The total knee endoprosthesis replaces the destroyed joint surfaces between the thigh bone, the shin bone and — if necessary — the kneecap with implants made of metal and plastic. Unlike a total hip replacement, the patient’s own bone is not completely replaced; rather, only the worn joint surfaces are removed and implants are fitted. The collateral ligaments and cruciate ligaments are — depending on the type of prosthesis — partly preserved.
Two main forms are to be distinguished:
Total endoprosthesis (total knee replacement)
The standard procedure for advanced knee joint osteoarthritis in old age with involvement of several compartments. All three bone surfaces are crowned. Durable in the long term, functionally very well established.
Sled prosthesis (unicondylar partial endoprosthesis)
In cases of isolated osteoarthritis in only one part of the joint (usually the inner side), only this part is replaced. A smaller procedure, preserved knee mechanics, faster rehabilitation. Prerequisites: intact collateral ligaments, a stable joint compartment on the opposite side, no inflammatory joint disease.
The choice between a partial and a total endoprosthesis is an orthopedic expert decision that takes into account the individual osteoarthritis pattern, the stability of the joint and the anatomy. Both procedures are very successful when the indication is right.
→ On the overall perspective of joint replacement in old age: Joint replacement in old age.
A central difference that many patients underestimate: rehabilitation after a total knee replacement is considerably more demanding than after a total hip replacement from age 80. The reasons are biomechanical and anatomical:
- Joint complexity: The knee is mechanically more complex than the spherical hip joint. It moves in several planes at the same time.
- Connective tissue and scar formation: After operations the knee is more prone to scarring (arthrofibrosis), which can restrict mobility if flexion is not worked on consistently.
- Pain perception: Knee pain after the operation is typically more intense and lasts longer than after a total hip replacement.
- Musculature: The thigh muscles must be rebuilt in a very targeted way after the operation — the first few weeks are decisive here. Pre-existing sarcopenia makes this process additionally difficult.
- Satisfaction rate: About 80 to 85 percent after a total knee replacement, compared with over 90 percent after a total hip replacement. This is not a sign of poorer surgery, but an expression of the anatomical complexity.
Realistically this means: full weight-bearing capacity and maximum mobility are only achieved three to six months after a total knee replacement. Anyone who knows this assesses the course appropriately — and is not disappointed after three weeks that not everything is yet “as it was before”.
The most important rule of knee rehabilitation: bend, bend, bend. The first few weeks determine how far the knee can later be bent. Anyone who practises consistently here benefits for years.
For patients over 75 — and all the more over 80 — the structured preoperative geriatric assessment before a total knee replacement is the standard of modern geriatric medicine:
- Frailty status: Clinical Frailty Scale. Decision-relevant before every major procedure. More on the frailty syndrome.
- Cognition: MMSE or MoCA. Pre-existing dementia in old age makes rehabilitation considerably more difficult — the postoperative exercises require understanding and cooperation.
- Mobility: Gait pattern, Timed-Up-and-Go, Tinetti test. The function of the other knee and the hips also determines the course of rehabilitation.
- Medication review: Particularly critical: anticoagulants, anti-inflammatory medications (NSAIDs), anticholinergic substances. The key terms being polypharmacy in old age and deprescribing.
- Nutrition and social environment: Particularly important with a total knee replacement, as recovery takes longer. Malnutrition in old age considerably increases the risk of complications.
→ On the comprehensive assessment of surgical risk: Surgical risk in old age.
→ On the frailty assessment: Frailty syndrome.
Studies on total knee replacement consistently show: patients who train in a structured way before the procedure have a faster return to mobility, less pain and higher satisfaction. Core components of prehabilitation:
- Strengthening of the thigh muscles (quadriceps, hamstrings)
- Mobility exercises for the affected knee, as far as possible
- Endurance training for cardiovascular conditioning
- Instruction in the postoperative exercises, so that the routine is familiar
- Medication optimization, in particular reducing potentially problematic preparations
- Weight reduction, if possible — every kilogram less relieves the knee joint by four times when walking
The total knee replacement usually takes 60 to 120 minutes. It is mostly performed under regional anesthesia (spinal anesthesia) with light sedation — this reduces postoperative complications compared with general anesthesia, in particular the risk of delirium in older people.
The postoperative care follows modern fast-track protocols:
- Mobilization on the day of surgery or at the latest on day 1
- Multimodal pain therapy with a minimal opioid dose
- Continuous passive motion (CPM) — today used in a differentiated way
- Early cold therapy and lymphatic drainage to reduce swelling
- Delirium screening and delirium prevention
- Thrombosis prophylaxis for at least two weeks
→ On postoperative delirium prevention: Delirium in older people.
Phase 1: acute phase (day 1 to discharge)
Goal: safe mobilization with a walking aid, pain-adapted weight-bearing, start of building up flexion. Typical length of stay in the acute hospital: 5 to 10 days.
Phase 2: inpatient follow-up rehabilitation (3 weeks)
Focus: improvement of flexion to at least 90 degrees, muscle building, gait training, pain-controlled increase in weight-bearing. The restriction of movement in this phase is normal and will improve with consistent training.
Phase 3: outpatient follow-up treatment (2 to 6 months)
Continuation of physiotherapy, further training at home, gradual building of full functionality. Final mobility and weight-bearing capacity are usually achieved after three to six months.
→ When geriatric early rehabilitation is indicated: Geriatric early rehabilitation.
- Pain: Pain that is too severe prevents the necessary exercises. Consistent multimodal pain therapy is a prerequisite, not an optional extra.
- Swelling: Normal in the first weeks, can be significantly reduced by consistent elevation, cooling and lymphatic drainage.
- Arthrofibrosis: Excessive scar formation with restricted movement. Consistent early movement is the most important prevention.
- Depression: The demanding course of rehabilitation is psychologically stressful. Depression in old age in the second postoperative week is common and can be named — not a matter of fate.
- Cognitive impairment: With pre-existing dementia in old age or postoperative delirium, cooperation with the exercises becomes more difficult. Here, structured, simplified, repeated instruction is particularly important.
The most important ones to know:
- Infection: 1 to 2 percent. Oral hygiene, a preparatory dental check-up and clean postoperative wound care reduce the risk.
- Thrombosis and pulmonary embolism: Rare with adequate prophylaxis.
- Arthrofibrosis: Restricted movement that sometimes has to be treated by mobilization under anesthesia or rare repeat procedures.
- Loosening of the prosthesis: Rare in the first 10 years, more common thereafter.
- Persistent pain: In 10 to 20 percent of patients, relevant pain persists despite a technically good prosthesis.
The long-term prognosis is very good: over 90 percent of total knee replacements are still functional after 15 years. The revision rate is about 1 percent per year. In older patients with osteoporosis in old age, the risk of fracture in the event of another fall should also be considered.
For a planned total knee replacement, the reasons for involvement apply analogously to the total hip replacement. Specifically:
Leading Medicine Guide lists a large number of orthopedic specialists for endoprosthetics. The combination of orthopedic expertise and geriatric co-care is the form of care that produces the best results in older patients — and is increasingly recognized as a quality feature of care.
→ How a comprehensive geriatric assessment supports the decision: Geriatric assessment.
