Views: 0 Author: Site Editor Publish Time: 2026-08-14 Origin: Site
Knee osteoarthritis is a degenerative joint disease that can progressively cause pain, stiffness, deformity, and loss of mobility.
The knee consists of three major compartments:
Medial tibiofemoral compartment
Lateral tibiofemoral compartment
Patellofemoral compartment
When osteoarthritis is confined primarily to the medial compartment, both UKA and TKA may be considered depending on the patient's symptoms, ligament status, deformity, range of motion, age, activity requirements, and overall joint condition.
Unicompartmental knee arthroplasty (UKA) replaces only the damaged compartment of the knee.
Because the lateral compartment and much of the native knee anatomy can be preserved, UKA may allow patients to retain more physiological knee kinematics.
Potential advantages include:
Less bone resection
Preservation of the cruciate ligaments in appropriately selected patients
Reduced soft-tissue disruption
Lower blood loss
Potentially faster early rehabilitation
However, UKA is highly dependent on appropriate patient selection and surgical technique.
Total knee arthroplasty (TKA) replaces the articular surfaces of the femur and tibia and, when indicated, addresses the patellofemoral compartment.
TKA is particularly useful when osteoarthritis involves multiple compartments or when the knee has substantial deformity, ligament insufficiency, inflammatory disease, or other characteristics that make UKA inappropriate.
Therefore, UKA and TKA should not simply be considered competing procedures. Rather, they are different surgical strategies for different clinical situations.
Many previous studies comparing UKA and TKA have relied heavily on patient-reported outcome measures (PROMs).
Examples include:
Oxford Knee Score
Knee Society Score
KOOS
Other pain and function questionnaires
PROMs are valuable because they capture the patient's perception of pain, symptoms, and function.
However, subjective scores do not necessarily reflect actual physical performance.
For example, two patients may report similar knee function while demonstrating different walking endurance or mobility during objective testing.
Therefore, performance-based tests can provide complementary information.
The 2-minute walk test (2MWT) evaluates the distance a patient can walk within two minutes.
It provides information about:
Walking endurance
Lower-extremity function
Mobility
Functional exercise capacity
A longer walking distance generally indicates better functional performance.
The timed up-and-go (TUG) test evaluates the time required for a patient to stand from a chair, walk a short distance, turn around, return, and sit down.
It incorporates several components of physical function:
Lower-extremity strength
Balance
Walking ability
Transitional movements
Overall mobility
These tests can therefore complement traditional patient-reported outcome measures when assessing recovery after knee arthroplasty.
The study was conducted between September 2016 and April 2019 by an orthopedic research team from Mahidol University in Thailand.
A total of 110 patients with isolated medial compartment knee osteoarthritis were initially randomized.
Patients were allocated to:
UKA group: 55 patients
TKA group: 55 patients
After exclusions, 99 patients were included in the final analysis:
UKA: 50 patients
TKA: 49 patients
The randomized design is important because it reduces the risk of selection bias when comparing postoperative recovery between the two surgical approaches.
The study included patients who met specific clinical and radiographic criteria.
Major inclusion criteria included:
Age between 50 and 85 years
Isolated medial compartment knee osteoarthritis
Anatomic tibiofemoral alignment within the specified range
Knee flexion of at least 90°
Flexion contracture of no more than 15°
No substantial joint-space narrowing in the lateral compartment or patellofemoral joint
American Society of Anesthesiologists physical status class I or II
Patients were excluded when they had conditions that could substantially influence the choice of arthroplasty procedure or postoperative function.
Examples included:
Significant disease in the opposite knee requiring surgery
Intraoperative anterior cruciate ligament insufficiency
Full-thickness cartilage loss in the lateral compartment
Severe bone defects
Significant lateral patellar facet wear
Spontaneous osteonecrosis of the knee
Inflammatory arthritis
Gout
Post-traumatic arthritis
These criteria are important when interpreting the study.
The findings apply primarily to appropriately selected patients with isolated medial compartment disease, rather than to all patients undergoing knee replacement.
