% across large cohorts irrespective of country, and the same modifiable risks (obesity, diabetes, smoking, malnutrition, inflammatory arthropathy) dominate globally.

Side-by-Side Guidance

Where guidance genuinely converges: optimise the host, prepare and handle skin meticulously, do not let a draining wound persist, sample deep tissue, and involve plastic surgery early. Where it diverges is mainly in the detail of decolonisation protocols and the role of adjuncts such as closed-incision NPWT.

Registry Notes

Major arthroplasty registries (NJR for England/Wales, AJRR in the US, AOANJRR in Australia, the Nordic registries) do not capture wound complications as a discrete endpoint, but they track the downstream signal — early revision for infection. Across these registries, infection is a dominant cause of revision in the first 2 years, underlining wound integrity as a modifiable lever on revision rates.

High- vs Limited-Resource Practice

The principles are universal; the resource-dependent variable is how quickly soft-tissue coverage and theatre can be mobilised — which is precisely the determinant of implant salvage.

The evidence base for managing TKA wound complications is largely retrospective; several core decisions remain genuinely contested and make excellent viva discussion points.

Prevention is Better Than Cure

• Optimize modifiable risk factors preoperatively (obesity, diabetes, smoking, nutrition)
• Meticulous surgical technique with emphasis on tissue handling
• Layered closure with attention to deep dermal layer
• Appropriate postoperative wound care

Early Recognition and Intervention

• Persistent drainage beyond 5-7 days is a red flag
• 48-72 hour rule: if conservative measures fail, proceed to theatre
• Trend of inflammatory markers more important than absolute values
• Low threshold for surgical exploration in high-risk patients

Definitive Management

• Aggressive debridement and lavage in theatre
• Direct closure if possible; NPWT as bridge if not
• Early plastic surgery involvement for complex wounds
• Gastrocnemius flap is the workhorse for soft tissue coverage

Outcomes

• Early treatment (less than 2 weeks) preserves 75-85% of prostheses
• Delayed treatment (greater than 4 weeks) drops to 50-60%
• Gastrocnemius flap has 90-95% success rate
• Functional outcomes reduced but acceptable with successful salvage

The evidence base for TKA wound complications is dominated by large retrospective cohorts and a small number of Level I trials on prevention (smoking cessation) and adjuncts (closed-incision NPWT). The verified key papers below are cross-referenced in their relevant sections above.