The way orthopaedic surgeons measure the effectiveness of total knee replacement surgery has, historically, been via a metric called the patient-reported outcome measure (PROM).
What are patient-reported outcome measures?
PROMs collect data directly from the patient using standardised questionnaires that measure how they feel and how well they are functioning after surgery. The questionnaires assess several important areas including health-related quality of life (how well they are managing day-to-day and their overall wellbeing); their symptoms including severity of pain and levels of fatigue; and how well they are recovering following the procedure.
How wearable sensors are used to evaluate surgical outcomes
The patient-reported outcome measure has long been regarded as the ‘gold standard’ when it comes to evaluating the outcomes of joint replacement surgery.
However, more recently wearable sensors have used to monitor patients. These sensors provide an accurate way of measuring joint function, capturing spatiotemporal gait characteristics (similar to 3D gait analysis) and providing estimates of impact loading, step count, load asymmetry and cumulative load exposure following a total knee replacement.
Research from New Zealand
A recent study by researchers at Auckland City Hospital in New Zealand[1] compared traditional patient-reported outcome measures (PROMs) with wearable sensors in assessing the early outcomes for patients following total knee replacement surgery. Just over half (56%) of the patients in the study had undergone conventional knee replacement surgery. The remaining 44% had received a robotic arm assisted total knee replacement.
Robotic arm assisted total knee replacement surgery
This innovative approach to joint replacement surgery uses innovative computer software to develop a 3D image of the patient’s unique knee anatomy and create a detailed pre-operative plan. On the operating table, the orthopaedic surgeon is supported by a high-tech robotic arm which help them achieve greater accuracy and precision, and to remain within the boundaries of the patient’s pre-operative plan. This means that patients undergoing a robotic arm assisted knee replacement benefit from personalised alignment of their new artificial knee – in other words, it is precisely located to match the structure of their natural knee joint.
Methodology
The researchers compared functional outcomes for patients using wearable devices called inertial measurement units (IMUs) and those using traditional PROMs measures (including the Oxford Knee Score, EuroQol five-dimension five-level questionnaire, EuroQol visual analogue scale and Forgotten Joint Score). Participants were evaluated pre-operatively as a baseline and then again at two weeks and six weeks postoperatively.
What the research showed
Six weeks after surgery, patients who’d received a robotic arm assisted total knee replacement showed improved function compared with those who’d undergone a conventional total knee replacement. The angle of maximum knee flexion was greater, limb loading symmetry was better, there was increased cumulative impact load and increased bone stimulus. Three weeks after surgery, patients who’d received a robotic arm assisted total knee replacement demonstrated an earlier return to symmetrical limb loading. All of these results were demonstrated by the IMUs. In contrast, no significant differences between the two groups were revealed in the patient reported outcome measures.
The researchers concluded that sensors worn by patients post-surgery revealed outcomes that were not detected by traditional patient-reported outcome measures. They suggest that IMUs may provide a “more nuanced understanding of the patients’ early postoperative progress” which “may be overlooked by traditional PROMs”.
In the early post-operative period, robotic arm assisted total knee replacements were associated with a faster return of symmetrical gait and improved range of motion compared with conventional total knee replacements.
For more information on total knee replacements, please contact us.
Frequently Asked Questions
What is a ‘total knee replacement’?
A total knee replacement means that the entire knee joint is removed and replaced by an artificial implant. By contrast, with partial knee replacements, only part of the joint is replaced, leaving undamaged sections of the knee intact.
Does the robotic arm perform the knee replacement surgery?
No. The robotic arm is there to support the orthopaedic surgeon, it does not perform the surgery itself.
What are patient reported outcome measures used to assess?
Patient reported outcome measures assess hip replacements and knee replacements from the patient’s perspective.
[1] Bone Joint J 2026;108-B(4):478–489.