The UKA group underwent Oxford mobile-bearing unicompartmental knee arthroplasty, while the TKA group underwent posterior-stabilized fixed-bearing total knee arthroplasty.
All procedures were performed by the same surgeon, and both groups underwent a minimally invasive midvastus approach.
The patella was not resurfaced in either group.
Using the same surgeon and a standardized surgical approach helped reduce variability between the two groups.
Patients were evaluated at multiple postoperative time points:
Preoperatively
6 weeks
3 months
6 months
1 year
2 years
At each stage, researchers assessed objective physical performance using:
2-minute walk test
and
Timed Up-and-Go test
The researchers also evaluated:
Knee Society Scores
Oxford Knee Scores
KOOS
Radiographic parameters
Implant positioning
Lower-limb alignment
Postoperative complications
This combination allowed investigators to compare both objective physical performance and patient-perceived outcomes.
The most important finding was the difference in early postoperative walking capacity.
At 6 weeks after surgery:
UKA patients walked approximately 96.5 ± 22.6 meters during the 2-minute walk test.
The corresponding distance in the TKA group was:
81.1 ± 19.1 meters.
The between-group difference was statistically significant, with P < 0.001.
The UKA group also demonstrated superior 2-minute walking performance at approximately 3 and 6 months after surgery.
However, this difference did not persist indefinitely.
By 1 year and 2 years, the difference between the two groups was no longer statistically significant.
The results suggest that UKA may allow patients to regain functional walking capacity more rapidly during the early postoperative period.
However, the study does not demonstrate that UKA produces superior long-term functional outcomes.
A more appropriate interpretation is:
UKA was associated with faster early functional recovery, whereas functional performance became broadly comparable between UKA and TKA over the longer term.
The same pattern was observed with the TUG test.
Patients who underwent UKA completed the test significantly faster at:
6 weeks
3 months
After 6 months, the difference between the groups was no longer statistically significant.
This provides a second objective measure supporting the concept of faster early mobility after UKA.
The consistency between the 2MWT and TUG results strengthens the interpretation that the difference was not limited to a single functional measurement.
Interestingly, the differences were less pronounced when researchers evaluated conventional patient-reported outcomes.
Except for certain measures at 6 weeks and 3 months, most patient-reported scores did not demonstrate significant differences between the two groups.
This finding highlights an important point in orthopedic outcomes research:
Objective functional recovery and patient-reported recovery are related, but they are not identical.
A patient may report satisfactory pain relief and knee function while still having measurable limitations in walking endurance or transitional mobility.
Therefore, postoperative assessment may be more informative when it combines:
PROMs + objective performance tests + radiographic evaluation.
The study identified differences in several perioperative parameters.
UKA:
75.6 ± 14.7 minutes
TKA:
93.7 ± 13.9 minutes
The difference was statistically significant:
P < 0.001
UKA:
16.8 ± 16.1 mL
TKA:
34.8 ± 36.6 mL
The difference was also statistically significant:
P = 0.014
These findings are consistent with the less extensive nature of UKA, which generally requires less bone and soft-tissue disruption than TKA.
However, operative time and blood loss are secondary outcomes and should not be used alone to determine the optimal procedure for an individual patient.
There are several possible biomechanical and surgical explanations.
UKA preserves substantial portions of the patient's native knee.
In appropriately selected patients, the:
ACL
PCL
Lateral compartment
Portions of the native joint capsule
can remain functional.
This may help maintain more natural knee kinematics.
Compared with TKA, UKA involves replacement of only the diseased compartment.
Less bone is therefore removed.
Because UKA does not require complete exposure and preparation of all three knee compartments, surgical trauma can be reduced.
This may contribute to:
Less postoperative pain
Earlier mobilization
Faster restoration of muscle function
The cruciate ligaments contribute to:
Anterior-posterior stability
Rotational stability
Dynamic knee control
Preservation of these structures may help patients achieve a movement pattern closer to their preoperative knee function.
However, these mechanisms should be viewed as plausible explanations for the observed recovery pattern, rather than direct causal conclusions established by this particular trial.
Although UKA is less extensive than TKA, it is technically demanding.
The success of UKA depends heavily on:
Appropriate patient selection
Accurate bone preparation
Correct implant positioning
Restoration of appropriate joint alignment
Proper flexion-extension gap balancing
Preservation of surrounding cartilage and ligaments
In the study, the UKA procedure involved preparation of the tibial and femoral components followed by implantation of a mobile-bearing prosthesis.
Particular attention was paid to:
The tibial cut must provide appropriate posterior slope and sufficient bone preservation.
The femoral component must be positioned to achieve appropriate flexion-extension balance.
The ACL and PCL should be preserved when performing UKA in appropriate candidates.
For mobile-bearing UKA, appropriate component positioning and balancing are essential for stable bearing function.
These principles emphasize an important distinction:
UKA is not simply a smaller TKA.
It is a different surgical procedure that requires specific indications and technical expertise.
TKA involves more extensive resurfacing of the knee.
Typical surgical principles include:
Distal femoral preparation
Femoral component rotation
Proximal tibial resection
Flexion and extension gap balancing
Femoral and tibial component implantation
Evaluation of overall alignment and stability
In posterior-stabilized TKA, the implant design provides additional constraint to compensate for the absence of the posterior cruciate ligament.
The ultimate objective is to achieve:
Stable knee motion
Appropriate alignment
Balanced flexion and extension gaps
Adequate component fixation
Reliable pain relief and functional improvement
Both groups in the study followed comparable rehabilitation protocols.
Early rehabilitation generally included:
Early mobilization
Assisted knee flexion and extension
Quadriceps activation
Progressive weight-bearing
Walking training
The goal is not simply to increase range of motion but to restore coordinated lower-extremity function.
Quadriceps recovery is particularly important because postoperative weakness can affect:
Walking speed
Stair climbing
Sit-to-stand performance
Balance
Overall mobility
The faster improvement observed in the UKA group in the 2MWT and TUG tests may therefore reflect a combination of less surgical trauma, preserved anatomy, and earlier restoration of lower-extremity function.
At 2 years, radiographic evaluation showed no significant differences between the groups in the assessed alignment and implant-position parameters.
The study also reported no cases of:
Implant loosening
Infection
Fracture
during the reported follow-up period.
Radiographic assessment remains essential after knee arthroplasty because implant alignment and positioning can influence:
Load distribution
Component wear
Stability
Long-term implant survival
The most clinically meaningful conclusion from this randomized trial is not that UKA is universally better than TKA.
Instead, the evidence supports a more nuanced interpretation.
| Outcome | UKA | TKA |
|---|---|---|
| Early walking performance | Better | Lower |
| Early mobility | Better | Lower |
| Operative time | Shorter | Longer |
| Blood loss | Lower | Higher |
| 1-year functional performance | Similar | Similar |
| 2-year functional performance | Similar | Similar |
| Surgical indication | Isolated compartment disease | Broader disease patterns |
| Technical requirements | High | High |
Therefore, patient selection remains more important than simply choosing the procedure associated with faster recovery.
▲Comparison of Average Two-Minute Walk Test Distances at Different Time Points Postoperatively between Unicompartmental Knee Arthroplasty and Total Knee Arthroplasty
UKA may be considered in carefully selected patients with:
Symptomatic isolated medial compartment osteoarthritis
Relatively preserved lateral compartment
Appropriate patellofemoral joint condition
Functional cruciate ligaments
Correctable deformity
Adequate range of motion
Appropriate bone quality
Acceptable overall limb alignment
The final decision should be based on comprehensive clinical and imaging assessment.
Patients with extensive multicompartmental disease or significant ligament insufficiency may be better candidates for TKA.
TKA may be preferred when osteoarthritis extends beyond a single compartment or when the knee has significant structural or functional abnormalities.
Potential indications include:
Multicompartmental osteoarthritis
Advanced lateral compartment disease
Significant patellofemoral disease
Severe deformity
Ligament insufficiency
Inflammatory arthritis
Extensive bone loss
Thus, the choice between UKA and TKA should be individualized rather than based solely on postoperative recovery speed.
This randomized controlled trial provides several practical lessons.
Patients receiving UKA demonstrated better objective walking performance during the first several months after surgery.
By 1 year, the functional differences were no longer significant.
Therefore, the main advantage demonstrated by this study is early recovery rather than proven long-term superiority.
The 2MWT and TUG identified differences that were not consistently apparent from patient-reported outcome measures.
This suggests that postoperative assessment may benefit from combining subjective and objective measurements.
The study included a highly selected population with isolated medial compartment disease.
Its findings should therefore not be extrapolated to patients with advanced multicompartmental osteoarthritis or substantial ligament dysfunction.
Although randomized controlled trials provide relatively strong clinical evidence, several limitations should be considered.
The study included carefully selected patients with isolated medial compartment osteoarthritis.
Therefore, the results may not apply to every patient undergoing knee arthroplasty.
Although patients were followed for 2 years, longer follow-up is required to determine whether early functional differences translate into differences in implant survival or revision rates.
All operations were performed by the same surgeon.
This improves procedural consistency but may limit generalizability to surgeons with different levels of UKA experience.
The 2MWT and TUG are useful performance measures, but they do not capture every dimension of knee function, such as high-demand sports performance, patient satisfaction, or long-term implant survivorship.
For appropriately selected patients with isolated medial compartment knee osteoarthritis:
UKA was associated with faster early functional recovery than TKA.
The strongest evidence from this study includes:
Greater 2-minute walking distance at 6 weeks, 3 months, and 6 months
Faster TUG performance at 6 weeks and 3 months
Shorter operative time
Lower intraoperative blood loss
No significant difference in objective functional performance at 1 and 2 years
The findings therefore support the concept that UKA can provide an early rehabilitation advantage while achieving broadly comparable functional outcomes to TKA in the longer term.
However, this does not mean UKA should replace TKA.
The appropriate procedure depends on the distribution of osteoarthritis, ligament integrity, deformity, range of motion, bone quality, patient expectations, and surgeon experience.
Not necessarily.
This randomized controlled trial found that UKA provided faster early functional recovery, but the functional differences were no longer significant at 1 and 2 years.
In appropriately selected patients, the study demonstrated better early performance on both the 2-minute walk test and TUG test after UKA.
Generally, yes. UKA involves replacement of only the diseased compartment and usually requires less bone and soft-tissue disruption.
No.
UKA requires appropriate patient selection. The status of the lateral compartment, patellofemoral joint, cruciate ligaments, alignment, deformity, range of motion, and bone condition must all be considered.
This study did not demonstrate a significant long-term functional advantage for either procedure at 1 or 2 years.
PROMs measure how patients perceive their pain and function, whereas performance tests directly evaluate physical capability. Using both provides a more comprehensive assessment.
For patients with isolated medial compartment knee osteoarthritis who meet appropriate selection criteria, unicompartmental knee arthroplasty may provide a meaningful advantage during the early postoperative recovery period.
In this randomized controlled trial, UKA patients demonstrated better walking endurance and mobility during the first several months, along with shorter operative time and lower intraoperative blood loss. However, the functional differences between UKA and TKA largely disappeared by 1 year and remained similar at 2 years.
The clinical message is therefore not simply that “UKA is better than TKA.”
Rather, the evidence suggests:
When UKA is appropriately indicated, preservation of native knee anatomy may facilitate faster early functional recovery, while both UKA and TKA can provide comparable functional outcomes over the longer term.
Consequently, surgical decision-making should remain patient-specific and evidence-based, with the extent of osteoarthritis, ligament function, alignment, deformity, activity requirements, and long-term treatment goals all considered before selecting UKA or TKA.
